CN112795848B - Free-cutting corrosion-resistant steel and preparation method thereof - Google Patents
Free-cutting corrosion-resistant steel and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
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- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- 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
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- 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
Abstract
The invention relates to free-cutting corrosion-resistant steel and a preparation method thereof. The free-cutting corrosion-resistant steel comprises the following components in percentage by mass: 0.015-0.024% of C; 0.4-0.5% of Si; 1.2-1.3% of Mn; 0.24-0.3% of S; 0.02-0.03% of P; 1.5-1.75% of Mo; 19-20% of Cr; 0.03-0.08% of Ca; 0.01-0.02% of Mg; 0.02-0.05% of Al; 0.012-0.03% of Te; the balance being Fe and impurities. The method comprises the following steps: mixing the free-cutting steel, the ferrochrome mixed material and the slag material uniformly, and completely melting at high temperature to obtain a molten material; and adding tellurium into the melting material, carrying out heat preservation treatment, and cooling to obtain the free-cutting corrosion-resistant steel. The free-cutting corrosion-resistant steel has the best component proportion and has the comprehensive best free-cutting performance and corrosion resistance.
Description
Technical Field
The invention belongs to the technical field of steel-making processes, and particularly relates to free-cutting corrosion-resistant steel and a preparation method thereof.
Background
Free-cutting steel occupies a large proportion in the steel market in China, and particularly in recent years, the consumption of the free-cutting steel is continuously increased, so that the free-cutting steel is mainly applied to the field of automobiles. The development history of the free-cutting steel is long, the first world war can be traced back, and the occasional chance that Americans find that the cutting performance of the high-sulfur steel is good is provided, and then research on the free-cutting steel is started, free-cutting elements or compounds formed by the free-cutting elements in the free-cutting steel can reduce the resistance of a cutter in the cutting process, and have the effect of lubricating the cutter, so that the cutting performance is improved, sulfur is the most widely applied free-cutting element at present, manganese sulfide is the most main free-cutting compound in the steel, and the manganese sulfide is easy to cause pitting corrosion of the steel, so that the free-cutting performance and the corrosion resistance are indispensable for the production of a transmission shaft, a crankshaft, a gear, a hub and a bolt nut in the automobile industry, particularly, and how to balance the two performances to achieve the best effect in the steel is an urgent problem to be solved.
Chinese patent application CN112195419A discloses a preparation method of corrosion-resistant high-nitrogen stainless steel, which mainly researches the heat treatment of steel, and makes the steel obtain the technical effects of corrosion resistance and difficult passivation through the heat treatment in a high-nitrogen environment, but the whole smelting process is not designed, and the easy-cutting performance of the corrosion-resistant high-nitrogen stainless steel is not considered. Chinese patent application CN112176151A discloses a method for regulating and controlling the form of MnS inclusions in free-cutting steel, which focuses on researching the free-cutting performance, controls the form of manganese sulfide by bismuth treatment, gives the component design and the production process design of the free-cutting steel, but does not give consideration to the improvement of the corrosion resistance of the free-cutting steel. Chinese patent application CN111850407A discloses a 850 MPa-grade titanium-containing free-cutting stainless steel forging bar and a preparation method thereof, the application considers the requirements of free-cutting performance and corrosion resistance, and meets the requirements of parts with higher strength, the component design and production process scheme are given, but the application focuses on the improvement of the strength of steel, and the application mainly depends on titanium treatment to modify sulfide in steel and control the form of sulfide, but when the sulfur content is less than 0.3%, the titanium treatment needs to depend on nitrogen as protective gas, when argon is used as protective gas, the titanium treatment cannot change the form of manganese sulfide, and the form of manganese sulfide cannot be effectively controlled and easily causes pitting corrosion of steel, thereby affecting the corrosion resistance; when the titanium treatment method adopts nitrogen as protective gas, the nitrogen content in the steel is difficult to control, and large-particle inclusions are easy to generate due to overhigh nitrogen content in the steel, thereby influencing the free-cutting performance of the steel.
Therefore, how to control the form of manganese sulfide to obtain the free-cutting performance, reduce the pitting phenomenon at the manganese sulfide position, improve the corrosion resistance of steel, control the distribution of manganese sulfide and chromium elements on the form of inclusions, and meet the requirement of the market on the performance of the free-cutting corrosion-resistant steel is a problem to be solved urgently.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides free-cutting corrosion-resistant steel and a preparation method thereof. The free-cutting corrosion-resistant steel has proper component content, combines the contradictory free-cutting performance and corrosion resistance, improves the corrosion resistance of the free-cutting steel to the maximum extent, reduces the free-cutting performance of the original finished product free-cutting steel to the minimum extent, and is suitable for the production requirements of the current automobile industry.
In order to achieve the above object, the present invention provides, in a first aspect, a free-cutting corrosion-resistant steel comprising, in mass percent: c, 0.015% -0.024%; 0.4 to 0.5 percent of Si; 1.2 to 1.3 percent of Mn; s, 0.24 to 0.3 percent; 0.02 to 0.03 percent of P; 1.5 to 1.75 percent of Mo; 19 to 20 percent of Cr; 0.03% -0.08% of Ca; 0.01% -0.02% of Mg; 0.02% -0.05% of Al; 0.012% -0.03% of Te; the balance being Fe and unavoidable impurities.
Preferably, the mass ratio of Mn to S is 4-5.42; and/or the mass ratio of Te to S is 0.04-0.125.
The present invention provides, in a second aspect, a method of producing the free-cutting corrosion-resistant steel of the first aspect of the invention, the method comprising the steps of:
(1) uniformly mixing the free-cutting steel, the ferrochrome mixed material and the slag to obtain a steel material; the free-cutting steel comprises the following components in percentage by mass: c, 0.02% -0.04%; 0.05% -0.15% of Si; 1.4% -1.6% of Mn; 0.32% -0.38% of S; 0.03% -0.06% of P; 2% -2.2% of Mo; the balance of Fe and inevitable impurities; the slag comprises the following components in percentage by mass: CaF2，50%~60%；Al2O335% -45%; 3% -8% of MgO; the ferrochrome mixed material comprises the following components in percentage by mass: 70% -80% of Cr; 1% -4% of Si; the balance being Fe;
(2) completely melting the steel material at high temperature to obtain a molten material;
(3) adding tellurium into the molten material, uniformly mixing, and then carrying out heat preservation treatment to obtain a tellurium-treated molten material; the addition amount of the tellurium is 0.014% -0.033% of the mass of the molten material;
(4) and cooling the tellurium treatment melting material to obtain the free-cutting corrosion-resistant steel.
Preferably, the free-cutting steel comprises the following components in percentage by mass: c, 0.028%; 0.1% of Si; 1.6 percent of Mn; s, 0.35 percent; p, 0.03%; 2.2 percent of Mo; the balance being Fe and unavoidable impurities.
Preferably, the slag comprises the following components in percentage by mass: CaF2，55%；Al2O3，40%；MgO，5%。
Preferably, the ferrochrome mixture comprises the following components in percentage by mass: 78% of Cr; si, 1.5%; 20.5 percent of Fe.
Preferably, the mass ratio of the usage amount of the free-cutting steel to the usage amount of the ferrochrome mixed material is (2.8-3.2): 1; and/or the mass ratio of the free-cutting steel to the slag charge is 100: (11-13).
Preferably, steps (2) to (4) are carried out in a vertical tube silicon molybdenum resistance furnace.
Preferably, in the step (2), the steel material is completely melted at 1600 ℃ to obtain a molten material; in the step (3), the heat preservation treatment time is 10-20 min; and/or in the step (4), the cooling mode is as follows: firstly, cooling to 200-300 ℃ along with the furnace, and then cooling to room temperature by adopting a water cooling mode.
