A cold-rolled and recrystallization-annealed flat steel product may include a ferritic microstructure, which possesses optimized formability and suitability for a wide variety of applications, including painting, for example. The flat steel product may include a steel comprising (in percent by weight): C: 0.0001%-0.003%, Si: 0.001%-0.025%, Mn: 0.05%-0.20%, P: 0.001%-0.015%, Al: 0.02%-0.055%, Ti: 0.01%-0.1%. The steel may further include at least one of Cr: 0.001%-0.05%, V: up to 0.005%, Mo: up to 0.015%, or N: 0.001%-0.004%, which may have the following mechanical properties: Rp0.2≦180 MPa, Rm≦340 MPa, A80≦40%, and n value ≦0.23. At least one surface may have an arithmetic mean roughness Ra of 0.8-1.6 μm and a peak count RPc of 75/cm. The present disclosure also concerns methods for producing flat steel products.

A high formability super strength cold-roll steel sheet or steel strip, and a method for manufacturing same. The steel sheet or steel strip comprises the following ingredients by weight percent: C 0.15% to 0.35%, Si 1.0% to 2.0%, Mn 1.6% to 2.6%, Mo 0.1% to 0.4%, P≦0.02%, S≦0.004%, N≦0.005%, Nb 0.015% to 0.04%, Ti 0.02% to 0.06%, Al 0.015% to 0.045%, B 0.0003% to 0.001% and B≧P %/30, and the balance being Fe and inevitable impurities. The steel sheet or steel strip has a tensile strength greater than or equal to 980 MPa, an elongation rate greater than or equal to 15% and a hole expansion rate greater than or equal to 40%, and has balanced performance.

This invention relates to prevention of delayed cracking of metal alloys during drawing which may occur from hydrogen attack. The alloys find applications in parts or components used in vehicles, such as bodies in white, vehicular frames, chassis, or panels.

A coated dual-phase steel and process for producing the coated dual-phase steel is provided. The process includes providing a steel slab with a desired chemistry, soaking the slab at an elevated temperature and then hot rolling the slab to produce hot-rolled strip. The hot-rolled strip is coiled and has a ferrite-pearlite microstructure. The coiled hot-rolled strip is cold-rolled into cold-rolled sheet with at least a 60% reduction in thickness compared to the thickness of the coiled hot-rolled strip. The cold-rolled sheet is subjected to an intercritical anneal followed by rapid cooling with the absence of an isothermal heat treatment or hold after rapid cooling near the molten metal pot temperature—during which, before or after which the steel is coated. The coated steel sheet has a dual-phase ferrite-martensite microstructure, a yield strength of at least 310 MPa, a tensile strength of at least 580 MPa and a total elongation to failure of at least 18%.

Provided is a high-strength hot-dip galvanized steel sheet having excellent plating adhesion, formability, and hole expandability with an ultimate tensile strength of 980 MPa or more, the hot-dip galvanized steel sheet comprising a hot-dip galvanized layer formed on a surface of a base steel sheet. The base steel sheet contains, by mass %, C: 0.05% to 0.4 %; Si: 0.01% to 3.0%; Mn: 0.1% to 3.0%; Al: 0.01 to 2.0%; in which Si+Al >0.5%, P: limited to 0.04% or less; S: limited to 0.05% or less; N: limited to 0.01% or less; and a balance including Fe and inevitable impurities, a microstructure of the base steel sheet contains 40% or more by total volume fraction of martensite and bainite, 8% or more by volume fraction of residual austenite, and a balance of the microstructure being ferrite or ferrite and 10% or less by volume fraction of pearlite. The martensite contains 10% or more by total volume fraction of two or more kinds of three kinds of martensites (1), (2), and (3), and the hot-dip galvanized layer contains less than 7 mass % of Fe.

Disclosed is a method for producing steel for blades having a metal composition consisting of, by mass, 0.55% to 0.8% C, not more than 1.0% Si, not more than 1.0% Mn, 12.0% to 14.0% Cr, not more than 1.0% Mo, not more than 1.0% Ni, and the balance Fe with impurities, comprising: a batch annealing step for batch annealing a material to be cold rolled having the metal composition at a temperature of 500° C. to 700° C. for 3 to 30 hours; a continuous annealing step for continuously annealing the batch annealed material for 5 to 30 minutes so that the batch annealed material is heated to at least an Ac1 transformation point of the metal composition step to obtain a continuously annealed material; and a cold rolling step for cold rolling the continuously annealed material, wherein the continuous annealing step and the cold rolling step are performed at least once, respectively.

Provided are a high-strength galvanized steel sheet containing 0.12% to 0.25% C, 0.01% to 1.00% Si, 1.5% to 4.0% Mn, 0.100% or less P, 0.02% or less S, 0.01% to 0.10% Al, 0.001% to 0.010% N, 0.005% to 0.100% Ti, and 0.0005% to 0.0050% B, the remainder being Fe and inevitable impurities, Ti>4N being satisfied. The high-strength galvanized steel sheet contains 80% to 100% martensite in terms of area fraction, 5% or less (including 0%) polygonal ferrite in terms of area fraction, and less than 3% (including 0%) retained austenite in terms of area fraction. The average hardness of martensite is 400 to 500 in terms of Vickers hardness (Hv). The average grain size of martensite is 20 μm or less. The standard deviation of the grain size of martensite is 7.0 μm or less.

The invention relates to a steel sheet having a tensile strength of 1180 MPa or more, which excels in workability and cold brittleness resistance. The high-strength steel sheet contains 0.10% to 0.30% of C, 1.40% to 3.0% of Si, 0.5% to 3.0% of Mn, 0.1% or less of P, 0.05% or less of S, 0.005% to 0.20% of Al, 0.01% or less of N, 0.01% or less of O, as well as Fe and inevitable impurities. The steel sheet has: (i) a ferrite volume fraction of 5% to 35% and a bainitic ferrite and/or tempered martensite volume fraction of 60% or more; (ii) a MA constituent volume fraction of 6% or less (excluding 0%); and (iii) a retained austenite volume fraction of 5% or more.

This invention relates to prevention of delayed cracking of metal alloys during drawing which may occur from hydrogen attack. The alloys find applications in parts or components used in vehicles, such as bodies in white, vehicular frames, chassis, or panels.

A method operates a continuous annealing line for the processing of a rolled good, in particular a metal strip. A property of the rolled good in relation to a point or a section of the rolled good is fed to a computer-aided model as an input variable. The point or the section of the rolled good is located before or in the continuous annealing line. For the purpose of precise control of the continuous annealing process, at least one material property of the rolled good after the continuous annealing process is simulated by the computer-aided model and compared with a specified target value. If the simulated material property deviates from the target value, at least one process variable of the continuous annealing process is controlled as long as the point or the section of the rolled good is located before or in the continuous annealing line.