Thermomechanisch hergestellter, extrem fester Bainit mit reduziertem C-Gehalt

一种生产极其坚固和廉价的钢的新方法正在开发中。该钢的强度可达2500mpa，硬度为600-670HV，断裂韧性超过30- 40mpam /2。这种新材料依赖于被称为贝氏体的微观结构，这种微观结构早在70多年前就已为人所知；新颖之处在于合金的设计，使其具有精细的组织和对热处理的控制反应。这些钢的高强度是由于它们非常精细的结构。观察到的细化主要是高碳含量和低转变温度提高奥氏体强度的结果。随着形成贝氏体的奥氏体屈服强度的增加，贝氏体板可望变薄。因此，高碳通过强化奥氏体直接细化组织，通过降低Ms温度间接细化组织，从而允许在较低温度下进行贝氏体转变过程。然而，高碳含量导致组织中存在大面积的未转化奥氏体，这对力学性能是有害的。T0曲线限制了在任何温度下可以形成的贝氏体的数量，这是这些大面积未转化奥氏体存在的原因。我们的初步预试结果表明，降低碳含量具有以下优点：-加速贝氏体转变反应。-在临界区域的一定温度范围内释放渗碳体，为合金的临界退火提供了可能。这种可能性导致了更大范围的机械性能。-观察到的拉伸和压缩性能与文献[1,6]中报道的结果相当。由于碳含量的降低，残余奥氏体含量的降低证明了这一点。通过本项目的工作，将研究以下几点：-研究合金元素对相变过程和机械性能的影响。-降低碳含量，同时通过热机械加工代替奥氏体强度的降低（10）。这一发展将导致在平面产品中获得这种类型的微观结构。

A novel method for producing extremely strong and cheap steel is under development. The steel is reaching strength up to 2500 MPa, a hardness of 600-670HV and fracture toughness in excess of 30-40MPam1/2. The new material relies on microstructure called bainite which is known since more than seven decades; the novelty is in the alloy design which leads to a fine structure and controlled response to heat treatment. The high strength of these steels is due to their very fine structure. The observed refinement is a consequence mainly of the ability of high carbon content and low transformation temperature to enhancing the strength of the austenite. It is expected that the bainite-plates will become thinner as the yield strength of the austenite, from which they are formed, increases. Thus, the high carbon directly refines the structure by strengthening the austenite and indirectly by lowering the Ms temperature and thus allowing performing the bainitic transformation process at lower temperature. However, the high carbon content results in the existence of large regions of untransformed austenite in the microstructure, which is known to be detrimental to the mechanical properties. The T0 curve, which limits the amount of bainite that can be formed at any temperature, is the reason for the existence of these large regions of untransformed austenite. Our first pre-tests results showed that decreasing the carbon content has the following advantages: - Accelerating the bainite transformation reaction. - Releasing the cementite in a certain temperature range in the intercritical region which provided the possibility of intercritical annealing of the alloys. This possibility results in a wider range of mechanical properties. - The observed tensile and compression properties are comparable with those reported in ref. [1, 6]. This is justified by the decrease in the retained austenite content as a result of decreasing the carbon content. Through out the work of this project the following points will be investigated: - Investigation of the effect of alloying elements on the phase transformation process and mechanical properties. - Lowering the carbon content and simultaneously substituting the decrease in austenite strength by thermomechanical processing (10). This development will result in obtaining this type of microstructure in flat products.