Inductive welding systems used to make metal tubes often incorporate a ferrite impeder to limit induced electrical current on the ID of the tube under the induction coil. This paper assesses the improvement that can be achieved through the use of soft magnetic composites, instead of ferrite, and the addition of an external magnetic controller or bridge. The authors explain how they simulated the potential impact of the two design modifications and experimentally verified the results.

The demand for lightweight, high performance components continues to grow in the transportation industry. However, the inevitable trade-off between strength, weight and cost is a limiting factor in design and implementation of many technologies. Load adapted tailored components with locally varying properties offer a potential solution to this problem. In sheet forming industry, use of tailored blanks has increased notably in the last two decades, whereas utilization of such concept is relatively new to bulk metal forming industry. The researchers have been exploring new possibilities for suitable process chains to manufacture massive hybrid components. The process chain involves manufacturing processes of joining, forming, heat treatment and machining. The interface characteristics between the two materials are decisive in the performance of the manufactured component. In this study, manufacturing of a bi-material shaft by tailored forming is covered. First of all, an overview of the tailored forming technology is given with an emphasis on the joining zone treatment by thermal and thermomechanical processing. In the following, a numerical and experimental analysis of induction heating of bi-material workpieces is presented.

Though electron beam welding (EBW) causes minimum destruction to the base metal, significantly different microstructure exists at weld zone. Rapid heating and cooling during electron beam welding results in dendritic microstructure, which lowers mechanical properties. In order to recover the original mechanical properties, post weld heat treatments (PWHT) needs to be performed after EBW. This paper presents effect of PWHTs on mechanical and microstructural properties of electron beam welded SAE 5137 H steel. Welded steel plates were processed through different heat treatments like stress relieving, normalizing and hardening & tempering. Micro-structural and mechanical testing were performed to characterize these specimens. It was perceived that, different PWHT’s can be employed and selection depends on final mechanical property requirement from the weld joint.

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.

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.

Induction heating is a very controlled and cost effective way of heating parts for bonding or joining applications. This presentation will talk about what induction is and why manufacturers are switching to induction over other heating processes for their joining and bonding needs. Applications covered include brazing and soldering, weld pre-heating, seam welding, shrink fitting, hard surfacing alloy bonding, adhesive and paint curing, heat staking, and heat sealing. Advantages to manufacturers include flexibility to process a variety of parts with relatively rapid changeover, efficient use of energy, time, and shop floor space, and economical processing of both large continuous production runs or small batch jobs.

Hot isostatic pressing or HIP has been used for diffusion bonding, casting densification, and powder consolidation. Continuous advances in HIP equipment design have allowed increasingly rapid cooling, recently reaching a point where true high-pressure gas quenching is now possible within the HIP unit. This capability further enables the integration of a heat treat and HIP processing. Within the heat treat industry, high pressure gas quenching has been an area of significant development, however, where typical high pressure gas quenching equipment offers quench pressures up to 15 or 20 bar, common HIP pressures are 1000 bar or higher. The ability to quench from HIP pressures appears to offer heat treat options not previously available. This paper examines ultra-high pressure gas quenching (from 1500 bar) within the HIP unit from a heat treating point of view using AISI 4140 steel, a well characterized, medium hardenability alloy, comparing the properties and microstructure of ultra-high pressure gas/HIP quenched steel to conventional water and oil quenched results.

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.

Transient liquid phase diffusion bonding was used to join stainless steel 304 with pure copper and aluminum foils as interlayers. The bonding process was conducted in a vacuum furnace at various temperatures and diffusion times. The joints were analyzed using optical and scanning electron microscopy, energy dispersive spectrometry, and microhardness measurements. Results indicated that the hardness of the bonds formed with the copper interlayer in a vacuum was higher than those formed with the aluminum interlayer. The poor mechanical properties of the bonds were attributed to the formation of intermetallic compounds within the bond region. Prolonged holding of the parent alloy at the bonding temperature likely led to complete isothermal solidification. The diffusion of the main elements from the interlayers into the base metal at bonding temperatures was the primary factor influencing the microstructural evolution of the joint interface. Selecting an appropriate bonding temperature to achieve the maximum concentration of melting point depressants depended on the duration of isothermal solidification. To assess the corrosion resistance of the joints, Tafel tests were conducted in a 3.5% NaCl solution. The presence of eutectoid γFe + eutectic Cu + Cr and Fe-Al intermetallics was detected at the interface of the joints bonded with copper and aluminum interlayers, respectively. The highest microhardness was observed in the diffusion zone, with hardness values gradually decreasing as the distance from the joint increased. The joints involving stainless steel and copper exhibited crevice corrosion due to the galvanic couple between the stainless steel and copper. Additionally, pitting occurred due to intergranular stress corrosion cracking on the copper surface.

Today’s “high tech” vacuum furnaces have evolved significantly as advancements in materials, controls, and process technologies have progressed. These furnaces were developed to enhance metallurgical quality, improve braze quality, reduce inter-granular oxide formation, and provide better control over heating and quenching processes. Since the introduction of the first vacuum furnace for brazing in the late 1950s and early 1960s, continuous improvements over the past 50 years have led to the development of the most advanced vacuum furnaces available today. A “high tech” vacuum furnace utilizes cutting-edge materials, innovative designs, sophisticated control systems, and advanced features to deliver high performance, efficiency, and productivity, all while maintaining low utility and maintenance costs.