CN114182177B - Sulfur-containing tellurium-containing free-cutting ferritic stainless steel and manufacturing method thereof - Google Patents

Sulfur-containing tellurium-containing free-cutting ferritic stainless steel and manufacturing method thereof Download PDF

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CN114182177B
CN114182177B CN202111490332.9A CN202111490332A CN114182177B CN 114182177 B CN114182177 B CN 114182177B CN 202111490332 A CN202111490332 A CN 202111490332A CN 114182177 B CN114182177 B CN 114182177B
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stainless steel
rolling
tellurium
steel
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CN114182177A (en
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严道聪
王贞应
马振宇
季灯平
李立
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Zhejiang Ruipu Technology Co ltd
Zhejiang Tsingshan Iron & Steel Co ltd
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Zhejiang Ruipu Technology Co ltd
Zhejiang Tsingshan Iron & Steel Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/46—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting
    • B21B1/463—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting in a continuous process, i.e. the cast not being cut before rolling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • B21B3/02—Rolling special iron alloys, e.g. stainless steel
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
    • B21B45/004—Heating the product
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
    • B22D11/002—Stainless steels
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/005—Manufacture of stainless steel
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C22C33/06—Making ferrous alloys by melting using master alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Abstract

The invention relates to free-cutting stainless steel, in particular to sulfur-containing tellurium-containing free-cutting ferritic stainless steel and a preparation method thereof. The invention relates to a sulfur-containing tellurium-containing free-cutting ferritic stainless steel, which comprises the following components in percentage by mass: less than or equal to 0.10 percent of C, less than or equal to 1.0 percent of Si, less than or equal to 1.25 percent of Mn, less than or equal to 0.03 percent of P, 0.20-0.30 percent of S, less than or equal to 0.60 percent of Ni, 17.0-18.0 percent of Cr, less than or equal to 0.60 percent of Mo, less than or equal to 0.05 percent of N, 0.005-0.015 percent of Te, 0.001-0.005 percent of B, and the balance of Fe and inevitable impurities. The sulfur-containing tellurium-containing free-cutting ferritic stainless steel is prepared by electric furnace smelting → AOD furnace refining → LF furnace refining → continuous casting → rolling → annealing, and the turning property, corrosion resistance and plasticity of the sulfur-containing tellurium-containing free-cutting ferritic stainless steel are completely superior to those of the common 430F material, so that the sulfur-containing tellurium-containing free-cutting ferritic stainless steel has a wider industrial application prospect.

Description

Sulfur-containing tellurium-containing free-cutting ferritic stainless steel and manufacturing method thereof
Technical Field
The invention relates to free-cutting stainless steel, in particular to sulfur-containing tellurium-containing free-cutting ferritic stainless steel and a preparation method thereof.
Background
Stainless steel is widely used due to its excellent corrosion resistance, plasticity and workability, and at present, it has a large amount of use in petroleum, chemical engineering, oceans and machinery, and also plays an important role in food, medical treatment, electronics, office and other fields. However, stainless steel has a large work hardening, which makes it inferior in machinability, resulting in low precision of the work and low efficiency of automated machining. With the increasing use of stainless steel, the requirements for automatic processing and high precision of stainless steel workpieces are increasingly stringent, and therefore, the improvement of the machinability of stainless steel products is extremely necessary.
The current ferritic stainless steel with the largest use amount is the mark 430F, the stainless steel realizes the free-cutting effect mainly by adding sulfur, the single sulfur has a limit on the improvement of the cutting property, and the addition of more sulfur can influence the hot workability and the plasticity of the steel, and the conventional 430F can not completely meet the processing requirements along with the requirements of fast turning of a high-speed lathe.
The invention patent with publication number CN 106591742A discloses a high-carbon sulfur-containing ferrite free-cutting stainless steel, which is characterized by comprising the following alloy elements in percentage by weight: 0.08 to 0.13 percent of C, less than or equal to 1.00 percent of Si, 0.5 to 1.25 percent of Mn, less than or equal to 0.045 percent of P, less than or equal to 0.15 to 0.35 percent of S, 15.00 to 20.00 percent of Cr, less than or equal to 0.60 percent of Ni, and the balance of Fe and inevitable impurities. The invention patent with publication number CN 102363869A discloses a free-cutting ferritic stainless steel 430FM, which is characterized by comprising the following alloy elements in percentage by weight: 0.10 to 0.16 percent of C, less than or equal to 1.00 percent of Si, less than or equal to 1.30 percent of Mn, less than or equal to 0.06 percent of P, more than or equal to 0.15 percent of S, 15.00 to 17.00 percent of Cr, less than or equal to 0.60 percent of Ni, 0.2 to 0.6 percent of Mo, 0.0005 to 0.003 percent of Ca0.001 to 0.006 percent of rare earth, and the balance of Fe and inevitable impurities. The invention patent with publication number CN 102851625A discloses a tellurium-containing high-performance stainless steel grinding, which is characterized in that the tellurium-containing high-performance stainless steel grinding is composed of the following alloy elements in percentage by weight: c is less than or equal to 0.05 percent, si is less than or equal to 0.70 percent, mn is 13.00 percent, S is less than or equal to 0.15 percent, cr is 11.00-12.00 percent, ni is 5.0-6.0 percent, cu is 2.5-3.0 percent, te is 0.035-0.08 percent, and the balance is iron and inevitable impurities. The invention patent with publication number CN 105132812A discloses a ferrite free-cutting stainless steel, which is characterized in that the invention comprises the following alloy elements by weight percent: less than or equal to 0.025 percent of C, 0.05 to 0.80 percent of Si, 0.5 to 0.8 percent of Mn, 0.02 to 0.04 percent of P, 0.01 to 0.1 percent of S, 15.0 to 20.0 percent of Cr, 0.05 to 0.5 percent of Ti, 0.04 to 0.06 percent of N, 0.8 to 1.2 percent of Mo, and the balance of Fe and inevitable impurities.
