1、Designation:G 79 83(Reapproved 1996)e1Standard Practice forEvaluation of Metals Exposed to CarburizationEnvironments1This standard is issued under the fixed designation G 79;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of
2、 last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon(e)indicates an editorial change since the last revision or reapproval.e1NOTEEditorial changes were made throughout in October 1996.1.Scope1.1 This practice covers procedures for the identificationand meas
3、urement of the extent of carburization in a metalsample and for the interpretation and evaluation of the effectsof carburization.It applies mainly to iron-and nickel-basedalloys for high temperature applications.Four methods aredescribed.Method ATotal Mass GainMethod BMetallographic EvaluationMethod
4、 CCarbon Diffusion ProfileMethod DChange in Mechanical Properties1.2 These methods are intended,within the interferences asnoted for each,to evaluate either laboratory specimens orcommercial product samples that have been exposed in eitherlaboratory or commercially produced environments.1.3 No attem
5、pt is made to recommend particular test expo-sure conditions,procedures,or specimen design as these mayvary with the test objectives.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establis
6、h appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:E 3 Methods of Preparation of Metallographic Specimens2E 8 Test Methods for Tension Testing of Metallic Materials2E 10 Test Method for Brinell H
7、ardness of Metallic Materi-als2E 18 Test Methods for Rockwell Hardness and RockwellSuperficial Hardness of Metallic Materials2E 23 Test Methods for Notched Bar Impact Testing ofMetallic Materials2E 139 Practice for Conducting Creep,Creep-Rupture,andStress-Rupture Tests of Metallic Materials2E 290 Te
8、st Method for Semi-Guided Bend Test for Ductilityof Metallic Materials2G 1 Practice for Preparing,Cleaning,and Evaluating Cor-rosion Test Specimens33.Terminology3.1 Definitions:3.1.1 carbon potentialthe amount of carbon available forreaction in an environment.This amount depends upon thechemical bal
9、ance of the carburizing and decarburizing agentsin the system such as carbon monoxide,hydrogen,carbondioxide,water vapor,methane,and nitrogen.3.1.2 carburizationthe absorption of carbon atoms into ametal surface at high temperatures.The carbon may remaindissolved or form metal carbides.This may or m
10、ay not bedesirable.METHOD ATOTAL MASS GAIN4.Summary of Method4.1 This method provides a relatively fast,simple,andinexpensive technique for comparing material or environmen-tal variables.The total mass gain of the sample during exposureis considered as a first approximation of total carbon pickup.5.
11、Significance and Use5.1 This method has an advantage over the other three,which are destructive single-determination techniques,in thatsuccessive measurements at selected time intervals can bemade without destroying the sample.If unwanted reactions(such as sulfidation and oxidation,which are usually
12、 minorunder intentionally carburizing conditions)are not important,amass gain plot versus time can provide some additional insightabout carburizing rate or intermittent variables,or both.6.Interferences6.1 The mass change of a sample may not be entirely theresult of carbon pickup.The environment may
13、 contain someother corroding species,such as oxygen,that may react withthe metal surface to form corrosion products which also affectmass change.This type of data also gives no indication ofcarbon distribution within the material which may be of more1This practice is under the jurisdiction of ASTM C
14、ommittee G-1 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.05 on LaboratoryCorrosion Tests.Current edition approved March 25,1983.Published June 1983.2Annual Book of ASTM Standards,Vol 03.01.3Annual Book of ASTM Standards,Vol 03.02.1Copyright ASTM,100 Barr Harbor Drive,W
15、est Conshohocken,PA 19428-2959,United States.importance than total pickup.Considering its limitations,thismethod is best used in combination with at least one of theother methods described in this practice or when considerableknowledge and understanding exist as to how materials usuallyperform in th
16、e particular conditions of the exposure environ-ment,or both.7.Procedure7.1 This method assumes the use of a sample that can bereadily measured to obtain exposed surface area and weighedboth before and after exposure to obtain mass gain per unitsurface area,that is,grams per square metre.See Practice G 1.8.Discussion of Results8.1 The successful application of this technique dependsprimarily upon the ability to measure small mass changes.Allweighing should be done to the nearest 0.1 mg.Sectionth
