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Significance Statement
Maraging steels are a special kind of steels, not only due to their remarkable combination of high strength and fracture toughness, but also for their excellent formability at both cold and hot temperature regimes, when compared to carbon containing martensitic steels. However, there are few studies that analyze the effect of deformation on the properties and aging behavior of these alloys, especially in the hot working regime.
The objective of the present study was to establish the effects of hot deformation on the microstructure and aging kinetics of a C300 Maraging steel. To do so, several samples were hot forged at 950°C and 1050°C with two different height reductions. They were also compared to non-deformed specimens that were solubilized at the same temperatures. The analyses showed that work-hardened and partially recrystallized austenite we formed at 950°C and 1050°C, respectively. Both conditions transformed to a refined lath martensite after cooling to room temperature. Regarding the aging process, the
precipitation and reverted austenite formation reactions were accelerated by deformation, particularly in the samples where forging produced work-hardened austenite. As a result, the deformed specimens presented faster hardening rates during the early stages of aging, bigger and more rounded precipitates at peak hardness conditions and an increased fraction of reverted austenite during overaging.
Following these discoveries, the authors are currently working on determining the effects of hot working on the mechanical properties of this steel, in order to establish the viability of using deformation processes as alternative methods of enhancing the properties of maraging steels without significantly raising their production costs.
Journal Reference
Materials Science and Engineering: A, Volume 655, 2016, Pages 142–151.
G.M. Castro Güiza , C.A.S. Oliveira
Mechanical Engineering Department, Universidade Federal de Santa Catarina (UFSC), Campus Universitário Trindade – CP 476, CEP 88040-900 Florianópolis, SC, Brazil
Abstract
Maraging steels are special steels with high strength and high toughness. Despite their desirable properties, their applications are limited due to their high production cost. In order to discover new processes that improve the mechanical properties of this alloy, the microstructural changes induced by hot forging in a maraging C300 steel were analyzed. Prismatic samples were deformed without lubrication using several forging conditions, and then were analyzed in both the as forged and aged stages employing different techniques such as: optical microscopy, hardness testing, SEM, TEM and XRD. The experimental results showed that an important refinement of the martensite block width was obtained when hot working produced either work-hardened or partially recrystallized austenite. In addition, the specimens in which the martensite phase was produced from a work-hardened austenite hardened faster in the early stages of precipitation than non-deformed ones. Besides, the amount of austenite in the former samples was higher than the one found in the latter. These two facts suggest that a significant acceleration of the precipitation and reverted austenite formation reactions might be taking place in the samples where hot forging produced a work-hardened austenite. Finally, the slight increase in hardness produced by deformation in the as forged condition was partially eliminated during aging. This fact was probably caused by the recovery of the martensite substructure.
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