Preferably, in the process of performing the step (2) and the step (3), introducing argon protective gas, wherein the flow rate of the introduced argon is 0.3-0.4 m3/h。
Compared with the prior art, the invention at least has the following beneficial effects:
(1) the free-cutting corrosion-resistant steel has the advantages that the carbon content is controlled to be 0.015-0.024%, the chromium content is controlled to be 19-20% and the tellurium content is controlled to be 0.012-0.03%.
(2) The method of the invention adjusts the components of the free-cutting steel by adding the ferrochrome mixed material and the slag material into the free-cutting steel, so that the carbon content in the finally prepared free-cutting corrosion-resistant steel is controlled within the range of 0.015-0.024%, the chromium content is controlled within the range of 19-20% and the tellurium content is controlled within the range of 0.012-0.03%; according to the invention, the appearance of the inclusions in the molten material is effectively improved by adding tellurium, the manganese telluride and the manganese sulfide form a eutectic with a low melting point after tellurium treatment, the eutectic is wrapped outside the manganese sulfide, the shape of the inclusions is better controlled, and the length-width ratio of the inclusions is reduced, so that the cutting performance is favorably improved.
(3) The invention provides the component design and the process flow of the free-cutting steel, the components and the appearance of non-metallic inclusions are controlled by controlling the components and the flow operation, the appearance and the wrapping mode of the inclusions are controlled by using a tellurium treatment mode, and the distribution of free-cutting phase manganese sulfide and corrosion-resistant element chromium is uniform, so that the free-cutting steel is ensured to have the free-cutting performance and the corrosion resistance with the best comprehensive performance.
Drawings
FIG. 1 is a schematic structural diagram of a vertical tube type silicon-molybdenum resistance furnace adopted by the invention.
In the figure: 1: an air inlet; 2: a temperature-resistant furnace cover; 3: a corundum furnace tube; 4: a silicon-molybdenum rod; 5: a MgO crucible; 6: protecting the crucible; 7: a thermocouple; 8: a thermal insulation material; 9: a refractory brick; 10: a tubular furnace sealing water jacket structure; 11: and (4) a bracket.
FIG. 2 is a graph showing the relationship between the flank wear and the cutting time of the cutting tools of examples 1 to 3 and comparative examples 1 to 3 of the present invention.
Fig. 3 is a morphology (SEM) of inclusions in the free-cutting corrosion-resistant steel prepared in example 1 of the present invention and an energy spectrum of each element. In the figure, (a) is an inclusion morphology map; in the figure, (b) is an energy spectrum of each element in the inclusion.
Fig. 4 is a morphology (SEM) of inclusions in the free-cutting corrosion-resistant steel prepared in comparative example 1 of the present invention and an energy spectrum of each element. In the figure, (a) is an inclusion morphology map; in the figure, (b) is an energy spectrum of each element in the inclusion.
Fig. 5 is a morphology (SEM) of inclusions in the free-cutting corrosion-resistant steel prepared in example 2 of the present invention and an energy spectrum of each element. In the figure, (a) is an inclusion morphology map; in the figure, (b) is an energy spectrum of each element in the inclusion.
Fig. 6 is a morphology (SEM) of inclusions in the free-cutting corrosion-resistant steel prepared in comparative example 2 of the present invention and an energy spectrum of each element. In the figure, (a) is an inclusion morphology map; in the figure, (b) is an energy spectrum of each element in the inclusion.
Fig. 7 is a morphology (SEM) of inclusions in the free-cutting corrosion-resistant steel prepared in example 3 of the present invention and an energy spectrum of each element. In the figure, (a) is an inclusion morphology map; in the figure, (b) is an energy spectrum of each element in the inclusion.
FIG. 8 is a morphology (SEM) chart of inclusions in the free-cutting corrosion-resistant steel prepared in comparative example 3 of the present invention and an energy spectrum of each element. In the figure, (a) is an inclusion morphology map; in the figure, (b) is an energy spectrum of each element in the inclusion.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
The invention provides in a first aspect a free-cutting corrosion-resistant steel comprising, in mass percent: c (carbon), 0.015% to 0.024% (e.g., 0.015%, 0.016%, 0.017%, 0.018%, 0.019%, 0.02%, 0.021%, 0.022%, 0.023%, or 0.024%); si (silicon), 0.4% to 0.5% (e.g., 0.4%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.46%, 0.47%, 0.48%, 0.49%, or 0.5%); mn (manganese), 1.2% to 1.3% (e.g., 1.2%, 1.21%, 1.22%, 1.23%, 1.24%, 1.25%, 1.26%, 1.27%, 1.28%, 1.29%, or 1.3%); s (sulfur), 0.24% to 0.3% (e.g., 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, or 0.3%); p (phosphorus), 0.02% to 0.03% (e.g., 0.02%, 0.021%, 0.022%, 0.023%, 0.024%, 0.025%, 0.026%, 0.027%, 0.028%, 0.029%, or 0.03%); mo (molybdenum), 1.5% to 1.75% (e.g., 1.5%, 1.52%, 1.55%, 1.58%, 1.6%, 1.61%, 1.62%, 1.65%, 1.68%, 1.7%, 1.72%, or 1.75%); cr (chromium), 19-20% (e.g., 19%, 19.1%, 19.2%, 19.3%, 19.4%, 19.5%, 19.6%, 19.7%, 19.8%, 19.9%, or 20%); ca (calcium), 0.03% -0.08% (e.g., 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, or 0.08%); mg (magnesium), 0.01% to 0.02% (e.g. 0.01%, 0.015% or 0.02%); al (aluminum), 0.02% -0.05% (e.g., 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, or 0.05%); te (tellurium), 0.012% -0.03% (e.g., 0.012%, 0.014%, 0.016%, 0.018%, 0.02%, 0.022%, 0.024%, 0.026%, 0.028%, or 0.03%); the balance of Fe and inevitable impurities; in the invention, the mass percentage of Fe contained in the free-cutting corrosion-resistant steel can be 75-76%, and the mass percentage of inevitable impurities in the free-cutting corrosion-resistant steel is less than 1%.
The free-cutting corrosion-resistant steel has the following functions in terms of components and contents:
c: the content of carbon directly influences the mechanical properties of steel, including plasticity, toughness and strength, and for the free-cutting corrosion-resistant steel, the strength and hardness of the steel are influenced if the carbon content is too low, so that the steel is too soft, the cutter is easily adhered in the cutting process, and the improvement of the cutting performance is not facilitated. Although certain strength and hardness must be ensured in the automobile industry, too high carbon content affects the machinability, and too hard steel accelerates the wear of the tool, so that the carbon content in the free-cutting corrosion-resistant steel is controlled within the range of 0.015-0.024%.
Si: the silicon element is mainly used as a deoxidizing element, the mechanical property of the steel is influenced by controlling the oxygen content, silicate inclusions are easily formed by deoxidizing products of the silicon, the service life of a cutter is influenced by the excessively high silicon content, the hardenability of the silicon can be improved, but if the silicon content is not controlled well, black net defects are easily formed at a crystal boundary, and the quality of steel is seriously influenced, so that the silicon content in the free-cutting corrosion-resistant steel is controlled within the range of 0.4-0.5%.
Mn: manganese is easy to form a compound manganese sulfide with sulfur, which is a main existing form of the sulfur and is an important free-cutting phase in free-cutting steel, and the principle that the manganese sulfide can improve the free-cutting performance of steel is that the manganese sulfide breaks the continuity of a matrix and serves as a stress concentration source in the matrix, chips are easy to break in the cutting process, and the manganese sulfide has the advantages of lubricating a cutter, reducing the cutting resistance, reducing the heat generated in the cutting process, improving the free-cutting performance and prolonging the service life of the cutter; however, the anisotropy of the steel is aggravated by the existence of manganese sulfide, and the toughness of the steel in the non-rolling direction is increased by the excessively high manganese content, so that the manganese content in the free-cutting corrosion-resistant steel is controlled within the range of 1.2-1.3%.
