CN113564470A - 1700MPa heat-resistant steel for agricultural machinery and manufacturing method thereof - Google Patents
1700MPa heat-resistant steel for agricultural machinery and manufacturing method thereof Download PDFInfo
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- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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- C23C24/00—Coating starting from inorganic powder
- C23C24/08—Coating starting from inorganic powder by application of heat or pressure and heat
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- C23C24/087—Coating with metal alloys or metal elements only
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
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- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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- C21D2211/009—Pearlite
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Abstract
1700MPa heat-resistant steel for agricultural machinery and a manufacturing method thereof, wherein the steel comprises the following chemical components in percentage by weight: 0.70 to 1.1 percent of C, less than or equal to 0.1 percent of Si, 0.4 to 1.5 percent of Mn0.06 percent of Al, 0.0005 to 0.05 percent of Ca0.001 to 0.5 percent of Re0.001 to 0.5 percent of Sn0.001 to 0.5 percent of Mg0.0008 to 0.05 percent of Ca/S, more than or equal to 0.2 percent of Ca/Mg, more than or equal to 1 percent of Ca/Re, less than or equal to 0.020 percent of P and less than or equal to 0.015 percent of S; the balance being Fe and unavoidable impurities. The agricultural machine steel hot rolled plate produced by the invention has high surface quality, the hardness of the matrix after heat treatment is more than 55HRC, the tensile strength is more than 1700MPa, the hardness of the surface spray-welded spherical chromium-copper alloy granular powder is more than 65HRC, and the surface wear resistance, the heat resistance and the corrosion resistance are excellent.
Description
Technical Field
The invention relates to the field of steel material preparation, in particular to 1700MPa heat-resistant agricultural steel and a manufacturing method thereof.
Background
The development and level of agricultural machinery equipment are related to the important safety of national food. The agricultural machine fittings are continuously updated with steel. At present, two types of steel for high-end soil-entering agricultural machine accessories are mainly used, one type is oil quenching of 65Mn steel, the hardness of a finished product is 42-45HRC, the strength is 1200MPa, the wear resistance is general, the environmental pollution is serious, the strength of a high-carbon hot-rolled plate is high, the hardness is high, the yield ratio is generally more than 80%, the processing and forming difficulty is high, the steel is easy to crack in heat treatment, and the heat resistance and the corrosion resistance are poor; the other one is medium carbon 30MnB5 agricultural machinery steel imported from abroad, the finished product has the hardness of 46-48HRC after tempering, the strength of about 1300MPa, the yield ratio generally reaches more than 70 percent, the cracking is easy to occur in heat treatment, the plate shape is not good, and the heat resistance and the corrosion resistance are not ideal. The wear resistance of the parts processed by the agricultural steel is reduced when the temperature is raised by the abrasion in the soil-entering work, and at present, no steel for agricultural parts with the hardness of more than 52HRC, the strength of more than 1500MPa and excellent surface heat resistance, wear resistance and corrosion resistance exists.
The patent document CN201510174384.3, a method for producing thin tool steel by CSP line without spheroidizing annealing, describes a method for producing thin tool steel plate with thickness of 1-2.5mm, which can not meet the use requirement of thick tool steel plate; the production process of reducing the hardness of the tempered sorbite by adopting low-temperature rolling, quick cooling to the temperature near the martensite transformation temperature for low-temperature coiling and tempering is adopted, on one hand, the requirement on the capability of a coiling machine is extremely high, on the other hand, the martensite transformation occurs in the coiling process, the martensite brittleness is extremely high, the strip is easily broken, and the high-temperature tempering treatment at the temperature of 550-700 ℃ is carried out after coiling, so that the cost is high. The process controls the decarburizing depth to not more than 1% of the plate thickness.
A method for manufacturing an annealing-free medium-high carbon steel plate CN201310076240.5 and a method for producing an annealing-free hot-rolled S45C plate CN201110411594.1 adopt two-phase region or ferrite region low-temperature large-pressure rolling, high-temperature coiling and stacking to obtain 60% ferrite and partial spheroidized pearlite, and the hardness of the steel plate is reduced to 80-85HRB through softening. The steel plate obtained by the process has large ferrite amount and large blocks, can be used only by quenching and tempering, has low hardness after heat treatment, and cannot meet the use requirements of high-end tool steel.
Patent document No. 201510687941.1 discloses an alloy tool steel and a production method thereof, relating to a medium carbon tool steel, which comprises: 0.5 percent of C, 0.2 percent of Si, 0.5 percent of Mn, 5.0 percent of Cr, 2.3 percent of Mo, 0.5 percent of V, less than or equal to 0.003 percent of S and less than or equal to 0.02 percent of P, more alloys such as Cr, Mo, V and the like are added into the alloy tool steel, electroslag remelting and casting ingot casting are needed for smelting, the yield is low, a plurality of heat treatment procedures such as softening annealing, spheroidizing annealing, quenching, tempering and the like are needed, the cost is high, and the alloy tool steel is not suitable for processing and manufacturing various tools with complex shapes.
The steel plate described in the patent document "a household gardening tool steel 55MnB and a preparation method thereof" filed as CN104630618A has a thickness of only 3-5 mm, has a limited application range, and cannot meet the requirements of thinner specifications or thicker specifications. This patent uses boron-containing composition design, but does not emphasize control of oxygen and nitrogen, and boron in molten steel is easily combined with oxygen and nitrogen to form a compound, which not only weakens the hardenability effect of solid solution boron, but also easily forms a network in the compound phase of B, N at the grain boundary to generate boron brittleness phenomenon, which causes a defect of high brittleness and the like. The boron-containing steel has large heat deformation resistance, the hot rolled plate shape is difficult to control, the hot rolled plate shape is poor, the subsequent processing heat treatment process is difficult to level again, and the quality of a finished product is seriously influenced. On the other hand, the yield strength of the steel plate described in the patent is 390 MPa-470 MPa, the tensile strength is 750-820 MPa, the elongation is 17-26%, the strength is still high, and the processing is still difficult to achieve. And the described production process adopts high-temperature coiling at 750 ℃, the surface of the steel plate is seriously decarbonized, the surface iron scale is thick, the polishing amount of a user is large, and the production efficiency is influenced.
