无缝钢管Gr.6轧制及正火后的组织和性能分析

Microstructure and Properties of Seamless Steel Pipe Gr.6 after Rolling and Normalizing

利用光学显微镜、扫描电镜、透射电镜分析及力学试验、腐蚀试验等,分析了热轧态和正火态Gr.6钢管组织形貌、低温性能及耐腐蚀性能。结果表明,研制的低温无缝钢管Gr.6热轧态及正火态低温力学性能及抗腐蚀性能满足标准要求,热轧态显微组织为珠光体+铁素体,晶粒均匀细小,但带状组织明显。析出相以TiN颗粒为主,在-60℃发生韧脆转变,经过900℃正火热处理后,晶粒更为细小,晶粒度达到10级以上,正火态试样大角度晶界差比例高于热轧态,大角度界面密度也有所增加。析出相主要为TiN+少量的VN颗粒,且在-80℃仍未发生韧脆转变。通过快、慢极化扫描速率的极化试验研究了材料的腐蚀行为。腐蚀试验表明,正火态试样在电化学模拟溶液中应力腐蚀敏感性较小,而热轧态试样的应力腐蚀敏感性较大。因此,正火态相比热轧态电化学腐蚀性能更优,适合更加苛刻的腐蚀环境。

The microstructure morphology,low-temperature performance,and corrosion resistance of hot-rolled and normalized condition Gr.6 steel pipes were analyzed using optical microscopy,scanning electron microscopy,transmission electron microscopy,mechanical testing,and corrosion testing.The results show that the low-temperature mechanical properties and corrosion resistance of the developed low-temperature seamless steel pipe Gr.6 in the hot-rolled and normalized states meet the standard requirements.The microstructure in the hot-rolled state is pearlite and ferrite,with uniform and fine grains,but the banded structure is obvious.The precipitated phase is mainly composed of TiN particles,which undergo a ductile brittle transition at-60℃.After 900℃normalizing heat treatment,the grains become finer,with a grain size of 10 grade or above.The proportion of large angle grain boundary differences in the normalized state sample is higher than that in the hot-rolled state,and the density of the large angle interface also increases.The precipitate phase is mainly TiN and a small amount of VN particles,and no ductile brittle transition has occurred at-80℃.The corrosion behavior of the material was studied through polarization tests with fast and slow polarization scanning rates.Corrosion tests have shown that the stress corrosion sensitivity of normalized specimens is relatively low in electrochemical simulation solutions,while the stress corrosion sensitivity of hot-rolled specimens is relatively high.Therefore,the electrochemical corrosion performance of the normalized state is better than that of the hot-rolled state,and it is suitable for more harsh corrosion environments.