S: the sulfur element belongs to harmful elements in general steel grades, is easy to cause hot brittleness, and is generally controlled at an extremely low level, but for the steel grade, the sulfur element belongs to easy-cutting elements, and needs to be reasonably utilized, and the sulfur-series easy-cutting steel can be generally divided into low-sulfur steel (S is less than or equal to 0.035%), sulfur steel (S =0.04% -0.09%) and high-sulfur steel (S =0.1% -0.3%); if the sulfur content is too low, the generation of the free-cutting phase manganese sulfide is not facilitated, and if the sulfur content is too high, the phenomena of sulfur element segregation and thermal brittleness are easily caused, so the sulfur content in the free-cutting corrosion-resistant steel is controlled within the range of 0.24-0.3%.
P: the phosphorus element is dissolved in ferrite to improve the strength and the hardenability of steel, is regarded as harmful element except special steel types such as shell steel and the like, is easy to cause cold brittleness phenomenon, and is generally controlled at a low level, and for the steel type, the phosphorus element is controlled within the range of 0.02-0.03 percent.
Mo: the molybdenum element can refine crystal grains and improve the hardenability and the heat strength, the molybdenum element and the chromium element act simultaneously in the corrosion-resistant steel to inhibit the temper brittleness, the content of the molybdenum element is high, the crystal grains are finer, the synergistic effect of the molybdenum element and the chromium element among the crystal grains is more favorable for improving the corrosion resistance, but the excessive molybdenum element can increase the production cost, so the molybdenum element in the free-cutting corrosion-resistant steel is controlled within the range of 1.5-1.75 percent.
Cr: the chromium element is the most important element for improving the corrosion resistance, the mechanical property of the steel can be improved under the combined action of the chromium element and other alloy elements, the chromium is easily wrapped outside the inclusion and is also easily enriched at the crystal boundary, and the interaction between the crystal boundaries is improved, so that the chromium element in the steel is not easy to be too high, the strength of the steel is improved by the excessively high chromium element, and the cutting performance of the steel is influenced, and therefore, the chromium element in the free-cutting corrosion-resistant steel is controlled within the range of 19-20%.
Te: the appearance of the inclusions can be improved by adding tellurium, manganese telluride and manganese sulfide are formed after tellurium treatment to form eutectic with low melting point, the eutectic is wrapped outside the manganese sulfide to control the morphology of the inclusions, the aspect ratio of the inclusions is increased, the improvement of the cutting performance is facilitated, meanwhile, the addition of tellurium relieves the contradiction that chromium and manganese sulfide are difficult to coexist, the tellurium and telluride strengthen the connection between the two, and play a vital role in improving the easy cutting performance and the corrosion resistance, the tellurium treatment is insufficient when the content of tellurium is too small, the morphology control of the inclusions is not ideal, and the production cost is influenced when the content of tellurium is too large, so that the chromium in the easy-cutting corrosion-resistant steel is controlled within the range of 0.012-0.03 percent.
The free-cutting corrosion-resistant steel has the advantages that the carbon content is controlled to be 0.015-0.024%, the chromium content is controlled to be 19-20% and the tellurium content is controlled to be 0.012-0.03%.
According to some preferred embodiments, the mass ratio of Mn to S (denoted as ω Mn/ω S) is from 4 to 5.42; and/or the mass ratio of Te to S (denoted as [ omega ] Te ]/[ omega ] S) is 0.04-0.125.
The present invention provides, in a second aspect, a method of producing the free-cutting corrosion-resistant steel of the first aspect of the invention, the method comprising the steps of:
(1) mixing the free-cutting steel (such as free-cutting pen point steel), the ferrochrome mixed material and the slag uniformly to obtain a steel material; the free-cutting steel comprises the following components in percentage by mass: c, 0.02% -0.04% (e.g., 0.02%, 0.03%, or 0.04%); si, 0.05% -0.15% (e.g., 0.05%, 0.08%, 0.1%, 0.12%, or 0.15%); mn, 1.4% -1.6% (e.g., 1.4%, 1.5%, or 1.6%); s, 0.32% -0.38% (e.g., 0.32%, 0.35%, or 0.38%); p, 0.03% -0.06% (e.g., 0.03%, 0.04%, 0.05% or 0.06%); mo, 2% -2.2% (e.g., 2%, 2.1%, or 2.2%); the balance of Fe and inevitable impurities; in the invention, the mass percentage of Fe in the free-cutting steel is 95-96%, and the mass percentage of inevitable impurities in the free-cutting steel is less than 1%; in the present invention, when the free-cutting steel contains the components in the above-mentioned ranges in percentage by mass, the free-cutting property and the corrosion resistance property of the free-cutting steel within the ranges do not differ greatly in performance index because the free-cutting steel does not contain chromium element and tellurium treatment; the slag comprises the following components in percentage by mass: CaF250% -60% (e.g., 50%, 52%, 55%, 58%, or 60%); al (Al)2O335% -45% (e.g., 35%, 38%, 40%, 42%, or 45%); MgO, 3% to 8% (e.g., 3%, 5%, or 8%); the ferrochrome mixture comprisesThe components by mass percentage are as follows: cr, 70-80% (e.g., 70%, 72%, 75%, 78%, or 80%); si, 1% to 4% (e.g., 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%) preferably 1.2% to 1.8% (e.g., 1.2%, 1.5%, or 1.8%); the balance being Fe; in the invention, the mass percentage of Fe contained in the ferrochrome mixture can be 18-26%; in the present invention, the free-cutting steel is a finished wire free-cutting steel block (finished free-cutting steel block) of known composition, and the finished free-cutting steel block is produced by using the existing production process: converter → LF refining → continuous casting → continuous rolling; in the invention, the components of the free-cutting steel are adjusted by adding the ferrochrome mixed material and the slag material into the free-cutting steel, so that the carbon content, the chromium content and the tellurium content in the finally prepared free-cutting corrosion-resistant steel are controlled within the ranges of 0.015-0.024%, 19-20% and 0.012-0.03%; in the invention, the addition of the slag can lead the free-cutting corrosion-resistant steel to contain extremely small amounts of calcium, magnesium and aluminum components, but the calcium, magnesium and aluminum elements are mostly present in the free-cutting corrosion-resistant steel in the form of oxides as the core of inclusions; in the invention, the addition of the slag can improve the yield of the tellurium powder, and can absorb large-sized impurities in the steel to promote the floating of the impurities; in the invention, the slag can finally suspend above the molten steel, and the slag basically has no influence on the content of each component of the finally prepared free-cutting corrosion-resistant steel;
(2) completely melting the steel material at a high temperature (for example, 1600 ℃) to obtain a molten material;
(3) adding tellurium (tellurium powder) into the molten material, uniformly mixing, and then carrying out heat preservation treatment to obtain a tellurium treatment molten material; the tellurium is added in an amount of 0.014% -0.033% (e.g., 0.014%, 0.015%, 0.016%, 0.017%, 0.018%, 0.019%, 0.02%, 0.021%, 0.022%, 0.023%, 0.024%, 0.025%, 0.026%, 0.027%, 0.028%, 0.029%, 0.03%, 0.031%, 0.032%, or 0.033%) of the mass of the frit); according to the invention, tellurium oxide smoke is generated under the high-temperature condition to influence the tellurium yield, and when the addition amount of tellurium is controlled to be 0.014% -0.033% of the mass of the molten material, the mass percentage content of Te in the finally prepared free-cutting corrosion-resistant steel can be effectively ensured to be 0.012% -0.03%;
(4) cooling the tellurium treatment melting stock to obtain the free-cutting corrosion-resistant steel; the free-cutting corrosion-resistant steel comprises the following components in percentage by mass: c, 0.015% -0.024%; 0.4 to 0.5 percent of Si; 1.2 to 1.3 percent of Mn; s, 0.24 to 0.3 percent; 0.02 to 0.03 percent of P; 1.5 to 1.75 percent of Mo; 19 to 20 percent of Cr; 0.03% -0.08% of Ca; 0.01% -0.02% of Mg; 0.02% -0.05% of Al; 0.012% -0.03% of Te; the balance being Fe and unavoidable impurities.
