cold working

[Coutel]

I have some steel specs from a supplier of 52100 where it goes on to describe various ways of heat treating 52100. In a section under 'machinability', it states that...'the machinability of 52100 can be somewhat enhanced by cold working, which accounts for the improved cutting characteristics of cold drawn or roto tubing'

What exactly is 'cold working'?, ......any one tried it?

Thanks.

[Quenchcrack]

Cold working is defined as deformation of the metal below the recrystalization temperture. In steel this is about 1100F. It is often expressed as a percentage reduction of the cross section. For instance, if I cold work a blade from 1/4" to 3/16" it would be 25% cold work. Because the work takes place below the recrystalization temperature, the crushed metal grains do not recrystalize as they would if done hot. The crushing of the grains disrupts the crystal lattice and makes dislocation movement much more difficult. Since deformation of the steel must take place by dislocation movement, it makes the steel harder and stronger. However, it is NOT a suitable substitute for quench and tempering. Hope that made sense...

[Coutel]

Thanks for the detailed answer...but I now have more questions

When forging the final hammer blows on the blade edge at a lower temperature, is this having the same effect (is this what some refer to as edge packing).?

and why is it not suitable for quenching and tempering?

[Quenchcrack]

If the cold work takes place at a low enough temperature, I suppose it could be considered edge packing. However, the entire concept of edge packing is questionable. First, one cannot pack the atoms in the metal any closer together than the interatomic forces will allow. Interatomic spacing is based upon charge and size of the atom. Pounding on it will not change that. Cold working prior to quench and tempering does nothing since the metal will re-crystalize and relieve the stresses when you austenitize it. I meant that cold working will not be as good as quench and tempering with regard to edge holding. Sythes are normally sharpened by cold working the edge but these cutting edges are not made for cutting flesh, bone, wood, etc.

As far as improved machinability of cold worked 52100, I can only guess that the distorted crystal lattice, being somewhat brittle from cold work, will readily form small chips and break away from the machined surface. Poor machinabilty is often a characteristic of very soft metals that do not form chips but peel off in long stringers. The addition of sulfur and lead to steel improves machinabilty because the lead and sulfur inclusions nucleate cracks that break the chips off quickly.

[Coutel]

Thank you for your replies.

I think you have answered my questions and helped me understand.