Nitrogen Absorption and Microstructure of Duplex Stainless Steel Weld Metal.

Abstract

A type 329J1 duplex stainless steel was welded by gas tungsten arc welding in argon-nitrogen gas mixture atmospheres. The penetration depth of weld metal increased with an increase of the nitrogen partial pressure of atmosphere. No porosity was observed in the weld metals. The nitrogen content and microstructure of the weld metal were studied. The nitrogen content increased and the ferrite content decreased with an increase of the nitrogen partial pressure of atmosphere. The ferrite content decreased linearly with an increase of nitrogen content. Fine chromium nitride precipitates were

Morphological Characteristics of Widmanstätten Austenite Formed in Laser Beam Welds of Lean Duplex Stainless Steels

“…1(a). Widmanstätten austenite precipitates along the grain boundary austenite, and it grows from the boundary to ferrite grain by maintaining a specific direction like the K-S relationship and grows up by obtaining the nitrogen in ferrite 7,8) . Therefore, the substances like chromium nitride, which also require nitrogen for precipitation and growth, are almost impossible to precipitate near the grain boundary austenite and at the end of the Widmanstätten austenite.…”

Effects of Welding Velocity and Short Time Post Weld Heat Treatment on Precipitation of Austenite in Laser Beam Welds of Duplex Stainless Steels

“…二相ステンレス鋼は，従来よりも優れた機械的性質及び 耐食性を有することから，化学プラント，海洋関連装置， 熱交換器など，種々の腐食環境にさらされる設備，機械に 幅広く使用されている．さらに，近年では水門等のインフ ラ設備等に適合するため，経済性とのバランスをとれる新 鋼種である省合金二相ステンレス鋼なども開発され実用化 されている [1][2][3][4][5] ．二相ステンレス鋼を構造材料として用いる 場合の課題として，溶接過程において溶接部での相比が崩 れ，とくに入熱量が大きい場合，著しくフェライト相量が 増加することから，鋼種の特性が劣化する可能性もあり， 十分な機械的特性，耐食性が発揮されない可能性があるこ とが挙げられる [6][7][8][9] ．これらの現象に関して議論した例には， 従来法による二相ステンレス鋼の溶接部に置いて，置換型 元素らは母材のような分配を起こさず，オーステンナイト 相の成長は窒素濃度から律速されるとの報告がある [10][11][12] ．さ らに，窒素を添加した溶接材及び窒素雰囲気での溶接も検 討されている [3][4][5][6][7][8][9][10][11][12][13][14][15] ．しかし，近年，実施工への応用が期待さ れているレーザ溶接法を種々の二相ステンレス鋼に適用し た事例については未だ十分には検討されていない [16][17][18] When conventional arc welding methods welded various kinds of duplex stainless steels, it is well known that the ferrite phase was enriched in welds. Notably, in the case of laser beam welding (LBW), due to high energy density and welding velocities, the phase balance might be remarkably changed from that in the base material.…”

Potential of grain boundary engineering to suppress welding degradations of austenitic stainless steels

“…Transmission electron microscopy studies have proved that low S CSL boundaries require longer time for 3 Corrosion rates of 304 BM and 304 GBEM sensitised during ferric sulphate-sulphuric acid test 14 Kokawa Potential of GBE to suppress welding degradations intergranular chromium carbide precipitation and corrosion than random boundaries in 304 austenitic stainless steel. [6][7][8] This suggests that GBE has a high potential to inhibit the weld decay caused for a short time exposure to the sensitisation temperature range in welding thermal cycles. 7 The 304 GBEM with optimised GBCD is expected to have a strong resistance to weld decay during arc welding.…”

“…Transmission electron microscopy studies have proved that low Σ CSL boundaries require longer time for intergranular chromium carbide precipitation and corrosion than random boundaries in 304 austenitic stainless steel 6 –. 8 This suggests that GBE has a high potential to inhibit the weld decay caused for a short time exposure to the sensitisation temperature range in welding thermal cycles 7.…”

“…Grain boundary studies have revealed that grain boundary phenomena strongly depend on the grain boundary structure and characteristics, and that low energy grain boundaries such as coincidence site lattice (CSL) boundaries have strong resistance to intergranular degradations, as contrasted with high energy random boundaries. [3][4][5][6][7][8] The concept of 'grain boundary design and control' 9 has been developed and refined as grain boundary engineering (GBE). [10][11][12] Grain boundary engineered materials which are characterised by high frequencies of CSL boundaries are resistant to intergranular degradations of materials.…”