JP2001226789A - Producing method for high tensile strength hot dip galvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a producing method for a high tensile strength hot dip galvanized steel sheet by which the problem of nonplating in hot dip galvanizing for an Si added high tensile strength steel sheet can be solved without adding equipment and process. SOLUTION: As to the producing method for a high tensile strength hot dip galvanized steel sheet, in the production of a zinc plated steel sheet containing, by mass, >=0.3% Si and moreover containing one or two kinds of <=3% Ni and <=3% Cu so as to satisfy (1.5×Ni+Cu)>=1.5%, pickling is performed for 1 to 15 min in a pickling bath in which the concentration of hydrochloric acid is 8 to 37 mass %, and the bath temperatue is 80 to 95 deg.C and, after that, hot dip galvanizing is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a high-strength hot-dip galvanized steel sheet using a high-strength steel sheet containing Si as a base material.

[0002]

2. Description of the Related Art Hot-dip galvanized steel sheets, including alloyed hot-dip galvanized steel sheets, are widely used mainly in automobiles and building materials because of their excellent corrosion resistance and coating adhesion after coating. However, raw materials of these hot-dip galvanized steel sheets are limited to soft working steel sheets having a low Si content, and hardly used particularly for high-strength steels to which Si is added. This is because when a steel sheet containing 0.3% by mass or more of Si is hot-dip galvanized, in the annealing step before plating, Si is concentrated on the steel sheet surface and the steel sheet surface is oxidized, so that the steel sheet becomes molten zinc. This is because they are not sufficiently wet, and non-plating occurs during plating.

In recent years, in order to reduce the weight of automobiles, there has been an increasing tendency to use high-strength steel sheets as a raw material, and a technique for enabling hot-dip galvanizing even for high-tensile steel sheets containing 0.3% by mass or more of Si. Is strongly desired. Conventional methods for improving non-plating in hot-dip galvanizing of a Si-added high-strength steel sheet include, for example, Japanese Patent Application Laid-Open No. 4-346.
There is a method disclosed in Japanese Patent No. 644. This method is a technique for improving the wettability of a steel sheet to hot-dip zinc by pre-plating Ni in a process before hot-dip galvanizing.

[0004] This method can improve the hot-dip galvanizing property of steel containing 0.3% by mass or more of Si, but has the disadvantage that new equipment must be installed for Ni pre-plating. There is. In addition to Ni pre-plating, methods for improving the plating wettability of high-strength steel have been proposed, but all of them involve new equipment and an increase in special pretreatment steps. It has become a major factor hindering the spread of tension hot-dip coated steel sheets.

[0005]

SUMMARY OF THE INVENTION The present invention does not require any new equipment or special pretreatment as in the prior art, and does not require any additional equipment or processes. It is an object of the present invention to provide a method for producing a high-strength hot-dip galvanized steel sheet that can solve the problem of non-plating in steel.

[0006]

Means for Solving the Problems The present inventors have conducted detailed research to solve such problems, and as a result, have found that Si.
In steel containing 0.3% by mass or more, one or both of Ni and Cu are simultaneously added, and the temperature, concentration, and time of the hydrochloric acid pickling are optimized, so that 1% of Ni and Cu can be added to the steel sheet surface. The present invention has found an excellent production method in which seeds or two kinds are substituted and precipitated, and non-plating does not occur in the subsequent hot-dip galvanizing. That is, the gist of the present invention is as follows: (1) By mass%, Si: 0.3% or more is contained, and 1.5 × Ni + Cu: 1.5% or more.
In the production of a galvanized steel sheet based on a high-tensile steel sheet containing one or two of i: 3% or less and Cu: 3% or less, hydrochloric acid concentration: 8 to 37% by mass, bath temperature: 80 to 95
A method for producing a high-strength hot-dip galvanized steel sheet, comprising performing pickling in a pickling bath at a temperature of 1 ° C. for 1 to 15 minutes, followed by hot-dip galvanizing. (2) The method for producing a high-strength hot-dip galvanized steel sheet according to (1), wherein after the hot-dip galvanizing, an alloying heat treatment is further performed at 450 to 550 ° C.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The present invention is directed to a high-tensile steel sheet containing 0.3% by mass or more of Si. With less than 0.3% by mass of Si, the influence of Si is small, and non-plating does not occur even if it is not according to the present invention. As a component of such a high-tensile steel sheet, Si:
A steel sheet containing 1.2% by mass and Ni: 2.3% by mass was immersed in hydrochloric acid at a concentration of 15% by mass and at a temperature of 85 ° C. for 3 minutes, and then subjected to normal hot-dip galvanizing to examine the plating property. As a comparison, Ni: 1.2 mass%
A similar experiment was performed for a steel sheet containing no. In addition, the determination of the plating property was performed by visually determining whether or not there was non-plating (a phenomenon that the plating does not wet) after hot-dip galvanizing.

