钢锭模用灰口铸铁热循环载荷下的微观组织与服役特性

Microstructure and Service Properties of Mould Grey Iron After the Experience of Periodic Thermal Loads

应用马弗炉对灰口铸铁试样进行热循环处理,并通过Gleeble-1500、光学显微镜、电子显微镜和能谱仪等手段重点分析了灰口铸铁拉伸性能、基体组织、化学成分与热历程的相关性。发现铸态试样珠光体片层间距较大,石墨片较厚,且其周围存在铁素体,这是其拉伸性能较差的根本原因。经800℃保温3h控温冷却后,试样组织均匀性显著改善,低温抗拉强度提高约30%。多次热循环处理后,试样各温度下的拉伸性能均有所下降,这与高温氧化、脱碳有关。试样经30次热处理后,碳的质量分数降至1.55%,致使珠光体转变难以完成。同时,在石墨片周围形成硅、锰、铁等氧化物的疏松带,二次渗碳体和晶粒粗化也均是试样抗拉强度下降的重要原因。

A kind of mould material of grey iron was adopted for the experimental thermal simulation to the large ingot mould and its service operation. The microstructure and tensile strength of grey iron after different thermal history was studied by Gleeble-1500, OM, SEM and EDS. The relationship among thermal pretreatment and graphite morphology, pearlite content was revealed. It is found that the homogeneousness and continuity of as-cast specimens are obviously weak. And the microstructure and tensile strength can be improved observably after one cycle pretreatment, which is similar to a normalizing scheme. For the specimens after different cycles of thermal loads, the tensile strength at various temperatures decreases with periodic thermal loads increasing, which should be related to the graphite and matrix oxidization and decarburization at high temperature. The carbon content in grey cast iron reduces to 1.55% after 30 cycles of high temperature thermal pretreatment. Meanwhile, the floccus band around the graphite with a composition of silicon, manganese and iron oxides has been observed.