With the rapid development of China's industry, urgently develop a variety of new surfacing materials to meet current production needs. Hardfacing currently in development at home and abroad more types of materials, mainly iron-based hardfacing material, cobalt-based hardfacing materials, nickel-based hardfacing materials, surfacing materials, alloy cast iron, high chromium cast iron pile welding materials. However, these materials add the W, Mo, V, Ni and other metals are expensive, the cost of electrode is very high.
B on the surfacing alloy has a strong strengthening effect, is very active chemical element of the. It is not only with nitrogen, oxygen has a strong affinity, but also the formation of carbide and carbon, such as: B4C (or BC), and chromium, iron and other metals to form extremely hard rigid material, such as: CrB, Cr2B, FeB, Fe2B and so on. These compounds dispersed in the surfacing alloy, there is help to improve the hardness and wear resistance, especially in small amounts of boron or boron in austenite formation of interstitial solid solutions, mainly in the lattice defects, its enhanced better , , . B to form boron carbide and other hard chrome diboride phase, to improve the wear resistance of electrode is very helpful. B is added to significantly improve the wear resistance of the alloy, but the crack is reduced, adding Ni alloy increases the toughness, reduce cracking tendency .
Hardfacing electrodes used in drug skin slag are: CaO-CaF2-SiO2 , CaO-CaF2-TiO2 , CaO-CaF2-TiO2-ZrO2 , CaCO3-CaF2-SiO2- TiO2, CaCO3-CaF2-graphite, CaCO3-CaF2-SiO2-rare earth oxide, and titanium calcium slag system. The electrodes used in the basic alloy system Cr-Mo-VBC, surfacing alloy according to the need to add a certain amount of Mn, Si elements.
The welding electrode core wire material for H08A.
2.1.2 Drug skin electrode
Skin from the drug electrode marble, dolomite, fluorite, rare earth silicon, mica, titanium dioxide, rutile, clay, ferrosilicon, ferromanganese, ilmenite, graphite, chrome iron, molybdenum, vanadium, iron, boron, iron and sodium water glass and other components.
2.2 Test Method
Calculated in accordance with good drug skin formula, made of hand-rubbing electrode and the skin completely finalized until after the drug electrode placed in the drying box-type resistance furnace.
After drying welding electrodes, welding, first along the test plate (material: A3) in the middle of a continuous longitudinal weld seam, and then welding slag cooling knock Layer 2, Layer 3.
To be welded specimens cooled to room temperature, the test plate surface slag grinding away, respectively, with a cutting machine to cut out sections 1, 2, 3 layers of weld specimens and polished specimens, as prepare follow-up performance testing, including hardness testing, the weld microstructure observation, anti-erosion experiments.
3 Experimental results and analysis
3.1 electrode process of
Through the welding process and welding seam after the observation that the stability of the arc of the electrode, arc, and then arc performance are excellent, weld slag removal performance and the performance is relatively good, and the dust generated when welding also and harmful gases are not many.
3.2 alloy elements in the welding Alloys
3.2.1 molybdenum, vanadium's role in the surfacing alloy
Figure 1 shows the molybdenum content of the weld metal impact. Can be obtained from Figure 1, with the molybdenum content increases, the weld significantly thinner. Mo solid solution strengthening elements are able to slow the diffusion process occurs when the lower molybdenum content alloy containing vanadium Figure 2 iron butt state's impact. Vanadium and carbon, nitrogen and oxygen have a strong affinity, and with them form a stable compound. As the vanadium carbides and nitrides have a high melting point, the liquid pool of metal in the solidification process soon became crystal nuclei, so that the cladding layer to the organization and grain refinement, the surfacing layer strength, hardness and toughness have been improved. 3.2.2 Boron's role in the surfacing alloy
Fixed iron content of 1.25% molybdenum, vanadium and iron content of 1% of the impact of B on the surfacing alloy.
B element of the macro-hardness of surfacing in Table 1. The surfacing alloy, when boron is low, due to boron and to generate low-melting eutectic alloy material, the surface is easy to weld a small amount of thermal cracking; when the amount of boron increases to a certain value, due to weld there are more in the low melting point eutectic material in the grain boundaries have a "healing" effect, so thermal cracks disappear; further increased when the amount of boron, is due to V, Mo and other elements of the role of carbon in the control of the weld the generation of boron, boron excess will not be able to form hard phase, but segregation at grain boundaries, increasing the sensitivity of crack, 8 # sample because the first cladding layer that can not be measured because cracks hardness. Table 2 6 #, 7 #, 8 # three kinds of sample No. 3 weld microhardness. Table 2 is based on data largely from the weld heat-affected zone along the surface to a direct measure of the encounter with borides or carbides place, as shown in Figure 3, which will be very high hardness. In addition, B and N to generate high melting point of BN, both to reduce the weld metal in solid solution in the harmful effects of N, but also as a weld metal solidification of the crystal core, played the role of grain refinement, as shown in Figure 3 . Surfacing alloy 3.3 crack resistance
In this paper, direct observation method of welding the weld crack resistance were observed and analyzed the site and observed cracks appear to analyze the number of crack resistance Aluminium Welding Electrode.
