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Making and Treating Iron and Steel

Many years ago as a student apprentice I spent a week of my life chiselling a block of cast iron. Such a seemingly mindless task taught me many things but three spring to mind:

  1. How soft cast iron can be.
  2. How hard the point of a chisel can be.
  3. How @&%$!ing painful it can be to hit yourself on the knuckle with a 2lb hammer.

Indeed my vocabulary was expanded by a handsome number of colourful words and I gained valuable experience should I ever wish to work in the 'enquiries' department of the CIA or perhaps the Muammar Gaddafi school of social etiquette.

Did you know that a 2 lb hammer is probably one of the most useful items anyone could ever have. They're very useful for repairing jewelry, fixing motor bikes, adjusting television sets, gently inserting straws into those little Aqua containers that always spew water down your front and for making fine adjustments to the delicate mechanism of that recalcitrant watch you bought last week on Kuta Beach.

As for you ethereal types sitting cross legged on your bamboo mats in your Ubud Bales with your eyes closed holding your fingers in the lobster claw position (that's the one that somehow makes me think of the Queen picking up something the royal corgi left on the carpet) trying to find your inner selves and gain enlightenment, - get real you lot! What you really need is a 2lb hammer and a pile of rather hard rocks.

I understand a rivetcatcher from Newcastle upon Tyne is opening a new enlightenment centre in Ubud next year to be called the Bill Bollock's School of Transcendental Catharsis. Bill is of course the famous author of that worldwide best seller “Rockbreaking for inner peace.” The hammers have already been ordered along with axes and clubs. Sponsored by Made's Firewood Supplies and the Agung Gravel and Aggregate Company the courses will cover such popular topics as “Bludgeoning for beginners”, “Chopping your way to internal wellness”, “Satisfying nightclubbing for frustrated housewives” and “Discovering the inner axeman.”

It is interesting to consider some of the items we have mentioned so far, a block of cast iron, a hammer, chisel, axe (and Bill Bollock for that matter) are all made from basically the same material, iron, though it does tend to come in different variations.

There are a handful of materials that have changed the whole nature of the way we live and probably nothing more so than iron. Iron is, of course, a material that has been around for quite a while (since the iron age really) and we do tend to take it for granted. It has become so ubiquitous we forget its involvement in just about everything we do (well, nearly everything).

How do we make iron and steel?

Unfortunately iron has a tendency to rust doesn't it and so iron as such doesn't occur naturally as iron, it exists as rust (iron oxide) or various forms of it. To make iron you take rock (iron ore) and you put it into a blast furnace with other rock (limestone) and yet other rock (coal that has been heated to turn it into coke), you burn it all and at around 1,250 degrees C the carbon in the coke removes the oxygen from the iron oxide, the carbon and oxygen mix to form carbon monoxide and carbon dioxide. Removing the oxygen in this way changes the iron oxide to iron which at somewhere around 1,538 degrees C (that's pretty hot isn't it?) it melts. When it cools the iron is not much use, it is called pig iron is very brittle and has a carbon content of around 4%.

So it has to be melted again (what!) so the contaminants can be removed, alloying elements can be added and the carbon content can be adjusted.

This is hardly straight forward is it? It makes you wonder how anyone ever found out how to make the stuff. Can you imagine Joe Muggins sitting in the pub staring into the fire?

“Hey I've got this idea”
“Oh dear.”
“Yes, we'll get some rock and we'll burn it.
“Burn it?”
“Yes, it'll melt and then we'll get iron.”
“Iron, what's that?”
“I don't know, we haven't made it yet.”
“It'll never take off you know.”

Finally after this tedious process and equally tedious explanation we have cast iron which is a mixture of ferrite (pure iron) and a lot of carbon (2.5 to 4%) in the from of graphite (there are lots of “ites” in iron you know). Iron is made up of crystals and the ferrite grows into large cubic crystals which are magnetic. Cast iron is strong, fairly heavy and does not rust much but it is also fairly soft and can crack. It is also easy to cast and machine. We use it for many things most notably car engine blocks and water pump housings.

