Engineering Materials E-Book

Henry Tindell

• Herausgeber: Crowood
• Kategorie: Fachliteratur
• Sprache: Englisch

Veröffentlichungsjahr: 2014

Beschreibung

A comprehensive guide to engineering materials used in the workshop, for processes such as milling, welding, and lathe and bench-work. Designed for the general enthusiast or amateur engineer, Engineering Materials provides in-depth information on the functions and limitations of commonly used metals, and valuable advice on material selection. With detailed diagrams and photographs throughout, the book covers: a history of engineering materials, and the forming and behaviour of a range of ferrous and non-ferrous metals; the practical application of materials in engineering and case studies on steam locomotive boilers, model aero engines and classic two-stroke motorcycle engines; authoritative advice on material selection for practical heat treatments, joining and other processes in the workshop; a review of the micro-structures and performance of familiar metals in critical applications, including fast fracture and fatigue, illustrated by a re-evaluation of some well-known dramatic engineering failures. Superbly illustrated with 144 colour photographs and 82 diagrams.

Leseprobe

First published in 2014 by The Crowood Press Ltd Ramsbury, Marlborough Wiltshire SN8 2HR

www.crowood.com

© The Crowood Press 2014

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers.

British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.

ISBN 978 1 84797 680 2

Safety is of the utmost importance in every aspect of metalworking. The practical workshop procedures and the tools and equipment used in metalworking are potentially dangerous. Tools should be used in strict accordance with the manufacturer’s recommended procedures and current health and safety regulations. The author and publisher cannot accept responsibility for any accident or injury caused by following the advice given in this book.

Photography by Colin Mills

Dedication

To Susan Elizabeth Tindell (1949–2012).

Contents

Preface

Introduction

1  Case studies: materials in action

2  Materials

3  Behaviour of metals

4  Material selection and limitations

5  Back to basics

Appendix I: Hardness measurement

Appendix II: Resources

Appendix III: Elements, Abbreviations, Symbols, Conversions

Glossary

Bibliography

Acknowledgments

Index

Preface

In a parallel universe there may exist the perfect material – as strong as an alloy steel, hard as diamond, malleable as gold, corrosion-resistant as titanium, weldable as mild steel, cheap as grey cast iron, abundant as wood, long-lasting as flint, etc. But, alas, it doesn’t occur here, hence the need to understand and select from the myriad materials commonly available. There are, for instance, literally thousands of different steels produced worldwide, although we need only know the details of a tiny selection.

Whilst the material in a project usually accounts for only a small part of the cost – and it is then the subject of considerable ‘added value’ in processing (e.g. machining) – it is surely appropriate to avoid this effort being wasted on the wrong material. Apparently invulnerable items may be rendered useless by the insidious effects of, for instance, vibration (slow crack growth – fatigue); stress-corrosion cracking (austenitic stainless steel in certain environments); or fatally cracked (incorrect welding procedure for a low-alloy steel).

This book should help as a guide through the labyrinth that is engineering material applications, based on well-established theory and practically available materials.

Henry Tindell

Cheadle Hulme, 2013

Introduction

‘It’s better to burn than rust…’, sang the Eagles in 1972 but, like the Rolling Stones, forty years later they’ve discovered that it’s better to rust gently than burn, just like my old bike…

For those of the gently rusting persuasion, this book aims to explain the application of engineering materials, essentially metals, for the engineer who is concerned with making things. The model engineer, the amateur or even professional experimental engineer, really needs a basic feeling for materials otherwise a lot of the enjoyment of these activities will never be realized; not to mention the pitfalls into which the unwary can fall, with expensive failures incurring lost time, money or worse…

In the post-industrial age now upon the West, practical skills and knowledge are at a premium, for not all things can be facilitated directly from the virtual world. And there is, despite the present information revolution, a common lack of basic understanding of the materials used in making things.

