201 results about "Delayed fracture" patented technology

The cold heading wire rod comprises the following components in percentage by mass: 0.20%-0.26% of C, less than or equal to 0.35% of Si, 1.2%-1.6% of Mn, less than or equal to 0.02% of P, less than or equal to 0.005% of S, 0.04%-0.14% of V, 0.02%-0.10% of Nb, less than or equal to 0.2% of Cr, less than or equal to 0.1% of Ni, 0.02%-0.06% of Al and the balance of Fe and inevitable impurities, the V + Nb is greater than or equal to 0.09%, the C / 4 + Si + Mn / 2 + Cr / 2 + 2Ni is greater than or equal to 1.1% and less than or equal to 1.3%, the F + P is greater than or equal to 95%, the F grain size is greater than or equal to grade 12, the longitudinal pearlite strip The steel plate prepared by the method does not crack at 1 / 5 of a hot rolling state, can meet the requirements of a user on strength and plasticity of cold heading forming after 5-50% of cold drawing deformation, and can meet the requirements of a 10.9-grade high-strength fastener on fatigue and delayed fracture resistance at the same time.

The invention discloses high-strength bolt steel and a preparation method thereof, and the high-strength bolt steel alloy comprises the following components in percentage by mass: 0.35%-0.45% of C, 0.03%-0.80% of O, 0.05%-1.20% of RE, 0.02%-0.70% of Si, 0.80%-1.20% of Cr, 0.05%-0.85% of Ti, 0.01%-0.05% of Nb, 0.02%-0.35% of V, 0.001%-0.1% of B, less than or equal to 0.005% of S, less than or equal to 0.015% of P and the balance of Fe. According to the high-strength bolt steel and the preparation method thereof, the obdurability and the hydrogen-induced delayed fracture resistance of the material are synchronously improved through dispersion strengthening of the high-number-density nanometer oxide, the high-strength bolt steel can be used for producing 15.8-grade high-strength bolts with the tensile strength being 1500 MPa or above, nanometer oxide particles serve as a dispersion strengthening phase and a hydrogen trap, and the high-strength bolt steel can be used for producing high-strength bolts with the tensile strength being 1500 MPa or above. While the strength and the toughness of the material are improved, the fatigue performance and the delayed fracture resistance of the material are greatly improved.

A method for producing a test material that can measure the amount of diffusible hydrogen in a metal material having a welded portion with high accuracy is provided. A method for preparing a test material for measuring the amount of diffusible hydrogen in a metallic material having a welded portion, the method comprising: a blowhole position identifying step of identifying the position of a blowhole in the test material, which is a metallic material having a welded portion; and a processing step of processing the blowhole identified in the blowhole position identifying step so that it does not have a closed structure, or of removing the blowhole.

To enable a more accurate assessment of delayed fracture characteristics in a sheared end surface. A method for assessing delayed fracture characteristics for assessing the delayed fracture characteristics of a sheared end surface of a metal sheet included: a test including a step of restraining a metal sheet in a state where a predetermined load stress is loaded to a sheared surface of the metal sheet and a step of placing the metal sheet for a predetermined time in a predetermined hydrogen entry environment in the restrained state; and a step of determining a limit load stress being a load stress at the limit where a delayed fracture in the sheared surface of the metal sheet does not occur based on the results of the test and setting a stress margin to the occurrence of the delayed fracture in the sheared end surface of the metal sheet based on the determined limit load stress, in which the determined stress margin is set as an index of the assessment of the delayed fracture characteristics of the sheared end surface of the metal sheet.

The invention relates to a delayed fracture resistant non-quenched and tempered 14.9-grade high-strength cold heading steel wire rod and a preparation method thereof. The wire rod comprises the following chemical components: 0.33%-0.55% of C, less than or equal to 0.10% of Si, 1.5%-2.3% of Mn, 0.4%-0.6% of Cr, 0-0.04% of Nb, 0-0.1% of V, 0-0.1% of Ti, 0.004%-0.008% of B, more than or equal to 0.020% of Als, less than or equal to 0.040% of Alt, less than or equal to 0.015% of P, less than or equal to 0.010% of S, less than or equal to 1ppm of H and the balance of Fe and impurity elements. Fine control is adopted in the steelmaking process, the H content is strictly controlled to be lower than 1 ppm, a hydrogen trap is manufactured by adding microalloy elements such as Nb, V and Ti, and the delayed fracture resistance is improved; the air cooling speed of the rolled hot-rolled wire rod is precisely controlled, so that the structure of the hot-rolled wire rod is lath bainite, and high strength is realized by utilizing a medium-carbon bainite structure; the finished wire rod has high strength, high plasticity, excellent low-temperature impact toughness and good delayed fracture resistance.

