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Technical Discussions
Chayan Maiti
Chayan Maiti
14:41 Jul-27-2017
Facing problem during UT

I am working in a ferrous foundry, making abrasion resistance cast iron (Grade ASTMA 532, Class-2, Type-D). Whose required hardness is 59-62HRC. We heat treated these casting as follows:
Normalising: 1050°c @ 100°c/hr.

We are facing problem during ultrasonic testing. The backwall echo is not upto the mark (max. time it shows upto 15-20%). Is there any special procedure for UT checking? Please help anybody.
We are using “ DIGISCAN DS 322” model UT machine which make EECI. And probe using 24mm dia and 2Megaharze.

 
 Reply 
 
Matthew Aguiar
Canada, Joined Jan 2017, 11

Matthew Aguiar

Canada,
Joined Jan 2017
11
15:21 Jul-27-2017
Re: Facing problem during UT
In Reply to Chayan Maiti at 14:41 Jul-27-2017 (Opening).

Hello Chayan,

Just out of curiosity what standard are you working to or is this a specific customer requirement? Are you performing UT for flaw detection or thickness monitoring? Anytime I have come across inspection of abrasion resistant cast iron it was usually only subject to a visual inspection for inherent casting defects like tears, cracks, inclusions etc.

Cheers,

Matthew

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 832

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
832
20:12 Jul-29-2017
Re: Facing problem during UT
In Reply to Chayan Maiti at 14:41 Jul-27-2017 (Opening).

The grain size in your casting is too large that results in high attenuation

 
 Reply 
 
Frank Hummus
Frank Hummus
09:14 Jul-30-2017
Re: Facing problem during UT
In Reply to Anmol Birring at 20:12 Jul-29-2017 .

anmol how can this be corrected?

thanks

 
 Reply 
 
Gokul Hrishikesh
Consultant, AUT Specialist
India, Joined Jul 2013, 76

Gokul Hrishikesh

Consultant, AUT Specialist
India,
Joined Jul 2013
76
09:50 Jul-30-2017
Re: Facing problem during UT
In Reply to Chayan Maiti at 14:41 Jul-27-2017 (Opening).

Few parametres that might help :

1) Lower frequency
2) Larger probes, good if focused to BW area
3) No/low damping (longer pulse)
4) Play with Voltage if your equipment supports
5) Shorter cables
6) Wide band filters
7) If you cannot add any more of gain (saturated) then use a remote pulser+pre amp

Take care that an additional scan is done for near surface with higher frequency

Regards,

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 832

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
832
13:05 Jul-30-2017
Re: Facing problem during UT
In Reply to Frank Hummus at 09:14 Jul-30-2017 .

The 2 MHz 24 mm probe you are using is the right probe for this test.
Grain size is reduced by heat treatment. Talk to the Materials Engineer in your plant

 
 Reply 
 
P V SASTRY
R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D, India, Joined Jan 2003, 195

P V SASTRY

R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
195
18:06 Jul-30-2017
Re: Facing problem during UT
In Reply to Chayan Maiti at 14:41 Jul-27-2017 (Opening).

You have not mentioned the section thickness and the details of the component.

You may also share with us, to what standards/recommendations, you are conducting UT.

But nevertheless it is very nice that you are getting 15 to 20% back wall echo after normalization treatment.

The micro structure of the as cast high chromium white cast iron consists of eutectic carbides in a matrix of Austenite, Pearlite with some Martensite.

After the so called normalization treatment at 1050° C (which is also called solutionizing or destabilization treatment) the micro structure consists of large sized Primary Chromium carbides, secondary Chromium carbides, some martensite and large amount of retained Austenite.

This high amount of retained Austenite contributes to high attenuation and as a result your back echo is not very high. The influence of the large primary Chromium carbides also contribute to scattering of the ultrasonic waves (and attenuation) but this a constant and we cannot do much about it.

But the large amount of retained Austenite can be reduced by tempering at about 550°C (for a period depending on the section thickness) whereby it is converted to mostly Martensite.

This treatment will not only increase the back wall echo but also the hardness from the present level and thereby the abrasion resistance.

The tempering treatment depends on the present hardness, micro structure, the composition etc. Please consult your metallurgist for the actual cycle.

Best wishes,

P V SASTRY

 
 Reply 
 

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