CN116536574B

CN116536574B - Austenitic stainless steel with excellent low-temperature performance and preparation method thereof

Info

Publication number: CN116536574B
Application number: CN202310299301.8A
Authority: CN
Inventors: 胡昕明; 欧阳鑫; 王储; 邢梦楠; 贾春堂; 刘晨希; 王勇; 胡海洋
Original assignee: Angang Steel Co Ltd
Current assignee: Angang Steel Co Ltd
Priority date: 2023-03-24
Filing date: 2023-03-24
Publication date: 2024-07-23
Anticipated expiration: 2043-03-24
Also published as: CN116536574A

Abstract

The invention provides austenitic stainless steel with excellent low-temperature performance and a preparation method thereof, wherein the stainless steel comprises the following ：C:0.04-0.08％、Si≤1.00％、Mn:2.10-3.50％、P≤0.020％、S≤0.010％、Ni:7.50-9.50％、Cr:20.00-25.00％、Mo:4.00-5.00％、N:0.15-0.30％、V:2.00-3.00％, weight percent of chemical components, and the balance of Fe and unavoidable impurities. The preparation method comprises smelting, continuous casting, forging, homogenizing, rolling and heat treatment. The austenitic stainless steel with excellent low-temperature performance has excellent low-temperature performance and high corrosion resistance.

Description

Austenitic stainless steel with excellent low-temperature performance and preparation method thereof

Technical Field

The invention relates to the technical field of steel preparation, in particular to corrosion-resistant urea-grade austenitic stainless steel with excellent low-temperature performance and a preparation method thereof, and especially relates to austenitic stainless steel with excellent low-temperature performance and a preparation method thereof.

Background

The traditional urea-grade austenitic stainless steel has the problem that the C content in the steel is required to be less than or equal to 0.03% in order to ensure that the ferrite content is low, so that the strength of the steel plate at normal temperature and low temperature is low, and the large-scale and high-pressure of urea production equipment cannot be met, which is an important development trend in the future. If the C element in the steel is greatly increased, the normal temperature and low temperature strength of the steel plate can be improved, but the corrosion resistance and low ferrite requirement of urea-grade austenitic stainless steel cannot be ensured, and the low temperature toughness is also adversely affected. In addition, the urea grade stainless steel commonly used at present is mainly 300-series austenitic stainless steel, for example, 316LMOD has good corrosion resistance, but cannot be used for manufacturing large-scale and high-pressure urea equipment due to relatively low strength. Meanwhile, the steel plate has high Ni content, so that the production cost of the steel plate is high.

The invention relates to an austenitic stainless steel with excellent ultralow temperature performance and a manufacturing method thereof (CN 109554608B), wherein the content of ferrite is less than 0.5% by controlling C to be less than or equal to 0.03% and Ni to be 11.5-12.8%, but the corrosion resistance, particularly pitting corrosion resistance, of the austenitic stainless steel is not more than 0.3% due to Mo.

The invention relates to an austenitic stainless steel plate with excellent medium-low temperature strength and a manufacturing method thereof (CN 101845605B), wherein C is less than or equal to 0.03 percent, ni is 10-13 percent, and the normal-temperature tensile strength is 660MPa, but the invention does not relate to the yield strength at-196 ℃ and the impact absorption energy at-250 ℃, and meanwhile, the invention also does not refer to the intergranular corrosion performance.

Therefore, in order to achieve excellent low temperature performance and high corrosion resistance of urea grade austenitic stainless steel, development of corrosion resistant urea grade austenitic stainless steel having excellent low temperature performance and a method for manufacturing the same are desired.

Disclosure of Invention

According to the above technical problems, an austenitic stainless steel excellent in low temperature properties and a method for preparing the same are provided.

The invention adopts the following technical means:

an austenitic stainless steel excellent in low temperature properties, which comprises the chemical components (in weight%) as follows:

C:0.04-0.08％、Si≤1.00％、Mn:2.10-3.50％、P≤0.020％、S≤0.010％、Ni:7.50-9.50％、Cr:20.00-25.00％、Mo:4.00-5.00％、N:0.15-0.30％、V:2.00-3.00％, The balance of Fe and unavoidable impurities.

The effect of the above chemical elements is analyzed as follows:

C is an important element of austenitic stainless steel, which can enlarge the austenite region while suppressing the formation of ferrite in the steel. In addition, the existence of the C element in the steel in the form of solid solution or carbide precipitation can also effectively improve the normal temperature and low temperature strength of the steel plate. However, too high a C content not only increases the hardness of the weld heat affected zone and post-weld heat treatment cracks, but also is detrimental to the intergranular corrosion resistance of the steel sheet. Therefore, the C content is limited to 0.04-0.08%.

