PRODUCTION OF SENSITIZATION-RESISTANT MATERIALS BY TWIN-INDUCED GRAIN BOUNDARY ENGINEERING

传统工艺如降低碳含量、稳定化处理、局部固溶-热处理等不能很好地防止奥氏体不锈钢晶界碳化铬析出引起的贫铬敏化。最近对晶界结构的研究表明，敏化强烈地依赖于晶界性质和原子结构，而低能晶界(如重位晶格(CSL)晶界)具有很强的抗晶间腐蚀能力。晶界设计与控制的概念被称为晶界工程(GBE)。GBEed材料的特点是CSL晶界频率高，可抵抗材料的晶间劣化，如晶间腐蚀。为了提高材料的抗GBE敏化性能，进行了热机械处理。A304型奥氏体不锈钢为冷轧…更多的热处理和固溶处理，然后敏化-热处理。用取向成像显微镜(OIM)观察了晶界特征的分布。通过电化学动电位再活化法(EPR)和硫酸铁-硫酸体系测试评价了涂层的耐晶间腐蚀性能。热机械处理降低了钢的晶间腐蚀敏感性，在较小的轧辊压下量时，敏感性最小。CSL边界的出现频率在小幅下降时达到最大。硫酸铁腐蚀试验表明，热机械处理后的试件的腐蚀速率远小于母材。在形变处理后的样品中观察到高密度的退火孪晶。结果表明，形变热处理可以通过孪晶的退火在晶界网络中引入低能段，阻止晶间腐蚀的渗流。还研究了碳含量和其他微量元素对晶界特征分布(GBCD)和热机械参数优化的影响。较少

Sensitization by chromium depletion due to chromium carbide precipitation at grain boundaries in austenitic stainless steels can not be prevented perfectly only by previous conventional techniques, such as reduction of carbon content, stabilization-treatment, local solution-heat-treatment, etc. Recent studies on grain boundary structure have revealed that the sensitization depends strongly on grain boundary character and atomic structure, and that low energy grain boundaries such as coincidence-site-lattice(CSL) boundaries have strong resistance to intergranular corrosion. The concept of "grain boundary design and control" has been developed as grain boundary engineering (GBE). GBEed materials are characterized by high frequencies of CSL boundaries which are resistant to intergranular deterioration of materials, such as intergranular corrosion. A thermomechanical treatment was hid to improve the resistance to the sensitization by GBE. A type 304 austenitic stainless steel was cold-roll … More ed and solution-heat-treated, and then sensitization-heat-treated. The grain boundary character distribution was examined by orientation imaging microscopy (OIM). The intergranular corrosion resistance was evaluated by electrochemical potentiokinetic reactivation (EPR) and ferric sulfate-sulfuric acid tests. The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of CSL boundaries indicated a maximum at the small reduction. The ferric sulfate-sulfuric acid test showed much smaller corrosion rate in the thermomechanical-treated specimen than in the base material. A high density of annealing twins were observed in the thermomechanical -treated specimen. The results suggest that the thermomechanical treatment can introduce low energy segments in the grain boundary network by annealing twins and can arrest the percolation of intergranular corrosion from the surface. The effects of carbon content and other minor elements on optimization in grain boundary character distribution (GBCD) and thermomechanical parameters wore also examined during GBE. Less