Moly in 300 Series Stainless

[vanci]

I am curious to know, what affect does molybdenum content have on 300 series stainless when producing autogenous welds? Also, how does the sulfur content and moly content relate to each other and weldability?

Thanks in advance!

 

[metengr]

vanci;
The effect of Mo on the weldability of austenitic stainless steels can be observed by the Cr _eq equation, where Mo behaves even stronger than chromium in ferrite formation during solidification. This is important to avoid hot cracking in austenitic stainless steel welds.

The effect of sulfur content is critical because increased sulfur content promotes improved wetting of the weld puddle (weld bead shape). However, hot cracking susceptibility is increased.

So, from my perspective, increased Mo content promotes ferrite formation to reduce hot cracking while sulfur increases wetting. I have not seen a specific interaction where Mo is deliberately added to allow increased sulfur content to promote wetting.

 

[EdStainless]

In general you can't see the Mo effect alone, since higher Mo alloys require more Ni to keep them fully austenitic. The higher Ni tends to make the welds slushy and penetration difficult. Adding a bit of S (0.007% - 0.012%) does help promote weld fluidity, but it also results in more sulfide inclusions in the welds.

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Plymouth Tube

 

[strider6]

The ferrite content in a weld is a function of the Cr and Ni equivalent. You can calculate the ferrite in the weld with the WRC or Delong or Shaeffler.

The presence of sulphur may cause cracks in the weld or HAZ, so it's important to clean the material to avoid Sulphur contamination and control the amount of ferrite in the weld.

here you can find software to calculate the ferrite in a weld:

http://www.corrosionist.com/corrosion_prevention_library_welding.htm

S

Corrosion Prevention & Corrosion Control