A tellurium-magnesium composite treated free-cutting martensitic stainless steel and a method for manufacturing the same

Abstract

The present application belongs to the field of steel manufacturing, and relates to a tellurium-magnesium composite treated free-cutting martensitic stainless steel and a manufacturing method thereof. The stainless steel contains, in percentage by weight, C: 0.08-0.15%, Si: 0.30-0.60%, Mn: 0.80-1.25%, P: not more than 0.050%, S: 0.25-0.35%, Ni: not more than 0.50%, Cr: 12.0-13.5%, Mg: 0.0010-0.005%, Te: 0.003-0.010%, and the rest is iron and inevitable impurities, wherein Mn / S is not less than 3, and 0.015 not more than Te / S not more than 0.04. The stainless steel provided by the present application can meet the cutting performance requirements of high-precision and high-surface-quality parts, has excellent mechanical properties, is convenient for subsequent processing applications, and still has excellent plasticity and corrosion resistance, and is suitable for manufacturing precision instrument parts, automobile shaft parts, electronic and electrical parts and other types of mechanical equipment parts with high precision and surface requirements, thus having a broad market application prospect. Meanwhile, the preparation method provided by the present application has a high yield, not less than 92%, and is suitable for large-scale industrial application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of steel manufacturing, and relates to an easy-to-cut stainless steel and a manufacturing method thereof, in particular to an easy-to-cut martensitic stainless steel with tellurium-magnesium composite treatment and a manufacturing method thereof. BACKGROUND

[0002] Stainless steel is widely used due to its good corrosion resistance, but the work hardening of stainless steel is large, and the thermal conductivity coefficient is small, which makes the machinability of stainless steel poor, and is not conducive to turning processing. Therefore, the current field pays more and more attention to the research and development of easy-to-cut stainless steel, and hopes to put the research results into practical industrial production.

[0003] Easy-to-cut stainless steel refers to an alloy steel in which one or more of sulfur, phosphorus, lead, calcium, selenium, tellurium and other easy-to-cut elements are added to improve its machinability. The commonly used easy-to-cut stainless steel is mainly sulfur-based, which obtains good machinability by adding easy-to-cut element sulfur. Sulfur is easy to combine with manganese in steel to form brittle and low-hardness manganese sulfide, which can be used as a stress concentration source during cutting processing to reduce cutting force and thus improve cutting performance. In addition, the production cost of sulfur-based easy-to-cut steel is low, and it is the most widely used easy-to-cut steel in the world. However, the cutting performance of single sulfur-based easy-to-cut steel is limited, and cannot meet the requirements of high-precision and high-surface-quality parts. In addition, the addition of single sulfur will significantly reduce the corrosion resistance and plasticity of the material.

[0004] Therefore, the current field workers add other elements on the basis of sulfur-based free-cutting stainless steel, and study the improvement effect on the cutting performance and other performances of the stainless steel. The Chinese patent with the publication number CN110117694 A discloses a magnesium adding process method of magnesium-containing free-cutting steel, provides a magnesium adding method in sulfur-containing steel, the sulfide is uniformly distributed by adding magnesium element, so that the cutting property is improved, but the cutting performance is still not ideal, and there is still room for improvement. The Chinese patent with the publication number CN112760576 A discloses a tellurium-containing Y1Cr13 free-cutting stainless steel and a manufacturing method thereof, the size and distribution of inclusions are more uniform by adding the free-cutting Te element, the inclusions tend to be spherical or ellipsoidal, the national standard GB / T10561 2005 rating and the German standard SEP1572-71 rating are significantly improved, the chip breaking morphology after steel cutting is good, the surface roughness of the workpiece is reduced, and the cutting performance of the steel is also significantly improved, but too little tellurium will not completely modify the manganese sulfide, and too much tellurium will seriously affect the hot workability of the material, thereby bringing difficulties to production. The Chinese patent with the publication number CN110656280 A discloses a low-oxygen calcium-magnesium-sulfur-based free-cutting steel and a preparation method thereof, by reducing the oxygen content and adding Ca and Mg elements, on the one hand, by adding Ca and Mg elements in the steel, finally forming a dispersed, particle size suitable, containing hard core composite sulfide in the steel, improving the anisotropy while ensuring the cutting performance of the steel, on the other hand, Ca and Mg composite treatment will inevitably reduce the respective addition amount, compared with calcium treatment or magnesium treatment alone, the production cost of the steel will not increase, but Ca and Mg are easy to form high-melting-point compounds to block the water gap, which also has certain hidden dangers to continuous casting batch production.

[0005] Therefore, in order to further improve the cutting property of the free-cutting stainless steel, meet the requirements of high-precision and high-surface-quality parts, and further improve the corrosion resistance and plasticity of the material, the present application proposes a method of treating sulfur-containing free-cutting stainless steel by tellurium-magnesium composite treatment, modifying the sulfide in the stainless steel, realizing uniform distribution of inclusions, and meeting the processing and use requirements. SUMMARY

[0006] To solve the above technical problems and overcome the shortcomings of the prior art, the present application provides a tellurium-magnesium composite treated free-cutting martensitic stainless steel, which has the following advantages: 1) changing the morphology and distribution of sulfides, improving the cutting property of the material, which is manifested as a reduction in cutting force and surface roughness during high-speed turning; 2) the transverse mechanical properties are improved, which is manifested as an increase in the reduction of area; the present application also provides a preparation method of the tellurium-magnesium composite treated free-cutting martensitic stainless steel, which has a high yield.