In order to obtain the best free-cutting and corrosion resistance properties of steel, the control of non-metallic inclusions in the steel is critical, including the composition and morphology of the inclusions. Manganese sulfide plays an important role in the free-cutting performance of steel, but because manganese sulfide has good deformability in the rolling process of steel, the aspect ratio of a pure manganese sulfide inclusion is relatively large in appearance, the mechanical property of steel is seriously influenced, the form of manganese sulfide is controlled by tellurium treatment, the aspect ratio of manganese sulfide is reduced, a low-melting-point eutectic of manganese telluride and manganese sulfide generated by adding tellurium is wrapped outside the manganese sulfide, spherical wrapping type inclusions are easily formed, the cutting resistance is reduced, heat generated in the cutting process is reduced, and the service life of a cutter is prolonged. However, the enrichment of manganese sulfide is very easy to cause pitting corrosion of steel, because chromium-poor areas are easily generated at the enriched place of manganese sulfide; chromium is an important element for controlling corrosion-resistant steel, and because the potential of chromium is negative than that of iron, chromium is easy to form an extremely thin passive film in the atmosphere and is stable in a humid atmosphere, chromium has the function of improving the corrosion resistance, and the chromium content cannot be too low to ensure the corrosion resistance, the existing corrosion-resistant steel generally adopts a method of 'decarbonizing and protecting chromium' in the production process, but the reported research of improving the corrosion resistance of free-cutting steel by chromium in free-cutting steel is not found in the prior art, because chromium can also refine crystal grains, the strength of the steel can also be improved, and the existing chromium with enough content capable of achieving the corrosion resistance can obviously reduce the free-cutting performance of the free-cutting steel due to the increase of the strength.
Chromium is an important element of corrosion resistance of steel, but in the prior art, manganese sulfide and chromium are generally considered to be difficult to coexist, and manganese sulfide and chromium are not easy to distribute uniformly, and sufficient chromium dosage capable of achieving corrosion resistance generally can increase the strength of the free-cutting steel and obviously reduce the free-cutting performance of the free-cutting steel, so that the improvement of the corrosion resistance of the free-cutting steel considering the free-cutting performance by adding chromium is generally considered to be undesirable, and in addition, the prior art does not see the related report that the chromium content of the free-cutting steel can be controlled within a reasonable range and the manganese sulfide and chromium are uniformly distributed, so that the free-cutting performance can be ensured, the corrosion resistance can be ensured, the comprehensive performance is optimal, and the free-cutting corrosion-resistant steel can be obtained. The invention just overcomes the technical prejudice, controls the appropriate components of the free-cutting corrosion-resistant steel and reasonable tellurium treatment, and links the contradictory free-cutting performance and corrosion resistance performance through certain smelting operation, and the reasonable tellurium treatment ensures the optimal comprehensive effect of the free-cutting performance and the corrosion resistance performance to the maximum extent in the appropriate component range, thereby being suitable for the production requirements of the current automobile industry; specifically, the method of the invention adjusts the components of the free-cutting steel by adding the ferrochrome mixed material and the slag material into the free-cutting steel, so that the carbon content, the chromium content and the tellurium content in the finally prepared free-cutting corrosion-resistant steel are respectively controlled within the ranges of 0.015-0.024%, 19-20% and 0.012-0.03%; the invention considers from the inclusion angle, for aluminum killed steel (free-cutting steel), the inclusion takes alumina or magnesium aluminate spinel as nucleation center, manganese sulfide is wrapped outside the oxide core, which can improve the free-cutting performance, in order to better control the form of the inclusion and make the distribution of chromium element and manganese sulfide uniform, the invention effectively improves the appearance of the inclusion in the melting stock by adding tellurium, the manganese telluride and manganese sulfide form eutectic with low melting point after tellurium treatment, the eutectic is wrapped outside the manganese sulfide to form telluride wrap, the addition of tellurium relieves the contradiction that chromium element and manganese sulfide are difficult to coexist, tellurium and telluride strengthens the connection between the two, avoids the rejection of the chromium element by manganese sulfide, makes the chromium and manganese sulfide uniformly distributed, makes the chromium element distributed at the periphery of telluride and the intersection of crystal boundary, the corrosion resistance is improved, the necessary mechanical property of the steel is ensured, the corrosion resistance is enhanced while the free-cutting property of the steel is influenced as little as possible by adding chromium, and the method plays a vital role in improving the free-cutting property and the corrosion resistance. In the invention, unexpectedly, the tellurium powder tellurium treatment is added to ensure that manganese telluride and manganese sulfide form eutectic with low melting point, the eutectic wraps the manganese sulfide to form telluride wrap, so that the addition of tellurium relieves the contradiction that chromium element and manganese sulfide are difficult to coexist, the rejection of manganese sulfide to chromium element is avoided, the chromium and manganese sulfide are uniformly distributed, the corrosion resistance of the free-cutting steel is improved to the maximum extent by adding a proper amount of chromium into the tellurium treated free-cutting steel, and the free-cutting performance of the original finished free-cutting steel is reduced to the minimum extent.
According to some preferred embodiments, the free-cutting steel comprises the following components in percentage by mass: c, 0.028%; 0.1% of Si; 1.6 percent of Mn; s, 0.35 percent; p, 0.03%; 2.2 percent of Mo; the balance being Fe and unavoidable impurities.
According to some preferred embodiments, the slag comprises the following components in percentage by mass: CaF2，55%；Al2O3，40%；MgO，5%。
According to some preferred embodiments, the ferrochrome mixture comprises the following components in percentage by mass: 78% of Cr; si, 1.5%; 20.5 percent of Fe.
According to some preferred embodiments, the mass ratio of the free-cutting steel to the ferrochrome mixture is (2.8-3.2): 1 (e.g., 2.8, 2.9, 3, 3.1, or 3.2) is preferably 3: 1; and/or the mass ratio of the free-cutting steel to the slag charge is 100: (11-13) (e.g., 100:11, 100:11.5, 100:12, 100:12.5, or 100: 13) is preferably 100: 12.5.
According to some more preferred embodiments, the free-cutting steel comprises the following components in percentage by mass: c, 0.028%; 0.1% of Si; 1.6 percent of Mn; s, 035%; p, 0.03%; 2.2 percent of Mo; the balance of Fe and inevitable impurities; the slag comprises the following components in percentage by mass: CaF2，55%；Al2O340%; 5% of MgO; the ferrochrome mixed material comprises the following components in percentage by mass: 78% of Cr; si, 1.5%; 20.5 percent of Fe; the mass ratio of the consumption of the free-cutting steel to the consumption of the ferrochrome mixed material is 3: 1; the mass ratio of the free-cutting steel to the slag charge is 100: 12.5; so that the finally prepared free-cutting corrosion-resistant steel is more favorably controlled to comprise the following components in percentage by mass: c, 0.015% -0.024%; 0.4 to 0.5 percent of Si; 1.2 to 1.3 percent of Mn; s, 0.24 to 0.3 percent; 0.02 to 0.03 percent of P; 1.5 to 1.75 percent of Mo; 19 to 20 percent of Cr; 0.03% -0.08% of Ca; 0.01% -0.02% of Mg; 0.02% -0.05% of Al; 0.012% -0.03% of Te; the balance being Fe and unavoidable impurities.
