Bohler CN 13/4-UP description: Sub-arc wire/flux combination for welding similar soft-martensitic steels like 1.4313 / CA 6 NM. BOHLER CN 13/4-UP // BB 203 yields a weld deposit featuring very good ductility and CVN toughness as well as high crack resistance. BOHLER BB 203 is a fluoride-basic, agglomerated flux providing good operating characteristics, smooth beads and a low hydrogen weld metal (HD d5 ml/100g).