Determining the BTR by conducting a Trans-Varestraint test using a high-speed camera and two-color pyrometry

Abstract

The Ni-Fe alloy consumable that applies to the welding of 9% nickel steel for LNG storage tanks is highly susceptible to solidification cracks. To evaluate susceptibilities such as the brittleness temperature range (BTR), a Trans-Varestraint test is generally conducted. However, it is difficult to evaluate the minimum strain value for the BTR and the real temperature at both ends of a solidification crack in a conventional Trans-Varestraint test because these values are measured indirectly. In this study, we propose determining the temperature range by conducting in-situ observations during a Trans-Varestraint test using a highspeed camera and two-color pyrometry so that the temperature range can be measured directly from the temperatures at both ends of the crack. Furthermore, we measured the augmented strain from the time elapsed since the initiation of bending. This method allowed us to successfully measure the augmented strain and the temperature range in the Trans-Varestraint test and to determine the BTR more accurately.

Quantitative evaluation of augmented strain at the weld metal during the Trans-Varestraint test

“…Therefore, it is desirable to avoid hot cracking on the material surface when measuring the strain via in-situ observation during the Trans-Varestraint test. According to a previous study [7][8][9]13] on hot cracking, solidification cracking occurs between the solidification starting temperature and solidification completion temperature. In other words, solidification cracking is less likely to occur in the case of a small solidliquid coexistence temperature range.…”

“…However, if such a method is adopted, the determination of the melting boundary when the yoke is dropped becomes unclear, and the measured crack length is inaccurate after the test [21]. Therefore, in this study, the method of dropping the yoke just after the extinction of the arc was adopted, as described by some researchers [7][8][9]13].…”

“…Although many researchers evaluated the hot cracking susceptibilities of various materials, few studies have measured the loaded strain experienced during the Trans-Varestraint test. In 2018, Abe [13] reported a measurement of this strain around the solidification crack using the Trans-Varestraint test. As the measured strain was in good agreement with the convention, there was no clear distinction between the crack occurrence and extension, and the measured minimum strain was the same as that of the conventional strain.…”

Assessment of the Solidification Cracking Susceptibility of Welding Consumables in the Varestraint Test by Means of an Extended Evaluation Methodology

“…The assumed shape of the BTR and the existence of critical strains for crack initiation were proven in experimental investigations by various research groups. [17][18][19][20][21] While the BTR was originally thought as a material related measure, it is significantly influenced by the welding parameters in some cases. [22] Investigations by Nakata et al and Matsuda et al have shown, that using slow bending Varestraint tests, the critical strain for crack initiation ε crit is a function of the strain rate applied.…”

A New Test Method for Evaluation of Solidification Cracking Susceptibility of Stainless Steel during Laser Welding

“…At present, the test methods for evaluating the solidification cracking susceptibility include mainly two categories. One is an external restraint test method, like Varestraint test [ 4 , 5 , 6 ], Sigmajig test [ 7 , 8 ], Rapid tensile test [ 9 , 10 ], etc. The other category is self-restraint test methods, like Houldcroft cracking test [ 11 , 12 ], FISCO hot cracking test [ 13 , 14 ], Circular patch test [ 15 , 16 ], etc.…”