THE ANALYSIS OF ULTRASONIC WAVE ATTENUATION SPECTRA IN STEELS

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THE ANALYSIS OF ULTRASONIC WAVE ATTENUATION SPECTRA IN STEELS

R. Smith, W. Reynolds, S. Perring

To cite this version:

R. Smith, W. Reynolds, S. Perring. THE ANALYSIS OF ULTRASONIC WAVE ATTENUA- TION SPECTRA IN STEELS. Journal de Physique Colloques, 1983, 44 (C9), pp.C9-337-C9-340.

�10.1051/jphyscol:1983948�. �jpa-00223395�

THE A N A L Y S I S OF ULTRASONIC WAVE ATTENUATION SPECTRA I N STEELS

R.L. S m i t h , W.N. R e y n o l d s and S. P e r r i n g r

NDT Centre, Materials Physics Division, AERE Harwell, U.K.

ABSTRACT

Detailed c a l c u l a t i o n s have been made o f the g r a i n scaf = r i n g spectra o f u l t r a s o n i c waves i n s t e e l , taking i n t o account not only the mean grain s i z e but also the d e t a i l e d d i s t r i b u t i o n o f sizes. I t i s now possible t o allow f o r t h i s term i n experimental data on any given a l l o y and thus t o i s o l a t e danping e f f e c t s generally associated w i t h dislocations.

Some exanlples are presented of p r a c t i c a l r e s u l t s , w i t h i l l u s t r a t i o n s of t y p i c a l danping spectra i n the 15-50 W z range. Their r e l a t i o n s h i p s t o macroscopic mechanical properties are now being investigated.

1. INTROWC TION

I n a recent series o f papers /1-5/ we have elucidated the r e l a t i o n s h i p between the frequency dependence o f the u l t r a s o n i c attenuation and the mean g r a i n s i z e , g r a i n s i z e d i s t r i b u t i o n and carbon content o f Fe-C a l l o y s . These experiments were c a r r i e d out t o i n v e s t i g a t e the p o t e n t i a l o f u l t r a s o n i c attenuation measurements as a nondestructive method o f assessing materials properties /6,7/ and i n t h i s context the d u c t i l e t o b r i t t l e t r a n s i t i o n tenperature was also determined f o r the Fe-C a l l o y s . The r e s u l t s o f these i n v e s t i g a t i o n s may be sumnarised as:-

-

-

I t i s obvious from the above that f o r the use o f u l t r a s o n i c attenuation t o be contenplated as a nondestructive t e s t i n g t o o l that the two e f f e c t s o f grain s i z e d i s t r i b u t i o n and the carbon content m s t be separated. I.t i s the purpose o f t h i s paper t o demonstrate a method o f analysis o f u l t r a s o n i c attenuation data which can achieve the separation of these variables.

2. THEORY

I t has been shown previously /2/ t h a t the conventional analysis o f u l t r a s o n i c attenuation i n terms o f s i n p l e power laws o f the frequency i s inadequate unless the grain s i z e o f the material i s very uniform. Subsequently i t was shown / 4 / t h a t i f a narrow g r a i n s i z e d i s t r i b u t i o n was present then the g r a i n s i z e s c a t t e r i n g c o n t r i b u t i o n could be subtracted from the t o t a l attenuation t o leave the c o n t r i b u t i o n dependent on the carbon content alone. This contribu tior! was shown t o have the frequency dependence properties associated w i t h absorption mechanisms such as d i s l o c a t i o n danping or magnetic domain darrping. The more l i k e l y o f these causes i s d i s l o c a t i o n danping as the magnetic c o n t r i b u t i o n has been shown t o be small for these a l l o y s 131.

+ M e t a l l u r g y D i v i s i o n

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983948

C9-338 JOURNAL DE PHYSIQUE

We propose therefore t o use an expression o f the form

where a i s the u l t r a s o n i c attenuation F i s the Frequency

D i s the g r a i n diameter alp a2 are constants

The f i r s t term has been associated w i t h d i s l o c a t i o n danping i n l i n e w i t h conventional theory / 8 / and the second term i s the s c a t t e r i n g c o n t r i b u t i o n from the grains w i t h i n the m a t e r i a l . I n the case o f a small g r a i n s i z e

I<<?, ,

the wavelength) w i t h a narrow d i s t r i b u t i o n t h i s s i m p l i f i e s t o

which then includes the c l a s s i c a l Rayleigh s c a t t e r i n g term.

