99results about How to "Improve solderability" patented technology

The invention belongs to the field of rail manufacturing, and specifically discloses a manufacturing method for improving the low temperature fracture resistance and contact fatigue damage resistance of rails and the rails obtained thereby. The method comprises the following steps: converter smelting, LF refining, RH vacuum treatment, billet continuous casting, billet cleaning and cooling, billet heating, rail rolling, online heat treatment and post-treatment, wherein: during the converter smelting process, bottom blowing of nitrogen is performed; after the RH vacuum treatment, iron-calcium wire feeding treatment is performed. Calculated by mass percentage, the chemical composition of the steel billet includes: C: 0.50-0.65%, Si: 0.45-0.95%, Mn: 0.35-0.85%, Cr: 030-0.80%, Cu: 0.20-0.55%, Ni: 0.10-0.30%, N: 0.007-0.030%, and the chemical composition of the steel billet also includes at least one of V, Nb, and Ti, wherein V: 0.02-0.15%, Ti: 0.001-0.030%, Nb: 0.01-0.08%, and the rest is Fe and unavoidable impurities. The steel rail obtained by the method provided by the present invention has excellent comprehensive properties such as resistance to low-temperature fracture, resistance to contact fatigue, corrosion resistance and weldability.

The present invention provides a stacked cascade GaN-based power device and a packaging method thereof. The device structure is a DBC double-sided ceramic substrate with through holes and grooves bonded on a TO-220 frame, a GaN-based chip bonded in the groove of the DBC ceramic substrate, and a vertically structured silicon-based MOSFET stacked on the source of the GaN-based chip to form a Cascode cascade structure. The present invention realizes the Cascode cascade structure by rationally arranging the GaN-based chip and the silicon-based MOSFET chip, thereby reducing the area of ​​the frame occupied by the chip, reducing the volume of the package body and improving the selectivity of the packaging form; the high thermal conductivity DBC double-sided ceramic substrate with through holes and groove structures increases the contact area between the chip and the high thermal conductivity material, improves the heat dissipation performance of the chip, optimizes the process steps, and improves the reliability and practicality of the device.

The invention relates to a method for improving the welding spot quality of resistance spot welding of a three-layer plate, which adopts an upper electrode cap and a lower electrode cap which are different from each other, effectively improves the spot welding nugget deviation of the three-layer steel plate, and widens the spot welding process window phenomenon. The spot welding method comprises the following steps: 1, performing surface treatment on a plate, and assembling in a lap joint form; 2, selecting an electrode cap; and thirdly, welding is conducted, and resistance spot welding of the three-layer steel plate is completed. The method has the advantages that the surface quality is good in the welding process, and no shrinkage cavity is generated; 2, the nugget deviation is small; thirdly, the spot welding process window reaches more than 2kA, and the spot welding process window is improved; and fourthly, the process is simple, production efficiency is high, cost is low, spot-welded joints are good in quality, and production and application are easy.

The invention discloses a hot-dip tinning copper plate strip capable of reducing the surface friction coefficient of a copper strip and a manufacturing method of the hot-dip tinning copper plate strip, relates to the field of hot-dip tinning of copper plate strips, and aims to solve the problem that a product cannot have high hardness and good weldability and corrosion resistance at the same time in the prior art. The method comprises the following steps: plating a pure tin layer on the surface of a copper plate strip in a hot dipping manner, cooling to room temperature, annealing, and preserving heat, so that a Cu6Sn5 layer grows between the copper plate strip and the pure tin layer until the Cu6Sn5 layer grows to occupy more than half of the overall thickness of the plating layer, thereby improving the hardness of the tin plating layer of the copper plate strip. Therefore, the hot-dip tin-plated copper plate strip has high hardness and good weldability and corrosion resistance, and the pure tin layer on the outermost layer can enable the copper plate strip to have low friction coefficient and low insertion and extraction rate and can be used for multi-piece insertion.