Metals have become ubiquitous since the early twentieth century; like computers in our age they are often overlooked. The great advances in understanding of metals’ behaviour, with many discoveries as recently as in the last fifty-odd years, may not be apparent to the non-specialist worker. Understanding how metals work has increasingly become the province of the materials specialist, as Further and Higher Education courses have moved on from metallurgy to the ‘newer’ materials like plastics and composites, with computer modelling rather than hands-on engagement. This is all very well, but it is leaving a great hole for expertise ‘in the shed’, when a substantial industrial manufacturing facility cannot be called upon for support.

Even a generation ago, it was not uncommon (in the UK, at least) for an engineering firm to be sufficiently vertically integrated that many trades were available in-house, from departments for electrics, plumbing and joinery, to design, fabrication, foundry-work, mechanical and non-destructive testing – even metallurgical analysis. This meant that often substantial domestic jobs could be tackled with access to these trades, like re-wiring a house and shed, or fitting a central heating system. It provided a source of material knowledge, even the materials themselves, for that special model or vehicle repair. (A downside of the latter I once saw was when a lunchtime welding repair on a car ended in it catching alight and being written off – but that’s the cost of experience!) Nowadays, this scenario is rare and the enterprising individual has to look elsewhere for help and guidance, with the result that an understanding of materials is becoming an impoverished area of expertise. There is, perhaps, a parallel with cooking, where time and circumstances have tempted a generation away from individual food preparation skills and into fast foods and takeaways. The burgeoning interest in cooking programmes and literature, however, shows the inherent desire for a practical connection with the process – the ‘making things’ drive, not dissimilar to that of the practical engineer.

Photo 1 Horizontal boiler, for use with a steam engine in a glass fibre model boat.

Photo 2 Vertical boiler, delivering 30psi, to power a Viper Vee twin, oscillator steam engine.

Photo 3 Early twentieth century vertical steam engine, from a German manufacturer.

Photo 4 Vertical parallel twin cylinder marine engine, often adapted as factory power source.

In this increasingly ethereal world of the virtual image, the benefit of making real things can be remarkably therapeutic, but in materials-driven engineering projects large or small, information and experience need to be steadily gained or disappointment and failure can overwhelm the enthusiastic worker. So, this book tries to describe the metals commonly available to the general enthusiast and how they can be selected and processed to a satisfactory product. As importantly, it points to the limitations of metals – an area that demands sufficient knowledge and experience.

Whilst considerable attention is normally paid to engineering processes, such as lathe-work, milling, bench-work and welding, a basic knowledge of the materials being worked is largely ignored. Indeed, there is a parallel with professional engineering, where the understanding of metals can surprisingly often be treated as a ‘black art’. But there is no good reason not to explore this fascinating field, and in the following chapters the aim is to describe the variety of materials available, and to show how the behaviour of metals can be understood, for their successful application and avoidance of failures.

‘Why not just make everything out of mild steel?’ is a question that will be explored, basically depending on the project undertaken. Only by understanding aspects like mechanical behaviour and corrosion resistance of the chosen material can we successfully fit it to the task. For instance, whilst mild steel is justifiably popular with the model engineer, it would be folly to employ it in highly stressed parts like vehicle transmissions, weight-sensitive applications in flying, or in corrosive environments.

The photographs in this chapter show some examples of small models connected with steam power, a favourite with model engineers worldwide, made largely from copper-base alloys, such as copper and brass, and mild steel.

A BRIEF HISTORY OF ENGINEERING MATERIALS

The history of materials has largely determined the way of life and progress of civilizations ever since mankind has inhabited the earth – the eponymous ages of Stone, Bronze and Iron are familiar to all, if somewhat misleading.

Instead, the great sweep of materials history can be seen as three distinct periods. The first, from 3500BC, continued until the Industrial Revolution around AD1700. This primarily made use of wood and stone with metals being deployed on only a small scale, despite the implied usage of metals in the Bronze and Iron Ages.

