JPS5913058A - Manufacture of galvanized steel plate - Google Patents

Abstract

PURPOSE:To obtain a galvanized steel plate having no blister in the zinc layers, by shot-blasting the surfaces of a steel pate and by galvanizing the plate. CONSTITUTION:The surfaces of a steel plate is shot-blasted with shot having grain size No. >=200 to apply some strains to the surfaces. The plate is then reduced under heating in an atmosphere contg. gaseous hydrogen, and it is dipped in a molten zinc bath to obtain a galvanized steel plate. By this method the formation of blister in the resulting zinc layers can be prevented, and descaling as pretreatment is carried out at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a hot-rolled galvanized steel sheet that prevents blisters from occurring in the plating layer after galvanizing.

Conventionally, hot-rolled steel sheets have been used as base sheets for thick hot-dip galvanized steel sheets. This hot-rolled steel sheet is pickled as necessary to remove acid scale, and then subjected to the Cirrus method.
Atmospheric gas containing hydrogen gas such as the Sendzimer method (in most cases, HII: 10 to 75 cm, N9 = 90 to 2
This is generally carried out by heating and reducing the zinc at step 5) and then immersing it in a molten zinc bath.

However, when a hot-rolled steel plate is used as the base plate, after plating,
There is a problem in that many blisters with a diameter of about 0.5 mm occur on the surface of the plated steel sheet after several days have passed. This is because when a steel sheet is heated in a hydrogen-containing reduction furnace, it absorbs a large amount of hydrogen, and when the steel sheet is plated and cooled, the hydrogen solubility of the steel sheet decreases, and supersaturated hydrogen is released from the steel sheet, causing the plating layer to deteriorate. This occurs when high-pressure gas gathers at the interface with the plated layer and pushes up the plated layer. This problem is based on Cirrus method, Sendzimer method, US
In general plating methods such as the steel method, in which the surface of a steel plate is heated and reduced in an atmospheric gas containing hydrogen, this problem occurs to varying degrees, and various solutions have been proposed to date.

For example, one method that has been proposed in the past as a solution to this problem is to improve the composition of the zinc bath. In the method described above, s and sθ are added as blister prevention agents in the zinc bath.

P s As r T e p S b r B i
A method of adding one or more of Fi2s or more (Japanese Unexamined Patent Publication No. 49-14325), a steel plate is reduced at a temperature in the range of 750 to Ac-5 points, and A7 is added in an amount of 0.22 to 0.35% by weight. A method of cleaning with a zinc bath containing
928), but in the former method, in order to uniformly disperse the blister prevention agent, it must be added in the form of a zinc alloy when adding the blister prevention agent. The disadvantage is that it costs a lot of money to manufacture. In addition, even with the latter method, the At concentration in the zinc bath increases, which impairs workability and quality, and increases manufacturing costs.The inventors of Banmoto et al. However, with this method, there arises a problem that the actual mounting is not carried out sufficiently and quality such as instant adhesion is deteriorated.

The present invention involves changing the zinc bath composition and reduction heating temperature as described above,
Another object of the present invention is to provide a method for producing a hot-dip galvanized steel sheet that can prevent blistering by a simple pretreatment without using methods such as reducing hydrogen concentration.

In order to prevent the occurrence of blisters, basically, as mentioned above, the amount of hydrogen absorbed can be reduced by lowering the hydrogen concentration in the atmosphere in the reduction furnace, or even if hydrogen is absorbed, It is thought that it would be better to increase the hydrogen storage capacity of the steel plate so that it is stored and not released even after plating. Therefore, the present inventors have conducted various studies on ways to increase the hydrogen storage capacity of steel sheets as a method of preventing the occurrence of blisters without causing quality deterioration such as poor plating adhesion. As a result, they discovered that blisters do not occur if galvanizing is applied in the usual manner after shot blasting is applied to the steel sheet surface before plating, and then galvanizing is applied in the usual manner. The reason why such shot blasting can prevent the occurrence of blisters is not necessarily clear, but it is thought that shot processing forms lattice defects near the surface of the steel sheet, and hydrogen is trapped there.

Next, we will discuss the particle size of shot blasting and its processing time.

The particle size of shot blasting is preferably in the range of #8.0 to #400, preferably T80 to #200.

If the grain size is less than #80, the surface of the steel sheet becomes rough, resulting in poor appearance after plating and loss of value as a product. Moreover, if the particle size exceeds 200, the effect will not be exhibited unless the treatment time is lengthened, which will be described later.

Also, a processing time of 10 seconds or more is sufficient, but particle size #
If the particle size is 80 to #200, some blistering may occur, so taking workability into consideration, the optimum range of particle size and processing time is 15 seconds for a particle size of 80 to #200.
- Hereinafter, the present invention will be described in detail with reference to Examples.

A hot-rolled steel plate with a thickness of 2-3mm x 1002-3mm x 100 was subjected to shot blasting using a shot blasting machine manufactured by Fuji Seisakusho using abrasive grains of different particle sizes manufactured by Ujiden Chemical Industry ■, and then subjected to hydrogen reduction annealing. A test material was prepared by hot-dip galvanizing for 2 seconds at a plating bath temperature of 460±2°C. Further, a plated steel plate not according to the present invention, that is, a plated plated conventionally without shot blasting, was used as a comparative example, and the occurrence of blisters after plating was visually observed on both plates. The test conditions and results are summarized in the table below.

The evaluation criteria are as follows: ◎ No blisters at all O Slightly observed in some areas, Δ Partially clearly observed Example 11 in
13-7 and 11-14 i.e. shot blast particle size #
80, the processing time is 15 seconds or more, and the shot blasting particle size is #200 and the processing time is 168 or more.
Even after the lapse of time, no blistering occurred. Furthermore, it was found that even if the particle size was the same, if the processing time was short, some blistering occurred as time progressed, as is clear from Example 1.2.8. - In the case of the strength wood obtained by the conventional method not based on the invention, that is, Comparative Examples 22 to 24, blistering occurred partially after 12 hours had passed after plating.

As described above, according to the present invention, blisters are generated on hot rolled galvanized steel sheets. 'Can be defended.

Furthermore, descaling as a pre-plating treatment is carried out at the same time, which is extremely effective in terms of productivity and has very high industrial value.

Patent applicant: Nisshin Steel Co., Ltd. Agent: Patent attorney Tadafu Noma Patent attorney Tadayuki Noma

Claims (1)

[Claims] 1. In a method for producing hot-dip galvanized steel sheets in which a hot-rolled steel sheet is heated and reduced in an atmosphere containing hydrogen gas and then immersed in a molten zinc bath for plating, the steel sheet surface is preliminarily coated with grain size 200.
A method for producing a hot-dip galvanized steel sheet, characterized by subjecting it to a shot blasting process of no.