U.S. patent application number 17/311886 was filed with the patent office on 2022-01-27 for impact and wear resistant component, and method for producing the same.
This patent application is currently assigned to KOMATSU LTD.. The applicant listed for this patent is KOMATSU LTD., NIPPON STEEL CORPORATION. Invention is credited to Eiji AMADA, Takafumi AMATA, Mamoru HATANO, Kouji KITAMURA, Naomi KOBAYASHI, Kazuo MAEDA, Kei MIYANISHI, Yutaka NEISHI, Ryoji NISHIJIMA, Takashi NODA, Daisuke TAKIGUCHI.
Application Number | 20220025475 17/311886 |
Document ID | / |
Family ID | |
Filed Date | 2022-01-27 |
United States Patent
Application |
20220025475 |
Kind Code |
A1 |
AMADA; Eiji ; et
al. |
January 27, 2022 |
IMPACT AND WEAR RESISTANT COMPONENT, AND METHOD FOR PRODUCING THE
SAME
Abstract
A ripper shank as the impact and wear resistant component is
made of a steel of a specific component composition which has a
hardness of HRC 53 or more and HRC 57 or less. The steel includes a
matrix including a martensite phase and a residual austenite phase,
and first nonmetallic particles dispersed in the matrix and
including at least one species selected from the group consisting
of MnS, TiCN, and NbCN. The steel does not include a M23C6
carbide.
Inventors: |
AMADA; Eiji; (Tokyo, JP)
; KITAMURA; Kouji; (Tokyo, JP) ; MAEDA; Kazuo;
(Tokyo, JP) ; KOBAYASHI; Naomi; (Tokyo, JP)
; NODA; Takashi; (Tokyo, JP) ; HATANO; Mamoru;
(Tokyo, JP) ; AMATA; Takafumi; (Tokyo, JP)
; NEISHI; Yutaka; (Tokyo, JP) ; MIYANISHI;
Kei; (Tokyo, JP) ; NISHIJIMA; Ryoji; (Tokyo,
JP) ; TAKIGUCHI; Daisuke; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOMATSU LTD.
NIPPON STEEL CORPORATION |
Tokyo
Tokyo |
|
JP
JP |
|
|
Assignee: |
KOMATSU LTD.
Tokyo
JP
NIPPON STEEL CORPORATION
Tokyo
JP
|
Appl. No.: |
17/311886 |
Filed: |
December 26, 2019 |
PCT Filed: |
December 26, 2019 |
PCT NO: |
PCT/JP2019/051137 |
371 Date: |
June 8, 2021 |
International
Class: |
C21D 9/00 20060101
C21D009/00; C21D 8/00 20060101 C21D008/00; C21D 6/00 20060101
C21D006/00; C21D 6/02 20060101 C21D006/02; C21D 1/18 20060101
C21D001/18; C22C 38/54 20060101 C22C038/54; C22C 38/50 20060101
C22C038/50; C22C 38/48 20060101 C22C038/48; C22C 38/46 20060101
C22C038/46; C22C 38/44 20060101 C22C038/44; C22C 38/04 20060101
C22C038/04; C22C 38/02 20060101 C22C038/02; C22C 38/00 20060101
C22C038/00; E02F 9/28 20060101 E02F009/28 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2018 |
JP |
2018-243881 |
Claims
1. An impact and wear resistant component made of a steel
containing not less than 0.41 mass % and not more than 0.44 mass %
C, not less than 0.2 mass % and not more than 0.5 mass % Si, not
less than 0.2 mass % and not more than 1.5 mass % Mn, not less than
0.0005 mass % and not more than 0.0050 mass % S, not less than 0.6
mass % and not more than 2.0 mass % Ni, not less than 0.7 mass %
and not more than 1.5 mass % Cr, not less than 0.1 mass % and not
more than 0.6 mass % Mo, not less than 0.02 mass % and not more
than 0.03 mass % Nb, not less than 0.01 mass % and not more than
0.04 mass % Ti, not less than 0.0005 mass % and not more than
0.0030 mass % B, and not less than 20 mass ppm and not more than 60
mass ppm N, with the balance consisting of iron and unavoidable
impurities, and having a hardness of HRC 53 or more and HRC 57 or
less, the steel including a matrix including a martensite phase and
a residual austenite phase, and first nonmetallic particles
dispersed in the matrix and including at least one species selected
from the group consisting of MnS, TiCN, and NbCN, the steel not
including a carbide represented as M.sub.23C.sub.6 (where M
represents the metallic elements constituting the steel).
2. The impact and wear resistant component according to claim 1,
wherein the steel further contains at least one species selected
from the group consisting of not less than 0.05 mass % and not more
than 0.20 mass % V, not less than 0.01 mass % and not more than
0.15 mass % Zr, and not less than 0.1 mass % and not more than 2.0
mass % Co.
3. The impact and wear resistant component according to claim 1,
wherein the matrix has a grain size number of 5 or more and 8 or
less.
4. The impact and wear resistant component according to claim 1,
wherein the martensite phase constituting the matrix is a low
temperature-tempered martensite phase.
5. A method for producing an impact and wear resistant component,
comprising the steps of: preparing a steel material made of a steel
containing not less than 0.41 mass % and not more than 0.44 mass %
C, not less than 0.2 mass % and not more than 0.5 mass % Si, not
less than 0.2 mass % and not more than 1.5 mass % Mn, not less than
0.0005 mass % and not more than 0.0050 mass % S, not less than 0.6
mass % and not more than 2.0 mass % Ni, not less than 0.7 mass %
and not more than 1.5 mass % Cr, not less than 0.1 mass % and not
more than 0.6 mass % Mo, not less than 0.02 mass % and not more
than 0.03 mass % Nb, not less than 0.01 mass % and not more than
0.04 mass % Ti, not less than 0.0005 mass % and not more than
0.0030 mass % B, and not less than 20 mass ppm and not more than 60
mass ppm N, with the balance consisting of iron and unavoidable
impurities; hot forging or hot rolling the steel material to obtain
a formed body; performing normalizing treatment on an entirety of
the formed body by cooling the formed body from a temperature not
lower than 945.degree. C. and not higher than 1000.degree. C. to a
temperature not higher than a temperature corresponding to the
M.sub.s point of the steel; and performing quench hardening
treatment on the formed body having undergone the normalizing
treatment and, thereafter, adjusting a hardness of the formed body
to be HRC 53 or more and HRC 57 or less by heating the formed body
to a temperature not lower than 150.degree. C. and not higher than
250.degree. C.
