HEAT-TREATED STEEL MATERIAL AND METHOD OF MANUFACTURING THE SAME

摘要

The present invention provides a heat-treated steel material having strength of 1.800 GPa or more with obtaining excellent toughness and weldability. The heat-treated steel material includes a chemical composition represented by, in mass %: C: 0.05% to 0.30%; Mn: 2.0% to 10.0%; Cr: 0.01% to 1.00%; Ti: 0.010% to 0.100%; B: 0.0010% to 0.0100%; Si: 0.08% or less; P: 0.050% or less; S: 0.0500% or less; N: 0.0100% or less; Ni: 0% to 2.0%; each of Cu, Mo, and V: 0% to 1.0%; each of Al and Nb: 0% to 1.00%; and the balance: Fe and impurities. “4612×[C]+102×[Mn]+605≧1800” is satisfied where [C] denotes a C content and [Mn] denotes a Mn content. The heat-treated steel material includes a microstructure in which 90 volume % or more is formed of martensite, and a dislocation density in the martensite is equal to or more than 9.0×1015 m−2.

主权项

1. A heat-treated steel material, comprising:
a chemical composition represented by, in mass %: C: 0.05% to 0.30%; Mn: 2.0% to 10.0%; Cr: 0.01% to 1.00%; Ti: 0.010% to 0.100%; B: 0.0010% to 0.0100%; Si: 0.08% or less; P: 0.050% or less; S: 0.0500% or less; N: 0.0100% or less; Ni: 0.0% to 2.0%; Cu: 0.0% to 1.0%; Mo: 0.0% to 1.0%; V: 0.0% to 1.0%; Al: 0.00% to 1.00%; Nb: 0.00% to 1.00%; and the balance: Fe and impurities, and a microstructure represented by martensite: 90 volume % or more, wherein an “Expression 1” is satisfied where [C] denotes a C content (mass %) and [Mn] denotes a Mn content (mass %),
4612×[C]+102×[Mn]+605≧1800   “Expression 1”; wherein a dislocation density in the martensite is equal to or more than 9.0×1015 m−2; and wherein a tensile strength is 1.800 GPa or more.