High Nitrogen Steels. Influence of Shielding Gas Composition and Welding Parameters on the N-content and Corrosion Properties of Welds in N-alloyed Stainless Steel Grades.

Abstract

TIG welding using different heat inputs, arc lengths and shielding gas nitrogen contents was performed, The aim was to evaluate the possibilities to avoid nitrogen losses on welding or even increase the weld metal nitrogen content and thereby improve the corrosion properties and, in the case of duplex grades, also to improve the phase balance, Three different nitrogen-alloyed duplex grades and one superaustenitic grade were investigated, Thecorrosion resistance in terms of CPT, Critical Pitting Temperature, of the super duplex material was found to be strongly correlated to the nitrogen content of the weld metal. In the case of the superaustenitic weld metal, the increased nitrogen content was found to be associated with an increased pore formation, Ieading to a lower corrosion resistance and thereby masking the positive effect of the increased nitrogen content.In order to illuminate the nitrogen exchange reactions between the arc, weld pool, and shielding gas, stationary weld experiments were also performed. The results from these stationary trials indicated that the net weld pool nitrogen content could be qualitatively understood if the various fluxes involved in the nitrogen transport between the plasma arc, weld pool and weld pool-shielding gas were considered. At short times the weld pool was limited in area and the nitrogen content of the weld pool increased due to high nitrogen activity in the arc. At longer times the nitrogen escaped from the weld pool to the shielding gas. This flux becamethen the dominating factor due to the increased weld pool area exposed to the shielding gas. The situation then approachedthe equilibrium conditions that were expected from the gas nitrogen activity and weld pool alloy composition according to thermodynamic calculations using the Thermo-Calc database.KEYWORDS: TIG welding; welding; duplex stainless steels; superaustenitic stainless steel; pitting corrosion resistance, nitrogen uptake; shielding gas; root gas composition.

Advances in Physical Metallurgy and Processing of Steels. The Influence of Nitrogen on Microstructure and Properties of Highly Alloyed Stainless Steel Welds.

“…16) A value of k 1 ϭ10 gave a good fit to the experimental results. Support for this value was also given by Bandopadhyay et al and Hertzman et al 27,31) The nitriding capacity of the plasma is thus about ten times larger than a molecular gas of the same composition.…”

“…Kokawa. 31) Cross et al 32) found that 250 ppm contamination of oxygen in the shielding gas increased significantly the weld metal nitrogen content in welding of duplex stainless steels under hyperbarric conditions. Hertzman and Wessman 33) investigated plates from five stainless steels including the duplex 2205 the super duplex SAF 2507 and the super austenitic 654 SMO.…”

Porosity and Nitrogen Content of Weld Metal in Laser Welding of High Nitrogen Austenitic Stainless Steel

“…19,20) The nitrogen flux between the weld pool and plasma is determined by the activity difference between them, and the direction of the nitrogen flux will be towards regions with lower nitrogen activity. 8,21) The nitrogen activity of the plasma is mainly determined by the nitrogen partial pressure in the plasma in this case, which is related to the nitrogen content in the shielding gas. The nitrogen activity of the plasma increases with the increase of the nitrogen content in the shielding gas.…”

“…Some problems will probably occur in welding of HNS, such as nitrogen loss, nitride, hot cracking and so on. [7][8][9][10][11][12] The nitrogen loss in the weld metal consists of the nitrogen desorption and nitrogen pore. Because high properties are attributed to high nitrogen content, the nitrogen loss in the weld metal will result in the decrease of mechanical properties during welding of HNS.…”

Σχέση Μικροδομής - Ιδιοτήτων Σε Υπερωστενιτικούς Ανοξείδωτους Χάλυβες

“…Οι αυξθμζνεσ τιμζσ ολκιμότθτασ δίνουν τθ δυνατότθτα μεγάλθσ ψυχρισ παραμόρφωςθσ *20+, ενϊ ςτισ ιδιότθτζσ τουσ πρζπει να προςτεκεί και θ πολφ καλι ςυγκολλθςιμότθτα, ιδιότθτα απαραίτθτθ ςχεδόν ςε όλεσ τισ εφαρμογζσ ενόσ μοντζρνου υλικοφ [21][22][23][24][25]. Κφρια κραματικά ςτοιχεία των υπερωςτενιτικϊν χαλφβων, εκτόσ των αυξθμζνων ποςοςτϊν χρωμίου και νικελίου, είναι το μολυβδαίνιο και το άηωτο, ενϊ διατθρείται πολφ χαμθλά το ποςοςτό του άνκρακα.…”