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.

Carburizing and induction hardening are two surface heat treatments commonly used to increase wear resistance and fatigue performance of steel parts subject to cyclical torsional loading. It was originally hypothesized that performing an induction surface hardening heat treatment on parts previously carburized could provide further increased fatigue life, however initial torsional fatigue results from previous work indicated the opposite as the as-carburized conditions exhibited better torsional fatigue strength than the carburized plus induction surface hardened conditions. The aim of this work is to further elucidate these torsional fatigue results through metallography and material property characterization, namely non-martensitic transformation product (NTMP) analysis, prior austenite grain size (PAGS) analysis, and residual stress vs depth analysis using x-ray diffraction (XRD). A carburizing heat treatment with a case depth of 1.0 or 1.5 mm and an induction hardening heat treatment with a case depth of 0, 2.0, or 3.0 mm were applied to torsional fatigue specimens of 4121 steel modified with 0.84 wt pct Cr. The carburized samples without further induction processing, the 0 mm induction case depth, served as a baseline for comparison. The as-received microstructure of the alloy was a combination of polygonal ferrite and upper bainite with area fractions of approximately 27% and 73% respectively. The only conditions that exhibited NMTP were the as-carburized conditions. These conditions also exhibited larger average PAGS and higher magnitude compressive residual stresses at the surface compared to the carburized plus induction hardened conditions. The compressive residual stresses offer the best explanation for the trends observed in the torsional fatigue results as the conditions with NMTP present and larger PAGS exhibited the best torsional fatigue performance, which is opposite of what has been observed in literature.

Controlled cooling conveyor system is known, as the starting point for quality processing of wire rod products, obtaining good mechanical properties. This process guarantees excellent performance with high production rates. In order to process several steel grades and different diameters, it is necessary to determine, the different austenitization temperatures and cooling rates that will control austenitic grain growth and, consequently, the pearlite interlamellar spacing. In this work, dilatometric analysis was performed to determine critical temperatures for an hypoeutectoid steel during heating and controlled continuous cooling, similar to the industry conditions for heat treatment. Metallographic analysis and microhardness test validated the results obtained during the dilatometry tests. The critical temperatures will be employed to understand the effect of the thermal conditions in controlled cooling process and adjust the conditions for better results in the austenitic grain size.

Heat Treatment represents one of the largest challenges for component risk management. Traditional metallurgical test methods do not meet AIAG/VDA Defect detection criteria for safety-critical components and can represent significant overhead costs. Newer non-destructive methods are difficult to implement with substantial upfront costs and must be integrated as 100% inspection to impact PFMEA detection ratings, which can introduce a throughput constraint. Production controls and automated escalation are imperative to minimizing risk. On the development side, it is impractical to physically evaluate all combinations of product/process variation, or even test specification limits. Consequently, designs which met requirements in validation may experience degraded functionality in production due to ‘normal’ process variation that cannot be eliminated, or inevitable differences between early development and production scale processes. With the accelerated pace of innovation seen in the automotive industry, use of FEA simulation to evaluate part sensitivities is essential to identify and optimize design/process, reducing risk. Increased confidence must be achieved in test and data processing methodology through robust implementation which often requires substantial investment in time and data analysis, which can be streamlined through machine learning.

A micro-alloyed 1045 steel was commercially rolled into 54 mm diameter bars by conventional hot rolling at 1000 °C and by lower temperature thermomechanical rolling at 800 °C. The lower rolling temperature refined the ferrite-pearlite microstructure and influenced the microstructural response to rapid heating at 200 °C·s -1 , a rate that is commonly encountered during single shot induction heating for case hardening. Specimens of both materials were rapidly heated to increasing temperatures in a dilatometer to determine the A c1 and A c3 transformation temperatures. Microscopy was used to characterize the dissolution of ferrite and cementite. Continuous cooling transformation (CCT) diagrams were developed for rapid austenitizing temperatures 25 °C above the A c3 determined by dilatometry. Dilatometry and microstructure evaluation along with hardness tests showed that thermomechanical rolling reduced the austenite grain size and lowered the heating temperature needed to dissolve the ferrite. With complete austenitization at 25 °C above the A c3 there was little effect on the CCT behavior.

Phase transformation and temper response of three martensitic alloys were investigated as an important portion of fundamental metallurgical information database related to heat treatment design for engine component applications. A limited metallographic evaluation has also been carried out with selected temper response run samples in this study. Basic descriptions on adequate hardening and tempering parameter design were provided in terms of optimizing the intended performance with these alloys.

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.

