A patented DANTE Controlled Gas Quench (DCGQ) process was developed for high precision distortion control during quench hardening. The DCGQ process follows a recipe of quenching time and the ambient gas temperature designed by computer modeling, with a specified maximum allowed temperature difference in the part section during the martensitic transformation.

This study examines the impact of thermal post processing, specifically induction hardening and tempering, on the fatigue performance of laser powder bed fusion (PBF-LB) manufactured AISI 4140 steel. Results highlight the importance of porosity control, with induction hardening effectively addressing near-surface porosity issues in non-machined parts.

Copper is expected to be increasingly used in electric vehicle components because of its high electrical and thermal conductivity. On the other hand, copper has the disadvantage of low fatigue strength compared to structural members such as steel and aluminum alloys. Therefore, the peening treatment is used in this study to increase the strength of copper. However, the projectile used in conventional peening treatments is much harder than copper, which may lead to deterioration of surface properties. Therefore, we decided to use a resin particle peening treatment that uses soft resin particles. For the projectile material, we used particles made from crushed walnut, apricot, and peach, which are natural material particles. Ceramic particles were used for comparison. Hardness measurements revealed that the near-surface hardness increased even when resin particles were used. In addition, compressive residual stresses were observed on the surface. Fatigue tests revealed that the fatigue strength improvement effect was higher than that of nontreated materials or hard particles. These results indicate that the resin particle peening treatment is an effective method for strengthening copper.

Liquid nitrocarburizing is a well-known surface treatment when it comes to tribological parts and systems. The surface layers formed through liquid nitrocarburizing processing (compound layer and diffusion zone) make it possible to combine the corrosion, wear, and fatigue resistance properties of the treated materials (mainly ferrous alloys, from low-carbon to high-alloy steels and even cast iron) while enhancing their tribological behavior. Based on its worldwide presence, its continuous improvement and high industrial maturity, HEF Groupe’s Liquid Nitrocarburizing is the technology ready for future with its CLIN 4.0 program and it ambitious ECOCLIN program which allow the recycling of wastes from nitriding installations and their transformation into directly reusable consumables. That is why HEF’s liquid nitrocarburizing is proven to be not only an alternative to other surface treatments (such as Chromium plating) on both technical aspects and price competitiveness but also a real solution answering the current environmental challenges. Thanks to the implementation of Life cycle Assessment methods, HEF’s liquid nitrocarburizing continuously improve its sustainability and continuously lower its impacts on global resources, making it an iterative routine to decrease environmental impact on all resources (Energy, water, raw materials,…)

One of the methods of evaluating the mechanical properties of a material in the case of its limited amount is the use of techniques that employ the miniaturized test specimens. The basic properties used mostly for residual life evaluation are tensile strength, impact notch toughness or impact notch toughness transition curve, fracture toughness, creep and high cycle fatigue. For example, by semi-destructive sampling of operating power equipment, actual material properties can be obtained which are crucial for predicting the residual life of the equipment. Furthermore, the local material properties of the weld joint in individual zones can be determined. In this paper applicability of these test methods is described, specific examples of use are given and reference is made to the existing ISO/ASTM 52909:2022 standard for the use of sub-size samples.

The increasing demand for accurate fatigue modeling of powder metallurgy components in automotive, aerospace, and medical industries necessitates improved knowledge of composition-microstructure interactions. Variations in feedstock composition and thermomechanical history can produce unique microstructures whose impact on fatigue performance has not been adequately quantified. When characterizing additively manufactured 316L that is within nominal standard chemistry limits, oxide and nitride species were observed preferentially in the specimen contour region. Thermodynamic simulations provide evidence of segregation of the low manganese and high nitrogen composition driving this precipitation of these phases. When present in the specimen, they promoted brittle fracture mechanisms during fatigue.

