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Lihua Technology(HK) Industrial Co., Ltd.

High-Frequency Induction Quenching Crack Analysis

Cracks occur during quenching of high-frequency quenching machines.The characteristics of these cracks are that cracks mostly occur at edges and corners; The crack depth is about the thickness of the quenched hardened layer and may also produce peeling cracks; There is no crack at all from the hardened layer to the heart. This kind of crack is caused by the structural transformation and internal stress caused by the high-frequency quenching. During high-frequency quenching, uneven heating temperature, local overheating, deep heating layer, violent or uneven cooling, improper or fast heating, and electric parameter selection can all be causes of quenching cracks.

Microstructural analysis of high-frequency quenched steel parts reveals that cracked workpieces are often caused by uneven microstructures within the quenched layer. For example, the boring tool made of T12 steel has cracks due to the overheating of edges and corners. The surface of the corners is super-heated, coarse acicular martensite and austenite, while the inner layer is “cryptocrystalline” martensite and remains carbonized. Further inward layer is the primitive structure.
The crack extends from the surface to the "cryptocrystalline" martensite area. The cracks are formed by sharp peeling or subcutaneous cracking.

The cracking tendency of high-frequency induction hardened steel is also related to the chemical composition, but mainly depends on carbon content. For example, 0.4%C chromium molybdenum steel, 0.3%C nickel chromium steel, 0.25%C of nickel chrome molybdenum steel, may have high-frequency quenching cracks. The high-frequency quenching agent made of USES oil and molten salt instead of water, generally does not produce cracks, but it cannot be used for spray quenching but immersed quenching.

Gear quenching cracking can generally be analyzed from the perspectives of the quenching cracking time and place as well as the crack size and shape and be solved from regulating the gear material, structure, heating temperature and uniformity, cooling media, self-tempering and tempering.

This article is written by the professional high-frequency induction quenching machine tool manufacturer - Dongguan Lihua Machinery ( specify the source when you copy the link.
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