Rensselaer Polytechnic transverse strength test (stainless/nickel alloy)

The Varestraint test as developed at RPI. Used to demonstrate liquation/solidification cracking by bending the plate during welding and exposing the partially-liquid grain boundaries.

I talked about this the other day when we were talking about stainless steels — the Rensselaer Polytechnic Varestraint test, where you weld on a stainless steel or a nickel-based alloy, some high alloy typically. You make the weld, and as you're welding you bend the plate along the weld. It's called a transverse-strain Varestraint test. You can see, when you apply the pressure, you just open up the cracks, because the cracks were partially liquid at the time. You open it up and make more space.

RPI in the 1970s as the leading US producer of welding PhDs. Developed the Varestraint test (TIG weld over a radius block under bending strain, count cracks afterward). Showed that three percent ferrite in austenitic weld metal scavenges sulfur and prevents solidification cracking.

They developed something called the Varestraint test. You'd have a TIG torch, you'd have the material you want to study the weldability of, you'd have a radius block, and you start making your TIG weld across here. As you did it you would load this thing and bend the thing over a certain radius block while it's hot. When you're all done you'd look at it and count the cracks. Here's the instantaneous solid-liquid interface when they applied the pressure. This was the time they started deforming it as it was being welded, and they would just open up little cracks. If they went in there and studied that, they'd find that the sulfur would go to the austenite — which likes hydrogen but doesn't like sulfur — and it would crack at the austenite boundaries. This metal could be all austenite, or it could be a little bit of austenite-ferrite, which was good, they found. They'd like to have a little bit of ferrite — about three percent ferrite was good, because it essentially absorbed most of the bad sulfur. These steels weren't high in sulfur; they just would crack, particularly in the highly restrained joints.