stainless steel welded assy

[brin]

Are there any complications or problems with welding AISI 301 1/4 Hard stainless? We have an approx 3 foot long weld joining two curved .040 inch thick skin panels.

I understand there are low carbon stainless alloys (eg: 316L) as well as stabilized (eg: 321) materials which are intended for welded applications. So far I can only find these alloys in annealled condition. Is there another (stronger) alloy that I should be using instead of 301?

Also, should the part be stress relieved after welding? What about heating the part to remove chance of intergranular corrosion (carbide precipitation)?

The welded assembly will form part of an aircraft fuselage skin panel, and will be subject to brief periods of heating.

Thanks

 

[Rich2001]

Type 301

Chemical Composition

Carbon 0.15 max
Manganese 2.00max
Silicon 1.00 max
Chromium 16.00 - 18.00
Nickel 6.00 - 8.00






Type 301 is adaptable to welding by SMAW, GTAW, GMAW, SAW A or electrical resistance processes. In this case, GTAW (tig) welding is the preferred mehod.

Since the material may be subject to carbide precipitation during welding, it is possible that areas adjacent (HAZ) to the weld may have poorer resistance to chemical attack. Restoration of normal corrosion resistance can be obtained by heating to 1750-2000°F and cooling rapidly.

If subsequent annealing is impractical, then Type 304 with 0.08 maximum carbon, one of the 0.03 maximum carbon grades such as Type 304L or one of the stabilized grades, Type 321 or 347, should be used.

Type 308 filler metal or electrodes are used for welding Type 301.


Hope this helps, Rich

 

[geoffWSNS]

What about the reduction in strength at the joint, the 1/4 hard will be soft at this point due to heating in our experience - is there a way to combat this?

 

[butelja]

I don't think that the strength reduction at the joint can be eliminated. The area affected can be minimized by stitch welding and by using a higher amperage with faster travel. GTAW (tig) welding will do better than other methods due to its more focused heat input.

 

[brin]

GeoffWSNS has my point exactly. Our goal is to replace a section of aluminum skin on a test aircraft with stainless steel. Because of complex curves, we are forced to form it in sections and weld together. The only problem is that annealed austenitic stainless (321, etc.)is not as strong as the original .040 thick 2024-T3 aluminum in compression (eg: MIL-HDBK-5H Tbl 2.7.1.0(b) vs. Tbl 3.2.3.0(e1). And 301 1/4 hard doesn't seem to provide any benefit either.

 

[geoffWSNS]

We use strip in a continuous process & have found the welded joint on 15% cracks every time it is formed not at the weld but at the HAZ. This material would seem to be of little use unless it is used without joining?

 

[syam2004]

We have fabricated a Tee Section from two pipes which in turn were fabricated from two halves of rolled Plate material of AISI 321 material, 70 mm thickness.

Welding Consumable used was 347, Welding Process used was SAW for Pipe longitudinal seams. SMAW for circular seams of T -section.
Weld bevels were prepared by milling for Longitudinal Joints.

For Circular seam of Tee Section Bevelling was done by Carbon Arc gouging and then grinding.

Due to this, The circular seam fit up was not good, with lot of gaps.The weld bevel also was very wide. so using SMAW Process, lot of weld metal was deposited.

After welding was done the whole Tee Section was solution annealed at 1050C.
After solution annealing numerous cracks were found on SMAW weld metal. When we tried to repair using SMAW process, new cracks were forming in HAZ of Reapir weld. After a while we noticed that when we were trying to repair this weld metal new pin holes or star cracks were forming.

Can any body throw light on the phenomenon that was causing the cracks

1)in weld metal after solution annealing
2) in HAZ of repair weld bead
3) pin holes and star cracks

 

[metengr]

The cracks, pin holes and crater cracks indicate either a problem with the SMAW weld consumable or base material. Double check the chemical composition of the tee base materials to verify T321 ss, and especially check to make sure the SMAW weld metal is a Grade 347. I have seen stranger things where weld rod was not marked, and placed into open cans thinking it was a specific grade of material. How much grinding of the base metal did you perform after arc gouging?

The original cracks reported in 1) above imply solidification cracks in the weld deposit that opened up after solution treatment and quenching.

The subsequent repair cracking and pin holes indicate a definite contamination or weld metal dilution problem again that points back to the weld metal used or joint preparation technique.

Typically, Type 321 ss is a titanium stabilized, high temperature grade of material that is readily weldable using Grade 347 ss consumables. You should go thru step by step to eliminate the possibilities as mentioned above - plate composition and weld metal composition.

If plates used for the tee piping are ok compositionally, remove the entire girth weld by machining or grinding, perform a liquid PT of the weld prep surfaces - very important, purchase new can(s) of SMAW weld rod, Grade 347 ss and start over.

 

[mcguire]

Can't you laser weld the two panels together? The cooling rate is fast enough with laser welding to avoid carbide precipitation. Also, the weld zone would be extremely small and minimize the area which is no longer 1/4 hard.

 

[btrueblood]

mcguire,

the problem is that the weld material will still have properties closer to annealed stainless rather than the 1/4-hard (strain hardened) stainless.

Geoff/brin,

You can look into a low-temp furnace braze (good luck finding a good alloy though) or mechanical joining. A better approach might be to look at using a precip-hardening stainless or one of the inconels, that you can re-solution treat after welding. Lastly, have you looked into hydroforming & other exotic techniques?

 

[mcguire]

From a yielding point of view I think a laser weld zone would be sufficiently thin that the elastic constraints of the surrounding material would prevent it from defroming separately. When it did deform, it would quickly exceed the flow stress of the surrounding material because of 301's high work hardening rate. That's why tensile specimens of 301 don't neck until final failure. The work hardening rate is greater than the local loss of cross section.