1. Scope
1.1 This specification covers several different types of chemical passivation treatments for stainless steel parts. It includes recommendations and precautions for descaling,cleaning, and passivation of stainless steel parts. It includes several alternative tests, with acceptance criteria, for confirma-tion of effectiveness of such treatments for stainless steel parts.
1.2 Practices for the mechanical and chemical treatments of stainless steel surfaces are discussed more thoroughly in Practice A 380.
1.3 Several alternative chemical treatments are defined for passivation of stainless steel parts. Appendix X1 gives some nonmandatory information and provides some general guide-lines regarding the selection of passivation treatment appropri-ate to particular grades of stainless steel but makes no
recommendations regarding the suitability of any grade, treat-ment, and acceptance criteria for any particular application or class of applications.
1.4 The tests in this specification are intended to confirm the effectiveness of passivation, particularly with regard to the removal of free iron and other exogenous matter. These tests include the following practices:
1.4.1 Practice A—Water Immersion Test,
1.4.2 Practice B—High Humidity Test,
1.4.3 Practice C—Salt Spray Test,
1.4.4 Practice D—Copper Sulfate Test,
1.4.5 Practice E—Potassium Ferricyanide–Nitric Acid Test,and
1.4.6 Practice F—Free Iron Test.
1.5 The values stated in inch-pound units are to be regarded as the standard. The SI units given in parentheses are for information only.
1.6 The following precautionary caveat pertains only to the test method portions, Sections 14 through 18 of this specifica-tion: This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
A 380 Practice for Cleaning, Descaling, and Depassivation of Stainless Steel Parts, Equipment, and Systems2
B 117 Practice for Operating Salt Spray (Fog) Apparatus3
B 254 Practice for Preparation of and Electroplating on Stainless Steel4
2.2 Federal Specification:
QQ-P-35C Passivation Treatments for Corrosion-Resistant Steels5 passivation may also include the removal of sulfides from the surface of the metal for the purpose of maximizing corrosion resistance.
3.1.1.2 The formation of the protective passive film on a stainless steel, also called passivation in a more general context, will occur spontaneously in air or other oxygen-containing environment when the stainless steel surface is free of oxide scale and exogenous matter.
3.1.1.3 Chemical treatments, such as sodium dichromate solutions, may facilitate the more rapid formation of the passive film on a stainless steel surface already free of scale or foreign matter. Such treatments, also sometimes called passi-vation in common usage, are designated as post-cleaning treatments in this specification in order to distinguish them from chemical treatments capable of removing free iron from stainless steels.
3.1.1.4 The chemical treatments capable of removing heat tint or oxide scale from stainless steel and capable of dissolving the stainless steel itself, typically called pickling, are substan-tially more aggressive than treatments used for passivation, as defined in 3.1.1.1. The surface of stainless steel that has been pickled is free of scale, free iron, and exogenous foreign matter, and does not require a separate treatment for passiva-tion as defined in 3.1.1.1. The passivation process defined in
3.1.1.2 will occur without further chemical treatment but maybe augmented and improved by the post-cleaning treatmentsdefined in 3.1.1.3.
3.1.1.5 Electrochemical treatments, including electropick-ling and electropolishing capable of removing heat tint or oxide scale from stainless steel and capable of dissolving the stainless steel itself, are substantially more aggressive than treatments used for passivation, as defined in 3.1.1.1. The surface of stainless steel resulting from these treatments is free of scale,free iron, and exogenous foreign matter, and does not require a separate treatment for passivation as defined in 3.1.1.1. The passivation process defined in 3.1.1.2 will occur without further chemical treatment, but may be augmented and im-proved by the post-cleaning treatments defined in 3.1.1.3.Statements regarding chemical treatments, unless otherwise specified, are taken to include electrochemical treatments.
4. Ordering Information
4.1 It is the responsibility of the purchaser to specify a test practice appropriate to any particular material and application.This specification was written for the purpose of providing an alternative to United States Federal Specification QQ-P-35C.Determination of the suitability of this specification for that purpose is the responsibility of the purchaser.
4.2 Unless specified by the purchaser, the chemical treat-ment applied to the stainless steel parts shall be selected by the seller from among the listed passivation treatments.
5. Materials and Preparation for Passivation Treatments
5.1 The passivation treatments shall be of one or more of the following types. The effectiveness of a particular treatment for a particular grade of stainless steel in a particular application is demonstrated by meeting the specified testing requirements:
5.1.1 Treatments in nitric acid,
5.1.2 Treatments in citric acid,
5.1.3 Other chemical treatments, including electrochemical
treatments,
5.1.4 Neutralization, and
5.1.5 Post-cleaning treatments.
5.2 Materials:
5.2.1 The chemicals used for passivation treatments shall produce passivated surfaces that meet the requirements of one or more of the tests of this specification. Attention shall be given to maintaining adequate volume, concentration, purity,and temperature control appropriate to the size and amount of stainless steel to be treated.
