Is it possible to make a blade stay blue after quenching?

[Zpyke]

Is it possible to make a blade stay blue after quenching? I just watched a video that showed Tony Swatton heat treat a sword made out of 5160 spring steel to a blue temper and then when the sword was completely finished it was still that same blue color. I am new to blacksmithing and the heat treating process but from all my research I did not think that was possible. So my question is is it possible? and if it is how is it done?

 

 

 

The part in question is at 3:58

[Maillemaker]

The phenomenon you  are describing is called temper coloring, or the temper spectrum.

Essentially, as the shiny steel is heated, a clear layer of oxide forms over the surface.  This layer bends the light bouncing off the steel, changing the color.  It starts out as a pale yellow, then deepens to gold, bronze, peacock (a brownish-purple), indigo, blue, light blue, and then a pale grey-green.  The color depends on the temperature the steel is subjected to, as well as the duration.

This is purely a cosmetic treatment in this case, but the temper spectrum is really useful in toughening steel that has been made hard and brittle from quenching.

If you would like more info, take a meander through the heat treat section.

[Zpyke]

I have read all about heat treating and tempering but I did not find anything that said the metal would stay blue after it was quenched and the heat treating was finished. So I am confused how the steel would stay blue or if it is even possible.

[Chinobi]

the blue oxide layer (and therefore color) remains on the surface of the steel until it is: thickened by continued application of heat(also known as running the colors); removed by chemical action (vinegar, etc); removed by mechanical abrasion (wire wheel/grinder); or altered slightly by application of a surface protectant (wax, clear coat, etc.)

 

you can also achieve a similar blue finish by application of something like a gun blueing chemical treatment.

 

the blue color is not a transient color like cherry red heat or yellow heat etc that are the result of heat radiating off the piece rather than a permanent change to the surface of the steel.

 

edit:

think of it like toasting white bread, put it in the toaster and watch the surface change from white, through shades of tan and golden brown, to dark brown, to black.  at any point if you take the toast(steel) out of the toaster (forge/tempering oven) the surface has been altered permanently and will not return to being white when it cools, the toasted/burnt (oxidized) layer has to be mechanically removed by scraping it off with a knife to reveal the original material color again.

[Zpyke]

So if I want the steel to stay blue I would anneal for a longer period of time and then apply a surface protectant?

[Chinobi]

not sure if thats just a terminology error or not, but no, no annealing.  look up anneal in the forum search for a more detailed explanation than i can readily provide, especially for blade steels, but thats not where you want to be going for this.

 

you are effectively exploiting a side effect of the tempering process.  you just want to apply a controlled low heat to cause the formation of a very thin layer of oxidation on the surface of the steel.  you will probably be at 400 deg F or less, if you see the steel beginning to glow you are far beyond the correct temperature and will need to grind or otherwise reclean the surface back to bare metal.  if you use a torch you can watch the colors develop as you heat the piece but its harder to get it even across the whole surface.  you can put it in the oven to get a more even finish, but its a little more difficult to control until you have some experience with it.

 

after you have achieved a pleasing color then you can apply whatever surface treatment you have available, hit up the alchemy section if you need some inspiration on that front.

[Rich Hale]

Blue color after part of the heat treat whole process may be cased during the final phase..tempering..and in most cases with blades that wouild indicate a blade that has beensoftening too much with tempering and would not hold an edge properly. You may have glanced through the heat treat informationhere but it is critical for youi to learn both the terminology and the steps involved,,,shoot they are so easy to learn tha4t I did!. But it will take more than a scan or two to get it right.
Now wot i think you likley saw in a blue blade is a blade that was finished entirely,,all heat treat steps and final finishing on the metal work...then it may have been gun blued...most likley hot blued..that makes a dureable finish just like it does on firearms. Any colors as a result of the heat treat process are very thin surface thick only and will not last..they will rub off when putting blade in and out of the sheathe.

[Zpyke]

Thank you for your help. That is exactly what I was looking for. I just noticed the toast analogy now and that was perfect. It's amazing how quickly you were able to clarify this for me when hours of reading could not answer it. Thank you again.

[Chinobi]

Happy to help :)

 

Rich, Tony states and shows that he does it via heat treat, at 4:00 he says hes going to temper it to blue and the clip shows him putting it into the kiln and pulling it out electric blue.  then he starts cutting stuff up with it :)

[Zpyke]

Blue color after part of the heat treat whole process may be cased during the final phaswe..tmepering..and in most cases with blades that wouild indicate a blade that has beensoftening too much with tempering and would not hold an edge properly. You may have glanced through the heat treat informationhere but it is critical for youi to learn both the terminology and the steps involved,,,shoot they are so easy to learn tha4t I did!. But it will take more than a scan or two to get it right.
Now wot i think you likley saw in a blue blade is a blade that was finished entirely,,all heat treat steps and final finishing on the metal work...then it may have been gun blued...most likley hot blued..that makes a dureable finish just like it does on firearms. Any colors as a result of the heat treat process are very thin surface thick only and will not last..they will rub off when putting blade in and out of the sheathe.

 
That makes sense. It goes along with what Maillemaker said that it is purely cosmetic. The sword in the video was basically made for a one time use so it would not have to be very durable. I will look into the gun blue though. Thank you for your help.

[ThomasPowers]

DEPENDING ON THE ALLOY blue would be a spring temper and not too bad for a sword where flex and impact resistance (toughness) might be more important than having a hard brittle edge DEPENDING ON THE ALLOY  

 

Knives are generally tempered harder for greater edge retention but are generally  not expected to have impact forces on them like a sword.