Recycled Carbon Steel: Physical and Chemical Properties

[bobbobwhite]

Due to the rapidly expanding practice of recycling used metals it makes me curious to know if, for example, recycled carbon steel is the same exact physical and chemical material it was before it was recycled. Or do recyclers have to add processes and carbon, etc. to get it back the exact material and performance specs it had before?

For example, if an old car's steel was melted down each day for a thousand days, ten thousand days, or a million days in a row, would it be substantially the same material afterward each time as it was before the very first smeltering? Or, would additional processes and metals, chemicals, carbon, etc. have to be added each/over time to insure the steel maintained the exact metalurgical and physical qualities such as composition, strength, hardness, durability, flexibility, etc. it had after initial smeltering?

I may have omitted some tech terms or words or used incorrect layman definitions in the above, but you get the idea, and thanks so much for all informed and detailed answers that will explain the process and results to a layman.

 

[Gokul43201]

It really comes down to the quality control during the recycling and the level of specification after. Some scrap recyclers will give you dirt cheap prices, but you can buy "brass rod" and find that it has an entire 1/2" SS bolt stuck in it! (that's a true story). But if you buy a slab of metal which has the correct ASTM specs for composition and heat treatment, then in theory, it shouldn't really matter if it came out of a local scrap foundry or a steel plant in Germany.

 

[bobbobwhite]

To get regain proper ASTM specs, do you happen to know what is/are usually added to the melted scrap to get it back to an acceptable ASTM rating for its intended usage? For example, a car frame from the 80's melted down to be used as a car frame in 2008 may require more or even less of something it had in it in the 80's? Just trying to get an idea of metalurgy requirements as a result of recycling steel compared to original smelting from iron ore. Or, any recycled metal actually, if the same concepts apply.

Thanks again.

 

[Astronuc]

Anything added to a melt has to be analyzed for composition, and then adjustments are made to whatever else is added. I would imagine that most melt shops use a blend list.

Dirty scrap will yield dirty alloys (i.e. higher impurities).

In some cases, heavily contaminated scrap may be processed chemically to remove impurities.

One can remelt a 1000 times, but the consituents would not change appreciably, except for possibly volatiles.