What kind of material is generally used for high-strength bolts?

1. The strength limit of common raw materials for high-strength bolts has a lot to do with heat treatment. After 40Cr heat treatment, it is generally difficult to meet the material requirements of 10.9S high-strength bolts. In the absence of strict testing, heat treatment can be used The processed surface strength is used to determine the strength limit of the material. In addition to the different properties in the process, high-strength bolts with different materials have different delayed rupture properties under high pressure. 2. The 40Cr high-strength bolts are mainly used in the spherical network frame of the bolt ball joint, and its design strength is generally 390MPa (d>=30mm) or 430MPa(d<30mm), no high pre-tension stress was found in the application. When it is used in the case of adding a high pre-tensioning force, attention should be paid to grasp and ensure its delayed rupture performance. The delayed time rupture performance of 20MnTiB high-strength bolts is better than that of 40B. 3. According to GB/T1231-91, the recommended material for 10.9S bolts is 20MnTiB (available specifications and models<=M24) and 35VB (available specification models<=M30). In the heat treatment process, large-diameter high-strength bolts are not easy to harden, so under normal circumstances do not use excessively large-sized high-strength bolts. If they are to be used, the internal stress during work should be reduced. Carbon steel and carbon steel bolts, mechanical equipment performance identification of screws and studs: (1) Carbon steel and carbon steel bolts, screws and studs (external thread diameter is 1.6-39mm, operating temperature is -50°C— 300°C) There are 10 performance level identification numbers, namely 3.6.4.6.4.8.5.6.5.8.6.8.8.8.9.8.10.9 and 12.9 (bolts manufactured with free-cutting steel. Operating temperature of screws and studs not higher than 250°C). Among them, bolts of grade 8.8 and above are made of low-carbon environmentally friendly carbon steel or medium-carbon steel and have undergone heat treatment (heat treatment. Quenching), collectively referred to as high-toughness bolts, and others are collectively referred to as general bolts. (2) Maijin introduced that the bolt performance level model consists of two parts of data, each indicating the nominal compressive strength and yield ratio of the bolt material. For example, a bolt with a performance level of 4.6 means: a. The nominal compressive strength of the bolt material reaches 400MPa; b. The yield ratio value of the bolt material is 0.6; c. The nominal tensile strength of the bolt material reaches 400×0.6= 240MPa grade. Performance level 10.9 high-toughness bolts, after the raw materials have passed the heat treatment process, can achieve: a. The nominal compressive strength of the bolt material reaches 1000MPa; b. The yield strength ratio of the bolt material is 0.9; c. The nominal tensile strength of the bolt material The strength reaches 1000×0.9=900MPa level.