121 results about "Martensitic microstructure" patented technology

The invention belongs to the technical field of bearing manufacturing, and particularly relates to a quenching and tempering heat treatment method for a large heavy-duty bearing ring piece, which is suitable for quenching and tempering heat treatment of a thick large-section ring piece. And the thick and large-section ferrule ring piece is heated to the quenching temperature in a segmented and stepped mode, the ferrule ring piece is hoisted to a circulating water pool to be subjected to water cooling after heat preservation is completed, cooling is conducted till the surface temperature of the ring piece is lower than 100 DEG C, and the quenched ferrule ring piece is timely charged into a furnace to be tempered twice. The surface of the ferrule ring subjected to quenching and tempering heat treatment is free of cracks, the deformation degree is small, a martensite structure with the full cross section quenched thoroughly can be obtained, and the uniformity of the surface layer, the core structure and the performance of the ferrule ring with the thick and large cross section can be greatly improved. In addition, the quenching and tempering heat treatment process is simple to operate, and the consistency of the performance of the ferrule ring pieces in all batches is easily ensured. The method is not limited to a process of a large heavy-duty bearing ring piece, is also very suitable for thermal refining of other large forgings, and solves the defect problems of non-uniform structure, unstable performance and the like.

The invention relates to the technical field of additive manufacturing, in particular to a direct aging treatment process of an SLM molded Ti-6Al-4V alloy and a product thereof, and the direct aging treatment process comprises the following steps: firstly, manufacturing a Ti-6Al-4V alloy sample by adopting an SLM technology, and then putting the SLM molded Ti-6Al-4V alloy sample into a vacuum heat treatment furnace for direct aging treatment, and finally, taking out the sample after furnace cooling or air cooling. According to the method, through direct aging treatment, a natural alpha'martensite structure in the Ti-6Al-4V alloy formed through SLM is decomposed into an alpha + beta double-phase structure, the front solid solution-quenching process in traditional solid solution aging treatment is not needed, and the purposes of optimizing structure uniformity and improving plasticity are achieved. The aging treatment cost and the quenching risk of the SLM titanium alloy are reduced, and the plasticity of the SLM titanium alloy can be remarkably improved while high strength is kept. The method is simple in process, low in cost and suitable for large-scale industrial application.

The invention discloses a heat treatment process for improving the obdurability of die steel, and belongs to the technical field of metal heat treatment. The invention relates to a heat treatment process for improving the toughness of die steel, which adopts a die steel material with a specific component proportion, and the die steel material comprises carbon, chromium, molybdenum, vanadium, tungsten, nickel, niobium, niobium carbide and trace boron element. By sequentially implementing austenitizing, quenching, deformation heat treatment, multi-stage subzero treatment, pulsed magnetic field assisted tempering, gradient surface hardening and nano-precipitation regulation treatment, the hardness and toughness of the die steel are remarkably improved. Particularly, through the synergistic effect of multiple advanced heat treatment means, the martensite structure is effectively refined, carbide precipitation is strengthened, the surface hardness and the core toughness are improved, the comprehensive performance of toughness and toughness is achieved, and the method is suitable for the field of high-performance injection molds and hot-working molds.

The invention relates to a high-strength complex-phase hot-rolled wire rod for a 2160MPa-grade stranded wire and a manufacturing method of the high-strength complex-phase hot-rolled wire rod, after high-carbon components containing trace Nb are rolled and spun into a wire rod, the wire rod is subjected to online molten salt micro-quenching isothermal treatment, so that the wire rod is firstly subjected to front-section molten salt treatment and enters a bainite phase region from an austenite state, part of the austenite is promoted to be converted into bainite, and then the high-strength complex-phase hot-rolled wire rod is obtained. The method comprises the following steps: carrying out high-temperature tempering on the residual austenite, carrying out post-section molten salt treatment, increasing the molten salt temperature, promoting the unconverted residual austenite to be decomposed and converted into sorbite, carrying out isothermal tempering, and finally carrying out roller way slow cooling to prepare the hot-rolled wire rod of which the microscopic structure comprises a complex-phase structure consisting of tempered bainite, ferrite and tempered sorbite, so that network carbides and martensite structures can be inhibited, and the tensile strength of the hot-rolled wire rod is improved. And the structure type and toughness are regulated and controlled on line, the tensile strength is 1472-1505MPa, the percentage reduction of area is 31%-36%, the work hardening rate and the production efficiency of the hot-rolled wire rod are improved, and the production energy consumption is reduced, so that a high-strength grade stranded wire is obtained.

