Influence of strain rate and temperature on tensile properties and flow behaviour of a reduced activation ferritic–martensitic steel
Introduction
In nuclear fusion reactor applications, the blanket module facing the plasma is expected to be exposed to the simultaneous effects of mechanical and thermo-mechanical stresses and intense neutron irradiation-induced damage at high temperatures. Ferritic steels as structural materials for the blanket module of fusion reactors are now under prime consideration because of their inherent void swelling resistance coupled with low thermal expansion coefficient and high thermal conductivity compared to austenitic steels [1], [2]. The requirement of safe operation and decommissioning of blanket module of fusion power plants and the disposal of radioactive wastes have also demanded the development of steels with reduced residual radioactive characteristics [3], [4]. High chromium ferritic–martensitic steels have been used extensively in power generation and petrochemical industries. The RAFM steels are modelled after the well established modified 9Cr–1Mo steel by replacing the highly radioactive elements residual molybdenum and niobium respectively with tungsten and tantalum having comparatively lower residual radioactivity. The steel is generally used in the normalised and tempered condition and has a tempered martensitic structure. It derives its high temperature strength from the complex microstructures consisting of high dislocation density, sub-boundaries decorated with M23C6 carbides and (Ta,V)-carbides of MX type in the intragranular region [5], [6], [7].
To predict the performance of the reactor components, an understanding of the plastic flow behaviour of the structural materials is essential. In the present work, detailed analysis of tensile deformation of a RAFM steel has been carried out to understand the high temperature plastic flow behaviour of the material. The plastic flow behaviour of the material has been studied in terms of the constitutive relationships proposed by Hollomon [8], Ludwik [9], Ludwigson [10] and Voce [11]. The appropriate constitutive relationship describing the tensile flow behaviour of the material over wide ranges of strain rate and temperature has been identified. The parameters of the relevant constitutive relationship have been examined in detail in order to gain an insight into the variations in strain-hardening characteristics of the steel at different temperatures and strain rates.
Section snippets
Experimental
The RAFM steel has been produced at M/s. Mishra Dhatu Nigam Limited (MIDHANI), Hyderabad, India. The ingot was produced by vacuum induction melting followed by vacuum arc refining processes. The ingot was hot-forged and subsequently rolled to a 12 mm thick plate. The steel plates were subjected to the final heat treatment consisting of normalisation at 1250 K for 30 min followed by tempering at 1033 K for 90 min. The chemical composition of the steel is shown in Table 1.
Button-head cylindrical
Tensile properties
Engineering stress–strain curves of the material tested at a strain rate of 3 × 10−3 s−1 over the temperature range of 300–873 K are shown in Fig. 1. Similar variation in stress–strain was also observed at other two investigated strain rates. The results revealed that the material exhibited monotonic stress–strain curves over the entire temperature range with no serrated flow in the intermediate temperature range as commonly observed in ferritic steels [12]. The strain to failure (ef) was found to
Conclusions
The following conclusions have been drawn from the investigation of tensile flow behaviour of the RAFM steel.
- (a)
Both the yield stress and ultimate tensile strength of the steel decrease with temperature with a relatively slower rate of decrease at the intermediate temperature range.
- (b)
Tensile strength of the steel was observed to increase with strain rate. Negative strain rate sensitivity of the flow stress in the intermediate temperature range revealed the occurrence of dynamic strain ageing in the
Acknowledgements
The authors thank Shri S. C. Chetal, Director, Indira Gandhi Centre for Atomic Research, Kalpakkam, India for his keen interest in this work. The collaboration with M/s. Mishra Dhatu Nigam Limited (MIDHANI), Hyderabad, India in melting the steel is acknowledged.
References (24)
J. Nucl. Mater.
(1991)- et al.
J. Nucl. Mater.
(2002) - et al.
Fusion Eng. Design
(2001) - et al.
Fusion Eng. Des.
(2006) - et al.
Int. J. Pres. Ves. Piping
(2004) - et al.
Acta Metall.
(1984) - et al.
J. Nucl. Mater.
(2011) - et al.
Mater. Sci. Eng. A
(2012) - et al.
Acta metall.
(1987) - et al.
J. Nucl. Mater.
(1994)
Nucl. Fission
Plasma Phys. Control Fusion
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