Q460GJCZ35特厚板Z向性能不合原因分析及优化措施

Causes analysis and optimization measures of unqualified Z-direction property of Q460GJCZ35 ultra-heavy plate

针对60~80 mm厚Q460GJCZ35钢板控轧后Z向性能不合的问题,采用金相检验、扫描电镜等检测手段,对钢板的组织、厚拉断口的形貌、夹杂物进行了检测分析。结果表明:Q460GJCZ35特厚板Z向性能不合是由于钢板心部存在贝氏体带状组织,以及厚拉断口存在MnS夹杂、(Nb、Ti)C夹杂而导致。为此,对Q460GJCZ35特厚板化学成分进行了优化,采用了降低C、Mn含量来减轻偏析,提高V、Ti含量及添加Cr元素来保证钢板强度的成分设计;炼钢及连铸工艺通过提高钢水的洁净度、加入钙线、降低拉速、增大二冷水量等措施,减少了钢坯的心部偏析及夹杂物;钢坯加热采用"低温长时间保温"工艺,控轧控冷工艺通过增大粗轧道次压下量、采用差温轧制工艺,提高精轧累计压下率、提高精轧温度、提高开冷温度、增大冷速等措施,保证了钢板的强度及Z向性能。

Aiming at the problem of unqualified Z-direction performance of 60-80 mm thickness Q460 GJCZ35 plate after controlled rolling, the metallographic inspection, scanning electron microscopy and other testing methods were used to detect and analyze the microstructure of the plate and the morphology and the inclusions of the thick-drawn fracture. The results show that the unqualified Z-direction performance of the Q460 GJCZ35 ultra-heavy plate is caused by the presence of a bainite band-like segregation zone in the core of the plate and the presence of MnS inclusions and(Nb, Ti) C inclusions in the thick-drawn fracture. For this reason, the chemical composition of the Q460 GJCZ35 plate was optimized, the contents of C and Mn were decreased to reduce segregation, the contents of V, Ti were increased and the Cr was added to ensure the strength of the plate. The steelmaking and continuous casting processes were improved, such as increasing the cleanliness of molten steel, adding calcium wires, lowering the drawing speed, and increasing the amount of secondary cooling water to reduced the core segregation and inclusions of the billet. The billet heating used the "low temperature and long-time holding" process, and the controlled rolling and controlled cooling process was improved by increasing roughing rolling pass reduction, adopting differential temperature rolling technology, increasing the cumulative reduction rate of finishing rolling, increasing finishing temperature, cooling temperature and cooling speed, and the strength and Z-direction performance of the plate were essured.