The objective of this work was conducted to investigate the influence of nickel (Ni) content and retained austenite on rolling-sliding contact fatigue (RSCF) life in carburized gear steel. In order to evaluate Ni and retained austenite effects, this study utilized carburized steel specimens of 4120 (0.13 wt pct Ni) and 4820 (3.38 wt pct Ni), which were subjected to RSCF testing. The specimens were gas carburized with a resulting case depth of approximately 1.3 mm, based on a hardness of 500 HV. The retained austenite was measured using x-ray diffraction at depths beneath the surface of 50, 250, 450, 650 μm. The 4120 specimens have a higher surface retained austenite content than the 4820. Specimens were surface ground to an average surface roughness of 0.2 μm to decrease the effect of as-carburized surface roughness on the fatigue life. The specimens underwent RSCF testing, with a surface contact stress of 2.5 GA and a slide to roll ratio of -20 pct, until a pit formed, as detected by an accelerometer. The pits that formed on the surface of the specimens were analysed with secondary electron microscopy, macrophotographs, and light optical microscopy. The pits that formed from the RSCF testing conditions were surface-initiated. The fatigue life of the 4820 specimens was higher than the fatigue life of the 4120 specimens, suggesting that the higher Ni level is beneficial to the fatigue life.

The proposition that compressive residual stresses are beneficial in improving the service life of components subject to rolling contact fatigue is well documented. However, the exact nature of the relationship between effective case depth (ECD) and the residual stress state is not well understood for components with deep case depth (>0.050inches, 1.27mm). It is expected that compressive residual stresses will gradually transition to tensile stresses as the case depth increases beyond a threshold value. In addition, the strain-induced transformation of retained austenite and its influence on the residual stress state of components resulting from service was explored. This study measured the residual stress state of components prepared with various ECD before and after simulated service with the goal of determining where the compressive to tensile transition occurs. Residual stress and retained austenite measurements were conducted using X-ray diffraction.

IN718 has good fabricability, high strength at elevated temperature, and corrosion resistance, and it is widely deployed in many aerospace and other high-performance applications. With the molten pool rapid solidification during laser powder bed fusion (L-PBF), the resulting microstructure is anisotropic and inhibits macro-segregation. The as-built condition usually exhibits lower mechanical properties. Four different heat treatment procedures were designed and tested to study the effect of different heat treatment parameters on the type of precipitates and grain size. The investigated heat treatment procedures showed the formation of equiaxed grain size and a significant amount of γ' and γ" particles at the grain boundary in addition to primary carbide types (MC). Three types of microstructure characteristics and grain size were achieved. Coarse grain size suitable for creep application was achieved by increasing the soaking time at the aging cycle. The formation of serrated grain boundaries suitable for good fatigue and creep properties was achieved by decreasing the stress relief cycle's soaking time and temperature. Fine-grain size, which is preferable for fatigue properties, was achieved by decreasing the soaking time at the solution annealing cycle.

Through hardened steel ball fatigue failure is an atypical mode of failure in a rolling element bearing. A recent full-scale bench test resulted in ball spalling well below calculated bearing life. Subsequent metallurgical analysis of the spalled balls found inferior microstructure and manufacturing methods. Microstructural analysis revealed significant carbide segregation and inclusions in the steel. These can result from substandard spheroidized annealing and steel making practices. In addition, the grain flow of the balls revealed a manufacturing anomaly which produced a stress riser in the material making it more susceptible to crack initiation. The inferior manufactured balls caused at least an 80% reduction in rolling contact fatigue life of the bearing.

Precision cold-forging processes are used to produce near-netshape parts that may then be carburized. During carburization thermal cycles, abnormal grain growth (AGG) after cold forging is known to develop microstructures which limit fatigue strength. In the present study, a small 0.04 wt.% Nb addition was made to a low-alloyed AISI 4121 steel containing 0.3 wt.% Mo. Subcritically annealed specimens were cold rolled (to simulate cold forging) at selected reduction ratios up to 50%, heated according to a simulated gas carburizing cycle at 930 °C, and water quenched to produce a final martensitic microstructure. The number density of abnormally grown grains increased rapidly as the cold rolling reduction ratio increased from 0 to 10%. With a further increase in reduction ratio, the extent of AGG decreased and was absent in samples subjected to the maximum reduction ratio of 50%. The evolution of fine (Nb, Mo)(C,N) precipitates at various stages of processing was characterized by thermodynamic calculations and electron microscopy and compared to the occurrence of abnormal austenite grain growth. The significance of these results for controlling AGG and thus optimizing fatigue performance in commercially-produced cold-forged and carburized components is discussed.

