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Thermal processing defects
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Proceedings Papers
IFHTSE2024, IFHTSE 2024: Proceedings of the 29th International Federation for Heat Treatment and Surface Engineering World Congress, 84-88, September 30–October 3, 2024,
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Gas carburizing with quenching is one of the most useful heat treatment processes for steel parts. However, after quenching distortion is still occurs. The nitriding and nitrocarburizing are the surface hardening heat treatment methods with low distortion, but these methods require the long treating time to obtain a thick hardened layer. Austenitic nitriding and quenching (ANQ) solves these problems. In ANQ process, nitrogen is infiltrated into the steel parts in austenite phase, and they are quenched to harden. The ANQ process can also be applied to cheap low carbon steel such as the Cold Rolled Carbon Steel Sheet. In this study, the effect of ANQ on mechanical properties was examined. For infiltrating the nitrogen into the steel parts, the steel parts were heating to 750°C or higher in an ammonia atmosphere and heating to 750°C or higher in a nitrogen glow discharge. After the ANQ process, hardness profiles, structure, nitrogen and carbon concentration profiles were observed. Also, distortion, tribological properties, impact value and fatigue strength were examined. The effective case depth, which is treated by ANQ, is larger than the effective case depth of gas nitrocarburizing for same period of time. Distortion of ANQ is much smaller than that of gas carbonitriding, and it is almost equal with that of gas nitrocarburizing. The seizure load is same as with other surface hardening heat treatment processes. The wear loss of ANQ is a lower, in the amount of about 1/2 that of the carbonitrided specimen and 1/3 that of the gas nitrocarburized specimen. The ANQ is an effective heat treatment process for parts which require wear resistance. The tempering softening resistance is improved by nitrogen infiltration. ANQ also improves the impact value and fatigue strength.
Proceedings Papers
IFHTSE2024, IFHTSE 2024: Proceedings of the 29th International Federation for Heat Treatment and Surface Engineering World Congress, 132-138, September 30–October 3, 2024,
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Heat treatment of steels is a process of modifying the mechanical properties by solid-state phase transformations or microstructural changes through heating and cooling. The material volume changes with phase transformations, which is one of the main sources of distortion. The thermal stress also contributes to the distortion, and its effect increases with solidstate phase transformations, as the material stays in the plastic deformation field due to the TRIP effect. With the basic understanding described above, the sources of distortion from a quench hardening process can be categorized as: 1) nonuniform austenitizing transformation during heating, 2) nonuniform austenite decomposing transformations to ferrite, pearlite, bainite or martensite during quenching, 3) adding of carbon or nitrogen to the material, and forming carbides or nitrides during carburizing or nitriding, 4) coarsening of carbide in tempered martensite during tempering, 5) stress relaxation from the initial state, 6) thermal stress caused by temperature gradient, and 7) nonhomogeneous material conditions, etc. With the help of computer modeling, the causes of distortion by these sources are analyzed and quantified independently. In this article, a series of modeling case studies are used to simulate the specific heat treatment process steps. Solutions for controlling and reducing distortion are proposed and validated from the modeling aspect. A thinwalled part with various wall section thickness is used to demonstrate the effectiveness of stepped heating on distortion caused by austenitizing. A patented gas quenching process is used to demonstrate the controlling of distortion with martensitic transformation for high temperature tempering steels. The effect of adding carbon to austenite on size change during carburizing is quantified by modeling, and the distortion can be compensated by adjusting the heat treat part size.
Proceedings Papers
IFHTSE2024, IFHTSE 2024: Proceedings of the 29th International Federation for Heat Treatment and Surface Engineering World Congress, 160-166, September 30–October 3, 2024,
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It is well known that distortion has and continues to present a challenge to the heat treater when hardening steel. However, recent advances in quenching technology are improving the opportunity for improved distortion control. 4 Dimension High-Pressure Gas Quenching (4DQ) is a unique gas quenching process that uses both quenching chamber design and part motion to minimize distortion during the quenching process. To understand 4DQ’s potential, the challenges of traditional batch quenching and press quenching techniques will be explored, emphasizing issues such as geometric distortion, residual thermal stresses, non-uniform microstructure transformation, safety, environmental, and handling concerns. In contrast, 4DQ is a process that enhances quenching uniformity and minimizes distortion by use of a specialized cooling chamber. Within the chamber it provides three-dimensional (3D) quenching by enveloping the part at specific areas with cooling gas while introducing the fourth dimension (4D) of part rotation during quenching that further optimizes quench uniformity. 4DQ gives the ability to “engineer” the quenching process by controlling quench pressure, gas velocity, gas manifold design, table rotation, table oscillation, and time-dependent gas flow. The system’s flexibility allows users to customize the quenching process for reduced distortion, repeatability, and precise accuracy. A case study on hypoid hears and coupling sleeves will demonstrate the effectiveness of the 4DQ system in minimizing distortion and achieving dimensional consistency. Results illustrate the system’s advantages over traditional quenching methods in terms of quality, repeatability, and cost-effectiveness. Considering the challenges of steel hardening processes, the 4DQ system has the potential to be a transformative solution for achieving enhanced quenching uniformity and reduced heat treatment distortion in manufacturing scenarios.
