Ductility dip cracking (DDC) is a detrimental solid-state cracking phenomenon that can occur during welding of copper-nickel (Cu-Ni) alloys used in naval vessels. The presence of these cracks has several deleterious effects, including reduced fatigue life and increased susceptibility to corrosion. The mechanism of DDC remains highly debated and understudied, especially in material systems outside of Ni-Cr-Fe alloys. The predominant mechanisms that have been proposed include: 1. Grain boundary sliding, 2. Precipitate-induced strain, and 3. Impurity element segregation. In the present body of research, thermal-mechanical testing over a wide range of strain rates and temperatures was performed using a Gleeble 3500. Both flow-stress and fracture morphology of wrought 70/30 Cu- Ni are considered. Following fracture, microstructural analyses using both scanning electron microscopy and optical microscopy were conducted to observe and quantify intergranular cracking and fracture surface features. Results show a strong correlation among fracture morphology, ductility, and temperature.

Decarburization of steel parts during heat treating results in a lower surface hardness, undesirable residual stress profiles, and poor part performance. Significant effort has been made towards preventing decarburization and determining the impact of annealing time and temperature on decarburization rate. Much of the published research has focused on medium carbon steels, ranging from 0.3wt% C to the eutectoid composition. The goal of the current research is to determine decarburization rates for steels with carbon concentrations above the eutectoid concentration. AISI 52100 steel was heated in air for 12, 24, and 36 hours at three temperature ranges (below A 1 , above A cm , and between A 1 and A cm ). Optical microscopy was used to determine the carbon concentration as a function of depth from the surface. The diffusion coefficients of carbon in austenite and ferrite plus cementite phase assemblages were calculated. These diffusion coefficients can be used in a finite difference simulation to predict decarburization at different temperatures and times.

Prof. Tatsuo Inoue passed away on September 23, 2023, at the age of 83. He held a professorship at Kyoto University from 1983 to 2003 and made significant contributions to the theory of heat treatment simulation, which is now widely used. His theory was reported at an international conference in Linkoping, Sweden in 1984. Fundamental equations in his theory cover metallurgical coupling effects caused by changes due to phase transformation, temperature, and inelastic stress/strain as well as carbon diffusion during the carburizing process. Prof. Inoue designated these effects as “metallothermo- mechanical coupling”. Software applying his theory was presented at ASM International’s 1st International Conference on Quenching and the Control of Distortion in 1992, where its advanced nature was recognized. In 1994, Prof. Inoue published a paper on the application of heat treatment simulation to the quenching of Japanese swords, revealing changes in temperature, curving, microstructure, and stress/strain in their model during the traditional quenching process. In 2017, he published “The Science of Japanese Swords” with Sumihira Manabe, a swordsmith, to communicate his specific achievements to the general public.

With the increasing amount of historical fatigue data for advanced manufacturing processes, such as additive manufacturing, it becomes increasingly feasible to use statistical and machine learning approaches to garner deeper insights into the contributions to fatigue performance in order to improve the design for fatigue failure or processing route parameters. Prior to model development, aggregated datasets, whether compiled through manual or automated processes, require extensive verification and profiling to eliminate systematic errors and identify insufficiently investigated parameter combinations. Without these steps, the veracity of any model, especially black-box models, is dubious. Once the structure and patterns of the dataset are established, proper implementation of random imputation can be used to expand the amount of usable data. This verified and augmented dataset can now be subjected to various statistical tools whose role in data exploration will be discussed, particularly regarding the role of distinguishing porosity- and microstructure-driven fatigue failure data.

Direct metal laser sintering (DMLS) is an established technology in metal additive manufacturing. This complex manufacturing process yields unique as-built material properties that influence mechanical performance and vary with different machine parameters. Part porosity and residual stresses, which lead to part failures, and grain structure, as it relates to mechanical properties and anisotropy of DMLS parts, require investigation for different print settings. This work presents results for density, residual stress, and microstructural inspections on designed test artifacts for the benchmarking of 3D metal printers. Results from printing artifacts on two separate DMLS printer models with default parameters show highly dense parts for both printers, with relative densities above 99.5%. Characterization of residual stress through cantilevered deflection specimens indicates similar resulting thermal stresses developed in both build processes, with deflection averages of 32.48% and 28.09% for the respective machines. Additionally, properties of the test artifact printed after adjusting default machine parameters for equal energy density are characterized.