The steel plate obtained by ZL201610727654.3 patent document 'a gardening tool steel with excellent processability and a production method thereof' has the structure of coarse lamellar pearlite + spheroidized pearlite, a surface decarburized layer of more than 0.01mm, poor surface quality, easy cracking during bending, high cost for adding Cr \ Ni \ Cu, 50HRC quenching hardness, strength of less than 1500MPa and lower strength and hardness after tempering.
A hot-rolled strip steel rake blade suitable for water quenching and a manufacturing method ZL 201410250576.3 thereof, a hot-rolled strip steel for the rake blade and a production method and a rake blade treatment method ZL 201410253770.7 thereof, a steel for the rake blade, a production method and a rake blade treatment method 201410253772.6 thereof, and a strip steel for the rake blade and a production method and a rake blade heat treatment method ZL 201410250902.0 thereof are disclosed, wherein the four patent documents adopt a design of medium-carbon boron-containing components, and meanwhile, Cr \ Ti \ V \ Nb is added, so that the cost is high, the boron activity is particularly difficult to control, the proportion of Ti \ V \ Nb and N needs to be controlled, the control precision requirement is high, the smelting difficulty is large, the plate shape is poor, the flatness after heat treatment is poor, the coiling temperature is high, and the surface oxidation and decarburization are serious.
The steel grade and the production method mentioned in the prior art do not refer to heat resistance and corrosion resistance technologies, and are not suitable for processing high-end heat-resistant and corrosion-resistant agricultural machinery accessories. In order to adapt to the development of times and meet the updating and upgrading requirements of agricultural machine accessories, the development of steel for the agricultural machine accessories, which has the hardness of 55HRC, the strength of more than 1500MPa and excellent heat resistance and corrosion resistance, is urgently needed.
Disclosure of Invention
The invention aims to provide 1700MPa heat-resistant agricultural steel and a manufacturing method thereof, the hot rolled plate structure of the agricultural steel produced by the invention is coarse lamellar pearlite with a lamellar spacing of more than 0.5 mu m, the diameter of a pearlite colony is less than 10 mu m, the yield ratio is less than 60%, the surface has no grain boundary oxide layer, the matrix hardness is more than 55HRC under the high-temperature working condition after heat treatment, and the tensile strength is more than 1700 MPa. The produced agricultural machinery parts have the surface hardness of more than 65HRC and excellent wear resistance, heat resistance and corrosion resistance.
In order to achieve the purpose, the invention adopts the following technical scheme:
1700MPa heat-resistant steel for agricultural machinery, which comprises the following chemical components in percentage by weight: 0.70 to 1.1 percent of C, less than or equal to 0.05 percent of Si, 0.4 to 1.5 percent of Mn, less than or equal to 0.06 percent of Al, 0.0005 to 0.05 percent of Ca, 0.05 to 0.5 percent of Re, 0.1 to 1.0 percent of Sn, 0.0008 to 0.05 percent of Mg0.0008, more than or equal to 0.2 percent of Ca/S, more than or equal to 1 percent of Ca/Mg, more than or equal to 0.05 percent of Ca/Re, less than or equal to 0.020 percent of P and less than or equal to 0.015 percent of S; the balance being Fe and unavoidable impurities.
The mechanism of action of each alloy component of the structural steel of the present invention is explained in detail below:
c is a main solid solution strengthening element in steel, and in the invention, sufficient C is required to be combined with Sn, Re and the like to improve the hardness, if the C content is lower than 0.70 percent, the hardness of a steel plate is difficult to ensure, and if the C content is higher than 1.1 percent, the strength of a hot rolled plate is too high, the toughness and plasticity of the steel are deteriorated, the yield ratio is influenced, and the formability is poor. Therefore, the C content is controlled to be 0.70-1.1%.
Mn is relatively cheap, is a good deoxidizer and desulfurizer, and is an essential element for ensuring the strength and toughness of steel. The manganese and the iron can be infinitely dissolved to form a solid solution, so that the hardness and the strength are improved, and the influence on the plasticity is relatively small. Mn and S are combined to form MnS, so that the influence of hot cracks caused by FeS formed at the grain boundary on the hot formability of the tool steel is avoided. Meanwhile, Mn is also a good deoxidizer and increases hardenability. The steel has low Mn content, cannot meet the requirement of high strength and hardness, and has over high Mn content, serious segregation, influence on welding performance and formability, and increase in production cost, so that the Mn content is controlled to be 0.4-1.5% by comprehensively considering factors such as cost, performance requirements and the like.
Si is one of common elements in steel and is used as a reducing agent and a deoxidizing agent in the steelmaking process, and the Si in a solid solution form can improve the yield strength and the ductile-brittle transition temperature, and is 0.17-0.37% in common agricultural steel. The method does not add Si, and controls the residual Si in the steel to be as little as possible. According to the invention, the surface of the cutting tool steel can be subjected to decarburization oxidation by Si, a loose oxidation layer is formed, and microcrack defects such as grain boundary oxidation exist in the oxidation layer, so that the surface hardness and the fatigue performance are seriously influenced. The invention has the advantages of less than or equal to 0.05 percent of Si, low cost, avoidance of steel surface oxidation, improvement of surface quality, compactness of an alloy layer which is beneficial to spray welding and guarantee of wear resistance and corrosion resistance.
Al is used as a deoxidizing and nitrogen-fixing agent in steelmaking, so that crystal grains are refined, the aging of steel is inhibited, the toughness of the steel at low temperature is improved, and the brittle transition temperature of the steel can be particularly reduced; al can also improve the oxidation resistance of the steel and improve the corrosion resistance to hydrogen sulfide. The Al content exceeds 0.06 percent, and the Al easily forms large-particle oxide inclusion with oxygen in steel, thereby influencing the fatigue performance.
