U.S. patent application number 16/349969 was filed with the patent office on 2019-09-19 for high-hardenability, medium-carbon, low-alloy round steel for fasteners and the manufacturing method thereof.
This patent application is currently assigned to JIANG YIN XING CHENG SPECIAL STEEL WORKS CO., LTD. The applicant listed for this patent is JIANG YIN XING CHENG SPECIAL STEEL WORKS CO., LTD. Invention is credited to Shaoxin HU, Zhen HUANG, Ling JI, Xiangwei KONG, Xuewen LIU, Shuyan SHAO, Xiaohong XU, Xudong ZHANG.
Application Number | 20190284654 16/349969 |
Document ID | / |
Family ID | 58351696 |
Filed Date | 2019-09-19 |
United States Patent
Application |
20190284654 |
Kind Code |
A1 |
JI; Ling ; et al. |
September 19, 2019 |
HIGH-HARDENABILITY, MEDIUM-CARBON, LOW-ALLOY ROUND STEEL FOR
FASTENERS AND THE MANUFACTURING METHOD THEREOF
Abstract
The present invention relates to a high-hardenability,
medium-carbon, low-alloy round steel for fasteners, the chemical
constituents by mass percentage are as follows: C:
0.36.about.0.44%, Si: 0.15.about.0.40%, Mn: 0.80.about.1.00%, Cr:
1.00.about.1.15%, Mo: 0.05.about.0.25%, Ni: 0.05.about.0.25%, Cu:
0.05.about.0.25%, Al: 0.015.about.0.050%, B: 0.0010.about.0.0050%,
Ti: 0.020.about.0.050%, the balance is Fe; the maximum diameter of
the round steel is 65 mm. The manufacturing process are as follows:
the raw materials are processed, in sequence, by converter
smelting, LF refining, RH/VD degassing to obtain molten steel,
feeding Ti wires and ferroboron, continuous casting, rolling into
the bar, obtaining the quenched and tempered round steel after
quenching and tempering treatment; the quenched and tempered round
steel is able to be directly used in processing fasteners which
meet ISO 898-1 standard for grade 10.9, such as bolts and the
like.
Inventors: |
JI; Ling; (Jiangyin,
Jiangsu, CN) ; XU; Xiaohong; (Jiangyin, Jiangsu,
CN) ; HUANG; Zhen; (Jiangyin, Jiangsu, CN) ;
SHAO; Shuyan; (Jiangyin, Jiangsu, CN) ; LIU;
Xuewen; (Jiangyin, Jiangsu, CN) ; KONG; Xiangwei;
(Jiangyin, Jiangsu, CN) ; HU; Shaoxin; (Jiangyin,
Jiangsu, CN) ; ZHANG; Xudong; (Jiangyin, Jiangsu,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JIANG YIN XING CHENG SPECIAL STEEL WORKS CO., LTD |
Jiangyin, Jiangsu |
|
CN |
|
|
Assignee: |
JIANG YIN XING CHENG SPECIAL STEEL
WORKS CO., LTD
Jiangyin, Jiangsu
CN
|
Family ID: |
58351696 |
Appl. No.: |
16/349969 |
Filed: |
August 10, 2017 |
PCT Filed: |
August 10, 2017 |
PCT NO: |
PCT/CN2017/096705 |
371 Date: |
May 14, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 9/0093 20130101;
C21D 6/008 20130101; C22C 38/42 20130101; C22C 38/44 20130101; C21D
8/065 20130101; C21D 2211/008 20130101; C21D 6/005 20130101; C22C
38/54 20130101; C22C 38/06 20130101; C22C 38/04 20130101; C22C
38/02 20130101; C21D 9/525 20130101; C21D 1/18 20130101; C22C 38/50
20130101; C21D 6/004 20130101 |
International
Class: |
C21D 6/00 20060101
C21D006/00; C22C 38/54 20060101 C22C038/54; C22C 38/50 20060101
C22C038/50; C22C 38/44 20060101 C22C038/44; C22C 38/42 20060101
C22C038/42; C22C 38/06 20060101 C22C038/06; C22C 38/04 20060101
C22C038/04; C22C 38/02 20060101 C22C038/02; C21D 1/18 20060101
C21D001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 15, 2016 |
CN |
201611003436.1 |
Claims
1. A high-hardenability, medium-carbon, low-alloy round steel for
fasteners, wherein its chemical constituents by mass percentage are
