A method for producing a high-strength steel sheet having high ductility, formability and weldability includes providing a cold-rolled sheet, with a composition containing: 0.15% ≤C≤0.23%, 1.4% ≤Mn≤2.6%, 0.6% ≤Si≤1.3%, with C+Si/10≤0.30%, 0.4% ≤Al≤1.0%, with Al≥6(C+Mn/10)−2.5%, 0.010% ≤Nb≤0.035%, 0.1% ≤Mo≤0.5%, annealing the sheet at 860° C.-900° C. to obtain a structure consisting of at least 90% austenite and at least 2% intercritical ferrite, quenching to a temperature between Ms-10° C. and Ms-60° C. at a rate Vc higher than 30° C./s, heating to a temperature PT between 410° C. and 470° C. for 60 s to 130 s, hot-dip coating the sheet, and cooling to room temperature. The microstructure includes 45% to 68% of martensite, consisting of 85% to 95% partitioned martensite having a C content of at most 0.45%, and fresh martensite; 10% to 15% retained austenite; 2% to 10% intercritical ferrite; 20% to 30% lower bainite.

Disclosed is an ultrahigh-strength maraging stainless steel with multiphase strengthening and a preparation method thereof. The stainless steel has a composition in mass percentage as follows: 1.0-5.0% of Co, 6.0-10.0% of Ni, 11.0-17.0% of Cr, 0.3-2.0% of Ti, 3.0-7.0% of Mo, 0.08-1.0% of Mn, 0.08-0.5% of Si, 0.02% or less of C, 0.003% or less of P, 0.003% or less of S, and Fe as a balance.

Disclosed is an ultrahigh-strength maraging stainless steel with multiphase strengthening and a preparation method thereof. The stainless steel has a composition in mass percentage as follows: 1.0-5.0% of Co, 6.0-10.0% of Ni, 11.0-17.0% of Cr, 0.3-2.0% of Ti, 3.0-7.0% of Mo, 0.08-1.0% of Mn, 0.08-0.5% of Si, 0.02% or less of C, 0.003% or less of P, 0.003% or less of S, and Fe as a balance.

A high-strength low-carbon bainitic fire-resistant steel and a preparation method thereof, belong to the technical field of low-carbon air-cooled bainitic fire-resistant steels. The problems of low yield strength, complicated production process and poor high-temperature mechanical properties of the fire-resistant steel in the prior art are solved herewith. The high-strength low-carbon bainitic fire-resistant steel disclosed herein have chemical components by mass percent of: 0.07%-0.1% of C, 0.7%-0.9% of Si, 1.0%-1.5% of Mn, 0.7%-0.8% of Cr, 1.0%-1.3% of Ni, 0.3%-0.35% of Cu, 0.6%-0.8% of Mo, 0.025%-0.035% of Nb, 0.09%-0.15% of V, 0.01%-0.015% of Ti, <0.2% of Nb+V+Ti, <0.02% of Alt, <0.003% of S, <0.008% of P, and the balance is Fe and inevitable impurities. Improvements are realized in the yield strength and high-temperature mechanical properties of the fire-resistant steel.

A high-strength low-carbon bainitic fire-resistant steel and a preparation method thereof, belong to the technical field of low-carbon air-cooled bainitic fire-resistant steels. The problems of low yield strength, complicated production process and poor high-temperature mechanical properties of the fire-resistant steel in the prior art are solved herewith. The high-strength low-carbon bainitic fire-resistant steel disclosed herein have chemical components by mass percent of: 0.07%-0.1% of C, 0.7%-0.9% of Si, 1.0%-1.5% of Mn, 0.7%-0.8% of Cr, 1.0%-1.3% of Ni, 0.3%-0.35% of Cu, 0.6%-0.8% of Mo, 0.025%-0.035% of Nb, 0.09%-0.15% of V, 0.01%-0.015% of Ti, <0.2% of Nb+V+Ti, <0.02% of Alt, <0.003% of S, <0.008% of P, and the balance is Fe and inevitable impurities. Improvements are realized in the yield strength and high-temperature mechanical properties of the fire-resistant steel.