Disclosure of Invention
The invention aims to provide a sulfur-containing tellurium-containing free-cutting ferritic stainless steel and a preparation method thereof, which improve the distribution and the form of sulfides by adding tellurium and controlling the contents of manganese, sulfur, chromium and molybdenum, improve the cutting performance and the corrosion resistance, improve the plasticity of the material by optimizing an annealing process, and can replace the ferritic free-cutting stainless steel 430F commonly used in the market.
In order to realize the purpose, the invention adopts the following technical scheme:
one of the purposes of the invention is to provide a sulfur-containing tellurium-containing free-cutting ferritic stainless steel, which comprises the following components in percentage by mass: less than or equal to 0.10 percent of C, less than or equal to 1.0 percent of Si, less than or equal to 1.25 percent of Mn, less than or equal to 0.03 percent of P, 0.20-0.30 percent of S, less than or equal to 0.60 percent of Ni, 17.0-18.0 percent of Cr, less than or equal to 0.60 percent of Mo, less than or equal to 0.05 percent of N, 0.005-0.015 percent of Te, 0.001-0.005 percent of B, and the balance of Fe and inevitable impurities.
Preferably, wherein the mass ratio of Mn to S satisfies Mn/S.gtoreq.3.
Preferably, the stainless steel comprises the following components: less than or equal to 0.065 percent of C, 0.3 to 0.6 percent of Si, 0.7 to 1.25 percent of Mn, less than or equal to 0.03 percent of P, 0.23 to 0.30 percent of S, less than or equal to 0.60 percent of Ni, 17.1 to 17.6 percent of Cr, 0.2 to 0.5 percent of Mo, less than or equal to 0.03 percent of N, 0.006 to 0.010 percent of Te, 0.0015 to 0.0045 percent of B, and the balance of iron and inevitable impurities, wherein the Mn/S is more than or equal to 3.
The second purpose of the invention is to provide a preparation method of the sulfur-containing tellurium-containing free-cutting ferritic stainless steel, which comprises the following steps: electric furnace smelting → AOD furnace refining → LF furnace refining → continuous casting → rolling → annealing, wherein:
electric furnace smelting: melting the raw materials into molten steel in an electric furnace;
refining in an AOD furnace: the molten steel is decarbonized and chromium-preserved in an AOD furnace, so that the content of C in the molten steel after decarbonization and chromium preservation is not higher than a target value; argon is blown and stirred in the whole refining process to ensure that the content of N is not higher than a target value;
refining in an LF furnace: adding materials into the molten steel in the previous step according to the target value of each component, then adding ferroboron to ensure that the content of B is the target value, and then feeding a tellurium wire to ensure that the content of Te is the target value;
continuous casting: casting the molten steel in the last step to obtain a steel billet;
steel rolling: preheating the billet in the previous step and then rolling to obtain a wire rod;
and (3) annealing: and annealing the wire rod obtained in the last step to obtain the sulfur-containing tellurium-containing free-cutting ferritic stainless steel.
Preferably, the raw material is waste stainless steel, and the waste stainless steel is low-P (P is less than or equal to 0.03%) and low-five-harmful-element (the sum of Pb, sn, as, sb and Bi is not more than 0.05%).
Preferably, the temperature of the electric furnace for electric furnace smelting is 1600-1700 ℃.
Preferably, the decarburization and chromium retention in the refining step of the AOD furnace are divided into an oxidation period and a reduction period, wherein the temperature of the oxidation period is controlled to 1650-1700 ℃, the time of the oxidation period is controlled to 30-60 min, the content of C at the end point of oxidation is controlled not to be higher than a target value, ferrosilicon is added in the reduction period for reduction, the reduction time is controlled to 10-15 min, and the temperature is controlled to 1610-1660 ℃; more preferably, the oxygen activity in the molten steel at the end of reduction is controlled to 10 to 80ppm.
Preferably, the AOD furnace refining step further comprises adding a ferro-sulphur alloy into the molten steel to enable the S content in the molten steel to reach a target value; more preferably, ferrosulfur is added to the molten steel and the temperature of the molten steel is adjusted to 1630-1670 ℃ for tapping, calculated according to the molten steel amount, the target sulfur content and 70% yield.
Preferably, the materials supplemented in the LF furnace refining step comprise ferrochrome, ferronickel, pure molybdenum, ferrosilicon, pure manganese and ferrosulfur, and are selectively supplemented according to the target content of each element.
Preferably, the temperature of the molten steel is adjusted to 1600-1630 ℃ in the LF furnace refining step.
Preferably, the tellurium wire is an iron sheet cored wire, the diameter of the tellurium wire is 13mm, the weight of an external iron sheet is 130-180 g/m, the weight of internal core powder is 500-550 g/m, and the core powder is pure tellurium powder.
Preferably, the wire feeding speed of the tellurium wires in the LF furnace refining step is 2-4 m/s; more preferably, argon is blown after the wire feeding to weakly stir for 5-15 min, the temperature of the molten steel is adjusted to 1620-1670 ℃, and the ladle is hung for continuous casting.
Preferably, the continuous casting step is performed by using an arc continuous casting machine.
Preferably, the superheat degree in the continuous casting step is controlled to be 25-45 ℃, the initial drawing speed is controlled to be 0.3m/min, and the stable drawing speed is controlled to be 0.7-1.0 m/min.
Preferably, the preheating of the steel billet in the steel rolling step is divided into two steps of low-temperature preheating and high-temperature preheating, the steel billet firstly enters a low-temperature region, the temperature is set to be 900-1000 ℃, the heating is carried out for 70-100 min, and then enters a high-temperature region, the temperature is set to be 1160-1200 ℃, and the heating is carried out for 40-80 min.
Preferably, the steel rolling step adopts 'dry head' rolling, namely, after the head of a rolled piece completely passes through the rolling mill, rolling roller cooling water is started.
Preferably, the rolling in the steel rolling step is divided into rough rolling, medium rolling and finish rolling; more preferably, the rough rolling is provided with 6 rolling mills, the middle rolling is provided with 18 rolling mills, the finish rolling is provided with 10 rolling mills, an online induction heating device is arranged between the rough rolling and the middle rolling, the temperature is set to be 1120-1200 ℃, the rolled piece is reheated in the process, and the rolling process is guaranteed not to crack.
