Effects of the hottest alloying elements and their

Effect of alloy elements and their content on the properties of laser cladding layer of iron-based alloy

laser cladding (also known as laser surfacing) refers to the process of placing selected coating materials on the clad substrate by different addition methods, melting them with the substrate surface after laser irradiation, and forming a low dilution surface coating combined with the substrate by rapid solidification. Compared with traditional surface treatment technologies, such as electroplating and thermal spray welding, laser cladding technology has the advantages of fine grains, small heat affected zone and thermal deformation zone. In the literature, the author studied the influence of carbon content on the properties of Fe based alloy laser surfacing layer, and obtained a high hardness and crack free cladding layer. Because alloy elements also play an important role in the properties of steel materials, the influence of alloy elements on the properties of laser cladding layers of iron-based alloys is further studied in this paper, in order to obtain cladding layers with different properties (such as different hardness) to meet different production needs

1 test materials and methods

laser cladding test adopts rofin tr050 fast axial flow CO2 laser manufactured by German rofin company. During the experiment, the laser power was 3.5kw and the laser beam wavelength was 10.6 μ m; The spot diameter was measured by ablation method, and the spot diameter was 4mm during the test by adjusting the defocusing amount; Single layer preset laser cladding is adopted, and the preset powder thickness is 1.5mm; The laser scanning rate is 6mm/s, and the scanning length is 30mm; AR is used as the shielding gas, which is mainly used to prevent the oxidation of alloy powder during the cladding process. The flow rate of AR is 3.6l/min. The base material is A3 steel, with a size of 100mmx40mmx5mm. The surface is pickled to remove rust, cleaned with acetone, and then dried for standby. The alloy powder fe202 with good performance was used as the basic alloy in the experiment. The powder is a self-made fe-ni-cr-b-si-c alloy with 150~200 mesh. The chemical composition (mass fraction,%) is 92.7fe, 3Ni, 2Cr, 1b, 1si, 0.3C. The results of laser cladding test show that using fe202 alloy powder as cladding powder, a high hardness and crack free Fe based laser cladding layer can be obtained. Different contents of Ni, Cr and mo were added to fe202 to study the influence of various alloy elements and their contents (mass fraction) on the properties of the cladding layer

in order to make the added pure alloy elements can be evenly mixed with the original alloy powder and achieve a certain degree of alloying, the mixed alloy powder is first mixed through a mechanical ball mill. The treatment process is: ball milling time is 10h, grinding ball is Φ For the cemented carbide ball of about 10mm, the mass ratio of grinding ball to alloy powder is 5:1, and the diluent during ball milling is an appropriate amount of anhydrous alcohol. After ball milling, the powder is dried at 100 ℃ for 2h, and then sieved for use

use Rockwell hardness tester to detect the surface hardness of various alloy cladding layers; There is only such amount of residual austenite (AR) in each cladding layer measured by X-ray diffraction; The number and length of cracks are observed and measured by a stereomicroscope with a magnification of 10 times; Cracking sensitivity of cladding α It is obtained by measuring the crack length per unit area, α= Σ li/a, Li is the length of the ith crack (mm), and a is the area of the cladding layer (cm2)

2 test results and analysis

2.1 the influence of alloy elements and content on the hardness of cladding layer

the influence of alloy elements and content on the surface hardness of cladding layer is shown in Figure 1. It can be seen that Ni can reduce the hardness of the cladding layer. With the increase of Ni content, the hardness of the cladding layer begins to decline steadily; When the Ni content exceeds 7%, the hardness of the cladding layer decreases sharply; A small amount of Cr can slightly increase the hardness of the cladding layer, but when the Cr content exceeds 4.6%, the hardness of the h+ cladding layer decreases slightly. When the Cr content further increases, the hardness of the cladding layer decreases significantly, but the decrease range is not as large as that of Ni; With the increase of Mo content, the hardness of the cladding layer increases, but when the Mo content exceeds 5.75, the hardness of the cladding layer decreases. When the Mo content further increases, the hardness of the cladding layer does not change significantly. The influence of alloy elements on the hardness of the cladding layer is mainly caused by the change of AR amount in the cladding layer. Due to the low ar hardness, if the AR in the cladding layer increases more, the hardness of the cladding layer will decrease. The influence of the change of alloy elements on the AR amount (volume fraction) of the cladding layer is shown in Figure 2 (measured)

2.2 effect of alloy elements and content on cracking sensitivity of cladding layer

the effect of alloy elements on cracking sensitivity of cladding layer is shown in Figure 3. Since the cladding layer prepared with fe202 alloy powder has no cracks, it can be seen that (1) no matter how much Ni element is added, the cladding layer cannot produce cracks. Because Ni element can increase the amount of AR in the cladding layer, it should reduce the cracking sensitivity of the cladding layer. Song Wulin's research also marked this point. Although in this test, because the sample size is relatively small, and the cladding layer without Ni element has no cracks, it does not reflect the effective role of Ni element, but if the cladding conditions are worse, such as the cooling rate of the cladding layer is higher or the surrounding restraint stress is more complex, this role of Ni element should be reflected. (2) With the increase of Cr content, the cracking sensitivity of the cladding layer increases, but when the Cr content reaches or exceeds 9.8%, the cracking sensitivity of the cladding layer is reduced due to the sharp increase of AR content, and the cladding layer does not produce cracks

2.3 effect of alloy elements and content on AR content of cladding layer

ar existence and content undoubtedly play an important role in the hardness and cracking sensitivity of cladding layer. It can be seen from the figure (1) with the increase of Ni content, the amount of AR in the cladding layer increases, almost in a positive proportion; (2) With the increase of Cr content, the amount of AR in the cladding layer increased slowly at first, and then increased rapidly after 20 ° angle deflection axial tensile test; (3) With the increase of Mo content, the amount of AR in the cladding layer increases slowly. The amount of AR in the cladding layer increases with the increase of Ni, Cr and Mo content, because these alloy elements reduce the martensitic transformation end temperature MF, and the level of MF point determines the amount of AR when the steel is quenched to room temperature

3 conclusion

with the increase of Ni content, the amount of AR in the cladding layer increases, the hardness decreases, and the cracking sensitivity remains unchanged; With the increase of Cr content, the amount of AR in the cladding layer increases, and the hardness first increases slightly, and then decreases. The cracking sensitivity of the cladding layer first increases, and then decreases. With the increase of Mo content, the amount of AR in the cladding layer slowly increases, and the hardness of the cladding layer first increases, then decreases, and then basically remains unchanged. The cracking sensitivity of the cladding layer continues to increase. (end)