6. The impact and wear resistant component producing method
according to claim 5, wherein the steel further contains at least
one species selected from the group consisting of not less than
0.05 mass % and not more than 0.20 mass % V, not less than 0.01
mass % and not more than 0.15 mass % Zr, and not less than 0.1 mass
% and not more than 2.0 mass % Co.
7. The impact and wear resistant component according to claim 2,
wherein the matrix has a grain size number of 5 or more and 8 or
less.
8. The impact and wear resistant component according to claim 2,
wherein the martensite phase constituting the matrix is a low
temperature-tempered martensite phase.
9. The impact and wear resistant component according to claim 3,
wherein the martensite phase constituting the matrix is a low
temperature-tempered martensite phase.
10. The impact and wear resistant component according to claim 7,
wherein the martensite phase constituting the matrix is a low
temperature-tempered martensite phase.
Description
TECHNICAL FIELD
[0001] The present invention relates to a component (impact and
wear resistant component) that is subjected to repeated impact and
wears by contact with earth and sand, such as a ground engaging
tool (hereinafter, GET) component used in construction or mining
equipment, and to a method for producing the same.
[0002] This application claims priority based on Japanese Patent
Application No. 2018-243881 filed on Dec. 27, 2018, the entire
contents of which are incorporated herein by reference.
BACKGROUND ART
[0003] A ripper device is a rear attachment of a work vehicle such
as a bulldozer, and is used to scrape up earth, sand, and bedrock.
Ripping work can be performed as the work machine is advanced with
a ripper point attached to the distal end of the ripper shank being
penetrated into the ground. While the ripper shank is a strength
member of the ripper device, it is an impact and wear resistant
component that suffers wear and deformation. Although SCrB steel,
JIS SNCM431H steel, etc. have conventionally been used as the steel
material constituting the ripper shank, a material having even
better durability is desired.
[0004] To improve the durability of an impact and wear resistant
component, it is necessary to impart high wear resistance and high
proof stress (strength) to the material constituting the component.
Simply increasing the strength of a component, however, leads to
reduction in toughness of the material constituting the component.
The surface of the component may crack or the component may break,
giving rise to the need for replacement of the component. As such,
in order to improve the durability of the impact and wear resistant
component, it is necessary to maintain ductility (toughness) at a
high level while achieving high proof stress (strength) of the
material.
[0005] As a steel material constituting a component of construction
equipment, a high-toughness and wear-resistant steel having
excellent durability has been proposed (see, for example, Japanese
Patent Application Laid-Open No. S61-166954 (Patent Literature 1)).
Further, as a steel for a tracked undercarriage component, a steel
containing about 0.4 mass % carbon and various alloy elements added
therein has been proposed (see, for example, Japanese Translation
of PCT International Publication No. 2014/185337 (Patent Literature
2)).
CITATION LIST
Patent Literature
[0006] Patent Literature 1: Japanese Patent Application Laid-Open
No. S61-166954
[0007] Patent Literature 2: Japanese Translation of PCT
International Publication No. 2014/185337
SUMMARY OF INVENTION
Technical Problem
[0008] When an impact and wear resistant component, particularly a
GET component, is produced using the steel disclosed in Patent
Literature 1 or 2, the resultant component will have a high
strength. Further, a steel having an improved 0.2% proof stress
will be able to, for example, suppress deformation (plastic flow)
of the contact surface with the ripper point in the ripper shank.
However, when the steel material disclosed in Patent Literature 1
is used to produce a large ripper shank having a wall thickness of
100 mm and a mass of about 1 ton, for example, the component will
suffer a decrease in strength (insufficient hardenability) at the
center in its wall thickness. Further, a component produced using
the steel disclosed in Patent Literature 2 through a common
production process tends to exhibit a small reduction of area in a
tensile test. According to the investigations conducted by the
present inventors, the smaller reduction of area in the tensile
test leads to lower resistance to breakage. That is, further
improvement in durability is desired for the impact and wear
resistant component produced through a common production process
using the steel disclosed in Patent Literature 2.
[0009] One of the objects of the present invention is to provide an
impact and wear resistant component excellent in durability and a
method for producing the same.
Solution to Problem
[0010] An impact and wear resistant component according to the
present invention is made of a steel containing not less than 0.41
mass % and not more than 0.44 mass % C, not less than 0.2 mass %
and not more than 0.5 mass % Si, not less than 0.2 mass % and not
more than 1.5 mass % Mn, not less than 0.0005 mass % and not more
than 0.0050 mass % S, not less than 0.6 mass % and not more than
2.0 mass % Ni, not less than 0.7 mass % and not more than 1.5 mass
% Cr, not less than 0.1 mass % and not more than 0.6 mass % Mo, not
less than 0.02 mass % and not more than 0.03 mass % Nb, not less
than 0.01 mass % and not more than 0.04 mass % Ti, not less than
0.0005 mass % and not more than 0.0030 mass % B, and not less than
20 mass ppm and not more than 60 mass ppm N, with the balance
consisting of iron and unavoidable impurities, and having a
hardness of HRC 53 or more and HRC 57 or less. The steel includes a
matrix including a martensite phase and a residual austenite phase,
and first nonmetallic particles dispersed in the matrix and
including at least one species selected from the group consisting
of MnS, TiCN, and NbCN. The steel does not include a carbide
represented as M.sub.23C.sub.6 (where M represents the metallic
elements constituting the steel).
