Performance characteristics of diathermic rods treated by medium frequency induction heating for quenching and tempering

The diathermic bar that has been quenched and tempered by medium-frequency induction heating can obtain a finer martensite structure after rapid heating of austenite and quenching, and then high-temperature tempering to obtain fine tempered sorbite. This tempered sorbite has high tensile strength and yield strength, as well as good plasticity and toughness.

Compared with traditional quenched and tempered steel, the new properties of this type of hot-rolled quenched and tempered steel have the following characteristics:

1) Medium frequency induction heating quenching and tempering process. The steel material with a diameter of 12-20mm rotates and advances along the conveyor roller, and is heated to 830-850°C by the quenching inductor and then quenched. Quenching adopts spray cooling method, the water pressure is 05MPa. After cooling to 100℃, it enters the tempering inductor. Temper by heating to 680-700°C. After tempering, air-cool at room temperature to complete the quenching and tempering process.

2) Mechanical properties of steel quenched and tempered by medium frequency induction heating. Steel quenched and tempered by induction heating has higher strength and toughness than ordinary heat treatment.

3) The strengthening effect of quenching during medium frequency induction heating quenching and tempering treatment. Because induction heating rapidly raises the temperature to austenitization and stays at the austenitizing temperature for a long time, fine initial austenite grains can be obtained. After spray quenching and rapid cooling, fine lath martensite is obtained, which is tempering. The treatment creates good quenching tissue conditions. During ordinary heating and quenching, due to the slow heating rate and long holding time at high temperature, the initial grains of austenite obtained are relatively coarse. In addition, the cooling rate of immersion quenching is slow, and the final martensite obtained is relatively coarse, which is the result of tempering. The effect is affected. It can be seen that the strengthening effect of quenching during induction heating quenching and tempering treatment is much stronger than that during ordinary heating. The difference between the two is that during the induction heating quenching process, the temperature rise rate is fast, the quenching cooling rate is fast, the high temperature retention time is short, and the resulting quenched structure is fine.

4) The strengthening effect of tempering during medium frequency induction heating quenching and tempering treatment. The strengthening effect of tempering heating rate is that it increases with the increase of heating rate. The strengthening effect of tempering heating rate is that as the heating rate increases, the tempered sorbite structure becomes refined, and the dispersion of carbides distributed on the ferrite matrix is high, resulting in high strength and good toughness of the steel. On the contrary, when heated and tempered slowly and with a long holding time, the tempered sorbite obtained is relatively coarse and the dispersion of carbides is low, so the mechanical properties are at a low level.

To sum up, the carbon structure and low alloy steel diathermic rods treated by induction heating and quenching and tempering have high strength and toughness. Compared with beryllium copper heating and quenching and tempering, they have faster heating speed, faster quenching and cooling speed, and better thermal insulation. time period and other process advantages. This process advantage leads to the acquisition of fine quenched lath martensitic structure, which is tempered at high temperature to form a troostite structure, resulting in steel with high strength, high toughness and excellent comprehensive properties. These characteristics are common to induction-heated, quenched and tempered carbon structures and low-alloy steels.