M2/FeV机械合金化及烧结过程中的碳化物形态转变

Carbide morphology transformation during M2/FeV mechanical alloying and sintering processes

对水雾化M2高速钢粉和FeV合金粉末进行混合高能球磨,制备V含量(质量分数,下同)为8%的M2高速钢/Fe V合金化粉末,研究机械合金化过程中粉末形貌的变化与显微组织结构演化,并在球磨48 h的粉末配碳至目标碳含量(质量分数)2.2%,研究真空烧结过程中的碳化物形态转变。结果表明,随球磨时间延长,粉末颗粒细化速率逐渐降低,球磨28 h后粉末粒度趋于稳定,D_(50)为15μm左右。球磨过程中Fe V颗粒先嵌入到M2的基体相α-Fe中,然后固溶进入基体,V元素逐步均匀分散于基体相α-Fe和M_6C型碳化物中;M_6C发生细化并呈流线形分布,含量逐渐减少,MC颗粒有一定的细化但仍维持粒状形态,含量基本不变。烧结过程中合金元素先脱溶,析出大量粒状M_6C与MC型碳化物,随烧结温度升高,M_6C颗粒长大的同时含量减少,温度过高时M_6C呈针片状;1 180℃之前MC颗粒长大不明显,1 210℃时MC颗粒异常粗大并呈芯环结构。1 180℃下烧结可获得优良组织,其孔隙度为0.8%,M_6C与MC的平均尺寸分别约为1μm和0.3μm。

M2/FeV alloy powder with V content(mass fraction,the same below)of8%was prepared by high energy ball milling method using M2high speed steel and FeV alloy powders as raw materials,and then the alloy powder was matched with carbon,pressed and sintered.The morphological and microstructural evolution of the powders during mechanical alloying were studied.When the ball milled powder matched with carbon to target carbon content of2.2%after48h milling,the transformation of carbide morphology in the vacuum sintering process were studied.The results show that,the powder particle refining rate gradually decreases with increasing the milling time,the particle size maintains stability after28h milling,the average size of the powder is about15μm.During the milling process,FeV particles are embedded intoα-Fe phase of M2matrix first,and then dissolve into M2.With increasing milling time,the V element disperses uniformly in M2and M6C type carbides.The M6C is refined and distributes in streamline form,and its content decreases gradually;MC particles in M2have a certain refinement but still maintain granular shape and the content is basically unchanged.During the sintering process,a large number of granular M6C and MC carbides are precipitated by the dissolution of the alloy elements.With the increase of temperature,the size of M6C particles increases and the content decreases,while M6C is needle-like when the temperature is too high.The growth of MC particles is not obvious below1180℃,and it is abnormally thick and changes into core-ring structure after sintered at1210℃.An optimal structure with the porosity of0.8%and an average size of M6C and MC of about1μm and0.3μm respectively can be obtained at1180℃sintering.