TIG question on A2 tool steel

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Hello.  I had a piece brought to me today at work from one of our other plants.  It's 1.25 x 2.00 x 24.00 piece of heat treated A2 tool steel that cracked by a 1/2" tapped hole.   It's still in one piece but not by much.  I pre-heated @ 350* for a few hours before attempting to weld this back together.  But as I start to weld, the crack wants to follow my puddle.  I increased my amperage to 125 and slowed down a little.  This seemed to help but wondering what the pro welders think or how they would handle this scenario.  Higher pre-heat?  Thanks.
Reply:I have no idea about welding that steel, but you need to give a bit more info for the guys who may know. Did you use any filler when welding it? Did you bevel it? What is the location of the hole/crack on the steel?Airco Ac/Dc 300 HeliwelderMillerMatic 200 (stolen)Miller Maxstar 150STLMiller AEAD200LE (welding and generating power) Hobart MIG
Reply:As squirmy said post more info for the guys that know this metal. What I do know is drill the start and end of a crack to stop the spread.
Reply:A2 is classified as a "cold work, medium alloy, air hardening" tool steel.   It's got 1% C, 5% Cr, 1% Mo.   It's been over 20 years but the last time I TIG welded on a stamping die that was made from A2 I recall using a 900 F. preheat.   Can't recall what I used for a filler.   I do know I use to have some air hardening TIG filler rod (had purple color coded ends) but I used that mainly for building up worn edges (so they could be reground) on plastic injection molding dies that where made from P-group mold steels. My best guess for now would be you need a lot higher preheat and maybe just plain old 70s-2 (or -6).  Your weld metal is going to pick up considerable alloying from dilution with the base metal.   In fact I'd be running small stringers and trying to minimize dilution.ER312 might be a good option for filler also.Last edited by HT2-4956; 12-29-2014 at 05:53 PM.
Reply:Ok A2 is not for the faint of heart. Most of the time its just better to have a machine shop make a new one.It is an air hardening tool steel. Its usually REALLY HARD. Hardened steels do not like to be welded in the hardened condition. Drilling holes near the ends is definitely out. The holes wont help anyway and its too hard to drill unless its annealed. Annealing isn't a bad idea by the way. Here is what I'd do.Grind the crack out as far as you can. This might involve a large v-groove that takes a while to fill but a part that has broken will never hold with just a surface weld. You will certainly have to pre-heat, the hotter the better. I wouldn't be afraid to heat to a dull red before welding. I would use Weld mold 880 filler. Its designed for welding tool and die steels and is also air hardening. Make sure the part stays hot until all welding is done. Then heat the part to hardening temp and allow to cool in still air on a fire brick.Good luckLincolin Power Wave 450, Lincoln Powermig 255, Lincoln Pro Mig 140, Lincoln Squarewave Tig 275, Miller Big 40 G(with Hobart Hefty suitcase), Thermal Arc 95S and Esab PCM875 in an already full machine shop.
Reply:my apologies for the lack of info.  I'm a self taught welder so many of the terms you guys speak are foreign to me.  I'll give my best description of my process so pardon if anything sounds hokey.  The 1/2" tapped hole is drilled through the 2" dimension.  So looking down at the hole, it lies on center of the 1.25" dimension 6" from the edge of the 24" dim.  The crack is visible on all 4 sides but the detail is still in one piece.  I grooved the crack roughly .100" deep and.100-.200" wide with a die grinder.  I then washed the detail with hot, soapy (Dawn dish soap) water and rinsed with hot water.  After heating @350* for a few hours I welded at 125 amps using .035" A2 filler rod.  As for the filler rod, that's how the container was labeled so that's all the info I can provide about it.  So, hopefully this is a little more help.  I'm nowhere near your guys level of welding knowledge.  I'm very grateful for the help.  Thanks.I did get to thinking if I would be better off using a filler of something soft (mild steel) and then laying a finish pass with the A2 rod.  I suspect with what I've already done it's going to crack again.  Increasing the pre heat temp sounds logical as well.  Thanks again.Also, the A2 filler rod I'm using has yellow coded ends (which I snip off before welding).Steve
Reply:You HAVE to use 312 stainless steel filler rod (or one of a couple other specialized fillers specifically designed for heat treated/hardened/tool steels).You don't need to do anything fancy, just grind out a V and fill it in nice and slow. Don't even bother trying anything else...Last edited by MikeGyver; 12-30-2014 at 12:26 AM.Welding/Fab Pics: www.UtahWeld.com
Reply:Metals And How To Weld Them by The James F Lincoln Arc Welding Foundation addresses the subject. The book was first printed in 1954 but I believe the information is still valid. It has you buttering all faces of a finished break with stainless to limit mixing, and provide needed ductility. Hard steel won't stretch much as it cools, stainless will.Last edited by Willie B; 12-30-2014 at 08:25 AM.
Reply:I worked in a tool and die shop as a maintenance guy. The tool makers taught me to tig. The forced me to weld up the cutting edges of shear blades.  I always V groved then used 312 as a base.  Maintaining 600F while welding. Allow the piece to normalize about an hour. Then finish the last 0.020" to 0.050" with A2.
Reply:Thanks for the replies.  The stainless worked great with no issues.
Reply:stevev,Good to hear you got it figured out and fixed.   Let us know how long it holds up back in service.
Reply:Can't take credit for this. The help you guys suggested led me to the solution. Thanks!