[0011] A method for producing an impact and wear resistant
component according to the present invention includes the steps of:
preparing a steel material made of a steel containing not less than
0.41 mass % and not more than 0.44 mass % C, not less than 0.2 mass
% and not more than 0.5 mass % Si, not less than 0.2 mass % and not
more than 1.5 mass % Mn, not less than 0.0005 mass % and not more
than 0.0050 mass % S, not less than 0.6 mass % and not more than
2.0 mass % Ni, not less than 0.7 mass % and not more than 1.5 mass
% Cr, not less than 0.1 mass % and not more than 0.6 mass % Mo, not
less than 0.02 mass % and not more than 0.03 mass % Nb, not less
than 0.01 mass % and not more than 0.04 mass % Ti, not less than
0.0005 mass % and not more than 0.0030 mass % B, and not less than
20 mass ppm and not more than 60 mass ppm N, with the balance
consisting of iron and unavoidable impurities; hot forging or hot
rolling the steel material to obtain a formed body; performing
normalizing treatment on an entirety of the formed body by cooling
the formed body from a temperature not lower than 945.degree. C.
and not higher than 1000.degree. C. to a temperature not higher
than a temperature corresponding to the M.sub.s point of the steel;
and performing quench hardening treatment on the formed body having
undergone the normalizing treatment and, thereafter, adjusting a
hardness of the formed body to be HRC 53 or more and HRC 57 or less
by heating the formed body to a temperature not lower than
150.degree. C. and not higher than 250.degree. C.
Effects of the Invention
[0012] According to the impact and wear resistant component and its
producing method described above, it is possible to provide an
impact and wear resistant component excellent in durability and a
method for producing the same.
BRIEF DESCRIPTION OF DRAWINGS
[0013] FIG. 1 is a schematic view showing the structure of a ripper
device including a ripper shank and a ripper point;
[0014] FIG. 2 is a schematic perspective view showing the state of
connection between the ripper shank and the ripper point;
[0015] FIG. 3 is a schematic cross-sectional view showing the
structure of the ripper shank;
[0016] FIG. 4 is a flowchart schematically illustrating the steps
of producing a ripper shank;
[0017] FIG. 5 shows optical micrographs of a microstructure of the
steel;
[0018] FIG. 6 shows SEM photographs of nonmetallic particles;
[0019] FIG. 7 shows observation results using an optical microscope
and SEM, and elemental mapping results;
[0020] FIG. 8 shows a result of identification of a product present
at a grain boundary; and
[0021] FIG. 9 shows a relationship between heating temperature and
reduction of area.
DESCRIPTION OF EMBODIMENT
Outline of Embodiment
[0022] An impact and wear resistant component of the present
application is made of a steel containing not less than 0.41 mass %
and not more than 0.44 mass % C, not less than 0.2 mass % and not
more than 0.5 mass % Si, not less than 0.2 mass % and not more than
1.5 mass % Mn, not less than 0.0005 mass % and not more than 0.0050
mass % S, not less than 0.6 mass % and not more than 2.0 mass % Ni,
not less than 0.7 mass % and not more than 1.5 mass % Cr, not less
than 0.1 mass % and not more than 0.6 mass % Mo, not less than 0.02
mass % and not more than 0.03 mass % Nb, not less than 0.01 mass %
and not more than 0.04 mass % Ti, not less than 0.0005 mass % and
not more than 0.0030 mass % B, and not less than 20 mass ppm and
not more than 60 mass ppm N, with the balance consisting of iron
and unavoidable impurities, and having a hardness of HRC 53 or more
and HRC 57 or less. The steel includes a matrix including a
martensite phase and a residual austenite phase, and first
nonmetallic particles dispersed in the matrix and including at
least one species selected from the group consisting of MnS, TiCN,
and NbCN. The steel does not include a carbide represented as
M.sub.23C.sub.6 (where M represents the metallic elements
constituting the steel).
[0023] In the impact and wear resistant component described above,
the steel may further contain at least one species selected from
the group consisting of not less than 0.05 mass % and not more than
0.20 mass % V, not less than 0.01 mass % and not more than 0.15
mass % Zr, and not less than 0.1 mass % and not more than 2.0 mass
% Co.
[0024] Firstly, a description will be made about the reasons for
limiting the component composition of the steel constituting the
impact and wear resistant component of the present application to
the above-described ranges.
[0025] Carbon (C): Not Less than 0.41 Mass % and Not More than 0.44
Mass %
[0026] Carbon is an element that greatly affects the hardness of
the steel. If the carbon content is less than 0.41 mass %, it will
be difficult to obtain a hardness of HRC 53 or more in a portion
having a wall thickness of about 100 mm, for example, with
quenching and tempering. On the other hand, the carbon content
exceeding 0.44 mass % will decrease the reduction of area and
reduce the breakage resistance. The carbon content is thus
necessary to be within the above-described range. From the
standpoint of readily securing a sufficient hardness, the carbon
content is preferably 0.42 mass % or more.
[0027] Silicon (Si): Not Less Than 0.2 Mass % and Not More Than 0.5
Mass %
[0028] Silicon is an element that has the effects of improving the
hardenability of the steel, enhancing the matrix of the steel, and
improving the resistance to temper softening, and also has a
deoxidizing effect in the steelmaking process. If the silicon
content is 0.2 mass % or less, the above effects cannot be obtained
sufficiently. If the silicon content exceeds 0.5 mass %, however,
the reduction of area tends to decrease. The silicon content is
thus necessary to be within the above-described range.
[0029] Manganese (Mn): Not Less Than 0.2 Mass % and Not More Than
1.5 Mass %
[0030] Manganese is an element effective in improving the
hardenability of the steel, and also having a deoxidizing effect in
the steelmaking process. If the manganese content is 0.2 mass % or
less, the above effects cannot be obtained sufficiently. If the
manganese content exceeds 1.5 mass %, however, the hardness before
quench hardening will increase, leading to degradation in
workability. From the standpoint of securing sufficient
hardenability of the steel, the manganese content is preferably 0.4
mass % or more. Further, focusing on the workability, the manganese
content is preferably 0.9 mass % or less, and more preferably 0.8
mass % or less.
[0031] Sulfur (S): Not Less Than 0.0005 Mass % and Not More Than
0.0050 Mass %
[0032] Sulfur is an element that improves the machinability of the
steel. Sulfur is also an element that is mixed during the
steelmaking process even if not added intentionally. If the sulfur
content is less than 0.0005 mass %, the machinability will
decrease, and the production cost of the steel will increase. On
the other hand, according to the investigations of the present
inventors, in the component composition of the steel of the present
application, the sulfur content greatly affects the reduction of
area. If the sulfur content exceeds 0.0050 mass %, the reduction of
area will decrease, making it difficult to obtain sufficient
breakage resistance. The sulfur content is thus necessary to be
within the above-described range. The sulfur content of 0.0040 mass
% or less can further improve the breakage resistance.
