Integrity Assessment of Grade 92 Welded Joint under Creep Condition

Abstract

Integrity of tempered martensitic grade 92 (9Cr-1.8W-0.5Mo-VNb) steel welded joint has been assessed by carrying out creep test at 923 K over a wide stress range. The failure location in the joint was found to shift from base metal to heat affected zone (HAZ) of the weld joint with decrease in applied stress. The HAZ of the weld joint consisted of coarse prior-austenite grain (CGHAZ), fine prior-austenite grain (FGHAZ) and intercritical (ICHAZ) regions in a sequence from the fusion boundary to unaffected base metal. The failure was associated with localized creep deformation coupled with creep cavitation. To have a better insight to the creep failure behaviour of the joint, the different microstructural constituents of HAZ of the joint has been simulated. Creep and tensile tests were carried out on the simulated HAZs specimens. The steel suffered degradation in creep rupture strength on subjecting heating in the intercritical (between Ac 1 and Ac 3 ) (ICHAZ) as well as at temperature just above the Ac 3 (FCHAZ). The extensive creep cavitation has been observed in the simulated FGHAZ of the joint. Similarly, localized extensive creep cavitation and precipitation of tungsten rich Laves phase has been observed in the FGHAZ of the weld joint. This caused the type IV failure in the FGHAZ of the weld joint. The integrity of grade 92 steel joint under creep condition is governed by the above microstructural modifications of the steel in HAZ by weld thermal cycle.

Characterisation of aluminium diffusion coatings elaborated on austenitic stainless steels and on ferritic-martensitic steels

“…The nitrogen in the interstitial sites of the matrix contained in the HR3C alloy combined with 0.4Nb, 25Cr and 20Ni (wt%) additions represent an effective measure of the enhancement of creep strength [8,13]. The P92 ferritic martensitic alloy is one of the most commonly employed high Cr creep resistant steels in large components of USC units because of its high creep rupture strength, its excellent mechanical properties, its good weldability, its low thermal expansion, its high thermal conductivity and its adequate corrosion resistance [8,[14][15][16][17]. However, despite the good properties of these three alloys, they need to be coated in order to enhance their lifetime at higher temperatures and pressures.…”

Residual stress analysis, microstructural characterization, and mechanical properties of tungsten inert gas-welded P92/AISI 304L dissimilar steel joints

“…The main composition of P92 steel is Cr: 9%, W: 1.8-2%, Mo: 0.5%, and B: 0.002-0.005 wt.%. 3 The other alloying elements in P92 steel are C, V, Mn, Nb, Ni, N, and Si. 4 The optimum combination of the W and Mo is required to get the maximum creep strength and low amount of δ ferrite.…”

Influence of microstructure on cavitation in the heat affected zone of a Grade 92 steel weld during long-term high temperature creep

“…The premature creep failure occurred in the HAZ is a known problem to 9% Cr steel welds, in which creep cavitation preferentially takes place in the HAZ regions that are close to the boundary with the parent metal [4,5,8,9]. The effect of microstructure on creep cavitation has been extensively investigated to understand the factors contributing to the formation of cavities in the HAZ.…”