Welding A2 Tool Steel

Date 04-22-2008 00:14

The MG 710 wire doesn't apear to be a standard designation. Can you tell us more about the wire? Also, since the welds cracked "as soon as the pass was laid down", seems to indicate that you were getting hot cracking in the weld metal as opposed to delayed or hydrogen cracking in the base metal or HAZ. Most times hot cracking is related to joint geometry &/or weld composition. So there is a good chance your preheat and slow cooling was adequate and you have discovered another problem.

By DaveBoyer (*****)

Date 04-22-2008 03:19

In Your post You mention that the part was "heated to 500F and then air cooled, and then TIG welded" The welding must be done while the parts [all of them] are hot and then cooled slowly.

In the auto frame plant when We did repair welds on tool steel [We commonly used A2] the majority of the weld was done with 9018 and just the working surfaces were layerd in with tool & die repair rod a few passes thick.

Welding tool steel is trickey busines, it is OK for repair work, but a poor choice in original manufacture. If You post a detailed drawing or picture and a good explanation of what You are making, I will give You My advice on alternative construction methods as a tool & die maker.

By msharma4 Date 04-22-2008 16:05 Edited 04-22-2008 16:07

Hi,

Thanks for the replies!

Ive attached a pdf of the machine drawing and a .jpeg of how the system would work as a metal diaphragm cutting system located inside a flange which is part of an air-driven facility (the upstream side of the knife blades would be exposed to about 44 atm pressure, causing the metal to rupture. The purpose of the knife-blade system would be to cut the metal so there is a clean break and no metal goes flying down to tube). The knife blades need to be very hard to assist with fatigue/wear resistance and capable of coping with the dynamic loading force due to the diaphragm rupture. I selected tool steel specifically because of their hardening properties and specifically A2, based on the department machine shop's recommendation that A2 is nice to machine and has excellent dimensional stability under heat treatment.

I made a mistake in the previous post: it was pre-heated to 500F, TIG welded and then air-cooled. The part was pre-heated using a torch only. The welder had one of those pyrometer guns (measures temperature using the laser red dot) and said that he checked in many locations to make sure the temp. was reasonably uniform. I have also attached a picture of one of the cracked welds if this helps in anyway.

The wire was called MG710, but is the exact same product as T5AH (from Eutectic corporation). I spoke to the sales representative and he said it was made for most air-hardening tool steels, including A2.

Thanks again!

Attachment: knifeblades.pdf (29k)

Attachment: knifeblades_weldstage.pdf (46k)

Attachment: IMG_0869Small_WeldCrack.JPG (38k)

Attachment: IMG_0863Small_Weld.JPG (32k)

Attachment: IMG_0870_WeldJig.JPG (49k)

By arrowside (**)

Date 04-22-2008 23:18

The first thing that i would check is that laser thermometer thing. Check it next to a temp stick. I had a situation a couple of weeks ago welding 6061-t6 Al. Another welder had one of those laser things and gave it to me. Well, long story short, it ends up that the battery in it was 4 yrs. old. The thing was off. Way off. I knew it didn't take that Al. that long to get to 150*.

   Next, i would preheat to your lower limit mentioned above, not 500*.

   It also looks like you are not getting adequate gas coverage, or your base metal has surface contaminants, or both.

   I would also cool it slower, rather than in still air. Wipe your filler clean also. And make sure that when the welder is preheating, that he's not using a sooty flame.

By DaveBoyer (*****)

Date 04-23-2008 03:25

I had a really in depth post typed up for You and managed to loose it. I will give You a greatly abreviated version now, and You can call Me at (610) 326-0113 if You want more details.

Some questions for You:
   1) What is the material this has to cut?
   2) How many cycles does this need to perform?

The MG 710 rod is not a good choice for the structural part of the weld. It is used to deposit the hard working surface ONLY.

   We used 9018 for the structural part of tool steel repairs, it might work out better for You.

   This is a poor design, structurally joining tool steel by welding is not really a good method.

A better alternative is to machine from a single piece of A2, if this really needs to be made from tool steel.

Alternatively, You could make the part from mild steel & weld it with simple and time proven methods. Then You could use the MG 710 rods to put a tool steel cutting edge where You need it. Pre & post weld heat treat is still mandatory, but You avoid heat treating the entire part.

   If You heat treat the entire part it will warp/distort quite a bit due to it's shape & size, in spite of being made from A2.

You could flame harden the edges and then draw at 400F for 60-62 RC or 700F for 57-59 RC, the softer temper gives greater toughness with some reduction in wear resistance. If You need more strength/toughness, there are other alloys that will better suit Your needs.

By 803056

Date 04-23-2008 19:44

A2 is air hardenable, so simply allowing it to air cool is going to harden it and the weak link, in your case; the weld, is going to fail.

Make sure the A2 is annealed before attemping to weld it. High preheat is required. Weld it with a 100 to 110 ksi filler metal and make sure the weld is of sufficient size to care any loads, including any residual stresses. The part should be stress relieved as soon as the weld is completed. Then it can be reheat treated to harden it.

Good luck.

Best regards - Al