309/312

[Hitch]

Not necessarily a MMA specific question...

Dissimilar materials, eg MS to SS, i have always used 309 consumables whether it me MMA or MIG.... got some 312 kicking about as well, i understand these are also dissimilar rods.... whats the difference, is 312 a better rod for 316 to mild due to the higher grade than the 309...?

 

[snowcat]

312 is a harder/stronger IIRC but if it gets over hot it can become brittle and crack OK in a few passes but not great on moosive stringers, 309 I tend to call a buttering rod, great for building worn parts that you want something soft and ductile to re machine, turns lovely..

I'm sure AL will be more suited to fill the gaps and the finner points..

 

[TechnicAl]

No in that respect there wont be much of a difference.

Simply, its just another way of doing the same thing. The main difference is that the 312 will have a much higher tensile strength (around 800 N/mm2) so it can also be used for welding grades like En 24T.

You have to be careful if you try to weld very thick joints with 312, if the weld metal gets hot and stays hot it can become brittle. To be honest the same applies to 309L but its much more unlikely.

 

[Hitch]

Nice one men.

So 309 is more forgiving for general dissimilar use then.

 

[TechnicAl]

in that the weld metal is softer, more ductile.....yes


and if youre buying them the 309L should be cheaper