Mechanism of Cracking Resistance of Hardfacing Specimens of Steel 5CrNiMo Improved by Rare Earth Oxide

The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure and modified inclusion in hardfacing metal with rare earth （RE） oxide were analyzed. The results show that, the hardfacing crack is initiated from the coarse dendritic crystal grain boundary, inclusions and coarse austenite grain boundary in the HAZ and propagated by the residual stress existing in the center of the hardfacing metal and HAZ. The primary columnar grain structure can be refined by adding RE oxide in the coating of the electrode. The inclusion in the hardfacing metal can be modified as well. Meanwhile, if the martensite transformation temperature is decreased, the largest value of the residual tensile stress in the dangerous region can be reduced.

Effect of CeO_2 on heat transfer and crystallization behavior of rare earth alloy steel mold fluxes

To improve the heat transfer capability and the crystallization property of the traditional mold flux, CaF_2 was replaced with B_2O_3. Then, the influences of CeO_2 on the heat transfer and the crystallization of the CaF_2-bearing mold flux and the new mold flux with 10 wt% B_2O_3 were studied using a slag film heat flux simulator and X-ray diffraction(XRD). The results revealed that the addition of CeO2 reduced the heat transfer by increasing the solid slag thickness and the crystallization of two mold fluxes. However, CeO_2 had less effect on the B_2O_3-containing mold flux compared with the CaF_2-bearing mold flux. According to the analyses, the CeO_2 contents in the CaF_2-bearing mold flux and the B_2O_3-containing mold flux should not exceed 8 wt% and 12 wt%, respectively. Therefore, these experimental results are beneficial to improve and develop the mold flux for casting rare earth alloy steels.

Effect of Rare Earth on Void Band of Diffusion Layer and Properties of Aluminized Steel

The effects of the addition of rare earth （RE） elements on the void band in the diffusion layer, and the re sistances to both oxidation and spalling of aluminized steel were investigated through high temperature oxidation and spalling tests. The results showed that RE had significant effects on the void band in the diffusion layer and the properties of aluminized steel. After diffusion treatment, a considerable number of the voids between the middle layer and transitional layer of pure aluminized coating, aggregated into wavy-line-shaped void bands parallel to the outer surface. For the RE added aluminized coating, only a few voids aggregated into intermittent block shapes. During high temperature oxidation at 800 ℃ for 200 h, the wavy void band of pure aluminized coating aggregated further into a linear crack parallel to the outer surface, and the internal oxidation occurred within them; the open cracks perpendicular to the surface penetrated through the diffusion layer. For the RE added aluminized coating, only a few voids aggregated into intermittent meniscus shapes. During cyclic spalling tests, the peeling, spallation, and pulver ulent cracking occurred along the void band in the diffusion layer of pure aluminized coating, but only a little spallation occurred in the diffusion layer of the RE-added aluminized coating, in which cracks perpendicular to the surface were much smaller than those of pure aluminized coating and did not penetrate through the diffusion layer. It is evident that RE addition can restrain the formation and aggregation of voids and subsequently improve the resistances to oxidation and spalling. The mechanism of the RE effect on the void band in the diffusion layer is also discussed.

High-Temperature Oxidation Behavior of 5Cr21Mn9Ni4N Steel Micro-Alloyed by Rare Earth

The oxidation resistance of 5Cr21Mn9Ni4N steel micro-alloying by RE at 700 - 900 ℃ was investigated. The results indicate that oxidation exponent n and oxidation activation energy are increased, and oxidation velocity constant kp is decreased when 0.2% RE is added in 5Cr21Mn9Ni4N steel. The addition of RE elements does not alter phase constitution of oxidation scale, however it improves the configuration of oxidation scale, and increases thermal stability and adhesivity of oxidation scale, which results in the raise of oxidation resistance of 5Cr21Mn9Ni4N steel at high temperature. The oxidation scale constitutes of refractory steel transfer from manganic oxide mostly to ferric oxide mostly with the increase of temperature, which leads to descend of compactness and desquamation resistance of oxidation scale. The mass increase of ferric oxide in the oxidation scale and the looseness of oxidation scale are the main reason to descend the oxidation resistance of refractory steel.

