Heat treatment refers to a metal thermal processing process in which materials are heated, insulated and cooled in a solid state to obtain the expected structure and properties.
Classification of heat treatment
1. Normalizing: Heat the steel or steel parts to the appropriate temperature above the critical point AC3 or ACM for a certain period of time and then cool it in the air to obtain a heat treatment process of pearlitic structure.
2. Annealing: The sub-eutectic steel workpiece is heated to 20~40 ℃ above AC3, and after holding for a period of time, it is slowly cooled with the furnace (or buried in sand or lime cooled) to below 500 ℃ and cooled in air.
3. Solution heat treatment: The alloy is heated to a constant temperature in the high-temperature single-phase zone, so that the excess phase is fully dissolved into the solid solution, and then quickly cooled to obtain the heat treatment process of the supersaturated solid solution.
4. Aging: The phenomenon that the performance of the alloy changes with time after solution heat treatment or cold plastic deformation, when it is placed at room temperature or slightly higher than room temperature.
5. Solid solution treatment: Fully dissolve various phases in the alloy, strengthen the solid solution and improve the toughness and corrosion resistance, eliminate stress and soften, so as to continue processing and molding.
6. Aging treatment: Heat and keep warm at the temperature of the precipitated phase of the strengthened phase, so that the precipitated precipitation of the strengthened phase can be hardened and the strength can be improved.
7. Quenching: Heat treatment process in which the steel is austenitized and cooled at an appropriate cooling rate, so that the workpiece can undergo martensite and other unstable microstructure transformation in all or a certain range within the cross-section.
8. Tempering: The quenched workpiece is heated to an appropriate temperature below the critical point AC1 for a certain time, and then cooled by a method that meets the requirements to obtain the required structure and performance of the heat treatment process.
9. Carbon nitriding of steel: Carbon nitriding is the process of infiltrating carbon and nitrogen into the surface layer of steel at the same time. Traditionally, carbonitriding, also known as cyanidation, is widely used in medium-temperature gas carbonitriding and low-temperature gas carbonitriding (i.e., gas soft nitriding). The main purpose of medium-temperature gas carbonitriding is to improve the hardness, wear resistance and fatigue strength of steel. Low-temperature gas carbonitriding is mainly nitriding, and its main purpose is to improve the wear resistance and seizure resistance of steel.
10. Quenching and tempering treatment: It is generally customary to combine quenching and tempering with high temperature tempering heat treatment. Quenching and tempering treatment is widely used in a variety of important structural parts, especially those connecting rods, bolts, gears and shafts that work under alternating loads. After quenching and tempering, the tempered sostenite structure was obtained, and its mechanical properties were better than that of the normalized sostenite microstructure of the same hardness. Its hardness depends on the high temperature tempering temperature and is related to the tempering stability of the steel and the cross-sectional size of the workpiece, generally between HB200~350.
11. Brazing:Heat treatment process that heats, melts, and bonds two kinds of workpieces together with brazing metal.