As a result, it has been found that non-plating is eliminated in the steel containing Ni, and good hot-dip galvanizing is performed. The exact mechanism of this mechanism is not known at present, but the present inventors presume as follows. As a result of analyzing the distribution of elements on the surface of the steel sheet immersed in hydrochloric acid by a glow discharge optical emission spectrometer, the steel sheet containing 2.3% by mass of Ni has a remarkably concentrated Ni on the steel sheet surface as shown in FIG. I understand. The mechanism of this concentration is that Ni in steel is once dissolved in hydrochloric acid and then reprecipitated on the steel sheet surface, or
It is unknown whether only Ni in the steel remains without dissolving in hydrochloric acid, and as a result, Ni is concentrated on the surface, but in any case, as in the case of pre-plating Ni, Ni is present on the surface. It can be considered that, as a result, the wettability to the molten zinc was improved even in the Si-containing steel sheet.

The inventors further conducted the same experiment by changing the concentration and temperature of hydrochloric acid. In each case, the immersion time of hydrochloric acid is 1 minute. As a result, as shown in FIG. 2, it was found that the wettability was improved when the hydrochloric acid concentration was 8% by mass or more. It is considered that the higher the concentration of hydrochloric acid, the higher the amount of Ni enrichment on the surface. However, the amount of commercially available hydrochloric acid is usually 37% by mass, and the production of concentrated hydrochloric acid exceeding 37% by mass is a negative cost. Therefore, the upper limit was set to 37% by mass.
Therefore, the hydrochloric acid concentration was specified to be 8% by mass or more and 37% by mass or less.

FIG. 2 shows that the wettability is improved when the temperature is 80 ° C. or higher. The higher the temperature of hydrochloric acid, the more N
It is considered that the surface concentration of i increases, but if it exceeds 95 ° C., the evaporation of hydrochloric acid increases, which is environmentally unfavorable. Therefore,
The hydrochloric acid temperature was specified to be 80 ° C. or more and 95 ° C. or less. further,
In order to clarify the appropriate range of the immersion time of hydrochloric acid, in the above experiment, the immersion time was changed and the effect of improving the wettability was similarly compared. As a result, as shown in FIG. 3, if the immersion time is less than 1 minute, the Ni concentration on the surface is unstable and non-plating may occur. It turned out to be. It should be noted that performing hydrochloric acid pickling for more than 15 minutes has a negative effect on production efficiency. Therefore, in the present invention, the hydrochloric acid pickling time is defined as 1 minute or more and 15 minutes or less.

It is considered that a steel sheet to which an element having good wettability to molten zinc is added has the same possibility, and a steel sheet to which Cu is added is also manufactured.
Steel sheets with different addition amounts and different Cu addition amounts were also manufactured, and an experiment was conducted to improve the plating properties by pickling with hydrochloric acid. The concentration of hydrochloric acid in the experiment was 13% by mass, the temperature was 85 ° C., and the pickling time was 2 minutes, and the plating properties after hot-dip galvanizing were determined. As shown in FIG. 4, it was found that the plating property was improved when 1.5 × Ni (% by mass) + Cu (% by mass) ≧ 1.5 (% by mass) was satisfied.

From the above examination results, the addition amounts of Cu and Ni are 1.5 × Ni (% by mass) + Cu (% by mass) ≧
A steel sheet satisfying 1.5 (% by mass) and containing one or both of Ni and Cu was used. On the other hand, Ni, Cu
When each element is added in excess of 3% by mass, not only the effect of improving non-plating is saturated, but it is not only disadvantageous in cost but also contaminates the pickling bath.
% By mass or less. Further, if Cu is added alone, hot brittleness is likely to occur, which is a problem in production. Therefore, the hot working temperature is set low, or 1/100 of the Cu addition amount.
Preferably, about two Nis are added simultaneously to minimize hot brittleness. FIG. 5 shows a process flow chart illustrating an example of the present embodiment. Hot rolled steel sheet,
Any of the cold-rolled steel sheets can be used. In any case, the hot-dip galvanizing is performed after the concentration, temperature, and time of hydrochloric acid pickling are performed under the conditions within the range of the present invention.
Implementation of the alloying treatment after hot-dip galvanizing can be selected according to the purpose of the product.

