U.S. patent application number 14/346740 was filed with the patent office on 2014-10-02 for stainless steel for cutlery and method of manufacturing the same.
This patent application is currently assigned to HITACHI METALS, LTD.. The applicant listed for this patent is Ichiro Kishigami, Tomonori Ueno, Goh Yoshiyama. Invention is credited to Ichiro Kishigami, Tomonori Ueno, Goh Yoshiyama.
Application Number | 20140294662 14/346740 |
Document ID | / |
Family ID | 47995270 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140294662 |
Kind Code |
A1 |
Ueno; Tomonori ; et
al. |
October 2, 2014 |
STAINLESS STEEL FOR CUTLERY AND METHOD OF MANUFACTURING THE
SAME
Abstract
The present invention has the ultimate purpose of obtaining
cutlery having marked characteristics such as high hardness and
high toughness, and provides an intermediate material, an annealed
material, and a cold-rolled steel strip for stainless steel for
cutlery, and a method for manufacturing them to achieve the
purpose. Provided is an intermediate material for stainless steel
for cutlery, the intermediate material being a material after hot
rolling but before annealing, having a composition, in terms of %
by mass, of from 0.46 to 0.72% C, from 0.15 to 0.55% Si, from 0.45
to 1.00% Mn, from 12.5 to 13.9% Cr, from 0 to 1.5% Mo, from 0 to
0.012% B, and the balance being Fe and impurities; and wherein a
ratio of a diffraction peak area from an fcc phase (a sum total of
diffraction peak areas from (200) plane, (220) plane, and (311)
plane) to a diffraction peak area from a bcc phase (a sum total of
diffraction peak areas from (200) plane and (211) plane) (the
diffraction peak area from the fcc phase/the diffraction peak area
from the bcc phase) is 30 or less in an X-ray diffraction of a
vertical section.
Inventors: |
Ueno; Tomonori; (Yasugi-shi,
JP) ; Yoshiyama; Goh; (Yasugi-shi, JP) ;
Kishigami; Ichiro; (Yasugi-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ueno; Tomonori
Yoshiyama; Goh
Kishigami; Ichiro |
Yasugi-shi
Yasugi-shi
Yasugi-shi |
|
JP
JP
JP |
|
|
Assignee: |
HITACHI METALS, LTD.
Minato-ku, Tokyo
JP
|
Family ID: |
47995270 |
Appl. No.: |
14/346740 |
Filed: |
September 14, 2012 |
PCT Filed: |
September 14, 2012 |
PCT NO: |
PCT/JP2012/073621 |
371 Date: |
March 24, 2014 |
Current U.S.
Class: |
420/64 ; 148/609;
72/202 |
Current CPC
Class: |
C22C 38/04 20130101;
C21D 9/18 20130101; C21D 9/46 20130101; C22C 38/24 20130101; C22C
38/28 20130101; C22C 38/001 20130101; C22C 38/50 20130101; C22C
38/02 20130101; C21D 8/02 20130101; C21D 8/0263 20130101; C22C
38/32 20130101; C22C 38/54 20130101; C22C 38/46 20130101; B21B 3/02
20130101; C22C 38/44 20130101; C22C 38/22 20130101; C22C 38/002
20130101; C22C 38/06 20130101 |
Class at
Publication: |
420/64 ; 148/609;
72/202 |
International
Class: |
C22C 38/54 20060101
C22C038/54; C22C 38/50 20060101 C22C038/50; C22C 38/46 20060101
C22C038/46; B21B 3/02 20060101 B21B003/02; C22C 38/06 20060101
C22C038/06; C22C 38/04 20060101 C22C038/04; C22C 38/02 20060101
C22C038/02; C22C 38/00 20060101 C22C038/00; C21D 8/02 20060101
C21D008/02; C22C 38/44 20060101 C22C038/44 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 26, 2011 |
JP |
2011-208430 |
Claims
1. An intermediate material for stainless steel for cutlery, the
intermediate material being a material after hot rolling but before
annealing, having a composition, in terms of % by mass, of from
0.46 to 0.72% C, from 0.15 to 0.55% Si, from 0.45 to 1.00% Mn, from
12.5 to 13.9% Cr, from 0 to 1.5% Mo, from 0 to 0.012% B, and the
balance being Fe and impurities; and wherein a ratio of a
diffraction peak area from an fcc phase (a sum total of diffraction
peak areas from (200) plane, (220) plane, and (311) plane) to a
diffraction peak area from a bcc phase (a sum total of diffraction
peak areas from (200) plane and (211) plane) (the diffraction peak
area from the fcc phase/the diffraction peak area from the bee
phase) is 30 or less in an X-ray diffraction of a vertical
section.
2. The intermediate material for stainless steel for cutlery
according to claim 1, wherein the content of B is from 0.0005 to
0.0050%.
3. A method of manufacturing an intermediate material for stainless
steel for cutlery, the intermediate material being a material after
hot rolling but before annealing, the method comprising: heating a
material, having a composition, in terms of % by mass, of from 0.46
to 0.72% C, from 0.15 to 0.55% Si, from 0.45 to 1.00% Mn, from 12.5
to 13.9% Cr, from 0 to 1.5% Mo, from 0 to 0.012% B, and the balance
being Fe and impurities, to from 1100 to 1250.degree. C., and hot
rolling the material at a hot rolling end temperature of from 700
to 1000.degree. C.; thereby manufacturing the intermediate
material, wherein a ratio of a diffraction peak area from an fcc
phase (a sum total of diffraction peak areas from (200) plane,
(220) plane, and (311) plane) to a diffraction peak area from a bcc
phase (a sum total of diffraction peak areas from (200) plane and
(211) plane) (the diffraction peak area from the fcc phase/the
diffraction peak area from the bcc phase) is 30 or less in an X-ray
diffraction of a vertical section.
