Method for Manufacturing a Low-Carbon Nitrogen-Containing Austenitic Stainless Steel Bar

Abstract

The present invention discloses a method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar, which sequentially includes the following steps: smelting, electroslag remelting and forging; in the electroslag remelting process, the steel ingot obtained in the smelting process is used as an electrode bar of an electroslag furnace, remelting with specific slag and crystallizing; in the forging process, forging the crystallized steel ingot into a material by a specific forging method; the specific slag comprises CaF.sub.2 (65-70%), Al.sub.2O.sub.3 (15-20%), CaO (5-10%) and MgO (2-5%) in percentage by weight; specific forging methods include upsetting-and-drawing and radial forging, wherein the upsetting-and-drawing includes: a pass deformation is less than 35%, a pass reduction is 50-80 mm, a pass heating temperature is 1130-1150 C., and a pass deformation method is ellipse-ellipse-circle. The method can obtain the low-carbon high-strength nitrogen-containing austenitic stainless steel with uniformly distributed chemical composition and tissues, high purity and high strength.

Claims

1. A method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar by sequentially comprising the following steps: smelting, electroslag remelting and forging; wherein, in the electroslag remelting process, the steel ingot obtained in the smelting process is taken as an electrode bar of an electroslag furnace, remelted with specific slag and crystallized; in the forging process, the crystallized steel ingot is forged into a material in a specific forging method; in the smelting process, the steelmaking raw materials are mixed in the way that the steel ingot obtained after smelting or the finally obtained stainless steel bar has specific composition components; the specific composition components comprise: C: 0.020-0.030%, Si: 0.3-0.6%, Mn: 1.3-1.8%, S: less than or equal to 0.002%, P: less than or equal to 0.015%, Cr: 19.20-19.70%, Ni: 9.20-9.80%, Cu: less than or equal to 1.00%, Co: less than or equal to 0.06%, N: 0.065-0.075%, B: less than or equal to 0.0018%, and Nb+Ta: less than or equal to 0.15% in percentage by weight; the specific slag comprises CaF.sub.2, Al.sub.2O.sub.3, CaO and MgO, and according to the weight percentage, the contents of the CaF.sub.2, Al.sub.2O.sub.3, CaO and MgO are 65%-68%, 18%-20%, 5%-10% and 3%-5% in sequence; the specific forging method comprises upsetting-and-drawing and radial forging, wherein the upsetting-and-drawing comprises: a pass deformation of less than 35%, a pass reduction of 50-80 mm, a pass heating temperature of 1130-1150 C., a pass deformation method of ellipse-ellipse-circle, an initial forging temperature of more than or equal to 1000 C., a final forging temperature of more than or equal to 800 C., and the number of upsetting-and-drawing of 2-3 times; and the radial forging is performed after upsetting-and-drawing with an initial forging temperature of 1000-1140 C., a final forging temperature of 800-900 C., air cooling the radial forged steel to obtain a low-carbon nitrogen-containing austenitic stainless steel bar, and the diameter of the low-carbon nitrogen-containing austenitic stainless steel bar is 200 mm; in the forging process, a soaking treatment is performed for the low-carbon nitrogen-containing austenitic stainless steel blank obtained by electroslag remelting before the upsetting-and-drawing, wherein the soaking treatment comprises heating up to 1130-1150 C. at a heating speed of 1-10 C./min.

2. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 1, wherein, according to the weight percentage, the contents of the CaF.sub.2, Al.sub.2O.sub.3, CaO and MgO are 65%, 20%, 10% and 5% in sequence.

3. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 1, wherein, in the smelting process, the steelmaking raw materials are mixed according to a method that the steel ingot obtained after smelting or the finally obtained stainless steel bar has specific composition components, and the specific composition components comprise: C: 0.025%, Si: 0.5%, Mn: 1.45%, S: less than or equal to 0.002%, P: less than or equal to 0.015%, Cr: 190.5%, Ni: 9.7%, Cu: less than or equal to 1.00%, Co: less than or equal to 0.06%, N: 0.07%, B: less than or equal to 0.0018%, Nb+Ta: less than or equal to 0.15% in percentage by weight.

4. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 1, wherein, the smelting process sequentially comprises a melting treatment, a refining treatment, a vacuum degassing treatment and a casting molding; the steelmaking raw materials comprise low-carbon ferrochrome, metallic nickel, electrolytic manganese, ferrosilicon, ferrochrome nitride and scrap steel.

5. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 4, wherein, before performing the electroslag remelting process, the steel ingot obtained in the smelting process is first subjected to a cutting treatment and a surface polishing treatment, and then used as an electrode bar for electroslag remelting.

6. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 5, wherein, in the electroslag remelting process, the current of the electroslag remelting is 11-13 KA.

7. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 6, wherein, in the electroslag remelting process, 1-10 wt % of the electrode bar is used for feeding the crystallized steel ingot; the steel ingot obtained by electroslag remelting is demoulded and cooled to room temperature to obtain the low-carbon nitrogen-containing austenitic stainless steel blank.

8. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 7, wherein, in the electroslag remelting process, 1-8 wt % of the electrode bar is used for feeding the crystallized steel ingot.

9. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 1, wherein, in the forging process, the low-carbon nitrogen-containing austenitic stainless steel blank obtained by electroslag remelting is firstly subjected to a soaking treatment before upsetting-and-drawing, and the heat preservation time of the soaking treatment is 3-5 hours.

10. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 1, wherein, in the forging process, the time of each upsetting-and-drawing is 5-20 minutes.

11. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 1, wherein, in the forging process, the upsetting-and-drawing conditions include upsetting and drawing by the specific forging method, wherein the initial forging temperature is 1050-1100 C., the final forging temperature is 800-900 C., and the time of each upsetting and drawing is 5-15 minutes; and the pass deformation is 30-32%, the pass reduction is 65-75 mm, and the pass heating temperature is 1130-1150 C.

12. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 11, wherein, in the upsetting-and-drawing of the forging process, the specific forging method includes that the pass deformation is 31%, the pass reduction is 70 mm, and the pass heating temperature is 1140 C.; and the upsetting-and-drawings are performed twice in a 4500t press, and the deformation of the second upsetting and drawing is larger than that of the first one.

13. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 1, wherein, during upsetting-and-drawing in the forging process, returning to the furnace to reburn is performed after each upsetting-and-drawing is finished, so as to reach the initial forging temperature required by the next upsetting-and-drawing, and the conditions for returning to the furnace to reburn and heat after each upsetting-and-drawing comprises: the temperature is 1130-1150 C., and the time is 90-120 minutes.

14. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 1, wherein, in the forging process, the time of the radial forging is 5-20 minutes.

15. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 14, wherein, the conditions of the radial forging include: the initial forging temperature is 1000-1100 C., the final forging temperature is 800-900 C., the time is 10-20 minutes; and the radial forging is performed by a 1600t radial forging machine.

16. The method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar according to claim 1, wherein, for the low-carbon nitrogen-containing austenitic stainless steel bar, the tensile strength at the high temperature of 350 C. is more than or equal to 410 MPa, the yield strength at the high temperature of 350 C. is more than or equal to 140 MPa, the tensile strength at the room temperature is more than or equal to 560 MPa, and the yield strength at the room temperature is more than or equal to 260 MPa.

Description

DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present invention will be described in detail below with reference to examples of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the invention and are not intended to limit the invention. Based on the embodiments in the invention, all other embodiments obtained by a person of ordinary skill in the art without any creative efforts shall fall within the protection scope of the present invention.

[0048] The invention provides a method for manufacturing a low-carbon high-strength nitrogen-containing austenitic stainless steel bar, which comprises the following steps: smelting, electroslag remelting and forging; wherein,

[0049] Smelting process: steelmaking raw materials are added into an electric arc furnace, an external refining furnace and a vacuum oxygen-blowing decarburization furnace for smelting, wherein the smelting sequentially comprises melting treatment, refining treatment, first sample adjustment treatment, oxygen-blowing decarburization treatment, degassing treatment, nitrogen-blowing treatment, second sample adjustment treatment and casting molding; the steelmaking raw materials are mixed according to a way that the finally obtained steel ingot has a specific composition; and the specific composition in percentage by weight comprises: C: 0.020 to 0.030%, Si: 0.3-0.6%, Mn: 1.3-1.8%, S: less than or equal to 0.002%, P: less than or equal to 0.015%, Cr: 19.20 to 19.70%, Ni: 9.20-9.80%, Cu: less than or equal to 1.00%, Co: less than or equal to 0.06%, N: 0.065-0.075%, B: less than or equal to 0.0018%, and Nb+Ta: less than or equal to 0.15%;

[0050] Electroslag remelting process: the steel ingots obtained from the smelting process are first cut and polished, and then used as an electrode bar for electroslag remelting, remelted with specific slag and crystallized, and then the crystallized steel ingot is cooled; and the specific slag includes CaF.sub.2, Al.sub.2O.sub.3, CaO and MgO, wherein the contents of the CaF.sub.2, Al.sub.2O.sub.3, CaO and MgO in percentage by weight are (65%-70%), (15%-20%), (8%-10%), (2%-5%) in sequence, and the sum of the final proportions is ensure to be 100%; Forging process: the crystallized steel ingot is cooled; and in the forging process, the crystallized steel ingot is forged into a material in a specific forging method. The specific forging comprises upsetting-and-drawing and radial forging; the upsetting-and-drawing comprising upsetting and drawing, wherein the upsetting-and-drawing comprises: the pass deformation is less than 35% (e.g. 28%, 30%, 32%, 33% and 34%), the pass reduction is 50-80 mm (e.g. 55 mm, 60 mm, 70 mm and 75 mm), the pass heating temperature is 1130-1150 C. (e.g. 1135 C., 1140 C. and 1145 C.), and the pass deformation method is: ellipse-ellipse-circle. The pass heating temperature refers to the temperature of the furnace for reheating after the deformation of each pass is finished.

[0051] In the present invention, the smelting process may adopt a conventional technical scheme in the field.

[0052] According to the present invention, as a preferred embodiment, the steelmaking raw materials includes low carbon ferrochrome, metallic nickel, electrolytic manganese, ferrosilicon, ferrochromium nitride, scrap steel, etc., and the low carbon ferrochrome, metallic nickel, electrolytic manganese, ferrosilicon, ferrochromium nitride, scrap steel, etc. may be various metals conventionally used for refining 304 series steel in the art, for example, the metallic nickel is 1 #Ni, etc.

