Aiming at the problems in easily fatigue failure at flat-end region of spring during service processing

the samples were taken from different period of heat-treatment spring to analyze the reason leading to fatigue broken in the region of flat-end rolling

and a measure to improving the technique parameter of flat-end rolling was persented.The results show that spring microstructure is increasingly coarsened with decreasing in distance toward the end.And then

the quenched martensite is coarsened

and the tempered structure is tended to be nonuniform due to the heredity

so then the tensile strength and hardness present fluctuation considerably in this region.The coarsening of microstructure is attributed to by the over-heating before flat-end rolling.Hence

the heating temperature and the holding time need to be controlled precisely to improve the quality of spring end.