Manufacturing method null of the non quality check tellurium free-cutting steel where the hot ductility which uses buckling die continuous casting equipment

摘要

PURPOSE:To produce a free-cutting steel having excellent high-temp. ductility by subjecting a non-tempered Te free-cutting steel material which contains Te as an element for improving machinability, is decreased in the contents of Al and N and is incorporated with a specific ratio of Zr to heating and forging under specific conditions. CONSTITUTION:The Te-contg. steel ingot contg., by weight%, 0.70% C, 1.5% Si, 2.0% Mn, 0.035% P, 0.10-0.50% S, 0.10% Te, 0.0002-0.0020% B, and Zr and N so as to satisfy ZrNX91.2/14.0% is heated to 1000-1300 deg.C and is then forged at 50% draft in the temp. region above 850 deg.C. The forged steel is subjected to accelerated cooling at =0.3 deg.C/sec cooling rate right after the forging. The machinability is improved by addition of the Te and S to the steel and the N in the steel is fixed as ZrN by addition of the Zr to prevent formation of AlN. The non-tempered Te free-cutting steel which does not generate ingot cracking during blooming and has the excellent high-temp. ductility is thereby produced.