RU2246554C2 - Chromium-nickel-manganese-copper austenite stainless steel with low nickel content - Google Patents

Abstract

FIELD: metallurgy, in particular chromium-nickel-manganese-copper austenite stainless steel.

SUBSTANCE: claimed steel contains (mass %) (a) C 0.03-0.12; (b) Si 0.2-1.0; (c) Mn 7.5-10.5; (d) Cr 14.0-16.0; (e) Ni 1.0-5.0; (f) N 0.04-0.25; (g) Cu 1.0-3.5; (h) Mo as trace element; and balance: Fe and inevitable impurities. Austenite stainless steel contains less, than 8.5 vol.% of δ-ferrite, determined as δ-ferrite = 6.77[(d)+(h)+1.5(b)]-4.85[(e)+30(a)+30(f)+0.5(c)+0.3(g)]-52.75.

EFFECT: austenite stainless steel of improved mechanical strength, high corrosion resistance, in particular in salt mist, and high phase stability during hot and cold treatment.

4 cl, 1 dwg, 4 tbl, 22 ex

Description

Technical field

The present invention relates to austenitic stainless steel, in particular to nickel-chromium-nickel-manganese-copper austenitic stainless steel.

State of the art

US Pat. No. 5,286,310 discloses chromium-nickel-manganese-copper austenitic stainless steel, which has a reduced nickel content and acceptable metallographic structure, mechanical strength, corrosion resistance and processability. Said austenitic stainless steel contains at least 16.5% by weight. chromium to ensure acceptable corrosion resistance. However, the chromium content should not exceed 17.5% wt. in order to avoid the undesired formation of delta ferrite (δ ferrite) during hot processing and the deterioration of suitability for hot processing. This austenitic stainless steel also contains at least 2.5% wt. nickel to improve cold workability and to inhibit the conversion of austenite to martensite. However, the nickel content should not exceed 5% wt. due to its relatively high price.

Although the austenitic stainless steel mentioned above has the ability to provide acceptable corrosion resistance and the ability to be processed in the cold or when heated, its chromium content is still high (previous research has shown that at least 17% by weight of chromium is required to ensure minimum levels of corrosion resistance) ), which can impair the stability of austenitic stainless steel and may cause cracking during hot rolling.

The disclosure of US Pat. No. 5,286,310 is incorporated by reference in this work.

Summary of invention

Thus, it is an object of the present invention to provide low nickel chromium nickel manganese-copper austenitic stainless steels that can overcome the disadvantages of the prior art.

According to the present invention, it is proposed austenitic stainless steel, which contains: (a) from 0.03 to 0.12% wt. FROM; (b) from 0.2 to 1.0% wt. Si; (c) from 7.5 to 10.5% by weight Mn; (vol.) from 14.0 to 16.0% wt. Cr; (e) from 1.0 to 5.0% by weight. Ni; (f) from 0.04 to 0.25% wt. N; (g) from 1.0 to 3.5% wt. Cu; (h) trace amount of Mo; the rest is Fe and random impurities. The content of δ-ferrite in austenitic stainless steel is less than 8.5 and satisfies the following formula:

δ-ferrite = 6.77 [(d) + (h) +1.5 (b)] - 4.85 [(e) +30 (a) +30 (f) +0.5 (c) +0 , 3 (g)] - 52.75.

A brief description of the graphic material

The drawing is a diagram illustrating the dependence of the content of δ-ferrite in a preferred embodiment of the austenitic stainless steel of the present invention from the temperature of the hot treatment.

Detailed Description of Preferred Option

A preferred embodiment of chromium nickel manganese-copper austenitic stainless steel with a low nickel content contains: (a) from 0.03 to 0.12% wt. FROM; (b) from 0.2 to 1.0% wt. Si; (c) from 7.5 to 10.5% by weight Mn; (d) from 14.0 to 16.0% by weight. Cr; (e) from 1.0 to 5.0% by weight. Ni; (f) from 0.04 to 0.25% by weight. N; (g) from 1.0 to 3.5% wt. Cu; (h) trace amount of Mo; the rest is Fe and random impurities. The content of δ-ferrite in austenitic stainless steel is less than 8.5 and satisfies the following formula:

δ-ferrite = 6.77 [(d) + (h) +1.5 (b)] - 4.85 [(e) +30 (a) +30 (f) +0.5 (s) +0 , 3 (g)] - 52.75,

in which (a), (b), (c), (d), (e), (f), (g), (h) denote the content of the corresponding elements (% wt.).

Austenitic stainless steel may also contain from 5 to 30 ppm. In to improve suitability for hot processing. The content of harmful impurities, such as S (sulfur) and P (phosphorus), should be as low as possible. However, for cost reasons associated with the removal of these impurities, the S content is limited to 150 ppm, and the P content is limited to 0.06% by weight.

The drawing shows a diagram of the dependence of the content of δ-ferrite in a preferred embodiment of the austenitic stainless steel of the present invention on temperature. The results show that when the temperature during hot rolling rises above 1250 ° C, the content of δ-ferrite increases sharply, which leads to the risk of cracking of the edges of the rolled sheet of austenitic stainless steel. At the same time, the minimum temperature for ensuring the required mechanical strength during hot rolling should be no lower than 1050 ° C.

Examples and comparative examples

The following examples and comparative examples illustrate unexpectedly improved results of the present invention compared with the results of the prior art.