A railroad tank car formed from steel alloy plates having improved toughness and puncture resistance. The steel alloy plates include a steel alloy including in wt. %: C: 0.1-0.15; Mn: 1.0-1.65; Si: 0.15-0.40; Al: 0.015-0.06; Mo: 0.1-0.3; Ni: 0.1-0.25; Nb: 0.015-0.045; Ti: up to 0.02; Cr: up to 0.22; V: up to 0.08; Cu: up to 0.35; P: max 0.025; S: max 0.015; and N: 0.004-0.01. The alloy plates may have been normalized for 30 minutes at 900° C. The alloy plates may have a tensile strength of at least 560 MPa; a yield strength of at least 345 MPa; a total elongation of at least 22%; a CVN impact toughness of at least 135.5J at −34.4° C.; a CVN impact toughness of at least 122J at −45.5° C. The alloy plates may have a ferrite-bainite microstructure, with 10% or less pearlite. The alloy plates of the inventive railroad tank car may have an absence of any banded ferrite-pearlite/martensite structure.

A railroad tank car formed from steel alloy plates having improved toughness and puncture resistance. The steel alloy plates include a steel alloy including in wt. %: C: 0.1-0.15; Mn: 1.0-1.65; Si: 0.15-0.40; Al: 0.015-0.06; Mo: 0.1-0.3; Ni: 0.1-0.25; Nb: 0.015-0.045; Ti: up to 0.02; Cr: up to 0.22; V: up to 0.08; Cu: up to 0.35; P: max 0.025; S: max 0.015; and N: 0.004-0.01. The alloy plates may have been normalized for 30 minutes at 900° C. The alloy plates may have a tensile strength of at least 560 MPa; a yield strength of at least 345 MPa; a total elongation of at least 22%; a CVN impact toughness of at least 135.5J at −34.4° C.; a CVN impact toughness of at least 122J at −45.5° C. The alloy plates may have a ferrite-bainite microstructure, with 10% or less pearlite. The alloy plates of the inventive railroad tank car may have an absence of any banded ferrite-pearlite/martensite structure.

Provided are a steel plate for high temperature applications having excellent strength at a high temperature and a method for manufacturing same. The steel plate for high temperature applications having excellent post-weld heat treatment resistance, according to the present invention, comprises by weight percent: C:0.05-0.25%; Mn:0.1-1.0%; Si:0.1-0.8%; Cr:1-3%; Cu:0.05-0.3%; Mo:0.5-1.5%; Ni:0.05-0.5%; Al:0.005-0.1%; and at least one of Ir:0.005-0.10% and Rh:0.005-0.10%, the balance being Fe and inevitable impurities.

Provided are a chromium-molybdenum steel plate having excellent creep strength and a method for manufacturing same. The chromium-molybdenum steel plate of the present invention comprises, by weight %, 0.11-0.15% of C, 0.10% or less of Si (exclusive of 0%), 0.3-0.6% of Mn, 0.010% or less of S (exclusive of 0%), 0.015% or less of P (exclusive of 0%), 2.0-2.5% of Cr, 0.9-1.1% of Mo, 0.65-1.0% of V, 0.25% or less of Ni (exclusive of 0%), 0.20% or less of Cu (exclusive of 0%), 0.07% or less of Nb (exclusive of 0%), 0.03% or less of Ti (exclusive of 0%), 0.015% or less of N (exclusive of 0%), 0.025% or less of Al (exclusive of 0%), 0.002% or less of B (exclusive of 0%), and the remainder of Fe and unavoidable impurities.

The present application provides a hot-work die steel and a preparation method thereof wherein the chemical constituents of the hot-work die steel in mass percentage are as follows: C: 0.20-0.32 wt %, Si: ≤0.5 wt %, Mn: ≤0.5 wt %, Cr: 1.5-2.8 wt %, Mo: 1.5-2.5 wt %, W: 0.5-1.2 wt %, Ni: 0.5-1.6 wt %, V: 0.15-0.7 wt %, Nb: 0.01-0.1 wt %, and a balance of iron, wherein an alloying degree is 5-7%; a tensile strength of the hot-work die steel at 700° C. is 560-700 MPa; a value of hardness of the hot-work die steel at room temperature is 32-38 HRC after holding at 700° C. for 3-5 h; and the hot-work die steel has an elongation of 14% to 16% at room temperature, a percentage reduction of area of 48% to 65%, and an impact toughness of 52-63 J at room temperature. The hot-work die steel of the present application has an excellent thermal stability as well as a good plasticity and a toughness at room temperature.