The Beneficial Effect of Niobium Alloying in Gray Cast Iron-Fundamentals and Applications
作者单位：Niobium Products Company GmbH Steinstrasse 2840210 DüsseldorfGermany
会议名称：《中国机械工程学会第十一届全国铸造年会》
会议日期：2006年
学科分类：080503[工学-材料加工工程] 08[工学] 0805[工学-材料科学与工程（可授工学、理学学位）] 0802[工学-机械工程] 080201[工学-机械制造及其自动化]
摘 要：正Abstract: Gray cast machinable iron consists of flake or spheroidal graphite in a ferritic, pearlitic, austenitic or martensitic matrix. This variety of microstructural combinations is used in a multitude of applications. Typical examples are vehicle brake systems, combustion engine blocks and machinery equipment. The particular microstructural design of gray iron and thus its characteristic properties is controlled by the alloying concept and by the casting as well as heat - treating process. The standard alloying elements in gray cast iron besides of carbon are silicon and manganese. Other elements like nickel, molybdenum, vanadium and magnesium are added to influence the microstructure. The research work on the effect of niobium in cast iron during the last 30 years allows to make the following general statements: - Nb additions up to 0. 3% improves the mechanical properties of gray iron resulting from a reduction in the cell size and correspondingly blunt graphite flake size. - Nb decreases the tendency to produce chill carbides due to an inoculating effect and the increase in cell count. - Nb is a mild pearlite stabilizer and refiner. - Nb additions of more than 0. 5 weight percent leads to the formation of primary MC - type carbides of high hardness improving the wear resistance of cast iron. Based on these effects specific applications of niobium - alloyed cast iron have been developed leading to appreciable technical and economical benefits. Work rolls for steel mills are often niobium - alloyed giving the advantage of reduced wear and thus longer endurance. Alloying of niobium to brake discs and drums allows to increase the graphite content at a given strength level and thus to optimize the heat conduction and damping behavior. The strength increasing effect of niobium can also be of advantage for the production of thin walled engine blocks. Additionally niobium helps to avoid the formation of chill structures which are difficult to machine. The present