TOOL STEEL FOR HOT WORKING, TOOL FOR HOT WORKING AND PLUG FOR PRODUCING SEAMLESS PIPE

摘要

A tool steel for hot working has a chemical composition: C: 0.05 to 0.5 %, Si: 0.1 to 1 %, Mn: 1.6 to 3.5 %, Ni: 0.05 to 0.5 %, Mo: 2 to 5 %, W: 2 to 5 %, Cu: 0.05 to 0.5 % and the balance: substantially Fe. The tool steel may further contain one or more of Cr, Co, REM, Ti, Nb, V, ZR and B; and a tool which is made of the above steel and has a surface covered with an oxide scale having a thickness of 50 to 1500 µm. The tool steel can have an oxide scale being formed on the surface thereof and exhibiting good adhesion to the surface and good lubricity, and has high strength. The tools include a drilling plug for use in producing a seamless pipe as a representative example.