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國際上X80級別螺旋焊管的鋼板厚度均未達到18.4mm。對如此極限規格和高性能要求,管線鋼的合金設計、軋制及冷卻工藝參數及其對組織、性能的影響等均需全面研究。
The thickness of the steel plate of the X80 grade spiral welded pipe is not up to 18.4mm. It is necessary to study the alloy design, rolling and cooling process parameters and their effects on the microstructure and properties of pipeline steel.
一般來說,熱連軋過程的物理冶金過程及現象與平板軋制有所不同,X80熱軋卷板管線鋼的成分設計思路和工藝也有其特點。首先,為了保證低溫沖擊韌性即DWTT性能,C含量應在0.07%(質量分數)以下,然而在該成分范圍,C含量的變化對屈服強度的影響需要認識;研究表明,低C2Mn2Nb+管線鋼添加Mo,可降低中溫轉變溫度,在較低冷卻速度下得到針狀鐵素體和貝氏體組織,但有必要通過工業軋制試驗確定Mo的最佳含量并進一步明確Mo的作用;當然,熱連軋工藝對組織和性能的影響也應通過工業試驗予以揭示,最終得到影響高性能管線鋼組織和性能的工藝因素。
Generally speaking, the physical metallurgical process and phenomena of the hot rolling process are different from those of the plate rolling. The design ideas and processes of the X80 hot rolled coil pipe steel also have their own characteristics. First of all, in order to ensure the low temperature impact toughness of DWTT performance, the content of C in 0.07% (mass fraction), however in the composition range, the change of C content requires understanding of the impact of yield strength; research shows that low C2Mn2Nb+ pipeline steel with Mo, can reduce the temperature change in temperature, low cooling speed are acicular ferrite and bainite, but it is necessary to determine the optimum content of Mo through the industrial rolling test and further clarify the role of Mo; of course, influence of hot rolling process on Microstructure and mechanical properties should also be revealed through the industrial test, finally obtain process factors affecting the microstructure and properties of high performance pipeline.
增加C含量會影響MA島的數量和形態,通過冷卻控制可得到細小而彌散的MA島。而在低碳范圍,C含量的增加并不是影響屈服強度的主要原因。添加質量分數為0.19%～0.25%的Mo,通過調整精軋工藝,能夠達到X80的強度要求;此外,添加Mo對抑制精軋時的動態再結晶有利。熱卷板的精軋開軋溫度應該控制在960℃以下,同時要控制壓下量,防止過大的應變積累,可避免靜態和動態再結晶的發生,實現平均流變應力的平穩積累,確保達到X80的強度、韌性和DWTT等性能的要求。
Increasing the content of C can affect the quantity and morphology of MA Island, and the small and dispersed MA island can be obtained by cooling control. In the low carbon range, the increase of C content is not the main cause of yield strength. Adding the mass fraction of 0.19% to, the strength of X80 can be achieved by adjusting the finishing process. In addition, the addition of Mo is beneficial to the dynamic recrystallization during the finishing process of Mo. Hot rolled plate finishing rolling temperature should be controlled at 960 DEG C, at the same time to control the amount of pressure, to prevent excessive strain accumulation, can prevent the occurrence of static and dynamic recrystallization, realize the steady accumulation of mean flow stress, ensure X80 strength, toughness and DWTT performance requirements.