Ingenieurwissenschaften und zugeordnete Tätigkeiten
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- Duplex stainless steels (2) (entfernen)
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When welding super duplex stainless steels a non-admissible pore formation can occur even if recommended processing guidelines are followed strictly. To investigate this phenomenon and to determine the influencing factors different claddings were produced using gas metal arc welding and submerged arc welding. The welding consumables, the shielding gas and the welding flux were varied. As shielding gases several mixtures, based on argon and 30 % helium, with various amounts of nitrogen, nitric oxide, carbondioxid and oxygen were applied. As welding flux agglomerated fluoride basic fluxes and aluminate fluoride basic fluxes were used. Different batches of the similar solid filler wire G 25 9 4 N L were used to produce the claddings on the base material UNS32750. To determine the pore formation X-ray examinations and microsections were used, to analyze the chemical composition of the claddings melt extractions and spectrometric examinations were applied. Additionally, the microhardness and the ferrite number were detected. The studies have shown the shielding gas, the welding flux and the filler metal possess a great influence on the pore formation. Even small variations in the chemical composition of the welding consumables lead to totally different results. In addition, the ferrite number and the chemical composition of the claddings depend strongly on the used gases and filler metals.
Manganese alloyed stainless steels represent a cost-effective alternative to conventional CrNi- stainless steels due to strong fl uctuations of the market prices for nickel seen during the last years. In CrMnNi steels, nickel is partially replaced by lower-cost manganese and small amounts of nitrogen for stabilization of the austenitic phase. This also brings benefi ts regarding the mechanical properties, as it results in an increased material strength. Laser beam welding of such materials was investigated for direct comparison with Standard CrNi steels. Main emphasis was laid on fi nding adequate process parameters to achieve a stable welding process and obtain a good weld quality. Two different laser sources, a 4.4 kW Nd:YAG and a 5 kW CO2 laser, were used to weld 1.5 mm stainless steel sheets in continuous wave mode. A high-Mn austenitic (1.4376) and a lean duplex (1.4162) steel, as well as the standard austenitic (1.4301) and duplex (1.4362) grades were selected as test materials. Both butt and lap joint confi gurations were studied. Experiments were carried out systematically, varying the welding speed, laser power and focal point position in order to determine adequate process windows. The infl uence of the shielding gas type and fl ow rate on the process stability and the weld quality were investigated. The effects of weld edge preparation on the weld appearance and quality levels attained were also examined. The obtained welded joints were subjected to radiographic tests for detection of internal imperfections. Also a metallurgical characterization of the samples regarding the resulting phase composition or balance and hardness depending on the welding process parameters was conducted. Furthermore, tensile and potentiodynamic tests were performed to evaluate the mechanical and corrosion properties, respectively. The results provide an insight into the advantages and limitations of the laser beam welding process for joining high-manganese alloyed stainless steels. Conditions for the production of defect-free and corrosion-resistant welds having good mechanical properties could be determined.