Research On The Microstructure And Properties Of High Nickel Compacted Graphite Wear Resistant Insert Ring

High nickel austenite in thermodynamics is a relatively stable phase, in some of the media has good resistance to corrosion and at high temperature, it has superior thermal damage resistance, antioxidant capacity, endurance strength, thermal shock and thermal fatigue life. In the same condition, the oxidation and thermal growth performance of the compacted graphite cast iron is between the nodular cast iron and gray cast iron. High nickel austenitic compacted graphite cast iron is the ideal material for high temperature environments with perfect hardness, thermal conductivity, and casting performance.The ring carrier has a direct contact with the high temperature and high pressure gas, under high thermal and mechanical loads, corrosion conditions, with a high speed back and forth movement within the cylinder of reciprocating swinging slightly. In ensure stable engine operation and safety of the premise, the engine is developing toward the direction of high power, lightweight, low fuel consumption, this research on improving material work of wear ring carrier try to use high nickel vermicular graphite austenitic cast iron material replace the original high nickel austenite gray cast iron to produce piston wear resistant insert ring and provide some experimental data and theoretical support for the development of future engine material.In the majority of the casting method, this kind of economic and easy to use technology, centrifugal, is adopted in this paper. With different doses (1%,0.8%, 0.6%,0.55%,0.5%,0.4%) and different kinds of B, A, the iron fluid was compacted and modified, and then the centrifugal casting was carried out. Scanning electron microscope and optical microscope were used to observe the microstructure of the joint, and the composition analysis was carried out by using the energy spectrum analyzer.The obtained samples can be roughly divided into:high nickel austenitic ductile cast iron, high nickel austenitic compacted graphite cast iron and high nickel austenitic gray cast iron. The mechanical properties of the material were analyzed in order to choose perfect wear resistant insert ring materials. The macro hardness, wear resistance, low temperature impact toughness and tensile properties of the samples were measured. In the macro hardness test which is closely related to the hardness of cast iron specimen and specimen of graphite morphology, matrix microstructure and carbide content, high Ni Austenitic Ductile Iron hardness is highest, the hardness value up to 220HBW around, high nickel austenite gray cast iron is lowest of three, about only 130 HBW, high nickel compacted graphite cast iron hardness values between the two, is about 160 HBW.Similar to the macro hardness test, results of wear resistance for high nickel austenite nodular cast iron is the best in the performance of wear resistance, high nickel austenite of compacted graphite cast iron is the second, third for the high nickel austenite gray cast iron, the worst for the nickel middle content in contrast sample. Due to casting in the aluminum pistons, the wear resistant insert ring and a piston ring assembly together have a high-speed reciprocating motion in the cylinder body, hardness value can not be too high, so high nickel austenite gray cast iron of the original and the high nickel austenite of compacted graphite cast iron related properties is conform to the material standards. For the two groups of samples in low temperature impact test and tensile test, it found that high Ni austenitic compacted cast iron s impact toughness and tensile properties are better than the original gray cast iron samples. It was also found that the impact toughness values of the cast iron samples with temperature change little, at room temperature (20℃),-20℃,-40℃. For several cases, the impact toughness value is almost the same. In the tensile test, the tensile properties of the cast iron sample are mainly determined by the matrix structure, and the three stage characteristics of the austenitic FCC crystal are found.In order to be more close to the actual application of piston and provide a reliable basis for the material, the thermophysical properties of wear-resistant ring material is analyzed, and this paper explores the materials positive performance of the thermal fatigue properties and thermal conductive, thermal fatigue test find that between 460 degrees and 20 ℃, the samples graphite morphology, matrix microstructure and carbide content are closely related with thermal fatigue property, through the observation of microstructure, high nickel austenitic matrix has excellent thermal fatigue resistance, thermal fatigue resistance is in graphite shape:ductile iron> vermicular cast iron> gray cast iron, the start position of thermal fatigue crack mainly appear between graphite and matrix, crack extension is mainly along the grain boundary or through graphite, only few crystal expansion. However, due to the existence of carbide, it hinders the expansion of the crack. In the observation of the crack propagation path and carbide intersection, the crack and carbide location are far away from each other. Thermal conductivity test find that there is a certain gap with the high nickel gray cast iron, the heat transfer capacity of compacted graphite cast iron is also excellent.High nickel austenite vermicular cast iron has wonderful high temperature performance, can keep good strength in a 500℃, has perfect thermal fatigue and thermal conductivity, combined with other related mechanical properties and casting properties, high nickel austenite of vermicular graphite cast iron can replace the original high nickel austenite grey cast iron to product piston wear resistant insert ring.