CN114395727A - Smelting and continuous casting process of martensite precipitation hardening stainless steel - Google Patents
Smelting and continuous casting process of martensite precipitation hardening stainless steel Download PDFInfo
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Abstract
The invention discloses a smelting and continuous casting process of martensite precipitation hardening stainless steel, which comprises the following steps of: s1) melting raw materials by EAF; s2) AOD smelting; s3) VOD smelting; s4) calcium treatment and weak stirring; s5), carrying out continuous casting in a straight arc-shaped slab continuous casting machine, wherein the ladle casting adopts a ladle nozzle and argon protection casting; s6) pouring the tundish into the crystallizer, and adopting an integral 2-hole submerged nozzle; s7), using the covering slag, and cooling the crystallizer for the first time; s8) secondary cooling of the crystallizer; s9) electromagnetic stirring; s10) adopting dynamic soft pressing at the solidification end; s11) water cooling of the slab. The casting method has the advantages of solving the problems of casting stability and solidification segregation, reducing the precipitation of large-scale impurities on the surface, reducing the occurrence of slag entrapment and longitudinal cracking through the selection of the continuous casting crystallizer casting powder, and improving the surface quality and the internal quality of a casting blank.
Description
Technical Field
The invention belongs to the technical field of alloy steel manufacturing, and particularly relates to a smelting and continuous casting process of martensite precipitation hardening stainless steel.
Background
High strength stainless steel is widely used in the fields of aviation, aerospace, marine, nuclear industries and the like, and martensite high strength stainless steel is most widely used. Martensitic high strength stainless steel is a stainless steel whose properties can be adjusted by heat treatment. According to the element composition, the martensite high-strength stainless steel is divided into aging stainless steel and precipitation hardening stainless steel. The martensite precipitation hardening stainless steel has the advantages of high strength, good toughness, excellent corrosion resistance and the like after heat treatment. The martensitic precipitation hardening stainless steel commonly used in the market at present is 0Cr17Ni4Cu4Nb, and the common chemical components thereof are as follows by mass percent: carbon (C) is less than or equal to 0.07 percent, manganese (Mn) is less than or equal to 1.00 percent, silicon (Si) is less than or equal to 1.00 percent, phosphorus (P) is less than or equal to 0.023 percent, sulfur (S) is less than or equal to 0.03 percent, chromium (Cr) is 15.50 to 17.50 percent, nickel (Ni) is 3.00 to 5.00 percent, copper (Cu) is 3.00 to 5.00 percent, niobium (Nb) is 0.15 to 0.45 percent, and the balance is iron and other inevitable impurities. 0Cr17Ni4Cu4Nb uses low carbon (C), high chromium (Cr) and copper (Cu), its strength, toughness and corrosion resistance are better than general martensitic stainless steel, it is used in structural member, it depends on Al, Nb and other elements to obtain higher service strength after aging treatment. The coiled material is produced according to the chemical components, and after aging treatment, the strength of about 1000-1400 Mpa can be obtained, which belongs to a low strength grade and can not meet the use requirement of the strength of stainless steel in some environments. Chinese patent application, application No. CN202010511297.3, 2020.06.08, application publication No. CN111575588A, application publication No. 2020.08.25, discloses a martensite precipitation hardening stainless steel, a preparation method and application thereof, wherein the chemical components comprise: 0.04-0.06% of C; 1.4-1.8% of Si; 0.5-0.9% of Mn0.5; p is less than or equal to 0.035%; s is less than or equal to 0.008 percent; cr 14-14.5%; ni 7-7.8%; al 0-0.15%; mo0.55-0.7%; 0.7-1.0% of Cu0; n0-0.03%; 0.28-0.35% of Ti0.28; the balance of iron and other inevitable impurities; the preparation method comprises the following steps: the raw materials are smelted, continuously cast, hot rolled, thermally annealed and pickled, cold rolled, annealed and pickled, leveled and aged. The method has the advantages that the chemical components of the stainless steel are proportioned, and a smelting process, a hot rolling and rolling process, a cold rolling and rolling process and an annealing process are improved, so that the martensite precipitation hardening stainless steel coil with the yield strength of 1480-1600 MPa is finally obtained. The defects that the martensite precipitation hardening stainless steel provided by the technical scheme does not disclose smelting and continuous casting processes; the martensitic precipitation hardening stainless steel has a high Ti content, so that it is required that the molten steel N, O content is as low as possible to prevent the formation of TiO in a large amount during casting2、TiN、TiCaCO3High-melting-point inclusions affect the castability of molten steel and the surface quality of a casting blank in the continuous casting process. Meanwhile, due to the high alloy content of the martensite precipitation hardening stainless steel, macroscopic and microscopic segregation of alloy elements is easily generated in the solidification process, so that martensite phase transformation is insufficient, and the hardness of a final product is uneven.
