The present invention relates to the field of laser additive repair technology, and specifically to a laser cladding material and a laser cladding method for strengthening a shield machine cutter.

Shield machines are widely used in the construction of various tunnel projects. The shield machine cutter directly acts on the excavation surface. Because of its harsh working environment, unstable load, and large impact load, it is one of the most easily damaged parts during the excavation process. When working on a complex rock surface, in order to ensure the station target of rock breaking, the mechanical thrust is increased, and the wear of the cutter is very serious. At the same time, due to the complexity of the shield machine working environment, the impact toughness of the cutter is also considered. The mechanical properties of the existing cutter have reached a peak value and are difficult to improve further. According to the friction and wear theory analysis, the increase in hardness will improve the wear resistance of the cutter. At present, the main tool modification method is to apply a wear-resistant coating.

As an emerging strengthening technology with high degree of freedom, laser cladding technology can be used for parts strengthening, parts repair and remanufacturing, etc. The combination of rapid heating and rapid cooling can effectively help refine the organization and improve the strengthening effect; the coating dilution rate is low, which further ensures that the coating performance is consistent with the original design intention; the cladding coating is easy to achieve metallurgical bonding, ensuring the reliability of the tool in future operations; hard wear-resistant particles improve hardness and wear resistance, while controlling the proportion of tough bonding phase to improve toughness and avoid brittleness. However, the laser cladding process is restricted by the performance of composite powder materials, and the cladding layer is prone to defects such as cracks and inclusions, which limits the use of laser cladding in the field of shield machine cutter strengthening. Combined with the theoretical support of the cutter rock breaking mechanism, rock parameters, and existing wear-resistant cladding layer research, the specific requirements of the shield machine cutter for strength, toughness and wear resistance are analyzed. Since the shield machine hob has strict requirements on toughness and wear resistance, it is necessary to use a laser cladding layer material with a dual mechanism of tough bonding phase and hard wear-resistant particles. However, as the mass proportion of hard wear-resistant particles increases, the factors affecting the performance of the cladding layer become complicated, and local stress concentration and crack sources increase.

In summary, under the premise of ensuring good bonding performance and excellent post-processing performance of the hob cladding layer, obtaining a strong and tough alloy coating that can meet the use of the shield machine is an urgent problem to be solved. In view of this, the present invention is specially proposed.

In order to solve the above-mentioned problems, the present invention provides a laser cladding material and a laser cladding method for strengthening the shield machine hob to solve the above-mentioned problems. The core of the present invention is: by mixing large-grained spherical tungsten carbide (diameter 50μm-100μm) and small-grained spherical tungsten carbide (diameter 20μm-45μm) with iron-based alloy powder and then cladding on the surface of the hob, by controlling the total tungsten carbide (WC) ratio and adjusting the ratio of large and small particles, the advantages of each particle size range of spherical tungsten carbide are maximized, and the mechanical properties of the cladding layer are comprehensively improved. WC particles have high hardness and wear resistance. As a hard phase in the composite coating, its own high hardness (over 2000HV0.3) performance and the shielding effect it brings can effectively strengthen the cladding layer. However, when the mass proportion of tungsten carbide in the iron-based cladding layer exceeds 50%, the crack sensitivity surges. Therefore, in order to meet the use requirements of the shield machine hob, the mass proportion of tungsten carbide needs to be controlled. The material matrix adopts high-strength iron-based alloy powder to obtain a laser cladding hob strengthening material that saves cobalt/nickel materials.

In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme:

A laser cladding material for strengthening the hob of a shield machine, comprising a base layer and a wear-resistant layer clad on the base layer; the base layer is clad by iron-based tungsten carbide composite alloy powder I, the iron-based tungsten carbide composite alloy powder I comprises spherical tungsten carbide I and iron-based alloy powder I, the mass percentage of the spherical tungsten carbide I is 25%-35%, the mass percentage of the iron-based alloy powder I is 65%-75%, the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide in the spherical tungsten carbide I is 3.5:1-2.5:1, the iron-based alloy powder I comprises C, Si, Cr, Ni, Mo, Mn, Fe, the mass percentage of C is 0.07%-0.13%, the mass percentage of Si is: 1.2%-2%, the mass percentage of Cr is: 21%-28%, the mass percentage of Ni is: 12%-20%, the mass percentage of Mo is: 0 .7%-1.3%, the mass percentage of Mn is: 0.7%-1.3%, and the balance is Fe;

The wear-resistant layer is formed by cladding of iron-based tungsten carbide composite alloy powder II, the iron-based tungsten carbide composite alloy powder II contains spherical tungsten carbide II and iron-based alloy powder II, the mass percentage of spherical tungsten carbide II is 35%-45%, the mass percentage of iron-based alloy powder I is 55%-65%, the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide in the spherical tungsten carbide II is 1:1-1.4:1, the iron-based alloy powder II contains C, Si, Cr, Ni, Mo, Mn, Fe, the mass percentage of C is 0.07%-0.13%, the mass percentage of Si is: 1.2%-2%, the mass percentage of Cr is: 21%-28%, the mass percentage of Ni is: 12%-20%, the mass percentage of Mo is: 0.7%-1 .3%, the mass percentage of Mn is: 0.7%-1.3%, and the balance is Fe.

