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本文用20Mn_2TiB、16CrMnB和40Cr钢制成的M24的10.9和12.9级高强度螺栓,进行静拉伸试验、偏斜角度为0°、5°和10°,测定其螺纹断裂强度和断面收缩率;对静拉伸载荷下的断裂过程、方式和特征进行宏观和微观观测分析。根据这些试验结果讨论了高强度螺栓是否要淬透问题,对ISO898/1—1978关于高强度螺栓的淬透性要求提出了商榷意见,并讨论了低碳马氏体高强度螺栓的优越性。试验结果表明:高强度螺栓断裂时,主裂纹往往在螺母下1～3扣萌生,而且裂纹沅一般是从牙沟亚表面萌生,向中心扩展的,剪切唇和稳定扩展区的总厚度一般小于螺纹内径的1/2。所以,在保证静强度满足设计要求前提下,只要获得一定层深全马氏体层,螺纹即具备良好的抗裂纹萌生和稳定扩展的能力,不必追求螺栓截面基本淬透。
In this paper, M24 10.9 and 12.9 high-strength bolts made of 20Mn_2TiB, 16CrMnB and 40Cr steel were used for static tensile test. The skew angles were 0 °, 5 ° and 10 °, and their thread rupture strength and reduction of area were measured. The fracture process, mode and characteristics under static tensile load were analyzed macroscopically and microscopically. Based on the results of these tests, the issue of whether to quench high strength bolts is discussed. The requirements of ISO898 / 1-1978 for hardenability of high strength bolts are discussed and the superiority of low carbon martensitic high strength bolts is discussed. The results show that when the high-strength bolts are broken, the main cracks tend to sprout 1 ~ 3 under the nuts, and the cracks are usually initiated from the subsurface of the sulcus and spread to the center. The total thickness of the shear lip and the stable expansion zone is generally Less than half the diameter of the thread. Therefore, under the premise of ensuring the static strength to meet the design requirements, as long as a certain depth of martensite layer is obtained, the thread has the good ability of anti-crack initiation and stable expansion, and does not have to pursue the basic quenching of the bolt cross section.