Hot Ductility Tests Research Articles

Effect of Cr on the Hot Ductility of Austenitic Fe-Mn-Al-C Lightweight Steel

In this study, a hot ductility test was performed for Fe-30Mn-10.5Al-0.9C-Cr austenitic lightweight steels. The test was carried out through a commercial Gleeble simulator at a heating rate of 350 °C/sec and cooling rate of 50 °C/sec, with a stroke rate of 50 mm/sec. Microstructural analysis for understanding the hot ductility behavior was conducted through optical and scanning electron microscopy. The lightweight steels exhibited similar hot ductility behavior in accordance with temperature despite the addition of Cr. The experimental results indicated that the κ-carbide precipitation had an insignificant influence on the hot ductility test. However, ductility at low temperature was induced by slip mechanism, while dynamic recrystallization had significant influence at high temperatures during the on-heating thermal cycle. In the on-cooling thermal cycle, the melted and re-solidified grain boundaries decreased the overall ductility, exhibiting the same tendency as that observed in the on-heating test.

Liquation cracking in laser powder bed fusion-fabricated Inconel718 of as-built, stress-relieved, and hot isostatic pressed conditions

A critical factor of the laser powder bed fusion (LPBF) additive manufacturing processed Inconel718 is its susceptibility to liquation cracking, primarily caused by the incipient melting of the grain boundary Laves phase or carbide (Nb-rich intermetallic phases). In this study, the liquation cracking behavior of the LPBF-processed Inconel718 was investigated using Gleeble® hot-ductility tests. In particular, the effect of commonly employed post-LPBF heat treatments, such as stress relieving, and hot isostatic pressing (HIP), on the liquation cracking resistance was examined. While the as-built Inconel718 exhibited good liquation cracking resistance, its liquation cracking resistance decreased after the stress relieving and HIP treatment. The variation in liquation cracking susceptibility was attributed to microstructural differences, including grain size, size and volume fraction of the low-melting carbides phase, and the segregation pattern of the solute element Nb. Good liquation cracking resistance of the as-built provides more flexibility in process design involving high temperatures. Meanwhile, HIP treatment can reduce internal defects but presents a significant disadvantage of increased liquation cracking susceptibility. These findings underscore the importance of carefully designing post-processing conditions for additively manufactured parts.

Weldability study of 304HCu stainless steel using varestraint and “Gleeble” based hot ductility tests

The susceptibilities of 304HCu SS to solidification and liquation cracking are assessed in the current work and the underlying mechanisms are clarified. The development of γ + Nb4C3 eutectic along the interdendritic areas in the fusion zone is attributed for solidification cracking in this stainless steel. To forecast and rank the susceptibility of an alloy to solidification cracking, a novel technique is put forth and experimentally confirmed. Using the measured temperature gradient, welding speed and Scheil's solidification module, a relationship between the liquid fraction and mushy zone width is derived. Liquation cracking susceptibility evaluated using “Gleeble™” based hot ductility test is observed to be high which is attributed to the constitutional liquation of primary Nb(C,N) and secondary M23C6 phases present in the base metal. Further, the influence of phosphorus on the local solidus temperature in the partially melted zone of the alloy is discussed in the context of liquation cracking.

HOT DUCTILITY BEHAVIOR OF Fe-0.05C-24Mn-3.5Si-1.6Al STEEL WITH Nb AND Ti MICROADDITIONS

"Hot ductility tests were carried out on Fe-0.05C24Mn-3.5Si-1.6Al high-manganese austenitic steel with Nb and Ti microadditions at a concentration of 0.029% and 0.075%, respectively. Hot tensile tests were performed using Gleeble 3800 thermomechanical simulator on specimens with a diameter of 6 mm and 116.5 mm in length. Deformation was carried out in a temperature range from 1050 °C to 1200 °C with a strain rate of 2.5 · 10-3 s -1 and 5.0 · 10-3 s -1 . Hot ductility was determined on the basis on evaluation of reduction in area (RA). Higher values of stress on the work-hardening curves were observed during tension carried out at higher strain rate. An analysis of the form and course of curves obtained in the tensile test allows to state that, in the studied range of hot plastic deformation parameters, the decrease of strain hardening is caused by the process of dynamic recrystallization (DRX). The reduction in area in a temperature range from 1050 °C to 1200 °C decreases from 90% to approx. 58% for the strain rate of 2.5 · 10-3 s -1 and from 82% to 48% – for the strain rate of 5.0 · 10-3 s -1 ."

