Economical high-nitrogen easy-to-form austenitic stainless steel and its manufacturing method

Abstract

Disclosed are an economical high-nitrogen, easy-to-form austenitic stainless steel and a manufacturing method thereof. The chemical composition of the stainless steel comprises the following components by mass: C 0.05-0.08%, Si 0.25-1.0%, Mn 5.0-8.0%, Cr 16.5-19.5%, Ni 2.5-4.5%, Cu 0.5-2.0%, P≤0.045%, S≤0.0020%, and N 0.20-0.30%, with the remainder comprising Fe and unavoidable impurities. The stainless steel also satisfies a bulging index FT≥50, where FT=551-162×(C%+N%)-9.2×Si%-8.1×Mn%-29×Ni%-39×Cu%-13.7×Cr%. By alloying Mn and N, the present invention further controls the bulging index FT ≥ 50 while reducing the Ni content and alloy cost, achieving an elongation ≥ 55% and a cupping value Er ≥ 11.0 mm, thereby achieving the goal of easy forming of economical high-nitrogen high-strength steel, and ultimately successfully applying it to products such as dishwasher door panels and range hood covers.

Description

Technical Field

[0001] The present invention relates to austenitic stainless steel and a manufacturing method thereof, and in particular to an economical high-nitrogen easy-to-form austenitic stainless steel and a manufacturing method thereof. Background Art

[0002] Austenitic stainless steel, represented by 304, boasts excellent corrosion resistance, processing properties, and formability, and is widely used in products such as dishwasher door panels and range hood covers. However, 304 stainless steel has a relatively high nickel content of approximately 8%, while my country's nickel resources are scarce, accounting for only 3.93% of the world's approximately 80 million tons of nickel metal reserves.

[0003] In recent years, two major types of nickel-saving austenitic stainless steels, namely 14% chromium content and 1% nickel content and 16% chromium content and 4% nickel content, have been industrialized at home and abroad. However, the pitting equivalent PREN (Cr+3.3Mo+30N-Mn) value is lower than 16.0, and the corrosion resistance is far inferior to 304 stainless steel (PREN value 18.5). It can only be used in dry areas and interior decoration fields, and its application range is severely limited.

[0004] Since 2018, domestic stainless steel companies have adopted the design concept of replacing Ni with Mn and N. For example, the 304-grade corrosion-resistant high-nitrogen nickel-saving austenitic stainless steel disclosed in Chinese patent announcement number CN112501493B has a PREN value of more than 18.5. The product has excellent corrosion resistance and has been widely used in many fields, such as containers, prefabricated buildings, and decorative welded pipes. However, the yield strength of this product exceeds 400MPa, and the elongation is slightly lower, only about 50%. It can replace 304 stainless steel stamping dishwasher door panels (see Figure 1 ) and range hood (see Figure 2 ) cracking occurs at large deformation locations. Summary of the Invention

[0005] The present invention aims to provide an economical, easily formable high-nitrogen austenitic stainless steel and a manufacturing method. The stainless steel has low cost, pitting corrosion resistance comparable to 304 stainless steel, a yield strength greater than 400 MPa, an elongation greater than 55%, a cupping value Er greater than 11.0 mm, and a pitting corrosion potential greater than 300 mV. The present invention overcomes the problem of cracking during forming of high-nitrogen, high-strength stainless steel and successfully replaces 304 stainless steel in applications such as dishwasher door panels and range hood covers.

[0006] To achieve the above objectives, the technical solutions of the present invention are as follows:

[0007] Economical high nitrogen easy-to-form austenitic stainless steel, its chemical composition by mass percentage is:

[0008] C: 0.05~0.08%,

[0009] Si: 0.25-1.0%,

[0010] Mn: 5.0~8.0%,

[0011] Cr: 16.5~19.5%,

[0012] Ni: 2.5-4.5%,

[0013] Cu: 0.5-2.0%,

[0014] P≤0.045%,

[0015] S≤0.0020%,

[0016] N: 0.20~0.30%,

[0017] The balance includes Fe and other unavoidable impurities, and the above elements must simultaneously satisfy the following relationship:

[0018] Bulging index FT≥50,

[0019] FT=551-162×(C%+N%)-9.2×Si%-8.1×Mn%-29×Ni%-39×Cu%-13.7×Cr%.

[0020] Furthermore, the balance is Fe and other inevitable impurities.

