Designation:A262−15
Standard Practices for
Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels1
This standard is issued under thefixed designation A262;the number immediately following the designation indicates the year of original adoption or,in the ca of revision,the year of last revision.A number in parenthes indicates the year of last reapproval.A superscript epsilon(´)indicates an editorial change since the last revision or reapproval.
This standard has been approved for u by agencies of the U.S.Department of Defen.
1.Scope*
1.1The practices cover the followingfive tests:
1.1.1Practice A—Oxalic Acid Etch Test for Classification of Etch Structures of Austenitic Stainless Steels(Sections4to 13,inclusive),
1.1.2Practice B—Ferric Sulfate-Sulfuric Acid Test for De-tecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels(Sections14to25,inclusive),
欧盟是什么意思1.1.3Practice C—Nitric Acid Test for Detecting Suscepti-bility to Intergranular Attack in Austenitic Stainless Steels (Sections26to36,inclusive),
1.1.4Practice E—Copper–Copper Sulfate–Sulfuric Acid Test for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels(Sections37to46,inclusive),and 1.1.5Practice F—Copper–Copper Sulfate–50%Sulfuric Acid Test for Detecting Susceptibility to Intergranular Attack in Molybdenum-Bearing Austenitic Stainless Steels(Sections 47to58,inclusive).
1.2The Oxalic Acid Etch Test is a rapid method of identifying,by simple etching,tho specimens of certain stainless steel grades that are esntially free of susceptibility to intergranular attack associat
ed with chromium carbide precipitates.The specimens will have low corrosion rates in certain corrosion tests and therefore can be eliminated (screened)from testing as“acceptable.”The etch test is applicable only to tho grades listed in the individual hot acid tests and classifies the specimens either as“acceptable”or as “suspect.”
1.3The ferric sulfate-sulfuric acid test,the copper–copper sulfate–50%sulfuric acid test,and the nitric acid test are bad on weight loss determinations and,thus,provide a quantitative measure of the relative performance of specimens evaluated.In contrast,the copper–copper sulfate–16%sulfuric acid test is bad on visual examination of bend specimens and,therefore, classifies the specimens only as acceptable or nonacceptable.
1.4The prence or abnce of intergranular attack in the tests is not necessarily a measure of the performance of the material in other corrosive environments.The tests do not provide a basis for predicting resistance to forms of corrosion other than intergranular,such as general corrosion,pitting,or stress-corrosion cracking.
N OTE1—See Appendix X1for information regarding test lection.
1.5The values stated in SI units are to be regarded as standard.The inch-pound equivalents are in p
arenthes and may be approximate.圣诞节快乐英文
1.6This standard does not purport to address all of the safety concerns,if any,associated with its u.It is the responsibility of the ur of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to u.Some specific hazards statements are given in10.1,20.1.1,20.1.9,31.3,34.4, 53.1.1,and53.1.10.
2.Referenced Documents
2.1ASTM Standards:2
A370Test Methods and Definitions for Mechanical Testing of Steel Products
A380/A380M Practice for Cleaning,Descaling,and Passi-vation of Stainless Steel Parts,Equipment,and Systems D1193Specification for Reagent Water
E3Guide for Preparation of Metallographic Specimens 2.2ASME Code:3
ASME Boiler&Pressure Vesl Code,Section IX
2.3ACS Specifications:4
Reagent Chemicals,Specifications and Procedures
1The practices are under the jurisdiction of ASTM Committee A01on Steel, Stainless Steel and Related Alloys and are the direct responsibility of Subcommittee A01.14on Methods of Corrosion Testing.
Current edition approved Sept.1,2015.Published September2015.Originally approved in1943.Last previous edition approved in2014as A262–14.DOI: 10.1520/A0262-15.
2For referenced ASTM standards,visit the ASTM website,,or contact ASTM Customer Service at For Annual Book of ASTM Standards volume information,refer to the standard’s Document Summary page on the ASTM website.
3Available from American Society of Mechanical Engineers(ASME),ASME International Headquarters,Two Park Ave.,New York,NY10016-5990,
4Available from American Chemical Society(ACS),1155Sixteenth Street,NW, Washington,DC20036,
*A Summary of Changes ction appears at the end of this standard Copyright©ASTM International,
100Barr Harbor Drive,PO Box C700,West Conshohocken,PA19428-2959.United States
2.4ISO Standard:5
ISO 3651-2Determination of Resistance to Intergranular Corrosion of Stainless Steels—Part 2:Ferritic,Austenitic,and Ferritic-Austenitic (Duplex)Stainless Steels—Corrosion Test in Media Containing Sulfuric Acid 3.Purity of Reagents
3.1Purity of Reagents—Reagent grade chemicals shall be ud in all tests.Unless otherwi indicated,it is intended that all reagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society 6where such specifications are available.Other grades may be ud,provided it is first ascertained that the reagent is of sufficiently high purity to permit its u without lesning the accuracy of the test result.