Temperature-dependent evolution of oxide inclusions during heat treatment of stainless steel with yttrium addition

The evolution of oxide inclusions during isothermal heating of 18Cr–8Ni stainless steel with yttrium addition at temperatures of 1273 to 1573 K was investigated systematically.Homogeneous spherical Al–Y–Si(–Mn–Cr)oxide inclusions were observed in as-cast steel.After heating,most of the homogeneous inclusions were transformed into heterogeneous inclusions with Y-rich and Al-rich parts,even though some homogeneous oxide particles were still observed at 1273 and 1573 K.With the increase in heating temperature,more large-sized inclusions were formed.The shape of the inclusions also changed from spherical to irregular.The maximum transformation temperature of inclusions was determined to be 1373 K.The evolution mechanism of inclusions during heating was proposed to be the combined effect of the(i)internal transformation of inclusions due to the crystallization of glassy oxide and(ii)interfacial reaction between inclusions and steel matrix.Meanwhile,the internal transformation of inclusions was considered to be the main factor at heating temperatures less than 1473 K.

Measurement of Residual Stress Field of Hardfacing Metal with RE Oxide and Its Numerical Simulation

The temperature and residual stress fields of a medium-high carbon steel, welded by a cracking resistance electrode with rare earth (RE) oxide, were measured by thermo-vision analyzer and X-ray stress analyzer respectively. Meanwhile, the martensitic transformation temperatures of matrix, hard-face welding (hardfacing) metal welded by conventional hardfacing electrode and that welded by cracking resistance electrode with RE oxide were determined. According to the experimental data and the thermo-physical, mechanical parameters of materials, finite element method (FEM) of temperature and stress fields was established. In this FEM, the effect of martensitic transformation on residual stress of hardfacing metal of medium-high carbon steel was taken into account. The results show that, by adding RE oxide in the coat of hardfacing electrode, the martensitic transformation temperature can be decreased, so that the residual tensile stress on the dangerous position can be decreased. Therefore, the cracking resistance of hardfacing metal can be improved.

OXIDE METALLURGY-ITS PURPOSES AND PRACTICAL APPROACHES

Under certain conditions, nonmetallic inclusions such as oxides, sulfides, nitrides and carbides are no longer harmful to steel service properties. With the new concept of oxide metallurgy, these properties can be improved by generating fine oxide inclusions which serve as heterogeneous nuclei for sulfide and fine ferrite. A novel continuous casting (CC) process is expected to be created with the utilization of oxide metallurgy. This is also useful for the forthcoming technologies of direct rolling and near-net-shape casting. The main idea of oxide metallurgy consists of an alternative oxidation technology. It is based on steels treated by complex metals such as Ti, Zr, Ti-Zr alloys and rare earth metals. The selected deoxidants should follow the required conditions which are concluded in this paper. (Author abstract) 45 Refs.

Effect of RE oxide on growth dynamics of primary austenite grain in hardfacing layer of medium-high carbon steel

The flux cored wires with different rare earth oxide additions for hardfacing the workpieces of medium-high carbon steel were developed. The microstrucmre of the hardfacing layer was observed using the optical microscopy. The average dimension of primary austenite grains in hardfacing layer was measured by image analyzer. The primary austenite grain growth activation energy and index were calculated according to Sellars＇s mode and Beck formula, respectively. Moreover, the effect of rare earth oxide on the growth dynamics of primary aus- tenite grain was analyzed, and then discussed with the misfit theory. The experimental results showed that, by adding rare earth oxide, the av- erage dimension of primary austenite grains in hardfacing layer of medium-high carbon steel decreased, and it was the smallest when the ad- dition of rare earth oxide was 5.17 wt.%. Meanwhile, at this rare earth oxide addition, the primary austenite grain growth activating energy in hardfacing layer was the largest, while its index was the smallest. The calculated results indicated that the primary austenite grain could be refined because LaAlO3 as heterogeneous nuclei of γ-Fe was the most effective.

S44535铁素体不锈钢高温氧化行为

为了探究稀土La对S44535铁素体不锈钢高温氧化行为的影响,采用加速氧化对添加0.26%La的S44535钢在800、900、1000℃下的静态空气中进行高温氧化研究。采用恒温氧化法对比S44535铁素体不锈钢在三种温度下的氧化动力学曲线,用扫描电镜(SEM)、能谱分析仪(EDS)和X射线衍射(XRD)对钢的氧化层进行表征分析,探究了稀土La对铁素体不锈钢高温抗氧化性能的影响。结果表明,氧化产物主要为Cr2O3和MnCr2O4,随着温度的升高,表面氧化膜增厚且更加致密,其外层富含Mn,内层富含Cr,说明稀土改变了氧化膜的生长方式,且呈现出较为优异的高温抗氧化性能。

