Further Development of the Cast Pin Tear Test for Evaluating Solidification Cracking in Ni-Base Alloys

Abstract

A modification of the original Cast Pin Tear Test (CPTT) developed by Hull in the 1970s is being used to quantify weld solidification cracking in Ni-base alloys, including both precipitation-strengthened “superalloys” and solid-solution strengthened alloys. This test uses a copper hearth and mold system to produce cast pins of different length. By changing the cast pin length, the thermal strain during solidification of the pin can be altered. Solidification cracking susceptibility is determined by the degree of cracking on the surface of the pin. As restraint level (pin length) increases, 360-degree circumferential cracking is observed and, eventually, complete pin separation occurs. The advantage of this test is that sample preparation is quite easy and only a few hundred grams of material are required to develop a complete cracking susceptibility curve for a given alloy or filler metal. Alloy additions can be made to the melted button in the hearth, allowing alloy development studies to be readily conducted. The CPTT has been applied to study the effect of dilution on the solidification cracking susceptibility of a new chromium-free welding consumable. In addition, the cracking susceptibility of a number of high-chromium Ni-base filler metals for use in nuclear power plant applications has been quantified and compared. The solidification behavior in these alloys has been studied utilizing the technique for Single Sensor Differential Thermal Analysis (SS DTA) and a button melting technique that closely reproduces the solidification in gas-tungsten arc welds.