The invention discloses martensite ultrahigh-strength steel and a preparation method thereof, and belongs to the technical field of steel and iron materials. The martensite ultrahigh-strength steel comprises the following chemical components in percentage by mass: 0.2 to 0.3 percent of C, 0.5 to 2 percent of Mn, 0.5 to 1.5 percent of Si, 6 to 10 percent of Ni, 1.5 to 2 percent of Al, 1 to 3 percent of Mo, 0.5 to 1 percent of Cr, 0.5 to 1 percent of W, 0.05 to 0.2 percent of V and the balance of Fe and inevitable impurity elements. By combining component design and a cyclic thermal mechanical treatment process, a nano-sized spherical precipitated phase and a band-shaped precipitated phase are introduced into a martensite lath at the same time, the dislocation storage density of a martensite structure in the deformation process is further improved, the tensile yield strength breaks through 2.4 GPa, the tensile strength reaches 2.5 GPa or above, and the tensile strength reaches 2.5 GPa or above. And good elongation at break is maintained, so that the alloy has excellent comprehensive mechanical properties.

The invention discloses a microalloyed high-toughness martensitic stainless steel cutter head as well as a preparation method and a preparation mold thereof. Stainless steel comprises the following components in percentage by weight: 0.3%-0.7% of C, 0.3%-1.0% of Si, 0.5%-1.5% of Mn, 16%-18.5% of Cr, 1%-2% of Ni, 0.3%-0.8% of Mo, 0.1%-0.35% of V, 0.1%-0.25% of Nb, less than or equal to 0.02% of S, less than or equal to 0.02% of P and the balance of Fe. Firstly, raw materials are smelted into molten iron; then adding a deoxidizing agent and precoated sand into the molten iron for molding, and performing sand mold casting and pouring to obtain a cutterhead blank; carrying out heat treatment on the cutter head blank; and finally, shot blasting and polishing are conducted on the cutterhead subjected to heat treatment. The martensitic stainless steel cutterhead has a metallographic structure which takes a martensitic structure as a main structure, takes austenite as an auxiliary structure and dispersedly distributes CrC, VC and NbC particles, the hardness of the martensitic stainless steel cutterhead is 40-45 HRC, the impact toughness of the martensitic stainless steel cutterhead reaches 92-95 J / cm < 2 >, the abrasion resistance of the cutterhead is longer, the service life of the cutterhead is longer, and the abrasion loss of the martensitic stainless steel cutterhead is reduced by 70% compared with a cutterhead without alloy elements.

The invention discloses a preparation method of medium and low carbon chromium manganese martensite cast steel. The preparation method comprises the following steps: step 1, preparing raw materials; 2, high-temperature smelting; step 3, deoxidizing and desulfurizing; step 4, casting molding; step 5, annealing treatment; step 6, quenching treatment; step 7, tempering treatment; step 8, surface treatment; according to the invention, the medium-low carbon martensitic cast steel is designed, and the hardness and toughness of the martensitic cast steel are balanced by controlling the content of carbon in the cast steel, so that the problem of lower toughness of the martensitic cast steel under high carbon is avoided; meanwhile, the phenomenon that carbon elements are combined with chromium elements to be dispersed and separated out from grain boundaries or martensite laths in a carbide mode is reduced in cooperation with a heat treatment process, the corrosion resistance of the martensite cast steel is improved, meanwhile, the heat treatment process more suitable for medium and low carbon chromium manganese martensite cast steel is matched, various properties are further balanced, internal stress is eliminated, and the corrosion resistance of the martensite cast steel is improved. And the martensite structure is more uniform and stable.