4. The method of manufacturing an intermediate material for
stainless steel for cutlery according to claim 3, wherein the
content of is from 0.0005 to 0.0050%.
5. A method of manufacturing an annealed material for stainless
steel for cutlery, the method comprising subjecting the
intermediate material for stainless steel for cutlery manufactured
by the method according to claim 3 to annealing at from 800 to
860.degree. C. for from 1 to 100 hours.
6. A method of manufacturing a cold-rolled steel strip for
stainless steel for cutlery, the method comprising subjecting the
annealed material for stainless steel for cutlery manufactured by
the method according to claim 5 to cold rolling and annealing,
thereby manufacturing a cold-rolled steel strip with a thickness of
less than 1.0 mm.
7. A method of manufacturing an annealed material for stainless
steel for cutlery, the method comprising subjecting the
intermediate material for stainless steel for cutlery manufactured
by the method according to claim 4 to annealing at from 800 to
860.degree. C. for from 1 to 100 hours.
8. A method of manufacturing a cold-rolled steel strip for
stainless steel for cutlery, the method comprising subjecting the
annealed material for stainless steel for cutlery manufactured by
the method according to claim 7 to cold rolling and annealing,
thereby manufacturing a cold-rolled steel strip with a thickness of
less than 1.0 mm.
Description
TECHNICAL FIELD
[0001] The present invention relates to stainless steel for cutlery
such as razors, cutters, kitchen knives, knives, and a method of
manufacturing the same.
BACKGROUND ART
[0002] Martensitic stainless steel has been widely used as the
material for cutlery such as razors, cutters, kitchen knives, and
knives. In particular, a strip of high carbon martensitic stainless
steel containing about 13% by mass of Cr and about 0.65% by mass of
C is known to be an optimum material for a razor. The high carbon
martensitic stainless steel (hereinafter referred to as "stainless
steel for cutlery") for these applications is usually used after
being subjected to hardening and tempering, and is required to have
high hardness and high toughness during use.
[0003] Stainless steel for cutlery is usually manufactured through
the following manufacturing process.
[0004] Firstly, a raw material is melted and cast to make a
material. Secondly, the material is hot-rolled to make an
intermediate material. The material may be subjected to a blooming
process such as hot forging or hot rolling.
[0005] Subsequently, the intermediate material is subjected to a
first annealing to make an annealed material. The annealed material
is subjected to cold rolling followed by annealing for removing
strain, which are repeated if necessary, thereby manufacturing a
cold-rolled steel strip having the intended thickness. The
cold-rolled steel strip is subjected to hardening and tempering,
thus obtaining stainless steel for cutlery.
[0006] Furthermore, the stainless steel for cutlery is subjected to
processing processes such as sharpening and cutting, and thus
making an end product. In usual cases, stainless steel for cutlery
is dealt on the market in the form of either an annealed material
or a cold-rolled steel strip.
[0007] For the above-described stainless steel for cutlery, various
proposals have been made as the techniques for achieving high
hardness and high toughness. For example, as a typical example,
Japanese Patent Application Laid-Open (JP-A) No. H05-039547 (Patent
Document 1), which is proposed by the present applicant, proposes
the increase in the carbide density of the cold-rolled steel strip
before hardening and tempering for stainless steel for cutlery.
According to this proposal, short time hardenability of the
cold-rolled steel strip is markedly improved, and the stainless
steel for cutlery after hardening improves hardness, and marks
sharpness of a razor.
PRIOR ART DOCUMENT
Patent Document
[0008] Patent Document 1: JP-A No. H05-039547
SUMMARY OF INVENTION
Technical Problem
[0009] As described above, various proposals have been made for the
techniques focusing the properties of the cold-rolled steel strip
before hardening and tempering for stainless steel for cutlery.
[0010] However, there is almost no study focusing on the properties
of the intermediate material after hot rolling but before
annealing, and the relationship between the characteristics of the
annealed material for stainless steel for cutlery after annealing
but before hardening, and the characteristics of the cold-rolled
steel strip, which are distributed in the form of half-finished
products, and the properties of the intermediate material, are not
thoroughly clarified.
[0011] Therefore, because of poor findings regarding the ideal
properties of the above-described intermediate material, there is a
problem that the excellent potential of stainless steel for cutlery
cannot be thoroughly exploited, and it was difficult to both of
high hardness and high toughness. In addition, even if the
properties of the intermediate material are varied by some kind of
factor, there was no known means for detecting the defect in the
stage of making the intermediate material for preventing the
occurrence of quality failure in the following processes.
Therefore, if any defect is not found in the stage of the
intermediate material and the decrease in hardness or toughness is
first revealed in the following process, the processes completed
until then come to nothing, and the cost of the product
increases.
[0012] The invention has a final purpose of efficiently obtaining
cutlery having marked characteristics such as high hardness and
high toughness by optimizing the intermediate material which
influences the structure of stainless steel for cutlery before
hardening, and provides an intermediate material, an annealed
material, and a cold-rolled steel strip for stainless steel for
cutlery, and a method of manufacture them to achieve the
purpose.
Solution to Problem
[0013] The inventors studied the properties of stainless steel for
cutlery, focusing on the form of carbides as the factor influencing
the hardness and toughness.
