Tool welding of A-2

By jer

Date 12-20-2003 03:38

I was welding on a A-2 block which I pre heated to 500 degrees in my oven, and then placed onto a electric hot plate which will keep die at 400- 500 throughout the welding process. I needed to raise one end up .150 and ramp down to 0. The block is 4" x 6" x 10"long, there is a angle cut out of block along the 10" length which I was to add the material onto this cut out ledge say.
Well I even tack welded a 2" x 3" plate to back edge to prevent the ledge from pulling or cracking at base of angle cut out.
I was using A-2 rod just outlining area and the base material still cracked, I had been welding with low heat making small stringers and peening.
Iv'e been told that I should use a more ductile rod then the A-2 rod when building up a larger area, and then cover with A-2.
My question, is 312 a good rod or would weldmold 888 a crack sensitive rod be better or what?
But again I only ran welds on the outline building it up and when I came inside and welded say two or three passes right in angle the die cracked.

Any insight into this matter with A-2 would be appreciated.

By flatjwl (*)

Date 12-21-2003 15:54

When I weld on a block of A-2, I draw it back with overnight cooldown in furnace, before striking an arc. Preheating just does not always work.

By jer

Date 12-21-2003 21:42

Iv'e recently heard where I should lay down a more ductile rod such as say 312, then cover with A-2. Do you have any thoughts on that? It seems to make sense to me for when I weld up cracked A-2 dies I use weldmold 888.

By flatjwl (*)

Date 12-22-2003 01:49

Using more ductile filler sounds logical, but I have seen dies crack vertically as well as adjacent to the toe, so I choose to draw the material first. Some of the results achieved, or lack thereof, can be attributed to the initial treatment as A-2 can be used in various levels of temper and can therefore be more or less susceptible to cracking.

By jer

Date 12-22-2003 20:29

Hello flatjwl, I would first like to say thank you and that I appreciate your reply's to this process. I am not aware on how to draw tool steel, the only thing I can say is that I've heard of this, yet I do not know anything about it. I have in past welded many smaller pieces of A-2 just welding on a cutting edge with good success. But like I said I have trouble on the larger blocks which need more area welded. If you could give me a little more insight I would be very grateful.

Thank you Jerry

By flatjwl (*)

Date 12-23-2003 00:53

There is more than one way to do this, but I usually put it in 500 degree preheated furnace and slowly elevate temperature to around 1500 at a rate of 200 degree increase per hour. When I am sure the block is at 1500, I switch the furnace off and allow it and the A-2 contents to cool overnight being certain not to open the furnace door prematurely. If it is a large block it will still be pretty warm at 8 AM, but ready for the welding operation. As a matter of information, I am refering to a small (approx 12"X12"X18") electric furnace in this discussion.

By jer

Date 12-23-2003 01:01

What effects to the hardness will this have? Will the block have to be hardened again? My oven I made will go only 750 or so I think.

By flatjwl (*)

Date 12-23-2003 12:43

YES, the block must be re-treated after the welding and machining is completed, so you need at least 1750.

By brande

Date 12-24-2003 06:49

Your preheat seems a bit low. I would have gone to 750-850 degF minimum, just to be sure. Just personal experience talking here.
Be sure to cover everything except exactly where you are welding.

Also, I would have started at the inside, and worked my way to the outside. This may have not been an absolute requirement if preheat was high enough, but the shape of the weldment often require this. This seems to work for me.

Preheat and interpass temps must be close. +/- 25 degF would be a good mark to shoot at, but +/- 50 degF would be the absolute max.

Remember, A2 is an air hardening steel. It will change hardness when a temp differential (base metal to weld metal) occurs. As long as it is in air, hopefully still air. Another point to consider-your hotplate probably keeps the bottom of the weldment at a good temp-but there is surely a temp differential from the bottom to the top. This temp differential is a killer on tool steels.

You also don't mention how the weldment was handled after welding-
was there a slow cool in an oven...was there insulation wrapped around it...and so on. This is really important.

312 is always a good choice when welding these types of steels.
The one problem is, 312, being an austenitic type stainless, will not respond to heat treatment,period.Very ductile and a high ferrite # seem to minimise cracking with this alloy, but unwise use can affect the integrity of the weldment.

If a tool steel weldment is to be re-heat treated for full strength, 312 isn't the best choice for underlayment. The overlay (even if it is A2) will always be in jeopardy. It will be hard, but the interface will not be.

I've had luck using 410 stainless (also an air hardening steel) on these A2 weldments, but this is something you'll have to try and evaluate.

Additionally, I don't think I would try the taper you mention-the depth to width ratio.
Put on what you can, reliably, and let the machinists or grinders take care of the final profile. Thin deposits of tool steel will crack-undercutting your weldment might be well advised to keep a decent amount (1/8-3/16) of buildup on your part.

All in all, I think a higher preheat and close interpass temp monitoring should solve your problem.

Letus know how you make out!!

Good Luck
brande