The 9% Cr steels were developed for ultra-supercritical (USC) power plants to meet the requirements of high operating temperature and pressure. These steels are produced to operate at high temperatures where impact toughness is not a concern; however, it becomes important for the welded joints to have good impact toughness at room temperature for manufacturing. The present work investigates the effect of the post-weld heat treatment (PWHT) parameters, i.e., temperature and time, on the impact toughness of multi-pass gas tungsten arc welded (GTAW) joints of ferritic/martensitic grade P92 steel. The microstructural evolution in welded joints given varying post-weld temperatures and times was studied. The lath martensitic structure of the weld metal for the as-welded joints resulted in high hardness and low impact toughness. The weld fusion zone toughness was 12 J, which was lower than the minimum specified values of 41 J (ASME standards) and 47 J (EN ISO 3580:2017). The PWHT temperature and time were found to have a significant effect on the impact toughness of the weld metal. A drastic increase in the impact toughness of the weld metal was noticed, which was attributed to lath break-up, reduction in dislocation density and reduction in solid solution hardening. The maximum impact toughness of 124 J was measured for PWHT temperature and time of 760 °C and 120 min, respectively. The effect of PWHT parameters on tensile strength was also investigated, and test results showed that the joint was safe for USC boiler application as it failed from the region of the P92 base metal. The variation in microstructural evolution along the weldments resulted in hardness variation. PWHT led to homogeneity in microstructure and, ultimately, reduction in hardness value. According to the study, the optimum temperature and time for PWHT of a GTAW joint of P92 steel were found to be 760 °C and 120 min, respectively.

The sun’s atmosphere is frequently disrupted by coronal mass ejections (CMEs) coupled with different solar happening like sun spot number (SSN), geomagnetic storms (GMS), solar energetic particle and solar flare. CMEs play the important role in the root cause of weather in earth’s space environment among all solar events. CMEs are considered as the major natural hazardous happening at the surface of sun because this event can cause several other phenomena like solar flare and many more. In this work, we report a statistical observation for the relationship of CMEs having linear speed >500 km/s with SSN and solar flares that were registered during the period 1997-2015. Test results of the annual correlation between SSN and CMEs is 0.77 and can be represented by a linear regression equation. We concluded that SSN and solar flares are well correlated with CMEs in most of the yearly compiled data for this time span.

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Geomagnetic storm (GMs) is a significant unsettling influence of Earth's magnetosphere that happens when there is an extremely productive trade of energy from the solar wind into the space climate encompassing Earth. Storms result from variations in the solar wind that produces significant changes in the flows, plasmas, and fields in Earth's magnetosphere. A southward directed solar wind magnetic field at the dayside of the magnetosphere is responsible to create GMs, large GMs are associated with coronal mass ejections (CMEs) also. In this work we take the GMs of magnitude ≤ -100 nT and CMEs having velocity more than 1000 km/s from 2010-2020. During this time span we have noted 28 geomagnetic storms (GMs).To analyze the GMs with other solar activities (Flares & CMEs) conducted a statistical analysis of the data of the Dst (disturbance storm time) index of Geomagnetic storms and Solar flare flux and CMEs. We found the low positive correlation between Dst index and the solar flare flux with correlation coefficient 0.21. We also found a correlation between the Dst index with different classes of flares (X and M), there is a strong positive correlation between Dst index and X class solar flare having coefficient 0.97, further the correlation of Dst index and M class flare is very low with correlation coefficient 0.04. We found that the CMEs are negatively correlated with Dst index with correlation -0.09. The present result implies that the geomagnetic storms formation dependent on the flares particularly x class but does not on the CMEs during the time taken.

Abstract