高强度钢内螺纹冷挤压成形与强化试验研究

内螺纹冷挤压成形是提高内螺纹疲劳强度的有效方法.作者研制出挤压扭矩和温度的测量系统,并从理论上证明了挤压变形区金属在挤压过程中受到三向压应力的作用,这可以大大增加金属的塑性,改善内螺纹的成形条件.高强度钢内螺纹成形与强化的关键在于挤压丝锥结构的优化设计以及工件底孔尺寸、挤压速度和冷却润滑液的合理选择.疲劳对比试验结果表明:在两个不同应力水平下,用挤压丝锥挤压强化的300M高强度钢螺纹,其寿命是切削螺纹的4～30倍.

Experimental Research on Forming and Strengthening of Internal Threads in High Strength Steels

Cold form tapping process is an effective method to enhance fatigue strength of in-ternal thread. It is theoretically verified that the metal in the deformed zone are forced in threedirection compressive stresses, this may greatly increase the plasticity of the metal which im-proves the forming condition of internal threads. The measuring system of forming torque andtemperature has been developed. The key to form and strengthen threads in high strengthsteels lies in optimal design of the structure of forming tap and suitable choice of cored holesize, forming speed and lubricants. The result of fatigue tests shows that fatigue lifes of thethreads in 300M steel formed and strengthened by forming tap are from several to thirty timeslonger than those of cut threads at two different levels.