Proceedings Papers
HT 2019, Heat Treat 2019: Proceedings from the 30th Heat Treating Society Conference and Exposition, 70-76, October 15–17, 2019,
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This paper describes some of the ways manufacturing data are being used to reduce variations in heat treat processes and achieve higher levels of conformance in treated parts. It also includes a review of quality management practices and demonstrates the use of Six Sigma statistical analysis in an induction heat treating application.
Proceedings Papers
HT 2019, Heat Treat 2019: Proceedings from the 30th Heat Treating Society Conference and Exposition, 185-192, October 15–17, 2019,
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This paper discusses the basic principles of multi-frequency eddy current testing and explains how it can be used on high-volume production lines to detect faulty heat-treated parts based on case depth, hardness patterns, tensile strength, carbon content, soft spots, and surface decarburization. It also presents examples showing how the method is used in high-speed inspection of cam shafts, screws, balls of various sizes and materials, distance pins, and complex bolts.
Proceedings Papers
HT 2019, Heat Treat 2019: Proceedings from the 30th Heat Treating Society Conference and Exposition, 316-321, October 15–17, 2019,
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Samples from forged and heat-treated steel products with known quench crack histories have been mapped in order to study a possible relation between banding segregation and quench cracking. The products were medium carbon low alloy steels produced by ingot and continuous casting. EDS X-ray mapping was used to characterize the banding pattern and tensile testing revealed corresponding properties. The experimental procedures are described in the paper along with test results and conclusions.
Proceedings Papers
HT2015, Heat Treat 2015: Proceedings from the 28th Heat Treating Society Conference, 107-110, October 20–22, 2015,
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Aluminum alloys are used intensively by the automotive industry to comply with environmental and fuel consumption regulations. These alloys were first used in the manufacture of power train components, and they have extended their use in parts and assemblies of structural components. Power train and structural components have to be heat treated to achieve the strength and hardness demanded, which imply solution treating, quenching and aging. Quenching is the most critical part of processing, as the material has to be cooled at rates high enough to allow for the hardening elements to remain in solution, but the rate has to be controlled to avoid distortion or, in some cases, catastrophic failure. Distortion is associated with the geometry of the piece, as heavy components have sections of different volume, which will cool at different rates, or, in the case of long thin pieces, warpage may arise from variations in cooling rate along the length of the part. This work presents the results of a series of tests carried out with the aim to evaluate the variation of the heat transfer coefficients that take occur in pieces made of a heat treatable wrought aluminum alloy cooled in different media. The heat transfer coefficients were used to compute the temperature distribution of a modified version of the Navy C specimen.
Proceedings Papers
HT2015, Heat Treat 2015: Proceedings from the 28th Heat Treating Society Conference, 123-128, October 20–22, 2015,
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Previous work was reported on the induction hardening process for a 1541 steel axle shaft. This presentation compares the previous results with the stress formation dynamics in the same shaft made from steels with lower hardenability. Hardened using a scan heating method and a trailing PAG spray quench, several steels having lower hardenability were modeled using the same heating schedule so that the depth of austenite formation is similar in all cases. During spray quenching, the hardened case is shallower as steel hardenability is reduced. This leads to differences in the magnitude of compressive and tensile stresses and their distributions. In turn, the potential for internal cracking is reduced as the stress transition zone is altered by the thickness of the diffusive phase layer between the martensitic case and the ferrite-pearlite core of the shaft. The next step is to investigate these effects on the torque carrying ability of the shaft.
Proceedings Papers
HT2015, Heat Treat 2015: Proceedings from the 28th Heat Treating Society Conference, 233-251, October 20–22, 2015,
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Press quenching is a specialized quenching technique used in heat treating operations to minimize the distortion of complex components such as spiral bevel gears and high quality bearing races. The quenching machine is designed to control the geometrical characteristics of components such as out-of-round, flatness, and (if the tooling is designed to accommodate it) taper. The achievement of final dimensional tolerances is accomplished through a trial and error process where the incoming machined sizes of the components are adjusted based upon measurement data taken from the initial sets of quenched and tempered components that have already been processed through the press quenching operation. Oil flow rates can be altered during the different stages of the quenching cycle, and through the use of specialized tooling the oil flow pathways can be selectively adjusted to meter the oil flow towards specific areas of the part surface while baffling it away from others in order to provide a more uniform overall quench. Complex metallurgical changes take place during austenitizing and quenching, resulting in corresponding mechanical property changes. Accompanying these changes are the generation of thermal and transformation induced stresses, which produce in-process and final residual stresses. During press quenching, dimensional restrictions add additional complexity to the combined effects of thermal and mechanical process sensitivities on these stresses. And if the stresses are severe enough, quench cracking can result. In this investigation the quench cracking of an asymmetrical AISI 52100 bearing ring is evaluated through physical experiments and through corresponding heat treatment process modeling using DANTE. The effects of quench rate, die load pulsing, and several other process variables are examined experimentally and/or analytically to illustrate how they can impact the resulting stresses generated during the press quenching operation.