The second age began with the Industrial Revolution and by the early 1800s steam began to challenge water power as the energy source of choice. By 1850 steam power, generated by extensive coal supplies in the UK, had supplanted water power. Steam engines were driving all forms of industry and enabling the explosive growth of the railways. These developments often required improved materials and knowledge. As this sometimes lagged behind construction, disasters resulted (the collapse of the Tay Bridge, for example) as the shortcomings of designs using non-ductile materials in tension, such as cast iron, were discovered.

The early twentieth century ushered in the third age which continues with the proliferation of truly ‘designer’ materials. The range of engineering metals is now being challenged by many developments in the synthetic non-metals, like ceramics and composites, which have taken several decades to reach application and are only now being extensively used in mainstream civil aircraft and high-performance sports products; these will continue to grow in the twenty-first century. Application of science to materials in the second age, like low-cost ductile steels, has undergone exponential growth in the third age, where we now understand how cast irons can be made almost as ductile as mild steel, why soft aluminium can be made as strong as the steel which is three times heavier, and how the debilitating effects of corrosion can be avoided – car bodies now lasting far longer than before. Indeed, air transport as we know it would be impossible without the long-term development of titanium and high-nickel alloys for jet engines.

Table 1 Materials timeline.

EARLY MATERIALS

Even as many as 250,000 years ago, materials were being deployed for hunting and, much later, agriculture. These were limited to the readily available stone (flint), animal bones, hair and skin, and wood from local forests. Sharpened flints provided powerful tools for the Stone Age, making hammers, saws, knives, needles, hooks and even arrow-heads for the wooden bows in use by 20,000BC. Ceramics (small items of glazed pottery) were available by 12,000BC. Even ornamental glass was being made in Egypt by 7,000BC.

Photo 5 Horizontal single cylinder steam engine, manufactured c. 1960, power source for small manufactory or workshop.

Early metals

The Middle East is generally regarded as the birthplace of the systematic use of metals and by 3,500BC the Sumerians, having already developed wooden wheels and axles, were casting, forging and forge-welding copper from local ores. Not until 2,000BC did the knowledge of bronze lead to its eponymous Age, with another 500 years before the widespread working of ferrous ores began the Iron Age. These were not, however, distinct periods, one supplanting the other like some latter-day vinyl/tape/CD/ANO development – rather the techniques were selected or co-existed over millennia, sometimes even into the modern era.

Photo 6 General purpose proprietary vertical engine, popular in factory mills and workshops, seen in the film The African Queen.

Stone

Stone buildings were being developed around the Mediterranean, in the Middle East and North Africa from 3,500BC – famously from 2,700BC for Egypt’s temples and pyramids. The use of 1,000-tonne blocks was a testament to their highly developed engineering in wood for the manipulation of these enormous pieces. This knowledge slowly spread across the western world, to the England of Stonehenge, 1,000BC. However, whilst one cannot but be impressed by the ancient Egyptians’ enterprises, it shouldn’t be forgotten that practices were often more ‘trial-and-error’ than scientific theory – witness the catastrophic collapse of the Fourth Dynasty King Sneferu’s pyramid at Mendum during, or just after, construction.

Photo 7 Simple beam engine as used in the early nineteenth century Industrial Revolution for general power source.

Wood

It has, fairly, been said that in the history of materials, wood has been the mild steel of every age until the latter part of the Industrial Revolution. Its properties are impressive (with careful selection), providing strength in tension, compression and bending, with predictable behaviour, light weight, ready availability and ease of shaping. The experience of centuries meant that it was not until the demands of industrial production and the factory system, plus the ever-present desire for advantage in warfare, finally led to metals largely superseding wood as the pre-eminent engineering material.

Photo 8 ‘Mamod Minor’ horizontal steam engine, manufactured late 1930s to 1940s.

EARLY METAL DEVELOPMENT

The development of kiln-dried bricks in Assyria in around 1,000BC enabled primitive hearths to be used for bronze, and then iron smelting at significantly higher temperatures. Perhaps the most important driver for metals was the rise and fall of the various empires around central Europe, and the deployment of their large armies. By 500BC the Egyptian empire was overtaken by the Persians, then Alexander the Great established the Greek supremacy which subsequently fell to the Romans who ruled from North Africa to Britain from 250BC to AD400.

