Tensile flow and work hardening behaviour of 9Cr–1Mo ferritic steel in the frame work of Voce relationship (original) (raw)
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Analysis of Tensile Stress-Strain and Work-Hardening Behavior in 9Cr-1Mo Ferritic Steel
Metallurgical and Materials Transactions A, 2013
Detailed analysis on tensile true stress (r)-true plastic strain (e) and work-hardening behavior of 9Cr-1Mo steel have been performed in the framework of the Voce relationship and Kocks-Mecking approach for wide range of temperatures, 300 K to 873 K (27°C to 600°C) and strain rates (6.33 9 10 À5 to 6.33 9 10 À3 s À1). At all test conditions, re data were adequately described by the Voce equation. 9Cr-1Mo steel exhibited two-stage work-hardening behavior characterized by a rapid decrease in instantaneous work-hardening rate (h = dr/de) with stress at low stresses (transient stage) followed by a gradual decrease in h at high stresses (stage III). The variations of work-hardening parameters and h-r as a function of temperature and strain rate exhibited three distinct temperature regimes. Both work-hardening parameters and h-r displayed signatures of dynamic strain aging at intermediate temperatures and dominance of dynamic recovery at high temperatures. Excellent correlations have been obtained between work-hardening parameters evaluated using the Voce relationship and the respective tensile properties. A comparison of work-hardening parameters obtained using the Voce equation and Kocks-Mecking approach suggested an analogy between the two for the steel.
Detailed analysis on true stress s-true plastic strain e 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?16610 25 to 1?26610 23 s 21 over the temperature range of 300-923 K. At room and intermediate temperatures, the Ludwigson equation follows the s-e data closely, whereas at high temperatures, the Ludwigson equation reduces to the Hollomon relation. The variations in s-e, workhardening parameters and h-s with temperature exhibited three distinct temperature regimes. At intermediate temperatures, anomalous variations in s-e, workhardening parameters and h-s 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. Sainath et al.
Tensile tests were performed at strain rates ranging from 3.16 9 10 À5 to 1.26 9 10 À3 s À1 over a temperature range of 300 K to 923 K (27°C to 650°C) to examine the effects of temperature and strain rate on tensile deformation and fracture behavior of P92 ferritic steel. The variations of flow stress/strength values, work hardening rate, and tensile ductility with respect to temperature exhibited distinct three temperature regimes. The fracture mode remained transgranular. The steel exhibited serrated flow, an important manifestation of dynamic strain aging, along with anomalous variations in tensile properties in terms of peaks in flow stress/strength and work hardening rate, negative strain rate sensitivity, and ductility minima at intermediate temperatures. At high temperatures, the rapid decrease in flow stress/strength values and work hardening rate, and increase in ductility with increase in temperature and decrease in strain rate, indicated the dominance of dynamic recovery.
Materials & Design (1980-2015), 2013
True stress (r)-true plastic strain (e) and work hardening behaviour of modified 9Cr-1Mo steel in normalised and tempered (N + T), and three different post weld heat treatment (PWHT) conditions have been examined in the framework of Hollomon, Ludwigson and Voce relationships in the temperature range 300-873 K. The analysis indicated that the re behaviour is described accurately by the combination of Ludwigson and Hollomon equations. Alternatively, Voce equation provides an adequate description of re behaviour in the range 300-873 K. The variations of work hardening parameters associated with Ludwigson/Hollomon and Voce relationships with temperature exhibited three distinct temperature regimes displaying signatures of dynamic strain ageing at intermediate temperatures and dominance of dynamic recovery at high temperatures. The influence of additional PWHTs is discussed in terms of the systematic variations in flow and work hardening parameters due to microstructural softening with increasing PWHT temperature observed for the steel.