The invention belongs to the technical field of metal processing technologies, and particularly relates to a gradient heat treatment steel strengthening and toughening technology optimization method which comprises the steps that a cooling tank is arranged, a vertical channel is formed in the inner side face of the cooling tank and communicates with a liquid layer in the cooling tank and the outer portion of the cooling tank, and quenching liquid is added into the cooling tank till the vertical channel is submerged; a proper amount of quenching oil is added, so that the quenching liquid and the quenching oil are layered, and a lower liquid layer and an upper oil layer are formed respectively; gradient heating is conducted on a target area of the workpiece in a local heating mode, and austenitizing is achieved; after the workpiece is austenitized, subarea gradient cooling is conducted, the workpiece is put into a cooling tank, quenching oil wraps the workpiece through an oil layer and continues to penetrate into a liquid layer, the surface layer of the workpiece reaches the martensite transformation termination temperature, and austenite is transformed into a martensite structure; the influence of a steam film generated when quenching liquid is used for quenching on the machining stability and the machining quality of a workpiece can be reduced.

The invention aims to provide a heat treatment-liquid nitrogen treatment-cryogenic forging composite forming method for obtaining an alpha '+ alpha' double-phase martensitic structure titanium alloy, and belongs to the technical field of titanium alloy plastic processing and heat treatment. Through liquid nitrogen treatment, the sample obtains a uniform cryogenic temperature and stabilizes an alpha'martensite phase structure; alpha'martensite to alpha '' martensite phase transformation of the alloy is promoted through cryogenic forging. And finally, obtaining the needle-shaped alpha '+ alpha' 'biphase martensitic structure titanium alloy forge piece based on the synergistic effect of heat treatment, liquid nitrogen treatment and cryogenic forging. Compared with traditional cryogenic forming of the titanium alloy, the method can achieve uniform distribution of nanoscale alpha '+ alpha' 'biphase martensite in the titanium alloy forge piece, meanwhile, the technological process is simple, and actual production is easy.

The invention discloses high-endurance-strength high-silicon martensite heat-resistant steel for a lead-bismuth reactor and a preparation method of the high-endurance-strength high-silicon martensite heat-resistant steel, and belongs to the technical field of corrosion-resistant and heat- The heat-resistant steel comprises C, Si, Cr, Ni, Mo, W, Mn, V, Nb and N, the Mo equivalent is 0.8-1.2, the CNB is smaller than 14, and the balance is Fe and inevitable impurities. The formation of a compact SiO2 protective film is promoted by increasing the content of Si, and meanwhile, Mo and W are adopted for synergistic solution strengthening and are matched with N, V and Nb to form a dispersed MX precipitated phase. The heat-resistant steel is prepared through the processes of smelting, homogenizing, forging, hot rolling, normalizing and tempering, and a full-martensite structure can be obtained. And the obtained material has good liquid lead and bismuth corrosion resistance, room-temperature and high-temperature mechanical properties and relatively high high-temperature endurance strength, and is suitable for structural materials serving in high-temperature liquid lead and bismuth environments such as a lead-cooled fast reactor and the like.

The invention belongs to the technical field of metal materials, and discloses precipitation-hardening stainless steel and a preparation method thereof. Through cooperative regulation and control of component design and process innovation, the traditional contradiction of'strength-plasticity inversion 'in additive manufacturing of the precipitation-hardened stainless steel is broken through, and the precipitation-hardened stainless steel with excellent strength and plasticity is prepared. On one hand, the N element is introduced into the precipitation-hardening stainless steel raw material powder, so that transformation from ferrite to austenite in the additive manufacturing process is promoted; on the other hand, in the additive manufacturing process, the substrate is subjected to in-situ heating to be close to the martensite phase transformation initial temperature, and transformation of austenite to martensite is restrained; and after printing is finished, global martensite phase transformation is triggered through natural cooling or air cooling, so that a total martensite structure with fine grains and high dislocation density is obtained. And finally, through aging treatment, precipitation of a nano Cu phase is induced, formation of austenite is reversed, and therefore the strength and plasticity of the precipitation-hardened stainless steel are improved at the same time.

