Metal finishing Q&As since 1989
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Hydrogen embrittlement in 17-4PH SS?
Q. Hi,
I need to supply hydraulic cylinders to a customer that he's asking for 17-4 PH SS h1150 piston rod . The rod is working in tension only at about 6000 psi tensile only what do you think about hydrogen embrittlement because we don't have the oven long enough (26 feet) to do it. Do you see any danger in not doing it.
Thanks for your help
PROJECT ENGENEER - QUEBEC, CANADA
May 12, 2009
A. What is it that you suspect might cause hydrogen embrittlement?
Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
May 18, 2009
A. It is not what we think that counts, it is what the print or spec calls for. If your firm is the controlling agency, if it is not plated or acid etched, it should not be required. If it is chemically treated and is over Rc39, then it should be heat treated to 375 °F for 3 hours. Hotter for longer if it is really harder.
James Watts- Navarre, Florida
May 18, 2009
A. In condition H1150, the hardness will be 30-33 HRc so by James' post you don't need to worry. My query as to why you thought it might be embrittled now seems irrelevant.
Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
May 20, 2009
Q. Sorry, I forgot to write the rod is going to be chrome plated but the Rockwell is between 28-35 Rc and the tensile is 135 Ksi.
MICHEL GAUDREAULT [returning]- Canada
May 21, 2009
A. I can not get my brain around a piston rod that is in tension only.
I also find it hard to believe that anyone that is good enough to chrome plate a 26' 17-4 stainless piston would not have a oven large enough to bake it.
Cover yourself. Get your customer to give you an exact specification to plate it by. It should give a bake or no bake requirement in it. If not, tell your customer that if he wants the part done without a bake, he should put it in the purchase order. Going by one or two book references that say that a bake is not required will probably not hold up in a serious injury liability lawsuit.
- Navarre, Florida
May 22, 2009
Second of two simultaneous responses --
A. Michel
ASTM A380
covers cleaning and passivation of stainless steel. Annex A1.6 suggests baking is required if the (heat treated) material is exposed to acid (pickling) due to HE concerns. I do not find any reference to tensile strength.
ASTM B849-02 & ASTM B850-98 deal with pre- & post- treatments of steels with respect to reducing the risk of HE. The threshold for either is 1000 MPa (31 HRc).
Your 135 Ksi translates to 930 MPa. So, ASTM A380
advises for baking HE relief, while the B-849 & 850 advise it is not necessary. I would do as James suggested and refer to the print / spec / purchase order.
- Colorado Springs Colorado
May 22, 2009
Q. Hi Willie,
In the ASTM B633 section 6.6 they are talking about tensile strength over 1200 Mpa.
The rod is working in tension only because cylinder is working up side down lifting a ramp.
Also in the specs AMSQQC320 ARTICLE 3.2.6. they are talking about 160 ksi and 36 Rc
Sorry I speak French so my translation is sometimes not too precise.
Thanks
- QUEBEC, CANADA
May 27, 2009
A. Michel
ASTM B633-98 does reference 1200 MPa as a threshold for baking for hydrogen embrittlement relief.
However, ASTM B633 sets the threshold at 1000 MPa, and includes ASTM B849-02 & ASTM B850-98 as referenced documents. All were revised or re-approved in 2004 or 2007 and seem to imply that hydrogen embrittlement may occur in materials of lower (than previously established) tensile strengths.
Keeping the hardness to the low end of your tolerance should help alleviate the need for HE baking.
- Colorado Springs, Colorado
May 27, 2009
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