Welding repair of the bucket body and bucket teeth of the WY25 excavator

1. Bucket material and its weldability

The bucket body material of the WY25 excavator is Q345, which has good weldability. The material of the bucket teeth is ZGMn13 (high manganese steel), which presents a single-phase austenitic structure at high temperatures and has excellent toughness. Under the action of impact loads, it has high wear resistance due to the work hardening of the surface layer. However, this type of steel has poor weldability: Firstly, carbides precipitate in the heat-affected zone during welding, causing material embrittlement; The second is that hot cracks occur in the weld seam, especially liquefaction cracks in the near-seam area.

(1) The precipitation of carbides in the heat-affected zone causes embrittlement

When ZGMn13 high manganese steel is heated above 250 ℃ again, carbides may precipitate along the grain boundaries, greatly reducing the material's toughness and seriously damaging the excellent properties of high manganese steel. After analysis, when high manganese steel is reheated and cooled at a relatively fast rate, carbides first precipitate at the grain boundaries. As the residence time increases, the carbides at the grain boundaries will change from a discontinuous granular state to a network distribution, and their brittleness will increase significantly. Therefore, when high manganese steel is welded or reheated after welding, carbides will precipitate to varying degrees in a section of the heat-affected zone of the welding, and may transform into martensite. This not only makes the material brittle but also reduces its wear resistance and impact toughness. Moreover, the longer the residence time within the temperature range (around 650 ℃) where carbides are prone to precipitate in the heat-affected zone, the more carbides precipitate.

To reduce the precipitation of carbides and prevent the material from losing its toughness and becoming brittle, measures should be taken to accelerate its cooling rate, that is, to shorten the residence time at high temperatures. For this reason, short-segment welding, intermittent welding, and submerged welding should be adopted during welding.

(2) Welding hot cracks

The way to prevent the occurrence of hot cracks is to reduce the content of S and P in the base metal or welding material. Measures can also be taken from the welding process to minimize welding stress as much as possible, such as using short-segment welding, intermittent welding, decentralized welding and post-weld hammering, etc. When surfacing high manganese steel on the bucket body, a layer of Cr-Ni, Cr-Ni-Mn or Cr-Mn austenitic steel can be welded first as an isolation weld bead to prevent cracks.

2 The welding process of the bucket body and bucket teeth

(1) Pre-welding preparation

First, remove the worn bucket teeth from the bucket body. Then, use an Angle grinder to clean the area where the bucket teeth are installed thoroughly, ensuring there is no dirt or rust. Carefully inspect for any cracks or other defects. A bevel was made at the welding area of the bucket teeth by carbon arc air gouging and cleaned thoroughly with an Angle grinder.

(2) Welding

First, perform surfacing welding on the bucket body (at the junction with the bucket teeth) using GB E309-15 welding rods. Before welding, the welding rods need to be treated at 350 ℃ and 1? After 5 hours of drying, the welding current should be relatively large and the welding speed slightly slow to ensure that the nickel content in the fusion zone is 5% to 6%, preventing the formation of martensite sensitive to cracks.

② Perform positioning welding. After the bucket teeth are assembled in place, use a diameter of 3? Use a 2mm D266 electrode for symmetrical positioning welding on both sides, with the weld length not exceeding 30mm. Immediately water cool and hammer after welding.

③ Base welding. With a diameter of 3? Perform the base welding with a 2mm D266 electrode. Use small current, direct current reverse polarity, intermittent welding, and short-segment welding. Each time the welding is stopped, water cooling should be carried out promptly, and the interlayer temperature should be controlled below 50 ℃.

④ Perform filler welding. After the base welding is completed, a D266 electrode with a diameter of 4mm is used for intermittent welding. The welding current is 160A. One electrode is welded in 3 to 4 steps. Each time the welding is stopped, the weld bead must still be cooled with water to below 50 ℃ in time and hammered to eliminate stress and prevent carbide precipitation. After each two layers are welded, rotate the left and right weld seams to ensure the symmetry of the welding until the weld toe reaches 16mm. After each weld is completed, inspect the crack condition with a magnifying glass. If there are cracks, eliminate them with carbon arc air gouging before welding.

After the bucket teeth were repaired by this method, the weld seam remained in good condition after more than a year of use. This method is highly efficient, low-cost and effective in repairing bucket teeth, and has certain practical value.