The invention discloses a dexterous four-foot cooperation robot welding system based on an industrial large model, belongs to the technical field of industrial robot welding, and provides the following scheme that the dexterous four-foot cooperation robot welding system comprises a four-foot robot body and is characterized in that a mounting base is arranged at the upper end of the four-foot robot body, and a mechanical arm body is arranged at the upper end of the mounting base; the arc-shaped guide groove formed in the outer side of the rolling cylinder is matched with the guide rod on one side of the positioning plate, so that the first spray head can flexibly swing left and right, the blowing cleaning range is remarkably expanded, and it is ensured that the periphery of a welding area is subjected to comprehensive and effective dust removal treatment; and meanwhile, the mounting plate and the cleaning brush at one end of the mounting plate are driven to synchronously swing, deep cleaning and removal of impurities on the surface of the iron plate are achieved, the adverse effect of the impurities on the welding quality is effectively avoided, and a solid technical support is provided for efficient and accurate welding operation of the four-foot cooperation robot in a complex environment.

The invention belongs to the technical field of precious metal electronic paste, and particularly relates to a preparation method and application of submicron spherical gold-platinum-palladium alloy powder used for being matched with low-temperature co-fired ceramics. The preparation method comprises the following steps: mixing a tetrachloroauric acid solution, a hexachloroplatinic acid solution and a tetrachloropalladium (II) acid solution to obtain a gold-platinum-palladium mixed solution; the gold-platinum-palladium mixed solution, the dispersing agent solution and the modified reducing agent solution are mixed for a second time, after a reduction reaction is conducted, static settlement and solid-liquid separation are conducted in sequence, obtained solids are washed and dried in sequence, and the obtained submicron spherical gold-platinum-palladium alloy powder used for being matched with the low-temperature co-fired ceramic has the advantages of being uniform in particle size, free of agglomeration, high in dispersity and the like. After low-temperature co-firing with a ceramic substrate, the substrate has the characteristics of flatness, no bubble, excellent weldability and soldering resistance, good batch stability and the like.

The invention relates to a high-reliability and high-integration microwave digital integrated module packaging method and a module, and belongs to the technical field of semiconductor device packaging, in the packaging method, welding of components on a low-temperature co-fired ceramic substrate is divided into two procedures, the welding procedure of a BGA packaging device is set after the welding procedures of other components, and the welding procedure of the BGA packaging device is set after the welding procedure of the other components. And the influence of other sintering procedures on the welding spots of the BGA packaging device is avoided. And meanwhile, the selectivity of the welding flux is also increased, and the Sn63Pb37 welding flux with better wettability is adopted for welding, so that the welding reliability of the BGA packaging device is improved.

The invention relates to the field of metal processing, and discloses a processing method of high-strength medium alloy carburizing steel, which comprises the following steps of: assembling parts and welding to form a product: aligning all the parts forming the product through corresponding grooves in a contact manner, and assembling all the parts to be welded to form a product prototype; carrying out integral preheating treatment on the to-be-welded parts which are integrally placed and assembled before welding, wherein the preheating temperature is 200-250 DEG C; after the temperature of all the to-be-welded parts is reached, welding the groove contact edges of the two to-be-welded parts which are placed and contacted one by one, so that a welding seam with a certain width is formed between the base materials of the two parts; all to-be-welded parts of the whole product are continuously heated in the welding process, and it is guaranteed that the temperature of the to-be-welded parts is always kept at 200-250 DEG C in the welding process; dehydrogenating the whole product; performing stress relief annealing on the whole product; and integrally tempering the product. According to the scheme, the overall performance of a welding product is effectively improved, and the performance homogenization of welding seams and part base metal is effectively improved.

The invention provides a machining device for metal powder tailored blank laser welding production. The machining device comprises a machining table, the machining table is connected with a welding room, the welding room is connected with a junction box, the junction box is provided with a magnetic attraction tool, the magnetic attraction tool is provided with a protective baffle, and the protective baffle is provided with a material frame; the welding room is connected with a welding head, the welding head is connected with a powder feeding pipe, the welding head is connected with a laser, the welding head is connected with a sealing ring, the sealing ring is connected with a powder storage barrel, the sealing ring is connected with a rotating disc, and the rotating disc is connected with a driving motor; the sealing ring is connected with an air pump which is connected with an air source. The powder flow is surrounded by the light beams emitted by the multiple lasers, powder can be fully melted on the molten pool and fused with the workpiece, meanwhile, the workpiece can be thoroughly welded, the workpiece is positioned and fixed through the magnetic attraction tool, the welding effect can be well improved, the feeding and discharging efficiency is improved, the production efficiency is improved, and the application cost is greatly reduced.

