ORIGINAL ARTICLE Analysis of heat-affected zone microstructures of steel P92 after welding and after post-weld heat treatment Marko Dunđer 1 & Tomaž Vuherer 2 & Ivan Samardžić 3 & Dejan Marić 3 Received: 16 October 2018 /Accepted: 20 February 2019 # Springer-Verlag London Ltd., part of Springer Nature 2019 Abstract Modern thermal power plant operating on fossil fuels has to be highly efficient and should emit low levels of CO 2 . One of possible ways to fulfil these requirements is to increase thermal power plant peak service temperature. P92 steel enables service temperature of up to 650 °C. It is stronger, more resistant to creep and enables higher service temperature than P91. During welding of steam boiler components made of P92, it is important to consider proper preheating, welding and post-weld heat treatment parameters in order to avoid cracks and diminish sensitivity to creep in service. The research focused on analysis of simulated heat-affected zone (HAZ) microstructures and distribution of carbides. The FG HAZ (fine-grain heat-affected zone) (T max is 950 °C) is the most problematic when it comes to occurrence of type IV cracks, as in this zone, the average representation of carbides on PAGB is 72%, while the average representation of carbides on PAGB in the P21 steel is 58%. After the heat treatment, maximum hardness is recorded in the CG HAZ (coarse-grain heat-affected Zone) (T max is 1300 °C), where the values reached 248 HV, which was below the maximum allowable value of 250 HV. Other areas of HAZ expressed the values from 218 to 227 HV. Charpy impact test at service temperatures of 650 °C showed that the CG HAZ was the most critical immediately after welding as the energy for crack initiation was 30 J. However, after obligatory post-weld heat treatment, FG HAZ appeared to be more problematic than CG HAZ, so this research showed that the crack initiation energy value increased due to the fine-grain microstructure, yet the crack propagation energy reduced. Keywords Heat-affected zone . Martensite . Impact toughness . Carbide . Toughness 1 Introduction In order to achieve better efficiency of modern thermal power plants operating on fossil fuels, it is necessary to use materials with higher creep resistance at operating temperatures in service. The heat resistant P92 steel al- lows service temperature of up to 650 °C and bears high pressure in the range of 270 bars and is therefore usually used in conventional power plants for piping systems, where all exploitation conditions have to be fulfilled (temperature, strain, medium) [1–3]. Further ad- vantage of this material is in reduction of wall thickness because it is stronger and more resistant to creep at higher temperatures. High service temperatures and pressures require high-quality welded joints to ensure safety of equipment and personnel. Welded structures need to be designed to bear high temperatures and pres- sures during service life of over 25 years. Therefore, welding has to be performed with the utmost care. Correct welding consumables, preheating, welding pa- rameters and post-weld heat treatment (PWHT) are of great importance for prevention of premature equipment failure. Previous studies have shown that the correct choice of parameters and proper process application * Dejan Marić dmaric@sfsb.hr Marko Dunđer marko.dundjer@uniri.hr Tomaž Vuherer tomaz.vuherer@um.si Ivan Samardžić Ivan.Samardzic@sfsb.hr 1 Department of Polytechnics, University of Rijeka, Rijeka, Croatia 2 Faculty of Mechanical Engineering, University of Maribor, Maribor, Slovenia 3 Mechanical Engineering Faculty, Josip Juraj Strossmayer University of Osijek, Slavonski Brod, Croatia The International Journal of Advanced Manufacturing Technology https://doi.org/10.1007/s00170-019-03513-8