Across all industries, material specifications are tightening beyond previously understood process capabilities. Slight shifts in material grade, microstructure, heat treatment, or alloy composition can significantly impact long term material integrity. This study examines the feasibility of noncontact, 100% inline magneto-inductive testing on materials and components to ensure material quality standards. To investigate the hypothesis that material grade, carbon content, density, and alloy composition can be accurately tested in real time during production, an experiment was conducted using magneto-inductive test instrumentation and an encircling coil. The results of the investigation confirmed that 100% of the material in a component could be thus tested, accurately, efficiently, and autonomously verifying that the specified material grade with the proper composition and properties had been used.

A physics-based software model is being developed to predict the nitriding and ferritic nitrocarburizing (FNC) performance of quenched and tempered steels with tempered martensitic microstructure. The microstructure of the nitrided and FNC steels is comprised of a white compound layer of nitrides (ε and γ’) and carbides below the surface with a hardened diffusion zone (i.e., case) that is rich in nitrogen and carbon. The composition of the compound layer is predicted using computational thermodynamics to develop alloy specific nitriding potential KN and carburizing potential KC phase diagrams. The thickness of the compound layer is predicted using parabolic kinetics. The diffusion in the tempered martensite case is modeled using diffusion with a reaction. Diffusion paths are also developed on these potential diagrams. These model predictions are compared with experimental results.

Determination of flow stress behavior of materials is a critical aspect of understanding and predicting behavior of materials during manufacturing and use. However, accurately capturing the flow stress behavior of a material at different strain rates and temperatures can be challenging. Non-uniform deformation and thermal gradients within the test sample make it difficult to match test results directly to constitutive equations that describe the material behavior. In this study, we have tested AISI 9310 steel using a Gleeble 3500 physical simulator and Digital Image Correlation system to capture transient mechanical properties at elevated temperatures (300°C – 600°C) while controlling strain rate (0.01 s -1 to 0.1 s -1 ). The data presented here illustrate the benefit of capturing non-uniform plastic strain of the test specimens along the sample length, and we characterize the differences between different test modes and the impact of the resulting data that describe the flow stress behavior.

This paper discuss recent developments in mesh belt heat treating systems used in the production of automotive fasteners. Methods for heat treating threaded fasteners have evolved significantly over the last 20 years as low-capacity shaker hearth, rotary hearth, and plate-belt systems are replaced by soft handling mesh belt heat treatment systems. Design innovations for improving the accuracy of tempering furnace tolerance bands and integrating inline zinc phosphate removal systems are discussed along with their respective benefits.

The objective of this work is to develop the material and numerical models needed to simulate the carburizing process of an automotive gear. The paper discusses the factors that influence calculation time and accuracy and presents important equations and material property data. It describes how the simulation predicts local carbon content based on diffusion and how quenching computation provides information on stress states and residual stresses. It also explains how to account for the effects of grain growth, volume variation due to phase changes, and transformation plasticity.

A study on the microstructural evolution of a Ni-base superalloy (Allvac 718plus) was conducted to better understand how solutionizing temperature affects the final microstructure of solutionized and aged test samples. Four different solutionizing temperatures were used to obtain different fractions of gamma prime (γ’) and delta (δ) phase precipitates. This paper describes the solutionizing treatments and presents and analyzes the results of SE-SEM, EBSD, EDS, and XRD testing.

This paper examines the causes of distortion in heat treated 1080 steel parts and the influence of quenchants and quenching temperature. A comparison of parts produced using a different oil and different quench temperatures shows that a significant improvement can be achieved in distortion with only minor grain growth and a slight reduction in hardness.

This work investigates the cooling performance of different salt solutions and quench bath parameters. The results show that increasing quenchant temperature can stabilize the vapor film, while the presence of various additives and the use of agitation can hasten its collapse. Ionic solutions containing NaCl, Na2SO4, NaOH, and NaNO2 were found to inhibit the vapor blanket at 35°C and improve cooling power. Adding salt-forming solutions promoted a more homogeneous cooling with high values of heat flux over most of the cooling cycle.