According to some preferred embodiments, the steps (2) to (4) are performed in a vertical tube type silicon-molybdenum resistance furnace, which is a vertical tube type silicon-molybdenum resistance furnace of a smelting device in the prior art, for example, a vertical tube type silicon-molybdenum resistance furnace as shown in fig. 1.
According to some preferred embodiments, in the step (2), the steel material is completely melted at 1600 ℃ to obtain a molten material; in the step (3), the heat preservation treatment time is 10-20 min (for example, 10, 15 or 20 min); the temperature of the heat preservation treatment is 1600 ℃; and/or in the step (4), the cooling mode is as follows: cooling to 200-300 ℃ with a furnace (such as 200 ℃, 250 ℃ or 300 ℃), and then cooling to room temperature (such as 20-30 ℃ at room temperature) by adopting a water cooling mode.
According to some preferred embodiments, during the step (2) and the step (3), argon protective gas is introduced, and the flow rate of the argon introduced is 0.3-0.4 m3H (e.g. 0.3, 0.35 or 0.4 m)3/h）。
According to some preferred embodiments, in step (4), the cooling is performed by: firstly, cooling to 200-300 ℃ along with the furnace, and then cooling to room temperature by adopting a water cooling mode; in step (4)In the furnace cooling process, the flow of the introduced argon is 0.2-0.3 m3H (e.g. 0.2, 0.25 or 0.3 m)3/h）。
According to some specific embodiments, the free-cutting corrosion-resistant steel is smelted by using a vertical tube type silicon-molybdenum resistance furnace (high-temperature tube furnace), and the specific operation flow is as follows: batching → melting in a high-temperature tube furnace → adding tellurium → sampling; the method specifically comprises the following steps:
preparing materials: cutting the finished wire of the free-cutting steel into free-cutting steel blocks with the length of 50mm by using a cutting machine, weighing 100g of free-cutting steel block samples, and putting the samples into a crucible (MgO crucible); weighing 33g of ferrochrome mixed material, selecting a chemical pure reagent to prepare slag materials and uniformly mixing, adding the prepared slag materials with the mass of 12.5g and the ferrochrome mixed material with the mass of 33g into a crucible and uniformly mixing to obtain steel materials, and putting the crucible filled with the steel materials into a vertical tube type silicon-molybdenum resistance furnace;
melting in a high-temperature tube furnace: setting a temperature-raising program to carry out temperature raising under the protection of argon, wherein the flow of the argon is set to be 0.4m3Heating the steel material to 1600 ℃ in a high-temperature tube furnace to completely melt the steel material (completely melt) to obtain a molten material;
adding tellurium: adding tellurium powder into the melting material, stirring by using a quartz glass tube to ensure uniform distribution, and carrying out heat preservation treatment at 1600 ℃ for 15min to obtain the tellurium treatment melting material.
Sampling: and cooling the tellurium treatment melting material in a furnace cooling mode (furnace cooling) to 200 ℃, and then cooling the melting material to room temperature by water to obtain the free-cutting corrosion-resistant steel.
The invention will be further illustrated by way of example, but the scope of protection is not limited to these examples.
Example 1
In this embodiment, the prepared free-cutting corrosion-resistant steel comprises the following components in percentage by mass: c, 0.02%; 0.45 percent of Si; 1.2 percent of Mn; s, 0.26%; p, 0.02%; 1.6 percent of Mo; 19.5 percent of Cr; ca, 0.05%; 0.01 percent of Mg; 0.03 percent of Al; 0.02% of Te; the balance of Fe and inevitable impurities; wherein ω [ Mn ]/ω [ S ] =4.62, and ω [ Te ]/ω [ S ] = 0.077.
In this embodiment, a vertical tube-type silicon-molybdenum resistance furnace (high-temperature tube furnace) is used for smelting, and the specific operation flow is as follows: burdening → melting in a high-temperature tube furnace → adding tellurium → sampling, which specifically comprises the following processes:
preparing materials: cutting the finished wire of the free-cutting steel into free-cutting steel blocks with the length of 50mm by using a cutting machine, weighing 100g of free-cutting steel block samples, and putting the samples into a crucible (MgO crucible); weighing 33g of ferrochrome mixed material, weighing 12.5g of slag, adding 12.5g of slag and 33g of ferrochrome mixed material into a crucible, and uniformly mixing to obtain steel material; the free-cutting steel comprises the following components in percentage by mass: c, 0.028%; 0.1% of Si; 1.6 percent of Mn; s, 0.35 percent; p, 0.03%; 2.2 percent of Mo; the balance of Fe and inevitable impurities; the slag comprises the following components in percentage by mass: CaF2，55%；Al2O340%; 5% of MgO; the ferrochrome mixed material comprises the following components in percentage by mass: 78% of Cr; si, 1.5%; 20.5 percent of Fe; the mass ratio of the consumption of the free-cutting steel to the consumption of the ferrochrome mixed material is 3: 1; and the mass ratio of the free-cutting steel to the slag charge is 100: 12.5.
Melting in a high-temperature tube furnace: setting a temperature-raising program to carry out temperature raising under the protection of argon, wherein the flow of the argon is set to be 0.4m3Heating the steel material in a high-temperature tube furnace to 1600 ℃ to completely melt the steel material to obtain a molten material; the set temperature-raising program is as follows: the heating rate is 10 ℃/min, the temperature is kept for 2min when the temperature is raised from the room temperature to 100 ℃, the temperature is kept for 2min when the temperature is continuously raised to 600 ℃, and the temperature is continuously raised to 1600 ℃ so that the steel material is completely melted.
Adding tellurium: adding tellurium powder into the molten material, stirring by using a quartz glass tube to ensure uniform distribution of the tellurium powder, and then carrying out heat preservation treatment at 1600 ℃ for 15min to obtain tellurium-treated molten material; the addition of the tellurium powder is 0.022% of the mass of the molten material.
Sampling: cooling the tellurium treatment melt in a furnace cooling mode (furnace cooling) to 200 ℃ and then cooling the tellurium treatment melt to room temperature; in the process of furnace cooling, the flow of the introduced argon is set to be 0.2 m3And h, setting the cooling rate to be 10 ℃/min, and finishing furnace cooling after cooling to 200 ℃.
Comparative example 1
In this comparative example, the produced free-cutting corrosion-resistant steel comprises the following components in percentage by mass: c, 0.02%; 0.45 percent of Si; 1.2 percent of Mn; s, 0.26%; p, 0.02%; 1.6 percent of Mo; 8 percent of Cr; 0.02% of Te; ca, 0.05%; 0.01 percent of Mg; 0.03 percent of Al; the balance of Fe and inevitable impurities; wherein ω [ Mn ]/ω [ S ] =4.62, and ω [ Te ]/ω [ S ] = 0.077.
In the comparative example, a vertical tube type silicon-molybdenum resistance furnace (high-temperature tube furnace) is adopted for smelting, and the specific operation flow is as follows: burdening → melting in a high-temperature tube furnace → adding tellurium → sampling, which specifically comprises the following processes:
preparing materials: cutting the finished wire of the free-cutting steel into free-cutting steel blocks with the length of 50mm by using a cutting machine, weighing 100g of free-cutting steel block samples, and putting the samples into a crucible (MgO crucible); weighing 12.5g of ferrochrome mixed material, weighing 12.5g of slag, adding 12.5g of slag and 12.5g of ferrochrome mixed material into a crucible, and uniformly mixing to obtain steel material; the free-cutting steel comprises the following components in percentage by mass: c, 0.025%; 0.12% of Si; 1.4 percent of Mn; s, 0.33%; p, 0.04%; 2% of Mo; the balance of Fe and inevitable impurities; the slag comprises the following components in percentage by mass: CaF2，55%；Al2O340%; 5% of MgO; the ferrochrome mixed material comprises the following components in percentage by mass: 72 percent of Cr; si, 3.8%; 24.2 percent of Fe; the mass ratio of the consumption of the free-cutting steel to the consumption of the ferrochrome mixed material is 8: 1; and the mass ratio of the free-cutting steel to the slag charge is 100: 12.5.