as follows: C: 0.36.about.0.44%, Si: 0.15.about.0.40%, Mn:
0.80.about.1.00%, Cr: 1.00.about.1.15%, Mo: 0.05.about.0.25%, Ni:
0.05.about.0.25%, Cu: 0.05.about.0.25%, Al: 0.015.about.0.050%, B:
0.0010.about.0.0050%, Ti: 0.020.about.0.050%, the balance is Fe and
unavoidable impurity elements; the maximum diameter of the round
steel is 65 mm, after quenching and tempering treatment, its
mechanical structure and performance meet the requirements of ISO
898-1 standard or other equivalent standards for grade 10.9
fasteners, specific requirements are as follows: quenched
martensite content is z,27 90%, after quenching and tempering
treatment, when a tensile sample is tested, the diameter of a
tensioned part of the sample is 75% of nominal size, yield strength
of the round steel Rp0.2 is z,27 3940 MPa, tensile strength Rm is
1040.about.1140 MPa, elongation is z,27 9% , reduction of area at
fracture is z,27 48%, Charpy impact energy measured at -20.degree.
C. is 27 J when a Akv2 impact sample is taken at 1/2 radius, HV0.3
hardness of the whole cross-section of round steel is 320.about.380
HV, difference of the hardness of the whole cross-section is within
30 HV.
2. A method of manufacturing the high-hardenability, medium-carbon,
low-alloy round steel for fasteners according to claim 1, wherein
the raw materials are processed, in sequence, by converter smelting
or electric furnace smelting, LF refining, RH/VD degassing to
obtain molten steel, feeding Ti wires and ferroboron after LF
refining; the molten steel is casted into a continuous casting
billet by adopting low superheat degree of 15.about.40.degree. C.
and under a full argon protection, the continuous casting billet is
fed warmly at a temperature of 300.about.600.degree. C. or
delivered to a slow-cooling pit and is slowly cooled for 32 hours
or more, and then is taken out of the pit; the continuous casting
billet is heated to 1200.about.1250.degree. C. and kept warm for
3.about.10 hours in the furnace, and then is taken out of the
furnace; after high-pressure water descaling, the continuous
casting billet is rolled in to round steel bar at a temperature of
1100.about.1150.degree. C.; the bar is processed by means of
quenching and tempering treatment in a continuous furnace thereby
to obtain quenched and tempered round steel; the quenched and
tempered round steel is able to be directly used in processing
fasteners which meet ISO 898-1 standard for grade 10.9, such as
bolts and the like; the above quenching and tempering treatment
includes quenching and tempering, the treatment can be performed in
a roller hearth continuous furnace or in induction lines, when in a
roller hearth continuous furnace, the quenching heating temperature
is 840.about.880.degree. C., the time in furnace is 60.about.360
min, the bar is water quenched by quenching ring; the tempering
heating temperature is 530.about.620.degree. C., the time in
furnace is 300.about.600 min, the bar is air-cooled outside the
furnace to room temperature or is water-cooled to room temperature;
when in induction lines, the quenching heating temperature is
880.about.950.degree. C., the time in furnace is 3.about.10 min,
the bar is water quenched by quenching ring; the tempering heating
temperature is 600.about.700.degree. C., the time in furnace is
3.about.10 min, the bar is air-cooled outside the furnace to room
temperature or is water-cooled to room temperature.
