U.S. patent application number 10/993674 was filed with the patent office on 2005-05-19 for low nickel containing chromim-nickel-mananese-copper austenitic stainless steel.
This patent application is currently assigned to Yieh United Steel Corp.. Invention is credited to Hsieh, Meng-Hsin, Huang, Pei-Te, Liu, Hao-Shang, Wu, Yi-Cheng.
Application Number | 20050103404 10/993674 |
Document ID | / |
Family ID | 34572639 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050103404 |
Kind Code |
A1 |
Hsieh, Meng-Hsin ; et
al. |
May 19, 2005 |
Low nickel containing chromim-nickel-mananese-copper austenitic
stainless steel
Abstract
An austenitic stainless steel includes (a) 0.03 wt % to 0.12 wt
% of C, (b) 0.2 wt % to 1.0 wt % of Si, (c) 7.5 wt % to 10.5 wt %
of Mn, (d) 14.0 wt % to 16.0 wt % of Cr, (e) 4.05 wt % to 4.31 wt %
of Ni, (f) 0.04 wt % to 0.07 wt % of N, (g) 1.0 wt % to 3.5 wt % of
Cu, (h) trace amount of Mo, and the balance being Fe and incidental
impurities. The austenitic stainless steel has a .delta.-ferrite
content less than 8.5 and equal to
6.77[(d)+(h)+1.5(b)]-4.85[(e)+30(a)+30(f)+0.5(c)+0.3(g)]-52.75.
Inventors: |
Hsieh, Meng-Hsin; (Tainan
City, TW) ; Wu, Yi-Cheng; (Kaohsiung City, TW)
; Huang, Pei-Te; (Kaohsiung Hsien, TW) ; Liu,
Hao-Shang; (Kaohsiung City, TW) |
Correspondence
Address: |
DARBY & DARBY P.C.
P. O. BOX 5257
NEW YORK
NY
10150-5257
US
|
Assignee: |
Yieh United Steel Corp.
Kaohsiung-Hsien
KR
|
Family ID: |
34572639 |
Appl. No.: |
10/993674 |
Filed: |
November 19, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10993674 |
Nov 19, 2004 |
|
|
|
10353167 |
Jan 28, 2003 |
|
|
|
Current U.S.
Class: |
148/327 ;
420/58 |
Current CPC
Class: |
C22C 38/58 20130101;
C22C 38/02 20130101; C22C 38/42 20130101; C22C 38/001 20130101 |
Class at
Publication: |
148/327 ;
420/058 |
International
Class: |
C22C 038/42 |
Claims
We claim:
1. An austenitic stainless steel comprising: (a) 0.03 wt % to 0.12
wt % of C; (b) 0.2 wt % to 1.0 wt % of Si; (c) 7.5 wt % to 10.5 wt
% of Mn; (d) 14.0 wt % to 16.0 wt % of Cr; (e) 4.05 wt % to 4.31 wt
% of Ni; (f) 0.04 wt % to 0.07 wt % of N; (g) 1.0 wt % to 3.5 wt %
of Cu; (h) trace amount of Mo; and the balance being Fe and
incidental impurities; wherein said austenitic stainless steel has
a .delta.-ferrite content that is less than 8.5 and that satisfies
the following formula .delta.-ferrite=6.77[(d-
)+(h)+1.5(b)]-4.85[(e)+30(a)+30(f)+0.5(c)+0.3(g)]-52.75.
2. The austenitic stainless steel of claim 1, further comprising 5
to 30 ppm of B.
3. The austenitic stainless steel of claim 1, further comprising no
more than 150 ppm of S.
4. The austenitic stainless steel of claim 1, further comprising no
more than 0.06 wt % of P.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part (CIP) of U.S.
patent application Ser. No. 10/353,167, filed by the applicant on
Jan. 28, 2003, and abandoned as of the filing date of this
application. The entire disclosure of the parent application is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to an austenitic stainless steel,
more particularly to a low nickel containing
chromium-nickel-manganese-copper austenitic stainless steel.
[0004] 2. Description of the Related Art
[0005] U.S. Pat. No. 5,286,310 discloses a low nickel containing
chromium-nickel-manganese-copper austenitic stainless steel that
has a reduced nickel content and acceptable metallographic
structure, mechanical strength, corrosion resistance and
workability. The aforesaid austenitic stainless steel contains at
least 16.5% by weight of chromium so as to provide acceptable
corrosion resistance. However, the chromium content should not
exceed 17.5% by weight so as to prevent undesired formation of
delta ferrite (.delta.-ferrite) during hot working and impairment
to hot workability. The aforesaid austenitic stainless steel
further contains at least 2.5% by weight of nickel so as to improve
cold workability and so as to inhibit transformation of austenite
into martensite. However, nickel content should not exceed 5% by
weight due to the relatively high price thereof.
[0006] Although the aforesaid austenitic stainless steel is capable
of providing acceptable corrosion resistance and cold or hot
workability, the chromium content thereof is still high (previous
investigation has shown that at least 17% by weight of chromium is
necessary to provide minimum levels of corrosion resistance), which
can impair stability of the austenitic stainless steel and which
can cause cracking during hot rolling.
