Study on Welding of High Silicon Containing Stainless Steels (II). HAZ Toughness of High Silicon Containing Duplex Stainless Steel.

The HAZ toughness was investigated in the high silicon containing duplex stainless steels from a metallurgical point of view. The increase of silicon content is effective for improving the corrosion resistance to nitric acid containing highly oxydizing ions. However, the effect of increasing in silicon content on the HAZ toughness of duplex stainless steels has been rarely clarified.The effects of nickel and nitrogen content as well as the ferrite ratio on the HAZ toughness were studied to obtain proper chemistry in 23%Cr-3.3%Si-Ni-N duplex stainless steels. The HAZ toughness was evaluated by using Charpy impact test specimens machined from GTA welded joints. It was clarified that there were two reasons for the HAZ embrittlement. One was the sigma phase precipitation in case of lower ferrite ratio. Another was the nitride precipitation in case of higher ferrite ratio. In the proper range of nickel and nitrogen content, the high HAZ toughness was obtained. The sigma phase precipitation was accelerated by the decrease of the ferrite ratio and the increase of the nickel content. The increasing in the silicon content accelerated the nitride precipitation in the HAZ. However the decrease of ferrite ratio could reduce the nitride precipitation in the HAZ even though in the 3.3% silicon containing duplex stainless steels. It was clarified it was important for the sound HAZ toughness to control the nickel and nitrogen content in the proper range.