1. The nature of the furnace gas:
The forging flame-heated furnace gas usually consists of an oxidizing gas, a reducing gas and a neutral gas. The nature of the furnace gas depends on the amount of air supplied when the fuel is burned. When the supply air is excessive, the nature of the furnace gas is oxidizing, then the oxidation is verified. On the contrary, if the supply air is insufficient, the furnace gas is reductive, the scale of the forging is very thin, and even oxidation is not generated in the forging manufacture.
2. Heating temperature:
The higher the temperature, the faster the oxidative diffusion rate of the forging, the more the oxidation process will be, and the resulting scale will be thicker. Generally, when the temperature is lower than 570 to 600 ° C, the oxidation is slow; after exceeding 900 to 950 ° C, the metal oxidation increases sharply.
3. Heating time:
The longer the heating time in the heating workshop of the forging factory, the more the scale of the forgings. Therefore, the use of rapid heating such as electric heating to shorten the heating time, especially the residence time at high temperatures, has great practical significance for reducing the generation of scale.
4. Chemical composition:
When the amount of carbon in the steel increases, the scale formed will decrease. This is because when the carbon content is high, CO is formed during the oxidation of the steel surface, which can weaken the effect of oxidation on the steel surface. There are also some metal elements, such as Cr, Ni, Ai, Mo, etc., which form a firm and tight film on the metal surface. The expansion coefficient is almost the same as that of steel. The forgings are not easy to fall off during heating, preventing oxygen from diffusing into the interior. Preventing the steel surface from continuing to oxidize, the film plays a certain protective role. Especially when the amount of Cr and Ni in the steel is more than 13% to 20%, almost no oxidation is produced.