What is the temperature and time for tempering large forgings with medium frequency induction heating equipment?

High-temperature tempering of large forgings after quenching is an effective means to improve impact toughness, which greatly reduces the risk of brittle cracking. When tempering the forgings, the tempering temperature should comply with the regulations and sufficient tempering treatment should be carried out. So, what is the temperature and time of medium frequency induction heating equipment when tempering large forgings? Today, Zhengzhou Gou's will tell you this answer.

The tempering of large forgings by medium frequency induction annealing equipment can be reasonably determined based on technical requirements, materials, shapes, etc., with reference to relevant technical information, experience, etc. The basic principle is to obtain the required hardness or yield strength, etc. The following points should be taken into consideration before tempering heating and cooling: cooling and residual stress after tempering, tempering brittleness, furnace entry temperature and time before heating, temperature rise, equalization and tempering insulation, etc.

1. Cooling and residual stress after tempering. There are four cooling methods after tempering, namely water quenching, oil cooling, water quenching, air cooling and blast cooling. Rapid cooling after high temperature tempering will cause large residual stress, so the cooling rate in the high temperature stage is usually reduced, and Below the elastic-plastic transition temperature range, rapid cooling occurs (400-450°C for carbon steel and low-alloy steel, 450-550°C for alloy steel). For important forgings, the residual stress on the surface after high-temperature tempering shall not be higher than 10% of its yield strength or 40MPa.

2. Control of temper brittleness (second type of temper brittleness). Some low-alloy structural steels are tempered brittle. If no measures are taken, it will directly lead to a reduction in impact toughness and an increase in brittleness. Therefore, rapid cooling after tempering is completed, but this may cause large residual stress for large forgings, so Supplementary tempering (below 450°C) should be carried out without causing temper brittleness. This measure can reduce the residual stress by about 50%.

3. Furnace temperature and time before heating. Generally speaking, when high alloy steel is quenched, there is untransformed supercooled austenite structure in the core, which is still cooling when entering the furnace for heating. Determine the furnace entry temperature according to the TTT curve, which is roughly near the Ms point. Pay attention to the residence time. It should be ensured that the supercooled austenite is fully transformed. As carbon steel and low alloy steel, the stay after entering the furnace is only to reduce the temperature difference between the inside and outside of the forging to reduce internal stress.

4. Heating, equalizing, tempering and heat preservation. Considering that the thermal stress generated during tempering heating is superimposed on the residual stress after quenching, the heating rate should be lower than the quenching heating rate, usually 30~100℃/h. As a high-temperature tempering, the temperature equalization starts when the temperature measuring instrument reaches the temperature. It can also be regarded as the end of the temperature equalization by observing that the color of the forging and the furnace are consistent, that is, it has entered the heat preservation stage. The length of the time should be The core continues to heat up to the tempering temperature and completes the structural transformation. The holding time is generally determined based on experience. Usually the holding time after quenching is calculated as 2h/100mm, and normalizing is calculated as 1.5h/100mm.

Medium frequency induction heating equipment is the best equipment for tempering and other heat treatments on large forgings. As a more advanced and professional manufacturer and seller of induction heating equipment, Zhengzhou Gou's has more experience in heat treatment of workpieces than other companies. You are welcome to call us for more information.