Ca is used as a microalloying element, so that crystal grains can be refined, partial desulfuration can be realized, the corrosion resistance, the wear resistance, the high temperature resistance and the low temperature resistance of the steel can be improved, and the impact toughness, the fatigue strength, the plasticity and the welding performance of the steel can be improved; the cold heading property, the shock resistance, the hardness and the contact endurance strength of the steel are improved. The invention adds calcium, changes the components, quantity and form of non-metallic inclusions, accelerates the flow of molten steel, promotes the inclusions to float sufficiently, improves the purity of steel, ensures that various non-metallic inclusions in finished steel do not exceed 1.5 grade, improves the surface smoothness of steel, eliminates the anisotropy of tissues, improves the hydrogen induced cracking resistance and the lamellar tearing resistance, and prolongs the service life of tools. The Ca inclusion denaturation has a great relation with the sulfur content, and the Ca/S ratio of the invention is more than or equal to 0.2, so that the Ca inclusion denaturation can be ensured to be sufficient. The invention can improve the yield of rare earth to more than 60 percent and the yield of Mg to more than 40 percent by adding calcium, effectively improve the utilization rate of rare earth and magnesium, and fully play the roles of improving high-temperature strength and hardness, oxidation resistance, corrosion resistance and heat resistance in steel.
The Re rare earth element can improve the oxidation resistance and corrosion resistance of the steel, so that the steel structure is compact, the high-temperature strength is improved, and the oxidation resistance effect of the RE element exceeds that of elements such as aluminum, titanium and the like. The Re can improve the fluidity of steel, improve the surface smoothness of the steel plate and improve the surface spray welding performance. Re also enables Al2O3Oxides and sulfide inclusions such as MnS become fine and dispersed spherical inclusions, so that the harmfulness of the inclusions is eliminated, and the fatigue performance is improved. The invention can improve the yield of the rare earth to more than 60 percent by enough Ca only when the Ca/Re is more than or equal to 0.05, and fully exert the effect of the rare earth on steelOxidation resistance, corrosion resistance and improved heat resistance. The rare earth of the invention enables the steel structure to be compact at high temperature, improves the high-temperature strength and improves the performance after heat treatment. Re, Mg and C in the steel generate series carbon magnesium rare earth compounds, further promote hot rolling to form a pearlite structure with the sheet spacing of more than 0.5 mu m, and have the advantages of quick diffusion of heat treatment carbon, no need of high temperature, energy conservation and consumption reduction.
Mg is a very active metal element, which has strong affinity with oxygen, nitrogen and sulfur. However, because Mg is too active, the Mg is not easy to control during smelting, and the yield is low. The invention adopts the self-created refining and Re-Mg smelting technology, strictly and accurately controls the Mg content in steel, and utilizes the combined action of Ca and Mg to generate CaO, MgO and Al2O3And CaO, MgO, MnS and other composite inclusions, and the inclusions have low melting point and are easy to solidify, float and remove in molten steel, thereby avoiding the problem of nozzle nodulation in the continuous casting process, reducing the inclusion content in the molten steel and controlling the inclusion level in the steel not to exceed 1.0 level. Enough Ca can be enough to improve the yield of Mg by more than 40 percent when the Ca/Mg is more than or equal to 1, the utilization rate of the magnesium is effectively improved, and CaO, MgO and Al are formed2O3And CaO, MgO and MnS composite inclusions, and the high-temperature strength and the hardness after heat treatment are improved. The other main function of Mg is to generate series carbon-magnesium rare earth compounds with Re and C, so that a pearlite structure with the sheet spacing of more than 0.5 mu m is formed in the hot-rolled plate, the diffusion of heat treatment carbon is fast, high temperature is not needed, and energy and consumption are saved.
Sn: the tin can improve the wear resistance and the molten steel fluidity of steel, and has good molten steel fluidity, full floating of inclusions and good steel purity. The invention improves the treatment hardness by dissolving Sn in solid solution. The method has high carbon content, the carbon is easy to segregate and gather at the solidification tail end of the dendritic crystal of the casting blank, and when the carbon segregates and gathers at the grain boundary of the surface of the steel plate, the serious surface oxidation is caused, and the grain boundary oxidation and the microcrack of the surface appear, which is the main reason for influencing the unqualified surface spray welding. On the other hand, the carbon content of the invention is high, the hot rolled plate is easy to generate liquid phase separation, and the graphite is further separated out by annealing and other heat treatments, thus influencing the service performances of bending forming, fatigue and the like. According to the invention, a certain amount of tin is added into the steel, so that the tool steel can be effectively prevented from gathering by carbon segregation, cementite and graphitized precipitation, the generation of microcracks on the surface of the steel plate is inhibited, the steel plate without surface grain boundary oxidation is obtained, and the comprehensive properties such as surface spray welding performance, strength, wear resistance and the like are improved.
The Re and Mg in solid solution are reacted with Sn and C under specific production process to form spherical tin carbide with diameter below 20nm, such as ReMgSnCM、ReSnCM、MgSnCMAnd the carbon is uniformly distributed in the steel to form nucleation particles of pearlite lamellar, so that the interval between the cementite plates in the pearlite of the coarsened hot rolled steel plate is more than 0.5 mu m, the carbon in the cementite is easy and quick to diffuse, high-temperature austenitization is not needed, the heating temperature during heat treatment is 670-750 ℃, and the energy consumption is saved. The spherical Re and Mg carbon tin compounds with the diameter of less than 20nm are more heat-resistant than common cementite, do not diffuse and decompose at 900 ℃, are still uniformly and dispersedly distributed in steel after heat treatment, improve the hardness after heat treatment, further improve the heat resistance and the wear resistance, and have the tensile strength of more than 1700MPa and the hardness of more than 55HRC under the high-temperature working condition of more than 200 ℃.
