3.1, clean bolt steel
From the steel to improve the cold heading, improve the steel is concerned, the need to minimize the content of impurities in steel impurities. Reducing the S content can improve the deformation ability of the steel and reduce the non-metallic inclusions in the steel to improve the toughness. Reduce the P content to reduce the deformation resistance of the steel while reducing the P and S content can also reduce its segregation at the grain boundary Reduce the grain boundary embrittlement, and can improve the steel resistance to delayed fracture performance; reduce the steel 0 content, can effectively reduce the oxide inclusions, thereby improving the steel cold working deformation capacity.
The KISCC of steel with high cleanliness is higher than that of commercial steel. Therefore, in order to ensure that the steel is still strengthened after high strength, the strength of the stress corrosion factor KISCC of ML42CrMo steel with high cleanliness is studied. With a high overall performance, high strength bolts steel P, S content to be further reduced.
3.2, economic high-strength bolt steel
3.2.1, micro-alloy non-quenched and tempered steel
The use of micro-alloy non-quenched and tempered steel manufacturing bolts can be omitted before the cold-drawn bolts bolts and bolts after forming the quenching and tempering treatment, but also reduce the deduction of screw thread deduction, improve the yield of bolts, economic benefits are obvious The