Disclosure of Invention
1. Technical problem to be solved
Aiming at the martensite precipitation hardening stainless steel provided in the prior art and the preparation method and the application thereof, the smelting and continuous casting process is not disclosed; the martensitic precipitation hardening stainless steel has a high Ti content, so that it is required that the molten steel N, O content is as low as possible to prevent the formation of TiO in a large amount during casting2、TiN、TiCaCO3Inclusions with high melting points affect the castability of molten steel and the surface quality of a casting blank in the continuous casting process; meanwhile, due to the high alloy content of the martensite precipitation hardening stainless steel, the macro and micro segregation of alloy elements is easily generated in the solidification process, the martensite phase transformation is insufficient, and the hardness of the final product is unevenThe invention aims to provide a smelting and continuous casting process of martensite precipitation hardening stainless steel, which solves the problems of casting stability and solidification segregation by adjusting the smelting and continuous casting process, reduces the precipitation of large-scale inclusions on the surface, and reduces the occurrence of slag entrapment and longitudinal cracking by selecting continuous casting crystallizer casting slag.
2. Technical scheme
In order to achieve the purpose and achieve the technical effect, the invention adopts the following technical scheme:
a smelting and continuous casting process of martensite precipitation hardening stainless steel comprises the following raw material components by mass percent: c: 0.04-0.06%; si: 1.4-1.8%; mn: 0.5-0.9%; p: less than or equal to 0.035%; s: less than or equal to 0.008 percent; cr:14 to 14.5 percent; ni: 7-7.8%; al is more than 0 and less than or equal to 0.1 percent; 0.55 to 0.7 percent of Mo; cu: 0.7-1.0%; 0 to 0.03 percent of N; 0.28 to 0.38 percent of Ti; the balance of iron and other inevitable impurities; the process steps of smelting and continuously casting each raw material of the martensite precipitation hardening stainless steel comprise:
s1) melting the raw material of the martensitic precipitation hardening stainless steel by EAF, and slagging off after tapping, wherein the temperature reaches 1550 ℃;
s2) AOD smelting, removing C to 0.2-0.25%, adding reducing agent SiFe alloy, adding lime, fluorite and aluminum balls, and continuing slagging, deoxidizing and desulfurizing; controlling the tapping temperature to be higher than 1620 ℃, and slagging off after tapping;
s3) VOD smelting, namely removing C to 0.04-0.06%, controlling the Al content of the continuous casting sample to be 500-1000ppm according to the aluminum-oxygen equilibrium solubility and the limitation of adopting ladle treatment, ensuring that the total oxygen content is below 10ppm in a deoxidation equilibrium state, and controlling the nitrogen content to be below 100 ppm; the nozzle and stopper nodulation caused by Ti precipitation is reduced, the castability is influenced, and the normal casting at the continuous casting speed is further influenced;
s4) calcium treatment, controlling the Ca content at 20-35ppm, ensuring the castability of the molten steel; weakly stirring for more than 30min to promote impurities to float and improve the purity of molten steel;
s5), carrying out continuous casting in a straight arc-shaped slab continuous casting machine, wherein the ladle casting adopts a ladle nozzle and argon protection casting; the superheat degree of the tundish is controlled at 30-40 ℃; the binary alkalinity R of a covering agent coated in the tundish is 1.5-2.0, and the covering agent adsorbs impurities and protects molten steel from being oxidized by air;
s6) pouring the tundish into the crystallizer, and adopting an integral 2-hole submerged nozzle with an inclination angle of 15 degrees; according to the section size of the plate blank of 200-220mm, the insertion depth is controlled to be 80-120 mm;
s7), using the covering slag, cooling the crystallizer for the first time, wherein the water flow of the wide surface is 2500-3500L/min, and the water flow of the narrow surface is 480-520L/min;
s8) secondary cooling of the crystallizer, wherein the secondary cooling water is 0.50-0.7L/kg;
s9), performing electromagnetic stirring by adopting 1500A and 7.5Hz unidirectional continuous stirring, breaking the columnar crystal dendrite, and increasing the equiaxed crystal rate;
s10), dynamically pressing down the solidification tail end by 2-5mm, increasing the backflow of molten steel, and reducing the segregation of a central solidification structure;
s11) water cooling the plate blank for 20-30 min; the grinding depth is 2-5 mm.
