Pokluda Jaroslav, Dlouhý Ivo, Kianicová Marta, Čupera Jan, Horníková Jana, Šandera Pavel
Faculty of Mechanical Engineering, Brno University of Technology, Technická 2, 616 69 Brno, Czech Republic.
Faculty of Special Technology, Alexander Dubcek University of Trencin, Ku kyselke 469, 911 06 Trenčín, Slovakia.
Materials (Basel). 2021 Oct 7;14(19):5875. doi: 10.3390/ma14195875.
The temperature dependence of tensile characteristics and fracture toughness of the standardly heat-treated low-alloyed steel OCHN3MFA along with three additionally heat-treated grades was experimentally studied. In the temperature range of ⟨-196; 22⟩ °C, all the additional heat treatments transferred the standard steel from a high- to ultra-high strength levels even with improved tensile ductility characteristics. This could be explained by a reduction of the inclusion content, refinement of the martensitic blocks, ductile retained austenite content, and homogenization of the shape ratio of martensitic laths as revealed by metallographic, X-ray, and EBSD techniques. On the other hand, the values of the fracture toughness of all grades were found to be comparable in the whole temperature range as the cause of a high stress triaxiality in the pre-cracked Charpy V-notch samples. The values of the fracture toughness of the standard steel grade could be predicted well using the fracture model proposed by Pokluda et al. based on the tensile characteristics. Such a prediction failed in the case of additionally heat-treated grades due to the different temperature dependence of the fracture mechanisms occurring in the tensile and fracture-toughness tests. While the tensile samples fractured in a ductile-dimple mode at all temperatures, the fracture-toughness specimens exhibited a transition from the ductile to quasi-brittle fracture mode with decreasing temperature. This transition could be interpreted in terms of a transfer from the model proposed by Rice and Johnson to the model of Tvergaard and Hutchinson.
对标准热处理的低合金钢OCHN3MFA以及另外三种热处理等级的钢的拉伸特性和断裂韧性的温度依赖性进行了实验研究。在⟨-196; 22⟩°C的温度范围内，所有额外的热处理都将标准钢从高强度水平转变为超高强度水平，同时拉伸延展性特性也得到改善。这可以通过金相、X射线和电子背散射衍射（EBSD）技术揭示的夹杂物含量降低、马氏体块细化、韧性残余奥氏体含量以及马氏体板条形状比的均匀化来解释。另一方面，由于预制裂纹夏比V型缺口试样中的高应力三轴性，发现所有等级的断裂韧性值在整个温度范围内具有可比性。使用Pokluda等人基于拉伸特性提出的断裂模型，可以很好地预测标准钢等级的断裂韧性值。对于额外热处理的等级，由于拉伸试验和断裂韧性试验中发生的断裂机制对温度的依赖性不同，这种预测失败了。虽然拉伸试样在所有温度下均以韧性韧窝模式断裂，但断裂韧性试样随着温度降低呈现从韧性断裂到准脆性断裂模式的转变。这种转变可以根据从Rice和Johnson提出的模型到Tvergaard和Hutchinson模型的转变来解释。
