An economical free-cutting high-formability austenitic stainless steel

Abstract

The present application relates to the technical field of special austenitic stainless steel preparation, and particularly relates to an economical easy-to-cut high-formability austenitic stainless steel and a preparation method thereof. The economical easy-to-cut high-formability austenitic stainless steel is composed of the following components: 5.5-6.8% of Ni, 1.5-3.5% of Mn, 16.5-18.5% of Cr, 0.15-0.20% of S, 0.8-1.5% of Cu, 0.01-0.03% of RE, 0.12-0.25% of Ca, 0.002-0.005% of Mg, C<=0.08%, Si<=1.0%, N<=0.05%, and the balance of iron and inevitable impurities. In the present application, the content of nickel is reduced to 5.5-6.8%, the material cost is reduced by 20-25%, the cutting force is obviously reduced, the tool life can be effectively prolonged, and the excellent mechanical properties and corrosion resistance are combined.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of special austenitic stainless steel, in particular to an economic easy-to-cut high-formability austenitic stainless steel. BACKGROUND

[0002] The easy-to-cut stainless steel has excellent cutting performance and corrosion resistance, and is widely used in precision machining, fastener industry, automobile industry, precision instrument industry, aerospace and household appliances.

[0003] At present, the easy-to-cut stainless steel is mainly formed by adding easy-to-cut elements (S, P, Pb, Bi, etc.) in the stainless steel series steel, among which the sulfur-based easy-to-cut stainless steel and the lead-based easy-to-cut stainless steel are widely used. The cutting performance of the lead-based easy-to-cut steel is good, but lead seriously pollutes the environment and has been gradually eliminated by lead-free environmentally friendly easy-to-cut stainless steel.

[0004] In order to obtain excellent cutting performance, the sulfur-based easy-to-cut steel needs to add a high sulfur content. For example, the Special Steel Branch of Baosteel Co., Ltd. uses the process of adding sulfur and iron in an electroslag furnace to produce sulfur-containing stainless steel, with a sulfur content of 0.06-0.10%. Although the cutting performance is improved, the sulfur content is unstable and too low, the cutting performance is not satisfactory, and it cannot well meet the needs of the consumer market, and the application field is narrow. Although increasing the sulfur content in the stainless steel can improve its cutting performance, it will significantly reduce the mechanical properties of the stainless steel and deteriorate its corrosion resistance. In addition, the sulfur segregation leads to hot rolling cracking and easy peeling defects, the product defect rate is high, it is difficult to realize large-scale stable production, and the production cost is high, the market industrial value is low.

[0005] In summary, the existing easy-to-cut stainless steel has the problems of high nickel cost, low sulfur cutting performance, and high sulfur steel forming deterioration, and there is an urgent need for an economic easy-to-cut high-formability austenitic stainless steel. SUMMARY

[0006] In order to solve the problems of high nickel cost, low sulfur cutting performance, and high sulfur steel forming deterioration of the existing stainless steel, the present application provides an economic easy-to-cut high-formability austenitic stainless steel and a preparation method thereof. The stainless steel in the present application reduces nickel and increases sulfur while stabilizing the austenitic structure, improves its cutting performance, formability and corrosion resistance, and solves the contradictory problems of cutting performance and hot rolling cracking, cold formability and material corrosion resistance.

[0007] The economic easy-to-cut high-formability austenitic stainless steel provided by the present application is realized by the following technical scheme:

[0008] An economical easy-to-cut high-formability austenitic stainless steel is composed of 5.5-6.8% Ni, 1.5-3.5% Mn, 16.5-18.5% Cr, 0.15-0.20% S, 0.8-1.5% Cu, 0.01-0.03% RE, 0.002-0.004% Ca, 0.002-0.005% Mg, P≤0.05%, C≤0.08%, Si≤1.0%, N≤0.05%, and the balance of iron and inevitable impurities.

[0009] Preferably, the RE element is cerium Ce and lanthanum La, and the mass ratio of cerium Ce to lanthanum La is 1:(0.5-2).

[0010] Preferably, the economical easy-to-cut high-formability austenitic stainless steel is composed of 6.0-6.5% Ni, 2.0-3.0% Mn, 16.8-17.5% Cr, 0.15-0.20% S, 1.0-1.5% Cu, 0.005-0.015% Ce, 0.005-0.015% La, 0.002-0.004% Ca, 0.003-0.005% Mg, P≤0.05%, C≤0.08%, Si≤1.0%, N≤0.05%, and the balance of iron and inevitable impurities, and Ca / S=0.8-1.2.

[0011] In the present application, the nickel content is reduced to 5.5-6.8%, which can reduce the cost of the produced stainless steel while stabilizing the austenite in cooperation with sulfur, copper and rare earth elements, thereby ensuring good corrosion resistance and mechanical properties.

[0012] In the present application, the sulfur content is 0.15-0.20%, which forms spherical sulfides in the stainless steel matrix, thereby improving the cutting performance of the stainless steel. By controlling the sulfur content, the cutting resistance of the stainless steel is effectively improved under the premise of ensuring the corrosion resistance and mechanical properties of the stainless steel, thereby effectively prolonging the service life of the cutting tool.

[0013] In the present application, the addition of an appropriate amount of copper element nano-precipitates in the stainless steel matrix, thereby improving the problem of insufficient strength of low nickel, and thereby ensuring good mechanical properties and corrosion resistance.

[0014] In the present application, the addition of an appropriate amount of rare earth elements can purify the grain boundary, improve the corrosion resistance, endow the stainless steel with good corrosion resistance, and improve the problem of hot working crack peeling defects.

[0015] This invention optimizes the stainless steel composition and preparation process. Specifically, the formulation uses a low-nickel + high-sulfur + copper / rare earth synergistic combination to control sulfide morphology (Ca-Mg composite treatment) and dynamic grain boundary regulation in the preparation process (three-stage rolling + gradient annealing). This results in the following technical effects in the prepared austenitic stainless steel: ① Nickel content is reduced to 5.5–6.8% (30% lower than 304), reducing material costs by 20–25%; ② Sulfur content is increased to 0.15–0.20%, resulting in a 45% reduction in cutting force and a more than 3-fold increase in tool life compared to 304 stainless steel; ③ Excellent forming performance, with a maximum drawing ratio (LDR) of 2.35, and rust-free performance after 1200 hours of salt spray corrosion resistance, exhibiting excellent mechanical properties and corrosion resistance.

[0016] The present invention provides an economical method for preparing free-machining, highly formable austenitic stainless steel, which is achieved through the following technical solution:

[0017] A method for preparing an economical, free-machining, highly formable austenitic stainless steel includes the following steps:

[0018] Step 1, Electric Furnace Smelting: Heat the scrap steel to 1600-1650℃, melt it into molten iron, then add low-phosphorus molten iron and nickel plates, maintain the melting temperature at 1600-1650℃ for 5-15 minutes, P≤0.05%, Ni content controlled at 5.5%-6.8%, then add manganese ingots and copper ingots, maintain the melting temperature at 1600-1650℃ for 5-15 minutes, Mn content controlled at 1.5-3.5%, Cu content controlled at 0.8%-1.5%, carbon content: C≤0.08%;

[0019] Step 2, AOD refining: Adjust the temperature to 1580~1600℃, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is (3~5):(5~7), decarburize to C≤0.03%, and then add sulfur-iron alloy at least three times at intervals, with the total sulfur content controlled at 0.15~0.20%;

[0020] Step 3, LF furnace calcium-magnesium composite treatment: Adjust the temperature to 1550~1580℃, feed in silicon-calcium alloy wire, the amount of silicon-calcium alloy wire added is calculated according to Ca / S ratio of 0.8~1.2, then add magnesium wire, the magnesium content is controlled at 0.002~0.005%, then feed in rare earth silicon-calcium alloy cored wire, the RE content is controlled at 0.01%~0.03%, the calcium content is controlled at 0.002~0.004%, and finally blow argon gas from the bottom of the ladle, the argon gas flow rate is 20~30L / min, and the soft blowing argon gas time is ≥10min;

[0021] Step four, continuous casting: adjusting the temperature of molten steel to 1550-1560 DEG C, drawing blank speed: 0.8-1.2 m / min, crystallizer vibration: amplitude 4-6 mm, frequency 120-150 times / min, two cold water: 0.8-1.2 L / kg molten steel, electromagnetic stirring: frequency 3-5 Hz, current 200-300 A;

[0022] Step five, three-stage hot rolling: rough rolling, low temperature finishing rolling and layer cooling in sequence;

[0023] Step six, gradient annealing of the rough product to obtain the finished economic easy-to-cut high-formability austenitic stainless steel.

