Short Notes K39

phys. stat. sol. 3, K39 (1968)

Subject classification: 18.2; 21.1.1

Higher Pedagogical College, Katowice

A Diffusional Magnetic Viscosity Effect in Iron-Carbon Martensite

BY

J. KINEL, J.W. MORO6, and J. PRZYBYU

Many papers have been devoted to internal friction in iron-carbon martensite

samples (e. g. 1 to 4). It has been found that in this material the following three

loss phenomena are occuring mainly (2) : 1. a background friction, which decreases

in a freshly quenched specimen during aging at room temperature, 2. a Snoek peak

at 20 to 30 C (for f = 1 Hz), observed only when the sample contains some ferrite,

3. a maximum in the region of the Koster peak (220 OC ht 1 Hz), the origin of which

is not quite clear.

0

Until now no magnetic investigations concerning after-effects in martensite

have been undertaken, although the material is ferromagnetic and its permeability

is rather high. An attempt to apply such methods has been undertaken in this inves-

tigation.

The permeability disaccommodation in a Fe-W-V-Cr steel sample (a so-called

diamond steel), containing 1.4% C , 5% W, 0.5% C r , 0.2% V, 0.25% Mn, 0.25% Si

has been investigated. The specimen consisted of 20 rings, 0 . 5 mm thick, 40 mm

outer and 30 mm inner diameter. Before measurements the rings were heated at

800 OC and then each of them was quenched in water. After this treatment they dis-

played the Rockwell hardness of about 65.

For the measurements a Wilde-type bridge, in detail described in (5), was

used. The magnetising field amounted to 2 mOe, at a frequency of 1000 Hz. After

quenching the sample was demagnetized with a 50 Oe, 50 Hz field.

Before each run a 50 Hz field changing from 5 to 0 Oe in 5 s was applied. The

bridge was compensated continuously.

Fig. 1 shows a typical All. /p x 100% temperature dependence ( A p is the

permeability decay between 0.5 and 15 min after demagnetization, p the permea-

bility at 15 min). In the region from -60 to 4 0 "C the results could be repeated

sufficiently well: 1. below -50 C the disaccommodation increased always, 2. be- 0

K40 physica status solidi 29

Fig. 1. Time decrease vs. temperature;

H = 2 mOe, f = 1000 Hz

0 tween -50 and -20 C there were no permeability

changes at all, 3. above -10 C A p / p increased

again with temperature.

0

0 The measurements above +80 C showed a 0 great influence qf heating, e . g. at 90 C, after an initial time decrease betweeu

t = 0.5 and t = 10 min, the permeability increased afterwards. Such heating caused

rlso an increashg of the disaccommodation at lower temperatures. Probably these

changes a re related to irreversible structural transformations occuring in martenslte

above 80 OC (first stage of tempering (6) ).

The discovered magnetic after-effect is not related neither to the Snoek relaxa-

tion, the disaccommodation of which occurs below -15 C (7), nor to the Koster pro-

cess, which causes a time decrease in the neighbourhood of 180 OC (8).

0

For this reason the second and third process, mentioned at the beginning of

this paper could be omitted in our discussion. The lack of any effect between -50 and

-20 C shows that the new disaccomodation is not related to a diffusional internal

friction background occuring at temperatures from +15 to 4 5 C (process 1).

0

0

It seems that the investigated effect is caused by single carbon atoms, jumping

between distorted lattice sites of the tetragonal martensite.

According to Johnson (9), in the case of a sample containing 1.5% C the migra-

tion energy of such an atom amounts to 1.05 eV in a plane perpendicular to the c -

axis and to 1.18 e V in a direction parallel to it. A s the disaccommodation maximum

of the carbon Snoek relaxation appears a t -23 OC (between 0.5 and 15 min (10) ),

frvm the Wert-Marx law (11) results that these energies ought to cause a time de-

crease at +42 C. 0

It is worth while to call attention to the fact that recently a similar process

has been discovered in aFe-C-N in the region above room temperature (10).

References

(1) R. WARD and J .M. CAPUS, J. Iron Steel Inst. 201, 1038 (1963).

(2) T. GLADMANN and F.B. PICKERING, J. Iron Steel Inst. 204, 112 (1966).

Short Notes K4 1

(3) G. W. KURDYUMOV, Fiz. Metallov i Metallovedenie z, 909 (1967). (4) J.N.MC GRATH and R. RAWLINGS, Metal Sci. J. 2, 37 (1968).

(5) J. KINEL, Thesis, Higher Pedagogical College, Katowice 1967.

(6) H. SCHUMANN, Metallographie, Leipzig 1964.

(7) P. BRISSONNEAU, J. Phys. Chem. Solids I, 22 (1958). (8) G. BIORCI, A. FERRO, and G. MONTALENTI, J. appl. Phys. 9, 1732

(1959).

(9) R.A. JOHNSON, Acta metall. 13, 1259 (1965). (10) J. W. MOROfi and J. RASEK, to be published.

(11) J. W. MORON, PAN OddziaYw Krakowie, Prace Komisji Nauk Technicznych, /

Metalurgia, Fizyka Metali i Stop6w, No. 3, 47 (1967).

(Received July 22, 1968)