JPS6296669A - Manufacture of galvanizing steel sheet by alloying vapor deposition - Google Patents

Abstract

PURPOSE:To obtain automatically a galvanizing steel sheet by alloying vapor deposition in a continuous and efficient manner by regulating the temp. of a steel strip immediately before plating to a value within a range defined by a prescribed formula. CONSTITUTION:A steel strip 1 is introduced into vapor deposition chambers 5, 5', where both sides of the strip 1 are plated by vapor deposition. At this time, the temp. T( deg.C) of the strip 1 immediately before plating is regulated to a value within a range defined by a formula [-80l/V+0.7W1+0.41(W1+W2)/t +403]<=T<=[420-0.41(W1+W2)/t] [where V is line speed (m/min), (l) is the distance (m) from a position just behind the 1st plating part to the final outlet of the vapor deposition line, (t) is the thickness (mm) of the steel strip, W1 is the amount (g/m<2>) of plating stuck to the front side of the steel strip and W2 is the amount (g/m<2>) of plating stuck to the rear side].

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for manufacturing a steel sheet having a 1-alloyed/A-coated galvanized layer.

<Prior art and its problems> Alloyed galvanized steel sheets are different from ordinary galvanized steel sheets.

b) Good continuous workability in spot welding.

(1) Good paint adhesion in electrodeposition coating, and therefore good corrosion resistance after pre-coating.

It is widely used because of its advantages.

How is alloyed galvanized steel sheet manufactured?

a) A method in which hot-dip galvanized zinc is heat-treated and alloyed before it solidifies.

b) A method of reheating and alloying electrogalvanized steel sheets.

It is broadly divided into Many methods have been proposed for applying zinc-iron alloy plating by electroplating, but since this is a problem with the electroplating method itself, it is not considered in the present invention.

Since method a) is a method using hot-dip galvanizing, it is difficult to obtain uniform thin plating of 30 g/m 2 or less per side, and it is extremely difficult to obtain plating on one side.

In addition, in the method b) above, the electroplated coil is heated to a temperature of 250 to 350
The mainstream is a method of alloying by heating at a low temperature of 0° C. for a long time, but this method uses i) a batch-type annealing furnace, so the process is complicated and takes a long time.

(Portrait) There is wide variation in quality and work management is troublesome.

It had problems such as: One way to solve these problems is to reheat the steel strip immediately after electrogalvanizing, but in this method, the steel strip that has been cooled to 50 to 60°C is continuously reheated and held at 300 to 430°C. The equipment required for this is huge and consumes a lot of energy.

Furthermore, since the method b) uses electrogalvanized steel sheets as the material, the cost will be extremely high if the adhesion exceeds 140 g/m2.

In order to solve these problems, a vacuum evaporation galvanized steel sheet is used as the entire material, and immediately after the vacuum evaporation galvanized steel strip is taken out of the vacuum evaporation equipment system, it is continuously reheated and alloyed. A method was developed to treat the
) However, even with this method, it is necessary to install a reheating furnace, which inevitably increases the size of the equipment.

Means for Solving the Problems The present invention has been made in view of these problems, and alloys the steel sheet by utilizing the rise in temperature of the steel sheet due to the release of the latent heat of condensation of the zinc vapor during vapor deposited galvanizing.

It has been discovered that by limiting the temperature of the steel strip immediately before vacuum evaporation galvanizing to a certain range, it is possible to continuously and efficiently produce alloyed evaporation galvanized steel sheets without installing a post-heating furnace.

<Structure of the Invention> The present invention is a method for automatically and continuously producing alloyed vapor-deposited galvanized steel sheets in a line, in which the steel strip temperature T''0 immediately before vapor-deposited galvanizing is determined by the following formula (7 ) % formula % However, in the formula, T: Steel strip temperature just before plating ("0") v: Line speed (wet/win) fL: Distance from immediately after evaporation plating to the final exit of the vacuum evaporation line (m) t: The method is characterized in that the thickness of the steel strip is within the range expressed by: wI: front surface plating amount (g/m2): back surface plating amount (g/m2) w2) provided.

The present invention will be specifically described below regarding double-sided plating, but it is obvious that it can also be applied to single-sided plating. <Specific Disclosure of the Invention> Next, the present invention will be described in detail with reference to the drawings.

