Study on the mechanical properties and defect detection of low alloy steel weldments for large cruise ships

Abstract

To study the influence of welding defects on welding quality and the detection effects of different nondestructive testing methods on welding defects in large cruise ships, tungsten inert gas welding tests were carried out on Q355 steel to prepare three types of welding specimens, including defect free, with porosity defects, and with slag inclusion. The microstructure, mechanical properties, and nondestructive testing of the three sample types were investigated. The results showed that weld zone microstructures of the three types were mostly formed of acicular ferrite, grain boundary ferrite, and pearlite, whereas heat-affected zone microstructures were primarily composed of martensite and bainite. Compared with weld without defects, the average Charpy impact toughness of welds with porosity defects in the weld and heat-affected zones decreased by 4.0 and 38.0%, respectively. The Charpy impact toughness of welds with slag defects in the weld zone was basically the same as those of welds without defects, while it increased by 5.6% in heat affected zones. The finer the grains in a weld were, the greater the microhardness. In terms of nondestructive testing, certain surface defects are related to internal defects, and they might be a symptom of internal problems in the weld.