440 MPa级高强钢焊条熔敷金属组织与低温冲击韧性研究

Study on microstructure and low-temperature impact toughness of deposited metal form covered electrodes for 440 MPa grade high-strength steel

为满足440 MPa级高强钢对焊接材料的需求,研制了三种焊条,并进行了熔敷金属焊接试验,使用光学显微镜、扫描电镜和透射电镜等手段研究了熔敷金属组织与低温冲击韧性.结果表明,随着Mn,Ni,Cr和Cu含量的增大,熔敷金属的-40℃平均冲击吸收功从35.7 J逐渐增至96.3 J,低温冲击韧性逐渐提高;随着Mn,Ni,Cr和Cu含量的增大,虽然熔敷金属中M23C6型碳化物含量逐渐增大,但是熔敷金属的CCT曲线逐渐右移,相变温度逐渐降低,使得针状铁素体含量逐渐增加,铁素体板条尺寸逐渐减小和板条间交织状分布趋势逐渐增强,M-A组元含量及尺寸逐渐减小,是低温冲击韧性逐渐提高的主要原因;含Cu熔敷金属中夹杂物外层会形成CuS,针状铁素体形核更容易,有利于低温冲击韧性提高.

To meet the welding material requirements of 440 MPa grade high-strength steel,three types of covered electrodes have been developed,and the welding test of deposited metal was carried out.The microstructure and low-temperature temperature impact toughness of deposited metal were analyzed by means of the optical microscope,scanning electron microscope,and transmission electron microscope.The results show that with the increase of Mn,Ni,Cr,and Cu contents,the average impact absorption energy of the deposited metal at−40℃gradually increases from 35.7 J to 96.3 J,and the low-temperature impact toughness gradually increases;With the increase of Mn,Ni,Cr and Cu contents,although the content of M23C6 type carbide in the deposited metals gradually increases,the CCT curve of the deposited metals gradually moves to the right,and the transformation temperature gradually decreases,which makes the content of acicular ferrite gradually increase,the size of ferrite lath gradually decreases,and the interlaced distribution trend between ferrite lath gradually increases,and the content and size of M-A constituent gradually decrease,which is the main reason for the gradual improvement of lowtemperature impact toughness;The outer layer of inclusions in the deposited metal containing Cu can form CuS,making it easier for acicular ferrite to form nuclei,which is conducive to improving low-temperature impact toughness.