A comprehensive study on the microstructure and mechanical properties of arc girth welded joints of spiral welded high strength API X70 steel pipe

In the paper, the effect of welding technology on the microstructure and mechanical properties of girth welded joints was presented. Metallographic examinations based on light microscopy and SEM were conducted on girth welded joints of API X70 steel pipe. Research has shown that microstructure of the heat-affected zone (HAZ) of MMA girth welded joints is not homogeneous and depends on the thermal history of each area during the welding process. Near the fusion line the zone is coarse, and further away there is a fine-grained zone. In the area of root passes the microstructure consists of recrystallized ferrite grains unlike to cap passes where the fine bainitic microstructure can be observed. In the case of MAG girth welded joints, the weld microstructure consists of primary austenite grains. The primary austenite boundaries serve as nucleation sites of ferrite. The microstructure of the HAZ varies continuously from a coarse—to fine-grained microstructure of the base material. The results of mechanical properties of girth welded joints are also presented. The hardness and strength of arc welded joints depend on welding filler materials as well as welding technology. The results of hardness distribution of MMA and MAG girth welded joints confirmed the results of microstructural evaluation

Osobliwości spawania łukowego metodą A-TIG tytanu i jego stopów

The paper contains the findings of investigation of the impact of activating flux and selected fluorides on A-TIG welding of Grade 2 titanium. The paper also presents the dimensions and macrostructure of welds and describes welded joints produced with BC-Ti activating flux as well as the mechanical properties such as strength, impact energy and hardness of specific weld zones. In addition, the article contains information about performed bend tests and results of macrostructure investigation.Przedstawiono wyniki badań wpływu topnika aktywującego oraz wybranych fluorków na proces spawania metodą A-TIG tytanu w gat. Grade 2 oraz wymiary i makrostrukturę spoin. Wykonano ponadto złącza spawane z zastosowaniem topnika aktywującego BC-Ti oraz określono ich własności mechaniczne, w tym wytrzymałość, pracę łamania oraz twardość poszczególnych stref złącza, jak również przeprowadzono próby gięcia i zbadano makrostrukturę

Corrosion Resistance and Mechanical Properties of TIG and A-TIG Welded Joints of Lean Duplex Stainless Steel S82441 / 1.4662

This paper presents results of pitting corrosion resistance of TIG (autogenous and with filler metal) and A-TIG welded lean duplex stainless steel S82441/1.4662 evaluated according to ASTM G48 method, where autogenous TIG welding process was applied using different amounts of heat input and shielding gases like pure Ar and Ar+N2 and Ar+He mixtures. The results of pitting corrosion resistance of the welded joints of lean duplex stainless steel S82441 were studied in as weld conditions and after different mechanical surface finish treatments. The results of the critical pitting temperature (CPT) determined according to ASTM G48 at temperatures of 15, 25 and 35°C were presented. Three different surface treatment after welding were applied: etching, milling, brushing + etching. The influence of post weld surface treatment was studied in respect to the pitting corrosion resistance, basing on CPT temperature. Research on TIG welding of lean duplex stainless steel S82441/1.4662 showed a clear influence of the applied shielding gas mixtures, where the addition of 5 to 15% N2 to Ar virtually no effect on the level of resistance to pitting corrosion, only 5% N2 addition has a positive effect, while use of a mixture of 50% Ar + 50% He compared with welding at 100% Ar atmosphere, can significantly reduce the resistance to pitting corrosion. Definite good results were obtained during TIG welding with the participation of activation flux (A-TIG). The weld surface of lean duplex stainless S82441/1.4662 obtained in A-TIG welding without the addition of filler metal has a much lower tendency to pitting corrosion than traditional welds made by TIG method. Pitting corrosion resistance of welds made by A-TIG improved with the increase of the heat input in the tested range of welding current 100-200 A. It was also found that the intensity of the occurrence of pitting does not affect the method of cleaning welds after welding, but the mechanical removal of a thin surface layer of metal significantly reduces their intensity

Pomiary ferrytu w stali lean duplex S32101 i jej złączach spawanych

Due to their mechanical and plastic properties as well as unique corrosion resistance, two-phase lean duplex steels are increasingly popular in industrial applications e.g. for building waterside fixtures, ships, pipelines or containers. A critical factor of welded joints made of such steels is the balance between austenite and ferrite; the latter being measured by a special device called ferritoscope. The article contains the results of tests focused on measurements of ferrite content in S32101 lean duplex steel and its welded joints. The text also presents the impact of such factors as test sample thickness or shape and condition of measurement surface etc. on test results. In addition, this paper discusses the use of correction factors, describes problems arising during measurements of ferrite in welded joints and presents manners of the elimination of the latter. The conducted tests revealed that MAG method welding parameters affect the content of ferrite in butt welded joints produced with S32101 lean duplex steel.Dwufazowe stale typu lean duplex z uwagi na ich własności wytrzymałościowe i plastyczne oraz szczególną odporność korozyjną są coraz częściej stosowane w przemyśle do budowy armatury nadbrzeżnej, statków, rurociągów lub zbiorników. W złączach spawanych z tych stali bardzo ważna jest równowaga pomiędzy austenitem i ferrytem. Pomiary zawartości ferrytu wykonuje sie za pomocą np. urządzenia typu ferrytoskop. W artykule przedstawiono wyniki badań zawartości ferrytu za pomocą ferrytoskopu w stali lean duplex S32101 i jej złączach spawanych oraz wpływ na wyniki pomiarów takich czynników jak: grubość mierzonej próbki, stan i kształt powierzchni pomiarowej itp. Omówiono stosowanie współczynników korekcyjnych. Wyszczególniono problemy powstające podczas wykonywania pomiarów ferrytu w złączach spawanych oraz sposoby ich niwelowania. Przeprowadzone badania wykazały, że parametry spawania metodą MAG mają wpływ na zawartość ferrytu w doczołowych złączach spawanych wykonanych ze stali lean duplex S32101

