Most Common Defects of Heat Treated Metals

23 August 2022

Most metal products being utilised by industries today must undergo heat treatment first. Heat treatment is a process wherein metal workpieces are subjected to heat without letting them reach their molten state. They are then cooled in a controlled way, ensuring that they attain the mechanical properties required by a specific industry.

With heat treatment, metal workpieces are expected to become more durable, tougher, and stronger. They can likewise attain improved wear resistance, better flexibility, and enhanced weldability. Their overall service life is also expected to increase significantly.

But heat-treated metals may still boast some defects because of a wide variety of reasons. Here are some most common defects of heat-treated metals you should know about.

Low Hardness and Strength

Metals, especially steel, need martensitic formation to achieve high hardness and strength. Without achieving these properties, it would be difficult for industries to acquire their needed products. The absence of better hardness and strength is due to improper austenitising temperature. It can likewise be caused by insufficient soaking duration, slow cooling rate, the existence of retained austenite, and low hardness during surface hardening treatment. 

Soft Spots

After quenching from austenitising temperature, metals are expected to attain an even hardness across their surfaces. But if their hardness becomes uneven from point to point, they may have acquired some soft spots. Soft spots in metals may be caused by quenching media issues. Once water generates a vapour blanket stage, it will ultimately reduce the critical cooling rate of specific workpiece areas. Soft spots can also happen due to high quenching media temperature, localised decarburisation, uneven heating, and improper cleaning of metal parts.

Quench Cracks

Quenching is essential to effectively cool metal workpieces so they can be subjected to martensitic transformation. Normally, this heat treatment phase is accompanied by various tensile and compressive stresses. But in some cases, these stresses may become severe, resulting in cracks during heat treatment. These cracks, also known as quench cracks, make metal workpieces useless and unusable.

Oxidation and Decarburisation

Oxidation and decarburisation are two more potential reasons heat-treated metals can become defective. Oxidation may happen once metals are exposed to carbon dioxide, air, and water vapours during specific phases of heat treatment. Without immediate mitigation, metals may become porous, resulting in material degradation and loss of properties. Decarburisation, alternatively, may occur when some metals are exposed to heat above 650 degrees Celsius. This issue may then result in loss of fatigue strength.

Distortion and Warping

These defects of heat-treated metals are normally irreversible, which makes them two of the costliest mistakes that heat treatment companies may commit. Distortion happens when metal workpieces acquire a symmetrical change in shape or size, while warping occurs if the changes are asymmetrical. Metals may undergo two types of distortion: size and shape distortions. Size distortion occurs during the expansion and contraction stages of heat treatment, while shape distortion happens due to the bending and twisting of metals. Some elements that must be checked to prevent these issues are initial composition, design, and machining processes.

To ensure that your heat-treated metals will not acquire any defects, you can work with us at Alpha Detroit Heat Treatment. Contact us today!

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