JPH03243754A - Production of alloyed galvanized steel sheet - Google Patents

Abstract

PURPOSE:To prevent the concentration phenomenon of P and to improve alloying velocity by specifying the coiling temp. of a hot rolled plate of P-added steel at the time of producing an alloyed galvanized steel sheet. CONSTITUTION:Coiling is applied to a hot rolled plate of P-added steel while regulating coiling temp. to <=700 deg.C (the lower limit is about 400 deg.C), and this steel plate is subjected, if necessary, to oxidation preventing treatment and, subsequently, is formed into a starting sheet for plating by the ordinary process. Then, this starting sheet for plating is galvanized and subjected to heating and alloying. By regulating coiling temp. to <=700 deg.C as mentioned above, the partial peeling of scale and also the concentration phenomenon of P can be prevented and alloying velocity can be improved, and further, the alloyed galvanized steel sheet excellnt in adhesive strength of plating, powdering characteristic, workability, and corrosion resistance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing an alloyed galvanized steel sheet.

(Prior art) The alloying rate of a galvanized steel sheet added with P is, for example,
It is assumed that a hot-dip galvanized steel sheet with excellent adhesion of the coating layer can be obtained by coating the surface of a galvanized steel sheet with phosphorus and then applying hot-dip galvanizing as described in JP-A No. 62-119880. is delayed,
It is disclosed that the r-phase, which impairs adhesion, can be reduced, in other words, it impairs alloying.

As described above, since the addition of P slows down alloying, there is a strong demand for improvement in alloying of galvannealed steel sheets.

(Problems to be Solved by the Invention) The present invention has been made to advantageously satisfy these requirements. The present invention provides a method for producing an excellent alloyed galvanized steel sheet.

(Means for Solving the Problems) In the production of alloyed galvanized steel sheets, the present invention involves coiling a P-added hot-rolled steel sheet at 700°C or lower, using it as a plating original sheet in a normal process, then plating, and heating the alloyed steel sheet. This is a method for producing an alloyed galvanized steel sheet characterized by the following: P-added hot-rolled steel sheet is rolled up at over 700°C, subjected to oxidation prevention measures, and then used as a plated original sheet in a normal process, and then plated. , a method for manufacturing an alloyed galvanized steel sheet, which is characterized by heating and alloying.

The galvanized steel sheet that is the object of the present invention is an alloyed galvanized steel sheet that is hot-rolled, pickled, cold-rolled, galvanized, and alloyed to which P is intentionally added, and other components are not particularly specified. do not. For example, hot-dip galvanized steel sheet (zinc or zinc-based Nl).

This is a steel sheet that has been heat-alloyed (including those plated with alloys such as Pb and Cr), a steel sheet that has been heat-alloyed from an electrogalvanized iron-zinc alloy steel sheet, and a steel sheet that has been heat-alloyed from a vapor-deposited galvanized steel sheet. This is a method for manufacturing steel plates, etc.

The present inventors believe that regardless of the type of galvanized steel sheet,
Increasing the alloying speed of P-added steel sheets prevents the scale of the hot-rolled steel sheets from partially peeling off before pickling, thereby suppressing the concentration of P in the grain boundaries on the surface of the steel sheets. , was found to significantly improve the alloying rate.

In the conventional plated steel sheet mentioned above, the alloying speed of the P-containing steel sheet is such that the passing speed of the steel sheet is, for example, 35 m/ll1.
Unless the temperature is extremely slow to n, alloying will not be completed, resulting in a so-called half-cooked state, and the alloyed galvanized steel sheet may not be obtained.

The present inventors conducted various experiments in order to improve the alloying speed of alloyed hot-dip galvanized steel sheets, and as a result, for example,
A high-strength steel sheet can be obtained by adding a small amount of P. O
By preventing partial peeling of scale on hot-rolled steel sheets before pickling, 1 to 0.2% was intentionally added. The action suppresses the reaction with the pickling solution, such as HC, Q, electrochemically becomes a cathode, the remaining scale becomes an anode, a local battery is formed, and the remaining scale is locally dissolved to the base iron. Although the reason is not clear, the grain boundaries of the dissolved portion remain as convex parts, and P is concentrated in the grain boundaries, resulting in a P-concentrated surface. It has become clear that cold rolling, galvanizing, and alloying cause poor alloying due to suppression of alloying of P.

Therefore, in order to prevent partial peeling of the scale of the hot-rolled steel sheet before pickling, the coiling temperature of the hot-rolled steel sheet should be set to 700°C or less to prevent partial peeling of the scale and prevent the above-mentioned problem. The P concentration phenomenon does not occur, and the alloying speed becomes faster.

Furthermore, when a large amount of scale is generated at high temperatures, P is concentrated on the surface of the hot-rolled steel sheet because P does not dissolve in the scale and concentrates on the grain boundaries of the base iron at the interface. In order to slow down the alloying rate in conjunction with partial peeling before pickling, the coiling temperature of the hot rolled steel sheet was set to 700°C or less, with the lower limit being about 400°C.

