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.

During forging operations, strain can occur through three primary mechanisms: strain due to load applied through dies, strain due to thermal contraction, and strain due to creep. In materials behavior models, strain due to applied load and thermal contraction are directly considered and predictions are based on thermophysical properties and flow stress behaviors as inputs to the models. Strain due to creep after forging (during cooling) is often more difficult to predict and capture due to lack of materials data. In particular, data that capture the changing flow stress behavior during cooling (rather than from isothermal testing) are not commonly available. In this project, creep strain behavior during cooling was investigated by physical simulations using a Gleeble 3500. Standard cylinder-shaped Ti-6Al-4V samples with 10 mm diameter were heated to below β-transus temperature (1775°F) or above β-transus (1925°F), followed by constant cooling rates of 250°F/min and 1000°F/min with and without applied load during cooling to 1000°F. Total strain for the tests ranged from 2 – 6%. Characterization of prior microstructure and texture was carried out using XRD, optical microscopy, and SEM. The results provide insights on the relationship of flow stress behavior and microstructure as a function of temperature and cooling rate and are applicable to forging practices. These materials data can be used as input for future process modeling, potentially giving better prediction accuracy in industry applications.

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.

This paper presents the preliminary results of experiments designed to mimic typical machining and thermal processing practices for aerospace titanium alloys. The most significant finding is that multiple side mill passes result in lower magnitude compressive stresses than a single side pass, which suggests that successive interactions with the milling tool serves to relieve residual stresses at the surface. The most likely mechanism for this is that Ti exhibits significant springback during machining, and multiple tool passes essentially remove the “springback” layer. Each successive removal of material allows stress relaxation in the remaining surface layer. By contrast, with only a single pass, surface residual stresses did not sufficiently relax.

Quench and tempering heat treating operations for tubular products are relying more on induction equipment. The reasons for this can be traced to the lower energy costs for operating induction equipment compared to gas furnaces and the greater flexibility that the induction lines offer compared to their furnace counterparts in regards to recipe control and product mix. However, there are limitations and special considerations for induction heat treating equipment and the induction coils used for these operations. This paper reports on the design and operation of a new induction heat treating line for API 5CT grade L80 and P110 casing and tubing with upset ends. Upset ends pose special technical challenges for induction heating; the generation of a uniform temperature distribution relies heavily on proper coil design as well as line layout and heating time. Simulations of induction heating have provided predictions of heating profiles, and on-the-line testing allowed recipe refinement and validation of simulation models. Results from this case study help to increase confidence in this heat treating process as well as create an improved induction heating line layout for future applications.

After several years’ effort, a new standard guide has been approved and published by ASTM International that will fill a lacunae in the field of induction heat treating. A1100 – Standard Guide for Qualification and Control of Induction Heat Treating, includes a detailed description of the process variables that can affect induction heat treated long products. ASTM A1100 also provides guidance on the creation of manufacturing procedures and evaluation of induction heating operations.

As heat treating equipment and processes are upgraded and redesigned, there is a significant push towards the inclusion of new sensor technologies, “smart” machines, and the Internet of Things for industrial heat treating operations. There is a clear benefit to being able to track the “health” of equipment in operation, as well as knowing and logging the processing parameters and quality control results in real-time. However, faced with ever increasing datasets containing complementary or contradicting information that are generated by multiple operators, different manufacturer’s equipment, and a variety of brands of PLCs and microprocessors, the heat treat industry is now challenged to create the infrastructure, procedures, and databases to make sense (and use) of these data. This paper explores the methods already in place in similar industries, the ways that data analytics are currently being applied to heat treat operations, and it provides recommendations for future Big Data efforts in our heat treat industry.

Martensitic steels must be tempered to increase their toughness and ductility. The tempering process requires heating from room temperature to the desired tempering temperature. In this paper, the effects of heating rates on carbide precipitate size distribution, chemistry, and precipitate density will be discussed. As-quenched martensite in AISI 4140 steel was heated to selected tempering temperatures in air furnaces as well as by induction. The heating rates for tempering vary from 30 seconds to 20 minutes. The experimental results are presented, and carbides were characterized using an extraction technique.

High frequency welding is a thermo-mechanical process that relies on precise heat input as well as mechanical control as strip edges are heated and forged together to result in a seam weld. Heat input can be defined as a way of characterizing the temperature distribution at the strip edges prior to forging them together. Heat input is affected by several process variables ranging from raw material properties to welder settings and weld area setup. These are summarized in this paper, with special attention on the effects of welder frequency, welder power, line speed, and steel alloy composition on heat input and the resulting weld quality. Frequencies in the range of 100 – 800 kHz are considered. Data from tube mills (including general data and controlled on-the-mill experiments) and laboratory evaluations are included in this paper.

Requirements for greater product flexibility in the heat treating industry, driven by lean strategies, have resulted in growing global capacity for induction heating operations as well as the re-examination of processes to save production time and line space. However, there are important considerations to keep in mind when developing and modifying heat treat recipes whether for full-body, full-length heat treating, or seam normalizing applications. These include consideration of specialty alloy requirements and the presence of micro-alloying elements, the prior microstructure and presence of heavily banded structures, heating and cooling rates, and phase transformation kinetics especially with overheating and undercooling situations. This paper focuses on the intersection of theory and practical application for induction heating operations. Particular attention is paid to induction heating principles and fundamentals as well as new and proven methods for recipe generation.