[0007] To achieve the above-mentioned purposes, the present application adopts the following technical solutions.

[0008] The application discloses a tellurium-magnesium composite treated free-cutting martensitic stainless steel, and chemical components of the free-cutting stainless steel include, in percentage by mass, C: 0.08-0.15%, Si: 0.30-0.60%, Mn: 0.80-1.25%, P: less than or equal to 0.050%, S: 0.25-0.35%, Ni: less than or equal to 0.50%, Cr: 12.0-13.5%, Mg: 0.0010-0.005%, Te: 0.003-0.010%, and the rest is iron and inevitable impurities, wherein Mn / S is greater than or equal to 3, and 0.015 is less than or equal to Te / S and is less than or equal to 0.04.

[0009] Preferably, the chemical components of the free-cutting stainless steel include, in percentage by mass, C: 0.10-0.13%, Si: 0.35-0.55%, Mn: 0.90-1.10%, P: less than or equal to 0.040%, S: 0.26-0.32%, Ni: less than or equal to 0.40%, Cr: 12.2-13.2%, Mg: 0.0012-0.0045%, Te: 0.004-0.009%, and the rest is iron and inevitable impurities.

[0010] Effects of the chemical components in the application:

[0011] Carbon (C): Carbon can expand the gamma zone, improve the hardenability of the steel, and also can improve the strength of the stainless steel, but significantly reduces the plasticity, toughness and welding performance of the steel, and the carbon content also has an influence on the cutting performance; higher carbon content makes the steel matrix harden, and it is easier to break chips during turning; according to the performance requirements of the material, the application sets C: 0.08-0.15%.

[0012] Silicon (Si): Silicon is a strong deoxidizing agent, which can reduce the oxygen content in the steel and improve the oxidized inclusions in the steel. However, too high silicon content can make the steel matrix brittle and is not conducive to the plasticity; the application controls the silicon content to be Si: 0.30-0.60%.

[0013] Manganese (Mn): Manganese can refine pearlite and significantly improve the strength of low-carbon pearlite steel, but the ductility is reduced; too high manganese content has an adverse effect on the welding performance; meanwhile, manganese can form manganese sulfide with sulfur in the steel, which is beneficial to the cutting performance; according to the performance requirements of the material, the application sets the manganese content to be 0.80-1.25%.

[0014] Phosphorus (P): Generally, phosphorus is a harmful element in the stainless steel, which increases the cold brittleness of the stainless steel, makes the welding performance worse, reduces the plasticity, and makes the cold working performance worse; in the conventional case, the lower the phosphorus content is, the better; a small amount of phosphorus is allowed to exist in the free-cutting stainless steel, and phosphorus has a certain beneficial effect on the cutting performance; the application controls the phosphorus content to be less than or equal to 0.050%.

[0015] Sulfur (S): Sulfur is a common impurity element in general steel, which can cause hot brittle phenomenon of steel, increase inclusions in steel, reduce corrosion resistance of material, and is an easy cutting element, which can form manganese sulfide with manganese in steel, the manganese sulfide becomes a stress notch during turning processing, reduces cutting resistance of steel, and improves cutting property of steel, but too much sulfur can make sulfide deform along the rolling direction, form long strips, and gather together, which seriously affects plasticity of stainless steel, especially transverse performance, in combination with various performance requirements of the material, therefore, the application controls S: 0.25-0.35%.

[0016] Nickel (Ni): Ni is a strong austenite forming element, and is generally not contained or contains a small amount of nickel in martensitic stainless steel, which is used to balance the martensitic structure, in combination with other component requirements, the application controls Ni≤0.50%.

[0017] Chromium (Cr): For stainless steel, Cr is a main element for stainless steel to achieve the purpose of stainless, when the chromium content in steel exceeds 10.5, a passivation film is formed on the surface, so that the stainless steel has remarkable corrosion resistance, for martensitic stainless steel, it is mainly low-carbon or high-carbon steel with chromium content in the range of 12%-18%, the application is Cr13 series of martensitic stainless steel, therefore, the application controls Cr: 12.0-13.5%.

[0018] Magnesium (Mg): Mg can be used as an easy cutting element and a deoxidizing element, can be combined with oxygen elements in stainless steel, can form MgO·Al2O3 complex type inclusions with aluminum and oxygen, and can form MgO·Al2O3·SiO2 complex type inclusions in silicon deoxidized steel, the size of the inclusions is small, is not easy to gather and grow, is dispersedly distributed in molten steel, can be used as a nucleation source of manganese sulfide inclusions, so that the manganese sulfide is uniformly and dispersedly distributed, too little magnesium can make too little nucleation, and too much magnesium can form a large amount of high-melting-point MgO and MgS inclusions, so that the water gap is blocked, and at the same time, is not conducive to turning, the application optimizes and designs Mg: 0.0010-0.0050%.