Proceedings Papers
HT2015, Heat Treat 2015: Proceedings from the 28th Heat Treating Society Conference, 350-357, October 20–22, 2015,
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The heat-treating industry is in need of heat-treatment furnace materials and fixtures that have a long service life and reduced heat capacity. Failure mechanisms on the effect of prolonged exposure to carburization heat treatment have been investigated. RA330, RA602CA, 304L, 316L and Inconel 625 alloys were selected to study the anti-corrosion properties. The alloys were exposed to 0.7%C carburizing atmosphere at around 900°C for 3 months, 6months, and 12months. Based on microstructural analysis of components that were used until failure in carburization furnace application, it was found that the primary reason for failure was the excessive carburization that leads to “metal dusting” and subsequent cracking. In addition, metallographic analysis indicated that “flake offs” of Fe-Cr-Ni alloys were mainly graphite and chromium carbides. In this paper the failure analysis of industrial components will be presented. In addition, the preliminary analysis of microstructural development during long term exposure experiments in an industrial carburizing furnace will be presented. These samples were characterized using optical and scanning electron microscope and x-ray diffraction.
Proceedings Papers
HT2015, Heat Treat 2015: Proceedings from the 28th Heat Treating Society Conference, 536-541, October 20–22, 2015,
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Quench cracks became a challenge in large serial production of martensitic components. The geometry is simple, and concentrations of stresses from the geometry itself were not indicated by numerical simulation. Grain boundary ferrite is presented in the component surface from where the cracks start. An example from another application is interesting to consider; titanium grade 5. Grain boundary alpha on prior beta grain boundaries is not accepted for aerospace applications. The volume for plastic deformation in the phases along the grain boundaries is restricted. The ductile part of the fracture indicates forces from unbalanced quenching and elevated temperature at time of crack start. The general focus for improvement will be overcritical surface temperature, vapor phase break and mix of turbulent/lamellar flow. More effective quenching around the whole component is, in this case, assumed to be better than slower quenching.
Proceedings Papers
HT2011, Heat Treating 2011: Proceedings from the 26th Heat Treating Society Conference, 182-188, October 31–November 2, 2011,
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Simulation of stresses during heat treating relates usually to furnace heating. Induction heating provides very different evolution of temperature in the part and therefore different stresses. This may be positive for service properties or negative, reducing component strength or even causing cracks. A method of coupled simulation between electromagnetic, thermal, structural, stress and deformation phenomena during induction tube hardening is described. Commercial software package ELTA is used to calculate the power density distribution in the load resulting from the induction heating process. The program DANTE is used to predict temperature distribution, phase transformations, stress state and deformation during heating and quenching. Analysis of stress and deformation evolution was made on a simple case of induction hardening of external (1st case) and internal (2nd case) surfaces of a thick-walled tubular body.
Proceedings Papers
HT2011, Heat Treating 2011: Proceedings from the 26th Heat Treating Society Conference, 199-204, October 31–November 2, 2011,
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The high-strength aluminum alloy V92Zr, part of the Al-Zn-Mg system, is a self-quenched alloy. Its primary alloying elements include 4.2 wt% Mg, 3.2 wt% Zn, 0.6 wt% Mn, and 0.15 wt% Zr. The most suitable filler wires for welding this alloy are V92W, AMg6, AMg4Zr, and No.11 (Al-Zn-Mg). This alloy is applicable in aircraft production. Prolonged heating at 50-70°C can lead to significant structural changes in the precipitation hardening of aluminum alloys due to the transition from zone aging to phase aging. Studies indicate that zone aging of Al-Zn-Mg alloys, particularly in weld seams, with repeated heating at 50-70°C, substantially increases strength while reducing elongation, cross-sectional area reduction, toughness, stress corrosion resistance, and increasing susceptibility to cracking. Research has shown that even heating at temperatures below the phase aging threshold can significantly alter the properties. This article examines the effects of prolonged low-temperature heating on the mechanical properties, crack sensitivity in impact bending, and corrosion resistance of semi-finished products and weldments of V92Zr aluminum alloys after solution treatment and aging at room and elevated temperatures.