稀土镧的添加对低合金高强钢粗晶热影响区韧性的影响

Effect of rare earth lanthanum addition on toughness of coarse-grained heat-affect zone of high strength low alloy steel

冶炼了不含La和含0.016 mass%La的两组钢,分别在Gleeb3800热模拟机上进行100 kJ·cm^(-1)线能量的焊接热模拟,并采用光学显微镜、场发射扫描电镜和透射电镜等观察了试验钢中粗晶热影响区的夹杂物和析出物特征、组织及断口形貌,分析了稀土La的添加对试验钢粗晶热影响区-20℃夏比冲击韧性的影响。结果表明:在钢中添加0.016 mass%La后,Mg-Al氧化物外附一层(Mn,Ca)S或TiN的复合夹杂物被改性为La_(2)O_(2)S和La_(x)S_(y),且夹杂物数量增多,尺寸减小,为针状铁素体的形成提供了更多的形核质点,导致在含0.016 mass%La试验钢中形成了较多的针状铁素体。同时,更加细小弥散的(Ti,Nb)(C,N)析出物在含0.016 mass%La试验钢中形成,在焊接热循环过程中可有效钉扎奥氏体晶界,有助于细化晶粒。此外,M-A岛的体积分数在含0.016 mass%La试验钢中也更少。这些结果使得含0.016 mass%La的试验钢的粗晶热影响区的低温韧性更好。

Two groups of steels without La and containing 0.016 mass%La were smelted,and the welding thermal simulation with line energy of 100 kJ·cm^(-1) of the steels was carried out on Gleeb3800 thermal simulator respectively.The characteristics of inclusions and precipitates,microstructure and fracture morphology of coarse grain heat affected zone in the experimental steel were observed by means of optical microscope,field emission scanning electron microscopy and transmission electron microscopy,and the effect of rare earth La on-20℃Charpy impact toughness of coarse grain heat affected zone of the experimental steel was analyzed.The results show that after adding 0.016 mass%La to the steel,the composite inclusions of Mg-Al oxide with a layer of(Mn,Ca)S or TiN are modified into La_(2)O_(2)S and La_(x)S_(y),and the number of inclusions increases,and the size decreases,which provides more nucleation particles for the formation of acicular ferrite,resulting in the formation of more acicular ferrite in the steel containing 0.016 mass%La.Meanwhile,the finer dispersed(Ti,Nb)(C,N)precipitates are formed in the steel containing 0.016 mass%La,which can effectively pinning the austenite grain boundary and help to refine the grain during the welding thermal cycle.In addition,the volume fraction of M-A island is also less in the steel containing 0.016 mass%La.These results make the low temperature impact toughness of the coarse grain heat affected zone of the steel containing 0.016 mass%La better.