[0033] Nickel (Ni): Not Less Than 0.6 Mass % and Not More Than 2.0
Mass %
[0034] Nickel is an effective element in improving the toughness of
the matrix of the steel. If the nickel content is less than 0.6
mass %, such an effect cannot be exerted sufficiently. If the
nickel content exceeds 2.0 mass %, however, nickel becomes more
likely to segregate in the steel. This may cause variation in the
mechanical properties of the steel. The nickel content is thus
necessary to be within the above-described range. Further, with the
nickel content exceeding 1.5 mass %, the improvement in toughness
will become moderate, and the production cost of the steel will
increase. From these standpoints, the nickel content is preferably
1.5 mass % or less. On the other hand, in the case of a steel
having a hardness of HRC 53 or more, in order to sufficiently exert
the effect of improving the toughness of the matrix of the steel,
the nickel content is preferably 1.0 mass % or more.
[0035] Chromium (Cr): Not Less Than 0.7 Mass % and Not More Than
1.5 Mass %
[0036] Chromium improves the hardenability of the steel and also
enhances the resistance to temper softening. In particular,
chromium being added in combination with molybdenum, niobium,
vanadium, and the like considerably enhances the resistance to
temper softening of the steel. If the chromium content is less than
0.7 mass %, the above effects cannot be exerted sufficiently. If
the chromium content exceeds 1.5 mass %, however, the improvement
of the resistance to temper softening will become moderate, and the
production cost of the steel will increase. The chromium content is
thus necessary to be within the above-described range.
[0037] Molybdenum (Mo): Not Less Than 0.1 Mass % and Not More Than
0.6 Mass %
[0038] Molybdenum improves the hardenability of the steel and
enhances the resistance to temper softening. Molybdenum also has
the function of improving the high temperature tempering
brittleness. If the molybdenum content is less than 0.1 mass %, the
above effects cannot be exerted sufficiently. If the molybdenum
content exceeds 0.6 mass %, however, the above effects will be
saturated. The molybdenum content is thus necessary to be within
the above-described range.
[0039] Niobium (Nb): Not Less Than 0.02 Mass % and Not More Than
0.03 Mass %
[0040] Niobium is effective in improving the strength and toughness
of the steel. In particular, niobium is a highly effective element
in improving the toughness because it makes the crystal grains of
the steel extremely fine when added in combination with chromium
and molybdenum. To secure such effects, the niobium content should
be 0.02 mass % or more. If the niobium content exceeds 0.03 mass %,
however, the crystallization of coarse eutectic NbC and the
formation of a large amount of NbC cause a decrease in the amount
of carbon in the matrix, leading to degradation in strength and
toughness of the steel. Further, the niobium content exceeding 0.03
mass % will increase the production cost of the steel. The niobium
content is thus necessary to be within the above-described
range.
[0041] Titanium (Ti): Not Less Than 0.01 Mass % and Not More Than
0.04 Mass %
[0042] Titanium is effective in improving the toughness of the
steel. Further, the addition of Ti can form Ti(C,N) and refine the
crystal grains of the steel. If the titanium content is less than
0.01 mass %, such effects are small. If the titanium content
exceeds 0.04 mass %, however, the toughness of the steel may rather
deteriorate. The titanium content is thus necessary to be within
the above-described range.
[0043] Boron (B): Not Less Than 0.0005 Mass % and Not More Than
0.0030 Mass %
[0044] Boron is an element that considerably improves the
hardenability of the steel. The addition of boron can decrease the
addition amounts of the other elements added for the purpose of
improving the hardenability, and can reduce the production cost of
the steel. As compared to phosphorus (P) and sulfur, boron is more
likely to segregate in the prior austenite grain boundary, and it
particularly expels sulfur from the grain boundary, thereby
improving the grain boundary strength. If the boron content is
0.0005 mass % or less, the above effects cannot be exerted
sufficiently. The boron content exceeding 0.0030 mass %, however,
may decrease the toughness of the steel. The boron content is thus
necessary to be within the above-described range.
[0045] Nitrogen (N): Not Less Than 20 Mass ppm and Not More Than 60
Mass ppm
[0046] Nitrogen may deteriorate the toughness of the steel, except
the case where nitrogen together with carbon forms carbonitrides
with Ti or Nb to refine the crystal grains. The nitrogen content is
thus necessary to be 60 mass ppm or less. The nitrogen content of
less than 20 mass ppm, however, will increase the production cost
of the steel. The nitrogen content is thus necessary to be within
the above-described range.
[0047] Vanadium (V): Not Less Than 0.05 Mass % and Not More Than
0.20 Mass %
[0048] Vanadium is not an indispensable element. Vanadium, however,
forms fine carbides, contributing to the refinement of crystal
grains. If the vanadium content is less than 0.05 mass %, the above
effect cannot be obtained sufficiently. If the vanadium content
exceeds 0.20 mass %, however, the above effect will be saturated.
Vanadium is a relatively expensive element, so it is preferably
added in a minimum required amount. Thus, in the case of adding
vanadium, the addition amount within the above-described range is
appropriate.
[0049] Zirconium (Zr): Not Less Than 0.01 Mass % and Not More Than
0.15 Mass %
[0050] Zirconium is not an indispensable element, but it has the
effect of further improving the toughness of the steel by making
carbides in the form of fine spherical particles dispersed in the
steel. If the zirconium content is less than 0.01 mass %, its
effect cannot be obtained sufficiently. If the zirconium content
exceeds 0.15 mass %, however, the toughness of the steel may rather
deteriorate. Thus, in the case of adding zirconium, the addition
amount within the above-described range is appropriate.
[0051] Cobalt (Co): Not Less Than 0.1 Mass % and Not More Than 2.0
Mass %
[0052] Cobalt is not an indispensable element, but it increases the
solid solubility of chromium, molybdenum, and other carbide-forming
elements to the matrix, and also improves the resistance to temper
softening of the steel. The addition of cobalt thus achieves finer
carbides and a higher tempering temperature, thereby improving the
strength and toughness of the steel. If the cobalt content is less
than 0.1 mass %, the above effects cannot be obtained sufficiently.
On the other hand, because of its expensiveness, cobalt added in a
large amount will increase the production cost of the steel. These
problems become prominent with a cobalt content exceeding 2.0 mass
%. Thus, in the case of adding cobalt, the addition amount within
the above-described range is appropriate.
