Hardness of steel rod…

[tmac1956]

All:

I need to thread some 3/16″dia. steel rod so I purchased S7 non-hardened steel which means I’ll need to harden it myself after I thread it (I suppose). Hardened rod is so cheap it seems to be a waste of time to buy the soft stuff for this purpose. If that is correct, then there seems to be several types available such as air, water, and oil hardened steel. My question is… what’s better and why?

Thanks!
Tom

[willofiam]

Hey Tom, I am in the dark somewhat when it comes to this also, I have read and read technical data referring to this subject, either I am not smart enough to grasp it or it is very complicated, how to harden, what temp, how fast, how much carbon in the steel, physical properties, molecular compositions, cooling parameters on and on. I hope someone here with a simple explanation for clock and watch applications will comment. A recent book I acquired talks of making watch parts with oil hardened steel, of course I have seen “oil hardened” and “oil hardening” steel for sale, now is that the same thing or not??? cant figure it out. the book also mentioned L.S. Starret Company, Starrett No. 469 oil hardened, precision ground stock, saying that it is less difficult to harden with a low hardening range of 1400 – 1500 degrees. not sure if this comes in rods though. I had also read somewhere simply to check if the steel has carbon just touch it to a grinding wheel and you’ll get alot of sparks compared to very little sparking, (thats about all I know with limited brain space). thanks for bringing it up Tom, William

[david pierce]

Tom,
It isn’t which steel is better, it is which steel will be best suited to a particular application. Air hardening steels harden in the air and are not subjected to the sudden shock of quenching. They are well suited to applications such as stamping dies where dimensional stability is important. Water hardening steels are used for sissors and knives and cost less than the other steels. This is because the mix of ingreadents to make the steel uses less exotic and costly materials than the other steels. S7 is used for high shock applications but will not wear as well as the others. Oil hardining steels are used for cutting tools such as end mill cutters. P series metals contain a high chromium content and can take an extremely high polish. They are used for injection mold cores and cavities. Some steels cost a lot more than other steels but it does not mean that they are better just because they cost more.
david

[Bob Tascione]

Hi guys,
Yes William you can purchase pre-hardened ground steels. I used to buy 4142 pre-hardened precision ground stock which was still low enough Rockwell for normal machining. There are so many different types of metals available now that you can easily become confused trying to figure out which to use when. As David says “It isn’t which steel is better, it is which steel will be best suited to a particular application“. With normal watch and clock parts I normally use high carbon oil hardening steels and temper them to the hardness needed for the parts purpose. I have been experimenting a bit this past year with making parts with different types of metal though and may begin moving over to some more modern metals. S7 is possibly one of them. I have a piece of 1/8” s7 that I’ve wanted to try making some staffs out of due to it’s high impact properties to see how they polish out and hold up. In horology though most parts are not subjected to much shock (other than balance staff pivots) so wear rather than impact is usually my greatest concern. S7 machines fairly well but can be a little rough on HSS tools. If you drop your spindle speed down a little and maybe take an extra pass or so when cutting those threads you should be OK Tom.
You didn’t mention what the threaded part will be used for so you may have good reason for choosing S7. For those that would like to practice some single point threading for the first time I would suggest starting out with a piece of 6061 aluminum until you get a feel for it. Not necessary but is a lot easier on tool bits and cuts like butter when compared to some steels.
I have a couple of pdf files on my other laptop that covers when to use what metals that may be of help. I’ll dig them up a little later today and will put them up here for you.
Enjoy,
Bob

[Bob Tascione]

Here are the two PDFs that I mentioned in my previous post. I don’t want to upload the files without having permission from the authors or owners so I dug up the links where I originally found them. They are informative and worth downloading.

http://www.eng.utoledo.edu/~tschrede/met1110/Unit%206.pdf
http://www.akronsteeltreating.com/docs/default-source/default-document-library/ast-book.pdf?sfvrsn=0

Enjoy Tom,
Bob

[tmac1956]

Thanks Bob and David!

