With groove type weld and multi pass I've done 2" steel with my Millermatic210. Answer, yes it can but what is the purpose, is it going to be structural if so check that it will with stand the rigor of service required.

What process' do you have available If it is a small piece tig would be OK but for larger areas and long weld beads with multipass MIG would be my choice. This large of thickness will require preheating and probably post heating or at least insulating the finished welded area to slow the cooling to prevent cracking during cooling. I would use 4043 filler material since it flows so well. Argon and helium mix for the gas will help penetration.

Good luck,
pjseaman

If you have GTAW, TIG process try DC and helium. Set the power source up like you would weld carbon steel and stainless steel, DC straight polarity, start- high frequency, 1/8 " dia. 2% thoriated tungsten, sharp point and 100% helium shielding gas. It takes getting used to the puddle and fluidity of the puddle but it will weld thick sections with no problem.