20th International Forgemasters Meeting - IFM 2017

Our company manufactures forged duplex and super duplex stainless steel products. These materials are called ASTM A182 F51, F53 and F55. These have high strength and high corrosion resistance. Super duplex stainless steels (SDSS) are by definition a duplex stainless steel with a pitting corrosion equivalent (PRE) > 40, where PRE = %Cr + 3.3x %Mo + 16x %N. So these are used injection pumps with oil and gas plant. Steel forgings have proof strength higher than cast steel and are able to increase in thickness. Therefore, these are used to drill for deep area oil. We supply forged SDSS products over 200 mm thickness. But these materials have critical thickness. Because SDSS precipitate sigma phase that is detrimental intermetallic phase with decreasing cooling rate. It causes of fragile material and could cause a problem of crack. We tested to decide critical thickness for forged SDSS. The forgings materials are thicken more and more. And test is stopped critical thickness that is crack exist. And thermal stress is analyzed by FEM. We compared difference result of analysis of existing crack thickness with no crack thickness and consider mechanism of crack for SDSS. As a result, we found critical thickness line. And in FEM analysis, we understand a difference in hydrostatic stress, maximum principal stress and trial stress state by some test thickness that is related cooling rate. In case of large thickness that is exist crack, it has high hydrostatic stress and doesn’t satisfy von Mises yield criterion. And it reaches the critical thickness after slight plastic deformation from elastic deformation. In conclusion, we understand maximum thickness of SDSS that is no existing crack thickness and relation of thermal stress and thickness of its material. We could manufacture thicker products and more multiple figure products.