[0007] The disclosure of U.S. Pat. No. 5,286,310 is incorporated
herein by reference.
SUMMARY OF THE INVENTION
[0008] Therefore, it is an object of the present invention to
provide a low nickel containing chromium-nickel-manganese-copper
austenitic stainless steel that is capable of overcoming the
aforesaid drawbacks of the prior art.
[0009] According to this invention, there is provided an austenitic
stainless steel that comprises: (a) 0.03 wt % to 0.12 wt % of C;
(b) 0.2 wt % to 1.0 wt % of Si; (c) 7.5 wt % to 10.5 wt % of Mn;
(d) 14.0 wt % to 16.0 wt % of Cr; (e) 4.05 wt % to 4.31 wt % of Ni;
(f) 0.04 wt % to 0.07 wt % of N; (g) 1.0 wt % to 3.5 wt % of Cu;
(h) trace amount of Mo; and the balance being Fe and incidental
impurities. The austenitic stainless steel has a .delta.-ferrite
content that is less than 8.5 and that satisfies the following
formula
.delta.-ferrite=6.77
[(d)+(h)+1.5(b)]-4.85[(e)+30(a)+30(f)+0.5(c)+0.3(g)]-- 52.75.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] In drawing which illustrates an embodiment of the
invention,
[0011] FIG. 1 is a diagram illustrating the relationship between
.delta.-ferrite content of the preferred embodiment of the
austenitic stainless steel of this invention and hot working
temperature.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] The preferred embodiment of the low nickel containing
chromium-nickel-manganese-copper austenitic stainless steel of the
present invention comprises: (a) 0.03 wt % to 0.12 wt % of C; (b)
0.2 wt % to 1.0 wt % of Si; (c) 7.5 wt % to 10.5 wt % of Mn; (d)
14.0 wt % to 16.0 wt % of Cr; (e) 4.05 wt % to 4.31 wt % of Ni; (f)
0.04 wt % to 0.07 wt % of N; (g) 1.0 wt % to 3.5 wt % of Cu; (h)
trace amount of Mo; and the balance being Fe and incidental
impurities. The austenitic stainless steel has a .delta.-ferrite
content that is less than 8.5 and that satisfies the following
formula
.delta.-ferrite=6.77[(d)+(h)+1.5(b)]-4.85[(e)+30(a)+30(f)+0.5(c)+0.3(g)]-5-
2.75,
[0013] wherein (a), (b), (c), (d), (e), (f), (g), (h) in the
formula mean the content of the respective elements (wt %).
[0014] The austenitic stainless steel can further comprise 5 to 30
ppm of B so as to improve hot workability. The contents of harmful
impurities, such as S (sulfur) and P (phosphorous), are as small as
possible. However, due to cost concerns associated with removal of
these impurities, the S content is limited to 150 ppm, and the P
content is limited to 0.06 wt %.
[0015] FIG. 1 illustrates the relationship between the
.delta.-ferrite content of the preferred embodiment of the
austenitic stainless steel of this invention and temperature. The
results show that when temperature is raised to above 1250.degree.
C. during hot rolling, the .delta.-ferrite content rises sharply,
which results in the risk of edge cracking of a rolled plate of the
austenitic stainless steel. In addition, a minimum temperature of
1050.degree. C. during hot rolling is required so as to obtain the
requisite mechanical strength.
EXAMPLES AND COMPARATIVE EXAMPLES
[0016] The following Examples and Comparative Examples illustrate
the unexpectedly better results of this invention over the prior
art.
[0017] Table 1 illustrates an edge crack effect test for different
test specimens of the austenitic stainless steel of Examples 1 to 9
and comparative Examples 1 to 5, which differ in composition (only
elements Ni, C, Si, Mn, Cr, Cu, and N are shown). The test was
conducted by hot rolling at a temperature ranging from 1050.degree.
C. to 1250.degree. C. The test results show that each Example of
the austenitic stainless steel of this invention has a
.delta.-ferrite content less than 8.5, and that no edge cracking
was observed for the test specimens of Examples 1 to 9. Each of the
test specimens of the Comparative Examples 1 to 5 has a
.delta.-ferrite content greater than 8.5. Edge cracks were found in
each of the test specimens of the Comparative Examples 1 to 5. The
results shown in Table 1 demonstrate that edge cracks can be
avoided when the Ni content ranges from 4.05% to 4.55% with the
Nitrogen content ranging from 0.04% to 0.061%.
