STEEL FOR CASE HARDENING WHICH HAS EXCELLENT COLD WORKABILITY AND MACHINABILITY AND WHICH EXHIBITS EXCELLENT FATIGUE CHARACTERISTICS AFTER CARBURIZING AND QUENCHING, AND PROCESS FOR PRODUCTION OF SAME

摘要

Cold worked, machined, and carburized quenched case-hardened steel prevented from formation of coarse grains, that is, case-hardened steel superior in cold workability, machinability, and fatigue characteristics after carburized quenching characterized by limiting, by mass%, S: 0.001 to 0.15%, Ti: 0.05 to 0.2%, Al: 0.04% or less, and N: 0.0050% or less, containing other specific ingredients in specific ranges, furthermore containing one or more of Mg: 0.003% or less, Zr: 0.01% or less, and Ca: 0.005% or less, limiting the amount of precipitation of AlN to 0.01% or less, and having a density d (/mm 2 ) of sulfides with a equivalent circle diameter of over 20 µm and an aspect ratio of over 3 and a content of S [S] (mass%) satisfying d‰¤1700[S]+20.