·Table of Contents
·Materials Characterization and testing
The Steel Grain Magnification Influence on the Ultrasound wave attenuationZ. CHERROUF, N. OUALI, S. OUALLAM, G. KAMEL,
Laboratory of Metallurgy
Scientific Research centre and Technique in Welding and Control
Road of Dely Ibrahim, BP 64, Cheraga. Algiers. Algeria.
|% in element|
||Z 6CNDT 17 - 12
||Table 1: Samples chemical composition|
These steels have sudden of the overheats thermal salary to high temperature during an important maintenance how presented on the picture 2 .
Overheats it is characterized by a grain magnification exaggerated.
This one is gotten to the extensively superior temperature to the Ac3 temperature criticizes and spreads until the one of limit solidus / liquidus.
This magnification is also accentuated by the increase in the maintenance time.
This thermal treatment choice is relative to difficulties that present the grain size steel when to the scattering and the acoustic wave absorption to grains joints (greatly anisotropy steel).
This problem is especially accentuated for the austenitic type rustproof steels.
The grain average diameter is: where m is the grains number by surface unit.
The grain magnification treatments, the gotten by the relation m = 8 x 2 G are given by the picture 2.
|initial grain||thermal treatment element||final grain|
|Steel||G||d (mm)||Maintenance temperature||Maintenance||Cooling nature||G||d (mm)|
|45SCD6||10||0,0110||1150°||1 h 30 min.||air||6||0,0442|
|Z 6 CNDT17-12||6||0,0442||1200°||4h||air||4||0,0884|
|Table 2: Thermal treatment parameters, middle diameters and numbers grains|
To discern the best treatments results undergone, micrographs have been achieved in order to put in evidence the grains structural magnification.
|Fig 1: XC48 (X200) a- no treated G =8 ; b-treated G =5||Fig 2: 45SCD6 (X200) a- no treated G=10 ; b- treated G=6|
|Fig 3: E24 (X200) a- no treated G=11 ; b- treated G=6||Fig 4: Z6CNDT 17-12 (X200) a- no treated G=6 ; b- treated G=4|
III-A - The attenuation
Grains have a disorganized orientation, ultrasonic wave undergoes a diffusion more or less pronounced anisotropy degrees function and the grain middle size. brWhile considering the case of structures single phased, one distinguishes three domains for which diffusion coefficients are given:
For the three domains Cm is the characteristic material constant, Fa the factor determining the anisotropy, d the grain average diameter, f and l
the frequency and the length of wave.
For the steels Ivens proposed the empiric law as :
ad=100.(d/l)3.dB/m for a perlitic structure and ad=35.(d/l)3.dB/m
for a bainitic structure.
Concerning this law, the wave diffusion remains negligible for a grains size understood between l /1000 et l /100 and increases quickly between l /100 and l .
The diffusion effect is boring, it reduces shortcomings echoes amplitudes and the bottom in their submerging addition in a bottom noise; that can not be adjusted by a simple signals amplification as in the absorption case.
In practice, the attenuation coefficient is determined while measuring corresponding successive signal amplitudes to the wave number go - return in the piece.
These signals are identified while measuring the time between every two consecutive signals top.
Curves (Fig. 5) representing the relative amplitude decrease according to the browsed course are illustrated for three frequencies: 5, 10 and 15 MHz.
The table gives all calculated essential values from the achieved measures.
It is place to note, for most cases, the average attenuation and the longitudinal speed wave increase for the treated steel.
|Average attenuations (dB/m )||longitudinal velocity (m/s)||Wave lengths (mm)|
|steel||5 MHz||10 MHz||15 MHz||5 MHz||10 MHz||15 MHz|
|No treaty||treaty||No treaty||treaty||No treaty||treaty||No treaty||treaty||No treaty||treaty||No treaty||treaty||No treaty||treaty|
|Z 6CNDT 17 - 12||68,02||78,13||120,76||136,15||156,16||173,57||6059||5937||1,21||1,19||0,61||0,59||0,40||0,40|
|Table 4: Essentiel ultrasonic parameters comparative table|
|Fig 6: Treaty and no treaty materials attenuations Gap according to the frequency|
With regard to the attenuation theory presented above, the application domain is the Rayleigh one being given the value of d (diameter of the grain) compared to the wave length.
These curves show the attenuation gap increase between steels treaties and no treaties thermally according to the frequency.
For it, histograms representing these gaps are represented by the figure 6 that shows that:
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