Further, in the step S6, the drawing speed of molten steel in the tundish entering the crystallizer through the submerged nozzle is 0.80-1.0 m/min.
Further, the mold flux comprises the following components in percentage by mass: CaO: 27.3 to 33.3% of SiO2：34.5～40.5％、Al2O3：2.4～4.4％、MgO：0.5～2.5％、Na2O: 11.3-14.3%, F: 5.8-8.8% and 1.5-3.5% of total carbon; since the martensite precipitation hardening stainless steel is high Ti steel, the covering slag is used in the continuous casting process, and the smooth casting is ensured.
Furthermore, the water content of the casting powder is less than or equal to 0.5 wt%, the melting point is 950-1055 ℃, and the viscosity at 1300 ℃ is 1.0-2.5 Poise.
In a specific embodiment of the present invention, the martensitic precipitation hardening stainless steel comprises the following chemical components by mass percent: c: 0.048 percent; si: 1.8 percent; mn: 0.70 percent; 0.027 percent of P; 0.0018 percent of S; 14.4 percent of Cr; ni: 7.1 percent; 0.05 percent of Al; 0.65 percent of Mo; cu: 0.76 percent; 0.008 percent of N; 0.35 percent of Ti; the balance being iron and other unavoidable impurities.
In a specific embodiment of the present invention, the martensitic precipitation hardening stainless steel comprises the following chemical components by mass percent: c: 0.050%; si: 1.78 percent; mn: 0.68 percent; 0.025 percent of P; 0.0025 percent of S; 14.2 percent of Cr; ni: 7.0 percent; 0.038 percent of Al; 0.60 percent of Mo; cu: 0.78%; 0.006 percent of N; 0.35 percent of Ti; the balance being iron and other unavoidable impurities.
In a specific embodiment of the present invention, the martensitic precipitation hardening stainless steel comprises the following chemical components by mass percent: c: 0.042 percent; si: 1.72 percent; mn: 0.69%; 0.028 percent of P; 0.0025 percent of S; 14.3 percent of Cr; ni: 7.1 percent; 0.055 percent of Al; 0.58 percent of Mo; cu: 0.79 percent; 0.007 percent of N; 0.38 percent of Ti; the balance being iron and other unavoidable impurities.
In a specific embodiment of the present invention, the martensitic precipitation hardening stainless steel comprises the following chemical components by mass percent: c: 0.043 percent; si: 1.7 percent; mn: 0.68 percent; 0.025 percent of P; 0.002 percent of S; 14.35 percent of Cr; ni: 7.2 percent; 0.06 percent of Al; 0.58 percent of Mo; cu: 0.77 percent; 0.008 percent of N; 0.37 percent of Ti; the balance being iron and other unavoidable impurities.
The invention also aims to provide the martensitic precipitation hardening stainless steel which is characterized by being obtained by the smelting and continuous casting process, the hot rolling, the hot annealing and pickling, the cold rolling, the annealing and pickling, the leveling and the aging of the martensitic precipitation hardening stainless steel.
The invention also aims to provide application of the martensitic precipitation hardening stainless steel prepared by the smelting and continuous casting process of the martensitic precipitation hardening stainless steel in manufacturing transmission belts of printed circuit equipment and food processing equipment.
