Heat-resistant steel for steel pipes and castings

A method of preparing a steel pipe, comprising:

• mixing raw materials according to mass percentage element proportioning of heat-resistant steel as follows:
• 0.08-0.14 wt % of C, 0.20-0.40 wt % of Si, 0.30-0.60 wt % of Mn, <0.020 wt % of P, <0.010 wt % of S, 9.00-10.00 wt % of Cr, 2.80-3.30 wt % of Co, 1.65-1.90 wt % of W, 0.55-0.80wt % of Mo, 0.15-0.25 wt % of V, 0.03-0.08 wt % of Nb, 0.006-0.015 wt % of N, 0.009-0.015 wt % of B, <0.20 wt % of Ni, <0.02 wt % of Al, <0.02 wt % of Ti, <0.02 wt % of Zr, <0.15 wt % of Cu, <0.02 wt % of Sn, <0.02 wt % of As, <0.005 wt % of Sb and the balance of Fe
• wherein a Cr equivalent is <8.5% based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, and a mass ratio of B to N is 0.65-2.40:1;
• smelting the mixed raw materials;
• making a pipe blank by any one of continuous casting, die casting, hot rolling or hot forging of the smelted mixed raw materials;
• making the pipe blank into a steel pipe by any one of hot rolling, hot extrusion, hot expansion, cold drawing, cold rolling, or forging and boring of the pipe blank;
• normalizing or quenching the steel pipe;
• and
• tempering the steel pipe,
• wherein the normalizing or quenching is carried out at a temperature of 1070-1160° C.;
• and the tempering is carried out at least one time, and the tempering is carried out at a temperature of 740-790° C.

A method of preparing a casting, comprising:

• mixing raw materials according to mass percentage element proportioning of heat-resistant steel as follows:
• 0.08-0.14 wt % of C, 0.20-0.40 wt % of Si, 0.30-0.60 wt % of Mn, <0.020 wt % of P, <0.010 wt % of S, 9.00-10.00 wt % of Cr, 2.80-3.30 wt % of Co, 1.65-1.90 wt % of W, 0.55-0.80 wt % of Mo, 0.15-0.25 wt % of V, 0.03-0.08 wt % of Nb, 0.006-0.015 wt % of N, 0.009-0.015 wt % of B, <0.20 wt % of Ni, <0.02 wt % of Al, <0.02 wt % of Ti, <0.02 wt % of Zr, <0.15 wt % of Cu, <0.02 wt % of Sn, <0.02 wt % of As, <0.005 wt % of Sb and the balance of Fe
• wherein a Cr equivalent is <8.5% based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, and a mass ratio of B to N is 0.65-2.40:1;
• smelting and pouring the mixed raw materials to obtain a casting;
• normalizing or quenching the casting, and
• tempering the casting,
• wherein the normalizing or quenching is carried out at a temperature of 1070-1160° C.;
• and the tempering is carried out at least one time, and the tempering is carried out at a temperature of 730-780° C.