Classic Summary of Heat Treatment Techniques

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1. Divide into two: Different materials, different equipment, and different process parameters result in different microstructures and qualities after heat treatment. Even when the material grade, equipment, and process parameters are identical, the microstructure and quality after heat treatment will differ due to variations in the upper and lower limits of chemical composition levels, heat treatment temperatures, and holding times. Even if the upper and lower limits for the chemical composition, as well as the upper and lower limits for the heat treatment temperature and holding time are the same, the structure and quality after heat treatment will still vary due to differences in the cold and hot working processes, quality, and microstructure prior to heat treatment. Therefore, when a problem arises, it is necessary to analyze it on a case-by-case basis, that is, to look at things from two different perspectives. 2. Two diagrams: Fe-C phase diagram, C curve. The Fe-C phase diagram is essential knowledge for those working with steel. The C curve shows the structural changes that occur in steel when it is heated and then cooled; these two diagrams form the basis of heat treatment. Only by mastering these two diagrams and gaining an in-depth understanding of them is it possible to carry out dry heat treatment, and only then can one get started with heat treatment. 3. Three processes: namely heating, holding temperature, and cooling. These three processes are present in all heat treatment techniques, and the quality of these processes determines the quality of the final heat treatment. Once these three processes are thoroughly understood, one can be considered to have entered the world of heat treatment. 4. The four heat treatments: namely annealing, normalizing, quenching, and tempering. These four types of heating are the most common forms of heat treatment, and the quality of these heat treatments reflects, to a certain extent, the level of expertise in heat treatment. If these four fires are managed well, one is a heat treatment technician. 5. Five types of structures: namely austenite, cementite, martensite, bainite, and pearlite. Only by gaining a thorough understanding of the characteristics, organizational structure, formation conditions, and performance of these five organizations can the level of heat treatment technology be improved. 6. Six major defects: namely oxidation, decarburization, overheating, overburning, deformation, and cracking. Among these, overburning and cracking are the most undesirable defects in operation, as they are irreversible; the other four should also be avoided as much as possible, since although they can be remedied, they significantly increase the workload and production costs. A qualified heat treatment engineer is one who can avoid or mitigate these six major defects. 7. Seven phase transformations: pearlite transforming into austenite (P→A), austenite transforming into pearlite (A→P), austenite transforming into sorbite (A→S), austenite transforming into troostite (A→T), austenite transforming into martensite (A→M), austenite transforming into bainite (A→B), and martensite transforming into tempered martensite (M→M back ). Mastering these seven phase transformations signifies a high level of expertise in heat treatment. 8. Eight major processing techniques: annealing, normalizing, quenching, tempering, surface quenching, chemical heat treatment, vacuum heat treatment, and special heat treatment methods (laser, ion nitriding, PCD, CVD, ion plating, etc.). Those who master these eight techniques can be considered experts in heat treatment!