E. Isaac Samuel

Influence of temperature and strain rate on tensile work hardening behaviour of type 316 LN austenitic stainless steel

Abstract The analysis of tensile work hardening of 316 LN steel revealed three-stage behaviour. The anomalous variation in work hardening rate observed at intermediate temperatures is ascribed to dynamic strain ageing. Increased dynamic recovery at high temperatures resulted in a rapid decrease in work hardening rate.

Influence of post-weld heat treatment on tensile properties of modified 9Cr–1Mo ferritic steel base metal

Abstract The paper presents the influence of post-weld heat treatment (PWHT) on tensile properties of modified 9Cr–1Mo ferritic steel base metal. Tensile tests at room and elevated temperatures (300–873 K) were performed on specimens in normalised and tempered condition as well as with additional PWHT (993 K for 1 h; 1013 K for 1 h and 1033 K for 1 h). The yield and ultimate tensile strengths decrease gradually up to intermediate temperatures followed by a rapid fall at high temperatures in all heat treatment conditions. At intermediate temperatures, the steel exhibited ductility minima, serrated flow, negative strain rate sensitivity on flow stress and peak in the average work hardening rate. The influence of additional PWHT is reflected in a systematic and gradual decrease in both the yield and tensile strength values with increasing PWHT temperature from 993 to 1033 K for 1 h. However, there has been no appreciable change in ductility values as well as the fracture mode in PWHT conditions compared with those observed in normalised and tempered condition. Comparison of strength values in PWHT conditions suggested that the strength values remained higher than the average values specified in the French Nuclear Design Code, RCC-MR.

Applicability of Kocks–Mecking approach for tensile work hardening in P9 steel

Abstract Work hardening behaviour of P9 steel in the temperature range 300–873 K has been examined in the framework of Kocks–Mecking (K–M) approach. At all temperatures, P9 steel exhibited two-stage work hardening behaviour characterised by a rapid decrease in instantaneous work hardening rate (i.e. θ = dσ/dϵ, where σ is the true stress and ϵ is the true plastic strain) with stress at low stresses (transient stage) followed by a gradual decrease at high stresses (stage III). Stage III work hardening of P9 steel was adequately described by K–M approach. The variations of work hardening parameters associated with K–M approach for stage III with temperature indicated three distinct temperature regimes. At all temperatures, good correlations between the respective work hardening parameters evaluated using K–M approach and from Voce equation and its derivative have been obtained for P9 steel.

Unified tensile work hardening behaviour of 9Cr-1Mo ferritic steel

Abstract Tensile work hardening behaviour of 9Cr–1Mo ferritic steel has been examined in terms of the variations in instantaneous work hardening rate (θ = dσ/dϵp, where σ is true stress and ϵp is true plastic strain) with stress and plastic strain rate for a wide range of temperatures (300–873 K) and strain rates (6·33×10−5–6·33×10−3 s−1). Both θ–σ and θσ–σ exhibited two stage work hardening behaviour and distinct three temperature regimes with signatures of dynamic strain aging at intermediate temperatures and dominance of dynamic recovery at high temperatures. The variations in θ with for 300–873 K exhibited unified work hardening in terms of separate master curves for different strain rates. At all the strain rates, θ varied linearly with reciprocal of plastic strain rate independent of temperature. As a consequence, direct proportionality between rate of change in true stress and plastic strain rate is obtained.

Effects of temperature and strain rate on tensile stress–strain and workhardening behaviour of P92 ferritic steel

Abstract Detailed analysis on true stress σ–true plastic strain ϵ data indicated that the tensile flow and workhardening behaviour of P92 ferritic steel can be described most accurately by the combination of Ludwigson and Hollomon relations at strain rates ranging from 3·16×10−5 to 1·26×10−3 s−1 over the temperature range of 300–923 K. At room and intermediate temperatures, the Ludwigson equation follows the σ–ϵ data closely, whereas at high temperatures, the Ludwigson equation reduces to the Hollomon relation. The variations in σ–ϵ, workhardening parameters and θ–σ with temperature exhibited three distinct temperature regimes. At intermediate temperatures, anomalous variations in σ–ϵ, workhardening parameters and θ–σ with respect to temperature and strain rate have been observed. At high temperatures, the dominance of recovery is reflected in the rapid decrease in flow stress and workhardening parameters associated with Ludwigson/Hollomon relations with increasing temperature and decreasing strain rate.

Kocks–Mecking approach to tensile work hardening behaviour of normalised and tempered and post-weld heat-treated modified 9Cr–1Mo steel

Abstract Detailed analysis performed on modified 9Cr–1Mo steel in normalised and tempered (N+T) and three different post-weld heat treatment (PWHT) conditions indicated that the work hardening behaviour can be adequately described by Kocks–Mecking approach in the temperature range 300–873 K. The steel in all test conditions exhibited two-stage work hardening behaviour in the variation of instantaneous work hardening rate (θ) with true stress (where θ = dσ/dε, σ is true stress and ε is true plastic strain). The variations of work hardening parameters and θ–σ with temperature exhibited three distinct temperature regimes. The influence of additional PWHTs is discussed in terms of the systematic variations in flow and work hardening parameters due to microstructural softening observed with increasing PWHT temperature in modified 9Cr–1Mo steel. Comparison of work hardening parameters obtained using Voce equation and Kocks–Mecking approach demonstrated an analogy between two approaches for the steel.

Unified Tensile Work Hardening Behaviour of Thin Section Plate and Forged Thick Section 9Cr-1Mo Ferritic Steel

Abstract Detailed investigation has been performed on tensile work hardening behaviour in terms of the variations of instantaneous work hardening rate (θ = dσ/dεp, where σ is true stress and εp is true plastic strain) with stress and true plastic strain rate (ε̇p) for temperature range 300–873 K in two different material conditions, (i) normalised and tempered plate and (ii) quenched and tempered tubeplate forging of 9Cr-1Mo ferritic steel. Both plate and tubeplate forging exhibited two-stage work hardening and three different temperature regimes in the variation of θ with σ. The variations of θ with respect to ε̇p exhibited unified work hardening in terms of a single master curve independent of temperature and initial microstructure. θ varied linearly with reciprocal of plastic strain rate, i.e. 1/ε̇p, and as a consequence, linear correlation between the rate of change of true stress and true plastic strain rate independent of temperature and microstructure has been obtained.

ac MH loop measurements on Mn doped YBa2Cu3O7-δ superconductors

Isothermal ac MH (magnetization-field) loops for varying field amplitudes were recorded at 77 K on YBa2(Cu1-xMnx)3O7-δ with x = 0, 0.010, 0.015, 0.020, 0.025, 0.035 and 0.050, YBa2(Cuo.o75Fe0.025)3O7-δ, YBa2(Cu0.075Ni0.025)3O7-δ and YBa2(Cu0.075Zn0.025)3O7-δ samples up to a maximum field amplitude of 80 Oe. Flat band susceptibility, ac losses and flux profiles were deduced from the ac MH loops. The undoped sample exhibited a minimum weak link ac loss and the 5.0% doped sample showed maximum weak link ac loss. Ni and Fe doped samples showed higher granular losses.Jcg estimated from the flux profiles decreases monotonically with increasing concentrations of Mn up to 2.5%.