Table 1 illustrates a test for the effect of cracking edges for different tested samples of austenitic stainless steel of examples 1-9 and comparative examples 1-5, which differ in composition (only elements Ni, C, Si, Mn, Cr and Cu are shown). A hot rolling test was conducted at temperatures ranging from 1050 to 1250 ° C. The test results show that in each example, the austenitic stainless steel of the present invention has a δ ferrite content lower than 8.5 and that no edge cracks were observed in the case of the test samples of Examples 1-9. Each of the tested samples of comparative examples 1-5, the content of δ-ferrite is higher than 8.5. Cracks at the edges were detected in each of the tested samples of comparative examples 1-5.

Table 1 Ni FROM Si δ ferrite Edge cracks Examples Mn Cr Cu 1 4.31 0,053 0.50 7.60 16.30 1,60 8.49 Not 2 4.05 0,032 0.53 7.85 15.36 1.71 6,636 Not 3 4.07 0,032 0.54 8.00 15.33 1,66 6,259 Not 4 4,55 0,032 0.58 7.54 15.23 1,59 4,984 Not 5 4.15 0.059 0.62 7.44 15.26 1.65 3,859 Not 6 4.24 0,046 0.42 7.86 15.68 1,66 3,278 Not 7 4.21 0.051 0.49 7.63 15.16 1,62 1,684 Not 8 4.09 0,060 0.50 8.08 15.14 1.70 0.109 Not nine 4.19 0,066 0.54 7.76 14,99 1.65 -1.989 Not Compares. Ni FROM Si Mn Cr Cu δ ferrite Edge cracks examples 1 4.31 0,039 0.47 7.07 19.04 2.15 28.58 Raster 2 4.36 0.05 0.45 7.58 17.53 2.03 15.82 Raster 3 4.37 0,046 0.47 7.96 18.33 1.71 22.60 Raster 4 4.11 0,052 0.51 7.54 18.13 1.73 19.85 Raster 5 4.45 0.051 0.53 7.5 16,20 1,5 9.1 Raster

Table 2 illustrates the corrosion test (ASTM B117) using salt spray for different test samples of austenitic stainless steel of examples 10-12 and comparative example 6 (stainless steel type 304), which differ in composition (only elements Ni, C, Si are shown , Mn, Cr and Cu). The test results show that in each example, austenitic stainless steel has a corrosion rate that is as low as the corrosion rate of type 304 stainless steel (not more than 0.1%) of the prior art.

It is noted that the chromium content in each of examples 1-12 of the austenitic stainless steel of the present invention is below 17 wt.%, Which is the minimum requirement of the prior art to ensure minimum levels of corrosion resistance.

Table 3 illustrates the compositions of the tested austenitic stainless steel samples of Examples 13-22 and Comparative Examples 7-10 (only elements Ni, C, Si, Mn, Cr and Cu are shown).

Table 4 illustrates the mechanical strength test of the tested austenitic stainless steel samples of Examples 13-22 and Comparative Examples 7-10. The test results show that the austenitic stainless steel of the present invention is characterized by a relative elongation greater than the elongation of type 304 stainless steel of the prior art. Other mechanical properties, such as tensile strength, yield strength and stiffness, of austenitic stainless steel of the present invention are comparable to the mechanical properties of type 304 stainless steel of the prior art.

Table 3 Examples Ni FROM Si Mn Cr Cu thirteen 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 fifteen 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 eighteen 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 twenty 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 Compares. Ni FROM Si Mn Cr Cu examples 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 nine 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

Table 4 Examples Tensile Strength (MPA) Yield Strength (MPa) Hardness (HRBO) Relative extension (%) thirteen 621.7 313.3 83.5 55.2 14 630.2 289.5 82.5 55.3 fifteen 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 eighteen 634.6 296.4 82.8 53.8 19 639.0 317.2 83.9 54.1 twenty 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 Compares. Tensile strength Limit Hardness Relative examples tensile strength (MPA) fluidity (HRBO) elongation (%) (MPa) 7 660.0 324.6 83,2 49.1 8 660.6 325,0 82.6 46.8 nine 663.8 328.9 82,4 48.8 10 657.8 322.8 81.8 48.5

The above tests show that the austenitic stainless steel of the present invention can exhibit excellent mechanical strength, corrosion resistance and phase stability during hot or cold processing with a relatively low nickel and low chromium content in comparison with the prior art steels.

It follows from the description of the invention that various modifications and changes may be made without departing from the scope of the present invention.

Claims (4)

1. Austenitic stainless steel containing (a) from 0.03 to 0.12 wt.% C; (b) from 0.2 to 1.0 wt.% Si; (c) from 7.5 to 10.5 wt.% Mn; (d) from 14.0 to 16.0 wt.% Cr; (e) from 1.0 to 5.0 wt.% Ni; (f) from 0.04 to 0.25 wt.% N; (g) from 1.0 to 3.5 wt.% Cu; (h) trace amount of Mo; the rest is Fe and random impurities, characterized in that the content of δ-ferrite in austenitic stainless steel is less than 8.5 and satisfies the following formula: δ-ferrite = 6.77 [(d) + (h) +1.5 (b)] - 4.85 [(e) +30 (a) +30 (f) +0.5 (c) +0 , 3 (g)] - 52.75. 2. Austenitic stainless steel according to claim 1, characterized in that it also contains 5-30 ppm. IN. 3. Austenitic stainless steel according to claim 1, characterized in that it also contains not more than 150 ppm. S. 4. Austenitic stainless steel according to claim 1, characterized in that it also contains not more than 0.06 wt.% R.