Through observation, resulting in cracks along the grain of both the development of more twists and turns of the thermal cracking, transgranular have developed along the grain ï¹‘ two trends, and more straight crack cold crack.
The welding electrode appears in the sample parallel to the crack with the parent material, indicating that drug skin electrode composition and thermal expansion coefficient of the base metal that much difference. Surfacing alloy linear expansion coefficient and the relatively large difference between the base metal, high hardness, low plasticity, and are added to improve the hardenability of the alloy elements more, such as Mo, Cr, B, making the welding seam is relatively high hardenability Therefore, after welding, easy to crack. Figure 5 shows the emergence of multi-layer welding of cracks can be seen from the graph is not smooth its rough crack fracture, there are some twists and turns both the straight part, part of the development along the grain, some transgranular development is cold and hot crack crack Integrated. 3.4 erosive wear resistance of the alloy welding performance
In this paper, the development of the surfacing alloy welded specimens 6 #, 7 # and 8 # of the third cladding layer erosion test, test conditions: room temperature experiments, using over 30 mesh sieve for quartz sand the impact specimens, using gas as compressed air, air 0.4MPa (ie impact of 4kg), the reference sample is 45 ~ 50HRC hardness of hardened steel (steel 45). Test first worn away the surface of the slag sample, the exposed weld metal, rinse and dry after a precision of one ten thousandth weighed on an electronic analytical balance, then the erosion test, weighing once every 3min . Weighing each sample surface should wash away the sand, and dry with a hair dryer. Adjacent is the absolute difference between the two weight wear. Among them, the relative wear resistance ε is the surfacing alloy with the ratio of the standard material wear, ε value is greater, the higher the wear resistance of said welding parts . ε = the absolute wear standard sample / specimen wear welding. Through access to information we can see: the macro-hardness wear resistance is increased with the increase. However, the data in the table, the conclusion is: with the increase in hardness, wear resistance decreased. After analysis, because of the following points: 3.4.1 Test conditions: self-test is used in erosion testing machine, the gas is compressed air. Slightly larger because of the humidity of quartz sand, sand often appear to stop leak case, and each test, the gas pressure regulator will have errors, so that the test results error. 3.4.2 wear inherent differences in the sample: the sample brittle, in the processing of the sample, the sample # 7 was broken, so that erosion area is reduced, and there are more pores on its surface, resistant to grinding of variation, while the surface quality of the sample # 6 is the best, which also makes testing errors. 3.4.3 where and how the impact of erosion: developed in this study sample brittle weld seam, is a brittle material. For brittle materials, the erosion angle of 90 °, that is, vertical jet of quartz sand in the surface of the sample, the wear volume is greatest. 45 steel is a ductile material, the smaller the angle erosion, the greater the wear. In the present experimental conditions, erosion, erosion can only maintain a 90 °, so the 45 steel is difficult to wear. 3.4.4 The brittle weld relatively large sample, but poor toughness, this material in low stress abrasion wear resistance when the better. But when the hardness, impact is large, the surface layer will be breaking up, so wear strict. 45 steel is ductile material, suitable for high-stress abrasion. Erosion of the erosion test force of 4kg, force is relatively large, so that the two materials of different degrees of wear and tear, resulting in inaccurate test results. In summary, the wear resistance of hardfacing alloys in addition to the hardness of the alloy, but also its crystal structure, crystal orientation, surface quality and service conditions. 4 Conclusion 4.1 arc of the electrode stability, arc, and then arc performance are excellent formability and weld slag removal performance is relatively good, and welding fumes are generated when the harmful gases and not many . 4.2 alloying elements on the performance of the surfacing alloy has a multiplicity, within a certain range, with increasing content of alloying elements, surfacing alloy hardness will increase, but more than a certain amount of time, but have a negative impact. 4.3 hardfacing alloy welded martensite, the internal distribution of a large number of carbides, borides, intermetallic compounds, such as strengthening phase, to improve the wear resistance of hardfacing alloys have great benefits. 4.4 the hardness of their abrasion resistance welding alloys have a certain influence, the basic trend is: the higher the hardness, wear resistance, the better. In addition to hardness, the wear resistance of the factors also affect the crystal structure, crystal phase, the alloy surface quality and service conditions. 4.5 in the high chromium cast iron alloy used in place of Mo and V B and other precious metals, can form boron carbide and other hard chromium diboride phase, to ensure the surfacing alloy wear resistance of the premise, lower electrode production costs.