Si is the main deoxidizing element of austenitic stainless steel, and can effectively reduce the oxygen content in the steel and improve the purity of the steel by improving the oxidation resistance of the steel. However, too high a Si content promotes brittle sigma phase formation or precipitation of a Si-rich G phase at grain boundaries while adversely affecting the stability of austenite. Therefore, the Si content is 1.00% or less.

Mn is an important element of austenitic stainless steel, and Mn element can enlarge an austenite region and improve the strength performance of the steel. In addition, mn is used to replace Ni to some extent in order to obtain an austenitic structure, and the addition of Mn can significantly improve the solubility of N. However, too high a Mn content may affect the weldability of the steel sheet. Therefore, the Mn content is limited to 2.10-3.50%.

Ni is an important element of austenitic stainless steel, and Ni element can inhibit ferrite formation in the steel while enlarging an austenite region. Meanwhile, the steel plate has good oxidation corrosion resistance when being matched with Cr element. Since it is expensive, the Ni content is limited to 7.50-9.50% for cost control.

Cr is an important element for oxidation resistance and corrosion resistance in austenitic stainless steel. In order to ensure the stainless steel to have excellent corrosion resistance, the phenomenon that a chromium-poor region appears near the grain boundary due to precipitation of M ₂₃C₆ carbide is prevented, and meanwhile, the increase of the Cr content is beneficial to improving the solubility of N in the steel, but excessive addition of the Cr content leads to coarsening of the carbide and further leads to reduction of the strength and toughness of the steel plate. Thus, the Cr content is limited to 25.00-30.00%.

Mo is an important element in austenitic stainless steel for improving high temperature strength and corrosion resistance, and in addition, it has a strong affinity for P, it can reduce the amount of segregated P at grain boundaries, and is advantageous for the reduction of weld heat treatment cracking sensitivity. Therefore, the Mo content is limited to 4.00-5.00%.

N is a strong austenite forming and stabilizing element, and can also replace part of Ni element in austenitic heat-resistant steel to form a more stable austenite structure. The low-temperature strength of the steel plate is obviously improved, and the ductility of the steel plate is not damaged. Therefore, the N content is limited to 0.15-0.30%.

The main function of V in steel is to form carbide and nitride with C, N preferentially, avoid the precipitation of chromium carbide and chromium nitride to form a 'chromium-poor zone' near the grain boundary, and increase the intergranular corrosion of the steel plate. Thus, the V content is limited to 2.00-3.00%.

P, S is a detrimental element of austenitic stainless steel, theoretically the lower the content, the better, but excessive reduction will lead to a significant increase in manufacturing costs. Therefore, the P content is limited to 0.020% or less and the S content is limited to 0.010% or less.

The invention also discloses a preparation method of the austenitic stainless steel with excellent low-temperature performance, which comprises the following steps: smelting, continuous casting, forging, homogenizing rolling, solution treatment and stabilization treatment, wherein the specific method comprises the following steps:

(1) Smelting: stainless steel smelting is carried out by adopting an electric furnace smelting method, an AOD (argon oxygen decarburization) and a VOD steelmaking method.

(2) Continuous casting: the pouring temperature of the molten steel in the tundish is 1570-1590 ℃, the superheat degree of the continuous casting billet is 60-80 ℃, and the pulling speed of the continuous casting billet is 1.0-1.3m/min; the rolling reduction of the continuous casting billet under light rolling is 5-8mm, and the rolling reduction rate is 0.6-1.2mm/m.

(3) Forging: the heating temperature is 1220-1250 ℃, the heat preservation is carried out for 5-10 hours, the deformation of each forging pass is controlled to be 20-30mm, and the deformation is accumulated for 4-5 passes until the forging process is completed.

(4) Homogenizing: heating to 1240-1260 ℃, carrying out net heat preservation for 80-100h, and then carrying out the last forging after the heat preservation is finished, wherein the deformation is 10-15mm, so as to ensure that the prior austenite structure is relatively fine before rolling.

