Patent ID: 8685177
Filing Date: 2014-04-01
Classification: B21K,C23C,F16C,Y10T

Abstract:
1. A manufacturing method of a crankshaft member, comprising the steps of: hot forging steel into a pre-crankshaft member's shape at an austenite single-phase region temperature, wherein said steel includes C, Ni, Mn, and Cr as required elements and Si, Cu, Mo, Ti, V, Nb, Ca and S as optional elements that may be included, in the amounts by weight of, C within the range of 0.20 to 0.50%, Si within the range of 0 to 0.6%, Mn within the range of 0.5 to 1.5%, S within the range of 0 to 0.10%, Cu within the range of 0 to 0.7%, Ni within the range of 0.05 to 1.5%, Cr within the range of 0.05 to 0.45%, and Mo within the range of 0 to 0.5%, to satisfy the condition 115≧70C+8Si+23Mn+11Cu+128Cr+83Mo>50; continuously cooling said steel at a cooling rate of 9.6 to 20 degrees Celsius per second from 800 degrees Celsius to 450 degrees Celsius by air blast, mist, oil cooling, or water-cooling so as to obtain a two-phase structure of ferrite and perlite having lamellar spacing of the perlite of 0.3 μm or less, and nitriding at least a portion of said steel to provide a hard nitride layer having an average hardness of the surface thereof within the range of 300 to 450HV.