> steel can work perpetually with deformations under a certain threshold[*] [*] Within a temperature range of about ~-30 °C to ~400 °C. Below that and the toug

> steel can work perpetually with deformations under a certain threshold[*] [*] Within a temperature range of about ~-30 °C to ~400 °C. Below that and the toughness goes way down so that it's prone to cracking. Above that and carbon starts to work its way into all those crystal structure discontinuities, preventing some percentage of the strain from being relieved each stress cycle (the "creep range"). That's just for carbon steels. Stainless has a different set of problems.