[0013]

EXAMPLES The effects of the present invention will be more specifically described below with reference to examples. In this embodiment, the steel components (Si content, Ni content,
(Cu content) and hydrochloric acid pickling conditions were variously examined. First, Table 1 shows the components of the steel sheet used as the sample. These steel sheets were pickled with hydrochloric acid under various conditions shown in Table 2 and then subjected to hot-dip galvanizing or subsequently to alloying treatment to evaluate the plating properties. Hot-dip galvanizing was performed by immersing in a galvanizing bath containing a bath temperature of 450 ° C. and Al: 0.1% by mass for 3 seconds. When alloying,
After immersion in the plating bath, an alloying treatment was performed at 500 ° C. for 10 seconds at a plating thickness of 60 g / m ^{2 by} nitrogen wiping.
After hot-dip galvanizing or subsequent alloying treatment, the plating property was evaluated visually. The case where non-plating (phenomenon that the plating is not wet) occurred even at one place on the surface of the steel sheet was determined as “non-plating occurred”, and the case where no plating was not observed on the surface of the steel sheet was determined as “good”.

[0014]

[Table 1]

[0015]

[Table 2]

In Table 2, Nos. 1 to 10 all belong to the present invention because the components of the steel sheet, the concentration of hydrochloric acid, the temperature and the pickling time are within the scope of the present invention. In these samples, no plating was not observed at all, and it was confirmed that a good plating appearance was exhibited. On the other hand, Nos. 11 to 16 are comparative examples. In No. 11, the amounts of Ni and Cu were small, these elements did not concentrate on the surface of the steel sheet, and the hot-dip galvanizing did not sufficiently adhere. No. 12 was within the scope of the present invention as a component, but non-plating occurred because the concentration of hydrochloric acid was as low as 6% by mass, so that sufficient Ni and Cu were not concentrated on the steel sheet surface.

No. 13 falls within the scope of the present invention as a component, but since the hydrochloric acid temperature was as low as 75 ° C., sufficient Ni and Cu were not concentrated on the surface of the steel sheet, so that non-plating occurred. No. 14 is an example in which non-plating occurred because the time for pickling with hydrochloric acid was 20 seconds, which was insufficient. No. 15 was a sample in which Ni and Cu were not intentionally added, and hardly any hot-dip galvanized coating was observed even after hydrochloric acid pickling. In No. 16, the plating was good because Ni and Cu were sufficiently added, but these elements were dissolved in the pickling bath in an allowable amount or more.

[0018]

From the above results, even in a high-tensile steel sheet containing 0.3% by mass or more of Si, an appropriate amount of Ni or Cu is added and hydrochloric acid pickling is performed at an appropriate hydrochloric acid concentration, temperature and time. This makes it possible to obtain a hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet exhibiting excellent appearance without non-plating. Therefore, it can be said that the present invention is an invention with remarkable industrial effects.

[Brief description of the drawings]

FIG. 1 is a diagram showing that Ni is concentrated on a steel sheet surface by hydrochloric acid pickling.

FIG. 2 is a diagram showing a range of hydrochloric acid concentration and temperature in the present invention.

FIG. 3 is a diagram showing a range of time of hydrochloric acid pickling in the present invention.

FIG. 4 is a view showing an addition range of Ni and Cu in the present invention.

FIG. 5 is a process flow chart showing a procedure of pickling with hydrochloric acid as an example of an embodiment of the present invention.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C23C 2/20 C23C 2/20 2/28 2/28 (72) Inventor Osamu Akizue 20 Shintomi, Futtsu City, Chiba Prefecture -1 F-term in Nippon Steel Corporation Technology Development Division (Reference) 4K027 AA02 AA05 AA23 AB05 AB07 AB09 AB15 AB28 AB42 AC02 AC32 AC52 AC73 4K053 PA02 PA12 QA01 RA05 RA19 SA06 TA04 TA09 YA02 YA03 ZA10

Claims (2)

[Claims] 1. An alloy containing not less than 0.3% of Si and not more than 3% of Ni and not more than 3% of Cu so that 1.5 × Ni + Cu is not less than 1.5% in mass%. Seed or 2
In the production of galvanized steel sheet based on a high-tensile steel sheet containing seeds, hydrochloric acid concentration: 8 to 37% by mass, bath temperature: 8
A method for producing a high-strength hot-dip galvanized steel sheet, comprising performing pickling in a pickling bath at 0 to 95 ° C for 1 to 15 minutes, and thereafter subjecting to hot-dip galvanizing. 2. After hot-dip galvanizing, further 450-55.
2. An alloying heat treatment at 0 ° C.
The method for producing a high-strength galvanized steel sheet according to item 1.