[0019] Tellurium (Te): Tellurium itself is an easy cutting element, a small amount of tellurium can significantly improve the cutting performance of stainless steel, when sulfur is contained in steel, tellurium is partly dissolved in manganese sulfide to form Mn(Te, S) complex type inclusions, which is not easy to deform during rolling, plays a role of spheroidizing sulfide inclusions, can significantly improve the cutting property and high plasticity of stainless steel, a part of it will directly form MnSe inclusions, and then exist alone or wrapped outside MnS, controls the shape of manganese sulfide after rolling, avoids the generation of long manganese sulfide, too little tellurium can not completely modify the manganese sulfide, and too much tellurium can form excessive MnTe, which reduces the thermal plasticity of the material, the application optimizes and controls Te: 0.003-0.010%.

[0020] The application discloses a preparation method of a tellurium-magnesium composite treated free-cutting martensitic stainless steel, and has the characteristics that raw materials are subjected to the following processes: electric arc furnace steelmaking, AOD smelting, LF refining, continuous casting, blank preheating, rolling, and annealing treatment, so that the tellurium-magnesium composite treated free-cutting martensitic stainless steel is obtained, wherein, in the LF refining step, the oxygen activity in the steel is controlled to be 10-40 ppm, and then the composition of the molten steel is finely adjusted so that the remaining elements except Mg and Te meet the target requirements; and then the Mg and Te contents are adjusted to meet the target requirements by wire feeding.

[0021] Preferably, the raw materials are selected from waste stainless steel raw materials with P≤0.04% and C<3.0%, so as to further reduce the production cost, improve the economic benefit, and further ensure that the phosphorus content meets the requirements by using low-phosphorus waste materials.

[0022] Preferably, in the LF refining process, the composition of the molten steel is finely adjusted by selectively adding ferrosilicon, ferromanganese, ferrosulfur, ferrochrome, pure nickel, and carbon additive.

[0023] Preferably, in the LF refining process, the wire for feeding includes at least one of magnesium wire, silicon-magnesium wire, tellurium wire, and magnesium-tellurium wire; more preferably, the wire for feeding is the silicon-magnesium wire and the tellurium wire, the silicon-magnesium wire can further effectively inhibit the oxygen increase in the steel caused by the wire feeding process, further improve the magnesium yield, and improve the economic benefit; it should be noted that the silicon-magnesium wire further introduces silicon elements, so the Si is adjusted to 0.30-0.45% when the composition of the molten steel is adjusted, so as to ensure that the introduction of the silicon elements does not cause the silicon content to exceed the range; more preferably, the silicon-magnesium wire and the tellurium wire are both a 10-12 mm diameter iron sheath core wire, the mass content of magnesium in the silicon-magnesium wire is 10-20%, the mass content of silicon is 10-20%, and the balance is iron; the mass content of tellurium in the tellurium wire is 40-60%, and the balance is iron; more preferably, the feeding sequence of the silicon-magnesium wire and the tellurium wire is not particular.

[0024] Preferably, in the LF refining process, the wire feeding speed is controlled to be 100-150 m / min, and the distance between the wire feeding nozzle and the liquid surface is controlled to be 20-50 cm; more preferably, after the wire feeding is completed, argon gas is blown for 5-8 min for weak stirring, and then the molten steel is directly lifted out of the ladle, so as to ensure that the interval time from the wire feeding completion to the molten steel lifting out of the ladle is not more than 10 min, thereby further effectively ensuring the high yield of magnesium and tellurium.

[0025] Preferably, in the continuous casting process, low superheat casting is adopted, the casting superheat is controlled to be 25-50℃, the whole process of the casting process is weakly cooled, the water flow of the mold is controlled to be 83-88 m 3 / h, the water flow of the foot roller is controlled to be 1.8-2.0 m 3 / h, and the water flow of the secondary cooling section is controlled to be 1.5-1.8 m 3 / h; the drawing speed is 0.7-1.0 m / min. The continuous casting parameters are optimized to make the continuous casting stable and further improve the surface quality of the continuous casting billet.

[0026] Preferably, during the billet preheating process, the billet preheating is divided into three stages. In the first stage, the heating temperature is 700-900 DEG C and the heating time is 50-60 min; in the second stage, the heating temperature is 1100-1150 DEG C and the heating time is 50-60 min; and in the third stage, the heating temperature is 1200-1220 DEG C and the heating time is 50-60 min. The temperature gradually increases, so that the billet is heated more uniformly and sufficiently, and the rolling cracking is prevented, and the stress cracking caused by the large temperature difference between the inside and the outside of the billet is avoided.

[0027] Preferably, during the rolling process, high-speed wire rolling is adopted, the rolling-in temperature is 1150-1220 DEG C, and the cooling water is not opened during the rough rolling. The head of the rolling piece needs to be kept away from the water during the whole rolling process, which can effectively reduce the rough rolling cracking and the rolling head splitting, and effectively solve the problem of poor thermal plasticity caused by the tellurium element. An induction heating process is arranged after the rough rolling to compensate the temperature of the rolling piece, and the temperature of the rolling piece needs to be increased by 80-150 DEG C. The final rolling temperature is required to be 1050-1150 DEG C. After rolling, the rolling piece is naturally cooled and coiled. More preferably, the temperature increased by the induction heating is 100-140 DEG C.

