U.S. patent application number 10/983709 was filed with the patent office on 2005-05-12 for ferritic free-cutting stainless steel excellent in surface roughness and outgass resistance.
This patent application is currently assigned to Daido Tokushuko Kabushiki Kaisha. Invention is credited to Ishikawa, Koichi, Shimizu, Tetsuya.
Application Number | 20050098240 10/983709 |
Document ID | / |
Family ID | 34510420 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050098240 |
Kind Code |
A1 |
Ishikawa, Koichi ; et
al. |
May 12, 2005 |
Ferritic free-cutting stainless steel excellent in surface
roughness and outgass resistance
Abstract
A ferritic free-cutting stainless steel excellent in surface
roughness and outgass resistance is disclosed which comprises in
weight percentage, 0.06% or less of C, 0.05 to 1.0% of Si, 2.0% or
less of Mn, 0.050% or less of P, 0.05 to 0.50% of S, 2.0% or less
of Cu, 2.0% or less of Ni, 9.0 to 25.0% of Cr, 4.0% or less of Mo,
0.065 to 2.0% of Ti, 0.0150% or less of 0, 0.020% or less of N,
0.001 to 0.100% of Al, and Fe and inevitable impurity in the rest
portion, wherein the steel satisfies Equations (1) and (2) of the
equations, [Ti].gtoreq.1.3.times.[S] Equation (1)
[Mn]/[Ti].ltoreq.3 Equation (2) (WTi+WCr) >2.times.WMn Equation
(3) where the amount of Ti contained in the steel is represented by
[Ti], that of S is represented by [S] and that of Mn is represented
by [Mn], and wherein the steel satisfies Equation (3) where the
amount of Ti contained in sulfide produced in the texture of the
steel is represented by WTi, that of Cr is represented by WCr and
that of Mn is represented by WMn.
Inventors: |
Ishikawa, Koichi;
(Nagoya-shi, JP) ; Shimizu, Tetsuya; (Nagoya-shi,
JP) |
Correspondence
Address: |
SNIDER & ASSOCIATES
P. O. BOX 27613
WASHINGTON
DC
20038-7613
US
|
Assignee: |
Daido Tokushuko Kabushiki
Kaisha
Nagoya-shi
JP
460-8581
|
Family ID: |
34510420 |
Appl. No.: |
10/983709 |
Filed: |
November 9, 2004 |
Current U.S.
Class: |
148/325 ; 420/40;
420/41; 420/61 |
Current CPC
Class: |
C22C 38/22 20130101;
C22C 38/60 20130101; C22C 38/20 20130101; C22C 38/28 20130101; C22C
38/40 20130101 |
Class at
Publication: |
148/325 ;
420/040; 420/041; 420/061 |
International
Class: |
C22C 038/42 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 10, 2003 |
JP |
2003-379633 |
Claims
What is claimed is:
1. A ferritic free-cutting stainless steel excellent in surface
roughness and outgass resistance, comprising: in weight percentage,
0.06% or less of C, 0.05 to 1.0% of Si, 2.0% or less of Mn, 0.050%
or less of P, 0.05 to 0.50% of S, 2.0% or less of Cu, 2.0% or less
of Ni, 9.0 to 25.0% of Cr, 4.0% or less of Mo, 0.065 to 2.0% of Ti,
0.0150% or less of O, 0.020% or less of N, 0.001 to 0.100% of Al,
and Fe and inevitable impurity in the rest portion, wherein the
steel satisfies Equations (1) and (2) of the equations,
[Ti].gtoreq.1.3.times.[S] Equation (1) [Mn]/[Ti].ltoreq.3 Equation
(2) (WTi+WCr)>2.times.WMn Equation (3) where the amount of Ti
contained in the steel is represented by [Ti], that of S is
represented by [S] and that of Mn is represented by [Mn], and
wherein the steel satisfies Equation (3) where the amount of Ti
contained in sulfide produced in the texture of the steel is
represented by WTi, that of Cr is represented by WCr and that of Mn
is represented by WMn.
