Greetings,

in the past I have had great luck with all tool and steels with respect to heat treating. However, PMM4 has perplexed my abilities, and it could be the capability of my home shop environment. 

I am preheating in kiln to 1500f equalizing 

rapidly heating to 1900f (recommend by supplier for cold working tools) soaking at this temperature for 20 minutes (in propane  forge)

quenching in oil to approx 8-900 f (blacked)

air cooling to 125f

tempering at 1000f for two hours. 

I don't have a HRC tester but it's clearly not upwards of 60-65. 

I have contacted some services who have great prices for a run of my chisels but I would love to do this myself as I have always done before.

Thank you in advance for any info or tips within the steps.

 

I just read the heat treatment requirements from Griggs and it says you might have to go as high as 2200 degrees before quenching. Soak for 5-15 minutes then quench in oil till black as ou said you did. It also mentions double tempering.

I've never heard of this steel and personally I don't think I'd try to use it myself. Looks like too many ways to go wrong.

41 minutes ago, Michael Cochran said:

I just read the heat treatment requirements from Griggs and it says you might have to go as high as 2200 degrees before quenching. Soak for 5-15 minutes then quench in oil till black as ou said you did. It also mentions double tempering.

I've never heard of this steel and personally I don't think I'd try to use it myself. Looks like too many ways to go wrong.

I didn't double temper,but you'd have to figure it would still be brittle right? Maybe my oil is forming a vapor barrier around it and not shocking it to solidify the grain structure... 

It is rather temperamental...

What kind of oil are you using? Are you moving it around some during the quench or are you just stickin in and lettin it set?

30 minutes ago, Michael Cochran said:

What kind of oil are you using? Are you moving it around some during the quench or are you just stickin in and lettin it set?

Using Canola, Also tried Peanut.

Yes sir on moving it around, but I have been getting flare up flaming with the canola.

I'm thinking of trying a heavy water / brine solution next. Just for testing purposes...

I am just stubborn, ill exhaust all my ideas and efforts before waving the white flag.

$170.00 for a run of 30 chisels to 62 HrC pick up and delivery free. Not a bad deal at all.

What temp is the oil? It's counter intuitive but you get a faster quench with warm oil

26 minutes ago, Charles R. Stevens said:

What temp is the oil? It's counter intuitive but you get a faster quench with warm oil

Oil approx 150 F, have the large pot of oil on an electric burner at the ready when the part comes out of the furnace.

 

Have you sacrificed a peice pre temper to see if it is brittle hard? 

19 hours ago, Charles R. Stevens said:

Have you sacrificed a piece pre temper to see if it is brittle hard? 

Now that is a XXXXXXX good Idea!

Haven't even thought of that, although I did skate a file over the piece. It didn't grab but I think it would be a great idea to attempt to shatter a piece for fun.

Thank you Charles.

Please review the terms of service you agreed to follow when joining.

 

If the file skates, then it's a good bet it's hard, is a 1000 degree to hot temper that alloy?

It's called destructive testing ;-) wrap a shop towel around it and place it in the vice. And whack it. We don't want deadly missiles flying around the shop.

When you get into the weird alloys you often have to go with the high grade engineered heat treat oils, cost of doing business...

48 minutes ago, Charles R. Stevens said:

If the file skates, then it's a good bet it's hard, is a 1000 degree to hot temper that alloy?

It's called destructive testing ;-) wrap a shop towel around it and place it in the vice. And whack it. We don't want deadly missiles flying around the shop.

The manufacture recommended 1000-1100 for two hours (double tempered) 

however they did not specify the HRC I would get.

it did also indicate to NOT temper below 1000... 

I had two pryo meters and both checked within +- 5 degree of each other.

Missle test tonight!

40 minutes ago, ThomasPowers said:

When you get into the weird alloys you often have to go with the high grade engineered heat treat oils, cost of doing business...

Very good point, I will look into this option. Thanks Thomas.

One may also try upping the oil temp a 100f

1 minute ago, Charles R. Stevens said:

One may also try upping the oil temp a 100f

Rodger that, will have a test run tonight. Won't machine this one down just destructive testing time. 

Update. 

Tried two different mediums for quench

peanut oil at approx 250f 

Boiling water approx 210f

result for oil, hard as XXXXX no grab from a coarse of fine file. (WONT BREAK) in quench form

result for water is the same (WONT BREAK)

grinded down to chisel point, hard as XXXXX won't chip or break, clamped XXXXX in vise struck with 3# double jack, will not break or bend... 

Even more confused.

i ran it opposite as well with the forge performing the preheat and the digital controlled fire box at 1950. 

Completely confused. Truth now is I'm just going to run some work with it in quench state. See how it goes...

cheers.

Please  actually read the Terms of Service you agreed to follow in order to be a member here. this is a G rated forum.  You have been warned before.

I have a theory.  

1)  i think you are at to  Low temp. When austenitizing.   Maybe not since there is some variance between suppliers end product and recommended  heat treats.  

2) i think the use of a propane oven is carbuerizing the steel.  

3) the two combined may have created something  special  here.   Id like to see some results of more intensive destructive  testing.  But it makes sense.  

I wonder if anyone has ever done propane vs electric oven  testing? 

 

Cheers

OP ha not chosen to return since his last post where he was warned about his repeated insistence of using bad language

This is getting ridiculous!   Boiling water is a TERRIBLE quenchant!!!!!!! Water abstracts heat by 1 raising it's temp to boiling and 2 converting to steam.  If you are already at boiling and forming steam you have pretty much destroyed it's ability to to take heat away.  Heating oil a bit helps it as it decreases the viscosity and allows for more convection and so more conduction cooling.  Heating water does not make that much a change in it's viscosity.