[0028] Preferably, during the annealing process, the annealing furnace is used for annealing. The temperature of the rolling piece is increased to 600 DEG C at a speed of 90-100 DEG C / h, then increased to 870 DEG C at a speed of 60-70 DEG C / h, and then kept at 870 DEG C for 8-10 h. After the heat preservation is finished, the temperature is first decreased to 650 DEG C at a speed of 30-40 DEG C / h, then decreased to 300 DEG C at a speed of 50-60 DEG C / h, and then the rolling piece is taken out of the furnace and cooled to room temperature in the air.

[0029] Preferably, the preparation method comprises the following steps:

[0030] 1) Electric furnace steelmaking: waste stainless steel raw material is melted into crude molten steel. After the steelmaking is finished, silicon iron is added to the molten steel for reduction, the C content is adjusted to 1.5%-3.0%, then all the steel slag is pulled out, 1 Kg of carbonized rice husk per ton of steel is added for heat preservation, and then the molten steel is tapped. The tapping temperature is 1550-1600 DEG C.

[0031] Further, the waste stainless steel raw material with P≤0.04% and C<3.0% is selected;

[0032] Further, after the steelmaking is finished, 7-10 Kg of silicon iron per ton of molten steel is added for reduction;

[0033] Further, after the reduction, the C content is adjusted by using a carbon additive according to the C content;

[0034] 2) AOD smelting: first into the oxygen decarburization stage, the temperature is controlled at 1650-1750℃, the time is 40-60min, the decarburization endpoint C≤0.05%; secondly, add silicon iron to reduce the temperature control at 1600-1650℃, the time is 6-12min; thirdly, the refining stage, the refining time is 6-10min, the temperature is 1620-1660℃, the slag basicity is controlled at 1.5-2.0; finally, add 12-14Kg of ferrous sulfide per ton of steel, stir for 5-8min and then tap, the tapping temperature is 1580-1630℃;

[0035] Further, in the reduction stage, 30-35Kg of silicon iron is added per ton of molten steel;

[0036] 3) LF refining: first, the temperature is raised in the LF stage, and the temperature is maintained at 1600-1630℃; the slag basicity is re-adjusted to maintain at 1.5-2.0, and the oxygen activity in the steel is controlled at 10-40ppm, then the composition is fine-tuned so that each element except Mg and Te meets the design requirements, and the Si element is preferably 0.30-0.45%; then the Mg and Te are adjusted by feeding wire, at this time the temperature is controlled at 1580-1610℃, the composition of the molten steel is adjusted to Mg: 0.0010-0.005%, Te: 0.003-0.010%, and finally the molten steel temperature is adjusted to 1590-1630℃ for tapping;

[0037] Further, in the LF refining process, silicon-magnesium wire and tellurium wire are fed, and the feeding sequence of the two wires is not distinguished, both the silicon-magnesium wire and the tellurium wire are a kind of iron sheath core wire with a diameter of 10-12mm, the mass content of magnesium in the silicon-magnesium wire is 10-20%, the mass content of silicon is 10-20%, and the balance is iron; the mass content of tellurium in the tellurium wire is 40-60%, and the balance is iron;

[0038] Further, the feeding speed is controlled at 100-150m / min, the distance between the feeding pipe and the liquid surface is controlled at 20-50cm, after the feeding is completed, argon gas is blown for 5-8min for weak stirring, and then the ladle is directly lifted for tapping, so that the interval time from the completion of feeding to the tapping is not more than 10min, which can effectively ensure a high recovery rate of magnesium and tellurium.

[0039] 4) Continuous casting: a 3-machine 3-flow continuous casting machine is used for casting, and the casting billet size is 180mm*180mm;

[0040] Further, in the continuous casting process, a long nozzle and an invasive nozzle are used for full-process protection casting, which can prevent oxygen increase during the process, low superheat casting is used, the casting superheat is controlled at 25-50℃, and full-process weak cooling is used during the casting process, the mold water flow is controlled at 83-88m 3 / h; the foot roller water flow is 1.8-2.0m 3 / h; the secondary cooling section water flow is 1.5-1.8m3 Speed: 0.7-1.0m / min;

[0041] 5) Steel billet preheating: the preheating of the billet is divided into three stages, the first stage, 700-900℃ heating for 50-60min; the second stage, 1100-1150℃ heating for 50-60min; the third stage, 1200-1220℃ heating for 50-60min, the temperature gradually increases, so that the billet is heated more evenly and fully, and at the same time, the stress cracking caused by the large temperature difference between the inside and outside of the billet is avoided.

[0042] 6) Rolling: high-speed wire rolling mill is used to roll the tellurium-magnesium composite treated free-cutting martensitic stainless steel wire rod with a specification of Φ5.5-32mm, and the wire rod is cooled and coiled after rolling;

[0043] Further, in the high-speed wire rolling process, the rough rolling temperature is 1150-1220℃, no cooling water is used in rough rolling, and the head needs to be kept away from water throughout the rolling process, which can effectively reduce the rough rolling cracking and rolling split head; an induction heating device is arranged after rough rolling, and the rolling piece is required to be increased by 80-150℃; the finish rolling temperature is required to be 1050-1150℃; and the wire rod is naturally cooled and coiled after rolling;

[0044] 7) Annealing: the wire rod needs to be annealed after rolling to obtain the tellurium-magnesium composite treated free-cutting martensitic stainless steel with stable performance.

