Incorrect passivation type for 17-4 PH

[anne_pe]

I have castings of 17-4 PH CRES that were passivated per AMS2700 Type 6 instead of Type 2. Could this cause any damage to the parts? Would it be okay to re-passivate per Type 2?

 

[EdStainless]

What was the actual acid concentration and temperature in the T6?
If both were on the high end you could see some pitting, but I doubt it.
Straight nitric should work fine and this isn't too hot.
Were they post treated is dichromate as required?
If so then they are fine.

 

[mfgenggear]

I have castings of 17-4 PH CRES that were passivated per AMS2700 Type 6 instead of Type 2. Could this cause any damage to the parts? Would it be okay to re-passivate per Type 2?

Please save me some time and give a little information.
Solutions use, was there post bake
Hardness of the material

 

[EdStainless]

Parts shall be cleaned so as to be free from water breaks and visible rust or scale (see 8.7).​

Method 1 - Passivation in Nitric Acid​

Passivation shall be accomplished by immersion in the specified bath type (see 1.3.2) in accordance with Table 1. When permitted by the cognizant engineering organization, other nitric acid solutions may be used (see 8.12).​

Table 1 - Method 1 passivation types

Type​	Feature​	Value(1)​
1​	Bath Composition	20 to 25% by volume of HNO3 2 to 3% by weight Na2Cr2O7·2H2O
​	Bath temperature	70 to 90 °F (21 to 32 °C)
​	Immersion time	30 minutes minimum
2​	Bath Composition	20 to 25% by volume of HNO3 2 to 3% by weight Na2Cr2O7·2H2O
​	Bath temperature	120 to 130 °F (49 to 54 °C)
​	Immersion time	20 minutes minimum
3​	Bath Composition	20 to 25% by volume of HNO3 2 to 3% by weight Na2Cr2O7·2H2O
​	Bath temperature	145 to 155 °F (63 to 68 °C)
​	Immersion time	10 minutes minimum
4​	Bath Composition	38 to 42% by volume of HNO3 2 to 3% by weight Na2Cr2O7·2H2O
​	Bath temperature	70 to 120 °F (21 to 49 °C)
​	Immersion time	30 minutes minimum
5​	Bath Composition	20 to 25% by volume of HNO3 2 to 3% by weight Na2Cr2O7·2H2O
​	Bath temperature	70 to 90 °F (21 to 32 °C)
​	Immersion time	2 minutes minimum
​	Voltage	Part anodic at 3 to 5 volts
6​	Bath Composition	25 to 45% by volume HNO3
​	Bath temperature	70 to 90 °F (21 to 32 °C)
​	Immersion time	30 minutes minimum
7​	Bath Composition	20 to 25% by volume HNO3
​	Bath temperature	120 to 140 °F (49 to 60 °C)
​	Immersion time	20 minutes minimum
8​	Bath Composition	45 to 55% by volume HNO3
	Bath temperature	120 to 130 °F (49 to 54 °C)
	Immersion time	30 minutes minimum
(1) Nitric acid concentration shown is by volume of 42° Baume (sp. gr. 1.4) nitric acid (see 8.11).

​

Final Rinse​

Immediately after removal from the passivating solution the parts shall be thoroughly rinsed. Final rinse shall be carried out in clean water (see 8.13).

Post Treatment​

When a post treatment is specified, directly after rinsing, parts made from ferritic, martensitic and precipitation hardening steels shall be immersed in a solution containing 4 to 6% by weight of sodium dichromate dihydrate (Na2Cr2O7·2H2O) at 140 to 160 °F (60 to 71 °C) for 1 hour, rinsed, and dried (see 8.2).

 

[mfgenggear]

Hi Ed
For type 6 The volume 23-45 % HNO3
please advise is this NITIC & H2O?

If not then no post bake.
But they use the wrong maybe drawing requirement. He will have to re due to type 2
It will require bake sorrect?

 

[EdStainless]

Passivation should not require a bake.
Passivation is a cleaning operation and should not be attacking the base metal at all.
Pickling is another matter altogether.
Yes, these are all either straight Nitric + water, or they have a dichromate addition.

 

[mfgenggear]

Passivation should not require a bake.
Passivation is a cleaning operation and should not be attacking the base metal at all.
Pickling is another matter altogether.
Yes, these are all either straight Nitric + water, or they have a dichromate addition.

Ed please reveiw AMS2759/9 latest. I have revision D
precipitation steels if etch require bake. if in the condition as shown
thank you

 

[EdStainless]

And if a passivation causes etching then you screwed up and used the wrong treatment.

 

[mfgenggear]

And if a passivation causes etching then you screwed up and used the wrong treatment.

So you interpreting passivation not an etch
Please explain.
What does nitric do

 

[EdStainless]

It is a cleaning operation.
It is supposed to remove iron and such from the surface.
It will not touch oxides and it should not touch the base metal either.
If you want to etch the surface (or remove oxides) then you would pickle (nitric + HF).
We used to run two different pickle baths.
One high concentration and hot, and the other lower concentration and lower temp. for ferritic and PH grades.

 

[mfgenggear]

It is a cleaning operation.
It is supposed to remove iron and such from the surface.
It will not touch oxides and it should not touch the base metal either.
If you want to etch the surface (or remove oxides) then you would pickle (nitric + HF).
We used to run two different pickle baths.
One high concentration and hot, and the other lower concentration and lower temp. for ferritic and PH grades.

thank for the correction

 

[EdStainless]

It isn't the clearest situation in the world.
I wish that we had better terminology.

 

[mfgenggear]

It isn't the clearest situation in the world.
I wish that we had better terminology.

All good . Some times it can be difficult.