Metallographic study of the plastic zone using magnetic etching and visual observation


  1. Roy, V.
  2. Hyatt, C.V.
  3. Matthews, J.R.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN)
To understand how fracture of ductile materials occurs, it is necessary to understand how the strain field, especially the plastic zone, develops around the crack as it advances by blunting and tearing. This has been examined in a number of ways experimentally and by calculation. Lacking however, has been a technique, which is highly sensitive to plastic strain in metals, which can also be easily applied to a large area. This paper describes the first stage of a program to overcome this difficulty. Briefly, it involves the magnetic etching of sections through cracked samples. Stainless steel AISI 304 is classified as an austenitic stainless steel grade because in its annealed state at room temperature its microstructure is entirely austenite. It is in fact a metastable austenitic stainless steel. Cooling to cryogenic temperatures or cold working can cause some transformation to beta-martensite. In contrast to the austenitic phase, the beta-martensite is magnetic. This fact has allowed percent cold work on a macroscopic scale to be assessed non-destructively and on a microscopic scale, the local plastic strain to be estimated with confidence. There are some important problems with this approach, notably that the transformation from which strain data is obtained is dependent on temperature, strain rate and composition. TRUNCATED
Magnetic etching;Stretch Zone Width;Plastic zone around the crack tip;Stretch zones
Report Number
DREA-TN-2001-096 — Technical Note
Date of publication
01 Jul 2001
Number of Pages
Hardcopy;Document Image stored on Optical Disk

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