CSP产线下汽车结构用热轧酸洗板中的夹杂物

Inclusions in hot rolled pickling plate for automobile structure through CSP process

为了提高CSP产线热轧酸洗板的洁净度与综合性能,研究了CSP工艺下QSTE500TM(汽车结构用热轧酸洗板)冶炼过程和热轧卷中的夹杂物。冶炼过程中夹杂物的变化路线是Al_(2)O_(3)-SiO_(2)-MnO→Al_(2)O_(3)→MgOAl_(2)O_(3)-CaO-CaS→Al_(2)O_(3)-CaO-CaS。LF钙处理前到中间包阶段,钢液中夹杂物总量基本不变,约为200μm^(2)/mm^(2)。热轧卷中夹杂物总量约是钢液中的2倍,组成主要是较大尺寸的MgO-Al_(2)O_(3)-CaO-CaS、小尺寸的TiN析出物以及中等尺寸的Al_(2)O_(3)-CaO-TiN复合夹杂。随着氮含量的增加,热轧卷中夹杂物总量增加、小尺寸夹杂物分布均匀,10μm以上的夹杂物在卷宽1/4处分布最多。由于选分结晶的作用,复合夹杂中TiN的质量分数在10%~100%之间变化,随着TiN含量的升高,夹杂物尺寸逐渐变小。CSP工艺下热轧卷中第二相析出物更均匀,有利于产品最终的力学性能。综合考虑过程控制能力和产品性能需求,建议CSP热轧酸洗板严格控制连铸保护浇铸,氮质量分数小于0.006 0%。

In order to improve the cleanliness and comprehensive properties of hot-rolled pickling plate produced by CSP process.The inclusions in QSTE500 TM(hot rolled pickling plate for automobile structure)smelting process and hot-rolled coil through the CSP process were studied.The variation route of inclusions in the process of smelting is Al_(2)O_(3)-SiO_(2)-MnO → Al_(2)O_(3) → MgO-Al_(2)O_(3)-CaO-CaS→ Al_(2)O_(3)-CaO-CaS.Before the LF calcium treatment to tundish,the total amount of inclusions in molten steel remains unchanged,is about 200μm^(2)/mm^(2).The total amount of inclusions in the hot-rolled coil is about 2 times of that in molten steel.The main inclusion is large MgOAl_(2)O_(3)-CaO-CaS,small TiN precipitates,and medium-size Al_(2)O_(3)-CaO-TiN complexes.The mass percent of TiN in complex inclusions varies from 10% to 100%.With the increase of TiN content,the size of inclusions decreases gradually.The density of inclusions below 10μm in different positions of the hot-rolled coil is almost the same,and the inclusions above 10μm are the most at 1/4 of coil width.With the increase of nitrogen content,the content of inclusions in hot rolled coil increases.The precipitation of the second phase in the hot-rolled coil is more uniform under the CSP process,which is beneficial to the final mechanical properties of the products.Considering the process control ability and product performance requirements,it is suggested to strictly control the protective casting of CSP hot-rolled pickling plate with nitrogen mass percent below 0.006 0%.