The fact that the microstructure of steel depends on its composition and the heat treatment given to it has been heavily exploited in the design of steel for power plant applications. To obtain a steel that can function at the higher temperature where power plants operate without failure for extended life, heat treatment is needed to produce fine and highly stable dispersion of carbides, nitrides, and intermetallic compounds in the microstructure of the material. A significant contribution also comes from solid solution strengthening by substitutional solutes. We review here various types of phases, microstructures, functions, and interacting effects of the various alloying elements in the design of steel for modern power plant application.

This paper presents a study on the effect of microstructure on the fatigue crack growth (FCG) rate in advanced S355 marine steels in the Paris Region of theda/dNversus ΔKlog–log plot. The environments of study were air and seawater (SW), under constant amplitude sinewave fatigue loading. Fundamentally, three phenomena (crack tip diversion, crack front bifurcation and metal crumb formation) were observed to influence the rate of FCG. These phenomena appear to be a function of the material microstructure, environment and crack tip loading conditions. The three factors retarded the crack growth by reducing or redistributing the effective driving force at the main active crack tip. A crack path containing extensively the three phenomena was observed to offer strong resistance to FCG. In SW, the degree of the electrochemical dissolution of themicroplastic zoneappears to be an additional primary factor influencing FCG in the steels.

The increasing need for materials and steel in particular for specific applications has led to development of theories, models, software, and practices which are now of immense value in the design of steel. The world stood still recently as the first bulk nanostructured metal was produced by Tata Steel and Rolls Royce Plc. This underscores the strategic position of steel in propelling technology. This paper reviews the theories, development, properties and application of this class of iron alloys in engineering design.

This work investigated the effect of cold wire gas metal arc welding (CW-GMAW) on the heat-affected zone (HAZ) and mechanical properties of structural steel designated as BS 970 Part 3:1991 080A15 steel. The study involved feeding cold ER70S-6 wire into the welding arc of energised hot wire (HW). Welds were produced at cold wire feed speeds (CWFS) of 2, 4, and 6 m per min labelled CW2, CW4, and CW6, and were compared with conventional welds (CW0) and the parent metal (PM). Metallographic examination, hardness testing, and cross joint tensile evaluation were carried out. Cold wire (CW) addition resulted in a more gradual cooling profile which increased the width of heat-affected sub-zones particularly the grain refined zone (GRZ). Hardness decreased across all weld zones with increasing CWFS indicating improved ductility and reduced potential for brittle phase formation. Although the 0.2% proof stress reduced by about 16% relative to the parent metal (PM), the tensile strength at CW6 approached that of the base material. Ductility loss of 35% in CW0 reduced to 22% in CW welds representing a 13-point improvement. For CW6, the tensile fracture location shifted from the partially transformed zone (PTZ) to the PM close to PTZ region confirming improved mechanical performance. However, at higher CWFS, weld penetration decreased due to reduced arc energy density. The study demonstrates that CW addition can improve ductility and tensile performance in conventional GMA welds while increasing productivity when welding parameters and joint design are optimised.