[0045] Further, in the annealing process, the wire rod is heated to 600℃ at a speed of 90-100℃ / h, then heated to 870℃ at a speed of 60-70℃ / h, and then kept at 870℃ for 8-10h, after the heat preservation is finished, the temperature is reduced, first reduced to 650℃ at a speed of 30-40℃ / h, then reduced to 300℃ at a speed of 50-60℃ / h, and then taken out of the furnace and cooled to room temperature in the air.

[0046] Compared with the prior art, the beneficial effects of the present application include:

[0047] 1. The tellurium-magnesium composite treated free-cutting martensitic stainless steel produced by the present application, by reasonably designing the S content in the stainless steel, adding Mg and Te free-cutting elements, and controlling the oxygen activity at 10-40 ppm, the original unevenly distributed MnS inclusions are modified into uniformly distributed MgO·Al2O3-MnS·MnTe, MgO·Al2O3·SiO2-MnS·MnTe composite inclusions, and the sulfides after rolling are changed from the original long strips into ellipsoidal or spherical shapes, improving the cutting property of the material, which is manifested as the reduction of cutting force and surface roughness during high-speed turning. The addition of Mg can combine with Al2O3 in the steel to produce composite inclusions MgO·Al2O3 and MgO·Al2O3·SiO2, the interaction force of the composite inclusions is smaller than that of Al2O3 and SiO2, and the composite inclusions are not easy to aggregate and grow, but can be dispersedly distributed in the molten steel, and can become the nucleation points of sulfides, so that the modified inclusions can be dispersedly distributed in the steel, and the addition of Mg can also reduce the addition amount of Te, thereby reducing the influence of Te on hot plasticity and ensuring high yield.

[0048] 2. The tellurium-magnesium composite treated free-cutting martensitic stainless steel produced by the present application has excellent mechanical properties, especially transverse mechanical properties, which is manifested as the increase of the reduction of area, because the addition of Mg and Te free-cutting elements makes the inclusions spheroidized and the long strip sulfides disappear, reducing the influence of sulfides on the mechanical properties. At the same time, the addition of Te and other elements still has a high yield, indicating that the hot plasticity of the stainless steel of the present application is good.

[0049] 3. The preparation method of the tellurium-magnesium composite treated free-cutting martensitic stainless steel designed by the present application, by designing the smelting process to stabilize the composition control; designing and optimizing the continuous casting parameters to make the continuous casting stable and the surface quality of the continuous casting billet good; optimizing the heating parameters to make the continuous casting billet uniformly heated and prevent rolling cracking; using high-temperature heating to control the rolling opening temperature, and using "induction heating" to compensate the temperature of the rolled piece, and keeping the head water-avoiding during the whole rolling process, effectively solving the problem of poor hot plasticity caused by tellurium, and the yield is still superior to that of conventional free-cutting materials, reaching more than 92%.

[0050] The tellurium-magnesium composite treated free-cutting martensitic stainless steel provided by the present application can meet the cutting performance requirements of high-precision and high-surface-quality parts, has excellent mechanical properties, is convenient for subsequent processing application, and still has excellent plasticity and corrosion resistance, is suitable for manufacturing precision instrument parts, automobile shaft parts, electronic and electrical parts and other types of mechanical equipment parts with high precision and surface requirements, and therefore has a broad market application prospect; meanwhile, the preparation method provided by the present application has a high material yield and is suitable for large-scale industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 The figure is a morphology and energy spectrum analysis diagram of inclusions of the present application embodiment 1.

[0052] Figure 2 The figure is a morphology and energy spectrum analysis diagram of inclusions of the present application embodiment 2.

[0053] Figure 3 The figure is an inclusion distribution diagram of the present application embodiment 1.

[0054] Figure 4 The figure is an inclusion distribution diagram of the comparative example 416.

[0055] Figure 5 The figure is a turning chip breaking morphology diagram of the present application embodiment 1.

[0056] Figure 6 The figure is a turning chip breaking morphology diagram of the comparative example 416. DETAILED DESCRIPTION

[0057] The technical solutions of the present application are further clearly and completely described below by means of specific embodiments and in combination with the drawings. It should be understood that the embodiments described in the present application are implemented on the premise of the technical solutions of the present application, and detailed implementation manners and specific operation processes are given, but only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0058] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional methods. The materials, reagents and the like used in the embodiments can be obtained from commercial channels unless otherwise specified.

