Abstract To obtain the ultrafine martensite for BR1500HS ultra-high-strength steel, a new preparation process of cyclic heat treatment (CHT) with descending heat temperature and holding time along with cycle steps was developed. First, a series of thermal dilation tests were conducted with the temperature range of 420–730°C and the heat rate of 5 K/s on a Gleeble-3800 thermomechanical physical simulator. According to the experimental data, the temperature ranges and the optimal holding time to completely austenitize BR1500HS were determined. Then, to confirm the optimal parameters of CHT for BR1500HS, several tests with various temperatures and cycle steps were conducted and analyzed by optical microscope and scanning electron microscope. Subsequently, the CHTs with decreasing heating temperature and holding time were studied due to the increasing internal energy of steel along with the CHT process. The lath width was measured as a criterion to evaluate the refinement degree in this article. After several loops of heat treatment, the lath width is reduced to 0.268 µm. Finally, the hardness evolution of the specimens subjected to CHT in this study was analyzed and compared with the lath width test results, which justified the effectiveness of the new developed process.

中文翻译：

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超细马氏体提高BR1500HS钢的韧性和硬度

摘要 为获得BR1500HS超高强钢超细马氏体，开发了一种随着循环步骤降低加热温度和保温时间的循环热处理(CHT)制备新工艺。首先，在 Gleeble-3800 热机械物理模拟器上进行了一系列热膨胀测试，温度范围为 420-730°C，热速率为 5 K/s。根据实验数据，确定了BR1500HS完全奥氏体化的温度范围和最佳保温时间。然后，为了确定 BR1500HS 的 CHT 的最佳参数，进行了多次不同温度和循环步骤的测试，并通过光学显微镜和扫描电子显微镜进行了分析。随后，由于钢的内能随着 CHT 过程的增加而增加，因此研究了随着加热温度和保温时间降低的 CHT。本文以板条宽度作为评价细化程度的标准。经过几次循环热处理后，板条宽度减小到 0.268 µm。最后，对本研究中经过 CHT 处理的试样的硬度演变进行了分析，并与板条宽度测试结果进行了比较，这证明了新开发工艺的有效性。