[bgd73]

I welded up an old differential bar, basically flat for an old Subaru.
26 years original. the springiness is no longer springy, and was acting like mild steel. so I welded the hell out of it with ingenuity, want to tow things anyway.

my question is.. after rinsing with water when still hot, attempting a quench..it turned carbon black for some seconds, then went right back to the metal colors origin.

does that mean anything? high carbon steel real hot, cool quick? never quenched anything.. I always slow cooled.

[Otto Nobedder]

The internal heat came to the surface, and tempered the metal at the surface. That's why the color changed.

A hard "quench" is more than a spray of water... Ideally you would submerge the part in water or oil (depending on the cooling rate you want).

Hardening and tempering is an arcane art, requiring practice and experience to get the desired result, and I'm no professional.

It is possible to over-harden the steel, making it brittle and easy to break, by quenching too long/too much.

Steve S

[bgd73]

ok thank you.

I tend to go the slow route cooling welding on a large object, like unibody framing.. well aware of too brittle.
the piece I refer to was unboltable, had in a vice, and had to be freakish strong.. like 1 ton in every direction, without counting extra "g-forces".

I am sure the surface version of quench, be it pretentious, did something good...it lasted a long time already. I simply volunteered to strengthen, 130mph.

This gets serious, good steel.
thanks for reply.