The application discloses a laser welding method for inhibiting formation of aluminum-rich phase in a weld, and belongs to the technical field of metal material processing. Firstly, welding edges of two steel plates are butted and fixed, laser wire filling welding is performed, the excess height on the surface of the weld is removed, and a welded plate is obtained; then the welded plate is kept in a heating furnace at 900-960 DEG C for 3-10 min, and the welded plate is taken out and quenched immediately; after quenching, the steel plate and the weld form martensite structures. The laser wire filling welding method is used to add welding wires into the weld, the composition of the weld metal is optimized, the aluminum-rich phase free weld structure is obtained, the welding wires entering the weld increase the volume and weight of the weld metal, the mass percentage content of the aluminum alloy in the weld metal is further reduced, the generation of the aluminum-rich phase in the weld is weakened, the joint strength after welding of the plated steel plate is greater than the base material strength, after hot forming of the welded joint, the weld is a complete martensite structure, and the weld strength is greater than or equal to 1500 MPa.

The present invention provides a steel sheet having a tensile strength of 1310 MPa or more and excellent press formability in a steel having a martensite structure as a main body and excellent delayed fracture resistance. The steel sheet is characterized by having a composition consisting of, in mass%, C: 0.12% to 0.40%, Si: 1.5% or less, Mn: 1.7% or less, P: 0.05% or less, S: 0.010% or less, sol. Al: 1.00% or less, N: 0.010% or less, Ti: 0.002% to 0.080%, and B: 0.0002% to 0.0050%, with the remainder being Fe and inevitable impurities, and a metal structure in which the area ratio of a martensite to the entire structure is 95% or more, the length L S of sub-block boundaries in the martensite is 0.5 to 2.0 μm, and the ratio L B / L S of the length L B of the sub-block boundaries to the length L of the block boundaries satisfies a prescribed formula (1), and the tensile strength is 1310 MPa or more.

The present application belongs to the field of metal materials, and particularly relates to a high-temperature carburizing process method of gear steel quenched by different media. The present application develops the carburizing process of gear alloy carburizing steel by finite element simulation mode, and proposes a double-medium quenching process to improve the phase organization of the core of the sample, reduce the martensite content of the core, increase the bainite content, thereby reduce the hardness of the core, and further improve the toughness of the core of the sample, on the basis of ensuring the control of production cost, without increasing the process flow and improving the use performance. The carburized surface is still martensite organization, and the high hardness of the surface layer is maintained.

The invention discloses martensite structure genetic effect-based ultrahigh strength and plasticity advanced high-strength steel and a preparation method thereof, and belongs to the technical field of metal materials. The advanced high-strength steel comprises the following chemical components: C, Mn, Si, Al, Nb, Ti, Fe and the like, and the core of the advanced high-strength steel is that a microstructure is regulated and controlled through the'structure genetic effect 'of martensite: full martensite formed by pre-quenching is used as an initial structure, and reverse transformed austenite is preferentially nucleated on a martensite lath interface through critical zone annealing and inherits the lath form of the martensite lath; the double-peak retained austenite with battens as the main part (the volume fraction is larger than or equal to 70%) and blocks as the auxiliary part (the volume fraction is smaller than or equal to 30%) is finally obtained, the Mn element of the batten retained austenite is obviously enriched, the mass fraction of the Mn element is larger than or equal to 3.5%, the tensile strength of the finally-obtained advanced high-strength steel reaches 840-900 MPa, the ductility is 35-40%, the product of strength and ductility is larger than or equal to 31.5 Pa%, and the tensile strength is larger than or equal to 31.5 Pa%. The method is suitable for the fields of automobile lightweight, high-end equipment manufacturing and the like with strict requirements on material performance.

A method for manufacturing a steel product includes providing a heated steel starting product at a temperature between 380° C. and 700° C., with a composition comprising, in percent by weight: 0.15%≤C≤0.40%, 1.5%≤Mn≤4.0%, 0.5%≤Si≤2.5%, 0.005%≤Al≤1.5%, with 0.8%≤Si+Al≤2.5%, S≤0.05%, P≤0.1%, at least one element chosen among Cr and Mo; subjecting the starting product to a hot forming step at a temperature between 700° C. and 380° C., to obtain a fully austenitic product; then quenching the product by cooling it down, to a quenching temperature QT lower than Ms in order to obtain a structure containing between 40% and 90% of martensite; then maintaining or reheating the product to a holding temperature PT between QT and 470° C. and holding the temperature PT for a duration Pt between 5 s and 600 s.