[0059] Embodiment 1:

[0060] The composition of the tellurium-magnesium composite treated free-cutting martensitic stainless steel is shown in Table 1. The specific implementation process includes the following steps:

[0061] 1) Electric furnace steelmaking: 32 tons of waste stainless steel raw material with P≤0.04%, C<3.0% is selected, 40t electric arc furnace is used for smelting, and the molten steel is melted into crude molten steel. After the steelmaking is finished, 270Kg of ferrosilicon is added for reduction, at this time the carbon content is 2.5%, then all the steel slag is pulled out, the temperature is adjusted to 1585℃, 32Kg of carbonized rice husk is added for insulation, and then the molten steel is tapped;

[0062] 2) AOD smelting: the crude molten steel is poured into the AOD furnace, first the oxygen blowing decarburization stage is entered, the minimum temperature is controlled at 1680, the maximum temperature is controlled at 1730℃, the duration is 42min, the decarburization endpoint C is 0.03%; secondly, the reduction stage is carried out, 1000Kg of ferrosilicon is added for reduction, the temperature is controlled at a minimum of 1610 and a maximum of 1648℃, the duration is 8min; thirdly, the refining stage is carried out, the refining time is 10min, the minimum temperature is 1622℃, the maximum temperature is 1650℃, the slag basicity is controlled at 1.9; finally, 400Kg of ferrous sulphur is added, stirring for 6min, and the molten steel is tapped, the tapping temperature is 1588℃.

[0063] 3) LF refining: the molten steel reaches the LF furnace, the temperature is adjusted to 1620℃; the slag basicity is re-adjusted to 1.7, the oxygen activity in the steel is controlled at 20ppm, then the composition is fine-tuned, so that all elements except Mg and Te meet the design requirements; then Mg and Te are adjusted, at this time the temperature is controlled at 1596℃, while 80m and 120m of silicon-magnesium wire and tellurium wire are fed respectively, the feeding speed is 110m / min, the distance between the wire feeding nozzle and the liquid surface is 45cm, the measured composition of the molten steel is Mg:0.0018%, Te:0.0045%; after the wire feeding is finished, argon gas is blown for weak stirring for 6min, and then the ladle is directly lifted out of the molten steel, the lifting temperature is 1610℃.

[0064] 4) Continuous casting: 3-machine 3-stream continuous casting machine is used for casting, the size of the cast billet is 180mm*180mm, long nozzle and invasive nozzle are used for full-process protective casting to prevent oxygen increase during the process, low superheat casting is used, the minimum superheat is 28℃, the maximum superheat is 49℃, the whole process is weakly cooled, the crystallizer water flow is controlled at 88m 3 / h; the foot roller water flow is 1.9m3 / h; the secondary cooling section water flow is 1.7m3 / h; the casting speed is 0.9m / min;

[0065] 5) Billet preheating: the billet preheating is divided into three stages, the first stage is heated at 700-900℃ for 53min; the second stage is heated at 1100-1150℃ for 55min; the third stage is heated at 1200-1220℃ for 58min, the temperature gradually increases, so that the billet is heated more uniformly and fully, and at the same time, stress cracking caused by too large temperature difference between the inside and outside of the billet is avoided.

[0066] 6) Rolling: the tellurium-magnesium composite treated free-cutting martensitic stainless steel wire rod with a rolling specification of Φ7.5 mm is rolled by using a high-speed wire rolling unit, the open rolling temperature is 1170℃, the rough rolling is not cooled by water, the head part needs to be kept from water during the whole rolling process, which effectively reduces the rough rolling cracking and rolling splitting; an induction heating device is arranged after the rough rolling to increase the temperature of the rolled piece by 100℃; the final rolling temperature is required to be 1080℃; and the rolled piece is naturally cooled and coiled after rolling.

[0067] 7) Annealing: the wire rod is annealed by using an annealing furnace, the wire rod is heated to 600℃ at a speed of 100℃ / h, then heated to 870℃ at a speed of 70℃ / h, and then kept at 870℃ for 8h, after the end of the keeping, the temperature is first decreased to 650℃ at a speed of 30℃ / h, then decreased to 300℃ at a speed of 50℃ / h, and then taken out of the furnace and cooled to room temperature in air, thereby obtaining the tellurium-magnesium composite treated free-cutting martensitic stainless steel with stable performance.

[0068] The material yield of the example is 92.8%, the Mg yield is 18%, and the Te yield is 45%.

[0069] Example 2: a preparation method of the tellurium-magnesium composite treated free-cutting martensitic stainless steel disclosed in the application, which is different from example 1 in that the parameter conditions of each step are shown in table 2, the obtained component composition is shown in table 1, the material yield of the implementation is 93.2%, the Mg yield is 19%, and the Te yield is 38%.

[0070] Example 3: a preparation method of the tellurium-magnesium composite treated free-cutting martensitic stainless steel disclosed in the application, which is different from example 1 in that the parameter conditions of each step are shown in table 2, the obtained component composition is shown in table 1, the material yield of the implementation is 94.2%, the Mg yield is 20%, and the Te yield is 38%.

[0071] Example 4: a preparation method of the tellurium-magnesium composite treated free-cutting martensitic stainless steel disclosed in the application, which is different from example 1 in that the parameter conditions of each step are shown in table 2, the obtained component composition is shown in table 1, the material yield of the implementation is 93.5%, the Mg yield is 21%, and the Te yield is 46%.

[0072] Example 5: a preparation method of the tellurium-magnesium composite treated free-cutting martensitic stainless steel disclosed in the application, which is different from example 1 in that the parameter conditions of each step are shown in table 2, the obtained component composition is shown in table 1, the material yield of the implementation is 93.0%, the Mg yield is 20%, and the Te yield is 44%.

