A method for producing a steel material for line pipes which has a tensile strength of 570 MPa or more, a compressive strength of 440 MPa or more, and a thickness of 30 mm or more, the method including heating a steel having a specific composition to a temperature of 1000 C. to 1200 C.; performing hot rolling such that a cumulative rolling reduction ratio in a non-recrystallization temperature range is 60% or more, a cumulative rolling reduction ratio in a temperature range of (a rolling finish temperature +20 C.) or less is 50% or more, and a rolling finish temperature is the Ar.sub.3 transformation point or more and 790 C. or less; and subsequently performing accelerated cooling from a cooling start temperature of the Ar.sub.3 transformation point or more, at a cooling rate of 10 C./s or more, until the temperature of a surface of a steel plate reaches 300 C. to 500 C.

A method for producing a steel material for line pipes including heating a steel having a specific composition to a temperature of 1000 C. to 1200 C.; performing hot rolling such that a cumulative rolling reduction ratio in a non-recrystallization temperature range is 60% or more, a cumulative rolling reduction ratio in a temperature range of (a rolling finish temperature +20 C.) or less is 50% or more, and a rolling finish temperature is the Ar.sub.3 transformation point or more and 790 C. or less; subsequently performing accelerated cooling from a temperature of the Ar.sub.3 transformation point or more, at a cooling rate of 10 C./s or more, to a cooling stop temperature of 200 C. to 450 C.; and then performing reheating such that the temperature of a surface of the steel plate is 350 C. to 550 C. and the temperature of the center of the steel plate is less than 550 C.

A hot dip galvanized steel sheet and hot dip galvannealed steel sheet improved in uniform ductility and local ductility, yield strength and tensile strength, and low temperature impact property, characterized by having a predetermined chemical composition, having a metal structure containing, by volume %, retained austenite: over 5.0% and tempered martensite: over 5.0%, having retained austenite containing C: 0.85 mass % or more, and having a ratio [C].sub.gb/[P].sub.gb of an amount of segregation of C (number of atoms/nm.sup.2): [C].sub.gb to an amount of segregation of P (number of atoms/nm.sup.2): [P].sub.gb at prior austenite grain boundaries of 4.0 or more.

The present invention provides a method for the fabrication of a steel sheet with a completely martensitic structure which has an average lath size of less than 1 micrometer and an average elongation factor of the laths is between 2 and 5. The elongation factor of a lath is defined as a maximum dimension l.sub.max divided by and a minimum dimension l.sub.min. The steel sheet has a yield stress greater than 1300 MPa and a mechanical strength greater than (3220(C)+958) megapascals. A composition of a semi-finished steel product includes, expressed in percent by weight, is, 0.15%C0.40%, 1.5%Mn3%, 0.005%Si2%, 0.005%Al0.1%, 1.8%Cr4%, 0%Mo2%, whereby: 2.7% 0.5 (Mn)+(Cr)+3(Mo)5.7%, S0.05%, P0.1%, optionally: 0%Nb0.050%, 0.01%Ti0.1%, 0.0005%B0.005%, 0.0005%Ca0.005%. The semi-finished product is reheated to a temperature T.sub.1 in the range between 1050 C. and 1250 C., then subjected to a roughing rolling at a temperature T.sub.2 in the range between 1000 and 880 C., with a cumulative rate of reduction .sub.a greater than 30%, to obtain a sheet with a completely recrystallized austenitic structure with an average grain size less than 40 micrometers and preferably less than 5 micrometers. The sheet is then partially cooled to prevent a transformation of the austenite at a rate V.sub.R1 greater than 2 C./s to a temperature T.sub.3 between 600 C. and 400 C. in the metastable austenitic range, and subjected to a finishing hot rolling at the temperature T.sub.3 of the partially cooled sheet, with a cumulative rate of reduction .sub.b greater than 30% to obtain a sheet that is then cooled at a rate V.sub.R2 which is greater than the critical martensitic quenching rate.

Provided is a cold-rolled steel plate for hot forming, which is excellent in corrosion-resistance and spot-weldability, contains, by weight %, C: 0.1-0.4%, Si: 0.5-2.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05%, S: 0.0001-0.02%, Cr: 0.5% to less than 3.0%, N: 0.001-0.02%, and a balance of Fe and inevitable impurities, satisfying formula (1) below, and includes an Si amorphous oxidation layer continuously or discontinuously formed at a thickness of 1 nm-100 nm on the surface thereof. Formula (1): 1.40.4*Cr+Si3.2 (wherein element symbols denote measurements of respective element contents by weight %).

A high-strength austenite-based high-manganese steel material and a manufacturing method for the same, the steel material comprising: manganese (Mn): 20 to 23 wt %, carbon (C): 0.3 to 0.5 wt %, silicon (Si): 0.05 to 0.50 wt %, phosphorus (P): 0.03 wt % or less, sulfur (S): 0.005 wt % or less, aluminum (Al): 0.050 wt % or less, chromium (Cr): 2.5 wt % or less, boron (B): 0.0005 to 0.01 wt %, nitrogen (N): 0.03 wt % or less, and a balance of iron (Fe) and other inevitable impurities, wherein stacked defect energy (SFE) represented by the following relationship 1 is 3.05 mJ/m.sup.2 or more, and a microstructure comprises 95 area % or more (including 100 area %) of austenite, and comprises 6 area % or more of strain grain boundaries in an austenite recrystallized grain, is provided.

SFE (mJ/m.sup.2)=24.2+0.950*Mn+39.0*C2.53*Si5.50*Al0.765*Cr[Relationship 1]

where Mn, C, Cr, Si, and Al denote weight percent of respective components.

A method of manufacturing an aluminium alloy strip article of variable width by means of continuously casting an aluminium alloy strip article, typically in a gauge range of 3 mm to 40 mm, and including the steps of, providing a first continuously cast aluminium alloy strip article at intermediate gauge and at least a second continuously cast aluminium alloy strip article at intermediate gauge, each of the aluminium alloy strip articles to be welded have the same thickness and are of the same aluminium alloy; welding the first aluminium alloy strip article at intermediate gauge to the second aluminium alloy strip article at intermediate gauge to form a welded aluminium alloy strip article; and rolling in at least one further rolling step of the welded strip article to a final gauge.

A steel part includes a steel sheet substrate and a coating on at least one surface of the steel sheet substrate. The coating includes between 0.2 and 0.7% by weight of Al, with a remainder of the metal coating being Zn and inevitable impurities. The steel sheet substrate and the coating have at least one deformation. An outer surface of the coating has a waviness Wa.sub.0.8 of less than or equal to 0.43 m.

The present invention provides a method for manufacturing a metal sheet. In this method, at least one of the following equations is satisfied: $\begin{array}{cc}\frac{Z}{d}+18\ln \left(\frac{Z}{d}\right)<8\ln \left(\frac{P}{V}\right)-27.52& \left(A\right)\\ f{O}_2<\frac{2.304.Math.{10}^{-3}}{{(27.52+\frac{Z}{d}+8\ln (}^{}}\end{array}$

Warming a metastable steel after coating and before or during cold rolling suppresses the transformation of austenite to martensite, resulting in lower mill loads and higher amounts of reduction at similar loads. As-warm rolled steel has enhanced mechanical properties when compared to steel reduced the same amount by cold rolling at room temperature.