Further, the mass percentage of the spherical tungsten carbide I is 30%, the mass percentage of the iron-based alloy powder I is 70%, the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide in the spherical tungsten carbide I is 3:1, the mass percentage of C in the iron-based alloy powder I is: 0.1%, the mass percentage of Si is: 1.6%, the mass percentage of Cr is: 23%, the mass percentage of Ni is: 14%, the mass percentage of Mo is: 1%, the mass percentage of Mn is: 1%, and the balance is Fe.

Further, the mass percentage of the spherical tungsten carbide II is 40%, the mass percentage of the iron-based alloy powder II is 60%, the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide in the spherical tungsten carbide II is 55:45, the mass percentage of C in the iron-based alloy powder II is: 0.1%, the mass percentage of Si is: 1.6%, the mass percentage of Cr is: 23%, the mass percentage of Ni is: 14%, the mass percentage of Mo is: 1%, the mass percentage of Mn is: 1%, and the remainder is Fe.

Further, the large-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 50μm-100μm, and the small-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 20μm-45μm. The present invention also provides a laser cladding method for the laser cladding material as described above, firstly using iron-based tungsten carbide composite alloy powder I as a base layer to be clad on the surface of the shield machine hob, and then cladding iron-based tungsten carbide composite alloy powder II on the upper surface of the base layer as a wear-resistant layer.

Further, the method specifically includes the following steps:

Step 1, substrate pretreatment
Use an angle grinder to remove oxides on the substrate surface, use sandpaper to grind the surface to be clad until the area to be clad is smooth, and then use acetone to clean and dry it to remove surface oil and residual dirt;

Step 2, powder pretreatment
The iron-based tungsten carbide composite alloy powder I and the iron-based tungsten carbide composite alloy powder II are placed in a vacuum drying oven for heat preservation and drying respectively;

Step 3, laser cladding base layer
The powder feeding adopts a coaxial powder feeding method of a double-barrel powder feeder, and the dried iron-based tungsten carbide composite alloy powder I and the iron-based tungsten carbide composite alloy powder II are placed in different powder feeding barrels of the powder feeder respectively, and the powder spot is adjusted to converge at the laser spot position;
A high-power semiconductor laser is used, and the mechanical arm and the tilting positioner are used to coordinately adjust the relative position of the laser and the hob and realize the rotation of the hob, adjust the laser mode and focal length, and clad two layers of iron-based tungsten carbide composite alloy powder I on the surface of the hob under a good argon protective atmosphere to prepare a laser cladding base layer;

Step 4, laser cladding wear-resistant layer
The surface of the base layer is polished and flattened, and the surface foreign matter is removed. After the treatment is completed, a layer of cladding layer is prepared on the upper part of the base layer using the iron-based tungsten carbide composite alloy powder II.

Furthermore, the substrate in step 1 is H13 steel.
Further, the laser cladding process parameters in step 3 are: laser cladding power is 1400W, spot diameter is 4mm, scanning speed is 600mm/min, overlap rate is 40%, powder feeding speed is 10.8g/min, shielding gas: argon, powder feeding gas: argon, shielding gas flow rate is 12L/min, and the base layer thickness is prepared to be 1mm.
Further, the laser cladding process parameters in step 4 are: laser cladding power is 1400W, spot diameter is 4mm, scanning speed is 420mm/min, overlap rate is 40%, powder feeding speed is 10.8g/min, shielding gas: argon, powder feeding gas: argon, shielding gas flow rate is 12L/min, and the wear-resistant layer is prepared to be 1mm.