[0073] The component of the tellurium-magnesium composite treated free-cutting martensitic stainless steel produced according to the mode of the application is shown in table 1. Meanwhile, the conventional 416 stainless steel produced by Qingshan Iron and Steel is taken as a comparative example, the material yield of the comparative example is about 93.5%, and the specific conditions are as follows:

[0074] Table 1 specific embodiment ingredients

[0075]

[0076]

[0077] The above embodiment ingredients all satisfy C: 0.08-0.15%, Si: 0.30-0.60%, Mn: 0.80-1.25%, P≤0.050%, S: 0.25-0.35%, Ni≤0.50%, Cr: 12.0-13.5%, Mg: 0.0010-0.005%, Te: 0.003-0.010%, Mn / S≥3; 0.015≤Te / S≤0.04, the rest being iron and inevitable impurities.

[0078] Table 2 is specific embodiment parameters of the tellurium-magnesium composite treated free-cutting martensitic stainless steel produced according to the mode of the present application:

[0079] Table 2 specific embodiment key parameters

[0080]

[0081]

[0082] The inclusion morphology and energy spectrum analysis of the tellurium-magnesium composite treated free-cutting martensitic stainless steel produced in Example 1 is shown in Table 1, which is MgO·Al2O3·SiO2-MnS·MnTe composite type inclusion, the inclusion morphology and energy spectrum analysis of the tellurium-magnesium composite treated free-cutting martensitic stainless steel produced in Example 2 is shown in Table 2, which is MgO·Al2O3-MnS·MnTe composite type inclusion, both of which present spindle or spherical shape. Figure 1 Figure 2 The sulfide distribution of the rolled material of Example 1 is shown in Table 3, the inclusions are uniformly distributed, the sulfide distribution of the rolled material of the comparative example is shown in Table 4, which obviously has longer connecting lines and is unevenly distributed, Table 3 shows that the proportion of sulfides with aspect ratio <3 is much higher than that of Comparative Example 416, the sulfide distribution of the rolled material of conventional production 416 is uneven and mostly in long strip shape, indicating that the sulfide modification of the present application is more thorough, and the improvement of inclusion morphology and distribution makes the cutting property and transverse mechanical property of the embodiment more excellent. Figure 3 Figure 4

[0083] Table 3 statistics of the proportion of sulfides with aspect ratio <3 of the embodiment and the comparative example

[0084]

[0085] Test Example:

[0086] (1) Turning performance evaluation:​​​

[0087] The tellurium-magnesium composite treated free-cutting martensitic stainless steel produced by the present application and the comparative example 416 were subjected to turning experiments at the same turning parameters of the materials, and were subjected to high-speed turning machining test on a M06J lathe equipped with a 9129AA type dynamometer, the cutting depth was 0.5mm, the feed rate was 0.15㎜ / r, and the cutting speed was 100m / min, and the results are shown in Table 4.

[0088] Table 4: Turning performance evaluation parameters

[0089]

[0090] It can be seen from the results that the turning force during cutting of the embodiment is significantly lower, and the turning force of the comparative example 416 is relatively high, and the low turning force is beneficial to precision control and tool wear; the surface roughness after turning of the embodiment is relatively significantly lower, and the surface roughness after turning of the comparative example 416 is relatively high. Figure 5 is the turning chip morphology after turning of the embodiment 1 of the present application, Figure 6 is the turning chip morphology after turning of the comparative example 416, and Figure 5 , Figure 6 It can be seen from the display that the chip effect after turning of the embodiment is better.

[0091] (2) Evaluation of mechanical properties and corrosion resistance:

[0092] According to the standards "GB / T 228.1-2010" "Metallic Materials Tensile Test Part 1: Room Temperature Test Method", "GB / T 231.1-2002" "Metallic Brinell Hardness Test Part 1: Test Method" and "GB / T 10125-2012" "Salt Spray Test for Artificial Atmosphere Corrosion Test", each embodiment and the comparative example were detected, and the results are shown in Table 5.

[0093] Table 5: Mechanical properties and corrosion resistance detection results

[0094]

[0095]

[0096] It can be seen that the area reduction of the embodiment is significantly higher than that of the conventional 416 product, and the difference in tensile strength and elongation after fracture is not obvious, which indicates that the transverse mechanical properties of the embodiment are more excellent, and the salt spray experiment shows that the corrosion resistance of the embodiment is more excellent.

[0097] The tellurium-magnesium composite treated free-cutting martensitic stainless steel produced by the application can improve the turning performance of the free-cutting stainless steel, can reduce the turning force and the surface roughness of the part in the high-speed turning process, can improve the transverse mechanical property and corrosion resistance of the free-cutting stainless steel, and can improve the broken chip, and the material yield of the free-cutting martensitic stainless steel produced by the application is not reduced, and the material yield is greater than or equal to 92%.

[0098] The above-mentioned embodiments are only the preferred schemes of the application, and do not limit the application in any form, and other variants and modifications can be made without exceeding the technical scheme recorded in the claims.

