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This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade TBT Committee. Standard Practice for. Macroetching Metals and Alloys 1. A number in parentheses indicates the year of last reapproval.
This standard has been approved for use by agencies of the U. Department of Defense. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard. It is the responsibility of the user of this standard to establish appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use. Referenced Documents.
Metallographic specimens and chemical. Current edition approved June 1, Published July, Originally approved in Last previous edition approved in as E — The information provided about varia- tions in chemical composition is strictly qualitative but the location of extremes in segregation will be shown. Chemical analyses or other means of determining the chemical compo- sition would have to be performed to determine the extent of.
It is also used in the heat-treating shop to determine location of hard or soft spots, tong marks, quenching cracks, case depth in shallow-hardening steels, case depth in carburization of dies, effectiveness of stop-off coatings in. In the machine shop, it can be used for the determination of grinding cracks in tools and dies. For an example of the use of macroetching in the steel forging industry see Method E Forging shops and foundries also use macroetching to determine the presence of internal faults.
The copper industry uses macroetching for control of surface porosity in wire bar. In the aluminum industry, macroetching is used to evaluate extrusions as well as the other products such as forgings, sheets, and so forth. United States. No further reproductions authorized. However, the sample should not be taken so early that further working can introduce serious defects.
Billets or blooms going into small sizes are sampled after initial breakdown. Sampling may be done systematically or on a random basis. The use of torch cutting or hot cutting should be used only when necessary to cut a sample from a large piece. The sample then is sectioned well away from the hot-cut surface. An example of permissible use of torch cutting is the excising of a piece from a large plate and then cutting a sample for macroetching 4 to 5 in.
Samples cut too. Disks from large blooms are sometimes cut into smaller pieces for ease in handling. In extrusions, coring and coarse grain are more commonly found in the back end of the extrusion.
An ideal length would be the circumference of the last roll, but this may be. Several samples totaling some given fraction of the circumference can be used; however, there is always a chance then that a defect arising from faulty rolls would not be detected. When seeking information on. In many cases, however, to reduce the size of the specimen, only a section out of the center of the plate may be taken.
Careful preparation is usually rewarded with highly detailed structures giving a large amount of information. Welds involving dissimilar metals will produce problems in etching. Occasionally an intermediary etchant may be required. The boundaries between etched and unetched portion will give an idea of weld penetration and dilution. In this case, other methods such as dye penetrant methods may be more desirable.
Any method. Disks may be faced on a lathe or a shaper. This will generate a smooth surface and remove cold work from prior operations. Sharp tools are necessary to produce a good specimen. Where necessary, details are given in the tabulation of procedures. Any grease, oil, or other residue. Once cleaned, care should be taken not to touch the sample surface or contaminate it in any way. In most cases a good grade of reagent should be used but need not be chemically pure or of analytical quality.
The so-called technical grades are usually satisfactory. The solution should be clean and clear, free of suspended particles, scum, and so forth.
Many of the. In all cases, the various chemicals. Etching should be done in a well-ventilated room, preferably under a fume hood. The solution should be mixed and placed in a corrosion resistant tray or dish and brought to the operating temperature. The specimen or specimens should be placed in a tray of stainless steel screen or on some non-reactive support. Glass rods often are placed on the bottom of the acid container and the specimens laid directly on the rods.
When etching is completed, remove the specimens from the dish taking great care not to touch the etched surface. When desmutting is required, dip the specimen into a second solution. After rinsing the specimen with hot water, blow dry with clean compressed air. High Si castings. High purity A1. All except high Si castings. High Cu alloys. NaOH H 2 O. Rinse in water, and remove smut in strong HNO 3 solution. Rinse and repeat etching if necessary. Rinse specimen in warm water and.
Use at room temperature. Immerse specimen at room temperature until desired contrast is developed. Rinse in warm water and dry. Same as above. May be used as an immersion etch or swabbed over.
When desired contrast is. Good general-purpose etchant, can be used on almost all aluminum alloys. Used to develop grain structure. General purpose etch for revealing microstructure of both cast and wrought aluminum.
Same as above, but slower acting. Best results are obtained with a ground surface. Saturate a large wad of cotton held in stainless steel or nickel tongs with the etchant and sweep over the surface of the specimen. An effort should be made to wet the entire surface as soon as possible. After the initial wetting, keep the swab saturated with solution and frequently sweep over the surface of the specimen to renew the solution. When the structure has been suitably developed, rinse the specimen, either with a swab saturated with water, or better still, by pouring water over the specimen.
After rinsing with hot water, blow the specimen dry with compressed air. Details of the procedure not discussed here are covered in the sections for the various metals and their alloys.
In fact, the progress of etching should be closely watched and etching stopped when the preferred structural details have been revealed. Specimens should be etched to develop structure. Generally, a light etch is better than a heavy etch; overetching can often lead to misinterpretation. The actual time to develop a structure properly may be quite different from the one suggested.
All these methods will cause cold work at the surface and will generate heat. The temperature rise can be enough to cause. For these reasons sharp tools and gener- ous lubrication are necessary for sectioning. Again sharp tools and copious lubrication. In these cases the specimen is periodically removed from the solution, cooled in running water, and reimmersed in the etchant.
This procedure is repeated until the desired degree of etching is obtained. Table 1. Warning— Before starting any work involving beryllium, a review of hazards and plans for han- dling should be made. A number of references on beryllium are available.
Standard Test Method for Macroetching Metals and Alloys
Standard Test Method f A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense. Scope 1. The SI equivalents of inch-pound units may be approximate. 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.
ASTM E340 (2015).pdf
Historical Version s - view previous versions of standard. More E Metallographic specimens and chemical analyses will provide the necessary detailed information about specific localities but they cannot give data about variation from one place to another unless an inordinate number of specimens are taken. The information provided about variations in chemical composition is strictly qualitative but the location of extremes in segregation will be shown. Chemical analyses or other means of determining the chemical composition would have to be performed to determine the extent of variation. Macroetching will also show the presence of discontinuities and voids, such as seams, laps, porosity, flakes, bursts, extrusion rupture, cracks, and so forth.