Thread: Quench metal by oxygen torch

Originally Posted by jackaroo

Hi All,

I need to quench the tip of a metal rod (say chisel or flat screwdriver). What is the procedure for this task? Is there any kind of powder/liquid to dip in in particular?

Thanks,
Jackaroo

OK - take a step back. What is it exactly that you are trying to achieve and what exactly is the type of steel in the metal rod - I also presume it is steel?

A rule of thumb is for heat treating metal you need to get it to the right temperature, for the right time then quench it at the right rate to get the right results....Luckily I have no facilities to do any of that so I just do what I think might work..

Firstly oxy's are generally too hot of a flame to do heat treating successfully....They generally overheat the metal in quick time..A LPG burner is much better...

Heat treating to harden steel works like this

Firstly the steel need to be able to be heat treated..Carbon is the sole element in the steel that determines the end hardness of the steel, other elements in the steel affect the way the steel can be heat treated...So low carbon steel like mild steel is not able to be heat treated by heating and quenching alone while high carbon steels like what springs are made out of is able to be hardened to a high state...

The treatment works like this, you heat the metal up to the correct temperature..You then put the piece into either oil, water or salty water to cool it down quickly..The piece of steel is now quite hard and brittle... Now you need to temper the steel. tempering makes it softer but tougher..So while the piece is still warmish, polish it until it is shiny then heat it slowly to a much lower temperature and as it gets hot you will see coloured oxide layers appearing on the steel....It starts with a light yellow (straw) colour and at the other end when it is really hot it gets a purple colour...The colour you want depends on what you are making...

This is only a very rough guide...

Thanks RC, I think I kind of get it but getting it right is another story. I'll give it a try.

@BobL, I am making the axle for my son ride-on car, I cut thread at 2 ends and I want to heat treat the ends.

Is the rod/axle high carbon steel, like spring steel? If so, I assume you are hoping to ensure the axle won't bend, or you want to prevent wear on the bearing surface. Was it easy to thread?
The threading process shouldn't have created enough stress to need relieving or annealing IMO.
If its plain old mild steel I don't think you will be acheiving anything, as it won't harden or toughen with heat treatment. Case hardening can be done on mild steel, and requires special powders which the heated metal is dipped in.

Good luck

Hi Andy,

The axle is mild steel, I just need to ensure the thread is hard enough so it hold the wheel in. What sort of powder and where can I get it from?

Cheers,
Jackaroo

Hi jackaroo,
There was a discussion here some time back.
Are you worried the whole threaded section is weak and maybe won't allow you to tighten up the nut fully before it strips (or worse)? Or is it just a security thing? If that's the case, use Locktite to glue on the nuts.

Cheers

Thanks for the link Andy, I am worried the thread section wont be strong enough for me to tight it and it might rip the thread away (M14x1.25)

Jackaroo

You shouldn't need to harden an axle that size

Is the axle just holding something along the lines of a pneumatic wheel barrow wheel,if so if your worried about the wheel coming off or loose I would suggest using a castalated nut.
If in the future you do more of these it would be better to use 5/8" UNF.

Better still just use an M14 nylon locking nut (Nylok). I can't see you will gain anything by heating an axle of that size for that use.

Originally Posted by jackaroo

Hi All,

I need to quench the tip of a metal rod (say chisel or flat screwdriver). What is the procedure for this task? Is there any kind of powder/liquid to dip in in particular?

Thanks,
Jackaroo

Hi jackaroo,
I think there is some misunderstanding and mixing of the terms.

In quenching a piece of red hot steel ,it would be done to a piece of steel that already had enough carbon content to effect a change in hardness when quenched.

The purpose is to harden the steel from its soft state
( before the heating and quench) and take it to a hrd state.

The quenching may possibly make the metal too hard and brittle for intended use. The quench would then be normally followed by a tempering to bring the steel to the degree of hardness and toughness require for the purpose of use.


The powder you refer to sounds like Casenite .My understanding of it is that it is to be applied to a steel to produce a surface hardness only.
It is applied by heating the metal and dipping it in the powder.

Mild steel with a carbon content of only around .03% can't be hardened by the quench method .

Quenching a piece of spring steel like Andy's mezzaluna herb knife would be an application of quenching and later tempering.

I am looking forward to learning more in how to do so.



Cheers
Grahame

Thanks All,

I didnt realise only high carbon steel can be quenched, I always thought I can heat up any steel and dip in carbon powder to make it hard.

Hi ,
Here's something that might help towards a better understanding of steel and carbon content.

A diagram form a An Eagle and Globe steel advisory booklet,I have for years.

We all learn by asking questions.

It may be a little hard to read but I had to resize down a bit to get it to load up.If you save as a jpg.file and load into windows picture file it can be zoomed up in there.
cheers

Grahame

The hot dip case hardening powders are basically a cyanide compound with some bulking agents - very poisonous if the kids decide to play Mad Scientist, and they may be hard to get, you'll have to go to a specialist supplier & I don't have any current information on suppliers - one can goes a loooooong way.

'Mild' steel comes in a number of grades and varying 'temper' numbers, but most stock is just sold without the necessary information (mate did a special prototype by hand and had to source all the correct steels) - I think the temper numbers relate to a work hardened state, like the difference between black & bright mild steel plate. The average person just does not have access to the needed equipment.

Useless information:

You can case harden the old fashioned way, but its not very precise. Just grind up a quantity of black charcoal fairly finely (or leather, dry bones ), then bury the part to be hardened in the charcoal inside a nearly airtight container - any leak much bigger than a pin hole will burn off the carbon/carbon monoxide before the carbon migrates into the steel, and no hole usually means the container explodes blowing burning bits everywhere. I have seen articles claiming you can use several layers of aluminium foil for the container - YMMV.

After preparing the parcel, heat it to a cheery bright red and keep it at that temperature for 1-3 hours. When cooked, break open the parcel & quickly dump the contents into cold water. You end up with a glass hard surface up to 3mm thick (variable, no way to tell) and a relatively soft core. Theoretically you could then temper the hard surface, but you have no real way of knowing its average carbon content.