The invention adopts a straight arc-shaped slab continuous casting machine for continuous casting, and compared with the prior method, the casting method has the main advantages of production stability, good surface quality and internal quality uniformity of the slab and the like. Specifically, the low oxygen and nitrogen content and the deoxidation mode can control the inclusions in a reasonable range, and prevent the nozzle and the stopper from nodulation to cause the fluctuation of the liquid level of the crystallizer; good surface quality, preventing surface longitudinal cracks and steel leakage accidents, reducing the grinding amount of the surface of the casting blank and improving the yield; the use of electromagnetic stirring and dynamic soft reduction can ensure the uniformity of chemical components of the casting blank, reduce the anisotropy to the maximum extent and ensure the uniformity of various properties of the product; the method is realized by adopting a straight arc-shaped slab continuous casting machine, and can improve the labor productivity through automatic control.
3. Advantageous effects
Compared with the prior art, the technical scheme of the invention has the following beneficial effects: by optimizing and adjusting the smelting and continuous casting processes, the problems of casting stability and solidification segregation are solved, the precipitation of large-scale impurities on the surface is reduced, the generation of slag entrapment and longitudinal cracking is reduced by selecting continuous casting crystallizer casting powder, and the surface quality and the internal quality of a casting blank are improved.
Drawings
The invention is further described below with reference to the accompanying drawings.
FIG. 1 is a macroscopic structural diagram of example 1.
FIG. 2 is a macroscopic structural view of example 2.
FIG. 3 is a low power tissue structure diagram of example 3.
Detailed Description
The present invention is further illustrated by the following specific examples.
Example 1
An enterprise uses a straight arc-shaped slab caster to produce a martensite precipitation hardening stainless steel slab, 1 furnace steel is produced, the slab specification is 220 (thickness) × 1540 (width) × Lmm, and L represents the slab length. The process conditions were as follows: actual chemical components of molten steel: c: 0.048 percent; si: 1.8 percent; mn: 0.70 percent; 0.027 percent of P; 0.0018 percent of S; 14.4 percent of Cr; ni: 7.1 percent; 0.05 percent of Al; 0.65 percent of Mo; cu: 0.76 percent; 0.008 percent of N; 0.35 percent of Ti; the balance of iron and other inevitable impurities, and the components meet the standard and the internal control requirement. Specifically, the method comprises the following steps:
A. smelting: through EAF + AOD + VOD + CCP, the oxygen and nitrogen contents of molten steel are reduced, and TiN and TiO are reduced2Is generated and preventedThe continuous casting water gap and the stopper rod have nodulation, which affects the castability and further affects the normal casting of continuous casting;
1) EAF melts alloy and scrap steel, the temperature reaches 1550 ℃, and slag is removed after tapping;
2) removing C to 0.2-0.25% by AOD smelting, adding a reducing agent SiFe alloy, adding lime, fluorite and aluminum balls after 3min, and continuously slagging, deoxidizing and desulfurizing; controlling the tapping temperature to be higher than 1620 ℃, and slagging off after tapping;
3) VOD smelting, VOD first adopts vacuum oxygen blowing decarbonization and high vacuum carbon deoxidation technology to remove C to 0.04-0.06%, then uses small aluminum balls to deoxidize to reduce Total [ O ] in steel, and impurities in molten steel float sufficiently, thereby reducing the formation of non-metallic oxide inclusions; further pumping to ensure that the vacuum degree is below 67pa, keeping the high vacuum for 25 minutes, and reducing the oxygen and nitrogen contents of molten steel, wherein the actual measurement of the oxygen content is 22ppm, and the nitrogen content is 75 ppm;
4) the Ca content in calcium treatment is controlled to be 20-35ppm, so that the castability of molten steel is ensured; weakly stirring for more than 30min to promote impurities to float and improve the purity of molten steel;
B. continuous casting: in the process of slab Continuous Casting (CCP), the casting speed is preferably not to generate speed fluctuation to cause the liquid level fluctuation of a crystallizer to cause slag entrapment; the most important indexes of the high-strength aging stainless steel, including the content and the form of inclusions have great influence on the toughness of the material;
1) casting the ladle by using a ladle nozzle and argon protection; tundish temperature 1505 and 1511 ℃; a covering agent with proper alkalinity is adopted in the tundish to adsorb impurities and protect molten steel from being oxidized by air;
2) an integral 2-hole submerged nozzle is adopted from the tundish to the crystallizer, and the inclination angle is 15 degrees; according to the sectional dimension of the slab of 220mm 1540mm, the insertion depth of the water gap is controlled at 100 and 120 mm;
3) the covering slag is special stainless steel covering slag, and is cooled for one time, wherein the water quantity of a narrow surface is 500L/min, and the water quantity of a wide surface is 3500L/min; the casting powder comprises the following components in percentage by mass: CaO: 27.3 to 33.3% of SiO2：34.5～40.5％、Al2O3：2.4～4.4％、MgO：0.5～2.5％、Na2O: 11.3-14.3%, F: 5.8-8.8% and 1.5-3.5% of total carbon;
4) secondary cooling, wherein the secondary cooling water is 0.6L/kg;
5) the electromagnetic stirring adopts 1500A and 7.5Hz unidirectional continuous stirring, breaks the columnar crystal dendrite and increases the equiaxed crystal rate.