3.2Purity of Water—Unless otherwi indicated,references to water shall be understood to mean reagent water as defined by Type IV of Specification D1193.
PRACTICE A—OXALIC ACID ETCH TEST FOR CLASSIFICATION OF ETCH STRUCTURES OF
AUSTENITIC STAINLESS STEELS (1)74.Scope
4.1The Oxalic Acid Etch Test is ud for acceptance of wrought or cast austenitic stainless steel material but not for rejection of material.U of A262Practice A as a stand-alone test may reject material that the applicable hot acid test would find acceptable;such u is outside the scope of this practice.4.2This test is intended to be ud in connection with other evaluation tests described in the practices to provide a rapid method for identifying qualitatively tho specimens that are certain to be free of susceptibility to rapid intergranular attack in the other tests.Such specimens have low corrosion rates in the various hot acid tests which require from 15to 240h of exposure.The specimens are identified by means of their etch structures,which are classified according to the criteria given in Section 11.
4.3The Oxalic Acid Etch Test may be ud to screen specimens intended for testing in Practice B—Ferric Sulfate-Sulfuric Acid Test,Practice C—Nitric Acid Test,Practice E—Copper-Copper Sulfate–16%Sulfuric Acid Test,and Prac-tice F—Copper-Copper Sulfate–50%Sulfuric Acid Test.4.4Each of the other practices contains a table showing which classifications of etch structures on a given stai
nless steel grade are equivalent to acceptable or suspect performance in that particular test.Specimens having acceptable etch structures need not be subjected to the hot acid test.Specimens having suspect etch structures must be tested in the specified hot acid solution.
4.5There are two class of specimens to be considered:ba metal,and process-affected metal.
4.5.1Process-affected metal contains any condition that affects the corrosion properties of the material in a non-uniform way,such as (but not limited to)welds;carburized.nitrided,or oxidized surfaces;mechanical deformation;and areas affected by heat.Ba metal has none of the conditions.
4.5.2Becau Practices B,C,and F involve immersing the entire specimen and averaging the mass loss over the total specimen area,and becau welding,carburization,mechanical deformation,and the like affect only part of a specimen,the prence of process-affected metal in a specimen can affect the test result in an unpredictable way depending on the propor-tions of the area affected.
4.5.3If the prence of the or other localized conditions is a concern to the purchar,then tests that do not average the mass loss over the total specimen surface area,such as Practice A,the Oxalic Acid Etch Test,or Practice E,the Copper–Copper Sulfate–Sulfuric Acid Test for Detecting Susc
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eptibility to Intergranular Attack in Austenitic Stainless Steels,should be considered.
5.Summary of Practice
5.1A specimen reprentative of the material to be evalu-ated is polished to a specified finish and over-etched using oxalic acid electrolytically.The etched specimen is then examined using a metallurgical microscope.The etched struc-ture is compared with reference photographs to determine whether the material is acceptable or suspect.Suspect material is then subjected to the specified hot acid immersion test.
6.Significance and U
6.1U of the etch test allows rapid acceptance of specific lots of material without the need to perform time-consuming and costly hot acid immersion tests on tho lots.
7.Apparatus
7.1Etching Cell:
7.1.1An etching cell may be asmbled using components as described in this ction.Alternatively,
a commercial electropolisher/etcher (as ud for metallographic sample preparation)may be ud for small specimens provided the current density requirement of 10.2is met.
7.1.2Source of Direct Current—Battery,generator,or rec-tifier capable of supplying about 15V and 20A.
7.1.3Ammeter—For direct current;ud to measure the current on the specimen to be etched.
7.1.4Variable Resistance—Ud to control the current on the specimen to be etched.
7.1.5Cathode—A stainless steel container,for example,a 1-L (1-qt)stainless steel beaker.
7.1.5.1Alternate Cathode—A piece of flat stainless steel at least as large as the specimen surface.
7.1.6Electrical Clamp—To hold the specimen to be etched and to complete the electrical circuit between the specimen and the power source such that the specimen is the anode of the cell.
