中文摘要：

采用Mn-Nb-B减量化成分设计的低碳贝氏体高强钢为研究对象,通过热模拟实验研究实验钢热变形行为和相变行为。结合中厚板生产线特点制定控制轧制与超快速冷却相结合生产工艺路线,充分利用超快速冷却条件下的细晶强化、析出强化等综合强化机制,实现综合力学性能优良的低成本高强工程机械用钢的试制和生产。产品屈服强度和抗拉强度分别达到678MPa和756MPa,伸长率A50为33%,-20℃低温冲击达到261J。产品显微组织由粒状贝氏体、针状铁素体和板条贝氏体组成,基体组织内弥散分布着细小的点状、粒状M/A岛和均匀细小的（Nb,Ti）（C,N）析出粒子以及大量位错组织。

英文摘要：

Using the Mn-Nb-B low carbon bainite high strength steel with the reducing production technology as the research target,the deformation behavior and phase transformation behavior were studied by the thermal simulation testing machine.Combining with the characteristics of the medium and heavy plate production line,the controlled rolling and controlled cooling technology based on ultra-fast cooling were designed to produce low cost high strength construction machinery steel with superior comprehensive mechanical properties.The strengthening mechanisms such as grain refinement strengthening,precipitation strengthening are effective to produce the Mn-Nb-B low carbon bainite high strength steel.The yield strength and tensile strength of the product reach to 678 MPa and 756 MPa respectively,the elongation A50 is 33%and the impact energy at-20℃is 261 J.The microstructure of the steel is composed of granular bainite,acicular ferrite and lath bainite.A large number of fine,point,granular M/A constituents and dislocation structures dispersively distributed inside the matrix,and also tiny and dispersed（Nb,Ti）（C,N）precipitates are observed by transmission electron microscopy.