[0053] Unavoidable Impurities
[0054] Besides the components intentionally added during the
production process, elements other than those described above may
be mixed into the steel as unavoidable impurities. Phosphorus (P)
as an unavoidable impurity is preferably contained in an amount of
0.010 mass % or less. Copper (Cu) as an unavoidable impurity is
contained in an amount of preferably 0.1 mass % or less and more
preferably 0.05 mass % or less. Aluminum (Al) as an unavoidable
impurity is contained in an amount of preferably 0.04 mass % or
less.
[0055] The impact and wear resistant component of the present
application is made of a steel having the above-described
appropriate component composition. Further, in the impact and wear
resistant component of the present application, the steel
constituting the impact and wear resistant component does not
include a carbide represented as M.sub.23C.sub.6 (where M
represents the metallic elements constituting the steel, mainly at
least one of Cr and Mo; hereinafter, referred to as
"M.sub.23C.sub.6 carbide").
[0056] According to the investigations conducted by the present
inventors, in the case of adopting a steel having the
above-described appropriate component composition as the steel
constituting an impact and wear resistant component, when the
component is produced with a common production process,
M.sub.23C.sub.6 carbides are generated at the grain boundaries of
the steel. With the M.sub.23C.sub.6 carbides generated, the Cr and
Mo contents decrease in the region around the M.sub.23C.sub.6
carbides. The hardenability in the region thus decreases, and a
bainite structure is formed. That the steel contains not only a
martensite structure, but also brittle M.sub.23C.sub.6 carbides at
the grain boundaries as well as brittle bainite structure near the
grain boundaries attributable thereto, results in a smaller
reduction of area in the tensile test of the steel. A lower
reduction of area of the steel leads to a reduced breakage
resistance of the impact and wear resistant component made of the
steel.
[0057] As a result of investigating the way of improving the
durability of the impact and wear resistant components, the present
inventors have obtained findings that adopting a steel having the
above-described appropriate component composition and eliminating
the M.sub.23C.sub.6 carbides from the steel structure can obtain an
impact and wear resistant component improved in breakage resistance
and excellent in durability. In the impact and wear resistant
component of the present application, the steel having the
above-described appropriate component composition is adopted as the
steel constituting the impact and wear resistant component, and no
M.sub.23C.sub.6 carbides are included in the steel structure. The
impact and wear resistant component of the present application is
thus an impact and wear resistant component excellent in
durability.
[0058] In the present application, the state where the steel
includes no M.sub.23C.sub.6 carbides means a state where
M.sub.23C.sub.6 carbides are not found when the cross section of
the impact and wear resistant component is observed using a
field-emission scanning electron microscope (FE-SEM) and an area of
80 .mu.m.sup.2 including the grain boundary of the steel is
examined for 10 or more fields of view. The M.sub.23C.sub.6 carbide
can be identified, when a possible product of M.sub.23C.sub.6
carbide is found for example in the above-described manner, by
detecting the product in a bright-field image of a scanning
transmission electron microscope (STEM) and then confirming the
selected area diffraction (SAD) pattern of the product.
[0059] In the impact and wear resistant component described above,
the matrix may have a grain size number of 5 or more and 8 or less.
With this configuration, excellent toughness can readily be
imparted to the impact and wear resistant component.
[0060] In the impact and wear resistant component described above,
the martensite phase constituting the matrix may be a low
temperature-tempered martensite phase. With this configuration,
excellent toughness can readily be imparted to the impact and wear
resistant component.
[0061] As used herein, the low temperature-tempered martensite
phase means a phase made up of a structure (obtained through low
temperature tempering) which is obtained when a steel that has been
quenched is tempered at a temperature not lower than 150.degree. C.
and not higher than 250.degree. C. The phase being the low
temperature-tempered martensite phase can be confirmed through
investigation of the hardness, carbide precipitation state, etc. of
the phase.
[0062] A method for producing an impact and wear resistant
component of the present application includes the steps of:
preparing a steel material made of a steel containing not less than
0.41 mass % and not more than 0.44 mass % C, not less than 0.2 mass
% and not more than 0.5 mass % Si, not less than 0.2 mass % and not
more than 1.5 mass % Mn, not less than 0.0005 mass % and not more
than 0.0050 mass % S, not less than 0.6 mass % and not more than
2.0 mass % Ni, not less than 0.7 mass % and not more than 1.5 mass
% Cr, not less than 0.1 mass % and not more than 0.6 mass % Mo, not
less than 0.02 mass % and not more than 0.03 mass % Nb, not less
than 0.01 mass % and not more than 0.04 mass % Ti, not less than
0.0005 mass % and not more than 0.0030 mass % B, and not less than
20 mass ppm and not more than 60 mass ppm N, with the balance
consisting of iron and unavoidable impurities; hot forging or hot
rolling the steel material to obtain a formed body; performing
normalizing treatment on an entirety of the formed body by cooling
the formed body from a temperature not lower than 945.degree. C.
and not higher than 1000.degree. C. to a temperature not higher
than a temperature corresponding to the M.sub.s point of the steel;
and performing quench hardening treatment on the formed body having
undergone the normalizing treatment and, thereafter, adjusting a
hardness of the formed body to be HRC 53 or more and HRC 57 or less
by heating the formed body to a temperature not lower than
150.degree. C. and not higher than 250.degree. C.
[0063] In the impact and wear resistant component producing method
described above, the steel may further contain at least one species
selected from the group consisting of not less than 0.05 mass % and
not more than 0.20 mass % V, not less than 0.01 mass % and not more
than 0.15 mass % Zr, and not less than 0.1 mass % and not more than
2.0 mass % Co.
[0064] In the impact and wear resistant component producing method
of the present application, after a steel material made of the
steel having the above-described appropriate component composition
is prepared, the steel material is hot forged or hot rolled to
obtain a formed body. In the cooling process following the hot
forging or hot rolling, M.sub.23C.sub.6 carbides are generated at
the grain boundaries of the steel. Thereafter, in the impact and
wear resistant component producing method of the present
application, normalizing treatment is performed on the entirety of
the formed body in which the formed body is cooled from a
temperature not lower than 945.degree. C. and not higher than
1000.degree. C. to a temperature not higher than the temperature
corresponding to the M.sub.s point of the steel. With the
normalizing treatment of heating to a temperature range of not
lower than 945.degree. C. and then cooling being performed, the
M.sub.23C.sub.6 carbides previously generated dissolve into the
matrix of the steel and disappear. Thereafter, quench hardening
treatment is performed and then the formed body is heated to a
temperature not lower than 150.degree. C. and not higher than
250.degree. C. to adjust the hardness of the steel to be HRC 53 or
more and HRC 57 or less. In this manner, it is readily possible to
produce the impact and wear resistant component of the present
application that is made of the steel including no M.sub.23C.sub.6
carbides.