Preferably, the temperature of the steel plate entering the finishing mill is controlled to be 950-1000 ℃ during finish rolling, the spinning temperature is 980-1050 ℃, the cooling speed is controlled to be 5-15 ℃/s after rolling, the steel plate is cooled to 200-300 ℃, and then the steel plate is air-cooled to the room temperature.
Preferably, the annealing step adopts a hood-type annealing furnace for annealing treatment.
Preferably, in the annealing step, the wire rod is heated to 860 ℃ at the speed of 15 ℃/min, is cooled to 450 ℃ in a furnace at the speed of 30 ℃/min after being kept at 860 ℃ for 8-10 h, and is taken out of the furnace and cooled in air.
Preferably, the specific production operation of each process is as follows:
electric furnace smelting: melting waste stainless steel with low P (P is less than or equal to 0.03%) and low five-harmful elements (the sum of Pb, sn, as, sb and Bi is not more than 0.05%) in an electric furnace;
refining in an AOD furnace: the decarbonization and chromium protection are carried out in AOD, which is divided into an oxidation period and a reduction period, oxygen is blown in the oxidation period to heat up, oxidize and decarbonize, and the oxygen blowing rate is controlled between 800 and 1200m 3 Controlling the temperature to 1650-1700 ℃, the time of the oxidation period to 30-60 min, controlling the oxidation end point C to be less than or equal to 0.01%, adding ferrosilicon for reduction in the reduction period, controlling the reduction time to 10-15 min, controlling the temperature to 1610-1660 ℃, controlling the oxygen activity in steel at the reduction end point to 10-80 ppm, adding ferrosulfur alloy into molten steel according to the molten steel amount, the target sulfur content and the 70% yield, and adjusting the temperature of the molten steel to 1630-1670 ℃ for tapping; argon is blown and stirred in the whole process to ensure that N is less than or equal to 0.05 percent;
refining in an LF furnace: adjusting the temperature of molten steel to 1600-1630 ℃, adding ferrochrome, ferronickel, pure molybdenum, ferrosilicon, pure manganese and ferro-sulphur alloy for supplementing when each element in the molten steel is insufficient, then adding ferroboron, adjusting B to 0.0015-0.0045%, then feeding a tellurium wire, adjusting Te to 0.006-0.010%, feeding wire at a speed of 2-4 m/s, blowing argon gas after feeding the wire, stirring for 5-15 min, adjusting the temperature to 1620-1670 ℃, and continuously casting on a ladle;
continuous casting: casting by adopting an arc continuous casting machine, wherein the superheat degree is controlled to be 25-45 ℃, the initial drawing speed is controlled to be 0.3m/min, and the stable drawing speed is controlled to be 0.7-1.0 m/min;
steel rolling: firstly heating a billet blank, entering a low-temperature region at 900-1000 ℃, heating for 70-100 min, entering a high-temperature region at 1160-1200 ℃, heating for 40-80 min, then discharging and starting rolling, adopting 'dry head' rolling, and starting rolling roller cooling water after the head of a rolled piece completely passes through a rolling mill; the rolling is divided into rough rolling, intermediate rolling and finish rolling, an online induction heating device is arranged after the rough rolling, the temperature is set to be 1120-1200 ℃, the rolled piece is reheated in the process, and the rolling process is guaranteed not to crack; controlling the temperature of the fine rolling mill to 950-1000 ℃ and the spinning temperature to 980-1050 ℃ by a water tank during fine rolling, controlling the cooling speed to 5-15 ℃/S by a heat preservation cover after rolling, cooling to 200-300 ℃, and then air cooling to room temperature;
annealing: the wire rod is heated to 860 ℃ at the speed of 15 ℃/min by adopting a hood-type annealing furnace, is cooled to 450 ℃ at the speed of 30 ℃/min after being kept at 860 ℃ for 8-10 h and then is cooled in the air, the process can fully anneal the material, the oxidation loss is less, and the sulfur-containing tellurium-containing free-cutting ferritic stainless steel is obtained.
The role of the respective chemical components in the material of the sulfur-containing tellurium-containing free-cutting ferritic stainless steel of the invention is explained below.
Carbon (C): carbon is a strong austenite forming element, the carbon directly influences the strength and hardness of the stainless steel, the carbon can improve the strength of the stainless steel and reduce the plasticity and toughness of the stainless steel when the carbon is higher, and the carbon can easily form a series of complex carbides with chromium in the stainless steel in order to form chromium-poor alloy and reduce the corrosion resistance of the stainless steel, so that the carbon content is controlled to be less than or equal to 0.10 percent.
Silicon (Si): silicon is a strong ferrite forming element, so that the stainless steel has a magnetic structure and is beneficial to enhancing the magnetic performance. The silicon has good effect on improving the oxidation resistance and heat strength of the stainless steel. However, the higher silicon content also reduces the plasticity and toughness of the stainless steel, and simultaneously influences the plasticity and the chloride ion corrosion resistance of the stainless steel. Therefore, the silicon content of the invention is controlled to be less than or equal to 1.0 percent.
Manganese (Mn): manganese is an austenite forming element and can influence the magnetism of the ferritic stainless steel, mnS generated by manganese and sulfur in the steel is an important free-cutting phase and can help to improve the cutting performance, the plasticity of the MnS is better, the hot working performance of the sulfur-containing steel can also be improved, and the content of manganese is controlled to be less than or equal to 1.25 percent.
Phosphorus (P): phosphorus is a harmful element in steel, the lower the phosphorus content is, the better the phosphorus content is, and the P content is less than or equal to 0.03 percent.
Sulfur (S): the sulfur is a free-cutting element, the sulfur and manganese (Mn) in the steel form manganese sulfide, the manganese sulfide can become a stress notch during turning, the cutting resistance of the stainless steel is reduced, and the effect of lubricating a cutter is achieved, the machinability of the stainless steel can be obviously improved along with the increase of the sulfur content, but the sulfide can be deformed along the rolling direction by too high sulfur to form a strip shape and be gathered together, the mechanical property of the material is seriously influenced, and the corrosion resistance is influenced, so the sulfur content is controlled to be 0.20-0.30%.
