Welding high speed steel

[tulmkr1]

Hopefully someone can help me out here. I have to weld high speed steel tools from time to time, and am looking to improve the quality of my welds. I am using a lincoln powermig 350 mp machine, and my filler metal is weld mold 966, and run straight argon gas. I am not the greatest tig welder, but have been able to muddle through so far. My biggest problem is cratering, and cracking. So far i have tried preheating the base metal to temps anywhere from 200- 800*f using heat sticks as a reference. I have tried different point grinds, flow settings, and amperage settings but i still get the cratering and cracks. What seems to have worked the best so far is a very fine point on the tungsten electrode which is 3/32, 2% thoriated. I run at about 150 amps depending on the thickness of the cross section. I have to use this particular filler metal because it is about 62 rc as deposited, and this is needed to maintain a cutting edge. Any help would be greatly appreciated.

[Kangi]

I think you need to post-heat also to relieve the stress in the welded piece. I don't know how much heat for how long, maybe someone else here knows more about it than I do.

[Oldiron2]

Without knowing more details, I'm just guessing, but could you grind it down a bit more, put on a thin but more ductile layer first and then apply the hard edge? What alloy is the base metal?

[tulmkr1]

base metal is m-2 high speed steel. These are cutting tools, broaches, milling cutters, and hard shank boring bits. when they break i can put a tee slot in the ends, and weld them back together. whats happening id they are cracking at the joints, o there is pitting in the weld. ive done preheats, post heats, and even an electric induction band under the part to keep the heat even. Im guessing its my tecnique, im not a great tig welder. looking for some pointers here. I am considering trying to mig weld these things, the filler is available in spools, and i am a much better mig welder than tig. still wondering about the cracking issue though.

[tanglediver]

You might have to anneal the base metal beforehand, then reharden & temper afterward. That is my best edumacated guess.

[A_DAB_will_do]

Here is some data for an M2 tool steel alloy I pulled down from the website shown below.

I agree with tanglediver. I don't think the problem is your welding technique, it's the condition of the material you're welding on. First off, it's a high carbon alloy steel. Second, as a cutting tool, it's been quenched and tempered to achieve that hardness you mentioned. Your best bet is going to be to fully anneal these parts, weld them, then re-heat, quench and temper them. There are some guidelines for doing so below.

The big problem that I see is that they recommend doing this in a vacuum furnace(to prevent scaling and damage to the part surface). I suspect you don't have a vacuum furnace. And unless these are custom tooling, worth a lot of money, it won't be worth the cost to send them out for annealing and re-heat treatment.

I hate to rain on your parade, but I think you're not going to find an easy solution to your problem. M2 tool steels have poor weldability in the heat treated condition. I think you'll find the annealed material tough to work on too; but it should be possible to weld the annealed parts with the right pre-heat, interpass, and post heat treatment.

Is it worth it to spend the money on these pieces of tooling?

http://www.crucibleservice.com/esele...d/rexm2sh.html

Typical Chemistry
Carbon 0.85%
Manganese 0.30%
Silicon 0.30%
Chromium 4.15%
Vanadium 1.95%
Tungsten 6.40%
Molybdenum 5.00%
Sulfur 0.03% max. (0.10%)

Typical Applications
Broaches Milling Cutters
Counterbores Punches
End Mills Taps
Form Tools Tool Bits


--------------------------------------------------------------------------------

Annealed Hardness: 217/255 BHN

Machinability in the annealed condition is approximately 45% of W1 Tool Steel (1%C).

Thermal Treatments

Critical Temperature: 1530F(830C).

Forging: 2075F(1135C) Do not forge below 1700F(925C). Slow cool after forging.

Annealing: 1600F(870C), hold 2 hours, slow cool 25F(15C)/ hr max. to 1000F(535C), then air or furnace cool. Hardness BHN 217/255. Stress Relieving: 1100-1300F(595-740C), hold 2 hrs. and air or furnace cool.

Straightening: Best done warm 400-800F(205-425C.)

Hardening: (Salt Baths or Vacuum Furnace preferred.)

Preheat: 1500-1550F(815-845C), equalize.

High Heat: 2100-2225F(1150-1220C), soak 2 to 5 minutes. For vacuum hardening, use the high side of the high heat range and soak times.

Quench: Salt or oil to 1000-1100F(540-595C), equalize, then air cool to hand warm, 150F(65C). Temper immediately. The vacuum quench rate to below 1000F(540C) is critical to achieve comparable results.

Temper: Tempering at 1000F(540C) or higher 2 times for at least 2 hours at temperature is recommended. Air cool to room temperature between tempers.

Hardening Data
Oil quenched.

[Oldiron2]

Most companies make a high-strength brazing alloy for high temperature use after repairing broken drills, milling cutters, attaching carbide tips and such. For MG, it is their #130 with an advertised tensile strength up to 113,800psi. All-State's # 11 or #13 have lower strengths, around 85,000 psi. while Unibraze #110 is advertised at 90,000psi. These can be oven or torch heated, but an oven would allow an inert atmosphere all around the whole part.
MG 700 stick electrode is made for build-up and hard-facing of metal-working tools including hot shears, reamers, lathe tools, etc. A preheat of from 800 to 1100*F is recommended. This also appears to come in bare sizes down to 1/16" for TIG welding. Probably is similar to what you're already using, with the same needs and problems.

[tulmkr1]

Thanks for the input. Unfortunatly because of the rush breakdown nature of the tooling i use, it is not timely to have the tools annealed before welding. I also cant use hard facing fillers because they do not retain a hardness of 62rc minimum. I have had tools welded like this from outside sourses, and they worked quite well. I am sure since they can do, i can do it. Finding the right combonation of material, and settings, preheat, and post heat seems to be the trick. Some of my welds turn out perfect, but its the consitant quality that im trying to maintain. Perhaps i will try larger corner radii in the hope of avoiding the cracks, and smaller tack welds to avoid carbon leeching..