METHOD FOR HEAT TREATMENT OF CAM FOR A LARGE SHIP

摘要

A method for heat treatment of a cam for a large ship is provided to improve physical properties such as hardness and wear resistance of the cam for the large ship by improving the cooling rate of quenching to a bout 680 deg.C/sec in a carburization step and increasing thickness of an effective hardening layer of a carburization layer to 3 mm, thereby reinforcing a surface hardening layer of the cam. A method for heat treatment of a cam for a large ship comprises a carburization step, a spheroidizing annealing step, a quenching step and a tempering step, wherein the carburization step comprises: a temperature raising process(1) of charging a cam workpiece for the large ship into a furnace and heating the cam workpiece from a temperature of 400 deg.C or lower to 850 deg.C at a heating rate of 100 to 120 deg.C/hr; a holding process(2) of holding the cam workpiece at 850 deg.C for 2 hours while pouring methanol onto the cam workpiece; a temperature raising process(3) of increasing a temperature of the cam workpiece to 950 deg.C, and continuously pouring methanol onto the cam workpiece; a carburization process(4) of holding the cam workpiece at 950 deg.C for 18 hours to form a carburization layer with a thickness of 3.0 mm on the cam workpiece; a diffusion process(5) of holding the cam workpiece at 950 deg.C for 17 hours to diffuse carburized carbon into the cam workpiece; a temperature lowering process(6) of lowering a temperature of the cam workpiece to a transformation point(A3) of 830 to 870 deg.C to obtain a cam workpiece with compact martensitic structure; a holding process(7); and a quenching process(8) of performing water cooling treatment by subjecting the cam workpiece to water quenching using water of 10 to 30 deg.C to obtain a cam for the large ship with a hardened martensitic structure.