heating of harden 1045 steel

[petedie]

... I was told that heating a preharden (42HRc) steel rule (1.5" high X 0.083 thick) for bending a bit is worst than heating it throughly (not melting). it has something to do with the fact that the steel becomes harder before it gets softer. now limited experimenting seems to support this notion.

has anyone else heard of this phenomena, and if so what is the proper term for it.

thanks
pete

 

[swall]

The only possible phenomenon that might support such a hypothesis would be strain ageing of a cold rolled spring strip material. This has been known to occur when hard drawn carbon steel spring wire or strip is heated in the range of 400F for an hour.But, if your 1045 was hardened by austenitizing, quenching and tempering, I would say no, nothing should be happening to harden the material when heating.

 

[unclesyd]

Some steels will become very brittle when heated in a range from 350-700F. A lot of people have mistakenly mistaken the brittle as an indication of hardness. A steel that undergoes this process with generally remain brittle after cooling to room temperature.

I don't have my reference any more so I don't know if 1045 has this problem.

 

[petedie]

FYI,

it is called blue brittleness in steel and is caused by "nitrogen atoms in the iron lattice hampering the movement of dislocations".