[0014] According to their finding, in a case in which the
distribution of carbides is not uniform because carbides are
maldistributed in the structure of the cold-rolled steel strip for
stainless steel for cutlery, or carbides having coarse crystal
grains and those having fine crystal grains are mixed, the
cold-rolled steel strip has lower hardness and toughness after
hardening and tempering in comparison with that containing
uniformly distributed carbides.
[0015] According to another finding, of the properties of the
intermediate material for stainless steel for cutlery, in
particular the composition and the amount of an fcc phase
influences the distribution of carbides in the structure of the
cold-rolled steel strip obtained from the intermediate
material.
[0016] Furthermore, they have found that the optimization of the
composition of the intermediate material for stainless steel for
cutlery and control of the amount of the fcc phase makes the
distribution of carbides in the cold-rolled steel strip uniform,
and markedly improves the characteristics of the cutlery as the end
product, and thus have accomplished the invention.
[0017] More specifically, an aspect of the invention is an
intermediate material for stainless steel for cutlery, the
intermediate material being a material after hot rolling but before
annealing, having a composition, in terms of % by mass, of from
0.46 to 0.72% C, from 0.15 to 0.55% Si, from 0.45 to 1.00% Mn, from
12.5 to 13.9% Cr, from 0 to 1.5% Mo, from 0 to 0.012% B, and the
balance being Fe and impurities; and wherein a ratio of a
diffraction peak area from an fcc phase (a sum total of diffraction
peak areas from (200) plane, (220) plane, and (311) plane) to a
diffraction peak area from a bcc phase (a sum total of diffraction
peak areas from (200) plane and (211) plane) (the diffraction peak
area from the fcc phase/the diffraction peak area from the bcc
phase) is 30 or less in an X-ray diffraction of a vertical
section.
[0018] The content of B is preferably from 0.0005 to 0.0050%.
[0019] Another aspect of the invention is a method of manufacturing
an intermediate material for stainless steel for cutlery, the
intermediate material being a material after hot rolling but before
annealing, the method including: heating a material, having a
composition, in terms of % by mass, of from 0.46 to 0.72% C, from
0.15 to 0.55% Si, from 0.45 to 1.00% Mn, from 12.5 to 13.9% Cr,
from 0 to 1.5% Mo, from 0 to 0.012% B, and the balance being Fe and
impurities, to from 1100 to 1250.degree. C., and hot rolling the
material at a hot rolling end temperature of from 700 to
1000.degree. C.; thereby manufacturing the intermediate material,
wherein a ratio of a diffraction peak area from an fcc phase (a sum
total of diffraction peak areas from (200) plane, (220) plane, and
(311) plane) to a diffraction peak area from a bcc phase (a sum
total of diffraction peak areas from (200) plane and (211) plane)
(the diffraction peak area from the fcc phase/the diffraction peak
area from the bcc phase) is 30 or less in an X-ray diffraction of a
vertical section.
[0020] Another aspect of the invention is a method of manufacturing
an annealed material for stainless steel for cutlery, including the
above-described hot rolling, followed by annealing at from 800 to
860.degree. C. for from 1 to 100 hours.
[0021] Another aspect of the invention is a method of manufacturing
a cold-rolled steel strip for stainless steel for cutlery,
including subjecting the above-described annealed material to cold
rolling and annealing, thereby manufacturing a cold-rolled steel
strip with a thickness less than 1.0 mm.
Advantageous Effects of Invention
[0022] Since the cutlery manufactured from the stainless steel for
cutlery of the invention has high hardness and high toughness, the
cutlery is particularly suitable for razors having a small
thickness. The invention also allows quality control not in the
stage of the end product but in the stage of the intermediate
material, whereby the occurrence of defects is prevented, and the
cost of manufacturing is reduced.
BRIEF DESCRIPTION OF DRAWINGS
[0023] FIG. 1 is a schematic view showing the position from which
the test piece is sampled, and the evaluated plane.
[0024] FIG. 2 is a photograph as a substitute of a drawing showing
an example of the metal structure of the intermediate material for
the stainless steel for cutlery of the invention.
[0025] FIG. 3 is a photograph as a substitute of a drawing showing
an example of the metal structure of the intermediate material for
the stainless steel for cutlery of a comparative example.
[0026] FIG. 4 is a photograph as a substitute of a drawing showing
an example of the metal structure of the intermediate material for
the stainless steel for cutlery of the invention.
[0027] FIG. 5 is a photograph as a substitute of a drawing showing
an example of the metal structure of the intermediate material for
the stainless steel for cutlery of a comparative example.
[0028] FIG. 6 is a photograph as a substitute of a drawing showing
an example of the metal structure of the intermediate material for
the stainless steel for cutlery of the invention.
[0029] FIG. 7 is a photograph as a substitute of a drawing showing
an example of the metal structure of the intermediate material for
the stainless steel for cutlery of the invention.
[0030] FIG. 8 is a photograph as a substitute of a drawing showing
an example of the metal structure of the annealed material for the
stainless steel for cutlery of the invention after
hardening-subzero-tempering.
[0031] FIG. 9 is a photograph as a substitute of a drawing showing
an example of the metal structure of the annealed material for the
stainless steel for cutlery of a comparative example after
hardening-subzero-tempering.
[0032] FIG. 10 is a photograph as a substitute of a drawing showing
an example of the metal structure of the annealed material for the
stainless steel for cutlery of the invention after
hardening-subzero-tempering.