Corrosion Resistance and Mechanical Properties of TIG and A-TIG Welded Joints of Lean Duplex Stainless Steel S82441 / 1.4662

This paper presents results of pitting corrosion resistance of TIG (autogenous and with filler metal) and A-TIG welded lean duplex stainless steel S82441/1.4662 evaluated according to ASTM G48 method, where autogenous TIG welding process was applied using different amounts of heat input and shielding gases like pure Ar and Ar+N2 and Ar+He mixtures. The results of pitting corrosion resistance of the welded joints of lean duplex stainless steel S82441 were studied in as weld conditions and after different mechanical surface finish treatments. The results of the critical pitting temperature (CPT) determined according to ASTM G48 at temperatures of 15, 25 and 35°C were presented. Three different surface treatment after welding were applied: etching, milling, brushing + etching. The influence of post weld surface treatment was studied in respect to the pitting corrosion resistance, basing on CPT temperature

Właściwości mechaniczne i mikrostruktura złączy doczołowych obwodowych rur ze stali API 5L X70 wykonanych metodami łukowymi

In the paper the results of welding of girth welded joints of steel pipe API 5L grade X70 (L485M) are presented. Manual metal arc (MMA) and metal active gas welding (MAG) were applied. Two welding filler metals for MMA were used to weld the girth welded joints and one for MAG process. The results of mechanical tests and distribution of residual stress of the girth welded joints are presented. Results indicated that MMA and MAG welding processes allowed to achieved the proper girth welded joints from the quality and mechanical properties point of view. Moreover, results of microscopic examination of welded joint, based on light microscopy are presented. In the root passes of MMA girth welded joint ferrite prevails with a grain size of several dozen micrometres. On the borders of ferrite grains, a second structural component, occurring as small islands of a few micrometres in diameter, can be distinguished, which may be either martensitic-austenitic (M/A) component, bainite or fine perlite. In the cap passes a bainitic structure was observed. In the case of MAG welded joints the weld microstructure consists of primary austenite grains, and on the primary boundaries the ferrite can be recognized. This ferrite forms a continuous phase and Widmanstätten ferrite, which lathes grow into the interior of the grains.W artykule przedstawiono wyniki badań spoin spawanych doczołowych obwodowych rur stalowych – gatunek API 5L X70 (L485M). Spoiny wykonano metodą spawania ręcznego elektrodą otuloną i spawania półautomatycznego MAG. Do spawania elektrodami otulonymi zastosowano dwa gatunki materiałów dodatkowych, natomiast do spawania metodą MAG jeden gatunek materiału. Przedstawiono analizę wyników badań właściwości mechanicznych połączeń spawanych obwodowych oraz określono rozkład naprężeń resztkowych. Stwierdzono, że procesy spawania ręcznego elektrodami otulonymi i półautomatycznego MAG pozwoliły na wykonanie spoin spełniających wymagania zarówno jakościowe, jak i właściwości mechanicznych. Wykonano badania mikroskopowe połączeń spawanych za pomocą mikroskopu świetlnego. Wykazano, że w obszarze grani (ściegi graniowe) dominuje struktura ferrytyczna o rozmiarze ziarna do kilkadziesiąt mikrometrów. Obserwowano na granicach ziaren ferrytu dodatkowe wydzielenia drugiego składnika mikrostruktury (o średnicy ziarna kilkanaście mikrometrów): wyspy martenzytyczno-austenityczne (M/A), bainit lub drobny perlit. Stwierdzono, że w obszarze ściegów licowych dominuje struktura bainityczna. Ustalono również, że w przypadku złączy spawanych półautomatu MAG mikrostrukturę cechują pierwotne ziarna austenitu o większych rozmiarach (także obserwowano na pierwotnych granicach austenitu ciągłe wydzielanie ferrytu oraz ferryt Widmanstättena o płytkach wrastających w kierunku wnętrza ziarn

Ferrite content measurement in super duplex stainless steel welds

Approaches to determining ferrite fraction (%) and ferrite number (FN) were examined for super duplex stainless steel (SDSS) welds. A reference sample was produced by bead-on-plate gas–tungsten arc welding of a type-2507 SDSS plate. By comparing different etchants and measurement practices, it was realized that etching with modified Beraha followed by computerized image analysis (IA) was the most accurate and quickest technique to measure ferrite fraction, which determined the same ferrite fraction (68.0 ± 2.6%) as that measured by electron diffraction backscattered analysis (67.6 ± 2.3%). A Round Robin test was performed on a reference sample at University West, Swerea KIMAB, Outokumpu Stainless, and Sandvik Materials Technology to investigate the repeatability of the technique. The ferrite fraction measurements performed at different laboratories showed very small variations, which were in the range of those seen when changing microscope in the same laboratory. After verification of the technique, the relationship between ferrite fraction and ferrite number (measured with FERITSCOPE®) was determined using 14 single (root) pass welds, including butt, corner, and T-, V-, and double V-joint geometries. The best-fit equation found in this study was ferrite number (FN) = 1.1 × ferrite fraction (%). To conclude, the ferrite fraction technique suggested in the present paper was accurate and repeatable, which made it possible to determine a ferrite fraction–ferrite number formula for SDSS single-pass welds.First Online: 05 December 2018</p