At the time of carburization heat treatment production manner null of the case hardening steel where the crystal grain does not coarsen

摘要

PURPOSE:To produce a case hardening steel free from coarsening of crystalline grains at the time of carburizing heat treatment by specifying the composition of a steel containing C, Si, Mn, S, N, Al, Ti, etc., regulating the dissolved oxygen content in the crude molten steel to a specific value, and then performing deoxidation with Al, Ti, etc. CONSTITUTION:At the time of producing a steel which has a composition containing, by weight, 0.10-0.30% C, 0.05-0.50% Si, 0.30-2.00% Mn, 0.02-0.20% S, 0.002-0.020% N, and 0.005-0.050% Al and/or 0.005-0.030% Ti and further containing, if necessary, one or more kinds among 0.20-2.00% Cr, 0.10-0.50% Mo, and 0.30-4.00% Ni and further one or more kinds among 0.010-0.070% Zr, 0.010-0.070% Ce, and 0.010-0.070% Hf, deoxidation is made by adding C, Si, Mn, etc., to a crude molten steel or by means of vacuum degassing. The resulting molten steel in which dissolved oxygen content is regulated to 10-150ppm is subjected to deoxidation by means of one or more kinds among Al, Ti, and alloys thereof. By this method, MnS can be finely precipitated, and the case hardening steel free from coarsening of crystalline grains at the time of carburizing heat treatment can be obtained.