I'm just trying to help out a friend, and he said the customer is recommending a 70 series filler, but the tensile of the 450 is something like 115ksi, which far exceeds the realm of a 70 series filler. I also think it is 450 to 450 and the pieces are pretty thick. I was thinking along the lines of a 90 series filler. Any suggestions would be appreciated. I didn't give enough information but I seem to think the thick pieces are cracking while using the 70 series filler. I think I might just suggest a preheat to slow the cooling rate and a 90 series filler. Thank you.

Just an FYI-
I have recently seen this material used in making the truck body for haul truck in the mining industry. (speaking of the monster haul trucks!)

The entire truck body is made of segments of Hardox 450. As Mr. Mankenberg suggested, these joining welds were also entirely welded with E71T1 FCAW.

These joints are full pen. butt welds (hardox 450 to 450) with a carbon steel backing bar and other assembly fillet welds.

Yes, the weld is way under the tensile of the 450 plate. But in this application, the welds never sees such stress anyway. The material is used for the bottom and sides of the truck body for -like you said, abrasion resistance.

note: Sometimes the manufacturer will apply a weld overlay (hardsurfacing) over the 70ksi butt weld joint seams.

Phil-

Thanks for posting the link to the Hardox info.
I was not aware of the low hydrogen welding requirements < 5ml/1000g