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Fastener Heat Treatment
Bolts are used in the largest amount in fasteners, and the materials manufactured mainly include steel, stainless steel, titanium alloys and non-ferrous metals. At present, except for a small number of large specifications that are manufactured by warm heading (warm extrusion) and cutting, most of them are manufactured by cold heading (cold extrusion) forming process. The final mechanical properties of bolts are determined by the material quality of the fasteners, and the lower limit of carbon content of 20MnTiB and ML20MnTiB is lower than 0.20%, which cannot meet the requirements of the standard for materials; the strength of 20MnTiB steel bolts is ≥1040MPa, and the hardness is 32—— The requirements of 39HRC are achieved by lowering the tempering temperature. When the tempering temperature is 425°C, the hardness and strength decrease, which cannot meet the performance requirements of the minimum tempering temperature in the standard. It can be seen from production practice that the excellent comprehensive mechanical properties of bolts not only depend on the heat treatment process and metallographic structure, but more importantly, they should have good chemical composition matching.