HIGH-STRENGTH STEEL, METHOD FOR MANUFACTURING HIGH-STRENGTH STEEL, STEEL PIPE AND METHOD FOR MANUFACTURING STEEL PIPE

摘要

Provided is a technique for manufacturing a high-strengthsteel pipe for steam transportation of API gradeX100 or higher.High-strength steel has a specified chemicalcomposition in which Ti/N is 2.0 to 4.0,and X(%) calculated by using equation (1) is 0.90% or more,a microstructure having a bainite phase fraction of 70% ormore, and a tensile strength of 760 MPa or more at atemperature of 350°C.X = 0.35Cr + 0.9Mo + 12.5Nb + 8V (1)The symbols of elements in equation (1) respectivelydenote the contents (mass%) of the corresponding chemicalelements. In addition, the symbol of a chemical elementwhich is not included is assigned a value of 0.