Heat Treatment Paths Research Articles

Effect of heat treatment paths on the aging and rejuvenation of metallic glasses

Effect of heat treatment paths on the aging and rejuvenation of metallic glasses

Evolution of the microstructure and mechanical properties of additively manufactured AlSi10Mg during room temperature holds and low temperature aging

Conventional thermal processing may not always be well-suited for modifying the unique, as-built microstructure of Additively Manufactured (AM) AlSi10Mg. Conventional post-build processing of AM AlSi10Mg components involves a Solution Heat Treatment (SHT) at elevated temperatures (∼500 °C) followed by low-temperature aging (170 °C). Here we characterize low-temperature aging (170 °C) of AM AlSi10Mg components both with and without a conventional solution heat treatment. The samples without a solution heat treatment are first held at room temperature for several months, during which we monitored the reduction of Si in the Al matrix, from 4.74 to 3.98 at% with limited changes in hardness. We also correlate the as-built microstructure back to the processing conditions. During the room temperature hold, and when these samples are subsequently aged at 170 °C without a solution heat treatment, they retain a eutectic ribbon microstructure but lose the supersaturation of Si within the Al matrix with aging. These samples reach a peak hardness after 2 h at 170 °C that is approximately 50 % higher than the peak hardness of SHT samples after 5 h at 170 °C. We contrast the microstructure and density changes resulting from both heat treatment paths and explain how this modified heat treatment complements AM AlSi10Mg’s unique, as-built microstructure.

Effect of heat treatment on microstructural evolution and creep behaviors of a conventionally cast nickel-based superalloy

The evolution of microstructures caused by heat treatment on Ni-based superalloy CM 247 LC was examined, and the creep behaviors were analyzed at various temperature and stress conditions. Secondary γ′ hardly precipitated in aged specimens subjected to solution treatment, but secondary γ′ precipitated in specimen subjected to two-step aging at 1080 °C and 871 °C without solution treatment, because the size and volume fraction of precipitated γ′ particles and the width of the γ channel depend on the heat-treatment path. The creep properties of the specimen subjected to two-step aging without solution heat treatment under low temperature and high stress was the best, owing to the uniform deformation and damage-relieving effect of the fine secondary γ′ particles in the γ channel and the eutectic γ/γ′ phase. At and above 871 °C, the effect of γ′ rafting on the creep properties was very important, and the creep lifetimes of the solution-treated specimens with better rafting were longer than those of the aged specimens.

High temperature characterization and material model calibration for hot stamping of AA7075 aluminium sheet

This paper presents an overview of the elevated temperature characterization of AA7075 aluminium sheet and calibration of a custom material model implemented in LS-DYNA. The plasticity characterization was performed by isothermal tensile testing while formability characterization was performed via isothermal Nakazima testing in a wide range of temperatures and strain rates. A special heat treatment path representative of the hot stamping was developed and applied in both series of tests. The material model included Hill’48 yield with a non-associated flow rule and phenomenological damage model similar to GISSMO but extended to cover non-isothermal conditions.

Effect of step quenching on microstructures and mechanical properties of HSLA steel

Step quenching and tempering (SQT) for HSLA multi-phases steel was designed to obtain the desirable multi-phases microstructure with the superior mechanical properties. Quenching and tempering (QT) and intercritical quenching and tempering (IQT) was also conducted as controls. Besides, Effects of austenitizing temperature for the different treatment routes on microstructural characteristics and mechanical properties were also investigated. Due to the cooperation of the “soft” ferrite/pearlite and “hard” martensite, the samples undergoing SQT possess the relatively high tensile strength and impact toughness, and the lowest yield ratio. Increase of austenitizing temperature results in the coarse austenite grains, and thus significantly decrease of tensile strength and impact energy, in spite of the heat treatment paths. Higher austenitizing temperature also leads to lower density of dislocations and higher grain size, which reduces the yield ratio for all samples.

Effects of Heat Treatment on the Microstructure and Mechanical Properties of Low-Carbon Steel with Magnesium-Based Inclusions

The effects of heat treatment on the microstructure and mechanical properties of Mg-containing (7 ppm), low-carbon commercial steel (SS400) were investigated. Twenty different heat treatment paths were performed using a Gleeble 1500 thermomechanical simulator. It was observed by using an optical microscope that as the cooling rate increased and holding temperature decreased, the volume fractions of pearlite, Widmanstatten ferrite, and grain boundary allotriomorphs ferrite fell, whereas that of acicular ferrite (AF) increased. Quantifying the fractions of AF and other phases by using electron backscatter diffraction shows that the heat treatment path with a cooling rate of 20 K/s and holding temperature of 723 K (450 °C) induced the highest volume fraction (44 pct) of AF. As such, the toughness of the sample was increased 12.4 times compared with that observed in the sample containing 4 pct AF. Typical inclusions were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy. The results showed that the magnesium-based complex inclusions could act as nucleation sites of AF. Inclusions with a size of about 5 μm can serve as heterogeneous nucleation sites for AF. Mg-containing SS400 steel also has excellent hot-ductility in the temperature range of 973 K to 1273 K (700 °C to 1000 °C), and the minimum percentage reduction in area (R.A pct) value of around 63 pct at 1073 K (800 °C).