[0024] The preparation method is relatively simple and mature, the finished product rate is high, and the scale manufacturing is facilitated.

[0025] Preferably, the sulfur-iron alloy is added in three intervals in step two, the interval time is 8-10 minutes, the first addition is 40wt% sulfur-iron alloy, the C content is controlled to be 0.15-0.20%, the second addition is 30wt% sulfur-iron alloy, the C content is controlled to be 0.05-0.08%, the third addition is 30wt% sulfur-iron alloy, the C content is controlled to be ≤0.03%, the chromium ingot and the nickel block are additionally added, and the composition is finely adjusted to control the Ni content to be 5.5%-6.8% and the Cr content to be 16.5%-18.5%.

[0026] The three-time interval addition of the sulfur-iron alloy in the preparation method has the following effects: ① preventing sulfur segregation (traditional one-time sulfur addition is easy to cause sulfur enrichment in a local area, forming coarse MnS inclusions, and the length-width ratio of the formed MnS inclusions is >5, which causes hot rolling cracks); ② improving sulfur recovery; and ③ making sulfur uniformly distributed (divided sulfur addition can make sulfur uniformly distributed, combined with subsequent calcium and magnesium treatment, forming fine spherical sulfides with a length-width ratio <2).

[0027] Preferably, in step three, the silicon-calcium alloy wire feeding speed is 3-5 m / min, the magnesium wire feeding speed is 1-2 m / min, and the rare earth silicon-calcium alloy cored wire feeding speed is 2-4 m / min.

[0028] The LF furnace calcium and magnesium composite treatment in the preparation method has the following advantages:

[0029] (1) Calcium treatment plays a core role in sulfide morphology control and sulfur segregation suppression. Sulfide morphology control: Calcium (Ca) combines with sulfur (S) to form CaS and forms (Ca, Mn) S complex inclusions with MnS. Technical effect: Sulfide changes from long strip (traditional MnS aspect ratio > 5) to spherical (aspect ratio < 2), reducing stress concentration, i.e. inclusion average size is refined from traditional 5-10 μm to 1-3 μm. Sulfur segregation suppression: The strong desulfurization ability of calcium reduces free sulfur content, suppresses sulfur segregation at grain boundaries, and avoids hot rolling cracking.

[0030] (2) The synergistic effect of magnesium treatment is complex sulfide modification and deoxidation purification. Complex sulfide modification: Magnesium (Mg) further reacts with CaS to form (Ca, Mg, Mn) S ternary complex inclusions. Technical effect: Inclusion melting point is raised (from traditional MnS 1610 °C to 1750 °C), and does not deform during high-temperature rolling. In addition, the inclusions are more dispersed, and the number density is increased to 2000-3000 / mm, while the number density of traditional process is only 500-800 / mm. Deoxidation purification: Magnesium combines with free oxygen in steel to form MgO, reducing oxide inclusions (oxygen content ≤30 ppm).

[0031] (3) Calcium-magnesium ratio design: Ca / S = 0.8-1.2. Calcium deficiency (Ca / S < 0.8): sulfides are mainly MnS, and morphology control is ineffective; calcium excess (Ca / S > 1.2): high melting point CaO-CaS complex inclusions are formed, which deteriorate cutting performance. And Mg addition amount is 0.002-0.005%, magnesium deficiency: unable to form stable (Ca, Mg, Mn) S phase; magnesium excess (> 0.005%): leads to increased nitrogen in molten steel (Mg reacts with N2 in air).

[0032] Single calcium treatment can only partially modify sulfides, while the addition of magnesium further optimizes the following mechanisms: reduce sulfur activity: Mg combines with S to reduce free sulfur content and reduce the tendency of sulfur segregation. Size refinement: the strong deoxidizing ability of Mg suppresses the growth of inclusions. High-temperature stability: ternary sulfides remain spherical at rolling temperature, avoiding elongation.

[0033] Preferably, the four-stage cooling of the secondary cooling zone in step four includes a foot roller stage, a first fan-shaped stage, a second fan-shaped stage, and a third fan-shaped stage. The foot roller stage has a cooling water flow rate of 0.4-0.6 L / kg of molten steel, the first fan-shaped stage has a cooling water flow rate of 0.35-0.45 L / kg of molten steel, the second fan-shaped stage has a cooling water flow rate of 0.25-0.35 L / kg of molten steel, and the third fan-shaped stage has a cooling water flow rate of 0.2-0.3 L / kg of molten steel.

[0034] The four-stage cooling mode in the application can control the solidification front temperature, reduce internal stress, prevent cracks, and improve the processing yield of finished products by controlling the cooling rate to be less than or equal to 100 DEG C / min.

[0035] Preferably, the electromagnetic stirring in the fourth step is divided into mold electromagnetic stirring M-EMS and end electromagnetic stirring F-EMS, the frequency of the mold electromagnetic stirring M-EMS is 3-5 Hz, and the current is 200-250 A; the frequency of the end electromagnetic stirring F-EMS is 2-3 Hz, and the current is 250-300 A.

[0036] By adopting the above technical scheme, equiaxed crystals can be refined, the uniformity of sulfide distribution is improved, and the overall mechanical properties and corrosion resistance are improved.

[0037] Preferably, the high-temperature large deformation roughing in the fifth step is specifically operated as follows: the cast blank is heated to 1150-1200 DEG C, is kept for 2-4 h, is rolled through 5-7 passes, the total deformation amount is 50-60%, and the single-pass deformation amount is 15-20%; and the rolling temperature is controlled to be 1100-1150 DEG C.

[0038] By adopting the above technical scheme, if the temperature is less than 1100 DEG C or the deformation amount is less than 50%, the dynamic recrystallization is not complete, and residual coarse grains lead to subsequent rolling cracking.

[0039] Preferably, the low-temperature finish rolling in the fifth step is specifically operated as follows: the finish rolling temperature is 900-950 DEG C, the total deformation amount is 30-40%, the single-pass deformation amount is 8-12%, and the final rolling thickness is 2-3 mm.

[0040] By adopting the above technical scheme, if the temperature is greater than 950 DEG C: the grains excessively grow, and the strength decreases; low-temperature rolling inhibits dynamic recrystallization, induces static recrystallization through strain accumulation, and refines the grains, thereby laying a good foundation for subsequent annealing mechanics.

[0041] Preferably, the layer cooling in the fifth step is specifically operated as follows: the water cooling is performed to 700 DEG C, and then the cast blank is input into a coiling device to be coiled, so that a crude steel coil is obtained.

[0042] Preferably, the gradient annealing in the sixth step is specifically operated as follows: after being rapidly heated to 1100 DEG C and kept for 5 min, the temperature is slowly cooled to 950 DEG C at a rate of 5-40 DEG C / min and is kept for 15-30 min, and then water cooling is performed to room temperature, so that the gradient annealing is completed.

[0043] The rapid heating to 1100 DEG C in the gradient annealing of the application is to completely austenitize and eliminate work hardening, and the slow cooling to 950 DEG C at 5-40 DEG C / min is to promote annealing twin formation and regulate grain boundary types, and the water cooling to room temperature at a cooling rate of 50 DEG C / s or more is to rapidly cool, fix the microstructure and inhibit grain growth.

[0044] It should be noted that 950 DEG C is critical, because if the temperature is >1000 DEG C, the proportion of twin boundaries decreases and the grains are coarsened, and if the temperature is <900 DEG C, the twin formation kinetics is insufficient, the proportion of small-angle grain boundaries is low, and other substances are easily precipitated. Copper (0.8-1.5%) forms nanoscale ε-Cu precipitates through gradient annealing, improves the tensile strength, and balances high strength and high formability. After gradient annealing, the LDR of the stainless steel can be improved to 2.35.

[0045] In summary, the application has the following advantages:

[0046] 1. In the application, the nickel content is reduced to 5.5-6.8%, the material cost is reduced by 20-25%, the cutting force is significantly reduced, the tool life is effectively improved, and excellent mechanical properties and corrosion resistance are achieved.

[0047] 2. In the application, the formation of spherical (Ca, Mg, Mn) S through sulfide control reduces hot rolling cracking, effectively improves the yield, and also improves the cutting performance and corrosion resistance.

[0048] 3. After gradient annealing, the LDR of the stainless steel provided by the application can be improved to 2.35, which can effectively improve the limit drawing ratio and forming performance of the stainless steel, further improve the yield, and reduce the overall production cost.

