Metallographic Inspection of Carbon Steel CO₂ GMAW Weld Joints

Metallographic examination of carbon steel weld joints fabricated via CO₂ gas metal arc welding serves as the core method to assess welding quality and process rationality.

Columnar grains, along with small amounts of proeutectoid ferrite, side-plate ferrite and pearlite are generally found in the weld metal zone. The heat-affected zone (HAZ) exhibits microstructural transitions between coarse-grained and fine-grained regions. Widmanstätten structures and martensitic hardened layers tend to form in the coarse-grained zone, which embrittles the welded joint.

Microscopic observation near the fusion line enables identification of internal defects such as incomplete fusion, microcracks, pores and inclusions. It also evaluates how overheating level and cooling rate affect microstructure morphology. Metallographic test results provide direct reference for adjusting welding heat input, preheating temperature and interpass temperature, effectively controlling hardening tendency and hydrogen-induced cracking risks.

Combined metallographic evaluation integrating hardness distribution and microstructure assessment is a reliable approach to verify welding procedure specifications and guarantee structural integrity.

Metallographic Preparation Parameters & Microstructure Showcase

1.Coarse Grinding: MET-M P400

2.Fine Grinding: POS + 9μm PD-WT

3.Polishing: ET-JP + 1μm PD-WT *Alternative for Step 2: P800 to P2000 abrasive paper