Cooling Rate Effects in the Welding of API 5L-X80 Steel

One of the main reasons for the development of the API 5L-X80 steel was its utilization in Polar Areas where a relatively high toughness in low temperatures is needed. The present work aimed at studying the welding cooling rate effects on the mechanical and metallurgical properties of this type of steel. These various cooling rates also simulate various heat input's. These different cooling rates were obtained through five distinct pre-heatings. The interpass temperature was the same of the pre-heating temperature presented by each one of the double V joints with root face; being the robotics weldings itself performed through gas metal arc welding (GMAW), using solid wire with matching mechanical resistance, and as a shielding gas a mixture of 75% Ar and 25% CO2. In order to analyze the welded joints, light microscope and scanning electron microscope (SEM) were utilized, as well as mechanical tests, such as tension, bending, impact (Charpy-V) and hardness (Vickers). The results of such mechanical tests were satisfactory and suitable correlated with the metallurgical analyses. The joint presented a high Charpy-V impact resistance in testing temperatures up to -40 degrees C.