铸轧不锈钢薄带表面质量与显微组织分析

为了提高铸轧不锈钢薄带的成材率，研究了铸轧不锈钢薄带的表面皱纹、重皮、裂纹、夹杂等缺陷和显微组织特征，分析了造成表面质量缺陷和不良显微组织可能形成的原因，并提出了防止这些质量缺陷的技术措施。     

钢中夹杂物与韧断机理

用平板拉伸试样直接观察夹杂物在裂纹成核和扩展中的行为得出:夹杂物开裂受应变控制:夹杂物开裂方式与加载方向有关;微裂纹在夹杂物上成核后主要按基体切变方式扩展;在夹杂物偏聚区微裂纹的扩展可按碰撞方式进行,从而加速裂纹的扩展,故在冶炼上需采取措施,以避免夹杂物的集聚。     

智能算法在双辊铸轧过程铸轧力计算中的应用

在双辊铸轧过程中,铸轧力的控制是铸轧过程稳定进行和提高薄带质量的关键.为了控制铸轧力,必须建立铸轧力计算数学模型,本文采用了一种基于贝叶斯方法的前向神经网络训练算法以提高网络的泛化能力,在网络的目标函数中引入了表示网络结构复杂性的惩罚项,融入“奥克姆剪刀”理论,避免了网络训练的过拟合.将上述网络应用于铸轧过程的铸轧力计算,具有很高的计算精度,同时在收敛速度、稳定性和泛化能力方面都优于传统的BP神经网络.     

不同铸轧条件下铸轧区温度场分析

依据建立的铝双辊铸轧区熔体流动凝固传热模型对铸轧区的温度场进行了数值模拟,研究了不同的铸轧工艺参数包括铸轧速度、带坯厚度、铸轧辊直径、内冷强度、铸轧区长度的变化对铸轧区温度场的影响规律,结果表明:铸轧速度增加,铸造区长度增加,带坯的出口温度增大;内冷强度的增加,铸造区长度变短,带坯的出口温度减小,这种影响随着内冷强度的增加而逐渐减弱.从而为优化铸轧工艺参数提供依据.     

SH波作用下圆形夹杂与裂纹的相互作用

利用特殊函数的加法公式,采用Green函数法研究圆形夹杂附近的裂纹对SH波的散射和裂纹尖端动应力强度因子的求解.取含有圆形夹杂的基体中任意一点承受时间谐和的出平面线源荷载作用时位移函数的基本解作为Green函数.首先求解圆形夹杂在SH波作用下的散射问题;然后利用Green函数在裂纹实际存在位置实施裂纹的"人工切割",以恢复存在的裂纹,建立裂纹尖端应力的求解积分,得到动应力强度因子的解答;最后对圆形夹杂附近单平行裂纹问题进行了研究.     

裂纹与拉剪型线夹杂相互作用之研究

本文采用奇异积分方程方法,对无限大板内一个裂纹与一个拉剪型线夹杂之间的相互作用问题进行了研究。与前人的研究不同,本文考虑的夹杂不但具有拉伸刚度而且具有剪切刚度。一对位错和一对集中力的格林函数被分别用以形成裂纹和夹杂。首先将裂纹与夹杂相应的混合边值问题归结为求解带有标准柯西核的奇异积分方程组,进而运用 Gauss—Chebyshev 求积公式求解,获得了裂纹与夹杂尖端的应力强度因子的数值解。通过对夹杂尖端附近应力场的奇异性分析,给出了夹杂尖端应力强度因子的定义。对若干种裂纹夹杂几何情况和夹杂拉伸与剪切刚度做了数值计算,分别讨论了裂纹与夹杂几何参数对裂纹与夹杂相互作用的影响。     

裂纹夹杂相互干涉问题

本文研究裂纹夹杂相互干涉的弹性力学的平面问题。一对位错和一对集中力的格林函数被分别用以形成裂纹和夹杂。所得积分方程适合于任意相对方位和尺寸的一个裂纹和一个夹杂。文中描述了裂纹尖端附近应力场的奇异性。对夹杂尖端附近应力场的奇异性给予了特别的注意,并为夹杂尖端的应力强度因子作了定义。对各种不同的裂纹夹杂几何情况和不同的夹杂刚度作了数值计算。根据这些数值结果--裂纹尖端和夹杂尖端的应力强度因子,分析、讨论了裂纹夹杂的各种几何参数以及夹杂-母体材料刚度比对裂纹夹杂相互干涉效应的影响。     

铝合金摩擦搅拌焊接焊区的Ⅰ/Ⅱ型复合断裂研究

采用二维计算机视觉-数字图像比对技术，进行裂纹稳定扩展实时表面位移测量，定量分析了铝合金2024-T351母材及摩擦搅拌焊接后不均匀、各向异性的焊区的Ⅰ/Ⅱ型复合裂纹稳定扩展的断裂性能、临界COD及其分量CODⅠ和CODⅡ并研究了母材及焊区裂纹的扩展路径．结果表明（1）距裂纹尖端后某一固定距离的临界COD可反映焊区的断裂韧性，（2）临界COD值反映复合裂纹的扩展受Ⅰ型或Ⅱ型裂纹扩展主导，（3）焊区的临界COD值对应地为母材的85％．（4）用数字图像比对技术分析Ⅰ/Ⅱ型裂纹的断裂性能是切实可行的一种新方法．     