2. A ferritic free-cutting stainless steel excellent in surface
roughness and outgass resistance, wherein in addition to the
components as claimed in claim 1, the steel contains in weight
percentage any one or more selected from the group consisting of
0.01 to 0.30% of Pb, 0.01 to 0.30% of Se, 0.10% or less of Te and
0.01 to 0.30% or less of Bi.
3. A ferritic free-cutting stainless steel excellent in surface
roughness and outgass resistance, wherein in addition to the
components as claimed in claim 1, the steel contains in weight
percentage any one or more selected from the group consisting of
0.05% or less of Ca, 0.02% or less of Mg, 0.02% or less of B, 0.02%
or less of REM, 0.50% or less of V, 0.50% or less of Nb, 2.0% or
less of W and 0.50% or less of Ta.
4. A ferritic free-cutting stainless steel excellent in surface
roughness and outgass resistance, wherein in addition to the
components as claimed in claim 2, the steel contains in weight
percentage any one or more selected from the group consisting of
0.05% or less of Ca, 0.02% or less of Mg, 0.02% or less of B, 0.02%
or less of REM, 0.50% or less of V, 0.50% or less of Nb, 2.0% or
less of W and 0.50% or less of Ta.
Description
RELATED APPLICATION
[0001] This application claims the priority of Japanese Patent
Application No. 2003-379633 filed on Nov. 10, 2003.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a ferritic free-cutting
stainless steel excellent in surface roughness and outgass
resistance.
[0004] 2. Description of the Related Art
[0005] In recent years, in order to facilitate the trend toward
making computers, their peripheral equipment or other electronic
products be maintenance-free, ferritic stainless steel with which
corrosion resistance can be obtained at a relatively low cost is
widely used as the material for parts thereof. Especially, since
improvement of machinability is regarded as important for a part to
which precise finish machining is required to secure the precision
of dimensions and a part having a complicated shape and including
large machining removal, the amount of elements giving the
free-cutting property to be contained tends to increase.
Furthermore, such elements are used in not only adding each of them
respectively but also adding them in combinations.
[0006] As the elements giving machinability, S, Pb, Se, Bi, Te and
Ca and so on are known. Among these, Pb tends to be hated gradually
in recent years during which the interest in environmental
protection is globally being raised. Therefore, the apparatuses and
parts for which use of Pb is restricted are getting more. Then, a
material in which S is used as the main element of the elements
improving machinability is considered as a substituting material
(see, e.g., Japanese Patent Application Laid-Open Publication Nos.
S56-16653, S62-258955, S54-17567 and H10-46292). By producing
Mn-based sulfide such as mainly MnS in these materials, they are
arranged to improve the stress concentration effect when forming
chips against sulfide, and machinability and grindability due to
lubricating action between a tool and chips.
[0007] However, when Mn-based sulfide is produced, the sulfide
becomes a cause to degrade the corrosion resistance and outgass
resistance of an alloy. Degrading outgass resistance means that,
when an alloy is exposed to the atmosphere, S component contained
in the alloy material produces a gas which contains sulfur and the
gas is released and tends to facilitate corrosion of peripheral
circuits of parts. Such a sulfur-containing gas especially tends to
cause troubles in components such as computer peripheral devices
often used in a sealed status, for example, Hard Disk Drive
(HDD).
SUMMARY OF THE INVENTION
[0008] The objective of the invention is to provide a ferritic
free-cutting stainless steel excellent in surface roughness,
corrosion resistance and outgass resistance while having an
excellent machinability.
[0009] In order to achieve the above objective, according to an
aspect of the present invention there is provided a ferritic
free-cutting stainless steel excellent in surface roughness and
outgass resistance, comprising:
[0010] in weight percentage, 0.06% or less of C, 0.05 to 1.0% of
Si, 2.0% or less of Mn, 0.050% or less of P, 0.05 to 0.50% of S,
2.0% or less of Cu, 2.0% or less of Ni, 9.0 to 25.0% of Cr, 4.0% or
less of Mo, 0.065 to 2.0% of Ti, 0.0150% or less of O, 0.020% or
less of N, 0.001 to 0.100% of Al, and Fe and inevitable impurity in
the rest portion, wherein
[0011] the steel satisfies Equations (1) and (2) of the
equations,
[Ti].gtoreq.1.3.times.[S] Equation (1)
[Mn]/[Ti].ltoreq.3 Equation (2)
(WTi+WCr)>2.times.WMn Equation (3)
[0012] where the amount of Ti contained in the steel is represented
by [Ti], that of S is represented by [S] and that of Mn is
represented by [Mn], and wherein
[0013] the steel satisfies Equation (3) where the amount of Ti
contained in sulfide produced in the texture of the steel is
represented by WTi, that of Cr is represented by WCr and that of Mn
is represented by WMn.
