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FH550 shipbuilding steel rolling process procedure

FH550 shipbuilding steel is a kind of ultra-high-strength ship plate steel, which is a low-carbon bainitic steel with acicular ferrite at room temperature. This paper mainly conducts rolling tests on FH550 shipbuilding steel, which lays a foundation for determining a reasonable controlled rolling and controlled cooling system, and focuses on the influence of TMCP process and tempering system on the microstructure and mechanical properties of the steel.

Using TMCP production process, the slab thickness is 80mm, the finished product thickness is 16mm, and the intermediate blank thickness is 45mm. According to the rolling mill capacity, heating capacity and cooling capacity, the heating temperature is set to 1200℃. The rolling of FH550 shipbuilding steel is carried out in two stages. The first three passes are high-temperature stage rolling, which is kept above 1120℃. The purpose is to fully refine the austenite structure through repeated recrystallization between rolling passes.

The last five passes are low-temperature stage rolling, and the rolling temperature is below 880℃. The purpose is to increase the nucleation position of the phase transformation through the deformation in the unrecrystallized area. Control different finishing rolling temperatures and cool down to 502℃ after rolling.

The hot-rolled FH550 shipbuilding steel was subjected to mechanical property test, microstructure observation and fracture analysis, and then 6 samples were taken from different positions of the FH550 shipbuilding steel and heated to 400, 450, 500, 550, 600 and 650℃ respectively. Fire treatment, hardness test, microstructure observation and mechanical property test were performed on the treated samples respectively.