Vacuum carburizing 9310 gear steel followed by austenitizing, oil quench, cryogenic treatment, and tempering is known to impact the residual stress state of the material. Residual stress magnitude and depth distribution can have adverse effects on part distortion during intermediary and finish machining steps. This study provides residual stress measurement, microstructural, and mechanical property data for test samples undergoing a specific heat treat sequence. Test rings of 9310 steel are subjected to a representative gear manufacturing sequence that includes normalizing, rough machining, vacuum carburizing to 0.03”, austenitizing, quench, cryo-treatment, temper, and finish machining. The rings along with metallurgical samples are characterized after each step in order to track residual stress and microstructural changes. The results presented here are particularly interesting because the highest compressive residual stresses appear after removal of copper masking, not after quenching as expected. Data can be used for future ICME models of the heat treat and subsequent machining steps. Analytical methods employed include X-ray diffraction, optical and electron microscopy, and hardness testing.

Nitriding is a surface hardening treatment used on steel components to improve their resistance to corrosion, fatigue, and wear. Iron nitrides at the nitrided steel surface form a compound layer known for its high hardness but also for its brittle nature. It is not uncommon for this layer to chip or break away during metallurgical sample preparation, making it difficult to accurately characterize the microstructure of the nitrided load. This paper presents the results of several studies that assess the effect of cutting and polishing operations along with polishing pressure, the use of foils, and Ni plating. A best practice procedure has been developed to prevent damage to nitrided samples and minimize uncertainty when evaluating part quality.

Microstructural examination of a nitrided part is the most commonly used method for evaluating nitriding material and process performance. Microstructural evaluation also helps to validate that the process ran as intended and produced the desired nitrided case characteristics. However, sample preparation is often complicated by the partial or complete breakaway of the compound layer and may affect the accuracy of the conclusions made. A set of experiments was performed to evaluate the effect of two saw cutting methods, the use of metal foil for sample mounting, and the use of Ni plating before cutting. Microstructures of 12 experimental conditions were analyzed. Recommendations were made for the nitrided sample preparation best practice to analyze compound layer uniformity and thickness.

The distortion behavior of carburized and fully heat treated Ni-Cr-Mo martensitic steel (S156) has been experimentally evaluated. Dimensional measurements of Navy C-ring distortion coupons during interrupted heat treatment process for parts manufactured from two forming routes, hot forging and machined from as received bar, was performed. Metallurgical analysis was carried out to attempt to relate the observed microstructural characteristics with measured process induced distortion. The carburization process was found to be the most severe in terms of inducing distortion. It was found that additional heat treatments during the process results in a larger final distortion. Machining parts from forgings results in higher distortions than that of those machined directly from as received bar due to the added thermal processing history. A finite element simulation of the carburization process for a C-ring coupon is presented.

The AISI 440B (DIN 1.2210, X90CrMoV18) steel is one of the hardest among martensitic stainless steels. This type of steel is used in a variety of industrial applications where wear and corrosion are determinant, such as molds, parts and tools for the automotive and biomedical industries. Their superior mechanical properties are due to its high carbon (0.75-0.95 % C) and chromium (16-18% Cr) contents. Suitable coatings can increase wear resistance and expand these materials usability range. Boride coatings, with their high hardness and wear resistance are good candidates for this purpose. Boride layers were obtained by boriding treatment in a salt bath (a mixture of sodium borate and aluminum). The layer properties, such as hardness, thickness, layer/substrate interface morphology and phases formed are influenced by steel composition. In this work, the layers produced on AISI 440B steel were harder, thinner, with a smoother interface when compared to plain carbon steels due the larger amount of alloying elements. In order to evaluate mechanical properties of borided layers in samples of stainless steel AISI 440B, Optical Microscopy (OM) microstructural analysis, Vickers microhardness tests and micro-adhesive and micro-abrasive wear resistance tests were performed. The layers produced exhibited a hardness close to 2250 HV and excellent wear resistance far superior to that of substrate.

The 13% Cr 0.2%C steel is extensively used in OCTG application. This steel was examined in the double hardened condition at 1040°C/OQ followed by 980°C/OQ as against conventional hardening treatment at 980°C/OQ. It was observed that the double hardening heat treatment resulted in higher carbon dissolution in the matrix without any residual grain boundary necklace carbides while single hardening at 980°C shows remnant grain boundary carbide. Double hardening heat treatment was found to refine the grain size by recrystallization of the defects introduced in first hardening. During double tempering heat treatment, the carbides in the 980°C treatment were coarse and found to nucleate along grain boundary. The double hardened sample on tempering showed an even distribution of carbide throughout without grain boundary carbide. The double hardened sample show improved strength and toughness compared to the single hardened sample at similar tempering conditions. The microstructural analyses at various stages of processing have been correlated to the mechanical properties obtained.

