Design of V containing line-pipe grades for improved strength and weldability

加拿大迫切需要新的大直径、高性能和耐用的先进高强度钢(AHSS)管线管，能够承受加拿大恶劣的条件。低温韧性、良好的应力腐蚀性能和优异的现场焊接性是一些主要要求。AHSS管材通常采用钛、Nb、V微合金化、控轧、加速冷却等加工工艺。虽然这些微合金化元素中的每一种对性能的单独影响都得到了很好的证实，但当存在两个或更多物种时，报告的结果不一致。在这里，我们首先将重点放在钒的单独作用上。钒对贝氏体有强化作用，是高强度管线钢的主要组织相之一，因此引起了人们的强烈兴趣。这种强化的原因尚有争议；一些作者认为这是由于贝氏体组织的细化，另一些人则认为是析出或聚集作用，还有一些人认为钒抑制了动态回复。我们将在实验室的铸件和热轧试件上进行试验，以确定这些假设的正确性，并开发一个更准确的含V贝氏体钢的组织-性能模型。随后，将研究同时包含V和Nb添加的更复杂的合金，以检查拮抗/协同效应。这一新知识将通过更好地优化成分和工艺参数，提高管道的强度、可靠性和成本。 因此，这项工作的目标是(A)通过精心设计的一系列实验和建模活动来解决这一知识差距，以及(B)在加拿大钢铁和管道行业非常感兴趣的领域培训一名HQP。

There is a strong need for new large-diameter, high-performance and durable advanced high strength steel (AHSS) line pipes in Canada that can withstand the harsh Canadian conditions. Low-temperature toughness, good stress corrosion properties and excellent field weldability are some of the main requirements. Microalloying with Ti, Nb and V, controlled rolling and accelerated cooling are commonly employed processing techniques for AHSS pipe. Whilst the individual effects of each of these microalloying elements on properties are well established, inconsistent results have been reported when two or more species are present. Here we will first focus on the effect of vanadium in isolation. Vanadium is of strong interest as it has been shown to have a strengthening effect on bainite, one of the main microstructural phases present in high strength line pipe steels. The origin of this strengthening is disputed; some authors claim that it is due to refinement of the bainitic microstructure, others claim that precipitation or clustering is involved, and still others believe that vanadium suppresses dynamic recovery. We will carry out trials on laboratory cast and hot-rolled specimens to determine the validity of each of these hypotheses and to develop a more accurate structure-properties model for V containing bainitic steels. Subsequently, a more complex alloy containing both V and Nb additions will be studied to check for antagonistic/synergistic effects. This new knowledge will lead to improvements in pipeline strength, reliability and costs through a better optimisation of the composition and process parameters. The objectives of this work are thus to (a) address this knowledge gap by a carefully designed series of experiments and modelling activities and (b) to train one HQP in an area of great interest to the Canadian Steel and Pipeline industries.