Statistical evaluation of low cycle durability for alloyed structural steels_ weld metals at room and elevated temperature

The low cycle loading in parts and structures appear near stress concentrators: in the zones of geometrical parameters change, near cracks, technological, weld and foundry defects [1]. Plastic strain in these areas appears in small material volumes. The conditions of loading in these zones are very similar to low cycle loading with limited strain, because plastic strains there are limited by adjacent elastic strained zones. In case of limitation of total strain, the cyclic hardened, softened or stabile materials accumulated only fatigue damage [2]. Therefore the conditions of loading with limited total strain are similar to the loading in real parts and constructions. Weld metals of alloyed structural steels were specified according the main metal, such as 22K, 19MN5, 10ChN I M, 10GN2MFA, 12Ch2NMFA, 15 Ch2MF, 15Ch2MFA, 15Ch2MFAA, 15Ch3NMFAA, etc. used in nuclear power equipments at room and elevated (250 deg C - 350 deg C) temperature. Different kinds of processing were used to get weld metals. Some of them are: welded by manual and automatic arc methods with electrodes such as UONI 13/45, UONI 13/55, 48N10, 48N3, 48N6, EA - 855/54, etc., automatic welding with wire, such as Sv - 1 OGSMT, Sv - 10G2, Sv - 08A, Sv - 10XMFT, etc., electroslag welding. In this work all the materials were divided into three groups according chemical composition. In our previous research [3] the parameters of Coffin curves and the durability dependence on main mechanical characteristics and their combinations were investigated. In this work it was shown that fatigue curves parameters the best correlate with modified plasticity (a' cry)Z at room and elevated (250 deg C - 350 deg C) temperature, conformed according to normal distribution. Analyses of the dependence of Coffin's curves parameters on modified plasticity for Cr - Ni, Cr - Ni - Mo, Cr - Ni - Mo - V alloyed structured steels weld metals at room and elevated temperature is represented in this work. The results of the investigation of 67 weld metals at room and 37 weld metals at elevated (250 deg C - 350 deg C) temperatures were selected from laboratories of Kaunas University of Technology and other countries (Czech Republic, Russia, Hungary).