KR100552545B1 - Austenitic Stainless Steel Having Excellent Corrosion Resistance and Workability - Google Patents

Abstract

Austenitic stainless steel according to the present invention comprises (a) 0.03% to 0.12% by weight of C; (b) 0.2% to 1.0% Si; (c) 7.5% to 10.5% by weight of Mn; (d) 14.0% to 16.0% Cr; (e) 1.0 wt% to 5.0 wt% Ni; (f) 0.04% to 0.25% by weight of N; (g) 1.0 wt% to 3.5 wt% Cu; (h) trace Mo; And Fe and incidental impurities as the balance component. The austenitic stainless steel is 6.77 [(d) + (h) + 1.5 (b)]-4.85 [(e) + 30 (a) + 30 (f) + 0.5 (c) + 0.3 (g) )]-52.75 and a δ-ferrite content of less than 8.5.

Nickel, Chromium, Manganese, Copper, Austenitic, Stainless Steel

Description

Austenitic Stainless Steel Having Excellent Corrosion Resistance and Workability}

1 is a diagram showing the relationship between the high temperature (or hot) processing temperature and δ-ferrite content of austenitic stainless steel according to a preferred embodiment of the present invention.

FIELD OF THE INVENTION The present invention relates to austenitic stainless steels, and more particularly to nickel-containing chromium-nickel-manganese-copper austenitic stainless steels.

U.S. Patent No. 5,286,310 discloses a nickel low chromium-nickel-manganese-copper auster having a reduced nickel content and having an acceptable metallographic structure, mechanical strength, corrosion resistance, and workability. Knight stainless steels are disclosed. The austenitic stainless steels described above contain at least 16.5% by weight of chromium to show acceptable collapse resistance. However, the chromium content should not exceed 17.5% by weight because it has defects on undesirable delta ferrite (δ-ferrite) formation and hot workability during hot working. The austenitic stainless steels described above further comprise at least 2.5% by weight of nickel to improve cold workability and to prevent the austenite from being transformed into martensite. However, nickel should not exceed 5% by weight because of its relatively high price.

Although the austenitic stainless steels described above have acceptable collapse resistance and cold or hot workability, the chromium content is still high (at least 17% by weight of chromium has been minimally collapsed in previous studies). This may adversely affect the stability of the austenitic stainless steel and may cause cracking during high temperature rolling.

U.S. Patent 5,286,310 is incorporated herein by reference.

Accordingly, an object of the present invention is to provide a nickel-containing chromium-nickel-manganese-copper austenitic stainless steel which can solve the above-mentioned problems of the prior art.

Austenitic stainless steel according to the present invention comprises (a) 0.03% to 0.12% by weight of C; (b) 0.2% to 1.0% Si; (c) 7.5% to 10.5% by weight of Mn; (d) 14.0% to 16.0% Cr; (e) 1.0 wt% to 5.0 wt% Ni; (f) 0.04% to 0.25% by weight of N; (g) 1.0 wt% to 3.5 wt% Cu; (h) trace Mo; And Fe and inevitable impurities as balance components. The austenitic stainless steel has a δ-ferrite content of less than 8.5 that satisfies Equation 1 below:

δ-ferrite = 6.77 [(d) + (h) +1.5 (b)]-4.85 [(e) +30 (a) +30 (f) +0.5 (c) +0.3 (g)]-52.75.

The low nickel content chromium-nickel-manganese-copper austenitic stainless steel according to the present invention comprises (a) 0.03% to 0.12% by weight of C; (b) 0.2% to 1.0% Si; (c) 7.5% to 10.5% by weight of Mn; (d) 14.0% to 16.0% Cr; (e) 1.0 wt% to 5.0 wt% Ni; (f) 0.04% to 0.25% by weight of N; (g) 1.0 wt% to 3.5 wt% Cu; (h) trace Mo; And Fe and incidental impurities as the balance component. The austenitic stainless steel has a δ-ferrite content of less than 8.5 that satisfies Equation 1 below:

Equation 1

δ-ferrite = 6.77 [(d) + (h) +1.5 (b)]-4.85 [(e) +30 (a) +30 (f) +0.5 (c) +0.3 (g)]-52.75,

In the above formula, (a), (b), (c), (d), (e), (f), (g) and (h) refer to the content (wt%) of each component.

The austenitic stainless steel may further include 5 to 30 ppm of B in order to improve hot working. The content of harmful impurities such as S (sulfur) and P (phosphorus) is as low as possible. However, due to the cost of removing such impurities, the S content is limited to 150 ppm and the P content is limited to 0.06% by weight.

1 is a diagram showing the relationship between the high temperature processing temperature and δ-ferrite content of austenitic stainless steel according to a preferred embodiment of the present invention. From the above results, if the temperature is elevated above 1250 ° C. during hot rolling, the δ-ferrite content is rapidly increased, which is a risk of edge cracking of the rolled plate of the austenitic stainless steel. Height results. In addition, to obtain satisfactory mechanical strength, a temperature of at least 1050 ° C. is required during hot rolling.

Examples and Comparative Examples

The following examples and comparative examples are intended to contrast the improved results of the present invention with respect to the prior art.

Table 1 shows edge crack effect tests for austenitic stainless steel samples according to Examples 1-9 and Comparative Examples 1-5 (only Ni, C, Si, Mn, Cr, and Cu elements) with different composition contents. It is shown. The test was performed by hot rolling at a temperature of 1050 ° C to 1250 ° C. From the test results, it was found that each example of the austenitic stainless steel according to the present invention had a δ-ferrite content of less than 8.5, and no edge cracks appeared in any of the samples of Examples 1-9. Each sample of Comparative Examples 1 to 5 has a δ-ferrite content of 8.5 or more. Edge cracks were observed in the test samples of Comparative Examples 1 to 5, respectively.

