Search Results for acicular ferrite

This article discusses the metallurgical aspects of underwater welds. It describes the microstructural development, which mainly includes three types of ferrite associated with low carbon steel weld metal: grain-boundary ferrite, sideplate ferrite, and acicular ferrite. The article explains the factors that affect heat-affected zone (HAZ) cracking. These include hydrogen from the weld pool, microstructures that develop in the HAZ, and stress levels that develop in the weld joint. The article describes the welding practices that can reduce residual stresses. It explains the effect of water pressure on the formation of porosity in underwater gravity welding. The article concludes with a discussion on the practical applications of underwater welding.

Two high-strength low-alloy (HSLA) families, acicular-ferrite steels and pearlite-reduced steels, contain microalloying additions of vanadium and niobium. Vanadium, niobium, and titanium combine preferentially with carbon and/or nitrogen to form a fine dispersion of precipitated particles in the steel matrix. This article summarizes the metallurgical effects of vanadium, niobium, molybdenum, and titanium. The metallurgical fundamentals were first applied to forgings in the early 1970s. The ultimate strength of first- and second-generation microalloy steels is adequate for many engineering applications, but these steels do not achieve the toughness of conventional quenched and tempered alloys under normal hot-forging conditions. Third-generation microalloy steels differ from their predecessors in that they are direct quenched from the forging temperature to produce microstructures of lath martensite with uniformly distributed temper carbides. Without subsequent heat treatment, these materials achieve properties, including toughness, similar to those of standard quenched and tempered steels.

The transformation of austenite of cast irons represents a more complex and less studied subject. This article discusses the general features of the decomposition of austenite into bainite. It describes the heat treatment cycles of austempered cast iron microstructure. The article reviews several factors, such as presence of graphite and austenite grain size, which affect the transformation rate of austenite during austempering of free-graphite cast irons.