Research On The Crack Failure Mechanism And Materials Improvement Of Cast Iron Mould

Glass mould is an important and consumptive tool for making glass wares, Theirquality has crucial effect on the quality and production cost of glass wares. D-typegraphite alloyed grey iron and compacted graphite iron have been widely used inmanufacturing of glass mould because of their good anti-oxidation and thermal fatigueresistance. However, with the increase of speed of glass forming machine anddiversification of the glass composition, the glass mould is prone to cracking andoxidation in service, which will lead to the reduction of quality and production efficiencyof glass ware. Therefore, it is significant to enhance the oxidation and thermal fatigueresistance by modifying the microstructure of cast iron for improvement of the level of theglass mould and the quality of the products.In this paper, the crack failure analysis of cast iron glass mould and the effectmicrostructure on the initiation and propagation of crack were examined. Based on theanalysis of crack failure mechanism, the experiments on melting, inoculating andannealing process of cast iron were carried out in order to improve the microstructure andproperties of D-type graphite alloyed gray iron. Based on the composition of RTM-7compacted graphite iron used for glass mould, the medium silicon and mediumsilicon-molybdenum compacted graphite iron were developed. The following results wereobtained.The crack formation reason of mould cavity was due to the formation of blockcementites and composite phosphide eutectics in the matrix of cast iron. During the cyclicheating and cooling process, dissolution and precipitation of cementites would result inphase transformation stress. And superposition of the phase transformation stress and the molten glass frictional stress led to the crack initiation on the grain boundaries andpropagation along the grain boundaries of the dendrite.The molten of D-type graphite alloyed gray iron was melted at1510℃~1520℃andstood for more than5min, which would improve the metallurgical quality of the molten.By using secondary inoculation with0.03-0.05wt%RE and in-mold inoculation with0.005-0.01wt%Bi-containing inoculants, the fine D-type graphite was obtained.Uniformity of the matrix was improved significantly, and the number of cementites andphosphide eutectic was reduced as well.High-temperature graphitization annealing temperature of D-type graphite alloyedgray iron was elevated from900℃-910℃to930℃-960℃, and Mid-temperaturegraphitization at720℃-750℃was added to annealing process. Fully ferritic matrixcould be obtained, and the distribution of cementites became dispersive. Compared withprevious process, the annealing process time was shorten by12h.With the process of REsecondary inoculation and Bi-inoculant in-mold inoculation the microstructure uniformityof cast iron mould was greatly improved and the service life of mould was significantlyprolonged.In the aspect of compacted graphite iron glass mould, the content of Mn in RTM-7compacted graphite iron was reduced from0.5wt%to0.3wt%or less, led to a remarkablereduction of quantities of the intergranular cementites and pearlite. By strengtheninginoculation and chilling, graphite nodularity in the mould cavity was increased and agradient graphite distribution (ductileâ†'ductile+compactedâ†'compacted graphite) wasobtained, the anti-oxidation and thermal fatigue resistance of glass mould were improved.Two novel kinds of compacted graphite iron glass mould, such as medium siliconcompacted graphite iron and medium silicon-molybdenum compacted graphite iron, weresuccessfully developed. For the higher content of Si, the oxidation resistance of the mouldwas apparently increased. The hardness of medium silicon and medium silicon-molybdenum compacted graphite iron after annealing was188HB and208HB,respectively. This is was beneficial to the strengthening of the wear resistance of the glassmould.