Melting in a high-temperature tube furnace: setting a temperature-raising program to carry out temperature raising under the protection of argon, wherein the flow of the argon is set to be 0.4m3Heating the steel material in a high-temperature tube furnace to 1600 ℃ to completely melt the steel material to obtain a molten material; the set temperature-raising program is as follows: the heating rate is 10 ℃/min, the temperature is kept for 2min when the temperature is raised from the room temperature to 100 ℃, the temperature is kept for 2min when the temperature is continuously raised to 600 ℃, and the temperature is continuously raised to 1600 ℃ so that the steel material is completely melted.
Adding tellurium: adding tellurium powder into the molten material, stirring by using a quartz glass tube to ensure uniform distribution of the tellurium powder, and then carrying out heat preservation treatment at 1600 ℃ for 15min to obtain tellurium-treated molten material; the addition of the tellurium powder is 0.022% of the mass of the molten material.
Sampling: cooling the tellurium treatment melt in a furnace cooling mode (furnace cooling) to 200 ℃ and then cooling the tellurium treatment melt to room temperature; in the process of furnace cooling, the flow of the introduced argon is set to be 0.2 m3And h, setting the cooling rate to be 10 ℃/min, and finishing furnace cooling after cooling to 200 ℃.
And (3) comparative experiment analysis:
compared with the embodiment 1, the content of the chromium element in the comparative example 1 is far lower than that in the embodiment 1, the chromium element is taken as the most key element in the corrosion-resistant steel and is an important influence factor for improving the corrosion resistance, and due to the deficiency of the chromium element, pitting corrosion is easily generated at the manganese sulfide rich part of the free-cutting phase, so that the corrosion resistance of the steel is reduced.
Example 2
In this embodiment, the prepared free-cutting corrosion-resistant steel comprises the following components in percentage by mass: c, 0.021%; si, 0.46%; 1.2 percent of Mn; s, 0.26%; p, 0.02%; 1.6 percent of Mo; 19.5 percent of Cr; ca, 0.05%; 0.01 percent of Mg; 0.03 percent of Al; 0.02% of Te; the balance of Fe and inevitable impurities; wherein ω [ Mn ]/ω [ S ] =4.62, and ω [ Te ]/ω [ S ] = 0.077.
In this embodiment, a vertical tube-type silicon-molybdenum resistance furnace (high-temperature tube furnace) is used for smelting, and the specific operation flow is as follows: burdening → melting in a high-temperature tube furnace → adding tellurium → sampling, which specifically comprises the following processes:
preparing materials: cutting the finished wire of the free-cutting steel into free-cutting steel blocks with the length of 50mm by using a cutting machine, weighing 100g of free-cutting steel block samples, and putting the samples into a crucible (MgO crucible); weighing 33g of ferrochrome mixed material, weighing 12.5g of slag, adding 12.5g of slag and 33g of ferrochrome mixed material into a crucible, and uniformly mixing to obtain steel material; the free-cutting steel comprises the following components in percentage by mass: c, 0.028%; 0.1% of Si; 1.6 percent of Mn; s, 0.35 percent; p, 0.03%; 2.2 percent of Mo; the balance of Fe and inevitable impurities; the slag comprises the following components in percentage by mass: CaF2，55%；Al2O3，40%；5% of MgO; the ferrochrome mixed material comprises the following components in percentage by mass: 78% of Cr; si, 1.5%; 20.5 percent of Fe; the mass ratio of the consumption of the free-cutting steel to the consumption of the ferrochrome mixed material is 3: 1; and the mass ratio of the free-cutting steel to the slag charge is 100: 12.5.
Melting in a high-temperature tube furnace: setting a temperature-raising program to carry out temperature raising under the protection of argon, wherein the flow of the argon is set to be 0.4m3Heating the steel material in a high-temperature tube furnace to 1600 ℃ to completely melt the steel material to obtain a molten material; the set temperature-raising program is as follows: the heating rate is 10 ℃/min, the temperature is kept for 2min when the temperature is raised from the room temperature to 100 ℃, the temperature is kept for 2min when the temperature is continuously raised to 600 ℃, and the temperature is continuously raised to 1600 ℃ so that the steel material is completely melted.
Adding tellurium: adding tellurium powder into the molten material, stirring by using a quartz glass tube to ensure uniform distribution of the tellurium powder, and then carrying out heat preservation treatment at 1600 ℃ for 15min to obtain tellurium-treated molten material; the addition of the tellurium powder is 0.022% of the mass of the molten material.
Sampling: cooling the tellurium treatment melt in a furnace cooling mode (furnace cooling) to 200 ℃ and then cooling the tellurium treatment melt to room temperature; in the process of furnace cooling, the flow of the introduced argon is set to be 0.2 m3And h, setting the cooling rate to be 10 ℃/min, and finishing furnace cooling after cooling to 200 ℃.
Comparative example 2
In this comparative example, the produced free-cutting corrosion-resistant steel comprises the following components in percentage by mass: c, 0.021%; si, 0.46%; 1.2 percent of Mn; s, 0.26%; p, 0.02%; 1.6 percent of Mo; 30% of Cr; ca, 0.05%; 0.01 percent of Mg; 0.03 percent of Al; 0.02% of Te; the balance of Fe and inevitable impurities; wherein ω [ Mn ]/ω [ S ] =4.62, and ω [ Te ]/ω [ S ] = 0.077.
In the comparative example, a vertical tube type silicon-molybdenum resistance furnace (high-temperature tube furnace) is adopted for smelting, and the specific operation flow is as follows: burdening → melting in a high-temperature tube furnace → adding tellurium → sampling, which specifically comprises the following processes:
preparing materials: cutting the finished wire of the free-cutting steel into free-cutting steel blocks with the length of 50mm by using a cutting machine, weighing 100g of free-cutting steel block samples, and putting the samples into a crucible (MgO crucible); weighing ferrochromeMixing 60g of materials, weighing 12.5g of slag, adding 12.5g of slag and 60g of ferrochrome mixed materials into a crucible, and uniformly mixing to obtain a steel material; the free-cutting steel comprises the following components in percentage by mass: c, 0.035%; 0.12% of Si; 1.6 percent of Mn; s, 0.38%; p, 0.04%; 2.2 percent of Mo; the balance of Fe and inevitable impurities; the slag comprises the following components in percentage by mass: CaF2，55%；Al2O340%; 5% of MgO; the ferrochrome mixed material comprises the following components in percentage by mass: 80% of Cr; si, 1.1%; 18.9 percent of Fe; the mass ratio of the consumption of the free-cutting steel to the consumption of the ferrochrome mixed material is 5: 3; and the mass ratio of the free-cutting steel to the slag charge is 100: 12.5.
Melting in a high-temperature tube furnace: setting a temperature-raising program to carry out temperature raising under the protection of argon, wherein the flow of the argon is set to be 0.4m3Heating the steel material in a high-temperature tube furnace to 1600 ℃ to completely melt the steel material to obtain a molten material; the set temperature-raising program is as follows: the heating rate is 10 ℃/min, the temperature is kept for 2min when the temperature is raised from the room temperature to 100 ℃, the temperature is kept for 2min when the temperature is continuously raised to 600 ℃, and the temperature is continuously raised to 1600 ℃ so that the steel material is completely melted.
