In this study,the welding thermal cycle curve exhibited two temperature peaks in high heat-input twin-wire separate-pool submerged-arc welding and coarse-grained heat affected zone existed in the welded joint. The inc...In this study,the welding thermal cycle curve exhibited two temperature peaks in high heat-input twin-wire separate-pool submerged-arc welding and coarse-grained heat affected zone existed in the welded joint. The inclusions of primary weld metal and coarse-grained heat affected zone of Ce-added SAW should be Al_2O_3,MnO,SiO_2,TiO,Ce_2S_3,CeS,Ce_2O_2S and Ce_2O_3. Under the effect of welding thermal cycle,oxy-sulfides inclusions of Ce,the diameter of which was less than 2. 0 μm,slightly grew larger,but the composition and type of the inclusions didn't change. The microstructure of the large heat input weld metal had acicular ferrite that Ce oxide sulphide particles induced nucleation and proeutectoid ferrite. In the coarse-grained heat affected zone of weld metal,home-position precipitation of acicular ferrite and sympathetic acicular ferrite were both observed. It was supposed that previous crystal cells of acicular ferrite in austenite grain promoted home-position precipitation of acicular ferrite. Meanwhile,sympathetic acicular ferrite tended to nucleate at the primary acicular ferrite grain boundaries,where high dislocation density was located,and grew inside the neighboring carbon-depleted austenitic regions. The granular bainite nucleated in the austenitic zone with high carbon content close to acicular ferrite and sympathetic acicular ferrite.展开更多
1000 MPa级高强钢在水电领域的应用已日趋成熟,但国内相应高性能焊材的研发较少,高强度熔敷金属保持低温高韧性是研发难点之一.通过添加Ce元素优化熔敷金属,并利用扫描电子显微镜(scanning electron microscope,SEM)、透射电子显微镜(tr...1000 MPa级高强钢在水电领域的应用已日趋成熟,但国内相应高性能焊材的研发较少,高强度熔敷金属保持低温高韧性是研发难点之一.通过添加Ce元素优化熔敷金属,并利用扫描电子显微镜(scanning electron microscope,SEM)、透射电子显微镜(transmission electron microscope,TEM)、高温激光共聚焦扫描显微镜(confocal laser scanning microscope,CLSM)等微观组织表征方法,研究了Ce含量对1000 MPa级高强钢埋弧焊熔敷金属组织强韧性及组织演变规律的影响.结果表明,Ce含量为0.02%时,抗拉和屈服强度分别提高3.7%和17.2%,此时强韧匹配效果最好,低温冲击韧性整体提升,Ce含量为0.01%时提升最大,-40℃和-60℃环境下分别为24.3%和42.2%.微观组织方面,Ce可细化晶粒,使M-A组元分布更弥散,增强组织韧性;含量为0.04%时会使块状铁素体和针状铁素体尺寸变大、大尺寸晶粒增多,影响抗拉强度.演变机理上,Ce与C协同富集引发晶格畸变促进M-A组元生成,含量为0.02%时使残余奥氏体含量增加,借助相变诱发塑性(transformationinduced plasticity,TRIP)效应提升塑性变形能力,促进下贝氏体转变实现强韧性协同提升;0.04%的Ce则导致晶界偏析加剧,形成含Ce脆性相析出物,降低奥氏体稳定性,使冲击韧性相对于0.02%时劣化.展开更多
Magnesium and its alloys have been used in many industries, but they are reactive and require protection against aggressive environments. In this study, oxide coatings were applied on AZ91D magnesium alloy using micro...Magnesium and its alloys have been used in many industries, but they are reactive and require protection against aggressive environments. In this study, oxide coatings were applied on AZ91D magnesium alloy using micro-arc oxidation （MAO） process. Then, in order to seal the pores of the MAO coatings, the samples were immersed in cerium bath for different times. The surface morphologies and compositions of the coatings were analyzed by scanning electron microscopy （SEM） and X-ray energy dispersive spectroscopy （EDS）, respectively. The corrosion behavior of the coatings was investigated with electrochemical impedance spectroscopy （EIS） and potentiodynamic polarization tests in 3.5 wt.% NaCl solution. The amount of the porosity of the coating was measured by electrochemical method. It was found that the sealing treatments by immersion in cerium bath successfully sealed the pores of the MAO coatings. The results of the corrosion tests showed that the MAO coating which was sealed in Ce bath for 10 min enhanced the corrosion resistance of the substrate significantly. Furthermore, this coating had the lowest amount of the porosity among the coatings.展开更多
基金supported by the National Natural Science Foundation of China,the Baoshan Iron&Steel Co.,Ltd(No.U1260103)
文摘In this study,the welding thermal cycle curve exhibited two temperature peaks in high heat-input twin-wire separate-pool submerged-arc welding and coarse-grained heat affected zone existed in the welded joint. The inclusions of primary weld metal and coarse-grained heat affected zone of Ce-added SAW should be Al_2O_3,MnO,SiO_2,TiO,Ce_2S_3,CeS,Ce_2O_2S and Ce_2O_3. Under the effect of welding thermal cycle,oxy-sulfides inclusions of Ce,the diameter of which was less than 2. 0 μm,slightly grew larger,but the composition and type of the inclusions didn't change. The microstructure of the large heat input weld metal had acicular ferrite that Ce oxide sulphide particles induced nucleation and proeutectoid ferrite. In the coarse-grained heat affected zone of weld metal,home-position precipitation of acicular ferrite and sympathetic acicular ferrite were both observed. It was supposed that previous crystal cells of acicular ferrite in austenite grain promoted home-position precipitation of acicular ferrite. Meanwhile,sympathetic acicular ferrite tended to nucleate at the primary acicular ferrite grain boundaries,where high dislocation density was located,and grew inside the neighboring carbon-depleted austenitic regions. The granular bainite nucleated in the austenitic zone with high carbon content close to acicular ferrite and sympathetic acicular ferrite.
文摘Magnesium and its alloys have been used in many industries, but they are reactive and require protection against aggressive environments. In this study, oxide coatings were applied on AZ91D magnesium alloy using micro-arc oxidation （MAO） process. Then, in order to seal the pores of the MAO coatings, the samples were immersed in cerium bath for different times. The surface morphologies and compositions of the coatings were analyzed by scanning electron microscopy （SEM） and X-ray energy dispersive spectroscopy （EDS）, respectively. The corrosion behavior of the coatings was investigated with electrochemical impedance spectroscopy （EIS） and potentiodynamic polarization tests in 3.5 wt.% NaCl solution. The amount of the porosity of the coating was measured by electrochemical method. It was found that the sealing treatments by immersion in cerium bath successfully sealed the pores of the MAO coatings. The results of the corrosion tests showed that the MAO coating which was sealed in Ce bath for 10 min enhanced the corrosion resistance of the substrate significantly. Furthermore, this coating had the lowest amount of the porosity among the coatings.
