Explanation

It refers to steel grades that adopt weld line energy weld with much higher weld conditions than normal, which will not significantly reduce the toughness of weld zone and will not produce weld cracks. The linear energy of weld is the energy input from outside during each weld, which is divided by the linear speed of weld. In order to improve weld efficiency, the method of reducing weld passes and increasing weld line speed is usually adopted, which makes weld line energy significantly increased. Generally, weld with input of line energy greater than 50kJ/cm is called high heat input welding. The increase of weld line energy will make the grain in the weld heat affected zone too coarse and cause obvious deterioration of performance (the loss of grain refinement effect will lead to the decrease of strength and toughness, and the increase of hardenabilhy will lead to the easy occurrence of weld cracks). In order to meet the needs of high heat input welding, steel for high heat input welding must be used to form high-temperature stable second phase particles (including TiN and oxide) in steel through micro alloying technology and oxide metallurgy technology to prevent grain growth. At the same time, the damage of these second phase particles to steel product properties and the expansion of weld hot cracks must be reduced or eliminated through intragranular ferrite technology. The thick and extra thick steel plates used in ships, oil platforms, bridges, storage tanks, offshore engineering structures, pipelines, etc. are widely used as steel for high heat input welding.

Classification