Specific Example of Embodiment
[0065] An embodiment of the impact and wear resistant component of
the present invention will be described below with reference to the
drawings. In the following drawings, the same or corresponding
parts are denoted by the same reference numerals, and the
description thereof will not be repeated.
[0066] Firstly, referring to FIGS. 1 to 3, a ripper shank as an
impact and wear resistant component in the present embodiment will
be described. FIG. 1 is a schematic view showing the structure of a
ripper device including a ripper shank and a ripper point. FIG. 2
is an exploded perspective view of the ripper shank and the ripper
point. FIG. 3 is a schematic cross-sectional view showing the
structure of the ripper shank.
[0067] Referring to FIG. 1, the ripper device 1 of the present
embodiment is, for example, a ripper device attached to a
bulldozer. The ripper device 1 is attached to the rear (opposite
the side on which a blade (soil removal plate) is disposed) of the
vehicle body of the bulldozer. The ripper device 1 includes an arm
31, a lift cylinder 32, a tilt cylinder 33, a ripper support member
34, a ripper shank 10, and a ripper point 20.
[0068] The arm 31 has a rod shape. The arm 31 has one end connected
to a bracket (not shown) mounted on the vehicle body of the
bulldozer, and the other end connected to the ripper support member
34. The ripper support member 34 is pivotably connected to the
other end of the arm 31.
[0069] The lift cylinder 32 and the tilt cylinder 33 have their one
ends connected to the bracket (not shown) mounted on the vehicle
body of the bulldozer. The lift cylinder 32 and the tilt cylinder
33 have their other ends connected to the ripper support member 34.
The lift cylinder 32 and the tilt cylinder 33 are hydraulic
cylinders that can be extended and contracted in the longitudinal
direction. The ripper support member 34 is pivotably connected to
the other ends of the lift cylinder 32 and the tilt cylinder 33. Of
the ripper support member 34, the region connected to the lift
cylinder 32 is located between the region connected to the arm 31
and the region connected to the tilt cylinder 33.
[0070] Referring to FIGS. 1 and 2, the ripper shank 10 is made of
steel. The ripper shank 10 includes a distal end 15 as one end and
a proximal end 14 as the other end in the longitudinal direction.
The region including the distal end of the ripper shank 10 is bent
toward the side approaching the vehicle body of the bulldozer. The
region of the ripper shank 10 between its distal end 15 and
proximal end 14 is supported by the ripper support member 34. The
ripper point 20 is attached to the distal end 15 of the ripper
shank 10. Of the ripper support member 34, the region connected to
the arm 31 is positioned closer to the ripper point 20 as compared
to the region connected to the tilt cylinder 33 and the region
connected to the lift cylinder 32.
[0071] In the ripper device 1, the extension and contraction of the
lift cylinder 32 cause the ripper shank 10 to move up and down. The
extension and contraction of the tilt cylinder 33 cause the ripper
shank 10 to tilt. With the ripper shank 10 in a lowered state and
tilted to cause the ripper point 20 to penetrate the ground the
vehicle body of the bulldozer is advanced, whereby earth, sand, and
bedrock are scraped up.
[0072] Referring to FIGS. 1 to 3, the ripper shank 10 has a through
hole, a ripper shank through hole 11, formed therein. The ripper
point 20 has a through hole, a ripper point through hole 25, formed
therein. In the state where the ripper point 20 is attached to the
ripper shank 10, the ripper point through hole 25 and the ripper
shank through hole 11 form a continuous through hole. A pin 51
inserted into the continuous through hole secures the ripper point
20 to the ripper shank 10.
[0073] Referring to FIG. 3, the ripper point 20 has a recess 22
formed to recess from its proximal end 23 side toward its distal
end 21 side. The ripper shank 10 includes a body portion 12
including its proximal end 14 and an insert portion 13 including
its distal end 15 on the side to be inserted into the recess 22.
The recess 22 formed in the ripper point 20 has its bottom region
22A not in contact with the distal end 15 of the ripper shank 10.
There is a space 29 between the bottom region 22A of the recess 22
and the distal end 15.
[0074] In the ripper device 1 in the present embodiment, the ripper
shank 10 as the impact and wear resistant component is made of a
steel containing not less than 0.41 mass % and not more than 0.44
mass % C, not less than 0.2 mass % and not more than 0.5 mass % Si,
not less than 0.2 mass % and not more than 1.5 mass % Mn, not less
than 0.0005 mass % and not more than 0.0050 mass % S, not less than
0.6 mass % and not more than 2.0 mass % Ni, not less than 0.7 mass
% and not more than 1.5 mass % Cr, not less than 0.1 mass % and not
more than 0.6 mass % Mo, not less than 0.02 mass % and not more
than 0.03 mass % Nb, not less than 0.01 mass % and not more than
0.04 mass % Ti, not less than 0.0005 mass % and not more than
0.0030 mass % B, and not less than 20 mass ppm and not more than 60
mass ppm N, with the balance consisting of iron and unavoidable
impurities, and having a hardness of HRC 53 or more and HRC 57 or
less. The steel includes a matrix including a martensite phase and
a residual austenite phase, and first nonmetallic particles
dispersed in the matrix and including at least one species selected
from the group consisting of MnS, TiCN, and NbCN. The steel does
not include a carbide represented as M.sub.23C.sub.6 (where M
represents the metallic elements constituting the steel). The
amount of the residual austenite included in the matrix is 10 vol %
or less, for example, and preferably 5 vol % or less.
[0075] The steel constituting the ripper shank 10 may further
contain at least one species selected from the group consisting of
not less than 0.05 mass % and not more than 0.20 mass % V, not less
than 0.01 mass % and not more than 0.15 mass % Zr, and not less
than 0.1 mass % and not more than 2.0 mass % Co.
