Development of NiCrSiBC Weld Hardfacing Approach for P91 Steels Used in Steam Turbine Components

Abstract

P91 steels are used as substrate material for steam turbine components like bush, valve seat internals, and engineering valves. These components have hardfacing of cobalt-based material to reduce the high temperature wear loss and to improve the surface hardness. However, delamination failure and higher heat affected zone (HAZ) hardness were identified challenges for P91 steels. Hence, this demands the development of a suitable weld hardfacing approach to resolve the said challenges. In this work, NiCrSiBC (Colmonoy 6) has been considered as a hardfacing material to replace cobalt-based Stellite 6 material due to elimination of radiation activity, lower cost, and higher coating hardness. FCAW and PTA techniques were used to deposit buffer layer (SS-309L) and hardfacing layer (NiCrSiBC) respectively. Sample WBL (with deposition of buffer layer) and sample WOBL (without deposition of buffer layer) are considered approaches to study the metallurgical characterization for each case. Higher coating hardness, lower HAZ hardness and lower Fe dilution were observed in sample WBL. Cr7C3, Cr2B, and Cr5B3 hard phases in block shape together with ϒ- nickel matrix solid solution was observed in coating region of sample WBL. Overall, sample WBL approach was considered to overcome weld hardfacing challenges for steam turbine industries.

Spark Plasma Sintering of NiCrSiBC Alloys

“…In all sintered samples, in addition to nickel, the presence of several important phases, such as borides (CrB, Ni 2 B, Cr 2 B, Ni 3 B, and Cr 5 B 3 ), as well as Cr 7 C 3 chromium carbide. The phases verified in the XRD analysis of the bodies sintered by SPS are the same obtained in the diffractograms of the initial powders, which is in perfect agreement with the works [11,21,22].…”

Влияние термической обработки на структуру и свойства наплавки NiCrSiBC на сталь P91

“…1. Òåõíîëîãè÷åñêèå ïàðàìåòðû ïðîöåññîâ íàíåñåíèÿ áóôåðíîãî (SS-309L) è èçíîñîñòîéêîãî (NiCrSiBC) ñëîåâ, âûáðàííûå íà îñíîâå ïðîáíûõ ýêñïåðèìåíòîâ è ëèòåðàòóðíûõ äàííûõ [10,17], ïðåäñòàâëåíû â òàáë. 2 è 3 ñîîòâåòñòâåííî.…”

“…Óñëîâíîå îáîçíà÷åíèå îáðàçöîâ â ýòèõ ñîñòîÿíèÿõ -PW 0 , PW 1 è PW 2 ñîîòâåòñòâåííî. Äëèòåëüíîñòü âûäåðaeêè ïðè òåðìè÷åñêîé îáðàáîòêå âûáèðàëè íà îñíîâå äàííûõ [3,5,17].…”