Nickel (Ni): nickel is a strong austenite forming element, a large amount of nickel should not exist in the ferritic stainless steel, but the ductility and toughness of the material can be improved by properly increasing the nickel, and the corrosion rate of the stainless steel in an acid environment can also be reduced, so that the content of the nickel is controlled to be less than or equal to 0.60 percent.
Chromium (Cr): chromium is an important ferrite forming element and an important guarantee element for the corrosion resistance of stainless steel, and with the increase of the chromium content in the stainless steel, the pitting point position of the ferritic stainless steel is increased, and the corrosion resistance is improved, but the stretching resistance of the stainless steel is reduced and the strength is improved due to the overhigh chromium content, so the chromium content is controlled to be 17.00-18.00 percent.
Molybdenum (Mo): molybdenum is a ferrite forming element, and molybdenum is added into ferrite to catalyze chromium to be aggregated in an oxide film, so that the stability of the oxide film is improved, and the pitting corrosion resistance and local corrosion resistance are enhanced, therefore, the content of molybdenum in the invention is controlled to be less than or equal to 0.60 percent.
Tellurium (Te): tellurium is an easy-cutting element, a small amount of tellurium can obviously improve the cutting performance of the stainless steel, when sulfur is contained in the steel, part of tellurium can be dissolved in manganese sulfide, and the part of tellurium usually exists in a MnTe form to wrap the outside of MnS, so that the manganese sulfide is not easy to extend during rolling, the sulfide is spheroidized, the sulfide is dispersed and finely distributed, the cutting performance of the stainless steel can be obviously improved, but the too high tellurium can influence the hot working performance of the material and is not beneficial to rolling, and therefore the tellurium content is controlled to be 0.005-0.015%.
Boron (B): boron can improve the grain boundary strength of austenitic stainless steel, improve the high-temperature plasticity of the material and reduce the problem of thermoplastic deterioration caused by tellurium addition, but the content of B element cannot be too high, otherwise, grain boundary segregation is caused, and harmful effects are caused, so the boron is controlled to be 0.001-0.005 percent.
Compared with the prior art, the invention has the beneficial effects that:
(1) Mn and S elements are adjusted, and Te element is added, so that most sulfides are spherical or spindle-shaped, the turning performance of the ferritic stainless steel is obviously improved, and the corrosion resistance and the plasticity can also be improved to a certain degree;
(2) Cr and Mo elements are adjusted, so that the corrosion resistance of the material is effectively improved;
(3) B element is added, and the rolling process is optimized by controlling the rolling heating temperature and setting the on-line induction heating process, so that the problem of thermoplastic deterioration caused by tellurium is effectively reduced, and the rolling yield is improved;
(4) A cover type annealing furnace is used, and a 860 ℃ complete annealing technology is adopted, so that the metallographic structure of the material is uniform, the plasticity of the material is further improved, and the subsequent straightening and drawing processing of the material is facilitated;
(5) The turning property, the corrosion resistance and the plasticity of the sulfur-containing tellurium-containing free-cutting ferritic stainless steel are completely superior to those of the common 430F material, and can completely replace the 430F material for use.
Drawings
FIG. 1 is a chip-breaking morphology of a sulfur-containing tellurium-containing free-cutting ferritic stainless steel of example 1 of the present invention after turning.
FIG. 2 shows the chip-breaking morphology of a conventional 430F ferritic stainless steel after turning.
FIG. 3 shows the sulfide morphology of the sulfur-containing tellurium-containing free-cutting ferritic stainless steel of example 1 of the present invention.
Fig. 4 shows the sulfide morphology of a common 430F ferritic stainless steel.
FIG. 5 shows the metallographic morphology of the sulfur-containing tellurium-containing free-cutting ferritic stainless steel of example 1 of the present invention.
Detailed Description
The technical solution of the present invention is further specifically described below by way of specific examples in conjunction with the accompanying drawings. The examples are merely illustrative of the best mode of carrying out the invention and do not limit the scope of the invention in any way.
The invention provides sulfur-containing tellurium-containing free-cutting ferritic stainless steel, which comprises the following components in percentage by mass: less than or equal to 0.10 percent of C, less than or equal to 1.0 percent of Si, less than or equal to 1.25 percent of Mn, less than or equal to 0.03 percent of P, 0.20-0.30 percent of S, less than or equal to 0.60 percent of Ni, 17.0-18.0 percent of Cr, less than or equal to 0.60 percent of Mo, less than or equal to 0.05 percent of N, 0.005-0.015 percent of Te, 0.001-0.005 percent of B, and the balance of Fe and inevitable impurities.
Wherein the mass ratio of Mn to S satisfies that Mn/S is not less than 3.
In the embodiment of the invention, the stainless steel comprises the following components: less than or equal to 0.065 percent of C, 0.3 to 0.6 percent of Si, 0.7 to 1.25 percent of Mn, less than or equal to 0.03 percent of P, 0.23 to 0.30 percent of S, less than or equal to 0.60 percent of Ni, 17.1 to 17.6 percent of Cr, 0.2 to 0.5 percent of Mo, less than or equal to 0.03 percent of N, 0.006 to 0.010 percent of Te, 0.0015 to 0.0045 percent of B, and the balance of iron and inevitable impurities, wherein the Mn/S is more than or equal to 3.
The invention provides a preparation method of the sulfur-containing tellurium-containing free-cutting ferritic stainless steel, which comprises the following steps: electric furnace smelting → AOD furnace refining → LF furnace refining → continuous casting → rolling → annealing, wherein:
electric furnace smelting: melting the raw materials into molten steel in an electric furnace;
refining in an AOD furnace: the molten steel is decarbonized and chromium-preserved in an AOD furnace, so that the content of C in the molten steel after decarbonization and chromium preservation is not higher than a target value; argon is blown and stirred in the whole refining process to ensure that the content of N is not higher than a target value;
refining in an LF furnace: adding materials into the molten steel in the previous step according to the target value of each component, then adding ferroboron to ensure that the content of B is the target value, and then feeding a tellurium wire to ensure that the content of Te is the target value;
continuous casting: casting the molten steel in the last step to obtain a steel billet;
steel rolling: preheating the steel billet in the last step and then rolling to obtain a wire rod;
annealing: and annealing the wire rod obtained in the last step to obtain the sulfur-containing tellurium-containing free-cutting ferritic stainless steel.
