Research On The Influence And Mechanism Of The Heat Treatment Parameters On Mechanical Properties Of ADI

ADI material can be obtained by isothermally quenching ductile iron (DI). By this treatment, its mechanical properties are greatly improved. To mechanical degree, ADI materials not only have a good strength, toughness, abrasion resistance, but also, its properties could be kept under a low temperature. Besides, its ratio of density to tensile strength is low, bending contact fatigue strength is high, it can absorb shocks and reduce noises. Its mechanical properties are excellent. To economic degree, cost of producing is low, economic benefit is great. Attributed to all its unique merits, ADI becomes one of the materials that can substitute steel, even aluminium alloy, copper alloy.In this paper, LZQT500-7 DI was isothermally quenched with the treatment parameters of austenitizing temperature 900℃, austenitizing time 90min, different isothermal quenching temperature and different isothermal quenching time.Then 9 different ADI materials with different mechanical properties were obtained. Their metallographic structures were qualitatively and quantitatively analyzed by scanning electron microscope and X-ray diffraction method. And the relationships among heat treatment parameters, content of retained austenite and carbon content of retained austenite were studied. Measure the strength, hardness, impact toughness, percentage of elongtation of all these 9 different materials and study the affecting rules of different parameters on mechanical properties. Analyze in detail and state the mechanical properties and macroscopic consequences of these materials by FEM simulation, macroscopical and microscopical analysis of fracture structures, comparing cutting force. Models that show the relationships between isothermal quenching temperature, isothermal quenching time, structures content and mechanical properties were built in the base of fuzzy subtractive clustering method. The reliability analysis method was used in the inference pattern of hardness, and the heat treatment parameters of ADI materials of different levels were predicted. 1. The results show that the metallographic structures and ingredients are changed totally after isothermal quenching, thus austenite structures with excellent mechanical properties are obtained. According to the statistic of the experiment, isothermal quenching temperature affects the structure content greatly, but isothermal quenching time is an inferior factor here. When the isothermal quenching temperature is 250℃, the austenite content and carbon content are the lowest in the experimental results, 300℃his medium, and 350℃is the highest. When the isothermal time ranges from 60min to 180min, the changing rules of austenite content and carbon content are not always same. When the isothermal quenching temperature is 250℃, austenite content and carbon content increase firstly, and then keep constant with the isothermal time increase. While 300℃, austenite content and carbon content are the highest when the quenching time is 60min, but when the quenching time is 120min or 180min, the contents reduce. And 350℃, the contents will increase at first and then reduce.2. The strength and hardness of ADI materials reduce as the isothermal quenching temperature raising. When the isothermal quenching time increases, the strength increases but then decreases, and the hardness decreases firstly and then increases. The percentage of elongtation and impact toughness increase as the isothermal quenching time increases, but they do not change regularly with the quenching time. The fractures of ADI tensile and impact specimens is the mix of ductile type and crisp type. When the isothermal quenching temperature increases, the fibrouszone increases; the plasticity, toughness increase too, brittleness decreases. The study of cutting force shows that the cylindrical specimens are not quenched thoroughly. The hardness of the top and surface is high, and the cutting force is great. The hardness of the inner part is low, and cutting force is small. Also, the quenching degree is not greatly relevant to the isothermal quenching temperature and time.3. Inferential models built on the ground of fuzzy subtractive clustering method. It shows the relationships between ADI structures content and mechanical properties are reliable, and heat treatment parameters can be predicted according to custom's requirement. The heat treatment parameters of ASTM ADI 4 could be 900℃-90min, 250℃-120min, are predicted by the models. And the heat treatment parameters of ASTM ADI 3 could be 900℃-90min, 330℃-90min. The heat treatment parameters of ASTM ADI 2 could be 900℃-90min, 360℃-60min. If high strength and high hardness are required, the isothermal quenching temperature should be reduced properly, but is not supposed to be lower than 230℃, which is the up transforming limit temperature of martensite.