Deep Learning to Predict Deterioration Region of Hot Ductility in High-Mn Steel by Using the Relationship between RA Behavior and Time-Temperature-Precipitation

Reduction of area (RA) measurement in a hot ductility test is widely used to define the susceptibility of surface crack of cast steel, but the test is complex because it entails processes such as specimen fabrication, heat treatment, tensile testing, and analysis. As an alternative, this study proposes a model that can predict RA. The model exploits the relationship between precipitation and RA behavior, which has a major effect on hot ductility degradation in high-Mn steels. Hot ductility tests were performed using four grades of high-Mn steels that had different V-Mo compositions, and the RA behavior was compared with the precipitation behavior obtained from a time-temperature-precipitation (TTP) graph. The ductility deterioration of high-Mn steels shows a tendency to start at the nose temperature TN at which precipitation is most severe. Using this relationship, we developed a model to predict the hot ductility degradation temperature of high-Mn steels. TN was calculated using J-matpro software (version 12) for 1500 compositions of high-Mn steels containing the precipitating elements V, Mo, Nb, and Ti, and by applying this to a deep neural network (DNN), then using the result to develop a model that can predict TN for various compositions of high-Mn steel. The model was tested by comparing its predicted RA degradation temperature with RAs extracted from reference data for five high-Mn steels. In all five steels, the temperature at which the RA decreases coincided with the value predicted by the DNN model. Use of this model can eliminate the cost and time required for hot ductility testing to measure RA.

Liquid metal embrittlement susceptibility of zinc-coated martensitic sheet steels

This paper investigates the liquid metal embrittlement (LME) behavior of three martensitic steels (MS-1, MS-2, and MS-3), each of 1500 MPa tensile strength. Their LME response was measured via hot ductility testing at a fixed strain rate over a range of temperatures (700–950 °C). Despite having the same room temperature strength and general lath martensitic microstructure, the three MS steels exhibited different LME responses. When LME occurred, it proceeded in an intergranular manner within a limited temperature range and with the most severe response at 850 °C. The lath martensitic microstructure was investigated in detail to correlate it to the differences in the LME response. It was found that the three MS steels had different microstructural morphologies and prior austenite grain sizes (PAGS). The LME sensitivity appears to correlate with these microstructural parameters. The MS-2 steel exhibited higher LME susceptibility and possessed the smallest PAGS and a high fraction of low-angle grain boundaries. In contrast, MS-1 was immune to LME at all tested temperatures and had a large PAGS and a high fraction of large-angle grain boundaries. To better compare hot ductility results between steels, a “LME index” was formulated based upon the measured LME severity over the tested temperature range, with a large LME index indicating a severe LME response. Among the three MS steels, MS-2 had the highest LME index while MS-1 had the lowest.

Interaction of Carbon, Titanium, and Boron in Micro-Alloy Steels and Its Effect on Hot Ductility

Varying contents of carbon, titanium and boron were used in the base steel composition of 0.30 wt% Si, 2.0 wt% Mn, 0.006 wt% S, 0.03 wt% Nb, and 30–35 ppm N. Hot ductility tests were performed with Gleeble-3800, after the steel sample was in-situ melted, solidified, and cooled to the test temperature. Investigation was completed with thermodynamic and kinetic simulations. The best results were obtained for steels containing 58–100 ppm B and 35 ppm Ti. They showed very good hot ductility of 80–50% RA within the temperature range between 1250 °C and 800 °C. It was shown that titanium and boron were effective in improving the hot ductility. Titanium protected boron from binding into BN and was low enough to prevent excessive (Ti,Nb) carbonitride precipitation, which both could decrease hot ductility. Boron that precipitated along austenite grain boundaries as iron boride Fe2B was very beneficial for the hot ductility of steel.

Effects of Sulfur on the Surface Crack in Medium Carbon Bloom

The surface cracking problem in medium carbon sulfur‐containing steel is gradually emerging in continuous casting production. Therefore, this article investigates the effect of sulfur content on the surface cracks of medium carbon steel. In addition to macroscopic cracks, network cracks are visible on the surface of medium carbon sulfur‐containing bloom. 3D confocal laser scanning microscopy and industrial computed tomography are used to characterize the 3D realistic morphology of the network and macroscopic cracks. Thermodynamic calculations and hot ductility tests’ results exhibit the higher precipitation of MnS in the sulfur‐containing steel, resulting in the second brittle zone of steel. The microstructure near the cracks revealed a high correlation between cracks and a high proportion of proeutectoid ferrite near the surface of the medium carbon sulfur‐containing bloom. In addition, the sulfur‐containing steel has 0.05% more linear shrinkage than the low‐sulfur steel during the transformation from austenite to ferrite, which increases its crack sensitivity. As a result, this article clarifies the effect of sulfur on the surface crack of medium carbon bloom.