Preferably, the raw material is waste stainless steel, and the waste stainless steel is low P (P is less than or equal to 0.03%) and low five-harmful element (the sum of Pb, sn, as, sb and Bi is not more than 0.05%).
In the embodiment of the invention, the temperature of the electric furnace for smelting by the electric furnace is 1600-1700 ℃.
In the embodiment of the invention, the decarbonization and chromium protection in the refining step of the AOD furnace are divided into an oxidation period and a reduction period, the temperature of the oxidation period is controlled to be 1650-1700 ℃, the time of the oxidation period is controlled to be 30-60 min, the content of C at the oxidation end point is controlled not to be higher than a target value, ferrosilicon is added in the reduction period for reduction, the reduction time is controlled to be 10-15 min, and the temperature is controlled to be 1610-1660 ℃; more preferably, the oxygen activity in the molten steel at the end of reduction is controlled to 10 to 80ppm.
In the embodiment of the invention, the AOD furnace refining step further comprises the step of adding ferrosulfur alloy into the molten steel to enable the content of S in the molten steel to reach a target value; more preferably, the ferro-sulphur alloy is added into the molten steel according to the molten steel amount, the target sulphur content and the yield of 70 percent, and the temperature of the molten steel is adjusted to 1630-1670 ℃ for tapping.
In the embodiment of the invention, the materials supplemented in the LF furnace refining step comprise ferrochrome, ferronickel, pure molybdenum, ferrosilicon, pure manganese and ferrosulfur, and are selectively supplemented according to the target content of each element.
In the embodiment of the invention, the molten steel temperature is adjusted to 1600-1630 ℃ in the LF furnace refining step.
In the embodiment of the invention, the tellurium wire is an iron sheet cored wire, the diameter is 13mm, the weight of an external iron sheet is 130-180 g/m, the weight of internal core powder is 500-550 g/m, and the core powder is pure tellurium powder.
In the embodiment of the invention, the wire feeding speed of the tellurium wires in the LF furnace refining step is 2-4 m/s; more preferably, argon is blown after the wire feeding to weakly stir for 5-15 min, the temperature of the molten steel is adjusted to 1620-1670 ℃, and the ladle is hung for continuous casting.
In the embodiment of the invention, an arc continuous casting machine is adopted for casting in the continuous casting step.
In the embodiment of the invention, the superheat degree in the continuous casting step is controlled at 25-45 ℃, the initial drawing speed is controlled at 0.3m/min, and the stable drawing speed is controlled at 0.7-1.0 m/min.
In the embodiment of the invention, the preheating of the steel billet in the steel rolling step is divided into two steps of low-temperature preheating and high-temperature preheating, the steel billet firstly enters a low-temperature region, the temperature is set at 900-1000 ℃, the heating is carried out for 70-100 min, and then enters a high-temperature region, the temperature is set at 1160-1200 ℃, and the heating is carried out for 40-80 min.
In the embodiment of the invention, the steel rolling step adopts 'dry head' rolling, namely rolling the head of a rolled piece completely through a rolling mill and then starting roller cooling water.
In the embodiment of the invention, the rolling in the steel rolling step comprises rough rolling, middle rolling and finish rolling, the rough rolling is provided with 6 rolling mills, the middle rolling is provided with 18 rolling mills, the finish rolling is provided with 10 rolling mills, an online induction heating step is arranged between the rough rolling and the middle rolling, the temperature is set to be 1120-1200 ℃, the rolled piece is reheated in the process, and the rolling process is ensured not to crack.
In the embodiment of the invention, the temperature of the steel wire entering a finishing mill is controlled to be 950-1000 ℃ during finish rolling, the spinning temperature is 980-1050 ℃, the cooling speed is controlled to be 5-15 ℃/s after rolling, the steel wire is cooled to 200-300 ℃, and then the steel wire is cooled to the room temperature.
In the embodiment of the invention, a hood-type annealing furnace is adopted in the annealing step for annealing treatment.
In the embodiment of the invention, in the annealing step, the wire rod is heated to 860 ℃ at the speed of 15 ℃/min, is cooled to 450 ℃ in the furnace at the speed of 30 ℃/min after being kept at 860 ℃ for 8-10 h, and is discharged from the furnace and cooled in the air.