This led to steady developments in metals, primarily for the military with the Greeks beginning to understand the rudiments of hardening by quenching of their iron (laboriously made with enough diffused carbon to permit hardening). The Romans progressed to tempering the quenched iron-carbon alloy, in their quest for the best combination of strength and toughness for critical weaponry like their famous short swords. Records exist that show how these swords helped to defeat the Celts, with their inferior swords bending on impact in the desperate struggle of pitched battle.

Photo 9 ‘ESL’ steam power unit of 1950s, popular for Meccano model operation.

Developments in the Far East

Long before the Greeks and Romans in the West, the early developments in metals technology split eastwards to India and China. This produced separate development, and superior advances in China with gunpowder, cast iron and high-calibre composite steels, a thousand years in advance of the West. This advantage, however, was lost with the chronic dislocation in communication and trade with the West until modern times when this is being redressed in dramatic fashion. While the West has lost much industrial power to the East, the amateur has at least benefited from the familiar high-quality, with low cost, tooling.

Early mechanics

Alongside their materials progress, the ancient Greeks developed an understanding of the elements of machines, like the wheel, lever, pulley and screw, but their mechanisms failed to make significant use of metal – one important limitation being the difficulty in working with hard materials, compared to the relative ease of working in wood.

We have records from Philo of Byzantium (2,000BC) which describe early experiments in elasticity, testing deflection of swords and bronze catapult springs under controlled loading. The Romans, as great miners, also made much use of lead and bronze for domestic as well as military use.

Materials in the Dark Ages

After the fall of the Roman Empire, the Dark Ages in Europe saw a return to stone and wood as primary materials, although some gradual improvement in machinery, such as waterwheels and quern mills, was made – albeit without significant deployment of metal. The two areas demanding use of metal instead of wood were armaments and clock-making. As the world’s first automatic machines, clocks, then watches, required all-metal construction as horology developed in the thirteenth and fourteenth century.

Materials in the Renaissance

In the fifteenth century the invention of printing, with moveable type, was enabled by fine casting methods, although lost-wax casting had been successfully developed in China a thousand years previously. This first Information Revolution presaged the Renaissance in Europe, with Leonardo da Vinci (1452–1519) undertaking studies into the properties of wires and beams. His simple tensile testing machine for wires was the principle used when the author worked at Fulmer Research Institute, Stoke-Poges, England, in the 1970s. We were studying the behaviour, for patent applications, of copper-base alloys (‘brasses’) exhibiting ‘memory’ properties associated with unusual strain-induced martensitic transformations. The device used a hopper which allowed lead shot to fall into a container attached to the specimen, thus loading it as desired for a special tensile test. Extremely simple and effective, it would surely have amused the great Leonardo!

Figure 1 Tensile testing – Leonardo da Vinci’s apparatus.

Developments in the strength of materials

In his book TwoNewSciences (1638), Galileo of Florence was the first to discuss ‘stress analysis’, a pioneering work on strength of materials. He even came close to correctly understanding the bending of beams theory which underpins structural analysis. In England, several decades later, Robert Hooke provided a framework for elasticity and the relation between stress and strain (load versus extension) that is at the heart of predicting a material’s behaviour. Hooke’s Law simply shows how the elastic (i.e. reversible) behaviour of metals can be confidently predicted from their unique stress–strain graph, upon which all stress analysis is based, as seen in Chapter 3.

There followed considerable efforts by the French theorists in the seventeenth and eighteenth centuries, such as Mariotte (internally pressurized pipes; laterally loaded plates) and Parent, who finally cracked the beam bending theory in 1713. Important theories from Poisson, Lame, Clapyron and St Venant of the École Polytechnique in Paris between the late eighteenth and late nineteenth centuries provided comprehensive analysis of beams, plates, shells and structures, laying the foundations of modern structural analysis and the pressure vessel codes that finally overcame the problem of harnessing high-pressure steam. This had dogged the use of steam power through the Industrial Revolution, leading to many unexpected and often catastrophic boiler explosions and the rise of the industrial insurance industry.

