The Study On Surface Alloying Of Heat-resistant Coating On Cast Iron By The Green Mold Casting

With the development of deep research on the surface technology in the world, through carious means, such as: mechanical physical, chemical and other methods to change the surface chemical composition, microstructure, stress and other properties, and hoping by these ways make the surface resistant to heat, corrosion, wear resistance properties to adapt the special work circumstances of the material.Green Sand casting is the most widely used and most convenient modeling approach accounts for all the sand, Green sand usage 60 to 70 percent, it has the features of production flexibility, high productivity, shot production cycle, easy to implement production machinery automation, materials, and low cost. If the use of Green sand casting method allows access to various features of the surface of cast alloy layer will very significant.Cast iron alloy has many advantages, alloying elements can be effectively used to eliminate waste, not only maintain their quality characteristics of cast iron but also makes a special performance of the local surface to adapt to specific environments, alloy layer composition, microstructure and the thickness can be chosen according to requirements and design, to the best use for the purpose.Home and abroad on the principle of metal casting penetration and there is no unified understanding of the early to cast infiltration is defined as: "In the mold cavity surface coated with a layer of high hardness material, casting, the metal coating layer of liquid penetration and high hardness (high melting point) of material particles, solidification, thus keeping them down to form a hardened layer."But it is not difficult to achieve an affordable way. Another way to get a cast iron surface alloying method is called "surface bred Law", defined as: "the specific position in the mold coated with paint containing alloy elements, use of liquid metal heat to melt and the diffusion of alloying elements to the metal liquid, which gradually formed on the surface alloying layer and obtain the required special performance. "Analysis of these two methods, the formation of their respective emphasize the different mechanism of alloy layer, through comparative study, previous proposed the "casting of metal coating," that is, surface alloying of cast iron and made a broad definition: "the prepared alloy coating must be able to produce pores after pouring liquid metal, so that liquid metal infiltration, and then makes the alloy elements in liquid metal melt and solvent coatings help to achieve alloyed with alloying elements. " Although the research project with the casting surface infiltration, and many of the expanding definition of perfect casting and mechanism of infiltration, but after testing and analysis of test results of the proposed surface alloying of cast iron casting penetration is more appropriate than the more specific. In this paper, the most widely used wet sand casting, and in which different amount of iron added to solid phenolic resin powder, prepared by coating the traditional way is to use liquid adhesives, powder coated alloy Review process not only easy but also difficult to control coating of even thickness, time consuming, and in the casting process because of problems caused by gas evolution binder holes, meets a direct impact on the defects such as the quality of the alloy layer. However, in this trial, as cast into the metal powder and binder are solid, you can adjust the thickness of a small brush to the problem of uneven simple results are satisfactory. Because the resin before casting had solidified completely or partially melted, so to casting process, gas evolution will be greatly reduced, and because the alloy powder has a certain intensity, it is not easy to be broken up when pouring, to solve the traditional use of sticky caking agent problems and access to high-quality coatings and rare fine pores and coarse surface.Alloy powder in the shape and the coating, the Heap up and down sand box, and marked, and in 1380℃under the temperature of liquid metal casting, cast iron surface in the successful preparation of the Fe-Cr-Ni-Mo and Fe-Cr-Ni-Si groups of heat-resistant alloy layer. Alloy layer by the outer layer, intermediate layer and the inner layer, using the interface method, the alloy layer by macro-morphology, microstructure, and thermal performance analysis.By Olympus optical microscope, scanning electron microscopy, X-ray diffraction, etc. The microstructure of the alloy layer and distribution of elements and the phase formation were observed and analyzed. The results show good performance for the dense outer layer of tissue block carbides, more common in the transition layer and diffusion layer plate-like, herringbone and network carbide, and various elements and compounds present in the alloy layer is not only the most outer layer, also exist in the transition layer and inner layer, Infer, mutual diffusion of alloying elements occurred, but that in the relevant literature obtained through diffusion alloy layer needs a certain thickness of insulation and a longer time period in this experiment is very short, so get alloy layer binding reaction is still the main mode.Contact front on the alloy layer microstructures, elements distribution and phase analysis, the Fe-Cr-Ni-Mo and Fe-Cr-Ni-Si groups in the A6 and B2 samples were analyzed hardness. Curve obtained from hardness, hardness of the transition is more uniform, compared to the selected sample morphologies, the base metal alloy layer and the bonding strength is ideal. Micro hardness results show that the alloy elements infiltrated into the region is abundant, and the response generated by the combination of hardness on the high carbon region, the closer the lower base metal hardness. This and the previous distribution of elements on the microstructure and phase analysis of the results were consistent, the closer the base metal, alloying elements to infiltrate into the more rarefied, and the reaction more difficult it is for.This article also analyzes the heat resistance of the alloy layer, mainly anti-fatigue and anti-oxidation by two aspects of the test. Thermal fatigue test is transferred to the furnace temperature of 800℃and 1000℃, 60S in the oven cavity insulation into the water after the fast quench cooling 5S, a cycle time for the 65S. In this more hostile environment, have a direct and effective results, the results show that the specimen with the alloy layers have different degrees of thermal fatigue properties of the matrix at 800℃test appeared in almost broken crack. Anti-oxidation tests at 800℃heat resistance furnace at different times, and find the different components of each test the temperature before and after oxidation weight change. The results showed that samples of different composition than the cast iron oxidation rate of 1.3 times to 2.6 times lower. Combination of alloy layer microstructure analysis found to contain dense and has a massive and plate-like carbide alloy layer of the best heat resistance.