掺杂氧化钇和富镧钐渣对连铸水口MgO-C耐火材料性能的影响

本研究分别考察了氧化钇(Y_(2)O_(3) )和富镧钐渣掺杂量对MgO-C耐火材料微观结构、烧结性能、力学性能和抗稀土钢侵蚀性能的影响。结果表明,Y_(2)O_(3) 和富镧钐渣通过与SiO_(2)和Al_(2)O_(3)反应而生成稀土硅酸盐和稀土铝酸盐,促进材料烧结,提高材料致密性。随着Y_(2)O_(3) 和富镧钐渣掺杂量增大,MgO-C耐火材料的体积密度、抗折强度和耐压强度均先增大后减小,而显气孔率的变化趋势相反。当Y_(2)O_(3) 和富镧钐渣的掺杂量分别为0.5%时,MgO-C耐火材料的体积密度分别为2.87 g/cm^(3)和2.85 g/cm^(3),显气孔率分别为9.6%和10.2%,抗折强度分别为7.6 MPa和6.8 MPa,抗压强度分别为46.4 MPa和41.2 MPa,致密性和常温力学性能提高的幅度最大,抗Ce基稀土钢侵蚀性能相比未掺杂稀土氧化物的试样分别提高了7.6%和10.2%。

Oxidation Behavior of Fe26Cr1Mo Stainless Steel in the Presence of Ni-La_2O_3 Electrodeposited Composite Film

The oxidation behaviors of Fe26Cr1Mo with and without the Ni La 2O 3 electrodeposited composite film have been investigated by thermogravimetric analysis (TGA) and a scanning electron microscope equipped with an energy dispersive analytical X ray system(SEM/EDAX). The experimental results show that the oxide scale growing on Fe26Cr1Mo exposed at 900 ℃ spalled severely during cooling, while after the stainless steel was coated with the Ni La 2O 3 electrodeposited composite film, its high temperature cyclic oxidation resistance was significantly improved. The reason is that a La 2O 3 modified NiO scale, which has a superior adhesion to the substrate, was formed on the Fe26Cr1Mo stainless steel coated with Ni La 2O 3 composite film.

Synergic Effect of Shot Blasting and Deposit RE on Corrosion Behavior of TP304H steel in SO_2-O_2 at 923K

The corrosion behavior of TP304H steel with combined treatment of shot blasting and electrophoresis deposited RE coating in l%SO2+14%O2+85%Ar mixture gaseous has been studied at 923K for 150 hours. The results show that both RE coating and shot blasting can improve the corrosion resistance of TP304H steel, and combined treatment has the best effect. Combined treatment reduces 50% mass gain, enhances the continuous and compactness of scale and changes the scale phase forms from FeaOs/Fe^S/Ni^/S to Cr2O3/FeCr2S4/Ni3_xS2. The synergistic effects of combined treatment on corrosion resistance and the effect of shot blasting on corrosion kinetics are discussed. Shot blasting increases the outward diffusion and surface concentration of Cr, Ce coating promotes the selective oxidation of Cr.

Effects of CeO_2 Coating on Oxidation Behavior of TP304H Steel in High-Temperature Water Vapor

Oxidation behaviors of TP304H steel with electrophoresis deposited CeO2 coating in water vapor were studied at 610℃～770℃ for 65 h. The results showed that CeO2 coating reduced effectively the oxidation rate of TP304H. Analysis with SEM and EDS showed the structure of oxide scale turned from multi-layer to mono-layer and oxide scale with high Cr content formed on the surface of CeO2 coating while inner oxidation disappeared. Based on test results and CeO2characters that Ce ion can vary between Ce4+ and Ce3+ under oxygen-rich and oxygen-poor environment, it is concluded that CeO2 coating acts as a barrier to prevent oxygen inner diffusion and the partial oxygen pressure of CeO2 coating-substrate interface is limited. Cr first diffuses outward across CeO2 coating and forms oxide scale on the surface, which delays formation of Fe oxide.

稀土镧对H13模具钢回火稳定性和抗氧化性的影响

本工作研究了稀土镧对H13模具钢在极限服役温度下的回火稳定性和抗氧化性的影响。随着镧元素的质量分数由0%增大至0.570%,H13模具钢在620℃下加热50 h后的硬度降低值先减小后增大,镧含量为0.052%时H13模具钢的回火稳定性最好,这主要是因为碳化物在回火过程中的融合长大受到了抑制。但是,当镧含量达到0.570%时,铁素体的再结晶受到显著抑制,基体组织为粗大的板条状铁素体,导致H13模具钢回火稳定性降低。添加0.052%的镧对长时间加热后的位错密度影响不显著,这说明稀土镧对H13模具钢回火稳定性的影响主要体现在碳化物和铁素体晶粒的演化。另外,随着镧元素的质量分数由0%增大至0.094%,在650℃加热100 h后H13模具钢的氧化层变得更加光滑和致密,氧化层厚度由48.4μm减小至30.6μm。添加镧元素促进了针状氧化物的形成,并减弱了内氧化。

