控轧控冷工艺对L450M管线钢屈强比的影响

为了提高管线用钢的安全服役性能，使其获得良好的强韧性和较低的屈强比，采用现场小批量试制试验，研究了不同控轧控冷工艺对L450M管线钢组织性能的影响。结果表明：L450M管线钢采用粗轧开轧温度1 010～1 050℃,精轧开轧温度920～960℃,精轧终轧温度790～830℃,终冷温度550～580℃,屈服强度可达到475～513 MPa,抗拉强度565～583 MPa,伸长率32%～38%,屈强比0.82～0.88,-20℃横向冲击功188～285 J,满足API SPEC 5L-2018标准要求；适当提高精轧终轧温度、降低粗轧阶段变形量、减少精轧阶段轧制道次，有利于降低L450M管线钢的屈强比；适当降低冷速、提高终冷温度，使L450M管线钢显微组织中先共析铁素体比例增加，有利于降低屈强比。

Influence of controlled rolling and controlled cooling process on yield ratio of L450M pipeline steel

In order to improve the safety service performance of pipeline steel and make it obtain good strength, toughness and low yield ratio, the effects of different controlled rolling and controlled cooling processes on the microstructure and properties of L450M pipeline steel were studied by field small batch trial production experiments. The results show that L450M pipeline steel can reach 475-513 MPa in yield strength, 565-583 MPa in tensile strength, 32%-38% in elongation, 0.82-0.88 in yield ratio, and 188-285 J in lateral impact energy at -20 ℃ when the roughing rolling starting temperature is 1 010-1 050 ℃, the finishing rolling starting temperature is 920-960 ℃, the finishing rolling temperature is 790-830 ℃, and the final cooling temperature is 550-580 ℃, meeting the requirements of API SPEC 5L-2018 standard. The yield ratio of L450M pipeline steel can be reduced by properly increasing finishing rolling temperature, reducing deformation in roughing rolling stage and reducing rolling passes in finishing rolling stage. The proportion of proeutectoid ferrite in the microstructure of L450M pipeline steel is increased by appropriately reducing the cooling rate and increasing the final cooling temperature, which is conducive to reducing the yield ratio.