[0076] The ripper shank 10 as the impact and wear resistant
component of the present embodiment adopts the steel having the
above-described appropriate component composition as the material,
and the steel structure does not include M.sub.23C.sub.6 carbides.
Accordingly, the ripper shank 10 as the impact and wear resistant
component of the present embodiment is an impact and wear resistant
component excellent in durability.
[0077] In the ripper shank 10, the matrix of the steel constituting
the ripper shank 10 preferably has the grain size number (ASTM) of
5 or more and 8 or less. This facilitates imparting excellent
toughness to the ripper shank 10.
[0078] In the ripper shank 10, the martensite phase constituting
the matrix of the steel is preferably a low temperature-tempered
martensite phase. This facilitates imparting excellent toughness to
the ripper shank 10.
[0079] An exemplary method of producing a ripper shank 10 as the
impact and wear resistant component of the present embodiment will
now be described with reference to FIG. 4. In the method of
producing the ripper shank 10 in the present embodiment, firstly, a
steel material preparing step is performed as a step S10. In the
step S10, a steel material made of the steel having the
above-described appropriate component composition is prepared.
[0080] Next, a hot working step is performed as a step S20. In the
step S20, the steel material prepared in the step S10 is subjected
to hot forging or hot rolling and forming processing. With this, a
formed body having an approximate shape of the ripper shank 10 is
obtained. Hot forging or hot rolling is performed by, for example,
heating the steel material prepared in the step S10 to a
temperature not lower than 1200.degree. C., such as 1250.degree. C.
In the cooling process following the hot forging or hot rolling,
M.sub.23C.sub.6 carbides are formed at the grain boundaries of the
steel.
[0081] Next, a normalizing step is performed as a step S30. In the
step S30, the formed body obtained in the step S20 is subjected to
normalizing treatment. Specifically, the formed body is firstly
heated to a temperature range of not lower than 945.degree. C. and
not higher than 1000.degree. C., and then cooled from the
temperature range to a temperature not higher than the temperature
corresponding to the M.sub.s point of the steel. In this manner,
the entirety of the formed body is normalized. Performing the
normalizing treatment of heating to the temperature range of
945.degree. C. or higher and 1000.degree. C. or lower and then
cooling causes the M.sub.23C.sub.6 carbides generated in the step
S20 to dissolve into the matrix of the steel and disappear.
[0082] Next, a hardening treatment step is performed as a step S40.
In the step S40, the formed body having undergone the normalizing
treatment in the step S30 is firstly heated to a temperature range
of 840.degree. C. or higher and 920.degree. C. or lower, for
example, and then cooled from the temperature range to a
temperature not higher than the M.sub.s point of the steel. In this
manner, the entirety of the formed body is quench hardened. The
cooling to the temperature not higher than the M.sub.s point of the
steel can be performed, for example, by water cooling or oil
cooling adopting water or oil as a cooling medium. The water
cooling or oil cooling is continued until, for example, the surface
temperature of the formed body becomes a temperature not lower than
50.degree. C. and not higher than 100.degree. C. Thereafter, the
formed body is heated to a temperature range of not lower than
150.degree. C. and not higher than 250.degree. C. and then cooled
to a room temperature (low temperature tempering). With this, the
hardness of the steel constituting the formed body is adjusted to a
range of HRC 53 or more and HRC 57 or less.
[0083] Next, a finishing step is performed as a step S50 as
required. In the step S50, the formed body obtained through the
steps S10 to S40 is subjected to any necessary finishing or other
treatment. The ripper shank 10 in the present embodiment can be
produced through the above-described process. The obtained ripper
shank 10 is combined with a separately prepared ripper point 20, to
obtain a ripper device 1.
[0084] According to the method for producing the ripper shank 10 of
the present embodiment, the M.sub.23C.sub.6 carbides, generated
along the grain boundaries of the steel during hot forging or hot
rolling and forming the steel material made of the steel having the
above-described appropriate component composition, are made to
disappear by the normalizing treatment in the step S30, before the
hardening treatment in the step S40. In this manner, the ripper
shank 10 as the impact and wear resistant component excellent in
durability can be produced.
[0085] Examples
[0086] Samples corresponding to the impact and wear resistant
component of the present application were prepared using four types
of steel materials, including one made of a steel having the
above-described appropriate component composition, and experiments
for evaluating their properties were conducted. The experimental
procedures were as follows.
[0087] Table 1 shows chemical compositions of the steels used in
the experiments. The values in Table 1 are in mass %. The steel
material A has a component composition corresponding to the steel
constituting the impact and wear resistant component of the present
invention (Inventive Example). The steel materials B, C, and D have
component compositions falling outside the scope of the present
invention (Comparative Examples). The steel materials B, C, and D
correspond to SCrB430H, JIS standard SNCM431H, and the steel
disclosed in the aforementioned Patent Literature 1,
respectively.
TABLE-US-00001 TABLE 1 C Si Mn P S Ni Cr Mo Nb Ti Al B N Fe A 0.43
0.30 0.40 0.008 0.004 1.29 0.99 0.48 0.03 0.02 0.033 0.0024 0.0035
Bal. B 0.30 0.23 0.93 0.021 0.015 0.05 1.09 0.03 not not 0.030
0.0017 not Bal. measured measured measured C 0.34 0.17 0.68 0.017
0.007 1.62 0.73 0.18 not not 0.028 not not Bal. measured measured
measured measured D 0.41 0.30 0.47 0.010 0.007 0.03 0.96 0.50 0.03
0.02 0.044 0.0022 0.0051 Bal.
[0088] (Experiments on Mechanical Properties)
[0089] The steel materials in Table 1 were used to prepare samples
through a process similar to the steps S10 to S40 in the above
embodiment. From the obtained samples, tensile test specimens and
Charpy impact test specimens (2 mm U-notch) were produced, and a
tensile test, an impact test, and a Rockwell hardness measurement
were conducted.
[0090] For the steel material A (Inventive Example) alone, the
amount of residual austenite was measured using an X ray. The test
results are shown in Table 2.