In addition, when hot-rolled steel sheets are coiled at a high temperature exceeding 700°C, partial peeling of scale may occur, and it is necessary to suppress this, and oxidation of scale after coiling is necessary. It is important to prevent the formation of Fe2O3, which is likely to progress and peel off. For this purpose, there are methods to prevent air from entering, such as covering the ends of the coil with glass wool from a hot-rolled steel strip.

In addition, after winding, it is water-cooled (water-cooled to below 500°C),
There are methods to shorten the oxidation time at high temperatures. In any case, by suppressing partial peeling of the scale of the hot rolled steel sheet, the alloying rate of the alloyed galvanized steel sheet can be improved.

It is believed that the presence of a large amount of P in steel, especially at grain boundaries, hinders the movement of Fe during alloying and slows down the alloying rate. It will be done. In addition, solid solution elements such as C and N are thought to have an adverse effect.

In this way, reducing solid solution elements such as P is effective in improving the alloying rate.

Therefore, the key to improving the alloying rate is to suppress the concentration of P on the surface grain boundaries, regardless of the surface concentration process.

By the way, as shown in Figure 1, the coiling temperature of a hot rolled steel sheet and the alloying speed of an alloyed galvanized steel sheet increase. The sheet threading speed tends to become slower. In this way, the alloying speed of alloyed galvanized steel sheets can be controlled by lowering the coiling temperature, etc., to suppress partial peeling of the scale of hot rolled steel sheets.
It is clear that improvement can be easily achieved by doing 1.

The specifications of FIG. 1 are as follows.

Added amount of P: 0.04% Plated double-sided AS basis weight + 60/80 (g/rrr) Alloyed plate temperature = 480°C x 5 sec Therefore, for example, the alloying speed of the above-mentioned alloyed galvanized steel sheet In other words, as a method to improve the threading speed of an alloyed galvanized steel sheet production line, the hot rolling coiling temperature should be increased to 70°C.
It is possible to improve the threading speed of galvannealed steel sheet production lines by suppressing partial peeling of the scale of hot-rolled steel sheets, such as by lowering the temperature to below 0°C or water-cooling it when coiling at temperatures above 0°C. can.

As a specific method, for example, a steel plate containing 0.04% P is hot-rolled at 0°C, pickled, cold-rolled,
Zinc plating, alloying, and alloying plate temperature of 480℃
The sheet can be passed at a sheet passing speed of 90 m/ll1n, and it is possible to reliably improve the alloying speed.

Alternatively, it can be applied when alloying a hot-dip galvanized steel sheet outside the line, when alloying an iron-zinc alloy electrogalvanized steel sheet, and when alloying a vapor-deposited galvanized steel sheet.

(Example) Examples of the present invention are listed in Table 1 along with comparative examples.

Note: Steel type #Nb-TI-5tlLC: Ultra-low carbon steel with Nb
- with addition of Tl.

・TI-8tlLC: Ultra low carbon steel with Tl added.

・A, 17- + aluminum killed low carbon steel.

Note 2 Method for preventing Niscale peeling ・- mark: No treatment.

・A: A hot-rolled steel plate whose end portion is covered with glass wool after being rolled up.

・B: A hot-rolled steel sheet that is water-cooled after being rolled up.

Note 3: Type of plated steel sheet ・Double-sided AS: Alloyed hot-dip galvanized steel sheet on both sides.

(80g/rrr/60g/m) ・Single-sided AS: Single-sided alloyed hot-dip galvanized steel sheet.

(45g/box 10) - Electric AS: Alloyed electrogalvanized steel sheet. (30g/rrr/30g/rr?) Vapor-deposited AS: Alloyed vapor-deposited galvanized steel sheet. (30sr/
m/30g/nf)Note 4 Bi-alloying treatment temperature/plate temperature when performing alloying treatment.

Note 5 = Alloying treatment time/Time maintained at alloying treatment temperature when performing alloying treatment.

Note 6 = Threading speed of galvanized steel sheet line/Limit speed at which alloying is possible at the threading speed of galvanized steel sheet line that performs alloying treatment.

(Effects of the Invention) According to the present invention, in manufacturing an alloyed galvanized steel sheet,
P addition can improve the alloying speed, that is, the threading speed during the production of alloyed galvanized steel sheets, and improve the properties, plating adhesion, powdering properties, and processing required for alloyed galvanized steel sheets. Effects such as durability and corrosion resistance can be obtained.

[Brief explanation of drawings]

FIG. 1 is a chart showing the relationship between the coiling temperature of a hot rolled steel sheet and the alloying speed of an alloyed galvanized steel sheet (the alloying limit threading speed during production of an alloyed galvanized steel sheet).

Claims (2)

[Claims] 1. In the production of alloyed galvanized steel sheets, the P-added hot-rolled steel sheet is coiled at a winding temperature of 700° C. or lower, and thereafter used as a plated original sheet in a normal process, and then plated and heat-alloyed. A method for producing plated steel sheets. 2. In the production of alloyed galvanized steel sheets, P-added hot-rolled steel sheets are wound up at over 700°C, subjected to oxidation prevention measures, and then used as a plated original sheet in the normal process, and then plated and heat-alloyed. Method for manufacturing alloyed galvanized steel sheet.