In the embodiment of the invention, the specific production operation of each process is as follows:
electric furnace smelting: melting waste stainless steel with low P (P is less than or equal to 0.03%) and low five-harmful elements (the sum of Pb, sn, as, sb and Bi is not more than 0.05%) in an electric furnace;
refining in an AOD furnace: the AOD is used for decarbonizing and chromium-protecting and is divided into an oxidation period and a reduction period, oxygen is blown in the oxidation period to raise the temperature for oxidation and decarbonization, and the oxygen blowing rate is controlled to be 1000-1200 m 3 The temperature is controlled to be 1650-1700 ℃, the time of an oxidation period is controlled to be 30-60 min, the oxidation end point C is controlled to be less than or equal to 0.01%, ferrosilicon is added for reduction in a reduction period, the reduction time is controlled to be 10-15 min, the temperature is controlled to be 1610-1660 ℃, the oxygen activity in steel at the reduction end point is controlled to be 10-80 ppm, ferrosulfur is added into molten steel according to the molten steel amount, the target sulfur content and the yield of 70%, and the molten steel temperature is adjusted to be 1630-1670 ℃ for tapping; argon is blown and stirred in the whole process to ensure that N is less than or equal to 0.05 percent;
refining in an LF furnace: adjusting the temperature of molten steel to 1600-1630 ℃, adding ferrochrome, ferronickel, pure molybdenum, ferrosilicon, pure manganese and ferro-sulphur alloy for supplementing when each element in the molten steel is insufficient, then adding ferroboron, adjusting B to 0.0015-0.0045%, then feeding a tellurium wire, adjusting Te to 0.006-0.010%, feeding wire at a speed of 2-4 m/s, blowing argon gas after feeding the wire, stirring for 5-15 min, adjusting the temperature to 1620-1670 ℃, and continuously casting on a ladle;
continuous casting: casting by adopting an arc continuous casting machine, wherein the superheat degree is controlled to be 25-45 ℃, the initial drawing speed is controlled to be 0.3m/min, and the stable drawing speed is controlled to be 0.7-1.0 m/min;
steel rolling: firstly heating a billet blank, entering a low-temperature region at 900-1000 ℃, heating for 70-100 min, entering a high-temperature region at 1160-1200 ℃, heating for 40-80 min, taking out of a furnace, starting rolling, adopting 'dry head' rolling, and then starting roll cooling water after the head of a rolled piece completely passes through a rolling mill; the rolling is divided into rough rolling, intermediate rolling and finish rolling, an online induction heating device is arranged after the rough rolling, the temperature is set to be 1120-1200 ℃, the rolled piece is reheated in the process, and the rolling process is guaranteed not to crack; controlling the temperature of the fine rolling mill to 950-1000 ℃ and the spinning temperature to 980-1050 ℃ by a water tank during fine rolling, controlling the cooling speed to 5-15 ℃/S by a heat preservation cover after rolling, cooling to 200-300 ℃, and then air cooling to room temperature; the on-line of the on-line induction heating device is synchronous with the production rolling process, the induction heating device is a conventional induction heater, and the induction heating device is as follows: the manufacturer: shanghai newly-researched industrial equipment, equipment model: MVP 2250SD induction heater.
And (3) annealing: the wire rod is heated to 860 ℃ at the speed of 15 ℃/min by adopting a hood-type annealing furnace, is cooled to 450 ℃ at the speed of 30 ℃/min after being kept at 860 ℃ for 8-10 h and then is cooled in the air, the process can fully anneal the material, the oxidation loss is less, and the sulfur-containing tellurium-containing free-cutting ferritic stainless steel is obtained.
The first embodiment is as follows:
the sulfur-containing tellurium-containing free-cutting ferritic stainless steel of the present embodiment comprises, by mass: 0.042% of C, 0.40% of Si, 0.81% of Mn, 0.023% of P, 0.25% of S, 0.22% of Ni, 17.23% of Cr, 0.26% of Mo, 0.018% of N, 0.0081% of Te and 0.0019% of B, and the balance of iron and inevitable impurities. The production process of the sulfur-containing tellurium-containing free-cutting ferritic stainless steel comprises the following steps: electric furnace → AOD → LF → continuous casting → rolling → annealing, concretely:
electric furnace: smelting by using 30 tons of electric furnaces, selecting 34 tons of waste stainless steel with low P and low five-harmful elements (Pb, sn, as, sb and Bi) As raw materials, firstly adding 20 tons of large raw materials, electrifying to melt for 1/3, then adding 14 tons of small raw materials, completely melting, wherein the P content is 0.023 percent, and the other elements comprise: 0.806 percent of C, 0.14 percent of Si, 0.68 percent of Mn, 0.017 percent of S, 0.22 percent of Ni, 16.99 percent of Cr, 0.26 percent of Mo and 0.072 percent of N, adjusting the temperature to 1670 ℃, and tapping after 2/3 of slag is pulled out.
AOD: decarbonizing and chromium-protecting in AOD, which is divided into an oxidation period and a reduction period, wherein the oxidation period is controlled to be 1650-1700 ℃, the time of the oxidation period is 44min, and the oxidation end point C:0.007 percent of the steel is reduced by adding 710Kg of ferrosilicon in the reduction period for 13min, the temperature is controlled to be 1610 to 1660 ℃, the oxygen activity in the molten steel at the reduction end point is 40ppm, then 330Kg of ferrosulfur alloy is added into the molten steel, argon is blown for weak stirring for 6min, at this moment, 0.018 percent of C, 0.40 percent of Si, 0.66 percent of Mn, 0.19 percent of S and 0.015 percent of N are added, the molten steel is tapped at 1650 ℃, and the tapping amount is 34 tons.
And (4) LF: adjusting the temperature of molten steel to 1625 ℃, ensuring that the elements Cr, mn and S in the molten steel are insufficient, supplementing 85Kg of ferrochrome, 80Kg of pure manganese and 100Kg of ferro-sulphur, then adding 40Kg of ferroboron, adjusting the B to 0.0019%, feeding 100 m/S of tellurium wire, adjusting the Te to 0.0081%, blowing argon after feeding the wire, stirring for 12min weakly, adjusting the temperature to 1655 ℃, and continuously casting on a ladle, wherein the molten steel amount is 34 tons.
Continuous casting: a three-machine three-arc continuous casting machine is adopted, the casting superheat degree is controlled at 38 ℃, the initial drawing speed is controlled at 0.3m/min, and the stable drawing speed is controlled at 0.7-1.0 m/min.
Steel rolling: firstly, heating a blank, firstly entering a low-temperature region, setting the temperature at 950 ℃, heating for 85min, then entering a high-temperature region, setting the temperature at 1180 ℃, heating for 66min, then taking the blank out of a furnace and starting rolling, adopting 'dry head' rolling, wherein the 'dry head' rolling is that the head of a rolled piece completely passes through a rolling mill and then rolling roller cooling water is started; the rough rolling is provided with 6 rolling mills, the billet is extruded and deformed, an online induction heating device is arranged after the rough rolling, and the temperature is set at 1170 ℃; the middle rolling is provided with 18 rolling mills, the finish rolling is provided with 10 rolling mills, the temperature of the middle rolling is controlled to be 980 ℃, the spinning temperature is 1021 ℃, and the cooling speed is controlled to be 10 ℃/S after the middle rolling is rolled.
Annealing: the wire rod is heated to 860 ℃ at the speed of 15 ℃/min by adopting a hood-type annealing furnace, is kept at 860 ℃ for 8h, is cooled to 450 ℃ at the speed of 30 ℃/min and is cooled in the air.