Different aspect of solidification cracking susceptibility and hot ductility behavior of borated stainless steels and the effects of boron content

A series of austenitic Fe-0.06wt%C-1.5wt%Mn-18wt%Cr-12wt%Ni stainless steels with B additions ranging from 0.2 to 1.76 wt% were prepared and the weldability of these samples was evaluated through Varestraint cracking tests and Gleeble hot ductility tests. The base steels consisted of the austenite(γ) matrix and borides of Cr-enriched M2B (Cr2B), and the fraction and size of the Cr2B borides increased with an increase in the B content. The results of the Varestraint cracking tests indicated that the resistance to solidification cracking in the fusion zone was improved with an increase in the B content and this is because the extent of solidification temperature range reduces with an increase in the B content. In the fusion zone, cracks occurred at the interphase between the primary γ and γ/Cr2B eutectic during solidification. At the heat-affected zone (HAZ) near the fusion zone, constitutional liquation occurred around the Cr2B borides, after which the γ/Cr2B eutectic formed surrounding Cr2B borides during cooling. Interestingly, the results of the hot ductility tests were in direct contrast to those of the Varestraint cracking tests; i.e., the hot ductility in the HAZ decreased with an increase in the B content. This occurred because cracks initiated and propagated along the γ/Cr2B interphase, and then the fraction and size of the brittle Cr2B borides acted as crack initiation site increased with an increase in the B content.

Converging criteria to characterize crack susceptibility in a micro-alloyed steel during continuous casting

The ductility drop and decrease in strength that lead to crack formation during continuous casting of steel is typically investigated by means of the hot ductility test. In this study, hot ductility tests are performed by using a thermo-mechanical Gleeble system to simulate the deformation of steels at high temperatures and low deformation rates similar to those during continuous casting. Thus, temperature was varied between 600 and 1000°C while strain rates covered a range from 0.001 to 0.1s−1. Tests are carried out to identify the temperature range at which the steel is susceptible to crack formation as well as the effect of strain rate. Characterization of fractured surfaces and phase transformation after thermo-mechanical tests are conducted in the SEM and Optical Microscope. The combination of these techniques makes possible to formulate cracking mechanisms during hot processing which show critical strain for failure at temperatures between 700 and 900°C based on the convergence of three different criteria: I) Reduction of area, II) True fracture strength-ductility and III) True total energy. This approach provides a better understanding of crack formation in steels at the high temperatures experienced during continuous casting. This information is key to productivity losses and avoid defect formation in the final cast products.

Hot ductility of Cr15Mn7Ni4N austenitic stainless steel slab

Hot ductility tests of Cr15Mn7Ni4N austenitic stainless steel slab were performed in a Gleeble-3500 thermomechanical simulator at a strain rate of 1×10−3s−1 and at temperatures ranging from 650°C to 1400°C, which are close to the continuous casting conditions of steel. The fracture morphology of tensile samples was examined using a scanning electron microscope (SEM). The ferrite structure of tensile samples was observed by using an optical microscope (OM). From 750°C to 1300°C, the reduction of area (RA) of tensile samples ranged from 50% to 70%. The hot ductility of Cr15Mn7Ni4N stainless steel is not appreciable with most of the reduction of area lower than 50% in the temperature range of 650–750°C. The volume fraction of ferrite of the tensile sample at 750°C was 5.8%, which was lower than 10 % of the tensile sample at 700°C. The equilibrium phase diagram indicated that ferrite began to form at 708°C and increased with the decrease of temperature. Meanwhile, the reduction of area decreased from 51.56% at 750°C to 39.68% at 700°C, which indicated that the formation of ferrite could lead to the decrease of the hot ductility at the temperature lower than 750°C.