Provided is a steel sheet that simultaneously achieves a strength of TS: 1310 MPa or more and excellent delayed fracture resistance. The steel sheet has a defined chemical composition and a complex structure consisting mainly of martensite and bainite, where carbides in the grains of martensite and bainite are 5% or more and 25% or less, the average circle equivalent diameter of carbides is 10 nm or more and 80 nm or less, and the particle size distribution of carbides satisfies Expression (1).

The purpose of the present invention is to provide a method for evaluating delayed fracture characteristics of a weld zone of a metal material, the method being capable of accurately and quantitatively evaluating delayed fracture characteristics of the weld zone of the metal material.　The method for evaluating delayed fracture characteristics of a weld zone of a metal material comprises: a hydrogen introduction step for introducing hydrogen into a test material composed of two or more metal material pieces having a weld zone; a tensile load application step for applying a tensile load to the hydrogen-introduced test material and acquiring a displacement-load curve; and a first evaluation step for evaluating an initial cracking load on the basis of the displacement-load curve.

The application belongs to the technical field of cold heading steel production, and particularly relates to a cold heading steel wire rod and a preparation method and application thereof. The mass percentage of each chemical component of the cold heading steel wire rod is shown in the specification. The cold heading steel wire rod provided by the application has good corrosion resistance, a weathering index I greater than or equal to 7, and good formability without cold heading cracking, and is suitable for the design and material selection of steel structures with strict requirements on the resistance to delayed fracture. The bolt prepared by the application has high strength, and the strength grade can be higher than or equal to 12.9.

The utility model relates to a device for testing hydrogen-induced delayed fracture of high-strength steel, which comprises an upper pressing cake, a lower pressing cake, an upper pressing block, a lower pressing block and a screw rod, a plurality of clamping grooves are uniformly distributed on the upper pressing block along the circumferential direction, the upper pressing block and the lower pressing block have the same structure, and the upper pressing cake and the lower pressing cake are connected on the screw rod in a penetrating manner; the upper pressing block and the lower pressing block are also connected to the threaded rod in a penetrating mode and are symmetrically arranged between the upper pressing cake and the lower pressing cake, a plurality of hydrogen-induced delayed fracture samples are arranged on corresponding clamping grooves of the upper pressing block and the lower pressing block respectively, the upper pressing cake and the upper pressing block can be locked and fixed to the threaded rod through nuts, and the lower pressing cake and the lower pressing block can be locked and fixed to the threaded rod through nuts. The hydrogen-induced delayed fracture experiment requirement of the high-strength steel with the pressure ranging from 1000 MPa to 2 GPa can be met, and reliable analysis data can be obtained when the hydrogen-induced delayed fracture experiment is carried out on the high-strength steel. Positioning and fixing holes are not required to be punched during sample preparation, a plurality of samples can be prepared by one clamp, and a bending test of a plurality of metal test pieces is allowed to be performed in one test.

The invention relates to a method for evaluating the hydrogen-induced delayed fracture risk of high-strength steel. The method comprises the following steps: stretching a notch sample to be measured at a strain rate in a range of 3.0 * 10 <-6 >-6.0 * 10 <-5 > s <-1 > until fracture so as to obtain a fracture stress sigma H, and stretching a reference notch sample at a strain rate in a range of 6.0 * 10 <-2 >-10.0 s <-1 > until fracture so as to obtain a reference fracture stress sigma 0; and evaluating the hydrogen-induced delayed fracture risk by using a hydrogen embrittlement risk index HERI = (sigma0-sigmaH) / sigma0 * 100%. According to the evaluation method, the influence of hydrogen in the high-strength steel on the performance can be accurately reflected, the test process is simplified, and rapid inspection on a production site is facilitated. The invention also relates to a method for determining the available dew point range of an austenitizing process for producing a hot-stamped product with an aluminum-silicon coating, which is resistant to hydrogen-induced delayed fracture.

