Bluing 12L14 Steel

[gmac]

Hello everyone;

I want to Blue - using heat in the way that tmuir does "Blue Screws" - some 12L14 air cooled finned cylinders (approx 1.5" dia, 2.0" long) for an Upshur engine. I've never done this and I'm not sure if it is possible with this size of part. Not looking for show class uniformity of color, just reasonable. I'd figured to pre-heat the parts in an oven then bring to final heat with a torch of some description - but what? What type of heat source will have the capacity to heat this size of part uniformly. Would propane/MAP do the trick or...?

I suppose my first question should have been does 12L14 respond and color in this way? Will the fins heat at a different rate and make uniforn color difficult to achieve?

Thanks for the help
Garry

 

[speakerme]

Hello,

This reference might help you: www.blindhogg.com/homeleamadesalts.html. You will not know how they come out until you give a sample a try.

best wishes

Chuck M

 

[tmuir]

I have no idea whether the grade of steel will make a diference but you will find it very hard to Blue an item evenly that big as you would need to heat the item evenly across it so it all reached the correct temperature to blue it at the same time.
This would be almost impossible to do with a blow torch. You might manage it with a kilm that gives even heat throughout it by setting it at the kilm at the correct temperature.
For items larger than a screw or small watch hands I think chemical bluing would be the only way to do it but that is not something I know anything about.

Also how hot does this engine get when running. If it gets too hot it will change the colour of your finish.
The other week I saw a motorbike with stainless exhaust pipe the most beutiful shades of yellow, blue and pink depending on how hot that part had got whilst the bike was ridden.

 

[shred]

12L14 will chemically 'blue' very well, but that is much more of a gray-to-black color; more gray with the DIY kits, more black with the hot salts. It will still rust even if blued, but less rapidly.

 

[JMI]

Hi gmac,
Here is a cold bluing product that I've used on 12L14 steel with IMHO pleasing results, Oxpho-Blue from Brownells:
http://www.brownells.com/.aspx/sid=3870/sku/8_oz_
Here's a picture where I used it:
http://www.homemodelenginemachinist.com/index.php?topic=2821.msg36071#msg36071
Very easy to use. Brownell's also has many other bluing products, hot and cold.

Jim

 

[GailInNM]

Garry,
Sometimes the easiest way to tell something is a direct experiment.

I looked up Steel Color Temperature with Google and while there was some differences, the first couple of hits showed that a dark blue needed about 550 degrees F. It seemed that I remembered that my kitchen oven went to 550 degrees F, and a quick check confirmed that it did. I think that is fairly standard.

Jogging the memory a little more, I remembered that I had a couple of hot air displacer cylinders that had become surplus to my needs at the time because I changed my mind about the design I was working on. They were made of 12L14. The fins are an inch in diameter and the overall length is about two inches. Largest cross section is about 1/8 by 3/16 inch.

Polished off the rust spots with some 600 grit abrasive paper, and then cleaned up one of them with CRC Brake Cleaner. Good stuff for oil removal. Don't touch with your fingers after cleaning unless you want finger prints on your finished part to prove it's yours. While the break cleaner was air drying I turned on the oven. Since it is a gas oven, I waited for the temperature to get to about 300 degrees so there would not be any free moisture from the flame to condense on the cold metal an the set the cleaned cylinder in the oven on a scrap of aluminium to bridge the bars of the rack. A few minutes later I checked the oven and it was up to 550 Degrees F. Back to the shop to do some other things. Ten minutes later I peeked at the part when I went to the kitchen to get more ice for my soda and it looked uniformly blue. So I gave it another ten minutes and pulled it out. Parts with a thicker cross section will take longer. Photo shows it after removal from oven and before oiling. You will have to oil the part as 12L14 likes to rust and the oxide coating will not slow it up much.

Gail in NM,USA

 

[tmuir]

What a great result, no way you could do that with a blow torch.

My kitchen oven is getting tired and struggles to 230C (445 F).
The wife wants a new one and now I can see a reason to get one too. :big:

 

[Joe Rollings]

Hi! I'm a newbe and thought I would respond to this with a little additional info. I have blued lots of tools and other parts we make in just that way in the kitchen oven. I now even have one in the shop for that pourpose that is electric. On smaller parts, a cheap toaster oven that will go to 550 F works well.

There are also some very nice colors with more reds and yellows in them at lower temps, so if I am making something that is one-off and does not need to match anything, I may stop it at a bronze color or even purple.

Also, if you finish a part and then do not like the color, you can go back to ground zero with a quick dip in some diluted muratic acid. That's an old trick around cutter grinding shops when they burn the edge on your cutters blue and don't want to regrind them. The acid takes the blue burn mark away. Follow with a dip in baking soda and water to kill the acid and prevent rust....Joe

 

[GailInNM]

Thanks for the information Joe.

And, welcome to HMEM wEc1
Glad to have you join us.

Gail in NM,USA

 

[Joe Rollings]

Thank you!...Joe

 

[gmac]

Thanks to all who replied! Virtual mentoring or what - I love this site. On the way home tonight I stopped into a sporting shop and picked up Birchwood Casey Perma Blue (only thing they had) - thinking heat bluing wasn't going to fly. I get home and check here to find a range of ways to accomplish bluing. Looks like the oven will get a workout and become part of the shop... Thanks for the ideas and support everyone - I'll report on my findings later.

Joe - I like your idea of stopping at the other colors - the bronze or purple may suit me better. Question - how much do you dilute the muratic acid for color removal?

