Study On The Application Of High-Strength Bolts

With the development of automobile, machinery, energy, light industry, construction and other industries, the material of all kinds of bolts is demanded, the material not only has lower cost but also has lighter weight materials, higher strength, better toughness, excellent corrosion resistance, long life and easy processing. So it has great signifiance to study the steel of high-strength bolts and to develop the high-strength bolts with better properties.In this thesis, the composition, microstructure and properties of class 8.8,10.9,12.9 bolts on the market at home and abroad were investigated by means of electron probe microscopy analysis, X-ray Diffraction analysis, hardness analysis, SEM morphology analysis, metallogra-phic analysis, tensile test analysis, impact test analysis and fracture analysis.Results show that:domestic bolts are made of carbon steel or alloying steel produced by quench and temper; Some of the imported bolts are made of strengthen non-quenched and tempered steel, and more strong carbide alloying elements were added in the quenched and tempered steel so that the grains of the organization are smaller, while reducing the grain boundary segregation, use of alloy carbide dispersion strengthening effect fully to make the strength, hardness, toughness, ductility and other mechanical properties of the organization better than domestic bolts. There is a gap in the material and the production process between domestic bolts and imported bolts.In this thesis, class 12.9 high-strength bolts are made of 42CrMoVNb by myself, and the tested mechanical properties of trial-produced bolts, such as the strength, hardness, toughness, ductility, can meet performance requirements of class 12.9 high-strength bolts in the national standard, and are better than domestic bolts'.