H.F.G. de Abreu

Simulations in multipass welds using low transformation temperature filler material

Transient thermal and residual stress fields in flux-cored arc welds were examined using a finite element (FE) model. Experimental multipass welds were produced using both conventional and low transformation temperature (LTT) filler metals. Temperature-dependent material properties and both convective and radiant heat loss boundary condition have been considered in the FE model. The effects of the transformation temperature and interpass intervals on residual stresses were examined. It was found that compressive longitudinal residual stresses were developed at the weld centreline in the LTT filler metal. A short-time interpass interval causes the weld fusion zone to be above the martensite start temperature allowing the optimal use of the phase transformation effect. The FE model is sensitive to alteration in welding parameters and can satisfactorily predict the residual stress distribution in welded parts.

Influence of tempering on microstructure and mechanical properties of Ti alloyed 13%Cr supermartensitic stainless steel

Abstract Tempering is the final heat treatment applied to martensitic steels. In conventional martensitic stainless steels or in the newly developed supermartensitic grades, the mechanical properties are strongly influenced by tempering. In the present work, several tempering treatments were performed in a Ti alloyed supermartensitic stainless steel. Tensile mechanical properties, hardness and impact toughness were measured and correlated to microstructural features. Microstructural analysis was conducted in a field emission gun scanning electron microscope and also by magnetic measurements. The ductility parameters continuously increased with tempering temperature, while yield and ultimate strength decreased. Secondary hardening and temper embrittlement were observed by hardness and low temperature impact tests respectively, while tensile tests were not sensitive to these phenomena.

Stress induced martensite transformation texture in AISI 304 austenitic stainless steel

Abstract The phenomenological theory of martensitic transformation was applied to a tension induced martensitic transformation in an AISI 304 austenitic stainless steel in order to estimate the transformation texture. Input data were obtained from the published literature. Calculated pole figures were constructed assuming a variant selection process based on Patel and Cohen’s theory, which emphasises that a mechanical component of free energy is the driving force for martensitic transformation at temperatures above martensite start Ms. The results showed a remarkably good match between the calculated and published measured data.