16MnDR与ZG20SiMn铸钢焊接接头的微观组织与低温性能

Micro-structure and cryogenic mechanical properties for welding joint of 16MnDR steel and ZG20SiMn cast steel

采用药芯焊丝气保焊方法焊接了压力容器用低温钢16MnDR和塑性、低温冲击韧性良好的ZG20SiMn铸钢。试验了焊接接头的低温拉伸、弯曲和冲击性能,结果为:焊缝和ZG20SiMn铸钢的低温强度都大于16MnDR,-40℃拉伸试验都断于16MnDR母材;-40℃侧弯试验弯曲角为90°时,在ZG20SiMn铸钢侧出现了大于3mm的裂缝;-40℃焊缝、16MnDR侧和ZG20SiMn侧热影响区的冲击值都大于标准要求的34J,-50℃时ZG20SiMn侧热影响区的冲击韧性已不足。焊缝金属中C、Si和Mn含量合适,并含有对提高低温性能有益的Ni和微量V,微观组织细小,有大量针状铁素体,故焊缝区域有很好的低温塑性和韧性。ZG20SiMn过热区的组织以贝氏体为主,有细小的缩松缺陷,故有较高的强度,弯曲试验在ZG20SiMn侧出现裂纹。

Welding joint of 16MnDR steel,one kind of cryogenic steels and ZG20SiMn cast steel which owns perfect cryogenic plasticity and toughness property was prepared by gas shielded metal arc welding with flux-cored wire.Tensile test ,bend test and impact test of the joints were carried out at low temperature.The result showed that all of the tensile samples tested at -40℃ were broken at the side of 16MnDR base metal,which meant that the strength of 16MnDR steel was lower than the weldmetal and the ZG20SiMn;Cracks longer than 3 mm were observed at the side of ZG2OSiMn when side bent tests at -40℃ were carried to 90° angles.The values of impact tests at -40℃Ceither located at weldmetal or located at HAZs of 16MnDR and ZG20SiMn were larger than 34 J, required by the code.While the impact values at heat affect zone（HAZ）of ZG20SiMn at -50℃ were lower than the code required. With OM and chemical composition analysis ,it showed that there were suitable contents of C ,Si ,Mn ,Ni and micro V ,and the microstructure of weldmetal was fined, so that the cryogenic mechanical properties were improved.The microstructure of over heated zone in ZG20SiMn HAZ was Bainite and shrinkage porosity was found ,caused to high tensile strength of ZG20SiMn and easy to crack when be bent.