JPS63161126A - Manufacture of steel sheet having bluing film by box annealing - Google Patents

Abstract

PURPOSE:To form a uniform bluing film at a low cost by loosely coiling a steel strip with spacers so as to leave a gap and by heating the steel strip at a specified temp. in an oxidizing atmosphere having a specified compsn. to carry out box annealing. CONSTITUTION:A steel strip is loosely coiled with spacers so as to leave >=1.0mm gap. The steel strip is then heated at 300-500 deg.C for >=1hr in an oxidizing atmosphere consisting of 5-75vol% H2 and the balance inert gas and having 30-60 deg.C dew point to carry out box annealing. By this box annealing, a steel sheet having a fine uniform bluing film is obtd. at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a steel plate with a bluing coating by box annealing.

[Prior Art] Steel strips, steel plates for hoops, and the like are subjected to a treatment called bluing, which oxidizes the surface of the steel plate blue for aesthetic reasons and corrosion resistance. In recent years, there has been an increase in the number of cases in which this bluing treatment is performed by steel plate manufacturers and shipped. Blueing treatment of steel strip is carried out by continuous annealing and heating in an oxidizing atmosphere in order to form a uniform film. Because the amount of bluing to be processed is small, there is no continuous annealing specifically for bluing in the production process, and the same equipment used for other non-oxidation annealing materials is often used.

[Problems to be solved by the invention] Since bluing treatment is performed in an oxidizing atmosphere, it is necessary to change the continuous annealing furnace to an atmosphere that allows non-oxidizing annealing after the treatment.Currently, it takes a long time to change the atmosphere. There is a problem in that it takes time and normal annealing cannot be performed during that time.

Therefore, box annealing is suitable for small-lot production such as blueing processing. However, when box annealing is performed, the steel strip is usually tightly wound, so the oxidizing atmosphere during annealing is not uniform over the entire length of the steel strip, making it impossible to form a uniform bluing coating over the entire length of the steel strip. The problem is that it cannot be done.

The present invention aims to solve the problems of the prior art described above and to provide a method for uniformly bluing by box annealing.

[Means for Solving the Problems] In order to achieve the above object, the present invention prevents the steel plates of a coil made by winding steel strips from coming into contact with each other, and
A spacer is sandwiched between the steel plates to ensure a gap of one or more layers, and the steel strip sandwiching the spacer is coated with 5 to 75 volume% H.
The mixture was heated to 300 to 500°C for over 1 hour in an oxidizing atmosphere with a dew point of 30 to 60°C, consisting of No. 2 and the rest being an inert gas.

The reason why the conditions of the box annealing method of the present invention are determined as described above will be described below.

The purpose of preventing the steel plates from coming into contact with each other is to ensure that the atmospheric gas for bluing comes into uniform contact with the entire steel plate.To satisfy this condition, the gap between the steel plates should be at least 1.0 seconds. There is no particular reason to limit the spacers sandwiched between the two (as long as a gap of 1.0 mm or more can be secured).

The annealing atmosphere must contain 5% by volume or more of H2 in order to obtain a beautiful and uniform bluing film. Increasing the H2 concentration beyond 75% by volume results in high costs.

Although the dew point is related to the hydrogen concentration, a temperature of 30°C or higher is required to form a bluing film, and if it exceeds 60°C, the bluing film becomes thick and peels off, reducing commercial value.

If the annealing temperature is below 300°C, bluing takes a very long time, and if it exceeds 500°C, the film will peel off.

Annealing time is required to be 1 hour or more; if the annealing time is shorter than this, bluing will be insufficient. However, if it exceeds 10 hours, the film may peel off, so there is no point in keeping it for too long.

[Example] A wire was inserted as a spacer into a 70% cold rolled steel strip with a thickness of 0.7m5t and a width of 1000+■, and box annealing was performed as an open coil under various annealing conditions.
Shown in the table.

No. 2.3, 5.11.12 show examples, and the others show comparative examples.

As can be seen from the table, all the examples of the present invention have good appearance and adhesion.

[Effects of the Invention] The method for producing a bluing film by box annealing of the present invention can produce a bluing film of the same quality as the conventional method at low cost without using a continuous annealing furnace.

Claims (1)

[Claims] In order to prevent the steel plates of the coil made by winding the steel strip from coming into contact with each other and to ensure a gap of 1.0 mm, a spacer is sandwiched between the steel plates, and the steel strip with the spacer sandwiched between 5 and 7
Dew point 3 consisting of 5% by volume H_2 and the balance inert gas
A method for manufacturing a steel plate with a bluing film by box annealing, which comprises heating at 300 to 500°C for 1 hour or more in an oxidizing atmosphere at 0 to 60°C.