By the end of the nineteenth century, studies in the strength of materials were sufficiently advanced for Giraud to produce his work on the subject, building on the work of Coulomb (1736–1806) who explored scientifically the effect of heat treatment upon the strength of iron. Whilst the French approached the subject theoretically, the experimental work characterized by the British approach provided significant practical advances. The rise of industry in the USA contributed rapid advances in machining processes with Capstan and automatic lathes, as well as steel structures with ever-larger bridges and buildings. In Germany, Wöhler started vital work on rotating shafts failing by fatigue, and Neumann (1798–1895) developed visualization of stress with photo-elasticity. This built on the work in England of Thomas Young, 1773–1829 (of Young’sModulus), founder of the Cambridge School of Materials. In St Petersburg an important Engineering School was established in the early nineteenth century, with prominent contributions from the French theoreticians and important Russian contributions to modern theory on shear stresses in beams, in current use.

Material limitations

As the Railway Age began in the early nineteenth century, it became increasingly clear that the current material of choice, cast iron, was going to limit progress. Earlier railway work undertaken in the eighteenth century by pioneers like Richard Trevithick foundered with cast-iron rails that were unable to take the loads imposed. Similarly, it could be argued that the early steam road-carriage produced by Trevithick prior to his railway exploits, failed to achieve its potential largely because of the massive components (like the 7ft/3.2m wheels) required from cast iron. Coupled with the appalling road system in England, neglected since Roman times, perhaps steam was abandoned prematurely for road transport. A century later, the internal combustion engine gained a foothold never since relinquished, and has now benefited from over one hundred years of incremental development to reach its present remarkable status.

Despite the limitations of cast iron, especially its lack of ductility in tension, the steam era progressed but not without the catastrophes noted earlier, until the development of economically produced steels as pioneered by Henry Bessemer in the mid-nineteenth century largely saved the situation. This was timely, with the railway revolution really getting underway after the Rainhill trials in 1829, famously won by George Stephenson’s Rocket, prior to construction of the Liverpool to Manchester line – itself a remarkable engineering feat.

Photo 10 c. 1905 German manufacture, possibly Johann Falke, fitted with injector pump from power take-off, for continuous operation. Often used on trolley to mobilize for farm contract use, such as threshing.

Photo 11 Detail of photo 10, gravity operated pressure relief valve, simple and effective!

Photo 12 Further detail of photo 10, injector pump and its exhaust.

Non-ferrous metals

During the nineteenth century, great advances were being made in the development and production of non-ferrous alloys. Brass and bronze were being produced in tubular form, importantly for the heating elements of steam boilers. Castings could be produced in extremely large proportions as the great Victorian engineers like I.K. Brunel pushed the boundaries of the possible with audacious designs culminating in the gigantic ‘Great Eastern’. Almost too large to be launched, it was too far ahead of its time to be wholly successful, but it later enabled another remarkable feat with the laying of the first transatlantic telecommunications cable in 1858 which, despite its composition of 98.5 per cent purity copper, achieved only 50 per cent of possible conductivity – leaving plenty of scope for material improvement!

The latter part of the nineteenth century saw the greater use of aluminium, discovered in 1827, although not deployed as a structural material until the first ‘Dural’ was produced in the aircraft era of the early twentieth century. Important alloys based on nickel were produced using the Mond process, as devised by Ludwig Mond in 1890 and then used commercially to convert nickel (Ni) oxides into pure Ni by utilizing the unique property of Ni to form a carbonyl compound in the presence of carbon monoxide. A three-stage process enables layers of Ni to be deposited onto Ni pellets. This was once also used for Ni plating work, but is too toxic a process and now ‘Electroless Nickel Plating’ (ENP) is used. Together with the rarer elements like tungsten, soon to be universally employed in the new electric light filaments, these alloys were produced on a commercial scale for use in the expanding range of alloy steels and high-performance metals. High strength, temperature- and creep-resistant alloys became the materials that enabled successors to the Steam Age to power the industry and transport of our modern world. The fact that over 90 per cent of the present world power is generated through steam turbines, however, arguably indicates that we are merely in a different steam age…

Materials testing

Great advances in materials testing were made as these newer alloys were developed – enabling strength, hardness, ductility, toughness, fatigue, creep and corrosion to be measured, even if a rigorous scientific understanding was not generally available until well into the twentieth century.

