X100高强管线钢焊接接头的断裂韧性

FRACTURE TOUGHNESS OF WELDED JOINTS OF X100 HIGH-STRENGTH PIPELINE STEEL

采用裂纹尖端张开位移(CTOD)实验对X100高强管线钢焊接接头母材、焊缝和热影响区(HAZ)进行了断裂韧性测试研究,并使用SEM和TEM对CTOD试样近断口区组织及夹杂物进行了观察.结果表明,温度对X100高强管线钢焊接接头断裂韧性有显著影响.在同一温度下,条件启裂值δ_(0.2)和δ_(0.2BL)均呈现母材最大、热影响区次之、焊缝最小,即母材低温断裂韧性最优、热影响区次之、焊缝最差,但随温度降低,其断裂韧性均下降.母材试样近断口区显微组织为粒状贝氏体(GB)和少量准多边形铁素体(QF)及板条贝氏体铁素体(BF),细小粒状M-A组元弥散分布于贝氏体铁素体板条界处;焊缝试样近断口区组织为针状铁素体(AF),M-A组元形态多样,尖角明显;热影响区粗晶区近断口组织为粒状贝氏体和平行排列的板条状贝氏体铁素体,M-A组元呈方形、楔形、条形分布于晶内、晶界和板条界处.大尺寸尖角型M-A组元是导致焊缝和热影响区粗晶区断裂韧性差的主要原因之一,而较高的夹杂物分布则使焊缝具有较低的断裂韧性.

Fracture toughness of base metal, weld seam and heat-affected-zone （HAZ） in X100 high-strength pipeline steel welded joints was investigated by three-point crack tip opening displacement （CTOD） test. Microstructure and inclusion near fracture zones were observed by means of SEM and TEM. The results indicated that fracture toughness of X100 high-strength pipeline steel welded joints was greatly influenced by test temperature. At the same temperature, the numerical values of apparent crack initiation 50.05, conditional crack initiation 50.2 and δ0.2BL of base metal are higher than that of weld seam and HAZ, and low temperature fracture toughness of base metal is better than those of weld seam and HAZ. With temperature decreasing, the fracture toughness of base metal, weld seam and HAZ decreased. The microstructure of near fracture zones of base metal specimen was composed of granular bainite （GB）, a small quasi polygonal ferrite （QF） and lath bainite ferrite （BF）, and the fine and equally dispersed M-A structure distributed on the grain boundary. The microstructure of near fracture zones of weld seam specimen was composed of acicular ferrite （AF）, and the form of M-A constituents shows diversity, sharp-angled clearly. The microstructure of near fracture zones of coarse grain HAZ was composed of GB and parallel LBF, and the square, wedged and bar M-A constituents distributed on the interior of grain, grain boundary and lath boundary. The poor fracture toughness of weld seam and HAZ specimen results from large size and cusp type M-A structure. While the higher distribution of inclusion in weld seam makes fracture toughness worse.