Description
TECHNICAL FIELD
[0001] The present invention relates to a field of manufacturing
special round steel, and specially relates to a high-hardenability,
medium-carbon, low-alloy round steel, which satisfies the
mechanical performance requirements of O65 mm fasteners after
quenching and tempering treatment, and the manufacturing method
thereof.
BACKGROUND ART
[0002] At present market, the fasteners are manufactured mostly
according to the requirements of standard ISO898-1: Mechanical
properties of fasteners--Part 1: Bolts, screws and studs. The table
3 of this standard puts forward very strict requirements of
mechanical and physical performance for fasteners, wherein the
difficulties are: {circle around (1)} after quenching, the
martensite structure in core of the steel should be 90% or more;
{circle around (2)} on the basis of satisfying the strength and the
hardness in each strength grades, the difference of HV 0.3 hardness
between surface and core should be less than 30 HV; {circle around
(3)} taking a whole tensile sample whose tensioned part has a
diameter of 75% to the diameter of fastener for testing the
mechanical performance of strength, elongation, reduction of
fracture and etc.; {circle around (4)} on the basis of satisfying a
high-grade strength and plastic properties, the impact energy Akv 2
measured at -20.degree. C. is equal to or more than 27 J. It
requires that the steel for fasteners has good hardenability, and
sufficient depth of quenched zone can be obtained in quenching, so
as to ensure martensite percentage, thereby to ensure the
uniformity of structure and hardness of the finished product to
match the strength and toughness. Bigger is the size of the
fastener, requirements of hardenability of the steel is higher and
the difficulty of manufacturing is greater. At present, the steels
such as 32CrB4 or 42CrMo etc. are used to manufacture fasteners of
diameter less than 45 mm, the steels such as 40CrNiMo, 4140MOD etc.
with higher contents of noble metals like Mo and Ni are used to
manufacture fasteners of diameter equal to or more than 45 mm.
Otherwise, the core quenched structure, the hardness distribution
in transversal cross-section, and the strength and toughness would
not satisfy the matching requirements.
DISCLOSURE OF INVENTION
[0003] Aiming at above technical requirements, the technical
problem to be solved in the present invention is to provide a round
steel of CrB class with medium carbon and low alloy, to replace the
steels such as 40CrNiMo, 34CrNiMo6 etc. having high content of Mo
and high content of Ni. It can manufacture fasteners with size up
to 65 mm and with mechanical performance satisfying standard of ISO
898-1, and achieve the purpose of reducing the cost.
[0004] The solution in the present invention is as follows: a
high-hardenability, medium-carbon, low-alloy round steel for
fasteners, wherein its chemical constituents by mass percentage are
as follows: C: 0.36.about.0.44%, Si: 0.15.about.0.40%, Mn:
0.80.about.1.00%, Cr: 1.00.about.1.15%, Mo: 0.05.about.0.25%, Ni:
0.05.about.0.25%, Cu: 0.05.about.0.25%, Al: 0.015.about.0.050%, B:
0.0010.about.0.0050%, Ti: 0.020.about.0.050%, the balance is Fe and
unavoidable impurity elements. The maximum diameter of the round
steel is 65 mm, after quenching and tempering treatment, its
mechanical structure and performance meet the requirements of ISO
898-1 standard or other equivalent standards for grade 10.9
fasteners, specific requirements are as follows: quenched
martensite content is 90% after quenching and tempering treatment,
when a tensile sample is tested, the diameter of a tensioned part
of the sample is 75% of nominal size, yield strength of the round
steel Rp0.2 is 940 MPa, tensile strength Rm is 1040.about.1140 MPa,
elongation is z,28 9% , reduction of area at fracture is z,28 48%
Charpy impact energy measured at -20.degree. C. is z,28 27 J when a
Akv2 impact sample is taken at 1/2 radius, HV0.3 hardness of the
whole cross-section of round steel is 320.about.380 HV, difference
of the hardness of the whole cross-section is within 30 HV.
