Selection of steel from hardening capacity
Hardening capacity refers to the degree of hardening that steel can achieve through quenching. It must be known to everyone that martensite hardness is mainly determined by carbon content but not related to alloy elements. The higher the carbon content in the steel, the higher the hardening capacity.
As mentioned above, with the increase of carbon content, the Ms point will decrease, and the tendency of quenching cracking will increase.
Therefore, when designing parts, in order to meet the requirements of hardness and strength, steel with low carbon content and high Ms point should be selected as far as possible. For example, important bolts (connecting rod bolts, cylinder head bolts and half shaft bolts) that are used in automobiles are made of 40Cr steel. Quenching cracks often occur in quenching and tempering treatment.
If 15MnVB steel is used, low carbon martensitic structure is obtained by quenching, which satisfies the bolts’ requirements of strength and hardness and exceeds 40Cr steel. The strength of low carbon martensite in 15MnVB steel is more than one third above the 40Cr steel of the tempered Soxhlet body. When the hardness is HRC40, the impact energy AK of 15MnVB steel can reach 72 ~96J while the impact energy AK of 40Cr steel with this hardness is only 20J. And 15MnVB steel does not produce quenching cracks
It has been seen from the diagram that hardening crack is difficult to occur when the Ms point is higher than 330 C, and the Ms point tends to crack at 330 degree below. The Ms point of 15MnVB steel is above 350 C while the Ms point of 40Cr steel is about 320 C.
What is a fully automatic high frequency quench machine
As the name suggests, it is the fully automatic high frequnency quenching
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