How can we prevent defects caused by heat treatment of large forgings using medium frequency induction heating machine？

Commonly used large forgings include large rolling mill work rolls and support rolls, large ship shafts, etc., which are usually directly forged from steel ingots. In order to make it work better, we usually use a medium frequency induction heating machine to heat treat large forgings. The heat treatment process is quite complicated and requires preparatory heat treatment and final heat treatment. Such a complex process, a small mistake , will cause defects in the workpiece, or even cause the workpiece to be scrapped.

1. Reticular carbides mostly occur in roll steel and bearing steel forgings and are formed during the forging and cooling processes. The measures taken are: control the final forging temperature to ensure that it is above 900°C <800~750°C is the range of large amounts of carbide precipitation). Secondly, high temperature normalizing treatment is adopted.

2. Cracks. The occurrence of cracks is a defect that every heat treatment worker does not want to encounter. but. Its flaws occur again and again. Cracks occur due to over-burning. The oxidation of the steel ingot at high temperature is more intense. The surface temperature is higher than the inside and over-burning occurs. Here is a short and thick crack. The two sides of the crack are severely decarburized and the grains are coarse. In addition, cracks occur due to copper brittleness, and the copper content exceeds 0.2%. During forging at high temperatures, the copper-rich metal melts and penetrates into the grain boundaries of the steel, causing the bonding force between the grains to weaken, and a network to form on the surface of the metal during thermal deformation. shaped cracks. Measures include changing the furnace loading position or changing the structure of the heating furnace to control the copper content in the steel ingot.

3. White spots and hydrogen embrittlement. The purpose of preparatory heat treatment for large forgings is to prevent white spots and hydrogen embrittlement. White spots are produced under the combined action of hydrogen and stress in the steel. The temperature range for their formation is between 200 and 50°C, and does not change with the chemical composition of the steel. The conditions for its formation are that the hydrogen in the steel must form a sufficient degree of segregation and embrittle the metal. Its nucleation sites are at grain boundaries, sub-grain boundaries, inclusion surfaces and defects in grains. We will take such preventive measures to limit the residual hydrogen in the steel below the white point-free limit of the steel.

a. Control the amount of retained austenite in steel

b. Control chemical composition and obtain a single tissue

c. Eliminated by isothermal annealing treatment after forging

d. Refine grains and carbonized material points, increase the number of flaking and dislocation density, etc.

e. Vacuum it

The medium frequency induction heating machine for heat treatment of large forgings has the advantages of complete functions, simple operation, energy saving and environmental protection, and it can also meet the needs of various occasions. If you are interested in the heat treatment of large forgings, and if you want to know more about the equipment, we welcome you to call us for consultation.