What is the quenching temperature of 45# steel?

45# steel is a medium carbon structural steel with good hot and cold workability, good mechanical properties, low price and wide source. Its biggest weakness is the low hardenability, large cross-section size and relatively high requirements of the workpiece should not be used.
 
    The quenching temperature of 45 # steel is A3 + (30 ~ 50) ℃. In practical operation, the upper limit is generally taken. Higher quenching temperature can speed up the workpiece heating speed, reduce surface oxidation, and improve work efficiency. In order to homogenize the austenite of the workpiece, sufficient holding time is required. If the actual furnace load is large, the holding time needs to be extended appropriately. Otherwise, insufficient hardness may occur due to uneven heating. However, if the holding time is too long, the grains will also be coarse, and the disadvantages of severe oxidation and decarburization will also affect the quenching quality. We believe that if the amount of furnace installed is greater than specified in the process documents, the heating and holding time needs to be extended by 1/5.

    Because 45# steel has low hardenability, a 10% saline solution with a large cooling rate should be used. After the workpiece enters water, it should be hardened, but not cold. If the workpiece is cold soaked in brine, it may crack the workpiece. This is because when the workpiece is cooled to about 180°C, austenite is rapidly transformed into martensite. Caused by excessive tissue stress. Therefore, when the quenched workpiece is rapidly cooled to this temperature region, a slow cooling method should be adopted. Because the temperature of the effluent is difficult to grasp, it must be operated by experience. When the jitter of the workpiece in the water stops, the effluent can be air-cooled (if oil cooling is better). In addition, the workpiece should not move or enter the water. It should be regularly moved according to the geometry of the workpiece. The stationary cooling medium plus the stationary workpiece results in uneven hardness and uneven stress, which deforms the workpiece and even cracks.
     The quenched hardness of 45# steel quenched and tempered part should reach HRC56 ~ 59. The possibility of large cross section is lower, but it cannot be lower than HRC48. Otherwise, it means that the workpiece has not been completely quenched, and sorbite or ferrite may appear in the structure. Body tissue, which is still retained in the matrix through tempering and cannot achieve the purpose of quenching and tempering.
     The high temperature tempering of 45 # steel after quenching, the heating temperature is usually 560 ~ 600℃, and the hardness is required to be HRC22 ~ 34. Because the purpose of quenching and tempering is to obtain comprehensive mechanical properties, the hardness range is relatively wide. However, if the drawing requires hardness, the tempering temperature should be adjusted according to the drawing to ensure the hardness.
 

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