MÖSSBAUER AUSTENITOMETRY AND MAGNETIC PROPERTIES OF STEEL

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MÖSSBAUER AUSTENITOMETRY AND MAGNETIC PROPERTIES OF STEEL

T. Zemčík, Z. Igut, Z. Lajs

To cite this version:

T. Zemčík, Z. Igut, Z. Lajs. MÖSSBAUER AUSTENITOMETRY AND MAGNETIC PROP- ERTIES OF STEEL. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-383-C1-383.

�10.1051/jphyscol:19801146�. �jpa-00219631�

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JOURNAL DE PHYSIQUE Colloque Cl, suppl6menl au n o 1 , Tome 41, janvier 1980, page (21-383

~@SSBAUER AUSTEN ITOMETRY AND M4GNETI C PROPERTIES OF STEEL

T. ~erneik, Z . 5iguZ(. ^and2. Slajs"

I n s t i t u t e of Physical Metallurgy, 616 62 Brno, Czechoslovakia.

n Central Research I n s t i t u t e , ~ K O D A Works, 316 00 PZzeE, Czechoslovakia.

Tie 5:~e M"osbauer spectroscopy facilitates a sensitive (down to ca 1 wt. % ) and accurate (bet- ter than

+

^{0.5 rt.}% ) determination of the retained austenite content in steels. Simultaneous ob- taining the phase composition and magnetic c h a r a ~ teristics proved to be valuable in cases where both mechanical and magnetic demands are to be fulfilled. In this paper, some results for the low-carbon CrNiMoV steels, used in magnetic cir- cuits (large generator rotors), are summarized.

~bssbauer backscattering spectra were taken with a toroidal Kr/CH4 counter. Least-squares de- composition was done into two magnetic and one non-magnetic components. From the hyperfine split- tings, the average magnetic moment of iron in the ferromagnetic matrix

zf

was derived. Using the em- piric calibration El], the area ratio yielded the retaingd austenite content A. From the two quanti- ties, the average iron moment was gained.

To verify the comection between the retained austenite and the magnetic induction, samples were austenitizeE at 860'~ and cooled at various rates (gradual transition from the ferritic through bai- nitic to martensitic structures). Along with A,

if

and

A,

the variations of the magnetic induction BE were followed, As a result, clear correlation of

the magnetic induction B, iron moment and the austenite content A was found (Fig. I). Constant ferromagnetic moments sf implicate unchanged satu- ration induction of the ferromagnetic phase. It is hence the paramagnetic austenite that suppresses

the magnetic induction;, in low fields there is an additional decrease due to the increased magnetic hardness. Both effects can be described by the in- ternal demagnetizing factor, reflecting the influence of the disperse paramagnetic phase [Z3.

Removing the inhomogeneities due to the non- -uniform cooling rates in bulky pieces is the c r u cia1 point of the production of rotating magnetic parts, One of the homogenizing measures is the isothermal annealing; its effectiveness was veri- fied by the same way (Fig. 2). The correlationbe

tween the values of A and BE (and constant

Gf)

for the unannealed samples is maintained, whereas the medium-temperature annealing (620°c/30 hrs ) brings a favourable induction increase to a value inde- pendent on the original structure of the samples.

References

[I] SCHWARTZ L.H.: Int. J. Nondestr. Testing 2 (1970) 353.

[2] SLAJS ^J., QXGUT 2. and Z E M ~ ~ K TI: Kovov6 ma- teri6ly (Bratislava) ( 1979)r in print.

7.

,

'-2 O F T

I Î Î Î I

10' lo1 10' 10' los lob

cooling rate [KI hr]

Fig. 1 Variations of magnetic induction B400 and El000 (subscript H in A/cm), iron magnetic moments N ~ , ,%A and austenite content A.

L I I L I I

10' $la lo3 lor

as

cooling rate [ ~ h d Fig. 2 Influence of isothermal anneal on magn_etic

induction BloOO, iron magnetic moment (uf

and austenite content A.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801146