heat treating question

[werowance]

ok, after hardening the steel then going back to "draw to straw" or some other color i understand. but right after i hit the color i am looking for to aneal the metal am i supposed to imediately quench it again as soon as it reaches the correct color?

or what if im using the oven trick 400 deg for 20 mins (for my application) do i just let it air cool, or do i need to dunk it in water or oil or something to quench it?

i have made screw drivers and other little projects, most called for draw to straw after hardening and i did, but looking at making a knife blade and saw one article that said, draw it to purple on top and wheat at the bottom - and then lower down he made mention of the old timers would quench it. so now i dont know whether to air cool after temper or quench after temper

 

[Steve J]

quench after temper. if you let it air cool the annealing process will continue. by quenching at a certain color you stop the anneal(or softening ) at that colors hardness. the hardness will vary depending on the type of steel you have. steve

 

[Sshire]

Search YouTube for "That Lazy Machinist". Just watched his heat treating video. The best explanation (both theoretical and practical) about heat treating I've seen. Highly recommended.

 

[werowance]

Thanks for the info!.

 

[Swifty]

Have done a lot of heat treating, and never quenched after tempering. You have to be very careful when heating for tempering with a torch, as the temper colour will still change a bit after you stop. For the home hobbiest, tempering is done by colour, but in a commercial operation the piece is brought up to a certain temperature, held for a while, then cooled naturally.

Paul.

 

[gus]

Have done a lot of heat treating, and never quenched after tempering. You have to be very careful when heating for tempering with a torch, as the temper colour will still change a bit after you stop. For the home hobbiest, tempering is done by colour, but in a commercial operation the piece is brought up to a certain temperature, held for a while, then cooled naturally.

Paul.

True. My bigger urgent jobs were sent to heat treatment shops and came back still warm. The neaby shop guys would call soon after heat treatment is done .

 

[abby]

It does of course depend upon the type of steel , there are air-hardening steels such as Jethete which is heated to 1050 °C air cooled , tempered at 650°C and air cooled .
I prefer to quench after tempering , safer if you don't have precise heat control like most of us and it doesn't do any harm.

 

[Chiptosser]

It depends on the metal alloys that are in the metal.
I don't know about all steels, But notice I said metals. This includes aluminum alloys.
All the steels that I have heat treated, D2, A1, A2 ,O1, 4140,ect. get quenched after initial heat and soak time. The soak time in heat is very important to allow proper transformation of the metal.
Then you quench the piece, in air (if air hard) or (oil if oil hard) or (water if water hard). Don't quench oil hard in water!!
The quench is if important to get proper hardness.

After quench, allow the piece to cool to touch, then you are ready to temper.

The drawing, annealing, tempering process is also critical to proper transformation.
This is to take the stress out of the part, and allows you to control the hardness of your part.
If you requench, the part you are setting up stresses in the part, you dont want that, you will stop the purpose of annealing, drawing, tempering.

Tempering,Drawing,Annealing all mean the same, just depends on the trade.
Some steels get double drawn, just depends on the properties of the steel.

There is a lot to heat treatment of steels. The best thing to do is read the manufacturers spec.'s and follow them. Or get a machinery"s hand book.

Some of the nonferrous allows, do get a quench after draw.

 

[Swifty]

Chiptosser, when I was working, we generally referred to annealing as bringing the steel back to a fully soft state after heat treatment.

Someone may have forgot to tap the holes before sending the piece for hardening, so the piece was sent back and brought up to temperature well above the tempering temperature, and allowed to cool very slowly. The piece was then tapped and sent back for hardening again.

Of course, in some cases, it was quicker just to remake the piece properly, depended on the size and the amount of work involved.

Paul.

 

[Chiptosser]

You are absolutely right, if you are annealing to the soft state.

When you get to the transforming temperature you are holding the temp. and allowing the steel to cool very slowly, you are not quenching.

The quench is what causes the transformation. When a piece has gone through the transformation stage, (heat and quench), Then temper and draw, it is still exposed to a partial annealing.
After quench, the part is usually a couple of points higher on the rockwell C scale, before draw, (temper).
It is going through an annealing stage, if slight, lowering the hardness a point or two, depending on the temperature that you temper the steel.
If you have 64 rc. after quench, then you draw or temper, ( draw back temp.) you can control to what rockwell number you want the piece to end up at, after (annealing, draw , temper).

If you have D2 , Heat to 1500F slowly, (816 c) raise to 1875F (1024c) soak for 15-45 min per inch of thickness
Quench medium: air
Temper: 400-1000F depending on rockwell c desired.

To Anneal: 1600-1650F---Pack and cool very slowly. DIFFERENT TEMP!

It depends an what industry you are in and terms used by each.
You have to know the materials that you are using and the properties of the material and what purpose it is to serve.

 

[werowance]

ok, i understand the point that it is important to know the material you are working with and its properties. but lets just say (and off topic from hmem forum) but that i was making a knife from an old tiller tine or truck leaf spring. thats somewhat a mystery metal. you want to make it really hard, but then releave it some so it doesnt shatter when bent a little.

does this process sound about right for just hobby use: heat to bright orange, hold it there a min or 2, then dump it metal bucket full of old motor oil (outside of course with all safety implied) then after its cooled, lightly sand it or steel wool it untill you can see the metal again. then if using torches, "draw it to straw" and once i see the straw color form dunk it back in the bucket of oil. or alternative cook it in the oven at 400 deg for 20 mins and either dunk it in oil or in pan of cold water? the oven trick when i brought it out the blade was a nice straw color and i doused it in the kitchen sink full of water. so far this blade is much better than the first one i made.

what do you all think of the process i used? for just hobby playing around in the garage stuff so to speak.

 

[Chiptosser]

Not knowing what the material is, but knowing what is was used for originally, does give information to start with. It is likely that type of item would have been HT in batches and a type of oil hard. Yes, as you stated, would be a safe starting point. It is a good practice, not to quench in water unless you know absolutely what temperature to heat the steel.

You can get hurt by over heating and then quenching in water, also over heating any steel can deteriorate the properties of the steel.

But,! I don't understand why do you want to requench after the initial quench?
After initial heat then quench, then you draw,temper at a lower temp. then allow to cool. Your done, unless you do a double draw.

The quench after the temper, sets up stresses that you are attempting to remove with the tempering.

 

[werowance]

honestly, the reason i did the "requench" was sort of my question, whether to quench during the "draw to straw" portion or to just set it aside once color is achieved and leave it alone.

i had originaly thought for just playing around so to speak with something i forged that i harden it first (bright orange then oil quench) then draw to color and then just sit it to the side to cool naturaly.

then i read an article that after drawing the color to quench it at that point also so then i bacame confused and thought i wasnt doing it correctly.

and im just using the straw color as an example, seems that just about every machine shop learning plans i have (machine shop projects) call for either straw or purple. and reading the color is pretty easy, its just the part of what to do once i hit the color. a little shakespear here: to quench or not to quench, that is the question

thanks for everyone who has replied

 

[abby]

The purpose of tempering is to reduce the brittleness of steel that has been hardened and so make it better able to withstand shock loads without breaking.
Example ; a lathe tool can be harder than a milling cutter because the shocks encountered are different (typically) a screwdriver does not need to be as hard as a lathe tool but needs more flex to withstand torque without breaking and a spring needs to stretch and return to it's original length.
All of these parameters are covered in the tempering chart.
To ensure that the heating process is thorough ,as a rule of thumb , a soak period of 1 hour per inch of thickness should be used which is pretty well impossible without a muffle furnace or kiln.
The majority of toolmakers will quench after the tempering colour has been reached , this ensures that the tool is not over tempered in situations where temperature control is by colour only.
You will find that it is very easy to reach dark straw for example , then it changes further and further towards the blue end of the chart.
This quenching after tempering does not set up any stresses .
Tempering is not annealing nor is it normalising , these are carried out at higher temperatures and require no quenching.
For carbon steels the quicker the cooling quench (following the hardening temperature) results in harder steel , but not necessarily the best hardness for the job.
Quenching baths can be iced brine solution , water or various oils , all they are doing is controlling the rate of cooling but be careful as cooling too fast may cause some steels to crack , cooling to slow in a thick oil may lose the hardness.