基于高强度钢的冷挤压内螺纹抗疲劳机理研究

摘要

According to the forming process of cold-extruded internal thread of high-strength steel,the effect of parts status on the fatigue properties of internal thread was studied from the microscopic viewpoint,such as residual stress,surface roughness,microhardness,hardened layer,etc.The results showed that the metal surface of cold-extruded internal thread had a long fibrous structure,and it appeared to be streamline type and distributed along the normal direction of the tooth surface.The grains were pressed and refined,and the dislocation density was increased significantly.The work hardening phenomenon was appeared,and made the strength and the hardness of the metal increase.The residual compressive stress field formed on the surface of the metal could eliminate the impact of stress concentration,reducing fatigue notch sensitive,extending period of crack forming and slowing or restraining the expanding of the crack.The surface of cold-extruded internal thread had obvious finish mark,and its smooth of the surface was well.The surface roughness could be eliminated effectively,and reducing stress concentration and contributing to increasing the fatigue properties of internal thread.%根据高强度钢内螺纹的成形过程,从微观的角度研究表层残余应力、表面粗糙度以及表面显微硬度与硬化层等零件状态方面的因素对内螺纹疲劳性能的影响。结果表明,冷挤压内螺纹表层金属具有细长纤维状结构,呈流线型沿牙面法相分布,晶粒被破碎和细化,位错密度显著增加,出现加工硬化现象,使得金属的强度与硬度增加。螺纹表层形成的残余压应力场,能够消除应力集中的影响,减小疲劳缺口敏感,延长裂纹萌生期,减慢或抑制裂纹的扩展。挤压螺纹的表面没有明显的加工痕迹,表面平整性较好,可有效地减小螺纹表面粗糙度,减少产生应力集中,有助于提高螺纹的疲劳性能。