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  • 方管的带状组织改善方法是什么
  • 本站编辑:杭州双惠金属材料有限公司发布日期:2019-12-17 17:38 浏览次数:

带状组织是钢材内部的一种缺陷,可分为一次带状组织和二次带状组织。带状组织的存在使钢的组织不平均,并严重影响方管性能,降低其塑性、冲击韧性、断裂韧性和断面收缩率,形成冷弯不合、冲压废品率高。并且在停止热处置时,方管容易变形、淬火开裂。要改善这一问题,我们能够采取以下四种办法:

  一轧钢工艺

  一次带状组织是在连铸过程中呈现的,但采用合理的轧钢工艺可有效抑止二次带状组织的呈现。轧钢工艺中加热制度、开轧温度、变形量、终轧温度和冷却速度等参数尤为重要。经过铸坯加热,可对铸态组织的成分偏析起到平均化作用,也能够方管降低轧制过程的变形抗力。在允许的条件下,都尽可能采用较高的加热温度,而且还要保证足够的加热时间。

  二钢种成分

  钢种成分设计的方面,要妥善处置升高转变温度的元素和降低转变温度的元素之间的关系。合金元素对转变温度是互相作用、互相影响的,假如能使几种元素的影响互相抵消,减小枝晶间和枝晶内转变温度的差别,就能减轻方管的带状组织。

  三热处置工艺

  方管在退火过程中,由于随炉冷却,使先共析铁素体析出充沛,加重带状组织级别。在正火过程中,冷速较快,能够减轻带状组织。采用等温正火工艺时,将钢材加热保温一段时间,快速冷却到珠光体转变区的某一温度,然后停止保温使其完成铁素体和珠光体的平均转变,随后在空气中停止冷却。

  四连铸工艺

  钢材轧后呈现的带状组织主要来源于连铸坯中产生的枝晶偏析,控制连铸坯的枝晶偏析和促进元素的平均散布是减轻或消弭带状组织的有效办法。从连铸工艺来看,扩展等轴晶区的范围和取得细小的二次枝晶能有效控制枝晶偏析。经过合理控制浇注温度并坚持恒定的速度浇注,能有效增大等轴晶区域。另外,采制定合理的二冷工艺,控制二冷区各段冷却水量的大小,能够控制方管外表温度,使其冷却平均,也能够得到大区域的等轴晶。

Banded structure is a defect in steel, which can be divided into primary banded structure and secondary banded structure. The existence of banded structure makes the structure of steel uneven, and seriously affects the property of square tube, reduces its plasticity, impact toughness, fracture toughness and section shrinkage rate, and forms cold-bending and high scrap rate. When the heat treatment is stopped, the square tube is easy to deform and crack during quenching. To improve this problem, we can take the following four methods: one rolling process, the first banded structure appears in the continuous casting process, but the reasonable rolling process can effectively restrain the second banded structure. The parameters such as heating system, starting temperature, deformation, finishing temperature and cooling rate are especially important in rolling process. The billet heating can homogenize the segregation of as-cast microstructure and reduce the deformation resistance of square tube during rolling. In the allowed conditions, as far as possible to use a higher heating temperature, but also to ensure that sufficient heating time. Two steel grade composition, steel grade composition design, to properly handle the increase in the transformation temperature of the elements and reduce the transformation temperature of the relationship between the elements. If the influence of several elements can be counteracted and the difference of transition temperature between Dendrite and in Dendrite can be reduced, the banded structure of square tube can be reduced. In the process of triple heat treatment, the pre-eutectoid ferrite precipitates abundantly and the banded structure is aggravated due to the cooling in the furnace. During normalizing, the cooling rate is faster and the banded structure can be reduced. In isothermal normalizing process, the steel is heated and kept warm for a period of time, rapidly cooled to a certain temperature in pearlite transformation zone, then stopped heat preservation to complete the average transformation of ferrite and Pearlite, and then stopped cooling in air. In the four continuous casting process, the banded structure of steel after rolling is mainly due to the dendrite segregation in the continuous casting slab. Controlling the dendrite segregation and promoting the average distribution of elements in the continuous casting slab are effective methods to reduce or eliminate the banded structure. From the view of continuous casting technology, extending the equiaxed zone and obtaining fine secondary dendrite can effectively control the dendrite segregation. The equiaxed crystal region can be increased effectively by controlling the pouring temperature reasonably and keeping the constant speed. In addition, the reasonable secondary cooling process can control the surface temperature of the square tube, make the cooling average, and obtain the equiaxed crystal in large area.