[0033] FIG. 11 is a photograph as a substitute of a drawing showing
an example of the metal structure of the annealed material for the
stainless steel for cutlery of a comparative example after
hardening-subzero-tempering.
[0034] FIG. 12 is a photograph as a substitute of a drawing showing
an example of the metal structure of the annealed material for the
stainless steel for cutlery of the invention after
hardening-subzero-tempering.
[0035] FIG. 13 is a photograph as a substitute of a drawing showing
an example of the metal structure of the annealed material for the
stainless steel for cutlery of the invention after
hardening-subzero-tempering.
[0036] FIG. 14 is a photograph as a substitute of a drawing showing
an example of the metal structure of the cold-rolled steel strip
for the stainless steel for cutlery of the invention.
[0037] FIG. 15 is a photograph as a substitute of a drawing showing
an example of the metal structure of the cold-rolled steel strip
for the stainless steel for cutlery of the invention after
hardening-subzero-tempering.
[0038] FIG. 16 is a photograph as a substitute of a drawing showing
an example of the metal structure of the cold-rolled steel strip
for the stainless steel for cutlery of the invention.
[0039] FIG. 17 is a photograph as a substitute of a drawing showing
an example of the metal structure of the cold-rolled steel strip
for the stainless steel for cutlery of the invention after
hardening-subzero-tempering.
DESCRIPTION OF EMBODIMENTS
[0040] As described above, the invention is characterized in that
it optimizes the alloy composition which influences the form of
carbides, and controls the amount of the fcc phase in the
intermediate material before annealing, thereby achieving both of
high hardness and high toughness in the cutlery as the end
product.
[0041] Firstly, the alloy composition contributing to the basic
properties defined herein is described below. The content of the
respective elements are based on % by mass.
[0042] C: from 0.46 to 0.72%
[0043] The C content is from 0.46 to 0.72%, thereby achieving
sufficient hardness of cutlery, and minimizing the crystallization
of the eutectic carbide during casting and solidification. When the
C content is less than 0.46%, sufficient hardness of cutlery cannot
be achieved. When the C content is more than 0.72%, the amount of
crystallization of the eutectic carbide increases because of the
balance with the Cr amount, which can cause blade chipping during
sharpening. The lower limit of the C content is preferably 0.50%,
and more preferably, 0.65%. The upper limit of the C content is
preferably 0.70%.
[0044] Si: from 0.15 to 0.55%
[0045] Si is added as a deoxidizing agent for smelting. In order to
achieve sufficient deoxidizing effect, the residual amount of Si
would be 0.15% or more. When the Si content is more than 0.55%, the
amount of inclusion increases, and can cause blade chipping during
sharpening. Therefore, the Si content is from 0.15 to 0.55%. In
addition, Si increases the tempering softening resistance. When Si
is added at a proportion of 0.20% or more, sufficient hardness of
cutlery will be achieved. Therefore, the lower limit of the Si
content is preferably 0.20%, and the upper limit of the Si content
is 0.35%.
[0046] Mn: from 0.45 to 1.00%
[0047] Mn is also added as a deoxidizing agent for smelting. In
order to achieve sufficient deoxidizing effect, the residual amount
of Mn would be 0.45% or more. When the Mn content is more than
1.00%, hot workability decreases. Therefore, the Mn content is from
0.45 to 1.00%. The lower limit of the Mn content is preferably
0.65%, and the upper limit of the Mn content is preferably
0.85%.
[0048] Cr: from 12.5 to 13.9%
[0049] The Cr content is from 12.5 to 13.9%, thereby achieving
sufficient corrosion resistance, and minimizing crystallization of
the eutectic carbide during casting and solidification. When the Cr
content is less than 12.5%, sufficient corrosion resistance of
stainless steel cannot be achieved, and when more than 13.9%,
crystallization of the eutectic carbide increases, and can cause
blade chipping during sharpening. The lower limit of the Cr amount
is preferably 13.0%. The upper limit of the Cr amount is preferably
13.6%.
[0050] Mo: from 0 to 1.5%
[0051] Mo is an element which improves corrosion resistance, so
that it may be added if necessary at a proportion of up to 1.5%.
However, when the Mo content is more than 1.5%, solid-solution
strengthening is increased, whereby deformation resistance is
increased, and hot workability is deteriorated. Therefore, the Mo
content is from 0 to 1.5%.
[0052] B: from 0 to 0.012%
[0053] B is an element effective at improving hardness and
toughness. In the invention, the toughness can be improved by
adjusting the below-described intensity ratio of X-ray, and the
improvement in the toughness is more reliably achieved by adding B
in advance. Therefore, B may be added at a proportion of up to
0.012%. However, when the B content is more than 0.012%, ductility
as hot workability markedly decreases. Therefore, the upper limit
of B is 0.012%. In order to more reliably improve hardness and
toughness by the addition of B, the B content is preferably from
0.0005 to 0.0050%, because the effect of B addition will be
insufficient when the B content is less than 0.0005%.
[0054] The remainder except for the above-described elements is
composed of Fe and impurities.
[0055] Typical impurity elements are P, S, Ni, W, V, Cu, Al, Ti, N,
and O. The contents of these elements are preferably controlled in
the following ranges. P.ltoreq.0.03%, S.ltoreq.0.005%,
Ni.ltoreq.0.15%, W.ltoreq.0.05%, V.ltoreq.0.2%, Cu.ltoreq.0.1%,
Al.ltoreq.0.01%, Ti.ltoreq.0.01%, N.ltoreq.0.05%, and
O.ltoreq.0.05%.
