Acid Pickling of ASTM A351 GR: CF3M
Acid Pickling of ASTM A351 GR: CF3M
(OP)
While acid pickling of castings made of grade cf8, cf8m ,cf3m, etc a kind of black deposition on the surface and inside the bore of casting is observed which gives a bad look and is tough to remove. Acid used is HNO3:HCl:H2O - 2:1:1 and dipped for approximately 30 to 40 min. please advice
A M CONTRACTOR





RE: Acid Pickling of ASTM A351 GR: CF3M
What is solution annealing, pickling, and passivation?
thread723-165497: What is solution annealing, pickling, and passivation?
If you can place your hand on Mcguire's book" Stainless steel for design engineers",it will make an excellent reading.
RE: Acid Pickling of ASTM A351 GR: CF3M
RE: Acid Pickling of ASTM A351 GR: CF3M
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: Acid Pickling of ASTM A351 GR: CF3M
RE: Acid Pickling of ASTM A351 GR: CF3M
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: Acid Pickling of ASTM A351 GR: CF3M
You even get the smut in the early stages of pickling in Nitric/HF.
The operator's solution is to pickle longer.
The right solution is to wash with high pressure water.
How warm is the pickle solution? This is worse in cold solutions. I like 20-25% Nitric/4-6% HF and about 130-140F.
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Plymouth Tube
RE: Acid Pickling of ASTM A351 GR: CF3M
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: Acid Pickling of ASTM A351 GR: CF3M
A M CONTRACTOR
RE: Acid Pickling of ASTM A351 GR: CF3M
Water is isn't a very good rinsing agent for removing pickling acids, I've found that a low pressure steam lance is the best approach. Knockoff what smut you can with the steam lance and then dip the part in a running water bath.
If smut is still a problem it can normally be removed by dipping the part in concentrated HNO3 at room temperature.
One thing to keep in mind is that a pickling and passivation system needs a dedicated operator. It can't be controlled by a hardcore unemployable as there is always a judgement factor to consider.
RE: Acid Pickling of ASTM A351 GR: CF3M
In general for alloys that are easy to pickle (easy to over pickle) like 430. 439, 17-4, 17-7 we would use 10-15% nitric/1% HF.
For standard 300 series alloys we use 20-25% nitric/4-5% HF.
For difficult to pickle alloys such as 6% Mo grades we go with 10% nitric/6% HF. The limit on HF is set by you permits and by the point where the bath starts to fume. HF fumes are deadly so it is good to avoid them.
If you have high Cr alloys (over 25%) a different approach is needed.
A final dip in 25% nitric is very good at cleaning the surface.
We like warm pickle baths since it helps prevent the re-precipitation of various salts back onto the product.
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