Identifying and Addressing the Most Common Heat-Treatment Metal Defects

Metals and Mining Review | Thursday, May 08, 2025

Without timely intervention, metals can develop porosity, resulting in material degradation and property damage. Conversely, heating certain metals above 650 degrees Celsius may trigger decarburization, potentially leading to a decrease in fatigue strength.

Fremont, CA: Most metal products used in industry nowadays require heat treatment beforehand. Heat treatment is applying heat to metal objects without letting them melt. The products then undergo a carefully regulated chilling procedure to guarantee that they acquire the mechanical qualities needed by certain sectors.

Heat treatment is expected to impart strength, resilience, and longevity to metal workpieces. Additionally, it can enhance weldability, flexibility, and wear resistance, potentially extending their overall service life significantly.

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Despite the benefits, heat-treated metals may still exhibit flaws for various reasons. Here are some of the most common flaws encountered in heat-treated metals that warrant attention:

Minimal Strength and Hardness:

For metals to reach high hardness and strength, martensitic development is necessary, notably for steel. It would be challenging for industries to obtain the required products if these qualities weren't achieved. Inadequate austenitizing temperature is the cause of the lack of improved hardness and strength. Moreover, insufficient soaking time, a sluggish cooling rate, residual austenite, and low hardness following surface hardening treatment can all contribute to it.

Soft Spots:

Upon quenching at the austenitizing temperature, metals should achieve a uniform hardness throughout their surfaces. However, they may have developed some soft places if their hardness becomes uneven throughout. Issues with quenching media may be the source of soft patches in metals. After the water reaches a level of vapor blanket generation, the critical cooling rate of particular workpiece regions will eventually be lower. Inadequate cleaning of metal parts, uneven heating, localized decarburization, high quenching media temperature, and uneven heating can also cause soft areas.

Quench Cracks:

In order to successfully cool metal workpieces and prepare them for martensitic transformation, quenching is necessary. This heat treatment step is typically accompanied by a range of compressive and tensile stresses. However, under certain circumstances, these strains could intensify to the point where heat treatment causes fissures. Metal workpieces with these cracks, sometimes referred to as quench cracks, are rendered useless and unusable.

Oxidation and Decarburization:

Two further possible causes of heat-treated metal defects are oxidation and decarburization. When metals are subjected to carbon dioxide, air, and water vapor during particular heat treatment stages, oxidation may occur. Metals may become porous in the absence of prompt remediation, which could lead to material degradation and property damage. On the other hand, some metals may undergo decarburization if they are heated above 650 degrees Celsius. Fatigue strength loss could then follow from this problem.

Distortion and Warping:

These two of the most expensive errors that heat treatment businesses can make are faults in heat-treated metals that are typically irreversible. Metal workpieces undergo warping if they undergo asymmetrical changes in shape or size, whereas distortion results from symmetrical alterations. Size and shape distortions are the two types of distortions that metals can experience. Shape distortion results from the bending and twisting of metals, whereas size distortion arises during the heat treatment process's expansion and contraction phases. To avoid these problems, some things that need to be examined include the initial design, machining procedures, and composition.

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