[0049] 4. The preparation method of the application is relatively simple and mature, has a high yield, and is easy to realize large-scale manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 is a TEM bright field image of the nanoscale ε-Cu precipitates in the austenitic stainless steel of Example 1.

[0051] Figure 2 is a SEM photo of the spherical sulfides in the austenitic stainless steel of Example 1. DETAILED DESCRIPTION

[0052] In order to further understand the creativity and technical progress of the application, the preferred embodiments of the application are discussed in detail below in combination with examples and comparative examples.

[0053] Embodiment: An economical easy-to-cut high-formability austenitic stainless steel consists of the following components: 5.5-6.8% Ni, 1.5-3.5% Mn, 16.5-18.5% Cr, 0.15-0.20% S, 0.8-1.5% Cu, 0.01-0.04% RE, 0.002-0.004% Ca, 0.002-0.005% Mg, P≤0.05%, C≤0.08%, Si≤1.0%, N≤0.05%, and the balance being iron and inevitable impurities. The RE element is cerium Ce and lanthanum La, the mass ratio of cerium Ce to lanthanum La is 1:(0.5-2), and Ca / S=0.8-1.2.

[0054] Preferably, the economical easy-to-cut high-formability austenitic stainless steel consists of the following components: 6.0-6.5% Ni, 2.0-3.0% Mn, 16.8-17.5% Cr, 0.15-0.20% S, 1.0-1.5% Cu, 0.005-0.015% Ce, 0.005-0.015% La, 0.002-0.004% Ca, 0.003-0.005% Mg, P≤0.05%, C≤0.08%, Si≤1.0%, N≤0.05%, and the balance being iron and inevitable impurities.

[0055] A method for preparing an economical easy-to-cut high-formability austenitic stainless steel, comprising the following steps:

[0056] Step one, electric furnace smelting: the scrap steel is heated to 1600-1650°C, melted into molten iron, and then low-phosphorus molten iron and nickel plates are added, and the molten state is maintained at 1600-1650°C for 5-15 min, P≤0.05%, the Ni content is controlled to be 5.5-6.8%, and then manganese ingots and copper ingots are added, and the molten state is maintained at 1600-1650°C for 5-15 min, the Mn content is controlled to be 1.5-3.5%, the Cu content is controlled to be 0.8-1.5%, and the carbon content is C≤0.08%;

[0057] Step two, AOD refining: adjust the temperature to 1580-1600°C, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is (3-5):(5-7), decarburize to C≤0.03%, and then add sulfur-iron alloy at least three times with intervals, and the total sulfur content is controlled to be 0.15-0.20%;

[0058] Preferably, the ferrous alloy is added in three intervals in step two, with an interval of 8-10 minutes, 40wt% ferrous alloy is added in the first interval, the C content is controlled to be 0.15-0.20%, 30wt% ferrous alloy is added in the second interval, the C content is controlled to be 0.05-0.08%, 30wt% ferrous alloy is added in the third interval, the C content is controlled to be ≤0.03%, and the chromium ingot and the nickel block are additionally added, and the components are finely adjusted to control the Ni content to be 5.5%-6.8% and the Cr content to be 16.5%-18.5%;

[0059] In step three, the LF furnace is subjected to calcium-magnesium composite treatment, the temperature is adjusted to be 1550-1580°C, silicon-calcium alloy wire is fed, the feeding speed is 3-5 m / min, the addition amount of the silicon-calcium alloy wire is calculated according to the ratio of Ca / S 0.8-1.2, then magnesium wire is added, the feeding speed is 1-2 m / min, the magnesium content is controlled to be 0.002-0.005%, rare earth silicon-calcium alloy cored wire is further fed, the feeding speed of the rare earth silicon-calcium alloy cored wire is 2-4 m / min, the RE content is controlled to be 0.01%-0.03%, the calcium content is controlled to be 0.002-0.004%, and finally argon is blown from the bottom of the ladle, the argon flow is 20-30 L / min, and the soft argon blowing time is ≥10 min;

[0060] In step four, continuous casting is performed, the temperature of the molten steel is adjusted to be 1550-1560°C, the casting speed is 0.8-1.2 m / min, the mold vibration is as follows: the amplitude is 4-6 mm, the frequency is 120-150 times / min, the water amount in the secondary cooling zone is 0.8-1.2 L / kg of molten steel, the water amount in the secondary cooling zone is divided into four stages of cooling, including the foot roller section, the first fan-shaped section, the second fan-shaped section, and the third fan-shaped section, the cooling water flow in the foot roller section is 0.4-0.6 L / kg of molten steel, the cooling water flow in the first fan-shaped section is 0.35-0.45 L / kg of molten steel, the cooling water flow in the second fan-shaped section is 0.25-0.35 L / kg of molten steel, the cooling water flow in the third fan-shaped section is 0.2-0.3 L / kg of molten steel, electromagnetic stirring is performed, the frequency is 3-5 Hz, and the current is 200-300 A, specifically, the electromagnetic stirring is divided into mold electromagnetic stirring M-EMS and end electromagnetic stirring F-EMS, in the mold electromagnetic stirring M-EMS, the frequency is 3-5 Hz, and the current is 200-250 A; in the end electromagnetic stirring F-EMS, the frequency is 2-3 Hz, and the current is 250-300 A;

[0061] In step five, three-stage hot rolling is performed, and the rough product is obtained through high-temperature large-deformation rough rolling, low-temperature finish rolling, and layer cooling in sequence;

[0062] The high-temperature large-deformation rough rolling is specifically performed as follows: the cast blank is heated to 1150-1200°C, is kept for 2-4 h, is rolled through 5-7 passes, the total deformation amount is 50-60%, and the single-pass deformation amount is 15-20%; the rolling temperature is controlled to be 1100-1150°C;

[0063] The low-temperature finish rolling is specifically operated as follows: the finish rolling temperature is 900-950℃, the total deformation is 30-40%, the single pass deformation is 8-12%, and the final rolling thickness is 2-3mm;

[0064] The layer cooling is specifically operated as follows: the water cooling to 700℃ is input into the coiling equipment to be coiled to obtain the crude steel coil;

[0065] Step six, gradient annealing is performed on the crude steel coil, and the specific operation is as follows: rapidly heated to 1100℃ and kept for 5min, then slowly cooled to 950℃ at a rate of 5-40℃ / min and kept for 15-30min, water cooled to room temperature, and the economic easy-to-cut high-formability austenitic stainless steel finished product is obtained.

[0066] The raw material sources are shown in Table 1:

[0067] Table 1 is a raw material source table of the economic easy-to-cut high-formability austenitic stainless steel

[0068]

[0069] Example 1: the preparation method of the economic easy-to-cut high-formability austenitic stainless steel, and the steps are as follows:

[0070] Step one, electric furnace smelting: the scrap steel is heated to 1650℃, melted into molten iron, and then low-phosphorus molten iron and nickel plate are added, and the melting is maintained at 1650℃ for 10min, P≤0.05%, the Ni content is detected to be 5.51%, then manganese ingot and copper ingot are added, and the melting is maintained at 1650℃ for 10min, the Mn content is detected to be 3.15%, the Cu content is detected to be 1.47%, and the carbon content is detected to be 0.072%;

[0071] Step two, AOD refining: the temperature is adjusted to 1590℃, and Ar / O2 mixed gas is blown in, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburization for 30min, the carbon content is detected to be 0.027%, then sulfur-iron alloy is added three times with an interval of 10min, the first time 40wt% sulfur-iron alloy is added, the carbon content is detected to be 0.187% after melting for 5min, the second time 30wt% sulfur-iron alloy is added after an interval of 10min, the carbon content is detected to be 0.069% after melting for 5min, the third time 30wt% sulfur-iron alloy is added after an interval of 10min, the carbon content is detected to be 0.016% after melting for 15min, chromium ingot and nickel block are supplemented to adjust the composition, the Ni content is detected to be 5.54% after melting for 10min, the Cr content is detected to be 17.46%, and the S content is detected to be 0.196%;

[0072] Step three, LF furnace calcium magnesium composite treatment: adjust the temperature to 1565℃, feed the silicon calcium alloy wire, the calcium content in the silicon calcium alloy wire is 30wt%, the feeding speed is 4m / min, the addition amount of the silicon calcium alloy wire is calculated according to the Ca / S=1.2:1 ratio, then add the magnesium wire with a purity of 99.95%, the feeding speed is 1m / min, the detected magnesium content is 0.004%, then feed the rare earth silicon calcium alloy cored wire, the silicon calcium alloy in the rare earth silicon calcium alloy cored wire is the carrier, the Ce content is 18wt% and the La content is 12wt%, the silicon calcium alloy content is 70wt%, the feeding speed of the rare earth silicon calcium alloy cored wire is 2.5m / min, the detected Ce content is 0.015%, the La content is 0.010%, the calcium content is 0.004%, finally blow argon from the bottom of the ladle, the argon flow is 25L / min, the soft argon blowing time is 12min;

