Tempering/annealing stainless steel for spring

[d13]

I like the spring you get from a windshield wiper insert, but I would like to be able to heat it if necessary to form it. After heating it, is it possible to temper/anneal the stainless in some fashion to a near-original level of springiness? Also, is it possible to heat it high enough with a propane torch and quench it to get it hard and brittle enough to crack like a carbon steel hacksaw blade? My torch can get it to around a dull orange color before I ice quench it, and it still isn't very hard, or at least I think. I'd like a really stiff head on my tension wrenches, if it can be done.

[bumber]

sorry but your questions are confusing, are you trying to get it stiff to break it or are you trying to get it as hard as it can get without breaking?

If you grab it with two pairs of pliers about an inch or so apart and bend really slowly you should be able to cold bend them and they should keep their springyness.

I hear so many different things about tempering I dont know what to say...and Ive heard you cant really temper stainless steel(SS) but im sure you can somehow....anyway I just get it a 'warm glowing' orange and dunk it in the coldest ice water I can make if Im not sure about the metal, like the first time you try a new brand of hacksaw blades. Seems to work.

[maintenanceguy]

Sort of.

Yes, you can harden the steel by heating it and quenching it. The hotter it is and the faster it is cooled, the harder it will become. However consider these two things.

First, the harder a steel is, the more brittle it is. Get a steel really hard and it will break easily.

Second, depending on the amount of carbon and other things in the steel, some steels can be very hard and other's just can't. I suspect the stainless in wiper blades just isn't formulated to be very hard.

Knife blades and saw blades often use a strip of hard steel right at the blade edge so it can be sharpened but the rest of the blade is a softer steel so the blade because very hard steel will break easliy.

Oh, one more thing, I've never heard of a stainless spring steel. Spring steel is a very specific type of steel that can deform elastically much further than other steels. Bend spring steel and it springs back to it's original shape. Bend mild steel and it stays bent, bend a hard steel and it just snaps off.

[d13]

Well, I don't know if I would need it hard enough to be brittle, but I would just like to know for future reference on it. Apparently the steel just isn't what I want from it. I keep forgetting that pesky carbon.

I've never heard of a stainless spring steel either. I can get the wiper inserts to bend cold just fine, but basically I'm asking if there is a simple and correct way to re-set the springiness, or at least I feel that it's rather springy, that you get before you heat the wiper blade.

[vitti]

You need to get it cherry red hot and quench it first. If your torch is only getting to a dull orange then that's not hot enough. Your torch needs to be capable of heating to just shy of 1500 F. Most butane pocket torches cannot get above 1200. If you are using a propane, mapp gas, oxy acetylene or other torch then it should be capable of reaching that temp no problem by adjusting the flame. Heat it slowly until it gets red hot then quench. It will be at it's hardest at this point. To temper it you can then put it in the oven at 400 F for about 30 minutes then quench it.

That will probably get you back to about the original springyness. You might have to experiment with the oven temp. Lower temperatures when tempering will retain more springyness but going lower than about 200 F will have no effect. If you do play around with the tempering temperature, keep in mind that you will need to harden it again (heat it back to cherry red) before trying a lower temperature temper.

If you've got the time to play with it you can probably get back to that original feel or possibly even stiffer depending on the original temper.

[bumber]

If you can bend them without heat, then why would you add heat and then worry about how to fix adding the heat you didn't need

I know you what to hear the 'correct' way to do it but Id have to say if it works for you then its the right way...

[d13]

bumber, I work with steel and stainless a fair bit, and wanted to know how to get the temper set on it right when I do have to heat it.

vitti, that's exactly what I wanted to know. Thank you! I've been looking for practical, exact directions for that for quite a while.

[Afisch]

This has been debated to death for about five pages somewhere on the site, if anyone is really interested it could be worth looking for. I remember it being interesting anyhow.

[bumber]

d13- Im not saying your wrong or anything but how do you bend them that you need heat? Are you talking about just bends, or twists?

I dont worry about tempering my SS wiper blade wrenches, i just like them however they turn out i guess. I never do any twists or anything extra to them...

[XOR]

You probably can't harden that stainless steel. You can harden and temper high-carbon steel like that in a file or hacksaw blade easily.

Depending on the type of stainless it is, you will probably have to do some exotic heat treating to get it to the level of hardness you require. It isn't something that can be done with a torch and some ice water.

For high-carbon steel you need a magnet. Yes, a magnet. Hold the steel to the magnet and it will stick. Now heat the steel up with your torch. As it goes through the red stage to the orange stage it will eventually hit a point where it is no longer magnetic. You should heat the metal, touch it to the magnet, heat, touch, etc. until this happens.