The beneficial effects of the present invention are as follows:
The present invention provides a laser cladding material and a laser cladding method for strengthening the hob cutter of a shield machine. The iron-based alloy is a bonding phase with good crack resistance and excellent wettability of the cutter ring substrate. Compared with the bonding phases of nickel-based alloys and cobalt-based alloys, it is a highly cost-effective choice. At the same time, due to its strong ability to hold the bonding phase, it can be better synergistically strengthened with tungsten carbide particles. Spherical tungsten carbide is selected to reduce the corner stress caused by the shape of tungsten carbide. Tungsten carbide particles with a diameter of 20μm-45μm are small in size, have a large interface area with the metal matrix, enhance the interface effect, and are evenly distributed. Tungsten carbide particles with a diameter of 50μm-100μm can provide better strengthening effects and increase the bearing capacity of the cladding layer.

First, when a high mass fraction of 50μm-100μm tungsten carbide powder is mixed with a smaller mass fraction of 20μm-45μm tungsten carbide powder, the good toughness of the matrix alloy can be maintained to a certain extent, while the strength and hardness will still be improved. Since the agglomeration of 50μm-100μm tungsten carbide powder in the laser cladding layer is lower than that of 20μm-45μm tungsten carbide powder, it is different from the obvious local hardening phenomenon caused by using large-grained tungsten carbide powder alone to prepare the laser cladding layer. The combination with a small amount of small-grained 20μm-45μm tungsten carbide powder can better fill the gaps and promote the uniformity of the quality of the mixture. Therefore, the iron-based tungsten carbide composite alloy powder I is suitable for preparing the base layer that plays a toughening role in the composite laser cladding coating.

Secondly, when 50μm-100μm tungsten carbide powder and 20μm-45μm tungsten carbide powder of similar proportions are mixed, a higher average hardness will appear, and a higher strength performance will also be obtained, which can significantly improve the wear resistance of the shield machine cutter ring. Based on this performance characteristic, the iron-based tungsten carbide composite alloy powder II is suitable for preparing the wear-resistant layer of the surface layer of the composite laser cladding coating.

In order to more clearly illustrate the specific implementation scheme of the method of the present invention, the specific implementation scheme will be introduced in conjunction with the accompanying drawings.
Figure 1 is a scanning electron microscope image of the selected alloy powder: (a) is the macroscopic morphology of the iron-based alloy powder; (b) is the macroscopic morphology of mixed-size tungsten carbide particles; (c) is the macroscopic morphology of 20-45μm tungsten carbide particles; (d) is the macroscopic morphology of 50-150μm tungsten carbide particles;

Figure 2 is a metallographic image of the iron-based tungsten carbide composite alloy powder laser cladding layer;

Figure 3 is a scanning electron microscope image of the iron-based tungsten carbide composite cladding layer;

Figure 4 is a schematic diagram of the hardness test results of the iron-based tungsten carbide composite alloy powder laser cladding layer;

Figure 5 is a knife ring cladding flow chart;

Figure 6 is a schematic diagram of the knife ring cladding device.

In the figure: 1 is a 6KW flexible laser processing system, 2 is a shield machine hob, and 3 is a positioner.

Specific implementation method
The present invention is further described below through specific embodiments, but the protection scope of the present invention is not limited to this.
In the following examples, the iron-based alloy powders are all prepared by the same atomization method and sieved to obtain 50-100μm particle size powders. The powder morphology is shown in Figure 1(a). The tungsten carbide in the following examples is all spherical cast tungsten carbide, as shown in Figure 1(b); the small-particle spherical tungsten carbide has a particle size of 20μm-45μm, as shown in Figure 1(c); the large-particle tungsten carbide powder has a particle size of 50μm-100μm, as shown in Figure 1(d). The iron-based alloy powder and tungsten carbide are mixed by vacuum ball milling.