[0056] According to the study by the inventors, a ratio of a
diffraction peak area from an fcc phase (a sum total of diffraction
peak areas from (200) plane, (220) plane, and (311) plane) to a
diffraction peak area from a bcc phase (a sum total of diffraction
peak areas from (200) plane and (211) plane) (the diffraction peak
area from the fcc phase/the diffraction peak area from the bcc
phase) in an X-ray diffraction of the intermediate material for
stainless steel for cutlery having the above-described composition
is correlated with the toughness of a stainless steel for cutlery
obtained using the intermediate material through a manufacturing
process including annealing, cold rolling, hardening, and
tempering.
[0057] Specifically, when the ratio of the diffraction peak area
from the fcc phase to the diffraction peak area from the bcc phase
is more than 30 in the X-ray diffraction of the intermediate
material for stainless steel for cutlery, the amount of the fcc
phase becomes too much. As a result of this, when annealing is
performed after hot working, carbides having a high aspect ratio
tend to precipitate at the grain boundaries. As a result of this,
for example, toughness markedly decreases after hardening and
tempering performed before used as cutlery. Therefore, the ratio of
the diffraction peak area from the fcc phase to the diffraction
peak area from the bcc phase must be 30 or less. The ratio is
preferably 20 or less, and more preferably 5 or less. The lower
limit may be 0.
[0058] The reason why (200) plane, (220) plane, and (311) plane of
an fcc phase and (200) plane and (211) plane of a bcc phase are
chosen in the invention is that the above-described direction is a
major peak in an X-ray diffraction of the alloy system having the
composition defined in the invention. The peaks other than the
major peak has a low peak intensity, so that the ratio of the
diffraction peak area from the fcc phase to the diffraction peak
area from the bcc phase is not so influential. Therefore, the
measurement of the major peak will suffice.
[0059] Since the ratio of the diffraction peak area from the fcc
phase to the diffraction peak area from the bcc phase is correlated
with the actual volume ratio between these phases, it can be
evaluated as the value corresponding to the proportion of the
constituting phases.
[0060] In a case in which the above-described X-ray diffraction is
performed, a vertical section of the intermediate material is
irradiated with an X-ray. The term "vertical section" herein means,
as shown in FIG. 1, in the surfaces of the test piece sampled in
the vicinity of the center of the width of the intermediate
material for stainless steel for cutlery 1, the cross section
corresponding to the evaluated plane 2 shown in FIG. 1, more
specifically the cross section perpendicular to the width direction
of the intermediate material. The reason why the vertical section
is used for evaluation is that the rolled material has anisotropy
that is dependent on the rolling direction, so that the fixity of
the evaluated plane allows evaluation under the same conditions. In
addition, in a case in which made into cutlery, the vertical
section most often corresponds to the blade edge which is most
required to have both of high strength and toughness.
[0061] The test piece used for the X-ray diffraction is subjected
to mirror plane polishing on the vertical section, and further
subjected to electrolytic polishing so as to be adjusted to a test
piece for the X-ray diffraction. Subsequently, the electrolytically
polished plane is subjected to the X-ray diffraction, and then the
ratio of the sum total of diffraction peak areas of (200) plane,
(220) plane, and (311) plane of an fcc phase to the sum total of
diffraction peak areas of (200) plane and (211) plane of a bcc
phase is calculated. In a case in which the area of each
diffraction peak is determined, the area of the diffraction peak
from which the background strength is subtracted is determined.
[0062] The following section describes the methods of the invention
for manufacturing the intermediate material for stainless steel for
cutlery, the annealed material for stainless steel for cutlery, and
the cold-rolled steel strip for stainless steel for cutlery.
[0063] Firstly, a material for stainless steel for cutlery is
manufactured by melting and casting. Examples of the melting
include a vacuum melting, an atmospheric melting, a vacuum arc
remelting, and an electroslag remelting. Examples of the casting
include die casting and continuous casting. If necessary, the
material thus obtained may be subjected to homogenization heat
treatment. Furthermore, the material may be subjected to a blooming
process by hot forging or hot rolling.
[0064] Thereafter, the material is hot-rolled, thereby
manufacturing the intermediate material for stainless steel for
cutlery. In the hot rolling process, the intermediate material for
stainless steel for cutlery is manufactured by hot rolling at a
heating temperature of from 1100 to 1250.degree. C., wherein the
end temperature of hot rolling is from 700 to 1000.degree. C.
[0065] The reason why the heating temperature is from 1100 to
1250.degree. C. is that this temperature range has relatively low
deformation resistance and marked hot workability. When the
temperature is higher than 1250.degree. C., the temperature range
extremely decreases ductility, and tends to cause cracking during
hot working. When the temperature is lower than 1100.degree. C.,
deformation resistance of the material during hot rolling is high,
working with a high reduction ratio is difficult, so that reheating
must be repeated during hot working. The lower limit of the heating
temperature is preferably 1150.degree. C.
[0066] In the invention, the reason why the end temperature of hot
rolling is from 700 to 1000.degree. C. is that the phase and metal
structure are controlled in consideration of the hot workability
during manufacturing the intermediate material for stainless steel
for cutlery. If the end temperature of hot rolling is higher than
1000.degree. C., the ratio of the diffraction peak area from the
fcc phase to the diffraction peak area from the bcc phase is more
than 30 in X-ray diffraction, so that the amount of the fcc phase
becomes too much. If the amount of the fcc phase is too much,
carbides tend to precipitate at the grain boundaries of the fcc
phase during annealing performed thereafter. In addition, if the
end temperature is too high, residual strain is low, and the
crystal grain diameter tends to increase, so that carbides which
precipitate at the grain boundaries of the fcc phase during
annealing tend to form networks.