Several types of continuous vacuum evaporation plating equipment have been proposed, but the one illustrated in FIG. 1 is a gas reduction pretreatment furnace 2. Reducing gas or air enters the vacuum deposition plating chamber 5.5°
A first pressurization chamber 3.3 consisting of a number of sealing rolls housed in a number of compartments equipped with individual evacuation means for stepwise depressurization or re-pressurization. and a second seal roll chamber 4.4', a first vacuum deposition plating chamber 5.4 for vacuum deposition plating on one side of the steel strip. A first step for vacuum deposition plating on the other side of the steel strip.
It consists of a second vacuum evaporation plating chamber 5' which communicates with the vacuum evaporation plating chamber. A zinc bath of 6.6° and a deflector roll of 7.7° are arranged inside the vacuum deposition plating chamber.

The seal roll chamber is for introducing and removing the steel strip while maintaining the vacuum in the vacuum deposition chamber.
As described in detail in No. 92574, the unit cells each containing a pair of rolls are evacuated, and the pressure of the entire unit is reduced in stages to maintain the vacuum deposition chamber at a predetermined vacuum.

The length of each part is determined appropriately depending on the set operating conditions, and the device itself can be designed and manufactured as necessary by a person skilled in the art who is familiar with the prior art according to the description of this specification.
Details are omitted.

The cold-rolled steel strip 1 is continuously introduced into the pretreatment furnace 2, where it is annealed and simultaneously pretreated by gas reduction. There are differences depending on the steel type, but in order for a steel strip to be annealed,
Holding for 20 to 180 seconds is required at a temperature range of 600 to 900°C. In order to obtain a vapor-deposited galvanized steel sheet with good adhesion, the inside of the furnace is heated to 3% H in the pretreatment by gas reduction.
Above (remaining N2), the steel strip is cooled in the latter half of the pretreatment furnace 2, where the atmosphere has a dew point of -15°C or less,
It is discharged from the pretreatment furnace at any temperature above 0°C. As disclosed in JP-A-57-15241!5, it is known that the temperature of the steel strip before the start of vapor deposition is preferably 200°C or higher in order to obtain good toughness and ductility of the vapor-deposited film. ing. The steel strip is further placed in a pressure chamber 3. It is introduced into the first vacuum deposition chamber 5 via the first seal roll chamber 4 . The zinc bath 6 is continuously supplied with zinc vapor heated by a suitable means (electrical resistance heating means, electron beam heating means, etc.) from a source not shown, so that the first surface of the steel strip is deposited. After being plated, the strip is turned over by a deflector roll 7.7 DEG and its second side is deposited and plated in the same manner as before in the second vacuum deposition chamber 5'. Then the steel strip
It exits the vacuum deposition system through the seal roll chamber 4' and the second pressure application chamber 6°.

When a steel strip is vacuum-deposited, its temperature rises due to the release of the latent heat of solidification of zinc vapor, and the temperature rise is determined by the following equation.

Δ”l”==q・W/ρ・t @c (
1) However, ΔT: Temperature rise of the steel strip (°C) q: Heat of condensation of the plated metal (kcal/g) wI: Front surface coating amount (g/m2) w2) 2: Back t)
Comes with S! t (g/m2) ρ: Density of steel strip (g/m2) t: Thickness of steel strip (-■) C: Specific heat of steel strip (kcal/kg・"0) Zinc is vapor-deposited on the steel strip. In the case, q: 0.415 k
cal/gp: ? , 85 g/am3 c: O, 13 kcal/kg -''C, and equation (1) can be rewritten as equation (2) below.

ΔT=0.41(w,+112)/l
(2) Since the steel strip is in a vacuum while passing through the second seal roll chamber 4', heat radiation is small and the strip temperature is substantially maintained. Immediately after vapor deposition plating, the second seal chamber 4
If the length up to the final roll 41' of ° is the cross (intestine), the plate temperature retention time S is line speed V (■/l1in)
as a function of.

5(see) = 60@J1/v (
3).

On the other hand, the heating conditions for alloying a zinc vapor-deposited steel sheet vary depending on the amount of zinc plating deposited.

As a result of repeated experiments using the apparatus for producing continuous vacuum-deposited galvanized steel sheets shown in FIG. 1, the possible alloying range as shown in FIG. 2 was found.