The analysis o f experimental data which we propose, w p c h i s discussed i n 2 f u l l by Reynolds and Smith / 5 / i s the presentation of a / F as dependent and F as

the independent v a r i a b l e , v i z ,

3. EXPERIMENTAL RESU L TS

We present here some r e s u l t s on Fe-C a l l o y s i n the annealed and normalised s t a t e s . The c h a r a c t e r i s t i c s o f these a l l o y s are sumnarised i n Table 1 and the u l t r a s o n i c attenuation measurements are shown i n Figure 1 . The a l l o y s M3/3/1 and M6/3/1 are i n the annealed s t a t e and have f e r r i t e grains decorated w i t h cementite a t the g r a i n boundaries whereas a l l o y s M3/3/1N and M6/3/1N are i n the normalised s t a t e showing a mixed f e r r i t e p e a r l i t e s t r u c t u r e . I n Figure 2 these r e s u l t s are presented i n the form o f Equation 3 along w i t h t h e o r e t i c a l curves derived from measure g r a i n s i z e d i s t r i b u t i o n s . These curves have been f i t t e d t o the experimental data b using least squares s t r a i g h t l i n e f i t s t o determine the i n t e r c e p t on the a / $ a x i s ( a 1 ) and appropriate scaling o f the constant a2.

From the micrographs o f these materials i t was obvious t h a t the only sanple which d i d not have a very narrow g r a i n s i z e d i s t r i b u t i o n was M3/3/1N and t h i s i s born out by the u l t r a s o n i c attenuation measurements. The change i n the DBTT r e f l e c t s t h i s change i n g r a i n s i z e . The other three sanples a l l show Rayleigh s c a t t e r i n g behaviour w i t h a s i g n i f i c a n t danping c o n t r i b u t i o n . These parameters are inportant f o r determining the a f f e c t s o f attenuation on u l t r a s o n i c inspection o f materials. U n t i l our recent work i t had been assumd t h a t damping a f f e c t s were n e g l i g i b l e a t MHz frequencies. The present work i l l u s t r a t e s that t h i s i s not so and i n some cases the danping term i s the more i n p o r t a n t . We have c a r r i e d out some i n i t i a l experiments on the temperature dependence of t h i s danping c o n t r i b u t i o n and the r e s u l t s i n d i c a t e a l i n e a r increase w i t h absolute tenperature i n accord w i t h conventional d i s l o c a t i o n danping theory / 8 / .

Although the theory p r e d i c t s the correct behaviour f o r a l l o y M3/3/1N, the predicted numerical values are larger than the experimental r e s u l t s . This could be due t o the sampling process used i n meashring the grain s i z e d i s t r i b u t i o n i n which l a r g e grains are over emphasised. These sanpling processes are being i n v e s t i g a t e d a t the present time.

A A

0

0 .

0 .

0 .

0 0

.

* .

FIG 1 THE FREQUENCY DEPENDENCE OF THE

10 2 0 3 0 ULTRASONIC ATTENUATION IN THE Fe-C ALUYS

Frequency MHz

-

- - -

FIG 2 PROPOSED ANALYSIS OF ULTRASONIC ATTENUATION DATA

I I I I I O / , ,

100 200 300 LOO 500 600 700 800 ( ~ r e ~ u e n c ~ ) ' M H ~ ~

C9-340 JOURNAL

DE

TABLE 1 Characteristics o f the Fe-C Alloys

A l l o y %C Heat Treatment Mean Grain DBTT

s i z e ,um OC

M3/3/1 0.10 700° f o r 1 hr 20 64

Furnace Cool

M3/3/1N 0.10 9 0 0 ° f o r 1 5 m i n 34 70

Argon Cool

M6/3/1 0.51 7 0 0 ° f o r 1 hr 20 120

Furnace Cool

M6/3/1N 0.51 8 2 0 ° f o r 1 5 m i n 20 120

Argon Cool 4. CONCLUSIONS

We have i l l u s t r a t e d i n the prese t pap the advantage o f analysi- o l t r a s o n i c attenuation data i n the form a 4 vs

7

REFERENCES

1 . SMITH R L , REYNOLDS W N and WADLEY H N G Metal Science

15,

2. SMITH R L

Ultrasonics

2,

Materials Science

17,

4. SMITH R L, RUSHBRIGCE K L, REYNOLDS W N and HUDSON 8 Materials Evaluation

2,

5. REYNOLDS W N and SMITH R L AERE R10753 (1983)

6. VARYA

M a t e r i a l s Evaluation

36,

7. KLINMAN R, WEBSTER G R , MARCH F J and STEPHENSON E T Materials Evaluation

38,

8. * BATIHA A B

U l t r a s o n i c Absorption Chap 13 (1967) OUP