Influence of inappropriate post weld heat treatment on HAZ hardness of creep resistant steel

Glavni cilj diplomske naloge je bilo preučiti vpliv nezadostne in previsoke toplotne obdelave TVP na trdoto za jekla za povišane temperature. Najprej so predstavljena sodobna jekla za povišane temperature ter toplotna obdelava vzorcev s simulirano mikrostrukturo. V nadaljevanju smo izdelali vzorce TVP na simulatorju termičnega cikla Smitweld in izvedli toplotno obdelavo na temperaturi, višji in nižji od priporočene (760°C). Sledila je še analiza mikrostrukture in meritev trdote TVP. Prikazali smo odvisnost časa in temperature termične obdelave na trdoto področij grobozrnatega, finozrnatega, medkritičnega ter podkritičnega TVP. Pri nezadostni toplotni obdelavi pride do padca žilavosti pod minimalno dovoljeno vrednost, pri preveliki pa do prenizke trdote materiala.The primary purpose of my study is to determine the influence of inappropriate post weld heat treatment on HAZ hardness of creep resistant steel. First the modern steels for high temperature environments and heat treatment of samples with simulated microstructure are presented. Then the examples of HAZ on thermal cycle simulator are made. Furthermore, the heat treatment with higher and lower temperature of recommended values is made. Then we analyse the microstructure and measure the hardness of HAZ. Moreover, the temperature and time dependence of thermal treatment on hardness of heat affected zones is shown. The results indicate that the unsufficient heat treatment means a mass reduction of impact toughness of steel. On the other hand oversufficient post weld heat treatment leads to reduction of hardness in welded joint