【作者】 贺龙威；

【导师】 王勇；

【作者基本信息】 中国石油大学 ， 材料科学与工程， 2011， 硕士

【摘要】 深水钻井隔水管是深海油气钻探的重要装备单元。深水钻井隔水管是由X80主管和30CrMo法兰焊接而成,焊接工艺和接头性能关系着隔水管制造技术和产品国产化的可行性。文中从焊接接头组织和性能入手,深入研究了焊接工艺对显微组织、接头硬度和冲击韧性的影响规律。采用维氏硬度计测试接头不同区域的宏观硬度,试验结果表明30CrMo热影响区存在局部硬化和局部软化,X80热影响区出现软化,焊缝区的硬度适中。30CrMo热影响区局部硬化是由于在该区形成了马氏体和上贝氏体组织,这两种组织的塑性变形抗力高,因此该区域出现硬化。30CrMo热影响区局部软化的原因是形成了粗大粒状铁素体、粗大碳化物和低碳奥氏体分解产物,导致这个区域的硬度与30CrMo母材相比较低。X80热影响区软化是由于受热作用,晶粒回复、再结晶长大形成多边形铁素体,同时质点粗化也引起焊接热影响区软化。经过500℃×1.5h焊后热处理,接头硬度发生变化。30CrMo局部硬化区和局部软化区硬度都有所降低,硬度降低是由于组织发生转变和焊接残余应力消除。经过热处理,30CrMo局部硬化区组织转变为回火索氏体和条状铁素体、块状铁素体。在热处理过程中,30CrMo局部软化区铁素体内分布的碳化物聚集和长大,不在弥散分布,碳化物的强化作用有所降低,所以经热处理后该区硬度进一步下降。冲击试验表明,X80侧熔合线+1mm处由于晶粒粗化和形成粒状贝氏体组织而发生脆化,热处理对此处的冲击韧性影响不明显。试验同时表明30CrMo侧熔合线+1mm处和熔合线+2mm处都发生脆化,原因是30CrMo侧熔合线+1mm处形成上贝氏体和硬脆马氏体,30CrMo侧熔合线+2mm处形成了粒状贝氏体和马氏体。经热处理后,这两区域的韧性都有所改善,冲击断口为韧窝状的,原因是30CrMo侧熔合线+1mm处组织转变为块状铁素体、回火索氏体和弥散分布的碳化物,30CrMo侧熔合线+2mm处形成了块状铁素体、粒状铁素体和粒状回火索氏体,而且碳化物弥散分布,这些组织的韧性较好,所以这两区域的冲击韧性有所改善。更多还原

【Abstract】 Deep water drilling riser is important Equipment unit in deep sea drilling and exploiting oil and gas. Welding of X80 and 30CrMo is used in manufacturing of deep water drilling riser. Welding procedure and welding joint properties is important to the localization of riser manufacturing technology and riser product.Microstructures and properties of welded joint are studied in this paper, the laws of effecting of welding procedure and microstructure on hardness and impact toughness of welding joint are intensively studied. Microstructures of different zones in welding joint are observed and analysed, The results show that the microstructures of welding joint are discontinuous, So the mechanical properties of welding joint is also discontinuous. Macrohardness of different zones in welding joint are tested by Vickers, The results show that local hardening and local softening exist in HAZ(heat affected zone) of 30CrMo. The results also show that local softening exists in HAZ of X80 and the hardness of weld metal is moderate. The reason of local hardening of 30CrMoHAZ is forming of martensite and upper bainite in this zone. Plastic deformation resistance of these microstructures is high, so the local hardening is tseted in this zone. Local softening of 30CrMoHAZ is caused by forming of coarse granular ferrite, coarse carbides and low carbon austenite decomposition products, Leading to hardness of this zone is lower than hardness of 30CrMo base matel. Softening of X80HAZ is originated from acicular ferrite, coarse polygonal ferrite and small quantities of carbide distributing among ferrite.Through 500℃×1.5h postweld heat treatment, the hardness of welding joint is changed. The hardness of local hardening zone and local softening zone in 30CrMoHAZ is reduced, which is caused by microstructure transformation and Welding residual stress releaseing. Through postweld heat treatment, microstructure of 30CrMo local hardening zone transform into tempered sorbite, ferrite band and granular ferrite. During postweld heat treatment, carbide precipitation, aggregation and growth occurred in ferrite of 30CrMo local softening zone. Strength rule of carbide is decreased, so the hardness of this zone is reducing after post weld heat treatment.Impact test show that embrittlement occurrs at X80 fusion-line+1mm because of forming of granular bainite, impact toughness of this zone is not improved through postweld heat treatment. Impact test show simultaneously that embrittlement occurred at 30CrMo fusion-line+1mm and 30CrMo fusion-line+2mm. After heat treatment, the toughness of these two zones are improved, impact fracture is dimple. Embrittlement is caused by brittle microstructure, there are upper bainite and hard and brittle martensite in the zone of 30CrMo fusion-line+1mm, and granular bainite martensite in the zone of 30CrMo fusion-line+2mm. Through heat treatment, the microstructures of the zone of 30CrMo fusion-line+1mm transform into granular ferrite, tempered sorbite and dispersed carbide. The microstructures of the zone of 30CrMo fusion-line+2mm transform into granular ferrite, granular bainite and granular tempered sorbite. These microstructure have good toughness, so the toughness of the two zones are improved.更多还原