[0005] The chemical constituents of round steel in the present
invention are determined by this way:
[0006] C is used for improving hardenability, strength and
hardness, but it decreases plasticity and toughness, and increases
ductile-brittle transition temperature. Medium carbon content is
applied in the present invention. The C content is controlled to be
0.36.about.0.44%.
[0007] Si is a deoxidizing element in steel, and is used for
increasing the strength by solid solution strengthening. When Si
content is lower than 0.1%, the deoxidation effect is poor, when Si
content is too high, the toughness is reduced. The Si content is
controlled to be 0.15.about.0.40%.
[0008] Mn is an element for improving hardenability of steel, and
has effect of solid solution strengthening to increase the
strength. But excessive Mn content is easy to reduce the plasticity
and toughness of steel. In order to match the strength, plasticity
and toughness, the Mn content is controlled to be
0.80.about.1.00%
[0009] Cr and Mo are used for improving hardenability and improving
the strength and toughness of material, Mo also has effects of
reducing ductile-brittle transition temperature, inhibiting
tempering brittleness, improving precipitation strengthening of
carbon and niobium nitride, inhibiting massive ferrite, and
hindering P segregation. However, Mo is a noble metal element,
excessive addition increases the manufacture cost. So the Cr
content is controlled to be 1.00.about.1.15%, Mo content is
controlled to be 0.05.about.0.25%.
[0010] Ni is an element for improving hardenability of steel and
obviously improving the toughness under low temperature, it has
good influence on impact toughness and ductile-brittle transition
temperature. In addition, Ni is also a noble metal element,
excessive addition increases the manufacture cost. Considering all
the above, the Ni content is controlled to be 0.05.about.0.25%,
helping to achieve the best cost performance.
[0011] Cu can improve hardenability of steel. However, excessive
addition of Cu is easy to cause copper brittleness, and worsens the
surface property. The Cu content of the present invention is
0.05.about.0.25%.
[0012] B is an element which most obviously improves the
hardenability of steel, and plays an important role in the present
invention in replacing noble metals Mo and Ni, thereby to reduce
cost. The B content of the present invention is controlled to be
0.0010.about.0.0050%.
[0013] Ti can mainly fixate nitrogen. Ti can combine with N in the
early stage of solidifying continuous casting billet, and forms TiN
particles in the grains, thereby to reduce the reactions between B
and N, to fully exert the effect of B on improving hardenability.
The Ti content is controlled to be 0.020.about.0.050%.
[0014] Al can mainly fixate nitrogen and deoxidize. The AlN formed
by the combination of Al and N can effectively refine grains.
However, excessive addition can destroy the toughness of steel, and
worsens the casting performance of molten steel. The Al content of
the present invention is controlled to be 0.015.about.0.050%.
[0015] A further object of present invention is to provide the
method of manufacturing the high-hardenability, medium-carbon,
low-alloy round steel for fasteners. Special steps are as follows:
the raw materials are processed, in sequence, by converter smelting
or electric furnace smelting, LF refining, RH/VD degassing to
obtain molten steel, feeding Ti wires and ferroboron after LF
refining; the molten steel is casted into a continuous casting
billet by adopting low superheat degree of 15.about.40.degree. C.
and under a full argon protection, the continuous casting billet is
fed warmly at a temperature of 300.about.600.degree. C. or
delivered to a slow-cooling pit and is slowly cooled for 32 hours
or more, and then is taken out of the pit; the continuous casting
billet is heated to 1200.about.1250.degree. C. and kept warm for
3.about.10 hours in the furnace, and then is taken out of the
furnace; after high-pressure water descaling, the continuous
casting billet is rolled in to round steel bar at a temperature of
1100.about.1150.degree. C.; the bar is processed by means of
quenching and tempering treatment in a continuous furnace thereby
to obtain quenched and tempered round steel; the quenched and
tempered round steel is able to be directly used in processing
fasteners which meet ISO 898-1 standard for grade 10.9 , such as
bolts and the like.
