The Use of Field Indentation Microprobe in Measuring Mechanical Properties of Welds

This paper establishes ABI®'s fundamental capability to characterize weld microstructural zones with millimeter-scale spatial resolution. The study demonstrates that ABI® can separately resolve the base metal, heat-affected zone (HAZ), and weld metal regions in HSLA (high-strength low-alloy) steel welds — a capability that conventional tensile specimens cannot achieve due to their minimum gauge-length requirements.

Weldments in structural steels contain three fundamentally different material zones within a span of just a few millimeters: the base metal (unaffected by welding), the heat-affected zone (base metal altered by the welding thermal cycle), and the deposited weld metal. Each zone has distinct mechanical properties, and the weakest zone often governs the structural integrity of the entire weldment.

Conventional tensile and Charpy specimens span 25 mm or more, inevitably averaging properties across multiple zones. Cross-weld tensile specimens measure the weakest zone but cannot identify which zone failed or characterize the property gradient. ABI®, with its approximately 1 mm indentation diameter, can systematically map properties across all zones and identify the exact location and magnitude of property minima.

This capability has proven to be one of ABI®'s most commercially valuable applications, supporting weld qualification, in-service weld assessment, and weld repair evaluation across the nuclear, pipeline, and petrochemical industries.