This study investigates the stress evolution and microstructural changes in TC4 titanium alloy through isothermal gradient solution quenching (900~1000°C solution treatment, water quenching at room temperature and 60°C), followed by annealing at 700~800°C and aging at 500~550°C.

Nickel-based Inconel 625 is widely used for both low and high-temperature applications. It has several applications in aerospace, marine, chemical, and petrochemical industries due to its high strength, corrosion resistance, good formability, and weldability. With the molten pool’s rapid solidification during laser powder bed fusion (LPBF), the resulting microstructures differ from those expected in equilibrium conditions. Residual stresses, microsegregation, anisotropy, undesirable phases, layered structure, and lower mechanical properties are the challenges that must be addressed before LPBF-ed Inconel 625 parts can be industrially implemented. Heat treatment of Inconel 625 after the LPBF process is widely discussed in the literature, and the proposed heat treatment processes do not address all the challenges mentioned above. For this reason, specific heat treatments should be designed to achieve desired mechanical properties. Five different high-temperature heat treatment procedures were developed and tested in recent work in comparison with the standard heat treatment for wrought alloy (AMS 5599), to study the effect of various heat treatment parameters on the type of precipitates, grain size, room, and elevated temperature mechanical properties, and to develop an elevated-temperature tensile curve between room temperature (RT) and 760°C of LPBF-ed Inconel 625. Four heat treatment procedures showed complete recrystallization and the formation of equiaxed grain size containing annealed twins and carbide precipitates. However, either eliminating the stress relief cycle or conducting it at a lower temperature resulted in microstructures having the same pool deposition morphology with grains containing dendritic microstructure and epitaxial grains. Two different grain sizes could be obtained, starting with the same as-built microstructure by controlling post-process heat treatment parameters. The first type, coarse grain size (ASTM grain size No. G 4.5), suitable for creep application, was achieved by applying hot isostatic pressing (HIP) followed by solution annealing. The second type, fine-grain size (ASTM grain size No. G 6), preferable for fatigue properties, was achieved by applying solution annealing followed by HIP. The mechanical properties at room and elevated temperature 540°C are higher than the available properties in the AMS 5599 for wrought Inconel 625 while maintaining a higher ductility above the average level found in the standards. It can be concluded that the performed heat treatment achieves higher mechanical properties. The values of ultimate tensile strength (UTS), yield strength (YS), elongation, and reduction of area percentages are similar in the XZ and XY orientations, revealing the presence of isotropic microstructure. The ultimate tensile strength values show an anomalous behavior as a function of the temperature. From the room temperature until around 500°C, there occurs a decrease in the yield strength and a slight increase up to 600°C, decreasing sharply at 700°C. An anomaly is also present in relation to the elongation, with a significant decrease in the elongation at temperatures after 600°C.

A hypoeutectoid steel was austenitized at 840 °C for one hour and cooled at two rates. Examination by optical and scanning electron microscopy showed a change in the pearlite microstructure. Cooling in air as compared to furnace cooling reduced the pearlite interlamellar spacing and increased the hardness. The slower cooling resulted in a lower tensile strength, higher tensile elongation, and different fracture appearance.

Ti-6Al-4V alloy is characterized to be sensitive to heat treatment and deformation. This paper focuses on microstructural evolution and variation in mechanical properties with respect to the deformation and change in the heat treatment cycle. Different heat treatment cycles such as mill annealing, solution treatment and beta solution treatment followed by annealing were carried out on deformed and undeformed Ti-6Al-4V samples. Heat treated samples were studied using optical and scanning electron microscopy. Also different mechanical tests (i.e. tensile test, fracture toughness test) were conducted and results were analyzed. Large variation in mechanical properties and microstructures were found out with different heat treatment cycles. Fracture toughness was found to be high for beta solution treatment samples than the mill annealed and solution treated samples and the reason for the same has been analyzed.