[0053] According to the invention, as a preferred embodiment, the specific composition comprises: C: 0.025%, Si: 0.5%, Mn: 1.45%, S: less than or equal to 0.002%, P: less than or equal to 0.015%, Cr: 19.5%, Ni: 9.7%, Cu: less than or equal to 1.00%, Co: less than or equal to 0.06%, N: 0.07%, B: less than or equal to 0.0018%, and Nb+Ta: less than or equal to 0.150% in percentage by weight.

[0054] Although the steelmaking raw material can be prepared according to the above composition, in order to obtain a better quality steel ingot, it is preferable that a part of the low-carbon ferrochrome and the nitrided ferrochrome in the steelmaking raw material is reserved in the smelting treatment process as the feed for the second sample preparation treatment.

[0055] According to a preferred embodiment of the present invention, the melting treatment is a process of melting and mixing steelmaking raw materials by electrode heating, oxygen blowing, and slag adding after the steelmaking raw materials are charged into an electric arc furnace such as a vacuum arc furnace. Preferably, the tapping conditions of the melting treatment include: c is less than or equal to 0.60%, and T is more than or equal to 1630 C.

[0056] According to a preferred embodiment of the present invention, the refining treatment is to pour molten steel from an electric furnace into an external refining furnace, and reducing the molten steel in the electric arc furnace by electrode heating and slag adding treatment, preferably, adding 5 to 10 kg/t of SiC powder, deoxidizing, and electrically burning slag for more than 10 minutes. Adjusting the slag to be proper (i.e. adjusting the slag to be white), sampling, fully analyzing, returning the sample and adjusting the components (compositions). Preferably, the tapping condition T is more than or equal to 1650 C., and the tapping components are: less than or equal to 0.80% of C, less than or equal to 0.30% of Si and less than or equal to 0.015% of S.

[0057] According to the invention, as a preferred embodiment, a vacuum oxygen decarburization treatment, degassing treatment and nitrogen blowing treatment are carried out in a vacuum oxygen decarburization furnace, which means that the molten steel in a refining furnace outside the furnace is subjected to the vacuum oxygen blowing treatment so as to remove the carbon content of the steel, and then a slag and a deoxidizing agent are added under vacuum to carry out a vacuum degassing treatment so as to remove oxides remained in the steel after the oxygen decarburization; the nitrogen blowing treatment is carried out at the bottom of the furnace after the deoxidation is finished so as to increase the nitrogen content in the steel, and finally the reserved low-carbon ferrochrome and the reserved nitrided ferrochrome are added according to chemical composition; preferably, the refining slag outside the furnace is scraped out before the molten steel enters the vacuum oxygen decarburization furnace, and the slag charge proportion of the vacuum degassing treatment is: 400 kg/furnace of lime, 50-100 kg/furnace of fluorite and 200-300 kg/furnace of pre-dissolved aluminum-calcium composite slag; the deoxidizer is Al particles, CaSi or FeSi; preferably, 1-3 kg/t of deoxidizer Al particles and 5-8 kg/t of CaSi or FeSi are added along with slag; the vacuum of vacuum degassing treatment is less than or equal to 100 Pa, and the holding time is more than or equal to 10 minutes.

[0058] According to a preferred embodiment of the present invention, the casting molding is that casting molten steel with acceptable (qualified) chemical composition obtained by vacuum degassing treatment into electrodes, preferably, argon gas is blown into the bottom of the furnace for 20 minutes before casting, and the molten steel is cast under the protection of argon gas, wherein the casting temperature is 1530-1550 C.

[0059] According to the present invention, as a preferred embodiment, a steel ingot having the composition of the present invention, particularly a steel ingot produced by the above-described production method, used as an electrode bar for electroslag remelting, is remelted and crystallized.

[0060] In the present invention, in order to obtain a steel material having a better surface quality, high purity, uniform structure and high strength, it is necessary to ensure that the chemical composition of the steel ingot after remelting are uniform and the surface quality is good, and it is preferable that the steel ingot used as the electrode bar should be first performed the cutting treatment and surface polishing treatment. The cutting treatment is used for cutting off the part with defective feeding; and the surface polishing treatment is used to obtain electrode bars with good surface quality.

[0061] According to a preferred embodiment of the present invention, in the electroslag remelting process, the steel ingot obtained by casting and shaping is used as an electrode bar of an electroslag furnace, the electrode bar will melt into molten steel in a slag under the condition of energization, and the molten steel is dripped into a crystallizer through the slag to be crystallized; preferably, the specific slag charge ratio is: CaF.sub.2:65%, Al.sub.2O.sub.3:20%, CaO:10%, and MgO:5% in percentage by weight, and the current of electroslag remelting is 11 KA.

[0062] According to the present invention, in order to obtain a steel with high surface quality, preferably, 1 to 10 wt % (more preferably, 1 to 8 wt %) of the electrode bar is used for feeding the crystallized steel ingot. That is, when molten steel drops into the crystallizer for crystallizing, shrinkage cavities will exist on the surface of the steel ingot due to the action of the surface tension of the molten steel. In order to avoid the problem that the quality of the processing plasticity of the steel ingot is affected due to the poor surface quality of the steel obtained after forging caused by the large shrinkage cavities formed in the steel ingot, it is preferable that 1 to 10 wt %, more preferably 1 to 8 wt % of an electrode bar is used to fill up the shrinkage cavities on the surface of the steel ingot formed after crystallizing at the later stage of crystallizing.

