Influence on martensite‐start‐temperature and volume expansion of low‐transformation‐temperature materials used for residual stress relief in beam welding

Abstract

Low-transformation-temperature materials (LTT) are used as high-alloy welding filler material for high-strength steels in order to minimize the tensile stresses and resulting distortion of the component during the welding process. The increase in the volume of the structure produced during martensitic transformation is utilized in order to counteract the volume shrinkage due to the cooling process. As stated in the field of study various elements influence the starting temperature of the martensite transformation, the influence on the volume expansion during the martensite formation is unknown. The influence of alloying elements nickel and chromium on the conversion behavior of low-transformation-temperature materials is to be investigated in detail. In particular, the effect of the variation of the mentioned elements on the starting temperature of the martensitic phase transformation and the extent of the volume expansion associated with that is investigated. In addition, the change in the hardness of the different low-transformation-temperature alloys is recorded and compared.

X-ray diffraction profile analysis of martensitic Ti6Al4V (ELI) parts produced by laser powder bed fusion

“…Various values for αˊ martensitic start temperature (Ms) have been reported in the range of 575 ͦ C -800 ͦ C [24,25]. Factors such as homogeneity of composition, initial microstructure and the presence and types of impurity elements are suggested in literature to affect the Ms [24,26,27].…”

“…This suggests that more than one slip system in this material is activated during deformation of these two different forms of LPBF Ti6Al4V (ELI) alloy. Thus, the method of calculating the average Burgers vector and average contrast factor used in [26,30,32] was adopted in this research. The method is well summarised in the authors' work published in Muiruri et al [18].…”

Residual oxygen content and powder recycling: effects on microstructure and mechanical properties of additively manufactured Ti-6Al-4V parts

“…Additionally, as a prerequisite for the formation of martensite, the martensite start temperature (M S ) needs to be lower than the build temperature. It depends on the initial microstructure, chemical composition, and composition homogeneity as well as on the presence of impurity elements [18,19]. Therefore, the type of powder and its recycling grade as well as the oxygen content present in the process atmosphere are also likely to have an impact on the resulting microstructure.…”

A Review of Heat Treatments on Improving the Quality and Residual Stresses of the Ti–6Al–4V Parts Produced by Additive Manufacturing

“…In addition to the quick cooling, the α phase will only form if the build temperature is kept below the martensite start temperature (Ms) [30]. The aforementioned temperature varies from 575 • C up to 800 • C [31][32][33] as the impure elements along with the initial microstructure and composition homogeneity affect the Ms temperature [34]. In Figure 2, it is possible to analyze how the phase transformation is affected by the distinct cooling rates, i.e., in the region of 525-410 • C/s the α phase will be formed; however, if the cooling rate is kept under 20 • C/s, it will lead to the formation of the phase α.…”