Preheating Before Welding
Before welding ASTM A588 Corten Plate, the workpiece should be preheated to a temperature between 350°C and 400°C. Preheating helps reduce the temperature differential between the welded area and surrounding metal.
This results in more uniform cooling and contraction after welding, significantly reducing welding stress and minimizing distortion.
Heating the "Stress Relief Zone"
In welding structures made from ASTM A588 Corten Plate, selecting appropriate areas for preheating can significantly reduce welding stress. These selected heating areas are called the "stress relief zones."
For example, when welding the fracture of a frame member, heating the middle of the frame's left and right rods before welding will elongate them and cause deformation in the opposite direction of the welding seam contraction.
During cooling, both the heated area and the weld seam contract together, reducing the restraint on the weld's free contraction and lowering the welding stress.
Reverse Deformation Method
The reverse deformation method involves calculating or estimating the expected deformation size and direction of the ASTM A588 Corten Plate after welding. Before assembly, place the workpiece in the opposite direction of the expected welding deformation.
This can be done based on calculations or practical experience. Alternatively, pre-deforming the workpiece in the opposite direction to counterbalance the deformation after welding can help maintain dimensional stability.
Rigid Clamping Method
The rigid clamping method uses clamps or spot welding to restrict welding deformation. This method is effective in preventing angular distortion and the wavy deformation of thin ASTM A588 Corten Plate structures.
However, rigid clamping is suitable only for materials with good plasticity, and the workpiece should be quickly annealed after welding to relieve internal stresses.
This method should not be used on materials with poor plasticity, such as steels with high hardenability or cast iron, as it may cause cracking after welding.
Post-Welding Heat Treatment
Post-welding heat treatment, specifically stress-relief annealing, is essential to eliminate residual welding stresses. To achieve this, the workpiece is uniformly heated to 600°C - 650°C, held at this temperature for a certain period, and then slowly cooled.
High-temperature tempering is the most effective method to eliminate welding stress, typically removing 80-90% of the residual stresses in the material.