Vanadium microalloying additions are common in medium carbon ferrite-pearlite steel shafts. The increased load capacity provided by vanadium carbonitride precipitation is beneficial in many applications. Induction hardening can further increase the surface strength of a component; however, the implications of the vanadium carbonitride precipitates on microstructural evolution during induction hardening are unclear. Evidence that vanadium microalloying influences the microstructural evolution of the induction hardened case as well as the case/core transition regions are presented in the current study. Vanadium increases the amount of non-martensitic transformation products in the case while decreasing austenite formation kinetics in the case/core transition region. Observations in induction-hardened shafts were supported by Gleeble physical simulations of computer simulated thermal profiles. Characterization was conducted using scanning electron microscopy, dilatometry, and microhardness testing.

Electromagnetic induction has provided reliable, predictable, and cost-effective heat treatment results for decades. Recently-developed inverter technology, providing instantaneous and calculated frequency control during heating, is dramatically advancing the heat treatment quality and equipment capability that induction heat treatment systems can deliver. This paper presents the many advantages of the technology in numerous real-world induction heat treatment applications, particularly in the scan hardening of shafts and shaft-like components. Coupled electromagnetic-thermal finite element analysis simulation results are utilized throughout to graphically and numerically illustrate the revolutionary nature of this new technology.

In single-shot hardening applications, heat treated components often feature a variety of geometric complexities including variable wall thicknesses, sharp diameter transitions, lightening holes, slots, etc. Due to the inherent 3D electromagnetic nature of single-shot coils and the complex geometry components which they must accommodate, the design and optimization of single-shot hardening coils is typically a demanding and intricate task. This paper presents combined electromagnetic-thermal and thermal-mechanical FEA simulation results for the single-shot induction hardening of a power transmission shaft. The simulation results, including electromagnetic, thermal, metallurgical, and mechanical data demonstrate the value of computer simulation in the design and development of single-shot induction hardening systems.

Previous work was reported on the induction hardening process for a 1541 steel axle shaft. This presentation compares the previous results with the stress formation dynamics in the same shaft made from steels with lower hardenability. Hardened using a scan heating method and a trailing PAG spray quench, several steels having lower hardenability were modeled using the same heating schedule so that the depth of austenite formation is similar in all cases. During spray quenching, the hardened case is shallower as steel hardenability is reduced. This leads to differences in the magnitude of compressive and tensile stresses and their distributions. In turn, the potential for internal cracking is reduced as the stress transition zone is altered by the thickness of the diffusive phase layer between the martensitic case and the ferrite-pearlite core of the shaft. The next step is to investigate these effects on the torque carrying ability of the shaft.

This presentation reviews selected innovations related to induction hardening of various automotive powertrain transmission and engine components, including but not limited to induction surface hardening of complex geometry shafts. Thanks to several innovative designs (patented and patent pending), important goals were achieved. Process flexibility in shaft scan hardening has been substantially enhanced thanks to a novel inverter design that allows controlling independently frequency and power during scanning. This innovation allows improving quality of induction hardened components maximizing production rate and process flexibility. When applying single-shot hardening for heat treatment of output shafts, flanged shafts, yoke shafts, sun shafts, intermediate shafts, drive shafts and others, coil life is often limited due to a necessity to “squeeze” coil current in a certain area, maximizing power density. This seemingly unavoidable feature of the great majority of single-shot inductors represents a “weak link”, limiting coil life expectancy. Thanks to innovative design (patent-pending) of a single-shot inductor, its life was increased approximately nine times. Process sensitivity has been dramatically reduced. Other benefits include measurable improvement in process robustness, coil reliability and maintainability.

Freight truck shipping is a massive industry and an important contributor to the US economy. Truck axle shafts for decades have been made from induction hardened carbon steel with 0.4% to 0.5% carbon. Associated metallurgical engineering of steel procurements, forging, processing, and applied machining, impacts axle shaft production and performance. This paper reviews metallurgical principles and controls currently applied to heavy truck axle shaft use and production in North America. Basic metallurgical engineering principles and controls, as historically and currently applied and specified, plus potential opportunities for increasing engineering value optimization, are reviewed. In particular, case depth, surface hardness, microstructure, grain size, chemical compositional interactions, procurement, processing, metallurgical evaluation, and overall engineering characterization and achievement targets are discussed.

Austempered irons and steels offer the design engineer alternatives to conventional material/process combinations. Depending on the material and the application, Austempering may provide the following benefits to producers of powertrain components like gears and shafts: ease of manufacturing, increased bending and/or contact fatigue strength, better wear resistance and enhanced dampening characteristics resulting in lower noise. Austempered materials have been used to improve the performance of powertrain components in numerous applications for a wide range of industries, from gears and shafts to clutch plates and crankshafts. This paper focuses on Austempered solutions for powertrain applications with an emphasis on gear and shaft solutions.