[0073] Step four, continuous casting: adjust the molten steel temperature to 1550℃, the casting speed is 1m / min, the mold vibration is amplitude 5mm, frequency 120 times / min, the water amount of the secondary cooling zone is divided into four stages including the foot roller section, the first fan-shaped section, the second fan-shaped section and the third fan-shaped section, the cooling water flow of the foot roller section is 0.5L / kg of molten steel, the cooling water flow of the first fan-shaped section is 0.4L / kg of molten steel, the cooling water flow of the second fan-shaped section is 0.3L / kg of molten steel, the cooling water flow of the third fan-shaped section is 0.25L / kg of molten steel, the electromagnetic stirring is divided into mold electromagnetic stirring M-EMS and end electromagnetic stirring F-EMS, the frequency of the mold electromagnetic stirring M-EMS is 5Hz, the current is 250A; the frequency of the end electromagnetic stirring F-EMS is 3Hz, the current is 300A;

[0074] Step five, three-stage hot rolling: rough product is obtained by high-temperature large deformation rough rolling, low-temperature finishing rolling and layer cooling in sequence;

[0075] The specific operation of high-temperature large deformation rough rolling is as follows: the casting blank is heated to 1180℃ and kept for 150min, then it is rolled by 6 passes, the total deformation is 60%, and the single pass deformation is 15%, and the rolling temperature is controlled at 1140℃;

[0076] The specific operation of low-temperature finishing rolling is as follows: the finishing rolling temperature is 950℃, it is rolled by 4 passes, the total deformation is 36%, the single pass deformation is 9%, and the final rolling thickness is 2.5±0.05mm;

[0077] The specific operation of layer cooling is as follows: water cooling to 700℃ at a cooling rate of 50℃ / s, then it is transferred to the coiling equipment for coiling, the coiling section temperature is 645℃, and the rough product steel coil is obtained;

[0078] Step six, gradient annealing of the crude steel coil, the specific operation is as follows: rapid heating to 1100℃ for 5min, then slowly cooling to 950℃ at 10℃ / min for 20min, water cooling to room temperature, the gradient annealing of the economic easy-to-cut high-formability austenitic stainless steel is completed.

[0079] The difference between example 2 and example 1 is that the preparation method of the economic easy-to-cut high-formability austenitic stainless steel in step one, electric furnace smelting: the scrap steel is heated to 1650℃, after melting into molten iron, low phosphorus molten iron and nickel plate are added, and the molten iron is maintained at 1650℃ for 10min, P≤0.05%, the Ni content is detected to be 6.14%, then manganese ingot and copper ingot are added, and the molten iron is maintained at 1650℃ for 10min, the Mn content is detected to be 2.21%, the Cu content is detected to be 1.05%, and the carbon content is detected to be 0.075%;

[0080] Step two, AOD refining: adjust the temperature to 1590℃, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburization for 30min, the carbon content is detected to be 0.025%, then add sulfur-iron alloy three times with an interval of 10min, the first time, add 40wt% sulfur-iron alloy, after melting for 5min, the carbon content is detected to be 0.185%, after an interval of 10min, the second time, add 30wt% sulfur-iron alloy, after melting for 5min, the carbon content is detected to be 0.067%, after an interval of 10min, the third time, add 30wt% sulfur-iron alloy, after melting for 15min, the carbon content is detected to be 0.015%, add chromium ingot and nickel block for composition fine-tuning, after melting for 10min, the Ni content is detected to be 6.19%, the Cr content is detected to be 17.08%, and the S content is detected to be 0.176%;

[0081] Step three, LF furnace calcium-magnesium composite treatment: adjust the temperature to 1565℃, feed in silicon-calcium alloy wire, the calcium content in the silicon-calcium alloy wire is 30wt%, the feeding speed is 4m / min, the addition amount of the silicon-calcium alloy wire is calculated according to the ratio of Ca / S=1:1, then add magnesium wire with a purity of 99.95%, the feeding speed is 1m / min, the magnesium content is detected to be 0.004%, then feed in rare earth silicon-calcium alloy cored wire, the silicon-calcium alloy in the rare earth silicon-calcium alloy cored wire is the carrier, the cerium Ce content is 18wt% and the lanthanum La content is 12wt%, the silicon-calcium alloy content is 70wt%, the feeding speed of the rare earth silicon-calcium alloy cored wire is 2.5m / min, the Ce content is detected to be 0.012%, the La content is detected to be 0.008%, the calcium content is detected to be 0.003%, finally, blow argon from the bottom of the ladle, the argon flow is 25L / min, and the soft argon blowing time is 12min.

[0082] Example 3 differs from Example 1 in that the step one of the preparation method of the economical easy-to-cut high-formability austenitic stainless steel is: electric furnace smelting: the scrap steel is heated to 1650℃, after melting into molten iron, low phosphorus molten iron and nickel plate are added, and the molten iron is maintained at 1650℃ for 10 minutes, P≤0.05%, the content of Ni is detected to be 6.78%, then manganese ingot and copper ingot are added, and the molten iron is maintained at 1650℃ for 10 minutes, the content of Mn is detected to be 1.87%, the content of Cu is detected to be 0.89%, and the content of carbon is detected to be 0.081%;

[0083] Step two, AOD refining: adjust the temperature to 1590℃, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburization for 35 minutes, the content of carbon is detected to be 0.025%, then add ferrosulphur in three times with an interval of 10 minutes, the first time, 40wt% ferrosulphur is added, the content of carbon is detected to be 0.185% after melting for 5 minutes, the second time, 30wt% ferrosulphur is added after an interval of 10 minutes, the content of carbon is detected to be 0.069% after melting for 5 minutes, the third time, 30wt% ferrosulphur is added after an interval of 10 minutes, the content of carbon is detected to be 0.016% after melting for 20 minutes, chromium ingot and nickel block are added for composition fine-tuning, the content of Ni is detected to be 6.78% after melting for 10 minutes, the content of Cr is detected to be 16.67%, and the content of S is detected to be 0.165%;

[0084] Step three, LF furnace calcium-magnesium composite treatment: adjust the temperature to 1565℃, feed in silicon-calcium alloy wire, the content of calcium in the silicon-calcium alloy wire is 30wt%, the feeding speed is 4m / min, the amount of the silicon-calcium alloy wire is calculated according to the ratio of Ca / S=0.8:1, then add magnesium wire with a purity of 99.95%, the feeding speed is 1m / min, the content of magnesium is detected to be 0.004%, then feed in rare earth silicon-calcium alloy cored wire, the silicon-calcium alloy is the carrier in the rare earth silicon-calcium alloy cored wire, the content of cerium Ce is 18wt% and the content of lanthanum La is 12wt%, the content of silicon-calcium alloy is 70wt%, the feeding speed of the rare earth silicon-calcium alloy cored wire is 2.5m / min, the content of Ce is detected to be 0.009%, the content of La is detected to be 0.006%, the content of calcium is detected to be 0.002%, finally, blow argon from the bottom of the ladle, the flow rate of argon is 25L / min, and the soft argon blowing time is 12 minutes.

[0085] Example 4 differs from Example 1 in that the step one of the preparation method of the economical easy-to-cut high-formability austenitic stainless steel is: electric furnace smelting: the scrap steel is heated to 1650℃, after melting into molten iron, low phosphorus molten iron and nickel plate are added, and the molten iron is maintained at 1650℃ for 10 minutes, P≤0.05%, the content of Ni is detected to be 6.65%, then manganese ingot and copper ingot are added, and the molten iron is maintained at 1650℃ for 10 minutes, the content of Mn is detected to be 2.48%, the content of Cu is detected to be 1.36%, and the content of carbon is detected to be 0.081%.