Computer simulations are increasingly being used in the automotive industry to evaluate the state of stress in cylinder blocks during casting and heat treat processes. With recent advancements, it is now possible to model casting and quenching processes as well as residual stress and high cycle fatigue. However, calculating the final stress in cylinder blocks requires the integration of several software tools with different meshing topologies, numerical methods, data structures, and post-processing capabilities. The intent of this research is to develop an integrated virtual engineering environment that combines casting simulation, computational fluid dynamics, and finite element methods in order to simulate the manufacturing process from the beginning of casting, through water quenching heat treatment, to engine dynamometer testing. The computational environment is built on three CAE tools, Magmasoft, AVL Fire, and Abaqus, and required considerable amounts of research and development to validate each numerical method and the tools that facilitate data exchange between them.

The notion that compressive residual stresses can extend the service life of components subject to rolling contact fatigue is well documented. However, the exact nature of the relationship between effective case depth and the residual stress state is not well understood for components with case depths greater than 0.050 in. (1.27 mm). It is expected that compressive residual stresses gradually transition to tensile stresses as case depth increases beyond a threshold value. This study will measure the residual stress state of components with different case depths before and after simulated service in order to determine where the compressive to tensile transition occurs. It will also investigate the role of retained austenite and the effect of strain-induced transformation caused by rolling contact. Residual stress and retained austenite measurements will be conducted using X-ray diffraction.

Low pressure carbonitriding (LPCN) has the potential to improve the impact and fatigue strength of steel components through the enrichment of nitrogen and the effect of carburizing at higher temperatures. The work described in this paper investigates the influence of boron on the LPCN response of 20MnCr5 steel and the effect of niobium on that of 8620. LPCN treatments were developed to achieve a surface hardness of ~700 HV and case depth of 0.65-0.75 mm in four alloys: 20MnCr5, 20MnCr5 + B, 8620, and 8620 + Nb. The hardness and case microstructure of treated and quenched test samples are correlated with bending fatigue measured in Brugger fatigue specimens, which simulate the root of a gear tooth.

The use of nitriding to improve a component’s resistance to wear, fatigue, and corrosion continues to increase across the industry. However, for nitrided components, no universally accepted definition of “case depth” is available to allow the comparison of different nitriding processes, cycles, and materials. This study documents currently published methods of specifying and determining case depth for nitrided components, and evaluates the reported case depth of multiple materials and cycles in an effort to determine an optimal and robust “universal” method of reporting case depth. After completing this exercise, it appears that the optimal “universal” method of specifying and reporting the case depth for a nitrided component is to report the depth at which a Vickers microhardness traverse crosses a threshold which is 50HV greater than the material hardness below the nitrided case.

Atmospheric case hardening of powertrain components may cause internal oxidation and thus reduce hardenability at the surface zone. This may affect the fatigue strength, which restricts the maximum cyclic load on steel components and hence is a major impediment for powertrain development and design. Here we have investigated the effect of furnace gas atmosphere composition and quenching path on fatigue properties of powertrain components. The results show that the detrimental effect of internal oxidation on fatigue may be compensated for by altering of the furnace atmosphere. Moreover, it is shown that the quenching path below the martensite start temperature also has an impact on the fatigue properties. These experiments were done in a full-scale industrial furnace on steel bars in 16MnCr5 and 20NiMo9-7F.

Gas Nitriding is a common industry process which can improve the hardness, wear resistance, and fatigue strength of steel components. Proper surface activation is reported to be critical in achieving a uniform and repeatable nitriding response, but little data is available to compare various activation techniques for common nitriding alloys. This paper reports the early hour compound layer formation for six activation techniques on both a low alloy steel and a specialized nitriding steel. Both grades of steel showed the best performance when a multi-stage nitride washer was used to prepare the surfaces. Two other processes, namely nitric acid etching and a neutral wash and rinse cycle, were also shown to provide acceptable early hour performance for both alloys under the test conditions in this study.

In the turbine airfoil refurbishment business, brazing cracks in investment cast parts made of expensive alloys is routinely required as hot section jet engine components are damaged due to oxidation, sulfidation, hot corrosion, fatigue, or foreign object damage. However proper brazing requires that all oxidation first be thoroughly removed from airfoil component surfaces, cooling passages and cracks, which can be very narrow and deep.

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.

In the turbine airfoil refurbishment business, brazing cracks in investment cast parts made of expensive alloys is routinely required as hot section jet engine components are damaged due to oxidation, sulfidation, hot corrosion, fatigue, or foreign object damage. However proper brazing requires that all oxidation first be thoroughly removed from airfoil component surfaces, cooling passages and cracks, which can be very narrow and deep.