(5) Rolling: the adding temperature of the continuous casting billet is 1200-1230 ℃; adopting two-stage rolling, wherein the initial rolling temperature of rough rolling is more than or equal to 1130 ℃, the final rolling temperature is more than or equal to 1000 ℃, the rolling passes in the stage are 4-6 times, the roller speed is controlled to be 40-60r/min, and the first pass reduction rate is more than or equal to 20%; the initial rolling temperature is more than or equal to 950 ℃ and the final rolling temperature is more than or equal to 850 ℃ in the finish rolling stage, the single pass rolling reduction is 8-10%, the rolling pass is 5-7 times in the stage, and the roller speed is controlled to be 20-25r/min.

(6) And (3) heat treatment: the solution heat treatment temperature is 980-1100 ℃, the net heat preservation time is 10-60mm, and the solution is cooled to room temperature after being discharged from the furnace.

The nitrogen-containing urea-grade austenitic stainless steel manufactured by the components and the process has the width of 2000-5000mm and the thickness of 10-35mm, and has the yield strength of more than or equal to 380MPa, the tensile strength of more than or equal to 710MPa and the elongation of more than or equal to 50 percent at room temperature; the yield strength at the temperature of minus 196 ℃ is more than or equal to 750MPa, and the impact absorption energy at the temperature of minus 250 ℃ is more than or equal to 150J; ferrite content less than 0.1%, grain size 4-6 grade; after the sensitization treatment at 650 ℃ and 2 hours, the method meets the requirement of GB/T4334-2018 method E of intergranular corrosion test method for corrosion stainless steel of metals and alloys, and simultaneously meets the requirement of average corrosion rate less than or equal to 3.0 mu m/48 hours in five corrosion periods according to the requirement of ASTMA262 standard method C for detecting intergranular corrosion sensitivity of austenitic stainless steel.

According to the invention, a large amount of C, N elements are added, so that the normal-temperature and low-temperature strength of the steel plate is improved, the Ni content of the noble metal element in the steel is reduced, and the manufacturing cost of the steel plate is greatly reduced; by increasing the Cr and Mo contents in the steel, the corrosion resistance of the steel plate is improved, and the increase of the Cr content is also beneficial to improving the solubility of N in the steel. In addition, the addition of the V element avoids the occurrence of a 'chromium-deficient zone' near a grain boundary, and further improves the corrosion resistance of the steel plate.

For the reasons, the invention can be widely popularized in the fields of high corrosion-resistant urea-grade austenitic stainless steel with excellent low-temperature performance and the like.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a photograph of ferrite in an austenitic stainless steel excellent in low-temperature properties according to an embodiment of the present invention.

FIG. 2 is a photograph showing grain size of an austenitic stainless steel excellent in low temperature properties according to an embodiment of the present invention.

Detailed Description

It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. The described embodiments are only some, but not all, embodiments of the invention. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The preparation method comprises the following steps:

The following describes the invention in more detail with reference to 10 examples. The chemical compositions of 10 examples are shown in table 1;

table 1 example chemical composition (wt%)

Examples	C	Si	Mn	Cr	Ni	N	V	Mo
									1	0.044	0.11	3.21	21.84	7.64	0.23	2.97	4.38
2	0.067	0.21	2.13	20.19	7.77	0.34	2.62	4.77
									3	0.078	0.35	3.21	22.86	8.51	0.26	2.23	4.98
4	0.065	0.47	3.13	21.83	8.64	0.34	2.46	4.14
									5	0.059	0.52	3.08	23.74	8.26	0.25	2.32	4.06
6	0.057	0.68	2.79	23.83	9.31	0.35	2.56	4.61
									7	0.056	0.72	3.42	24.29	9.16	0.38	2.73	4.31
8	0.064	0.85	2.19	23.74	8.43	0.27	2.84	4.35
									9	0.041	0.95	2.13	20.11	7.53	0.15	2.01	4.02
10	0.079	0.93	3.48	24.98	9.47	0.30	2.99	4.98

The smelting and continuous casting processes of 10 examples are shown in Table 2;

table 2 example smelting and continuous casting process

Examples	Molten steel temperature DEG C	Degree of superheat	Pulling speed m/min	Reduction in mm	Reduction percentage%
						1	1576	78	1.1	6.7	1.14
2	1583	72	1.2	7.9	1.03
						3	1575	66	1.2	5.9	0.83
4	1586	67	1.0	7.3	0.98
						5	1584	74	1.2	6.4	1.19
6	1576	77	1.2	6.5	0.66
						7	1580	60	1.1	7.6	1.05
8	1577	65	1.3	5.3	0.76
						9	1570	60	1.0	5.0	0.61
10	1590	80	1.3	8.0	1.20

