| The effect is discussed of carbon and nickel on mechanical properties, metallurgical structure and fracture surface microstructures of iron based P/M materials. On this basis, both carbon and nickel were added in iron powder, and we study on mechanical properties and microstructures of Fe-xC-yNi(x=0.4、0.6、0.8、 1.0, y=1、2、........、8). All of the study was based on atomized iron powder LAP 100.29 which was made by Laiwu iron and steel powder Co. Ltd. The work of this thesis could provide the basis for synthetising low cost and high plastic powder metallurgy materials.The results showed that the Fe-xC(x=0,8wt%) alloy possess the best comprehensive performance:its strength is 56.8HRB, hardness is 358Mpa and elongation is 1.85%. When carbon content is 1.0wt%, the tensile strength and elongation decreased rapidly. Microstructure observations indicated that porosity, grain size and content of pearlite of alloy are increased with the increase of carbon content. The fracture morphology of alloys changed from dimple to cleavage fracture with river pattern.Mechanical property and microstructure of Fe-yNi(y=1,2,3...8wt%) alloy prepared by conventional sintering (CS) were studied, it is found that the hardness, tensile strength and elongation were increased with the increase of nickel content. Fe-7%Ni alloy’ the strength and hardness are 50.6HRB and 292MPa, the elongation increased to 7.68%. Microstructure observations indicated porosity and the grain size of alloy were reduced with nickel content increased. The microstructure of the alloy mainly contained a lot of solid solution of iron and nickel. When the nickel content is 8wt%, nickel-rich region was observed in the microstructure of Fe-yNi alloy. The dimple of the fracture morphology of alloys was increased while the river pattern was reduced, the transformation of alloy by quasi cleavage fracture to ductile fracture. The fracture mode of the alloy change from Quasi-cleavage fracture to Cleavage fracture.Based on anterior respective studies about the effect of carbon and nickel on iron-base. We studied the combined action of carbon and nickel on iron-based alloy. the results showed that the comprehensive performance of Fe-7Ni-1.0C alloy is best, The hardness and tensile strength of Fe-7Ni-1.0C alloy are respectively 85.3HRB,511MPa,the elongation is 4.76%. Microstructure observations indicated:in the case of nickel content remain unchanged, porosity of alloy was increased and the spheroidization degrees of pores were enhanced with the increase of carbon content. In the case of carbon content remain unchanged, the numbers of pores along the grain boundary were increased and the porosity was decreased with the increase of nickel content. It is found the grain has been refined when both carbon and nickel powder added to the iron powder; Carbon hindered nickel, martensite presence around the nickel-rich austenite and the martensite content is increased with the carbon content increased; alloy fracture morphology was observed, when the nickel content is constant, the pore distribution and river pattern in the cross section were increases with the increase of carbon content, When the carbon content is constant, the fracture mechanism of the alloy changes from brittle fracture to quasi cleavage fracture with the increase of carbon content. |
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