GMAW for Ferritic 430 1

[sawhney]

I am facing a problem of regular breakage in welding of ferritic 430 and 409 grade.Material is actually strip of 4to 6mm thickness.The strip get broke down during processing on CR mill.

 

[metengr]

Several important questions;
1. Was the MIG welding performed in one pass or multi-pass for joining the strip sections?

2. What was the filler metal, if any?


Ferritic stainless steels can form coarse grains in the weld HAZ and can result in significant loss of toughness, especially during forming operations

 

[sawhney]

The passes in the process depends on the thickness of the strip to be welded.right now we have employed 308L wire for this solution.theres a recommendation to go for inconel wire but that ll be quite expensive.

 

[metengr]

First off, I would have a sample of a typical failure subjected to metallurgical analysis to confirm what I will be recommending below.

The 308 filler metal is acceptable for this application. Inconel will not help because the problem is most likely in the base metal heat affected zone.

Several Recommendations, pending the results of your analysis;

1. You need to reduce heat input for the multipass welds - keep the interpass temperature below 575 deg F. Stick with multi-pass welds.

I would try the following post weld heat treatment - locally heat the weld zone to about 1450 deg F for about 10 minutes. This short PWHT should restore ductility to the weld HAZ.

Grind the weld cap flush to reduce any stress concentration prior to forming.

 

[mcguire]

430 is generally considered to not be weldable in the sense that it forms martensite in any segments that were austenitized during welding.
You need to:
a)switch to 439, a stabilized 430 or
b)anneal the weld

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[EdStainless]

430 should weld fine. We autogenously weld and cold draw tubing in 430.
The trick is to temper the welds. You don't need full anneal, but a temper is esential. Check some hardnesses. The welds should pass bend tests.
Due to the matersite that forms you get fine grained welds. 439 is a problem becuase the welds are very coarse grained.

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Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[mcguire]

Ed
When you temper the welds is the idea to do it at a low enough temp that you don't sensitize?

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/