Hot-rolled stainless steel annealing process under protection of full hydrogen gas

Abstract

The present invention relates to a hot-rolled stainlesss steel annealing process under the condition of full hydrogen protection, in particular, it is applicable for annealing ferritic and martensitic hot-rolled stainless steel roll, and includes the following steps: a). in the course of heating adopting hydrogen gas whose hydrogen gas content is above 99.99% oxygen content is below 10 to the minus fifth and dew-point is -60 deg.C--30 deg.C as protection gas to make sweeping, and controlling the dew-point of atmosphere in the furnace at -30 deg.C--50 deg.C; b). adopting heating and heat-insulating temp. of 830-870 deg.C, after the centre of bottom of steel roll is reached to heat-insulating temp. for 1-3 hr., stopping heating; and c). using heating cover to slowly cool for 3-5 hr., using cooling cover to quickly cool to control temp. of bottom of steel roll to 200-300 deg.C, tapping and naturally cooling.

Description

technical field [0001] The invention relates to a processing method of hot-rolled stainless steel, which is particularly suitable for ferrite and martensitic hot-rolled stainless steel coils, and is a hot-rolled stainless steel annealing process under full hydrogen protection for annealing. Background technique [0002] For stainless steel manufacturers, the annealing of ferritic and martensitic hot-rolled stainless steel coils is done in a bell furnace under a protective gas atmosphere. Some manufacturers use 5-7% hydrogen and 95-93% nitrogen as the protective gas. Due to the low thermal conductivity of nitrogen, the annealing heating and cooling time is long, although a higher furnace temperature of about 600 ° C is used to reduce Cooling time, but the total production cycle of the hearth is still very long, and the production capacity of the hearth is low (for the existing process 1). [0003] Although some manufacturers also use 100% hydrogen as a protective gas, due to...

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Problems solved by technology

Some manufacturers use 5-7% hydrogen and 95-93% nitrogen as the protective gas. Due to the low thermal conductivity of nitrogen, the annealing heating and cooling time is long, although a higher furnace temperature of about 600 ° C is used to reduce Cooling time, but the total production cycle of the hearth is still very long, and the production capacity of the hearth is low (for the existing process 1)

[0003] Although some manufacturers also use 100% hydrogen as a protective gas, due to the high thermal conductivity of hydrogen, its thermal conductivity is about 7 times that of nitrogen, although the annealing heating and cooling time is more than 90% higher than that of bell annealing with nitrogen as a protective gas. The furnace is reduced by about 45%, but the cooling time is prolonged due to the lower furnace temperature of about 100°C. As a result, the total production cycle of the furnace base is still very long, and the production capacity of the furnace base is low (for the existing process 2)

[0004] In addition, when the existing process is annealed, the water content (or dew point) in the atmosphere during the annealing process is not controlled

Therefore, the oxide layer on the surface of the steel coil after annealing with the existing process is relatively thick and uneven. When pickling in the next process, there will be a large pickling effect on the surface of the strip, including the length and width directions. The oxide layer remains in the center of the steel coil, and there is pickling at the edge

In order to remove this surface defect, it is necessary to increase the treatment process, such as surface grinding treatment or pickling treatment again, which increases the processing time and production cost