Recent destructive analysis of six ASTM A350 LF2 flanges has revealed vastly different low temperature (-50°F) Charpy impact toughness from 4 J (3 ft-lbs) to greater than 298 J (220 ft-lbs). These relatively low strength flanges, minimum 248 MPa (36 ksi) yield and 483-655 MPa (70-95 ksi) tensile strength, had nominally the same yield and UTS despite the difference in toughness. Detailed chemical and microstructural analysis was undertaken to elucidate the cause of the toughness range. The majority of the flanges had aluminum additions and a fine grain size with the toughness differences mostly explained by the cooling rate after normalizing with the still air cool showing the lowest toughness and the fastest air cooled sample the highest. For flanges of this strength level a quench and temper operation is not required to obtain good low temperature toughness but forced air cooling after normalizing is a minimum cooling rate to ensure good toughness and overall strength.

A study was conducted on a set of H13 steels to enhance their performance as matrices and pins. The steels were austenitized in a high-pressure vacuum furnace at 1015 °C for 180 minutes, followed by nitrogen quenching in a high vacuum (2 bar). Two tempering treatments were applied: one at 540 °C and another at 580 °C, each for 180 minutes, with subsequent nitrogen cooling to room temperature. The nitrocarburizing process was carried out in a liquid bath salt furnace at 580 °C for varying durations of 45, 60, 90, 120, 150, and 180 minutes to assess the impact of treatment time on the quality of the nitrocarburizing layer. Post quenching and tempering, the steels exhibited hardness values ranging from 550 to 570 HV. After nitrocarburizing, the surface hardness increased to between 740 and 810 HV, with a nitrocarburizing layer thickness of less than 14 μm. The microstructural evolution of the compound layer was analyzed using scanning electron microscopy and X-ray diffraction. The characterization revealed a continuous nitrocarburizing ε-Fe 2–3 (C,N) layer. Specimens treated for 45 to 60 minutes demonstrated superior wear performance compared to those treated for 90 to 180 minutes.

An investigation was carried out to examine the influence of cryogenic processing on the microstructure and mechanical properties of Austempered Ductile Cast Iron (ADI). ADI has emerged as a major engineering material in recent years because of its many attractive properties. These include high yield strength with good ductility, good fatigue strength, fracture toughness and wear resistance. In this investigation, compact tension and cylindrical tensile specimens were prepared from ductile cast iron as per ASTM standards and were austempered at a lower bainitic temperature of 288°C (550°F). These specimens were then cryogenically processed. The mechanical properties and fracture toughness of these samples were evaluated and compared with the noncryogenically treated samples. The influence of cryogenic heat treatment on the microstructure of these samples was also examined. Test results show that the cryogenic processing can improve the mechanical properties without compromising the fracture resistance of the material.

The dissolution of second phase particles in a 319-type (Al-Si- Cu-Mg) aluminum casting alloy has been quantified by image analysis of metallographic specimens as well as an electron microprobe technique. The initial phase content of the as-cast material, and the change in volume fraction of each phase following solution treatment for various times at 480°C and 505°C, was determined by analysis of particles observed by backscattered electron microscopy. Furthermore, the change in dendritic alloy content during solution treatment was measured using electron microprobe analysis in order to estimate the relative volume fraction of second phase particles dissolved. Finally, a non-isothermal dissolution model was used to predict the dissolution behaviour during solution treatment and comparisons are made between the model predictions and experimental measurements.

Current heat treatment standards do not adequately define tempers for thin-walled castings that solidify at high rates. Emerging casting processes, such as vacuum high-pressure die casting, benefit from rapid solidification rates, which result in fine microstructures and reduce the need for prolonged solution treatment times. Studies on rapidly solidified samples with secondary dendrite arm spacing between 35-10 μm were conducted, with solution times ranging from 30 minutes to 9 hours, and various aging parameters were evaluated. Metallurgical analysis revealed that increased microstructure refinement could reduce solution time by up to 50% without compromising the alloy’s mechanical properties. The highest strengths, with an ultimate tensile strength of 330 MPa (47.9 ksi) and a yield strength of 300 MPa (43.5 ksi), were achieved under T6 peak aging conditions. Additionally, thermal analysis and dilatometer results are presented to evaluate phase dissolution during solution treatment, aging kinetics, and dimensional stability.