Research On The Modification Of High Chromium White Cast Iron Spherical Plug

High chromium white cast iron is a kind of material which is very widely used inwear-resistant field. Its microstructure and performance quality directly affect the actualproduction efficiency and cost. So it has a very vital significance on the research of themicrostructure and performance of high chromium white cast iron. According to theactual production of the spherical plug in seamless steel tube rolling pipe bender and onthe basis of the failure analysis of the spherical plug and the summary of plenty researchresults of domestic and foreign relevant, appropriate composition optimization,inoculation treatment and heat treatment process improvement for high chromium whitecast iron were carries out in this thesis. Effects of heat treatment and the inoculationtreatment with RE and V on microstructure and properties were systematically studiedusing the metallurgical structure, rockwell hardness, impact toughness, sliding wear,XRD, SEM and EDS.The results show that the cast austenitic microstructure of the modified highchromium white cast iron (2.03%C,18.02%Cr) transfers to the martensitemicrostructure when destabilization treatment in770℃~1200℃, and some secondarycarbides precipitate simultaneously. With increasing the temperature, the hardness andthe wear resistance increase firstly, reaching a maximum value at1010℃, and thendecrease. The impact toughness of high chromium white cast iron by destabilizationheat treatment (1010℃×4hâ†'sand coolingâ†'400℃×5hâ†'sand cooling) is4.9J/cm2, andthe hardness reaches up to55.2HRC, and the wear weight loss decreases almost16%compared with the as-cast state. Grading insulation heat treatment can make thehardness of high chromium white cast iron vastly improve, at the same time, the impacttoughness remains at a high level. Within this experiment temperature range, with risingthe first-class insulation temperature, the hardness of high chromium white cast irondecreases, the impact toughness increases and the wear weight loss decreases firstly,and then increases. At the same time, with increasing the second-class insulationtemperature, the hardness of high chromium white cast iron increases, the impacttoughness decreases and the wear weight loss decreases firstly, and then increases. Thehardness of high chromium white cast iron by grading insulation heat treatment(1150℃×2hâ†'furnace coolingâ†'890℃×4hâ†'sand coolingâ†'400℃×5hâ†'sand cooling)is52HRC. At the same time, the impact toughness reaches up to5.76J/cm2and the wearweight loss decreases almost24%compared with the as-cast state and decreases almost10%compared with the destabilization treatment state (1010℃×5hâ†'sand coolingâ†'400℃×5hâ†'sand cooling).The results indicate that the grain size of the modified high chromium white castiron (2.03%C,18.02%Cr) can be refined by adding RE, V appropriately. Moreover, thedistribution and appearance of the carbides can be changed from continuous, mesh, andbulky board strips to isolated, disjointed and tiny strips, which results in improvementof the continuity of the matrix microstructure. The hardness of the modified highchromium white cast iron by composite treatment process (inoculation treatmen (0.9%V+1.0%RE)+heat treatmen (1150℃×2hâ†'furnace coolingâ†'890℃×4hâ†'sandcoolingâ†'400℃×5hâ†'sand cooling)) is53HRC, the impact toughness reach up to6.72J/cm2, and the wear weight loss decreasing almost35%compared with the as-caststate. With this process, the spherical plug service life is nearly three times comparedwith the non-improved one.