Welding Tips and Tricks

I'm trying to establish a welding procedure for a heavy-section repair using the TIG process.

The workpiece is a 30 inch cube of alloy steel that has a 12" diameter hole bored through its center. The rough machined part was then clad with a skin of material compatible with ER 307-Si stainless and the bore was ground to close tolerance in order to accept a piston. Somewhere along the line, the piston froze up inside the block and had to be pressed out with a 100 ton jack causing some serious scoring to the cylinder wall.

All the material and metallurgical criteria have been met, the wire has been selected and I am now trying to determine the best route to follow with regard to preheat and post heat treatment in order to prevent cracks or defects since the workpiece will need to be re-machined and honed after the welded repairs are made.

The filler wire manufacturer recommends a 150 degree F interpass temperature but I somehow think that's a little unrealistic in view of the section's thickness. I have the capability to to bring the block up to about 450 deg. F with nearly infinite temperature control for slow cooling in stages if necessary.

If anyone out there has some info on this type of heavy section procedure I'd be very grateful.

JG

Do you know the composition of the alloy block?

Funny you should ask.....The manufacturer in Germany steadfastly refused to furnish any information on this issue. Best guess is that it's a common, garden variety of low carbon steel. The Germans are noted for using stuff like 285-C when cost is a big issue and a 30 inch cube would definitely be a big issue.

The cladding, which was probably spray welded on, is what makes the thing tick under high temperature (it operates at 485 deg. F) and conditions of moderate abrasion with very little impact. Hence the ER-307-Si filler which is noted for stainless to carbon steel compatibility as well as abrasion resistance due to the Mg content while having sufficient Cr and Ni in the alloying recipe to deal with the temperature. What I'm actually doing here is repairing a series of defects to the cladding while ensuring that the deposited material bonds properly with the base material.

The expansion coefficients are in the ballpark with a 7.3 for the carbon steel base material and an estimated range of 8.0-9.6 for the Austenitic ER-307 filler/cladding material (that's my own average interpolated from the tables given for 304 and 310 SS). My biggest concern is getting a proper temperature gradient during the first pass to avoid an under-bead cracking condition and then maintaining this equilibrium during a "stepped down" cooling /aging process.

I do a lot of cast iron as well as very heavy sections of aluminum. In all these cases the material is homogeneous and quite predictable. This one is a little different due to the nature of the two somewhat dissimilar materials involved.

It is probably a fair assumption to say that it is not an A285C. This specification covers carbon steel plates of low- and intermediate-tensile strengths. The maximum thickness of plates under this specification, for reasons of internal soundness, is limited to a maximum thickness of 2 in. for all grades. Any ways, without really knowing what your working with it is kinda like a crapshoot. The weld deposit of 307 has little or no ferrite. Care must be taken to avoid hot cracks. That is accomplished by low heat input and making “convex” bead profiles, hence the 150 deg. interpass temp. Without knowing what the base metal is, the best thing to do is go with the 450 deg. preheat (obviously not reccommended for the 307 filler) and with a controlled post weld cool. Maybe they can choose a different filler. Send your question directly to Jody and see if he got anything for ya. He is more knowledgeable in this area than I am. Sorry I couldn't be more help.

Thanks much.....You're right; it's a crap shoot....Perhaps a block that large is actually a steel casting but without any cooperation from the manufacturer, we're working with a lot less information that I'd like. I may have to try one of the more accessible spots first as a control and take it from there.

Again, thanks for the effort.

JG

In TIG welding an arc is formed between a no consumable tungsten electrode and the metal being welded. Gas is fed through the torch to shield the electrode and molten weld pool. If filler wire is used, it is added to the weld pool separately.