Provided is a method for manufacturing a test material with which it is possible for the diffusible hydrogen content of a metal material having a welded portion to be measured accurately.　The method for manufacturing a test material for measuring the diffusible hydrogen content of a metal material including a welded portion includes: a blow hole position identification step for identifying a blow hole position in a test material, which is a metal material having a welded portion; and a machining step for machining the blow hole identified in the blow hole position identification step so as not to have a closed structure, or for removing the blow hole.

Provided is a method for producing a high-strength hot-dip galvanized steel sheet which has excellent LME cracking resistance while ensuring the appearance quality of the steel sheet, and in which the deterioration of delayed fracture resistance characteristics due to hydrogen embrittlement is suppressed. This method for producing a hot-dip galvanized steel sheet is a method in which a steel sheet containing a prescribed amount of Si is subjected to oxidation treatment, then reduction annealing is performed, and then hot-dip galvanizing is performed. The oxidation treatment is carried out in an atmosphere containing N2 and 500 ppm by volume or more of O2 at a temperature of 500-800 DEG C (inclusive). The reduction annealing is performed by means of a first reduction annealing of a front stage, in which the reduction annealing is held at a predetermined temperature for a predetermined time in an atmosphere containing 5.0-25 vol% of hydrogen gas with a dew point of-45 DEG C or more and + 20 DEG C or less and a remainder of N2, and a second reduction annealing of a rear stage, in which the reduction annealing is held at a predetermined temperature for a predetermined time in an atmosphere containing 5.0-25 vol% of hydrogen gas with a dew point of-45 DEG C or more and + 20 DEG C or less and the remainder of N2. The steel sheet is held at a predetermined temperature for a predetermined time in an atmosphere having a dew point of-10 DEG C to + 20 DEG C inclusive and containing 2.0 vol% to 8.0 vol% inclusive of hydrogen and a remainder of N2. In addition, the hydrogen gas concentration is adjusted so that the hydrogen gas concentration in the first reduction annealing in the front stage is higher than the hydrogen gas concentration in the second reduction annealing in the rear stage.

Provided is a method for evaluating the delayed fracture characteristics of a metal material, the method being capable of accurately evaluating delayed fracture characteristics caused by hydrogen entering the inside of a metal material due to atmospheric corrosion in which a chloride is a dominant factor of corrosion.　This method for evaluating the delayed fracture characteristics of a metal material carries out, at least one time, a process involving: a chloride adhesion step (A) in which droplets of a chloride-containing aqueous solution are adhered to an evaluation surface of a metal material so as to achieve a predetermined adhesion amount of a chloride; and a corrosion step (B) in which a cycle having a predetermined drying step (b1), a wetting step (b2), a transition step (b3), and a transition step (b4) is regarded as one cycle, and the cycle is performed at least one time, wherein, regarding the distribution of the droplets on the evaluation surface of the metal material in at least the first chloride adhesion step (A), the average contact area of the droplets is at least 0.1 mm2 and less than 3.0 mm2, the area ratio of the total contact area of the droplets to the area of the evaluation surface is 40-80%, and the standard deviation of the contact area of the droplets is at most 3.0 mm2.

A method for manufacturing high-strength, hydrogen-embrittlement-resistant bolts based on microsphere shot peening, and the bolts themselves, are disclosed. The manufacturing method includes: S1, cold heading and thread rolling of alloy structural steel billets to obtain bolt forming parts; S2, surface cleaning of the bolt forming parts, followed by overall surface peening with microspheres driven by high-pressure air; after overall peening, targeted strengthening peening treatment is performed on stress concentration areas such as thread roots, undercut grooves, and flange transition corners to obtain reinforced bolt parts; S3, the reinforced bolt parts are cleaned, dried, and phosphated to obtain finished bolt parts. This design, through a "overall + targeted" composite microsphere shot peening strategy, introduces a uniform residual compressive stress field and a micron-level fine-grained plastic deformation layer on the bolt surface, forming a thicker strengthening layer in stress concentration areas, significantly improving the fatigue strength and delayed fracture resistance of high-strength bolts, while ensuring uniform surface roughness and stable assembly friction coefficient.