[0021] Yield strength Rp of the stainless steel of the present invention 0.2 >400MPa, elongation ≥55%, cupping value Er ≥11.0mm, pitting potential >300mV.

[0022] In the composition design of the economical high nitrogen easy-to-form austenitic stainless steel of the present invention:

[0023] In order to obtain 304 grade corrosion resistant stainless steel, the Cr content of the product is controlled at 16.5-19.5%. Furthermore, since N exists in the form of NH3 in the passivation film, when the passivation film dissolves, NH3 can combine with the dissolved site H + Formation of NH4 + , which increases the local pH and inhibits the further dissolution of the passivation film, thereby improving the pitting corrosion resistance of the passivation film. Therefore, the present invention further improves the pitting corrosion resistance of the product through N alloying, and ultimately obtains 304-grade corrosion-resistant stainless steel. To ensure that the added N remains in the material during the solidification process and does not escape from the molten steel in the form of nitrogen gas, Mn is simultaneously added to increase the nitrogen solubility of the molten steel. In addition, by alloying Mn and N, it can also replace some Ni elements, thereby saving Ni resources and reducing alloy costs.

[0024] N exists in the form of interstitial solid solution atoms in austenite, which significantly improves the yield strength of the product and slightly reduces the elongation. In order to make the steel of the present invention have excellent bulging properties on the basis of high-strength mechanical properties, the present invention studies the relationship between the bulging index FT and the content of each element. FT is a characterization of the bulging performance of the product. The bulging performance of the material is not only related to the yield strength, but also to the work hardening ability after plastic deformation. The work hardening ability is mainly affected by the content of deformation-induced martensite. The higher its content, the stronger the work hardening ability and the better the bulging performance. Traditionally, M d30 / 50 Characterizes the ability of deformation-induced martensite, that is, the temperature at which 30% deformation produces 50% martensite. The empirical formula is: M d30 / 50＝ 551-462×(C%+N%)-9.2×Si%-8.1×Mn%-29×Ni%-29×Cu%-13.7×Cr%-18.5Mo%. This empirical formula is fitted based on the basic data of Cr-Ni austenitic stainless steel represented by 304. The interstitial C and N contents of Cr-Ni austenitic stainless steel are relatively low (C%+N%<0.15%). C and N cannot completely occupy the interstitial Fe atoms, resulting in insufficient austenite stability. In this case, increasing the C and N contents can significantly improve austenite stability and significantly reduce M d30 / 50 , and sharply reduce the cupping value ( Figure 3 ).

[0025] However, the high nitrogen austenitic stainless steel of the present invention has a high content of C and N (C% + N% > 0.25%). C and N atoms fully occupy the interstitial spaces between Fe atoms in the form of interstitial solid solution atoms, and the austenite stability is relatively high. At this time, increasing the C and N content can only slightly improve the austenite stability and slightly reduce the M d30 / 50 , and slightly reduce the cupping value ( Figure 4 ). Therefore, in the steel of the present invention, M d30 / 50 It cannot be used directly to characterize the stability of high nitrogen austenite. d30 / 50 Correct the C and N coefficients. Low C+N content Figure 3 The slope is -20.4, which is a high C+N content Figure 4 The slope is 2.85 times of -7.16, so the corresponding M d30 / 50 The C and N coefficients of the steel are reduced by 2.85 times. At the same time, considering that the steel of the present invention contains a higher Mn content, the effect of Cu in stabilizing austenite and inhibiting the formation of deformation martensite in high manganese steel is more significant than in low manganese Cr-Ni stainless steel, so the influence coefficient of Cu content is also corrected accordingly. The corrected M d30 / 50 That is, the relationship between the bulging index FT and each alloy element is:

[0026] FT=551-162×(C%+N%)-9.2×Si%-8.1×Mn%-29×Ni%-39×Cu%-13.7×Cr%.

[0027] The influence coefficients of C and N were revised from -462 to -162, the influence coefficient of Cu was revised from -29 to -39, and the fitting degree R between the bulging index FT and the actual cupping value of industrialized high nitrogen austenitic stainless steel was 2 ( Figure 5 ) is 0.90, and M d30 / 50 The fitting degree R with the actual cupping value of industrialized high nitrogen austenitic stainless steel 2 Only 0.71( Figure 6 ), it can be seen that the bulging index FT fitted by the present invention is more suitable for characterizing the stability of high nitrogen austenitic stainless steel, and then characterizing the bulging performance of high nitrogen austenitic stainless steel.