稀土微合金化5Cr21Mn9Ni4N钢高温氧化行为

研究了稀土微合金化5Cr21Mn9Ni4N钢在700-900℃范围内的抗氧化性能。结果表明：在700～900℃范围内，5Cr21Mn9Ni4N钢中加入0．2％（质量分数）稀土后，均使氧化指数n增大，氧化速率常数kp减小，氧化激活能增大，稀土的加入没有改变耐热钢氧化膜的相组成，而是改善了氧化膜的结构，提高了氧化膜的热稳定性和粘附性，从而提高了耐热钢的高温抗氧化性能。随着氧化温度的升高，耐热钢氧化膜组成从锰的氧化物为主向铁的氧化物占较大比重转变，致密度和抗剥落性下降，氧化膜中铁的氧化物大量出现和氧化膜疏松是抗氧化性能降低的主要原因。

稀土对热浸镀铝钢Al_2O_3／渗铝层界面空洞生长的影响

通过高温氧化试验以及测量空洞平均直径和形核数量随氧化时间的变化,研究稀土对Al2O3／渗铝层界面空洞生长和抗高温氧化性能的影响,并与渗纯铝试样进行比较。结果表明,渗铝稀土试样空洞平均直径的增长速率仅是渗纯铝试样的1／2,空洞平均深度随平均直径的增长速率仅是渗纯铝试样的3／5,单位面积上的空洞数量少于渗纯铝试样。稀土可抑制界面空洞的形核和生长,阻止空洞向渗铝层纵深扩展,提高渗铝钢的抗高温氧化性能。探讨了稀土抑制空洞形核和生长的机理。

稀土对渗铝层/基体界面空洞生长和抗高温剥落性能的影响

通过高温氧化实验以及测量空洞平均直径和形核数量随氧化时间的变化,研究稀土对渗铝层抗高温剥落性能和渗铝层/基体界面空洞生长的影响,并与渗纯铝试样进行了比较。结果表明:渗铝层/基体界面空洞的生长可划分为快速生长和稳定生长两个阶段;但当渗稀土铝后,空洞生长速度比渗纯铝试样降低约1/3;稀土可抑制界面空洞的形核和生长,阻止空洞聚集成波浪线状空洞带和线状裂纹,提高渗铝钢的抗高温剥落性能;热浸镀稀土铝后,试样表面自由铝层减薄,从而降低了高温下渗铝层/基体界面铝的浓度梯度,这是稀土抑制空洞形核和生长的主要原因。

Al与Re脱氧对取向硅钢铸态组织的影响

在真空冶炼过程中,分别采用铝和稀土两种元素对取向硅钢进行脱氧,并对两种脱氧剂所冶炼的试验钢的铸态组织与夹杂物的类型、尺寸、形貌等方面进行分析。结果表明:与铝脱氧剂相比,稀土元素作为脱氧剂所冶炼的取向硅钢,其铸坯的宏观缺陷更少,夹杂物多为变质的硫化锰及少量的稀土铝酸盐,使得取向硅钢铸态组织和性能得到改善。

稀土元素对60CrMnMo热轧辊用钢抗氧化性能的影响

研究了６０ＣｒＭｎＭｏ钢中氧化对热疲劳裂纹萌生和长大过程的作用，同时对不同稀土加入量的６０ＣｒＭｎＭｏ钢试样在不同温度、不同保温时间进行了氧化增重对比试验，并采用金相、电镜和Ｘ射线衍射方法进行了氧化皮形貌观察和晶体结构分析。结果表明：随着稀土加入量的增加，试样的氧化速度降低，氧化物颗粒细化，从而抑制了热疲劳裂纹处的氧化，提高了热疲劳寿命。

喷丸与电泳沉积稀土薄膜复合处理提高T91钢抗水蒸气氧化性能的研究

采用喷丸与电泳沉积稀土薄膜复合处理工艺对T91钢进行表面处理 .在管式高温水蒸气氧化实验装置中 ,以 6 0 0℃脱氧水蒸气氧化 30 0h的试验条件评价其抗水蒸汽氧化性能 .结果表明 ,该处理方法可以减小氧化抛物线速度常数 ,有效改善抗氧化性能 ,较单一沉积稀土薄膜效果更为显著 .与原材料相比 ,氧化物晶粒直径可由 3～ 5 μm细化至约 0 .5 μm .分析了喷丸与沉积稀土薄膜对氧化机理的影响 ,并讨论了复合处理工艺对氧化过程中扩散机理的影响以及氧化膜物相组成的变化 .