Gleeble Testing Research Articles

Investigation of the effects of thermal gradients present in Gleeble high-temperature tensile tests on the strain state for free cutting steel

A common feature of uniaxial high-temperature tension tests, and to a certain extent compression tests, performed using a Gleeble thermomechanical testing system that employs direct resistance heating for the characterisation of the rheological behaviour of materials is longitudinal and radial thermal gradients. The aim of this article is to experimentally quantify the axial thermal gradients for a given tensile specimen geometry of free cutting steel during heating and deformation, and design a modelling methodology to simulate their influence on the strain distribution as compared to the assumption of isothermal heating and deformation. For this purpose, a feedback algorithm was developed to control the electric current input in a similar manner to that applied by the Gleeble testing system, which implemented via the UAMP user subroutine in ABAQUS for use in electro-thermal simulations of the direct resistance Joule heating used by the Gleeble testing system. The predicted temperature fields were compared with the temperature distributions recorded experimentally along the gauge section of the tensile specimens. Finite element simulations of Gleeble tensile tests were carried out under isothermal conditions and using the temperature distributions calculated by the feedback algorithm for a range of strain rates and temperatures in order to evaluate the difference in predicted stress state. The results show that an isothermal assumption should only be used conservatively in finite element simulation of the Gleeble thermomechanical test employing direct resistance heating to avoid significant errors.

Flow Stress and Pyroplastic Behaviour of Ultra-Low Carbon Steel in Warm Temperature Range

In order to analyze the mechanical behaviour of ultra-low carbon steel in warm rolling, the flow stress and pyroplastric behaviour were investigated on the Gleeble-3500 with the deformation temperatures in the warm range. The strain rates of 0.1, 1 and 10s-1 were applied to the temperatures above. A series of stress-strain curves were obtained after the compression Gleeble tests with different parameters. The result indicates the flow stress increases with the decreasing deformation temperatures during the compression. And it increases with the increasing strain rate as well. The constitutive equation, which includes the deformation activation energy Q and the Kelvin temperature T, was developed by using the concept that proposed by C. M. Sellars and W.J. M. Tegart. These equation results can be verified by the results of Gleeble compression test. It indicates the average error is reasonable and acceptable for predicting the flow stress and pyroplastic deformation behaviour of ultra-low carbon steel in warm temperature range. The achieved constitutive equation provides theoretical fundaments for designing the warm rolling process of ultra-low carbon steel. The experimental data also can be used as material property parameters for the establishment of finite element (FE) model.

Hot compression behavior and deformation microstructure of Mg-6Zn-1Al-0.3Mn magnesium alloy

The hot compression behavior of a wrought Mg-6Zn-1Al-0.3Mn magnesium alloy was investigated using Gleeble test at 200–400 °C with strain rates ranging from 0.01 to 7 s−1. The true stress-strain curves show that the hot deformation behavior significantly depends on the deformation temperature and strain rate. The calculated hot deformation activation energy Q is 166 kJ/mol with a stress exponent n=5.99, and the constitutive equation is deduced to be ɛ˙=3.16×1013[sinh(0.010σ)]5.99 exp [−1.66×105/(RT)]. Deformation microstructure shows that the incompletely dynamically recrystallized grains can be found at grain boundaries and twins with the strain rates ranging from 0.01 to 1 s−1 at 250 °C, and completely dynamic recrystallization occurs when the temperature is 350 °C or above during hot compression, the size of recrystallized grains decreases with the increment of the strain rate at the same temperature. The relatively suitable deformation condition is considered temperature 330–400 °C and strain rate of 0.01–0.03 s−1, and temperature of 350 °C and strain rate of 1 s−1.

Effects of different solution heat treatments on the hot ductility of superalloys

The susceptibility to heat affected zone cracking of Waspaloy has been investigated in terms of its hot ductility, measured as the reduction of area (RA). Gleeble testing with on-heating as well as on-cooling test cycles was carried out to illuminate the influence of different 4 h solution heat treatments between 996 and 1080°C. A ductility maximum of between 80 and 90%RA was found at 1050–1100°C for all conditions in the on-heating tests. Although the different heat treatment conditions showed similar macrohardness, the particle size and distribution of the γ′ and M23C6 phases differed, which significantly affected the on-heating ductility in the lower temperature test region. The ductile to brittle transition was initiated at 1100°C in the on-heating testing with indications of grain boundary liquation at the higher test temperatures. Ductility recovery, as measured in the on-cooling tests from 1240°C, was very limited with <30%RA for all conditions and test temperatures except for the 1080°C/4 h treatment, which exhibited 60%RA at 980°C.