[0086] Step two, AOD refining: adjust the temperature to 1590℃, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in Ar / O2 mixed gas is 4:6, after decarburization for 35 min, the carbon content is detected to be 0.026%, then add ferrous sulphur alloy three times at intervals of 10 minutes, 40wt% ferrous sulphur alloy is added for the first time, the carbon content is detected to be 0.189% after melting for 5 min, 30wt% ferrous sulphur alloy is added for the second time after 10 min, the carbon content is detected to be 0.067% after melting for 5 min, 30wt% ferrous sulphur alloy is added for the third time after 10 min, the carbon content is detected to be 0.015% after melting for 20 min, add chromium ingot and nickel block for composition fine-tuning, the Ni content is detected to be 6.78%, the Cr content is detected to be 17.25%, and the S content is detected to be 0.188% after melting for 10 min;

[0087] Step three, LF furnace calcium-magnesium composite treatment: adjust the temperature to 1565℃, feed in silicon-calcium alloy wire, the calcium content in the silicon-calcium alloy wire is 30wt%, the feeding speed is 4m / min, the silicon-calcium alloy wire is added according to the Ca / S=1:1 ratio, then add magnesium wire with a purity of 99.95%, the feeding speed is 1m / min, the magnesium content is detected to be 0.004%, then feed in rare earth silicon-calcium alloy cored wire, the silicon-calcium alloy in the rare earth silicon-calcium alloy cored wire is the carrier, the cerium Ce content is 18wt% and the lanthanum La content is 12wt%, the silicon-calcium alloy content is 70wt%, the feeding speed of the rare earth silicon-calcium alloy cored wire is 2.5m / min, the Ce content is detected to be 0.018%, the La content is detected to be 0.012%, and the calcium content is detected to be 0.003%, finally blow argon from the bottom of the ladle, the argon flow is 25L / min, and the soft argon blowing time is 12min.

[0088] Example 5 differs from Example 1 in that the preparation method of the economical free-cutting high-formability austenitic stainless steel in step one, electric furnace smelting: heat the scrap steel to 1650℃, after melting into molten iron, add low-phosphorus molten iron and nickel plate, maintain 1650℃ melting for 10 min, P≤0.05%, detect the Ni content to be 5.51%, then add manganese ingot and copper ingot, maintain 1650℃ melting for 10 min, detect the Mn to be 3.15%, detect the Cu content to be 0.83%, and detect the carbon content to be 0.081%;

[0089] Step two, AOD refining: adjust the temperature to 1590 °C, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in Ar / O2 mixed gas is 4:6, after decarburization for 35 min, the carbon content is 0.026%, then add ferrous sulphur alloy three times at intervals of 10 minutes, 40wt% ferrous sulphur alloy is added for the first time, the carbon content is 0.191% after melting for 5 min, 30wt% ferrous sulphur alloy is added for the second time after 10 min, the carbon content is 0.071% after melting for 5 min, 30wt% ferrous sulphur alloy is added for the third time after 10 min, the carbon content is 0.016% after melting for 20 min, add chromium ingot and nickel block to adjust the composition, the Ni content is 5.54%, the Cr content is 17.46%, and the S content is 0.195% after melting for 10 min;

[0090] Step three, LF furnace calcium and magnesium composite treatment: adjust the temperature to 1565 °C, feed in silicon-calcium alloy wire, the calcium content in the silicon-calcium alloy wire is 30wt%, the feeding speed is 4 m / min, the addition amount of the silicon-calcium alloy wire is calculated according to the Ca / S=1.2:1 ratio, then add magnesium wire with a purity of 99.95%, the feeding speed is 1 m / min, the magnesium content is 0.004%, then feed in rare earth silicon-calcium alloy cored wire, the silicon-calcium alloy in the rare earth silicon-calcium alloy cored wire is the carrier, the cerium Ce content is 18wt% and the lanthanum La content is 12wt%, the silicon-calcium alloy content is 70wt%, the feeding speed of the rare earth silicon-calcium alloy cored wire is 2.5 m / min, the Ce content is 0.018%, the La content is 0.012%, and the calcium content is 0.004%, finally blow argon from the bottom of the ladle, the argon flow is 25 L / min, and the soft argon blowing time is 12 min.

[0091] Example 6 differs from example 1 in that the preparation method of the economical free-cutting high-formability austenitic stainless steel of step one, electric furnace smelting: heat the scrap steel to 1650 °C, after melting into molten iron, add low-phosphorus molten iron and nickel plate, maintain 1650 °C for 10 min, P≤0.05%, the Ni content is 5.51%, then add manganese ingot and copper ingot, maintain 1650 °C for 10 min, the Mn content is 3.15%, the Cu content is 1.19%, and the carbon content is 0.081%;

[0092] Step two, AOD refining: adjust the temperature to 1590℃, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburization for 35 min, the carbon content is detected to be 0.026%, then add ferrous sulphide alloy three times at intervals of 10 minutes, 40wt% ferrous sulphide alloy is added for the first time, the carbon content is detected to be 0.181% after melting for 5 min, 30wt% ferrous sulphide alloy is added for the second time after 10 min, the carbon content is detected to be 0.065% after melting for 5 min, 30wt% ferrous sulphide alloy is added for the third time after 10 min, the carbon content is detected to be 0.015% after melting for 20 min, add chromium ingot and nickel block to fine-tune the composition, the Ni content is detected to be 5.54%, the Cr content is detected to be 17.46%, and the S content is detected to be 0.196% after melting for 10 min;

[0093] Step three, LF furnace calcium and magnesium composite treatment: adjust the temperature to 1565℃, feed in silicon-calcium alloy wire, the calcium content in the silicon-calcium alloy wire is 30wt%, the feeding speed is 4m / min, the addition amount of the silicon-calcium alloy wire is calculated according to the Ca / S=1.2:1 ratio, then add magnesium wire with a purity of 99.95%, the feeding speed is 1m / min, the magnesium content is detected to be 0.004%, then feed in rare earth silicon-calcium alloy cored wire, the silicon-calcium alloy in the rare earth silicon-calcium alloy cored wire is the carrier, the cerium Ce content is 18wt% and the lanthanum La content is 12wt%, the silicon-calcium alloy content is 70wt%, the feeding speed of the rare earth silicon-calcium alloy cored wire is 2.5m / min, the Ce content is detected to be 0.018%, the La content is detected to be 0.012%, the calcium content is detected to be 0.004%, and finally blow argon from the bottom of the ladle, the argon flow is 25L / min, and the soft argon blowing time is 12min.

[0094] Example 7 is different from example 1 in that the preparation method of the economical free-cutting high-formability austenitic stainless steel of step one, electric furnace smelting: heat the scrap steel to 1650℃, after melting into molten iron, add low-phosphorus molten iron and nickel plate, maintain 1650℃ melting for 10 min, P≤0.05%, detect the Ni content to be 5.51%, then add manganese ingot and copper ingot, maintain 1650℃ melting for 10 min, detect the Mn to be 3.15%, detect the Cu content to be 1.47%, and detect the carbon content to be 0.074%;

[0095] Step two, AOD refining: adjust the temperature to 1590 °C, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburization for 35 min, the carbon content is 0.025%, then add ferrous sulphur alloy three times at intervals of 10 minutes, 40wt% ferrous sulphur alloy is added for the first time, the carbon content is 0.183% after melting for 5 min, 30wt% ferrous sulphur alloy is added for the second time after 10 min, the carbon content is 0.066% after melting for 5 min, 30wt% ferrous sulphur alloy is added for the third time after 10 min, the carbon content is 0.015% after melting for 20 min, add chromium ingot and nickel block to fine-tune the composition, the Ni content is 5.54%, the Cr content is 17.46%, and the S content is 0.195% after melting for 10 min;

[0096] Step three, LF furnace calcium and magnesium composite treatment: adjust the temperature to 1565 °C, feed in silicon-calcium alloy wire, the calcium content in the silicon-calcium alloy wire is 30wt%, the feeding speed is 4 m / min, the amount of silicon-calcium alloy wire is calculated according to the Ca / S=1.2:1 ratio, then add magnesium wire with a purity of 99.95%, the feeding speed is 1 m / min, the magnesium content is 0.004%, then feed in rare earth silicon-calcium alloy cored wire, the silicon-calcium alloy in the rare earth silicon-calcium alloy cored wire is the carrier, the cerium Ce content is 18wt% and the lanthanum La content is 12wt%, the silicon-calcium alloy content is 70wt%, the feeding speed of the rare earth silicon-calcium alloy cored wire is 2.5 m / min, until the Ce content is 0.006% and the La content is 0.004%, then feed in silicon-calcium alloy wire, the feeding speed is 2.5 m / min, adjust the calcium content to 0.004%, finally blow argon from the bottom of the ladle, the argon flow is 25 L / min, the soft argon blowing time is 12 min.