In Fig. 2, straight line a is a straight line that changes depending on the amount of coating, and is a straight line that changes depending on the coating amount, and the plate temperature T' (℃) after vapor deposition plating and the plate temperature holding time S.
(see) and adhesion as a function of T' = -4/
3 S ÷ 403 Medium 0.7 Wt
It is expressed as (4). Note that the straight line a in Figure 2
In this case, the adhesion Wk log/m2 is shown as an example.

The straight line is the upper limit of the plate temperature T' after vapor deposition, and T'=
420 (5). The reason why the temperature is limited to 420°C is that at higher temperatures, zinc on the surface of the steel strip may melt and adhere to the rolls in the vacuum roll chamber. This value remains unchanged with respect to the amount of adhesion.

Although the straight line C indicates the lower limit of the plate temperature retention time, this is the lower limit that can be accommodated for practical reasons, and there is no further limitation.

straight! id indicates the upper limit of the plate temperature retention time, and depending on the equipment,
Considering operational economics, etc., the time is preferably 25 seconds or less,
Although this is shown as an example, it is not limited to this.

The plate temperature T' after vapor deposition is calculated from the substrate temperature (steel strip temperature before vapor deposition) T and equation (2), T' = T + 0.41 (w1 + 2) /
It is expressed as l (8).

When the range shown in Fig. 2 is expressed using equations (3), (4), (5), and (6), -80 l/v + 0.7 wl -0,41 (ill +
w2 )/1+403≦T≦420−0.41Cwt
+112)/l (7) Therefore, by controlling the pre-plating steel strip temperature within the range expressed by equation (7), it is possible to automatically and continuously manufacture alloyed vapor-deposited galvanized steel sheets within the line.

<Embodiment> The invention will now be illustrated by examples.

Completed I1 using the continuous vacuum evaporation plating equipment shown in Figure 1.
By method 1, vacuum evaporation galvanization was performed by controlling the substrate temperature before evaporation within the range of formula (7), and a single-sided alloyed differential thickness evaporation galvanized steel sheet was automatically and continuously produced.

Example 1 Calculation examples and examples based on formula (7) using a low carbon cold rolled steel plate with a plate thickness of 0.6 cm are shown in Tables 1-1 and 1-2.

Table 1-2 ○・・・Alloying X: Not fully alloyed ×・・・Plating layer melting The manufacturing conditions were as follows.

Steel strip dimensions: 0.8mm thickness, 300mm width Threading speed:
12 to 80 m/win Holding length = 5I Vapor deposition chamber pressure 0.01 torr The alloyed vapor deposited galvanized steel sheet thus produced had a uniform and beautiful skin and had good workability.

Example 2 Tables 2-1 and 2-2 show calculation examples and examples of formula (7) using a low carbon cold rolled steel plate with a thickness of 1 mm.

The manufacturing conditions were as follows.

Steel strip dimensions: 1.0 mm thickness, 300 ■ layer width Threading speed: 1
2~EtOm/m2) Win holding length: 5-layer holding chamber pressure 0.01 torr The alloyed vapor deposited galvanized steel sheet manufactured in this way has a uniform and beautiful skin and has good workability. Ta.

Table 2-2 O: Alloying X: Not fully alloyed ×: Plating layer melting

[Brief explanation of drawings]

The attached FIG. 1 is a schematic cross-sectional view showing the concept of an example of an apparatus for carrying out the method of the present invention. FIG. 2 is a graph showing the relationship between the steel strip temperature after vapor deposition and the steel strip temperature holding time, which shows the conditions under which the method of the present invention can be carried out.

Claims (1)

[Claims] 1. A method for automatically and continuously manufacturing an alloyed vapor-deposited galvanized steel sheet within a line, wherein the steel strip temperature T°C immediately before vapor-deposited galvanizing is expressed by the following formula (7). A method characterized in that the range being represented. -80l/v+0.7w_1+0.41(w_1+w_
2)/t+403≦T≦420−0.41(w_1+w
_2)/t(7) In the formula, T: Steel strip temperature just before plating (℃) v: Line speed (m/min) l: Distance from immediately after vapor deposition plating to the final exit of the vacuum evaporation line (m) t: Thickness of steel strip (mm) w_1: Front side plating amount (g/m^2) w_2: Back side plating amount (g/m^2)