Claims

1. A free-cutting martensitic stainless steel treated with tellurium and magnesium, characterized in that, The stainless steel contains, by mass percent: C: 0.08-0.15%, Si: 0.30-0.60%, Mn: 0.80-1.25%, P≤0.050%, S: 0.25-0.35%, Ni≤0.50%, Cr: 12.0-13.5%, Mg: 0.0010-0.005%, Te: 0.003-0.010%, and the balance of iron and inevitable impurities, wherein Mn / S≥3, 0.015≤Te / S≤0.04; the preparation method of the tellurium-magnesium composite treated free-cutting martensitic stainless steel comprises the following steps: electric arc furnace steelmaking, AOD smelting, LF refining, continuous casting, billet preheating, rolling, annealing treatment, and the balance of iron and inevitable impurities, wherein in the LF refining step, the oxygen activity in the steel is controlled to be 10-40ppm, and then the composition of the molten steel is finely adjusted so that the remaining elements except Mg and Te meet the target requirements; and then the Mg and Te contents are adjusted to meet the target requirements by feeding wire.

2. A free machining martensitic stainless steel with tellurium and magnesium composite treatment according to claim 1, characterized in that, The stainless steel contains, by mass percent: C: 0.10-0.13%, Si: 0.35-0.55%, Mn: 0.90-1.10%, P≤0.040%, S: 0.26-0.32%, Ni≤0.40%, Cr: 12.2-13.2%, Mg: 0.0012-0.0045%, Te: 0.004-0.009%, and the balance of iron and inevitable impurities.

3. A method of producing the tellurium-magnesium composite-treated free-cutting martensitic stainless steel according to claim 1 or 2, characterized by, The raw material is subjected to the following processes: electric arc furnace steelmaking, AOD smelting, LF refining, continuous casting, billet preheating, rolling, annealing treatment, and the balance of iron and inevitable impurities, wherein in the LF refining step, the oxygen activity in the steel is controlled to be 10-40ppm, and then the composition of the molten steel is finely adjusted so that the remaining elements except Mg and Te meet the target requirements; and then the Mg and Te contents are adjusted to meet the target requirements by feeding wire.

4. The method of producing a free-machining martensitic stainless steel with tellurium and magnesium composite treatment according to claim 3, characterized by, In the LF refining process, the wire fed includes at least one of magnesium wire, silicon-magnesium wire, tellurium wire and magnesium-tellurium wire.

5. The method for preparing free-machining martensitic stainless steel with tellurium-magnesium composite treatment according to claim 3, characterized in that, In the LF refining process, the wire fed is silicon-magnesium wire and tellurium wire, and both the silicon-magnesium wire and the tellurium wire are iron sheath core wires with a diameter of 10-12mm, the mass content of magnesium in the silicon-magnesium wire is 10-20%, the mass content of silicon in the silicon-magnesium wire is 10-20%, and the balance is iron; the mass content of tellurium in the tellurium wire is 40-60%, and the balance is iron.

6. The method of producing a free-machining martensitic stainless steel according to claim 3, wherein In the LF refining process, the wire feeding speed is controlled to be 100-150m / min, and the distance between the wire feeding pipe and the liquid surface is controlled to be 20-50cm.

7. The method for preparing free-machining martensitic stainless steel with tellurium-magnesium composite treatment according to claim 3, characterized in that, In the continuous casting process, low superheat casting is adopted, the casting superheat is controlled to be 25-50℃, the water flow rate is controlled to be 83-88m 3 / h in the whole process of the crystallizer, the water flow rate is controlled to be 1.8-2.0m 3 / h in the foot roller, the water flow rate is controlled to be 1.5-1.8m 3 / h in the secondary cooling section, and the pulling speed is controlled to be 0.7-1.0m / min.

8. The method of producing a free-machining martensitic stainless steel according to claim 3, wherein The billet preheating process is divided into three stages, the first stage is heating at 700-900 DEG C for 50-60 min, the second stage is heating at 1100-1150 DEG C for 50-60 min, and the third stage is heating at 1200-1220 DEG C for 50-60 min.

9. The method of producing a free-machining martensitic stainless steel according to claim 3, wherein In the rolling process, high-speed wire rolling is adopted, the opening rolling temperature is 1150-1220 DEG C, no cooling water is used in rough rolling, and the head needs to be kept away from water in the whole rolling process; an induction heating process is arranged after rough rolling to compensate the temperature of the rolled piece, and the temperature of the rolled piece is required to be increased by 80-150 DEG C; the finish rolling temperature is required to be 1050-1150 DEG C; and natural cooling and coiling are carried out after rolling.

10. The method of producing a free-machining martensitic stainless steel according to claim 3, wherein In the annealing process, the annealing furnace is used for annealing, the rolled piece wire rod is heated to 600 DEG C at a speed of 90-100 DEG C / h, then heated to 870 DEG C at a speed of 60-70 DEG C / h, then kept at 870 DEG C for 8-10 h, after the keeping, the temperature is decreased, first decreased to 650 DEG C at a speed of 30-40 DEG C / h, then decreased to 300 DEG C at a speed of 50-60 DEG C / h, and after decreased to 300 DEG C, the furnace is discharged and cooled to room temperature in air.

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