Effect of Mo concentration and aging time on the magnetic and mechanical hardness of Fe-xMo-5Ni-0.05C alloys (x = 5, 8, 11 and 15 wt. (%))

Mauro Carlos Lopes Souza,Hamilton Ferreira Gomes De Abreu,Manoel Antonio Da Fonseca Costa Filho,Sérgio Souto Maior Tavares

doi:10.1590/s1516-14392009000400009

Abstract

Changes to the microestructure during thermal aging treatment at 610 ºC in Fe-xMo-5Ni-0.05C alloys were studied for different aging times with different Mo concentrations. The heat treatment at 610 ºC induces carbide precipitation into the metallic matrix near Fe2Mo phase. The X-ray diffraction studies revealed a more intense precipitation of α-FeMo, Fe3Mo, R(Fe63Mo37) phases and MoC, Fe2MoC carbides for the alloys containing 15 and 11% Mo, respectively. This work shows that hardness and coercive force changes are function of the molybdenum content and aging time variation. Vickers hardness and coercive force both increase with the increase of molybdenum content and reach maximum values at 4 and 1h of aging, respectively.

Highlights

The alloys based on the Fe-Mo-Ni-C system used for permanent magnets may achieve similar magnetic properties to Vicalloy II (FeCoV) and other Fe-Co alloys, but are advantageous since they do not have cobalt, which is a strategic and expensive alloying element[1]
In this work the coercive force and mechanical hardness values of Fe-Mo-Ni-C alloys were compared for alloys with Mo contents 5, 8, 11 and 15 wt. (%) heat treated by aging at 610 and 650 °C
Sato et al.[11] studied the mechanism of precipitation of Fe-Mo-Ni alloys without carbon, and concluded that alloys containing less than 20% Mo and less than 5% Ni contained preferential regions in which platelet shapes were produced by nucleation and growth, and increased in number and size with the magnetic aging time

Summary

Introduction

The alloys based on the Fe-Mo-Ni-C system used for permanent magnets may achieve similar magnetic properties to Vicalloy II (FeCoV) and other Fe-Co alloys, but are advantageous since they do not have cobalt, which is a strategic and expensive alloying element[1] These alloys are ductile, and tolerate cold deformations larger than 99% without intermediary thermal treatment[2]. The magnetic and mechanical hardening of the Fe-Mo and Fe-Mo-Ni alloys are attributed to λ(Fe2Mo)[4] and/or μ (Fe7Mo6)[5] precipitation during the aging. (%) show a more intense precipitation of the αFeMo, Fe3Mo, R(Fe63Mo37) phases, and MoC, Fe2MoC carbides for alloys containing 15 and 11% Mo, respectively. This clearly shows the influence of precipitates on the magnetic properties of Fe-Mo-Ni-C alloys. In this work the coercive force and mechanical hardness values of Fe-Mo-Ni-C alloys were compared for alloys with Mo contents 5, 8, 11 and 15 wt. (%) heat treated by aging at 610 and 650 °C

Experimental

Results and Discussion

Conclusions