[0014] Usually, S tends to form sulfide with Mn, a component of a
steel material. However, as described above, Mn-based sulfide
becomes a cause to degrade the corrosion resistance and outgass
resistance of an alloy. Then, according to the invention,. by
producing Ti-based sulfide such as TiS but not Mn-based sulfide by
adding Ti in the texture of the steel, the corrosion resistance and
the outgass resistance are improved. Furthermore, since the
Ti-based sulfide takes a form of a sphere and disperses finely, the
ferritic free-cutting stainless steel of the invention has
excellent machinability and is excellent in the inclusion falling
property, especially surface roughness in precision machining.
Moreover, the same effect can be obtained when the sulfide contains
Cr. "A"-based sulfide used herein refers to sulfide for which the
component (element) contained in the sulfide at the highest ratio
in weight is "A" among the components bonding with S. That is, in
Ti-based sulfide, more Ti bonds with S compared to other elements
(such as Mn).
[0015] Next, reasons for restriction of the claims of the invention
will be described.
[0016] C (Carbon): 0.06% or Less
[0017] When the amount of C contained is excessive, C prevents
improvement of machinability by producing much carbide in the form
of simple substance. Therefore, the upper limit is 0.06% and the
preferable range is 0.03% or less. More preferably, the range is
0.015% or less.
[0018] Si(Silicon): 0.05 to 1.0%
[0019] Si is added as a deoxidizer for steel. In order to obtain
the effect of the deoxidizer, 0.05% or more of Si is necessary.
However, when the amount of Si contained is excessive, the hot
workability of the steel is degraded. Therefore, the upper limit is
1.0%. A preferable range emphasizing the hot workability is 0.05 to
0.5%.
[0020] Mn (Manganese): 2.0% or Less
[0021] Mn is added as a deoxidizer for steel and, in addition, has
an effect of improving machinability since it produces Mn-based
sulfide (MnS). However, since the Mn-based sulfide (MnS) degrades
the corrosion resistance, the upper limit of the amount is 2.0%.
When the corrosion resistance is especially emphasized, the range
of the amount is 1.0% or less. More preferably, it is 0.5% or
less.
[0022] P (Phosphorus): 0.050% or Less
[0023] As lower amount as possible of P contained is desirable
since P causes decrease of the toughness in addition to increasing
intergranular corrosion sensitivity by segregating in the grain
boundary. The range of the amount of P contained is desirably
0.050% or less. Preferably, it is 0.030% or less.
[0024] S (Sulfur): 0.05 to 0.50%
[0025] S is a constituent element of sulfide, that improves the
machinability and 0.05% of S is necessary to obtain this effect.
However, since hot workability is degraded when the amount of S
contained is excessive, the upper limit is 0.50%. The range of the
amount of S contained is desirably 0.15 to 0.40% taking into
consideration the balance between the improvement of machinability
and the degradation of hot workability.
[0026] Cu (Copper): 2.0% or Less
[0027] Cu may be added when necessary since Cu is effective for
improving the corrosion resistance, especially the corrosion
resistance in a reducing acid environment. However, since excessive
addition of Cu degrades the hot workability, the upper limit is
2.0%. It is desirably 1.0% or less.
[0028] Ni (Nickel): 2.0% or Less
[0029] Ni is an element necessary for supplementing the corrosion
resistance that is insufficient when only Cr is contained. However,
since excessive addition of Ni causes increase of cost, the upper
limit is 2.0%. Furthermore, the amount of Ni contained is desirably
1.0% or less taking into consideration the balance between the
efficient corrosion resistance and the blending cost.
