Although one of the most hotly debated microstructure topics, control of bainitic transformation can lead to a range of diversified gains over the mechanical properties of the finished product.
Specific studies of the relationship between cooling rate and finished cooling temperature show interesting findings related to the distribution of granular bainite, martensite-austenite constituent, bainitic ferrite, and polygonal ferrite.
Although extrusion processes vary considerably in detail, they are identical in principle. The press consists of the die, a pressure cylinder, the ram, and a container which receives the preheated ingot, or billet, to be extruded. The billet to be extruded is placed in the cylinder which is closed at one end by the die and at the other end by the ram. The metal is forced, by ram pressure, through the die, taking the shape of the orifice in the die.
Creep is defined as the time-dependent strain that occurs under load at elevated temperature and operates in most applications of heat-resistant high-alloy castings at normal service temperatures. In time, creep may lead to excessive deformation and even fracture at stresses considerably below those determined in room temperature and elevated-temperature short-term tension tests.
With weathering steel, the specific alloying elements in the steel produce a stable rust layer that adheres to the base metal. This rust ‘patina’ develops under conditions of alternate wetting and drying to produce a protective barrier, which impedes further access of oxygen and moisture.
The anticorrosive properties of weather resistant steel are better than those of other structural steels in many applications. This steel is self-protecting: the rust layer on the surface becomes a tight oxide layer that slows down the progress of corrosion.