[0016] Above quenching and tempering treatment includes quenching
and tempering, the treatment can be performed in a roller hearth
continuous furnace or in induction lines, when in a roller hearth
continuous furnace, the quenching heating temperature is
840.about.880.degree. C., the time in furnace is 60.about.360 min,
the bar is water quenched by quenching ring; the tempering heating
temperature is 530.about.620.degree. C., the time in furnace is
300.about.600 min, the bar is air-cooled outside the furnace to
room temperature or is water-cooled to room temperature; when in
induction lines, the quenching heating temperature is
880.about.950.degree. C., the time in furnace is 3.about.10 min,
the bar is water quenched by quenching ring; the tempering heating
temperature is 600.about.700.degree. C., the time in furnace is
3.about.10 min, the bar is air-cooled outside the furnace to room
temperature or is water-cooled to room temperature.
[0017] Compared with prior arts, the advantages of present
invention focus on: taking a very small amount of alloy elements B
and Ti to replace parts of noble metal elements Mo and Ni so as to
improve hardenability of steel bar, manufacturing the fasteners
with maximum diameter up to 65 mm, and on the basis of satisfying
the mechanical and physical requirements of quenched martensite
content in steel core being more than 90%, difference of the
hardness of the whole cross-section being within 30 HV, impact
energy measured at -20.degree. C. being z,28 27 J in standard ISO
898-1, obviously reducing the manufacture cost of alloy raw
material.
BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS
[0018] FIG. 1 is quenched and tempered core structure (100.times.)
of embodiment 1;
[0019] FIG. 2 is quenched and tempered core structure (100.times.)
of embodiment 2;
[0020] FIG. 3 is quenched and tempered core structure (100.times.)
of embodiment 3.
MODE(S) FOR CARRYING OUT THE INVENTION
[0021] The present invention is further described in details with
reference to embodiments.
Embodiment 1
[0022] The diameter of the steel for fastener relating to the
present embodiment is 64 mm, and the steel is processed with heat
treatment according to the requirements of 10.9 grade fastener, the
chemical constituents by mass percentage are as follows: C: 0.42%,
Si: 0.25%, Mn: 0.95%, Cr: 1.10%, Mo: 0.10%, Ni: 0.12%, Cu: 0.12%,
Al: 0.018%, B: 0.0020%, Ti: 0.025%, the balance is Fe and
unavoidable impurity elements.
[0023] The manufacturing processes are as follows: the main raw
materials are processed, in sequence, by electric furnace smelting,
LF refining, VD degassing to obtain molten steel, feeding Ti wires
and ferroboron after LF refining; the molten steel is casted into a
continuous casting billet by adopting low superheat degree of
15.about.30.degree. C. and under a full argon protection, the
continuous casting billet is slowly cooled for 32 hours; the
continuous casting billet is heated to 1250.degree. C. and kept
warm for 4 hours in the furnace, and then is taken out of the
furnace; after high-pressure water descaling, the continuous
casting billet is rolled in to round steel bar at a temperature of
1150.degree. C.; in a roller hearth continuous furnace, the bar is
heated to 840.degree. C. for 3 hours for austenization, after
austenization, the bar is high-press water quenched by quenching
ring, and the bar is further heated to 620.degree. C. for 6 hours
for tempering, the bar is air-cooled outside the furnace to room
temperature. Comparison with the chemical constituents, the
mechanical performance and the metallographic structure of 40CrNiMo
steel which is usually used for manufacturing the fasteners with
large size, is shown in table 1, table 2 and FIG. 1. It can be seen
that Mo content and Ni content in the present embodiment are
greatly reduced, the noble metal addition is less and at the same
time the mechanical performance, the distribution of hardness in
transversal cross-section and the metallographic structure at the
core all satisfy the requirements of standard ISO 898-1.
