Optical observation of real materials using laser scanning confocal microscopy Part 1 – techniques and observed examples of microstructural changes

Abstract

Owing to the good thermal response of an infrared image furnace, the thermal cycle of welds (weld metal or heat affected zone) can be reproduced, while a laser scanning confocal microscope has a suitable light source and optical geometry for observing metal irradiated at high temperatures. The combination of an infrared image furnace and a laser scanning confocal microscope provides a useful tool for determining the microstructural changes in metals at the micrometre scale during the thermal cycle of welding. The technique of using such a combined system is called high temperature laser scanning confocal microscopy. Both macro‐ and microviews expand the understanding of the microstructural formation of welds and are useful in developing microstructure control methods. This is the first part of a report on the application of laser scanning confocal microscopy to observe microstructural changes for various types of steel samples and thermal cycles. The micro‐ or macroviews of different microstructural formations are presented, including the solidification cell, austenite from δ‐ferrite, pearlite, martensite, Widmanstätten ferrite and bainite.