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How to deal with the phenomena of burning and oxidative decarbonization in box furnace heating?

In the heating process of the box furnace, materials are easy to be oxidized and decarbonized, which will dilute the metal elements on the surface of the workpiece, which will affect the surface quality, and also reduce the mechanical properties and corrosion resistance of the metal.
 
The punch and concave dies of dies usually need to be quenched. After quenching, they are slightly ground and reassembled. If the die produces serious oxidative decarbonization during heating, the oxidative decarbonization layer can not be completely eliminated during assembly, which affects the use of accessories.
 
If we want to avoid the formation of overburning and oxidative decarbonization, we must first understand how overburning and oxidative decarbonization are formed.
First of all, we need to understand several phenomena, which can help us better understand.
 
Overburning phenomenon: The so-called over-burning refers to the phenomenon that the austenite grains are coarser and the grain boundaries are oxidized or melted locally, resulting in the weakening of grain boundaries caused by the excessive heating temperature of industrial electric furnaces. After overburning, the performance of steel will deteriorate seriously, and even cracks will appear during quenching. The overburning structure of tubular furnace can not be recovered and must be scrapped. So we must avoid overburning in the actual operation process.
 
Decarbonization phenomenon: When the industrial electric furnace is heating the steel, the carbon on the surface reacts with oxygen, hydrogen, carbon dioxide and water vapor in the medium, which reduces the carbon concentration on the surface. This is called decarbonization. After quenching, not only the surface hardness and fatigue strength of the decarbonized steel will be greatly reduced, but also it will reduce. The wear resistance is weakened and the residual tensile stress on the surface is easy to form a network crack path on the surface.
 
OXIDATION: OXIDATION occurs when iron and alloys on the surface of steel react with oxygen, carbon dioxide and water vapor in the medium to form oxide film, which is usually called oxidation. For this kind of problem, the surface coating of workpiece is usually used to prevent oxidation and decarbonization of workpiece by sealing heating with stainless steel foil and heating with salt bath furnace. Ordinary workpiece will be oxidized above 570 degrees. Hardening softening point will easily occur on steel parts with poor hardenability when both the single dimension accuracy and surface brightness of the oxidized workpiece are deteriorated.
 
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