I've spent hours but can't find the answer...

[schmittie]

Howdy again. You guys are sharp, so I'm sorry if this is a stupid question. But I've done hours of reading and can't find out for sure what the answer is to this question: Can steel be cut and or modified after it has been HT? If it is modified after HT (I realize it is backwards way to do things, I'm just curious if it is possible) does it have to be HT and tempered again? Would the easier route be to just anneal it and start over? Will it ruin steel to go through these processes over and over again and render it useless?

Again, my apologies if this is a stupid question. I read through the newbies thread info last night and again today but can't find the answer there either. Go easy on my guys, maybe I'm just missing it.....

 

[Nathan the Machinist]

Thank you for making the effort to find the answer to your question yourself first. It is my pleasure to answer your well phrased question.

Steel can be worked in the hard condition, but it is more difficult. It can be cut with carbide tooling if you are setup for it, but generally most work on hard steel is done by grinding.

Grinding hard steel works fine unless you get it hot, which is easy to do. If you get it over the tempering temperature used when it was heat treated, that spot will loose hardness. For example, a blade that was tempered at 450 will be damaged if, while grinding, the very edge hits 500 deg. Sometimes it will run color, leaving a blue or colored oxide on the surface to tell you ya screwed up. Sometimes you'll get no clue at all, except it just doesn't hold an edge like it should. Keep it cool with frequent dunks.

In practice, you do not want to anneal and re heat treat steel too many times because the repeated heats will deplete the steel of carbon if it is not in a protected environment, which most of us don't have. If you want to anneal it and reshape it and reharden it, that should be fine (assuming you are capable of a heat treat as good as the original). But I wouldn't recommend doing it over and over again.

So the short answer is yes, you can work hard steel. But sometimes it is simpler to anneal and re heat treat.

 

[jdm61]

When I was visiting Bailey Bradshaw last spring, he had a complex damascus blade blank that had been surface ground and then heat treated. He left the grinding of the bevels for after heat treating. Just keep the blade cool. Grind with bare hands so you can feel the blade.

 

[schmittie]

Thanks for the help Nathan. You spelled it out pretty well. One more thing though. What would be better to dunk in in while grinding hardened steel? Water bath or oil?

 

[galadduin]

Water is the best for grinding, don't do it with oil as it will be pretty messy while grinding. Some abrasive belts don't like water and it will get dull, for example with simple AlO belts as it gets hot dunk the blade and wipe with a cloth, then continue grinding.

 

[Nathan the Machinist]

Thanks for the help Nathan. You spelled it out pretty well. One more thing though. What would be better to dunk in in while grinding hardened steel? Water bath or oil?

Water. You're just dunking it in water to keep it cool while grinding.

Oil is frequently used as a quench from austenitizing temperatures when hardening steel. Assuming the steel isn't glowing bright red (yeah, that would be bad), it isn't hot enough that the quench medium makes any difference. That is a different kind of quench and a different set of circumstances when you would use oil.

 

[Stacy E. Apelt - Bladesmith]

Good question, and good answers.

To add:
Many thin knives are ground from hardened steel. Fillet knives are a prime example. When the blade is that thin, there is no easy way to pre-grind the bevels ( and not have the edge too thin for HT), so you often just profile the knife, harden the steel, and grind the bevels in last.

Other times when a hardened steel is used, is grinding hard objects into knife blades. This is done with planer blades, old saw blades, and files. A final temper to make the blade less brittle is usually done in the kitchen oven at about 400F.

When grinding a hardened blade, or any grinding after HT, put a pan/bucket of water by the grinder. Put it where you can dunk the blade easily and quickly. Grind bare handed, and when the blade is hot....DUNK. This will protect the temper of the steel from being ruined. If it turns blue, you have overheated that spot. A little blue spot won't be the death of the blade, but a lot will make it so it won't keep an edge.

As was pointed out, if the steel is easily annealed and re-hardened, it is better, and usually easier, to anneal ( soften) it , grind the blade, then re-harden it.

Stacy