More recent developments have enabled ever-more sophisticated measurements to be made, but the basic principles have been long-established. The advances in examination of the microstructure of metals, achieved with the advent of the (transmission) electron microscope (TEM), could almost be compared to the unravelling of the mysteries of DNA in biology. Such is the power of resolution on the atomic scale to confirm, for instance, the theory of dislocations that explains the vast difference between the theoretical and actual strength of metals. The scanning electron microscope (SEM) and its derivatives provide remarkable depth-of-field, enabling a view of fracture faces at multi-thousand times magnification, so that the fine detail of fatigue fracture can be observed. A vital tool in understanding modes of failure, it has been extensively used in accident investigations to determine the difference between mechanical failure and sabotage.

Many processes, like the vital strengthening of aluminium alloys upon which much of the aircraft industry has been based, have been observed and theories postulated – unproven until the minute particles responsible for pinning dislocations during the heating process of ‘precipitation hardening’ were seen with the TEM. Even our old friend, the Fe-C (iron-carbon, as steel) alloy system has yielded remarkable complexity with its variety of phases that can provide a wide range of properties from such apparently simple variants as ‘EN 8’ (ASTM 1040, or 0.4 C steel), providing an easily worked, almost mild-steel strength material, to a tough, a medium strength, or quite high-strength/low-ductility product. We shall see later how this is achieved and how alternative alloys can complement a particular application – the higher alloys primarily being required to achieve properties in larger items, the ‘ruling section’ effect. Thus the secrets of the heat treatment of steels first tackled by the ancient Greeks and Romans have yielded to modern science.

Iron and steel

Iron has been known to man since ancient Egypt, with necklaces of iron beads found in pre-dynastic tombs, where it was clearly rated as more valuable than their precious stones. However, these were obtained from meteorites and easily identified by their high nickel (Ni) content, typically 10 per cent Ni. Early Eskimos had also found similar iron, and this possibly explains the perpetual association with the ancient gods, like Zeus and Thor, who have been linked throughout the ages with metalworking and blacksmithing.

These early finds were of no engineering importance whatsoever, but by 2,000BC the Egyptians were displaying foundry-work in their tomb paintings. The early bifurcation of metals knowledge eastwards led to the Indian ‘Wootz’ iron, produced directly from iron ore subjected to laborious hammering and heating in charcoal. This diffused sufficient carbon to enable heat-treatment by quenching, as we would today. Wootz metal, despite little progress for a thousand years, provided steel forgings the envy of the world until the crucible process was perfected in the west by the mid-nineteenth century. China was, again, far ahead with cast iron produced some 1,500 years before the west. Even until the mid-sixteenth century in the west it was normal for there to be no specialization in the manufacture and application of metals – remarkably one man would often prospect the ore, manage the mine, design the smelting furnaces, supervise the foundry and blacksmith the product – and likely even finance the business and engineer the application. Talk about multi-tasking, but little wonder that progress was slow!

Until the Industrial Revolution the ‘demand pull’ was insufficient to force the pace of iron production, with small-scale production deemed adequate to produce ‘wrought iron’, analogous to present-day mild steel with ultra-low carbon content, and thus offering no scope for direct hardening. Where strength was essential, as for swords, the time-consuming business of heating in a carboniferous packing was used, similar to present-day ‘case hardening’. Indeed, the Greeks were familiar with this process, as alluded to in Homer’s Odyssey, where the giant Polyphemus is blinded by the grizzly quenching of Odysseus’s sword.