[0028] In view of the above relationship, by controlling the content of each alloy element, it is found that when the bulging index FT≥50, the material elongation ≥55% and the bulging cupping value Er≥11.0mm can be achieved, which meets the performance requirements of the dishwasher door panel and range hood cover forming process.

[0029] The method for manufacturing the economical high-nitrogen easily formable austenitic stainless steel of the present invention comprises the following steps:

[0030] 1) Smelting and casting

[0031] According to the above composition, smelting, AOD, LF refining and continuous casting are carried out to form ingots; wherein the casting temperature is controlled at 1450°C to 1500°C, preferably 1460°C to 1480°C; the cooling rate of the crystallizer is controlled at 8°C to 10°C / s, preferably 9°C to 10°C / s;

[0032] 2) Hot rolling

[0033] The heating temperature of the slab is controlled to be 1200-1300°C, preferably 1200-1250°C; the heating time is controlled to be 180-280 minutes, preferably 200-240 minutes, and then the slab is rolled to the desired thickness through rough rolling and finish rolling, and then coiled, wherein the finish rolling outlet temperature, i.e., the final rolling temperature, is ≥1000°C;

[0034] 3) One annealing and one pickling

[0035] The primary annealing is carried out in an annealing furnace at a temperature of 1050-1150° C., preferably 1100-1150° C.; the annealing time is 1-10 minutes, preferably 3-10 minutes; after annealing, the steel coil is mechanically dephosphorized and finally pickled once to obtain a steel coil that meets the requirements;

[0036] 4) Cold rolling

[0037] Use conventional continuous rolling mill or reversible single rolling mill to roll to the required thickness specification;

[0038] 5) Secondary annealing and secondary pickling

[0039] The secondary annealing is carried out in an annealing furnace at a temperature of 1080-1160°C for 3-5 minutes, followed by secondary pickling.

[0040] Preferably, the first pickling in step 3) adopts a sulfuric acid section + a mixed acid section, wherein the sulfuric acid concentration in the sulfuric acid section is 250-400 g / L, preferably 300-350 g / L; the mixed acid section is nitric acid + hydrofluoric acid, the nitric acid concentration is 140-240 g / L, preferably 180-220 g / L, and the hydrofluoric acid concentration is 10-25 g / L, preferably 15-20 g / L.

[0041] Preferably, in step 5), the secondary pickling is an electrolysis + mixed acid process, the electrolysis section medium is Na2SO4, the electrolysis current is 3000-4000A, preferably 3500-4000A; the mixed acid section is nitric acid + hydrofluoric acid, the nitric acid concentration is 140-240g / L, preferably 180-220g / L, and the hydrofluoric acid concentration is 10-25g / L, preferably 15-20g / L.

[0042] In the method for manufacturing the economical high nitrogen easy-to-form austenitic stainless steel of the present invention:

[0043] During the continuous casting process, the pouring temperature is controlled at 1450℃~1500℃, preferably 1460~1480℃, which is lower than the conventional 304 steel casting temperature of 1475~1490℃. High nitrogen steel has the risk of nitrogen escaping during the continuous casting process. Lowering the pouring temperature is beneficial to improving the nitrogen solubility of the molten steel (see Figure 7 ), reducing the risk of nitrogen escape. In addition, the cooling rate of the crystallizer is controlled to 8-10°C / s, preferably 9-10°C / s, which is much higher than the cooling rate of 6-8°C / s of conventional 304 steel. Accelerated cooling during crystallization and solidification is conducive to quickly crossing the "ferrite trap", reducing the precipitation of high-temperature ferrite, and then reducing the discharged N atoms, reducing the risk of nitrogen escape. However, the cooling rate should not be too fast, otherwise cracks may appear in the shell due to uneven cooling, and severe steel leakage accidents may even occur. Therefore, the cooling rate of the crystallizer is controlled to 8-10°C / s, preferably 9-10°C / s.

[0044] During the hot rolling process, the heating temperature is controlled at 1200-1300°C, preferably 1200-1250°C. High nitrogen steel has high strength and high deformation resistance. Compared with conventional 304 steel, the heating temperature should be set higher to soften the slab, which is conducive to smooth rolling. However, the heating temperature should not be too high, otherwise the Cu in the steel will be enriched to form liquid copper during the oxidation process, causing "copper brittleness" and causing scaling defects on the surface of the steel coil. The heating time is controlled to 180-280 minutes, preferably 200-240 minutes, in order to fully dissolve the high-temperature ferrite phase during the solidification process of the slab, while avoiding the coarse austenite structure and affecting the hot working performance. In particular, in the subsequent rolling process, it is necessary to ensure that the final rolling temperature at the end of rolling is ≥1000°C to avoid the high-viscosity oxide scale produced by too low temperature from being embedded in the steel plate surface and causing rust defects.

