Spring steel wire is quenched and tempered using a medium frequency induction heating machine. How should the tempering temperature and holding time be selected?

Quenching and tempering, we all know that it is a comprehensive heat treatment process of quenching and tempering. Therefore, the spring steel wire uses an intermediate frequency heating machine for quenching and tempering heat treatment. It is not only the quenching temperature that affects the heat treatment effect, but also the tempering temperature and its holding time. . Today, the editor will tell you how to choose the induction heating tempering temperature and holding time of spring steel wire.

Select the tempering temperature according to the tempering structure of the spring steel wire. The tempering structure of eutectoid and hypoeutectoid spring wire can be divided into three categories (see the table below). Among them, pearlite is a high-temperature tempering product with low strength and is not suitable for spring materials; troostite is a medium-temperature tempering product with high strength and toughness and can be used as some spring materials; troostite is a low-temperature tempering product. , has the smallest organizational structure, the highest strength and toughness, and more importantly, has better resistance to stress relaxation, that is, a low relaxation rate. Therefore, the tempered troostite structure should be obtained as much as possible during tempering treatment. In order to obtain tempered troostite, the conditions that should be met are: first, a quenched structure formed by quenching fine austenite grains must be obtained; secondly, a lower tempering temperature must be selected so that the proportion of troostite can be obtained More tempering tissue. The tempered structure of induction heating spring steel wire should be composed of troostite and troostite, and the higher the proportion of the former, the better.

Characteristics of induction heating tempering temperature and tempering structure of eutectoid steel

① Determination of tempering and holding time. The principle of determining the induction heating tempering holding time is to ensure that the steel wire is heated through and complete the structural transformation. In fact, the time required to complete the tissue transformation is very short, mainly the time it takes to equalize the surface and heart temperatures. If the designed surface heating power density is not very high, there is no need for holding time for steel wires with a diameter of less than 6 mm. For steel wires with a small surface power density and a diameter greater than 6mm, the tempering and heat preservation time can be 5-10s.

②The cooling method of steel wire after tempering treatment. Cooling after induction heating and tempering has little effect on the performance of the steel wire. Water spray cooling should be used for silicon-manganese, silicon-chromium, and silicon-chromium vanadium steel wires that tend to be tempered brittle. However, in order to shorten the length of the production line, the spring steel wire can be cooled by water spray, but it is best to keep the steel wire at a residual temperature of about 50°C so that the surface moisture can evaporate and be removed by itself.

Today, the editor briefly tells you how to choose the tempering temperature and holding time when tempering spring steel wire. If you still don’t understand anything about this, you can consult our technical staff.