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本文通过光学显微镜观察了Q550D与SM570-H的光学显微金相组织,通过扫描电镜观察其微观组织并利用能谱分析其夹杂物的成分。得到了两种钢的组织精细结构以及非金属夹杂物的形貌及成分,分析了这些夹杂物对低碳贝氏体钢性能的影响。
通过在显微镜下观察到Q550D组织为板条状的上贝氏体组织,在大致平行的铁素体板条中镶嵌着很多细小的不易辨认的渗碳体。而SM570-D的组织属于粒状贝氏体组织,在板条状的铁素体基体上弥散分布着由残余奥氏体和马氏体组成的小岛(也称M/A岛),从微观组织上观察,SM570-H的组织比Q550D更为细小。
通过扫描电镜图,可以观察到在两种钢中都含有非金属夹杂物,这些非金属夹杂物大多都分布在奥氏体晶界处,主要是一些复杂的钙铝酸盐和硫化物,其导致组织的不均匀,从而使得钢的性能出现不均匀,除了钙铝酸盐和硫化物之外,组织中也有一些细小的颗粒,这些颗粒主要是合金元素通过过饱和固溶体的时效处理而沉淀出来,从而提高钢的强度。钢中其它的一些微量元素如钛、铝等,这些元素的第二相弥散分布在铁基体中,形成弥散强化。
低碳贝氏体钢的性能还与轧制工艺有着密切的关系,特别是控制终轧温度能够明显改善低碳贝氏体钢的组织,一般把低碳贝氏体钢的终轧温度降低到1000℃左右能够明显提高低碳贝氏体钢的强韧性。
研究发现低碳贝氏体钢由于贝氏体组织结构精细,分布均匀,且碳当量小,因而贝氏体钢具有良好强韧性和焊接性能。
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关键词: 贝氏体组织, 金相组织,贝氏体转变,非金属夹杂
Research on the Microstructure Property of Low-carbon Bainite Steel
Abstract
The microstructure of Q550-D and SM570-H were studied by optical microscope and electron microscope in this paper, and positions was analyzed by energy spectrum. The microstructures of the two steels and positions of nonmetallic inclusions were obtained, also the effections of nonmetallic inclusions for the steels’ property was analyzed.
Through observation by microscopy we can get that there are parallel bainite-ferrite strip distributed in microstructure of Q550-D. And more fine cementites are inlayed in the bainite-ferrite strip, It’s uneasy to identify. It belongs to upper bainite. the microstructure of SM570-H belongs to granular bainite, the sand island consisted of retained austenite and martensite distributed in the lath-like ferrites,observing in the microstructure, The microstructure of SM570-H is finer than Q550D.
We can observed there were more nonmetallic inclusions in the Bainitic steels, and these nonmetallic inclusions always distributed in austenite grain boundary and always some calcium-aluminate and sulfides. These nonmetallic inclusions can decrease the strength of steels because of uneven microstructure. besides the calcium-al