[willofiam]

thanks guys, will be some very helpful info , William

[david pierce]

Bob,
Holy cow, you don’t look like the guy in the videos. As far as the steel goes, if the application is for a pivot, then wear resistance would be an important factor in the material selection. A pivot will rub against an extremely hard bearing surface and must be able to withstand the abrasion. Usually when an entire industry used a particular material for many years it is because it worked. If you watch some of the old videos of the Hamilton Watch Company you can get a strong impression that they put out an immense effort to find the proper materials for watch parts. There may be other materials that have sufficient shock resistance but can be made a little harder and take a better polish than S7. The material that the rest of the watch industry uses is probably the best material for a particular application. We used to use S7 for punch press dogs because in some applications no other material would stand up to the force from the flywheel. Heat treating these items was a bit tricky. If it was too soft it would begin to mushroom, if too hard it would crack. We had to send these out to a heat treating company that had computer controlled vacuum furnaces as the blow tourch and quench when it looked right method could not give us the control needed to make the part work.
david

[david pierce]

Tom,
Brass rod is a great material to practice on. Enco is constantly running sales on brass rod but there may be some local suppliers of metal near you that can beat their prices. If you live in Dothan Alabama you may be not that far from me. I live in Stone Mountain Georgia and used to run to Dothan quite often. On Ross Clark Circle near the old West Lumber Company is a Waffle House. SAIA LTL is just across from that Waffle House.
david

[Bob Tascione]

Hi David,
Ha…Ahhh yes. I was 43 when I made those clock videos 17 years ago. Have a few more greys now at 60. The hair’s still all there though…just tied back and hidden for the pic.
Yes you are absolutely correct about S7 not being a good choice for ‘balance’ staff pivots. Wear would be too much for that application. I will be testing S7 for something much different though. I think I had mentioned the project I’m working on when we spoke on the phone a while back. They (the staffs/arbors) will rarely be in operation and then only briefly when manually activated. Wear will not be a factor. There is the possibility of shock though and this is where S7 may prove itself a worthy metal. Using S7 should allow me to scale down the pivot size a little and also go from a typical squared pivot to a lesser dia. conical staff pivot and at the same time reduce the parts mass. IF I can get a decent finish then friction should be reduced significantly. Friction is the big enemy here but I think it will be an improvement overall. I’ve managed to successfully heat treat tiny S7 parts with flame using both oil and water. Water’s difficult. Any sharp corners will usually result in cracks. The shape of the staff though has no sharp shoulders or edges. S7 get’s up into the mid 50s rc which is plenty hard enough for these parts. I had to pull the high carbon arbors back to at least this hardness to keep the parts tough enough. I’ve experimented with the shape and all’s well so far. It’s the surface finish I’ll be dealing with next. If all turns out well I’ll replace the arbors that I’ve already made with S7 staffs and will run some tests. I have one length of 1/8″ dia. left to mess with down here with me. We probably didn’t use S7 in our toolroom as much as you did as it’s not needed that often for jigs and fixtures so if you know of any trick or have any ideas that might work for polishing this stuff I’m all ears…as you can clearly see in my Avatar pic.!
Thanks David,
Bob

[tmac1956]

@david pierce wrote:

Tom,
Brass rod is a great material to practice on. Enco is constantly running sales on brass rod but there may be some local suppliers of metal near you that can beat their prices. If you live in Dothan Alabama you may be not that far from me. I live in Stone Mountain Georgia and used to run to Dothan quite often. On Ross Clark Circle near the old West Lumber Company is a Waffle House. SAIA LTL is just across from that Waffle House.
david

David:

Yes – I live in Circle City where even New Yorkers fear to drive – those farmers driving 15 mph in the left lane can be killer.

Stone Mountain is a little over 200 miles from here. The old West Lumber is now closed – we have two Lowes and a Home Depot so I guess they just couldn’t compete. On the bright side, we now have a Harbor Freight just down the road from there on 431.

If you’re ever down this way again let me know and I’ll treat you to lunch or a brew – or both. Of course it won’t be free cause I’ll be pickin’ your brain. Some day, I might talk my wife into visiting Stone Moutain – I’m a big Civil War buff.

