Thread: Heat treatment of 4140

Originally Posted by bevinp

Some more questions:
1. What quenching should I use?

2. Apparently the SS wrap becomes soft at high temperatures and can tear easily particularly on sharp corners of the tool. Any tear would cause oxygen to be drawn into the packet and cause scale. So my question is what would be a good way to avoid tearing when transferring the wrapped tool from furnace to quench bucket? I have in mind to wrap wire around the tool shank on the outside of the wrapping, but then again the QA advises against having the wrap held tightly due to likelihood of wrap welding itself to the item.

Ueee,
Where do you get your O-1 steel, and do we call it O-1 in Australia? Google tells me even the Brits call it BO-1, so I guess O-1 or O1 would work here.
Bevin

Hi Bevan,

Oil quench. If you can find it, try to get some Aqua Quench, which is a water based quenchant that has quenching properties like oil.

The temperature for 4140 won't be high enough to cause welding. As far as handling goes, work out in advance how you are going to hold the part, maybe a wire hook that allows the part to hang from a pair of pliers and try to go into the quench vertically, so as to avoid and side to side stresses that might cause warping. Once you go into the oil, don't lift out until it's cooled. ( I remember lifting a red hot plane blade out of the oil, and it not only caught fire but set the oil bucket on fire as well... for excitement like this you need to take it outside... )

I wouldn't worry about the foil tearing, when you are handling it hot, it's right at the latter stages and you are almost done anyway. Just handle with care.

I think Ewan has a supplier of O1 steel, it might be called 1095? I've bought O1 from the US, much cheaper for some reason. Flat Ground stock - O1 oil hardening tool steel - up to 1/8 inch.

Regards
Ray

PS I got your PM, and will post some cooking foil for you to play with...

Hi Bevan,
Far be it for offer advice when you have so many well informed people responding, but my 'other' hobby is knife making and that entails just the sort of problems you are experiencing. May I suggest you contact Tharwa Valley Forge who could be just down the road from you. I believe he is fairly knowledgeable with hardening and tempering.
For what its worth you an buy 'blood and bone' at any garden shop, this saves you graverobbing.
Instead of hard refractory bricks if you have pottery supply place nearby you may be able to buy just one soft refractory brick that can have a 25mm hole bored through the long axis and one half way down the short axis at right angles with an ordinary wood drill to make a simple furnace. Angle your flame so its swirling down the length of the cavity, and not directly onto your workpiece.
Set the flame at 'reduction' so its more yellow than blue-this prevents oxidation of the steel.. I find that hydraulic oil works well for quenching--especially used stuff. Theres a whole pseudo-science on quenching mediums in the States.
A toaster oven works well to temper if you can pick one up at a thrift shop for a few bucks all the better. Otherwise wait until your wife is out before you use her oven.
regards Brian

Originally Posted by RayG

The temperature for 4140 won't be high enough to cause welding.

The bulk temperature of the 4140 might not be hot enough but a MAPP flame applied like this may be hot enough to cause local welding at the edges.



Last year I made a 3/4" B26 die (26 TPI) using a piece of 1/4" O1 tool steel and hardened it using a MAPP torch in the same minicave furnace method you describe.
I can't find the die right now so this is the only photo I have of it.
I did not use any anti scale coating so as you can see there is a lot of scaling and the threads are compromised somewhat, but it still worked fine on mild steel.



Now I have a small 20kW+ gas forge and would probably use the cast iron box method

Hi Bevin,
O-1 is otherwise known as silver steel, or drill rod in the USA. I get smaller sizes from m&g's in fyshwick, but it gets pricey. Best bet is to order a bit from victor tools, they are the cheapest I have found. Sorry no link I'm on my phone. I don't want to count my chickens just yet but I may be able to help you with a heat treatment oven in a few weeks.
Cheers,
Ew

Here's the stuff from victors, as a reference 18"? (or 16") length of 12mm will cost you $30 from M&G's. Oil Hardening O1 Steel Drill Rod - metric sizes

Hi all,

OK so 01 is the same as silver steel? I was wondering. There is an ebay site that sells 300mm lengths of silver steel at reasonable prices. My local steel supplier sells it but you have to buy a length....

16mm Diameter X 333mm Long Silver Steel ROD Crusader Steel | eBay

Cheers,

Simon

Originally Posted by RayG

PS I got your PM, and will post some cooking foil for you to play with...

Thanks very much Ray. You're very generous. I hope to be able to return the favour sometime.

By the way, who is Ewan who has a supplier of O-1?
Bevin

Originally Posted by bevinp

Thanks very much Ray. You're very generous. I hope to be able to return the favour sometime.

By the way, who is Ewan who has a supplier of O-1?
Bevin

Thats me....and no i can't help with the heat treatment oven.....

Cheers,
Ewan

Thanks everyone for the info.
I am now in the process of making a new cutter which I will heat treat in Ray's SS wrap.
Bevin

Just an afterthought guys, could you use standard plumbers brazing flux as a anti scaling treatment?

It is a bit easier than trying to find SS foil.

G'Day Bevin,

Try Amazon.com for O1, aluminium or brass rod. That's where I've got mine from:
O1 Tool Steel Round Rod, Polished Finish, Precision Ground, Standard Tolerance, Metric, ASTM A681: Amazon.com: Industrial & Scientific

Delivery was quite reasonable especially if you're ordering books anyway.

Christian

I just tested out using standard plumbers brazing flux on a pair of flaring dies I made up for SS tube. It worked a treat with no scale where I put the flux.

I don't know that I would have used it on the tap though. It had some very hard (small) spots of glazed flux after the heat treatment that were easy enough to remove on on a simple smooth die. If you could soak it in something to soften the flux after the heat treatment then it might be an option.
It was very old flux.. That might be the reason for the hard glaze? Not sure at all on that.

I used a mapp gas torch on the 4140 water quenched and they came out damn hard.