Microstructural changes produced by hot forging in a C300 Maraging Steel

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.  

About the author

Gabriel Mauricio Castro Güiza received his bachelor degree in Mechanical Engineering at Universidad de los Andes (Bogotá – Colombia, 2012) and his master’s degree in Materials Science and Engineering at Universidade Federal de Santa Catarina (Florianópolis – Brazil, 2015).

During his undergraduate studies, G.M. Castro Güiza worked as a teaching and research assistant in the areas of Materials Science and Failure Analysis. Also, he has published two research papers in academic journals, two articles in industrial magazines and has contributed with 15 papers to several conferences around the world. Currently, he is finishing his studies in Chemical Engineering at Universidad de los Andes and is working as an independent researcher in Metallurgy, Materials Science and Engineering and Failure Analysis in Colombia.  

About the author

Prof. Carlos Augusto Silva de Oliveira received his bachelor degree in Metallurgical Engineering from Universidade Federal Fluminense (1979), his master’s degree in Metallurgical Engineering from Pontifical Catholic University of Rio de Janeiro (1985) and his Ph.D. in Metallurgical and Materials Engineering from Federal University of Rio de Janeiro, Brazil (1994).

From May 2008 to May 2012, Prof. C.A.S. Oliveira was chair of the graduate program in Materials Science and Engineering from Federal University of Santa Catarina (UFSC). He is currently vice-chair of the same program and professor of UFSC. He was also a volunteer contributor of the Brazilian Association of Metallurgy, Mining and Materials (ABM), between 2002 and 2011, acting in this period as chair and vice-chair of the technical division of Santa Catarina State and as teaching division chair. He has experience in the area of Materials and Metallurgical Engineering, with emphasis in Mechanical Forming, acting on the following topics: heat treatment and forming.

 

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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