Effects of Processing Parameters on Microstructure and Properties of Ultra High Strength Linepipe Steel

To examine the effect of processing parameters on microstructural evolution and to obtain the excellent combination of strength and toughness, simulation of thermo-mechanical processing was conducted using the Gleeble machine. Trial production was then conducted under the conditions obtained by Gleeble tests. Based on the results of microstructure analysis and mechanical property evaluation, the relationship between microstructural features and mechanical properties was elucidated. The result shows that the volume fraction of constituted phases can be controlled through adjusting the cooling rate and finish cooling temperature in order to get different strength levels. As cooling rate increases, the volume fraction of upper bainite increases, which leads to the increase of strength. The upper shelf energy (USE) increases with increasing volume fraction of acicular ferrite in bainite base because of the small effective acicular ferrite grain size. Ductile-brittle transition temperature (DBTT) decreases with increasing acicular ferrite volume fraction. High reduction in the rough stage has great influence on grain refinement.

Gleeble Testing to Assess Solid/Liquid Metal Embrittlement of Gun Steels by Copper

Gleeble testing was performed to assess the solid/liquid metal embrittlement of gun steels by copper. An interior ballistics and finite element model provided the maximum bore temperatures in a 155 mm gun after aggressive firing. Specimens were manufactured out of three different steels. Testing was performed on bare steel as well as copper plated specimens at temperatures ranging from 868°C to 1,100°C. Additionally, notched and un-notched specimens were tested. After testing, metallography, scanning electron microscopy, and energy dispersive spectroscopy were performed. Embrittlement occurred in all copper plated steels tested at 1,100°C. Below 1,100°C, there was only slight evidence of embrittlement.

Effect of different solution heattreatments on hot ductility of superalloysPart 2 – Allvac 718Plus

The hot ductility of Allvac 718Plus for different solution heat treatments (954°C–15 h, 954°C–1 h, 982°C–1 h and 1050°C–3 h+954°C–1 h) has been investigated using Gleeble testing. Substantial variations in the microstructure among the heat treatments affected the Gleeble test hot ductility only to a very limited extent. Constitutional liquation of the NbC phase was found to be the main cause for the poor ductility at high testing temperatures in the on-heating cycle as well as at the lower temperatures on-cooling. Grain boundary δ phase was seen to assist the constitutional liquation of the NbC phase. Based on established evaluation criteria for Gleeble ductility testing, a ranked indicator for weldability is suggested.

Effect Of Phosphorous and Silicon On Hot Cracking Susceptibility Of 14Cr-15Ni-2.3 Mo Ti-Modified Fully-Austenitic Stainless Steel

Alloy D9, fully-austenitic stainless steel containing 15Cr, 15Ni, 2.3Mo and 0.3Ti [wt. %] is being used as the material for the fuel clad and wrapper in Fast Breeder Reactors (FBRs). An improved version of this alloy containing higher nickel, silicon and phosphorous than present in D9 is being developed, with the objective of enhancing the radiation swelling resistance of this alloy to achieve higher burn-up for the fuel. Fabrication of this alloy involves autogenous welding to seal the fuel pins and fuel bundle containers. In fully-austenitic stainless steels like D9, hot cracking is a major concern during welding, especially in the absence of any residual delta-ferrite in the prior austenitic mode of solidification. In this study, both Varestraint and hot ductility tests were used to evaluate the hot cracking susceptibility of these alloys. The Varestraint test results indicated that these new alloys have a very high hot cracking susceptibility during autogenous welding, as the total crack length and maximum crack length in both the weld and heat-affected zone and also the BTR values were very high, compared to that of alloy D9. Hot ductility (Gleeble) testing was also carried out to determine the temperature range at which the material is prone to hot cracking when subjected to a thermal cycle that simulates actual welding. The Gleeble test results are also unfavourable to the weldability of these alloys since the nil ductility range of these alloys is much higher compared to that of reasonably weldable alloys. This paper discusses the results of the hot cracking behaviour of this fully-austenitic SS material using the Varestraint and hot ductility tests.

Effect of solution heat treatments on superalloys Part 1 – alloy 718

The hot ductility as measured by Gleeble testing of Alloy 718 at four different solution heat treatments (954°C/15 h, 954°C/1 h, 982°C/1 h and 1050°C/3 h+954°C/1 h) has been investigated. It is concluded that constitutional liquation of NbC assisted by δ phase takes place and deteriorates the ductility. Parameters established by analysing the ductility dependence on temperature indicate a reduced weldability of the material in the coarse grain size state (ASTM 3) while indicating an increased weldability when containing a large amount of δ phase due to a grain boundary pinning effect. The accumulation of trace elements during grain growth at the highest temperature is believed to be the cause for the observed reduced on-cooling ductility.

