Big-End Hardening process

[G-Man]

The copper coating was used on crankshafts, con-rods and other parts as a 'resist' during the carburising process. This process is designed to put more carbon into the areas of lower carbon steel to increase hardenability. The purpose of the copper is to keep the carbon away from the parts that just require a tough steel without the super-hard (and potentially brittle) surface that you need for bearings to run.

One of my metallurgy friends kindly sectioned a scrap (rust and fatigue damaged) rod so that I could see how the process worked and possibly gauge whether it might be possible to remove some of the hardened layer and create a new bearing surface by grinding or honing.

Here is the rod cut up with the sample. The sample is just a thin section taken from opposite sides of the big-end, set in resin, and then mirror-polished.

002 Sectioned Con-rod by Graham Curtis, on Flickr

And here is a close-up of the sample.




You can see a feint (darker) outline of the 'hardened' steel layer around the important inner surface and side faces of the rod. On the coppered areas - the outside surface and that little indentation where one of the oil-retention slots is placed show no hardened layer. I really need a microscope to get a picture of the actual changes in material structure and will try and do that. It is also possible with modern hardness testing equipment to check the change in hardness across the layer.

Not very useful in itself but fascinating for the curious mind...... :-)

G

[brewsky]

Interesting...I wonder how that process compares with cryogenic treatment?

[G-Man]

Brewsky

Not heard of that for steel. How does it work?

G

Interesting...I wonder how that process compares with cryogenic treatment?

[brewsky]

It's basically a controlled deep freeze process that alters the mechanical properties of the whole piece instead of just the wear edge. It doesn't increase hardness per se, but does increase durability.

Or at least that's how I read it.

My brother in law built an 1100 HP Ford V-8 drag car and had the internal parts treated with this process.

Supposedly, it is in common use in the US racing engine business.

Another reported benefit, is that it will show up any manufacturing defect during the process.
http://www.300below.com/motorsports/

[G-Man]

Brewsky

Thanks for that - I did have a look on Wikipedia. Very interesting.

G

It's basically a controlled deep freeze process that alters the mechanical properties of the whole piece instead of just the wear edge. It doesn't increase hardness per se, but does increase durability.

Or at least that's how I read it.

My brother in law built an 1100 HP Ford V-8 drag car and had the internal parts treated with this process.

Supposedly, it is in common use in the US racing engine business.

Another reported benefit, is that it will show up any manufacturing defect during the process.
http://www.300below.com/motorsports/