热输入对X70管线钢焊接热影响区组织和韧性的影响  

Influence of heat input on the microstructure and properties of welding heat affected zone of X70 pipeline steel

作　　者：张忠发[1] 朱亮[1] 蔡淑娟[1] 

机构地区：[1]兰州理工大学省部共建有色金属先进加工与再利用国家重点实验室,甘肃兰州730050

出　　处：《电焊机》2015年第9期29-33,共5页Electric Welding Machine

基　　金：国家自然科学基金资助项目(51264026)

摘　　要：管线钢焊接突出的问题是热影响区晶粒粗化会导致接头韧性下降。利用热模拟技术和超窄间隙焊接方法对X70管线钢进行试验,得到了不同热输入下焊接热影响区粗晶区的组织,并测试了其韧性。结果表明,在室温下,当热输入低于8 k J/cm时,以板条贝氏体和少量针状铁素体组织为主,原奥氏体晶粒尺寸小于48μm,韧性与母材相当;高于8 k J/cm时,随着热输入增加,板条贝氏体和针状铁素体逐渐减少,原奥氏体晶粒逐渐长大,韧性开始急剧下降。分析认为,对于这类C含量低的管线钢,板条贝氏体的形成并不会导致韧性降低,原奥氏体晶粒不断长大才是造成韧性下降的主要原因。采用超窄间隙焊接方法,可以有效缩短高温停留时间,防止原奥氏体晶粒长大,从而避免焊接热影响区粗晶区的韧性下降。The outstanding problem of welding pipeline steel is the toughness of welded joint will be decreased by grain coarsening of heat affected zone.The microstructures of X70 pipeline steel coarse-grained heat affect zone （CGHAZ） under different welding heat inputs are obtained by using thermal simulation technique and the ultra-narrow gap welding method ,and the toughness of CGHAZ is tested.The results show that under room temperature,the microstructure is lath bainite and acicular ferrite,the original austenite grain size is lower than 48 μm and the impact energy is equal to base metal when the welding heat input is less than 8 kJ/cm;When the welding heat input is above 8 kJ/cm,the amount of lath bainite and acicular ferrite decreases gradually,the original austenite grain size grows gradually and the impact energy decreases drastically with the increase of heat input.Through analysis, it is concluded that the lath bainite can not make the toughness reduce and the growth of original austenite grain is the main reason for the decrease of the toughness for this type of low C content of pipeline steel.The narrow-gap welding can decrease the holding time in high temperature and prevent the original austenite grain grow ,so it can avoid the decrease of the toughness of CGHAZ.

关 键 词：热模拟 超窄间隙焊接 焊接热输入 热影响区粗晶区 

分 类 号：TG457.11[金属学及工艺—焊接]