Studies on magnetically aged Fe-Mo-Ni-C alloys with different carbon additions
A.A. Braida J.R. Teodosio* H.F.G. Abreub* J.M. Neto° M.R. Silvaa
*Metollorgical ansd Materials Deparnsmt; COPPE; Fedleral Uitersity ef Rio de Janeiro Brazi Mechanical Department - Federal Uwitersity af Ceari Brazil“Plysical Institate - Federal Unfeersity of Rio de Janeiro Brazi?
Abstract
solution treatment water quenching and magnetic aging at two different temperatures. Coercive force and maximum Magnetic properties of the Fe20Mo5NixC (wt% x varying from 0.016 to 0.14) aloys were studied after hot rolling.energetic product as high as 450 Oe and 1.8 MGOe respectively were obtained. C 2001 Elsevier Science B.V. Allrightsreserved.
Keywonds: Magnetic materials; Magnets; Cobalt free magnets
1. Introduction
aging treatmenl on the magnetic properties of The aim of this work is to determine the influence ofFe20Mo-5Ni alloys with carbon additions ranging from 0.016% to 0.14% (w1%) and aging time varyingfrom 0 to 1080min.
alloys show high mechanicalplasticity when cold Since the 1980s it has been known that FeMoNiVicalloy L deformed as well as magnetic properties similar to
with coercive force H = 210 Oe and maximum energetic Tiefel et al. [1] obtained a Fe20Mo5Ni (wt%) alloyproduct (BH) 1.1 MGOe after hot rolling solutiontreatment at 1200°C and magnetic aging at 610°C for 4 h. With aging temperature of 650°C the resuls were similar[1].
2. Materials and methods
melting furnace using high-purity materials. The chem- The ingots were prepared in a vacuum induction-ical position of the alloys is given in Table 1. The ingots were soaked at 1250°C hot rolled (60% reduc-tion) water quenched and magnetically aged at two different temperatures 610°C and 650°C. The magneticproperties were determined in a vibrating sample mag- netometer. A maximum field of 10000 Oe was appliedduring measuremenL.
Recently Teodosio et al. [2] studied the influence ofon the magnetic properties of the Fe20Mo5Ni alloy. small contents of carbon from 0.016% to 0.14% (wt%) The alloys containing carbon achieved H = 262267 Oe and (BH)mx = 0.830.97 MGOe after hot rolling solu-the necessty of any aging heat treatments or cold defor- tion treatment at 1250°C and water quenching withoutmation.
3. Results and discussion
with the aging time for the temperatures of 610°C and Figs. 1 and 2 present the variation of coercive force650°C respectively. It can be seen that there is a very similar behavior for all the alloys with different carboncontent. The coercive force starts from about 260 Oe
Table 1 Chemical position of the alloys (wt%)
Alloy C% S% Mo% Ni% Fe%A 0.016 0.006 19.0 5.1 Bal.B C 0.026 0.038 0.003 0.002 20.2 19.2 5.2 5.1 Bal. Bal.G D 0.075 900 0.011 0.005 19.3 21.2 5.0 5.0 Bal. Bal.H 0.12 0.085 0.004 0.01 20.1 20.2 5.2 5.0 Bal. Bal.J 0.14 0.01 20.0 5.0 Bal.
Fig. 1. Coercive foroe H against aging time after aging at610°C.
pides soseao n ug pue “(uean Sue ou qm)until 4 h of aging time for 610°C and 1 h for 650°C and stabilizes in a plateau around 450 Oe for both temper-atures. The alloys that present the highest coercive forceare in the region of 0.046% and 0.075% (wt%) of carbon content. There is a great similarity between the behaviorof H for 610°C and 650°C of aging temperature. The only difference between the two plots is that at 650°C theincrease of Hf is even faster than the increase observed a1 610°C because of the kinetic effect of the temperature.
time for the alloys with different carbon content for an Fig 3 shows B saturation induction against aginga great symmetry with the equivalent H plot (Fig. 1). For aging temperature of 610°C. From this figure one can seeall alloys B stats around 17 500 G with no aging treal-ment) drops very fast until 4h of aging time and stabil- izes at a plateau around 14 000 G. The B behavior wasalso investigated at 650°C; the values obtained were similar to those obtained at 610°C. The only differencebetween the two temperatures is that the drop of B a1 650°C is faster than the drop observed at 610°C becauseof the kinetic effect of the temperature.
According to Becker et al. [3] the microstructure ofthe material has no influence on B . On the other hand
Fig. 2. Coercive fore H against aging time after aging at650°C.
Fig.3. Maximm eergetic produet (BH) against agingtime after aging at 610°C.
this property is strongly influenoed by the chemical - position of the alloy. The precipitation of carbides cha-nges the x-matrix position. But the microstructure ofthe material has a strong influence on the coercive force.
Tiefel et al. [1] and Magat et al. [4] proposed thatFe Mo precipitates are responsible for the high H values. More recently Teodosio et al. [5] showed thepresence of M C carbide precipitates in the alloys con- taining carbon where M can be Fe or Mo. These carbideshancing H values. The precipitation of carbides during are ferromagnetic and hinder domain wall motion en-magnetic aging decreases the quantity of Mo dissolved increases. the z-matrix and consequently the saturation B de-
alloys after magnetic aging at 610°C. This value of max- Fig 4 shows the maximum energetic product of theimum energetic product is higher than that obtained for the alloy without carbon (1.1 MGOe) [1]. The time ofheat treatment (4 h) for the highest value of the maximum energetic product is the same that gives the highest valueof H. The temperature of 650°C was also investigated
1. After 4h of aging al 610°C and 1h at 650°C the coercive forces of the alloys reached the maximumvalues from 400 to 450 Oe and maximum energeticproduct reached the maximum values from 1.3 to 1.8 MGOe These values of H and (BH)x are aboutcarbon and aged at the same temperatures. twice as high as those of the same alloy without2.The highest magnetic properties were obtained for the alloys with carbon contents between 0.046 and3. The perfect symmetry between H and B together 0.075% (wt%).with the presence of precipitates observed in previous works shows a strong indication that the mechanismof magnetic hardening is developed by the formationof precipitates in the x-matrix during low-temperature aging.
Fig. 4. Saturation B agains aging time after aging at610°C.
and the maximum energetic product was achieved after1 h of aging time. The values obtained for (BHf) were similar to those obtained at 610°C.
References
[2] B. Adolfo J.R. Teodosio Joel M. Neto Julio Scr. Mater. 42 [1] S. Jin T.H. Tiefel J. Appl. Phyx. 52 (3) (1981) .[3] JJ. Becker F.E. Luborsky D.L. Martin IEEE Trans. (2000) 711.[4] L M. Magat G.M. Makarova L.P. Lapina E. Belozerov Magn. MAG-4 (1968) 8498.[5] S.S.M. Tavares J.R. Teodosio M.M. Pires Scr. Metall. Fiz. Met. Metalloved. T. 5 (6) (1981) .Mater. 33 (2) (1995) 251257.
4. Conclusions
Fe20Mo-5NixC(w1%) magnetic allys x varyingfrom 0.016 to 0.14 were hot rolled solution treated a1 1250°C and magnetic aged at 610°C and 650°C. Thefollowing conclusions can be made:
