Microstructure and High-Temperature Properties of TIG Welded Joints of 1Cr12Ni3MoVN Steel

Literature Overview

This paper, authored by Zhou Qingquan and colleagues from Nanchang Hangkong University, investigates the welding performance of 1Cr12Ni3MoVN (S/SJ2) steel, a low-carbon martensitic stainless steel containing approximately 12% chromium, which is extensively used in aeroengine components. The study employs TIG (Gas Tungsten Arc) welding to fabricate specimens from steel plate, followed by high-temperature instantaneous tensile testing, high-temperature creep (durable) tensile testing, and microstructural analysis. The work was published in Hot Working Technology (2016, Vol. 45, Issue 17, pp. 62–65) and is classified under TG457.1.

Core Technical Findings

The central finding of this study is that TIG welding can produce joints in 1Cr12Ni3MoVN steel with high-temperature properties comparable to the base metal. The following table summarizes the key quantitative results:

Both the base metal and the welded joint exhibited shallow dimple fracture morphology under both instantaneous tensile and creep conditions, indicating a consistent ductile fracture mode. The fracture location during tensile testing was consistently at the tempered zone of the heat-affected zone (HAZ), not at the weld metal itself. This is a critical observation for engineers: the weld metal, despite being cast martensite, is not the weakest link in the joint at elevated temperatures.

Microstructural Analysis

The base metal of 1Cr12Ni3MoVN steel exhibits tempered sorbite at room temperature, which provides excellent comprehensive mechanical properties. The weld metal, by contrast, displays acicular (platelet) martensite in the as-cast condition. After high-temperature tensile and creep testing, the martensite in the weld metal underwent significant coarsening. However, as the duration of high-temperature exposure increased, the rate of microstructural coarsening decelerated, and further growth became negligible. This suggests a degree of microstructural stability under prolonged thermal exposure, which is favorable for engineering applications in aeroengine hot sections.

Interpretation of HAZ Behavior

The fracture occurring in the tempered zone of the HAZ rather than in the weld metal or the base metal is a well-documented phenomenon in martensitic stainless steel welding. The tempered zone corresponds to the region where peak temperatures during welding were between approximately 550°C and 750°C, sufficient to cause tempering of the pre-existing martensitic structure without full recrystallization. This zone typically exhibits reduced hardness and potentially reduced strength compared to both the base metal and the weld metal. For 1Cr12Ni3MoVN steel, the high chromium content (12%) promotes the formation of stable chromium carbides during tempering, which can further soften the microstructure. Engineers working with this material should pay close attention to the HAZ, particularly when designing for high-temperature creep service, as this zone represents the most likely initiation site for failure.

Engineering Practice Implications

For aeroengine applications where 1Cr12Ni3MoVN steel components are welded, the following practical recommendations emerge from this study:

1. TIG welding is a viable and reliable process for producing joints with high-temperature performance equivalent to the base metal, provided appropriate welding parameters and post-weld heat treatment are applied.
2. The weld metal, in its as-welded acicular martensite condition, must be followed by proper tempering treatment to relieve residual stresses and improve ductility, as the study implicitly assumes a tempered condition for the welded specimens.
3. Non-destructive testing (NDT) protocols should focus on the HAZ tempered zone region, as this is the critical area for crack initiation under high-temperature loading.
4. Creep life predictions for welded components should account for the 3.2% reduction in creep life relative to base metal (240.71 h vs. 248.56 h), which, while small, may be significant in life-limited aeroengine components.

Key Reflections

This study reinforces the principle that in martensitic stainless steel welding, the weld metal is often not the weakest link; rather, the HAZ tempered zone frequently governs joint performance. The microstructural evolution observed under high-temperature exposure—initial rapid coarsening followed by stabilization—is consistent with classical precipitation hardening and coarsening kinetics described by Ostwald ripening. For engineers involved in aeroengine component manufacturing, this finding provides confidence that TIG-welded 1Cr12Ni3MoVN steel joints can be designed for long-term high-temperature service with well-understood failure modes. The shallow dimple fracture morphology across all test conditions further confirms that the joints maintain adequate toughness even under elevated temperature and sustained load conditions.