ASTM A 561 Standard Practice for Macroetch Testing of Tool Steel Bars

Scope:

This standard practice is used as a quality control and inspection test carried out by deep acid etching the microstructure of the specimen to reveal cuts from the bars. Also, to show the presence of such conditions as cracks, porosity, segregation and foreign material. The etched surface is examined by magnification. 

Test procedure:

In this practice, the detailed procedure to micro etch the tool steel bars is given, in this initially the micro etching temperature is maintained at 71ºC. at this temperature the etching reaction is vigorous and solution loss is negligible. Temperature control is an important factor to get the desired output from the test. Then etching time is also an important factor. Etching is not done below 10min or over 40min. As the specimen and conditions got ready the specimen is cleaned with solvent to remove dirt and grease. The specimen is placed in an etching solution that was already heated. Ensured that the specimen is properly immersed. The etching solution is moderately agitated to promote uniform development by eliminating temperature and composition gradients. at the end removed the specimen and rinse with water and flushed off the sludge which formed during the test. Then the specimen is dried with alcohol and a clean air blast.

Video 01:macroetching

Test Specimen:

Specimens are usually cut from hot-rolled annealed bars but may be cut from machined or ground bars if the bars are to be finished machined or ground. For ease in handling, use specimens 1⁄4 to 1⁄2 inch thick. The specimen is cut to expose the transverse section of bars.

Data:

The specimen is examined etched surface visually or at up to 10X magnification to determine its structure.  Noted the following condition in the specimen

• Internal

Pipe, Bursts, Carbide or alloy segregation, Concentrations of nonmetallic inclusions, Porosity, and Internal cracks or thermal flakes

• Surface and Subsurface

Seams, laps, cracks, Ingot corner segregation or cracks, Pinholes, Miscellaneous, Entrapped metallic or nonmetallic material and Ingot pattern (dendritic segregation, columnar grain structure, etc.).

Conclusion:  

ASTM A 561 gives guidelines for macro etch testing of steel tool bars. This test method gives photographs of the condition but that can not be used as a standard for rejection or acceptance.