High-Temperature Behaviour of Austenitic Alloys

Theoretical and Applied Mechanics Letters

2014

Self Cite

In this study, slow strain rate tensile testing at elevated temperature is used to evaluate the influence of temperature and strain rate on deformation behaviour in two different austenitic alloys. One austenitic stainless steel (AISI 316L) and one nickel-base alloy (Alloy 617) have been investigated. Scanning electron microscopy related techniques as electron channelling contrast imaging and electron backscattering diffraction have been used to study the damage and fracture micromechanisms. For both alloys the dominante damage micromechanisms are slip bands and planar slip interacting with grain bounderies or precipitates causing strain concentrations. The dominante fracture micromechanism when using a slow strain rate at elevated temperature, is microcracks at grain bounderies due to grain boundery embrittlement caused by precipitates. The decrease in strain rate seems to have a small influence on dynamic strain ageing at 650 • C.Energy production by power plants must be more efficient to meet the increasing energy consumption. A higher efficiency can be established by increasing temperature and pressure in the boiler sections. This gives higher demands on the materials that should operate within these power plants. Not only is great high-temperature corrosion resistance of importance but also the mechanical behaviour during slow deformation because these alloys can undertake low deformation rates from 10 −5 s −1 (low cycle fatigue) to 10 −7 s −1 (creep) during service. 1,2 Current study was focused on damage and fracture micromechanisms related to low strain rate and high-temperature in two austenitic materials. Using uniaxial slow strain rate tensile testing (SSRT) at high-temperatures, the influence of low strain rates on these mechanisms could be investigated. Also precipitation due to high-temperature and deformation could be coupled to the damage and fracture behaviours.The austenitic stainless steel, AISI 316L and the nickel-base alloy, Alloy 617 were used in this study. Both types were solution treated before testing, AISI 316L at 1 050 • C for 10 min and Alloy 617 at 1 175 • C for 20 min. Table 1 shows the chemical composition of the materials.For the SSRT a Roell-Korthaus and an Instron 5982 tensile test machines were employed. The tensile test machines were equipped with a MTS 653 furnace and Magtec PMA-12/2/VV7-1 a) Corresponding author.

mentioning

confidence: 99%

Deformation behaviour in advanced heat resistant materials during slow strain rate testing at elevated temperature

Theoretical and Applied Mechanics Letters

2014

Self Cite

“…At elevated temperature serrated yielding, also called jerky flow, can be seen in the stress-strain curve giving support for the existence of dynamic strain ageing (DSA) [9,10]. Earlier studies [11,12] have shown that AISI 316L has decreasing ductility and strength with increasing temperature when using a strain rate of 2x10 -3 /s in the temperature regime where DSA are active. DSA could be responsible for giving a contribution to the lower ductility at elevated temperatures when using a higher strain rate (2*10 -3 /s) [13].…”

Section: Resultsmentioning

confidence: 87%

Influence of Deformation Rate on Mechanical Response of an AISI 316L Austenitic Stainless Steel

2014

AMR

Austenitic stainless steels are often used for components in demanding environment. These materials can withstand elevated temperatures and corrosive atmosphere like in energy producing power plants. They can be plastically deformed at slow strain rates and high alternating or constant tensile loads such as fatigue and creep at elevated temperatures. This study investigates how deformation rates influence mechanical properties of an austenitic stainless steel. The investigation includes tensile testing using strain rates of 2*10-3/ and 10-6/s at elevated temperatures up to 700°C. The material used in this study is AISI 316L. When the temperature is increasing the strength decreases. At a slow strain rate and elevated temperature the stress level decreases gradually with increasing plastic deformation probably due to dynamic recovery and dynamic recrystallization. However, with increasing strain rate elongation to failure is decreasing. AISI 316L show larger elongation to failure when using a strain rate of 10-6/s compared with 2*10-3/s at each temperature. Electron channelling contrast imaging is used to characterize the microstructure and discuss features in the microstructure related to changes in mechanical properties. Dynamic recrystallization has been observed and is related to damage and cavity initiation and propagation.

“…AISI 304 shows less serrated yielding at the low strain rate at 700°C than for a higher straining rate. For aged samples of Alloy 617 serrated yielding is not present at 700°C using a strain rate of 2*10 -3 /s, but DSA occur in the stress-strain curve for the non-aged sample under same conditions [7]. However, the serrated yielding occurs when using a strain rate of 10 -6 /s at 700°C, probably due to a decrease in dislocation motion rate.…”

Section: Resultsmentioning

confidence: 94%

Damage and Fracture Behaviours in Aged Austenitic Materials during High-Temperature Slow Strain Rate Testing

2013

KEM

Keywords: High-temperature, ageing, slow strain rate, biomass power plant, austenitic stainless steel, nickel base alloy and dynamic strain ageing.Abstract. Biomass power plants with high efficiency are desired as a renewable energy resource. High efficiency can be obtained by increasing temperature and pressure. An upgrade of the material performance to high temperature material is therefore required in order to meet the increased demands due to the higher temperature and the more corrosive environment. In this study, the material's high-temperature behaviours of AISI 304 and Alloy617 under slow deformation rate are evaluated using high-temperature long-term aged specimens subjected to slow strain rate tensile testing (SSRT) with strain rates down to 10 -6 /s at 700°C. Both materials show decreasing stress levels and elongation to fracture when tensile deformed using low strain rate and elevated temperature. At high-temperature and low strain rates cracking in grain boundaries due to larger precipitates formed during deformation is the most common fracture mechanism.