The invention relates to a normalizing type low-alloy container steel plate for an ultrahigh-temperature molten salt storage tank and a manufacturing method of the normalizing type low-alloy container steel plate. The normalizing type low-alloy container steel plate comprises the following chemical components in percentage by mass: 0.14-0.18% of C, 0.30-0.50% of Si, 1.30-1.60% of Mn, less than or equal to 0.010% of P, less than or equal to 0.002% of S, more than or equal to 0.020% of Al, less than or equal to 0.10% of Cu, less than or equal to 0.10% of Cr, less than or equal to 0.10% of Ni, 0.12-0.20% of Mo, 0.02-0.04% of Nb, 0.02-0.04% of V, 0.01-0.03% of Ti and the balance of Fe and inevitable impurities. The steel plate is produced through the procedures of converter smelting, external refining, vacuum treatment, slab continuous casting, controlled rolling and controlled cooling, normalizing heat treatment and the like, the thickness of the steel plate is 20-60 mm, and the steel plate has good weldability, forming machinability, high-temperature tensile property and low-temperature impact toughness, the room-temperature tensile yield strength Rp0.2 is larger than or equal to 350 MPa, the tensile strength Rm is larger than or equal to 540-620 MPa, and the percentage elongation after fracture A50 is larger than or equal to 25%; the-20 DEG C transverse impact unit value of the core part is not less than 100J; the tensile yield strength Rp0.2 at the high temperature of 300-400 DEG C is greater than or equal to 300 MPa, the tensile strength Rm is greater than or equal to 505 MPa, and the percentage elongation after fracture A50 is greater than or equal to 25%; and the surface hardness is less than or equal to 180 HB.

The invention relates to a voltage stabilizing diode chip manufacturing method, and belongs to the field of electronic accessories. According to the method for plating nickel and silver on the metal, the adhesion among all layers of the metal is improved, the metal is not prone to falling off, and the weldability and the uniformity are improved. And by adopting a silicon wafer diffusion method, only one-time photoetching is adopted, so that the cost is greatly reduced. Besides, the glass powder is adopted for glass passivation, the glass powder of the formula is easier and faster to melt after being subjected to high temperature, inconsistent thickness caused by non-uniform melting and cracks of a glass layer are avoided, the uniformity of glass passivation is improved, PN junctions are better protected while the area of the PN junctions is increased, and the reject ratio of electric leakage is avoided. And the working current is improved. According to the method disclosed by the invention, the mode of grooving the glass of which the grooves are removed by the ultraviolet laser on the front surface, grooving the back surface by the infrared laser and then splitting is adopted, so that the loss in the cutting process and the damage to a glass passivation layer are greatly reduced, and the product yield and the yield are effectively improved.

The invention relates to a method for solving interface failure of a resistance spot-welded joint of a 980MPa-grade galvanized complex-phase steel plate. The method comprises the following steps: determining preheating current and preheating time according to the plate thickness of a welding sample; determining the number of welding pulses and the single-pulse welding time according to the plate thickness of the welding sample; according to the plate thickness of the welding sample, the cooling interval time of preheating pulse and welding pulse and the welding pulse interval time are determined; determining welding pressure according to the steel plate thickness of the welding sample; and determining the dwell time according to the plate thickness of the welding sample. The method has the advantages that the pulse form with ultra-large preheating current and small preheating time is used, the content of a zinc layer in a weld nugget is greatly reduced, then the multi-pulse interval time is determined according to the plate thickness of a welding sample, the cooling interval time between welding pulses is long, and the welding precision is high. The method aims at providing sufficient time to enable nugget structures to tend to be relatively stable after a previous welding pulse is finished, and a next pulse is applied when the temperature of a welding spot is close to the normal temperature state, so that the nugget is further increased.

The utility model discloses a flexible anti-electromagnetic pulse cable assembly which comprises a cable lead, a copper net sleeve, a PTFE film, a flexible anti-wave sleeve, a braided sheath and an electric connector. The cable conductor is fixedly connected with the electric connector, the cable conductor is sleeved with a copper net sleeve in a penetrating mode, the copper net sleeve is wrapped with a PTFE film, the PTFE film is sleeved with a soft wave-proof sleeve in a penetrating mode, and the soft wave-proof sleeve is sleeved with a woven sheath in a penetrating mode; according to the technical scheme, the copper net sleeve and the soft wave-proof sleeve which have the advantages of being light in weight, small in hole, good in shielding performance, good in weldability and the like, and the PTFE film and the woven sheath which have the advantages of being large in expansibility, high in strength, resistant to abrasion, soft, light in weight and the like are adopted for shielding protection, and therefore the assembly is light in weight, good in signal shielding effect and high in strength.

