Tempering/annealing stainless steel for spring

[TMIB]

Good comments in this last post on drawing the temper colors. One of my other hobbies is blacksmithing, and what was said in the previous post is right on the money.

A bit more information for those interested:

Steel below about 25 points carbon won't harden up with heating/quenching. The higher the carbon amount in the steel, the harder and more brittle the steel will be when you quench it. Really high carbon steel will often crack when quenched in water, so it's needed to quench it in oil, as it cools it just slightly slower.

When quenching it's best to move the metal stock up and down vertically; you don't want to move it back and forth as it can warp or crack, but if you don't move it at all it can form a vapor barrier in the fluid and not cool quickly enough.

"Mild" steel is usually 1018. The last two digits "18" refer to the amount of carbon in the steel, or in this case, "18 points". Unfortunately, less and less things are being made from actual 1018 these days, and more often what you're using is A36, or recycled steel. Anything goes with that stuff, and you really have no way of knowing what its actual content is. You just have to treat it as though it were mild steel, and be prepared for the occasional cracking or breaking when you quench it, if it happens to have a bit of higher-carbon steel in it somewhere.


Tempering is a softening process; you're drawing the temper in the steel to a specific amount by heating it in a controlled manner. You can do this by heating it for a period of time in an oven, or like many smiths do, by drawing the temper colors. The oxides present on the surface of steel change color as they reach specific temperatures, and by these colors, you can judge what temperature the metal has reached (and thus, how much you've softened the metal.)

There is no hard and fast rule for things like wiper blade inserts and street cleaner bristles- I'm pretty sure they are not made to a standard, and as such, one batch you get may be of a much higher or lower carbon steel than another batch. As with any unknown steel, it's best to just try it and see what works. On larger pieces you can sometimes do a "spark test" on a grinder to see how the sparks look; a higher carbon steel will have very short, explosive "firework" sparks, and a low carbon or mild steel will have longer burning "streak" sparks.

If you're making your picks and tools out of hacksaw blades, sawzall blades, or jigsaw blades, then they are likely going to be a higher carbon steel, and will react more predictably to tempering or heat treating. I'm guessing they are probably around 45 or 50 points carbon, but I'm not sure. Stuff like valve springs are aroudn 60 points carbon and work really well for center punches and the like.

On the pick I made (only one so far) I used a hacksaw blade, and didn't bother with trying to keep it cool as I cut it, as I knew I'd be tempering it when done.

I first normalized it by heating it to the Curie point then letting it air cool. Next I heated it up again to the same temperature and quenched it in oil. I then heated the back (handle) end lightly with a torch until the temper colors ran to the tip. I stopped it with a blue just behind the tip. I figure that this should make the handle portion the most flexible/tough, with the tip being slightly harder than the "neck" portion just behind the tip.

--TMIB

[TMIB]

Oh, also, I wanted to add:

Annealing is also a softening process, but much more so than tempering. With a ferrous metal such as steel, annealing is done by heating it up, then letting it cool *very* slowly. This can be done by burying in wood ash or vermiculite, or via a slowly cooling heat source. When I'm smithing, I often anneal pieces by leaving them in my gas forge after I shut it down for the night. The forge keeps a good heat for 4-5 hours at least, and may still be warm to the touch in the morning.

With non-ferrous metals, such as brass or copper, this slow cooling is not need. (though you wouldn't want to make brass or copper picks. ) You can quench non-ferrous metals immediately and they will be annealed.

--TMIB

[ToolyMcgee]

You have opened up a huge can of worms here. Since everyone is being so accomodating with giving info on different steel annealing and hardening, I'm going to add just a very small bit of info about stainless steel.

Surface hardening of stainless steel is next to useless it has a very low to low carbon content. It is possible to surface harden austenitic stainless steels through a process called nitriding, but it really isn't worth it and you would have to know the composition of the stainless stock you are working with. In fact even heating stainless past it's original annealing temperature will release some chromium from the molecular bonds on the surface of the steel and change it's corrosion resistance properties. You do not want to go through the hassle of heating stainless steel to work with it period.

