Study On Smelting And Rolling Processing For X80 Pipeline Steel In Shouqin Co., Ltd.

In recent decades, controlled rolling and controlled cooling pipeline steel develop ed on the basis of high-strength low-alloy steel is widely used in the oil and gas transp ortation of pipeline engineering. With the increasing of transport pressure and distance, the study of the pipeline steel turned around to the improvement of its high strength, high toughness, good weldability and corrosion resistance of high performance. Shou Qin metal material co.,ltd. solve the problems of traditional X80 pipeline steel, such a s low temperature Charpy impact toughness and poor structure uniformity by composi tion designed, smelting process control and find out the suitable controlled rolling and cooling process parameters.In this paper, the smelting and rolling processing of X80 pipeline steel has been optimitzed by Shou Qin metal material co.,ltd. The microstructure characteristics and mechanical properties of X80 pipeline steel has been studied systematically. The main results are as follows:In this thesis, we focused on the effects of the trace elements and optimized the combination to reduce the cost of alloy and increased the degree of freedom. The alloy components of the new designed X80 pipeline steel are C: 0.045 ~ 0.065, Mn: 1.60 ~ 1.85, Si: 0.10 ~ 0.25, Nb: 0.06 ~ 0.085, Cr: 0.2 ~ 0.3, V: 0.040 ~ 0.040, Ti: 0.01 ~ 0.03, Al: 0.025 ~ 0.025, Cu: 0.15 ~ 0.15, Ni: 0.15 ~ 0.30, Mo: 0.10 ~ 0.25, and the rest is Fe.The microstructure of the continuous casting X80 pipeline steel is ferrite matrix with pearlite colony distributed on it. The grain of the cast ingot’s surface layer is very fine(about 10μm), while the ingot center portion is larger(approximately 25μm). After hot-rolled, the grain size of X80 pipeline steel has been refined obviously, and t he "banded structure" appeared along the rolling direction.The smelting of X80 pipeline steel is based on iron ladle co-injection desulfurization, roughing and finishing preventing rephosphorization, strong deoxidizing and deep desulfurization process by secondary refining. Continuous casting protections prevent the secondary oxidation.The blank thickness of X80 pipeline steel is 300 mm and the rolled product’s thickness is 22 mm. The specific rolling process is as follow: The rough rolling process of the X80 pipeline steel blank was carried out up to 10 gates with total reduction of 74.33%. The temperature of rolling is began in 1180~1200℃ and ended in 1000℃. The finishing rolling process was 9 gates with total reduction of 71.43%, and ended in 830 ℃. And the cooling speed is 15~20℃/s after rolling process.The mechanical properties of the industrial pilot produced rolled X80 pipeline steel fully meet the design requirements, and the rolling process with strong operational can meet the Shou Qin metal materials company’s actual production.