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Letter 1747 Chrome plating-- After chrome plating, how important is it to get a part into an oven for embrittlement relief bake? If the time until baking extends too long, will the hydrogen tie up and be unable to diffuse out of the steel. Also, what time is sufficient to bake a high strength steel that has just been chrome plated? What benefit does shot peening provide during chrome plating? Does chrome plating induce a stress on the substrate during plating and how large? What causes hydrogen embrittlement? Drake Clarke
Hydrogen Embrittlement is caused by the Hydrogen evolved during electroysis being, to some extent, absorbed into the crystal structure of the steel at its' surface. Normally baking at 200 deg. C will remove the atomic Hydrogen before it has had chance to migrate and become molecular. Documented tests carried out by the Spring Research Institute in the UK have suggested that if baking is carried out within 24 hrs. of plating the Hydrogen can be removed. However it appears that many specifications request that the treatment be carried out within a much tighter timescale. I have heard evidence that suggests that this may, in some cases, be due to the desirability to ensure that the operation is carried out and not forgotten! If the baking operation is not carried out on High Strength Steels then almost certainly it will be to late after the 24 hr. period and the Hydrogen will become molecular, being tied up with an inability to remove and provide a high degree of risk to failure. The degree of baking of High Stregth Steel would be suficient at 24 hrs at not less than 200 deg. C. Consultation with UK Defence Standard DEF STAN 03-4/2 would provide more specific info (sorry don't have one to hand to quote at present). sorry no details on the third and second last points. Regards Martyn Grimes
-- The present aircraft standards and AMS-2406 [link is to spec at TechStreet] , average 3 hours post plating bake at 190 centigrade . Dependent on the weight of the part . Hard Chrome does have a tendency to increase crack propagation sites in steel , due to the micro cracked structure of the coating . There is also a drop in the fatigue strength of the material which can be as much as fifty percent . Shotpeening will increase the fatigue life of some steels as much as 200 percent . Normal treatment of high strength steel parts would be : pre heat treat 190 c for 2 hrs after grind , shotpeen 12A2 , Chromium plate , heat treat 190 c for 3 hrs , final grind , heat treat 1 hr at 190 c to relieve grinding stress , magnetic particle inspect . As for the embrittlement problem it is to be taken very seriously when dealing with Chrome due to the high ammount of hydrogen evolved at the cathode surface , in the process . Dave Brackenridge
- I am interested to know if there is any conclusive data to support or oppose the use of sodium (alkaline) based cleaning solutions on T22 and if there is potential for caustic embrittlement. Any data appreciated. SQUADZRT Ed. note: Real name next time please, Squadzrt.
- Hello, This is not really relevant to the discussion, but I was wondering if you could help me. I am doing some research for a mini-project at uni on the chromium electroplating industry and I need some information on plating baths : what they are, what chemicals are used in them, how long the electroplating process actually takes, etc...I have not been able to find out these basic facts, although there is a lot of really technical stuff on the net. Any help anyone can offer will be greatly appreciated. Thank you. Bethany Mason Bangor, Gwynedd, UK
- Bethany, Please see our 'must have' booklist. On that page you will see a good selection of electroplating introductions. Probably the Garden State AESF 'Basic Practical Electroplating' would be the most responsive to your situation. You are not going to find the info you seek on the web for a few more years, and you'll probably never find it on the web for free.
Dear Reader, please --
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