A flux cored wire 2209 for duplex stainless steel was developed and different weight percent of content of CaF

2

were added in it. The microstructure of slag was observed by Olympus-PMG30 and the gas porosity rate on the weld was tested. The results showed that when the weight percent of CaF

2

were less than 2%

the contents of "FeO" decreased with increasing of the content of CaF

2

which are beneficial to the detachability. If the weight percent of CaF

2

was more than 3%

the detachability of the slag became more compact which could worsen the detachability of slag. In addition

the processing properties become deteriorated. With increasing of the content of CaF

2

the gas porosity reduced.