Investigation to Self-Piercing Riveting of Wrought Magnesium AZ31 Sheets

In this study, the fabrication of the desired SPR joints was investigated as a function of the preheat temperature and strain rate. To determine the optimum preheat temperature, Gleeble thermal analogue testing of 2mm thick magnesium AZ31 was used to assess the combined influence of preheat temperature and strain rate on the strength and total elongation of magnesium AZ31. Magnesium alloy AZ31 with a thickness of 2mm was preheated with various temperatures prior to self-piercing riveting. The appearances, cross-sections and mechanical tests of the SPR magnesium AZ31 joints were investigated. It was found that a preheat temperature of 180 to 200oC largely eliminated the cracking in magnesium AZ31 joints. The joint strength increases with increasing preheat temperature from ambient to 200oC. The strength increase is attributed to the reduction in joint cracking and an increase in mechanical interlock between the rivet and work pieces.

Solid Welding Conditions for Seam and Hollow Extrusion Process of 7075 Aluminum Alloy

Direct extrusion by porthole – bridge die configuration has been successfully used to fabricate products with hollow cross sections for 6000 series aluminum alloys. However, if for 7000 series aluminum alloys, this situation alerts since different alloy composition such as Cu causing hollow extrusion failed due to not enough welding strength in seam. In order to determine the solid welding conditions during hollow extrusion with porthole die structure for high strength aluminum alloy, an easy tooling configuration has been designed. The proposed method is easy and cheap because there is no necessary to conduct experiment in controlled environment such as in vacuum chamber of Gleeble test or in a protective atmosphere. A seam and hollow extrusion for square tube has been conducted to obtain the welding strength comparison to the proposed solid welding method which shows good agreement.

Inverse finite element modelling and identification of constitutive parameters of UHS steel based on Gleeble tensile tests at high temperature

The rheological behaviour of an ultra high strength (UHS) steel is investigated by Gleeble tensile tests at low-deformation rates and high temperature, from 1200°C to solidus temperature. Results show that large thermal gradients exist in specimens, resulting in heterogeneous deformation, which makes the identification of constitutive parameters difficult from the directly deduced nominal stress–strain curves. The advantages of an inverse identification method – associating a direct finite element model of Gleeble tests and an optimization module – are demonstrated in such conditions. The constitutive parameters identified by this technique have been successfully applied to additional tests, more complex in nature than those used for the identification of parameters. However, such tests combining successive loading and relaxation stages have revealed some limitations of the considered constitutive model.

A critical analysis of plastic flow behaviour in axisymmetric isothermal and Gleeble compression testing

Coupled thermo-mechanical finite element modelling of both isothermal axisymmetric compression and compression testing using the Gleeble thermo-mechanical simulator has been carried out in order to compare the levels of relative stress error which can arise during each test. A Norton-Hoff material model has been used as a basis for evaluating the testing methods and the calculation of the relative error by providing reference stress–strain curves. The errors arise from effects such as interface friction causing non-uniform deformation fields and heat generation in both testing cases and from initial specimen temperature profiles in the case of the Gleeble testing. These errors are shown to be up to approximately 20% and vary throughout the test from positive to negative and are therefore important to consider when processing experimental data.

A Finite Element Analysis of Errors in Axisymmetricisothermal and Gleeble Compression Testing of Ti-6Al-4V

Coupled thermo-mechanical finite element modelling of both the isothermal axisymmetric and Gleeble compression testing of Ti-6Al-4V has been carried out in order to give insight into errors which occur when generating flow stress data for process modelling by these methods. A strain-rate and temperature-dependent Norton-Hoff material model is used to represent the material in the analyses and also for calculation of relative stress error. Significant errors are predicted for both testing methods caused by interface friction between the platens and the specimen and plastically-induced heat generation. An axial temperature profile is also predicted in the Gleeble test specimen from resistance heating which increases deformation at the axial centre of the specimen and introduces further errors. Stress errors of up to 25% are predicted.

A Weldability Study of Nickel-Iron-Cobalt Hydrogen Resistant Alloys Using Weld Simulation in Parallel with Variable Restraint Testing

Incoloy 903 overlays have been used to provide hydrogen environment embrittlement (HEE) resistance to welds in nickel alloy 718 structures. This is problematic because application of the required overlays has a history of high rejection and rework due to interpass microfissuring. Kovar has been identified as a potential hydrogen resistant replacement for Incoloy 903. A weldability study was initiated to compare the hot crack (microfissure) resistance of the two alloys to determine if substitution of Kovar for Incoloy 903 has the potential to improve the fabricability of HEE overlays. Varestraint testing indicates that Kovar has much higher crack initiation strains for both HAZ and weld metal cracking. Crack initiation strains were approximately 2% for Kovar while Incoloy 903 crack initiation strains were only 0.25% . Maximum crack lengths (MCL) observed on Kovar Varestraint tests were 0.12mm and 0.58mm for base and weld metal respectively, while 903 MCLs were 0.56mm and 2.3mm. Gleeble hot ductility testing indicates that Kovar has a nil ductility range of 7 degrees C while Incoloy 903 has a range of approximately 45 degrees C. The larger range observed for 903 is an indication of its greater crack susceptibility. Fabricability was correlated to material microstructure using optical microscopy, scanning electron microscopy and microprobe analysis.

