Embrittlement in the Heat-Affected Zone (HAZ): Understanding the Threats

Embrittlement in the welding HAZ is a leading cause of cracks and brittle failures in welded joints. Understanding its mechanisms is essential for developing strategies to prevent it.

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Types of HAZ Embrittlement

Coarse Grain Embrittlement

Grain coarsening near the fusion line due to thermal cycles

Larger grains increase the ductile-to-brittle transition temperature

Precipitation Embrittlement

Formation of carbides, nitrides, and intermetallic compounds during aging or tempering

Strength, hardness, and brittleness all increase

Structural Embrittlement

Formation of brittle phases like Martensite-Austenite (M-A) constituents, upper bainite, or coarse Widmanstätten structures

Especially critical in low-carbon, high-strength steels

Thermal Strain Aging Embrittlement

Caused by local strain and deformation during fabrication (e.g., cutting, forming, welding)

Includes both static and dynamic strain aging (e.g., “blue brittleness”)

Heat affected zone of welding

Identifying and mitigating the various types of embrittlement in the HAZ is key to ensuring the long-term safety and performance of welded structures.

Related Articles:

The causes and effects of hardening in the heat-affected zone (HAZ) of welding

Welding Heat-Affected Zone (HAZ) vs Weld Metal: Why the HAZ matters more than you think