ACOUSTIC EMISSION DURING TENSILE DEFORMATION OF 2.25Cr-1Mo STEEL A.B. Pattnaik 1* and B.B. Jha 1 1 CSIR-Institute of Minerals and Materials Technology Acharya vihar, Bhubaneswar, Odisha, India *amulyapattnaik@gmail.com;amulya@immt.res.in Abstract In this paper a systematic study has been undertaken to correlate the microstuctural variation with acoustic emission parameters during tensile deformation of 2.25Cr-1Mo steel. Tensile testing of normalised and thermally aged samples has been carried out at a strain rate of 6.66 x 10 -4 s -1 with simultaneous monitoring of acoustic emission (AE) time domain parameters. Results have shown that acoustic emission activities are higher for normalised condition and the same decreased as the severity of tempering is increased. The microstructural characterisation has been done using optical microscopy and Field emission scanning electron microscope (FESEM). Keywords: 2.25Cr-1Mo steel; Acoustic emission; tensile deformation; Strain rate Introduction 2.25Cr-1Mo steel has long been used as a structural material in power generating utilities and petrochemical industries for high temperature applications [1]. This steel undergoes microstructural degradation when exposed to extremely high temperature and pressure due to precipitation and coarsening of carbides [2-3]. It is also used as core component material in fast breeder nuclear reactors [4]. The presence of fine molybdenum carbide is responsible for high creep strength of the steel [5]. Acoustic emission (AE) is a non destructive evaluation (NDE) procedure in which material itself generates transient elastic or stress waves upon deformation which are detected by a transducer. Thermal ageing of 2.25Cr-1Mo steel produces different types of carbides. B.B Jha et al. [2] studied the microstructural degradation in thermally aged 2.25Cr-1Mo steel. They found that the carbide precipitation was in the sequence of M 3 C, M 7 C 3 , M 23 C 6 , and M 6 C. Experimental Procedure 2.25Cr-1Mo ferritic steel having nominal chemical composition (wt. %) C – 0.07, Mn – 0.42, Si – 0.019, S – 0.025, Cr – 2.28, P – 0.02, Mo – 0.98, Ni– 0.09, Fe – balance, has been used in the present investigation. The plate was cut into strips of size 115mmx14mmx12mm using BAINCUT-XL cutting machine. These strips were normalised at 1223K for 2hrs in an evacuated quartz tube. The normalised strips were tempered at 873K/10hrs, 923K/20hrs, 973K/40hrs, 973K/80hrs using a tubular furnace. Tensile tests were carried out on a Tinius Olsen make screw driven material testing machine at a strain rate of 6.66 x 10 -4 s -1 . The tests were carried out at room temperature (300K). Acoustic emission (AE) time domain parameters were studied using a four channel PCI-DiSP with an AE win v2.19 AE system (Physical Acoustic Corporation, USA). Two miniature sensors of resonant frequency 225 kHz and 325 kHz were mounted on the specimen using high vacuum silicone grease and tape. Results and Discussion The initial microstructure of normalised steel is found to be consists of bainite and very little amounts of ferrite. Bainitic microstructures have a better creep resistance but degrade rapidly at high Proceedings of the 3rd Asian Symposium on Materials & Processing ASMP 2012, IIT Madras, Chennai, 30-31, August 2012 NDTC2