FIG. 5 shows the metallographic structure of example 1, which is uniform in structure, completely annealed, and excellent in plasticity.
Example two:
the sulfur-containing tellurium-containing free-cutting ferritic stainless steel of the present embodiment comprises, by mass: 0.049% of C, 0.51% of Si, 0.99% of Mn, 0.014% of P, 0.28% of S, 0.30% of Ni, 17.33% of Cr, 0.32% of Mo, 0.009% of N, 0.0062% of Te and 0.0021% of B, and the balance of iron and inevitable impurities. The production process of the sulfur-containing tellurium-containing free-cutting ferritic stainless steel comprises the following steps: electric furnace → AOD → LF → continuous casting → rolling → annealing, concretely:
electric furnace: smelting by using an electric furnace of 30 tons, selecting 33 tons of waste stainless steel with low P and low five-harmful elements (Pb, sn, as, sb and Bi) As raw materials, firstly adding 25 tons of large raw materials, electrifying and melting for 1/3, then adding 8 tons of small raw materials, completely melting to ensure that the P content is 0.014 percent, and the other elements are As follows: 0.780% of C, 0.16% of Si, 0.61% of Mn, 0.016% of S, 0.32% of Ni, 16.81% of Cr, 0.34% of Mo and 0.016% of N, adjusting the temperature to 1675 ℃, and tapping after 2/3 of slag is pulled out.
AOD: decarbonizing and chromium-protecting in AOD, which is divided into an oxidation period and a reduction period, wherein the oxidation period is controlled to be 1650-1700 ℃, the time of the oxidation period is 50min, and the oxidation end point C is as follows: 0.009%, adding 680Kg of ferrosilicon in the reduction period for reduction for 15min, controlling the temperature at 1610-1660 ℃, controlling the oxygen activity in the molten steel at the reduction end point to be 25ppm, then adding 280Kg of ferrosulfur alloy into the molten steel, blowing argon gas and weakly stirring for 8min, wherein 0.030% of C, 0.52% of Si, 0.66% of Mn, 0.23% of S and 0.008% of N, adjusting the temperature of the molten steel to 1655 ℃ for tapping, and the tapping amount is 31 tons.
LF: adjusting the temperature of molten steel to 1628 ℃, supplementing 155Kg of ferrochromium, 91Kg of pure manganese and 60Kg of ferro-sulphur when the elements Cr, mn and S in the molten steel are insufficient, then adding 47Kg of ferroboron, adjusting the B to be 0.0021%, feeding a tellurium wire by 80m at the speed of 2m/S, adjusting the Te to be 0.0062%, blowing argon after feeding the wire, stirring for 11min, adjusting the temperature to 1650 ℃, and continuously casting on a ladle, wherein the amount of the molten steel is 31 tons.
Continuous casting: a three-machine three-arc continuous casting machine is adopted, the casting superheat degree is controlled at 35 ℃, the initial drawing speed is controlled at 0.3m/min, and the stable drawing speed is controlled at 0.7-1.0 m/min.
Steel rolling: firstly, heating a blank, firstly entering a low-temperature region, setting the temperature at 950 ℃, heating for 88min, then entering a high-temperature region, setting the temperature at 1180 ℃, heating for 53min, then taking the blank out of a furnace and starting rolling, adopting 'dry head' rolling, wherein the 'dry head' rolling is that the head of a rolled piece completely passes through a rolling mill and then rolling roller cooling water is started; an online induction heating device is arranged after rough rolling, and the temperature is set at 1150 ℃; the temperature of the finishing mill is controlled to 970 ℃, the spinning temperature is controlled to 1005 ℃, and the cooling speed is controlled to 12 ℃/S after rolling.
Annealing: the wire rod is heated to 860 ℃ at the speed of 15 ℃/min by adopting a hood-type annealing furnace, is kept at 860 ℃ for 10 hours, is cooled to 450 ℃ at the speed of 30 ℃/min, and is cooled in the air.
Test example 1
The sulfur-containing and tellurium-containing free-cutting ferritic stainless steel produced by the invention and the common ferritic stainless steel 430F (Qingshan steel of manufacturers) are subjected to turning experiments at the same time, the turning parameters of the materials are the same, the experiments are carried out on a CA6140 lathe, a hard alloy blade is adopted, the turning speed is 1600r/min, the cutting depth is 0.5mm, the feed speed is 0.15mm/r, and the results are shown in table 1 after continuous 10-minute turning experiments. Wherein, the surface roughness of the turning piece obtained after cutting in the examples 1 and 2 is low and is obviously superior to 430F; the chip breaking morphology of the embodiment 1 is shown in FIG. 1, the proportion of C-type chips is high, and the chip effect is better than 430F; the values of the tool flank wear widths VB of examples 1 and 2 were lower than 430F, indicating that the tool wear was less for examples 1 and 2. In combination with the above evaluations, the turning performance of the present example was superior to that of the conventionally produced 430F.
TABLE 1 turning Performance evaluation parameters
Figure BDA0003398202590000131
Test example two
The tensile property test data of examples 1 and 2 are shown in Table 2, and the elongation and shrinkage of examples 1 and 2 are significantly higher than those of 430F produced conventionally, which shows that the sulfur-containing tellurium-containing free-cutting ferritic stainless steel of the present invention has better plasticity and is beneficial to the production and processing of downstream customers.
TABLE 2 tensile Property test results
Figure BDA0003398202590000132
In summary, the sulfur-containing tellurium-containing free-cutting ferritic stainless steel designed and manufactured by the invention adjusts the contents of S, mn and Cr on the basis of 430F, adds Mo and Te elements, and combines with a complete annealing process, so that the material has better cutting performance, and simultaneously, the corrosion resistance and the plasticity of the material are improved. Through turning experiments, the stainless steel turning scraps produced by the method are thinner and smoother in turning surface and smaller in cutter wear, and the method is beneficial to improving the machining efficiency of downstream customers and the precision and the smoothness of workpieces. The invention also can effectively solve the problem of poor hot processing performance caused by tellurium addition by adding the element B and optimally designing the rolling process, and has high production yield. The invention has simple design and operation, meets the requirement of mass production, and can completely replace 430F commonly used in the market.
