Zhengzhou Gou's tells you the causes of quenching cracks and their preventive measures of large forging dies quenching by medium frequency induction quenching equipment

As we all know, in order to improve the hardness, wear resistance and service life of large forging dies, we need to perform quenching heat treatment on large forging dies. Now, the more common quenching equipment is medium frequency induction quenching equipment. When large forging dies are quenched using medium-frequency induction quenching equipment, they are affected by many factors and may produce quenching defects such as insufficient hardness and cracks. Today, we will talk about the causes of quenching cracks in large forging dies and their preventive measures.

The large forging die is quenched using medium frequency induction quenching equipment. The reasons for crack defects are:

(1) The quenching and heating of the large forging die is not preheated. Due to the large size of the workpiece and the high alloying elements, its thermal conductivity is poor. When heated, the surface expands rapidly, but the internal heat transfer is slow, resulting in tensile stress inside the workpiece. The tensile stress can easily cause quenching cracks in the forging die.

(2) No pre-cooling before quenching. Due to the large size of the workpiece, the working surface is always immersed in oil during oil cooling quenching, and the quenching residual stress is very large, which induces microcracks. This is the main reason for quenching cracks in the workpiece.

(3) Failure to temper in time. The bulging deformation of the workpiece after quenching is a typical thermal stress deformation, and the crack fracture appears black oxidation color. It shows that the cracks occur after quenching and before tempering. The forging die quenching oil immersion time is too long and the oil outlet temperature is too low, which will increase the cracks. Because the workpiece has been tempered for too long and the workpiece has not been tempered in time, the quenching stress still exists and the cracks in the workpiece have further deteriorated.

(4) When using medium frequency induction quenching equipment for quenching, the quenching heating temperature is too high. Because the heating temperature is too high (8℃) and the heating time is long (7h), the austenite grains develop fire cracks.

After continuous research, we have proposed the following measures to improve the large forging die process:

(1) Add preheating treatment, (600~650)℃x(3-4)h, calculated as 0.6min/mm.

(2) The large forging die is pre-cooled to 760°C before quenching and then quenched by oil cooling. The oil outlet temperature is controlled above 200AC (200 -300°C). After oil outlet, the workpiece is placed in the furnace above 200°C for uniform heating.

(3) After soaking, take out the workpiece and temper it immediately. The tempering temperature is 540°C, and the oil is slowly cooled above 20WC to reduce the thermal stress in the workpiece and prevent deformation or cracks caused by high stress on the workpiece.

(4) The quenching temperature is reduced to 830°C, and the holding time is 4-5h, calculated as 0.8-1.Omin/mm.

The medium frequency induction quenching equipment produced by Zhengzhou Gou's has complete functions and is easy to operate. It is a good equipment for heat treatment of workpieces. Zhengzhou Gao's has been engaged in the production and sales of induction heating equipment for fifteen years, and has a good understanding of the heat treatment of workpieces. If you want to know more about equipment and workpiece heat treatment, please feel free to contact us.