Effect of heating temperature on the mechanical properties and microstructures of X80M pipeline steels
The effects of heating temperatures on the prior austenite grain size,microstructure and mechanical properties of X80M pipeline steels with a large wall thickness were investigated in this pa-per.The results showed that the heating temperature has a great effect on the drop weight tear test(DWTT)properties of X80M pipeline steels.The austenite grains continued to coarsen with enhancing the heating temperatures.The average austenite grain size was within 35 μm by controlling the heating temperature below 1 210 ℃.The finer prior austenite grains provide more nucleation sites of acicular ferrite(AF)and granular bainite(GB),and improve the low temperature toughness of steel plates dur-ing the subsequent rolling and cooling processes.Moreover,the higher solution degree of alloy ele-ments in the casting blank promotes the formation of finer NbC precipitates with the sizes less than 20 nm by increasing heating temperature.It also leads to the grain coarsening and the decrease of AF and GB proportions in the microstructure.Therefore,the DWTT properties of X80M pipeline steels with the large wall thickness can obviously be improved by controlling the heating temperatures below 1 210 C and ensuring the acicular ferrite(AF)and granular bainite(GB)phase contents more than 60％.
X80M pipeline steelheating temperaturedrop weight tear test propertiesacicular ferritegranular bainite
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