[0063] The low-carbon nitrogen-containing austenitic stainless steel obtained by the manufacturing method of the invention has the advantages of uniform distribution of chemical composition, high purity and no segregation defect, and can be used for manufacturing a low-carbon high-strength nitrogen-containing austenitic stainless steel bar.

[0064] In the above manufacturing method, as a preferred embodiment, in the forging process, the specific forging method is to upset-and-draw and radially forge the steel ingot after soaking treatment. The soaking treatment is to cool and then heat the steel ingot obtained in the electroslag remelting process, which comprises: heating up to 1130-1150 C. at a heating speed of 1-10 C./min, and then preserving heat for 3-5 hours. The upsetting-and-drawing comprises upsetting and drawing.

[0065] In the above manufacturing method, as a preferred embodiment, the condition of the upsetting-and-drawing in the forging process includes that the initial forging temperature is more than or equal to 1000 C., the final forging temperature is more than or equal to 800 C., and the time of each upsetting-and-drawing is 5-20 minutes; the pass deformation is 30-32%, the pass reduction is 65-75 mm, the pass heating temperature is 1130-1150 C., and the pass deformation method is ellipse-ellipse-circle.

[0066] Preferably, the condition of upsetting-and-drawing comprises that the initial forging temperature is 1050-1100 C., the final forging temperature is 800-900 C., and the time of each upsetting-and-drawing is 5-15 minutes; the number of upsetting-and-drawing can be 1-3 times, preferably 2-3 times; more preferably, two upsetting and two drawing are carried out in a 4500t press, and the deformation of the second upsetting-drawing is larger than that of the first one, so that the problem of coarse structure caused by the process of returning to furnace after the first upsetting-drawing can be solved, and thus the obtained steel has better grain size.

[0067] Wherein, every time upsetting-and-drawing (including upsetting and drawing) is finished, it's returned to the furnace to be re-burnt to reach the required initial forging temperature for upsetting-and-drawing. Preferably, the conditions of returning to furnace and re-burning after each upsetting-and-drawing include that the temperature is 1130-1150 C., and the time is 90-120 minutes, and the returning condition after the final upsetting-and-drawing can adopt the condition of the returning to the furnace, the pass deformation is 310%, the pass reduction is 70 mm, the pass heating temperature is 1140 C., and the pass deformation method is ellipse-ellipse-circle.

[0068] In the above manufacturing method, as a preferred embodiment, in the forging process, the radial forging is performed after the completion of the upsetting-and-drawing, and the initial forging temperature of the radial forging is the temperature of the steel after returning to the furnace to reheat. Preferably, the conditions of the radial forging include that the initial forging temperature is 1120-1140 C., the final forging temperature is 800-900 C. and the time is 5-20 minutes. Still preferably, the conditions of the radial forging include: the initial forging temperature is 1000-1100 C., the final forging temperature is 800-900 C., and the time is 10-20 minutes; still preferably, the radial forging is performed on a 1600-ton radial forging machine, one-pass forging is performed, and the radial forged steel is air-cooled.

[0069] The low-carbon high-strength nitrogen-containing austenitic stainless steel prepared by the method of the present invention can be used for preparing a steel bar with a diameter of more than 200 mm. The tensile strength at the high temperature of 350 C. of the obtained low-carbon high-strength nitrogen-containing austenitic stainless steel is more than or equal to 410 MPa, the yield strength at the high temperature of 350 C. is more than or equal to 140 MPa, the tensile strength at the room temperature is more than or equal to 560 MPa, the yield strength at the room temperature is more than or equal to 260 MPa, the chemical composition and microstructure are uniform, and the purity of the steel is high.

[0070] The present invention will be described in detail below by way of examples.

[0071] In the examples, the tensile strength Rm, the yield strength Rp0.2, the elongation after fracture A, and the reduction of area Z are measured by the methods described in RCCM M1000.

Example 1

[0072] The embodiment provides a method for manufacturing a low-carbon high-strength nitrogen-containing austenitic stainless steel bar, which sequentially comprises the following steps of: smelting, electroslag remelting and forging. In particular,

[0073] Smelting Process:

[0074] (1) Batching: low carbon ferrochrome, metal nickel, electrolytic manganese, ferrosilicon, nitrided ferrochrome and scrap steel are batched in the way that the steel ingot prepared contains C: 0.026%, Si: 0.54%, Mn: 1.45%, S: less than or equal to 0.002%, P: 0.017%, Cr: 19.7%, Ni: 9.7%, Cu: less than or equal to 1.00%, Co: less than or equal to 0.06%, N: 0.072%, B: less than or equal to 0.0018%, Nb+Ta: less than or equal to 0.15%, wherein of the weight of the low-carbon ferrochrome and the nitrided ferrochrome are reserved respectively.

[0075] (2) Melting treatment: adding the steelmaking raw materials obtained after proportioning (batching) into an electric arc furnace for melting treatment, firstly inserting an electrode into an alloy material for feeding the material, simultaneously inserting an oxygen lance into the furnace bottom for blowing oxygen for fluxing (to assist melting), adding lime onto the surface of the steelmaking raw materials, and melting and mixing the steelmaking raw materials through electrode heating, oxygen blowing and slag adding. When tapping from the electric furnace, C is 0.56 wt % and tapping temperature is 1690 C.