5.2.2 The processor shall maintain a record with regard to concentration and temperature of the passivation solution sufficient to demonstrate that the specified passivation condi-tions were maintained for each lot of stainless steel parts processed. Such records shall be available for inspection when specified in the purchase order. The processor is not required to reveal the precise composition of proprietary chemical mix-tures but shall maintain a unique identification of the mixture that will ensure its accurate representation for subsequent use.
5.2.3 The processor shall be responsible for the safe dis-posal of all material generated by this process.
5.3 Preparation for Passivation Treatments:
5.3.1 The pretreatment methods and procedures used prior to the passivation treatment, including mechanical and chemi-cal methods, singly or in combination, for descaling and pickling, shall be in accordance with Practice A 380. When electrochemical cleaning is required, it shall be performed in accordance with Practice B 254.
5.3.2 The resulting pretreated surface shall be substantially free of oil, grease, rust, scale, and other foreign matter.
5.3.3 When the final pretreatment of a part includes pickling of the entire surface of the part, no further passivation treatment is required prior to testing of the surface unless specified by the purchaser.
6. Treatments in Nitric Acid Solutions
6.1 Passivation Treatment:
6.1.1 Stainless steel parts shall be treated in one of the following aqueous solutions and maintained within the speci- fied temperature range for the specified time.
6.1.1.1 Nitric 1—The solution shall contain 20 to 25 volume percent of nitric acid and 2.5 + 0.5 weight percent of sodium dichromate. The parts shall be immersed for a minimum of 20 min at a temperature in the range from 120 to 130°F (49 to 54°C).
6.1.1.2 Nitric 2—The solution shall contain 20 to 45 volume percent of nitric acid. The parts shall be immersed for a minimum of 30 min at a temperature in the range from 70 to 90°F (21 to 32°C).
6.1.1.3 Nitric 3—The solution shall contain 20 to 25 volume
percent nitric acid. The parts shall be immersed for a minimum of 20 min at a temperature in the range from 120 to 140°F (49 to 60°C).
6.1.1.4 Nitric 4—The solution shall contain 45 to 55 volume percent of nitric acid. The parts shall be immersed for a minimum of 30 min at a temperature in the range from 120 to 130°F (49 to 54°C).
6.1.1.5 Nitric 5—Other combinations of temperature, time, and concentration of nitric acid, with or without other chemi-cals, including accelerants, inhibitors, or proprietary solutions,capable of producing parts that pass the specified test require-ments.
6.2 Water Rinse—Immediately after removal from the pas-sivating solution the parts shall be thoroughly rinsed, using stagnant, countercurrent, or spray washes singly or in combi-nation, with or without a separate chemical treatment for neutralization (see 9.1) of the passivation media, with a final rinse being carried out using water with a maximum total solids content of 200 ppm.
7. Treatments in Citric Acid
7.1 Passivation Treatment:
7.1.1 Stainless steel parts shall be treated in one of the following aqueous solutions and maintained within the speci- fied temperature range for the specified time.
7.1.1.1 Citric 1—The solution shall contain 4 to 10 weight percent of citric acid. The parts shall be immersed for a minimum of 4 min at a temperature in the range from 140 to 160°F (60 to 71°C).
7.1.1.2 Citric 2—The solution shall contain 4 to 10 weight percent of citric acid. The parts shall be immersed for a minimum of 10 min at a temperature in the range from 120 to 140°F (49 to 60°C).
7.1.1.3 Citric 3—The solution shall contain 4 to 10 weight percent of citric acid. The parts shall be immersed for a minimum of 20 min at a temperature in the range from 70 to 120°F (21 to 49°C).
7.1.1.4 Citric 4—Other combinations of temperature, time, and concentration of citric acid, with or without other chemi-cals to enhance cleaning, including accelerants, inhibitors, or proprietary solutions capable of producing parts that pass the specified test requirements.
7.1.1.5 Citric 5—Other combinations of temperature, time, and concentrations of citric acid, with or without other chemi-cals to enhance cleaning, including accelerants, inhibitors, or proprietary solutions capable of producing parts that pass the specified test requirements. Immersion bath to be controlled at a pH of 1.8–2.2.