夹杂对粉末冶金CT试样断裂性能影响的计算研究

采用GURSON本构方程对含夹杂粉末冶金材料紧凑拉伸试样进行了有限元分析,模拟了裂尖与夹杂的相互作用对基体的损伤及裂纹扩展性能的影响.圆形夹杂对基体材料的损伤及裂纹扩展性能是最保守的形状,对于椭圆形夹杂,硬夹杂在椭圆横向受力较为安全,而软夹杂则相反,在椭圆纵向受力对基体的损伤更小.     

GH80A镍合金电子束焊接接头旋转弯曲高周疲劳行为研究

随着镍合金电子束焊接在工业中的大量应用,尤其是在航空发动机和燃气轮机等关键长寿命服役设备中的使用,有必要对镍合金电子束焊接接头的高周疲劳属性和断裂机理进行系统的分析研究。本文利用旋转弯曲高周疲劳试验机进行疲劳试验,获得了母材和焊接接头的应力-寿命(S-N)曲线和疲劳断口,同时利用扫描电镜（Scanning Electron Microscope,SEM）对疲劳断口进行了微观特征分析,确定了母材和焊接接头在不同应力幅下的疲劳裂纹萌生区和扩展区,分析了裂纹萌生区位置与应力幅的相互关系。最后,利用有限元分析了焊接接头热影响区微裂纹位置与大小对材料疲劳性能的影响。从现有的试验和模拟结果可以得到：1)母材和电子束焊接接头应力-寿命(S-N)曲线分布趋势一致,但焊接接头疲劳强度要低于母材,在靠近107周次时,两者疲劳强度差距最小;2)在高应力幅（低周疲劳寿命阶段）母材和焊接接头的疲劳裂纹均起源于试件表面并且都是多点萌生断裂,焊接接头疲劳断口位置位于焊接熔合区或热影响区;3)在低应力幅（高周疲劳寿命阶段）疲劳裂纹在试件次表面萌生,焊接接头疲劳断口位于热影响区或焊接母材靠近热影响区处;4) 通过有限元模拟发现微裂纹的存在有利于裂纹的扩展。在拉应力作用下,横向微裂纹更优于纵向裂纹沿着应力方向进行裂纹扩展;随着微裂纹尺寸增大,微裂纹间更易于相互贯通,形成更长的裂纹,从而降低了材料的疲劳性能。综上可知,电子束焊接仅仅影响材料的疲劳强度。疲劳断裂机理和母材一致都为穿晶解理断裂,疲劳裂纹萌生区域位置也和母材一样都受应力幅的直接影响。     

Nonmetallic inclusions in SUS304 strip produced by twin-roll strip casting

The shape, type, content, and dimension of nonmetallic inclusions in SUS304 strip produced by twin-roll strip casting were studied using scanning electron microscopy （SEM）. The results show that the inclusions are mainly spherical Al2O3 and complex oxides composed of MnO, Al2O3 , and SiO2. The percentage of fine oxides smaller than 3 μm reaches up to 51.8%. The theoretical calculations show that fine oxides have precipitated during solidification. Therefore, it is concluded that during twin-roll strip casting, because of high cooling rate, the size of inclusions precipitated during solidification decreases, and the amount increases.     

Kinetics of recrystallization for twin-roll casting AZ31 magnesium alloy during homogenization

The kinetics of recrystallization for twin-roll casting AZ31 magnesium alloy with different thicknesses during homogenization was analyzed.It is shown that fine grains are first formed at the boundaries of deformed bands in the twin-roll casting slab.The recrystallized grains with no strain are gradually substituted for the deformed microstructure of twin-roll casting AZ31 magnesium alloy.The incubation temperature and time for the recrystallization of a twin-roll casting AZ31 magnesium alloy strip with a thickness of 3 mm are lower and shorter than those of the 6-mm thick strip,respectively.The 3-mm thick twin-roll casting magnesium alloy has finer grains than the 6-mm thick strip.The activation energies of recrystallization for twin-roll casting AZ31 magnesium alloy slabs with the thickness of 3 and 6 mm are 88 and 69 kJ/mol,respectively.The kinetics curves of recrystallization for twin-roll casting AZ31 magnesium alloy were obtained.     

Microstructure of AISI 304 stainless steel strips produced by a twin-roll caster

By optical inspection of macro-etched metallography and electron back-scattered diffraction (EBSD) mapping,this paper analyzed the microstructure of anstenitic stainless steel strips produced with an equal-diameter twin-roll strip caster.The results indicate that the microstructure of the strips includes two columnar zones with highly compact dendrites and one equiaxed zone.The characteristics,such as grain size and growing direction of columnar grains and equiaxed grains,were investigated.An additional transitional area with many freer grains between the columnar zone and the equiaxed zone was found.As shown in EBSD analysis,small angle boundaries exist both in the columnar zone and the equiaxed zone,although they are especially more in the transitional area.Additionally,some <111> twin boundaries were found in the mierostructure of the strips.     

