TiO_(2)对自保护药芯焊丝熔敷金属组织与性能的影响

Effect of TiO_(2)in the Self-Shielded Flux-Cored Wire on Microstructures and Properties of Deposited Metal

针对自保护药芯焊丝焊接熔渣中TiO_(2)和Al、Mg的冶金反应引起熔敷金属成分变化的问题,本文以CaF_(2)-Al-Mg为基础渣系,制备了不含TiO_(2)和在药粉中分别添加5%、10%和20%TiO_(2)的4种自保护药芯焊丝,并以熔化极自保护焊接方式堆焊了相应的熔敷金属,通过落锤冲击试验、直读光谱仪、光学显微镜、SEM、拉伸试验和冲击试验,研究了TiO_(2)对脱渣率以及熔敷金属成分、组织、夹杂物和力学性能的影响规律.试验结果表明,TiO_(2)能有效改善脱渣性,并会与Al、Mg发生冶金反应:2Al+Mg+2TiO_(2)→2Ti+MgAl_(2)O_(4),还原出来的Ti经过渣-金属界面进入熔敷金属,导致熔敷金属中的Ti含量明显升高,C、Si、N含量降低;无TiO_(2)焊丝的熔敷金属组织主要为针状铁素体,夹杂物主要为直径<1μm的圆形MgO·Al_(2)O_(3),此时的屈服强度为411MPa,0℃冲击功为86 J,冲击断口放射区的微观形貌由韧窝和河流花样构成,属于混合断裂;添加5%的TiO_(2)后,熔敷金属中形成大量细小准多边形铁素体组织,并出现了多边形TiN夹杂物,屈服强度提高到489 MPa,韧性稍许下降;当TiO_(2)添加达到10%后,由于熔敷金属中过高Ti含量的影响,组织转变为粒状贝氏体,TiN夹杂物增多并发生粗化,此时屈服强度增高至615 MPa,但韧性急剧恶化,冲击断口放射区完全为河流花样,属于脆性断裂;更高的TiO_(2)含量(20%)对应的熔敷金属,组织仍为粒状贝氏体,因形成大量的晶界Ti_(4)C_(2)S_(2),强度及韧性均降低.

In this study,four types of self-shielded flux-cored wires containing 0,5%,10%,and 20%TiO_(2)in flux were prepared with CaF_(2)-Al-Mg as the basic slag system.This study aims to solve the composition change of the deposited metal caused by the metallurgical reaction between TiO_(2)and Al-Mg.The corresponding metal was deposited through self-shielded arc welding.The effect of TiO_(2)on slag detachability was investigated through drop weight impact,tensile,and impact tests,and the composition,microstructure,inclusions,and mechanical properties of the deposited metal were determined using optical emission spectroscopy,optical microscopy,and scanning electron microscopy.The results indicate that TiO_(2)can effectively improve slag detachability and react with Al and Mg:2Al+Mg+2TiO_(2)→2Ti+MgAl_(2)O_(4).The reduced Ti enters the deposited metal through the slag-metal interface,resulting in a significant increase in the Ti content in the deposited metal and a decrease in the C,Si,and N contents.The deposited metal microstructure of the wire without TiO_(2)is mainly acicular ferrite,and the inclusions are mainly round MgO·Al_(2)O_(3)of less than 1μm.The yield strength and impact energy at 0℃are 411MPa and 86 J,respectively.The radiation zone of the impact fracture comprises dimples and river patterns,which belong to mixed fracture.After adding 5%TiO_(2),the microstructure of the deposited metal is fine quasipolygonal ferrite and contains polygonal TiN inclusions.The yield strength increases to 489 MPa but toughness slightly decreases.When the TiO_(2)content reaches 10%,due to the high Ti content in the deposited metal,the microstructure is granular bainite,and TiN inclusions increase and become coarser.The yield strength reaches a maximum of 615 MPa,but the toughness sharply deteriorates.The radiation zone of impact fracture is of river patterns completely,which belong to brittle fracture.The microstructure of deposited metal corresponding to a higher TiO_(2)content(20%)remains granular bainite.However,the strength and toughness are both reduced due to the formation of a large number of Ti_(4)C_(2)S_(2)at grain boundaries.