HCCM水平连铸黄铜管材表面质量、组织性能控制与冷轧加工

发布时间：2018-01-20 15:24

本文关键词： 黄铜管材热冷组合铸型水平连铸表面质量凝固组织冷轧　出处：《北京科技大学》2017年博士论文　论文类型：学位论文

【摘要】：黄铜合金管材具有较高的强度、优良的导热性能和耐腐蚀性能,在石油化工、海洋工程、建筑装饰等领域应用广泛。目前,工业上主要采用传统的“半连铸实心铸锭→热挤压管材→冷轧→中间退火→拉拔”工艺主产黄铜管材,存在流程长、能耗大、成材率低、生产成本高等问题。本课题组前期开发了一种基于热冷组合铸型(Heating-Cooling Combined Mold,HCCM)水平连铸技术的铜合金管材短流程生产新工艺,并成功应用于BFe10-1-1白铜管材的工业生产,显著缩短了白铜管材生产工艺流程,提高了成材率,降低了生产成本。该新工艺也为解决黄铜管材传统生产工艺存在的问题提供了可行的技术途径。本文在课题组前期研究工作的基础上,重点开展了以下研究工作：针对黄铜管材水平连铸过程中表面点状缺陷和裂纹严重的问题,研究了缺陷的形成机理,提出消除缺陷的措施；研究了HCCM水平连铸HA177-2铝黄铜管材凝固组织的形成规律,确定了合理的连铸制备参数；探明了晶粒尺寸和取向对合金力学性能的影响规律及作用机制,提出通过控制柱状晶晶粒尺寸和取向,提高合金的塑性变形能力的方案,为连铸管材凝固组织工艺控制提供了理论依据。在此基础上,采用HCCM水平连铸工艺制备了具有高表面质量和优异冷加工成形性能的HA177-2铝黄铜管坯,并在不需进行表面处理和中间退火的条件下,实现了累积变形量达95%以上的大变形冷轧加工。本文的主要创新性成果如下：以高锌含量的H62黄铜为典型合金,研究发现,HCCM水平连铸管材外表面出现的点状缺陷主要为富锌低熔点物质,锌含量达80 wt%。连铸过程中,凝固界面附近挥发的锌在铸型内表面形成的锌液滴与高温管材外表面接触后发生熔蚀作用,导致管材表面形成点状缺陷。通过快速降低冷型段内管材温度以减少管材锌元素挥发,可消除点状缺陷。连铸H62黄铜管材上部周期性裂纹是由于凝固时下部早于上部凝固,导致上部受到附加轴向拉伸应力而形成的,提高合金熔体温度、热型加热温度或连铸速度,提高了凝固界面附近的温度梯度,减小了处于凝固两相区的凝固区宽度,可有效消除裂纹。采用连铸实验和凝固组织模拟相结合的方法探明了HCCM水平连铸HA177-2铝黄铜管材凝固组织的形成规律。保持其他参数不变,提高热型加热温度(1040℃→1080℃)使管材下部激冷形核数量减少,同时使凝固前沿温度梯度与凝固速率之间的比值增大,有利于促进柱状晶组织生长,获得沿周向较为均匀的轴向梓状晶组织管材。确定J’合金管材连铸制备参数：熔体温度1100℃,热型加热温度1080-1100℃,连铸速度90-100 mm/min,冷型段冷却水流量500-600 L/h,二次冷却水流量400 L/h。所制备的管材各部位轴向拉伸试样的断后伸长率均超过80.0%,具有优异的塑性变形能力。与小晶粒柱状晶试样相比,大晶粒柱状晶HA177-2铝黄铜具有更优的塑性变形能力,断后伸长率由晶粒直径2.0 mm时的70.4%增大到晶粒直径6.0mm时的84.4%；较好的晶内变形均匀性足大晶粒柱状晶试样具有较优塑性变形能力的主要原因。加载方向与柱状晶生长方向之间夹角为0-300的合金试样,室温拉伸过程中以位错平面滑移为主要变形机制,具有较高的塑性变形能力,断后伸长率大于80.0%；而45-90°试样晶内变形集中程度高,断后伸长率为62.9-65.2%。为获得冷加工成形性能优良的HA177-2合金,应控制定向凝固时柱状晶生长方向与主延伸变形方向之间的夹角在0-30°范围内。与等轴晶组织HA177-2铝黄铜管材由于晶粒随机取向,在冷轧过程中易形成相互交叉的平面位错、形变孪晶和切变带的特点相比,柱状晶管材晶粒取向度高且具有平直的小角度晶界,主要形成平行分布的变形组织,具有较低的残余应力。70%变形量时,柱状晶管材的周向和轴向残余应力分别为201MPa和175 MPa,低于等轴晶管材的281 MPa和238 MPa。等轴晶组织管材累积冷轧变形量达到75%时,表面出现可肉眼观察的宏观裂纹,而柱状晶组织管材累积冷轧变形量可达95%以上。柱状晶管材晶粒取向度高且具有平直的小角度晶界,使其冷轧变形组织较均匀,残余应力较低,因而具有优异冷加工成形性能。在上述结果的基础上,采用HCCM水平连铸工艺制备了高表面质量和优异冷加工性能的柱状晶组织HA177-2铝黄铜管材,将管材直接进行冷轧加工,获得了累积冷加工大于95%的大变形量,从而可省略传统生产工艺中的热挤压、表面处理、中间退火和酸洗等工序,实现HA177-2铝黄铜管材高效短流程制备。
[Abstract]:Brass alloy tube with high strength, good thermal conductivity and corrosion resistance in the petrochemical, marine engineering, architectural decoration and other fields are widely used. At present, the industry is mainly using the traditional "semi continuous casting ingot, solid extruded tube, cold rolling, intermediate annealing and drawing process of producing brass pipe, there is a flow long, high energy consumption, low yield, high cost of production. Ourprevious developed a mold based on a combination of hot and cold (Heating-Cooling Combined Mold, HCCM) of copper alloy tubes for horizontal continuous casting of short flow production process, and successfully applied to the industrial production of BFe10-1-1 copper tube, significantly shorten the process copper pipe production, improve the production efficiency, reduce production costs. The new technology provides a feasible technical way to solve the existing problems of the traditional production process of brass tube in this paper. Based on our previous work, focus on the following contents: on the surface of brass pipes in the continuous casting process of point defects and crack problems, the defect formation mechanism is studied and put forward measures to eliminate defects; formation of HCCM horizontal continuous casting HA177-2 aluminum brass tube microstructure on the parameters of continuous casting for the reasonable; proved the influence and mechanism of the mechanical properties of the alloy grain size and orientation, proposed by controlling the columnar grain size and orientation, improve the alloy plastic deformation ability of the scheme, and provides a theoretical basis for controlling the solidification structure of casting pipe technology. Based on this, with HA177-2 aluminum yellow the copper billet with high surface quality and excellent cold forming properties of HCCM prepared by horizontal continuous casting process, and surface treatment and intermediate annealing are not in need of Under the condition, realizes the cumulative deformation of large deformation in cold rolling process. More than 95% of the main innovations of this paper are as follows: To study the high zinc content of H62 brass alloy is typical, found punctate defects in HCCM horizontal continuous casting tube material surface is the main material of low melting point of zinc, zinc content of 80 wt%. continuous casting process in the occurrence of