METHOD FOR PRODUCING COLD-FINISHED STEEL MATERIAL HAVING EXCELLENT MACHINABILITY, DRILL-WORKABILITY AND STRAIGHT ADVANCING PROPERTY BY OMITTING HEAT-TREATMENT

摘要

PROBLEM TO BE SOLVED: To provide a cold-finished steel material which reduces the cost and has excellent machinability by omitting conventional intermediate heat-treatment where a hot-rolled coil is annealed and by applying reduction-working with control-rolling and low reduction.;SOLUTION: In a method for producing the cold-finished steel material having excellent machinability, a drill-workability and a straight advancing property, steel having ≤0.55% C content, that is, SC(carbon steel), SCr(chromium steel), SCM(chromium-molybdenum steel), SMn(manganese steel) or SBC(boron steel) as stipulated in the JIS is control-rolled at elevated temperature, then the rolling speed is reduced, and the rolling finishing temperature is lowered to 850 to 880°C. Further, thereafter, this rolled steel material is slowly cooled to soften this steel material into 79 to 82 HRB hardness maintaining ferrite+pearlite structure in a rolled state. The softened steel material is subjected to reduction-working at a low reduction of 8.5 to 9.5% to make the steel material to 92 to 95 HRB hardness.;COPYRIGHT: (C)2005,JPO&NCIPI