Tempering.... and home made tools.

[Romstar]

Vapouring is indeed a problem at these temperatures, and the type of heat treating required to turn carbon steel into a spring steel is a two step process. First hardened, and then tempered. This process is required for HSS hacksaw blades.

Most wiper blades with stainless inserts use type 302 stainless. This is a very common, and cheap stainless that is very suitable to this purpose. Some other wiper blades use a half hard blued carbon steel. It has some minor characteristics of spring steel, and is also quite suitable for this application. Brief grinding, while paying attention to the spark plume will normally give you a very good idea of the type of steel.

Hacksaw blades are generally standard carbon steel, or in some cases D-2 tool steel. Although these are less common. The exception to this is bi-metal blades. Bi-metal blades are terrible for making picks, so these don't concern us.

Oh, 5" x 5/16 steel, heated to 1450 degrees for 30 minutes, plunged into 5w30 motor oil does nothing but smoke. Lighter weight oil hasn't caused any problems either. Absolutely no argument on the eye protection.

I'm only going to say this one more time though, water is not the cooling medium you want to be using.

Romstar

[raimundo]

sweeper bristle pick are made of such a tiny amount of metal that water quenching is very rapid. almost instant. larger pieces of metal will hold heat deeper inside. in any case, when I make picks of sweeper bristle, I hold the bend and the twist over a bic lighter for about 30 seconds, til it gets a blue surface, then I water quench. Red color in metal is light coming from super excited molecules, just like the filament in a light bulb, but straw yellow and blue are oxidation effects on the surface of the metal and will remain that color after quenching. Some posts seem to confuse this with the blue of certain flames, which are less hot than white but hotter than yellow. As far as the shaft and the tips of the pick, I leave them exactly as the metal was tempered for the bristle. There are problems with the bristle sometimes, brittleness could be a tempering/hardening effect or a failure to control the alloy. Modern steel is recycled from melted cars and such, so it contains elements of aluminum zinc copper etc although these are largly separated in the melt, some remains mixed in the steel. special steels for rocket engines or turbine blades are not made of this recycled metal, but for street sweeper bristles, stiffness is the only quality required, and price is the determining factor the manufacturer will consider.

[Hojo]

Ok, my dad is a tech studies teacher and hes taugh me to harden and temper, first a few notes...

-Tempering and Hardening are two different things
-The deffenition of a temper is: To harden a metal by quickly heating and cooling the metal
-Heating the metal for two long will weaken the metal and make it soft and really easy to bend
-Heating it and letting it cool down slowly will do the same as above
-Tempering a metal more than once will make it brittle
-Tempering oils can vary, also I will say through this post you need to cool it quickly, this is not always the case, but for picks and such you will need to

Ok, so firstly depending on the metal you might have to harden it, but most things people use to make picks with you dont need to bother, there are a few things your going to need...

-Blowtorch --Used to heat the metal QUICKLY!
-Oil --Used to cool the metal, can use water but oil is faster at cooling and is what you need
-Some sort of polisher --to clean your work so you can see the "Temper lines"

Ok, firstly clean up your work, then say if your doing a pick, heat the tang to a dull red, if it goes bright red, let it cool in the air back down to a dull red, but this will weaken the metal so try to avoid heating too much, then once its a dull red drop the whole pick into a deep oil bath, dipping just the tang will cool it but heat is still in the handle, so when you do that make sure the WHOLE tang is a dull red, now, polish it up nice and shiney again, might take a while, then get your blowtorch and aim it about 1 inch from the pick tip, heat at the one point and try nor to let it go bright red, watch the straw brown lines going down the shaft could be a blue or another color then one the lines hit the tip, drop it in the oil bath, and you have yourself a hardened temper...

This is the metod I used for my picks ages ago and tension tools, hope it works and hope to get some feedback...

[Beginner]

-Oil --Used to cool the metal, can use water but oil is faster at cooling and is what you need

Actually the water does transfer the heat more quickly from such small piece of metal than oil. The heat transfer rate goes from the fastest to slowest something like this

-Salt water
-Water
-Oil
-Air

Some polymer-water mixes does have same heat transfer rate than oil, and they dont have enviroment hazard's like oil when boiling.

Low heat transfer rate is needed for metals that does crack when they are cooled too fast, this happends too when using very big pieces.

[Chucklz]

Has anyone tried pickling/acid dipping for cleaning/rust removal on either sweeper bristles or wiper inserts?

[D_Shane]

Here's a link to a heat treating "course". it's from a free-ed type of site. Basic theory on tempering and temp charts and such.

http://64.78.42.182/free-ed/BldgConst/Welding01/modulemain.asp?lesNum=2

[ToolMan]

An easy way to harden steel is to 'carbonise' it. We used to do this at school to harden screwdriver blades we made in metalwork class.

Basically, get an empty metal can and fill it with carbon powder (you can make your own by crushing lumps of barbecue charcoal into powder).

Heat the tip of whatever you want to harden until it's orange, then dip it into the charcoal for a few seconds. Quench the piece in cold water. The steel gets a carbon coating (you've just made carbon steel) which is very tough and quenching it in cold water also helped the hardening process by 'annealing' the piece. Try filing or polishing the piece now and you'll find it's much tougher to work with.

Carbonising is good for tension wrenches, but take care with fine picks, carbonising makes steel hard, but if you overdo it the steel may become brittle, as usual, some experimentation will be required to get the best results.

[Peaky]

Chris B got it right and im sure romstar knows what hes talking about.
It depends on the type of steel, a high carbon steel should be heated up till its a bright cherry red then quenched in an oil somthing like a 25/40w(motor oil is fine for this as long as it is mineral based) the item should then be polished up and heated again untill a straw colour then quenched again you will be left with the correct hardness needed for picks and wrenches.
If the steel is low carbon steel it needs to have the carbon added to get the hardness required, this is done by a process called case hardening, this is done by heating the metal up untill it is bright red (it will get brighter than a high carbon steel) and then dipping it in to carbon powder leave it in the carbon powder until it is cool, when you take it out you will notice that it is furry with the carbon, heat it up again untill it is cherry red (you will not get it as bright as before) and quench it in oil as before, when cool polish back (dont grind as the hardness is only skin deep) and heat again until straw coloured and quench again. water is fine for small items but on larger items water def is not the way to go as romstar has explained.