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 invention provides a hydrogen-induced delayed fracture resistant ultrahigh-strength steel plate and a preparation method thereof, and belongs to the technical field of metal materials. The hydrogen induced delayed fracture resistant type ultrahigh strength steel plate comprises the following components in percentage by mass: 0.18 to 0.25 percent of C, 2.0 to 2.8 percent of Mn, 0.3 to 1.0 percent of Si, 3.0 to 6.0 percent of Al, 0.001 to 0.015 percent of Ce, 0.05 to 0.25 percent of Mo, 0.02 to 0.10 percent of Ti, less than or equal to 0.01 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.004 percent of N and the balance of Fe and inevitable impurities. The steel plate with ultrahigh strength, high elongation and excellent hydrogen-induced delayed fracture resistance can be stably produced through rare earth microalloying and precise structure regulation and control in cooperation with a proper process.

Provided is a high-strength steel sheet having a tensile strength of 1180 MPa or more, excellent bendability and delayed fracture resistance, and a wide optimal gap range for bending and forming a sheared end surface. The high-strength steel sheet comprises, in mass%, 0.030 to 0.500% of C, 0.50 to 2.50% of Si, 1.50 to 5.00% of Mn, 0.100% or less of P, 0.0200% or less of S, 1.000% or less of Al, 0.0100% or less of N, 0.0100% or less of O, and 0.005 to 0.100% of Nb, with the remainder comprising Fe and unavoidable impurities, and has a martensite content of 70% or more, a retained austenite content of 3 to 20%, and a total of a ferrite content and a bainitic ferrite content of 10% or less, the instability index k of the retained austenite is less than 6.1, and the instability index d of the retained austenite at the initial stage of processing is less than 5.7.

Provided is a hot-pressed member having excellent delayed fracture resistance and capable of releasing intruded hydrogen in a short time while reducing the amount of intruded hydrogen in a hot-pressing step. This hot-pressed member is provided with a steel material, an Al-Fe-based intermetallic compound layer which is arranged on at least one surface of the steel material and has a thickness of 10-35 [mu] m, and a diffusion layer which is arranged on the interface between the Al-Fe-based intermetallic compound layer and the steel material. The Al-Fe-based intermetallic compound layer contains an Al-rich phase having an Al concentration of 40 mass% or more and an Fe-rich phase having an Al concentration of less than 40 mass%, and the average length of the cross section of the Fe-rich phase in the direction perpendicular to the sheet thickness direction is 10 [mu] m or less.

The invention discloses a high-strength bolt, a steel material and a preparation method of the high-strength bolt, and relates to the technical field of alloy smelting, and the high-strength bolt is characterized by comprising the following components in percentage by mass: 0.18%-0.22% of C, 0.08%-0.12% of Nb, 0.02%-0.05% of Al, 0.004%-0.02% of Ti, 0.05%-0.08% of V, 0.0001%-0.002% of S, 0.00%-0.05% of Cu, 0.70%-0.90% of Mn, 0.20%-0.30% of Si, 0.90%-1.10% of Cr, 0.30%-0.50% of Ni, 0.15%-0.30% of Mo and the balance of Fe. The high-strength steel material has the advantages that the components of the high-strength steel material are optimized, an alloy structure composed of fine and uniform martensite, nanoscale precipitated phases and low internal stress is obtained, and the effects of improving the strength and the delayed fracture resistance are achieved.

The present invention provides a resistance spot welding method that can alleviate residual stress during resistance spot welding and can suppress occurrence of delayed fracture. In the resistance spot welding method, a pair of plate-shaped members having a hat-shaped cross section with a top plate portion and a pair of vertical wall portions extending from both ends of the top plate portion are overlapped, and resistance spot welding is performed on the pair of plate-shaped members. In the resistance spot welding method, there are included a step of detecting a contact load required for mutual contact of a portion where a gap between the pair of vertical wall portions becomes the largest due to a part tolerance of the plate-shaped members after the top plate portions of the pair of plate-shaped members are overlapped and resistance spot welding is performed on the top plate portions; and a step of setting a pressing force of a pair of electrodes that sandwich the pair of vertical wall portions during resistance spot welding on the overlapped pair of vertical wall portions in such a manner that the pressing force of the electrodes is greater than half of the contact load and smaller than the contact load, and performing resistance spot welding on the pair of vertical wall portions with the pressing force of the electrodes.