[0076] (3) Refining treatment: pouring molten steel melted by an electric furnace into a out-of-furnace refining furnace, adding 15 kg of SiC powder and 400 kg of synthetic slag, electrically burning the slag for 15 minutes, taking a sample after power failure for full analysis, returning the sample to adjust the composition (namely, a first sample adjustment treatment). Tapping condition T is 1670 C. In discharge composition, C is 0.40%, Si is 0.25%, and S is 0.005%.

[0077] (4) Oxygen blowing decarburization treatment, degassing treatment and nitrogen blowing treatment, the second sample adjustment treatment and casting molding:

[0078] Pouring the molten steel after refining treatment and tapping into a vacuum oxygen blowing decarburization furnace for oxygen blowing treatment under vacuum, sampling after oxygen blowing until the carbon content in the steel is 0.005%, then pouring 400 kg of lime, 80 kg of fluorite and 200 kg of synthetic slag into the molten steel, adding 20 kg of deoxidizer Al particles and 20 kg of CaSi along with slag materials, and degassing at the vacuum degree of 67 Pa and the retention time of 15 minutes.

[0079] And blowing nitrogen into the molten steel after degassing is finished, then adding reserved low-carbon ferrochromium and manganese metal, blowing argon into the molten steel for 20 minutes after the metal materials are melted, and then casting 2.5 tons of electrode molds with the diameter of 410 mm under argon protection. Blowing argon gas at the bottom of the furnace for 20 minutes before casting, and then casting under the protection of argon gas, wherein the casting temperature is 1530-1550 C., and leaving 400 kg of residual casting after casting.

[0080] Cutting Treatment and Surface Polishing Treatment:

[0081] Cut off the filling part of the steel ingot obtained in the smelting process, and polish the surface of the steel ingot.

[0082] Electroslag Remelting Process:

[0083] Remelting is performed by using the polished steel ingot as an electrode bar of an electroslag furnace, wherein the weight of slag in the remelting process is 130 kg, and the slag proportion is as follows: CaF.sub.2: Al.sub.2O.sub.3:CaO:MgO=65%:20%:10%:5%, remelting current is 11 KA, and remelting voltage is 45V. The molten steel drops into a crystallizer having a diameter of 510 mm (510 mm) to be crystallized, and when 360 kg of the electrode bar remained, it is used as a feeding material for the steel ingot in the mold to feed the shrinkage cavity of the steel ingot.

[0084] After the smelting is finished, demould the steel ingot and cool to room temperature to obtain D510 mm steel ingot.

[0085] Forging process: Forging process is carried out in a specific forging method, including soaking treatment and forging, wherein the forging comprises upsetting-and-drawing and radial forging, and the specific forging method comprises that the pass deformation is 31%, the pass reduction is 70 mm, the pass heating temperature is 1140 C., and the pass deformation method is ellipse-ellipse-circle. In particular,

[0086] Soaking treatment: The air-cooled steel ingot of 2.5 tons (510 mm) is subjected to soaking treatment, the condition of soaking is as follows. Firstly, heat the air-cooled steel ingot up to 1150 C. at the heating speed of 2.3 C./min, and then preserve the heat for 4 hours.

[0087] Upsetting-and-drawing (including upsetting and drawing) and radial forging: The steel ingot after the soaking treatment is fed into a 4500t press for first upsetting-and-drawing for 8 minutes, the final forging temperature is 850 C. until the diameter is 530 mm, the reduction is 70 mm, and the deformation mode is 540 mm ellipse-535 mm ellipse-530 mm circle (the ellipse herein is also called a rough circle in the production process, namely an irregular circle, and the diameter refers to the average value of the major diameter and the minor diameter); then the blank is returned to the furnace for heating at 1140 C. for 90 minutes, and then sent into a press of 4500t for second upsetting-and-drawing for 10 minutes, wherein the final forging temperature is 850 C. until the diameter is 510 mm, the reduction is 70 mm, and the deformation method is 520 mm ellipse-515 mm ellipse-510 mm circle; then the steel is returned to the furnace and heated at 1140 C. for 90 minutes and fed into a press of 4500t for first drawing for 15 minutes until the diameter is 420 mm, wherein the reduction is 70 mm, the deformation is 31%, and the deformation mode is 430 mm ellipse-425 mm ellipse-420 mm circle; then the steel is returned to the furnace and heated at 1140 C. for 90 minutes, and sent into a press of 4500t for the second drawing for 15 minutes until the diameter is 350 mm, wherein the reduction is 70 mm, the deformation is 31%, and the deformation mode is 360 mm ellipse-355 mm ellipse-350 mm circle; then the steel is returned to the furnace and heated for 90 minutes at 1140 C., and then is forged for 20 minutes in a 1600t radial forging machine for one fire time, wherein the final forging temperature is 850 C., the diameter after forging is 200 mm; and then the steel is air-cooled to room temperature to obtain the 00Cr19Ni10N steel bar with the diameter of 200 mm, wherein the tensile strength at 350 C., yield strength at 350 C., tensile strength at room temperature and yield strength at room temperature all meet the requirements of the RCCMM3306 standard, and the chemical composition and microstructure are uniform, and the purity of steel products is high, which are shown in Tables 1 and 2.