P and S are inevitable harmful impurities in steel, and the presence of P and S seriously deteriorates the toughness of steel, so that measures are taken to reduce the contents of P and S in steel as much as possible. According to the invention, the maximum P content is limited to 0.020% and the maximum S content to 0.015%. Sulfur exists in the steel in the form of FeS and MnS, and in this invention, Mn is high, MnS tends to be formed, and although the melting point is high to avoid hot embrittlement, MnS is elongated in the machine direction during machine deformation, and plasticity, toughness, and fatigue strength of the steel are significantly reduced, so Ca and Mg are added to the steel to perform inclusion deformation.
The hot rolled steel plate for the agricultural machine steel is a coarse lamellar pearlite structure, the spacing between pearlite plates is more than 0.5 mu m, and the diameter of pearlite colony is not more than 10 mu m; the structure after heat treatment is a lath-shaped martensite structure with spherical tin carbide with the diameter of less than 20nm in a dispersion distribution manner.
The yield ratio of the steel plate for the agricultural machine is less than 60%; after heat treatment, under the working condition of high temperature above 200 ℃, the matrix hardness is above 55HRC, and the tensile strength is above 1700 MPa.
The non-metallic inclusions in the steel plate for the agricultural machinery do not exceed 1.0 level; the grain boundary oxide layer of the steel plate is 0 mm; segregation does not exceed 1.5 grade.
The invention relates to a method for manufacturing 1700MPa heat-resistant agricultural steel, which is rolled by a continuous casting billet obtained by converter smelting, electric furnace refining and pouring, and comprises the following steps:
1) the smelting process comprises the following steps:
a) deoxidizing by using an Al deoxidizer, adding Ca for at least 5 minutes after the refining oxygen content is less than or equal to 0.0020%, then adding Mn, Re and Mg, and finally adding Sn alloy;
b) the argon blowing time of the tundish is 5-8 minutes, so that impurities are fully floated, and the degree of superheat of pouring is less than or equal to 25 ℃;
c) electromagnetic stirring is carried out on the continuous casting by adopting a crystallizer, and the thickness of a casting blank is 170-250 mm; the rolling reduction is 2 mm-10 mm; the electromagnetic stirring current intensity of the continuous casting crystallizer is 500A-1000A, and the electromagnetic stirring is carried out for 1 minute-3 minutes;
d) the continuous casting speed is 1.0m/min to 1.4 m/min;
2) the casting blank treatment process comprises the following steps:
a) the casting blank is inserted into a slow cooling pit for slow cooling for more than 72 hours, and a stepping heating furnace is adopted for heating before rolling the casting blank;
b) the heating furnace adopts reducing atmosphere, the temperature of the preheating section is more than 500 ℃, the temperature of the heating section is 1200-1350 ℃, the time of the heating section is 30-50 minutes, and the total time in the furnace is 2-4 hours;
3) the rolling process comprises three processes of rough rolling, finish rolling and third rolling:
multi-pass high-pressure water descaling is adopted before rough rolling, finish rolling and third rolling, and the high-pressure water pressure is not less than 30MPa, so that the surface quality of the steel plate is ensured;
a) the rough rolling adopts the first rolling with a large reduction rate of more than or equal to 50 percent to fully break the coarse grains of the casting blank;
b) the finish rolling is carried out for at least 6 times in a continuous rolling mode, the total rolling reduction rate is more than or equal to 80 percent, the primary rolling reduction rate is more than or equal to 30 percent, the high-temperature rapid rolling is carried out, the rolling speed is more than or equal to 20m/s, the rolling temperature is 1100-1150 ℃, and the rolling speed temperature is 900-980 ℃;
c) after finish rolling, the mixture is cooled to 600-750 ℃ at the cooling speed of more than or equal to 20 ℃/s and then is put into a double-vertical-roller four-horizontal-roller mill for continuous two-pass rolling, wherein the upper and lower reduction rate is 2-8 percent, and the side pressure reduction rate is 5-25 percent;
4) and (3) a cooling process:
a) the steel plate enters laminar flow cooling, and is quenched at the cooling speed of more than or equal to 20 ℃/s;
b) in order to ensure the performance uniformity of the whole-roll structure and no surface oxidation crystal boundary oxidation of the whole roll, a roll head, a roll middle and a roll tail are adopted for sectional cooling, the roll head is rolled at 500-550 ℃ in a range of 0-30 m, the roll tail is rolled at 550-600 ℃ in a range of 0-30 m, the other parts in the roll are rolled at 520-580 ℃, the whole roll is rolled to obtain a coarse lamellar pearlite structure, the spacing between pearlite plates is more than 0.5 mu m, and the diameter of the pearlite mass is not more than 10 mu m;
5) machining and manufacturing the shape required by the soil-entering agricultural machine part by using the hot rolled steel plate obtained in the step 4), heating to 670-750 ℃, preserving heat for 10-30 minutes, performing oil quenching to below 200 ℃, preserving heat for 24-36 hours in a tempering furnace at 300-500 ℃, and performing air cooling.
A spray welding method for agricultural machinery parts processed by 1700MPa heat-resistant agricultural machinery steel comprises
1) After the surface treatment of the agricultural machinery parts for 10 to 30 minutes by sand casting and 10 to 30 minutes by roll finishing, the surface is heated to 800 to 900 ℃, a chromium-copper alloy powder layer containing 70 to 80 percent of chromium is thermally sprayed and welded, and the powder layer is cooled to the room temperature by air;
2) the chromium-copper alloy powder sprayed and welded on the surface of the agricultural machine fittings is spherical granular powder with the diameter of 80-150 mu m.