Influence of the heat treatment path on the martensite phase and dry reciprocating wear behavior of dual-phase steels

In order to explore the tribological potential of dual-phase (DP) steel as a wear-resistant material, the wear and friction characteristics of this steel, which consists of soft ferrite and hard martensite phases, was investigated. A low-carbon (0.11% C) steel was subjected to three different annealing heat treatments in order to develop different martensite percentages and morphologies, i.e., island types, a bulky and interconnected network, and fibrous (fine, needle-like), respectively. Dry reciprocating wear tests were performed under atmospheric conditions of 25 °C using a pin-on-disk apparatus at different loading conditions ranging from 18.9 N to 43.6 N and at a constant sliding velocity of 0.22 m/s. The lowest wear rate was obtained for the DP steel with an ~87% volume fraction (V F ) of martensite, reflecting the effect of hardness imparted by the increasing amount of martensite, which is a hard and load-bearing phase, while the highest wear rate was for the DP steel with a ~36% martensite V F . The analysis of the surface, subsurface and wear debris of specimens using a scanning electron microscope (SEM) showed that the wear mechanism was mainly mild oxidative wear. The friction and wear rate of the steels are explained with respect to the microstructure and the wear mechanism.

Ultra-Hard Bainitic Steels Processed through Low Temperature Heat Treatment

Relative high carbon steel bearing Cr and Mo with microstructure consisting of nanoscaled bainitic laths and certain amount of retained austenite was produced through the combination of rolling and isothermal/multi-step heat treatment at low temperatures. The effect of the heat treatment temperature, time and path on the volume fraction of retained austenite and the width of bainitic lath was investigated. Nanoindentation was applied to inspect the separate hardness of the tiny bainite and retained austenite for different heat treatment parameters. The results showed that bainitic lath treatedt at 250°C was much thinner than that at 300°C and the volume fraction of retained austenite changed with different heat treatment temperatures, time and paths. The nanohardness of the baintic lath and retained austenite also changed with the processing of both carbon partitioning and displacive transformation for different heat treatment paths.

Effects of Tempering Temperature and Heat-Treatment Path on the Microstructural and Mechanical Properties of ASTM Gr.92 Steel

Effects of Tempering Temperature and Heat-Treatment Path on the Microstructural and Mechanical Properties of ASTM Gr.92 Steel

Effects of microstructure on fatigue crack growth behavior of Ti–6Al–2Zr–1Mo–1V ELI alloy

In this paper, fatigue crack growth behavior of Ti–6Al–2Zr–1Mo–1V ELI alloy with differences in the lamellar structure was investigated at room temperature. Heat treatments were performed in order to produce the microstructures that vary in α lamella width and colony size. Results show that, with adequate mechanical properties, the microstructure formed through air cooling from the β-phase field presents better fatigue crack propagation behavior than microstructures formed by other heat treatment paths. The fatigue crack growth proceeds along the planes either perpendicular or parallel to the long axis of α lamellae. The explanation for this behavior is related to prismatic slip along the a 1 [21¯1¯0] and a 2 [112¯0]/a 3 [1¯21¯0] directions.

Effect of heat treatment path on the cold formability of drawn dual-phase steels

Dual-phase steel has received much attention as a candidate for non-heat treated steel due to its high strain hardening capability. Present study was performed to examine the optimum microstructure and corresponding heat treatment path revealing excellent cold formability of drawn dual-phase steel. Microstructures were varied by three different heat treatments (or quenching paths), namely intercritical quenching (IcQ), intermediate quenching (ImQ), and step quenching. Resulting microstructures consisted of ferrite and martensite phases, but the volume fraction and morphology were largely varied by the quenching paths. Tensile and compression tests for all three microstructures showed continuous yielding curves with high strain hardening exponent. However, after imposing some amounts of drawing strain, all the specimens were significantly strengthened losing strain hardening capability. Cold formability was studied by estimating both the forming limit and the deformation resistance. The IcQ microstructure showed excellent forming limit and deformation resistance as compared to other two microstructures. It was attributed to the beneficial morphology of the IcQ microstructure, which effectively suppressed crack propagation.

Properties of Nimonic 80A alloy with change in the chemical compositions and Heat Treatment Paths

Properties of Ni-base superalloys of Nimonic 80A alloy system were investigated by the observation of microstructures, precipitates ana hardness as a function of the chemical compositions ana the paths of heat treatment. The higher hardness values showed, the higher Ti/Al ratio among high compositions of Cr and Co element. The lower (Ti+Al) and Fe contents decreased in the same Ti/Al ratio, the higher hardness values showed. This results are considered that coherent deformation was increased with increasing Ti/Al ratio. Hardness showed higher value when Cr contents was <TEX>$18 wt\%$</TEX> less than <TEX>$21wt\%Cr$</TEX>. In <TEX>$3.15 wt\%$</TEX>Co alloy, <TEX>$\gamma'$</TEX> phase was very fine as around 50nm and, its volume fraction and hardness showed the highest value by 2step-aging treatment.

Intermetallic TiAlNb alloys based on strengthening of the orthorhombic phase by ω-type phases

The microstructure of an alloy, with composition Ti30Al20Nb (atomic percent), when annealed at temperatures between 700 and 900°C for up to 18 days, consists of two intermetallic phases: orthorhombic Ti 2AlNb and ω-type B8 2 Ti 4Al 3Nb. The presence of the two phases in the microstructure is independent of the heat treatment path and, thus, the two phases appear to be in thermodynamic equilibrium. The potential for high strength alloys in this two-phase field, based on the combination of properties of the two different phases, is demonstrated by microhardness measurements.

The relative stability of? and??-phases in Na2O-Al2O3 beta alumina

To reveal the relative stability of β and β″-phases in beta alumina, effects of Na20 content and calcination and annealing history on the relative content of β and β″-phases have been studied for compositions ranging from Na2O-5Al2O3 to Na2O-9.5Al2O3. The relative stability appears to be dependent on the calcination or annealing history, except holding time such as annealing or re-annealing time, but independent of the Na2O content and the holding time. From these results it can be demonstrated that the relative stability of β and β″-phases is sensitive to the heat treatment path, except the holding time. The “two stage model” on the β/α. polytypic transition in silicon carbide has been quoted to explain the heat treatment pathdependent characteristics.