question regarding 0-1 drill rod?

[Tony Wells]

Thanks for posting that, Bill. It nicely expands on what I was saying.

Ray, I respect theory and reference materials, but having gone down this road innumerable times, experience tells me that despite the physics behind it (which are solid), things don't work exactly like they <edit>should</edit> in real life. THAT is a fact. As you continue to study and do your own evaluations, I'm confident that you will come to the same conclusion. I've discussed this subject with so many people over the years (including several Metallurgists holding valid PhD's and Masters degrees that I am weary of it, and resigned to design and machine around the facts as they really are, not as they are "supposed" to be. Just part of the game.

 

[OldMachinist]

Thanks for posting that, Bill. It nicely expands on what I was saying.

Ray, I respect theory and reference materials, but having gone down this road innumerable times, experience tells me that despite the physics behind it (which are solid), things don't work exactly like they do in real life. THAT is a fact. As you continue to study and do your own evaluations, I'm confident that you will come to the same conclusion. I've discussed this subject with so many people over the years (including several Metallurgists holding valid PhD's and Masters degrees that I am weary of it, and resigned to design and machine around the facts as they really are, not as they are "supposed" to be. Just part of the game.

Tony,
Very well stated.
:goodjob2:

 

[DMS]

If you have not checked out the article that Bill Grubby linked above, it was quite interesting. They only talk about 2 alloys (D2, and 17-2 stainless), but one grows, and one shrinks. The D2 appears to be affected by not only the initial quench, but also the temper, and the effects are non-linear (I guess that is to be expected if you have read anything about the crazy chemistry going on in chrome steel).

I think the question regarding whether the whole shrinks or grows is interesting, but take a step back and lets have a look at the OPs question. It seems like there are two things you have to deal with

1) Growth/shrinkage
2) distortion (things changing shape)

If the two pieces are round mating parts, and you make them out of A2 or D2 (something that is not likely to distort), and you run them through the same HT cycle at the same time, at the end of the road, I would guess they would mate pretty well (but.. I wouldn't bet money on it).

O1 is going to distort more than A2 or D2. I'm guessing the best bet is to leave allowances for finishing after, which is the common practice.

As far as undersized taps, I though those were for parts that were going to be plated afterwards?

 

[Ray C]

Trust me, I'm the first to know that theory and reality have different views of each other. In the last 32 years of engineering and R&D (now an adviser and leader of a group of senior scientists) I'm well aware that engineers and technicians often have an unfavorable view of "theory". I've spent my career bridging that gap and having come from a family of machinists and metallurgists -and having put myself through school working every kind of job imaginable, I've gotten my snoot full of crash courses with reality. And FWIW, I do not accept assignments unless I see the project through from conception to field test and initial manufacturing -only after that others take over and I move on to the next thing. Sometimes I have 2-3 such grand project in the works at one time.

Another thing I'd like to mention is I'm well aware of comments like "what stupid engineer designed XYZ thing this way?", "They should be shot". Easy answer. We're under pressure from the business teams (or in some cases, the executive VP and/or CEO acting on direction from the BoD) to cut every corner possible. In days past, we had the power to stand-up and say "No-way, it's not done until I say so". -Do that now and you won't be working in that town and will be looking for different ways to pay the mortgage and feed the family. ( You'll be happy to know that I push the limits to extent possible).

That said, I never disbelieved anyone that dimensions changed. I will admit that my initial response in this thread came across as a little grumpy -and for that, I apologize if it was taken that way. Truth be know, I was responding while taking breaks from the sun while fixing my backyard deck and my responses may not have been as cordial as they should have been. What can I say? I'm getting to be a grumpy/crusty guy as time goes... -And rather enjoying the privilege .

We'll get to the bottom of this...

Ray

Thanks for posting that, Bill. It nicely expands on what I was saying.

Ray, I respect theory and reference materials, but having gone down this road innumerable times, experience tells me that despite the physics behind it (which are solid), things don't work exactly like they do in real life. THAT is a fact. As you continue to study and do your own evaluations, I'm confident that you will come to the same conclusion. I've discussed this subject with so many people over the years (including several Metallurgists holding valid PhD's and Masters degrees that I am weary of it, and resigned to design and machine around the facts as they really are, not as they are "supposed" to be. Just part of the game.

 

[cdhknives]

There are 2 different things happening with the heating discussed in this thread.

1) Standard heating. Heat a fully annealed disc/tube/cylinder and both the inside and outside get larger as the metal expands...to a point. IF it is a hardenable steel, and IF you go above the critical temperature you get:

2) ...a change in crystal structure. Yes, steel is a crystalline solid. When the crystal structure rearranges, the atoms pack differently and the alloy USUALLY expands slightly. Previous grain structure affects future grain structure to some degree, some alloys do strange things, effects may take more or less time to fully develop, etc. Now IF you:

a) ...allow the alloy to cool slowly enough, it returns to an annealed state and returns essentially to the original dimensions
b) ...cool rapidly enough the high temperate crystal structure is (partially or completely depending on how fast it cools, the metal alloying elements, etc.) 'frozen' in place, and the change in dimension is also frozen (though the new crystal structure also expands and contracts with standard heating...but from a different starting/zero point). This is the basic principle of thermally (as opposed to work hardening) hardening steels.

One of the first things you learn when digging deeply into metallurgy is to NOT make absolute statements. Metal solutions are extremely complex and well deserving of a status of specialty chemistry. Much if what is known is still the result of trial and error, though most of the common alloys are pretty well understood by now. The exotic superalloy stuff is still, well, exotic.

Want to get really confused? Heat treat some precision ground cylinder of an exotic air quenching stainless alloy. Let it sit. Measure it each day. Plot the result. Some continue to move for days or longer as the quench time is measured in days+ at room temperature...another reason some alloys need a cryo quench!

Annealing can also affect final dimensions. In fact, if your heating enough to stress relieve, you risk changing dimensions.

Fun stuff...too much to lean in my lifetime but worth the effort!

- - - Updated - - -

To the OP: O-1 is a simple enough steel that you should expect your internal bore to increase slightly when the rod is hardened. I would recommend a trial and error approach...bore a disc, harden, measure, and assume similar results for similarly dimensioned items from that rod. If your heat treatment is not uniform, neither will your dimensional change...but O-1 is relatively forgiving.