Can steel be recycled repeatedly?

Question

Can steel be recycled repeatedly?

(OP)

14 Oct 20 09:08

Hi all,

I have embarked on a research project in view of establishing steel strength after several melting cycles. I intend to use a vacuum furnace using temperature of around 1500 C. My hypothesis is that repeated recycling of steel renders the material weaker and more prone to rusting. I have practically exhausted the literature search and surprisingly I cannot find any published study to support my thinking. Can someone please reassure me? That is all I want because I am dubious whether I would be the first person to be performing this experiment or not. I only use the English language for my search needs. So, it could be that there is a study in Japanese or French or other language that I would be missing and that has already showed that there is a limit on how much steel cam be melted and reused or it might be that steel can be kept recycled indefinitely!

Kind regards,

Charles Micallef
NB. Honesty is the best policy. I am not a student. I am an independent researcher but this Forum does not cater for people like me. My papers on materials science include:
'Can rust spread through temporary contact?'
'Blu-Tack can stop transmission oil leaks'

Ron (Structural) · Answer 1 · 2020-10-14 10:10:16

Charles, steel can be repeatedly recycled. It is done every day. The chemistry of steel can be controlled and any deviation in the furnace charge can be accommodated.

IRstuff (Aerospace) · Answer 2 · 2020-10-14 13:49:47

Up to a point, yes, but you have to be careful of contaminants and alloying components that might oxidize or otherwise change along the way and change the apparent chemical composition of the steel. Note also, that there are known trace materials that are not assayed in typical steels.

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drawoh (Mechanical) · Answer 3 · 2020-10-14 16:15:15

IRstuff,

This is a metallurgy question, and so far, none of us are metallurgists. When metal is removed from the ground, it is full of contaminants, i.e. it is ore. I am sure you can take some rusty piece of junk and separate everything but the pure iron. I just don't know how economical it is.

My understanding is that automobiles are very thoroughly recycled.

--
JHG

handleman (Automotive) · Answer 4 · 2020-10-14 17:02:29

The idea that steel properties change with just melting and resolidifying multiple times is ludicrous.
The idea that steel properties may change with contamination is obvious.
Any link between what contamination occurs from this experiment and the contamination from actual recycling of steel is tenuous.
The ability of a pharmacist to actually remelt and test the same lump of steel while preventing, monitoring and/or introducing/controlling contamination over multiple remelts is dubious.
Any conclusion drawn from this "research" is likely to be spurious.

arunmrao (Materials) · Answer 5 · 2020-10-15 03:44:26

Steel founders are recyclers. All,the waste generated by other industries, are collected, sorted and processed before melting.
However, there will be requirements of chemistry correction, gas removal and most importantly grain refining . AOD refiners are common nowadays to remove impurities.
For primary products like billets, ingots etc which undergo further mechanical processing, grain size control will depend on thermomechanical process.
For castings,it is very important not to use beyond 35% of foundry returns for recycling.

I hope,,I have cleared some of your concerns.

Happy Remelting

MintJulep (Mechanical) · Answer 6 · 2020-10-15 12:38:01

Quote (arunmrao)
For castings,it is very important not to use beyond 35% of foundry returns for recycling.

Hello Arun,

Could you explain why please.

arunmrao (Materials) · Answer 7 · 2020-10-15 13:15:26

Hello MintJulep

It is considered a good foundry practice to generally avoid increasing returns. This is true mostly for air-melted induction furnace castings.

Induction melting offers very little or no scope for refining. Also, the mechanical properties like elongation and impact strength get reduced. These are attributed to grain coarsening and also literature supports problems due to heredity.

In case of stainless steel castings, the castings are more prone to gas pickup. I am presently handling a situation for 316L pump casting.

I am stuck at home in India, as there are no flights, and the foundry has used 100% 316L returns. I have asked them to scrap the casting and reprocess using 35% returns maximum.

Situation becomes more acute while processing different grades of Bronze castings. The golden rule, Do not use any inhouse returns.

I hope,I have shared my experience convincingly.

GregLocock (Automotive) · Answer 8 · 2020-10-18 03:01:16

Student forum QC expert system v0.1 alpha

Recommendation - Attempt to answer

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Cheers

Greg Locock

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Can steel be recycled repeatedly?