Case hardening

Hi Folks,

I want to case harden the eyes of a small link, 5/8" C/Cs with 0.096" dia holes. I understand that I heat to red/ pack hardening compound in and repeat a few times before quenching in water.

How will I know I have done enough treatment and will I need to re-drill to return to original hole size, but will this remove case hardening?

Thanks
Dave

Dave, its the length of time it stays at the red heat that matters and if you have an idea that you will have a size problem then allow for it but I dont think you will.

Perhaps two sessions will give you about 5 to 10thou. depth of hardness. The surfaces will be glass hard and almost untouchable by drills etc. You could perhaps lap out the holes.

I personally have never had size change yet !

Clive

How does the inner bearing surface become adequately hardened without losing bore?

Dave

It is unlikely to change dimension. If a small distortion is apparent you could easily lap it, as already suggested, with a suitable pin and lapping paste. Colin

Thanks for these thoughts. I have case hardening compound but not enough old shoes or belts to make up the leather carbon source. I did wonder if I had enough steel plate I could spare but I realised it may be okay to use a tin can. We only recently had corned beef so the box tin might do the job.

But, is it work waiting for some leather scraps?

I will try the process on a drilled bar stock before I try it on the machined links.

Also, for lapping compound, I suppose a fine grade grinding paste would do?

Thanks again

Dave

Edited By David Haynes on 17/10/2012 19:23:09

Hi David, search this forum with "Case Hardening" and you will see a couple of posts from me on this subject.

If you use the corned beef tin, fine but you must seal the lid with fire clay to prevent oxidising you work.

With hardening compound and a torch you will only get a very thin case unless you hold it in the flame for a great deal of time --- penetration is usually in the order of 0.005"per hour for pack hardening but there are several factors that affect this.

Good luck John

Hi David, search this forum with "Case Hardening" and you will see a couple of posts from me on this subject.

If you use the corned beef tin, fine but you must seal the lid with fire clay to prevent oxidising you work.

With hardening compound and a torch you will only get a very thin case unless you hold it in the flame for a great deal of time --- penetration is usually in the order of 0.005"per hour for pack hardening but there are several factors that affect this.

Good luck John

Doe's anyone know if it is possible to case harden plated bolts I don't know what the plating is

Thanks Roy

Not without removing the plating first Roy. Why would you want to do this?

Russell.

Russell They are square headed for my tool post

Roy

My Oxford arc welder has a 12V tapping which can be used with a carbon rod in the electrode holder to heat and solder, etc. The brief instructions also claim that the carbon can be used to harden steel. I had never tried this until very recently when I found that it seemed to work after a fashion.

Has anyone any experience of this method or helpful comment to make?

Roy,

I would leave them as bought. If they are working on hard tools it isn't a good idea to harden them. Just turn the thread off the end for a short distance to stop them jamming.

Russell.

Russell Eberhardt:

I agree that hard on hard seems wrong and, in any event, suspect you know more about this than I. However, one authority (the late Cliff Bower) said "clamping screws for tool-posts should always be made of high-tensile and case hardened material and the lower ends bevelled neatly". He went on to suggest drilling the ends and inserting a standard (presumably, hardened) steel ball-bearing making the interesting point that screws treated in this way do not tend to shift the toolshank when tightened.

I personally use standard HT capscrews treated as you suggest and try to avoid overtightening.

The supplied M6 cap screws in y 4-way toolpost burred over at the ends and some of the sockets were worn after 14 years of abuse with mixed metric and imperial allen keys.

I replaced them with cheap stainless ones from Screwfix which come with nicely finished ends that are much less likelty to burr. I also use these on my QCTP holders.

Neil

I have an old oilcooled Arcmobile welder which has a 200 amp tapping for brazing and case hardening using a carbon rod. I have only used the hardening facility on the ends of a push rod and got a good case but rough result. Stoning it produced a satisfactory finish. Colin

colin hawes:

Thanks for your post. What intrigued me about this method was that I had always understood that case hardening was a two-stage process - first introduce the carbon under heat then quench to complete. I seemed to get some kind of effect without quenching. Tubal Cain (WPS1) is very good on this subject and makes a good argument for choosing case hardening mild steel over through hardening silver steel, etc.

If you quench, you shopuld get a near glass-hard case. If yoiyu don'[t, but it cools quickly, you will just toughen the steel somewhat by turning the surface into an annealed high-carbon steel.

Neil

ega, It is some time since I used my welder's case hardening facility but i'm pretty sure I would have either quenched it quickly in water or reheated it with a propane torch and quenched it. Colin