5
Available from International Organization for Standardization (ISO),1,ch.de la V oie-Creu,CP 56,CH-1211Geneva 20,Switzerland,6
For suggestions on the testing of reagents not listed by the American Chemical Society,e Analar Standards for Laboratory Chemicals ,BDH Ltd.,Poole,Dort,U.K.,and the United States Pharmacopeia and National Formulary ,U.S.Pharma-copeial Convention,Inc.(USPC),Rockville,MD.7
The boldface numbers in parenthes refer to a list of references at the end of this
standard.
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7.1.7The power source,resistor,and ammeter must be sized appropriately for providing and controlling the current as specified in10.2of this practice.
7.1.8As described,the electrolyte container is the cathode; it may be a stainless steel beaker or fabricated from stainless steel such as by welding a ction of tube or pipe to aflat plate or sheet.Alternatively,the electrolyte container may be glass (or other non-conducting,corrosion resisting material)in lieu of a stainless steel container,and the cathode may be aflat plate or sheet of a corrosion resisting alloy.In this latter ca,theflat surface of the cathode must be at least as large as,facing,and approximately centered on,the prepared surface of the speci-men.Other configurations
of the electrodes might not provide uniform etching over the specimen surface.In any ca,the size and shape of the specimen dictate the size and construction of the etching cell and of the power source and controls.The overriding principle is that the etch needs to be uniform over the surface to be examined.
7.2Metallurgical Microscope—For examination of etched microstructures at250to500diameters.
8.Reagents and Materials
8.1Etching Solution(10%)—Dissolve100g of reagent grade oxalic acid crystals(H2C2O4·2H2O)in900mL of reagent water.Stir until all crystals are dissolved.
8.1.1Alternate Etching Solution(See10.7)—Dissolve100g of reagent grade ammonium persulfate((NH4)2S2O8)in 900mL of reagent water.Stir until dissolved.
9.Sampling and Test Specimens
9.1The specified hot acid test provides instructions for sampling and for specimen preparation such as a nsitization heat treatment.Additional instructions specific to Practice A follow:
9.2The preferred specimen is a cross-ction including the product surface to be expod in rvice.Only suchfinishing of the product surface should be performed as is required to remove foreign material.
9.3Whenever practical,u a cross-ctional area of1cm2 or more.If any cross-ctional dimension is less than1cm, then the other dimension of the cross-ction should be a minimum of1cm.When both dimensions of the product are less than1cm,u a full cross ction.
9.4Polishing—On all types of materials,polish cross c-tional surfaces through CAMI/ANSI600[FEPA/ISO P1200]in accordance with Guide E3prior to etching and examination. Not all scratches need to be removed.
opposites10.Procedure
10.1(Warning—Etching should be carried out under a ventilated hood.Gas,which is rapidly evolved at the electrodes with some entrainment of oxalic acid,is poisonous and irritating to mucous membranes.)
10.2Etch the polished specimen at1A/cm2for1.5min.
10.2.1To obtain the correct specified current density: 10.2.1.1Measure the total immerd area of the specimen to be etched in square centimetres.
10.2.1.2Adjust the variable resistance until the ammeter reading in amperes is equal to the total immerd area of the specimen in square centimetres.
10.3A yellow-greenfilm is gradually formed on the cath-ode.This increas the resistance of the etching cell.When this occurs,remove thefilm by rinsing the inside of the stainless steel beaker(or the steel ud as the cathode)with an acid such as30%HNO3.
10.4The temperature of the etching solution gradually increas during etching.Keep the temperature below50°C. This may be done by alternating two containers.One may be cooled in tap water while the other is ud for etching.
10.4.1The rate of heating depends on the total current (ammeter reading)passing through the cell.Therefore,keep the area to be etched as small as possible while at the same time meeting the requirements of desirable minimum area to be etched.
10.5Avoid immersing the clamp holding the specimen in the etching solution.
10.6Rinsing—Following etching,rin the specimen thor-oughly in hot water and then in acetone or alcohol to avoid crystallization of oxalic acid on the etched surface during drying.
richstar10.7It may be difficult to reveal the prence of step structures on some specimens containing molybdenum(AISI 316,316L,317,317L),which are free of chromium carbide nsitization,by electrolytic etching with oxalic acid.In such cas,an alternate electrolyte of ammonium persulfate may be ud in place of oxalic acid.(See8.1.1.)An etch for5or10 min at1A/cm2in a solution at room temperature readily develops step structures on such specimens.
11.Classification of Etch Structures
11.1Examine the etched surface on a metallurgical micro-scope at250×to500×for wrought steels and at about250×for cast steels.
11.2Examine the etched cross-ctional areas thoroughly by complete traver from inside to outside diameters of rods and tubes,from face to face on plates.
11.2.1Microscopical examination of a specimen shall be made on metal unaffected by cold-working,carburization, welding,and the like.If any of the conditions are found,note their prence in the report.
