Evaluation of Weld Solidification Cracking in Ni-Base Superalloys Using the Cast Pin Tear Test

Abstract

A second-generation cast pin tear test (CPTT) that is capable of ranking the weldability of Ni-base superalloys has been developed at the Ohio State University. The CPTT utilizes an optimized testing procedure and apparatus design that provide controllable and repeatable testing conditions, and yield reproducible and reliable test results.The CPTT provided a weldability ranking of four highly alloyed stainless steels that is in very good correlation to the results of a round robin study on six externally restrained weld hot-cracking tests. The solidification microstructure of the test samples (cast pins) closely simulates the microstructure of low to medium heat input welds, such as those made by the GTAW process. The CPTT fracture surfaces exhibit dendritic "eggcrate" fracture morphology, which is a characteristic of solidification cracking. This fracture morphology is similar to the high and medium temperature regime of solidification cracks generated using the Varestraint test. The nature of crack nucleation and propagation, and the crack healing phenomenon in CPTT closely resemble weld solidification cracking.The CPTT technique was applied for evaluating the solidification cracking susceptibility of a series of high performance turbine engine alloys. These alloys were ranked in order of decreasing susceptibility to solidification cracking as follows: René alloys 142, 125, and 77, alloy 718, René 80, Waspaloy, and alloy 600. These rankings are in good correlation to field experience with the solidification cracking susceptibility of the tested alloys.The second generation CPTT proved to be capable of ranking the solidification cracking susceptibility of both "difficult-to-weld" alloys and "standard" alloys, and to differentiate their solidification cracking behavior. It also provides an efficient and inexpensive tool for weldability testing in the process of alloy and consumable development. Pin Tear Test

The Effects of Chemistry Variations on Hot Cracking Susceptibility of Haynes® 282® for Aerospace Applications

“…The CPTT was developed and extensively used as a tool for evaluation of the solidification cracking susceptibility in Ni-based alloys [26,[30][31][32][33][34]. The test set up of CPTT is shown in Fig.…”

Weldability of Nickel-Base Alloys

“…Another method known as the Cast Pin Tear test, which was originally developed in the 1950s, has been revived and modified by researchers at The Ohio State University (66). These tests have been reviewed elsewhere in-depth (51) and general focus on evaluating an alloy's BTR, which corresponds to the welding temperatures where weld restrain overcomes material ductility to induce solidification and liquation cracks.…”

Corrosion Behavior of CW6MC Nickel Cast Alloy (Inconel 625) Welded by Shielded Metal Arc Welding

“…This optimum composition results in low segregation of alloying elements and the formation of NbC instead of the chromium carbides (such as M 23 C 6 ). This favors the hardening of the alloy and reduces the occurrence of ductility-dip cracking, being associated with the presence of chromium carbides [10][11][12][13]. However, during the final stages of solidification (casting or welding), the segregation of alloying elements (Nb, Mo and Si) promotes the formation of secondary phases, such as the Laves phases, which can degrade the corrosion resistance of the material [9,11,[14][15][16].…”