7.2 Water Rinse—Immediately after removal from the pas-sivating solution, the parts shall be thoroughly rinsed, using stagnant, countercurrent, or spray washes, singly or in combi-nation, with or without a separate chemical treatment for neutralization of the passivation media (see 9.2), with a final rinse being carried out using water with a maximum total solids
content of 200 ppm
8. Treatments in Other Chemical Solutions, Including Electrochemical Treatments
8.1 It is recognized that the purpose of removal of all exogenous matter from a stainless steel surface, including the removal of free iron, can be accomplished by different media,with potential for benefits to be gained from use of proprietary skills and art, including proprietary passivation media. Such treatments may include externally applying an electrical po-tential on the stainless steel parts, as in the case of electropol-ishing. The suitability of such passivation treatments for use in.
3 meeting the requirements of this specification shall be deter-mined by the capability of the processed parts meeting the specified test requirements.
8.2 Stainless steel parts shall be treated in a specified aqueous solution, with or without externally applied electrical potential, and maintained within a specified temperature range for a time sufficient for the processed parts to meet the specified test requirement.
8.3 Water Rinse—Immediately after removal from the pas- sivating solution, the parts shall be thoroughly rinsed, using stagnant, countercurrent, or spray washes, singly or in combi-nation, with or without a separate chemical treatment for neutralization of the passivation media (see 9.2), with a final rinse being carried out using water with a maximum total solids content of 200 ppm.
9. Neutralization
9.1 The chemical reactions of the passivating media on the surface of the stainless steel shall be stopped by rinsing of the stainless steel part, with or without a separate neutralization treatment.
9.2 The suitability of a neutralization procedure is deter- mined by the capability of the processed parts meeting the specified test requirements. (See Note 1.)
NOTE 1—The selection of medium and procedures for a neutralization depends of the chemistry of the passivation and on economic consider-ations. An example of a neutralizing treatment would be immersion of the part for a minimum of 30 min in a solution of 5 % NaOH at 160 to 180°F(71 to 82°C), followed by a water rinse.
10. Post-Cleaning Treatments
10.1 Although the passive film characteristic of stainless steel will form spontaneously in air or any other oxygen-containing environment, the processor shall, when specified, apply a chemical treatment that will accelerate the formation of the passive film on a chemically clean stainless steel surface. An example of a medium that serves to accelerate the forma-
tion of the passive film but does not contribute to the removal of free iron from the stainless steel surface would be an aqueous solution of sodium dichromate.
10.2 When specified, within one hour after the final water rinse as required in 6.2, 7.2, or 8.3, all ferritic and martensitic steel parts shall be immersed in an aqueous solution containing 4 to 6 weight percent of sodium dichromate at a temperature in the range from 140 to 160°F (60 to 71°C) for a minimum of 30 min, followed by a rinse in accordance with 6.2, 7.2, or 8.3.The parts shall then be thoroughly dried.
10.3 The purchaser may specify other post-cleaning treat-ments.
11. Finish
11.1 The passivated parts shall exhibit a chemically clean surface and shall, on visual inspection, show no etching, pitting, or frosting resulting from the passivation procedures.
12. Testing Agency
12.1 When required, the purchaser shall be permitted to perform such inspections as necessary to determine that the testing agency is capable of performing the specified test.
13. Lot, Frequency of Testing, and Selection of Test
13.1 Definition of Lot—A lot shall consist of one of the following, at the option of the processor:
13.1.1 The passivated parts of similar alloy and manufac-turing methods that are pretreated and passivated in a single day or within a time frame that will ensure consistent passiva-tion results;
13.1.2 The passivated parts of the same product of one size from one heat in one shipment; or
13.1.3 When few parts are involved, the passivated parts from an entire production run.
13.2 Unless a greater frequency of testing is specified on the purchase order, one test per lot shall be sufficient.
13.3 One or more of the following tests, when specified on the purchase order, shall be performed on each lot of stainless steel parts. Not all of the following tests are suitable for all grades of stainless steel. (See Note 2.)
13.3.1 Practice A—Water Immersion Test,
13.3.2 Practice B—High Humidity Test,
13.3.3 Practice C—Salt Spray Test,
13.3.4 Practice D—Copper Sulfate Test, and
13.3.5 Practice E—Potassium Ferricyanide–Nitric Acid
Test.
NOTE 2—Some of the tests may produce positive indications not
associated with the presence of free iron on the stainless steel surface. An
example would be application of Practice C on some lesser-alloyed
martensitic or ferritic stainless steels.
14. Practice A—Water Immersion Test
14.1 This test is used for the detection of free iron or any
other anodic surface contaminants on stainless steel.
14.2 The sample representing the lot of passivated parts
shall be alternately immersed in a non-rusting tank of distilled
water for 1 h and allowed to dry in air for 1 h. This cycle shall
be repeated a minimum of twelve times.