[0097] Example 8 differs from Example 1 in that the preparation method of the economical free-cutting high-formability austenitic stainless steel of step one, electric furnace smelting: heat the scrap steel to 1650 °C, after melting into molten iron, add low-phosphorus molten iron and nickel plate, maintain 1650 °C for 10 min, P≤0.05%, the Ni content is 5.51%, then add manganese ingot and copper ingot, maintain 1650 °C for 10 min, the Mn content is 3.15%, the Cu content is 1.47%, and the carbon content is 0.079%;

[0098] Step two, AOD refining: adjust the temperature to 1590℃, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburization for 35 min, the carbon content is detected to be 0.026%, then add ferrous sulphide alloy three times at intervals of 10 minutes, 40wt% ferrous sulphide alloy is added for the first time, the carbon content is detected to be 0.188% after melting for 5 min, 30wt% ferrous sulphide alloy is added for the second time after 10 min, the carbon content is detected to be 0.071% after melting for 5 min, 30wt% ferrous sulphide alloy is added for the third time after 10 min, the carbon content is detected to be 0.016% after melting for 20 min, add chromium ingot and nickel block to fine-tune the composition, the Ni content is detected to be 5.54%, the Cr content is detected to be 17.46%, and the S content is detected to be 0.196% after melting for 10 min;

[0099] Step three, LF furnace calcium and magnesium composite treatment: adjust the temperature to 1565℃, feed in silicon-calcium alloy wire, the calcium content in the silicon-calcium alloy wire is 30wt%, the feeding speed is 4m / min, the silicon-calcium alloy wire is added according to the Ca / S=1.2:1 ratio, then add magnesium wire with a purity of 99.95%, the feeding speed is 1m / min, the magnesium content is detected to be 0.004%, then feed in rare earth silicon-calcium alloy cored wire, the silicon-calcium alloy in the rare earth silicon-calcium alloy cored wire is the carrier, the cerium (Ce) content is 18wt% and the lanthanum (La) content is 12wt%, the silicon-calcium alloy content is 70wt%, the feeding speed of the rare earth silicon-calcium alloy cored wire is 2.5m / min, the Ce content is detected to be 0.021%, the La content is detected to be 0.014%, the calcium content is detected to be 0.004%, finally blow argon from the bottom of the ladle, the argon flow is 25L / min, and the soft argon blowing time is 12min.

[0100] The control group is a traditional 304 J1 steel, and the element composition of the traditional 304 J1 steel is as follows: Ni: 8.5%, S: 0.04%, C: 0.031%, Si: 1.15%, Mn: 2.20%, P: 0.032%, Cr: 18.50%, Cu: 1.50%, N: 0.025%, and the balance is iron and inevitable impurities.

[0101] The difference between the comparative example 1 and the example 1 lies in that the step one, electric furnace smelting, of the preparation method of the economical easy-to-cut high-formability austenitic stainless steel is as follows: heat the scrap steel to 1650℃, after melting into molten iron, add low-phosphorus molten iron and nickel plate, maintain 1650℃ melting for 10 min, P≤0.05%, detect the Ni content to be 5.51%, then add manganese ingot, maintain 1650℃ melting for 10 min, detect the Mn to be 3.15%, and detect the carbon content to be 0.071%;

[0102] Step two, AOD refining: adjust the temperature to 1590℃, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburization for 30 min, the carbon content is detected to be 0.027%, then add ferrous sulphide alloy three times at intervals of 10 minutes, the first time 40wt% ferrous sulphide alloy, after melting for 5 min, the carbon content is detected to be 0.182%, after 10 min, the second time 30wt% ferrous sulphide alloy, after melting for 5 min, the carbon content is detected to be 0.065%, after 10 min, the third time 30wt% ferrous sulphide alloy, after melting for 15 min, the carbon content is detected to be 0.015%, supplement chromium ingot and nickel block for composition fine-tuning, after melting for 10 min, the Ni content is detected to be 5.54%, the Cr content is detected to be 17.46%, and the S content is detected to be 0.196%;

[0103] Step three, LF furnace calcium-magnesium composite treatment: adjust the temperature to 1565℃, feed in silicon-calcium alloy wire, the calcium content in the silicon-calcium alloy wire is 30wt%, the feeding speed is 4m / min, the addition amount of the silicon-calcium alloy wire is calculated according to the Ca / S=1.2:1 ratio, then add magnesium wire with a purity of 99.95%, the feeding speed is 1m / min, the magnesium content is detected to be 0.004%, again feed in silicon-calcium alloy wire, the feeding speed is 2.5m / min, the calcium content is 0.004%, finally blow argon from the bottom of the ladle, the argon flow is 25L / min, the soft argon blowing time is 12min.

[0104] The difference between Comparative Example 2 and Example 1 is that the preparation method of the economical easy-to-cut high-formability austenitic stainless steel in Step one of the electric furnace smelting: heat the scrap steel to 1650℃, after melting into molten iron, add low-phosphorus molten iron and nickel plate, maintain 1650℃ melting for 10 min, P≤0.05%, the Ni content is detected to be 5.51%, then add manganese ingot and copper ingot, maintain 1650℃ melting for 10 min, the Mn is detected to be 3.15%, the Cu content is detected to be 1.47%, and the carbon content is detected to be 0.074%;

[0105] Step two, AOD refining: adjust the temperature to 1590℃, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburization for 30 min, the carbon content is detected to be 0.026%, then add ferrous sulphur alloy three times at intervals, the interval time is 10 minutes, the first time adds 40wt% ferrous sulphur alloy, after melting for 5 min, the carbon content is detected to be 0.189%, after 10 min, the second time adds 30wt% ferrous sulphur alloy, after melting for 5 min, the carbon content is detected to be 0.071%, after 10 min, the third time adds 30wt% ferrous sulphur alloy, after melting for 15 min, the carbon content is detected to be 0.016%, supplementally add chromium ingot and nickel block to fine tune the composition, after melting for 10 min, the Ni content is detected to be 5.54%, the Cr content is detected to be 17.46%, and the S content is detected to be 0.195%;

[0106] Step three, LF furnace calcium magnesium composite treatment: adjust the temperature to 1565℃, feed in silicon calcium alloy wire, the calcium content in the silicon calcium alloy wire is 30wt%, the feeding speed is 4m / min, the addition amount of the silicon calcium alloy wire is calculated according to the ratio of Ca / S=1.2:1, then add magnesium wire with a purity of 99.95%, the feeding speed is 1m / min, the magnesium content is detected to be 0.004%, then feed in the silicon calcium alloy wire again, the feeding speed is 2.5m / min, and the calcium content is 0.004%, finally, blow argon from the bottom of the ladle, the argon flow is 25L / min, and the soft argon blowing time is 12min.

[0107] The difference between Comparative Example 3 and Example 1 lies in that the preparation method of the economical easy-to-cut high-formability austenitic stainless steel in step one of the electric furnace smelting is that: the scrap steel is heated to 1650℃, after melting into molten iron, low-phosphorus molten iron and nickel plate are added, and the molten iron is maintained at 1650℃ for 10 min, P≤0.05%, the Ni content is detected to be 5.51%, then manganese ingot is added, the molten iron is maintained at 1650℃ for 10 min, the Mn is detected to be 3.15%, and the carbon content is detected to be 0.071%;

[0108] Step two, AOD refining: adjust the temperature to 1590℃, blow in Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburization for 30 min, the carbon content is detected to be 0.027%, then add ferrous sulphur alloy three times at intervals, the interval time is 10 minutes, the first time adds 40wt% ferrous sulphur alloy, after melting for 5 min, the carbon content is detected to be 0.185%, after 10 min, the second time adds 30wt% ferrous sulphur alloy, after melting for 5 min, the carbon content is detected to be 0.067%, after 10 min, the third time adds 30wt% ferrous sulphur alloy, after melting for 15 min, the carbon content is detected to be 0.015%, supplementally add chromium ingot and nickel block to fine tune the composition, after melting for 10 min, the Ni content is detected to be 5.54%, the Cr content is detected to be 17.46%, and the S content is detected to be 0.196%;

[0109] Step three, LF furnace calcium magnesium composite treatment: adjust the temperature to 1565 °C, feed in silicon calcium alloy wire, the calcium content in the silicon calcium alloy wire is 30 wt%, the feeding speed is 4 m / min, the addition amount of the silicon calcium alloy wire is calculated according to the Ca / S = 1.2:1 ratio, then add magnesium wire with a purity of 99.95%, the feeding speed is 1 m / min, the magnesium content is detected to be 0.004%, then feed in rare earth silicon calcium alloy cored wire, the silicon calcium alloy in the rare earth silicon calcium alloy cored wire is a carrier, the Ce content is 18 wt% and the La content is 12 wt%, the silicon calcium alloy content is 70 wt%, the feeding speed of the rare earth silicon calcium alloy cored wire is 2.5 m / min, the Ce content is detected to be 0.015%, the La content is detected to be 0.010%, the calcium content is detected to be 0.004%, finally blow argon from the bottom of the ladle, the argon flow is 25 L / min, the soft argon blowing time is 12 min.

