Research And Development Of N-type High-grade GCI And Its Cutting Machinability

GCI has become the preferred material for many castings in casting production practice due to its excellent casting formability,cutting machinability,wear resistance,vibration resistance and thermal conductivity.But the most advanced China VI engine puts higher demands on GCI.Aiming at the urgent demand of high-strength GCI,in this paper,a series of experiments were carried out to study the preparation,metallographic structure and cutting machinability of high strength GCI.The main work and conclusions are as follows:First of all,the paper introduces the experimental scheme and equipment needed,clarifies the source and rationality of the paper data,paving the way for the development of the paper.Secondly,orthogonal experiment and single factor test scheme were used to study the effects of nitrogen addition medium,process and amount on nitrogen absorption rate and mechanical properties of GCI.The results of orthogonal experiments show that the addition medium and process is the main factor affecting the absorption rate of nitrogen,and the medium of Mn3N2 and process of adding in furnace is an excellent level.The influence degree of each factor on the graphite morphology and metallographic structure of GCI is:adding process>medium>amount;the influence degree of each factor on the mechanical properties of GCI is:adding amount>medium>process.The graphite morphology and metallographic structure of nitrogen strengthened GCI was studied by single factor test of additive amount of adding Mn3N2 in furnace.The results show that with the increase of N addition,the graphite length decreases slightly,the graphite body becomes thicker gradually,the graphite end is passivated,the graphite curvature increases;the pearlite volume increases,the pearlite fines,and the pearlite layer spacing decreases;the mechanical properties increase linearly.When the addition amount is 0.024wt%,due to the formation of nitrogen pore defects,the tensile strength and the specified plastic elongation strength are slightly decreased and the hardness growth rate is slowed down.When the addition amount is 0.018wt%,the tensile strength showed a maximum value of 332MPa.Finally,the cutting machinability of the coated cemented carbide tools in cutting normal/N-type HT250 was comprehensive comparative studied by the orthogonal test and the single factor test program of significant factors.The results show that the wear of the front and rear cutter faces of coated carbide tools when cutting the N-type HT250 is higher than that of the ordinary HT250.The significant factor affecting the amount of flank wear on the tool cutting N-type HT250 is the cutting speed.When Vc=100m/min,the tool produces severe bond wear,which causes the flank wear to be abnormal serious.When Vc=100～200m/min,the tool wear is mainly caused by abrasive wear and bond wear,which causes the tool wear to decrease sharply with the increase of cutting speed.When Vc=200～450 m/min,the tool wears is mainly caused by diffusion wear and oxidative wear,and tool wear tends to increase slowly with increasing cutting speed.The surface roughness of coated carbide tool cutting N-type HT250 is better than that of ordinary HT250,especially in the case of high cutting speed(Vc=250～400m/min)and high feed rate(f=0.3mm/r),the superiority of the N-type HT250 with respect to surface roughness is more pronounced.The significant factor affecting the surface roughness of the N-type HT250 is the feed amount,and the surface roughness increases linearly with the increase of the feed amount.