Temperature Processing Inc. has offered merchant heat treating in the northern NJ town of North Arlington for over 60 years. Their 10,000 sq ft facility, expanded in 1998, offers broad thermal processing capability in a compact plant. Diverse services offered include annealing, tempering, bright hardening, ageing and nitriding.

Nitrogen (N 2 ) atmospheres with different, not always optimized levels of reducing and carburizing gases are often used to prevent decarburizing and oxidation of steel parts during annealing in continuous furnaces. The type and concentration of these additives in N 2 should correlate to the extent of air leakage into furnace, entrainment of air with loaded parts, steel composition, and complex reaction kinetics in the gradients of oxygen (O 2 ) and temperature existing between the entrance and hot zones of the furnace. This study explores the effect of small, 0.1 vol.% - 0.4 vol.% propane (C 3 H 8 ) additions on composition of air-contaminated N 2 atmosphere in the temperature range of 500°C - 860°C. Microstructures are presented for AISI 1045 steel exposed to the atmospheres produced. Atmosphere compositions compared include those produced by a new type of plasma activated, in-situ reformer for N 2 -diluted C 3 H 8 . The latter method extends the atmosphere protection to the lower range of annealing temperatures. Present results may assist heat treaters in optimizing their neutral hardening operations.

This paper presents the results of an experimental investigation of the effect of three types of post-heat treatments: 1) solution treatment and aging, 2) stress relieving, and 3) annealing on the corrosion behavior of Ti-6Al-4V fabricated via direct metal laser sintering (DMLS). The microstructure and phase evolution as affected by heat treatment temperature were examined through scanning electron microscopy and via x-ray diffraction. The Vicker’s microhardness, as it was affected by various heat treatments, was compared. The corrosion behavior of the specimens was measured electrochemically in simulated body fluid at 37°C. It was found that the nonequilibrium α’ phase with a small amount of β nuclei was formed in the as-fabricated sample. Heat treatments allow the formation of the β phase and the agglomeration of β precipitates to occur at elevated temperatures. Transformed β phase with various morphologies was observed as a result of the heat treatments. Different degrees of improvement in the corrosion resistance were observed in the solution-treated and aged samples, 650 °C stress relieved, and annealed samples.

Case carburizing grade steel forgings are often normalized or iso-annealed to improve machinability. The aim here is to get a uniform ferrite-pearlite microstructure and controlled, uniform hardness. Since during forging material is above austenitizing temperature, controlled slow cooling after trimming can give similar results. In this work, the effect of forging temperature and cooling rate at different stages on microstructure is studied. Further the effect of this process on machinability and distortion behavior of gears during case carburizing is studied. It was observed that the controlled cooled gear blanks had coarse grain size resulting in superior machinability, and no change was observed in the distortion behavior of the gears during case carburizing.

Since the invention of the vacuum furnace in the 1950s and up until the 1970s, its primary use was for annealing aerospace components. In the 1980s, vacuum equipment began to be used for heat treating tools and dies. By the 1990s, the need for faster quenching of high-alloy steels led to the development of vacuum furnaces capable of quenching at pressures up to 20 bar. Prior to this, only certain hot-work steels and a few tool steels with small cross-sections could be satisfactorily hardened in vacuum furnaces. Today, it is understood that simply increasing quenching pressure does not necessarily yield optimal results. Modern vacuum furnace technology allows for the precise design of the entire quench curve to maximize material performance while minimizing distortion. Continuous advancements and new concepts, such as multi-directional cooling systems, separate quenching chambers, and integrated cryo-cooling systems, have led to oxidation-free and low-distortion vacuum heat treatment for a wide range of parts and materials. This paper demonstrates how modern vacuum furnace designs and processes can improve quenching and cooling. It includes proven heat treatment results and examples from the international tool and die industry, which has been utilizing this technology over the past 25 years.