A variety of test systems have been developed to determine the cooling characteristics of quenchants. Although current test standards specify cylindrical probes for measuring quenchant temperatures and cooling rates, this review concerns the development, implementation, and potential of test systems that use ball probes instead. It assesses the strengths and limitations of different types of ball probes and describes prototype test systems that leverage ball probe capabilities while compensating for inherent weaknesses.

This paper presents the results of a study on the cooling performance of hot oil and molten salt quench media. It describes the tests performed, analyzes the results, and interprets the findings. It explains how the heat extraction mechanism in hot oil differs from that of NaNO2 eutectic mixtures and how it translates to differences in cooling rate, spatial uniformity, and hardness in quenched steel parts.

Gas nitriding is proving to be a viable low temperature case hardening process for stainless steels used in numerous applications. In this study, a comparison between austenitic (grade 304) and martensitic (grade 401) stainless steels shows how pre-oxidation temperature affects the thickness and porosity of the compound layer produced as well as hardness and nitriding diffusion depth. The results indicate that austenitic stainless steel would be the best choice for a part requiring wear resistance and strength, and that a standard rolled martensitic stainless steel would suffice if only a wear resistant surface is needed.

Accurate simulation of phase transformation during quenching of steels requires comprehensive knowledge of thermal and physical properties of the material. In cases when reliable material data are not available they can be obtained by a two-stage inverse method proposed in the paper. It includes a Jominy test of a specimen with thermocouples. At the first stage, we obtain TTT diagrams by means of analyzing cooling curves for several regions of the specimen obtained from experimental results. The second stage includes correction of material thermo-physical properties, i.e. the thermal conductivity and specific heat for each phase as well as estimation of the latent heat for each phase transformation. Parameters fitting is carried out iteratively by comparing FEM simulation and experimental results. Varying of parameters is performed with evolutionary methods of multi-parameter optimization. The developed method is implemented in QForm commercial software.

Blade curving due to quenching in the Japanese sword has been recognized by swordsmiths through the ages. In the late 1920s, Hattori noted that the sword curving is induced from not only martensitic transformation expansion in the near-edge region but also non-uniform elastic and plastic strains distributed in the section, based on his experimental results using cylindrical specimens. Our research for an updated explanation on the subject prepared Japanese sword (JS) type specimens made of the same steel and process as the Japanese sword, and model JS (MJS) type specimens with the almost same shape as the JS type specimens, which were machined from commercial carbon steel and austenite stainless steel bars. All specimens quenched by a swordsmith using the traditional way showed a usual curved shape with different curvatures. Curving, temperature, hardness, metallic structure and residual stress measurements for the specimens were performed to prepare their future simulation works.

The temperature profile in the Heat Affected Zone (HAZ) during induction welding is one of the most important factors determining the weld quality of High-Frequency Induction (HFI) welded steel tubes. In this work, numerical computation of the 3D temperature profile in the steel tube has been done by coupling the electromagnetic model with the thermal model. The high-frequency current and the magnetic fields in the tube, coil and impeder have been evaluated. The resulting power from the induced current is used to evaluate the temperature in the joining edges of the tube. The continuous tube movement has been implemented by considering an additional transport term in the heat equation. The simulations consider non-linear electromagnetic and thermal properties of the steel when it undergoes temperature rise to the welding temperature. The temperature profile from the resulting simulation gives information to control the subsequent process of joining the edges of the steel tube.

Larsen Miller is a formula used to calculate broad equivalent Thermal Effect (TE) stress relieving and tempering recipes. However, results are not precise. The purpose of this work is to determine a more exact procedure. ANOVA design of experiment was used and three supplemental variables were identified as a source of thermal effect variances added to temperature and time: ramp rate, soak time and correlation between Temperature and Soak time. It was then possible to predict the most effective process temperature and soak time necessary to produce the desired stress relief as defined by the angle position of a torsion spring. The results apply to one spring type and one configuration. More work is necessary to expand the methodology to families of parts, i.e. compression springs.