Adding tellurium: adding tellurium powder into the molten material, stirring by using a quartz glass tube to ensure uniform distribution of the tellurium powder, and then carrying out heat preservation treatment at 1600 ℃ for 15min to obtain tellurium-treated molten material; the addition of the tellurium powder is 0.022% of the mass of the molten material.
Sampling: cooling the tellurium treatment melt in a furnace cooling mode (furnace cooling) to 200 ℃ and then cooling the tellurium treatment melt to room temperature; in the process of furnace cooling, the flow of the introduced argon is set to be 0.2 m3And h, setting the cooling rate to be 10 ℃/min, and finishing furnace cooling after cooling to 200 ℃.
And (3) comparative experiment analysis:
comparative example 2 compared with example 2, the composition of chromium element in the steel of comparative example 2 is as high as 30%, and chromium element is the most important element in corrosion-resistant steel, but since chromium element has the effect of improving the strength of steel, excessively high content of chromium is not favorable for improving the free-cutting performance.
Example 3
In this embodiment, the prepared free-cutting corrosion-resistant steel comprises the following components in percentage by mass: c, 0.019%; 0.45 percent of Si; 1.2 percent of Mn; s, 0.26%; p, 0.02%; 1.61 percent of Mo; 19.5 percent of Cr; ca, 0.05%; 0.01 percent of Mg; 0.03 percent of Al; 0.02% of Te; the balance of Fe and inevitable impurities; wherein ω [ Mn ]/ω [ S ] =4.62, and ω [ Te ]/ω [ S ] = 0.077.
In this embodiment, a vertical tube-type silicon-molybdenum resistance furnace (high-temperature tube furnace) is used for smelting, and the specific operation flow is as follows: burdening → melting in a high-temperature tube furnace → adding tellurium → sampling, which specifically comprises the following processes:
preparing materials: cutting the finished wire of the free-cutting steel into free-cutting steel blocks with the length of 50mm by using a cutting machine, weighing 100g of free-cutting steel block samples, and putting the samples into a crucible (MgO crucible); weighing 33g of ferrochrome mixed material, weighing 12.5g of slag, adding 12.5g of slag and 33g of ferrochrome mixed material into a crucible, and uniformly mixing to obtain steel material; the free-cutting steel comprises the following components in percentage by mass: c, 0.028%; 0.1% of Si; 1.6 percent of Mn; s, 0.35 percent; p, 0.03%; 2.2 percent of Mo; the balance of Fe and inevitable impurities; the slag comprises the following components in percentage by mass: CaF2，55%；Al2O340%; 5% of MgO; the ferrochrome mixed material comprises the following components in percentage by mass: 78% of Cr; si, 1.5%; 20.5 percent of Fe; the mass ratio of the consumption of the free-cutting steel to the consumption of the ferrochrome mixed material is 3: 1; and the mass ratio of the free-cutting steel to the slag charge is 100: 12.5.
Melting in a high-temperature tube furnace: setting a temperature-raising program to carry out temperature raising under the protection of argon, wherein the flow of the argon is set to be 0.4m3Heating the steel material in a high-temperature tube furnace to 1600 ℃ to completely melt the steel material to obtain a molten material; the set temperature-raising program is as follows: the heating rate is 10 ℃/min, the temperature is kept for 2min when the temperature is raised from the room temperature to 100 ℃, the temperature is kept for 2min when the temperature is continuously raised to 600 ℃, and the temperature is continuously raised to 1600 ℃ so that the steel material is completely melted.
Adding tellurium: adding tellurium powder into the molten material, stirring by using a quartz glass tube to ensure uniform distribution of the tellurium powder, and then carrying out heat preservation treatment at 1600 ℃ for 15min to obtain tellurium-treated molten material; the addition of the tellurium powder is 0.022% of the mass of the molten material.
Sampling: cooling the tellurium treatment melt in a furnace cooling mode (furnace cooling) to 200 ℃ and then cooling the tellurium treatment melt to room temperature; in the process of furnace cooling, the flow of the introduced argon is set to be 0.2 m3And h, setting the cooling rate to be 10 ℃/min, and finishing furnace cooling after cooling to 200 ℃.
Comparative example 3
In this comparative example, the produced free-cutting corrosion-resistant steel comprises the following components in percentage by mass: c, 0.019%; 0.45 percent of Si; 1.2 percent of Mn; s, 0.26%; p, 0.02%; 1.61 percent of Mo; 19.5 percent of Cr; ca, 0.05%; 0.01 percent of Mg; 0.03 percent of Al; 0.002% of Te; the balance of Fe and inevitable impurities; wherein ω [ Mn ]/ω [ S ] =4.62, and ω [ Te ]/ω [ S ] = 0.077.
In the comparative example, a vertical tube type silicon-molybdenum resistance furnace (high-temperature tube furnace) is adopted for smelting, and the specific operation flow is as follows: burdening → melting in a high-temperature tube furnace → adding tellurium → sampling, which specifically comprises the following processes:
preparing materials: cutting the finished wire of the free-cutting steel into free-cutting steel blocks with the length of 50mm by using a cutting machine, weighing 100g of free-cutting steel block samples, and putting the samples into a crucible (MgO crucible); weighing 33g of ferrochrome mixed material, weighing 12.5g of slag, adding 12.5g of slag and 33g of ferrochrome mixed material into a crucible, and uniformly mixing to obtain steel material; the free-cutting steel comprises the following components in percentage by mass: c, 0.028%; 0.1% of Si; 1.6 percent of Mn; s, 0.35 percent; p, 0.03%; 2.2 percent of Mo; the balance of Fe and inevitable impurities; the slag comprises the following components in percentage by mass: CaF2，55%；Al2O340%; 5% of MgO; the ferrochrome mixed material comprises the following components in percentage by mass: 78% of Cr; si, 1.5%; 20.5 percent of Fe; the mass ratio of the consumption of the free-cutting steel to the consumption of the ferrochrome mixed material is 3: 1; and the mass ratio of the free-cutting steel to the slag charge is 100: 12.5.
Melting in a high-temperature tube furnace: setting a temperature-raising program to carry out temperature raising under the protection of argon, wherein the flow of the argon is set to be 0.4m3H, heating the steel material in a high-temperature tube furnace to 1600 ℃ to finish the steel materialFully melting to obtain a molten material; the set temperature-raising program is as follows: the heating rate is 10 ℃/min, the temperature is kept for 2min when the temperature is raised from the room temperature to 100 ℃, the temperature is kept for 2min when the temperature is continuously raised to 600 ℃, and the temperature is continuously raised to 1600 ℃ so that the steel material is completely melted.
Adding tellurium: adding tellurium powder into the molten material, stirring by using a quartz glass tube to ensure uniform distribution of the tellurium powder, and then carrying out heat preservation treatment at 1600 ℃ for 15min to obtain tellurium-treated molten material; the addition of the tellurium powder is 0.0025% of the mass of the molten material.
Sampling: cooling the tellurium treatment melt in a furnace cooling mode (furnace cooling) to 200 ℃ and then cooling the tellurium treatment melt to room temperature; in the process of furnace cooling, the flow of the introduced argon is set to be 0.2 m3And h, setting the cooling rate to be 10 ℃/min, and finishing furnace cooling after cooling to 200 ℃.
And (3) comparative experiment analysis:
compared with the example 3, the tellurium added in the comparative example 3 is one tenth of that of the example 3, the difference is one order of magnitude, namely the tellurium treatment of the comparative example 3 is insufficient, the tellurium treatment is not basically carried out, although the smelting cost of the comparative example 3 is greatly reduced, the control on the shape of the inclusion is not ideal, the distribution of the corrosion resisting element chromium and the free-cutting phase manganese sulfide is not uniform, and the free-cutting performance and the corrosion resisting performance cannot be balanced and improved.
