The Phoenix Patchett - No 2627

[Vincent]

I think the Mk4 casings might have been made from different steel than the Patchett casings. When welding the Patchett I noticed the steel seemed less prone to Martensite, glass like crystals. Too much Martensite will make the steel too hard, brittle and prone to “cold cracking.” It was cold cracking that sent some Liberty Ships to the bottom. Not enough Martensite will leave the steel soft.

It turns out the Mk4 casing steel contains a high level of manganese. That means it’s probably a Reynolds steel. Though it’s not the one I thought it might be. It’s definitely not the Accles and Pollock chromium-molybdenum.

My guess is Sterling changed to the high CE manganese steel when they stopped welding components to the casing and started using only induction brazing. The few small spot welds are insignificant. The manganese steel is perfect for brazing but poor for welding due to the high CE, equivalent carbon content.

Those Sterling engineers really knew their onions. They used the right steel for their manufacturing process. They must also have known how strong and durable it would be.

Using manganese has been around for a long time. The Spartans swords were made from iron ore containing manganese. It made them stronger than their enemy’s swords and gave them an edge in battle. But it wasn’t widely used until around WWI. That’s when items made from “Hadfield steel” or “Mangalloy” began to be mass produced. It has a very high manganese content. It’s also non-magnetic. The Type B Brodie helmet was made from it.

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