14.3 The tested sample shall not exhibit rust or staining
attributable to the presence of free iron particles embedded in
the surface.
15. Practice B—High Humidity Test
15.1 This test is used for the detection of free iron or any
other anodic surface contaminants on stainless steel.
15.2 The test shall be performed using a humidity cabinet
capable of maintaining the specified test conditions.
15.3 The sample representing the lot of passivated parts
shall be cleaned by immersion in acetone or methyl alcohol or
by swabbing with a clean gauze saturated with acetone or
methyl alcohol, and dried in an inert atmosphere or desiccated
container. The cleaned and dried part shall be subjected to 97
6 3 % humidity at 100 6 5°F (38 6 3°C) for a minimum of
24 h.
15.4 The tested sample shall not exhibit rust or staining
attributable to the presence of free iron particles imbedded in
the surface.
16. Practice C—Salt Spray Test
16.1 This test is used for the detection of free iron or any
other anodic surface contaminants on stainless steel.
16.2 The sample representing the lot of passivated parts
shall be tested by the salt spray test conducted in accordance
with Practice B 117 for a minimum of 2 h using a 5 % salt
solution.
16.3 The tested sample shall not exhibit rust or staining
attributable to the presence of free iron particles imbedded in
the surface.
17. Practice D—Copper Sulfate Test
17.1 This test is recommended for the detection of free iron
on the surface of austenitic stainless steels in the 200 and 300
series, precipitation hardened stainless steels, and ferritic 400
series stainless steels having a minimum of 16 % chromium.
This test is not recommended for martensitic 400 series
stainless steels or for ferritic 400 series stainless steels with less
than 16 % chromium because these steels will give a positive
indication irrespective of the presence or absence of anodic
surface contaminants. This test shall not be applied to parts to
be used in food processing.
17.2 The test solution is prepared by dissolving 4 g of
copper sulfate pentahydrate (CuSO4·5H2O) in 250 mL of
distilled water to which 1 mL of sulfuric acid (H2SO4, sp gr
1.84) has been added. Aqueous copper sulfate solutions more
than two weeks old shall not be used for this test.
17.3 The test solution is swabbed on the surface of the
sample representing the lot of passivated parts, applying
additional solution as needed to keep the surface wet for a
period of at least 6 min. At the end of this period, the surface
shall be carefully rinsed and dried with care taken not to disturb
copper deposits if present.
17.4 The tested sample shall not exhibit copper deposits.
18. Practice E—Potassium Ferricyanide–Nitric Acid Test
18.1 This test is recommended when detection of very small
amounts of free iron is required. It is recommended for
detection of free iron on austenitic 200 and 300 series stainless
steels. This test is not recommended for detection of free iron
on ferritic or martensitic 400 series stainless steels, because
these steels will give a positive indication irrespective of the
presence or absence of anodic surface contaminants. This test
shall not be applied to parts to be used in food processing.
18.2 The test solution is prepared by adding 10 g of
chemically pure potassium ferricyanide to 500 mL of distilled
water, adding 30 mL of 70 % nitric acid, agitating until all of
the ferricyanide is dissolved, and diluting to 1000 mL with
distilled water. The test solution shall be mixed fresh on the day
of the test.
18.3 The test solution is swabbed on the surface of the
sample representing the lot of passivated parts. The formation
of a dark blue color within 30 s denotes the presence of
metallic iron.
18.4 The tested sample shall not exhibit the dark blue color
indicative of free iron on the surface.
18.5 When the test is negative, the surface shall be thor-
oughly washed with warm water to removal all traces of the
test solution. When the test is positive, the dark blue stain shall
be removed with a solution of 10 % acetic acid and 8 % oxalic
acid, followed by a thorough hot water rinse
19. Practice F—Free Iron Test
19.1 This test is used for the detection of free iron on the
surface of stainless steel. It is especially useful for large parts
that have been uniformly cleaned but that are inconvenient for
reasons of size of equipment or ease of handling of the part to
place in the environments defined in Practice A (Section 14) or
Practice B (Section 15). Unless otherwise specified by the
purchaser, the number of tests and the locations of the tests
shall be at the option of the processor to assure a representative
testing of the part.
19.2 The test is performed by placing a clean cloth pad that
has been thoroughly soaked with distilled or deminaralized
water on the surface of the part at a part temperature of 50°F
(10°C) or greater for a period of not less than 60 minutes. The
cloth shall be in contact with the steel for an area of at least 20
square inches (130 cm2). The pad shall be maintained wet
through the test period, either by a method of retarding external
evaporation, by the further addition of potable water, or by
backing the pad with a sponge or similar water source. The
cloth pad used shall be used for only one such test, being
changed for each test so as to avoid risk of contamination.