The 2524 aluminum alloy was cold rolled to 70% reduction and then annealed at 500? for 0.5h in an air furnace with a heating rate of 5?/min and in a salt bath with a heating rate of 75?/s, respectively. The effect of heating rate on the microstructure, tensile properties and fatigue crack growth (FCG) rate of the alloy was investigated. The microstructure and mechanical properties of the alloy were studied by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), optical microscopy (OM), tensile and FCG rate tests. In the case of slow heating the alloy exhibited a coarse elongated grain structure (~75μm), while a fine equiaxed grain structure (~13μm) was obtained in the case of rapid heating. The sheet annealed with rapid heating has slightly higher tensile strength and yield strength, but a slightly lower elongation than the sheet annealed with slow heating. The FCG rate of the sheet annealed with slow heating is 20% lower than the sheet annealed with rapid heating.

Advanced electrolysis hydrogen technology has demonstrated utility in providing hydrogen for brazing, annealing, MIM, P/M, flame spray and other thermal treatment techniques, in both continuous and batch modes. Advantages include low flammable inventory, elimination of pressure hazards, eliminating of the need to move cylinders and elimination of deliveries. By combining on-site hydrogen generation with a small amount of in-process hydrogen surge storage, on-site hydrogen generation can be used to meet the needs of batch process such as batch furnaces. By carefully choosing generation pressure and surge storage vessel volume, the process can provide maximum flexibility while minimizing the amount of hydrogen actually stored. As compared with dissociated ammonia, advanced electrolysis hydrogen generation provides drier gas, and the ability to vary furnace atmosphere from no hydrogen to 100% hydrogen, enhancing processing flexibility. Additionally, advanced electrolysis can be turned off when not in use saving power as compared with ammonia retorts.

Direct fired and electrically heated box furnaces are used to normalize and anneal long products. The two different processing temperatures for annealing and normalizing stainless, or alloy, steel introduce the need to optimize furnace performance at two distinct temperature ranges, both on the high end and low end. Furnace designs to achieve a benchmark temperature spread are reported. Considerations such as combustion control, PID tuning and controls will be discussed.

Forgings traditionally undergo normalizing or iso-annealing processes to achieve consistent hardness within controlled bands and to improve machinability. The need for these heat treatments stems primarily from the uncontrolled cooling of forgings after trimming operations. This paper demonstrates that similar results can be achieved through controlled cooling rates after trimming, with only minor differences in specific properties. The microstructure obtained through controlled cooling is predominantly coarse-grained, consisting of pearlite and ferrite matrices, contributing to improved machinability. Notably, the controlled cooling process offers potential energy savings of approximately 20 kg of oil per metric ton of net forging weight, with corresponding reductions in CO₂ emissions of up to 250 kg per metric ton. Implementation requires a specially designed cooling tunnel to regulate cooling rates precisely. This paper details the mechanical properties achieved for a carburizing grade steel, discusses necessary refinements to steel specifications, and outlines the process controls required to replace conventional normalizing/iso-annealing with controlled cooling effectively. Additionally, the paper presents the established cycles and cooling rates that produce optimal results in production environments.

This paper and presentation will provide an overview of the processing implications of select atmosphere and vacuum heat treating processes. Fundamentals of both vacuum and atmosphere processing will be compared and contrasted with a survey of current practices for each. Processes to be reviewed include Annealing, Tempering, Brazing, Hardening, Aging, and Carburizing.

Atmospheric pressure carburizing and neutral carbon potential annealing in nitrogen containing small additions of hydrocarbon gases can offer cost and steel surface quality alternatives to the comparable, endothermic atmosphere or vacuum operations. An experimental program was conducted for refining real-time process control methods in carburizing of AISI 8620 steel under N 2 -C 3 H 8 blends containing from 1 to 4 vol% of propane at 900°C and 930°C. Multiple types of gas analyzers were used to monitor residual concentrations of H 2 , CO, CO 2 , H 2 O, O 2 , CH 4 , C 3 H 8 , and other hydrocarbons inside furnace. A modified shim stock technique and the conventional oxygen probe (mV) were additionally evaluated for correlation with gas analysis and diffusional modeling using measured carbon mass flux values (g/cm 2 /s). Results of this evaluation work are presented.