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Bead on Plate Temper Pass Study: Thermal and Microhardness Study

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Technical Report

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Defence R and D Canada - Atlantic Dartmouth, Nova Scotia Canada

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During multiple pass welding, subsequent welding passes provide the heat required to effectively temper underlying welds and their heat affected zones. In low alloy quenched and tempered steels, high cooling rates associated with the welding thermal cycle lead to high hardness phases such as martensite in the heat affected zone. This study measures the cause cooling rate, and effect hardness associated shielded manual arc weld beads deposited on alow alloy quenched and tempered steel. The welds were deposited on a fully instrumented panel which had a series of thermocouples positioned along the weld path and were used to validate analytical peak temperature and cooling rate expressions. Following welding, metallurgical analyses including micro-hardness maps revealed the microstructural evolution during subsequent welding passes. The hardness and metallurgical survey indicated that tempering is most effective for locations which have a peak temperature less than the lower critical AC1 below which the ferrite to austenite transformation is suppressed and is located adjacent to the visible heat affected zone. This knowledge can be used to develop effective weld tempering strategies required to reduce the prevalence of hard i.e. brittle microstructural phases.


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