The application discloses a high-aluminum-titanium heavy-duty combustion turbine vane crack repairing and tissue recovering method, and belongs to the field of heavy-duty combustion turbine vane repairing. The method adopts a repairing process route of complete solid solution heat treatment-welding repair-partial solid solution heat treatment-aging heat treatment, melts the matrix gamma' strengthening phase through complete solid solution heat treatment, reduces the volume fraction of the gamma' phase, reduces the liquefaction crack sensitivity, and improves the weldability of the matrix; the matrix surface layer crack of the turbine vane is completely exposed through complete solid solution heat treatment, the turbine vane crack repairing qualified rate is improved, the IN625 welding wire with low aluminum titanium content is used in the welding stage, the strengthening phase in the weld heat affected zone in the welding process is reduced, and the crack tendency of the weld is reduced; and the matrix gamma' strengthening phase is recovered through aging heat treatment. The method can effectively solve the heavy-duty combustion turbine vane crack repairing process of the high-aluminum-titanium turbine vane, and effectively improves the high-aluminum-titanium turbine vane repairing qualified rate.

The invention provides a preparation method for metallizing an electrode on the surface of a ceramic element by aluminum plating or aluminum alloy coating through a magnetron sputtering process. Comprising the following steps: cleaning and drying the surface of a ceramic element, putting the ceramic element into magnetron sputtering equipment with aluminum or aluminum alloy as a target material, and directly depositing the aluminum or aluminum alloy material on the surface of the ceramic element through magnetron sputtering to form a metallized electrode. A layer of aluminum or aluminum alloy metallization can be directly deposited on the surface of the ceramic element to serve as an electrode instead of silver, copper and other materials, the material cost is greatly reduced, the binding force and conductivity are good, and the process is simple and controllable.

This invention relates to the field of metallurgical technology, specifically to an ultra-low yield strength ratio, high-phosphorus, atmospheric corrosion-resistant steel and its preparation method. The preparation method includes: placing a cut billet into a slow-cooling pit, with the initial slow-cooling temperature ≥500℃ and the final slow-cooling temperature not lower than 300℃; heating the slow-cooled billet, controlling the billet's exit temperature from the furnace to 1140~1170℃, and the furnace time coefficient to be 10~11 min / cm; employing a two-stage rolling process, with the billet undergoing the first stage of rolling after descaling, and the surface temperature of the rolled piece at the start of the second stage of rolling being T2=(T+1600 / H-1.8H)℃, and the rolled steel plate not being water-cooled; and then placing the rolled steel plate between steel plates at 500~600℃ for at least 48 hours to achieve stacking cooling. This invention utilizes a fine, uniform microstructure and phosphorus and chromium compounds to improve the material's corrosion resistance, meeting the requirements for corrosion resistance and high toughness of steel used in building and engineering structures in coastal atmospheric environments.

The invention discloses superaustenitic stainless steel based on the synergistic effect of Mo and N and a preparation method of the superaustenitic stainless steel, and belongs to the technical field of high-performance metal materials. The stainless steel comprises the following components in percentage by mass: 26.0%-26.5% of Cr, 3.48%-4.52% of Mo, 0.29%-0.51% of N, 23.0%-25.0% of Ni, less than or equal to 0.01% of C, 0.40%-0.65% of Mn and the balance of Fe and inevitable impurities. According to the method, on the premise that the PREN value is kept basically unchanged, the point corrosion resistance of the stainless steel in a chloride ion-containing medium is remarkably improved by synergistically reducing the Mo content and increasing the N content and utilizing the interaction effect of Mo and N. The synergistic effect is embodied in inhibiting pitting initiation, slowing down pitting extension, promoting repassivation and forming a more protective passive film structure. The material is especially suitable for harsh corrosive environments such as offshore oil and gas exploitation and seawater desalination.

The utility model relates to medical instrument technical field especially, more particularly to a kind of adapter applied to monitor, including shell, shell is covered with plug, connecting seat and socket connected in sequence, wherein, the front end of plug is provided with two rows of connecting holes, the rear end of plug is equipped with two rows of elastic sheet corresponding with connecting hole and two skeletons for fixing elastic sheet, and skeleton is connected with plug.The elastic sheet is installed in the plug in the application, the connecting hole is corresponding with the elastic sheet, when the adapter is inserted or pulled out from the connector of monitor, the convex needle is contacted or disconnected with the elastic sheet, so that the elastic sheet occurs elastic deformation or rebound movement, the structure and manufacturing process of elastic sheet are simple, and have good elasticity, conductivity and weldability, the production cost is lower, meet the demand of disposable wrapping use.

