KM bearings for you to introduce 45 steel heat treatment
Tempering has a hardness range, generally between 225-297HB. If no. 45 steel is tempered, that is, quenched + high-temperature tempering, its hardness should be as high as 297HB, i.e. 31-32HRC! That's the ideal. This value may not be reached in general.
45 steel is quenched. If quenched with water, it can generally reach 40-- 60HRC (depending on the water temperature and the size of the material), and oil quenching is generally between 30-- 55HRC (depending on the thickness of the material and the type of quenching oil).
It has nothing to do with the degree of hardness achieved, but with the shape of the workpiece and the way of heat treatment.
Medium and low carbon steel is generally normalized. After normalizing, pearlite structure is obtained, which is convenient for machining. High carbon steel and alloy steel are annealed (ordinary, spheroidized, isothermal).
Quenching and tempering is a double heat treatment with quenching and tempering at high temperature, the purpose of which is to make the workpiece have good comprehensive mechanical properties.
There are two kinds of tempered steel, carbon tempered steel and alloy tempered steel. If the carbon content is too high, the strength of tempered workpiece is high, but the toughness is not enough. If the carbon content is too low, the toughness will be increased and the strength will be insufficient. In order to get a good comprehensive performance, the carbon content is generally controlled within 0.30~0.50%.
During quenching and tempering, the whole section of the workpiece is required to be quenched through, so that the workpiece is mainly composed of fine needle-like quenched Martensite. The microstructure of uniform tempered soxhlet was obtained by high temperature tempering. It is impossible for a small factory to conduct metallographic analysis on each furnace. Generally, only hardness test is carried out. That is to say, the hardness after quenching must reach the quenching hardness of the material, and the hardness after tempering should be checked according to the requirements in the figure.
The operation of tempering the workpiece must be carried out strictly in accordance with the process document. We just give some opinions on how to implement the process in the operation process.
1. Tempering 45 steel
45 steel is medium carbon structural steel, cold and hot processing performance is good, mechanical performance is better, and low price, wide source, so it is widely used. Its biggest weakness is low hardenability, large section size requirements of higher workpiece should not be used.
45 steel quenching temperature in A3+(30~50)℃, in practice, generally is the upper limit. The higher quenching temperature can accelerate the heating speed of workpiece, reduce the surface oxidation, and improve the work efficiency. In order to homogenize austenite of the workpiece, sufficient holding time is required. If the actual amount of furnace, it is necessary to extend the insulation time. Otherwise, the phenomenon of insufficient hardness caused by uneven heating may occur. However, if the heat preservation time is too long, serious defects such as coarse grain and oxidation and decarburization will also occur, which will affect the quenching quality. In our opinion, if the amount of furnace loading is greater than that stipulated in the process document, the heating and holding time should be extended by 1/5.
Because of the low hardenability of steel 45, a 10% brine solution with a high cooling rate should be used. After the workpiece is put into water, it should be quenched through, but not through cold. If the workpiece is cooled through salt water, it may crack the workpiece, because when the workpiece is cooled to about 180℃, austenite rapidly changes into martensite, causing excessive stress of the tissue. Therefore, when the quench workpiece quickly cooled to the temperature region, should take the slow cooling method. As the water outlet temperature is difficult to grasp, it must be operated by experience. When the workpiece in the water stops shaking, the water outlet can be air-cooled (if it can be oil cooled better). In addition, the workpiece into the water should not be static, according to the workpiece geometry, make regular motion. The static cooling medium plus the static workpiece, resulting in uneven hardness, uneven stress and the workpiece deformation, even cracking.
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