The present application belongs to the technical field of metal materials, and discloses a precipitation hardening stainless steel and a preparation method thereof. Through synergistic regulation of component design and process innovation, the present application breaks through the traditional contradiction of "strength-plasticity inversion" in additive manufacturing of precipitation hardening stainless steel, and prepares a precipitation hardening stainless steel with excellent strength and plasticity. On the one hand, by introducing N element in the raw material powder of the precipitation hardening stainless steel, the transformation of ferrite to austenite in the additive manufacturing process is promoted; on the other hand, the substrate is heated in situ to the vicinity of the martensite transformation starting temperature in the additive manufacturing process, and the transformation of austenite to martensite is inhibited; and after the printing is completed, global martensite transformation is triggered by natural cooling or air cooling, so that the full martensite structure with fine grains and high dislocation density is obtained. Finally, through aging treatment, the precipitation of nano Cu phase is induced, and the formation of austenite is reversed, so that the strength and plasticity of the precipitation hardening stainless steel are simultaneously improved.

The application provides a 1700MPa-grade hot forming steel with high cold bending performance and a preparation method and application thereof. A surface layer of the hot forming steel has soft ferrite structure, a subsurface layer has mixed structure of soft ferrite and martensite, and a core layer has carbon-poor martensite structure. The preparation method comprises any one or a combination of at least two of the following conditions: (A) the coiling temperature after hot rolling is 650-700 DEG C; (B) the pickling speed is less than or equal to 150 m / min; (C) the temperature of continuous annealing is 780-830 DEG C; (D) the atmosphere in the furnace is a mixture of nitrogen and hydrogen; (E) the dew point temperature is-35 DEG C to-17 DEG C. Through fine component design and process integration, the application successfully solves the contradiction between material strength and toughness, realizes double guarantee of high strength and high toughness, simultaneously meets the light weight requirement, and improves the competitiveness of existing products.

The invention belongs to the technical field of in-service repair of pressure pipelines, particularly discloses a B-type sleeve ring fillet weld welding method based on phase change stress compensation and application of the B-type sleeve ring fillet weld welding method, and aims to solve the problem of cold cracks caused by residual stress concentration at weld toes. Through specific alloy element ratio and control, the special welding wire with excellent cold crack resistance can be prepared through the design method. Comparative analysis results show that in the deposited metal welded by adopting the low-temperature phase change welding wire and the matched welding process, the martensite structure content (55-60%) is slightly higher than that of the deposited metal welded by using the welding wire of a control group; the level of welding residual stress generated by the special welding wire in a welding line area (especially a welding site area) is obviously lower than that of a control group welding wire, and the risk of generating cold cracks at the weld toe of the B-type sleeve repair ring fillet welding line is obviously reduced in cooperation with optimization of a welding line structure. And an effective technical solution is provided for improving the welding quality and the service reliability of B-type sleeve repair.

The invention relates to a black skin heat treatment method for a 05Cr15Ni5Cu4Nb forge piece with the diameter being smaller than phi 200 mm. After forging is finished, the temperature of a forging stock is controlled when the forging stock is loaded into a heating furnace, and it is guaranteed that the grain size of the forging stock is in a fine state; heating to a high temperature at a limited temperature rising speed to promote structure homogenization, and cooling to a room temperature in a furnace cooling or air cooling manner after heat preservation, so as to avoid a cracking phenomenon caused by relatively large stress generated by too fast structure transformation; fine calibration is conducted on the black skin forging stock, the straightness is controlled to be smaller than or equal to 5 mm, and large deformation caused by follow-up heat treatment is avoided; the medium with the weak cooling effect is adopted for solid solution cooling, the solid solution cooling effect is guaranteed, the needed fine lath-shaped martensite structure is obtained, it is guaranteed that the minimum thermal stress and the minimum structural stress are obtained in the solid solution cooling process, and the phenomenon that a forging stock cracks is avoided; the final mechanical property is ensured through high-temperature aging, so that relatively good strength, plasticity, toughness and hardness are obtained; through the heat treatment of the forge piece black skin, the surface rough turning allowance of the forge piece is reduced by 10-15 mm, and the production cost is effectively reduced; the surface quality is good, the phenomena of surface cracking, uneven structures and the like are avoided, and the manufacturing cost can be reduced.