[0045] During the hot rolling annealing and pickling process, the annealing temperature is 1050-1150°C, preferably 1100-1150°C; the annealing time is 1-10 minutes, preferably 3-10 minutes. During the annealing and recrystallization process of high nitrogen steel, nitrogen will increase the recrystallization nucleation energy and hinder grain growth. In order to ensure sufficient grain growth and obtain high-strength steel with good plasticity, which is conducive to cold rolling thin specifications, the annealing temperature needs to be increased as much as possible and the annealing time needs to be extended.

[0046] The hot acid pickling process preferably uses a sulfuric acid stage + mixed acid stage (nitric acid + hydrofluoric acid) process. The sulfuric acid concentration in the sulfuric acid stage is 250-400 g / L, preferably 300-350 g / L; the nitric acid concentration in the mixed acid stage is 140-240 g / L, preferably 180-220 g / L; and the hydrofluoric acid concentration is 10-25 g / L, preferably 15-20 g / L. The sulfuric acid stage primarily removes the loose outer layer of iron oxide scale, while the mixed acid stage primarily removes the dense inner layer of chromium oxide scale and re-passivates the steel to form a stable passivation film.

[0047] The annealing time during the cold pickling process is 3 to 5 minutes, which is longer than the 1 to 2 minutes annealing time for 304 stainless steel. High-nitrogen steel has a high yield strength, so extending the annealing time allows for full recrystallization and growth of the grain structure after cold rolling, reducing yield strength and improving bulging properties. However, the annealing time should not be too long, as otherwise the grain structure will become too coarse, which can easily cause orange peel defects on the surface of the product after stamping.

[0048] Beneficial effects of the present invention:

[0049] The present invention ensures that the product has excellent corrosion resistance by designing a Cr content of 16.5-19.5%, and further improves the corrosion resistance of the product by alloying with Mn and N, and finally obtains 304-grade corrosion-resistant austenitic stainless steel; at the same time, it replaces part of the Ni element to save Ni resources and reduce alloy costs.

[0050] On the basis of the composition of Mn-N replacing Ni, the bulging index FT≥50 is controlled by adjusting the content of C, Si and Cu alloy elements. Combined with controlling the cold rolling annealing time to 3-5min, the elongation can be made ≥55% and the cupping value Er≥11.0mm, so that the product has excellent bulging performance on the basis of high strength mechanical properties.

[0051] The present invention obtains surface-defective continuous casting slabs by controlling the pouring temperature and the cooling rate of the crystallizer during the continuous casting stage; obtains surface-defective hot-rolled steel coils by controlling the heating temperature, heating time, and final rolling temperature during the hot rolling stage; and obtains finished stainless steel coils with both high strength and excellent bulging properties by controlling the annealing temperature and time during the annealing stage. These finished coils successfully replace 304 stainless steel in applications such as dishwasher door panels and range hood covers. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a photo of a dishwasher door panel cracked after being stamped from high-nitrogen, nickel-saving austenitic stainless steel (Chinese Patent Announcement No. CN112501493B).

[0053] Figure 2 This is a real picture of cracking in the range hood body stamped with high-nitrogen nickel-saving austenitic stainless steel (Chinese patent announcement number CN112501493B).

[0054] Figure 3 is the cupping value of 304 stainless steel with different C+N contents.

[0055] Figure 4 is the cupping value of the stainless steel of the present invention with different C+N contents.

[0056] Figure 5 This is a fitting diagram of the bulging index FT and the cupping value of industrialized high nitrogen austenitic stainless steel.

[0057] Figure 6 M d30 / 50 Fitting diagram with the cupping value of industrialized high nitrogen austenitic stainless steel.

[0058] Figure 7 Effect of pouring temperature on nitrogen solubility in molten steel.

[0059] Figure 8 This is a real picture of nitrogen holes on the surface of the continuous casting slab in comparative example 3.

[0060] Figure 9 This is a real picture of the cracked edge of the hot-rolled steel coil in comparative example 4.

[0061] Figure 10 This is the SEM image of the cracked edge of the hot-rolled steel coil in comparative example 4.

