I’m currently writing an overview course on heat treating metals for welding. I’ll save you all of the details, but I will tell you this one thing: the key to the strength of a bond is the temperature it cools at.
If a metal is cooled suddenly, it likely to break altogether when pressure or force is exerted on it. It’s extremely hard, and seems like it would never break, but once it reaches its max pressure, it will suddenly give way and the bond will be broken.
If a metal is cooled slowly over time, it won’t be seen as a “hard” bond, but it’s more likely to flex when pressure is applied to it.
Sudden bonds don’t allow impurities to escape from the metal – they get caught in the bond and eventually lead to breakage. Slow bonds allow the impurities to escape and result in less breakage and rust.
Maybe Paul knew what he meant when he said “work out your salvation with fear and trembling…”