By the late fifteenth century in Europe it had become possible, with forced draught, to achieve the temperatures required for iron to be produced in the fully molten state, thus providing cast iron for the first time in the West. However, this was not adopted on an industrial scale until the demands of the Industrial Revolution some two hundred years later.

In 1740 the clockmaker, Huntsman, was perhaps the first to produce molten steel to overcome the unreliability of supplier quality. As Huntsman’s steel contained 0.6 to 1.5 per cent carbon, however, it proved too difficult to work and expensive for general use. Not until Bessemer developed his innovative ‘Bessemer Converter’ process in 1856 did the supply of steel, rather than cast iron, become economically viable, and then not without some traumatic struggles to finally perfect the process. However, the tenacity of the great Victorians like Bessemer, Thomas and Gilchrist, experimenting with furnace linings and different iron charges, finally produced the reliable and cheap steel that we would today recognize as (naturally) – mild steel. The process took the familiar cast iron, of around 2 to 4 per cent carbon, and by forcing oxygen through the molten charge, reduced the carbon to around 0.2 per cent. Thus was provided the strong and ductile material perfectly suited to manufacture of the high-pressure steam boilers, when used in a good engineering design based on the new science of stress analysis, which powered the Industrial Revolution. This material overcame the weakness in tension of nineteenth-century cast iron, but not until much later, with the Liberty Ships in the Second World War, was it appreciated that even these low-carbon steels could suffer devastating brittle-fracture under particular conditions of stress, low temperature, and design, as will be seen in Chapter 4.

After the basic Bessemer Converter process became established and the Victorian entrepreneurs made their fortunes, the range of steels expanded rapidly with the introduction of the many, often rare, elements to produce the range of ‘low alloy’ steels familiar today. We will see later how a small palette of these alloys, from the several thousand listed in present-day specifications, is quite sufficient to meet the requirements of even the most demanding task, with the aid of careful heat treatment. Although data is fragmented, sufficient information is provided to achieve the requisite ends, not normally available in texts for the practical worker.

Where corrosion resistance is of concern, and coatings are not the solution, we turn firstly to the high alloy ‘stainless steels’. In 1912, at Krupp in Germany, it was discovered that a minimum of 10 per cent chromium (Cr) in steel conferred a remarkable resistance to corrosion, leading to the austenitic stainless steels, such as the ‘18/8’ (Cr Ni) familiar as cutlery. At the Portland Works, Sheffield, the world’s first stainless steel cutlery was produced in 1913. Since then, the range of stainless steels has expanded enormously, in order to satisfy the demand for use in a wide range of corrosive environments as, perhaps surprisingly, austenitic stainless can be rendered useless in certain important applications, including some marine uses. Austenitic stainless steels, such as the familiar 304 or 316 types, can be susceptable to crevice and pitting corrosion in the presence of environments such as chlorides, as found in seawater. Another risk is Stress Corrosion Cracking (SCC) in similar environments and where there is a tensile stress, producing a brittle failure mechanism that, ironically, is not normally found in rust-prone steel.

By the twentieth century, steels had become an integral part of the fabric of life, but this is far from meaning that, even including low- and high-alloy steels, they provide the solution to all engineering requirements. Indeed, world consumption is still outstripped by cast iron, itself now existing in many forms, as described in Chapter 2.

1 Case studies: materials in action

This chapter introduces materials used in three practical applications: model locomotive or steam engines (Case Study 1), a small model aero engine (Case Study 2), and a two-stroke motorcycle engine (Case Study 3). It is to be hoped that these items will be of interest to the amateur engineer: often the steam engine from earlier and later life; the aero engine from sore fingers flicking propellers when growing up; even the small two-stroke motorcycle might resonate with those Baby Boomers who were sufficiently fortunate (or otherwise) to encounter them as early personal transport, even if this particular model’s failings and missed potential reflect on the demise of this sector of UK manufacturing.