Assume there was a carbon steel part that was normalized a year ago. If we want to determine the prior austenite grain size of the part, we follow ASTM E112. Lets say we carburized it, cooled it slowly, and etched it to reveal the p.a.g. boundaries.
Does this mean we are determining what the size of the austenite grains was during normalizing a year ago or during our carburizing HT?
Let me generalise, the methods for prior austenite determinatio, and this one, are aimed at measuring the 'prior' austenite grain size, I.e. That which existed previously during the prior austentenitising treatment. In essence we 'decorate' in some way those 'old' boundaries. On re-transformation (on cooling) back to some mixture of ferrite and cementite, hopefully that decorated network remains which one can measure by standard quantitative metallography techniques. These second excursions above the eutectoid temperature are hopefully brief enough that the 'action' occurs only at the old austenite boundaries.
So the brief answer is it is the former austenite grain size. Hopefully, I have conveyed the basic principle behind these methods. Other methods may use the fact of tramp element segregation to the austenite grain boundaries during the heat treatment cycle.
Thank you for the response John.
I understand we are looking at the prior-austenite grain boundaries, but which 'prior-austenite grain boundaries' are we looking at? The grain boundaries of the austenite from the normalizing or from the carburizing?
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Metals
- Alloys
- Steel