基于应变设计的L485海洋管材开发

为了满足海底管道用高应变钢管的需求，采用基于应变设计方法进行了L485海洋管材的开发。采用低C、Nb、Ti 微合金化成分设计和多边形铁素体+贝氏体的双相组织设计，开发出屈强比≤0.80、均匀延伸率≥12.0%、-20 ℃下平均冲击功＞400 J的31.8mm厚壁L485钢板，并采用此钢板进行了Φ559 mm×31.8 mm规格L485钢管的试制。对试制出的钢管进行了力学性能测试，测试结果显示，钢管的纵向屈服强度为485～585 MPa，抗拉强度为570～700 MPa，屈强比≤0.85，总伸长率≥25%，均匀延伸率≥7%。试制结果表明，钢管的强度、塑性、韧性等均已达到高应变海洋管研制目标要求。同时，针对存在的屈服强度和应变硬化指数偏下限、热影响区软化等问题，需要从钢板成分及性能、钢管成型及焊接工艺等方面进一步优化设计。

Development of L485 Marine Pipe based on Strain Design

In order to meet the demand of high strain steel pipe for marine pipeline, L485 ocean pipe was developed by strain based design method. The L485 pipeline steel plate of wall thickness 31.8 mm with the strength ratio≤0.80, uniform elongation≥12.0% and average impact energy＞400 J at -20 ℃ was developed by using the microalloy-composition design of low C, Nb and Ti and dual phase microstructure design of "polytope ferrite+bainite". The steel plate was used for the trial production of Φ559 mm×31.8 mm L485 steel pipe. The mechanical property test results show that the longitudinal yield strength of the steel pipe is 485~585 MPa, the tensile strength is 570~700 MPa, the strength ratio is 0.85, the total elongation rate is 25%, and the uniform elongation rate is 7%. The test results indicate that the strength, plasticity and toughness of the steel pipe have reached the target requirements of high strain marine pipe development. At the same time, in view of the existing problems such as the lower limit of yield strength and strain hardening index, and the softening of heat affected zone, it is necessary to further optimize the design from the aspects of steel plate composition and performance, and steel pipe forming and welding process.