Hi Dougie,

I assume you are looking for something like this:

The example above is a low resoloution chart. Here is another in higher resoloution.

Have you done a web search?

Thor

A good article Michael, and I’m particularly pleased to see that it also makes reference to the time effect on the level of colouring.

Many years ago I used to receive reports on failed bearings. These would claim that, based on the colours of the inner and outer rings, and the tables showing ‘temper colours’ in various books, the bearings had reached ridiculously high temperatures during their operation. This of course raised many questions about what the user had been doing.

I would often try to challenge these reports based on lubrication evidence, but when plastic cages were involved and these showed absolutely no evidence of temperature distress I still received push-back on the lines that the “books can’t be wrong”!

Eventually I did manage to persuade the inspection group to carry out a test in a laboratory oven to try to settle the matter once and for all. About ten small bearings were placed inside and the temperature set at precisely 120C.  Every hour I got them to remove one of the bearings. When the test was complete it was clear that within 10 hours the steel rings of the bearings would progress all the way through the range of temper colours described in the books the quoted, despite not ever exceeding the relatively mild 120C.

The quality of the reports improved after this simple test.

Gerry

And people often confuse tempering colours with colours due to oxide film thickness.