[0110] The difference between Comparative Example 4 and Example 1 is that the step three, LF furnace calcium magnesium composite treatment, of the preparation method of the economical easy-to-cut high-formability austenitic stainless steel is as follows: adjust the temperature to 1565 °C, feed in silicon calcium alloy wire, the calcium content in the silicon calcium alloy wire is 30 wt%, the feeding speed is 4 m / min, the addition amount of the silicon calcium alloy wire is calculated according to the Ca / S = 1.3:1 ratio, then add magnesium wire with a purity of 99.95%, the feeding speed is 1 m / min, the magnesium content is detected to be 0.004%, then feed in rare earth silicon calcium alloy cored wire, the silicon calcium alloy in the rare earth silicon calcium alloy cored wire is a carrier, the Ce content is 18 wt% and the La content is 12 wt%, the silicon calcium alloy content is 70 wt%, the feeding speed of the rare earth silicon calcium alloy cored wire is 2.5 m / min, the Ce content is detected to be 0.015%, the La content is detected to be 0.010%, the calcium content is detected to be 0.005%, finally blow argon from the bottom of the ladle, the argon flow is 25 L / min, the soft argon blowing time is 12 min.

[0111] Comparative Example 5 differs from Example 1 in that the preparation method of the economical easy-to-cut high-formability austenitic stainless steel in Step 1, electric furnace smelting: the scrap steel is heated to 1650℃, after melting into molten iron, low phosphorus molten iron and nickel plate are added, maintaining 1650℃ melting for 10 min, P≤0.05%, the Ni content is detected to be 5.21%, then manganese ingot and copper ingot are added, maintaining 1650℃ melting for 10 min, the Mn content is detected to be 3.15%, the Cu content is detected to be 1.47%, and the carbon content is detected to be 0.071%; Step 2, AOD refining: adjusting the temperature to 1590℃, blowing Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburizing for 30 min, the carbon content is detected to be 0.025%, then sulfur-iron alloy is added in three times with an interval of 10 minutes, the first time 40wt% sulfur-iron alloy is added, after melting for 5 min, the carbon content is detected to be 0.185%, after an interval of 10 min, the second time 30wt% sulfur-iron alloy is added, after melting for 5 min, the carbon content is detected to be 0.064%, after an interval of 10 min, the third time 30wt% sulfur-iron alloy is added, after melting for 15 min, the carbon content is detected to be 0.015%, chromium ingot and nickel block are added for composition fine adjustment, after melting for 10 min, the Ni content is detected to be 5.29%, the Cr content is detected to be 17.46%, and the S content is detected to be 0.196%; Step 3, LF furnace calcium-magnesium composite treatment: adjusting the temperature to 1565℃, feeding silicon-calcium alloy wire, the calcium content in the silicon-calcium alloy wire is 30wt%, the feeding speed is 4m / min, the amount of the silicon-calcium alloy wire is added according to the ratio of Ca / S=0.7:1, then pure magnesium wire with a purity of 99.95% is added, the feeding speed is 1m / min, the magnesium content is detected to be 0.004%, rare earth silicon-calcium alloy cored wire is further fed, the silicon-calcium alloy is the carrier in the rare earth silicon-calcium alloy cored wire, the Ce content is 18wt% and the La content is 12wt%, the silicon-calcium alloy content is 70wt%, the feeding speed of the rare earth silicon-calcium alloy cored wire is 2.5m / min, the Ce content is adjusted to be 0.015%, the La content is adjusted to be 0.010%, the Ca content is adjusted to be 0.002%, finally argon gas is blown from the bottom of the ladle, the argon gas flow is 25L / min, and the soft argon blowing time is 12min.

[0112] Comparative Example 6 differs from Example 1 in that the preparation method of the economical easy-to-cut high-formability austenitic stainless steel in Step 2, AOD refining: adjusting the temperature to 1590℃, blowing Ar / O2 mixed gas, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is 4:6, after decarburizing for 30 min, the carbon content is detected to be 0.027%, then sulfur-iron alloy is added at one time, continuously blowing Ar / O2 mixed gas, after decarburizing for 30 min, the carbon content is detected to be 0.027%, chromium ingot and nickel block are added for composition fine adjustment, after melting for 10 min, the Ni content is detected to be 5.54%, the Cr content is detected to be 17.46%, and the S content is detected to be 0.196%.

[0113] Performance test: 1, mechanical properties were determined according to ISO 6892-1:2021. 2, salt spray resistance was determined according to ISO9227:2017. 3, cutting force was determined according to ISO 3685:1993. 4, limit drawing ratio (LDR) was determined according to GB / T15825.3-2008.

[0114] Table 2: Element composition table of austenitic stainless steel in examples 1-8 and comparative examples 1-5

[0115]

[0116] Table 3: Performance test parameter table of austenitic stainless steel in examples 1-8 and comparative examples 1-6

[0117]

[0118] It can be seen from the combination of examples 1-6 and the control group and the combination of tables 2-3 that the nickel content in the application is reduced to 5.5-6.8%, the material cost is reduced by 20-25%, the cutting force is significantly reduced, the tool life is effectively prolonged, and excellent mechanical properties and corrosion resistance are achieved.

[0119] It can be seen from the combination of examples 1 and comparative examples 1-3 and the combination of tables 2-3 that the low nickel + high sulfur + copper / rare earth synergistic can improve the cutting performance, mechanical properties and corrosion resistance of the prepared stainless steel.

[0120] It can be seen from the combination of examples 1 and comparative examples 2 and the combination of tables 2-3 and Figure 1 It can be seen that the addition of copper improves the mechanical properties and corrosion resistance of the prepared stainless steel through nano precipitation strengthening. And it can be seen from the combination of examples 1, examples 5-6 and comparative examples 1-3 and the combination of tables 2-3 that the copper addition amount is preferably controlled to be 0.8-1.5%, when the copper addition amount is less than 0.8%, the mechanical strength of the stainless steel is low, and the reinforcement effect is not obvious; when the copper addition amount is higher than 1.5%, the increase of the mechanical strength of the stainless steel is low, and the overall production cost is increased.

[0121] It can be seen from the combination of examples 1 and comparative examples 4-5 and the combination of tables 2-3 that Ca / S=0.8-1.2 can improve the cutting performance, mechanical properties and corrosion resistance of the prepared stainless steel. Insufficient calcium (Ca / S<0.8): sulfides are mainly MnS, the morphology control fails, and the mechanical properties and corrosion resistance decrease significantly; excessive calcium (Ca / S>1.2): high melting point CaO-CaS complex inclusions are generated, which significantly deteriorate the cutting performance.

[0122] It can be seen from the combination of examples 1 and comparative examples 6 and the combination of tables 2-3 and Figure 2It can be seen that the cutting performance, mechanical properties and corrosion resistance of the stainless steel prepared by adding ferrous sulphur alloy three times at intervals, the reduction of hot rolling crack incidence and the improvement of chromium recovery rate, the role of preventing sulfur segregation and the role of improving sulfur recovery rate, the traditional one-time sulfur addition is easy to cause sulfur enrichment in local area, forming coarse MnS inclusions, the length-width ratio of the formed MnS inclusions is > 5, which causes hot rolling crack; in addition, it also makes the sulfur evenly distributed, forming fine spherical sulfide, the length-width ratio < 2.

[0123] It can be seen from the combination of examples 1 and 7-8 and tables 1-2 that the rare earth elements cerium Ce and lanthanum La improve the mechanical properties and corrosion resistance of the prepared stainless steel, and the addition amount of rare earth elements RE is preferably 0.1-0.4wt%. When the addition amount of rare earth elements RE is less than 0.1wt%, the improvement of the mechanical properties and corrosion resistance of the stainless steel is not obvious, and when the addition amount of rare earth elements RE is higher than 0.4wt%, the increase of the mechanical strength and corrosion resistance of the stainless steel is lower, and the overall production cost is increased.