Example 1
The laser cladding material in this embodiment includes a base layer and a wear-resistant layer clad on the base layer. The base layer is clad by iron-based tungsten carbide composite alloy powder I. The iron-based tungsten carbide composite alloy powder I includes spherical tungsten carbide I and iron-based alloy powder I. Spherical tungsten carbide I accounts for 30%, iron-based alloy powder I accounts for 70%, and the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide in spherical tungsten carbide I is 3:1;
The wear-resistant layer is clad by iron-based tungsten carbide composite alloy powder II. The iron-based tungsten carbide composite alloy powder II includes spherical tungsten carbide II and iron-based alloy powder II. Spherical tungsten carbide II accounts for 40%, iron-based alloy powder II accounts for 60%, and the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide is 55:45.
The above-mentioned iron-based alloy powder I and iron-based alloy powder II use the same iron-based alloy powder, and the composition mass percentage is C: 0.1%, Si: 1.6%, Cr: 23%, Ni: 12%, Mo: 1%, Mn: 1%, and the balance is Fe.
The above-mentioned large-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 50μm-100μm, and the small-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 20μm-45μm.
The single-pass laser cladding strengthening test was carried out on the shield machine hob substrate material, and the specific operation method is as follows:
Cladding substrate pretreatment: The hob cutter ring is used as the cladding substrate, and the specific material is H13 steel. Referring to Figure 6, the cutter ring is clamped on the positioner, and the surface oxide is removed by an angle grinder. The surface to be clad is polished with 80 mesh, 240 mesh, and 500 mesh sandpaper successively, and then cleaned and dried with acetone to remove residual oil and residual rust on the surface.
Cladding powder pretreatment: Place the iron-based tungsten carbide composite alloy powder I and iron-based tungsten carbide composite alloy powder II in a vacuum drying oven at 130°C for 2 hours. The powder is fed by a coaxial powder feeding method of a double-barrel powder feeder. The dried iron-based tungsten carbide composite alloy powder I and iron-based tungsten carbide composite alloy powder II are placed in different powder feeding barrels of the powder feeder, and the powder spots are adjusted to converge at the laser spot position.
Base layer cladding process: Adjust the positioner speed so that the outer peripheral rotation speed of the hob is equal to 600mm/s, the powder feeding speed is 10.8g/min, the laser power is 1400W, the base layer thickness is prepared to be about 1mm, the protective gas is argon, the powder feeding gas is argon, and the protective gas flow rate is 12L/min. Re-adjust the focal length after each cladding layer to keep the light powder spots converged. Cladding two layers of base layer.
Wear-resistant layer cladding process: The surface of the base layer is polished and flattened, and foreign matter on the surface is removed; after the treatment, the wear-resistant layer is prepared. Two layers of cladding layers are prepared on the upper part of the base layer using iron-based tungsten carbide composite alloy powder II. The positioner speed is adjusted so that the outer peripheral rotation speed of the hob is equal to 600mm/s, the powder feeding speed is 10.8g/min, the laser power is 1400W, and the wear-resistant layer is prepared. The thickness of the wear-resistant layer is prepared to be about 1mm.
Post-processing: The cladding layer after cladding is subjected to coloring flaw detection. The flaw detection results show that there are no obvious crack defects in the coating and the cladding layer has good quality. The knife ring after cladding is placed in a heat treatment furnace at 260℃ for 4h and then cooled in the furnace to remove the residual stress caused by different material shrinkage ratios during laser cladding. The single-pass cladding layer on the hob surface is sampled by wire cutting. Subsequently, the metallographic and scanning electron microscope observations were performed on the bonding of tungsten carbide in the hob cladding layer after cladding. The results are shown in Figures 2 and 3. The tungsten carbide is well bonded in the matrix and has a dense structure. The tungsten carbide shape remains spherical. The thermal damage phenomenon of tungsten carbide under this process is effectively controlled, and the formation of brittle phases is reduced. The hardness of the sample was tested, and the results are shown in Figure 4. The hardness is significantly improved compared with the substrate.

Example 2
In this embodiment, the laser cladding material includes a base layer and a wear-resistant layer clad on the base layer. The base layer is clad by iron-based tungsten carbide composite alloy powder I. The iron-based tungsten carbide composite alloy powder I contains spherical tungsten carbide I and iron-based alloy powder I. The spherical tungsten carbide I accounts for 25%, the iron-based alloy powder I accounts for 75%, and the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide in the spherical tungsten carbide I is 3.5:1.
The wear-resistant layer is formed by cladding of iron-based tungsten carbide composite alloy powder II. The iron-based tungsten carbide composite alloy powder II contains spherical tungsten carbide II and iron-based alloy powder II. Spherical tungsten carbide II accounts for 35%, iron-based alloy powder II accounts for 65%, and the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide is 1:1.
The above-mentioned iron-based alloy powder I and iron-based alloy powder II use the same iron-based alloy powder, and the composition mass percentage is C: 0.07%, Si: 1.2%, Cr: 28%, Ni: 14%, Mo: 1%, Mn: 1.3%, and the balance is Fe.
The above-mentioned large-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 50μm-100μm, and the small-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 20μm-45μm.
The powder processing, sample preparation and testing methods refer to Example 1. After testing, the hardness of the element ratio is relatively high, the average hardness of the wear-resistant layer reaches 795HV0.3, and the average hardness of the base layer reaches 662HV0.3.

