Heat treatment method of spring steel

Spring steel heat treatment methods are divided into cold forming and hot forming. Due to the different processing methods, the subsequent heat treatment methods are not the same. Therefore, Zhengyi Spring Manufacturing Co., Ltd. will give you a brief introduction here.

◆Heat treatment of cold formed springs

①. Quenched and tempered steel wire

After the steel wire is drawn to the treated size, it is oil quenched and tempered. The strength of this type of steel wire is not as good as that of the lead bath treated steel wire, but the performance is uniform and the cost is lower. After the cold coil is formed, it is subjected to stress relief treatment.

②. Lead bath treated cold drawn steel wire

The steel wire is continuously drawn three times to make the total deformation reach 50%, and then heated to a temperature above Ac3 to make it austenitized, and then treated at an isothermal temperature in a lead bath at 450-550°C to transform austenite into sorbite Organization. Yield strength is 1600Mpa, after cold roll forming, annealing can be done at 200-300℃ to eliminate stress.

③. Steel wire in annealed condition

The steel wire is drawn to the specified size, and then annealed. After the softened steel wire is cold coiled, it needs to be quenched and tempered at medium temperature to obtain the required mechanical properties.

The commonly used springs with a diameter of less than 8mm are generally formed by cold drawn steel wire and cold coil.

◆Heat treatment of thermoformed springs

The process of hot-rolled spring steel is roughly as follows: first, the flat steel is cut, and then the heating and bending forming waste heat quenching + medium temperature tempering + shot peening is adopted, and finally the packaging is placed.

This heat treatment is to first heat the spring steel wire to a condition of 50-80°C higher than the normal quenching temperature, and then heat it to form, in the case of quenching, add medium temperature tempering to obtain excellent elastic limit and fatigue strength Tempered sorbite. When spring steel is quenched and heated, equipment with less oxygen or no oxidation should be selected, such as salt bath furnaces, protective atmosphere furnaces, etc., to prevent the occurrence of oxidative decarburization.

After the heat treatment of spring steel, shot peening is required to strengthen the surface, generate residual compressive stress, and improve fatigue strength.

Under normal circumstances, large spring parts with a diameter or plate thickness greater than 10-15mm are mostly made of steel wire or steel plate drawn by hot-rolled wire rod.

Commonly used cold-drawn steel wire and cold-rolled bullets with a diameter of less than 8mm and less than 8mm in diameter.