Abstract
The Hollomon-Jaffe parameter is usually used to stablish a equivalence between time and temperature in a tempering treatment, but not to predict the harness of the alloy after the treatment. In this paper this last possibility has been studied. A group of cast iron samples was annealed and cooled at different rates in order to obtain samples with three different hardness values. These samples were tempered using different times and temperatures. The Hollomon-Jaffe parameter was calculated for each case and a relationship based on a logistic function between that parameter and the final hardness was stablished. This relationship was found to depend on the initial hardness and the lowest hardness achievable.
Highlights
Introduction in Quenched and Tempered NodularThe heat treatment known as tempering, which consists in heating the hardened material to a temperature below the lower critical temperature, is a common procedure carried out after quenching in order to improve toughness and ductility of an iron alloy with martensitic microstructure, including welds [1,2,3] and the newest generations of steels [4,5]. the cost is a hardness reduction, the benefits clearly outweigh the inconveniences as the material properties are adapted to the in-service demands
The combination of a quenching and tempering treatment is technically a lot easier to perform than a quenching where the cooling rate must be accurately controlled or a certain temperature must be maintained during a certain period of time
The main aim of this work has been to study the applicability of the Hollomon-Jaffe parameter TP on the tempering of nodular cast iron after quenching, to determine the best value for the constant C and to use TP to predict the hardness of the samples after a hardening and tempering treatment. The results show this parameter is useful in the study of the tempering process over a wide range of C values and that the final hardness of the cast iron can be estimated from the initial hardness of the alloy and the HollomonJaffe parameter
Summary
Introduction in Quenched and Tempered NodularThe heat treatment known as tempering, which consists in heating the hardened material to a temperature below the lower critical temperature, is a common procedure carried out after quenching in order to improve toughness and ductility of an iron alloy with martensitic microstructure, including welds [1,2,3] and the newest generations of steels [4,5]. the cost is a hardness reduction, the benefits clearly outweigh the inconveniences as the material properties are adapted to the in-service demands. The heat treatment known as tempering, which consists in heating the hardened material to a temperature below the lower critical temperature, is a common procedure carried out after quenching in order to improve toughness and ductility of an iron alloy with martensitic microstructure, including welds [1,2,3] and the newest generations of steels [4,5]. The two main parameters of the process are the temperature and the time the material is held at that temperature, being those two parameters complementary and interchangeable. This means a lower temperature can be compensated by a longer soaking time and a higher temperature should be accompanied by a lower soaking time if the same hardness reduction is to be obtained. Several equations have been proposed as a means to study the combined effect of time and temperature and other variables [6,7,8], the most known and used worldwide is the Hollomon-Jaffe equation [9], which is expressed as: Cast Iron Using the Hollomon-Jaffe
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