Armor plate isn't structural steel. The heat input requirements, preheat, interpass temperature control, and post-weld treatment are all fundamentally different — and getting them wrong means one thing: rejection. Here's what to know before you put a torch to MIL-DTL-12560.
Why Armor Plate Is Different
MIL-DTL-12560 rolled homogeneous armor (RHA) plate is a high-hardness, high-strength steel designed to resist ballistic penetration. That hardness comes from the alloying and heat treatment process — and it's also what makes it challenging to weld. The same properties that make it effective as armor make it susceptible to hydrogen-induced cracking (HIC) in the heat-affected zone if the weld process isn't properly controlled.
The Three Things Most Shops Get Wrong
1. Skipping or Underestimating Preheat
Preheat is non-negotiable on armor plate. The exact temperature depends on the plate thickness, the carbon equivalent, and the applicable specification — but it's there for a reason: it slows the cooling rate in the heat-affected zone and reduces the risk of hydrogen cracking.
Shops that treat armor plate like A36 and skip the preheat are gambling. The weld might look fine visually. It might even pass a basic visual inspection. But hydrogen cracking can be delayed — showing up hours or even days after the weld is complete. By then, the part may have moved further down the line.
2. No Qualified Procedure
MIL-spec work requires documented, qualified welding procedures. A WPS that says "weld per AWS D1.1" with no armor-specific parameters isn't sufficient. The procedure needs to address the specific base material, filler metal selection, preheat and interpass temperatures, heat input limits, and any post-weld requirements called out by the prime or the applicable specification.
We have qualified procedures for MIL-DTL-12560 and MIL-DTL-46100 in-house. That qualification documentation is part of every job package we ship.
3. Wrong Filler Metal Selection
Filler metal selection for armor plate isn't just about matching base metal strength. You need to account for the diffusible hydrogen content of the filler, the joint configuration, and the preheat being used. Low-hydrogen electrodes and proper storage aren't suggestions — they're requirements.
The cost of a rejected weld on a defense program — rework, re-inspection, timeline impact — almost always exceeds the cost of doing the procedure qualification correctly upfront.
How We Approach Armor Plate Work
Every armor plate job at Jack & Sons runs against a qualified WPS. Preheat is verified and documented before welding starts. Interpass temperature is monitored and controlled throughout. Filler metals are stored and handled per manufacturer and specification requirements.
Our affiliate United Technical provides CWI oversight and NDT inspection on programs that require it — all on-site, same facility. For defense programs where the documentation package matters as much as the part itself, that integrated capability makes a difference.
The Bottom Line
If a shop tells you they can weld MIL-DTL-12560 without showing you a qualified procedure, walk away. This isn't a material where you improvise and hope it passes. It's a material where you qualify your procedure, control your process, and document everything — or you deal with the consequences at inspection.