Instead you would be better off trying something like low temperature stress relieving. You know what it isn't really worth me getting into here is a snippet from a website:
When austenitic stainless steels have been cold worked to develop high strength, low temperature stress relieving will increase the proportional limit and yield strength (particularly compressive yield strength). This is a common practice for austenitic stainless steel spring wire. A two hour treatment at 345 to 400°C is normally used; temperatures up to 425°C may be used if resistance to intergranular corrosion is not required for the application. Higher temperatures will reduce strength and sensitise the metal, and generally are not used for stress relieving cold worked products.

http://www.azom.com/details.asp?articleid=1141That is the website. First one that popped up when I googled.

Sound familiar? Very similar to the instructions given for re-tempering steel. Honestly I find one hour to be more than sufficient, but generally speaking just cold bending and using a low heat torch or cigarette lighter for around a minute removes the tendency of most stainless steel to want to return to it's original shape. Thank Raimundo for that little tip.

Have fun with it, but try not to go through to much toil. You don't need a full blow forge to do a little jimmy smithing.

-Tooly

[der_fisherman]

My take on stainless steel (from windscreen wipers mainly) is that you can make some good tension wrenches with it cold, but for picks it is simply not good enough.

I see blog entries where people have used it for picks, but my simple answer is that they may never have had a good springy hard spring steel pick, so do not know what they are missing! The same goes for picks from paper clips, great in an emergency only.

The best homemade ones are from hacksaw blades as there you have relatively high quality, high carbon steel.

By the way, final tempering and quenching in oil can give a hacksaw blade steel pick a coating that resists rusting to a far greater degree than one without (look at gun barrels made in the old manner).

I personally only use it on my homemade tools for fishing, due to the fact that getting the colors right on a good thin pick is so difficult unless you have a proper oven for the job, it is so easy to ruin a good pick if one part remains too hard and brittle.....and the lock that it breaks off in!!! WD40 protects my finished picks against rust.

The method I described in my previous blog entry is quite simple and easy to do and has the beauty that if you get the colors wrong the first time, you can repeat it again till its right! and even if that bit of hacksaw blade is eventually useless while you are learning, you have invested very little money and no time in making the pick either......therefore its the best method I know of for people with simple home tools to get that hard springy effect.....

.....but of course if anyone has an even better method to achieve this, I am not averse to learning something new!!! as are the rest of us are on this blog!!

[ToolyMcgee]

When you are picking wiper inserts out of the garbage you certainly have to expect the occasional failure. Tthe material is somewhat of an unknown and a couple basic tests on the stock isn't going to assure you a top quality stainless piece, but to group them with a safety pin is a bit extreme.

I like the rigid feedback a tempered piece of steel gives, but I know a few great pickers on here that use stainless steel picks because of the durability and flex that it has. I know the heavy handed beginner can appreciate not having a case of picks bend on them before they get it in their head to lighten up on the wrench a bit.

I like steel and surely a very thin pick made from good steel is going to be more rigid than even the best stainless pick of the same size. Such is the nature of the material. A good stainless, rigid, pick can be made though, and I have more than a few to prove it. Have a look around the forums and I think you'll see many pick makers agree it can be done.

I like the way you think der_fisherman, and I'm not trying to start a debate about what is better because it is ultimately personal preference. I would encourage anyone curious to try a good piece of hardened steel for a pick. Enough people have posted good info in this forum alone to make a good attempt at one. In fact try any material you want, but you'll be back to some kind of steel. Anything else just doesn't cut it.

I'm gonna go burn some hacksaw blade hooks and get to tempering them. I just needed to vent over the safety pin thing.

[Engineer]

There are different types of stainless steel, that is why some info coflicts with other info.

I could try explaining, but I would never do as good a job as this site has done already:

http://www.aalco.co.uk/technical/stainless.html

Hopefully you will be able to get the best from the picks!

[der_fisherman]

Hi TooleyMcGee,

I liked your post and I agree with you fully on all points.

But just to try out what was said about stainless wiper blades, I made a couple of picks, but they were too "floppy" for me when thin enough to work in most locks..... (could have been substandard wipers of course)

I will be staying with hacksaw blades that I have both hardened and tempered myself for the forseeable future.

I am planning on making an electric tempering oven shortly, so that I can properly temper thin picks without having uneven temperatures along its length.

Once I have figured out the details, I will be building something and if anyone is interested, I could post details here. First and foremost, it will be cheap!! I figure around $20 or so.......my aim will be to keep it as cheap as possible......I already have a simple design in mind......with a little bit of home made electronics to control the power/heat.