Contents
Annealing
Heating steel to a specific temperature, holding it for a certain period, and then allowing it to cool slowly is called annealing. Steel annealing is when the steel is heated to the temperature of the phase change or part of the phase change after holding it in a slowly cooled heat treatment method. The purpose of annealing is to eliminate organizational defects, improve the organization so that the composition of the uniformity and grain refinement, improve the mechanical properties of steel, and reduce residual stress; at the same time, it can reduce the hardness, improve the plasticity and toughness, and improve the performance of cutting and machining. So, annealing eliminates and improves the organization of the previous process left defects and internal stress, but also for the subsequent process to prepare, so annealing is a semi-finished heat treatment, also known as pre-finish heat treatment.
Normalizing
Normalizing is to heat the steel above the critical temperature so that all the steel is transformed into a homogeneous austenite and then naturally cooled in the air heat treatment method. It can eliminate the over-eutectic steel network carburization body, for sub-eutectic steel normalizing can refine the lattice and improve the overall mechanical properties, and the requirements of the parts are not high with normalizing instead of annealing process is more economical.
Quenching
Quenching is a heat treatment method in which steel is heated above a critical temperature, held for some time, and then quickly placed into a quenchant to reduce its temperature abruptly and cool it rapidly at a rate more significant than the critical cooling rate while obtaining an unbalanced organization dominated by martensite. Quenching increases the strength and hardness of steel but reduces its plasticity. The quenching agents commonly used are water, oil, alkaline water, and salt solutions.
Tempering
It will have been quenched and reheated to a specific temperature, and then a particular cooling method is called tempering. Its purpose is to eliminate the internal stress produced by quenching and reduce the hardness and brittleness to obtain the expected mechanical properties. Tempering high-temperature tempering, medium-temperature tempering, and low-temperature tempering are three categories. Tempering is used in conjunction with quenching and normalizing.
(1) Tempering treatment: The heat treatment method of high-temperature tempering after quenching is called tempering treatment. High-temperature tempering refers to tempering between 500-650 ℃. Tempering can improve the performance of the steel; the material is adjusted to a large extent, and its strength, plasticity, and toughness are better, with good overall mechanical properties.
(2) Aging treatment: to eliminate precision gauges or molds, parts in long-term use of the size, and shape changes, often in the low-temperature tempering (low-temperature tempering temperature of 150-250 ° C) before finishing, the workpiece reheating to 100-150 ° C, to maintain the 5-20 hours, this treatment for the stabilization of the quality of precision parts, known as aging. The aging of steel components at low temperatures or under dynamic loading conditions to eliminate residual stresses and stabilize the steel organization and size is especially important.
Surface heat treatment
(1) Surface quenching is the surface of the steel parts by rapid heating to the critical temperature above. The heat has not had time to transfer to the heart before rapid cooling so that the surface layer can be quenched in the martensite organization. The heart does not phase change, which achieves the purpose of the surface quenching and hardening of the heart of the unchanged. It is suitable for medium carbon steel.
(2) Chemical heat treatment refers to the chemical elements of the atoms. Using high-temperature atomic diffusion, it penetrates the surface layer of the workpiece to change its chemical composition and structure, achieving a surface layer of steel that meets specific requirements for the organization and performance of a heat treatment process. Chemical heat treatment can be divided into carburization, nitriding, cyanidation, and metal penetration methods, depending on the infiltration of different elements.
Carburizing
Carburizing is the process of infiltrating carbon atoms into the surface layer of steel. It is also the process of making a low-carbon steel workpiece with a surface layer of high-carbon steel, and then after quenching and low-temperature tempering, the surface layer of the workpiece has high hardness and wear resistance. In contrast, the center part of the workpiece still maintains the toughness and plasticity of low-carbon steel.
Nitriding
Nitriding is the process of infiltrating nitrogen atoms into the surface layer of steel. Its purpose is to improve the hardness and wear resistance of the surface layer, fatigue strength, corrosion resistance, and so on. At present, the production of the gas nitriding method.
Cyanitriding
Also known as carbonitriding, it is the process of simultaneously infiltrating carbon and nitrogen atoms into steel. This gives the steel’s surface the characteristics of both carburization and nitriding.
Metalizing
It is the process of infiltrating the surface layer of steel with metal atoms. It is to make the surface layer of steel alloying in order to make the surface of the workpiece with particular alloy steel, unique steel characteristics, such as heat resistance, wear resistance, oxidation resistance, corrosion resistance, etc. It is commonly used in producing aluminum infiltration, chromium infiltration, boron infiltration, silicon infiltration, etc.
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