[0067] When the end temperature of hot rolling is lower than
700.degree. C., deformation resistance is high, and hot rolling is
difficult. Accordingly, the heating temperature in the hot rolling
process is from 1100 to 1250.degree. C., and the end temperature of
hot rolling is from 700 to 1000.degree. C. The lower limit of the
heating temperature is preferably 1150.degree. C., the upper limit
of the end temperature is preferably 950.degree. C., the upper
limit of the end temperature is more preferably 900.degree. C., and
the lower limit of the end temperature is preferably 750.degree.
C.
[0068] The intermediate material for stainless steel for cutlery
obtained by the hot rolling wherein the end temperature of hot
working is from 700 to 1000.degree. C. is preferably cooled with
water during passing the runout table, and/or during winding with a
winding device. The cooling is preferably performed with a water
flow which can cool the wound coil to 600.degree. C. or lower
within 5 minutes from the finishing point of the last pass of hot
rolling.
[0069] The reason for this is as follows: the wound coil is once
cooled on the surface exposed to atmosphere, but the temperature of
the once cooled coil surface is increased again by the heat
retained by the coil, so that the metal structures can differ
between the front end, center, and rear end of the coil. When the
temperature of a part of the wound coil exceeds 600.degree. C.
within 5 minutes from the finishing point of the final pass of hot
rolling, toughness of cutlery may decrease.
[0070] Therefore, it is preferred that the wound coil be cooled
with water to 600.degree. C. or lower within 5 minutes from the
finishing point of the final pass of hot rolling.
[0071] When the above-described hot rolling process is completed,
the intermediate material for stainless steel for cutlery having
the structure defined in the invention is obtained.
[0072] The intermediate material for stainless steel for cutlery
manufactured by the above-described manufacture method is subjected
to the first annealing at from 700.degree. C. to 860.degree. C. for
from 1 to 100 hours, and thus manufacturing an annealed material
for stainless steel for cutlery in which carbides are
precipitated.
[0073] Furthermore, in a case in which the annealed material for
stainless steel for cutlery is repeatedly subjected to cold rolling
and annealing, a cold-rolled steel strip for stainless steel for
cutlery having a thickness of 1.0 mm or less is obtained.
[0074] In a case in which the above-described cold-rolled steel
strip for stainless steel for cutlery is subjected to hardening,
tempering, and sharpening to make cutlery, if necessary, subzero
treatment may be performed after hardening, and surface coating may
be performed after tempering.
EXAMPLES
[0075] The invention is further described below with reference to
examples.
[0076] Six 10 kg steel ingots (materials), A to F, were made by
vacuum melting. The chemical compositions of the steel ingots A to
F are shown in Table 1.
TABLE-US-00001 TABLE 1 (mass %) Steel ingot C Si Mn Cr Mo B A 0.69
0.28 0.68 13.39 0.01 0.0001 B 0.70 0.29 0.73 13.29 0.01 0.0018 C
0.70 0.29 0.73 13.25 0.01 0.0102 D 0.58 0.39 0.85 13.29 0.89 0.0002
E 0.70 0.29 0.74 13.19 0.02 0.0005 F 0.50 0.45 0.82 13.42 1.27
0.0004 Steel ingot P S Ni W V Cu Al Ti [N] [O] A 0.024 0.0012 0.01
<0.01 0.02 <0.01 0.002 0.001 13 61 B 0.024 0.0015 0.01
<0.01 0.02 <0.01 0.002 0.001 12 34 C 0.022 0.0015 0.01
<0.01 0.02 <0.01 0.003 0.001 12 30 D 0.023 0.0016 0.01
<0.01 0.02 <0.01 0.005 0.001 13 28 E 0.021 0.0029 0.01 0.01
0.02 0.01 0.006 0.003 11 31 F 0.026 0.0029 0.01 0.01 0.01 <0.01
0.009 0.002 10 33 *1. The value of the element within [ ] is ppm.
*2. The balance other than the above elements is composed of Fe and
unavoidable impurities.
[0077] The materials to be hot-rolled having a width of 45 mm, a
length of 1000 mm, and a thickness of 20 mm were made from the
steel ingots A to D. These materials to be hot-rolled are subjected
to hot rolling under the following three types of conditions, and
the intermediate materials of stainless steel for cutlery were
obtained.
[0078] (1) Materials A to D: heated to 1180.degree. C., and
hot-rolled at an end temperature of 850.degree. C.
[0079] (2) Materials A to C: heated to 1200.degree. C., and
hot-rolled at an end temperature of 1050.degree. C.
[0080] (3) Materials E and F: heated to 1180.degree. C., and
hot-rolled at an end temperature of 900.degree. C.
[0081] The alloy C which had been hot-rolled under the conditions
(2) caused cracking during hot rolling, so that the operation was
suspended.
[0082] In this test, the length was insufficient for being wound
into a coil, but it was confirmed that the intermediate material
for stainless steel for cutlery was cooled to 600.degree. C. within
5 minutes from the finishing point of the final pass of hot
rolling.
[0083] A test piece was sampled in the vicinity of the center of
the width of each of the intermediate material for stainless steel
for cutlery. The sampling position of the test piece is the
position shown in FIG. 1, and the vertical section as the evaluated
plane 2 is subjected to an observation of a metal structure, an
X-ray diffraction, and an evaluation of hardness.
