Welding Techniques for Low Alloy High Strength Steel
Low Alloy High Strength Steel (LAHSS) is becoming increasingly popular in the fabrication of components and structures due to its low cost, high strength and excellent weldability. As with any material, however, there are some challenges in welding LAHSS that require careful consideration in order to ensure a successful weld.
One of the most important considerations when welding LAHSS is preheating. Preheating the steel helps to reduce the risk of cracking by eliminating or reducing the thermal and mechanical stresses created during welding. Depending on the alloy and thickness of the steel, preheating temperatures between 150 - 250 °C (300 - 500 °F) are recommended. It is important to note that preheating temperatures should not exceed the tempering temperature for that material as this may reduce the strength of the weld joint.
Another important factor to consider when welding LAHSS is suitable filler metals. Filler metals should match the composition of the base metal in order to ensure adequate fusion and strength. The material specification for the LAHSS and the correct type of electrodes should be determined prior to welding in order to select the appropriate filler materials.
In order to control the heat input and keep distortion and residual stresses to a minimum, a careful selection of welding parameters is also required when welding LAHSS. Generally, the welding speed should be kept as low as possible while still providing sufficient heat input to ensure complete fusion. It is important to avoid excessive amounts of heat input as this may affect the microstructure of the steel and result in a loss of ductility.
It is also important to ensure that adequate preparation of the joint surfaces is undertaken prior to welding. Grinding or machining of the joint surface should be used to ensure its cleanliness and a smooth, uniform surface.
Finally, a post weld heat treatment (PWHT) can be used to relieve any residual stresses remaining in the welded joint and further improve its strength. Depending on the type and thickness of the steel, PWHTs at temperatures of between 400°C-850°C (750°F-1560°F) can be used.
In conclusion, proper techniques and considerations should be taken when welding LAHSS in order to ensure a successful weld. Preheating, the selection of suitable filler metals, welding parameters and preparation of the joint surfaces all contribute to the success of the weld. Furthermore, post weld heat treatment can further reduce residual stresses and enhance the strength of the joint.
