Method of continuous annealing of steel strip, and method of manufacturing hot-dip galvanized steel strip

Abstract

Provided is a method of continuous annealing of steel strips capable of realizing at low cost a low-dew-point annealing atmosphere suitable to annealing steel strips containing an easily oxidizable element such as Si. A vertical annealing furnace is configured such that: a heating zone and a soaking zone are provided in which the steel strip is conveyed vertically; an atmosphere gas is supplied from outside of the furnace into the furnace, and gas in the furnace is discharged from a steel strip introduction section at the bottom of the heating zone; part of the gas in the furnace is sucked in and discharged to a refiner having a deoxygenation device and a dehumidifier device disposed outside the furnace, oxygen and water in the gas are removed to lower the dew point, and the gas with the lowered dew point is returned back into the furnace. When annealing a steel strip in this vertical annealing furnace, a gas injection device having multiple gas outlets in the steel strip sheet-passing direction is provided in the heating zone-soaking zone, suppressing mixing of the furnace atmosphere upstream of the gas injection device and the furnace atmosphere downstream thereof, and the temperature of the steel strip when passing the gas injection device is controlled to 600-700°C.

Description

technical field [0001] The invention relates to a continuous annealing method for steel strips and a manufacturing method for hot-dip galvanized steel strips. Background technique [0002] In recent years, demand for high-strength steel (high-strength material) that may contribute to weight reduction of structures has increased in the fields of automobiles, home appliances, and building materials. In this high-strength material technology, when Si is added to steel, it is possible to manufacture a high-strength steel strip with good hole expandability. In addition, when Si and Al are contained, residual γ is easily formed, and it is shown that it can provide ductility. Possibility of good steel belt. [0003] However, for high-strength cold-rolled steel strips, when containing easily oxidizable elements such as Si and Mn, these easily oxidizable elements are enriched on the surface of the steel strip during annealing to form oxides such as Si and Mn, resulting in Poor appe...

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Problems solved by technology

In addition, this method has the following problems: Since the atmosphere in the furnace is oxidative, when the control is wrong, oxides will adhere to the furnace rollers to cause pick-up defects and damage the furnace wall.

These technologies are related to relatively small-scale single-pass vertical annealing furnaces, and do not consider the annealing of steel strips containing easily oxidizable elements such as Si and Mn in multi-pass vertical annealing furnaces such as CGL-CAL.

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