Flow Behaviour of Modified 9Cr–1Mo Steel at Elevated Temperatures (original) (raw)
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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.
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.
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.
Dynamic Strain Ageing Behaviour of Modified 9Cr-1Mo Steel Under Monotonic and Cyclic Loading
Procedia Engineering, 2017
Dynamic strain ageing (DSA) behavior of modified 9Cr-1Mo steel under uniaxial tensile and constant strain cyclic loading is presented in this paper. Tensile tests are carried out at different strain rates from 10-3 to 10-5 s-1 in the temperature range from room temperature to 600 °C. DSA has been established in the temperature range between 250 and 400°C in terms of peak in tensile strength, minima in ductility, serrated plastic flow and negative strain rate sensitivity. In the region of DSA dislocation substructure revealed high density of dislocations and features like kinks and bowing of dislocations are observed. Low cycle fatigue behavior was studied at 300°C, over a wide range of strain amplitudes at different strain rates. An inverse effect of strain rate was observed on cyclic stress response and fatigue life at 300 °C due to DSA.
Effect of microstructure on the critical strain to onset of serrated flow in modified 9Cr–1Mo steel
International Journal of Pressure Vessels and Piping, 2012
The influence of microstructure on the strain to onset of serrated flow in modified 9Cre1Mo steel has been studied at 573 K. The different microstructures have been developed by soaking the steel at different temperatures starts at a temperature below Ac 1 to temperature above Ac 4 followed by oil quenching and tempering at 1033 K for 1 h. Soaking the steel in the intercritical temperature range (between Ac 1 and Ac 3) reduced the hardness and tensile strength of the steel whereas soaking at temperatures above Ac 3 increased the hardness and tensile strength until the occurrence of relatively soft d-ferrite for soaking at temperatures above Ac 4. The d-ferrite formation reduced the hardness of the steel. The steel showed serrated flow in the load-elongation curves at 573 K in all the microstructural conditions except for those having coarse prior austenite grain. The critical plastic strain to the onset of serrated flow was found to increase with hardness of the steel, as influenced by different microstructures. The variation of hardness, tensile strength and the critical plastic strain to onset of serration flow had been rationalized on the basis of the inter-barrier spacing to dislocation motion in the steel.
This article reports on the comparative study of the hot deformation behaviour of virgin (steel A) and rejuvenated heat treatment creep-exhausted (steel B) P91 steels. Hot uniaxial compression tests were conducted on the two steels at the deformation temperature range of 900°C-1050°C and a strain rate range of 0.01-10s-1 to 0.6 strain using Gleeble® 3500 equipment. The results showed that the flow stress largely depends on the deformation conditions. The flow stress for the two steels increased with an increase in strain rate at a given deformation temperature and vice versa. The flow stress-strain curves exhibited a dynamic recovery as the softening mechanism. The material constants determined using Arrhenius constitutive equations were: stress exponent was: steel A (5.76) and steel B (6.67), and the apparent activation energy was: steel A (473.1 kJ mol-1) and steel B (564.5 kJmol-1). From these results, steel A exhibited better workability than steel B. Statistical parameters anal...
Resisting stress for constitutive analysis of hot deformation in modified 9Cr–1Mo (P91) steel
Materials Science and Engineering: A, 2013
Flow stress data from isothermal hot compression tests on modified 9Cr-1Mo steel over a wide range of strain rate (0.001-100 s À 1) and temperature (1173-1373 K) were found to follow the universal Dorn power-law equation. Distinct stress regimes were observed with stress exponent values of $ 5 and $ 10 for low and high stress regimes, respectively. The flow behavior is rationalized by invoking resisting stress s R for dislocation motion and the modified stress exponent n 0 was close to 5 for the entire stress regime. At low stresses, s R /G ¼ K(s/G) and approaches a constant threshold stress (s R /G ¼ s H /G) in the high stress regime. This has been attributed to the transition in the mechanism from dislocation climb bypass over particles at low stresses to Orowan bowing at high stresses. The stress dependence is found to obey rate equation of the form ð_ ekT=D L GbÞ ¼ A 0 ½ðsÀs R Þ=G n0 and the constitutive parameters A 0 , n 0 , K and s H /G evaluated at different strains were employed for predicting flow stress. The successful prediction of flow stress is reflected by a higher correlation coefficient (R ¼0.99) and a lower average absolute relative error (6.62%) for the entire investigated hot working domain.
Metal flow behaviour and processing maps of high heat resistant steel during hot compression
Research Square (Research Square), 2022
This article reports the flow stress behaviour of ASTM A335 P92 steel. Uniaxial isothermal compression experiments were conducted to examine the hot deformation behaviour of P92 steel in a Gleeble® 3500 thermal-mechanical simulator. The test conditions were: 0.01-10 s-1 strain rate and 850-1000°C deformation temperature. Constitutive equations and processing maps developed were used to describe the hot deformation process. The results showed that the flow stress-strain curves exhibited a dynamic recovery (DRV) behaviour as the dominant softening mechanism. The flow stress decreased with an increase in the deformation temperature or a decrease in strain rate. Using the Arrhenius equation, the stress exponent and the activation energy values were: 8.0 and 487.56 kJmol-1 , respectively. The correlation between the constructed processing maps and microstructure showed that the optimal process parameters occurred at a lower strain rate in the region of 0.1 s-1 and deformation temperatures of 900-950 °C and 1000 °C for the steel investigated.
The Iso 5832-9 Steel Hot Flow Curves, an Analytical Study
ABM Proceedings
An austenitic stainless steel ISO 5832-9 was deformed in a torsion test machine over the temperature range of 1,000°C-1,200°C and strain rates of 0.05, 0.1, 1.0 and 5.0s-1. The Steel plastic behavior was studied by analyzing the flow curves shapes and using the constitutive equations under the conditions of thermomechanical treatment. The curves initially presented an increase in stress characterized by hardening work, followed by a drop in stress to an intermediate level that reached or not, for certain conditions, the steady state softening. The plastic flow curves of ISO 5832-9 steel displayed in three different ways: (i) Curves with continuous softening presenting plastic instability for low temperatures and high strain rates; (ii) curves type flat, here after the peak there is little variation of stress with strain presenting softening mechanism by higher contribution of dynamic recovery at low temperatures and low and intermediate strain rates; (iii) curves with softening after the critical deformation favored by high temperatures and low strain rates. These behaviors indicate the influence of the stacking fault energy (SFE) and precipitated particles on the softening kinetics of this steel.
Hot workability behaviour of two P92 creep resistant steels: Constitutive analysis
The International Journal of Advanced Manufacturing Technology, 2023
This article reports the flow stress behaviour of two P92 steels at a temperature range of 850-1000°C and a strain rate of 0.1-10 s −1 using the Gleeble® 3500 thermomechanical simulator. A physically-based constitutive model was used to analyse the effects of deformation conditions on the flow stress behaviour during deformation. This model incorporates the influence in the variation of Young's modulus and the self-diffusion coefficient as affected by temperature. The study developed constitutive equations that predict the flow stress behaviour of the two steels investigated. From the constitutive analysis of the results, the stress exponent n was: 9.8 (steel A) and 10.3 (steel B). The model used the self-diffusion activation energy of steel. The statistical parameters: correlation coefficient of 0.99 (for steel A and B), the absolute average relative error of 2.18% (steel A) and 2.20% (steel B) quantified the applicability of the model. The quantification results show that the constitutive equations developed have high accuracy in predicting the workability of the two P92 steels. The study has shown that this method is applicable in predicting the metal flow pattern of two P92 steels in the metalworking processes.