6) The solidification tail end adopts dynamic soft pressing, the pressing amount is 5mm, the backflow of molten steel is increased, and the segregation of a central solidification structure is reduced;
7) water cooling the plate blank for 20-30 min; the grinding depth is 2-5 mm.
Example 2
An enterprise uses a straight arc-shaped slab caster to produce a martensite precipitation hardening stainless steel slab, 1 furnace steel is produced, the slab specification is 220 (thickness) × 1540 (width) × Lmm, and L represents the slab length. The process conditions were as follows: actual chemical components of molten steel: c: 0.050%; si: 1.78 percent; mn: 0.68 percent; 0.025 percent of P; 0.0025 percent of S; 14.2 percent of Cr; ni: 7.0 percent; 0.038 percent of Al; 0.60 percent of Mo; cu: 0.78%; 0.006 percent of N; 0.35 percent of Ti; the balance of iron and other inevitable impurities, and the components meet the standard and the internal control requirement. Specifically, the method comprises the following steps:
A. smelting: through EAF + AOD + VOD + CCP, the oxygen and nitrogen contents of molten steel are reduced, and TiN and TiO are reduced2The generation of the slag can prevent the continuous casting water gap and the stopper rod from nodulation, and influence the castability, thereby influencing the normal casting of the continuous casting.
1) EAF melts alloy and scrap steel, the temperature reaches 1550 ℃, and slag is removed after tapping;
2) removing C to 0.2-0.25% by AOD smelting, adding a reducing agent SiFe alloy, adding lime, fluorite and aluminum balls after 3min, and continuously slagging, deoxidizing and desulfurizing; controlling the tapping temperature to be higher than 1620 ℃, and slagging off after tapping;
3) VOD smelting, VOD first adopts vacuum oxygen blowing decarbonization and high vacuum carbon deoxidation technology to remove C to 0.04-0.06%, and uses small aluminum balls to deoxidize again to reduce Total [ O ] in steel, and impurities in molten steel float sufficiently, thereby reducing the formation of non-metallic oxide inclusions; further pumping to make the vacuum degree reach below 67pa, maintaining the high vacuum for 25 minutes, and reducing the oxygen and nitrogen contents of molten steel, wherein the actual measurement of the oxygen content is 18ppm, and the nitrogen content is 55 ppm.
4) The Ca content in calcium treatment is controlled to be 20-35ppm, so that the castability of molten steel is ensured; weakly stirring for more than 30min to promote impurities to float and improve the purity of molten steel;
B. continuous casting: in the process of slab Continuous Casting (CCP), the casting speed is preferably not to generate speed fluctuation to cause the liquid level fluctuation of a crystallizer to cause slag entrapment; the most important indexes of the high-strength aging stainless steel, including the content and the form of inclusions have great influence on the toughness of the material;
1) casting the ladle by using a ladle nozzle and argon protection; tundish temperature 1505 and 1511 ℃; a covering agent with proper alkalinity is adopted in the tundish to adsorb impurities and protect molten steel from being oxidized by air;
2) an integral 2-hole submerged nozzle is adopted from the tundish to the crystallizer, and the inclination angle is 15 degrees; according to the sectional dimension of the slab of 220mm 1540mm, the insertion depth of the water gap is controlled at 100 and 120 mm;
3) the covering slag is special stainless steel covering slag, and is cooled for one time, wherein the water quantity of a narrow surface is 500L/min, and the water quantity of a wide surface is 3500L/min; the casting powder comprises the following components in percentage by mass: CaO: 27.3 to 33.3% of SiO2：34.5～40.5％、Al2O3：2.4～4.4％、MgO：0.5～2.5％、Na2O: 11.3-14.3%, F: 5.8-8.8% and 1.5-3.5% of total carbon;
4) secondary cooling, wherein the secondary cooling water is 0.6L/kg;
5) the electromagnetic stirring adopts 1500A and 7.5Hz unidirectional continuous stirring, breaks the columnar crystal dendrite and increases the equiaxed crystal rate.
