how heating metal and quenching makes it stronger, but heat cycling over time makes it more likely to break

Question

I’m just an amateur guy who messed with metal on occasion

And straight up not following the logic

I know heating and quenching makes it harder, which is good for knives and such, but also makes it more brittle I guess? And likely to crack?

The descriptions on this subject are literally “over explaining the scientific molecular composition of metal” or “so anyway make hot then make un hot, dat good”

But I was trying to bend some metal today, heated it up a few times and got it near its shape, then cooled it by quenching so no one would grab it and burn their hands on it while I stepped away, came back and heated again and it just broke lol

In: Other

Answer 1

I worked in a copper alloy producing plant. Typically annealing was done at a higher temperature (~1450F) and water quenched to preserve the grain structure. The product was either then left in that condition or it would be cold drawn, cold drawn and heat treated (600F) or just heated treated and air cooled. These treatments would create the grain structures and physical properties required by the customer or specification. All metal heat treatments, either annealing or ageing (hardening) are performed at different temps specific to the material.