The invention provides an OLIF approach lumbar vertebra fusion cage and fixing piece device and a manufacturing method of the OLIF approach lumbar vertebra fusion cage and fixing piece device. According to the device, reinforcing ribs and grids are arranged on a fusion cage, a right upper through hole and a left lower through hole which are vertically and obliquely crossed are formed in the right rear end of the fusion cage, the front end of the exterior of a fixing part body is conical and provided with self-tapping threads, the rear end of the exterior of the fixing part body is provided with external threads, and a stretching mechanism is arranged in the fixing part body. The anti-retreating mechanisms are arranged on the two sides of the front outer portion of the fixing piece body and connected with the stretching mechanism through the medical steel wires. The method comprises the following steps: 1, constructing a model; 2, 3D printing manufacturing; 3, assembling the fixing piece main body; 4, preparing a bone induction factor solution; 5, soaking the fusion cage; 6, disinfection treatment; and 7, storing at low temperature. According to the device, the fusion cage is in threaded connection with the fixing part main body, so that the stability of the fusion cage in the gap between the upper vertebral body and the lower vertebral body is improved, and the postoperative displacement and retreating of the fusion cage are effectively prevented.

The invention belongs to the technical field of medium-thickness plate production, and relates to a production method of a thick steel plate with a low-alloy structure. The steel plate comprises the following chemical components in percentage by mass: 0.09%-0.12% of C, 0.15%-0.55% of Si, 1.40%-1.70% of Mn, less than or equal to 0.014% of P, less than or equal to 0.005% of S, less than or equal to 0.30% of Cr, less than or equal to 0.25% of Ni, 0.025%-0.035% of Nb, 0.008%-0.020% of Ti, 0.020%-0.050% of Al and the balance of Fe and inevitable impurities. The key production steps include converter smelting, refining, continuous casting, heating, rolling and heat treatment. The problem that the uniformity of the mechanical property in the thickness direction of the medium-thickness plate is poor is solved. The adopted production method combines the advantages of a hot rolling process and a heat treatment process, the produced thick steel plate has excellent low-temperature toughness and good welding performance, and medium-thickness plate production with a wide chemical component range is achieved.

The invention discloses a PCB (Printed Circuit Board) substrate for LED (Light Emitting Diode) packaging and a surface anti-oxidation treatment method thereof. The PCB substrate is composed of the base layer, the heat conduction layer, the conductive layer and the insulating layer, the base layer is made of a high-strength and high-temperature-resistant material so as to provide stable support for the whole PCB substrate, meanwhile, the heat conduction layer is made of a material with a high heat conductivity coefficient, heat generated by an LED chip can be rapidly conducted out, and the heat dissipation efficiency is improved; the surface of the PCB substrate provided by the invention is subjected to special treatment, so that the PCB substrate has good weldability and corrosion resistance, and packaging and long-term use of an LED chip are facilitated; in order to improve the dimensional stability of the PCB substrate, the buffer layer is arranged between the base layer and the heat conduction layer, and the buffer layer is made of an elastic material and can absorb dimensional changes caused by factors such as temperature changes.

The present invention relates to C23C18, and more specifically, to a stable tin chemical plating solution and its application. The raw materials for preparing the plating solution include stannous salt, organic acid, thiourea accelerator and reducing agent, and the organic acid includes C1-C5 organic acid. The present invention provides a chemical plating solution, which can realize continuous tin plating under acidic conditions by using suitable thiourea accelerator and reducing agent, and realize higher smoothness and brightness on the tin layer with higher thickness. By adding suitable dispersant and organic acid, the stability of the plating solution can be improved while reducing the aggressiveness to ink. Through the joint action of the components of the plating solution provided by the present invention, a dense plating layer can be achieved at a faster plating speed, and the solderability of subsequent electronic components such as PCB boards can be improved.