The thickness of the chromium-copper alloy granular powder layer sprayed and welded on the surface of the agricultural machine accessory is 0.2-0.5mm, the chromium-copper alloy granular powder layer and carbon in a matrix below the surface of steel form a compact CrCuC transition layer with the thickness of 0.1-0.2 mm, the surface hardness is more than 65HRC under the high-temperature working condition of more than 200 ℃, the abrasion rate is less than 20mg/km under the conditions of the rotating speed of a grinding pin of 300r/min and the load of 120N, and the corrosion rate is less than 15g/m under the soil environment2·h。
The steel for agricultural machinery of the present invention has high carbon content, difficult control of oxygen content and poor molten steel fluidity, and in order to improve the molten steel fluidity, the present invention has sufficient deoxidation, firstly uses Al deoxidant to deoxidize, after the oxygen content is less than or equal to 0.0020%, adds Ca to treat for at least 5 minutes, and then adds Re and Mg alloy. In the components of the invention, Ca, Mg, Re and Sn are active elements, which are difficult to control during smelting, and the addition sequence is very important. Al is generated in the steel after Al addition and deoxidation2O3Inclusion of, if lining of furnaceRefractory material is poor, and MgO & Al are generated2O3And the melting point of the Al oxide inclusions is high, the Al oxide inclusions are not easy to solidify and float in steel, on one hand, the fluidity of molten steel is reduced, a pouring nozzle is blocked, on the other hand, the inclusions in the steel are increased, and the bending and fatigue properties of the steel are influenced. Adding Al for deoxidation, and then adding Ca for treatment, wherein the Ca can break the original long-strip-shaped Al2O3And MgO. Al2O3And MnS inclusions, which are wrapped outside the intermittent inclusions to generate spherical CaO, MgO, Al in a dispersed distribution2O3Or CaO. Al2O3And CaO & MnS composite oxides, the inclusions are refined and spheroidized, and the small-particle calcium aluminate composite inclusions have low melting point and are easy to solidify, float and remove in molten steel, so that the problem of nozzle nodulation in the continuous casting process is avoided, the inclusion content in the molten steel is reduced, and the inclusion level in the steel is ensured not to exceed 1.0 level. After Ca treatment for 5 minutes, the denatured inclusion floats sufficiently, after the molten steel is purified, Re and Mg alloy are added, the yield of R, Mg is improved by redundant free Ca in the molten steel, the yield of Re is improved to more than 60% by Ca, and the yield of Mg is as high as more than 40%. Fully exerts the functions of improving the high-temperature strength and hardness, oxidation resistance, corrosion resistance and heat resistance in steel.
According to the invention, the Ca, the Re and the Sn enable oxide and sulfide inclusions to be denatured, the fluidity of molten steel is increased, the floating speed of the inclusions is increased, and the argon blowing time of the tundish is 5-8 minutes, so that the inclusions can be fully floated after being denatured, the purity of various non-metal inclusions in the steel is ensured not to exceed 1.0 level, nearly half time is saved compared with that of common tool steel, energy is saved, consumption is reduced, and the productivity is improved.
The invention has high carbon content, and the continuous casting is easy to generate component segregation and influence the uniformity of the structure, so the continuous casting adopts a reduction technology and controls the superheat degree to improve the macrosegregation of the casting blank. The superheat degree is less than or equal to 25 ℃, the continuous casting reduction is 2-10 mm, the segregation is reduced, and the casting blank is prevented from cracking. Segregation is serious when the reduction is less than 2mm and exceeds 1.5 grade, and the casting blank with the reduction more than 10mm is easy to crack.
The invention has high carbon content, is easy to form liquid micro segregation at the solidification tail end of columnar crystal of a casting blank, is easy to produce liquid precipitation phase of a hot rolled plate, and further separates out graphite by heat treatment, thereby influencing the service performances such as tensile strength, fatigue and the like. According to the invention, a certain amount of tin is added into steel, and meanwhile, a crystallizer is adopted for electromagnetic stirring, the current intensity is 500-1000A, the time is 1-3 minutes, the continuous casting pulling speed is 1.0-1.4 m/min, the liquid micro-segregation of the alloy at the tail end of the columnar crystal is controlled, and the aggregation of carbon segregation and the graphitization precipitation are effectively hindered. The electromagnetic stirring current intensity is lower than 500A, the stirring time is less than 1 minute, the carbon segregation aggregation and graphite precipitation are prevented from being obvious, the electromagnetic stirring current intensity is higher than 1000A, the energy is wasted, the stirring time is more than 3 minutes, the temperature of molten steel is reduced, and a water blocking opening is poured. Tin can effectively prevent carbon segregation aggregation, cementite and graphitization precipitation, inhibit the oxidation of the surface grain boundary of the steel plate, and improve the comprehensive properties of surface spray welding performance, strength, wear resistance and the like.
The casting blank is inserted into a slow cooling pit for slow cooling for more than 72 hours, so that the high-carbon steel casting blank with relatively high alloy content is prevented from being easily cracked under the action of stress, and the segregation of the casting blank is reduced.
The casting blank is heated by a stepping heating furnace before rolling, the temperature of the casting blank in a preheating section of the heating furnace is above 500 ℃, and the phenomenon that the temperature difference between the inside and the outside of the casting blank in the heating section is too large to generate internal stress and thermal stress cracking is prevented; the heating furnace adopts reducing atmosphere to resist the surface oxidation and decarburization of the casting blank. The heating temperature of the heating section is 1200-1350 ℃, the time of the heating section is 30-50 minutes, and the total time of the heating section in the furnace is 2-4 hours, so that the uniform heating and the uniform composition of the casting blank are ensured, and the segregation is reduced. Inhibiting the oxidation and decarburization of the grain boundary on the surface of the steel plate, and improving the comprehensive properties of surface spray welding performance, strength, wear resistance and the like.
Descaling for 2 times before rough rolling, descaling for 2 times before finish rolling, descaling for 1 time before third rolling, wherein the descaling pressure is over 30MPa, the iron scale on the surface of the steel plate is completely removed, and the surface of the steel plate has no obvious oxidation and decarburization, thereby being beneficial to surface spray welding and improving the strength and hardness in a high-temperature working environment. The rough rolling adopts 3 times of rolling with the large reduction rate of more than or equal to 50 percent, the coarse columnar grains of the casting blank are fully crushed, and Re, Mg and C in the steel generate series carbon magnesium rare earth compounds, thereby further promoting the hot rolling to form a pearlite structure with the inter-sheet distance of more than 0.5 mu m.