Unified description of tensile work hardening behaviour of P92 steel
Tensile work hardening behaviour of P92 steel has been examined over wide range of temperatures (300-923 K) and strain rates (3.16 Â 10 À 5 -1.26 Â 10 À 3 s À 1 ) in terms of the variations of instantaneous work hardening rate (θ) with true stress (s) and true plastic strain rate (ε̇p). At all the temperatures and applied strain rates, θ vs. s exhibited two-stage work hardening behaviour characterised by a rapid decrease in θ at low stresses (transient stage) followed by a gradual decrease at high stresses (stage-III). θ vs. s also exhibited three distinct temperature regimes along with signatures of dynamic strain ageing at intermediate temperatures and dominance of dynamic recovery at high temperatures. Analysis in terms of the variations of θ with ε̇p displayed a unified curvilinear behaviour independent of temperature. For a given applied strain rate, a linear correlation between θ and the reciprocal of plastic strain rate (1/ε̇p) was observed. As a consequence, the rate of change of true stress was observed to be directly proportional to plastic strain rate independent of temperature. Further, a unified description of tensile work hardening in terms of a master curve between work hardening rate (θ) and plastic strain rate normalised by applied strain rate (ε̇p/ε̇a) has been obtained for the range of strain rates and temperatures examined.
Temperature and strain rate effect on tensile properties of 9Cr–1·8W–0·5Mo–VNb steel
Materials at High Temperatures, 2014
Tensile tests have been carried out on 9Cr-1?8W-0?5Mo-VNb steel (grade 92) over wide ranges of temperature (300-923 K) and strain rate (3610 23-3610 25 s 21). The tensile strength of the steel decreased slowly with temperature at relatively lower temperature range, whereas rapidly in the higher temperature range with a plateau in the intermediate temperature range. The decrease in strain rate decreased the tensile strength of the steel both at lower and higher temperature ranges. Elongation to fracture and reduction in area increased with increase in temperatures and decrease in strain rate at higher temperature regime with a plateau in the intermediate temperature regime. The ductile mode of tensile failure has been observed in the investigated temperatures and strain rates. The plateau in the variation of tensile strength with temperature, the negative strain rate sensitivity of tensile strength and minimum in ductility of the steel in the intermediate temperature range are considered as a consequence of dynamic strain ageing. The rapid decrease in tensile strengths and increase in ductility at high temperatures have been attributed to the dynamic recovery.
Materials Science and Technology, 2007
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.
Influence of strain rate and temperature on serrated flow in 9Cr–1Mo ferritic steel
Tensile tests were performed on specimens in normalised and tempered condition at temperatures ranging from 300 to 873 K and at four strain rates in the range 6.33 Â 10 À 5 to 6.33 Â 10 À 3 s À 1 to examine serrated flow behaviour in 9Cr-1Mo ferritic steel. At all strain rates, the steel exhibited different types of serrations namely type A, B and C serrations at intermediate temperatures, and the nature and type of serrations were strongly dependent on temperature and applied strain rate. Serrations were observed only after a specimen was deformed beyond a critical plastic strain. Critical strain for type A and A þB serrations decreases with increase in temperature and decrease in strain rate. Inverse temperature dependence of critical strain for type C serrations was observed. The activation energy of 86 kJ mol À 1 obtained for serrated flow suggested that diffusion of an interstitial solute such as carbon is responsible for dynamic strain ageing in 9Cr-1Mo steel.
EFFECTS OF STRAIN RATE ON WORK HARDENING OF HSLA AND Ti-IF STEELS
Metallurgy and Foundry Engineering, 2006
B-a coefficient dependent on the chemical composition and strain rate and directly correlates to the stage of austenite decomposition c 1…5-Zerilli-Armstrong model's constants d-grain size, μm, mm D-Cowper-Symonds coefficient f-the volume fraction of precipitates (for Nb-microalloyed steels: f = 1.13⋅10-4 [Nb]) G-shear modulus, MPa K-microstructural stress intensity, MPa k-Boltzmann's constant, J/K K p-dispersion strengthening contribution coefficient k s-constant associated with subgrain boundary strength Δl-the distance between dislocation barriers M-orientation factor [M]-chemical composition n-hardening exponent P-constant dependent on ferrite grain size, MPa