Gas Soft Nitriding of Ductile Iron Crankshaft Zhu Jiacai; Ma Yeying; Tang Xiaohua (Assoc. Prof.,Northeast University of Forestry, Changchun 130118,China.)Through the tear-and-wear experiment of ductile iron before and after its gas saft nitriding,this paper explores the effect of friction velocity,friction time,and load supported by friction of slidingfriction,etc, factors,on friction performance. Meanwhile,it demonstraftes that the fine processing before soft nitriding can improve the surface roughness so as to decrease the surface friction coefficient, and after soft nitriding,even, compact and high hardness compound layer with e and r' phases as the main can be formed on the surface, resulting in the great increase of the abrasion-resistance and working life of ductile iron crankshaft.: soft nitriding; sliding friction