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Cleaning rust from high tensile steel
April 2, 2009
Q. Hi, my name is Frank and I am involved in the restoration of vintage cars.
I have been using a very diluted retarded phosphoric acid based solution as a bath for removing rust and scale from steel, as a pre-treatment for painting.
I have been using this phosphoric acid based bath for a while with great success and generally find that I can leave steel automotive bits and pieces, etc., in the bath for a few days and any rust is removed without visually affecting the metal. Metal usually comes out nice and bright and clean.
On this occasion I put some bare steel rods (not zinc plated) 40 cm long and 1.5 cm in diameter, into the bath. I have subsequently found out they are a high tensile steel probably grade 10.8 (well, so I am told by someone who tested them for me).
After leaving the rods in the bath for about 4 - 6 hours I checked on them they were bubbling away. By this I mean there were hundreds and thousands of very tiny bubbles coming from the steel rods.
I pulled them out and they were coated with some sort of black substance which partially rubbed come off on my fingers. It tried to wash the black off with water, however the rods still retained this tainted black color and they had a funny sort of smell to them.
I finally got the rods shinny clean again by using a scotch brite scouring disk mounted on an angle grinder
[on
eBay or
Amazon]
.
I would still like to paint and use these rods, however, my concern is that because they are high tensile steel that they may have been affected by the phosphoric acid bath that I put them in.
I am particularly concerned that this may have weakened the steel or may have led to some sort of embrittlement.
Would the high tensile steel rods have been affected in any way by the phosphoric acid bath?
Do the high tensile steel rods now have hydrogen embrittlement and will I have to get them de-embrittled by having them placed in an appropriate oven?
Your assistance would be appreciated.
Frank
A. I'm not sure what 10.8 rod is. If it's similar to the ISO class 10.9 for bolts, then you have high strength alloy steel, and it may well be hydrogen embrittled. Baking must be done within one hour of the process which caused the embrittlement. After that it cannot be removed, and if these rods are subject to any sort of stress in use, you should scrap them as they may experience catastrophic failure.
Jeffrey Holmes, CEF
Spartanburg, South Carolina
April 6, 2009
Jeffrey,
It's the standard strength designation for metric bolts. The first number is the minimum ultimate tensile strength, the second is the minimum yield strength, both in units of a hundred megapascals.
Remember, you guys in America are the only ones who still use the old Imperial measures :)
Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
April 7, 2009
A. You can clean stressed parts only in oil or petroleum based rust remover (simple DIY formula 1 lit petroleum/30 gm paraffin). Acid or electrolytic processes are useless and destructive on that type of material. Hope it helps and good luck!
Goran Budija- Cerovski vrh Croatia
April 8, 2009
April 9, 2009
Q. These rods are part of the cars suspension and are known as radius rods / strut rods.
I believe the rods may be 10.9 I asked an engineer to look at them for me and can only rely on what I have been told. Mind you he only had a quick look at them and he did not perform any type of test on them.
Although, I must say I have seen many similar rods that have come from other vintage cars that are bent. Some people actually hammer them straight. So this makes me wonder whether they are actually high tensile or just mild steel.
What test or tests could be performed on these to determine what type of steel they are made from?
After I posted my question, someone else advised me that hydrogen embrittlement only occurs if the metal is electroplated. Is this correct?
How can I tell if they have hydrogen embrittlement? Is there any sort of test?
I also have another set of high tensile rods which I did not place into the bath because I saw what happened to the first lot.
I gave these rods a thin coat of a rust converter [on
eBay or
Amazon]
called "phoscoate". This converter is phosphoric acid based and is only applied very thinly and allowed to dry overnight.
Would this also cause hydrogen embrittlement?
Your assistance would be appreciated.
- Melbourne, VIC, AUSTRALIA
A. I'll try to respond to your questions -
First off, you need to know *for certain* what your radius rods are made of. Some alloys are very sensitive to hydrogen embrittlement, some are not. Guessing they "might" be xxxx or xxxx isn't good enough.
Whoever told you that only electroplating can cause hydrogen embrittlement is just plain wrong. Exposure to acids can cause the problem, and acid pickling which causes the myriad hydrogen bubbles you observed can absolutely cause hydrogen embrittlement.
There is no non-destructive test you can perform, since the only definitive tests are destructive.
The problem with hydrogen embrittlement is that failures are impossible to predict and are catastrophic. Everything seems fine and then...SNAP!
I'll describe for you the first hydrogen embrittlement failure I experienced: We were asked to zinc plate Belleville spring washers, which were made from high carbon (AISI 1090), hardened and tempered spring steel. Prior to plating you could hold them in a vise and hammer them over, no problem. After plating, a hammer blow would shatter them like soda crackers.
Now, do you have a problem with the radius rods you have exposed to phosphoric acid? No one here can know. We don't know what the alloy is, what heat treatment there has been, we don't know how badly embrittled they might be.
Maybe they'll be just fine and give no trouble. Maybe they'll fail in a high speed maneuver.
Don't install them on my car.
Jeffrey Holmes, CEF
Spartanburg, South Carolina
April 17, 2009
Hi Jeffrey,
Firstly thank you for the information and advice provided to date.
I have been doing some research on the affects of rust converter [on
eBay or
Amazon]
s on high tensile / stress steels. During this I came across a test done by the United States Navy, who immersed two different types of high tensile steels in different rust converter [on
eBay or
Amazon]
s for 24 hrs and then subjected them to a number of tests. Makes for interesting reading.
Basically , the United States Navy conducted tests on the affects of two types of rust converter [on
eBay or
Amazon]
s on fasteners made from different types of steels including high tensile.
One of the rust converter [on
eBay or
Amazon]
s also contained phosphoric acid.
In their conclusions they found no evidence of "Environmentally assisted cracking resistance" in the tested fasteners when the rust converter [on
eBay or
Amazon]
s were applied.
The Navy document is available on the internet and is as titled as follows:
Paper No. 05206 Corrosion 2005
EFFECT OF COMMERCIAL rust converter [on
eBay or
Amazon]
COATINGS ON THE ENVIRONMENTALLY ASSISTED CRACKING RESISTANCE OF HY-100 STEELS AND HIGH STRENGTH ALLOY STEEL FASTENERS
Link : http://content.nace.org/Store/Downloads/05206.pdf
Regards,
Frank Ventura
- Dandenong, VIC, AUSTRALIA
A. First, there is a non destructive test, but extremely few companies have one, so it is relatively terribly expensive. Also, the problem is with penetration as well as quantity, so how much is too much?
Second, no two bolts are affected identically by the acid.
Third, if you saw gas bubbles, it is hydrogen, therefore the bolts are affected to some degree.
4th, I have never seen Naval Jelly (phosphoric acid in jellied alcohol) bubble on steel. It is generally considered to be safe, but I am not going to bet the ranch on it.
I would sleep better if I replaced the bolts with new ones.
- Navarre, Florida
May 12, 2009
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