论高强度螺栓的材料及其强度问题

本文从高强度螺栓的服役条件出发论述了高强度螺栓选材的考虑因素。用低碳马氏体钢和中碳调质钢进行了静拉伸、偏斜拉伸、冲击韧性、疲劳强度和延迟断裂强度等试验。试验结果表明，与中碳调质钢相比，低碳马氏体钢的强度提高1/3以上，同时保持较高的塑性和韧性，螺栓的承载能力提高45～70%，而缺口偏斜敏感性并不显著升高；螺栓的疲劳强度与中碳钢调质态螺栓大体相同：低碳马氏体钢的延迟断裂敏感性比相同强度水平的40Cr钢小，并且在盐水和水中对延迟断裂是不敏感的。因此，选用低碳马氏体钢作高强度螺栓材料，不仅在综合机械性能方向有许多优点，而且其优良的工艺性能更是中碳钢不能比拟的。本文还进行了热处理前和后滚制螺纹对螺栓疲劳强度的影响试验，结果表明，热处后滚制螺纹可有效地提高螺栓的疲劳强度。根据本文的试验结果，作者对低碳马氏体螺栓钢的成分设计作了某些探讨。

ON THE MATERIALS OF HIGH STRENGTH BOLTS AND ITS STRENGTH

Factors to be considered in materials selection for high strength bolts are discussed in view of their service conditions. Axial and inclined tensile, impact, tensile fatigue and delayed fracture tests were made on low carbon martensite steels and tempered medium carbon steels. The experimental results have shown that the strength of lowcarbon marten sites is about 1/3 higher than that of 600℃ tempered medium carbon steels, while maintaining comparatively higher ductility and toughness; the load carrying capacity of bolts made from low carbon martensite steels is 45-70% higher as compared with that made of 600℃ tempered medium carbon steels, but the former shows no higher sensitivity to notches and inclination over the latter; fatigue strength of bolts made from both steels is basically the same; low carbon martensite steels have lower sensitivity to delayed fracture than steel 40Cr at the same strength level, and are insensitive to delayed fracture in brine and water, Therfore to choose low carbon martensite steels for making high strength bolts is advantageous not only for their superior comprehensive mechanical properties, but also for their much better forming characteristic. Tests were made on the influence of rolling thread before or after heat-treatment upon the fatigue strength of bolts. Results have shown, rolling screws after heat-treatment can effectivelly increase their fatigue strength. According to these experimental results, the auther also presents a discussion on composition design for low cardon martensite bolt steels.