The invention discloses a high-speed steel heat treatment machining method for a precise valve needle, and relates to the field of high-speed steel heat treatment. High-speed steel continuous resistance furnace heat treatment processing; high-speed steel is straightened, straightened and cut off on line; and performing subzero treatment on the high-speed steel straight rod. According to the SKH51 high-speed steel treated through the method, internal carbide distribution is more uniform and fine, a quenched martensite structure and a part of retained austenite structure are fully tempered and converted into tempered martensite, and the content of a small amount of retained austenite is accurately controlled, so that the high hardness is guaranteed, and meanwhile, the service life of the SKH51 high-speed steel is prolonged. The toughness, the fatigue resistance and the dimensional stability of the material are greatly improved; the high-end precision valve needle processed by the high-speed steel has the advantages that the wear resistance is obviously enhanced, the fatigue resistance is outstanding, and the service life is prolonged.

The application discloses a high-strength dual-phase steel with excellent low-temperature toughness and corrosion resistance and a production method thereof, and belongs to the technical field of steel rolling production. The chemical composition and mass content of the dual-phase steel are as follows: C: 0.06-0.12%, Si: 0.15-0.4%, Mn: 1.8-2.5%, Cr: 0.3-0.6%, Nb: 0.015-0.03%, Mo: 0.20-0.25%, Cu: 0.2-0.4%, Ni: 0.3-0.8%, Ti: 0.008-0.018%, N: 0.0030% or less, P: 0.025% or less, S: 0.002% or less, and the balance of Fe and inevitable impurity elements. The production method comprises a slab heating, rolling and continuous annealing process. The obtained dual-phase steel has uniform ferrite and martensite structures, good strength and toughness matching, and excellent low-temperature toughness and corrosion resistance.

A cast lip for an excavator bucket composed of a ferrous alloy having at least seven percent chromium by weight, between 3%-6% nickel by weight, and =0.12% carbon by weight, and a mainly martensitic structure.

The application discloses a preparation method of a heat-resistant and radiation-resistant ultra-fine grain martensitic steel and belongs to the field of metal structural materials. 12 The ceramic oxide powder replaces Y2O3 and Ti powder added in preparation of a traditional oxide dispersion strengthened steel (ODS); the ODS steel with an ultra-fine grain structure is prepared through high-energy ball milling and spark plasma sintering, and a martensitic structure is obtained through a special heat treatment process. Compared with the preparation processes of the traditional ODS steel and the martensitic steel, the method can obtain the martensitic structure with small grains without a complex thermal mechanical treatment process. The material has a tensile strength of 1000-1200 MPa at room temperature, has an elongation of 16-20%, and has a high-temperature strength of 280-320 MPa at 650 DEG C.

This disclosure provides an electrolytic corrosion method for martensitic structures in FeMnSi alloys, relating to the field of materials processing technology. The method includes: pretreatment operations such as grinding and polishing the FeMnSi alloy; mixing sodium hydroxide, sulfuric acid, and water to obtain an electrolyte for electrolytic corrosion; placing the pretreated FeMnSi alloy as the anode and a stainless steel plate as the cathode in an electrolytic cell containing the electrolyte to perform the electrolytic corrosion process; after the electrolytic corrosion process, removing the FeMnSi alloy, cleaning, and drying it. This disclosure can obtain a well-defined microstructure, meeting the needs of microscopic observation and analysis.

This invention relates to the field of shape memory alloy technology, specifically providing a zero-hysteresis giant linear elastic Ni-Fe-Ga shape memory alloy microwire and its preparation method. The preparation method of the alloy microwire includes: ① preparing austenitic alloy microwires using a glass coating method; ② inducing the austenite in the microwires into a full martensite structure through stress aging treatment and maintaining it at room temperature; ③ finally introducing some austenite into the martensite alloy microwires through annealing treatment, obtaining a wire material with a stable austenite / martensite coexistence structure at room temperature. The Ni-Fe-Ga ternary shape memory alloy microwires provided by this invention exhibit both zero hysteresis and giant linear elasticity characteristics under external force, with a maximum elastic strain of up to 7.7%, and the preparation method is simple, showing broad application prospects in high-precision micro-actuators and sensing fields.