The invention relates to a 10.9-grade high-Si non-quenched and tempered steel wire rod for a fastener and a manufacturing method of the 10.9-grade high-Si non-quenched and tempered steel wire rod. The 10.9-grade high-Si non-quenched and tempered steel wire rod for the fastener comprises the following chemical components in percentage by weight: 0.08 to 0.12 percent of C, 1.45 to 1.90 percent of Si, 1.50 to 1.80 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.010 percent of S, 0.0005 to 0.0030 percent of B, 0.01 to 0.03 percent of Ti, 0.010 to 0.050 percent of Als, 0.02 to 0.04 percent of Nb and the balance of iron and trace impurities. The manufacturing process of the hot-rolled wire rod comprises the following steps: preparing raw materials according to chemical components, and sequentially carrying out converter / electric furnace-LF refining-vacuum degassing-casting-wire rod controlled rolling-wire rod controlled cooling. The steel wire rod produced by the method can obtain a uniform bainite structure at a relatively large range of cooling speed, and has the characteristics of uniform structure, good plasticity and excellent cleaning performance, and a fastener produced by drawing with relatively small area reduction rate, relatively small cold heading deformation and aging subsequently has the characteristics of stable mechanical property and excellent delayed fracture resistance; and the requirement of a 10.9-level fastener is met.

The application relates to the technical field of denture welding processing, in particular to a flexible support fastening component for denture root part in denture welding processing, which comprises a support table, an arc-shaped groove for loading a denture root part component is arranged on the inner side of the support table, a support assembly is arranged below the support table, and a flexible support fastener for fixing the denture root part component is arranged above the support table. The flexible support fastener comprises a support seat, a sliding seat is slidably arranged in the support seat, a positioning shaft with a conical top is detachably arranged on the top side of the sliding seat, and a return spring is fixed to one side of the sliding seat. The flexible support fastening component for the denture root part in the denture welding processing can pull the end part of the e-bar, effectively eliminates welding residual stress, prevents post-welding deformation and delayed fracture, the pulling force can effectively eliminate the internal stress of the e-bar welding position caused by high welding temperature, deformation and cracking of the e-bar caused by stress concentration are avoided, and the structural stability of the e-bar after welding is improved.

The present application relates to the technical field of metallurgical materials, and particularly relates to a rare earth micro-alloyed cold heading steel wire rod for 14.9-grade ultra-high strength fasteners and a preparation method thereof. Through reasonable alloy component design, synergistic micro-alloying of rare earth elements and precise control of process parameters, the plasticity and delayed fracture resistance of the fastener are significantly improved while meeting the ultra-high strength requirement of the 14.9-grade fastener, and the stability of rare earth addition and the industrial applicability of the process are realized. After the fastener prepared by the present application is subjected to a quenching and tempering heat treatment, the tensile strength is greater than or equal to 1400 MPa, the yield strength is greater than or equal to 1260 MPa, the elongation after fracture is greater than or equal to 9%, the reduction of area is greater than or equal to 48%, the core hardness is HRC 44-49, and the mechanical performance requirement of the 14.9-grade fastener is fully met.

The present invention provides a method, device, and program for predicting delayed fracture of a press-formed product, which predicts locations where delayed fracture will occur in a press-formed product made of high-tensile steel plate, and a method for manufacturing the press-formed product. [Solution] The method for predicting delayed fracture of a press-formed product of the present invention calculates the stress distribution and strain distribution of the press-formed product (S1), calculates the stress gradient in the direction in which a crack will propagate due to delayed fracture in a portion of the press-formed product where delayed fracture is a concern (S3), sets a hydrogen concentration distribution corresponding to the strain distribution of the press-formed product (S5), performs a hydrogen diffusion analysis of the press-formed product based on the stress distribution and the hydrogen concentration distribution, calculates the hydrogen concentration distribution after hydrogen diffusion (S7), and predicts whether delayed fracture will occur in the portion of concern based on delayed fracture judgment conditions based on the stress, strain, and hydrogen concentration at the stress gradient in the portion of concern, and the stress, strain, and hydrogen concentration in the portion of concern (S9).

Provided is a high-strength steel sheet having excellent member strength, stretch flangeability, bendability, and delayed fracture resistance under atmospheric corrosion and in a coated state. The steel sheet has a prescribed component composition, microstructure and the like, the average value [tau q] of the plastic deformation initiation stress [tau q] measured by nanoindentation at a position 1 / 4 of the sheet thickness of the steel sheet is 2.50-4.10 GPa, the standard deviation [sigma q] of the tau q is 0.30 GPa or less, and the average value [tau q] of the plastic deformation initiation stress [tau q] is 0.30 GPa or less. When [tau s] is the average value of the plastic deformation start stress [tau] s measured by the nanoindentation method at a position 10 [mu] m from the surface of the steel sheet, the ratio of measurement points less than 0.85 * [tau s] is 25.0% or less.