[0062] Figure 11This is a physical picture of the rust defects of the hot-rolled pickled steel coil in comparative example 4. DETAILED DESCRIPTION

[0063] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0064] The compositions of the embodiments and comparative examples of the present invention are shown in Table 1, with the remainder comprising Fe and other unavoidable impurities. The manufacturing processes and properties of the embodiments and comparative examples are shown in Table 2 and Table 3, respectively.

[0065] The tensile properties test of the material is carried out in accordance with GB / T 228.1 "Tensile tests on metallic materials - Part 1: Room temperature test methods".

[0066] The pitting potential test was carried out in accordance with GB / T 17899-1999 “Measurement Method for Pitting Potential of Stainless Steel”, the test solution was 3.5% NaCl solution, and the test temperature was 30±1°C.

[0067] The bulging performance cupping value Er test is carried out in accordance with GB / T 4156-2007 "Erichsen cupping test for metal sheets and strips".

[0068] The Ni content in Comparative Example 1 exceeds the upper limit of the constraint of the present invention, resulting in a bulging index FT of only 32.7, which is lower than 50. The deformation martensite content is reduced during the stamping process, and the work hardening ability is reduced, resulting in an elongation of 50.8%, which is lower than 55%. The bulging cupping value Er is 10.62 mm, which does not reach above 11.0 mm, and the stamped dishwasher door panel cracks.

[0069] In Comparative Example 2, the contents of each element are within the control range, and the bulging index FT>50, but the cold rolling annealing time is insufficient, only 1.6 min, which is not within the control range of 3 to 5 min of the present invention, and the grains are not fully grown, resulting in the yield strength Rp of the material. 0.2 The elongation is too high and the expansion cup value Er is 10.56mm, which does not reach above 11.0mm. The stamped dishwasher door panel also cracks.

[0070] In Comparative Example 3, the continuous casting temperature was 1505°C, which was beyond the control range of 1450-1500°C of the present invention; the cooling rate of the crystallizer was 7.6°C / s, which was beyond the control range of 8-10°C / s of the present invention. Nitrogen escape occurred during the continuous casting process, and pores appeared on the surface of the continuous casting slab ( Figure 8 ).

[0071] In comparative example 4, the heating time is 175 min, which is beyond the control range of the present invention, 180 to 280 min, and the hot-rolled steel coil has cracked edges ( Figure 9 ). Sampling analysis at the crack edge revealed a large number of strip-shaped precipitation phases near the crack ( Figure 10Electron probe microanalysis revealed that Cr content in Precipitation Phases 1, 2, and 3 exceeded 30%, significantly higher than the approximately 18% found in the austenite matrix. Mn and Ni content were 3.2% and 1.2%, respectively, significantly lower than the 6.3% and 2.92% found in the austenite matrix, respectively. The precipitates were identified as ferrite. Due to the short heating time, the residual ferrite in the ingot was not fully dissolved, leading to cracks forming at the interface between the two phases during rolling and ultimately causing edge cracking defects.

[0072] In addition, the final rolling temperature in Comparative Example 4 was 906°C, which did not reach the process requirement of 1000°C or above, resulting in the high-viscosity oxide scale formed at low temperature being embedded in the surface of the steel plate, which was difficult to remove by pickling and eventually formed rust defects on the surface of the steel strip ( Figure 11 ).

[0073] Tables 1 to 3 also list the composition of Comparative Example 5 (Chinese Patent CN112501493B) and the bulging index FT fitted according to the present invention. Its value is 34, far below 50, indicating insufficient work hardening ability. Furthermore, the secondary annealing time is 2 minutes, and the grains do not fully grow, resulting in a yield strength of 446 MPa that is too high and an elongation of 52.1% that is too low. It is foreseeable that this comparative patented steel will crack during the stamping process of dishwasher door panels.

[0074] Tables 1-3 also list the typical composition and bulge index (FT) of 304 stainless steel. Its value is 65.6, exceeding 50, indicating good work hardening capability. Although the cold-rolling annealing time is relatively short, only 1.5 minutes, due to the low nitrogen content and yield strength of 304 stainless steel, its cupping value is still as high as 12.4mm, fully meeting the bulge performance requirements for forming dishwasher door panels.

[0075] Examples 1-10 are all designed according to the composition, composition constraints, and consistent processing technology control of the present invention, so that the products not only have high-strength mechanical properties, but also have excellent bulging properties and corrosion resistance, realizing the application of economical high-nitrogen austenitic stainless steel in products such as dishwasher door panels and range hood covers.