TABLE-US-00001 TABLE 1 Comparison of chemical constituents between
CrB middle-carbon steel in Embodiment 1 and round steel in
Comparative Example 1 (wt %) C Si Mn Cr Mo Ni Cu Al Ti B
Comparative 0.40 0.25 0.70 0.78 0.18 1.30 0.03 0.022 0.003 0.0001
Example 1 Embodiment 1 0.42 0.25 0.95 1.10 0.10 0.12 0.12 0.018
0.025 0.0020
TABLE-US-00002 TABLE 2 Comparison of performance after quenching
and tempering treatment between bar in Embodiment 1 and round steel
in Comparative Example 1 Hardness Yield Tensile of Vickers hardness
of Strength Strength Reduction -20.degree. C. tempered transversal
cross section Rp0.2 Rm Elongation of Area Akv core HV0.3 Steel
Grade (MPa) (MPa) A % Z % J HRC Surface 1/2R Core Requirement 930
1040 9 48 27 30 + 1/2*C % 320-380 Comparative 1000 1100 13 52
62/56/60 55 354 348 342 Example 1 Embodiment 1 970 1050 11 49
42/43/38 53 335 332 328 .asterisk-pseud.take a whole sample for
measuring tensile properties; Vickers hardness of transversal cross
section: max-min .ltoreq. 30HV.
Embodiment 2
[0024] The diameter of the steel for fastener relating to the
present embodiment is 54 mm, and the steel is processed with heat
treatment according to the requirements of 10.9 grade fastener, the
chemical constituents by mass percentage are as follows: C: 0.37%,
Si: 0.22%, Mn: 0.95%, Cr: 1.10%, Mo: 0.08%, Ni: 0.10%, Cu: 0.10%,
Al: 0.022%, B: 0.0023%, Ti: 0.028%, the balance is Fe and
unavoidable impurity elements.
[0025] Above round steel is processed, in sequence, by electric
furnace smelting, LF refining, VD degassing to obtain molten steel,
feeding Ti wires and ferroboron after LF refining; the molten steel
is casted into a continuous casting billet by adopting low
superheat degree of 15.about.30.degree. C. and under a full argon
protection, the continuous casting billet is fed warmly at a
temperature of 400.degree. C.; the continuous casting billet is
heated to 1200.degree. C. and kept warm for 4 hours in the furnace,
and then is taken out of the furnace; after high-pressure water
descaling, the continuous casting billet is rolled in to round
steel bar at a temperature of 1100.degree. C.; in induction lines,
the bar is heated to 880.degree. C. for 5 minutes for
austenization, after austenization, the bar is quenched by
quenching ring, and the bar is further heated to 550.degree. C. for
5 hours for tempering in a roller hearth continuous furnace, the
bar is air-cooled outside the furnace to room temperature.
Comparison with the chemical constituents, the mechanical
performance and the metallographic structure of the conventional
40CrNiMo steel, is shown in table 3, table 4 and FIG. 2. It can be
seen that Mo content and Ni content in the present embodiment are
greatly reduced, and at the same time the mechanical performance,
the distribution of hardness in transversal cross-section and the
metallographic structure at the core all satisfy the requirements
of standard ISO 898-1.
TABLE-US-00003 TABLE 3 Comparison of chemical constituents between
CrB middle-carbon steel in Embodiment 2 and round steel in
Comparative Example 2 (wt %) C Si Mn Cr Mo Ni Cu Al Ti B
Comparative 0.41 0.23 0.72 0.80 0.18 1.31 0.05 0.028 0.003 0.0001
Example 2 Embodiment 2 0.37 0.22 0.95 1.10 0.08 0.10 0.10 0.022
0.028 0.0023
TABLE-US-00004 TABLE 4 Comparison of performance after quenching
and tempering treatment between bar in Embodiment 2 and round steel
in Comparative Example 2 Hardness of Vickers hardness of Yield
Tensile Reduction -20.degree. C. tempered transversal cross
Strength Strength Elongation of Area Akv core section HV0.3 Steel
Grade Rp0.2(MPa) Rm(MPa) A % Z % J HRC Surface 1/2R Core
Requirements 930 1040 9 48 27 30 + 1/2*C % 320-380 Comparative 1020
1120 14 55 65/60/68 55 350 348 345 Example 2 Embodiment 980 1060 11
51 47/47/45 52 342 337 335 2 .asterisk-pseud.take a whole sample
for measuring tensile properties; Vickers hardness of transversal
cross section: max-min .ltoreq. 30HV.