Provided are a steel sheet and a member, having high strength and high delayed fracture resistance, and methods for manufacturing the steel sheet and the member. The steel sheet has a specific chemical composition and a microstructure in which the area fraction of martensite is 95% to 100%, with the balance being one or more of bainite, ferrite, and retained austenite. In the steel sheet, prior-austenite grains have an average grain size of 18 μm or less, 90 mass % or more of the total content of Nb and Ti contained is present as a carbonitride having an equivalent circular diameter of 100 nm or more, and a Nb carbonitride and a Ti carbonitride, having an equivalent circular diameter of 1.0 μm or more, are present at a rate of 800 pieces / mm2 or less in total. The steel sheet has a tensile strength of 1310 MPa or more.

Provided is a hot pressed member for which an amount of hydrogen entering during the hot press process is small, that can release hydrogen that has entered in a short period of time, and that has excellent delayed fracture resistance. The hot pressed member includes: steel material; an Al-Fe intermetallic compound layer having a thickness of 10 µm to 35 µm, on at least one side of the steel material; and a diffusion layer at an interface between the Al-Fe intermetallic compound layer and the steel material. The Al-Fe intermetallic compound layer includes an Al-rich phase having an Al concentration of 40 mass% or more and an Fe-rich phase having an Al concentration of less than 40 mass%. Average length of the Fe-rich phase in a cross-section in a direction perpendicular to the thickness direction is 10 µm or less.

The invention provides a high-strength high-toughness hydrogen-induced delayed fracture-resistant oil casing material, and belongs to the field of oil exploitation equipment. The contents of Mn, Mo and V are optimized, and other components are matched, so that the material has good hydrogen-induced delayed fracture resistance while having high strength and high toughness. Experimental results show that the mechanical properties of the casing material provided by the invention are as follows: the tensile strength is not less than 1260Mpa, the yield strength is not less than 1200Mpa, the longitudinal impact energy at 0 DEG C is not less than 100J, and the transverse impact energy is not less than 70J; a notch constant-load delayed fracture test is carried out, the notch constant-load critical fracture stress ratio n is not smaller than 0.8, and fracture does not occur after more than 100 h.

The present invention contains 0.090-0.390% of C, 0.25-2.00% of Si, 2.00-3.70% of Mn, 0.100% or less of P, 0.0200% or less of S, 1.000% or less of Al, 0.0100% or less of N, and 0.0100% or less of O. At a position 1 / 4 through the sheet thickness, tempered martensite (M) is included at a proportion of 80% or more, fresh martensite (FM) is included at a proportion of less than 8%, ferrite (F) and bainite (B) are included at a total proportion of 15% or less, and retained austenite is included at a proportion of 15% or less. At a position located at the interface with respect to a zinc plating layer, tempered M and FM are included at a total proportion of 40% or less, F and B are included at a total proportion of 60% or more, and oxide particles (average aspect ratio of 1.2-6.0 and average long diameter of 0.10-0.70 µm) are included at a proportion of 2-18%. As a result, a high-strength zinc-coated steel sheet having excellent impact resistance, stretch flange properties, bendability, and shear disturbance stability for delayed fracture resistance can be obtained.

According to the bolt delayed fracture resistance test method, a torque sensor is arranged on a transmission arm of a transmission motor, a screwing sleeve is arranged at the tail end of the transmission arm of the transmission motor, a positioning tool is arranged on the side, provided with the transmission arm, of the transmission motor, a positioning sleeve is arranged on the positioning tool, and the end, provided with a nut, of a test bolt is embedded into the screwing sleeve. The stud end of the test bolt sequentially penetrates through the inclined washer and the positioning baffle and is inserted into the positioning sleeve to be connected with the test nut; and a pressure sensor is arranged between the positioning sleeve and the positioning baffle. The device has the advantages that the inclined pad with a certain angle is placed below the nut of the test bolt, the installation torque required by a customer is applied, the installation mode is close to the actual installation mode, and the stress distribution condition of the test bolt is equal to the stress condition of the test bolt under the actual working condition; if the test bolt is fractured, the delayed fracture resistance of the test bolt is insufficient, and the test is accurate.