[0124] It should be noted that: the specific embodiments are only an explanation and description of the technical scheme of the present application, and are not a limitation of the present application, and those skilled in the art can make non-creative contribution modifications to the embodiments according to the needs after reading the specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. An economical free-cutting high formability austenitic stainless steel, characterized by: The economic easy-to-cut high-formability austenitic stainless steel is prepared from the following components: 5.5-6.8% Ni, 1.5-3.5% Mn, 16.5-18.5% Cr, 0.15-0.20% S, 0.8-1.5% Cu, 0.01-0.04% RE, 0.002-0.004% Ca, 0.002-0.005% Mg, P≤0.05%, C≤0.08%, Si≤1.0%, N≤0.05%, and the balance of iron and inevitable impurities; the RE element is cerium (Ce) and lanthanum (La), and the mass ratio of Ce to La is 1:(0.5-2); The preparation method of the economic easy-to-cut high-formability austenitic stainless steel comprises the following steps: Step one, electric furnace smelting: the scrap steel is heated to 1600-1650 ℃, and then melted into molten iron, and then low-phosphorus molten iron and nickel plate are added, and the molten iron is maintained at 1600-1650 ℃ for 5-15 min, P≤0.05%, the content of Ni is controlled to be 5.5-6.8%, then manganese ingot and copper ingot are added, and the molten iron is maintained at 1600-1650 ℃ for 5-15 min, the content of Mn is controlled to be 1.5-3.5%, the content of Cu is controlled to be 0.8-1.5%, and the content of C is controlled to be≤0.08%; Step two, AOD refining: the temperature is adjusted to 1580-1600 ℃, and Ar / O2 mixed gas is blown in, the volume ratio of O2 to Ar in the Ar / O2 mixed gas is (3-5):(5-7), and the carbon content is reduced to≤0.03%, then at least three times of sulfur-iron alloy is added, and the total sulfur content is controlled to be 0.15-0.20%; Step three, LF furnace calcium-magnesium composite treatment: the temperature is adjusted to 1550-1580 ℃, silicon-calcium alloy wire is fed in, the addition amount of the silicon-calcium alloy wire is calculated according to Ca / S 0.8-1.2, then magnesium wire is added, the content of Mg is controlled to be 0.002-0.005%, then rare earth silicon-calcium alloy cored wire is fed in, the content of RE is controlled to be 0.01-0.03%, the content of Ca is controlled to be 0.002-0.004%, and finally argon gas is blown from the bottom of the ladle, the argon gas flow is 20-30 L / min, and the soft argon blowing time is≥10 min; Step four, continuous casting: the temperature of the molten iron is adjusted to 1550-1560 ℃, the casting speed is 0.8-1.2 m / min, the mold vibration is 4-6 mm in amplitude and 120-150 times / min in frequency, the water amount in the secondary cooling zone is 0.8-1.2 L / kg of molten iron, and the electromagnetic stirring is 3-5 Hz in frequency and 200-300 A in current; Step five, three-stage hot rolling: the crude product is obtained by high-temperature large-deformation rough rolling, low-temperature precision rolling and layer cooling in sequence; Step six, gradient annealing is performed on the crude product to obtain the economic easy-to-cut high-formability austenitic stainless steel finished product.

2. The economical free-machining high formability austenitic stainless steel according to claim 1, characterized in that: Consist of the following ingredients: 6.0%~6.5%Ni, 2.0~3.0%Mn, 16.8~17.5%Cr, 0.15%~0.20%S, 1.0%~1.5%Cu, 0.005%~0.015%Ce, 0.005%~0.015%La, 0.002~0.004%Ca, 0.003~0.005%Mg, P≤0.05%, C≤0.08%, Si≤1.0%, N≤0.05%, the balance is iron and inevitable impurities.

3. A method of producing the economical free-cutting high-formability austenitic stainless steel according to any one of claims 1 to 2, characterized by: Comprise the following steps: Step one, electric furnace smelting: scrap steel is heated to 1600~1650℃, after molten into molten iron, add low phosphorus molten iron and nickel plate, maintain 1600~1650℃ melt 5~15min, P≤0.05%, Ni content control is 5.5%~6.8%, then add manganese ingot, copper ingot, maintain 1600~1650℃ melt 5~15min, Mn content control is 1.5~3.5%, Cu content control is 0.8%~1.5%, carbon content: C≤0.08%; Step two, AOD refining: adjust the temperature to 1580~1600℃, blow in Ar / O2 mixed gas, the volume ratio of O2 and Ar in Ar / O2 mixed gas is (3~5):(5~7), decarburization to C≤0.03%, then add ferrous sulphide alloy at least three times interval, total sulfur content control is 0.15~0.20%; Step three, LF furnace calcium magnesium composite treatment: adjust the temperature to 1550~1580℃, feed in silicon calcium alloy wire, the addition amount of silicon calcium alloy wire is calculated according to Ca / S 0.8~1.2 ratio, then add magnesium wire, magnesium content control is 0.002~0.005%, then feed in rare earth silicon calcium alloy cored wire, RE content control is 0.01%~0.03%, calcium content control is 0.002~0.004%, finally blow argon from the bottom of the ladle, argon flow is 20~30 L / min, soft blowing argon time≥10 min; Step four, continuous casting: adjust the temperature of molten iron to 1550~1560℃, blank drawing speed: 0.8~1.2 m / min, mold vibration: amplitude 4~6mm, frequency 120~150 times / min, two cooling zone water quantity: 0.8~1.2 L / kg molten iron, electromagnetic stirring: frequency 3~5Hz, current 200~300A; Step five, three stage hot rolling: rough product is obtained by high temperature large deformation roughing, low temperature finishing and layer cooling in turn; Step six, gradient annealing is carried out on the rough product to obtain economic easy cutting high formability austenitic stainless steel finished product.

4. The method of producing an economical free-machining high formability austenitic stainless steel according to claim 3, characterized in that: The step two is divided into three times interval adding ferrous sulphur alloy, interval time is 8-10 minutes, first time adding 40wt% ferrous sulphur alloy, C content control is 0.15-0.20%, second time adding 30wt% ferrous sulphur alloy, C content control is 0.05-0.08%, third time adding 30wt% ferrous sulphur alloy, C content control is ≤0.03%, supplement adding chromium ingot, nickel block, component fine adjustment to Ni content control is 5.5%-6.8%, Cr content control is 16.5%-18.5%.

5. The method of producing an economical free-machining high formability austenitic stainless steel according to claim 3, characterized in that: The step three is that the feeding speed of silicon-calcium alloy wire is 3-5 m / min, the feeding speed of magnesium wire is 1-2 m / min, and the feeding speed of rare earth silicon-calcium alloy cored wire is 2-4 m / min.

6. The method of producing an economical free-machining high formability austenitic stainless steel according to claim 3, characterized in that: The step four is that the water quantity of the two cooling zones is divided into four sections, including foot roller section, first fan-shaped section, second fan-shaped section and third fan-shaped section, the cooling water flow of the foot roller section is 0.4-0.6 L / kg molten steel, the cooling water flow of the first fan-shaped section is 0.35-0.45 L / kg molten steel, the cooling water flow of the second fan-shaped section is 0.25-0.35 L / kg molten steel, and the cooling water flow of the third fan-shaped section is 0.2-0.3 L / kg molten steel.

7. The method of producing an economical free-machining high formability austenitic stainless steel according to claim 3, characterized in that: The step four is that the electromagnetic stirring is divided into mold electromagnetic stirring M-EMS and end electromagnetic stirring F-EMS, the frequency of the mold electromagnetic stirring M-EMS is 3-5 Hz, and the current is 200-250 A; the frequency of the end electromagnetic stirring F-EMS is 2-3 Hz, and the current is 250-300 A.

8. The method of producing an economical free-machining high formability austenitic stainless steel according to claim 3, characterized by: The step five is that the high-temperature large deformation rough rolling is specifically operated as follows: the cast blank is heated to 1150-1200 ℃, and the temperature is kept for 2-4 h, and the cast blank is rolled by 5-7 passes, the total deformation is 50-60%, and the single pass deformation is 15-20%; the rolling temperature is controlled at 1100-1150 ℃; the step five is that the low-temperature finish rolling is specifically operated as follows: the finish rolling temperature is 900-950 ℃, the total deformation is 30-40%, the single pass deformation is 8-12%, and the final rolling thickness is 2-3 mm; the step five is that the layer cooling is specifically operated as follows: the water cooling is performed to 700 ℃, and then the cast blank is input into the coiling equipment to be coiled, and the crude steel coil is obtained.

9. The method of producing an economical free-machining high formability austenitic stainless steel according to claim 3, characterized in that: The step six is that the gradient annealing is specifically operated as follows: the temperature is rapidly increased to 1100 ℃, and the temperature is kept for 5 min, then the temperature is slowly cooled to 950 ℃ at a speed of 5-40 ℃ / min, and the temperature is kept for 15-30 min, and then the temperature is water-cooled to room temperature, and the gradient annealing is completed.

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