Shielding Gas In Welding Research Articles

Influence of nitrogen-doped shielding gas for welding of medium manganese austenites for cryogenic applications

The relevance of technical gases is constantly increasing due to environmental and climate policy requirements. The storage and transport of liquefied natural gas (LNG) takes place under cryogenic conditions with substantial volume reduction due to significant storage efficiency. Consequently, there are specific requirements for the mechanical properties of the applied materials at cryogenic temperatures. The materials used so far have been cold-hard, high-nickel austenites, and martensitic steels of the X8Ni9 type. The austenitic materials offer good processing properties, but due to their comparatively low strength and high costs, these materials are not attractive. In contrast, the welding of the martensite has a significant negative impact on the processing quality and the automation of the process. In order to address the problems of automation, material costs, and mechanical properties, particularly high strength and cold toughness, the application of innovative austenitic steels with a medium as well as a high manganese content is suggested. For the qualification of medium manganese austenites as a substitute for maritime applications, the welding processing of an X2CrMnNiN17-7–5 (1.4371) is considered under the aspects of the standards and guidelines of the International Association of Classification Societies (IACS), the International Maritime Organization (IMO) and the classification society Det Norske Veritas (DNV). Preliminary investigations have revealed that the application of a conventional filler metal of type G 20 16 3 Mn N L in combination with nitrogen doping of the M12-ArC-2.5 shielding gas according to DIN EN ISO 14175 results in a significant enhancement of the mechanical properties. The addition of 4% nitrogen into the shielding gas caused a diffusion-induced increase in the nitrogen content of the weld metal and a simultaneous increase in strength. Additionally, there were no negative influences on the austenitic microstructure. In consideration of the qualification specifications for welded joints and filler metals of the standards and guidelines according to IACS, IMO, and DNV, the joint welds are examined, and the qualification of the welding process is envisaged. For this purpose, comparative welds of the mentioned material combination are carried out and compared with both the initial gas mixtures and the nitrogen-doped shielding gas.

Investigations on the use of Nitrogen Shielding Gas in Welding and its Influence on the Hot Crack Behaviour of High-Temperature Resistant Fully Austenitic Ni- and Fe-Base Alloys

Due to their excellent high-temperature behaviour and corrosion-resistance properties, as well as to their equally good high-temperature strength and long time strength, high-temperature resistant fully austenitic Ni-base alloys are widely employed in industrial branches for especially demanding and exacting use. The outspoken tendency of the weld metal to hot cracking, however, considerably restricts the outstanding working-life properties of this group of materials. In our research project is investigated systematically the metallurgical effect of nitrogen for avoidance of hot cracks in fully austenitic weld metal. As objects of the investigation, were selected hot-crack sensitive fully austenitic high-temperature Ni- and Fe-base alloys (alloy 602 CA, alloy 601 H, alloy 617, alloy 690, alloy 800), which were processed with GTAW and pulsed GMAW procedures under the use of suitable weld filler materials as applied in practical use. The element nitrogen was added as gaseous component with the weld shielding gas. The hot-crack behaviour of the base metals and of the welds was evaluated by the Programmed Deformation Rate-Test. As results of the hot cracking tests, the positive effect of nitrogen was shown at first and foremost only with the primary carbide containing Ni-base alloy 602 CA and slightly with alloy 601 H. The reasons for this effect are metallurgical. Starting from the presented results and the experience meanwhile gained in practice in matched arc welding the high-temperature resistant Ni-base alloy 602 CA, nitrogen additions between 1 and 3 % for the GTAW process and between 5 and 12% for the pulsed GMAW process are recommended.

Atmospheric Physics or Putting The Air To Good Use

Separating air into its individual constituents is a major industry and manufacturing processes which employ oxygen, nitrogen and argon are as ubiquitous as the air from which these gases are derived. Most readers will be familiar with the use of oxygen in steel making and the application of argon as a shielding gas for welding.

Effects of nitrogen and helium shielding mixtures on semiaustenitic stainless steel welds

AbstractThe effect of nitrogen-helium atmos pheres used as a shielding gas for welding of some semiaustenitic stainless steels was studied. Nitrogen, being a strong austenite stabilizer, has the tendency to suppress the amount of retained delta ferrite in the weldment. The addition of 1.0 per cent nitrogen by volume to the helium shielding gas increased the tensile strength of the weldment approximately 4000 psi to within about 1 per cent of the parent metal, and the ductility approximately 33 per cent to within 95 per cent of the parent metal.The additions of nitrogen to the shielding gas significantly reduced the a mo unt of retained ferrite. However, increasing the nitrogen in excess of 1 per cent by volume drastically reduced the tensile strength and ductility. It is suggested that this reduction in strength and ductility is the result of pertinent alloying components being used up in the formation of nitrides. Resume Les auteurs ont etudie 1'influence de melanges d'helium et d'azote utilises comme ga...