6) The solidification tail end adopts dynamic soft pressing, the pressing amount is 5mm, the molten steel backflow is increased, and the central solidification structure segregation is reduced
7) Water cooling the plate blank for 20-30 min; the grinding depth is 2-5 mm.
Example 3
An enterprise uses a straight arc-shaped slab caster to produce a martensite precipitation hardening stainless steel slab, 2 furnaces of steel are produced, the specification of the slab is 220 (thickness) × 1540 (width) × Lmm, and L represents the length of the slab. The process conditions were as follows: heat 1 molten steel actual chemical composition: c: 0.042 percent; si: 1.72 percent; mn: 0.69%; 0.028 percent of P; 0.0025 percent of S; 14.3 percent of Cr; ni: 7.1 percent; 0.055 percent of Al; 0.58 percent of Mo; cu: 0.79 percent; 0.007 percent of N; 0.38 percent of Ti; the balance of iron and other inevitable impurities; heat 2 molten steel actual chemical composition: c: 0.043 percent; si: 1.7 percent; mn: 0.68 percent; 0.025 percent of P; 0.002 percent of S; 14.35 percent of Cr; ni: 7.2 percent; 0.06 percent of Al; 0.58 percent of Mo; cu: 0.77 percent; 0.008 percent of N; 0.37 percent of Ti; the balance of iron and other inevitable impurities, and the components meet the standard and the internal control requirement. Specifically, the method comprises the following steps:
A. smelting: through EAF + AOD + VOD + CCP, the oxygen and nitrogen contents of molten steel are reduced, and TiN and TiO are reduced2The generation of the slag can prevent the continuous casting water gap and the stopper rod from nodulation, and influence the castability, thereby influencing the normal casting of the continuous casting.
1) EAF melts alloy and scrap steel, the temperature reaches 1550 ℃, and slag is removed after tapping;
2) removing C to 0.2-0.25% by AOD smelting, adding a reducing agent SiFe alloy, adding lime, fluorite and aluminum balls after 3min, and continuously slagging, deoxidizing and desulfurizing; controlling the tapping temperature to be higher than 1620 ℃, and slagging off after tapping;
3) VOD smelting, VOD first adopts vacuum oxygen blowing decarbonization and high vacuum carbon deoxidation technology to remove C to 0.04-0.06%, and uses small aluminum balls to deoxidize again to reduce Total [ O ] in steel, and impurities in molten steel float sufficiently, thereby reducing the formation of non-metallic oxide inclusions; further pumping to ensure that the vacuum degree is below 67pa, keeping the high vacuum for 25 minutes, and reducing the oxygen and nitrogen contents of molten steel, wherein the actual measurement of the oxygen content is 20-23ppm, and the nitrogen content is 70-90 ppm;
4) the Ca content in calcium treatment is controlled to be 20-35ppm, so that the castability of molten steel is ensured; weakly stirring for more than 30min to promote impurities to float and improve the purity of molten steel;
B. continuous casting: in the process of slab Continuous Casting (CCP), the casting speed is preferably not to generate speed fluctuation to cause the liquid level fluctuation of a crystallizer to cause slag entrapment; the most important indexes of the high-strength aging stainless steel, including the content and the form of inclusions have great influence on the toughness of the material;
1) casting the ladle by using a ladle nozzle and argon protection; the temperature of the tundish is 1510-1515 ℃; a covering agent with proper alkalinity is adopted in the tundish to adsorb impurities and protect molten steel from being oxidized by air;
2) an integral 2-hole submerged nozzle is adopted from the tundish to the crystallizer, and the inclination angle is 15 degrees; according to the sectional dimension of the slab of 220mm 1540mm, the insertion depth of the water gap is controlled at 100 and 120 mm;
3) the covering slag is special stainless steel covering slag, and is cooled for one time, wherein the water quantity of a narrow surface is 500L/min, and the water quantity of a wide surface is 3500L/min; the casting powder comprises the following components in percentage by mass: CaO: 27.3 to 33.3% of SiO2：34.5～40.5％、Al2O3：2.4～4.4％、MgO：0.5～2.5％、Na2O: 11.3-14.3%, F: 5.8-8.8% and 1.5-3.5% of total carbon;
4) secondary cooling, wherein the secondary cooling water is 0.6L/kg;
5) the electromagnetic stirring adopts 1500A and 7.5Hz unidirectional continuous stirring, breaks the columnar crystal dendrite and increases the equiaxed crystal rate.
