Ultrasonic Characterization of High Manganese Austenitic Steel Parts for Longevity and Service Life

High Manganese Steel containing 11-15% Mn often referred to as Hadfield steel are often used in applications that require high strength, wear resistance, and corrosion resistance. Hadfield steel is a work hardening steel; its surface becomes harder when subjected to impact and abrasion while the core remains ductile. This property makes Hadfield steel a suitable material for casting heavy hammers for rotary crushers, Jaw crusher blades, forklift forks, etc. Failure of such parts is often results in safety issues as well as work stoppage and equipment damage. Regular UT flaw detection offers limited possibility due to high attenuation of austenitic steel. Metallurgical research at MME indicates that there is a predictable relationship between grain size of Hadfield steel parts and their service life. Grain size of up to 0.5 mm indicates reasonable service life. For some applications grain size of up to 1.0 mm may be acceptable but larger grain size almost always lead to short service life or sudden breakage mainly due excessive softness of austenite in the core of grains. In order to predict service life of such part, a dedicated ultrasonic test system was developed. The system acquires raw RF data from a 2.25 MHz probe and performs a sequence of signal processing to obtain ultrasound attenuation coefficient at selected frequency. An empirical relationship between grain size and attenuation coefficient has been established based on which the grain size can be measured with reasonable consistency. This in turn provides a measure of longevity for the part. The instrument provides a quick and inexpensive procedure to determine the service life of parts cast from Hadfield steel.

References
1. Vary, Alex, “Material Property Characterization,” Nondestructive Testing Handbook, third addition: Volume 7, Ultrasonic Testing, Columbus, OH, American Society for Nondestructive Testing. 2. Vary, A., “Ultrasonic Measurement of Material Properties,” Research Techniques in Nondestructive Testing, Volume 4, London, Academic Press, 1980. 3. Truell, R., C. Elbaum and B. Chick, Ultrasonic Methods in Solid State Physics, Academic Press, 1969. 4. Lynnworth, L., Ultrasonic Measurements for Process Control, Academic Press, London, 1989
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