[0030] Cr (Chromium): 9.0 to 25.0%
[0031] Cr is an element which improves the corrosion resistance,
and 9.0% or more of Cr should be contained in order to obtain the
effect. On the other hand, since the hot workability is degraded in
addition to increasing of cost when the amount contained is
excessive, the upper limit is 25.0%. Furthermore, the range of the
amount of Cr contained may desirably be 13.0 to 21.0% taking into
consideration the balance between the efficient corrosion
resistance and the blending cost.
[0032] Mo (Molybdenum): 4.0% or Less
[0033] Mo can further improve the corrosion resistance and
strength. However, since excessive addition of Mo degrades the hot
workability and, in addition, causes increase of cost, the upper
limit is 4.0%. The range of the Mo contained is desirably 1.5% or
less taking into account the increase of cost.
[0034] Ti (Titanium): 0.065 to 2.0%
[0035] Ti is an element necessary for producing Ti-based sulfide
that improves the machinability, and 0.065% or more of Ti is
necessary in order to obtain this effect. On the other hand, since
cost is increased when the amount of Ti contained is excessive, the
upper limit of the amount of Ti contained is 2.0%. Furthermore, the
range of the amount of Ti contained may desirably be 0.075 to 2.0%
in order to obtain further sufficient machinability.
[0036] O (Oxygen): 0.0150% or Less
[0037] The upper limit of the amount of O contained is 0.0150%
since O bonds with Ti which is a constituent element of a compound
effective for improving machinability and forms oxide which does
not contribute to improvement of the machinability. The range of
the amount of O contained may be desirably 0.0080% or less, and is
further desirably 0.0050% taking into consideration of.
manufacturing cost and in order to secure the effective amount of
Ti necessary for forming Ti-based sulfide.
[0038] N (Nitrogen): 0.020% or Less
[0039] The upper limit of the amount of N contained is 0.020% since
N bonds with Ti which is a constituent element of a compound
effective for improving machinability and forms nitride which does
not contribute to improvement of the machinability. The range of
the amount of N contained may be desirably 0.010% or less and is
further desirably 0.006% or less taking into consideration of
manufacturing cost and in order to secure the effective amount of
Ti necessary for forming Ti-based sulfide.
[0040] Al (aluminum): 0.001 to 0.100%
[0041] Al is added as a deoxidizer for the steel. However, the
upper limit of the amount of Al contained is 0.100% since oxide
harmful to machinability is formed when the amount of Al contained
is excessive. The range of the amount of Al contained is desirably
0.050% or less.
[Ti].gtoreq.1.3.times.[S] Equation (1)
[0042] The amount of Ti contained is 1.3 times as much the amount
of S contained or more in order to suppress the production of
Mn-based sulfide (MnS) that degrades the corrosion resistance and
the outgass resistance and to fix all S in the texture of the steel
onto Ti. More desirably, [Ti].gtoreq.1.5.times.[S], that is, the
amount of Ti contained may be 1.5 times as much the amount of S
contained or more. [ ] indicates the amount of a component
contained in the steel.
[Mn]/[Ti].ltoreq.3 Equation (2)
[0043] The amount of Mn contained is three times as much the amount
of Ti contained or less in order to suppress the production of
Mn-based sulfide (MnS) that degrades the corrosion resistance and
the outgass resistance, and (in order to decrease the amount of Mn
contained and to increase the amount of Ti contained in the
sulfide) to cause Ti-based sulfide to be produced.
(WTi+WCr)>2.times.WMn Equation (3)
[0044] In order to make the corrosion resistance and the outgass
resistance of the steel excellent, it is preferable that, in the
sulfide, the sum of the amount of Ti contained and the amount of Cr
contained exceeds the double of the amount of Mn contained. Here,
"W" indicates the amount of a component following it contained in
the sulfide.
[0045] In a ferritic free-cutting stainless steel of the invention,
the steel may further contain in addition to the components
described above, in weight percentage any one or more selected from
the group consisting of 0.01 to 0.30% of Pb, 0.01 to 0.30% of Se,
0.10% or less of Te and 0.01 to 0.30% of Bi.