[0084] On the vertical section of the sampled test piece, the metal
structure was observed, and hardness and a ratio of a diffraction
peak area from an fcc phase to a diffraction peak area from a bcc
phase in an X-ray diffraction were measured. The test piece used
for the X-ray diffraction was subjected to mirror polishing on the
vertical section, and further subjected to electrolytic polishing
to be suitable as a test piece for the X-ray diffraction.
[0085] FIGS. 2 to 7 show the photographs as substitutes of drawings
showing the metal structure of the materials Nos. 1 to 6 whose
metal structures were observed. Table 2 shows hardness and the
ratio of the diffraction peak area from the fcc phase to the
diffraction peak area from the bcc phase in X-ray diffraction. In
addition, Table 3 shows the diffraction peak area from the fcc and
bcc phases for each plane index.
[0086] The observation of the metal structure was performed by
mirror-polishing the vertical section of the test piece, corroding
it in a ferric chloride aqueous solution, and then observing it
using a scanning electron microscope.
[0087] The ratio of the diffraction peak area from the fcc phase to
the diffraction peak area from the bcc phase in the X-ray
diffraction was determined by a ratio of a diffraction peak area
from an fcc phase (a sum total of diffraction peak areas from (200)
plane, (220) plane, and (311) plane) to a diffraction peak area
from a bcc phase (a sum total of diffraction peak areas from (200)
plane and (211) plane) (the diffraction peak area from the fcc
phase/the diffraction peak area from the bcc phase) in an X-ray
diffraction. The X-ray diffraction measurement used RINT2500V
manufactured by Rigaku Corporation, the radiation source used
Co.
[0088] The hardness was determined by polishing the sampled test
piece with #1200 abrasive paper, and then measuring a hardness
using Vickers hardness tester under a load of 98.1 (N). The
hardness is the average of five points.
TABLE-US-00002 TABLE 2 fcc/bcc Heating End ratio Hard- Mate-
temper- temper- (X-ray ness No. rial ature ature diffraction) (Hv)
Remarks 1 A 1180.degree. C. 850.degree. C. 5.0 385 The invention 2
A 1200.degree. C. 1050.degree. C. 31.3 324 Comparative example 3 B
1180.degree. C. 850.degree. C. 2.3 515 The invention 4 B
1200.degree. C. 1050.degree. C. 36.0 290 Comparative example 5 C
1180.degree. C. 850.degree. C. 1.2 575 The invention 6 D
1180.degree. C. 850.degree. C. 2.3 423 The invention 7 E
1180.degree. C. 900.degree. C. 15.9 422 The invention 8 F
1180.degree. C. 900.degree. C. 3.3 477 The invention
TABLE-US-00003 TABLE 3 fcc phase bcc phase diffraction peak area
Sum total diffraction peak area Sum total (arbitrary unit) of fcc
(arbitrary unit) of bcc No. (200) (220) (311) phase (200) (211)
phase fcc/bcc Remarks 1 50.0 13.6 19.7 83.3 5.4 11.2 16.7 5.0 The
invention 2 40.9 24.4 31.6 96.9 1.4 1.7 3.1 31.3 Comparative
example 3 34.8 14.0 20.8 69.7 9.1 21.2 30.3 2.3 The invention 4
50.9 16.9 29.5 97.3 0.8 1.9 2.7 36.0 Comparative example 5 29.2 9.7
15.6 54.5 15.3 30.2 45.5 1.2 The invention 6 34.8 14.0 20.8 69.7
9.1 21.1 30.3 2.3 The invention 7 48.8 18.6 26.7 94.1 1.5 4.4 5.9
15.9 The invention 8 29.5 21.7 25.4 76.6 7.6 15.8 23.4 3.3 The
invention
[0089] Subsequently, the intermediate materials of stainless steel
for cutlery shown in Table 2 were subjected to hardening, subzero
treatment, and tempering, which are performed before used as
cutlery.
[0090] An intermediate material for sampling a test piece having a
width of 40 mm, a length of 100 mm, and a thickness of 1 mm was cut
out from each of the intermediate material for stainless steel for
cutlery. At this time, the intermediate material for sampling a
test piece was cut out so as to contain the vicinity of the center
of the width of the rolled material shown in FIG. 1.
[0091] The intermediate material for sampling a test piece was
annealed at 840.degree. C. for 5 hours to make an annealed
material, and then, for hardening, maintained at 1100.degree. C.
for 3 minutes and water-cooled. Furthermore, after the hardening,
the material was maintained at -75.degree. C. for 30 minutes for
subzero treatment, and then tempered at 150.degree. C. for 3
minutes.
[0092] Five pieces of test pieces for three point bending test
having a width of 5 mm, a length of 70 mm, and a thickness of 0.5
mm were made from the intermediate materials for sampling a test
piece after the above-described heat treatment.
[0093] In addition, other test pieces were sampled from the
position corresponding to the position shown in FIG. 1 (in the
vicinity of the center of the width of the rolled material) in such
a manner that the vertical section as the evaluated plane 2 is used
for the observation of the metal structure and the evaluation of
hardness. FIGS. 8 to 13 show the photographs of the metal structure
(Nos. 1 to 6). Table 4 shows hardness, absorption energy by the
three point bending test, bending strength by the three point
bending test, and deflection by the three point bending test.