Solidification and Liquation Cracking Behavior of Dual-Phase Steel DP600

In this work, the solidification and liquation cracking behavior of a dual-phase steel DP600 was examined using longitudinal Varestraint testing and hot ductility testing. Varestraint tests showed only limited cracking even at 4 pct augmented strain. Hot ductility tests showed that the nil-strength temperature of the steel was 1459 °C, while the nil-ductility and the ductility-recovery temperatures were 1435 °C and 1420 °C, respectively. The brittleness temperature range was found to be 39 °C, and the DP600 steel was highly resistant to both weld metal solidification cracking and heat-affected zone liquation cracking. The reasons for the high hot cracking resistance of dual-phase steel DP600 are discussed.

Liquation cracking susceptibility of partially melted zone in 304B4 SS multipass weldments

AISI 304B4 stainless steel (SS) containing 1.3 wt% boron is reported to be weldable under moderate restraint forces provided welding parameters are chosen carefully. However, during fabrication of components, extensive cracking issues are being reported. Hence, a study involving assessment of base metal, unmixed zone and partially melted zone (PMZ) of 304B4 steel and its welds made using E309 and boron containing consumables on hot cracking is carried out. In this article, results obtained on cracking susceptibility of PMZ formed in this steel are presented and discussed. In order to evaluate hot ductility behavior of PMZ formed in unmixed zone in a multipass weld, PMZ was first simulated using “Gleeble™” thermo-mechanical simulator. Subsequently, hot ductility tests were conducted on this simulated PMZ. Results of the study showed that liquation cracking susceptibility of PMZ of this steel subjected to repeated thermal cycle is higher than that of 304B4 base material. Microstructural analysis of tested specimens showed that formation of Fe-rich ((Fe,Cr)2B + Cr2B) borides in PMZ lowers ductility recovery temperature by 50 °C which results in an increase in cracking factor by 84% of that of base metal. Reasons for high cracking susceptibility of PMZ formed on fused 304B4 have been deduced.

Roles of (Fe, Mn)3Al Precipitates and MBIP on the Hot Ductility Behavior of Fe–30Mn–9Al–0.9C Lightweight Steels

In the automotive industry, lightweight steel has received much attention because steel comprises a significant portion of a vehicle’s total weight. Fe–Mn–Al–C steel is a representative lightweight steel due to its high performance and low density. However, there is insufficient research into the welding characteristics of Fe–Mn–Al–C lightweight steels. In this study, hot ductility tests were conducted on austenitic Fe–30Mn–9Al–0.9C steel in order to understand the welding characteristics (cracking resistance) of the heat affected zone. During the on-heating thermal cycle, ductility was altered by a decrease in microband induced plasticity (MBIP) (softening) and an increase in dynamic recrystallization (DRX) (softening) as the temperature increased. Specifically, in the range of 773–1073 K, ductility was fairly degraded because neither MBIP nor DRX took place. During the on-cooling thermal cycle, ductility behavior was changed by both softening and hardening factors, including formation of brittle (Fe, Mn)3Al intermetallic compounds with grain growth and re-solidified grain boundaries. However, the hardening effect of precipitated κ-carbide was insignificant and might not play a significant role in the hot ductility behavior of the lightweight alloy used in this study.

Effect of Boron Content on Hot Ductility and Hot Cracking Susceptibility in 316L Austenitic Stainless Steel for Welding Components

Liquation cracking may occur in the heat-affected zone during welding. Two factors influence this phenomenon: the tensile stresses generated during welding and the potential loss of ductility due to the presence of a liquid film at grain boundaries depending on their chemical composition. Gleeble hot ductility tests have been used to study the combined effect of boron content and holding time on ductility drop in the liquation temperature range of a 316L type austenitic stainless steel. It is shown that high boron contents and short holding times promote the loss of ductility in this temperature range. Secondary ion mass spectrometry has been used to correlate mechanical results to boron distribution either at grain boundaries or in the bulk. Other welding tests have been performed to confirm the influence of boron content on hot cracking sensitivity of AISI 316L stainless steels. Results indicate that cracks appear on all specimens but at different strain levels. The higher the boron content is, the more the specimen exhibits tendency to hot cracking.

Weld Solidification Cracking Behaviour of AA2195 Al–Cu–Li Alloy

In this study, weld solidification cracking behaviour of AA2195 Al–Cu–Li alloy was studied and compared with conventional AA2219 and AA2014 aluminium alloys. Cracking susceptibility was evaluated using varestraint test and Gleeble® hot ductility test and the slope of liquidus temperature as function of liquid fraction was also evaluated. Solidification cracking susceptibility of AA2195, AA2219 and AA2014 alloys was ranked based on the above methods. Consistent trend in cracking susceptibility was observed in all the methods where AA2195 and AA2219 alloys showed highest and lowest cracking susceptibility, respectively.

