Hardfacing is a critical technique used to extend the service life of components subject to wear. However, cracking is a common challenge in hardfacing applications. This document addresses the types, causes, and mitigation strategies for cracks in hardfacing welds, focusing primarily on SMAW (Shielded Metal Arc Welding), FCAW (Flux Cored Arc Welding), and other consumable-based methods.
Cracking can generally be divided into three categories:
Check Cracking (also called relief or stress-relief cracking):
Normal and expected in many hardfacing deposits, especially with high-carbon or carbide-forming alloys.
Typically runs perpendicular to the weld bead and occurs shortly after cooling.
Serves a purpose: it relieves internal stresses caused by shrinkage and prevents larger, more dangerous cracks.
Cross Cracking:
Occurs across multiple passes or through multiple layers.
Indicative of high stress or poor technique/materials.
Should be avoided—may lead to premature failure.
Base Metal Cracking:
Cracking that penetrates into the substrate, generally caused by:
Excessive dilution
Improper preheat
Poor choice of buffer layer
This type of crack is critical and must be addressed immediately.
Several variables contribute to cracking:
Alloy Chemistry:
Higher carbon and alloy content increases crack sensitivity.
Chromium and niobium carbides are more prone to check cracking.
Welding Parameters:
High travel speeds, large weave beads, and poor interpass temperature control contribute to internal stress.
Dilution and Base Metal Compatibility:
Excessive dilution increases hardness and brittleness.
Mismatch in thermal expansion between base metal and overlay can induce stress.
Poor Preparation:
Contaminants, improper joint design, and lack of preheat/postheat can exacerbate cracking.
To minimize undesirable cracking, the following practices are recommended:
Preheat:
Reduces thermal shock and slows the cooling rate.
Helps avoid hydrogen-related cracking and base metal hardening.
Buffer Layers:
Soft, ductile layers between the hardfacing and base metal absorb stress.
Commonly low-alloy or austenitic stainless materials are used.
Heat Input Control:
Use correct amperage/voltage settings.
Maintain proper interpass temperature (often 300°F–600°F, depending on the alloy).
Stress Relief Cracks:
Acceptable in high-hardness overlays like chromium carbide and are part of normal performance.
Visual inspection should distinguish between acceptable check cracking and dangerous cross or base metal cracking.
When in doubt, grind and reapply with correct procedures and ensure full fusion in repair areas.
Cracking in hardfacing is a manageable phenomenon when understood correctly. Check cracking is not a defect, but a stress-relief mechanism, especially in chromium or complex carbide overlays. However, base metal cracks indicate procedural flaws or mismatched materials. Successful hardfacing depends on the proper selection of consumables, controlled procedures, and an understanding of the metallurgy involved.