Finish rolling6-pass high-temperature fast rolling is adopted, the initial rolling temperature is more than or equal to 1100 ℃, the finishing temperature is 900-980 ℃, Sn and the like dissolved in austenite react with carbon to form a series of spherical fine SnC with the diameter of less than 10nmMTin carbide. The total reduction rate is more than or equal to 80 percent, the first-pass reduction rate is more than or equal to 30 percent, austenite is refined, and sufficient phase transformation energy is provided for forming tin carbide; these SnCsMThe carbon stannide is prepared for forming a carbon stannide compound of Re and Mg with high temperature resistance. In order to reduce the heating temperature of heat treatment, high-temperature rapid rolling is adopted, and the interval between the carbide pieces in the coarsened pearlite is more than 0.5 mu m by the process with the rolling speed more than or equal to 20 m/s. The rolling speed is more than or equal to 20m/s, the carbon stannides are not long enough to grow up and are uniformly and dispersedly distributed in the steel to prepare for forming carbon stannide compounds of Re and Mg. On the other hand, these fine tin carbides also serve as nucleation sites for pearlite cementite lamellae, and since these tin carbides tend to aggregate carbon more easily, the cementite lamellae are mostly based on these tin carbides, and since they are distributed dispersedly, the distance between the cementite lamellae in the formed pearlite is greater than 0.5 μm, and no high temperature is required for the heat treatment. However, after the finish rolling process, the cementite sheet grows fast, which results in large pearlite colony diameter, poor ductility and bending formability of the steel sheet, and large martensite of the lath after heat treatment, which affects the performance after heat treatment.
After the steel plate is taken out of the finishing mill, the steel plate is subjected to finish rolling, then is quenched to 600-750 ℃ at the cooling speed of more than or equal to 20 ℃/s, and then is put into a double-vertical-roller four-horizontal-roller mill for continuous two-pass rolling, wherein the upper and lower reduction rate is 2-8%, and the side pressure reduction rate is 5-25%. The third low-temperature rolling is mainly SnCMReaction of tin carbide with Re and Mg to generate ReMgSnCM、ReSnCM、MgSnCM2The carbon-tin composite provides phase transformation energy and supercooling degree required by reaction. The uniform and fine carbon-tin compound reduces the yield ratio to below 60% in a hot rolled plate and improves the formability. The carbon-tin composites are more heat-resistant than common cementite, do not diffuse and decompose at 900 ℃, are still uniformly and dispersedly distributed in the martensite low-strip after heat treatment, improve the hardness after heat treatment, further improve the heat resistance and the wear resistance, and have the tensile strength of more than 1700MPa and the matrix hardness of more than 55HRC under the high-temperature working condition of more than 200 ℃. On the other hand, thirdThe secondary low-temperature rolling can crush large pearlite colonies formed in the finish rolling for coarsening pearlite plates, the diameter of the pearlite colonies is not more than 10 mu m, the toughness and the plasticity are improved, the yield ratio is less than 60%, the formability is excellent, and a structure guarantee is provided for forming fine martensite laths after subsequent heat treatment. 20 ℃/s is the critical supercooling degree required by the reaction for generating the carbon-tin compound, so the cooling speed after the finishing mill is more than or equal to 20 ℃/s, and meanwhile, the overlarge pearlite colony is inhibited. The rolling temperature is 600-750 ℃, the upper and lower reduction rate is 2-8%, the side pressure reduction rate is 5-25%, and the enough generated ReMgSnC is ensured to be providedM、ReSnCM、MgSnCM2The deformation energy of the carbon-tin composite reaction is equal, the pearlite colony is broken to be less than 10 mu m in diameter, the yield ratio of the steel plate is less than 60%, and the bending formability is excellent. And a four-horizontal-roller mill is adopted for continuous two-pass rolling, so that the phase transformation energy is increased. The rolling temperature is higher than 750 ℃, the reduction rate is lower than 2 percent, the lateral pressure reduction rate is lower than 5 percent, large pearlite colonies are not easy to break, the phase transformation energy of the generated carbon-tin composite is insufficient, and the quantity is small. The rolling temperature is lower than 600 ℃, the reduction rate is more than 8%, the rolling force is large when the side pressure reduction rate is more than 25%, the load of a rolling mill is overlarge, the storage energy in steel is overlarge, the carbon-tin compound grows to be more than 20nm, the high-temperature resistant effect cannot be achieved, fine flaky carbide is easily generated in a ferrite matrix of the coarse flaky cementite pearlite, the pearlite lamella becomes thin, carbon is not easy to diffuse during heat treatment, and austenitizing is difficult.
20 ℃/s is also the critical cooling rate of the invention for obtaining the pearlite, and more than the critical cooling rate, no ferrite is precipitated, and the surface oxidation and decarburization are reduced. The temperature of 500-600 ℃ is the final cooling temperature of the invention for generating the complete pearlite, a head-rolling, middle-rolling and tail-rolling segmented cooling mode is adopted, the head-rolling is rolled at the temperature of 0-30 m and 500-550 ℃, the tail-rolling is rolled at the temperature of 0-30 m and 550-600 ℃, and the other part in the rolling is rolled at the temperature of 520-580 ℃, so that the structure performance of the whole-rolling steel plate is uniform, the surface of the whole-rolling steel plate is fine, the surface quality of the whole-rolling steel plate is improved, and the surface is smooth, free of oxidation and decarburization. Coiling in the temperature range can effectively inhibit surface grain boundary oxidation and decarburization, and simultaneously contributes to fine dispersion and uniform distribution of carbon-tin compounds of Re and Mg, coarse lamellar pearlite with the interplate distance of more than 0.5 mu m is formed, the diameter of pearlite colony is not more than 10 mu m, and the uniformity of the whole coil structure performance is improved. The coiling temperature is lower than 500 ℃, bainite or martensite brittle-hard phase can be generated, the hardness of the steel plate is too high, and the steel plate is easy to crack. The coiling temperature is higher than 600 ℃, the cooling speed is less than 20 ℃/s, large blocks of ferrite which is precipitated first can be precipitated, the strength is low, the surface is secondarily oxidized, the surface spray welding is influenced, and the forming is easy to crack.
