Hardness Measurement of Welded Materials by Micro-Vickers Hardness Tester

Hardness Measurement of Welded Materials Using the HMV-G31-FA Micro-Vickers Hardness Tester

Significance of the topic:
Welded joints are ubiquitous in structures across automotive, construction, and energy sectors. Local variations in heat input and cooling during welding produce heterogenous microstructures that strongly influence mechanical properties such as strength, toughness, and crack susceptibility. Rapid, spatially resolved hardness mapping is therefore a practical and widely used proxy to assess variations in these properties across base metal, heat-affected zone (HAZ), and weld metal. The methodology described demonstrates an efficient workflow to generate high-density hardness distribution maps for welded dissimilar metals, useful in QA/QC, failure analysis, and process optimization.

Objectives and overview of the study:

• Evaluate spatial hardness differences in a dissimilar-metal weld composed of SUS304 (austenitic stainless steel) and SS400 (carbon steel) joined with TG308 filler by TIG welding.
• Demonstrate the capabilities of the HMV-G31-FA Micro-Vickers Hardness Tester combined with stage imaging and pattern-based multi-point automated measurement to produce a hardness distribution map across the welded region.

Methodology and measurement protocol:

• Sample preparation: Two metals (SUS304 and SS400) were TIG-welded around the circumference using TG308 filler. The welded specimen was embedded in resin and polished to reveal the welded cross section and permit clear indentation imaging.
• Measurement pattern: A rectangular grid of 101 points along X and 11 rows along Y (total 1,111 indentations) with 200 μm spacing was defined to ensure non-interacting indentations and full coverage across base metals, HAZ, and weld metal.
• Indentation parameters: Vickers indenter, applied force 980.7 mN (HV0.1), dwell/hold time 14 s.
• Automation: Stage viewer imaging and pattern-setting software controlled motorized XYZ stage for automated positioning, focus adjustment, indentation, and automatic optical reading of diagonal lengths.

Used instrumentation:

• HMV-G31-FA Micro-Vickers Hardness Tester (Shimadzu) with motorized XYZ stage.
• Vickers indenter (for HV0.1 measurements).
• PC-based dedicated software providing stage viewer, pattern setting, automated multi-point testing, and automatic indentation size acquisition.

Main results and discussion:

• High-density hardness mapping produced clear separation of mechanical response across regions: SUS304 exhibited highest hardness (~HV 300–350), SS400 showed intermediate hardness (~HV 200–250), and the TG308 weld metal region averaged around HV 200.
• Profiles along representative rows revealed lateral asymmetry: hardness tended to be higher on the left side of the sample and lower in the central weld area, with local hardness peaks inside the weld at some positions.
• Localized hardening was observed near boundaries where TG308 weld metal contacts SUS304 and SS400; these are attributed to microstructural changes (e.g., rapid solidification, phase transformations, local alloying effects) produced by welding thermal cycles.
• The HAZ adjacent to both base metals showed modest softening relative to the bulk base metals, consistent with grain coarsening and residual-stress changes caused by welding heat input.
• Automated image capture before and after indentation confirmed regular indentation spacing and enabled reliable automated measurement of diagonal lengths for conversion to HV values.

Benefits and practical applications of the method:

• Rapid generation of quantitative hardness distribution maps across welds enables localized assessment of mechanical property changes without labor-intensive single-point testing.
• Useful for weld process qualification, post-weld inspection, and comparative studies of filler materials or welding parameters.
• Supports failure analysis by correlating regions of abnormal hardness (hardening or softening) with potential crack initiation sites or brittle zones.
• Pattern-driven automated measurements improve throughput and reproducibility, reducing operator bias and measurement time for dense mapping.

Future trends and potential uses:

• Integration with correlative microscopy (SEM, EBSD) to link hardness maps with grain structure, phase distribution, and crystallographic texture for mechanistic interpretation.
• Higher-throughput automated mapping and increased spatial resolution to resolve finer microstructural features in complex weldments.
• Application of machine learning to classify hardness map patterns and predict microstructural states or likely failure modes from large datasets.
• In-situ or near-real-time monitoring workflows combining thermal simulation, welding process control, and post-weld hardness mapping for closed-loop process optimization.
• Extension to cross-disciplinary inspections, e.g., coatings, additive-manufactured parts, and multi-material joins.

Conclusion:
This application demonstrates that the HMV-G31-FA Micro-Vickers Hardness Tester, when combined with motorized staging and pattern-based automation, provides an effective approach for detailed hardness mapping of welded dissimilar metals. The study identified expected differences between SUS304, SS400, and TG308 weld metal, localized weld-boundary hardening, and HAZ softening—observations that are directly relevant for weld integrity assessment and process optimization. Automated multi-point measurement substantially improves data density and repeatability, making the method suitable for research and industrial quality assurance workflows.

References:

1. Matsushita T., Yamamoto T., Yano F., Hardness Measurement of Welded Materials by Micro-Vickers Hardness Tester, Shimadzu Application News, First Edition: Mar. 2026, Publication No. 01-01148-EN.
2. Related application: Three-Point Bending Fatigue Tests of Welded Material Using the SEM Servopulser, Shimadzu Application News No. 01-00792.