Falanx

Yeah. No probs. It'll be long though....;

Up until the mid-to-late 1940s, some applications - often military ones where components were subject to very high loading were through-hardened and stress relieved (a process that is often referred to as tempering, but demonstrates no martensite decomposition, so is really a lie). The components were, in other words untempered, meaning the martensite that was responsible for their hardness (and also the component most suceptible to the effects of trapped hydrogen) had not begun to decompose and liberate carbon as fine carbide particles and ferrite.

Now, as long as your component is redundant and never going to see contaminated water, or and corrosive environments this is acceptable. How many applications can you think of that fit that bill? Not many, I'll wager.

Then something wonderful happened...

In the fifties, Inco laboratories made some groundbreaking discoveries. First they developed the maraging steels, which suffer little from hydrogen issues due to their very soft high-nickel, carbon-free lath martensites and their enormous, ultrafine and profuse intermetallic precipitate strengthening (which is on a scale that conincides with the most efficient hydrogen sinks).

Alongside them came the nickel-cobalt secondary hardening steels, of which things like Aermet is a family member. These steels use the martensite of a sonventional maraging steel and intead of intermetallics, they strengthen it with profuse, incredibly stable ultrafine mixed carbides. This which Aermet was such a ***** to work with for cycle frame tubing manufacturers. It just eats tooling, unlike conventional maraging steels.

From this point forward, the approach to use of steel changed. In 1948, when the Basic Oxygen process for producing high quality clean, low carbon and nitrogen steel was developed, we had a way to ensure clean, and then with AOD/VIMVAR/etc electric vacuum secondary steelmaking techniques, ultra, ultra, just plain silly-clean steels, it became very easy to produce these ultra high strength, ultra high toughness, ultra clean steels just the way we wanted them.

Suddenly super-high mechanical properties didn't require us to quench high-carbon steels and leave them full of quenched in stresses to ensure they were hard/strong enough. We could get 2/3/4GPa UTS from a steel containing NO carbon. We could make a steel, harden it in still air and then temper it to death and it would only get stronger while sacrificing no toughness.

These days you'd have to be either nuts or just plain tight to go back to quenching the living daylights out of a 0.6% carbon steel just so you could have 55+Rockwell C hardness.


What's most important about this is that our inventory steels, our national standard grades - all the ones we use to make bicycle frames - now all contain either molybdenum or vanadium or both (with a couple of really stupid exceptions), both of which produce fine scale carbides when you temper a steel at about 550-650C. These carbides are perfect trapping sites for any hydrogen that has been absorbed by the steel. And they will trap a hell of a lot, trap it stably, trap it safely.