The agricultural machine accessory processed and manufactured by the hot rolled plate is quenched at 670-750 ℃, insulated for 10-30 minutes, tempered at 300-500 ℃ and insulated for 24-36 hours. Because the structure is coarse lamellar pearlite and the diameter of pearlite colony is small, the quenching temperature of the invention is lower than that of common high-carbon steel, the quenching and tempering heat preservation time is short, the energy consumption is saved, and the invention meets the requirements of energy conservation, emission reduction and environmental protection. The quenching temperature is below 750 ℃, cementite in the coarse pearlite sheet with the sheet spacing of more than 0.5 mu m can be completely diffused and decomposed to form martensite. The alloy is quenched at low temperature, the Re and Mg carbon tin compounds are not diffused and decomposed and are still uniformly dispersed and distributed in the steel, the hardness after heat treatment is improved, the heat resistance and the wear resistance are further improved, and the tensile strength is more than 1700MPa and the matrix hardness is more than 55HRC under the high-temperature working condition of more than 200 ℃. On the other hand, the low-temperature heat treatment helps to suppress oxidation and decarburization of the steel surface.
After sand polishing for 10-30 minutes and roll finishing for 10-30 minutes, the surface is heated to 800-900 ℃, a chromium-copper alloy powder layer containing 70-80% of chromium is thermally sprayed and welded, the thickness of the layer is 0.2-0.5mm, the powder consists of spherical particles with the diameter of 80-150 mu m, the spherical particle powder is attached to the surface of steel, the heat resistance and the wear resistance of the surface are effectively improved, the surface hardness is more than 65HRC under the high-temperature working condition of more than 200 ℃, and the wear rate is less than 20mg/km (the rotating speed of a grinding pin is 300r/min, the load is 120N). The spherical particles constituting the powder have poor wear resistance, either less than 80 μm or more than 150. mu.m in diameter. On the other hand, a part of powder subjected to surface spray welding seeps into a lower matrix of the steel surface at high temperature to form a compact CrCuC layer with the thickness of 0.1-0.2 mm with carbon, so that the corrosion resistance of the steel is improved, and the corrosion rate is lower than 15g/m in a soil environment2·h。
In summary, compared with the prior art, the invention has the beneficial effects that:
1) the Sn, Re, Mg and carbon are used for forming spherical carbon tin compounds with high temperature resistance and the diameter of less than 20nm to improve the high-temperature hardness, the structure after heat treatment is a lath-shaped martensite structure with the diameter of less than 20nm and uniformly distributed fine carbon tin compounds, the hardness of a matrix is more than 55HRC under the high-temperature working condition of more than 200 ℃, the tensile strength is more than 1700MPa, and the heat resistance and the wear resistance are obviously improved;
2) the interlayer spacing of the dispersedly distributed carbon stannide coarsening pearlite plates generated by Sn, Re, Mg and carbon reaches more than 0.5 mu m, the heat treatment temperature is reduced, and the heat treatment energy is saved;
3) the large pearlite colony is crushed by adopting a three-time rolling technology, the size of the pearlite colony of the hot rolled plate is not more than 10 mu m, the yield ratio is below 60%, and the formability is excellent;
4) according to the invention, Ca and Mg are combined for deoxidation to carry out denaturation treatment on inclusions in steel, and various non-metallic inclusions do not exceed 1.0 level;
5) sn is added and electromagnetic stirring is adopted to effectively prevent carbon segregation aggregation and graphitization precipitation;
6) adopting a pressing technology, wherein the segregation is not more than 1.5 grade;
7) the surface oxidation is inhibited by adopting the low Si and Sn component design, and the crystal boundary oxidation microcrack is avoided;
8) spherical chromium-copper powder particles with the diameter of 80-150 mu m are subjected to spray welding on the surface, the thickness of the chromium-copper layer is 0.2-0.5mm, the chromium-copper layer and carbon in the base form a compact CrCuC layer with the thickness of 0.1-0.2 mm, the surface hardness, the wear resistance, the heat resistance and the corrosion resistance are effectively improved, the surface hardness is more than 65HRC under the high-temperature working condition of more than 200 ℃, the abrasion loss rate is less than 20mg/km under the conditions of the rotating speed of a grinding pin of 300r/min and the load of 120N, and the corrosion rate is less than 15g/m under the soil environment2·h。
Detailed Description
The present invention is described in more detail by way of examples, which are merely illustrative of the best mode of carrying out the invention and are not intended to limit the scope of the invention in any way.
The chemical compositions of the steels of the examples are shown in Table 1; the production process of the hot-rolled strip steel is shown in tables 2 and 3; the spray welding process is shown in table 4; the properties of the finished product are shown in Table 5.
TABLE 1 chemical composition in the steel of the examples%
TABLE 2 smelting process
TABLE 3 casting blank treatment and Hot Rolling, Cooling Process
TABLE 4 Heat treatment and spray welding Process parameters
TABLE 5 Steel plate and finished product Properties
Claims (9)
1.1700MPa heat-resistant agricultural steel, which is characterized in that the steel comprises the following chemical components by weight percent: 0.70 to 1.1 percent of C, less than or equal to 0.05 percent of Si, 0.4 to 1.5 percent of Mn, less than or equal to 0.06 percent of Al, 0.0005 to 0.05 percent of Ca, 0.05 to 0.5 percent of Re, 0.1 to 1.0 percent of Sn, 0.0008 to 0.05 percent of Mg0.0008, more than or equal to 0.2 percent of Ca/S, more than or equal to 1 percent of Ca/Mg, more than or equal to 0.05 percent of Ca/Re, less than or equal to 0.020 percent of P and less than or equal to 0.015 percent of S; the balance being Fe and unavoidable impurities.