Cheers
Garry

 

[Joe Rollings]

Muratic dilution and temperature are almost equally important, and I never have found a good road to repeatability. I use muratic to eat rust, too, and fire scale. It only takes a minute or less to strip off blue oxidation, so if I were doing it in warm weather, I'd probably start with 1 part acid and 3 parts water and go from there. concentration does not seem to be as important as temperature. The fumes make rust on tools and machines if you use it inside, so keep the process outdoors. I strip railroad spikes and horseshoes to bare metal with it all the time, laying out a bunch of bricks in a square on the ground, then laying clear plastic or a garbage bag over the bricks to make a tank.

For rust stripping, the solution is strong enough when you start getting bubbles rising from the metal.....Joe

 

[vlmarshall]

That displacer cylinder is beautiful, I'll never use chemical bluing again! My 12L14 Cracker wheels that I dipped (the extra set) look just like Shred describes, grey-black.

 

[vlmarshall]

Well, I tried it today, with that extra set of 12L14 wheels. A quick glassbeading to knock off the chemical black, degreasing, and then into the oven at 550 degrees.
After 20 minutes or so, they looked like "straw" tempering color.

I bumped the heat up to 650, and they blackened, sort of.

Dring all of this, my coworker with 30-something years of heat-treating experience, is telling me that it's not gonna work until 900 degrees.
So, up to 900 I went, and after probably an hour at that temperature, they looked like this:

Well, without the paint stripe. ;D

What'd I do wrong? Was it the beadblasted finish?

 

[gmac]

Vernon;

It's unlikely the glassbeading had an effect on the color - the beading reduces the stress in the surface skin of the metal, which is why it is useful as a tool to improve fatigue life of loaded parts.

I found two color charts (went looking after Gail's comments) and it looks as if you needed 1000 F to get to black, medium gray at 900 F looks about right;

http://www.anvilfire.com/index.php?...per Colors and Steel Hardness : anvilfire.com

The colors in these charts look kind of "loud" to me, I like the photo strip at the bottom of this article;

http://home.att.net/~ShipModelFAQ/ShopNotes/smf-SN-Metals.html

It raises the question - are you reading the air temperature in the oven or the actual metal temperature?

Cheers
Garry

PS - the wheels still look good to me!

 

[vlmarshall]

Thanks!
Yeah, I knew about blasting and stress.
So, I should have gone even hotter, eh? I should have listened to Mark (at work). ;D

These ovens read air temperature with a little thermocouple.

;D I'm happy with the wheels, too! I just wondered why they don't look as good as Gail's Stirling hotcap.

 

[GailInNM]

Vernon,
You got me curious, so test #2.

I had a Gauge 1 locomotive wheel 2 inch diameter that I had made as a extra when building one of my locomotives. It is 2 inch diameter 12L14. Since I had made it over 5 years ago, and not oiled it, it had quite a few rust spots on it. I don't have a bead blaster, but a few minutes with a fine silica sand (with respirator) in a portable sand blast gun got rid of all the rust spots and left a satin finish. Degreased and into the oven it went at 550 degrees. I think the oven is fairly close on temperature. I checked it when I bought it about 5 years ago at lower temperatures. It has an electronic control.

The color is definitely different. I am partially color blind so I can't really tell you what it is. But it is quite dark as you can see in the photo.

I think that you may have gone through the "blue" zone when you heat treated your parts. The temperature range for blues is fairly narrow. Look at the color chart on the links.

If you wanted a black finish, you could probably spray with oil and then bake some more. Not a recommended procedure for the domestic oven unless you live alone. If you have ever tried to remove a little baked on cooking oil from a frying pan you know how tough it is. Maybe one of the spray cans of cooking oil for frying would work. Getting it ever might be a problem however. Maybe I will try it on this wheel a bit later.

Gail in NM,USA

 

[vlmarshall]

Maybe I did go through the "blues", and missed it! I'm using one of the heat-treating ovens at work, so I can't bake my parts while oily, but I CAN heat them with a torch and oil-quench them... I guess it won't look as good though.
I don't mind the finish I've gotten, I'll be using it again...it just doesn't look as good as that displacer cylinder! :bow:

Still, it's quite believable for a railroad wheel. Thanks for all of the help!

 

[gmac]

Another clue;

"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."

Found this in some material on stainless steel. Vernon - perhaps if you'd soaked longer at the temp you were using you may have gotten to black (or run at a higher temp for less time).

Gail - Test #1 looks medium black with a blue tint to it (somewhat like the chemical bluing with Brownell's products). Test #2 looks black/black - at least on my monitor. How long did you soak Test #2 at temperature?

Garry

 

[GailInNM]

Garry,
Both test were about 20 to 30 minutes at 550 degrees F.

OK, last test and now I have to get back to my own shop projects. Not that this has not been worth while as I have learned a lot with this project.

I sprayed the wheel with Canola non stick cooking oil. Not a real good plan as the spray was very uneven and bubbled on the surface from the propellant. So, I blotted it with a paper towel and blew it off with an air gun to spread it around and make it even. Baked for 30 minutes at 550 degrees F. It definitely got darker.

In the attached photo I tried to get a decent white balance and put in a couple of reference black objects. To my eye, the color is about the same as the matte black section on my calipers, maybe a little bit lighter. I can see the darkness difference between the wheel and the black lens cap from my Cannon camera, but it is not a lot.

Some further thoughts. My propane BBQ gets up to 600 degrees F with the hood closed and both burners on high. Takes about ten minutes from cold. Temperature probe is about 4 inches down from the high point of the hood, and a little higher than the keep hot rack that folds up and down with the hood. I think it would work for carbonizing the oil on oil treatment, but the temperature control would not work well for just a blue oxide coloring. It would keep any smells on the outside of the house, although I did not notice any odors stronger than what I get with normal cooking using the Canola oil.

Gail in NM,USA