The Study Of Controlled Rolling And Coldding For Pipeline Steel X70

The demands for pipeline steels are being increased dramatically with the national economy development. Driven by cost considerations, gas and oil transportation companies have readily adopted higher strength pipeline steels with thicker gauges to permit gas and oil transportation at higher pressures. As a result, recent construction of pipelines has shown a trend towards higher operation pressure with greater wall thickness and higher strength pipe. At the same time, acicular ferrite pipeline steels are becoming accepted as the prevalence for this new construction because of their high strength, excellent tough-ness, good weldability and satisfied hydrogen sulfide resistance.The controlled rolling and controlled cooling technology is very important in modern steel products. This paper, apply controlled rolling and controlled cooling technology on the production of micro-alloyed pipeline steel. The experimental aims were to clarify the characteristics of the change of microstructures and mechanical properties at various deformation conditions and to offer theoretical foundation and technological basis for industrial manufacture. The main contents are given as follows:1. The dynamic recovery and dynamic recrystallization of X70 during hot deformation were investigated by single pass compression test. The flow stress curves and microstructures of test steel at different temperature, strain rate and strain amount were obtained.2. By multi-pass thermal simulation test, the effects of the strain amount, strain rate, finishing temperature, final cooling temperature and the cooling rate on austenite-ferrite transformation behavior and the microstructure were studied on the thermo-mechanical simulator for pipeline steel X70.3. Based on the investigation results of multi-pass hot simulation deformation test, the practical controlled-rolling and controlled-cooling tests were performed by using the rolling mill in ANSteel ASP 2150, the improved TMCP schedules containing a multi-pass controlled rolling coupled with moderate cooling rates were applied to hot rolling experiments. And the effects of technological parameters of controlled rolling and controlled cooling on the microstructures and mechanical properties of pipeline steel were investigated to obtain flexible rolling of pipeline only by optimized TMCP, without changing the chemical compositions of existing pipeline steels.