Research and Development Into Low Temperature Toughness of Large Diameter Heavy Wall X80 Pipeline Steel at Shougang Steel

Abstract

In recent years the trend in oil and gas transmission pipelines has been toward higher operating pressures. This trend, while the desire to keep steel costs low, has resulted in an increased demand for large diameter heavy wall X80 with good low temperature toughness. It is well known that improving the low temperature toughness with increasing wall thickness of the pipeline is very difficult. To overcome the difficulty of producing consistent low temperature toughness in heavy wall pipe Shougang Steel Research in cooperation with the Shougang Steel Qinhuangdao China (Shouqin) 4.3 m heavy wide plate mill research was conducted. This paper describes the background, composition design and process strategy to produce good low temperature toughness in heavy wall API plate. The importance of the slab reheating schedule and recrystallized rolling process/schedule that occurs during the roughing process will be discussed. The effect of per pass reductions and work roll speed rotation on the strain introduced was analyzed by means of the numerical simulation technology. Furthermore, the center thickness microstructure and low temperature toughness of plate under the different rolling schedules were researched. The results showed a low reheating temperature and slow rough rolling speed should be implemented. The per pass reductions during recrystallized rough rolling should be increased in a steady fashion, with special emphasis on the reduction of the final roughing pass prior to the intermediate hold (transfer thickness for finishing). When the final roughing pass had a per pass reduction of more than 15%, the main microstructure of plate consists of uniform (surface to center) fine ferrite/acicular ferrite with a small volume fraction of M-A constituent. This fine uniform microstructure results in good low temperature fracture toughness in heavier plate thicknesses. Results of this research and development work will be discussed.

Hot Deformation Behavior of C-Mn Steel with Incomplete Recrystallization during Roughing Phase with and without Nb Addition

“…from R1 to R7. It is obvious that according to Figure 4a,b, the stress uniformity increases with the last roughing passes, similar to that observed in the case of equivalent strain, where uniformity increases with increased per-pass reduction and control of work roll rotation speed [24]. However, the strain distribution is usually more stable as related to rolling parameters than stress as related also to material characteristics and therefore reveals the true nature of rolling complexity under low energy deformation rolling schedule and the unstable austenite conditioning degrading the needed mechanical properties.…”

“…For FEM simulation a complete SRX was considered; a common to full recrystallization-controlled rolling (RCR) or recrystallization rough rolling (RRR) process was used to identify the minimum penetration depth as a boundary condition of the proposed rolling schedule. FEM methods are well-accepted methods for optimization of deformable materials [24] and were therefore used also in this study.…”

Numerical Simulation on Rolling Process of Medium Plate

“…3, along with rising of pass reduction, total equivalent strain of core metal become greater. And the occurrence tendentious of birth defects would be decreased, making metal structure crystal grain refine, reach the goal of increasing steel plate's toughness and intensity,especially for the low temperature toughness, thanks to completely strain without dead corner by increasing of core metal strain [5] . But, its overlarge pass reduction may bring low the condition of roll bite, prolong rolling time, reduce rolling efficiency.…”

Developing of X65 steel coils making at Steckel mill using thermo-mechanical control process

“…The processes of Steckel mill rolling high-strength steels, intended mainly for the production of large pipe, were investigated in papers [20][21][22][23]. The processes proposed by the authors of works [20, 21,24], related to the production of rolled products for large diameter pipes of steel grade X80, are of practical importance. It should be noted that these technologies are implemented on the equipment created in the 1990's, which allows to conduct a particular analysis of technical capabilities and differences of equipment built earlier.…”