heat colored stainless steel

[hotrodlincoln]

Hello, this is my first post as a new member, back in the 80's I bought a ss rugger redhauk from a gun smith in vallejo ca., the gun was brass colored, all the guns he was selling at the time had the same treatment (some were light and some were darker, but the color was always very uniform), he also worked as metallurgist for a fixture company that specialized in coloring stainless fixtures, he said that they slow heated them in ovens at i think 275 degrees for 4 days, he said that they lost no temper, and he re assembled the steel parts after the coloring, everyone who saw the gun found it very interesting and I had countless offers to sell it. I have never been able to find another gun with the same finish, BTW the color ran deep and scratches still showed the same color. I shot many regular magnum and hot loads over the years, and cracks never appeared. Has anyone ever seen this done before? do you thing a low temp would compromise the heat treatment? It was a gorgeous gun.

 

[NIGHTLORD40K]

Welcome to the forum!

Not sure what process he used, but it sounds interesting. I take it you no longer have the gun? No pics?

 

[silicosys4]

An article on the process
https://www.bssa.org.uk/topics.php?article=140

 

[Lucky Derby]

Sounds interesting. I'm not a metallurgist, so I can't say anything about the process.

 

[BigBlue 94]

Low temperature heating is known as tempering in the knife world. It will not hurt the heat treat. This toughens the outer shell of the metal, similar to case hardening, but not exactly.

What hurts heat treating is heating up to a high temp (about 1250° for 1018 steel) then letting it cool in the shut down oven. This is known as annealing, and completely renders the metal soft and workable.

Heating to the same critical temp then quenching in the correct medium will produce a heat treat.

For steel, 290° will turn it pale yellow. As you increase the temps, itll darken, then turn brown, purple, blue, and finally varying shades of red, then white. Red however means the molecules are starting to turn molten. White is forging temps. It was using these colors that old timey blacksmiths knew how hot their steel was.

Stainless is a funny metal in that the more it's worked, the harder the surface gets. A dull cutting tool will turn the piece yellow with heat, making the surface harder, and exacerbate problem.

This is the hot side of a Stirling engine. Its made of stainless and gets heated by an alcohol burner. You can see the various shades cause by different temps

 

[Mizar]

Some companies, like Colt and Luger P08 manufacturers, used heat bluing, but it was reserved for the small parts because it was not really durable. And in the case of blue color heat (salts) bluing it was not suitable for critical parts as the high temperature for obtaining the blue color would damage the heat treating. But it is just a thin oxide layer, it will not penetrate the steel - what you are describing, scratches showing the same color, cannot happen.

 

[Speedo66]

The pale yellow, according to the chart, starts at 290C (554F), that's twice the temp indicated by the OP.

 

[silicosys4]

The pale yellow, according to the chart, starts at 290C (554F), that's twice the temp indicated by the OP.

The OP mentions that the parts were left in an oven for days, my guess it probably takes that long at a low heat to show any effects.

The article mentions

"Time

Laboratory tests done to establish the published heat tint colour charts have usually been based on heating for one hour. As exposure time is increased, the temper colours can be expected to deepen ie make it appear that a higher exposure temperature may have been used."

 

[BigBlue 94]

Yes time plays a factor in all heat treating. It's kind of like baking a turkey, so much time per inch of thickness.

I didnt get into much heat treating in school but we did some. For instance, the punches we made as our first project were 1" diameter, and were baked for 1 hour at the critical temp, which was somewhere over 1200°F. Then they were removed and quenched in a saline bath.