The Nitrocarburizing Process: Part One

Nitrocarburizing, by definition, is a thermochemical treatment that is applied to a ferrous object in order to produce surface enrichment in nitrogen and carbon which in turn form a compound layer.
The composition, function and control of the furnace atmosphere are of crucial importance for the result of all hardening and thermochemical operations. Continue reading

Semi-Solid Rheocasting of Alumina Alloys: Part One

Aluminum is well established at the front of the pack with regards to providing the technological answer to the increasing challenges of light weighting whilst maintaining integrity of the material for the desired applications.
Semi solid rheocasting is a development within the casting sector which enables improved quality in die casting without increasing cost. Continue reading

Intercritical Annealing of Ductile Iron: Part One

Heat treatment can be performed on ductile iron to increase strength, wear resistance, ductility, toughness, and/or improve machinability by controlling the matrix microstructure. In F, an intercritical heat treatment starts with partial austenitization in the intercritical region where ferrite and austenite are present. The amount of austenite depends on the chemistry of the alloy and the temperature. Continue reading

Principles of Heat Treating of Steels

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.

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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.

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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.

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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.

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