Structure And Performance Research Of Helical Spring With Residual Heat Quenching For Higher Speed Lorry

Helical compressed spring is an important component of lorry and plays an important part in shock absorption and support of the whole lorry. In order to meet the demand of higher speed and heavy loading, higher performance is asked. Heat treatment procedure for the spring determines its ultimate service performance. Roll residual heat quenching procedure has features with energy saving, small operation area, high productivity, grain refinement, less oxidation decarburization and deformation enforcement at high temperature. Now this procedure is adopted to produce springs in developed countries. because of unenlightened technique and diversification in spring steel,in china no one has carried out the research on whether residual heat quenching procedure can meet new demand since the speed of lorry is enhanced. The spring steel from the same group is selected as the test sample in this research. Helical circumcircle spring and inscribed circle spring of lorry are produced with two types of procedures ,such as roll residual heat quenching and re-heat treatment quenching. First metallurgical structure of such spring is analyzed with optical microscope, penetrating electric microscope and scanning electric microscope. The results show that: a. the martensite in roll residual heat quenching structure of circumcircle spring is finer than that in heat quenching structure. The surface of roll residual heat quenching structure of has no decarburization layer, but there is much spiculate Bainite and the structure is asymmetrical; b. The distributing of cementite in roll residual heat quenching and tempering structure of circumcircle spring is more asymmetrical than that in heat quenching and tempering structure and the size of grains in this two structures is different too. The structure of roll residual heat quenching inscribed circle spring is the same with that of heat quenching inscribed circle spring, but the structure of roll residual heat quenching inscribed circle spring is finer and distributes more symmetrically; The structure of spring tine is not the same with that of any other parts and there is quenching. Hardness, tensile and fatigue test are carried with different heat treatment helical spring. Results show that: a. hardness difference of roll residual heat quenching and heat quenching is obvious. Quenching procedure makes hardness distributing of circumcircle spring asymmetrical. Hardness of tine is higher than that of column and hardness of center is lower than that of edge. The hardness of residual heat quenching spring is more asymmetrical; Column hardness of inscribed circle spring is almost the same under different heat treatment procedure. Hardness difference of tine is obvious and tine hardness of residual heat quenching spring is obviously lower than that of heat quenching; tempering treatment not only reduces hardness difference of roll residual heat quenching spring and heat quenching spring, but also eliminates asymmetrical hardness distributing phenomenon that is caused by quenching;. σb, δand ψare all a little lower than that of heat quenching spring and tempering sample. Fatigue performance of roll residual heat quenching and tempering is almost the same as that of heat quenching and tempering. Fatiguel life of spring produced under this two quenching procedure can both meet the demand;. Through examining 7200 roll residual heat quenching spring already used, all performance can meet the demand of lorry of higher speed. There is no quality problem and helical compressed spring can be widely used in lorry of higher speed.