Induction Hardening by the Numbers

About this book

Induction hardening puts a hard, wear-resistant case on a steel part in seconds, by inducing currents in its surface, heating that surface above its hardening temperature and quenching it, while the core stays tough. It is fast, clean and precise, and it is unforgiving: a few seconds’ difference in time, a millimetre in the coil’s position, a different delivery of steel or a warm quench bath can change the case without anything visible on the part.

This book follows one induction-hardened journal through every stage. It starts with the electromagnetics, the reference depth and its jump at the steel’s Curie point, then sets the power and heating time, the coil and its coupling, the steel’s response, the quench and the temper. It then covers how the case is measured, why hardened parts distort and crack and how to prevent it, and how the whole process is held steady in production.

It is for manufacturing, process and quality engineers, heat treatment supervisors, laboratory technicians and the designers and buyers of induction-hardened parts. It assumes school physics and algebra. Each chapter works the running case with real numbers, includes one plausible mistake and how it was found, links the KEVOS® tools that do the chapter’s calculations, and ends with an exercise and its worked answer.

The running case

Every chapter follows one part. This is an illustration. A drive-line manufacturer in Dandenong, Victoria, induction hardens the bearing journal of the IH-40 drive shaft.

• Shaft: 400 mm long, 40 mm journal, 3.95 kg, a 0.45% carbon steel of the 1045 type, bought as normalised bar at 180 to 230 HB.
• Case: a 100 mm journal hardened to 600 to 720 HV1 at the surface, with an effective case depth of 2.0 to 3.0 mm to 500 HV1, stopping 5 mm short of the shoulder fillet.
• Equipment: a 30 kHz, 80 kW generator, a single-shot coil with an integral spray quench, a 2,000 L polymer quench tank with a 10 kW chiller, and tempering ovens running 2 hours at 180 °C.
• Production: 120 shafts an hour, with one section per shift for case depth.

Resistivities, permeabilities, efficiencies, energies, test results, prices and times are the case manufacturer’s working figures or are calculated from stated assumptions. They do not describe KEVOS® work or any real business, machine maker or steel supplier’s data.

How to use the book

Read Chapters 1 to 3 first: they set out the process, the reference depth and the energy that every later chapter uses. Chapters 4 to 7 cover the coil, the steel, the quench and the temper and can be read in any order. Chapter 8 covers measurement, Chapter 9 distortion and cracking, and Chapter 10 control in production.

Every calculation in the book was checked by running it, and the KEVOS® tools linked from each chapter were checked against the calculations they perform. The formulas, reference depth, layer heat balances, interpolation and control chart arithmetic, are sound starting points; sectioned parts are the final word on every recipe.

Source limits and professional responsibility

This book is educational. Its methods give first estimates of frequency, energy, quench and temper loads and show how case depth is measured and controlled; real recipes are proved by sectioned parts, hardness traverses and crack testing against the customer’s specification, and steel data come from the supplier and the applicable standards. Induction machines carry high currents and voltages, strong magnetic fields, hot parts and quench spray, and must be guarded, interlocked and operated under a safe system of work as the model WHS laws require; people with active medical implants should get medical advice before working near them. Decisions about real parts and processes remain with the competent people responsible for them.