But then one day someone came up with the German Finery process. He was a gentleman who said “Ah Hah Hah, Vee haff vays off making zee steel koz vee haff zee mussels in zee spittle.” It was found that if you blow air over the molten iron, the oxygen in the air burns and removes impurities from the iron. It also mixes with the carbon in the iron which is given off as carbon monoxide and carbon dioxide. When the iron cools it is purer and has less carbon in it.

“Donner undt Blitzen, zee iron haff becum zee steel!”
“But just a minute, we added carbon to iron ore to get rid of oxygen and turn iron oxide into iron. Now we we want to add oxygen to remove carbon and turn iron into steel. Isn't it all a bit pointless?”
“Stop asking zee seely, seely kvestions schvinehundt. Do you vant zee steel or vot?”

Steel is made up of crystals of pure iron (ferrite) and pearlite and/or cementite (oh dear two more “ites” which are mixtures of iron and carbon). The crystals are smaller than in cast iron and steel is much harder and stronger.

It was all very difficult at first but then in 1855 along came a man called Bessemer, he was one tough cookie. He found that by putting a straw into a vat of molten iron and blowing into it you could convert a whole lot of iron into steel quickly and easily - provided your lungs were big enough.

Even to this day we use the same process of blowing air (these days oxygen is used rather than air) through molten iron to dramatically reduce the amount of carbon in the iron and produce what is known as low carbon or “mild” steel. A strong material we use for really useful things such as tools for taking stones out of horses hooves and skyhooks.

Over time we have also become very clever at further modifying what is already a very useful material by changing its qualities to suit our purpose.

Heat Treatment of steel to change its properties

The first thing we found was that if you drop red hot steel into water (known as quenching) the steel cools very quickly, the crystals cannot grow large and small crystals make the steel harder and more brittle. By experimentation it was found that by heating the steel up to different shades of redhottedness (that's a good word isn't it?) before dropping it into water we can control the size of the crystals and the degree of hardness and brittleness. This is called heat treatment.

By heating steel then cooling it very slowly we can allow the crystals to grow large making the steel softer and more malleable. This is known as annealing.

It was then found that if you heat the end of something sharp (such as an axehead) dip it into charcoal (carbon) and quench it in water just the edge could be hardened. This technique is very useful for such things as swords, scissors, axes, knives, chisels and, as the French all know, guillotines where we want the edge to be very hard so we can sharpen it and it won't blunt easily but we don't want the main body of the thing to be to brittle and break, all very useful when you need to chop off the head of some belligerent king with rather tough neck.

Finally we found that by adding impurities and alloying elements we could change the form of the crystals in a million and one different forms allowing us to make squillions of different types of steel for different purposes.

So what is the relevance of all this?

The importance of the right grade of steel

In our daily lives this is all very relevant. We need hard steel for car springs and soft steel for coat hangers. We need very tough steel for spanners and socket sets. For hinges we need steel that doesn't wear or bend easily. For knives and scissors we need tough steel but with hard sharp edges. The list is endless.

Of major importance we need to use the correct steel for steel reinforcing bars when we build our houses. This is an important issue in Bali where the temptation for builders to buy cheaper steel is ever present.

Of particular importance is the use of steel in tools.

  • Screwdrivers need to be of tough steel but with the tip hardened so they don't bend but not so hard that they shatter.
  • Files are made hard to be able to abrade softer steel, unfortunately this also makes them brittle and they tend to break easily. Drill bits are similar.
  • Hammers need to be tough but not brittle.
  • Chisels need to be of tough steel but with a hardened tip so they can be ground to a sharp edge but not so they will shatter. If a chisel shatters you can easily lose an eye.
  • Saws need to be flexible and strong, you certainly don't want them to break but you do need hard sharp teeth.

It pays to buy good quality tools. Take care when you buy them and they will last you a lifetime and justify the cost. Many of the tools you buy in Indonesia are of such poor quality that they can be considered throw away items and sadly you may well be throwing them away in disgust before you have completed the job.

Pay attention to the steel used and the quality of finish. Bear in mind that low quality tools are often cheap copies of high quality tools, they may look good but have been made without any understanding of the need to get the steel right. I suggest you look out for respected brand names, I always like Stanley as a brand that is of good reliable quality without being over the top price wise. Germany has a history of making high quality tools. Certain other countries have well earned reputations for sub standard copies.

“Vee haff vays off making zee tools.”

Copyright © Phil Wilson 2011
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