2. The 1700MPa heat-resistant agricultural steel of claim 1, wherein the hot rolled steel sheet structure of the agricultural steel is a coarse lamellar pearlite structure having a cementite piece spacing of 0.5 μm or more with a particle of tin carbide, and a pearlite colony diameter is not more than 10 μm; the structure after heat treatment is a lath-shaped martensite structure with spherical tin carbide with the diameter of less than 20nm in a dispersion distribution manner.
3. The 1700MPa heat resistant agricultural steel of claim 1, wherein the hot rolled steel sheet for agricultural steel has a yield ratio of 60% or less; the hardness of the steel plate matrix is above 55HRC and the tensile strength of the steel plate is above 1700MPa under the working condition of the temperature of above 200 ℃ after heat treatment.
4. The 1700MPa heat-resistant agricultural steel sheet of claim 1, wherein non-metallic inclusions in the agricultural steel sheet are not more than 1.0 level; the grain boundary oxide layer of the steel plate is 0 mm; segregation does not exceed 1.5 grade.
5. The method of manufacturing 1700MPa heat resistant agricultural steel according to any one of claims 1 to 4, comprising:
1) the smelting process comprises the following steps:
a) deoxidizing by using an Al deoxidizer, adding Ca for at least 5 minutes after the refined oxygen content is less than or equal to 0.0020%, then adding Mn, Re and Mg alloy, and adding Sn to J;
b) the continuous casting adopts a reduction process and electromagnetic stirring of a crystallizer, the thickness of a casting blank is 170-250 mm, and the reduction amount is 2-10 mm; the electromagnetic stirring current intensity of the continuous casting crystallizer is 500A-1000A, the electromagnetic stirring is carried out for 1 min-3 min, and the continuous casting drawing speed is 1.0 m/min-1.4 m/min;
2) the rolling process comprises the following steps:
the method comprises three processes of rough rolling, finish rolling and third rolling:
a) the rough rolling adopts rolling with a large reduction rate of more than or equal to 50 percent;
b) the finish rolling adopts a continuous rolling mode, the total rolling reduction rate is more than or equal to 80 percent, the primary rolling reduction rate is more than or equal to 30 percent, the rolling speed is more than or equal to 20m/s, the rolling temperature is 1100-1150 ℃, and the finishing temperature is 900-980 ℃;
c) after finish rolling, the mixture is cooled to 600-750 ℃ at the cooling speed of more than or equal to 20 ℃/s and then is put into a double-vertical-roller four-horizontal-roller mill for continuous two-pass rolling, wherein the upper and lower reduction rate is 2-8 percent, and the side pressure reduction rate is 5-25 percent;
3) and (3) a cooling process:
a) the steel plate enters laminar cooling, and the cooling speed is more than or equal to 20 ℃/s;
b) adopting a head-coiling, middle-coiling and tail-coiling sectional cooling mode, coiling the head at 0-30 m and 500-550 ℃, coiling the tail at 0-30 m and 550-600 ℃, and coiling the other parts in the coil at 520-580 ℃;
4) processing and manufacturing the shape required by the agricultural machinery accessory by using the hot rolled steel plate obtained in the step 3), heating to 670-750 ℃, preserving heat for 10-30 minutes, performing oil quenching to below 200 ℃, putting into a tempering furnace, preserving heat for 24-36 hours at 300-500 ℃, and performing air cooling.
6. The method of manufacturing 1700MPa heat resistant agricultural steel for a steel product according to claim 5, further comprising a billet treatment process: the casting blank is inserted into a slow cooling pit for slow cooling for more than 72 hours, and a stepping heating furnace is adopted for heating before rolling the casting blank; the heating furnace adopts reducing atmosphere, the temperature of the preheating section is more than 500 ℃, the temperature of the heating section is 1200-1350 ℃, the time of the heating section is 30-50 minutes, and the total time in the furnace is 2-4 hours.
7. The method of spray welding agricultural machinery parts processed with the 1700MPa heat resistant agricultural steel of claim 1, comprising
1) After the surface treatment of the agricultural machinery parts for 10 to 30 minutes by sand blasting and 10 to 30 minutes by roll finishing, the surface is heated to 800 to 900 ℃, a chromium-copper alloy powder layer containing 70 to 80 percent of chromium is thermally sprayed and welded, and the powder layer is cooled to the room temperature by air;
2) the chromium-copper alloy powder sprayed and welded on the surface of the agricultural machine part is spherical granular powder with the diameter of 80-150 mu m.
8. The spray welding method of the agricultural machinery part processed by the 1700MPa heat-resistant agricultural machinery steel according to claim 7, wherein the thickness of the chromium-copper alloy granular powder layer sprayed and welded on the surface of the agricultural machinery part is 0.2-0.5mm, and the thickness of the CrCuC transition layer is 0.1-0.2 mm.
9. The spray welding method of the agricultural machinery accessory processed by the 1700MPa heat-resistant agricultural machinery steel according to claim 7, wherein the surface hardness of the agricultural machinery accessory after spray welding is more than 65HRC, the abrasion rate is less than 20mg/km under the conditions of 300r/min of pin grinding rotation speed and 120N of load, and the corrosion rate is less than 15gg/m under the soil environment2·h。
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| CN108315644A (en) * | 2018-02-09 | 2018-07-24 | 天津荣程联合钢铁集团有限公司 | Hot-rolled round steel for high carbon manganese and chrome grinding ball and its manufacturing method |
| CN110423939A (en) * | 2019-07-25 | 2019-11-08 | 芜湖市春正农业科技有限公司 | A kind of farm machinery corrosion-resistant steel and preparation method thereof |
| CN112458378A (en) * | 2020-12-02 | 2021-03-09 | 山东泰山钢铁集团有限公司 | Production method of high-strength hot-rolled coiled plate for soil contact accessory of agricultural implement |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115505852A (en) * | 2022-10-26 | 2022-12-23 | 河北普阳钢铁有限公司 | Corrosion-resistant steel for agricultural machinery and manufacturing method thereof |
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