Think you’re getting hardness & toughness mixed-up. The two properties are very different.
As an example, glass is hard but brittle = not tough. Chrome steel with such a high Carbon content (0.5% is a LOT of Carbon) can be very brittle indeed. I quickly read those reports but a quick summary would be.
The Jominey quench is all about showing that the hardness varies with depth from the quenched surface. It may be obvious but, the thicker the plate, the more difficult it is to harden it through its entire thickness. Whilst the US analysts seem to dismiss this as poor quality work, the Germans may have been constrained by “operational factors’. For example, cooling steel reduces in volume and a solid piece of steel that’s shrinking and hardening on one side while still hot on the other could break due to the internal stress. Try pouring boiling water in to a cold glass & you’ll see what I mean. Consequently, this limited rate of cooling would result in the heat from the remainder of the plate, especially very thick plate, preventing the quenching effect in some areas altogether.
It’s an interesting problem (to me anyway) which would have been solved if Germany had had access to Molybdenum.
You see, what you’re picking-up on about the quality getting poorer as time goes on is actually clearly stated in one section about the chemical analysis. The % of Molybdenum steadily reduces with time from about 0.5% to almost nothing. Make no mistake, Mo is a critical alloying element in these kinds of steels. Chromium & Carbon can both make steel very hard but together, in large quantities, they’re a recipe for disaster. Too much Carbon and you’ll get Chromium carbides forming. The documents then go on to describe the effects witnessed when welding this material. Cracks
Welding a steel that’s been carefully heat treated is probably the worst thing you can do to it. And the only way you can stop it from cracking is…
To heat it up a lot before you start welding.
Obviously, this screws with the properties the heat treatment was intend to give in the first place. The only way I can think of to weld it would be to use a temper bead procedure. This would take a LONG time which would really screw your production rates
and promote carbide formation due to prolonged periods at high temperature, further degrading the armour plate.
It's another critical component in making really hard steel for armour.