corrosion of zinc droplets formed on the surface of zinc volatilization near the solidification interface in the mould with high temperature tube outer surface after contact, resulting in the formation of point defects. Through the tube surface rapidly reduce the temperature of cold type pipe section to reduce pipe zinc volatilization, can eliminate the point defects of casting H62 brass pipe. The upper cycle the crack is due to the solidification of lower early in the upper solidification, lead to the upper part of the additional axial tensile stress and the formation, increase the melt temperature of the alloy, heat type heating temperature and casting speed, improve the solidification The temperature gradient near the interface, reduced in width of solidification zone in solidifying mushy zone, which can effectively eliminate the crack. By the experiments of continuous casting and solidification simulation combined proved the formation rule of HCCM horizontal continuous casting HA177-2 aluminum brass pipe solidification. Keeping the other parameters unchanged, increasing heat type heating temperature (1040 DEG to 1080 DEG C to reduce the lower cooling pipe) number of nuclei, and the ratio between the solidification temperature gradient and solidification rate increasing, is conducive to promote the growth of columnar grains, obtained along the circumferential axial Zi morphology pipe is relatively uniform. To determine the J 'alloy preparation parameters: melt casting temperature is 1100 degrees centigrade, hot the heating temperature of 1080-1100 DEG C, the casting speed of 90-100 mm/min, the cold type section cooling water flow rate of 500-600 L/h, the two cooling water flow rate of 400 L/h. prepared by different parts of the pipe axial tensile specimen after elongation Rate of more than 80%, with excellent ability of plastic deformation. Compared with small columnar grain samples, large columnar grain HA177-2 aluminum brass with plastic deformation ability better, elongation by the grain diameter of 2 mm at 70.4% 6.0mm when the grain diameter increases to 84.4%; good grain deformation foot large columnar grain sample has better capability of plastic deformation is the main reason. The angle between the loading direction and the growth direction of columnar crystals for 0-300 alloy specimens, tensile process with planar slip of dislocations is the main deformation mechanism is plastic deformation ability, elongation is greater than 80% DEG 45-90; the specimen deformation inside the grains with high concentration degree, the elongation of 62.9-65.2%. for cold forming of HA177-2 alloy with excellent performance, should be columnar crystal growth direction and extension deformation control during directional solidification direction between The angle in 0-30 degrees. And the equiaxed microstructure of HA177-2 aluminum brass pipe due to randomly oriented grains, easy to form planar dislocation cross in the cold rolling process, compared with the characteristics of deformation twinning and shear bands, small angle columnar grain orientation degree is high and the pipe having a flat crystal boundary, formed mainly parallel deformation structure the distribution, with low residual stress.70% deformation, the columnar pipe circumferential and axial residual stress were 201MPa and 175 MPa, lower than that of equiaxed crystal tubes of 281 MPa and 238 MPa. equiaxed grains accumulated pipe cold rolling deformation reaches 75%, the surface appears to the naked eye crack observation, and columnar structure pipe cumulative cold deformation can reach more than 95%. The small angle columnar grain orientation degree is high and the pipe with straight grain boundaries, the uniform deformation of cold rolled microstructure, residual stress is low, so it has excellent cold Processing properties. On the basis of the above results, high surface quality and excellent cold workability of the columnar structure of HA177-2 brass pipe prepared by HCCM horizontal continuous casting system, pipe will direct the processing of cold rolling, the deformation accumulation of cold processing more than 95%, which can be omitted in the traditional production process hot extrusion, surface treatment, intermediate annealing and pickling, HA177-2 aluminum brass pipe, short process of preparation.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG291;TG339

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