Surface- and volume-based investigation on influences of different Varestraint testing parameters and chemical compositions on solidification cracking in LTT filler metals

• Published in: Welding in the world Vol. 64; no. 5; pp. 913 - 923
• Main Authors: Thomas, Maximilian, Vollert, Florian, Weidemann, Jens, Gibmeier, Jens, Kromm, Arne, Kannengießer, Thomas
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.05.2020; Springer Nature B.V
• Subjects: Alloying; Chemical composition; Chemistry and Materials Science; Chromium; Computed tomography; Materials Science; Metallic Materials; Nickel; Process parameters; Research Paper; Solid Mechanics; Solidification; Superalloys; Theoretical and Applied Mechanics; Transformation temperature; LTT filler metal; Varestraint testing; Microfocus X-ray computer tomography (μCT); Solidification cracking
• ISSN: 0043-2288; 1878-6669
• DOI: 10.1007/s40194-020-00895-2

The subject of this study is how, and to what extent, Varestraint/Transvarestraint test results are influenced by both testing parameters and characteristics of evaluation methods. Several different high-alloyed martensitic LTT (low transformation temperature) filler materials, CrNi and CrMn type, were selected for examination due to their rather distinctive solidification cracking behaviour, which aroused interest after previous studies. First, the effects of different process parameter sets on the solidification cracking response were measured using standard approaches. Subsequently, microfocus X-ray computer tomography (μCT) scans were performed on the specimens. The results consistently show sub-surface cracking to significant yet varying extents. Different primary solidification types were found using wavelength dispersive X-ray (WDX) analysis conducted on filler metals with varying Cr/Ni equivalent ratios. This aspect is regarded as the main difference between the CrNi- and CrMn-type materials in matters of cracking characteristics. Results show that when it comes to testing of modern high-performance alloys, one set of standard Varestraint testing parameters might not be equally suitable for all materials. Also, to properly accommodate different solidification types, sub-surface cracking has to be taken into account.