本文關(guān)鍵詞： 黃銅管材 熱冷組合鑄型水平連鑄 表面質(zhì)量 凝固組織 冷軋　出處：《北京科技大學》2017年博士論文　論文類型：學位論文

【摘要】：黃銅合金管材具有較高的強度、優(yōu)良的導熱性能和耐腐蝕性能,在石油化工、海洋工程、建筑裝飾等領(lǐng)域應用廣泛。目前,工業(yè)上主要采用傳統(tǒng)的“半連鑄實心鑄錠→熱擠壓管材→冷軋→中間退火→拉拔”工藝主產(chǎn)黃銅管材,存在流程長、能耗大、成材率低、生產(chǎn)成本高等問題。本課題組前期開發(fā)了一種基于熱冷組合鑄型(Heating-Cooling Combined Mold,HCCM)水平連鑄技術(shù)的銅合金管材短流程生產(chǎn)新工藝,并成功應用于BFe10-1-1白銅管材的工業(yè)生產(chǎn),顯著縮短了白銅管材生產(chǎn)工藝流程,提高了成材率,降低了生產(chǎn)成本。該新工藝也為解決黃銅管材傳統(tǒng)生產(chǎn)工藝存在的問題提供了可行的技術(shù)途徑。本文在課題組前期研究工作的基礎(chǔ)上,重點開展了以下研究工作：針對黃銅管材水平連鑄過程中表面點狀缺陷和裂紋嚴重的問題,研究了缺陷的形成機理,提出消除缺陷的措施；研究了HCCM水平連鑄HA177-2鋁黃銅管材凝固組織的形成規(guī)律,確定了合理的連鑄制備參數(shù)；探明了晶粒尺寸和取向?qū)辖鹆W性能的影響規(guī)律及作用機制,提出通過控制柱狀晶晶粒尺寸和取向,提高合金的塑性變形能力的方案,為連鑄管材凝固組織工藝控制提供了理論依據(jù)。在此基礎(chǔ)上,采用HCCM水平連鑄工藝制備了具有高表面質(zhì)量和優(yōu)異冷加工成形性能的HA177-2鋁黃銅管坯,并在不需進行表面處理和中間退火的條件下,實現(xiàn)了累積變形量達95%以上的大變形冷軋加工。本文的主要創(chuàng)新性成果如下：以高鋅含量的H62黃銅為典型合金,研究發(fā)現(xiàn),HCCM水平連鑄管材外表面出現(xiàn)的點狀缺陷主要為富鋅低熔點物質(zhì),鋅含量達80 wt%。連鑄過程中,凝固界面附近揮發(fā)的鋅在鑄型內(nèi)表面形成的鋅液滴與高溫管材外表面接觸后發(fā)生熔蝕作用,導致管材表面形成點狀缺陷。通過快速降低冷型段內(nèi)管材溫度以減少管材鋅元素揮發(fā),可消除點狀缺陷。連鑄H62黃銅管材上部周期性裂紋是由于凝固時下部早于上部凝固,導致上部受到附加軸向拉伸應力而形成的,提高合金熔體溫度、熱型加熱溫度或連鑄速度,提高了凝固界面附近的溫度梯度,減小了處于凝固兩相區(qū)的凝固區(qū)寬度,可有效消除裂紋。采用連鑄實驗和凝固組織模擬相結(jié)合的方法探明了HCCM水平連鑄HA177-2鋁黃銅管材凝固組織的形成規(guī)律。保持其他參數(shù)不變,提高熱型加熱溫度(1040℃→1080℃)使管材下部激冷形核數(shù)量減少,同時使凝固前沿溫度梯度與凝固速率之間的比值增大,有利于促進柱狀晶組織生長,獲得沿周向較為均勻的軸向梓狀晶組織管材。確定J’合金管材連鑄制備參數(shù)：熔體溫度1100℃,熱型加熱溫度1080-1100℃,連鑄速度90-100 mm/min,冷型段冷卻水流量500-600 L/h,二次冷卻水流量400 L/h。所制備的管材各部位軸向拉伸試樣的斷后伸長率均超過80.0%,具有優(yōu)異的塑性變形能力。與小晶粒柱狀晶試樣相比,大晶粒柱狀晶HA177-2鋁黃銅具有更優(yōu)的塑性變形能力,斷后伸長率由晶粒直徑2.0 mm時的70.4%增大到晶粒直徑6.0mm時的84.4%；較好的晶內(nèi)變形均勻性足大晶粒柱狀晶試樣具有較優(yōu)塑性變形能力的主要原因。加載方向與柱狀晶生長方向之間夾角為0-300的合金試樣,室溫拉伸過程中以位錯平面滑移為主要變形機制,具有較高的塑性變形能力,斷后伸長率大于80.0%；而45-90°試樣晶內(nèi)變形集中程度高,斷后伸長率為62.9-65.2%。為獲得冷加工成形性能優(yōu)良的HA177-2合金,應控制定向凝固時柱狀晶生長方向與主延伸變形方向之間的夾角在0-30°范圍內(nèi)。與等軸晶組織HA177-2鋁黃銅管材由于晶粒隨機取向,在冷軋過程中易形成相互交叉的平面位錯、形變孿晶和切變帶的特點相比,柱狀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變形組織,具有較低的殘余應力。70%變形量時,柱狀晶管材的周向和軸向殘余應力分別為201MPa和175 MPa,低于等軸晶管材的281 MPa和238 MPa。等軸晶組織管材累積冷軋變形量達到75%時,表面出現(xiàn)可肉眼觀察的宏觀裂紋,而柱狀晶組織管材累積冷軋變形量可達95%以上。柱狀晶管材晶粒取向度高且具有平直的小角度晶界,使其冷軋變形組織較均勻,殘余應力較低,因而具有優(yōu)異冷加工成形性能。在上述結(jié)果的基礎(chǔ)上,采用HCCM水平連鑄工藝制備了高表面質(zhì)量和優(yōu)異冷加工性能的柱狀晶組織HA177-2鋁黃銅管材,將管材直接進行冷軋加工,獲得了累積冷加工大于95%的大變形量,從而可省略傳統(tǒng)生產(chǎn)工藝中的熱擠壓、表面處理、中間退火和酸洗等工序,實現(xiàn)HA177-2鋁黃銅管材高效短流程制備。
[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.

【學位授予單位】：北京科技大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG291;TG339

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