Metallurgical Functionality of Mo Alloying and Nb Microalloying in Automotive Multiphase Steels
- 作者：Mohrbacher Hardy
- 会议时间：2011-10-26
- 关键词：multiphase steel ; molybdenum ; niobium ; strength ; formability ; microstructure ; hardenability
- 作者单位：NiobelCon bvba, Schilde, Belgium
- 母体文献：第八届(2011)中国钢铁年会论文集
- 会议名称：第八届(2011)中国钢铁年会
- 会议地点：北京
- 主办单位：中国金属学会
- 语种：chi
- 分类号：TG1;TQ1
摘要
No other industrial sector has pursued weight reduction as consequently as the automotive industry since the reduction of fuel consumption and emissions as well as the improvement of crash safety continue to be major technical targets. The body-in-white (BIW), I.e., the body structure including all hang-on parts such as fenders, doors and lids constitutes the largest contributor to the total vehicle weight. Modern car bodies using an advanced steel design usually account for 25 to 35% of the total vehicle weight. The advanced steel BIW is also the most cost-efficient way of reducing the vehicle weight. Weight reductions of 20 to 25% compared to a conventional steel body could be achieved at a simultaneous cost reduction of around 10%. Multiphase steel grades come as hot rolled and cold rolled grades and play an essential role in advanced automotive BIW construction. The strength and elongation of multiphase steels are principally determined by the ratio of ferrite, bainite, retained austenite and martensite in the microstructure. The alloying concept as well as the metallurgical processing route determine to what extend these phases will be present in the microstructure. Molybdenum is a very powerful element for controlling the phase composition. It offers better hardenability than Mn or Cr. Molybdenum particularly has a strong effect on the carbon diffusivity which can be used to tailor particular phases and to control precipitation of microalloying elements. With regard to forming operations in the press shop additional properties are important such as bendability and hole expansion ratio. These characteristics relate to the morphology and distribution of the phases in the microstructure. Niobium microalloying can influence not only the strength of multiphase steels but also particularly the phase morphology and homogeneity leading to significant improvement of the mechanical properties. The paper will demonstrate alloying and processing strategies involving Mo and Nb alloying in multiphase steel production and provide options on tailoring mechanical properties to the needs of applications. The metallurgical mechanisms induced by either element and the synergies between both elements are being discussed.