[0046] Since Pb (lead), Se (selenium), Te (tellurium) and Bi
(bismuth) can improve the machinability furthermore, they can be
added as necessary. However, since excessive addition of them
degrades the hot workability, the upper limit of the amount to be
added for each of them is respectively 0.3% for Pb, 0.30% for Se,
0.10% for Te and 0.30% for Bi. In order to obtain sufficiently the
effect of improving the machinability, it is desirable to add 0.01%
or more of each of the above components respectively.
[0047] In a ferritic free-cutting stainless steel of the invention,
the steel may further contain in addition to the components
described above, in weight percentage any one or more selected from
the group consisting of 0.05% or less of Ca, 0.02% or less of Mg,
0.02% or less of B, 0.02% or less of REM, 0.50% or less of V, 0.50%
or less of Nb, 2.0% or less of W and 0.50% or less of Ta.
[0048] Since Ca (calcium), Mg (magnesium), B (boron) and REM (one
or more of rare-earth elements) can improve the hot workability of
the steel, they can be added as necessary. However, since excessive
addition of them makes the effect saturate and, on the contrary,
degrades the hot workability, the upper limit of the amount to be
added is 0.05% for Ca, 0.02% for Mg, 0.02% for B and 0.02% for
REM.
[0049] Since W (tungsten) can improve the corrosion resistance and
the strength of the steel, it can be added as necessary. However,
since excessive addition of it degrades the hot workability and
causes increase of cost, the upper limit of the amount to be added
is 2.0%.
[0050] Since Nb (niobium), V (vanadium) and Ta (tantalum) have the
effect of improving toughness by forming carbon nitride and making
the crystal grain in the steel very fine, each of them can be added
respectively in the range of 0.50% or less.
EXAMPLE
[0051] In order to verify the effect of the invention, the
following experiment was performed.
[0052] First, after producing by melting in a high-frequency
induction furnace a 50 kg-ingot of each type of steel having the
component composition shown in Table 1, ingots were produced by
cooling the melted steel. Then, each ingot was heated to 1,050 to
1,100.degree. C. and shaped into a round bar having a length of 20
mm by hot-forging. After further heating those round bars at
800.degree. C. for one hour, they were air-cooled (annealing) and
supplied to each test. The result of each test is shown in Table
1.
1TABLE 1 Pb Se wt % Te C Si Mn P S Cu Ni Cr Mo Ti Al O N Bi Steel
of 1 0.003 0.21 0.04 0.019 0.206 0.30 0.05 16.5 0.05 0.56 0.020
0.0040 0.0057 the 2 0.021 0.40 0.16 0.007 0.253 0.14 0.23 19.0 0.30
0.75 0.017 0.0023 0.0043 Invention 3 0.005 0.35 0.50 0.019 0.196
0.02 0.97 18.3 0.32 0.47 0.007 0.0009 0.0053 Bi: 0.11 4 0.014 0.33
0.43 0.032 0.151 0.28 0.28 13.4 0.95 0.28 0.043 0.0037 0.0038 5