The application discloses a preparation method of diamond / Ti / W / Cu composite material, which comprises the following steps: sequentially depositing a titanium layer, a tungsten layer and a copper layer on one surface of a diamond sheet to obtain a preform; placing the copper layer of the preform on a copper-molybdenum plating pad, and then placing the copper-molybdenum plating pad in an MPCVD device; vacuumizing a cavity of the MPCVD device to a background vacuum of 5*10 ‑ 3Torr; introducing hydrogen gas, controlling the hydrogen gas flow to be 400sccm-500sccm, adjusting the cavity pressure to be 60Torr-70Torr, starting a microwave system of the MPCVD device, controlling the microwave power to be 2000W-2750W, exciting the hydrogen gas to form a hydrogen plasma, increasing the temperature of the preform to 720-800, keeping the temperature for 15-30min, and then reducing the temperature to room temperature to obtain the diamond / Ti / W / Cu composite material. The application relies on an MPCVD hydrogen plasma annealing system to simultaneously achieve the technical effects of oxidation resistance and diffusion suppression, and obtains the diamond / Ti / W / Cu composite material with stable interface structure and excellent performance.

The invention belongs to the technical field of magnetic pulse welding, and particularly relates to a busbar aluminum bar structure and a magnetic pulse welding method of a busbar aluminum bar and an FPC, the busbar aluminum bar structure comprises an aluminum bar main body and a to-be-welded part used for carrying out magnetic pulse welding with the FPC, the to-be-welded part is integrally arranged at one end of the aluminum bar main body, and the to-be-welded part is arranged in a downward concave shape relative to the aluminum bar main body; the upper surface of the to-be-welded part is lower than the upper surface of the aluminum bar body, the lower surface of the to-be-welded part is lower than the lower surface of the aluminum bar body, the width of the to-be-welded part is larger than or equal to the width of the end, used for welding, of the FPC, and the end, used for welding, of the FPC is located above the upper surface of the to-be-welded part during magnetic pulse welding. During welding, the controllability of the to-be-welded part is higher, the overall surface of the welded busbar aluminum bar is smoother, the welding effect is more stable, and the welding quality is better.

The invention discloses a heterostructure hydrogen-resistant pipe as well as a preparation method and application thereof, and belongs to the technical field of pipe preparation. The preparation method comprises the following steps that raw materials of the heterostructure hydrogen-resistant pipe are smelted and stirred at the set temperature, then the raw materials are poured into a plate, hot rolling is conducted, and a hot-rolled plate is obtained; the hot-rolled plate is heated to be subjected to heat preservation for set time at the set temperature, then quenching and cold rolling are conducted till the target thickness is achieved, and a plate with a martensite structure is obtained; carrying out heat treatment on one side of the plate to obtain a heterostructure plate; and after the plate is subjected to hot pipe coiling at the set temperature, heat preservation is conducted for set time, so that the martensite structure of the heterostructure plate is subjected to phase change into tempered sorbite, then aftertreatment is conducted, and the heterostructure hydrogen-resistant pipe is obtained.

The present invention discloses an electrode slurry, a preparation method and a photovoltaic cell, and relates to the technical field of solar cells, in order to solve the problem that the existing electrode slurry silver layer and the welding strip are prone to produce cold welding, resulting in low tension. The electrode slurry includes a first conductive material and a second conductive material, the first conductive material at least includes nano silver powder, the second conductive material is a Sn-Zn-Ga-Nd alloy, and the melting point of the second conductive material is 176°C to 198°C. The preparation method is used to prepare the electrode slurry, and the photovoltaic cell uses the electrode slurry. The electrode slurry, preparation method and photovoltaic cell provided by the present invention are used to improve the welding bonding strength between the electrode slurry and the welding strip of the component string welding when printing the main grid during the battery manufacturing process.

Provided is a steel sheet having a predetermined chemical composition, wherein precipitates having a diameter of less than 0.1 µm are present in a number density of 10 to 200 / µm2 in a depth region of 1 to 10 µm from a surface, an amount of dissolved C in a depth region of 10 to 60 µm from the surface is less than 0.20 mass%, and a tensile strength is 1200 MPa or more. Further, provided is a method for producing a steel sheet comprising a step of hot rolling a steel slab having a predetermined chemical composition, then coiling it at 580°C or less, a step of pickling the hot rolled steel sheet to remove oxide scale and remove the surface layer of the hot rolled steel sheet down to at least 5 µm, and a step of cold rolling the hot rolled steel sheet, then holding it in an atmosphere of a dew point of -20 to 20°C at a temperature region of 200 to 400°C for 20 to 180 seconds and holding it at a temperature region of 740 to 900°C for 40 to 300 seconds.