Preparation before welding of cast steel components for railway vehicles

Before welding and repairing cast steel components, necessary pre welding preparations should be carried out. Firstly, it is necessary to determine whether welding repair grooves are needed based on the defect properties of the cast steel components that need to be welded. When necessary, the shape of the grooves should be determined based on factors such as the defect size, position, depth, cross-sectional thickness, and welding repair operation conditions of the components. The groove preparation should be carried out according to the specified method.

There are various methods for removing defects and preparing grooves. Common groove processing methods include mechanical machining such as drilling and milling, as well as pneumatic shovel cutting and polishing; Thermal cutting methods can also be used, such as oxygen cutting (neutral flame, flame core not less than 10mm from the surface of the casting), carbon arc gouging (only applicable to ZG230-450 and B-grade steel). If thermal cutting methods such as flame cutting and arc gouging are used to prepare the groove, the decarburization or carburization layer on the surface of the groove must also be removed after the groove is prepared to prevent the increase or decrease of carbon element at the groove interface from affecting the mechanical properties of the welding repair area.

For the crack defects of cast steel components, it is necessary to first determine the starting end of the crack through certain methods. If necessary, it is necessary to drill a crack stop hole at the starting end of the crack, and then thoroughly remove the crack defects according to the above requirements to prevent the continued expansion and extension of the crack.

The processing of the groove surface should be based on exposing the metallic luster of the cast steel base material, and the transition between the bottom of the groove and the side wall must be through an arc with a radius of not less than 5mm, without sharp corners. The 20mm range around the groove should also be cleaned to remove clean water, oil stains, rust, and other debris.

Before welding repair, the defective parts need to be visually inspected and confirmed again. For the preparation of crack grooves with a defect length greater than 50mm, non-destructive testing methods such as MT magnetic powder or PT penetration need to be used for inspection. Only after confirming that the crack defects are completely removed can welding repair operations be carried out.

When repairing a single sided groove that runs through, a backing can be added to the back of the groove or a sealing weld can be performed, but the backing used should be kept smooth and clean. If a steel lining is used, the chemical composition of the steel lining used should be the same or similar to that of the cast steel components to be welded and repaired; When using non-metallic gaskets, ensure that the gaskets are not flammable. The gasket after welding should be removed.

For thick sections with through defects, double-sided grooves should be opened, and a gap of no less than 3mm should be left at the root of the weld seam to ensure full penetration during welding repair. For the welding repair of double-sided grooves, before welding the reverse groove, the root of the front groove should be cleaned first to ensure that defects such as incomplete penetration, welding slag, and welding overlap at the root of the front groove are completely removed before welding the reverse groove.