Hydrogen Embrittlement Measured Hydrogen Amount
Hydrogen Embrittlement Measured Hydrogen Amount
(OP)
Assume a chrome-plated alloy-steel component that can be susceptible to hydrogen embrittlement (>40 HRC). Questions:
1.Would hydrogen always be present in identifiable quantities if hydrogen embrittlement occurred either because of insufficient bake-out or baking starting too late?
2. If so, what amount of hydrogen (in ppm) would be a minimum threshold as an identifier that hydrogen embrittlement occurred?
3. Any references for this threshold?
Thanks!
1.Would hydrogen always be present in identifiable quantities if hydrogen embrittlement occurred either because of insufficient bake-out or baking starting too late?
2. If so, what amount of hydrogen (in ppm) would be a minimum threshold as an identifier that hydrogen embrittlement occurred?
3. Any references for this threshold?
Thanks!





RE: Hydrogen Embrittlement Measured Hydrogen Amount
Dissolved hydrogen only causes embrittlement if the steel is under stress (i.e. an installed fastener). Because the hydrogen levels go down over time, any failure due to hydrogen embrittlement will occur within a short time frame (hours to days) after the part is installed or otherwise stressed. A failure that occurs later (weeks) cannot be due to hydrogen embrittlement.
For the same reason, testing days or weeks after the failure may not detect hydrogen. Any testing, to be accurate, would have to be done close in time to the failure.
The exact ppm of hydrogen that can cause problems I'm not familiar with, unfortunately.
RE: Hydrogen Embrittlement Measured Hydrogen Amount
Take a look at the publication below. I believe there is good information on hydrogen contents in ppm that can cause hydrogen embrittlement in high strength steels and other metals.
http://ftp.rta.nato.int/public/PubFullText/RTO/AG/...
RE: Hydrogen Embrittlement Measured Hydrogen Amount
He was reporting 4ppm as having an influence on ductility.
The measurement of hydrogen were made using a Balzers Thermo-Balance and the value reported was around or just below the limits that this machine so I never liked the results.
I understand that using neutron scattering techniques it is possible to measure 2ppm by weight but wonder if anyone has good data with regard to this.
RE: Hydrogen Embrittlement Measured Hydrogen Amount
One is if the residual stress in the parts is high enough that combined with H you initiate cracking. In this case the bake out can't be started soon enough to prevent cracks.
The other is an in service condition where H is generated, usually by a corrosion mechanism. They often correctly identify these as HIC failures, but then look into the fasteners production and not the application.
The threshold in H and stress have a lot to do with the alloy and the stress level.
Considering that there are not many Fe based alloys that at full H charging will have more than 10ppm H the low end of the range is very low.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: Hydrogen Embrittlement Measured Hydrogen Amount
1.) No
2.) N/A
3.) N/A
The amount of hydrogen required to cause embrittlement depends on the material in question and it's condition. For example, high strength alloy steels and tool steels with tempered martensitic microstructures and yield strengths between 175 and 320 ksi can be severely embrittled by less than 5 ppm of hydrogen. But austenitic stainless steels, unhardened steels, and steels hardened below about 35 Rockwell C are generally only mildly affected, or not affected at all regardless of the hydrogen concentration.
Here is a very good paper on the subject of hydrogen assisted cracking:
http://www.dtic.mil/dtic/tr/fulltext/u2/601116.pdf
Maui
RE: Hydrogen Embrittlement Measured Hydrogen Amount
http://www.boltcouncil.org/files/2014PSalimBrahimi...
2. Here are hydrogen concentration data, but not threshold values, for high strength steel fasteners such as you mentioned:
as-received: < 1 ppm
after acid pickling: < 1 ppm
after acid zinc electroplating (higher probability to embrittle): 7 ppm
after 4-hour bake: 5.5 ppm
after 8-hour bake: 5 ppm
as-received: < 1 ppm
after acid pickling: < 1 ppm
after alkaline zinc electroplating (lower probability to embrittle): 5.5 ppm
after 4-hour bake: 3.5 ppm
after 8-hour bake: 2 ppm
3. SAE 960312 Hydrogen Embrittlement in Automotive Fastener Applications
RE: Hydrogen Embrittlement Measured Hydrogen Amount
This is false. Hydrogen is trapped in steel. Some trap sites are weak/reversible, and others are strong/irreversible. Baking treatments not only increase the speed (rate with respect to time) that hydrogen leaves the steel, it also increases the total amount of hydrogen that leaves the steel.
Most of the rest of that post is wrong too. Terminology is a problem in this field, but hydrogen embrittlement can be divided into internal hydrogen embrittlement (IHE) and environmental hydrogen embrittlement. EHE certainly can occur if the fastener is not stressed, and can take longer than hours/days to occur. The recent problem with fasteners on the San Francisco-Oakland Bay Bridge took years to occur.
RE: Hydrogen Embrittlement Measured Hydrogen Amount
RE: Hydrogen Embrittlement Measured Hydrogen Amount
What is generally considered the hydrogen content is the free, dissolved interstitial hydrogen, which is the trivially small one or two PPM one usually hear cited.
Because the bound hydrogen seeks dislocation, it loves to go to the high dislocation density crack tips and cause it's famous trouble.
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: Hydrogen Embrittlement Measured Hydrogen Amount
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/