Small Punch Creep Studies for Optimization of Nitrogen Content in 316LN SS for Enhanced Creep Resistance
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THE small punch creep (SPC) test has attracted the attention of several researchers as an innovative tool to study the creep properties of materials.[1–9] The SPC testing technique has several advantages when compared with conventional creep tests: (i) It is material noninvasive and requires a very small amount of material for the tests. Hence, it is attractive for remnant life evaluation and structural integrity assessment studies where it is not desirable to remove a large amount of material from an operating component; (ii) it enables rapid screening of creep properties of several laboratory heats for optimizing the chemical composition in any alloy development program since the SPC test time is relatively short and (iii) characterization of creep properties of different narrow microstructural regions in the heat-affected zones in weld joints, which is impossible to be determined in conventional creep tests. Despite these advantages, the SPC testing technique has some limitations such as the following: (i) The type of loading is bending and stretching unlike conventional creep tests in which the loading is tensile, (ii) since the test time is generally short, typically a few hundreds of hours, creep behavior due to long-time microstructural changes occurring during creep in engineering alloys cannot be evaluated, and (iii) although the test is relatively easy to perform and requires shorter time, interpretation of the results is difficult on account of the complex multi-axial nature of loading. Parker and James[10] and Ule et al.[11] were the pioneers who developed the SPC test. M.D. MATHEW, Head, Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu, 603 102, India. Contact e-mail: [email protected], [email protected] J. GANESH KUMAR and V. GANESAN, Scientific Officers, and K. LAHA, Head, are with the Creep Studies Section, Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research. Manuscript submitted May 27, 2013. Article published online October 1, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
The small punch (SP) test is generally used for evaluating the ductile to brittle transition temperature, tensile properties, fracture toughness, and creep strength of materials. The test can be carried out in a loadcontrolled mode and displacement-controlled mode. The SP test was developed originally for evaluating mechanical properties of irradiated materials since it is not possible to irradiate the standard size of tensile, impact, and creep specimens. The SP test conducted in the load-controlled mode is known as the SPC test. The SPC test technique has been undergoing continuous evolution and standardization over the past many years. An international SPC standard is still some time away, but a code of practice for SPC testing has been evolved by several European researchers and it is called the CEN code of practice. This code of practice mainly deals with the testing equipment, testing procedures, specimen size, and procedures for analysis of data.[12
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