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Study on narrow gap welding of martensitic grade P92 and austenitic grade AISI 304L SS steel for ultra-supercritical power plant application

Dak Gaurav, Khanna Navneet, Pandey Chandan

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e14, 2023

EN

The present work investigated the microstructural feature, mechanical properties, and residual stress variation for the dissimilar welded joints (DWJs) of P92 and AISI 304L steel. The multi-pass DWJs were attempted for narrow gap geometry using the tungsten inert gas (TIG) welding process employing the ERNiCrMo-3 filler metal. The martensitic microstructure produced in the P92 HAZ region after welding is brittle due to quenched martensite and the dissolution of precipitates. Thus, the post-weld heat treatment (PWHT) known as tempering was carried out at 760 °C for a period of 2 h to get tempered martensitic microstructure and re-precipitation of dissolved precipitates. The radiographic examination and macrostructure analysis showed defect-free P92/304L SS DWJs. The weld metal showed the complete austenitic microstructure with a Ni weight percentage of 36%. However, segregation of the alloying elements along with the inter-dendritic areas and variation in grain growth during solidification was observed. There is columnar grain morphology at interface, cellular, and equiaxed in the center. The major segregation along the inter-dendritic areas was observed for Nb, Mo, Ti, and Cr that led to the formation of the carbides of type Mo6C, TiC, and NbC, which was confirmed from the energy dispersive spectroscopy (EDS) analysis. From the tensile test result, 304L SS base metal (BM) was inferred as the weakest region in P92/304L SS DWJs. The ultimate tensile strength (UTS) of the as-weld joint was about 626 MPa, along with fracture location in 304L SS base metal. The Charpy impact test results showed that the region with relatively poor impact toughness was austenitic ERNiCrMo-3 filler weld (57 J) which might be due to the segregation of the Nb and Mo along the inter-dendritic areas. However, the impact toughness of the ERNiCrMo-3 filler weld met the minimum requirement of 47J (EN ISO 3580:2017). The micro-hardness result showed that in the as-welded condition, the coarse grain heat affected zone (CGHAZ) has the highest micro-hardness value (340 HV) due to the high weight percentage of Cr and N resulting from the dissolution of M23C6 precipitates followed by the fine grain heat affected zone (FGHAZ, 270 HV), and the inter-critical heat affected zone (ICHAZ, 205 HV). After PWHT, the hardness value was decreased below the maximum allowable value of 265 HV due to the tempering of the martensite. The residual stresses developed in the case of the narrow groove design were less due to the less quantity of weld metal available for volumetric contraction in the case of the narrow groove geometry. The tensile stress was dominant in the weld fusion zone due to the volumetric contraction of the weld metal, while compressive stress was dominant in P92 HAZ because of the martensitic phase transformation.

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Zastosowanie metody spawania wąskoszczelinowego w energetyce

Cecotka M., Wnuk M.

Przegląd Spawalnictwa

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2014

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R. 86, nr 7

17--21

PL

Metoda spawania wąskoszczelinowego ma te zalety w stosunku do standardowego spawania łukiem krytym, że z uwagi na ma przekrój rowka pod spoinę mniejsza jest objętość spoiny, co wiąże się ze zmniejszeniem zużycia materiału dodatkowego, energii oraz krótszym czasem wykonania złącza. Dodatkowo w wariancie spawania wąskoszczelinowego, wdrożonym i stosowanym w Wydziale Produkcji Warsztatowej Elektrowni Bełchatów, dzięki opanowaniu ciągłego, jednoetapowego wykonywania spoiny, wyeliminowano występującą w tradycyjnej technologii fazę wstępną, a tym samym uniknięto ryzyka jej wpływu na jakość złącza spawanego.

EN

Advantages of narrow-gap welding method, compared with normal hidden arc welding: – due to more narrow weld groove, weld volume is lesser, – lesser welding material consumption, – lesser energy consumption and welding time. Additionally, in narrow-gap welding method, implemented and used in Belchatow Power Station by know-how of continuous, one stage weld making, preliminary stage in traditional technology was eliminated, and by this, risk of preliminary welding stage influence for welded joint quality was excluded.

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Spawanie wąskoszczelinowe szyn elektrodami otulonymi

Stembalski S., Banach J.

Przegląd Spawalnictwa

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2000

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R. 72, nr 2-3

10-17

PL

Przedstawiono problemy występowania podczas spawania wąskoszczelinowego pęknięć gorących i zimnych w konstrukcjach dźwignicowych i kolejowych. Wyniki badań wykazały konieczność w przypadku spawania dźwignic zastosowania dwóch rodzajów elektrod zasadowych oraz zasadowych z chromem.

EN

Problems of hot and cold cracks arising in crane and railway structures during narrow-slit welding. The test results have revealed that for welding crane structures it is necessary to two kinds of electrodes: basic and basic with chromium.