At this point the steel is "in solution" or what is called the Curie point. Once it goes non-magnetic, you heat it just a little longer and then quench it in oil (mineral oil works great). Do not shake the metal around or it will warp during the quench if it is too thin. Just hold it under until it cools completely.

Now the metal is quite brittle. If you don't temper the steel it may crack quickly. What you'll do now is put it in an oven and heat the oven to about 375-400 degrees and set it in there for an hour. Then shut the oven off. Then heat it again to the same temp for an hour. Then shut it off and let it cool and do it one more time.

If you clean the steel off with a brush/sandpaper after the quench and then temper it in the oven it will come out a nice straw-color. This is a good temper. The steel at this point will be nice and springy but not so brittle as to break easily.

Again the above only works for high-carbon steel. Stainless is a whole different beast.

Finally, if you are making tools out of a hacksaw you probably don't want to mess with the steel as it is a good quality temper already. In this case you should just work slowly with your tools and not allow the metal to heat up too much when you are working on it. If you allow the metal to heat up to the point where you can't hold it then you are going to wreck the temper.

When I'm working on heat-treated steel I am very careful not to heat up the metal with power tools. I keep a bucket of water nearby and dip the implement in it to cool off during the process. It's very important for it not to get too hot or you will ruin the metal and have to start over.

[Safety0ff]

Wow thanks XOR! That helps so much, I was always missing the part where it goes into the oven.

[XOR]

Wow thanks XOR! That helps so much, I was always missing the part where it goes into the oven.

Much of that advice comes from knife making where you need to be careful about the steel. If you harden a steel but don't temper it in the oven it will likely crack. It may crack within an hour, or it may crack a few days later, or it may never crack until you start using it. The important thing is that a quench process introduces a lot of stress into the metal and you need the tempering to draw out the hardness and relax the metal.

The other important and neat trick is to use a magnet and wait for the steel to get heated up enough to go non-magnetic. Only at this point will an oil quench do you any good. If you do it too soon it won't harden. If you heat it too much you'll cook out the carbon from the steel and ruin it.

If you want to get fancy you use a molten salt bath to control the temps, but that's probably more than us garage fabricators want to get into.

[Havoc]

d13- Im not saying your wrong or anything but how do you bend them that you need heat?

This whole heat and temper thing is all about the long term use of the tool, sure you can bend metal just fine in a lot of cases without heat, but say you wanted a flexible metal? Or maybe you don't? Maybe you want a twist in your tension wrench and don't want it to break? Or keep it flexible? It's really a chemistry question about how the metal is made-up and what kinds of characteristics you want in the end.

I'm sure when it comes to steak you have a preference between the super flexible steak knives, and the solid ones? It's something like that. A steak knife is a steak knife, but if they had their choice, some people would pick one over the other.

[nothumbs]

I think anyone interested in this topic would find this subject quite useful.

[der_fisherman]

I found some of this blog quite useful and some of it to be wrong with regard to tempering steel (not stainless, I have no idea about this metal).

Straw or yellow color tempering is still a bit too hard and probably also too brittle to my mind and will easily crack or break. From memory, it is the color used for making metal scrapers for bearings, sharpness being required.

I use the cheapest hacksaw blades around and re-temper them myself to be strong and springy, its quite easy to do.

I like a long pick, so I first just break the blade in half, this is far longer than most people like though....I temper before grinding the shape as tempering a small thin pick after grinding is quite difficult to do correctly and uniformly, in fact the only method that really works is the oven method then, mentioned elsewhere.

I (as mentioned earlier by someone else) heat the end of the blade (about the last 1 to 1.5 inches only) to cherry red and quench in water, now the blade is very hard, but also very brittle and easily broken.

I then clean the blade using wet and dry 240 until the steel is nice and clean, this is to allow you to see the color as you reheat the blade in the same area again, but use a lower temperature flame and keeping that part of the blade moving back and forth as otherwise you will miss the correct point in the color changes.

Heat gently, making sure that as the colors go over the surface, it is as even as possible over the area that will become your pick, when you see it turn to somewhere between brown & blue, quench then as quickly as possible in water and you will have a good springy but hard pick. I personally find blue best, but experiment and see what suits you.

Before grinding to the correct shape, clean both sides of the blade using wet and dry 240 so that each side is shiny again, this is so that when grinding, you will see any color change that happen if the metal gets too hot from grinding too long without cooling, sometimes also called burning. Avoid this like the plague, keep cooling it frequently while grinding.

If the metal is dirty, or still blue from tempering, you will not see burning so easily.....

Final polish as per usual and you have a good pick ready for anything you can throw at it!

For more detail on colors & tempering, use the following link:

http://www.threeplanes.net/toolsteel.html

Sorry, I have not understood how to make it an active URL, you will need to copy it and paste it into your browser!![/url]