退火工艺对Q195冷轧钢板组织及屈强比的影响

发布时间：2017-12-28 12:35

本文关键词：退火工艺对Q195冷轧钢板组织及屈强比的影响　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：Q195冷轧钢板因其具有优良的塑、韧性和加工性能,被广泛应用于轻工、机械、交通运输等行业,在我国低碳薄钢板中占据较大市场份额。但在进行Q195冷轧钢板生产时,普遍存在屈强比偏高问题。屈强比(YieldRatio=ReL/Rm)是衡量材料冷变形和均匀延伸能力的重要指标。屈强比高的钢板由开始发生塑性变形到最终断裂的形变容量小,严重影响了钢板的成型性能和结构设计安全性。因此,研究屈强比影响因素对钢板屈强比控制和开发低屈强比钢材具有重要意义。本课题以泰钢1780产线(板宽1780mm)和950产线(板宽950mm)生产的Q195钢板为研究对象,采用组织表征和力学性能分析相结合的方法,首先探讨了导致Q195钢板屈强比偏高的主要原因,再系统研究了退火工艺对Q195冷轧钢板微观组织及屈强比的影响,以此探究退火工艺是否可以解决Q195钢板屈强比过高的问题。对泰钢Q195钢板的力学性能进行分析可知,其屈强比为0.68～0.83,高于普通碳素钢屈强比要求(0.60～0.65),主要因为屈服强度偏高(281～338MPa)。进行组织观察和夹杂物分析可知,1780产线Q195钢板屈强比偏高的原因主要为:热轧钢板组织在厚度方向上不均匀,心部组织细小,表层组织粗大;钢中难变形的A1203及其复合夹杂物含量过高且细小弥散。950产线Q195钢板屈强比偏高的原因主要为:热轧及退火钢板组织均匀但过于细小;钢中难变形的A1203及其复合夹杂物含量过高且细小弥散。细小弥散的夹杂物造成了弥散强化和细晶强化,提高了钢板的屈强比。对Q195冷轧钢板进行了模拟罩式退火,研究了退火温度和保温时间对Q195冷轧钢板显微组织及屈强比的影响。研究结果表明,在3小时恒时退火时,1780产线Q195冷轧钢板在610℃时完成再结晶;随着退火温度从610℃升高到760℃,钢板组织均匀性得到提高,但晶粒没有明显长大,因此屈服强度未明显降低,屈强比依然偏高。950产线压下率为58.5%和86.1%的Q195冷轧钢板分别在580℃和550℃时完成再结晶,大压下率钢板的再结晶温度更低,且再结晶晶粒越细小;随着退火温度由640℃升高至760℃,950产线Q195冷轧钢板组织均匀性得到提高,晶粒略微长大,故屈服强度随之降低,屈强比由0.92降至0.84,但仍高于普碳钢屈强比要求。在670℃和730℃恒温退火时,两条产线的Q195冷轧钢均在5min内完成了再结晶,说明冷变形金属在高于再结晶临界温度条件下,再结晶过程可以迅速完成。保温时间在30min内,硬度下降较明显,而保温时间由30min延长至7h过程中,硬度降低较小,晶粒尺寸仅略微长大。综上所述,两条产线生产的Q195钢板都无法单纯通过调整退火工艺来改善因夹杂物过多而造成的晶粒细小问题,降低屈强比的效果不明显。两条产线都需要优化冶炼除杂工艺,提高钢水纯净度;1780产线还需要在热轧过程进行工艺优化,提高热轧组织均匀性。
[Abstract]:Q195 cold-rolled steel sheet is widely used in light industry, machinery, transportation and other industries because of its excellent plasticity, toughness and processability. It occupies a large market share in China's low carbon steel sheet. But in the production of Q195 cold rolled steel plate, there is a widespread problem of high ratio of flexion to strength. The ratio of flexion and strength (YieldRatio=ReL/Rm) is an important index to measure the cold deformation and the uniform extension ability of the material. The deformation capacity of the steel plate with high bending strength from the beginning of plastic deformation to the final fracture is small, which seriously affects the forming and structural design safety of the steel plate. Therefore, it is of great significance to study the influence factors of the flexion ratio for steel plate bending strength ratio control and the development of low yield strength ratio steel. This topic in Taigang 1780 production lines (board width 1780mm) and the 950 production line (width 950mm) Q195 steel production as the research object, using the method of tissue characterization and mechanical properties analysis unifies, first discusses the cause of Q195 plate yield ratio of the main reasons for the high, and then studied the annealing process on the yield and effect of high ratio of Q195 cold rolled steel microstructure, in order to explore whether the annealing process can solve the Q195 problem of high yield ratio of steel plate. The analysis on the mechanical properties of Taishan steel Q195 plate, the yield ratio is 0.68 ~ 0.83 higher than that of ordinary carbon steel, yield ratio requirements (0.60 ~ 0.65), mainly because of the high yield strength (281 ~ 338MPa). By metallographical analysis, 1780 production line of steel Q195 high yield ratio of the main reason for the organization: hot rolled steel plate is not uniform in the thickness direction, heart tissue surface fine and coarse microstructure; steel deformed A1203 and its composite inclusion content is too high and fine dispersion. The main reason for the high yield ratio of Q195 steel plate on the 950 production line is that the hot rolled and annealed steel plate is homogeneous but too small, and the A1203 and its complex inclusions in the steel are difficult to deform. The fine dispersion of inclusions resulted in dispersion strengthening and fine grain strengthening, and increased the ratio of flexion to strength of the steel plate. The simulated annealing of Q195 cold rolled steel sheet was carried out. The effects of annealing temperature and holding time on the microstructure and yield ratio of Q195 cold rolled steel sheet were studied. The results show that in the 3 hours of constant time during annealing, 1780 Q195 production line of cold rolled steel plate at 610 DEG C to complete recrystallization; with the increase of the annealing temperature from 610 degrees to 760 degrees, the microstructure uniformity is improved, but the grain size does not grow significantly, so the yield strength has been significantly reduced, yield ratio is still high. The 950 line pressure rate of Q195 cold rolled steel plate 58.5% and 86.1% are completed in 580 degrees and 550 degrees when the recrystallization rate under the pressure plate, the recrystallization temperature is lower, and the recrystallization grain size; with the increase of the annealing temperature from 640 DEG to 760 DEG C, Q195 cold rolled steel production line 950 uniformity to improve the grain grow up slightly, the yield strength decreases, yield ratio decreased from 0.92 to 0.84, but still higher than the carbon yield ratio requirements. The recrystallization of Q195 cold rolled steel produced by two production lines was completed in 5min at 670 and 730 degrees constant temperature, indicating that the recrystallization process of cold formed metal can be completed at a higher critical temperature than that of recrystallization. When the holding time is in 30min, the hardness decreases obviously. While the heat preservation time is extended from 30min to 7h, the hardness decreases less, and the grain size is only slightly grown. To sum up, the Q195 steel plates produced by two production lines can not only improve the grain size problem caused by too much inclusions by adjusting the annealing process, but the effect of decreasing the ratio of yield to strength is not obvious. The two production lines need to optimize the smelting and impurity removal process and improve the purity of molten steel. The 1780 production line also needs to optimize the process in hot rolling process and improve the homogeneity of hot rolled structure.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1;TG335.5;TG162.83

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