| Dual-phase steels consisting of ferrite and martensite exhibit better combination of strength and formability, lower yield stress, higher Hardening rate than other steels. This has led to the increased use of them in the automobile industry.Most mechanical and other engineering structures are exposed in the course of alternating load. Since fatigue is often no obvious macroscopic plastic deformation, and is often sudden rupture, causing great harm and economic loss. Dual-phase steel is more and more widely used in the automotive industry, so the security of it is more and more important.This work was carried on in order to investigate the fatigue properties of DP as part of the cooperation project between Changchun University of Technology and the China First Auto Work Group Corporation Development of800MPa and1000MPa High Strength Dual-phase for Automobile.The micro structures of DP800andDP1000are investigated and fatigue property test were carried out. Then we can understand the complex phase structure of dual-phase steel and determine the fatigue properties of dual phase steel (S-N fitting line). Then use the data to identify the fatigue life of DP at the cyclic state of Lara in8Hz loading frequency conditions, determine the Fatigue life calculation formula of DP800andDP1000.These results can provide some theoretical and data support for the applications of DP1000and DP800steel in FAW relevant automobiles.The results are concluded as follows:1、At the state of Lara cyclic and8Hz loading frequency conditions, the fatigue limit of DP800is490MPa, DP1000is690MPa,2、DP800fatigue life is calculated as, DP1000fatigue life is calculated as:lgN=127.3206-42.437491gσa3、The obvious fatigue striations can be seen from the fatigue pictures. And the fatigue extension has toughness characteristics; the instant-off area is the brittle fracture mode. |
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