Cold-drawn square steel has the advantages of fast forming speed, high output and no damage to coating, and can be made into various cross-sectional forms to meet the needs of service conditions. Cold rolling can cause great plastic deformation of steel, thus improving the yield point of steel. Delamination will occur, resulting in interlayer tearing; Residual stress has a certain influence on the performance of steel members. It affects the surface treatment and local buckling characteristics of steel, with low free torsional stiffness, poor torsional performance and weak local concentrated bearing capacity. Cold-rolled steel allows local buckling of the section, which can make full use of the bearing capacity of the buckled bar; However, local buckling of hot rolled steel is not allowed. The causes of residual stress in hot rolled steel and cold rolled steel are different, so the distribution of residual stress in cross section is also very different. The residual stress distribution on the section of cold-formed thin-walled steel is curved, while the residual stress distribution on the section of hot-rolled steel or welded steel is thin film. The free torsional stiffness of hot rolled steel plate is higher than that of cold rolled steel plate, so the torsional performance of hot rolled steel plate is better than that of cold rolled steel plate and cold drawn square steel. Quenching of cold-drawn square steel is a kind of heat treatment method, which heats the steel above the critical temperature, keeps the temperature for a period of time, and then quickly puts it into quenching agent, so that its temperature suddenly drops, and quickly cools the cold-drawn square steel at a speed greater than the critical cooling rate, thus obtaining an unbalanced structure dominated by martensite. Quenching can improve the strength and hardness of steel, but reduce its plasticity.
Quenching agents commonly used in quenching are: water, oil, alkaline water and salt solution. The quenching agent of high-speed steel can be "wind", so the heat treatment process of cold-drawn square steel of high-speed steel is to heat the steel above the critical temperature, transform it into average austenite, and then naturally cool it in the air. Normalization Normalization is a heat treatment method that heats the square steel above the critical temperature, transforms the steel into average austenite, and then naturally cools it in the air. It can eliminate the reticular cementite in which * * * steel precipitates, refine the crystal lattice for sub * * * steel precipitation, improve the comprehensive synergy of cold-drawn square steel, and it is more economical to replace annealing process with normalizing for parts with low requirements.