THE INFLUENCE OF MOLYBDENUM ON THE TEXTURE AND MAGNETIC ANISOTROPY OF Fe-xMo-5 Ni-0 . 05 C ALLOYS

Diagrams ofremanent induction, Br, versus saturation induction, Bs, for Fe-5Ni-xMo0.05C alloys, where x is equal to 11%, 15% or 19%, were determined for samples 60%, 80%, 90% and 97% cold rolled and magnetically age-annealed at 610C for h. The texture evolution in those alloys was analysed as a function ofrolling reduction, by means of the orientation distribution function (ODF). The results show that a sharp 100}(110) texture component develops in the 11%-Mo alloy for rolling reductions in excess of90%. This leads to the highest values ofthe remanent induction, Br, and ofthe Br/Bs ratio for this alloy as a result of (100) directions, the easy magnetization directions, lying at 45 to the rolling direction.


INTRODUCTION
Fe-Mo-Ni alloys are highly ductile materials with magnetic properties similar to those displayed by commercial Fe-50Co-(3-14)V. Their main advantage over the latter is the absence of the expensive element cobalt. These alloys have a bcc structure from room temperature to 232 H. ABREU et al.
1200C (Jim and Tiefel, 1981) which, together with their high ductility, makes them amenable to magnetic property improvement via thermomechanical treatments. Magat et al. (1988) showed that severe cold deformation prior to magnetic aging improves the remanent induction Br and coercive force Hc of  alloys. They showed that both the textural and magnetic anisotropies are a result of the cold deformation introduced in these alloys. Tavares et al. (1994) showed that the addition of 0.12% carbon improves Br and Hc but the alloys become brittle, probably as a result of grain boundary carbide precipitation. Jim and Tiefel (1981), studying Fe-Mo-Ni alloys, found very low values of He for the compositions with low Mo content.
In a previous work in this same journal, Abreu et al. (1998)

cold rolled
Fe-20Mo-5Ni-xC, with x varying between 0.020% and 0.092% in weight, to different reductions up to 99%. They showed that in the samples cold rolled between 80% and 90% there was a decrease in the volume fraction of the {001 } (100) orientation while in those cold rolled 97% and 99% an increase was observed, after age-annealing. Their results also indicated that the increase in the {001 } (100) volume fraction depended strongly on alloy composition. The goal of the present work is to determine the influence of the Mo content on the textural changes in Fe-Mo-5Ni-0.05C alloys and relate these changes to the observed variation in magnetic properties. This is part of a more comprehensive investigation on Fe-Mo-Ni-C alloys being carried out by the authors.

EXPERIMENTAL
Three Fe-Mo-5Ni-0.05C ingots were prepared by induction melting under vacuum. The composition of each ingot is shown in Table I. The ingots were soaked at 1250C for 30 min and hot rolled to 60% reduction in one pass. The strips were reheated to 1220C and quenched in water. The hot-rolled strips were cold rolled to 60%, 80%, 90% and 97% whence samples were removed. Magnetic aging of these samples was carried out at 610C for h. The magnetic properties and the hysteresis loops were measured in a vibrating sample magnetometer EGG-PAR model 4500.
The samples for texture measurement were 20 mm x 14 mm rectangles cut from the sheets with the smaller dimension parallel to the rolling direction. These were ground to a 600-mesh finishing and chemically polished in a solution of HF in H202.
The crystallographic textures were determined by calculating the orientation distribution function ODF using the Roe method (Roe, 1965 (Bunge, 1993). cold rolled 80%, 90% and 97% and magnetically aged at 610C for h. It can be seen that the fibres that characterize the bcc texture become sharper for reductions above 80%. The increase in sharpness with rolling reduction is better observed in Fig. l(a), for alloy B (11% Mo); the sharpness decreases with increasing Mo content. The texture development is similar to that observed in rimming steels, but it is retarded with respect to the latter when the textures for the same rolling reduction are compared. The texture seems to be the result ofa normal cold rolling and recrystallization behaviour when the latter is hindered by the presence of fine precipitates (not confirmed in this work). The  to an increase in the magnetic anisotropy on account of the (100) directions, the direction of easy magnetization, lying in the sheet plane at 45 to the rolling direction. Figure 3 shows the variation ofthe texture severity parameter TSP with cold rolling reduction for the three alloys. The TSP measures the depart of the texture from random and is equal to unity for the uniform distribution. It can be seen that the increase in TSP is larger for alloy B, in agreement with the trend observed in Fig. 1 Figure 4 shows the variation of the ratio between remanent induction and saturation induction, B,/Bs with cold reduction. It is generally accepted that this ratio, when larger than 0.8, is an indication of magnetic anisotropy. It can be seen that all three alloys show magnetic anisotropy for reductions equal to and higher than about 80%. In fact, both  CONCLUSIONS Three Fe-5Ni-xMo-0.05C alloys, where x is 11%, 15% or 19%, were cold rolled 60%, 80%, 90% and 97% and magnetically aged at 610C for h. The texture in these alloys shows the typical carbon steel-like increasing Mo content. The ODF intensity ofthe {001 } (110) component continuously increase with rolling reduction, for the 11% Mo alloy only, and reaches a maximum at 97% reduction. This increase is responsible for the high Br/Bs ratios observed in this alloy. Taking into account the results obtained by Abreu et al. (1998) on the influence of the carbon content in Fe-Mo-Ni-C alloys, the alloy Fe-11Mo-5Ni-0.05C seems to be an optimized composition, displaying high magnetic properties and cold ductility and having the advantage of being less costly than Co-containing alloys.