Microstructure evolution of hot-work tool steels during tempering and definition of a kinetic law based on hardness measurements

Microstructural evolutions of the 55NiCrMoV7 steel during tempering were investigated by transmission electron microscopy, scanning electron microscopy and X-ray diffraction in order to describe the main mechanisms of softening. The softening resistance is strongly associated with evolution of obsta...

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Bibliographic Details
Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2004-08, Vol.380 (1), p.222-230
Main Authors: Zhang, Z, Delagnes, D, Bernhart, G
Format: Article
Language:English
Subjects:
Applied sciences
Carbides
Engineering Sciences
Exact sciences and technology
Hardening. Tempering
Hardness
Heat treatment
Kinetic law of tempering
Martensitic steel
Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology
Metals. Metallurgy
Microstructure
Production techniques
Tempering ratio
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Summary:Microstructural evolutions of the 55NiCrMoV7 steel during tempering were investigated by transmission electron microscopy, scanning electron microscopy and X-ray diffraction in order to describe the main mechanisms of softening. The softening resistance is strongly associated with evolution of obstacles to the movement of dislocations (prior austenitic grain boundary, lath boundary, secondary carbides, etc.). Only the average size of carbides was found to be influenced by tempering conditions. Moreover, a strong correlation observed between the hardness measured after tempering and the average size of carbides showing that this easy test could in this case partially characterize the state of the microstructure after tempering. Performing hardness measurements at the as-quenched, tempered and annealed states, a kinetic law of tempering based on the work of Johnson, Mehl and Avrami has been proposed. This law was validated in the case of complex tempering and for other steels and can well describe the evolution of hardness during tempering.
ISSN:0921-5093
1873-4936
DOI:10.1016/j.msea.2004.03.067