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Claims

1. Economical high nitrogen easy-to-form austenitic stainless steel, its chemical composition mass percentage is as follows: C：0.05～0.08％， Si: 0.25-1.0%, Mn: 5.0~8.0%, Cr：16.5～19.5％， Ni: 2.5-4.5%, Cu: 0.5-2.0%, P≤0.045％， S≤0.0020％， N：0.20～0.30％， The balance is Fe and other unavoidable impurities, and the above elements must simultaneously satisfy the following relationship: Bulging index FT≥50, FT=551-162×(C%+N%)-9.2×Si%-8.1×Mn%-29×Ni%-39×Cu%-13.7×Cr%.

2. The economical high nitrogen easy-to-form austenitic stainless steel according to claim 1, characterized in that: The yield strength Rp of the stainless steel 0.2 >400MPa, elongation ≥55%, cupping value Er ≥11.0mm, pitting potential >300mV.

3. The method for producing economical high nitrogen easily formable austenitic stainless steel according to claim 1 or 2, characterized in that: The steps include: 1) Smelting and casting According to claim 1, the composition is smelted, AOD, LF refined, and continuously cast into a casting billet; wherein the casting temperature is controlled at 1450°C to 1500°C; the crystallizer cooling rate is controlled at 8 to 10°C / s; 2) Hot rolling The heating temperature of the ingot is controlled at 1200-1300℃; the heating time is controlled at 180-280min, and then the ingot is rolled to the required thickness through rough rolling and finish rolling before being coiled. The finish rolling outlet temperature, i.e., the final rolling temperature, is ≥1000℃. 3) One annealing and one pickling The primary annealing is carried out in an annealing furnace at a temperature of 1050-1150°C for 1-10 minutes. After annealing, the steel coil is mechanically descaled and finally pickled once to obtain a steel coil that meets the requirements. 4) Cold rolling Use conventional continuous rolling mill or reversible single rolling mill to roll to the required thickness specification; 5) Secondary annealing and secondary pickling The secondary annealing is carried out in an annealing furnace at a temperature of 1080-1160°C for 3-5 minutes, followed by secondary pickling.

4. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 3, characterized in that: Step 3) The primary pickling adopts a sulfuric acid section + a mixed acid section, wherein the sulfuric acid concentration in the sulfuric acid section is 250-400 g / L; the mixed acid section is nitric acid + hydrofluoric acid, the nitric acid concentration is 140-240 g / L, and the hydrofluoric acid concentration is 10-25 g / L.

5. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 4, characterized in that: In step 3), the sulfuric acid concentration in the sulfuric acid section is 300-350 g / L.

6. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 4 or 5, characterized in that: In step 3), the concentration of nitric acid is 180-220 g / L.

7. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 4 or 5, characterized in that: In step 3), the concentration of hydrofluoric acid is 15-20 g / L.

8. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 6, characterized in that: In step 3), the concentration of hydrofluoric acid is 15-20 g / L.

9. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 3, characterized in that: Step 5) The secondary pickling is an electrolysis + mixed acid process, the electrolysis medium is Na2SO4, and the electrolysis current is 3000-4000A; the mixed acid section is nitric acid + hydrofluoric acid, the nitric acid concentration is 140-240g / L, and the hydrofluoric acid concentration is 10-25g / L.

10. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 9, characterized in that: In step 5), the electrolysis current is 3500-4000A.

11. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 9 or 10, characterized in that: In step 5), the concentration of nitric acid is 180-220 g / L.

12. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 9 or 10, characterized in that: In step 5), the concentration of hydrofluoric acid is 15-20 g / L.

13. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 11, characterized in that: In step 5), the concentration of hydrofluoric acid is 15-20 g / L.

14. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 3, characterized in that: In step 1), the casting temperature is controlled at 1460-1480°C.

15. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 3 or 14, characterized in that: In step 1), the cooling rate of the crystallizer is controlled to be 9-10°C / s.

16. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 3, characterized in that: In step 2), the heating temperature of the casting is controlled to be 1200-1250°C.

17. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 3 or 16, characterized in that: In step 2), the heating time is controlled to be 200 to 240 minutes.

18. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 3, characterized in that: In step 3), the annealing temperature is 1100-1150°C.

19. The economical high nitrogen easy-to-form austenitic stainless steel manufacturing method according to claim 3 or 18, characterized in that: In step 3), the annealing time is 3 to 10 minutes.

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