1 TABLE 1 Ni C Si Mn Cr Cu N .delta.-ferrite Edge crack Examples 1
4.31 0.053 0.50 7.60 16.30 1.60 0.041 8.49 None 2 4.05 0.032 0.53
7.85 15.36 1.71 0.04 6.636 None 3 4.07 0.032 0.54 8.00 15.33 1.66
0.043 6.259 Noen 4 4.55 0.032 0.58 7.54 15.23 1.59 0.041 4.984 None
5 4.15 0.059 0.62 7.44 15.26 1.65 0.042 3.859 None 6 4.24 0.046
0.42 7.86 15.68 1.66 0.061 3.278 None 7 4.21 0.051 0.49 7.63 15.16
1.62 0.041 1.684 None 8 4.09 0.060 0.50 8.08 15.14 1.70 0.042 0.109
None 9 4.19 0.066 0.54 7.76 14.99 1.65 0.044 -1.989 None
Comparative Examples 1 4.31 0.039 0.47 7.07 19.04 2.15 0.039 28.58
Cracking 2 4.36 0.05 0.45 7.58 17.53 2.03 0.039 15.82 Cracking 3
4.37 0.046 0.47 7.96 18.33 1.71 0.035 22.60 Cracking 4 4.77 0.052
0.51 7.54 18.13 1.73 0.032 19.85 Cracking 5 4.45 0.051 0.53 7.5
16.20 1.5 0.031 9.1 cracking
[0018] Table 2 illustrates a corrosion resistance test (ASTM B117)
using salt fog for different test specimens of the austenitic
stainless steel of Examples 10 to 12 and comparative Example 6
(type 304 stainless steel), which differ in composition (only
elements Ni, C, Si, Mn, Cr, Cu, and B are shown) The test results
show that each Example of the austenitic stainless steel of this
invention has a corrosion rate that is as low as that of the type
304 stainless steel (no more than 0.1%) of the prior art.
2 TABLE 2 Corro- sion Ni C Si Mn Cr Cu B rate Exam- ples 10 4.40
0.058 0.48 7.56 15.26 1.79 0.0001 .ltoreq.0.1 wt % 11 4.11 0.051
0.54 7.86 15.35 1.69 0.0032 .ltoreq.0.1 wt % 12 3.40 0.059 0.77
7.84 14.94 1.78 0.0001 .ltoreq.0.1 wt % Compar- ative Exam- ple 6
8.02 0.045 0.53 1.25 18.19 0.23 0.0008 .ltoreq.0.1 wt %
[0019] It is noted that the chromium content in each of the
Examples 1 to 12 of the austenitic stainless steel of this
invention is less than 17 wt %, which is a minimum requirement of
the prior art for providing minimum levels of corrosion
resistance.
[0020] Table 3 illustrates compositions of test specimens of the
austenitic stainless steel of Examples 13 to 22 and comparative
Examples 7 to 10 (only elements Ni, C, Si, Mn, Cr, and Cu are
shown). Table 4 illustrates a mechanical strength test for the test
specimens of the austenitic stainless steel of the Examples 13 to
22 and the comparative Examples 7 to 10. The test results show that
the austenitic stainless steel of this invention has an elongation
better than those of type 304 stainless steel of the prior art.
Other mechanical properties, such as tensile strength, yield
strength, and hardness, of the austenitic stainless steel of this
invention are comparable to those of type 304 stainless steel of
the prior art.
3 TABLE 3 Ni C Si Mn Cr Cu Examples 13 4.26 0.036 0.56 7.7 15.12
1.67 14 4.21 0.039 0.47 7.97 15.32 1.66 15 4.21 0.056 0.54 7.69
15.26 1.79 16 4.15 0.049 0.48 7.7 15.26 1.66 17 4.20 0.040 0.49
7.93 15.35 1.67 18 4.21 0.039 0.48 7.96 15.29 1.66 19 4.22 0.044
0.46 7.93 15.01 1.70 20 4.17 0.064 0.5 7.71 15.16 1.65 21 4.20
0.055 0.52 7.70 15.32 1.68 22 4.41 0.058 0.48 7.56 15.27 1.80
Comparative Example 7 8.06 0.039 0.53 1.17 18.14 0.23 8 8.04 0.041
0.50 1.15 18.15 0.21 9 8.08 0.039 0.49 1.18 18.17 0.24 10 8.03
0.040 0.52 1.11 18.09 0.22
[0021]
4TABLE 4 Tensile strength, Yield strength, Hardness, Elongation,
(MPa) (MPa) (HRBO) (%) Examples 13 621.7 313.3 83.5 55.2 14 630.2
289.5 82.5 55.3 15 628.5 287.6 82.3 55.0 16 642.3 291.3 82.8 53.1
17 618.4 312.0 84.3 53.7 18 634.6 296.4 82.8 53.8 19 639.0 317.2
83.9 54.1 20 642.6 319.7 84.7 54.3 21 621.7 313.3 83.5 55.2 22
641.9 301.6 83.4 53.4 Comparative Examples 7 660.0 324.6 83.2 49.1
8 660.6 325.0 82.6 46.8 9 663.8 328.9 82.4 48.8 10 657.8 322.8 81.8
48.5
[0022] The aforesaid tests show that the austenitic stainless steel
of this invention is capable of exhibiting excellent mechanical
strength, corrosion resistance, and phase stability during hot or
cold working with a relatively low nickel content and a low
chromium content as compared to those of the prior art.
[0023] With the invention thus explained, it is apparent that
various modifications and variations can be made without departing
from the spirit of the present invention.
* * * * *