DETAILED MÖSSBAUER STUDY OF AGE HARDENING OF Fe-Co-Cr-Mo MARAGING STEEL

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DETAILED MÖSSBAUER STUDY OF AGE

HARDENING OF Fe-Co-Cr-Mo MARAGING STEEL

M. Uhlig, J. Kansy, T. Panek

To cite this version:

M. Uhlig, J. Kansy, T. Panek. DETAILED MÖSSBAUER STUDY OF AGE HARDENING OF Fe- Co-Cr-Mo MARAGING STEEL. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-381-C1-382.

�10.1051/jphyscol:19801145�. �jpa-00219630�

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JOURNAL DE PHYSIQUE Co~oque Cl , supplkment au n " 1 , Tome 41, janvier 1980, page C1-381

DETAI LED NSSBAUER STUDY OF AGE HARDENING OF Fe-Co-Cr-Mo NMAGING STEEL

M.R. Uhlig, J. Kansy and T . J . Panek

I n s t i t u t e of Physics and Chemistry of Metals, S i l e s i a n University, Bankma 22, 40-007 Katowice, Poland

1. Introduction,

-

^In^I⁹⁶⁷^Caton^[I] ^de-

signed a aaraging steel ;vith iron matrix, containing 20 wt % Co, 15 wt % Cr, 2.9 wt 5 170 and 0.03 wt % C. Till now the mechanism of dispersion hardening of this alloy has not been investigated in detail. Par- ticularly, Caton [I] could not distinguish which of intermetallic compounds

-

^{chi or}

R phase

-

caused strengthening of the matrix during the ageing of the steel.

We presented already [ 2 ] our initial results of MGesbauer study of the dispersion hardening mechanism in the steel with aim- ilar composition. One of our conclusions was that at the first stage of ageing the precipitation of an a3most iron-free phase took place. This phase could not be obvi- ously aeen in Yiissbauer spectrum when Lo- rentzians fitting did not give exact e- rzough results concerning composition of the matrix in order to calculate the chemical composition of the precipitated compound. It co-dd not be then identified.

In the present paper, main aim of which is to show the possibility of solving the structural problems in case of rnulticompo- nent dloys through the appropriate analysis of N6ssbauer data, we describe further detailed study of the problem with more developed analysis of Ebssbauer spectra.

2. Experimental,

-

^Theindustrially mel- ted specimens of the steel contained 21 .I wt% Co, 14.1 wt% Cr, 3.2 wt % lo and 0.06 wt % C. 40

pm

thick foils of the material were solution treated by annealing in 1273 K for 10.8 ks and quenching into water.

Then the samples were aged in 803 K for 0.3, 0.6, 0.9, 1.8, 3.6, 18, 54and180ks in argon atmosphere and room temperature Mossbauer measurement was performed after each stage of heat treatment using conven- tional constant acceleration spectrometer

with a 10 mCi, P ~ ( c o ~ ~ ) aource. Iil~reover, electrolytically isolated extract from overaged by ageing in 923 X for 720 ks sample was subjected to the PSssbauer ex- aminat ion.

3. Results and discussion.

-

^{The spec-}

trum of the solution treated steel is very complex s i ~ l i n e Zeeman pattern with small paramagnetic line at the central part. As a result of ageing Zeeman pattern lines slim. Simultaneously one can observe per- manent increase in paramagnetic line intensity. The Idossbauer spectrum of the extract is composed of two lines with dif- ferent intensities.

We have applied two independent methods for IiIossbauer data analysis:

a/. The model of Nossbauer spectrum of the alloy has been based on the following ae sumptions: i. the matrix of the alloy c o ~ posed of iron, cobalt and chromium has bcc disordered structure. Nolybdenm is disrk garded due to its relatively small amount in the alloy (1.9 at

$1.

ii. the shape of the spectrwn can be described as the first term of series expansion of the transmis- sion integral [3,4]

.

iii. hyperf ine magnetic field at iron nucleus and isomer shift of the spectrum linearly depend on the number of cobalt and chromium atoms in the first and the second coordination shells of an iron atom. Considering that in the cenkral parts of the spectra the paramagnetic line is found we have eliminated these parts from model calculations.

This model is characterized by fifteen parameters which have been varied to mini- mize the sum of squares for each spectrum.

!Cwo parameters among of above ones were concentrations of cob4t and chromium in the matrix. Just these parameters were used for calculations of the chemical c o s

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801145

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JOURNAL DE PHYSIQUE

HYPERFINE MAGNETIC FIELD

Mg. 1. Comparison of hyperfine field dis- tributions for 180 ks aged sample.

position of precipitates (Pig. 2).

b/. 'Phe independent on any physical model Hesse and Rubartsch method

151

of finding hyperfine field distributions has been used as a test of the previously chosen model.

The agreement of hyperfine field distri- butions obtained independently by these two methods (Fig. 1 ) entitles us to come to the conclusion that our model of the spectra is correct at least in the ques- tion under investigation.

We have obtained very good fits of the calculated spectra to the measured ones using both of two above methods.

On the grounds of informations obtained as the result of both methods we are able to suggeet the model of precipitation pro- cess in the steel. After solution treat- ment the steel has martensitic structure with slight amount of retained auetenite, which decomposes almost completely during the first 0.6 ks of ageing. For all period of ageing ( ~ r , l ? e ) ~ ~ ~ ~ carbide is found in

r Fe

C

0.3 0.8 1.8 3.6 18 54 180 TIME OF AGEING [ks]

Fig. 2. Relation between amount of alloy components in the precipitates and time of ageing. TJ means here number of precipitac ted atoms per 100 atoms of the alloy.

the matrix. This phase has been identified taking into account the isomer shift of its low intensity Mossbauer single line in the spectrum of the extract which is equal to the one reported in [6] for this kind of carbide. Intermetallic phase precipita- ted in the steel is R phase containing al- most equal amounts of cobalt and chromium

(Fig. 2

1.

'Phe atomic composition of the precipitated R phase changes slightly' dur- ing ageing, It c m be seen that the ini- tidly precipitated phase does not contain iron, so it can not be chi phase. High in- tensity line in the extract spectrum as well as the paramagnetic line in the spec- trum of the alloy arise from PeCr sigma phase. The increasing with time of ageing amount of iron in the precipitates is c o l ~ nected with precipitation of this inter- metallic compound 121.

4. Conclusion, -. It has been found that intermetallic compound causing increase in the strength of the Fe-Co-Crdbo maraging steel is R phase, Caton's supposition

[I]

being this way confirmed. Precipitation of chi phase has not been found.

References

1 CATOI?,R.L,, Metal Progress,~(l967)106 [4] BYKOV,G.A. a n d p w ZmmEN, Zh.

[2

[I

UHLIG,DB.R., JAEKOWSKI,B.J., KUlSY,J., & Teor. Fie.,

42

(1962) 909.

PFR,T.J, ~ ~ S A L A M O I ? , A . , BOC. kt. [5] HESSE,J. a n d ~ i j ~ ~ ~ ~ s c ~ , A . , J.Phys.E Conf. on Nossbauer Spectroscopy, Cr+ ~ ( 1 9 7 4 ) 526.

cow, 1975, vol, 1, p. 117, [6] VOZNPUR,P.O., V I Y T J W I K , I . I . , DUBIITIE,

[3]

RMISY,J., PRACKOWIAK,J.E., JAMKOWSRI, V.N.,

Mz.

Met.

8;

Ketalloved,, B., PANEK, I.J., Physics Papers, z(1973) 1310.

Silesian University,

2

⁽¹⁹⁷⁶⁾^{1 1}7.