Passivation Problems with 17-4 SS
Passivation Problems with 17-4 SS
(OP)
Has anyone experienced a coloration between this and improper heat treat? I am a quality/process engineer running a passivation line for medical devices. If we get product (17-4 H900) back from our heat treat vendor that is slightly discolored, and we don’t properly finish it thru polishing or bead blasting, we get dark grey or black discoloration. (I posted this in another forum before I found this one.)





RE: Passivation Problems with 17-4 SS
RE: Passivation Problems with 17-4 SS
RE: Passivation Problems with 17-4 SS
17/4 that has been mistreated during heat treatment can be a little hard to clean. The best way to eliminate cleaning problems is to correct the heat treatment problems.
The recommended cleaning procedure is a Nitric/Hydrofluoric bath, normally 12% HNO3 / 2% HF v/v @ RT. The bath can go up to 20% HNO3 / 3% HF v/v @ RT if the scale is stubborn.
If a quick dip in a HNO3/HF bath doesn’t do the job you will have to go with an oxidizing pretreatment.
RE: Passivation Problems with 17-4 SS
Please don't use HCl. Nitric and Nitric/HF are the way to go. Some people passivate in Citric or Phosphoric, but they are less effective.
When you have oxide from the heat treatment the passivation will not remove it.
= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Passivation Problems with 17-4 SS
You must remove the heat tint before passivation. Even with good vacuum heat treatment oven you may get a slightly discolored surface. So, the best is to use mechanical cleaning process such as fine glass bead blasting. However, beware of excess metal removal which may affect the part dimensions.
Using a chemical etching process to remove the heat tint may result in hydrogen embrittlement and will surely remove too much metal which can be as much as 0.05mm from the surface. The chemical removal process is not accurate and it is difficult to control the metal removal thickness.
Your best bet is to rough machine the part accurate dimensions (leave enough material to remove after heat treatment) then heat treat it to H900. Now use fine mesh glass beads to mechanically clean the part and then machine/grind the accurate dimensions of the part to final dimensions. This way you will have a clean part ready for passivation.