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 34.0 to 43.0; 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 2.00% or less and an amount of precipitated Mo is 0.50% or less.

Provided is a round billet capable of reducing damage on a piercing plug in a method of producing a seamless metal tube with a Mannesmann process. The round billet (5), for use in a seamless metal tube, to be produced into a seamless metal tube with a Mannesmann process includes a body having a hole (6) formed in an axial direction of the body. The hole (6) includes an aperture (6a) opening at least at one end face of the round billet (5), and a tapered portion (61) continued to the aperture (6a) and having a diameter gradually increasing toward the aperture (6a).

Provided is a round billet capable of reducing damage on a piercing plug in a method of producing a seamless metal tube with a Mannesmann process. The round billet (5), for use in a seamless metal tube, to be produced into a seamless metal tube with a Mannesmann process includes a body having a hole (6) formed in an axial direction of the body. The hole (6) includes an aperture (6a) opening at least at one end face of the round billet (5), and a tapered portion (61) continued to the aperture (6a) and having a diameter gradually increasing toward the aperture (6a).

The present disclosure relates to a hot working method for stainless steel bars, comprising: step (1) heating a steel ingot at a heating temperature in a range from 1200 C. to 1270 C.; step (2) subjecting the heated steel ingot to radial forging and cogging down according to a total compression ratio greater than 3 to obtain a square billet; step (3) heating the square billet at a heating temperature in a range from 1200 C. to 1270 C.; and step (4) subjecting the heated square billet to hot rolling to obtain a bar. The processing method of the present disclosure can avoid the quality defect of surface crack while ensuring production efficiency by optimizing the process flow and controlling key process parameters, so that niobium-containing high-alloy austenitic heat-resistant stainless steel bars with good surface quality and structure can be prepared.

The present disclosure relates to a hot working method for stainless steel bars, comprising: step (1) heating a steel ingot at a heating temperature in a range from 1200 C. to 1270 C.; step (2) subjecting the heated steel ingot to radial forging and cogging down according to a total compression ratio greater than 3 to obtain a square billet; step (3) heating the square billet at a heating temperature in a range from 1200 C. to 1270 C.; and step (4) subjecting the heated square billet to hot rolling to obtain a bar. The processing method of the present disclosure can avoid the quality defect of surface crack while ensuring production efficiency by optimizing the process flow and controlling key process parameters, so that niobium-containing high-alloy austenitic heat-resistant stainless steel bars with good surface quality and structure can be prepared.

A cold rolled heat treated steel sheet having a composition with the following elements, expressed in percentage by weight 0.1%Carbon0.5%, 1%Manganese3.4%, 0.5%Silicon2.5%, 0.03%Aluminum1.5%, 0%Sulfur0.003%, 0.002%Phosphorus0.02%, 0%Nitrogen0.01% and can contain one or more of the following optional elements 0.05%Chromium1%, 0.001%Molybdenum0.5%, 0.001%Niobium0.1%, 0.001%Titanium0.1%, 0.01%Copper2%, 0.01%Nickel3%, 0.0001%Calcium0.005%, 0%Vanadium0.1%, 0%Boron0.003%, 0%Cerium0.1%, 0%Magnesium0.010%, 0%Zirconium0.010%, the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet having in area fraction, 10 to 30% Residual Austenite, 50 to 85% Bainite, 1 to 20% Quenched Martensite, and less than 30% Tempered Martensite.

A cold rolled heat treated steel sheet having a composition with the following elements, expressed in percentage by weight 0.1%Carbon0.5%, 1%Manganese3.4%, 0.5%Silicon2.5%, 0.03%Aluminum1.5%, 0%Sulfur0.003%, 0.002%Phosphorus0.02%, 0%Nitrogen0.01% and can contain one or more of the following optional elements 0.05%Chromium1%, 0.001%Molybdenum0.5%, 0.001%Niobium0.1%, 0.001%Titanium0.1%, 0.01%Copper2%, 0.01%Nickel3%, 0.0001%Calcium0.005%, 0%Vanadium0.1%, 0%Boron0.003%, 0%Cerium0.1%, 0%Magnesium0.010%, 0%Zirconium0.010%, the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of the steel sheet having in area fraction, 10 to 30% Residual Austenite, 50 to 85% Bainite, 1 to 20% Quenched Martensite, and less than 30% Tempered Martensite.

Provided are a high-strength cold-rolled steel sheet that has a tensile strength of 1320 MPa or more, excellent ductility and stretch flangeability, and a low failure rate in a hole expanding test, and a method for manufacturing the same. A high-strength cold-rolled steel sheet comprises a specific composition, wherein a total area ratio of ferrite and bainitic ferrite is 10% to 50%, an area ratio of retained austenite (RA) is more than 15% and 50% or less, an area ratio of tempered martensite is more than 15% and 60% or less, a ratio of RA with an aspect ratio of 0.6 or less is 70% or more, a ratio of RA with an aspect ratio of 0.6 or less in ferrite grain boundaries is 50% or more, and an average KAM value of bcc phase is 1 or less.

Provided are a high-strength cold-rolled steel sheet that has a tensile strength of 1320 MPa or more, excellent ductility and stretch flangeability, and a low failure rate in a hole expanding test, and a method for manufacturing the same. A high-strength cold-rolled steel sheet comprises a specific composition, wherein a total area ratio of ferrite and bainitic ferrite is 10% to 50%, an area ratio of retained austenite (RA) is more than 15% and 50% or less, an area ratio of tempered martensite is more than 15% and 60% or less, a ratio of RA with an aspect ratio of 0.6 or less is 70% or more, a ratio of RA with an aspect ratio of 0.6 or less in ferrite grain boundaries is 50% or more, and an average KAM value of bcc phase is 1 or less.

The present invention provides a hot-rolled and annealed ferritic stainless steel sheet which has sufficient corrosion resistance and in which cracks can be prevented during blanking into a thick flange, and a method for manufacturing the same. A hot-rolled and annealed ferritic stainless steel sheet has a chemical composition containing, in percent by mass, C: 0.001% to 0.020%, Si: 0.05% to 1.00%, Mn: 0.05% to 1.00%, P: 0.04% or less, S: 0.01% or less, Al: 0.001% to 0.100%, Cr: 10.0% to 19.0%, Ni: 0.65% to 1.50%, Ti: 0.10% to 0.40%, and N: 0.001% to 0.020%, with the balance being Fe and unavoidable impurities, and has a threshold stress intensity factor K.sub.IC of 35 MPa.Math.m.sup.1/2 or more.