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Rising prices of nickel and molybdenum in the recent past years have led to unprecedented interest in substituting leaner-content alloys for standard 300-series austenitic stainless steels in many applications. Due to the price volatility of various alloying elements, many new materials have entered the market, yet no direct comparison of corrosion resistance of these new materials exists. In this project, comparative investigations were carried out and in each case one or several representatives of a material group were taken into account. The material groups covered were: lean duplex stainless steels, manganese alloyed austenitic and duplex stainless steels and ferritic stainless steels. In addition to electrochemical investigations, all materials were exposed to various atmospheric conditions in different surface states.
The second part of this paper looks continues the comparative investigation of lean duplex stainless steels, manganese alloyed austenitic and duplex stainless steels and ferritic stainless steels. These new materials were investigated in many different test procedures and in different conditions focused on the application in civil engineering and common use. In addition to electrochemical investigations, all materials were exposed to atmospheric conditions in different surface states. In Part 2, Prof. Gümpel and his team examine the effects of coastal and urban atmospheres on the samples, and presents their final conclusions.
Because of its excellent corrosion resistance, a high tensile strength together with a high ductility, duplex stainless steel 2205 offers many areas of application in the chemical and the offshore industry, to name just two. Though welding, especially laser beam welding accompanied by high cooling rates, duplex steels tend to perform higher ferrite contents in weld metal upon cooling down from melting temperature as the base metal. This trend leads to a reduction of the ductility as well as the corrosion resistance of the weld joint. To overcome this problem a solution, based on buffering the plate edges by laser metal deposition with material containing higher Ni concentrations prior to the laser welding was suggested. This method offers more benefits in comparison to conventional usage of higher Ni-alloyed filler wire due to the better control over Ni-distribution in the weld seam, resulting in balanced austenite- ferrite ratio everywhere in the weld metal.
In this context different mixtures of duplex and nickel powder were investigated as well as different process parameters, that enable a smooth surface structure with slightly reduced ferrite contents. In a second step the possibility of welding those edges defect free with standard parameters while achieving balanced austenite- ferrite ratio was verified with metallographic analysis of the microstructure, Electron Backscatter Diffraction (EBSD) and impact testing according to Charpy. The improved corrosion resistance of the welds in comparison to unbuffered ones was observed with the ASTM G48 standard test method.
Because of its excellent corrosion resistance, high tensile strength and high ductility, duplex stainless steel 2205 offers many areas of application. Though laser beam welding accompanied by high cooling rates, duplex steels tend to perform higher ferrite contents in weld metal as the base metal, which leads to a reduction of ductility and corrosion resistance of the weld joint. To overcome this problem, a solution, based on buttering the plate edges by laser metal deposition (LMD) with material containing higher Ni concentrations prior to laser welding was suggested.
In this context different process parameters for LMD and different mixtures of duplex and nickel powder, were investigated. In a second step the possibility of welding those edges defect free while achieving balanced austenite-ferrite ratio was verified with metallographic analysis, Electron Backscatter Diffraction (EBSD) and impact testing according to Charpy. The improved corrosion resistance was observed with ASTM G48 standard test method.