低碳贝氏体钢的组织类型及其对性能的影响

Microstructure and Mechanical Properties of Low Carbon Bainitic Steel

低碳贝氏体钢受控冷工艺的影响会得到不同类型的组织, 在较慢速冷却时,在奥氏体中先形成针状铁素体,残余奥氏体会被包裹在铁素体之中,形成粒状贝氏体团。工业轧制试验表明,不同控制冷却工艺可得到两类组织,一类出现黑珠组织(富碳马氏体组织),具有该组织的钢轧态冲击韧性低。另外一类为细化的板条贝氏体组织,具有该组织的钢轧态强度高,冲击韧性好,但伸长率不足。通过回火处理,存在黑珠组织钢的冲击韧性能得到提高,超细化板条贝氏体组织钢的伸长率也能得到改善,但后者屈服强度会比前者高100 MPa左右。

In low carbon bainitic steel, different microstructure is formed depending on the cooling rate. From a thermo-simulation study, it was found that during slowly continuous cooling, the acicular ferrite nucleates at the prior austenite grain boundary or other interfaces first; the retained austenite remains beside the acicular ferrite to form M/A constituents. Industrial test showed that, two kinds of microstructure can be formed depending on the thermo-mechanical control processes: one is granular bainite with coarse block-like M/A phase, and the other is ultrafine lath-like bainitic ferrite. The steel as rolled with granular bainite and coarse M/A phase has lower strength and toughness compared with the steel with ultrafine bainitic ferrite, but the elongation of the former is relatively higher than the later one. Tempering for 1 h at about 600 ℃ can improve the toughness of steel with granular bainite, and the elongation of steel with ultrafine bainite ferrite, and the strength of the tempered ultrafine bainitic ferrite steel is higher by about 100 MPa than that of granular bainite steel.