双辊薄带连铸中分配器的优化设计

薄带生产过程中,熔池内钢液的分布以及熔池液面的波动是影响带钢质量的重要因素.分配器对实现稳定的薄带连铸过程和保证薄带的质量具有重要的作用.针对所设计的不同结构的分配器,进行了流场、压力场计算,并对其进行分析,为优选出满足双辊薄带连铸要求的分配器提供依据.     

CSP工艺Q235 B热轧带钢边部裂纹成因分析

为减少采用CSP工艺生产的Q235B热轧带钢边部裂纹缺陷,分别在Q235 B连铸坯和热轧带钢裂纹处进行取样,通过宏观形貌、金相组织、扫描电镜及能谱分析等方法,研究铸坯角部横裂纹与热轧带钢边部裂纹的演变规律和形态变化. 结果表明,结晶器卷渣、冷却不均匀是产生连铸坯角部裂纹的主要原因;第2道次过渡带钢的金相组织中出现混晶现象,裂纹边上存在脱碳现象;热轧带钢边部裂纹主要源自于铸坯裂纹,并在轧制过程中得到扩展. 根据连铸工艺参数,对边部裂纹缺陷率与液渣层厚度、保护渣消耗量、结晶器振动参数、中间包过热度、结晶器传热参数以及铸坯宽度的关系进行统计分析,并提出相应的边部裂纹控制工艺措施.     

不同水口角度对熔池内温度场的影响

基于ANSYS软件,建立了双辊带材铸轧过程的浇铸模型,同时选用AISB04不锈钢,模拟了不同水口角度下熔池温度场及铸带的温度变化。研究发现,水口的出口角度对熔池内温度场有一定影响,随着水口出口角度的增大,凝固终了点的位置向出口方向移动,熔池表面温度变化较大,铸带的表面温度略有变化。水口角度是实现稳定铸轧和保证铸带质量的重要条件。     

Metallurgical quality of CSP thin slabs

The casting structure, chemical composition segregation, dendrite arm space, inclusiona and during the CSP (compact strip production) rolling process were investigated. The results show that the CSP thin slab has a feature of uniform fine grains, more columnar crystals, less central porosity and segregation etc. There is no great difference in macrostructure between the CSP thin slab and conventional slab; however, the fine dendrite structure of the CSP slab is more uniform. Moreover, the central porosity and segregation are obviously improved after the first pass; and the dendrite is bent along the rolling direction rather than broken into pieces.Small inclusions with the diameter less than 10 p.m in the CSP slab are dominantly consisted of aluminates formed by A1 deoxidation and Ca treatment and not floating out of the melt. The large size inclusions found in the continuous casting slab are very few.     

Microstructure analysis of AISI 304 stainless steel produced by twin-roll thin strip casting process

The microstructure of AISI 304 austenite stainless steel fabricated by the thin strip casting process were investigated using optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). The microstructures of the casting strips show a duplex structure consisting of delta ferrite and austenite. The volume fraction of the delta ferrite is about 9.74vol% at the center and 6.77vol% at the surface of the casting thin strip, in vermicular and band shapes. On account of rapid cooling and solidification in the continuous casting process, many kinds of inclusions and precipitates have been found. Most of the inclusions and precipitates are spherical complex compounds consisting of oxides, such as, SiO2, MnO, Al2O3, Cr2O3, and FeO or their multiplicity oxides of MnO·Al2O3, 2FeO·SiO2, and 2MnO·SiO2. Many defects including dislocations and stacking faults have also formed during the rapid cooling and solidification process, which is helpful to improve the mechanical properties of the casting strips.     

双辊薄带连铸侧封板热应力模拟及试验研究

采用有限元法模拟了双辊薄带连铸带钢工艺中侧封板的三维温度场和热应力.通过对侧封板的温度和应力的耦合数据模拟,得到在薄带连铸过程中侧封板的温度和应力分布规律,结合试验分析了造成侧封板破损的主要原因.     

Effects of ultrasonic treatment on structure of roll casting aluminum strip

The experiment of ultrasonic treatment of roll casting aluminum strip on plane twin-roll cast-roller with double-heads ultrasonic tools was carried out, and the metallographic structure of the roll casting aluminum strip treated by ultrasonic was studied. The results show that ultrasonic treatment can refine the grain of the roll casting aluminum strips and make the structure of the strips more homogeneous. The effect is the best when the power of ultrasonic is 300 W and the incident angle of the guide rod is 45^＋. The mechanism of acoustic cavitations and acoustic flow on grain refinement was also discussed. The heat effect of intensity ultrasonic was studied. The present problems during ultrasonic roll casting process, such as the imperfect cooling system, the inaccurate calculation of ultrasonic energy, and the shape and position of the guide rod to be improved were pointed out.