Disclosed is a duplex stainless clad steel plate in which a duplex stainless steel plate as a cladding metal is bonded or joined to one or both surfaces of a base steel plate, in which the base steel plate comprises a predetermined chemical composition such that Nb/N is 3.0 or more and Ceq is 0.35 to 0.45, and the duplex stainless steel plate comprises: a predetermined chemical composition such that PI is 33.0 to 38.0; and a microstructure containing a ferrite phase in an area fraction of 35% to 65%, and in the microstructure, an amount of precipitated Cr is 1.00% or less and an amount of precipitated Mo is 0.50% or less.

Provided is a steel used for chassis parts, etc. of an automobile and, more specifically, to a hot rolled steel plate for an electric resistance welded steel pipe, which shows an excellent weldability in electric resistance welding, and a manufacturing method thereof.

Provided is a steel used for chassis parts, etc. of an automobile and, more specifically, to a hot rolled steel plate for an electric resistance welded steel pipe, which shows an excellent weldability in electric resistance welding, and a manufacturing method thereof.

In a tandem type cold rolling mill of a circulating oil-feeding system for continuously rolling a steel sheet by feeding a coolant serving as a rolling oil and a cooling water to each stand, an edge heater for heating both edge portions of the steel sheet to not lower than 60° C. as a steel sheet temperature at an entry side of a roll bite is arranged at an upstream side of the first stand in the cold rolling mill and a device for jetting a coolant having a concentration higher than that of the coolant fed to the firsts stand onto surfaces of both edge portions of the steel sheet is arranged between the edge heater and the first stand. The cold rolling mill can be used to roll a hard-to-roll material such as silicon or stainless steel sheet without causing an edge crack or sheet breakage in low-speed rolling.

A bar-shaped stainless steel product contains, by mass %, 0.001 to 0.030% of C, 0.01 to 4.00% of Si, 0.01 to 2.00% of Mn, 0.01 to 4.00% of Ni, 6.0 to 35.0% of Cr, 0.01 to 5.00% of Mo, 0.01 to 2.00% of Cu, and 0.001 to 0.050% of N. In the product, an F value is 20 or less, a rolling-direction-crystal-orientation RD//<100> fraction is 0.05 or more, and preferably a rolling-direction-crystal-orientation RD//<334> fraction is 0.2 or less. The above RD//<100> fraction means an area ratio of crystal having 25 degrees or less of an orientation difference between a <100> orientation and a rolling direction, and the above RD//<334> fraction means an area ratio of crystal having 10 degrees or less of an orientation difference between a <334> orientation and a rolling direction. F value=700C+800N+20Ni+10Cu+10Mn−6.2Cr−9.2Si−9.3Mo−74.4Ti−37.2A1−3.1Nb+63.2

A raw blank for vacuum carburization is provided. The raw blank for vacuum carburization has a chemical composition containing, by mass, C: 0.13 to 0.28%, Si: 0.01 to 1.20%, Mn: 0.10 to 1.50%, P: 0.030% or less, S: 0.050% or less, Cr: 0.30 to 2.20%, Al: 0.027 to 0.090%, N: 0.0060 to less than 0.0140%, and, as an optional element, Mo: 0.60% or less, the remainder being Fe and unavoidable impurities, and satisfying the following formula (1). AlN precipitates having an equivalent circle diameter of 100 nm or more exist at 1.5 pieces/100 μm.sup.2 or less in a cross section of the raw blank.

Al×N≤0.00090  (1)

It is noted that element symbols in the formula (1) denote a value of content (% by mass) of each element.

A raw blank for vacuum carburization is provided. The raw blank for vacuum carburization has a chemical composition containing, by mass, C: 0.13 to 0.28%, Si: 0.01 to 1.20%, Mn: 0.10 to 1.50%, P: 0.030% or less, S: 0.050% or less, Cr: 0.30 to 2.20%, Al: 0.027 to 0.090%, N: 0.0060 to less than 0.0140%, and, as an optional element, Mo: 0.60% or less, the remainder being Fe and unavoidable impurities, and satisfying the following formula (1). AlN precipitates having an equivalent circle diameter of 100 nm or more exist at 1.5 pieces/100 μm.sup.2 or less in a cross section of the raw blank.

Al×N≤0.00090  (1)

It is noted that element symbols in the formula (1) denote a value of content (% by mass) of each element.

An aspect of the present invention relates to 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): 1.4≤0.4*Cr+Si≤3.2 (wherein element symbols denote measurements of respective element contents by weight %).

An aspect of the present invention relates to 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): 1.4≤0.4*Cr+Si≤3.2 (wherein element symbols denote measurements of respective element contents by weight %).

A thick-walled, high-toughness, high-strength steel plate manufactured from steel having a particular composition and casted under conditions where the cooling rate of a surface during solidification is 1° C./s or less. The surface of the steel plate has a toughness (vE-40) of 70 J or more, and the steel plate has a thickness of 100 mm or more.