There’s literally everything in scrap metal, aren’t there compounds that will worsen the quality of the steel produced?
In: Chemistry
I work in the steel industry, and have been for nearly 20 years. This includes the melting and casting operations.
We can guesstimate what impurities are in the various types of scrap by the source of the metal. Light-gauge metal gets shredded, and so do cars – that means that *shred* will usually contain a high percentage of copper (from electric motors and wiring). *Heavy melt* consists of thicker sections (rails, I-beams, railway wheels, plate sections from ships and barges and bridges) that are more likely to have higher silicon and manganese and *pig iron* or *cast iron* is going to have a lot more carbon and silicon (note: North American scrap is usually further categorised). During loading of the scrap buckets prior to charging into the furnace, a blend of scrap types is chosen depending on what grade of steel is being made, as well as taking into account scrap density, price (shred is ususally cheaper than heavy melt) and other operational factors. For example, if the meltshop knows low-copper grades are scheduled, the scrap yard will be asked to load a low-copper scrap blend.
During and after melting, oxygen is blown into the steel to burn out some impurities (aluminium, silicon, manganese, carbon, phosphorous, sulphur) so that when the furnace is ready to be empited (tapped), the liquid steel ends up with about 0.1% carbon, 0.1% silicon and 0.1% manganese. This can be confirmed by taking a sample of the steel and analysing it on a spectrometer – usually takes no more than 5 minutes to get a result. The spectrometer will also report on other elements like chromium, copper, nickel and molybdenum – these elements can make the steel too strong for cold working, or (in the case of copper) make it too weak at high temperatures to be rolled down to size. The problem is, these four elements can’t be removed with oxygen (which is why they’re known as *residuals*), so if there’s too much of them in the steel, then the steel has to be diverted to a grade which can handle them, or diluted or tipped out. Normally if the scrap has been sorted, picked and loaded correctly, then the level of residuals is low.
Edit: spelling and clarity, plus a video link that briefly shows and explains sampling and spectrometry
[https://www.youtube.com/watch?v=ou9vNsVhk8M](https://www.youtube.com/watch?v=ou9vNsVhk8M)
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