A zinc-coated steel may be produced by performing a pre-alloying heat treatment after galvannealing the steel and prior to the hot stamping the steel. The pre-alloying heat treatment is conducted at a temperature between about 850 F. and about 950 F. in an open coil annealing process. The pre-alloying heat treatment allows for shorter time at the austenitization temperature to form a desired -Fe phase in the coating by increasing the concentration of iron. This also decreases the loss of zinc, and a more adherent oxide exists after hot stamping.

A coated metallic substrate including at least a first coating of aluminum, such first coating having a thickness below 5 m and being directly topped by a second coating including from 0.5 to 5.9% by weight of magnesium, the balance being zinc.

A coated metallic substrate including at least a first coating of aluminum, such first coating having a thickness below 5 m and being directly topped by a second coating including from 0.5 to 5.9% by weight of magnesium, the balance being zinc.

A high-strength galvanized steel sheet having a chemical composition containing, by mass %, C: 0.07% to 0.25%, Si: 0.01% to 3.00%, Mn: 1.5% to 4.0%, P: 0.100% or less, S: 0.02% or less, Al: 0.01% to 1.50%, N: 0.001% to 0.008%, Ti: 0.003% to 0.200%, B: 0.0003% to 0.0050%, and the balance being Fe and inevitable impurities, in which the relationship Ti>4N is satisfied, and a microstructure including, in terms of area ratio in a cross section located at of the thickness from the surface of a base steel sheet, a ferrite phase in an amount of 70% or less (including 0%), a bainite phase in an amount of 20% or less (including 0%), a martensite phase in an amount of 25% or more, and a retained austenite phase in an amount of less than 3% (including 0%), in which the average crystal grain diameter of the martensite phase is 20 m or less, and in which a variation in the Vickers hardness of the martensite phase is 20 or less in terms of standard deviation, as well as a method for manufacturing the steel sheet, is disclosed.

A high-strength galvanized steel sheet having a chemical composition containing, by mass %, C: 0.07% to 0.25%, Si: 0.01% to 3.00%, Mn: 1.5% to 4.0%, P: 0.100% or less, S: 0.02% or less, Al: 0.01% to 1.50%, N: 0.001% to 0.008%, Ti: 0.003% to 0.200%, B: 0.0003% to 0.0050%, and the balance being Fe and inevitable impurities, in which the relationship Ti>4N is satisfied, and a microstructure including, in terms of area ratio in a cross section located at of the thickness from the surface of a base steel sheet, a ferrite phase in an amount of 70% or less (including 0%), a bainite phase in an amount of 20% or less (including 0%), a martensite phase in an amount of 25% or more, and a retained austenite phase in an amount of less than 3% (including 0%), in which the average crystal grain diameter of the martensite phase is 20 m or less, and in which a variation in the Vickers hardness of the martensite phase is 20 or less in terms of standard deviation, as well as a method for manufacturing the steel sheet, is disclosed.

To provide a technique capable of preventing or suppressing fatigue failure of a vehicle underbody part material by 3DQ. A vehicle underbody part material relating to this disclosure includes: a quenched and bent steel pipe; and a plating film layer provided on a surface of the steel pipe and containing 30 mass % or more of Al and having an AlFe alloy existing in a surface thereof.

A cold-rolled and annealed steel sheet is provided, the chemical composition of which comprises, the contents being expressed by weight percent: 0.10C0.13% 2.4Mn2.8% 0.30Si0.55% 0.30Cr0.56% 0.020Ti0.050% 0.0020B0.0040% 0.005Al0.050% Mo0.010% Nb0.040% 0.002N0.008% S0.005% P0.020%,
the remainder consisting of iron and unavoidable impurities resulting from the smelting, the steel sheet having a microstructure consisting of, in surface proportion, martensite and/or lower bainite, said martensite comprising fresh martensite and/or self-tempered martensite, the sum of the surface proportions of martensite and lower bainite being comprised between 60 to 95%, 4 to 35% of low carbide containing bainite, 0 to 5% of ferrite, and less than 5% of retained austenite in island form.

A cold-rolled and annealed steel sheet is provided, the chemical composition of which comprises, the contents being expressed by weight percent: 0.10C0.13% 2.4Mn2.8% 0.30Si0.55% 0.30Cr0.56% 0.020Ti0.050% 0.0020B0.0040% 0.005Al0.050% Mo0.010% Nb0.040% 0.002N0.008% S0.005% P0.020%,
the remainder consisting of iron and unavoidable impurities resulting from the smelting, the steel sheet having a microstructure consisting of, in surface proportion, martensite and/or lower bainite, said martensite comprising fresh martensite and/or self-tempered martensite, the sum of the surface proportions of martensite and lower bainite being comprised between 60 to 95%, 4 to 35% of low carbide containing bainite, 0 to 5% of ferrite, and less than 5% of retained austenite in island form.

Provided are a high-strength galvanized steel sheet which can preferably be used as a material for automobile parts and a method for manufacturing the steel sheet. The steel sheet has a C content of 0.15% or less, in which an area ratio of ferrite is 10% or less, an area ratio of bainitic ferrite is 2% or more and 30% or less, an area ratio of martensite is 60% or more and 98% or less, an area ratio of retained austenite is less than 2%, an average grain diameter of martensite adjacent to bainite is 15 m or less, a proportion of massive martensite adjacent only to bainite to the whole metallographic structure is 10% or less, and a value (Hv) calculated by subtracting the Vickers hardness at a position located at 20 m from the surface of the steel sheet from the Vickers hardness at a position located at 100 m from the surface of the steel sheet is 30 or more.

Provided are a high-strength galvanized steel sheet which can preferably be used as a material for automobile parts and a method for manufacturing the steel sheet. The steel sheet has a C content of 0.15% or less, in which an area ratio of ferrite is 10% or less, an area ratio of bainitic ferrite is 2% or more and 30% or less, an area ratio of martensite is 60% or more and 98% or less, an area ratio of retained austenite is less than 2%, an average grain diameter of martensite adjacent to bainite is 15 m or less, a proportion of massive martensite adjacent only to bainite to the whole metallographic structure is 10% or less, and a value (Hv) calculated by subtracting the Vickers hardness at a position located at 20 m from the surface of the steel sheet from the Vickers hardness at a position located at 100 m from the surface of the steel sheet is 30 or more.