[0094] The observation of the metal structure was performed by
mirror-polishing the vertical section of the test piece, corroding
it in a ferric chloride aqueous solution, and then observing it
using a scanning electron microscope. In the three point bending
test, a test piece having a width of 5 mm, a length of 70 mm, and a
thickness of 0.5 mm was measured over a span of 50 mm. The data of
the hardness and three point bending test are the average of five
points.
TABLE-US-00004 TABLE 4 Absorbed Bending Hardness energy strength
Deflection No. (Hv) (N mm) (N mm.sup.2) (mm) Remarks 1 770 593 2799
6.24 The invention 2 762 421 2289 5.16 Comparative example 3 792
704 2880 6.62 The invention 4 786 230 1825 3.77 Comparative example
5 792 580 2721 5.94 The invention 6 719 757 2861 6.93 The invention
7 752 553 2524 5.91 The invention 8 696 444 2341 5.21 The
invention
[0095] From Tables 2 and 4, in a case in which the ratio of the
diffraction peak area from the fcc phase to the diffraction peak
area from the bcc phase is 30 or less in the X-ray diffraction of
the intermediate material for stainless steel for cutlery after
heat treatment including annealing-hardening-subzero
treatment-tempering, the material has high toughness, which is
evaluated by the absorption energy in the three point bending test,
while maintaining high hardness even after heat treatment including
annealing-hardening-subzero treatment-tempering.
[0096] The reason for this is likely due to the difference in the
metal structure after heat treatment including
annealing-hardening-subzero treatment-tempering. Specifically, in a
case in which the ratio of the diffraction peak area from the fcc
phase to the diffraction peak area from the bcc phase is more than
30 in the X-ray diffraction of the rolled material for stainless
steel for cutlery, as shown in FIGS. 9 and 11, the carbides having
a high aspect ratio are linked at the boundaries in the rolled
material for stainless steel for cutlery after heat treatment,
which likely causes the decrease in toughness.
[0097] In this regard, in a case in which the ratio of the
diffraction peak area from the fcc phase to the diffraction peak
area from the bcc phase in the X-ray diffraction is 30 or less, as
shown by FIGS. 8, 10, 12, and 13, the carbides after heat treatment
are more dispersed, so that the structure is likely more preferable
from the viewpoint of toughness.
[0098] These results suggest that cutlery having high hardness and
high toughness is produced from the intermediate material for
stainless steel for cutlery of the invention by subjecting it to
heat treatment including annealing-hardening-subzero
treatment-tempering.
[0099] Furthermore, besides the ratio of the diffraction peak area
from the fcc phase to the diffraction peak area from the bcc phase
in the X-ray diffraction, the inclusion of B in the proportion of
0.0050% or less further improves the balance between hardness and
toughness.
[0100] Subsequently, an intermediate material for sampling a test
piece having a width of 40 mm, a length of 100 mm, and a thickness
of 1.5 mm was cut out from each of the intermediate materials of
stainless steel for cutlery shown in the above-described Nos. 1 and
3. At this time, the intermediate material for sampling a test
piece so as to contain the vicinity of the center of the width of
the intermediate material shown in FIG. 1.
[0101] The intermediate material for sampling a test piece was
annealed at 840.degree. C. for 10 hours, and then cold-rolled using
a compact cold rolling machine; a cold-rolled material was obtained
without rupture until the thickness became 0.075 mm. As a result of
this, it was confirmed that a cold-rolled steel strip can also be
obtained.
[0102] Subsequently, the cold-rolled material was, for hardening,
maintained at 1100.degree. C. for 40 seconds and then water-cooled.
Furthermore, after the above-described hardening, the material was
maintained at -75.degree. C. for 30 minutes for subzero treatment,
and then maintained at 150.degree. C. for 30 seconds for
tempering.
[0103] Using the cold-rolled material and the material for sampling
a test after the heat treatment including
annealing-hardening-subzero treatment-tempering, test pieces were
sampled from the position corresponding to the position shown in
FIG. 1 (in the vicinity of the center of the width of the rolled
material), and the test pieces were sampled in such a manner that
the vertical section as the evaluated plane 2 is used for the
observation of the metal structure and the evaluation of hardness.
FIGS. 14 to 17 show the photographs as substitutes of drawings
showing the metal structure before and after the above-described
heat treatment (Nos. 1 and 3), and Table 5 show the hardness.
TABLE-US-00005 TABLE 5 Hardness before heat Hardness after heat No.
treatment (HV) treatment (HV) Remarks 1 398 796 The invention 3 400
798 The invention
[0104] The results shown in FIGS. 14 to 17 and Table 5 indicate
that the cold-rolled material of the invention, and the stainless
steel for cutlery after hardening, subzero treatment, and tempering
contained no carbide having a high aspect ratio which can
deteriorate toughness, and spherical carbides contributing to good
toughness are finely dispersed in them. In addition, the hardness
after hardening, subzero treatment, and tempering was 790 HV or
more.
[0105] From the above results, it was confirmed that a metal
structure and hardness suitable for cutlery are achieved by
subjecting the intermediate material for stainless steel for
cutlery of the invention to annealing and cold rolling, followed by
hardening, subzero treatment, and tempering.
INDUSTRIAL APPLICABILITY
[0106] The cutlery made from the intermediate material and
cold-rolled steel strip for stainless steel for cutlery of the
invention has marked hardness and toughness, and thus can be used
for razors and other applications.
EXPLANATION OF REFERENCES
[0107] 1 intermediate material for stainless steel for cutlery
[0108] 2 vertical section
* * * * *