0.006 0.05 0.03 0.050 0.394 0.80 0.80 20.9 1.32 0.86 0.032 0.0049
0.0029 6 0.016 0.50 0.01 0.029 0.298 0.47 0.47 19.4 0.27 0.94 0.022
0.0031 0.0049 7 0.011 0.27 0.22 0.035 0.179 0.31 0.31 17.8 0.63
0.54 0.038 0.0018 0.0021 8 0.024 0.46 0.32 0.009 0.161 0.88 0.88
20.5 0.83 0.43 0.001 0.0035 0.0047 Pb: 0.29 9 0.018 0.13 0.28 0.011
0.368 0.56 0.56 13.1 0.02 0.78 0.012 0.0043 0.0034 Se: 0.19 10
0.023 0.19 0.11 0.001 0.188 0.41 0.01 15.2 0.22 0.35 0.028 0.0029
0.0060 Te: 0.05 Pb: 0.17 11 0.032 0.41 0.02 0.031 0.163 0.54 0.68
18.4 0.33 0.56 0.038 0.0048 0.0059 12 0.031 0.89 0.38 0.008 0.289
0.33 0.19 19.5 0.05 0.88 0.021 0.0029 0.0059 13 0.048 0.33 0.43
0.032 0.432 0.03 0.29 16.7 0.58 0.89 0.028 0.0039 0.0041 14 0.037
0.05 0.53 0.019 0.263 0.21 0.09 19.2 0.50 0.86 0.029 0.0034 0.0078
15 0.028 0.33 0.16 0.045 0.147 0.12 0.19 18.2 0.34 0.23 0.061
0.0029 0.0051 16 0.013 0.07 0.22 0.035 0.051 0.31 0.31 17.8 0.63
0.32 0.038 0.0089 0.0043 17 0.009 0.37 0.43 0.022 0.264 0.88 1.09
9.3 0.85 0.43 0.032 0.0034 0.0045 18 0.002 0.13 0.25 0.019 0.296
1.59 1.97 16.8 0.50 0.49 0.014 0.0048 0.0058 19 0.007 0.19 1.97
0.041 0.290 0.41 0.32 15.2 0.22 0.91 0.041 0.0021 0.0089 20 0.021
0.98 0.43 0.032 0.182 0.28 0.28 13.4 0.95 1.96 0.030 0.0069 0.0041
Pb: 0.11 21 0.019 0.39 0.63 0.050 0.485 0.32 0.48 23.8 0.49 1.43
0.029 0.0042 0.0059 22 0.010 0.50 1.06 0.029 0.278 0.59 0.19 24.9
0.27 0.70 0.022 0.0031 0.0049 23 0.059 0.27 0.49 0.035 0.354 0.31
0.21 12.3 0.33 0.87 0.023 0.0030 0.0060 Te: 0.03 24 0.005 0.43 0.31
0.028 0.234 0.88 0.35 21.0 0.15 0.58 0.081 0.0035 0.0055 Bi: 0.28
25 0.007 0.14 0.22 0.011 0.334 0.44 0.27 19.7 0.87 0.64 0.028
0.0043 0.0034 26 0.036 0.19 0.11 0.041 0.188 0.41 0.32 15.2 0.22
0.35 0.028 0.0043 0.0139 27 0.001 0.39 0.10 0.011 0.051 0.33 0.33
18.9 0.07 0.07 0.039 0.0023 0.0054 28 0.013 0.80 1.04 0.019 0.278
0.09 0.11 14.9 0.01 0.41 0.011 0.0010 0.0210 29 0.001 0.41 0.19
0.025 0.348 0.02 0.31 22.3 1.48 0.47 0.038 0.0020 0.0170 Se: 0.25
30 0.009 0.08 0.13 0.013 0.158 1.41 0.38 20.8 0.08 0.21 0.019
0.0050 0.0080 Steel for 1 0.060 0.29 0.34 0.008 0.043 0.95 0.12
19.3 0.20 -- 0.052 0.0048 0.0168 Comparison 2 0.045 1.32 0.60 0.019
0.031 0.37 0.09 18.4 0.54 -- 0.011 0.0086 0.0253 3 0.094 0.58 0.19
0.041 0.002 0.18 0.43 19.1 1.04 -- 0.121 0.0091 0.0178 4 0.032 0.39
1.67 0.032 0.189 0.65 0.32 15.7 0.21 0.17 0.068 0.0072 0.0089 5
0.019 1.98 0.14 0.050 0.034 0.51 0.55 17.9 0.62 -- 0.082 0.0089
0.0048 6 0.081 0.67 0.38 0.029 0.009 1.88 0.41 18.5 0.87 -- 0.290
0.0029 0.0073 7 0.105 0.78 0.67 0.028 0.038 0.12 0.11 16.2 0.03 --
0.019 0.0233 0.0067 8 0.089 0.11 1.32 0.011 0.233 0.09 0.32 21.4
0.15 -- 0.088 0.0083 0.0149 9 0.021 0.25 0.11 0.041 0.008 0.59 0.07
8.5 0.54 -- 0.059 0.0091 0.0111 10 0.093 0.60 0.55 0.032 0.652 0.44
1.34 19.4 0.21 -- 0.078 0.0022 0.0121 11 0.056 0.18 2.60 0.050
0.285 0.89 0.63 16.8 0.08 -- 0.092 0.0148 0.0198 12 0.009 0.43 0.50
