The different grades of malleable iron are essentially the result of different heat treatments. Just as a medium carbon steel can be heat treated to a wide range in properties so can malleable iron, but malleable is even more versatile. The combined carbon content, on which heat treatment depends, can be adjusted from none, as when the microstructure is entirely ferritic, to that of a fully pearlitic structure. Read more
An important group of alloyed irons that fall outside of the ordinary types of Alloy Die castings have been designated the white and high alloy irons, or the special irons. The high alloy irons are considered separately because their alloy content exceeds 3% and they cannot be produced by ladle additions to irons of otherwise standard compositions.
The high alloy irons are usually produced in foundries that are specially equipped to produce the highly alloyed compositions. These irons are often melted in electric arc or induction furnaces, which provide for precise control of composition and temperature. The high alloy irons are sold at premium prices and are expected to outperform ordinary compositions in applications that involve severe service conditions. The foundries that produce these irons may be equipped with heat treating furnaces and quenching equipment or cooling facilities to provide for the most economical use of alloys. Read more
A Basic Guide to Choosing Aluminum Casting Alloys Part 2
Alloys 319.0, A319.0, B319.0 & 320.0
Alloys 319.0 and A319.0 exhibit very good castability, weldability, pressure tightness and moderate strength. They are very stable alloys (i.e., their good casting and mechanical properties are not affected seriously by fluctuations in the impurity content). Alloys B319.0 and 320.0 show higher strength and hardness than 319.0 and A319.0 and are generally used with the permanent mold casting process. Characteristics other than strength and hardness are similar to those of 319.0 and A319.0. Read more
The mechanical properties of alumi- num casting alloys are obtainable only if the chemical and heat treating specifications are followed carefully. It should be noted that the properties obtained from one particular combination of casting alloy, foundry practice and thermal treatment may not necessarily be identical to those achieved with the same alloy in a different foundry or with a different thermal treating source. In all aluminum casting alloys, the percentages of alloying elements and impurities must be controlled carefully. If they are not, characteristics such as soundness, machinability, corrosion resistance and conductivity are affected adversely. Read more
Ductile iron is characterized by having all of its graphite occur in microscopic spheroids. Although this graphite constitutes about 10% by volume of ductile iron, its compact spherical shape minimizes the effect on mechanical properties. The graphite in commercially produced ductile iron is not always in perfect spheres. It can occur in a somewhat irregular form, but if it is still chunky as Type II in ASTM Standard A247, the properties of the iron will be similar to cast iron with spheroidal graphite. Of course, further degradation can influence mechanical properties. The shape of the graphite is established when the metal solidifies, and it cannot be changed in any way except by remelting the metal. Read more
Microscopically, all gray irons contain flake graphite dispersed in a silicon-iron matrix. How much graphite is present, the length of the flakes and how they are distributed in the matrix directly influence the properties of the iron.
The basic strength and hardness of the iron is provided by the metallic matrix in which the graphite occurs. The properties of the metallic matrix can range from those of a soft, low carbon steel to those of hardened, high carbon steel. The matrix can be entirely ferrite for maximum machinability but the iron will have reduced wear resistance and strength. An entirely pearlitic matrix is characteristic of high strength gray irons, and many castings are produced with a matrix microstructure of both ferrite and pearlite to obtain intermediate hardness and strength. Alloy additions and/or heat treatment can be used to produce gray iron with very fine pearlite or with an acicular matrix structure. Read more