Example 3
The laser cladding material in this embodiment includes a base layer and a wear-resistant layer clad on the base layer. The base layer is clad by iron-based tungsten carbide composite alloy powder I. The iron-based tungsten carbide composite alloy powder I contains spherical tungsten carbide I and iron-based alloy powder I. The spherical tungsten carbide I accounts for 35%, the iron-based alloy powder I accounts for 65%, and the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide in the spherical tungsten carbide I is 2.5:1.
The wear-resistant layer is formed by cladding of iron-based tungsten carbide composite alloy powder II. The iron-based tungsten carbide composite alloy powder II contains spherical tungsten carbide II and iron-based alloy powder II. Spherical tungsten carbide II accounts for 45%, iron-based alloy powder II accounts for 55%, and the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide is 1.4:1.
The above-mentioned iron-based alloy powder I and iron-based alloy powder II use the same iron-based alloy powder, and the composition mass percentage is C: 0.13%, Si: 1.2%, Cr: 21%, Ni: 14%, Mo: 0.7%, Mn: 1%, and the balance is Fe.
The above-mentioned large-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 50μm-100μm, and the small-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 20μm-45μm.
The powder processing, sample preparation and testing methods refer to Example 1. After testing, the average hardness of the wear-resistant layer is 675HV0.3, and the average hardness of the base layer is 507HV0.3. This example has good impact toughness performance.

Example 4
The laser cladding material in this embodiment includes a base layer and a wear-resistant layer clad on the base layer. The base layer is clad by iron-based tungsten carbide composite alloy powder I. The iron-based tungsten carbide composite alloy powder I includes spherical tungsten carbide I and iron-based alloy powder I. Spherical tungsten carbide I accounts for 30%, iron-based alloy powder I accounts for 70%, and the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide in spherical tungsten carbide I is 3:1;
The wear-resistant layer is clad by iron-based tungsten carbide composite alloy powder II. The iron-based tungsten carbide composite alloy powder II includes spherical tungsten carbide II and iron-based alloy powder II. Spherical tungsten carbide II accounts for 40%, iron-based alloy powder II accounts for 60%, and the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide is 55:45.
The above-mentioned iron-based alloy powder I and iron-based alloy powder II use the same iron-based alloy powder, and the composition mass percentage is C: 0.1%, Si: 2%, Cr: 23%, Ni: 20%, Mo: 1%, Mn: 0.7%, and the balance is Fe.
The above-mentioned large-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 50μm-100μm, and the small-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 20μm-45μm.
The powder processing, sample preparation and testing method refer to Example 1. After testing, when the proportion of large-grained tungsten carbide increases, the relative contact area between tungsten carbide and the molten pool in the cladding layer decreases, and the thermal damage of tungsten carbide is further controlled.

Example 5
In this example, the laser cladding material includes a base layer and a wear-resistant layer clad on the base layer. The base layer is clad by iron-based tungsten carbide composite alloy powder I. The iron-based tungsten carbide composite alloy powder I includes spherical tungsten carbide I and iron-based alloy powder I. Spherical tungsten carbide I accounts for 35%, iron-based alloy powder I accounts for 65%, and the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide in spherical tungsten carbide I is 2.5:1.
The wear-resistant layer is clad by iron-based tungsten carbide composite alloy powder II. The iron-based tungsten carbide composite alloy powder II includes spherical tungsten carbide II and iron-based alloy powder II. Spherical tungsten carbide II accounts for 45%, iron-based alloy powder II accounts for 55%, and the ratio of large-grained spherical tungsten carbide to small-grained spherical tungsten carbide is 1.4:1.
The above-mentioned iron-based alloy powder I and iron-based alloy powder II use the same iron-based alloy powder, and the composition mass percentage is C: 0.1%, Si: 1.6%, Cr: 21%, Ni: 14%, Mo: 1.3%, Mn: 1%, and the balance is Fe.
The above-mentioned large-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 50μm-100μm, and the small-grained spherical tungsten carbide is a tungsten carbide particle with a diameter of 20μm-45μm.
The powder processing, sample preparation and testing method refer to Example 1.
The five samples of the embodiments and the H13 substrate were subjected to color flaw detection tests, and the results showed that the cladding layer had no macro crack defects; the Charpy pendulum impact toughness test was carried out on each embodiment, and the impact absorption energy results all exceeded the cutter ring substrate material; the room temperature sliding friction and wear test was carried out, and the data are shown in the following table: Example 1 (7.95E-6), Example 2 (1.26E-5), Example 3 (2.80E-5), Example 4 (5.34E-5), Example 5 (3.90E-6), H13 substrate (1.83E-4).
In summary, the laser cladding layer prepared by the iron-based composite alloy powder can effectively improve the surface performance of the hob, meet the operation needs under complex rock conditions, reduce the consumption of metals such as nickel and cobalt, save the time of replacing cutters during shield tunneling, improve the operation efficiency of the shield machine, and have good economic benefits.