11.3Classify the etch structures into the following types (Note2):
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11.3.1Step Structure(Fig.1)—Steps only between grains, no ditches at grain boundaries.
11.3.2Dual Structure(Fig.2)—Some ditches at grain boundaries in addition to steps,but no single grain completely surrounded by ditches.
11.3.3Ditch Structure(Fig.3)—One or more grains com-pletely surrounded by ditches.
11.3.4Isolated Ferrite(Fig.4)—Obrved in castings and welds.Steps between austenite matrix and ferrite pools. 11.3.5Interdendritic Ditches(Fig.5)—Obrved in castings and welds.Deep interconnected
ditches.--` , ` , ` ` , ` ` , ` , , ` , , , , , , ` ` ` , ` , , ` ` ` -` -` , , ` , , ` , ` , , ` ---
11.3.6End-Grain Pitting I (Fig.6)—Structure contains a few deep end-grain pits along with some shallow etch pits at 500×.(Of importance only when the nitric acid test is ud.)11.3.7End-Grain Pittin
g II (Fig.7)—Structure contains numerous,deep end-grain pits at 500×.(Of importance only when nitric acid test is ud.)
N OTE 2—All photomicrographs were made with specimens that were etched under standard conditions:10%oxalic acid,room temperature,1.5min at 1A/cm 2.
11.4The evaluation of etch structures containing only steps and of tho showing grains completely surrounded by ditches in every field can be carried out relatively rapidly.In cas that appear to be dual structures,more extensive examination is required to determine if there are any grains completely encircled.If an encircled grain is found,classify the steel as a ditch structure.lfridges
11.4.1On stainless steel castings (also on weld metal),the steps between grains formed by electrolytic oxalic acid etching tend to be less prominent than tho on wrought materials
or
FIG.1Step Structure (500×)(Steps Between Grains,No Ditches
at Grain
Boundaries)
FIG.2Dual Structure (250×)(Some Ditches at Grain Boundaries in Addition to Steps,but No One Grain Completely
Surrounded)
FIG.3Ditch Structure (500×)(One or More Grains Completely
Surrounded by
Ditches)
FIG.4Isolated Ferrite Pools (250×)(Obrved in Castings and Welds.Steps Between Austenite Matrix and Ferrite
Pools)
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are entirely abnt.However,any susceptibility to intergranular attack is readily detected by pronounced ditches.
11.4.2Some wrought specimens,especially from bar stock,may contain a random pattern of pits.If the pits are sharp and so deep that they appear black (Fig.7)it is possible that the specimen may be susceptible to end grain attack in nitric acid only.Therefore,even though the grain boundaries all have step
structures,specimens having as much or more end grain pitting than that shown in Fig.7cannot be safely assumed to have low nitric acid rates and should be subjected to the nitric acid test whenever it is specified.Such sharp,deep pits should not be confud with the shallow pits shown in Figs.1and 6.12.U of Etch Structure Classifications
12.1The u of the classifications depends on the hot acid corrosion test for which stainless steel specimens are being screened by etching in oxalic acid and is described in each of the practices.
13.Precision and Bias
13.1Precision and Bias—No information is prented about either the precision or bias of Practice A—Oxalic Acid Etch Test for classification of Etch Structures of Austenitic Stainless Steels since the test result is nonquantitative.
PRACTICE B—FERRIC SULFATE–SULFURIC ACID TEST FOR DETECTING SUSCEPTIBILITY
TO INTERGRANULAR ATTACK IN AUSTENITIC STAINLESS STEELS (2)14.Scope
14.1This practice describes the procedure for conducting the boiling 120-h ferric sulfate–50%sulfuric acid test which measures the susceptibility of austenitic stainless steels to intergranular attack.
14.2The prence or abnce of intergranular attack in this test is not necessarily a measure of the performance of the material in other corrosive environments.The test does not provide a basis for predicting resistance to forms of
corrosion
FIG.5Interdendritic Ditches (250×)(Obrved in Castings and
Welds.Deep Interconnected
Ditches)
N OTE 1—To differentiate between the types of pits,u a magnification of 500×and focus in the plane of etched surface.The pits which now appear completely black are end grain pits.
FIG.6End Grain Pitting I (500×)(A Few Deep End Grain Pits
(See 1in Figure)and Shallow Etch Pits
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N OTE 1—This or a greater concentration of end grain pits at 500×(using standard etching conditions)indicates that the specimen must be tested when screening is for nitric acid test.爱丽丝梦游仙境真人版
FIG.7End Grain Pitting II
(500×)
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