6) The solidification tail end adopts dynamic soft pressing, the pressing amount is 5mm, the molten steel backflow is increased, and the central solidification structure segregation is reduced
7) Water cooling the plate blank for 20-30 min; the grinding depth is 2-5 mm.
The surface of the billet obtained in the embodiment 1, 2 and 3 is inspected, and the billet has no defects such as rolling slag, depression, cracks and the like; fig. 1, 2, and 3 are macrostructural diagrams of examples 1, 2, and 3, respectively, and it can be seen from the diagrams that the macrostructure of example 1 is uniform columnar crystal, the macrostructure of example 2 is uniform equiaxial crystal, the macrostructure of example 3 is uniform columnar crystal, the central equiaxial crystal ratio of examples 1, 2, and 3 is > 50%, and the central porosity rating is 1.0.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other substitutions, modifications, combinations, changes, simplifications, etc., which are made without departing from the spirit and principle of the present invention, should be construed as equivalents and included in the protection scope of the present invention.
Claims (7)
1. A smelting and continuous casting process of martensite precipitation hardening stainless steel comprises the following raw material components by mass percent: c: 0.04-0.06%; si: 1.4-1.8%; mn: 0.5-0.9%; p: less than or equal to 0.035%; s: less than or equal to 0.008 percent; cr:14 to 14.5 percent; ni: 7-7.8%; al is more than 0 and less than or equal to 0.15 percent; 0.55 to 0.7 percent of Mo; cu: 0.7-1.0%; 0 to 0.03 percent of N; 0.28 to 0.38 percent of Ti; the balance of iron and other inevitable impurities; the method is characterized in that the process steps of smelting and continuously casting each raw material of the martensite precipitation hardening stainless steel comprise:
s1) melting the raw material of the martensitic precipitation hardening stainless steel by EAF, and slagging off after tapping, wherein the temperature reaches 1550 ℃;
s2) AOD smelting, removing C to 0.2-0.25%, adding reducing agent SiFe alloy, adding lime, fluorite and aluminum balls, and continuing slagging, deoxidizing and desulfurizing; controlling the tapping temperature to be higher than 1620 ℃, and slagging off after tapping;
s3) VOD smelting, namely removing C to 0.04-0.06%, controlling the continuous casting sampling Al content to be 500-1000ppm, ensuring that the total oxygen content is below 10ppm and the nitrogen content is below 100ppm under the deoxidation equilibrium state; the nozzle and stopper nodulation caused by Ti precipitation is reduced, the castability is influenced, and the normal casting at the continuous casting speed is further influenced;
s4) calcium treatment, controlling the Ca content at 20-35ppm, ensuring the castability of the molten steel; weakly stirring for more than 30min to promote impurities to float and improve the purity of molten steel;
s5), carrying out continuous casting in a straight arc-shaped slab continuous casting machine, wherein the ladle casting adopts a ladle nozzle and argon protection casting; the superheat degree of the tundish is controlled at 30-40 ℃; the binary alkalinity R of a covering agent coated in the tundish is 1.5-2.0, and the covering agent adsorbs impurities and protects molten steel from being oxidized by air;
s6) pouring the tundish into the crystallizer, and adopting an integral 2-hole submerged nozzle with an inclination angle of 15 degrees; according to the section size of the plate blank of 200-220mm, the insertion depth is controlled to be 80-120 mm;
s7), using the covering slag, cooling the crystallizer for the first time, wherein the water flow of the wide surface is 2500-3500L/min, and the water flow of the narrow surface is 480-520L/min;
s8) secondary cooling of the crystallizer, wherein the secondary cooling water is 0.50-0.7L/kg;
s9), performing electromagnetic stirring by adopting 1500A and 7.5Hz unidirectional continuous stirring, breaking the columnar crystal dendrite, and increasing the equiaxed crystal rate;
s10), dynamically pressing down the solidification tail end by 2-5mm, increasing the backflow of molten steel, and reducing the segregation of a central solidification structure;
s11) water cooling the plate blank for 20-30 min; the grinding depth is 2-5 mm.