The above-described embodiments are merely preferred embodiments of the present invention, which is not intended to be limiting in any way, and other variations and modifications are possible without departing from the scope of the invention as set forth in the appended claims.

Claims (8)

1. The sulfur-containing tellurium-containing free-cutting ferritic stainless steel is characterized by comprising the following components in percentage by mass: less than or equal to 0.10 percent of C, less than or equal to 1.0 percent of Si, less than or equal to 1.25 percent of Mn, less than or equal to 0.03 percent of P, 0.20-0.30 percent of S, less than or equal to 0.60 percent of Ni, 17.0-18.0 percent of Cr, less than or equal to 0.60 percent of Mo, less than or equal to 0.05 percent of N, 0.005-0.015 percent of Te, 0.001-0.005 percent of B, and the balance of Fe and inevitable impurities; wherein the mass ratio of Mn to S satisfies that Mn/S is more than or equal to 3; the stainless steel is prepared by the following method:
electric furnace smelting: melting the raw materials into molten steel in an electric furnace;
refining in an AOD furnace: the molten steel is decarbonized and chromium-preserved in an AOD furnace, so that the content of C in the molten steel after decarbonization and chromium preservation is not higher than a target value; argon is blown in the whole refining process to ensure that the content of N is not higher than a target value;
refining in an LF furnace: adding materials into the molten steel in the previous step according to the target value of each component, then adding ferroboron to ensure that the content of B is the target value, and then feeding a tellurium wire to ensure that the content of Te is the target value;
continuous casting: casting the molten steel in the last step to obtain a steel billet;
steel rolling: preheating a steel billet and then rolling to obtain a wire rod;
annealing: annealing the wire rod to obtain sulfur-containing tellurium-containing free-cutting ferritic stainless steel;
wherein in the annealing step, the wire rod is heated to 860 ℃ at the speed of 15 ℃/min, is kept at 860 ℃ for 8-10 h, is cooled to 450 ℃ in the furnace at the speed of 30 ℃/min, and is discharged and cooled in the air.
2. The sulfur-containing tellurium-containing free-cutting ferritic stainless steel as set forth in claim 1, characterized in that the stainless steel comprises the following components in mass percent: less than or equal to 0.065 percent of C, 0.3 to 0.6 percent of Si, 0.7 to 1.25 percent of Mn, less than or equal to 0.03 percent of P, 0.23 to 0.30 percent of S, less than or equal to 0.60 percent of Ni, 17.1 to 17.6 percent of Cr, 0.2 to 0.5 percent of Mo, less than or equal to 0.03 percent of N, 0.006 to 0.010 percent of Te, 0.0015 to 0.0045 percent of B, and the balance of iron and inevitable impurities, wherein the Mn/S is more than or equal to 3.
3. A method for producing a sulfur-containing tellurium-containing free-cutting ferritic stainless steel as set forth in any one of claims 1 through 2, which comprises the steps of: electric furnace smelting → AOD furnace refining → LF furnace refining → continuous casting → steel rolling → annealing, wherein:
electric furnace smelting: melting the raw materials into molten steel in an electric furnace;
refining in an AOD furnace: the molten steel is decarbonized and chromium-preserved in an AOD furnace, so that the content of C in the molten steel after decarbonization and chromium preservation is not higher than a target value; argon is blown in the whole refining process to ensure that the content of N is not higher than a target value;
refining in an LF furnace: adding materials into the molten steel in the previous step according to the target value of each component, then adding ferroboron to ensure that the content of B is the target value, and then feeding a tellurium wire to ensure that the content of Te is the target value;
continuous casting: casting the molten steel in the last step to obtain a steel billet;
steel rolling: preheating a steel billet and then rolling to obtain a wire rod;
and (3) annealing: annealing the wire rod to obtain sulfur-containing tellurium-containing free-cutting ferritic stainless steel;
wherein in the annealing step, the wire rod is heated to 860 ℃ at the speed of 15 ℃/min, is kept at 860 ℃ for 8-10 h, is cooled to 450 ℃ in the furnace at the speed of 30 ℃/min, and is discharged and cooled in the air.
4. The method of producing a sulfur-and tellurium-containing free-cutting ferritic stainless steel as set forth in claim 3, wherein the raw material is a scrap stainless steel.
5. The method of producing a sulfur-and tellurium-containing free-cutting ferritic stainless steel as set forth in claim 3, wherein the AOD furnace refining step further comprises adding a ferrosulfur alloy to the molten steel to make the S content in the molten steel a target value.
6. The method of producing a sulfur-and tellurium-containing free-cutting ferritic stainless steel as set forth in claim 3, wherein the materials supplemented in the LF furnace refining step include ferrochrome, ferronickel, pure molybdenum, ferrosilicon, pure manganese and ferrosulfur, which are selectively supplemented according to the target contents of the respective elements.
7. The method for producing a sulfur-and tellurium-containing free-cutting ferritic stainless steel as set forth in claim 3, wherein the tellurium wire is a sheet iron cored wire having a diameter of 13mm, an outer iron sheet weight of 130 to 180g/m, an inner core powder weight of 500 to 550g/m, and a core powder composition of pure tellurium powder; and the wire feeding speed of the tellurium wires in the LF furnace refining step is 2-4 m/s.
8. The method of manufacturing a sulfur-and tellurium-containing free-cutting ferritic stainless steel as set forth in claim 3, wherein the preheating of the steel slab in the steel rolling step is divided into two steps of low temperature preheating and high temperature preheating, the steel slab is first introduced into the low temperature region at a temperature of 900 to 1000 ℃ for 70 to 100min and then introduced into the high temperature region at a temperature of 1160 to 1200 ℃ for 40 to 80min; the rolling in the steel rolling step comprises rough rolling, intermediate rolling and finish rolling, wherein an online induction heating device is arranged between the rough rolling and the intermediate rolling, and the temperature is set to be 1120-1200 ℃.
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Denomination of invention: A sulfur-containing tellurium free cutting ferritic stainless steel and its manufacturing method

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