Numerical method applied to duplex stainless steel welding

Abstract

Microstructure plays an essential role in the attractive properties of the duplex stainless steels (DSSs) such as toughness and corrosion resistance. These properties are obtained by an adequate balance between the fractions of the ferrite and austenite phases, which can be modified when DSSs are welded. Besides the unbalanced fractions of ferrite and austenite, the precipitation of deleterious compounds at high temperatures such as sigma phase can also occur during DSS welding. In this work, a model based on transport equations was numerically implemented by the finite volume method in a computational code in order to simulate the 2205 DSS welding. It was able to evaluate qualitatively the sigma phase precipitation and the formation of the ferrite and austenite phases by calculating the cooling rates reached during 2205 DSS welding. The results are discussed in light of the previous work, and good agreement between numerical and experimental results was obtained.     

Mechanomaking of nanostructured hypereutectic white irons: powder fabrication

Abstract

White irons containing 5·7 wt-%C were produced by room temperature, high energy milling from iron and carbon elemental powders. Both iron and cementite phases have crystal sizes of less than 10 nm in the powders which have fully dense particles of 50 μm mean size. The gas content is 0·5 wt-% and the powder is stable up to 550°C. Above 550°C decomposition of cementite occurs, involving a decrease in combined carbon content from 5·7 to 3·5 wt-% (annealing at 1050°C). The crystal growth kinetics has two temperature regions with lower activation energies in the high temperature (above 800°C) region. Crystal sizes still below 100 nm were observed for annealing up to 800°C. The size distribution in mechanosynthesised powders was modified by tumbling (dry) and attritor (wet) milling down to mean sizes of 4 μm and 1·4 μm respectively. Whereas tumbling milling does not alter the properties of MS powders, wet attritor milling produced higher gas content (7 wt-%) and much decreased thermal stability. Mechanosynthesised and tumbling milled powders can be degassed prior to consolidation, while wet attritor milled ones cannot.     

焊接热影响区针状铁素体的形核长大及其对组织的细化作用

通过观察焊接热循环冷却过程中不同温度取样直接淬火后的微观组织,研究了焊接热影响区(HAZ)晶内针状铁素体(IAF)的形核长大过程,论证了针状铁素体分割原奥氏体晶粒及细化晶内组织的机理.Auger电子能谱(AES)证实,在TiOx-MnS型复合夹杂物边界附近存在贫Mn区,IAF易于在这类复合夹杂物上形核,单个复合夹杂物能...     

焊缝管液压胀形模拟建模及变形规律的研究

基于周向显微硬度的分布及经验公式法,确立了STKM11A焊缝管热影响区的流动应力;通过对热影响区进行分片的方式,建立了包含焊缝和热影响区的焊缝管液压胀形的有限元模拟模型。基于该模型,模拟分析了STKM11A焊缝管液压胀形时的变形规律,如截面轮廓形状、周向壁厚分布和成形极限等,并与胀形实验结果进行对比。结果表明,液压胀形后焊缝管的截面轮廓形状不对称、壁厚分布不均匀,最小壁厚位于热影响区;包含焊缝及热影响区的有限元模型在预测焊缝管液压胀形的变形规律、极限载荷和潜在胀裂位置等方面,较其他常规模型更加精确。     

Formulation of grain growth diagram in simulated weld HAZ of Ti-microalloyed steel

In this paper,the response of TiN particles to welding thermal cycle and the kinetic behavior of the grain growth in weld heat-affected zone of the Ti-microalloyed steel have been studied by using the simulation technology.Based on the theory of the TiN particle dissolution and coarsening kinetic models in weld thermal cycle and some metallographic data from thermal simulated samples,the grain growth diagram of Ti-microalloyed steel is presented.The experimental data from thermal simulated weld samples agre...     

汽车桥壳用热连轧微合金高强钢板的研究

测试了一种微合金钢（０．０８％Ｃ,１．６４％Ｍｎ,０．０３３％Ｎｂ,０．０１９％Ｔｉ）经１２００℃加热,奥氏体分别在未经变形、８５０℃经５０％压缩变形条件下的ＣＣＴ曲线和暧时加热到１３３０℃的ＣＣＴ曲线。在二辊实验轧机和控冷设备上模拟热轧和控冷工艺。结果表明,实验钢经控轧控冷中温卷取可获得针状铁素体组织,抗拉强度达到５７０ＭＰａ,总伸长率大于２５％,冷弯成形性能优良。     

大线能量焊接用船体结构钢的研究进展

介绍了大线能量焊接在船舶建造中的应用,对比了船体结构钢与其它钢种对大线能量焊接适应性的不同要求。针对大线能量焊接热影响区韧性下降问题,提出了目前提高热影响区韧性的主要措施。指出降低碳当量、细化热影响区奥氏体晶粒尺寸、利用有益氧化物诱导晶内铁素体析出是提高船体结构钢大线能量焊接适应性的有效途径。介绍了鞍钢在热影响区组织调控技术和氧化物诱导机理研究等方面取得的成果。     

焊缝管液压成形技术及热影响区对成形的影响

结合研究成果讨论了焊缝材料性能对管材液压成形规律的影响,阐述了焊缝管液压成形的研究现状及发展趋势,以及亟待解决的关键问题.论述焊缝及热影响区材料性能的测定技术,包含焊缝及热影响区材料特性的有限元数值模拟模型的建立方法.结果表明:焊缝及热影响区的存在造成焊缝管的液压胀形特点及成形规律不同于无缝管.有缝管自由胀形后轮廓形状不对称;在距焊缝对称中心0°～15°之间的壁厚沿环向分布不均匀,在15～180°之间的壁厚基本上呈均匀分布,且壁厚值和与同种材料的无缝管在相同条件下胀形的壁厚值接近;焊缝材料比基体材料强度高,则极限胀形高度大.     

低合金奥-贝球铁焊接峰值温度(Tm)对热影响区组织与力学性能的影响

利用Ｇｌｅｅｂｌｅ－１５００焊接热模拟试验机，在固定的加热速度（１５０℃／ｓ）、峰值温度保温时间（７ｓ）与８００～５００℃冷却时间为７ｓ的条件下，研究了峰值温度（Ｔｍ）在１０５０～８５０℃内变化对低合金奥－贝球墨铸铁热影响区组织及力学性能的影响。研究结果表明，随Ｔｍ的增高，高碳马氏体占基体组织百分数增加，马氏体片随之增长、变粗，σｂ和αｋ值显著下降，同时分析了共晶团各点马氏体含碳量不同，点阵畸变程度发生变化的原因     

STT焊机在超细晶粒钢焊接中的试验研究

采用STT焊接电源进行了400 MPa级超细晶粒钢焊接试验.结果表明,在表面张力过渡CO2气保焊条件下,超细晶粒钢热影响区宽度极窄约为1 mm,随着线能量增大,热影响区中过热区的晶粒尺寸随之增大,但低线能量的表面张力过渡使晶粒长大的程度得到控制.各焊接线能量下,热影响区各区平均硬度不低于母材,不存在软化现象.过热区为多相组织混合形貌,为低碳马氏体、贝氏体、珠光体、铁素体的不平衡混合组织.对线能量3.68 kJ/cm时的焊接接头进行综合力学试验,发现超细晶粒钢的热影响区硬度、强度和韧性均高于母材.