Speaking of Precision Blog

Speaking of Precision

Speaking of Precision is a knowledge preservation and thought leadership blog covering the precision machining industry, its materials and services. With over 36 years of hands on experience in steelmaking, manufacturing, quality, and management, Miles Free (Milo) Director of Industry Research and Technology at PMPA helps answer "How?" "With what?" and occasionally "Really?"

Previous in Blog: 5 Reasons To Anneal Steel   Next in Blog: 6 Ways Barstock Can Lose Straightness
Close
Close
Close
11 comments

5 Contributions of Chromium to Steels

Posted July 06, 2010 11:08 AM by Milo

Chromium is added to steel to

1. Increase resistance to corrosion;

2. Increase resistance to oxidation;

3. Increase hardenability;

4. Improve high temperature strength;

5. Improve abrasion resistance in higher carbon grades.

Chromium forms complex chromium-iron carbides. These carbides go into solution into austenite very slowly, so assuring a long enough heating (soak) time before quenching is very important.

In stainless steels, ~18 % chromium is typical, (303, 304 austenitics), while analyses as low as ~12 % (403, 420), and as high as 26-28% grades are available.

In non-stainless steels, chromium is essentially a hardening element. It is often used in combination with nickel (a toughening element) to produce improved mechanical properties. In combination with molybdenum, chromium contributes to higher strength at elevated temperatures.

Chromium's principal use is in stainless steels, where its resistance to oxidation provides the protection from oxidation and corrosion.

Chromium's decorative properties made it a favorite among automotive and motorcycle enthusiasts. Its resistance to oxidation and staining and ability to take a high polish make it an easy choice for decorative yet functional parts. Chromium's hardness and chemical resistance makes it ideal for protecting our tools.

Chromium has several oxidation states, Hexavalent chromium (CRVI) is of concern as an industrial environmental issue. Metallic chromium is not hexavalent, but flame cutting or welding of chromium materials may release haxavalent chromium. Chromic acid used for some chrome plating applications is hexavalent. Newer environmentally acceptable chromium finishes are trivalent. (CRIII) Link.

Chromium is named for the Greek word chroma, meaning color, as its salts are brightly colored. Chromium is a constituent of rubies, and is why ruby lasers give off their characteristic red light.

Final chromium fact: your body requires chromium. Chromium in your body ranges from 6-100 ppb in blood, up to 800 ppb in various tissues. Depending on your mass, you might contain as much as 12 milligrams of chromium in your body.

Reference

Editor's Note: CR4 would like to thank Milo for sharing this blog entry, which was originally posted here.

Register to Reply

Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Power-User

Join Date: Dec 2009
Location: New Zealand
Posts: 122
Good Answers: 4
#1

Re: 5 Contributions of Chromium to Steels

07/06/2010 10:59 PM

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.

Register to Reply
Guru
Engineering Fields - Electromechanical Engineering - Technical Services Manager Canada - Member - Army brat Popular Science - Cosmology - What is Time and what is Energy? Technical Fields - Architecture - Draftsperson Hobbies - RC Aircraft - New Member

Join Date: Sep 2006
Location: Clive, Alberta, Canada
Posts: 5907
Good Answers: 204
#2

Re: 5 Contributions of Chromium to Steels

07/07/2010 12:18 AM

Is Chromium recycled... or should it be?

Register to Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21012
Good Answers: 783
#3

Re: 5 Contributions of Chromium to Steels

07/07/2010 1:55 AM

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.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Anonymous Poster
#4
In reply to #3

Re: 5 Contributions of Chromium to Steels

07/07/2010 6:57 AM

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)

Register to Reply
Guru
Engineering Fields - Instrumentation Engineering - EE from the the Wilds of Pa.

Join Date: Feb 2006
Location: middle of nowhere, Pennsylvania
Posts: 2603
Good Answers: 63
#5

Re: 5 Contributions of Chromium to Steels

07/07/2010 8:51 AM

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.

__________________
Remember when reading my post: (-1)^½ m (2)^½
Register to Reply
Guru
Engineering Fields - Electromechanical Engineering - Technical Services Manager Canada - Member - Army brat Popular Science - Cosmology - What is Time and what is Energy? Technical Fields - Architecture - Draftsperson Hobbies - RC Aircraft - New Member

Join Date: Sep 2006
Location: Clive, Alberta, Canada
Posts: 5907
Good Answers: 204
#6
In reply to #5

Re: 5 Contributions of Chromium to Steels

07/07/2010 1:54 PM

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

Register to Reply
Guru
Engineering Fields - Instrumentation Engineering - EE from the the Wilds of Pa.

Join Date: Feb 2006
Location: middle of nowhere, Pennsylvania
Posts: 2603
Good Answers: 63
#7
In reply to #6

Re: 5 Contributions of Chromium to Steels

07/07/2010 2:12 PM

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.

__________________
Remember when reading my post: (-1)^½ m (2)^½
Register to Reply
Guru

Join Date: Jul 2006
Location: "Dancing over the abyss."
Posts: 4884
Good Answers: 243
#8
In reply to #6

Re: 5 Contributions of Chromium to Steels

07/07/2010 2:42 PM

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

__________________
People say between two opposed opinions the truth lies in the middle. Not at all! Between them lies the problem, what is unseeable,eternally active life, contemplated in repose. Goethe
Register to Reply
Guru
Engineering Fields - Electromechanical Engineering - Technical Services Manager Canada - Member - Army brat Popular Science - Cosmology - What is Time and what is Energy? Technical Fields - Architecture - Draftsperson Hobbies - RC Aircraft - New Member

Join Date: Sep 2006
Location: Clive, Alberta, Canada
Posts: 5907
Good Answers: 204
#9
In reply to #8

Re: 5 Contributions of Chromium to Steels

07/07/2010 2:56 PM

"Great query."

What did you just call me?!

Thanks Milo.

Register to Reply
Anonymous Poster
#10

Re: 5 Contributions of Chromium to Steels

07/12/2010 10:40 AM

" 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?

Register to Reply
Guru

Join Date: Jul 2006
Location: "Dancing over the abyss."
Posts: 4884
Good Answers: 243
#11
In reply to #10

Re: 5 Contributions of Chromium to Steels

07/12/2010 11:11 AM

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

__________________
People say between two opposed opinions the truth lies in the middle. Not at all! Between them lies the problem, what is unseeable,eternally active life, contemplated in repose. Goethe
Register to Reply
Register to Reply 11 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Copy to Clipboard

Users who posted comments:

Anonymous Poster (2); chrisg288 (3); Milo (2); Phys (2); Smeaton (1); Tornado (1)

Previous in Blog: 5 Reasons To Anneal Steel   Next in Blog: 6 Ways Barstock Can Lose Straightness

Advertisement