TABLE-US-00001 TABLE 1 Properties and structure of the low-carbon nitrogen-containing austenitic stainless steel bar obtained in Example 1 Tensile Yield strength strength Tensile Yield at high at high strength strength temperature temperature at room at room Specification of 350 C. of 350 C. temperature temperature Macro- (mm) (MPa) (MPa) (MPa) (MPa) Non-metal inclusions Grain size structure 200 424 144 568 262 A, B, C, D all the types Uniform Uniform of inclusion are is less grade 5 and no than or equal to grade 0.5 grain size segregation

TABLE-US-00002 TABLE 2 Chemical composition (wt %) of the low-carbon nitrogen-containing austeniticstainless steel bar prepared in Example 1 C Si Mn P S Cr Ni N Nb + Ta Co Cu B 0.026 0.54 1.45 0.017 0.002 19.7 9.7 0.072 0.008 0.03 0.2 0.0009

Example 2

[0088] The embodiment provides a method for manufacturing a low-carbon and high-strength nitrogen-containing austenitic stainless steel bar, which sequentially comprises the following steps of: smelting, electroslag remelting and forging. Wherein, except the material preparation step in the smelting procedure adopts the following technical scheme, the other steps of the smelting process and the electroslag remelting and forging process adopt the technical scheme in Example 1.

[0089] Smelting Process:

[0090] (1) Batching: Low carbon ferrochrome, metal nickel, electrolytic manganese, ferrosilicon, nitrided ferrochrome and scrap steel are batched in the way that the steel ingot prepared contains C: 0.026%, Si: 0.54%, Mn: 1.45%, S: less than or equal to 0.002%, P: less than or equal to 0.017%, Cr: 190.2%, Ni: 9.2%, Cu: less than or equal to 1.00%, Co: less than or equal to 0.06%, N: 0.072%, B: less than or equal to 0.0018%, and Nb+Ta: less than or equal to 0.15%, wherein of the weight of the low-carbon ferrochrome and the nitrided ferrochrome are reserved respectively.

[0091] The above batching are adopted for smelting, electroslag remelting and forging, the diameter is 200 mm through final forging, then the steel bar is air-cooled to room temperature, and the 00Cr19Ni10N steel bar with the diameter of 200 mm is obtained, and the tensile strength at the high temperature of 350 C., the yield strength at the high temperature of 350 C., the tensile strength at the room temperature and the yield strength at the room temperature all can not meet the requirements of the RCCMM3306 standard, and are specifically shown in Tables 3 and 4.

TABLE-US-00003 TABLE 3 Properties and structure of the low-carbon nitrogen-containing austenitic stainless steel bar prepared in Example 2 Tensile Yield strength strength Tensile Yield at high at high strength strength temperature temperature at room at room Specification of 350 C. of 350 C. temperature temperature Macro- (mm) (MPa) (MPa) (MPa) (MPa) Non-metal inclusions Grain size structure 200 420 140 558 258 A, B, C, D all the types of Uniform Uniform inclusion are is less than grade 5 and no or equal to grade 0.5 grain size segregation

TABLE-US-00004 TABLE 4 Chemical composition (wt %) of the low-carbon nitrogen-containing austenitic stainless steel bar prepared in Example 2 C Si Mn P S Cr Ni N Nb + Ta Co Cu B 0.026 0.54 1.45 0.017 0.002 19.2 9.2 0.072 0.008 0.03 0.2 0.0009

Example 3

[0092] The embodiment provides a method for manufacturing a low-carbon high-strength nitrogen-containing austenitic stainless steel bar, which sequentially comprises the following steps of smelting, electroslag remelting and forging. Wherein the smelting and electroslag remelting process adopts the same technical scheme as that of Example 2, and the forging process adopts the following technical scheme.

[0093] Forging process: Forging process is carried out in a specific forging method, including soaking treatment and forging, wherein the forging method comprises upsetting-and-drawing and radial forging, and the specific forging method comprises that the pass deformation is 31%, the pass reduction is 65 mm, the pass heating temperature is 1140 C., and the pass deformation method is ellipse-ellipse-circle. The reduction herein is the single reduction height of the press, and the deformation is the change in the area of the steel before and after the press. Specifically,

[0094] Soaking treatment:The steel ingot of 2.5 tons (510 mm) after the air cooling is soaked, and the conditions of soaking are firstly heating up to 1150 C. at the heating speed of 2.3 C./min and then preserving the heat for 4 hours.

[0095] Upsetting-and-drawing and radial forging: The steel ingot after the soaking treatment is fed into a 4500t press for first upsetting-and-drawing for 15 minutes, wherein the final forging temperature is 800 C., the diameter is 530 mm, the reduction is 65 mm, and the deformation method is 540 mm ellipse-535 mm ellipse-530 mm circle; then the steel ingot is returned to the furnace to heat for 90 minutes at 1130 C., and then fed into a press of 4500t for the second upsetting-and-drawing for 15 minutes, wherein the final forging temperature is 800 C., the diameter is 510 mm, the reduction is 65 mm, and the deformation method is 520 mm ellipse-515 mm ellipse-510 mm circle; then the steel ingot is returned to the furnace to heat for 90 minutes at 1130 C., and then fed into a press of 4500t for first drawing for 15 minutes until the diameter is 420 mm, the reduction is 65 mm, the deformation is 31%, and the deformation mode is 430 mm ellipse-425 mm ellipse-420 mm circle; then the steel ingot is returned to the furnace to heat for 90 minutes at 1130 C., and then fed into a press of 4500t for secondary drawing for 15 minutes until the diameter is 350 mm, wherein the reduction is 65 mm, the deformation is 31%, and the deformation mode is 360 mm ellipse-355 mm ellipse-350 mm circle; then the steel ingot is returned to the furnace to heat for 90 minutes at 1140 C., and performed one-shot forging for 20 minutes in a 1600t radial forging machine, wherein the final forging temperature is 850 C., and the diameter after forging is 200 mm; and then the steel ingot is air-cooled to room temperature to obtain the 00Cr19Ni10N steel bar with the diameter of 200 mm.

