Analysis of LePera's etching of the heat affected zone of a microalloyed steel

LePera's etching combined with optical microscopy is an effective way to distinguish various microstructures that can form in microalloyed steels, especially within the heat affected zone (HAZ) of steels that have been welded. Ferritic and bainitic constituents tend to be tinted by the etchant and show up as various shades of tan, while martensite-austenite (M-A) regions are not tinted and exhibit a white color or bright contrast. This paper reveals that LePera's etchant also provides a similar contrast effect, as that for M-A, for any cementite particles in the microstructure. In addition, it is shown that heat tinting of the steel, which is a common imaging aid after fracture toughness testing (including the crack tip opening displacement (CTOD) method), can alter the steel microstructure. These effects can be important when trying to correlate microstructure with mechanical properties.