Steels can exhibit a wide variety of properties depending on composition as well as the phases and micro-constituents present, which in turn depend on the heat treatment.
The basis for the understanding of the heat treatment of steels is the Fe-C phase diagram. It actually includes two diagrams; the stable iron-graphite diagram and the metastable Fe-Fe3C diagram. The stable condition usually takes a very long time to develop, especially in the low-temperature and low-carbon range, and therefore the metastable diagram is of more interest.
Category Archives: Heat Treatment
Precipitation Hardening of Aluminum Alloys
Precipitation hardening, or age hardening, provides one of the most widely used mechanisms for the strengthening of metal alloys. The strongest aluminum alloys (2xxx, 6xxx and 7xxx) are produced by age hardening.
In order for an alloy system to be able to be precipitation-strengthened, there must be a terminal solid solution that has a decreasing solid solubility as the temperature decreases. The precipitation-hardening process involves three basic steps: solution treatment, quenching and aging.
Strain Ageing of Steel: Part Two
Strain ageing can have a serious detrimental effect on low carbon structural steels and so two material examples are examined to see how different pre-strain and ageing conditions affect material mechanical properties.
A carbon steel (40% martensite) and a microalloyed steel (20% martensite) were both treated under the same parameters and then the UTS and stress strain curves were evaluated to gain some valuable conclusions.
Strain Ageing of Steel: Part One
Strain ageing of steel was first observed during the 19th century when the maximum load carrying capacity of a test piece was increased after it had been retested after a previous series of testing in the plastic range.
General acceptance has been recognized that strain ageing is due to the diffusion of carbon and/or nitrogen atoms in solution to dislocations that have been generated by plastic deformation however the resulting characteristics are the result of a complex series of metallurgical reactions.