Rapid Flow Stress Characterization of Steel

This rapid flow stress characterization concept involves rapid heating to an initial test temperature, T1, followed by loading and short-time stress relaxation measurement, followed by heating to a higher temperature, T2, followed by loading and short-time stress relaxation measurement, followed by heating to T3, and so on. This test sequence can generate stress-strain rate-temperature data over a wide spectrum, with a single specimen. The principal advantage of this method of flow stress characterization is its short-time format. The cost of specimen preparation is modest, as well. Beyond this, the test methodology provides very accurate temperature control. It also tests a given metallurgical structure, with minimal complications from structural evolution due to plastic deformation. This study has demonstrated the feasibility of this method on plain carbon and austenitic stainless steels, using a Gleeble testing machine. This includes demonstrated consistency between single-test-per-specimen data and data derived from sequential testing on a single specimen, as well as consistency with conventionally developed flow stress data.

Thermomechanical Processing of Pipeline Steels with a Reduced Mn Content

Lowering the Mn content of hot rolled pipeline steel can economise the steel making process by eliminating costly desulphurisation and at the same time improve product properties, particularly toughness, by reducing the formation of MnS inclusions. Lower Mn contents, however, have significant implications for austenite recrystallization and austenite (γ) to ferrite (a) transformation behaviour. This study compares the recrystallization start (T nr ) and y to a transformation (A r3 ) temperatures of two low Mn steels to those of a commercial steel with a conventional Mn content. Simulations of thermomechanical processing were carried out using a Gleeble 3500 testing machine. The T nr for the low Mn alloy design were found to be ∼25°C higher than for the high Mn steel, while the A r3 of the low Mn steel were some 50°C higher. The higher A r3 promotes the formation of coarse ferrite grains, thus reducing the strengthening and toughening benefits of a fine grain size. However, this could largely be overcome by maximising the degree of deformation performed between T nr and A r3 and maintaining a combination of high cooling rates and low stop cooling temperatures below A r3 , thus providing a high density of nucleation sites and promoting high nucleation rates. Production trials validated the results from the Gleeble tests.

변형지도 모델링을 통한 몰리브데늄의 고온 변형에 따른 미세조직 변화 연구

The hot deformation characteristics of pure molybdenum was investigated in the temperature range of <TEX>$600{\sim}1200^{\circ}C$</TEX> and strain rate range of <TEX>$0.01{\sim}10.0/s$</TEX> using a Gleeble test machine. The power dissipation map for hot working was developed on the basis of the Dynamic Materials Model. According to the map, dynamic recrystallization (DRX) occurs in the temperature range of <TEX>$1000{\sim}1100^{\circ}C$</TEX> and the strain rate range of <TEX>$0.01{\sim}10.0/s$</TEX>, which are the optimum conditions for hot working of this material. The average grain size after DRX is <TEX>$5{\mu}m$</TEX>. The material undergoes flow instabilities at temperatures of <TEX>$900{\sim}1200^{\circ}C$</TEX> and the strain rates of <TEX>$0.01{\sim}10.0/s$</TEX>, as calculated by the continuum instability criterion.

The Electrical Contact Resistance in Resistance Welding Evaluated by Gleeble Testing Machine

Electrical contact resistance is an important parameter in resistance welding. In this article, a Gleeble 3500 thermal-mechanical testing machine was employed to measure the contact resistance. The machine is equipped with a special electrical resistance measuring system. The contact resistance is experimentally investigated for welding low carbon steel to themselves. A detailed work was carried out to investigate the influence of pressure, temperature on the contact resistance of low carbon steel. The experimental results show that the contact resistance decreases when pressure or temperature increases.

Deformation behavior and mechanisms of Ti-1023 alloy

The deformation behavior and mechanisms of Ti-1023 alloy were studied in the temperature range of 650–900 °C and strain rate range of 0.001–10 s −1 by compression and tensile tests. The results show that in a limited strain rate range of 0.001–0.1 s −1, the kinetic rate equation is obeyed and a linear fit is obtained at all the temperatures. The apparent activation energy is 322 kJ/mol in the α-β region and 160 kJ/mol in the β region, respectively. Power dissipation maps of this alloy developed by using Gleeble test data show three domains in the tested range. Superplasticity, marked by abnormal elongation at 700 °C, occurs in the temperature range of 650–750 °C and at strain rates below about 0.03 s −1. Large grain superplasticity takes place in the temperature range of 750–850 °C and strain rates range of 0.001–0.03 s −1. Dynamic recrystallization occurs in the temperature range of 850–900 °C and at strain rates below about 1 s −1. The instability maps of this alloy were also developed.