Effect of electroslag remelting on carbides in 8Cr13MoV martensitic stainless steel

The effect of electroslag remelting (ESR) on carbides in 8Cr13MoV martensitic stainless steel was experimentally studied. Phases precipitated from liquid steel during solidification were calculated using the Thermo-Calc software. The carbon segregation was analyzed by original position analysis (OPA), and the carbides were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), energy- dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results indicated that more uniform carbon distribution and less segregation were obtained in the case of samples subjected to the ESR process. After ESR, the amount of netty carbides decreased significantly, and the chromium and vanadium contents in the grain-boundary carbides was reduced. The total area and average size of carbides were obviously smaller after the ESR process. In the sample subjected to ESR, the morphology of carbides changed from lamellar and angular to globular or lump, whereas the types of carbides did not change; both M₂₃C₆ and M₇C₃ were present before and after the ESR process.     

Effect of mold rotation on the bifilar electroslag remelting process

A novel electroslag furnace with a rotating mold was fabricated, and the effects of mold rotational speed on the electroslag remelting process were investigated. The results showed that the chemical element distribution in ingots became uniform and that their compact density increased when the mold rotational speed was increased from 0 to 28 r/min. These results were attributed to a reasonable mold speed, which resulted in a uniform temperature in the slag pool and scattered the metal droplets randomly in the metal pool. However, an excessive rotational speed caused deterioration of the solidification structure. When the mold rotational speeds was increased from 0 to 28 r/min, the size of Al₂O₃ inclusions in the electroslag ingot decreased from 4.4 to 1.9 μm. But the excessive mold rotational speed would decrease the ability of the electroslag remelting to remove the inclusions. The remelting speed gradually increased, which resulted in reduced power consumption with increasing mold rotational speed. This effect was attributed to accelerated heat exchange between the consumable electrode and the molten slag, which resulted from mold rotation. Nevertheless, when the rotational speed reached 28 r/min, the remelting speed did not change because of limitations of metal heat conduction. Mold rotation also improved the surface quality of the ingots by promoting a uniform temperature distribution in the slag pool.     

不锈钢接头的宽间隙真空钎焊

采用先在钎缝间隙中预填合金粉,然后在钎缝外置放钎料进行钎焊的方法,解决不锈钢接头宽间隙的钎焊问题.当钎缝内预填３１６粉（或１Ｃｒ１８Ｎｉ９粉）及用ＢＮｉ－１ａ（或ＢＮｉ－２）钎料钎焊时,预填粉不熔化,焊后保持原来的形状。钎料中的硼沿晶界向预填粉中扩散,在晶界处与铁结合形成Ｆｅ２Ｂ,钎料获得固溶体组织。用ＢＮｉ－１ａ钎料钎焊钎缝内预填３１６粉时,钎绀缝强度高达５０４．７ＭＰａ。用ＢＮｉ－５钎料钎焊针缝内预填３１６粉时,针缝组织内的固溶体相中夹带少量的化合物相,钎缝的重熔温度高达１３２５℃。对同一种钎料而言,宽间隙针缝的抗拉强度与重熔温度有较好的对应性,即重熔温度高,抗拉强度也高。     

电渣重熔过程中金属熔池形状的数学模拟

本文利用了前人关于熔滴在渣池中行为的研究成果和渣池中有关传热规律的实验资料,确定了渣池一金属熔池界面上的边界条件,通过实验确定了输入功率与熔化速度的关系,建立了包括有金属熔池、两相区,凝周锭在内的电渣锭温度场的数学模型,经数值计算,得到6种不同熔化速度的熔池形状,与实验进行比较,其结果令人满意。     

激光焊接与重熔自由表面温度分布及熔池形状的数值分析

以固液相变的统一模型方程为基础,计算了激光焊接与表面重熔不同加热模型条件下,液态熔池的形成过程,以及温度场和流场.主要考察了激光诱导的合金元素汽化和表面张力驱动流对自由表面温度分布及熔池形状的影响.结果发现,熔池自由表面温度和溶池形状主要受表面张力驱动的流体流动的影响,它在限制自由表面最高温度方面起着主要作用,合金元素汽化热损失的影响是第二位的.熔池的形状主要受液态金属涡旋方向的影响,在负的表面张力温度系数条件下,熔池浅而宽;在正的表面张力温度系数下,熔池深而窄.     

电渣重熔过程中熔滴滴落的影响因素

采用VOF方法来追踪钢渣两相界面,磁流体力学模块(MHD)来加载电流、电压对电渣重熔过程中熔滴滴落行为进行数值模拟.结果表明:电渣重熔过程中自耗电极端部熔滴的数目随着充填比的增加而增多;熔滴的尺寸随着自耗电极端部形状和界面张力的增加而增大.然而,熔滴的尺寸和数量随着输入电流的增大而减小.而且一些尺寸较大的熔滴在滴落的过程中受到了电磁力、重力以及浮力等力作用被分裂成几个尺寸较小的熔滴.从自耗电极端部滴落的熔滴不具有对称性,从而导致了渣池的流场不对称性.     

电渣重熔过程的数值模拟

以电渣重熔电极、渣池和铸锭为研究对象,建立了电渣重熔体系三维准稳态数学模型.利用商业软件ANSYS得到了电渣重熔过程的电磁场、流场与温度场.计算结果表明,在电极和钢锭内,电流主要集中在外表面,在渣池内主要集中在电极角部;由于电流密度分布不同导致的电磁力和焦耳热及冷却条件共同影响渣池内流场和温度场;随着熔速的增加,熔池深度和两相区最大宽度增加;本工况下,700~800kg/h的熔速将对应一个最短的局部凝固时间.     

电渣重熔中脱氧剂种类影响炉渣脱氧的热力学分析

以工业纯铁为研究对象,熔渣-金属中各个组元间的热力学平衡反应和质量守恒为基础,计算了不同的脱氧剂添加量下钢中的Si,Al的平衡质量分数,建立了脱氧剂Al,CaSi,CaSiBa的脱氧热力学模型.结果表明:基于本模型对多种脱氧剂进行的研究能够符合实验结果,在采用Al,CaSi,CaSiBa脱氧时,渣中FeO质量分数分别能降低到0.04%,0.08%,0.08%,铝脱氧可以使得熔渣中氧势降到最低,且渣中Al2O3由于脱氧而增加的量相对于原始质量分数变化幅度较小,与CaSi,CaSiBa相比具有良好的氧势控制能力.     

变流四探针法测定炉渣电导率的研究

介绍了利用四探针组成的电极及DC—1新型电导仪测定炉渣电导率的装置和原理,根据对我国广泛应用的L_4(15％CaF_2-30％CaO-50％Al_2O_3-5％Mgo)渣在1230～1650℃所测熔态和固态的结果,求出了电导率与温度的经验式,为使测定结果能有较高的准确性和重现性,以KCl为标准溶液,讨论了电流频率、探针插入深度、溶液深度及电极二维偏心度等因素对测试结果的影响,并求得了电导池常数与探针插入深度及温度的关系式,此法简单而可靠。     

铝合金表面激光改质工艺效果的研究

表面重熔、表面合金化及表面熔覆是铝合金激光表面改质的３个主要方法．重熔工艺虽然简单,但强化潜力有限,以重熔为基础的后两种工艺比较复杂,但强化潜力大．通过一系列实验,对比性地揭示了这些工艺对铝合金表面组织的影响及强化效果．