Study on Thermal Deformation Behavior and Mechanism of Difficult-to-process Boron-containing Stainless Steel
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摘要: 硼在钢中的固溶度较低，采用熔铸法制备的含硼不锈钢在凝固过程中容易形成大量粗大硬脆的共晶硼化物，导致其坯料的热加工性能较差。针对这一难题，本文以18.5Cr-14.0Ni-2.1B含硼不锈钢作为研究材料，采用热力模拟实验机进行单道次热压缩实验，建立了流变应力本构方程，构建了热加工图并明确了该不锈钢合理的加工窗口，揭示了含硼不锈钢热变形行为及其机制。实验结果表明：18.5Cr-14.0Ni-2.1B不锈钢的表观热变形激活能Q和应力指数n分别为501.08 kJ·mol−1和8.13；热压缩过程中，共晶硼化物主要发生破碎、转动并诱发形成大量微孔洞，塑性流动的奥氏体基体可将大部分孔洞填充；热压缩过程的应变量越大，其加工窗口越小，18.5Cr-14.0Ni-2.1B含硼不锈钢在1000~1100℃以0.01~1.0 s−1的应变速率进行变形时，呈现较为良好的可加工性。Abstract: The solid solubility of boron in steel is low, and a large number of coarse, hard and brittle eutectic borides are easily formed in the solidification process of Boron-containing stainless steel prepared by fusion casting, which leads to poor hot processibility of its billets. In order to solve this problem, using 18.5Cr-14.0Ni-2.1B stainless steel as the research material, the single-pass hot compression experiment was carried out on a thermal simulation machine, the flow stress constitutive equation was established, the hot processing map was constructed, the reasonable processing window of the stainless steel was defined, and the thermal deformation behavior and mechanism of boron-containing stainless steel were revealed. The results show that the apparent thermal deformation activation energy Q and stress exponent n of 18.5Cr-14.0Ni-2.1B stainless steel are 501.08 kJ·mol−1 and 8.13 respectively; In the process of hot compression, eutectic borides are mainly broken, rotated and induced to form a large number of micropores, most of which can be filled by the plastic flowing austenitic matrix; The larger the strain of the hot compression process is, the smaller the processing window is. When the 18.5Cr-14.0Ni-2.1B boron-containing stainless steel is deformed at 1000~1100℃ and at the rate of 0.01~1.0 s−1, it shows good processibility.
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图 1 18.5Cr-14.0Ni-2.1B不锈钢铸锭1/4厚度的金相和高倍显微组织
Figure 1. Metallographic and High Magnification Microstructure of a Quarter Thick Layer of 18.5Cr-14.0Ni-2.1B Stainless Steel Ingot
图 2 不同变形温度及应变速率条件下应力-应变曲线
Figure 2. True Stress-True Strain Curves under Different Deformation Temperatures and Strain Rates
图 3 流变应力与应变速率和变形温度关系
Figure 3. Relationship between Flow Stress, Strain Rate and Deformation Temperature
图 5 18.5Cr-14.0Ni-2.1B不锈钢在不同应变量时的热加工图
Figure 5. Hot Processing Map of 18.5Cr-14.0Ni-2.1B Stainless Steel under Different Strains
图 6 应变速率为10 s−1时不同变形温度条件下的EBSD显微组织
Figure 6. Microstructure of EBSD under Different Deformation Temperatures at a Strain Rate of 10 s−1
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