TABLE-US-00002 TABLE 2 0.2% Proof Tensile Reduction Impact Residual
Stress Strength Elongation of Area Value Hardness .gamma. Amount
(MPa) (MPa) (%) (%) (J/cm.sup.2) (HRC) (vol %) A 1592 2131 14 44 62
56 2.3 B 1417 1655 13 47 65 48 not measured C 1414 1752 15 44 60 50
not measured D 1599 1935 13 43 59 53 not measured
[0091] Referring to Table 2, when comparing the Inventive Example
with the Comparative Examples, the Inventive Example has achieved
high values for the 0.2% proof stress, tensile strength, and impact
value, while maintaining the reduction of area comparable to those
of the Comparative Examples. Further, for the steel material A as
the Inventive Example, as compared to the steel material D, the
tensile strength has improved considerably despite their comparable
0.2% proof stress. The above demonstrates that the impact and wear
resistant component of the present application is excellent in
durability.
[0092] (Experiment on Steel Structure)
[0093] The steel material A in Table 1 (the steel material
corresponding to the example of the present invention) was used to
prepare a sample of a ripper shank in a similar procedure as in the
above embodiment. A test specimen was taken from the sample. The
surface of the obtained test specimen was polished and then etched
with a nitric acid alcohol solution, and a microstructure was
observed using an optical microscope. FIG. 5 shows optical
micrographs showing the microstructure of the steel.
[0094] Referring to FIG. 5, it can be seen from the microstructure
of the steel that the matrix includes a low temperature-tempered
martensite phase. In the impact and wear resistant component of the
present application, the presence of some residual austenite (of 10
vol % or less) is acceptable. For the sample obtained in a similar
manner, the amount of residual austenite was measured using an X
ray, and it was found that the residual austenite of 1 vol % to 3
vol % was present. The above demonstrates that the matrix of the
steel includes the martensite phase and the residual austenite
phase.
[0095] FIG. 6 shows photographs indicating the results of analysis
by energy dispersive X-ray spectroscopy (EDX) of products that were
found through observation of the steel structure with SEM. As shown
in FIG. 6, it is confirmed that nonmetallic particles having a size
of about 1 .mu.m to about 20 .mu.m (first nonmetallic particles
including at least one species selected from the group consisting
of MnS, TiCN, and NbCN) are dispersed in the matrix of the
steel.
[0096] (Experiments on Carbides Formed at Grain Boundaries)
[0097] The steel material A (the steel material corresponding to
the example of the present invention) in Table 1 was used to
prepare a test specimen (as quenched; sample A) by performing the
process of the above embodiment up to the step S20 (with the
forging temperature of 1250.degree. C.), not performing the step
S30, and performing quenching treatment in the step S40 after
heating the material to 870.degree. C. A test specimen (as
quenched; sample B) was also prepared, by similarly performing the
process up to the step S20, performing normalizing treatment in the
step S30 by heating the material to 970.degree. C., and further
performing quenching treatment in the step S40 after heating the
material to 870.degree. C. For the samples A and B, the
microstructures were observed with an optical microscope and SEM,
and for products present along the grain boundaries, elemental
mapping was conducted with EDX. The experimental results are shown
in FIG. 7.
[0098] Referring to FIG. 7, it can be seen that carbides of Mo and
Cr are present along the grain boundaries in the sample A for which
the step S30 was omitted, and that a bainite structure is formed
around the carbides. The formation of the bainite structure is
conceivably attributable to the local decrease in the amount of
alloy elements because of the formation of the above carbides, and
the resultant reduction in hardenability. In contrast, in the
sample B corresponding to the impact and wear resistant component
of the present invention for which normalizing treatment was
conducted in the step S30 with the heating temperature of
970.degree. C., no carbides as described above were found. The
above experimental results show that although the above-described
carbides formed during the hot working process remain with the
quenching temperature of 870.degree. C., the carbides dissolve and
disappear with the normalizing temperature of 970.degree. C.
[0099] An example of the identification of carbides present in the
sample A is shown in FIG. 8, in which a carbide was detected in a
bright-field image of STEM and then the selected area diffraction
(SAD) pattern of the carbide was confirmed. As shown in FIG. 8, it
can be seen that the carbide is a M.sub.23C.sub.6 carbide. That is
to say, it has been confirmed that in the method of producing an
impact and wear resistant component of the present application, the
M.sub.23C.sub.6 carbides formed during the hot working process
disappear by the heating during the normalizing conducted in the
step S30.
[0100] (Experiment on Relationship between Heating Temperature and
Reduction of Area)
[0101] The steel material A in Table 1 was used to prepare test
specimens which were quench hardened by rapid cooling from various
temperatures and then tempered at high temperature. The test
specimens were subjected to a tensile test. At this time, the
heating temperature upon quenching was varied to investigate the
effect of the heating temperature on the reduction of area in the
tensile test. The experimental results are shown in FIG. 9.
[0102] Referring to FIG. 9, it can be seen that the reduction of
area clearly increases with the heating temperature of 945.degree.
C. or higher. This temperature range of not lower than 945.degree.
C. agrees with the temperature range in which M.sub.23C.sub.6
carbides cease to be seen in the experiment on the carbides formed
at the grain boundaries. This indicates that the M.sub.23C.sub.6
carbides generated at the grain boundaries of the steel can be
eliminated by the heating to the temperature range of not lower
than 945.degree. C., whereby the reduction of area is improved.
[0103] While the ripper shank was described as an example of the
impact and wear resistant component of the present application in
the above embodiment, the impact and wear resistant component of
the present application is applicable to a variety of impact and
wear resistant components made of a steel having a hardness of HRC
53 or more and HRC 57 or less, such as bucket teeth, bucket
adapters, bucket shrouds, ripper points, protectors, cutting edges,
end bits, crusher teeth, sprocket teeth, springs, shoe plates, shoe
bolts, and the like.
[0104] It should be understood that the embodiment and examples
disclosed herein are illustrative and non-restrictive in every
respect. The scope of the present invention is defined by the terms
of the claims, rather than the description above, and is intended
to include any modifications within the scope and meaning
equivalent to the terms of the claims.
REFERENCE SIGNS LIST
[0105] 1: ripper device; 10: ripper shank; 11: ripper shank through
hole; 12: body portion; 13: insert portion; 14: proximal end; 15:
distal end; 20: ripper point; 21: distal end; 22: recess; 22A:
bottom region; 23: proximal end; 25: ripper point through hole; 29:
space; 31: arm; 32: lift cylinder; 33: tilt cylinder; 34: ripper
support member; and 51: pin.
* * * * *