2. The process of smelting and continuously casting a martensitic precipitation hardened stainless steel according to claim 1, wherein: and in the step S6, the drawing speed of molten steel in the tundish entering the crystallizer through the submerged nozzle is 0.80-1.0 m/min.
3. The process of smelting and continuously casting a martensitic precipitation hardened stainless steel according to claim 1, wherein: the casting powder comprises the following components in percentage by mass: CaO: 27.3 to 33.3% of SiO2：34.5～40.5％、Al2O3：2.4～4.4％、MgO：0.5～2.5％、Na2O: 11.3-14.3%, F: 5.8-8.8% and 1.5-3.5% of total carbon; the water content of the covering slag is less than or equal to 0.5 wt%, the melting point is 950-1055 ℃, and the viscosity at 1300 ℃ is 1.0-2.5 Poise.
4. A process for smelting and continuously casting a martensitic precipitation hardened stainless steel according to any one of claims 1 to 3, characterized in that: the martensite precipitation hardening stainless steel comprises the following chemical components in percentage by mass: c: 0.048 percent; si: 1.8 percent; mn: 0.70 percent; 0.027 percent of P; 0.0018 percent of S; 14.4 percent of Cr; ni: 7.1 percent; 0.05 percent of Al; 0.65 percent of Mo; cu: 0.76 percent; 0.008 percent of N; 0.35 percent of Ti; the balance being iron and other unavoidable impurities.
5. A process for smelting and continuously casting a martensitic precipitation hardened stainless steel according to any one of claims 1 to 3, characterized in that: the martensite precipitation hardening stainless steel comprises the following chemical components in percentage by mass: c: 0.050%; si: 1.78 percent; mn: 0.68 percent; 0.025 percent of P; 0.0025 percent of S; 14.2 percent of Cr; ni: 7.0 percent; 0.038 percent of Al; 0.60 percent of Mo; cu: 0.78%; 0.006 percent of N; 0.35 percent of Ti; the balance being iron and other unavoidable impurities.
6. A process for smelting and continuously casting a martensitic precipitation hardened stainless steel according to any one of claims 1 to 3, characterized in that: the martensite precipitation hardening stainless steel comprises the following chemical components in percentage by mass: c: 0.042 percent; si: 1.72 percent; mn: 0.69%; 0.028 percent of P; 0.0025 percent of S; 14.3 percent of Cr; ni: 7.1 percent; 0.055 percent of Al; 0.58 percent of Mo; cu: 0.79 percent; 0.007 percent of N; 0.38 percent of Ti; the balance being iron and other unavoidable impurities.
7. A process for smelting and continuously casting a martensitic precipitation hardened stainless steel according to any one of claims 1 to 3, characterized in that: the martensite precipitation hardening stainless steel comprises the following chemical components in percentage by mass: c: 0.043 percent; si: 1.7 percent; mn: 0.68 percent; 0.025 percent of P; 0.002 percent of S; 14.35 percent of Cr; ni: 7.2 percent; 0.06 percent of Al; 0.58 percent of Mo; cu: 0.77 percent; 0.008 percent of N; 0.37 percent of Ti; the balance being iron and other unavoidable impurities.
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