摘要
本论文通过从生产现场取样然后和实验室实验相配合的方式,针对以唐山建龙热轧二厂生产出的热轧带钢为原料采用酸洗后进行冷轧而获得的SPCC冷轧低碳带钢进行研究,研究影响冷轧深冲钢性能的各种因素,研究对象包括生产工艺、织构、加工硬化系数n、塑性应变比r值及析出相等。
从生产现场进行取样,再在实验室分析。热轧生产现场设定590℃和650℃两种不同热轧卷取温度,分别选取在这两种不同的卷取温度下生产出的热轧、冷轧、退火以及平整后的带钢作为试样。在冷轧实验室通过拉伸实验测定试样的n、r值,结果显示热轧、退火和平整后带钢试样的塑性应变比r值均随着卷取温度的升高而逐渐降低,590℃热轧卷取所得带钢试样的深冲性能较理想。发现带钢试样退火后的凸耳系数Δr随卷取温度的升高略微升高除外,卷取温度对带钢试样的Δr值、应变硬化指数n值还有抗拉强度等力学性能的影响很不明显。
观察所取生产中试样的组织和析出,通过SEM实验和TEM实验发现,热轧、平整和退火后的带钢试样的晶粒均为饼形,同时发现高的热轧卷取温度下晶粒变细小,且容易出现混晶现象。在650℃的较高温度卷取时,热轧试样有粗大的条块状游离渗碳体和少量珠光体在晶界处析出,冷轧过程中的带钢渗碳体被压碎,压碎后形成的微观空隙会为带钢组织在退火时渗碳体的析出提供大量的位置,容易使带钢退火后的试样沿晶界甚至在晶内形成粗大的渗碳体,其他还有新析出渗碳体并未把空隙填满,这对深冲带钢的成形性能造成不利影响。细小弥散析出的AlN粒子,细化晶粒,并且还可以提高带钢强度。
在实验室用X射线衍射仪测定所取带钢试样的织构,测定结果发现热轧、冷轧、退火、平整各带钢试样的组织织构之间有一定的联系。结果发现带唐山建龙钢组织织构的发展具有一定遗传性。热轧带钢中的{111}有利织构伴随着生产的延伸得到逐渐的加强。再结合带钢试样拉伸实验和组织析出观察可以最终确定,温度较低的卷取温度更对提高带钢r值有利,获得均匀的组织和较少的渗碳体析出,在带钢退火后中更容易获得更多有利的{111}织构。
The combination of laboratorial and plant experiments was adopted on the research of microstructures and deep drawing properties of SPCC cold-rolled low-carbon steel sheets of Tangshan Jianlong Steel Group after sulfuric.
The plant experiments included sample taking from Jianlong Steel and analysis in laboratory.The coiling temperatures were separately set as 590℃and 650℃during plant production.Then samples were taken respectively from hot-rolled,annealed and temper-rolled sheets.The values of r and n were measured by tensile test in the laboratory.The results show the r values reduces with the increase of coiling temperature and the samples subjected to 590℃coiling temperature enjoy desirable deep drawing properties.The coiling temperature has no obvious effect on the r and n values of annealed sheets rises a little with the coiling temperature.
SEM and TEM were adapted to investigate the microstructure and precipitation of plant samples.The results show that the grAlNs of hot-rolled,annealed and temper-rolled sheets are prolate.The higher the coiling temperature,the smaller the grAlNs,which can even results in mix grAlN sizes.When subjected to the coiling temperature of 650℃,coarse chAlN cementities were observed along the grAlN boundaries of hot-rolled samples.The cenmentites were cracked after being cold rolled,which makes room for more cementite to precipitate along or even within grAlN boundaries during the following annealing process.The cementite particles of the cold rolled low-carbon steel sheets.The small precipitates of AlN,oxidation and sulfide can increase strength of steel sheets by anchoring the dislocations.
The results of texture test show that there is a connection between the hot-rolled, cold-rolled,annealed and temper-rolled sheets.The {111} texture formed in hot-rolling period can be further strengthened during the following processes.Take into account of the tensile test results and the microstructure investigation, conclusions can be made that low coiling temperature is conductive to microstructures; texture and deep drawing properties.
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