Embodiment 3
[0026] The diameter of the steel for fastener relating to present
embodiment is 48 mm, and the steel is processed with heat treatment
according to the requirements of 8.8 grade fastener, the chemical
constituents by mass percentage are as follows: C: 0.36%, Si:
0.21%, Mn: 0.92%, Cr: 1.08%, Mo: 0.08%, Ni: 0.06%, Cu: 0.08%, Al:
0.023%, B: 0.0025%, Ti: 0.026%, the balance is Fe and unavoidable
impurity elements.
[0027] Above round steel is processed, in sequence, by KR
pre-treatment, converter smelting, LF refining, RH degassing to
obtain molten steel, feeding Ti wires and ferroboron after LF
refining; the molten steel is casted into a continuous casting
billet by adopting low superheat degree of 15.about.30.degree. C.
and under a full argon protection, the continuous casting billet is
fed warmly at a temperature of 400.degree. C.; the continuous
casting billet is heated to 1200.degree. C. and kept warm for 4
hours in the furnace, and then is taken out of the furnace; after
high-pressure water descaling, the continuous casting billet is
rolled in to round steel bar at a temperature of 1100.degree. C.;
in continuous induction lines, the bar is heated to 950.degree. C.
for 4 minutes for austenization, after austenization, the bar is
quenched by quenching ring, and the bar is further heated to
700.degree. C. for 4 minutes for tempering, the bar is air-cooled
outside the furnace. Comparison with the chemical constituents, the
mechanical performance and the metallographic structure of the
conventional 4140MOD steel, is shown in table 5, table 6 and FIG.
3. It can be seen that Mo content and Ni content in the present
embodiment are greatly reduced, and at the same time the mechanical
performance, the distribution of hardness in transversal
cross-section and the metallographic structure at the core all
satisfy the requirements of standard ISO 898-1.
TABLE-US-00005 TABLE 5 Comparison of chemical constituents between
CrB middle-carbon steel in Embodiment 3 and 40CrNiMo round steel in
Comparative Example 3 (wt %) C Si Mn Cr Mo Ni Cu Al Ti B
Comparative 0.41 0.25 0.95 1.05 0.23 1.31 0.05 0.028 0.003 0.0001
Example 3 Embodiment 3 0.36 0.21 0.92 1.08 0.08 0.06 0.08 0.023
0.026 0.0025
TABLE-US-00006 TABLE 6 Comparison of performance after quenching
and tempering treatment between Embodiment 3 and 40CrNiMo round
steel Yield Tensile Hardness of Vickers hardness of Strength
Strength Reduction -20.degree. C. tempered transversal cross Rp0.2
Rm Elongation of Area Akv core section HV0.3 Steel Grade (MPa)
(MPa) A % Z % J HRC Surface 1/2R Core Requirements 660 830 12 52 27
30 + 1/2*C % 255-335 Comparative 790 900 18 60 100/98/90 56 288 283
279 Example 3 Embodiment 3 760 880 15 56 78/72/65 52 280 280 270
.asterisk-pseud.take a whole sample for measuring tensile
properties; Vickers hardness of transversal cross section: max-min
.ltoreq. 30HV.
[0028] Besides above embodiments, the present invention further
includes other embodiments, and any technical solution formed by
equivalent transformation or equivalent substitution shall fall
within the protection scope of claims of the present invention.
* * * * *