0.029 0.032 0.48 0.45 17.3 0.09 -- 0.034 0.0105 0.0184 13 0.023
0.58 1.95 0.044 0.285 0.34 0.24 16.4 0.15 0.40 0.049 0.0111 0.0135
Machinability Ca V Variation Mg Nb [Tl]/ [Mn]/ of Outer Surface B W
[S] .gtoreq. [Tl] .ltoreq. Diameter Roughness Shape of Corrosion
Outgass REM Ta 1.3 3 (.mu.m) (.mu.m) Chips Resistance Resistance
Steel of 1 2.72 0.07 Small 0.07 Good Good A the 2 2.96 0.21 Small
0.14 Good Good A Invention 3 2.40 1.06 Small 0.11 Good Good B 4
1.85 1.54 Small 0.08 Good Good B 5 2.18 0.03 Small 0.09 Good Good A
6 Mg: 0.0012 3.15 0.01 Small 0.05 Good Good A 7 3.02 0.41 Small
0.09 Good Good A 8 V: 0.43 2.67 0.74 Small 0.12 Good Good A 9 2.12
0.36 Small 0.11 Good Good A 10 1.86 0.31 Small 0.10 Good Good A 11
Nb: 0.19 3.44 0.04 Small 0.10 Good Good A 12 3.04 0.43 Small 0.15
Good Good A 13 Ca: 0.0132 2.06 0.48 Small 0.11 Good Good A Mg:
0.0021 14 3.27 0.62 Small 0.08 Good Good A 15 1.56 0.70 Small 0.09
Good Good A 16 B: 0.01 V: 0.33 6.27 0.69 Small 0.10 Good Good A 17
1.63 1.00 Small 0.14 Good Good B 18 1.66 0.51 Small 0.13 Good Good
A 19 B: 0.005 Ta: 0.50 3.14 2.16 Small 0.11 Good Good A 20 10.77
0.22 Small 0.12 Good Good A 21 W: 1.7 2.95 0.44 Small 0.13 Good
Good A 22 2.52 1.51 Small 0.15 Good Good B 23 2.46 0.56 Small 0.13
Good Good A 24 Ta: 0.41 2.48 0.53 Small 0.12 Good Good A 25 1.92
0.34 Small 0.09 Good Good A 26 Ca: 0.0085 1.86 0.31 Small 0.06 Good
Good A 27 Mg: 0.0013 1.37 1.43 Small 0.14 Good Good B 28 1.47 2.54
Small 0.13 Good Good B 29 1.35 0.40 Small 0.09 Good Good A 30 Nb:
0.28 1.33 0.62 Small 0.10 Good Good A Steel for 1 Large 0.44 Bad
Good B Comparison 2 Large 0.54 Bad Good B 3 Large 0.42 Bad Bad C 4
0.90 9.82 Intermediate 0.69 Good Good C 5 Large 0.29 Bad Good A 6
Large 0.58 Bad Bad A 7 Large 0.45 Bad Bad B 8 Intermediate 0.34
Good Bad C 9 Large 0.32 Bad Bad A 10 Nb: 0.86 Large 0.89 Good Bad C
11 Small 0.83 Good Bad C 12 Large 0.41 Bad Good B 13 1.40 4.88
Intermediate 0.65 Good Bad C
[0053] (1) Evaluation of Machinability
[0054] Machinability was evaluated by evaluating the variation of
the outer diameter of the works after machining, the surface
roughness and the shape of chips.
[0055] Machining was performed under the following conditions using
Carbide tool in insoluble oil: 100 mm/min. of cutting speed; 0.10
mm of depth of cut, and; 0.01 mm/rev of feed amount for one
rotation. Machining was performed to 50 samples and the outer
diameter of the test pieces and the wear of the tool after
machining were measured.
[0056] The variation of the outer diameter is the variation from
that of an initial work. The criterion for judging the variation
was determined as "small" for the case where the wear of the
lateral relief is less than 50 .mu.m and "intermediate" for the
case where it is 50 .mu.m or more and 100 .mu.m or less, and
"large" for the case where it exceeds 100 .mu.m.