Example Ni C Si Mn Cr Cu δ-ferrite Edge crack One 4.31 0.053 0.50 7.60 16.30 1.60 8.49 none 2 4.05 0.032 0.53 7.85 15.36 1.71 6.636 none 3 4.07 0.032 0.54 8.00 15.33 1.66 6.259 none 4 4.55 0.032 0.58 7.54 15.23 1.59 4.984 none 5 4.15 0.059 0.62 7.44 15.26 1.65 3.859 none 6 4.24 0.046 0.42 7.86 15.68 1.66 3.278 none 7 4.21 0.051 0.49 7.63 15.16 1.62 1.684 none 8 4.09 0.060 0.50 8.08 15.14 1.70 0.109 none 9 4.19 0.066 0.54 7.76 14.99 1.65 -1.989 none Comparative example Ni C Si Mn Cr Cu δ-ferrite Edge crack One 4.31 0.039 0.47 7.07 19.04 2.15 28.58 Cracking 2 4.36 0.05 0.45 7.58 17.53 2.03 15.82 Cracking 3 4.37 0.046 0.47 7.96 18.33 1.71 22.60 Cracking 4 4.77 0.052 0.51 7.54 18.13 1.73 19.85 Cracking 5 4.45 0.051 0.53 7.5 16.20 1.5 9.1 Cracking

Table 2 shows austenitic stainless steel samples of Examples 10-12 and Comparative Example 6 (304 stainless steel type) (only Ni, C, Si, Mn, Cr, Cu and B elements shown) having different composition contents. The collapse resistance test (ASTM B117) using salt fog is shown. From the above results, it can be seen that each embodiment of the austenitic stainless steel according to the present invention has a lower decay rate than 304 stainless steel according to the prior art (0.1% or less).

Example Ni C Si Mn Cr Cu B Decay rate 10 4.40 0.058 0.48 7.56 15.26 1.79 0.0001 ≤0.1 wt% 11 4.11 0.051 0.54 7.86 15.35 1.69 0.0032 ≤0.1 wt% 12 3.40 0.059 0.77 7.84 14.94 1.78 0.0001 ≤0.1 wt% Comparative example Ni C Si Mn Cr Cu B Decay rate 6 8.02 0.045 0.53 1.25 18.19 0.23 0.0008 ≤0.1 wt%

It can be seen that the chromium content of Examples 1 to 12 of the austenitic stainless steel according to the invention is less than 17% by weight, which is the minimum level of collapse resistance required in the prior art.

Table 3 shows the test sample compositions (only Ni, C, Si, Mn, Cr, and Cu) of the austenitic stainless steels of Examples 13-22 and Comparative Examples 7-10. Table 4 shows the mechanical strength tests for the test samples of Examples 13 to 22 and Comparative Examples 7 to 10. It can be seen from the Tess results that the austenitic stainless steel of the present invention exhibits excellent elongation compared to the 304 type stainless steel according to the prior art. The tensile strength, yield strength, and hardness of the austenitic stainless steel of the present invention and the 304 type stainless steel according to the prior art are compared.

Example Ni C Si Mn Cr Cu 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 Ni C Si Mn Cr Cu 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

Example Tensile strength (MPa) Yield strength (MPa) Hardness (HRBO) Elongation (%) 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 example Tensile strength (MPa) Yield strength (MPa) Hardness (HRBO) Elongation (%) 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

From the above test, the austenitic stainless steel of the present invention has a relatively low nickel content and a low chromium content compared to the prior art, and exhibits excellent mechanical strength, collapse resistance, and phase stability during hot or cold processing. It can be seen.

The present invention is not limited to the above-described embodiments, and it is apparent that various modifications and changes can be made without departing from the spirit of the present invention.

As described above, according to the present invention, it is possible to provide an austenitic stainless steel having a relatively low nickel content and a low chromium content compared to the prior art, which exhibits excellent mechanical strength, collapse resistance, and phase stability at high temperature or cold working. have.

Claims (7)

(a) 0.03% to 0.12% by weight of C; (b) 0.2% to 1.0% Si; (c) 7.5% to 10.5% by weight of Mn; (d) 14.0% to 16.0% Cr; (e) 4.15% to 4.41% by weight of Ni; (f) 0.04% to 0.25% by weight of N; (g) 1.0 wt% to 3.5 wt% Cu; (h) trace amount of Mo; And A balance component containing Fe and incidental impurities; Has a δ-ferrite content of less than 8.5 that satisfies Equation 1 below, Austenitic stainless steels with good collapse resistance and processability, characterized by a tensile strength in the range of 621.7 to 642.6 MPa: Equation 1 δ-ferrite = 6.77 [(d) + (h) +1.5 (b)]-4.85 [(e) +30 (a) +30 (f) +0.5 (c) +0.3 (g)]-52.75. The austenitic stainless steel of claim 1, wherein the austenitic stainless steel further comprises 5 to 30 ppm of B. The austenitic stainless steel of claim 1, wherein the austenitic stainless steel further comprises S of 150 ppm or less. The austenitic stainless steel of claim 1, wherein the austenitic stainless steel further comprises up to 0.06% by weight of P. 5. 2. The austenitic stainless steel according to claim 1, wherein the yield strength of the austenitic stainless steel is in the range of 287.6 to 319.7 MPa. The austenitic stainless steel according to claim 1, wherein the elongation of the austenitic stainless steel is in the range of 53.1 to 55.3%. The austenitic stainless steel according to claim 1, wherein the austenitic stainless steel has a hardness in the range of 82.3 to 84.7.

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