The weldability of D6AC ultra-high strength steel is analyzed, and the fundamental of
tandem sequence submerged arc welding with thin-wire is introduced. Welding tests are carried out
to study the procedure of D6AC ultra-high strength steel welding with the tandem sequence
submerged arc welding technology, and the character of welding ultra-high strength steels by use of
this method is analyzed. With the thin-wire tandem sequence submerged arc welding technology,
the cracking problem existing in the welding of D6AC ultra-high strength steel can be solved, the
welding automation can be realized at low cost, and the low efficiency of TIG pulse welding and the
high cost of high-energy density welding are avoided.