Strange steel for a cutter

[44man]

I need a better crimp starter for my shotgun loader (MEC) and Ballistic Products sells one machined from brass but it is $30 plus shipping. I have some brass so I was going to buy a cutter but they are $32. Being cheap and poor, I decided to make a cutter. The first was made from 3/8" tool steel with a label on the back that says oil hardening. I hack sawed a chunk and gas welded it to a 3/8" shank. Then the trouble started. I let it cool slow but the steel got so hard it wore out two carbide cutters. I have never seen this before, it acted like air hardening. I don't know what the stuff is!
I then went to a 1/2" shank and used a stainless aircraft bolt to hold the tool steel on. I made the cutter and ran a test cut today. It cut brass like butter. I have to work out a better index because I don't have an index head and I have to center it better. Small problems to work out. All I have is a vise.
Anyone know why heating oil hardening steel and letting it cool slow will make it super hard?

[grumpy one]

A lot more information would be required to give you the full answer you want, but if the steel hardens fully with an oil quench, which cools it more slowly than water quenching, its transformation to martensite happens even with a slower-than-normal cooling from the austenitic state. Hence making it as soft as possible - i.e. annealing it - may require a slower rate of cooling than you are used to. Annealing, to a heat-treatment works, means cooling from the A1-3 temperature (723*C) over about 8 hours. Sounds like you let it cool quite a bit faster than that. Letting it air-cool isn't called annealing, it's called normalising, and many alloy steels will not be nearly as soft after normalising as they would be after annealing.

Some alloy steels, including tool steels, are very difficult to machine even when they are annealed.

You might consider making up a simple indexing device to get your cutter teeth to come out with an even thickness, perhaps using a bench drill as the indexable spindle. However if you are only going to use this cutter once, why not use a single-point cutter and just take longer to machine your part? That's the traditional solution. Then you make the cutter from a high speed steel lathe tool.

[Nueces]

My take on it is that your success with the non-welded metal indicates that the first shank acted as a heat sink for the hot cutter material, thus quenching it. I've heard of others having similar trouble welding relatively small bits of tool steel to larger chunks.

By the way, really nice job on both the cutter and the crimper. I'd sorta like to live near you. :drinks:

Mark

[grumpy one]

No disagreement from me, Mark. It can't harden anyway unless it's heated above 723*C, and that wouldn't have happened with the second one. I thought his question was why the first one hardened when he'd tried to cool it slowly - and the answer is that he didn't cool it slowly enough. Of course the welding heated it hot enough to harden, so unless he heated it back up above 723*C after welding, then cooled the whole thing very, very slowly, it was going to end up hard.

[44man]

Grumpy, the new cutter was easy to index with my plate I use for cherries and it cuts great. It took a little work to back cut from the edges with my Moto tool. The brass is 7/8" though and won't fit my jig so I need to make something else.
I understand why the steel hardened and I have annealed a lot of steel over the years. It just got way, way harder then I expected. Carbide would not cut it, all it did was shine it and wear out the cutter. The little piece of 3/8" rod got red hot almost to the top and could not have acted like a heat sink. I held it by the cooler end with pliers until it was almost cold. It took a long time. I could cut the shank but not the piece I welded on.
The new one was heated with a torch while spinning in the drill press. I opened the chuck and dropped it straight into my oil. Then I put it in the oven at 300 degrees for an hour and let it cool down in the oven. It seems very tough and none of the edges or points chipped or got dull. I only need two crimp starters so it won't be used for anything else. Saves me about $75.

[shooter575]

I allways have a bucket of dry lime around the shop to to use as a insulation to throw hot work into to slow down the cooling.Does not work every time.But enough to make it worth having around.
BTW nice work.

[44man]

I fixed the index plate I made by elongating the holes so I could seat the brass rod to the bottom of my vise. I cut two starters today and both came out perfect. Now I need to figure out the length, cut them and drill and tap the tops. I also need a smaller hole all the way through for a relief at the top of the shell.
I will let you know how they work when the press arrives. It was back ordered.
This cutter might never be used again but it did the job.
Oh well, no more welding cutters! I still think this steel was labeled wrong and it was air hardening. I have hardened and annealed oil hardening rod to stop warp, then cut cherries with no problems. This stuff was so hard I could cut glass.

[Willbird]

The critical temp to heat treat A2 is 1750/1800. Thats pretty hot to be welding :-)

[44man]

I know, it never got that hot. It just blows my mind. Maybe this metal was from Roswell! Sneaky little aliens!