MACHINE-STRUCTURAL CARBON STEEL EXCELLENT IN MACHINABILITY AND COLD FORGEABILITY

摘要

PURPOSE: To improve machinability and cold forgeability by incorporating specific amounts of Zr into a carbon steel and also adding elements for making cementite in a structure unstable and accelerating graphitization, elements for improving hardenability, and elements for improving machinability. ;CONSTITUTION: A carbon steel containing 0.1-1.5% C, 0.5% Si, and 0.1-2.0% Mn is used, and 0.005-0.2% Zr, 0.0015-0.0150% N, 0.003O% O, and 0.1-3.0% of one or more elements among Ni, Cu, and Co, or further, B, Al, Ti, and REM as elements for accelerating graphitization in a structure and Cr, Mo, V, and Nb as hardenability-improving elements, or further, one or more kinds among Pb, Te, P, Ca, Bi, Se, S, etc., as machinability-improving elements are incorporated into this carbon steel, independently or in combination. Cold forgeability is improved by decomposing hard and brittle cementite into soft ferrite and graphite by forming solid-solution nitrogen as cementitestabilizing element in the carbon steel into ZrN together with Zr and superior machinability is provided by the addition of machinability-improving elements, by which the machine-structural carbon steel use can be obtained.;COPYRIGHT: (C)1995,JPO