Modeling Solid-State Phase Transformations of 13Cr-4Ni Steels in Welding Heat-Affected Zone

J B Lévesque,D Paquet,J Lanteigne,H Champliaud

doi:10.1007/s11661-019-05587-1

Abstract

Fatigue damage is commonly encountered by operators of Francis type hydraulic turbine runners made of 13Cr-4Ni soft martensitic stainless steel. These large and complex welded casting assemblies are subjected to fatigue crack initiation and growth in the vicinity of their welded regions. It is well known that fatigue behavior is influenced by residual stresses and the microstructure. By including solid-state phase transformation models in welding simulations, phase distribution can be evaluated along with their respective volumetric change and their effect on residual stresses. Thus, it enables the assessment of welding process on fatigue crack behavior by numerical methods. This paper focuses on modeling solid-state phase transformations of 13Cr-4Ni soft martensitic stainless steel, used for manufacturing hydraulic turbine runners, occurring upon welding. It proposes to determine the material parameters of the models for both the austenitic and the martensitic transformation by nonisothermal dilatometry tests. The experiments are conducted in a quenching dilatometer with applied thermal conditions as experienced in the heat-affected zone of homogeneous welds. The activation energy and the kinetic parameters of the austenitic transformation from fully martensitic state are measured from the experimental results. The martensitic transformation modeling from a fully austenitic domain is also presented.

Highlights

SINCE its elaboration in the late fifties, 13Cr-4Ni soft martensitic stainless steel has been extensively preferred to low carbon steel for the manufacturing of hydraulic turbines as it offers better mechanical properties, toughness, and corrosion resistance.[1,2] this steel is weldable, has a higher yield strength than common austenitic stainless steels, and it is less expensive, owing to a low alloying nickel content
Rate is reflected in an increase in the austenitic transformation start temperature, which leads to a shift of the curves towards higher temperatures
According to the study of Bojack et al.[36] on 13Cr6NiMo steel, this could result from a change of transformation mechanism during the austenitic transformation attributed to a mechanism of nickel and molybdenum partitioning

Summary

Introduction

SINCE its elaboration in the late fifties, 13Cr-4Ni soft martensitic stainless steel has been extensively preferred to low carbon steel for the manufacturing of hydraulic turbines as it offers better mechanical properties, toughness, and corrosion resistance.[1,2] this steel is weldable, has a higher yield strength than common austenitic stainless steels, and it is less expensive, owing to a low alloying nickel content. These benefits made this material a good candidate for the manufacturing of Francis type hydraulic turbines, which are large and complex structures generally made of multiple cast components assembled with homogeneous Flux Cored Arc Welding (FCAW) deposits.

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