Hello Milton, I am by no means an expert in this area, yet everything that I could find would not qualify 4130 as being a type of armor plate. I looked at some of the British, Swedish, and U.S. sites and none of them make any mention, of any kind, of this being the case. I did not do a chemical composition comparison so I couldn't say for sure that the various armor plates don't share similar chemical make-up to that of 4130. Hopefully others might be able to shed a more precise light on your question. Best regards, Allan

Milton,
I have the U.S. Army Ground Combat Vehicle Welding Code. It has plenty of info in it pertaining to pre-qualified Base metals and Filler metals in table 3.1 on page 21 of the code. if You would like a copy sent to You in pdf format, I will gladly send it to You. I believe this is the acceptable test for what qualifies as Armor. However I am No metallurgist, so deciphering the information proves to be a bit ellusive for me. I can only use this information for referencing questions that may arise...then i can find the section that provides the needed technical data.
Let me know if You want it and I'll send it to you via email.
respectfully, Jeffrey

Armor plate might be 4130 [I really don't know], however there is most likely some heat treat done to it. In the old days armor plate was carbourized on the impact side so that that side could be case hardened. Improvements have probably been made since then.