Microstructure And Properties of High-speed Laser Cladding Ni60 Coating On Surface of High Manganese Steel

Under the impact load, high manganese steel will produce a large number of dislocation plugging near the surface, resulting in significant work hardening, while the interior maintains a certain toughness, so it has good surface wear resistance and overall toughness, and is widely used in the crushing hammer processing and manufacturing of mining machinery, with irreplaceable role. In the long working process, due to the corrosion and impact of water, ore, etc., the hammer head is easy to produce one side of the wear, the formation of the size is out of whack, and the need to stop for replacement or repair affects the production efficiency. Due to the high carbon equivalent of high manganese steel, the weldability is poor, especially
In the welding process, cracks are easily caused near the fusion line of the heat affected zone due to carbide precipitation, which makes it difficult to repair high-manganese steel by traditional surfacing welding methods, and it is necessary to use small heat input, forced cooling, secondary water toughen and other methods to repair the surfacing welding, which is difficult and requires high technical requirements for repair personnel. It can also use stainless steel electrode arc welding as the bottom and surfacing welding electrode cover, but the production efficiency is low and the subsequent machining workload is large, which improves the repair cost of parts and reduces the production efficiency of enterprises.

The main feature of high-speed laser cladding technology is that by changing the position of the laser beam and the metal powder, the powder can be melted in the flight space, and only a small solution pool is formed on the surface of the matrix. The heat input of the cladding process is further reduced on the premise of ensuring metallurgical bonding. At the same time, the thickness of cladding layer is controllable. Dilution rate is less than 1%. Low surface roughness. It can greatly reduce the machining amount of the parts after cladding, and provide a new idea and a new method for the repair of high manganese steel.

In this paper, ZGMn13, a material used for the hammer head of a mine crusher, is taken as an example. High speed laser cladding system was used to cladding Ni60 powder on its surface, and the optimal process parameters were obtained by orthogonal test and range analysis. It can provide some technical parameters basis for mining enterprises to use high speed laser cladding technology to repair high manganese steel.

1. Specimen preparation

The test material was ZGMn13 steel plate after water toughening treatment, and the chemical composition was shown in Table 1. The steel plate is processed into 200 mm × 100 mm × 10 mm sample by milling machine. The upper and lower surfaces of the sample are processed by grinding machine to Ra1.6, and the remaining four surfaces are not required for roughness. The upper surface of the sample to be melted was wiped with acetone and ethanol respectively for degreasing and drying. Ni60 self-fusible alloy powder of 45 ~ 106 μm is selected for cladding layer, and its chemical composition is shown in Table 1. Before cladding, the powder should be sent to the drying box and dried at 150 ℃ for 1 h to remove the moisture contained in the powder, prevent powder clusters, and ensure the uniform continuity of powder delivery during the cladding process.

                                                            Table 1 Chemical composition of ZGMn13 and Ni60 powder (mass fraction, %)

2. Test method

High-speed laser cladding equipment was used to prepare the cladding sample. Ni60 coatings with an area of 40 mm × 10 mm and a thickness of 1.5 ~ 2.0 mm were prepared by six single-layer processes. In order to avoid cracks and excessive internal stress in the process of cladding, the sample was pre-heated before cladding, preheated and held at 150 ℃ for 1 h, and the cladding test was carried out immediately after the preheating according to the test parameters in Table 2. The laser spot diameter is 1.5 mm, the bonding rate is 60%, and the defocusing capacity is 15 mm. Argon gas is used as the powder feeding and protecting gas.

                                                                                           Table 2 Laser cladding test parameters

1. The color penetration test shows that the surface forming quality of the cladding layer is better and there are no defects such as cracks and pores when the high-speed laser cladding test is carried out after holding at 150 ℃ for 1h.

2. The range analysis of orthogonal test and the test results of cladding samples show that the best process parameters of cladding Ni60 powder on ZGMn13 material are laser power 1 200 W, scanning speed 4 mm/s and powder feeding rate 7.5 g/min. Under such conditions, the hardness can reach 811.41 HV. It is about 2.8 times that of the base material, and the friction coefficient is 0.367, which is reduced by 37.7% compared with the base material, the wear resistance is increased by 1.6 times, and the wear amount is about 38% of the base material.

3. Through OM, XRD and BSE analysis, it can be seen that the cladding layer is mainly composed of γ-Ni dendrites, dendritic dendrites, floral hard boride phases CrB and gray hard carbide phases Cr7C3 and Cr23C6. The above hard phase improves the wear resistance of the cladding layer.