CLADDING TECHNOLOGY SHANXI CO., LTDCracking Mechanisms in TIG Welded Joints of 12Cr1MoVG Steel
Literature Overview
The paper by Pei Lixia, Zeng Min, Wang Wenxian, Du Jijun, Zhou Lidan, and Yan Hao, published in Physical Testing and Analysis (2026), investigates the root causes of cracking in TIG welded joints of 12Cr1MoVG steel. This austenitic stainless steel grade is widely employed in high-temperature and high-pressure service environments, particularly in power plant boiler tubes, superheater headers, and nuclear-grade piping systems. The study adopts a systematic failure analysis approach combining macroscopic examination, metallographic observation, scanning electron microscopy (SEM), and fractographic analysis to identify the cracking mechanism.
Core Technical Points
Material Characteristics of 12Cr1MoVG
12Cr1MoVG is a modified austenitic stainless steel containing approximately 12% Cr, 1.0% Mo, and 0.03–0.05% V. The alloying elements provide excellent resistance to high-temperature oxidation and creep deformation, making it suitable for service temperatures up to 600–650 °C. However, the high alloy content also introduces susceptibility to solidification cracking and sensitization during welding.
| Parameter | Value |
|---|---|
| Cr content | 11.0–13.0 wt% |
| Mo content | 0.90–1.20 wt% |
| V content | 0.03–0.05 wt% |
| Carbon max | 0.08 wt% |
| Typical service temperature | 450–650 °C |
| Welding method | GTAW (TIG) |
| Filler wire | ER309L / ER316L |
Identified Cracking Mechanisms
The research identifies two primary cracking mechanisms:
- Solidification cracking occurring in the weld bead due to high sulfur and phosphorus impurity concentrations in the base metal combined with excessive heat input during TIG welding. The dendritic solidification structure creates microchannels rich in low-melting-point eutectic phases (Cr23C6, Mo-rich carbides), which become crack initiation sites under thermal stress.
- Intergranular cracking in the heat-affected zone (HAZ) caused by sensitization. During the TIG welding thermal cycle, chromium carbides precipitate at grain boundaries in the temperature range of 500–800 °C, depleting adjacent regions of chromium and reducing corrosion resistance. Subsequent exposure to corrosive environments leads to intergranular stress corrosion cracking.
FMEA Analysis of Contributing Factors
| Failure Mode | Potential Cause | Effect | Detection Method | Preventive Action |
|---|---|---|---|---|
| Weld bead cracking | Excessive heat input (>25 kJ/cm) | Loss of structural integrity | Visual + MT | Reduce travel speed, use lower current |
| HAZ sensitization | Dwell time in 500–800 °C range | Intergranular corrosion | ASTM A262 Practice A/E | Preheat control, rapid cooling |
| Root cracking | Inadequate root cleaning | Hydrogen-assisted cracking | PT/MT | Thorough surface preparation, low hydrogen filler |
Engineering Practice Implications
In pressure vessel fabrication, particularly for hydrogenation reactors and superheater headers utilizing 12Cr1MoVG, the following engineering controls are critical:
- Preheating strategy: Maintain preheat temperature between 100–150 °C to reduce cooling rate and minimize HAZ susceptibility to sensitization, while avoiding excessive temperatures that promote grain growth.
- Interpass temperature control: Limit interpass temperature to below 250 °C for multi-pass welds to prevent prolonged exposure to the sensitization temperature window.
- Filler metal selection: Use low-carbon fillers (ER309L, ER316L) with carbon content below 0.03% to minimize chromium carbide precipitation.
- Post-weld heat treatment: Apply solution heat treatment at 1050–1100 °C followed by water quenching to dissolve precipitated carbides and restore corrosion resistance.
Key Reflections
The study underscores that cracking in 12Cr1MoVG TIG welds is rarely attributable to a single factor but rather emerges from the interplay of material chemistry, thermal cycle parameters, and residual stress states. For engineers involved in pressure vessel fabrication, this reinforces the necessity of a holistic approach to welding procedure qualification — not merely achieving code compliance but understanding the metallurgical consequences of each parameter selection. The findings are particularly relevant for applications governed by ASME VIII Div.2 and NB/T 47014, where weld procedure qualification must account for both mechanical performance and corrosion resistance requirements.