The forging and homogenization processes for 10 examples are shown in table 3;

table 3 example forging and homogenizing process

The rolling process of 10 examples is shown in table 4;

table 4 example rolling process

The heat treatment process for 10 examples is shown in table 5;

table 5 example heat treatment process

Examples	Temperature (DEG C)	Clean incubation time min
			1	991	14
2	1067	47
			3	999	37
4	1070	26
			5	1090	56
6	1033	13
			7	1088	35
8	1018	46
			9	980	10
10	1100	60

The performance parameters of an austenitic stainless steel with excellent low-temperature performance prepared according to the above components and the preparation process are shown in table 6;

Table 6 example overall performance

Note that: the steel plates of examples 1-10 meet the requirements of GB/T4334-2018 method E of intergranular corrosion test method for corrosion stainless steel of metals and alloys after being sensitized at 650 ℃ for 3 hours.

As is clear from Table 6, the austenitic stainless steel excellent in low-temperature performance provided by the present invention has excellent corrosion resistance and excellent low-temperature performance while reducing the manufacturing cost.

As shown in fig. 1, the residual ferrite content in the stainless steel was 0.02%, and as shown in fig. 2, the grain size in the stainless steel was 4.5 grade.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims

1. An austenitic stainless steel with excellent low-temperature performance is characterized by comprising the following chemical components in percentage by weight:

C:0.04-0.08%、Si≤1.00%、Mn:2.10-3.50%、P≤0.020%、S≤0.010%、Ni:7.50-9.50%、Cr:20.00-25.00%、Mo:4.00-5.00%、N:0.15-0.30%、V:2.00-3.00%, The balance of Fe and unavoidable impurities;

The stainless steel is urea-grade austenitic stainless steel;

The preparation method of the stainless steel comprises the following steps:

(1) Smelting:

Smelting according to the components to obtain molten steel;

(2) Continuous casting;

(3) Forging;

(4) Homogenizing:

heating to 1240-1260 ℃, carrying out net heat preservation for 80-100h, and forging for the last time after heat preservation is finished, wherein the deformation is 10-15mm, so that a relatively fine original austenite structure is ensured before rolling;

(5) Rolling:

The heating temperature of the continuous casting billet is 1200-1230 ℃; adopting two-stage rolling, wherein the initial rolling temperature of rough rolling is more than or equal to 1130 ℃, the final rolling temperature is more than or equal to 1000 ℃, the rolling passes in the stage are 4-6 times, the roller speed is controlled to be 40-60r/min, and the first pass reduction rate is more than or equal to 20%; the initial rolling temperature is more than or equal to 950 ℃ in the finish rolling stage, the final rolling temperature is more than or equal to 850 ℃, the single pass rolling reduction is 8-10%, the rolling passes in the stage are 5-7 times, and the roller speed is controlled to be 20-25r/min;

(6) Heat treatment is carried out to obtain the stainless steel;

The heat treatment adopts solution heat treatment, and the specific process is as follows: the solution heat treatment temperature is 980-1100 ℃, the clean heat preservation time is 10-60min, and the water cooling is carried out to the room temperature after the furnace is taken out.

2. The austenitic stainless steel excellent in low-temperature properties according to claim 1, wherein the stainless steel has a width of 2000-5000mm and a thickness of 10-35mm.

3. The austenitic stainless steel excellent in low-temperature properties according to claim 1, wherein the yield strength at room temperature of the stainless steel is not less than 380MPa, the tensile strength is not less than 710MPa, and the elongation is not less than 50%.

4. The austenitic stainless steel excellent in low-temperature properties according to claim 1, wherein the yield strength of the stainless steel is not less than 750MPa at-196 ℃ and the impact absorption energy is not less than 150J at-250 ℃.

5. The austenitic stainless steel excellent in low-temperature properties according to claim 1, wherein the ferrite content in the stainless steel is < 0.1%, and the grain size of the stainless steel is 4-6 grade.

6. The austenitic stainless steel excellent in low-temperature properties according to claim 1, wherein in said step (2), the specific process of continuous casting is as follows: the pouring temperature of the molten steel in the tundish is 1570-1590 ℃, the superheat degree of the continuous casting billet is 60-80 ℃, and the pulling speed of the continuous casting billet is 1.0-1.3m/min; the rolling reduction of the continuous casting billet is 5-8mm.

7. The austenitic stainless steel excellent in low-temperature properties according to claim 1, wherein in the step (3), the specific process of forging is as follows: heating at 1220-1250 ℃, preserving heat for 5-10h, controlling the deformation of each forging pass to be 20-30mm, and carrying out deformation accumulation for 4-5 passes.