[0057] The surface roughness is the arithmetic mean (Ra: .mu.m) of
the work surface after machining, measured in a method designated
in JIS-B0601.
[0058] Furthermore, the shape of the chips was visual-inspected and
the chip of the size of approximately 10 mm or less, having a good
fragmenting property were evaluated and represented as "good" and
other chips that were not separated from each other were evaluated
and represented as "bad".
[0059] (2) Corrosion Resistance
[0060] The corrosion resistance evaluation test was performed in
the form of wet-type test. As the test pieces, those having a
cylindrical shape, the diameter of 10 mm and the height of 50 mm
were used and their surface was polished to the count number 400
with emery paper and was washed to degrease. Thereafter, these
pieces were stored in a high-temperature and high-humidity
atmosphere at 50.degree. C. of temperature and 98% RH of humidity
for 98 hours. Then, whether or not there is rust on the pieces was
evaluated by visual inspection of their appearance.
[0061] (3) Outgass Resistance
[0062] The evaluation of the outgass resistance was performed by
determining the amount of S generated. More specifically, test
pieces having a shape of rectangular parallelepiped and dimensions
of 15 mm in height, 3 mm in width and 25 mm in depth, of which the
entire surface has been polished with emery paper of count number
400 were used. Then, the test pieces, a sheet of silver foil
(dimensions: 0.1 mm in height, 5 mm in width and 10 mm in depth;
and purity: 99.9% or higher) and 0.5 cc of pure water were put in a
sealed container having the volume of 250 cc. Then, the temperature
inside the container was maintained at 85.degree. C. for 20 hours.
The sheet of silver foil acts as the getter when gas containing S
is generated and the surface of the sheet of the silver foil turns
black due to production of silver sulfide when S component adsorbed
by the sheet of the silver foil becomes excessive. Then, the change
of the color of the silver foil surface was checked by visual
inspection and the outgass resistance was evaluated in three (3)
ranks in which those without any change of the color were evaluated
as "A", those with a little change of the color were evaluated as
"B" and those with apparent change of the color were evaluated as
"C". Those that obtained the evaluation result of A or B were
judged as excellent in outgass resistance.
[0063] According to the test results listed in Table 1, it can be
seen that any type of the steel according to the invention has
excellent machinability and surface roughness as well as is
excellent in the corrosion resistance and the outgass
resistance.
[0064] Next, for some of the steel types of the invention and steel
types for comparison, a composition analysis of sulfide produced in
the texture of the steel was performed in electron beam probe
micro-analysis (EPMA) method. The results of this analysis are
shown in Table 2. According to Table 2, it can be seen that, the
composition of sulfide satisfies Equation (3) for the steel of the
invention and the sulfide has a high ratio of Ti contained. In
contrast, for the steel for comparison No. 4 for which the
composition of the steel does not satisfy Equations (1) and (2) and
steel for comparison No. 7 for which the composition of the steel
does not satisfy Equation (1), almost same amount of Ti and Mn are
contained in sulfide and the composition of the sulfide does not
satisfy Equation (3). The steel for comparison Nos. 4 and 7 having
such sulfide are poor in the corrosion resistance and the outgass
resistance as also apparent from Table 1.
[Ti].gtoreq.1.3.times.[S] Equation (1)
[Mn]/[Ti].ltoreq.3 Equation (2)
(WTi+WCr)>2.times.WMn Equation (3)
2 TABLE 2 Composition of Sulfide (wt %) Ti Cr Mn (Ti + Cr)/Mn Steel
of the Invention No. 1 58.9 0.7 0.4 149.0 No. 4 48.5 1.5 10.5 4.8
No. 8 56.5 0.8 2.8 20.5 No. 17 48.3 1.2 8.1 6.1 No. 19 51.9 0.3 8.1
6.4 No. 27 42.8 8.2 9.6 5.3 No. 28 42.6 1.1 17.0 2.6 Steel for
Comparison No. 4 33.3 1.2 26.8 1.3 No. 14 38.4 0.8 22.3 1.8
* * * * *