Types of Heat Treatment

Heat treatment is a processing technique that putting metal material into to a certain medium to heat, preserve and cool down, so that to change the material surface or internal metallographic structure to control its performance. Next are some ways of heat treatment which are commonly used:

Normalizing

Heat the steel materials or parts up to the critical point AC3 or ACM, and keep it in air for a period. Then, cool it down to obtain the steel with pearlite structure.

Annealing

Heating hypoeutectoid steel up to over AC3 or 20 to 40 Celsius Degree. After preserving it for a period, cooling it down in the air (or buried in sand or cooled in lime) until the temperature goes below 500 Celsius Degree.

 

Heat treatment for solid solution

Heat the alloy to high temperature in its single-phase zone and maintain a constant temperature. After the excess phases are fully dissolved into the solid solution, do the fast cooling to obtain the supersaturated solid solution. Solid solution also named solution annealing, it is the heat treated of stainless steel pipe and fittings, the temperature is 1040 °C for common grade, such as 304, 316L stainless steels and fittings. And 1020-1100 °C for duplex pipe and fittings.

 

Quenching

After austenitizing steel, cooling it down with an appropriate speed, so that the unstable structure transformation of martensite of the workpiece can be achieved in the cross section or a certain range.

Tempering

Heat the quenched workpiece to the critical point AC1 and keep it for a period. After this, cool it down in an appropriate way to obtain the desired structure and properties.

 

Carbonitriding of steel

Carbonitriding refers to the simultaneous infiltration of carbon and nitrogen into the surface of steel, and it is also known as cyanidation. Currently, the most widely-used ones are medium-temperature gas carbonitriding and low-temperature gas carbonitriding. Medium-temperature gas carbonitriding can improve the hardness, wear resistance and fatigue strength of steel. Low temperature gas carbonitriding is participated by nitriding and it can improve the wear resistance and bite resistance of steel.

 

Ion nitriding:

It refers to using the glow discharge generated between the workpiece (cathode) and the anode in the nitriding atmosphere whose pressure is below barometric pressure. This process is fast in nitriding, and its structure is easy to be controlled. Besides, it has small brittleness in its layer and little deformation. It can be easily protected, energy-saving, and has less pollution.

Quenching and tempering treatment

It refers to the heat treatment combining quenching and tempering. This process is widely used in all kinds of important structural parts, especially for the connecting rods, bolts, gears and shafts that work under alternating loads. After this process, tempered sox-austenite can be obtained, and it has better mechanical properties than normalizing sox-austenite with the same hardness. The hardness of sox-austenite depends on the tempering temperature and the tempering stability of steel as well as the section size of workpiece. Generally, it is between HB200 to 350.

Brazing

It refers to a heat treatment process that bonding two kinds of workpiece together with a filler metal. With the development of modern science and technology, heat treatment technology is becoming more advanced, which brings a great convenience for industrial enterprises. However, for traditional heat treatment processing, it always requires a lot of resources and raw material to obtain high quality metal products, which will also produce large amounts of waste, or the raw materials will not be fully used. For ion nitriding, it now can save a lot energy, reduce the emission of pollutants and gases, and improve the work efficiency. This process is another important creation in the history of heat treatment.

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