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Work Hardening

Work Hardening

(OP)
Hello,

I have a question about work hardening. I was in a discussion with a friend of mine about work hardening. We were trying to drill a hole through a piece of HARDENED steel and my friend told me to drill slow to prevent work hardening. My thought is the steel is already hardened, and therefore cannot get harder. I would like to have some other input on this.

Thank you,
Pat Wilkosz

RE: Work Hardening

If you want to drill through, e.g., a file, you use a special 'hard steel drill'. Which may be made of carbide. I think it has three flutes and a negative rake, and is run at very high rpm and high thrust, so that it basically rubs/melts its way through, leaving a blued HAZ around the hole.

If you want to drill through something that work hardens, like stainless steel, you use a low speed and a positive feed, so you are never 'rubbing' the metal, and it cuts like it's soft and gummy, which it is. ... if your setup is rigid and you have enough torque. The drill point geometry makes a difference, so you may need to get friendly with your Guhring dealer.

Another way to drill through hardened metal is to use an EDM machine, or a 'disintegrator', which is a very low-tech version of the same thing.

OR, build a putty dam around where you want the hole, fill it with grinding compound, and run a copper tube through, backing often to re-charge the 'lap'. Works on glass, too.

But just spinning an ordinary twist drill slowly against a hard surface will just destroy the twist drill and probably never make a usable hole.





Mike Halloran
Pembroke Pines, FL, USA

RE: Work Hardening

When I was an apprentice (many years ago), if you were a naughty boy in the workshop, as a reprimand, you had to cut half an inch off a railway track section manually, with a hacksaw.

Railway track is a manganese work-hardening steel. You were given a new hacksaw blade. Get nearly to the end and one "slip" where the blade just rubbed rather than cut and there was then no chance of finishing the job! A new hacksaw blade was supplied for you to start again...

Good training really - a bit of metallurgy regarding properties of alloy steels and how to use a hacksaw correctly!

Cheers

H

www.tynevalleyplastics.co.uk

Politicians like to panic, they need activity. It is their substitute for achievement.

RE: Work Hardening

How hard is "hardened" ?

Harder than a Grade 5 Bolt?

harder than a US made inch series socket head cap screw?

Harder than a sharp name brand file ?
http://toolguyd.com/blog/wp-content/uploads/2011/0...

Harder than a quality ball bearing outer race?

RE: Work Hardening

I would think the effect would more likely consist of overheating (and softening) the drill bit, rather than work-hardening the substance drilled.

RE: Work Hardening

(OP)
Thank you for all the quick and detailed responses. The item that was being drilled was a hardened steel gear from a socket wrench. We did end up getting the 1/8" hole through with a general purpose carbide bit and a masonry drill. Took a total of about 4 hours.

RE: Work Hardening

Definitely depends on what you mean by "hardened steel". A typical HSS drill will not likely cut into a steel surface that has been case hardened. But a carbide drill will cut into a steel material through hardened (Q&T) to a fairly high strength level if used carefully. One common mistake you see made by people attempting to manually drill thru carbon steels with HSS drills is using too high of a speed, using dull drill bits, starting with a drill that is too large, or spraying oil onto a steel surface excessively heated by drilling so that it gets quenched hardened.

RE: Work Hardening

As others have said, it depends on how hard it already is, and how, and what its metallurgy is in the first place.

Remember that there are different mechanisms of hardening. For example, your steel could already be highly martensitic, but have large grains and few dislocations. Plastically deforming it could therefore still strain harden it. Or, it could be e.g. heavily cold worked high carbon steel and thus have a very fine grain size, but still no hard phases. In which case, you can push it around, but you need to be careful not to overheat it.

If it's in a full hard condition, with both Q&T and fine grain size, you probably aren't going to make it any worse.

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