After removal of the cloth pad, the surface of the part shall be
allowed to dry in air before inspection.
19.3 The tested part shall not exhibit rust or stainingattributable to the presence of free iron particles embedded inthe surface.
20. Rejection and Retest
20.1 Any lot failing to meet the specifed test requirementsof the purchase order shall be rejected. A rejected lot may, atthe option of the processor, be re-passivated, with or withoutre-pretreatment, and then be retested. The number of samplestested from a lot subject to retest shall be twice the originalspecifed test frequency, to the limit of the number of pieces inthe lot. All samples must pass the specified acceptance criterionfor the specified test for the retested lot to be accepted.
21.Precision and Bias
21.1 No statement is made concerning either the precisionor bias of Practices A,B,C, D. and E because the results statemerely whether there is confomnance to the criteria for successspecifed in the procedure.
22.Certifcation
22.1 When specifed in the purchase order, a report of thepractice and tests used, including the record of process condi-tions when specifed in accordance with 3.1.1.2. shall besupplied to the purchaser.
X1.INFORMATION REGARDING PASSIVATION TREATMENTS
NoTE X1.1-The following information is based on a section ofFederalSpecification 00-P-35C(0ct.28,1988)identifed as information of ageneral or explanatory nature that may be helpful, but is not mandatoryMinor changes have been made in the text to facilitate references to themain document and to correct technical inaccuracies.
X1.1 Intended Use The passivation treatments providedby this specification are intended to improve the corrosionresistance of parts made from stainless steels of all types.
X1.1.1 During processing operations such as forming, ma-chining, tumbling, and lapping, iron particles or other foreignparticles may become smeared over or imbedded into thesurface of stainless steel paits. These particles must be remnoved or they will appear as rust or stain spots. This conditionmay be prevented by chemically treating the parts to removethe iron particles or other foreign particles, and then allowingthe passive flm to fomn on the cleaned surface. with or withoutchemical enhancement of the fomation of this oxide flm.X1.1.2 This specifcation is not intended for the black oxidecoating of parts typically used for photographic or opticalinstruinents.
Ordering Data Purchasers should select the preX1.2ferred options pemitted by this specifcation and include thefollowing infommation in the purchase order:
X1.2.1 Title, number, and date of this specifcation;
X1.2.2 Identification of material by type and applicableproduct specifcation:X1.2.3 Test practices to be imposed (see 1.4);X1.2.4 Defnition of lot size, if other than described in thisspecification; andX1.2.5 Required documentation, if other than the inimumrequired by this specifcation.
X1.3 Grades ofStainless Steel-Different types of stainlesssteel are selected on a basis of properties required, for exammple.corrosion resistance and design criteria, and fabrication requirements. Table X1.l is a compilation that serves as a guidefor the selection of passivation treatient for different grades.but is far from complete either in grades or in passivationtreatments.
X1.4 Clean WaterClean water is defined as water con-taining a maximum total solid content of 200 ppm. Rinsing canbe accomplished by a combination of stagnant, countercurrentor spray rinses, or both, prior to fnal rinse.
X1.5 Chemically Clean Surace-A chemically clean surface is defined as a surface upon which water, when appliedmomentarily to the surface, will remain on that surface in aneven, continuous flm, and in addition is free of any foreignmaterial or residual flm deposit which would be detrimental tothe quality of the part.
X1.6 Test Specimens When using test specimens insteadof parts, the specimens can efectively represent the parts onlyif they have been exposed to the same processing steps, such asmachining, grinding, heat treating, welding, and so forth, as theparts they are to represent.
Carburized Suraces-Stainless steel parts with carX1.7burized surfaces cannot be passivated because the carboncombines with the chromiun fomming chromium carbides onthe surface.
X1.8 Nitided Suraces,Stainless steel parts with nitridedsurfaces should not be passivated because the treatment wil!severely corrode the nitrided case
X1.9 This specifcation provides for the same passivationtreatments as Fed. Spec.Q0-P-35C,but also includes anumber of altemnative passivation treatments. The efectivenessof any passivation treatment is demonstrated by the partsmeeting the specifed testing requirements after treatent.
X1.10 Martensitic Grade 440c-High-strength gradessuch as 440C are subject to hydrogen embrittlement orintergranular attack when exposed to acids.Cleaning bymechanical methods or other chemical methods is recommended.
X1.1l The salt spray test is typically used to evaluateaustenitic stainless steels and may not be applicable to allmartensitic or ferritic stainless steels.
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