TABLE-US-00005 TABLE 5 Properties and structure of the low-carbon nitrogen-containing austenitic stainless steel bar obtained in Example 3 Tensile Yield strength strength Tensile Yield temperature at high strength strength at high temperature at room at room Specification of 350 C. of 350 C. temperature temperature Macro- (mm) (MPa) (MPa) (MPa) (MPa) Non-metal inclusions Grain size structure 200 426 143 566 264 A, B, C, D all the types of Uniform Uniform inclusion are is less than grade 5 and no or equal to grade 0.5 grain size segregation

[0096] The 350 C. high-temperature tensile strength, 350 C. high-temperature yield strength, room temperature tensile strength and room temperature yield strength of the 00Cr19Ni10N steel bar all meet the requirements of the RCCMM3306 standard, and the steel bar has uniform chemical composition and high-magnification tissues and high purity, as shown in Tables 5 and 6.

TABLE-US-00006 TABLE 6 Chemical composition (wt %) of low-carbon nitrogen-containing austenitic stainless steel bar prepared in Example 3 C Si Mn P S Cr Ni N Nb + Ta Co Cu B 0.026 0.54 1.45 0.017 0.002 19.2 9.2 0.072 0.008 0.03 0.2 0.0009

Comparative Example 1

[0097] The comparative example provides a method for manufacturing the low-carbon high-strength nitrogen-containing austenitic stainless steel bar by adopting a conventional electroslag process, which sequentially comprises the following steps: smelting, electroslag remelting and forging. The smelting and forging process adopts the same technical scheme as the smelting and forging process in Example 1, and the electroslag remelting process adopts the following technical scheme.

[0098] Electroslag Remelting Process:

[0099] The steel ingot with the polished surface as an electrode bar of an electroslag furnace is remelted, wherein the weight of slag in the remelting process is 130 kg, and the slag ratio is: CaF.sub.2: Al.sub.2O.sub.3=70%: 30%, remelting current is 12 KA, and remelting voltage is 45V; the molten steel drops into a crystallizer with the diameter of 510 mm for crystallizing, and when 360 kg of the electrode bar left, it is used as a feeding material of the steel ingot in the crystallizer to perform feeding treatment on the shrinkage cavity of the steel ingot.

[0100] The steel ingot is demolded after the smelting is finished and cooled to room temperature.

[0101] Then, the steel ingot obtained in the electroslag remelting process is forged to obtain a steel bar with the diameter of 200 mm, and then the steel bar is air-cooled to room temperature to obtain a 00Cr19Ni10N steel bar with the diameter of 200 mm, wherein the tensile strength at the high temperature of 350 C., the yield strength at the high temperature of 350 C., the tensile strength at the room temperature and the yield strength at the room temperature all can not meet the requirements of the RCCMM3306 standard, the purity of the steel is low, and the macrostructure is uneven, which is specifically shown in Tables 7 and 8.

TABLE-US-00007 TABLE 7 Properties and structure of the low-carbon nitrogen-containing austenitic stainless steel bar obtained in Comparative example Tensile Yield strength strength Tensile Yield at high at high strength strength temperature temperature at room at room Specification of 350 C. of 350 C. temperature temperature Macro- (mm) (MPa) (MPa) (MPa) (MPa) Non-metal inclusions Grain size structure 200 390 113 533 232 A, B, C, D all the types of Grade 5-4 Having inclusion are grade 1.5 segregation

TABLE-US-00008 TABLE 8 Chemical composition (wt %) of the low-carbon nitrogen-containing austenitic stainless steel bar prepared in Comparative example 1 C Si Mn P S Cr Ni N Nb + Ta Co Cu B 0.026 0.54 1.45 0.017 0.002 19.7 9.6 0.072 0.008 0.03 0.2 0.0009

Comparative Example 2

[0102] The comparative example provides a method for manufacturing a low-carbon high-strength nitrogen-containing austenitic stainless steel bar produced by adopting a conventional forging process, which sequentially comprises the following steps: smelting, electroslag remelting and forging. The smelting and electroslag remelting process adopts the same technical scheme as that of Example 1, and the forging process adopts the following technical scheme.

[0103] Forging: Forging in a specific forging method, including soaking treatment and forging, wherein the forging method comprises upsetting-and-drawing and radial forging, and the specific forging method comprises: the pass deformation is 50%, the pass reduction is 120 mm, the pass heating temperature is 1170 C., and the pass deformation method is square-ellipse-circle. In particular,

[0104] Soaking treatment:The steel ingot of 2.5 tons (510 mm) after the air cooling is soaked, and the conditions of soaking are firstly heating up to 1170 C. at the heating speed of 2.3 C./min and preserving heat for 4 hours.