On the Role of Boride in the Structural Integrity of a Turbine Disc Superalloy’s Solid State Weld

This work reports the melting of boride precipitates along the grain boundary of a supposedly solid state welding of a polycrystalline superalloy, and discusses its attendant effect on the hot ductility behaviour of the alloy. Nickel-based superalloy used for this study was previously processed by hot extrusion of argon atomized powered followed by forging. The alloy was solution heat treated at 1120 °C, aged at 760 °C and subsequently air cooled to room temperature. Thereafter, it was welded by inertial friction welding (IFW) at a forging pressure of 250 MPa and finally stressed relieved at 760 °C for 8 hours. The microstructures of welded samples were studied by scanning and scanning transmission electron microscopes. Gleeble hot ductility test was carried out on tensile specimen machined from the welded sample. The microstructures of the welded alloy shows that boride precipitates liquated along the grain boundary within the heat affected zone (HAZ) as a result of rapid heating of IFW. The results of hot ductility test revealed that the melting of boride lowered the hot ductility of the alloy. It was concluded that the boride precipitates liquated along the grain boundary of the nickel-based superalloy during solid state welding and lowered its hot ductility.

Use of Friction Stir Processing for Improving Heat-Affected Zone Liquation Cracking Resistance of a Cast Magnesium Alloy AZ91D

In this work, a cast magnesium alloy AZ91D was friction stir processed. Detailed microstructural studies and Gleeble hot ductility tests were conducted on the as-cast and the FSPed samples to comparatively assess their heat-affected zone liquation cracking behavior. The results show that the use of FSP as a pretreatment to fusion welding can strikingly improve the heat-affected zone liquation cracking resistance of alloy AZ91D by reducing the amount and size of the low-melting eutectic β (Mg17Al12) as well as by refining the matrix grain size.

Hot Ductility and Compression Deformation Behavior of TRIP980 at Elevated Temperatures

The hot ductility tests of a kind of 980 MPa class Fe-0.31C (wt pct) TRIP steel (TRIP980) with the addition of Ti/V/Nb were conducted on a Gleeble-3500 thermomechanical simulator in the temperatures ranging from 873 K to 1573 K (600 °C to 1300 °C) at a constant strain rate of 0.001 s−1. It is found that the hot ductility trough ranges from 873 K to 1123 K (600 °C to 850 °C). The recommended straightening temperatures are from 1173 K to 1523 K (900 °C to 1250 °C). The isothermal hot compression deformation behavior was also studied by means of Gleeble-3500 in the temperatures ranging from 1173 K to 1373 K (900 °C to 1100 °C) at strain rates ranging from 0.01 s−1 to 10 s−1. The results show that the peak stress decreases with the increasing temperature and the decreasing strain rate. The deformation activation energy of the test steel is 436.7 kJ/mol. The hot deformation equation of the steel has been established, and the processing maps have been developed on the basis of experimental data and the principle of dynamic materials model (DMM). By analyzing the processing maps of strains of 0.5, 0.7, and 0.9, it is found that dynamic recrystallization occurs in the peak power dissipation efficiency domain, which is the optimal area of hot working. Finally, the factors influencing hot ductility and thermal activation energy of the test steel were investigated by means of microscopic analysis. It indicates that the additional microalloying elements play important roles both in the loss of hot ductility and in the enormous increase of deformation activation energy for the TRIP980 steel.

Heat-Affected Zone Liquation Cracking Resistance of Friction Stir Processed Aluminum-Copper Alloy AA 2219

In the current work, the effect of friction stir processing on heat-affected zone (HAZ) liquation cracking resistance of aluminum-copper alloy AA 2219 was evaluated. In Gleeble hot-ductility tests and longitudinal Varestraint tests, the FSPed material, despite its very fine dynamically recrystallized equiaxed grain structure, showed considerably higher susceptibility to HAZ liquation cracking when compared to the base material. Detailed microstructural studies showed that the increased cracking susceptibility of the FSPed material is due to (i) increase in the amount of liquating θ phase (equilibrium Al2Cu) and (ii) increase in the population of grain boundary θ particles. An important learning from the current work is that, in certain materials like alloy 2219, the use of FSP as a pretreatment to fusion welding can be counterproductive.