The performance indexes of examples 1 to 3 and comparative examples 1 to 3 measured by the present invention are shown in table 1. The cutting performance measurement indexes mainly comprise the service life of a cutter, the chip and chip breaking performance and the roughness of the surface of a workpiece; the service life of the tool is the cutting operation time until a new tool is scrapped or worn to a predetermined extent, and in the present invention, the tool is scrapped when the flank wear width VB =0.3mm of the tool is considered, and the longer the corresponding cutting time is, the better the free-cutting performance is. For the corrosion resistance test, the self-corrosion potential and the self-corrosion current of the steel sample are measured, and the larger the self-corrosion potential is, the smaller the self-corrosion current is, and the stronger the corrosion resistance of the sample is. In the present invention, the corrosion resistance and the machinability of each example, each comparative example and the finished free-cutting steel block were measured as shown in table 1, the flank wear amount of the tool and each comparative example was measured as a graph of the cutting time, as shown in fig. 2, and the cutting time corresponding to each example and each comparative example when the flank wear width VB =0.3mm was obtained from fig. 2 is shown in table 1.
Table 1: the performance indexes of examples 1 to 3 and comparative examples 1 to 3.
The results in table 1 show that the corrosion resistance of the embodiment of the invention is superior to that of the comparative example, and the improvement range is about 10%; the cutting performance of the embodiment 1 of the invention is lower than that of the comparative example 1, because the chromium element content of the comparative example 1 is low, the strength of steel is lower, the improvement of the cutting performance is facilitated, but the corrosion resistance of the comparative example 1 is poorer; the cutting time of the embodiment 3 is 25min, and the cutting time of the comparative example 3 is 21min, because the tellurium treatment of the comparative example 3 is insufficient, the length-width ratio of manganese sulfide is too large, the contradiction that chromium element and manganese sulfide are difficult to coexist cannot be effectively relieved, and the free-cutting performance of the free-cutting steel is obviously reduced due to the addition of chromium. The results in table 1 show that the free-cutting corrosion-resistant steel prepared by the embodiment of the invention has the best component proportion, combines the contradictory free-cutting performance and corrosion resistance, improves the corrosion resistance of the free-cutting steel to the maximum extent, reduces the free-cutting performance of the original finished free-cutting steel to the minimum extent, widens the application range of the free-cutting steel, and meets the production requirements of the current automobile industry; for example, in the field of automobiles, the adopted steel is required to have good corrosion resistance in places which are easy to cut and process and are contacted with the outside or easy to scratch, in the field of automobiles, the production of bolts, nuts, brake parts and the like is indispensable in both the easy-cutting performance and the corrosion resistance, and the easy-cutting corrosion-resistant steel prepared by the method is particularly suitable for the production requirements of the current automobile industry.
The invention also tests the morphology (SEM image) of the inclusions in the free-cutting corrosion-resistant steels prepared in examples 1-3 and comparative examples 1-3 and the energy spectrum of each element in the inclusions, and the results of example 1, comparative example 1, example 2, comparative example 2, example 3 and comparative example 3 are shown in FIGS. 3-8 respectively. Comparing example 1 with comparative example 1, comparative example 1 has a low chromium content, corresponding to insufficient chromium wrapping of the outermost layer of inclusions in fig. 4, and although the strength reduction is advantageous for improving the free-cutting property, the corrosion resistance is seriously affected. Comparing example 2 with comparative example 2, the comparative example 2 has an excessive chromium content, which reflects on the inclusion in fig. 6, and thus causes concentration of chromium elements and further causes segregation of tellurium elements, which has a bad influence on both free-cutting performance and corrosion resistance; compared with the comparative example 3, in the comparative example 3, tellurium treatment is insufficient, so that the inclusion in the figure 8 is mostly in a strip shape, the contradiction that chromium element and manganese sulfide are difficult to coexist cannot be effectively relieved, and the free-cutting performance is obviously reduced due to the addition of chromium.
The invention has not been described in detail and is in part known to those of skill in the art.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (9)
1. A method for preparing free-cutting corrosion-resistant steel, which is characterized by comprising the following steps:
(1) uniformly mixing the free-cutting steel, the ferrochrome mixed material and the slag to obtain a steel material; the free-cutting steel comprises the following components in percentage by mass: c, 0.02% -0.04%; 0.05% -0.15% of Si; 1.4% -1.6% of Mn; 0.32% -0.38% of S; 0.03% -0.06% of P; 2% -2.2% of Mo; the balance of Fe and inevitable impurities; the slag comprises the following components in percentage by mass: CaF2，50%~60%；Al2O335% -45%; 3% -8% of MgO; the ferrochrome mixed material comprises the following components in percentage by mass: 70% -80% of Cr; 1% -4% of Si; the balance being Fe;
(2) completely melting the steel material at high temperature to obtain a molten material;
(3) adding tellurium into the molten material, uniformly mixing, and then carrying out heat preservation treatment to obtain a tellurium-treated molten material; the addition amount of the tellurium is 0.014% -0.033% of the mass of the molten material;
(4) cooling the tellurium treatment melting stock to obtain the free-cutting corrosion-resistant steel; the free-cutting corrosion-resistant steel comprises the following components in percentage by mass: c, 0.015% -0.024%; 0.4 to 0.5 percent of Si; 1.2 to 1.3 percent of Mn; s, 0.24 to 0.3 percent; 0.02 to 0.03 percent of P; 1.5 to 1.75 percent of Mo; 19 to 20 percent of Cr; 0.03% -0.08% of Ca; 0.01% -0.02% of Mg; 0.02% -0.05% of Al; 0.012% -0.03% of Te; the balance being Fe and unavoidable impurities.
2. The production method according to claim 1, wherein in the free-cutting corrosion-resistant steel:
the mass ratio of Mn to S is 4-5.42; and/or
The mass ratio of Te to S is 0.04-0.125.
3. The method of claim 1, wherein:
the free-cutting steel comprises the following components in percentage by mass: c, 0.028%; 0.1% of Si; 1.6 percent of Mn; s, 0.35 percent; p, 0.03%; 2.2 percent of Mo; the balance being Fe and unavoidable impurities.
4. The method of claim 1, wherein:
the slag comprises the following components in percentage by mass: CaF2，55%；Al2O3，40%；MgO，5%。
5. The method of claim 1, wherein:
the ferrochrome mixed material comprises the following components in percentage by mass: 78% of Cr; si, 1.5%; 20.5 percent of Fe.
6. The method of claim 1, wherein:
the mass ratio of the free-cutting steel to the ferrochrome mixed material is (2.8-3.2): 1; and/or
The mass ratio of the free-cutting steel to the slag charge is 100: (11-13).
7. The method of claim 1, wherein:
and (4) performing the steps (2) to (4) in a vertical tube type silicon-molybdenum resistance furnace.
8. The method of claim 1, wherein:
in the step (2), completely melting the steel material at 1600 ℃ to obtain a molten material;
in the step (3), the heat preservation treatment time is 10-20 min; and/or
In the step (4), the cooling mode is as follows: firstly, cooling to 200-300 ℃ along with the furnace, and then cooling to room temperature by adopting a water cooling mode.
9. The method of claim 1, wherein:
introducing argon protective gas in the process of the step (2) and the step (3), wherein the flow of the introduced argon is 0.3-0.4 m3/h。
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| CN113913704B (en) * | 2021-12-13 | 2022-03-11 | 北京科技大学 | Tellurium-sulfur co-processed aluminum deoxidized steel and preparation method and application thereof |
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