AHSS: Development of a High Strength, High Toughness Ausferritic Steel

该研究奖项的目的是促进对高强度，高韧性贝氏体钢的合成的基本理解，该钢具有由铁素体和碳稳定奥氏体组成的极细尺度组织。这种新型钢将采用等温球墨铸铁技术的概念，并在高硅含量的中碳低合金钢中应用一种新的绝热变形概念和两步等温淬火工艺合成。这种新工艺将产生极细的贝氏体铁素体和碳稳定奥氏体，从而同时提供高屈服强度、断裂韧性、冲击强度和疲劳强度。目前，这种独特性能的结合在传统的低合金钢中是无法获得的。如果成功，这项研究的结果将开创一种新技术，用于创造一系列具有优异机械性能组合的奥氏体钢。确定绝热变形和两步等温回火相结合是否会导致大的过冷和碳分配，从而导致极细尺度的贝氏体铁素体和碳稳定奥氏体。此外，它将验证这种微观结构是否能提供所需的机械性能组合，即同时具有高屈服强度、疲劳强度、断裂韧性和冲击强度。奥氏体钢的产生将是一个全新的概念。奥氏体钢的概念将对铁合金相变理论作出有价值的贡献。除此之外，我们还建立了一个热力学模型，在推导这个热力学模型时所做的假设也将被检查。因此，本文的研究将推动铁物理冶金以及基本相变热力学和动力学的知识水平。这种新型钢材将使结构部件更轻，更节能，从而提高燃油经济性，减少污染。这种新工艺也将导致钢的近净形状生产技术。等温回火工艺是一种更节能的热处理工艺，因为淬火后不需要后处理。因此，这一过程将显著节省能源。

The objective of this research award is to advance fundamental understanding of the synthesis of a high strength, high toughness bainitic steel with extremely fine scale microstructure consisting of ferrite and carbon stabilized austenite. This novel steel will be synthesized using the concept of austempered ductile cast iron technology and by applying a novel concept of adiabatic deformation together with a two-step austempering process in a medium carbon low alloy steel with high silicon content. This novel process will result in extremely fine bainitic ferrite and carbon stabilized austenite which will in turn provide simultaneous high yield strength, fracture toughness, impact strength and fatigue strength. Currently such combination of unique properties can not be obtained in conventional low alloy steels.If successful, the results of this research will pioneer a novel technology for creation of a series of Ausferritic Steels with excellent combination of mechanical properties. It will establish whether a combination of adiabatic deformation and two-step austempering will lead to large super cooling and carbon partitioning, and thus lead to an extremely fine scale bainitic ferrite and carbon stabilized austenite. Moreover it will validate whether such a microstructure will impart the desired combination of mechanical properties i.e. simultaneous high yield strength, fatigue strength, fracture toughness and impact strength. The creation of Ausferritic steel will be totally new and a novel concept. The concept of Ausferritic steel will make a valuable contribution to the theory of phase transformation in ferrous alloys. In addition to this, we have also developed a thermodynamic model and the assumptions made in derivation of this thermodynamic model will also be examined. Thus this proposed research will advance the state of knowledge in the ferrous physical metallurgy as well as basic thermodynamics and kinetics of phase transformation. This novel steel will make the structural components lighter, more energy efficient and consequently improve fuel economy and reduce pollution. This novel process will also lead to a near net shape production technology for steels. The austempering process is a more energy efficient heat treatment process since no post heat treatment after quenching is required. Therefore, this process will lead to significant energy savings.