[0105] Upsetting-and-drawing and radial forging: the steel ingot after the soaking treatment is fed into a 4500t press for first upsetting-and-drawing for 8 minutes, wherein the final forging temperature is 850 C. until the diameter is 530 mm, the reduction is 120 mm, and the deformation method is 530 mm square-535 mm ellipse-530 mm circle; then the blank is returned to the furnace and heated at 1170 C. for 90 minutes, and then fed into a press of 4500t for second upsetting-and-drawing for 10 minutes, wherein the final forging temperature is 750 C., the diameter is 450 mm, the reduction is 120 mm, and the deformation method is 440 mm-square-billet-455 mm-ellipse-450 mm-circle; then the steel is returned to the furnace and heated at 1170 C. for 90 minutes, and then fed into a press of 4500t for drawing for 15 minutes until the diameter is 300 mm, wherein the reduction is 120 mm, the deformation is 55%, and the deformation method is 310 mm-square-billet-305 mm-ellipse-300 mm-circle; then the steel is returned to the furnace and heated again at 1170 C. for 90 minutes, then performed one-fire forging for 20 minutes in a 1600t radial forging machine, wherein the final forging temperature is 850 C., the diameter after forging is 200 mm; then the steel is air-cooled to room temperature to obtain a 200 mm diameter 00Cr19Ni10N steel bar. The 350 C. high temperature tensile strength, the 350 C. high temperature yield strength, the room temperature tensile strength and the room temperature yield strength of the steel bar can not meet the requirements of the RCCMM3306 standard, and the high-magnification structure (microstructure) and the low-magnification structure (macrostructure) are not uniform, which is shown in Tables 9 and 10.

TABLE-US-00009 TABLE 9 Properties and structure of the low-carbon nitrogen-containing austenitic stainless steel bar obtained in Comparative Example 2 Tensile Yield strength strength Tensile Yield at high at high strength strength temperature temperature at room at room Specification of 350 C. of 350 C. temperature temperature Macro- (mm) (MPa) (MPa) (MPa) (MPa) Non-metal inclusions Grain size structure 200 385 121 527 210 A, B, C, D all the types of Grades 5-2 Non- inclusion are is less than mixed uniform or equal to Grade 0.5 crystal tissue

TABLE-US-00010 TABLE 10 Chemical composition (wt %) of low-carbon nitrogen-containing austenitic stainless steel bar prepared in Comparative Example 2 C Si Mn P S Cr Ni N Nb + Ta Co Cu B 0.026 0.54 1.45 0.017 0.002 19.7 9.6 0.072 0.008 0.03 0.2 0.0009

Comparative Example 3

[0106] The comparative example provides a method for manufacturing a low-carbon high-strength nitrogen-containing austenitic stainless steel bar produced in a conventional chemical component control range, which sequentially comprises the following steps: smelting, electroslag remelting and forging. Wherein, except the material preparation step in the smelting procedure adopts the following technical scheme, the other steps of the smelting process, the electroslag remelting process and the forging process all adopt the technical scheme in Example 1. In particular,

[0107] Smelting Process:

[0108] (1) Batching: Low carbon ferrochrome, metal nickel, electrolytic manganese, ferrosilicon, nitrided ferrochrome and scrap steel are batched in the way that the steel ingot prepared contains C: 0.026%, Si: 0.54%, Mn: 1.45%, S: less than or equal to 0.002%, P: less than or equal to 0.017%, Cr: 18.8%, Ni: 9.3%, Cu: less than or equal to 1.00%, Co: less than or equal to 0.06%, N: 0.05%, B: less than or equal to 0.0018%, Nb+Ta: less than or equal to 0.15%, wherein of the weight of the low-carbon ferrochrome and the weight of the nitrided ferrochrome are reserved respectively.

[0109] The above ingredients are adopted for smelting, electroslag remelting and forging, the diameter is 200 mm after final forging; and then, 200 mm-diameter 00Cr19Ni10N steel bar is obtained though air-cooling to room temperature. The tensile strength at the high temperature of 350 C., the yield strength at the high temperature of 350 C., the tensile strength at the room temperature and the yield strength at the room temperature of the steel bar all can not meet the requirements of the RCCMM3306 standard, which are specifically shown in Tables 11 and 12.

TABLE-US-00011 TABLE 11 Properties and structure of the low-carbon nitrogen-containing austenitic stainless steel bar obtained in Comparative Example 3 Tensile Yield strength strength Tensile Yield at high at high strength strength temperature temperature at room at room Specification of 350 C. of 350 C. temperature temperature Macro- (mm) (MPa) (MPa) (MPa) (MPa) Non-metal inclusions Grain size structure 200 370 109 518 202 A, B, C, D all the types of Uniform Uniform inclusion are less than or Grade 5 and no equal to Grade 0.5 grain size segregation

TABLE-US-00012 TABLE 12 Chemical composition (wt %) of low-carbon nitrogen-containing austenitic stainless steel bar prepared in Comparative Example 3 C Si Mn P S Cr Ni N Nb + Ta Co Cu B 0.026 0.54 1.45 0.017 0.002 18.8 9.3 0.05 0.008 0.03 0.2 0.0009

[0110] In conclusion, by adopting the technical scheme of the invention, the low-carbon high-strength nitrogen-containing austenitic stainless steel with uniformly distributed chemical composition and tissues, high purity and high strength can be obtained.