Q345H型钢Z向性能的研究

发布时间：2018-01-05 06:01

本文关键词：Q345H型钢Z向性能的研究　出处：《山东大学》2016年硕士论文　论文类型：学位论文

更多相关文章： H型钢 Z向性能 带状组织 夹杂物

【摘要】：近年来具有高强度、塑性、抗疲劳强度和焊接性能的优质钢越来越受到人们的青睐。H型钢具有截面模量高、重量轻、容易组装等特点,被广泛应用于高层建筑上。由于其受力环境比较复杂,因此还需要较好的Z向性能(即抗层状撕裂性能)。目前我国广泛使用的要求Z向性能的H型钢大多是通过Z向钢板焊接而成,焊接接头金属冷却过程中发生收缩现象会产生很大的拉应力,引起应力集中,易形成微裂纹,发生层状撕裂。因此研究影响钢材Z向性能的因素,开发出具有较好Z向性能的热轧H型钢具有重要意义。本课题以莱钢生产的精炼Q345B、未精炼Q345B和Q345ELH型钢为研究对象,在精炼Q345B钢翼缘和腹板、未精炼Q345B钢翼缘和腹板、Q345EL钢翼缘分别进行取样,做厚度方向拉伸试验测量其厚度方向力学性能,然后对其金相组织,断口形貌和夹杂物等进行研究,总结出影响Q345H型钢Z向性能的因素。研究发现,试验钢中精炼Q345B钢的Z向性能最好,Q345EL钢次之,未精炼Q345B钢的Z向性能最差。从微观组织方面分析,影响Q345H型钢Z向性能的主要因素是带状组织和晶粒度等级,带状组织越明显,晶粒度等级越小,Z向性能越差。Q345EL和未精炼Q345B钢组织均为铁素体和珠光体组成的带状组织,而Q345EL钢在冶炼的过程中添加了B、Nb等微量合金元素,晶粒得到细化, Z向性能相对较好。而经钢包精炼的Q345B钢组织中没有出现明显的对Z向性能不利的带状组织,原因是它在轧制过程中应用了控轧控冷技术,带状组织消失,改善了钢板的各向异性,Z向性能相对更好。从夹杂物方面分析,影响Q345H型钢Z向性能的主要因素是夹杂物的含量、形状和尺寸,夹杂物含量越多,尺寸越大,Z向性能越差。精炼Q345B和Q345EL钢中的长条状硫化物、硅酸盐类夹杂物均明显少于未精炼Q345B钢,Z向性能相对较好。同一种型钢中,翼缘和腹板部位的夹杂物种类一致,且含量基本相同,但是腹板部位的硫化物夹杂物的尺寸较大,作为裂纹源扩展的倾向性较大,Z向性能较差。断口形貌分析发现,五组试样断口均属于韧性断口。精炼Q345B钢翼缘和腹板试样断口出现大量等轴韧窝,尺寸较小,韧坑较深,可以观察到少量微小夹杂物。Q345EL钢翼缘试样断口出现较多长条状韧窝,尺寸较大、韧坑较浅,也可以观察到少量微小夹杂物。未精炼Q345B钢翼缘与腹板试样断口出现较多长条状韧窝,尺寸较大、韧坑较浅,同时出现了一些解理面形貌,并且可明显的观察到较多长条状夹杂物。韧窝尺寸越小、深度越深,断面收缩率越大,材料的Z向性能越好。因此工业化生产具有优良Z向性能的热轧H型钢时需应用精炼技术降低其夹杂物的含量,尤其是硫化物、硅酸盐等塑性夹杂物,同时采用控轧控冷工艺改善带状组织,细化晶粒,提高材料的Z向性能。
[Abstract]:In recent years, high quality steels with high strength, plasticity, fatigue strength and welding properties have been more and more favored by people. H section steel has the characteristics of high section modulus, light weight, easy assembly and so on. It is widely used in high-rise buildings, because of its stress environment is more complex. Therefore, we also need better Z performance (that is, layer tearing resistance). At present, the H-section steel which is widely used in our country, which requires Z-direction performance, is mostly welded by Z-direction steel plate. The shrinkage phenomenon of welded joint metal during cooling will produce great tensile stress, cause stress concentration, and easily form micro-cracks and lamellar tear. Therefore, the factors that affect the Z-direction properties of steel are studied. It is of great significance to develop hot rolled H-section steel with good Z-direction properties. In this paper, the refined Q345B, unrefined Q345B and Q345ELH sections produced by Laiwu Iron and Steel Co. The flange and web plate of refined Q345B steel, unrefined Q345B steel flange and web plate steel Q345EL steel flange were sampled, and the thickness direction mechanical properties were measured by tensile test in thickness direction. Then the metallographic structure, fracture morphology and inclusion of Q345H steel were studied, and the factors affecting the Z-direction properties of Q345H steel were summarized. It was found that the Z-direction property of Q345B steel was the best in the test steel. Q345EL steel followed by unrefined Q345B steel in Z direction properties. From the microstructure analysis, the main factors affecting the Z direction properties of Q345H steel are strip structure and grain size grade. The more obvious the strip structure is, the smaller the grain size grade is, the worse the Z direction property. Q345EL and the unrefined Q345B steel structure are both ferrite and pearlite. However, in the process of smelting Q345EL steel, some trace alloying elements, such as Bnb, were added, and the grain size was refined. The Z direction property is relatively good, but there is no obvious strip structure which is unfavorable to the Z direction property in the Q345B steel structure refined by ladle, because it has applied the controlled rolling and cooling control technology in the rolling process. The disappearance of strip structure improves the anisotropic zigzag property of steel plate. From the analysis of inclusions, the main factors affecting the Z-direction properties of Q345H steel are the content, shape and size of inclusions. The larger the size of the inclusions, the worse the Z direction properties of the steel. In the refined Q345B and Q345EL steels, the silicate inclusions are obviously lower than those of the unrefined Q345B steels. The long stripe sulfides in the refined Q345B and Q345EL steels are obviously lower than those of the unrefined steels. The type of inclusions in flange and web are the same, and the content is basically the same, but the size of sulfide inclusion in web is larger. The fracture morphology analysis shows that the fracture surface of five groups of specimens belongs to ductile fracture. A large number of equiaxed dimples appear in the flange of refined Q345B steel and the fracture surface of web specimen. The size is small and the toughness is deep. A small amount of micro-inclusions. Q345EL steel flange specimen fracture surface appears more long stripe dimples, larger size, shallow toughness. A small amount of small inclusions can also be observed. The fracture surface of unrefined Q345B steel flange and web specimen has more long dimples, larger size, shallow toughness, and some cleavage surface morphology. The smaller the dimple size, the deeper the depth and the greater the section shrinkage. The better the Z direction property of the material is, the better the content of inclusions, especially the plastic inclusions such as sulphide, silicate and so on, should be reduced by refining technology when producing hot rolled H-section steel with good Z-direction properties. At the same time, the controlled rolling and cooling process was used to improve the strip structure, refine the grain and improve the Z direction properties of the material.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG142.1

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