表面强化与组织强韧化提高汽车钢板弹簧疲劳寿命研究

Leaf spring normally plays great roles in reducing vibration, adjusting orientation and carrying loading during the service of automobiles. Once failure of the leaf spring occurs, there will be great personnel casualty and property loss. In order to improve the fatigue lives of the spring steels, in this project, we will cooperate with the Changchun First Automobile Works (FAW) and Liaoning Fawer Automobile Spring Co. Ltd to carry out the experimental studies and theoretical analysis of the fatigue lives of the FAS3550 spring steel. The following studies will be performed. 1) To improve the surface strength and surface finish quality of the leaf spring through the Surface Spinning Strengthening (3S) technique, and further to introduce the residual compressive stress into the surface layer, in order to enhance the fatigue life of crack nucleation. 2) Through suitable rolling, quenching and consequent tempering treatments of the spring steel, one can control and optimize the microstructure in order to adjust the combination of strength and ductility. Then, the fatigue crack propagation rate of the spring steel may be minimized and the highest fatigue life may be achieved. 3) To optimize the new composition of the FAS3550 spring steel, one may obtain the better combination of strength and ductility of the new steel than the current FAS3550 spring steel. After that, one may have chance to further improve the total fatigue lives of the spring steel by combing the 3S technique in practice. The current project may provide some new technique standards for the optimization of composition, microstructure and combination of strength and ductility in order to improve the fatigue lives of the string steel. It may also give rise to some theoretical clues or models for the reliability of the automobile.

钢板弹簧在汽车服役过程中起着减震、方向调整及承担载荷的重要作用，一旦钢板弹簧发生断裂失效将导致财产损失与人员伤亡。为提高汽车钢板弹簧的疲劳寿命，本项目拟与中国第一汽车集团公司和富奥辽宁汽车弹簧有限公司合作，分别采取实验研究与理论分析来提高FAS3550钢板弹簧的疲劳寿命，具体提高疲劳寿命的途径主要包括三方面内容：1）通过表面旋压强化技术（简称3S技术）提高钢板弹簧的表面强度与光洁度，引入残余压应力来提高钢板弹簧的疲劳裂纹萌生寿命；2）对钢板弹簧进行合适的轧制+淬火+回火调质工艺处理，通过优化其微观组织使钢板弹簧的强度与韧性达到最优匹配，降低疲劳裂纹扩展速率并提高裂纹扩展寿命；3）对现有FAS3550钢板弹簧进行成分优化，使其具有更高强度与韧性配合，结合3S技术进一步提高其疲劳总寿命，为钢板弹簧通过表面强化与成分组织强韧化设计提高疲劳寿命提供技术标准，为汽车钢板弹簧的服役可靠性提供理论指导。

本项目提出采用表面强化提高疲劳裂纹萌生寿命和组织强韧化提高疲劳裂纹扩展寿命的研究思路，分别在表面强化设备设计与制造、材料表面强化微观机制与钢板弹簧强化疲劳延寿效果方面开展了大量实验研究，设计和制造了表面旋压强化试验机，并通过该旋压强化试验机对钢板弹簧钢强化，使钢板弹簧台架疲劳寿命超过24万周；在金属材料疲劳性能预测与优化理论方面开展了系统性与创新性研究工作，提出了金属材料疲劳强度最优判据、疲劳强度预测Y-T-F模型、疲劳裂纹扩展速率预测模型、疲劳强度临界夹杂物尺寸模型等若干疲劳性能预测新理论，上述模型用于指导钢板弹簧抗疲劳组织结构设计与制造。经过对组织强韧化设计的钢板弹簧台架疲劳实验测试表明：其疲劳寿命超过30万周。上述研究成果成功地将原有汽车钢板弹簧的疲劳寿命8万周次，分别从表面强化和组织抗疲劳设计两个方面都到超过16万周次的目标（24万和30万周）。研究成果在Acta Mater.、Mater. Res. Lett.、J. Mater. Sci. Tech.、Mater. Sci. Eng. A等SCI刊物上发表学术论文31篇，被SCI论文他引200余次，申请或授权发明专利19项，培养研究生8名，在国内外学术会议做邀请报告10次。