Thanks!
Tom

[david pierce]

Bob, Tom, William and anyone else interested,
The 41xx series is known as chromium-molybdenum steel, has a very high tinsile & yield stringth and is generally used in shafting applications and high strength bolts. 4142 in particular has .4-.45 carbon, .75-1.0 manganese, .8-1.1 chromium and .15-.25 molybdenum. The shock resisting tool steels are S1, S2, S5, and S7. S7 is an air hardening tool steel but the rest are not. S7 can also be oil hardened but suffers a stability loss if hardened this way. It is known for high stability if air hardened, poor wear resistance and good toughness (obviously if it is shock resistant). The mix for S7 is .5 carbon 1.4 molybdenum and 3.25 chromium. The hardining temperature is higher than most other tool steels (1700-1750) and the tempering range is 400-1150. The hardness will fall between Rockwell 45-57 on the C scale.
david

[Bob Tascione]

Thanks David!
My reason for an oil quench hardening is to try and carburize the outer layer a bit for polishing purposes. Figure if I can case harden it a little that I should be able to hit the upper Rc range for S7 and possibly beyond and come up with a better finish while retaining S7s toughness. In most cases if the base metal is .5% or above in carbon content then carburizing will have little to no effect but I think going to higher temp. and soak times can sometimes change this. My reasoning is most likely all wrong but figure it’s worth a try and I enjoy messing with things like that. I’ve done pack hardening with low carbon steels used in old timepieces with success and have enjoyed the process. Once in a while stuff actually works out but mostly end up proving myself wrong. I wish I had an oven to leave the part in to test different duration’s and temps where the effects on penetration depths (if any) could be tested when packed in the carbon environment (charcoal and ground up cow bone wrapped in stainless foil.) I’m really just after about .001 or .002 penetration and hoping this might work using a flame. Sodium Cyanide and a gas or vacuum environment works better but that’s not happening in my shop. I’d probably kill myself. There are a lot of reasons for this to fail (S7 having some element that would prevent carbon infusion for one) and little that I can see that would give good results. I know that under ‘perfect’ conditions a depth of around 1/16 inch is possible but that would be for low carbon steel (like .2% or lower carbon content) and well controlled carborizing process. But what the heck…just need a couple of .001″. Also I have to wonder why this would prove to be any better than just making the parts out of a tough low carbon steel in the first place and then case hardening it. My hope is that there ‘IS’ some resistance to infusion that prevents a penetration beyond .002 or .003. The pivots are now around .021 dia. and I would like to cut that dia. by 1/3 or so. So with a dia. of .013 to .014 and a penetration of .002 I’d be looking at a ratio of tough material to hard outer layer that may just work. With regular low carbon steels it’s difficult for me to accomplish this shallow depth using a flame and repeatability would be a big issue. If S7 repeatedly resists penetration to about the same depth then that might help to control the depth to a shallow limit. I could be fairly certain that future parts made using S7 would be within the desired tolerance since the depth of penetration would be determined more by the characteristics of S7 rather than slight variations in my heat treating process. That’s a big if. Only one way I can think of to find out considering my limited tooling resources. If the case hardening works then I can try to figure out a way to run some comparison tests of the old way against S7. If the old way holds it’s own against S7 then pretty much proved myself wrong again, but if S7 comes out ahead then it possibly solves a pesky problem I’m having with my little project.
Not much S7 stock left here and difficult getting it shipped to my location. Would like to experiment with larger diameters but limited to what’s on hand for now. Will try to do this tonight or Sat. morning if I can get some playtime! If this works I’ll post the results up here in case there’s some interest since carburizing steel can play an important role in true horological restoration work . I didn’t intend to hijack Toms thread though.

Bob

[tmac1956]

Bob and David:

Guys – please post away. While I probably get maybe 50% of what you are discussing, I’m still getting some of it and I wouldn’t get this information anywhere else. You probably don’t know how much these discussions help me/us. I’m becomming acclimated!

Thanks,
Tom

[david pierce]

Tom,
No, I thank you. I have probably learned far more from your questions than you learned from my answers. I spent more than 30 years of my life in the manufacturing industry and enjoy having at least some link to my past. Because of Bob’s similar background and the way he set up and conducts this program, I feel that I can look back and at least know I do not have to throw that portion of my life down the sewer. The job I currently have is dull mindless drugery interlaced with moronic numbskulls constantly making bad decisions. Outside of the fact that it pays well, it has little else to offer. My career has changed from working out a mathematical algorithm and writing a computer program to generate the surface of a propeller blade, to, make sure I wear my company uniform properly and leave and arrive on time. My shop gives me a small glimmer of hope that I can someday do something a little more challenging and rewarding in my later years.
david

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