5 Contributions of Chromium to Steels

Good Post Milo,

I would like to add that extended operation at high temperatures highlights a problem of chromium oxide in that it is volatile. This may be okay in thicker sections where sufficient chromium can migrate to the surface to replace what is lost but in thinner sections the Cr can be depleted and the protective properties are lost. The use of a non-volatile oxide such as alumina (alonising etc.) can provide protection in itself and/or by slowing the Cr loss.

Is Chromium recycled... or should it be?

This is another of an excellent series of metallurgy topics. It is appealing and understandable to the layperson as well as the expert. I would enjoy seeing it published in book form.

Ask and you shall recieve, check out:

Understanding Stainless Steel by Alan Harrison, published by BSSA (British Stainless steel Association). Cost £30GP + post and packaging. website www.bssa.org.uk

John (no connection with BSSA, I just recently purchase this book)

Without chromium I would not have my job. I am a controls engineer, but I put those controls on all stainless steel pharmaceutical process skids manufactured by the company that employees me.

I also appreciate wht it does for my bicycle. I have recently salvaged an old road frame built in Japan in 1983. The entire fork and the rear stays are polished chromoly steel.

I know about the down side to it as well. I spent a few years as the saftey and environmental co-ordinator here, until the company could actually hire a trained EHS man. (technically I was job trained by a large corporation in a previous job, but never college trained) EPA doesn't care much for chromium, nor does OSHA. The hexavalent form is a particularly bad actor. Causes cancer. I had many a test done on the fumes from the welding operations and the dusts created by the polishing operations, and had many TCLP tests done to insure what we had to dispose of (polishing dusts/acid baths that were worn out) were not loaded with chromium. (actually, the real reason is for a record for EPA to see how much is actually getting loose in the environment - used these figures to estimate yearly losses)

As to the post wondering about recycling - all scraps are definitely recycled. Saves on environmental paper work - you do not have to report recycled metals as a "lost waste". What escapes in the acids and the dust is lost. This is miniscule. The highest I ever saw on an acid bath was 500 parts per million chromium. The dust is in the tens of parts per million. At this time, not economically worth trying to capture.

Thank you. By recycling.. I meant, aren't there 50 million cars and trucks sitting in junkyards with the chromium bumpers etc going back into the ground, when, as a limited resource, it should somehow be recovered for future use?

Chris

If it is a chrome plated bumper, or any other trim part, and it was in the junkyard, it isn't now. Some auto buff or hot rodder has it. My son has a hot rod '50 Ford and at least three sets of bumpers for it, and a small pile of extra trim parts. I see they are restoring and/or hot rodding old Ramblers and Larks now, so if even those old lemons are in demand, no part should go to waste.

Hi Chris, Intellectually, yes.

Pragmatically, well, it could be very expensive.

The chrome plating on the bumpers is just 100 microns thick.

So my rough calculation using 7.2 g per cubic cm is 0.0324 grams per large bumper.

times 2 bumpers times 50 million cars=

3240 kg= 3.240 tonnes

If i could get the chrome off each car for $1, I'd spend $50,000,000 to get that 3.240 tonnes; each tonne of Chrome so reclaimed would cost me $15432099.

New chrome is probably $7000 per tonne, reclaimed would be 2204 times more expensive than new.

And that is if it only costs a buck per car to strip it off.

This is why Design is so important, and engineers need to look at the entire product life cycle. End of Life vehicles regulations are 'driving' designers to avoid these kinds of applications.

As a side note, presuming that the bumper stays attached to the car as a crushed bundle or as shredded scrap, it will be reclaimed in the remelt and show up as a residual or tramp element in the steel analysis. We permitted residual Chrome in the ladle analysis of the remelt to be as high as 0.35 wt % for merchant and structural qualities.

Some of the chrome may also oxidize off into the slag.

Great query.

Milo

"Great query."

What did you just call me?!

Thanks Milo.

" Chromium is added to steel to

1. Increase resistance to corrosion

2. Increase resistance to oxidation..."

3. ... ... ... hmmm...

According to Corrosionists (National Association of Corrosion Engineers International) the corrosion of metals takes many forms. However, any time that we refer-to the breaking-down via electrochemical processes, corrosion is exhibited as REDOX reactions (one cannot take place without the other); thus, corrosion is Oxidation occurring at the anodic sites with the corresponding Reduction occurring at the cathodic sites ... and for those multitudinous misguided souls:

Oxidation has nuthin whatsoever to do with oxygen. Oxidation is defined as the "giving-up of an electron".

Reduction is nothing more than the "gaining (or 'picking-up') of an electron".

So, for your Listing to meticulously itemize itself thoroughly, should it not read:

" Chromium is added to steel to

1. Increase resistance to corrosion

2. Increase resistance to oxidation

3. Increase resistance to reduction ..."

etc. ???

_{or was #2 simply redundancy and adding the above would be superarrogantly redundant?}

When writing for a broad public, one tends not to get to the finest points of defining whether one means "electron transfer," or "rusting" or "Scaling in high temperatures." These are synonyms which are also well know to those of us in the field as 'oxidation.' Why turn off the reader with lengthy definitions before you make your point?

In the Corrosionist's National Clubhouse, Oxygen may well not be involved in certain redox (Oxidation) reactions, but for those of us who make things of steel in the current earths atmosphere, when we say oxidation we generally mean that our material is in fact involved with the element with atomic number 8...

Had I been writing for the Corrosionists, I would likely have had a very different post.

When writing for scholarly purposes, such exacting descriptions are necessary and appropriate. For purposes of informing practitioners and providing sensemaking on material issues, such minutiae may actually interfere with getting the message out.

We appreciate your close semantic examination of our writing as it motivates us to continue to do our best in communicating what it is we think we know.

Milo