Heating defects and emergency control methods of circuit heat treatment equipment

When the phenomenon of overheating in an electric furnace occurs, we all know that overheating during the heat treatment process of the electric furnace can easily lead to the coarsening of austenite grains, which can lead to a decrease in the mechanical properties of the parts. Everything has its two sides, and in practical work, some people use this phenomenon to serve people, such as the crushing treatment of alloys.
Inheritance of coarse structure When steel parts with coarse martensite, bainite, and widmanstatten are re austenitized, they are heated slowly to the conventional quenching temperature, or even lower, and their austenite grains are still coarse. This phenomenon is called structural heredity. To eliminate the heritability of coarse structure, intermediate annealing or multiple high-temperature tempering treatments can be used.
When the overheating phenomenon occurs, the heating temperature is too high, which not only causes coarse austenite grains, but also local oxidation or melting of grain boundaries, leading to weakening of grain boundaries, which is called overheating. The performance of steel severely deteriorates after being burned, and cracks form during quenching. Burned tissue cannot be restored and can only be scrapped. Therefore, it is necessary to avoid the occurrence of overheating in work.
When decarburization and oxidation steel are heated, the surface carbon reacts with oxygen, hydrogen, carbon dioxide, and water vapor in the medium atmosphere, reducing the surface carbon concentration, which is called decarburization. After quenching, the surface hardness, fatigue strength, and wear resistance of decarburization steel decrease, and residual tensile stress forms on the surface, which is easy to form surface network cracks. After oxidation of workpieces at temperatures above 570 degrees Celsius, the dimensional accuracy and surface brightness deteriorate, and steel parts with poor hardenability of oxide films are prone to quenching soft spots.
Measures to prevent oxidation and reduce decarburization: Coating the surface of the workpiece, using stainless steel foil packaging for sealing and heating, using a salt bath furnace for heating, using a protective atmosphere for heating (such as purified inert gas, controlling the carbon potential inside the furnace), and a flame combustion furnace (making the furnace gas reducible). The phenomenon of iron and alloy on the surface of steel reacting with elements such as oxygen, carbon dioxide, and water vapor in the medium (or atmosphere) to form an oxide film is called oxidation.
Overheating is generally caused by excessive heating temperature or prolonged holding time at high temperatures, resulting in coarsening of austenite grains. Coarse austenite grains can lead to a decrease in the strength and toughness of steel, an increase in the brittle transition temperature, and an increase in the tendency for deformation and cracking during quenching in tubular electric furnaces. The reason for overheating is that the furnace temperature instrument is out of control or mixed materials (often caused by not understanding the process). The overheated structure can undergo annealing, normalizing, or multiple high-temperature tempering, and under normal circumstances, undergo re austenitization to refine the grains.
After being reheated and quenched, it can refine the austenite grains, but sometimes coarse and granular fractures still appear. There are many controversies about the theory of fracture inheritance. It is generally believed that impurities such as MnS were dissolved into austenite and enriched at the grain interface due to excessive heating temperature. However, during cooling, these inclusions precipitate along the grain interface and are prone to fracture along the coarse austenite grain boundary when subjected to impact.
The phenomenon of hydrogen embrittlement refers to the decrease in plasticity and toughness of high-strength steel heated in a hydrogen rich atmosphere. Workpieces that exhibit hydrogen embrittlement can also be eliminated through hydrogen removal treatment (such as tempering, aging, etc.). Heating in vacuum, low hydrogen atmosphere, or inert atmosphere can avoid hydrogen embrittlement. Like the current continuous heat treatment furnace, which can provide timely tempering treatment after quenching, oxygen displacement treatment can be considered during the tempering process. According to current usage and statistics, products treated in continuous controllable atmosphere heat treatment furnaces generally do not exhibit hydrogen embrittlement.

The above content is organized by Superb heater Company, super heater. Mainly professional production: industrial heating elements, temperature measuring elements, production equipment, accessories, and raw materials such as tubular heaters, tubular heaters, belt heaters, ceramic heaters, silicone rubber heaters, thermocouples, etc.

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