This invention provides a steel plate with a tensile strength of 1310 MPa or higher, which achieves excellent compressibility in a steel primarily composed of martensite with excellent resistance to delayed fracture. The steel plate is characterized by having the following composition and microstructure, wherein the composition, by mass%, contains C: 0.12%–0.40%, Si: less than 1.5%, Mn: greater than 1.7% and less than 3.5%, P: less than 0.05%, S: less than 0.010%, sol.Al: less than 1.00%, N: less than 0.010%, Ti: 0.002%–0.080%, and B: 0.0002%–0.0050%, with the remainder being Fe and unavoidable impurities. The martensite in the microstructure has an area fraction of 85% or more relative to the overall microstructure, and the length L of the subplate boundaries in this martensite is... S Length L of the lath boundary B The ratio of L S / L B It satisfies the specified formula (1) and has a tensile strength of 1310 MPa or more.

The application relates to a 1450MPa-grade high-strength tool steel wire rod and a manufacturing method thereof. After rolling and wire drawing into a wire rod by adopting a Nb-V chemical composition design, the wire rod is subjected to on-line molten salt phase transformation control quenching isothermal treatment. The wire rod is cooled at a cooling speed of greater than or equal to 36 DEG C / s from a high-temperature austenite state in a front-stage molten salt, partial austenite is promoted to transform into a martensite structure, the wire rod is heated to a sorbite phase zone in a rear-stage molten salt, residual austenite is promoted to transform into a sorbite structure, isothermal tempering and stress relief treatment is performed on the structure, and finally, the wire rod is slowly cooled on a roller bed, the wire rod is prepared, the microstructure of the wire rod comprises isothermal sorbite and tempered martensite, the strength and plasticity matching of the wire rod is improved, the tensile strength is 1410-1460MPa, the reduction of area is 37%-42%, after cold working, additional heat treatment is not needed, the tool steel part is directly processed, the production energy consumption and cost of the high-strength tool steel are reduced, and the production efficiency is improved.

The application discloses a kind of bar finish rolling control cooling system and control cooling method, control cooling system includes the front cooling device, finish rolling entrance flying shear, finishing rolling unit, rear cooling device and finish rolling exit flying shear sequentially arranged on rolling line, the finishing rolling unit is made of multiple rolling mills in series, the front cooling device is connected with middle rolling unit rolling line before, the finish rolling exit flying shear is connected with cooling bed after, the front cooling device, rear cooling device are made of one or more cooling device;Control cooling method includes finish rolling front cooling, entrance flying shear cut head tail, finishing rolling unit rolling, finish rolling rear cooling, exit flying shear cut fixed size and cooling bed air cooling and so on process.The application can effectively reduce the cooling intensity of finish rolling exit rolling after rolling by reasonable equipment configuration and cooling process, so as to avoid the appearance of water cooling closed loop and martensite organization, and the resulting yin and yang surface and its bending phenomenon, can provide size precision high, surface quality good, temperature uniform, better microstructure and performance bar finished product.

The application provides a kind of straw returning to field with self-hardening broken blade steel and its preparation method, and belongs to the field of steel preparation.The broken blade steel chemical composition includes C, Si, Mn, Cr, Ni, Mo, Nb, Ti, V, B and Fe; wherein, the content of C is 0.30%~0.55%, the content of Si is 0.15%~0.25%, the content of Mn is 0.45%~0.75%, the content of Cr is 0.85%~2.0%, the content of Ni is 3.0%~4.5%, the content of Mo is 0.4%~1.2%, the content of Nb is 0.01%~0.060%, the content of Ti is 0.015%~0.03%, the content of V is 0.3%~0.9%, and the content of B is 0.002%~0.005% by mass fraction.By limiting the addition of C, Si and Mn to improve the tensile strength of steel, adding Ti and Nb elements for fine-grain strengthening and second phase particle precipitation strengthening, adding B and Cr elements to improve the hardenability of steel, adding Ni to improve the toughness of steel, adding Mo element to improve the ability of anti-tempering brittleness, and adding V element to ensure hardenability at local high temperature, the metallographic structure of the steel is obtained in the form of lath martensite, thereby improving the performance of the broken blade.