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== Theory of steel forging ==
[Draw the iron-carbon phase diagram on the board covering 0-1.5% carbon and 0-1500 ºC]
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! Topic !! Detailed Contents !! Rationale
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| States of steel and their properties ||
* Ferrite - Soft, workable
* Cementite - Hard, Brittle
* Pearlite - Soft layered structure, normal resting state for most steels
* Austentite - High temperature structure, soft, malleable, workable, dynamic structure
* Martensite - Not a natural structure, formed by heat treatment, very hard, very strong quite brittle
Using a magnet to test for critical, but learn to use colour▼
* Spheralite and Banite - Useful industrially but we can't make them here
|| Need to know the basics of how steels respond to heat in order to know how to work
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| Critical Temperature ||
* Is at least 727ºC and can be more depending on %age carbon
* Steels are generally magnetic below critical and non-magnetic above it.
* Steel is formed above critical temperature and plannished below it.
* Other alloys can have different critical temperatures
** Bronze is much lower
** Stainless steel is higher
** Damascus steel is much higher
|| Vital concept for forging
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| Hot hardness || Is a measure of how easy to forge the material is, small changes in composition can cause large changes in hot-hardness || Key concept in working with different steels.
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| Heat treatment processes ||
* Annealing
** Heat slowly to above critical temperature
** Soak till even temperature
** Cool as slowly as possible, either in vermiculite or in the furnace
** Results in a soft steel that's cold-workable
* Normalizing
** Heat slowly to above critical temperature
** Hold it there for some time, time depends on thickness and your patience
** Cool reasonably slowly
** Relieves stress and lowers risk of cracking subsequent treatments
** Not all steels can or should be normalised
* Hardening
** Heat to specified hardening temperature
** Quench in air, oil, water or brine according to specification sheet
** Leaves steel very hard and very brittle
** Too slow cooling leaves metal soft, too fast will crack it
* Tempering
** Heat to temperature and time specified in datasheet
** Reduces brittleness in hardened steels to make them useable
|| Basic ways to change the properties of steels
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| Heating Errors ||
* Working a steel too cold - Very hard work and risk of cracking
* Working a steel too hot - Hard to control and risk of crumbling from hot-shortness
* Overly oxidising flames - Lots of scale and risk of decarburization
* Overly reducing flames - Poor heat, Carbon monoxide risk, case-hardening, but unlikely to ever happen in our furnace
|| Knowing the serious errors and how to avoid them
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== Practical Forging ==
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