Solidification Behavior and Microstructure in Stainless Steel Welds

Stainless steel welding involves local melting and re-solidification during fusion-based processes. Solidification behaviour in the weld pool dictates the emergent microstructure, which in turn governs mechanical integrity, corrosion resistance and service performance. Cooling rate, thermal gradient and composition determine whether primary austenite or primary ferrite phases form, whether cellular or dendritic arrays evolve, and whether segregation or eutectic structures appear at intercellular boundaries. At moderate cooling rates typical of directed energy deposition (DED), a ferritic primary mode often prevails, while rapid solidification such as in selective laser melting (SLM) can induce dual solidification with austenite nucleating at the fusion boundary followed by ferrite within. Surface morphology, including ripple formations, influences local dendrite arm spacing and heterogeneity of microstructural features. Control of welding parameters and targeted alloy design enable grain refinement, phase distribution control and minimisation of defects such as hot cracking, porosity or undesirable delta ferrite networks. Advances in computational tool-chains, from thermodynamic constitution diagrams through phase-field models to machine-learning predictions, are enhancing predictive capability for industrially relevant stainless steel grades. These developments support the design of weld schedules and alloy chemistries optimised for global applications ranging from chemical processing to energy systems.

Research from Nature Portfolio

A recent study introduced a unified phase stabilising parameter, termed γ stabilising efficiency, which quantifies the influence of each alloying element on the balance between austenite and ferrite during solidification. By analysing the slopes of phase boundary lines, the work provides a single metric applicable across a wide range of stainless steel chemistries, streamlining the prediction of primary solidification modes. This framework replaces separate equivalents for γ and α stabilisers and offers a more coherent approach to alloy design for controlled microstructure in welded joints.

Solidification Behavior and Microstructure in Stainless Steel Welds publication trend

The graph below shows the total number of articles in solidification behavior and microstructure in stainless steel welds across all publications each year (not limited to Nature Index journals).

Technical terms

Dendrite: Tree-like crystal structure formed during solidification, composed of a primary trunk and secondary arms.

Austenite (γ): Face-centred cubic phase of iron-based alloys stable at high temperatures, often the primary phase in stainless steel weld pools.

Ferrite (α): Body-centred cubic phase that can form during solidification under certain cooling rates or chemistries, influencing toughness and crack sensitivity.

Cooling rate: Rate of temperature decrease in the molten pool, controlling microstructural scale, phase selection and defect formation.

Phase stabilising parameter: Quantitative measure of an alloying element’s tendency to promote austenite or ferrite formation during solidification.

References

1. Ripple formations determine the heterogeneous microstructure of directed energy deposition (DED)-printed 316L components. Materials & Design (2023).
2. Predictive tools for the cooling rate-dependent microstructure evolution of AISI 316L stainless steel in additive manufacturing. Journal of Materials Research and Technology (2024).
3. Composition equivalents of stainless steels understood via gamma stabilizing efficiency. Scientific Reports (2021).