JPS61204332A - Production of metal hot dipped thin steel sheet having excellent ridging resistance and plating adhesiveness - Google Patents

Abstract

PURPOSE:To obtain a titled thin steel sheet having good workability with lessened stages without including cold rolling by specifying rolling conditions and coiling temp. in a stage for warm rolling a low-carbon steel to a prescribed sheet thickness and subjecting the steel strip to a recrystallization and plating treatment in a continuous metal hot dipping line in succession to the rolling. CONSTITUTION:The low-carbon steel is finished in the temp. range of 300-800 deg.C and at >=300 s<-1> strain rate in at least one pass and is coiled at <=400 deg.C coiling temp. in the stage for warm rolling the low-carbon steel to the prescribed sheet thickness. The steel strip is subjected to the recrystallization and plating treatment in the continuous metal hot dipping line of an inline annealing system. The plated thin steel sheet exhibiting high ductility r value and having the excellent plating adhesiveness and ridging resistance is thus obtd. by the high- strain rate warm rolling without executing the conventional cold rolling stage.

Description

[Detailed Description of the Invention] (Industrial Application Field) This specification describes the production of thin steel sheets with excellent ridging resistance, workability, and hot-dip metal plating adhesion. It is related to the evolving results of development research based on experimental findings that it is possible to save processes without involving.

Thin steel plates with a thickness of approximately 2 mm or less used for applications such as building materials, automobile body materials, can stock, and various surface-treated original sheets have good mechanical properties such as bending workability, stretch formability, and drawing workability. In order to obtain high ductility and high Lankford value (r value), high ductility and high Lankford value (r value) are required. Furthermore, since these materials are mainly used on the outermost side of the final processed product, the surface condition after processing has become particularly important.

Furthermore, in recent years, the requirements for corrosion resistance of thin steel sheets for processing have become more and more severe, and the use of surface-treated sheets has been rapidly increasing.

Particularly in the case of automobiles, those used in Northern Europe and North America are required to have even stricter corrosion resistance in order to withstand corrosion caused by snow melting base materials.

On the other hand, even if a surface-treated steel sheet is used, if it is easily damaged during processing, its corrosion resistance will deteriorate, so the adhesion between the base steel sheet and the surface treatment layer is extremely important for surface-treated steel sheets.

The general manufacturing procedure for these thin steel sheets for processing is as follows.

Low-carbon steel is mainly used as the steel material, and steel slabs with a thickness of approximately 200 m111 are made by continuous casting or ingot-blowing and rolling, and then hot-rolled steel with a thickness of approximately 311 III is produced by a hot rolling process. The copper strip is then pickled and cold-rolled into a copper strip of a predetermined thickness, and then recrystallized using a box annealing method or a continuous annealing method to produce a final product.

The biggest drawback of this practice is that it is a long process; not only does it take a lot of energy, manpower, and time to produce a product, but during this long process, there are some problems with the quality of the product, especially its surface properties. There is also the added disadvantage of causing

As mentioned above, it has been essential to include a cold rolling process (rolling temperature less than 300° C.) in the manufacturing procedure of thin steel sheets for processing.

This cold rolling process not only aims to reduce the desired thickness, but also improves deep drawability in the final annealing process by utilizing the plastic strain introduced by cold working (111). It helps to promote the growth of oriented grains.

However, in cold working, the deformation resistance of the steel strip is significantly higher than in hot working, so the energy required for rolling is also significant, the rolling rolls are severely worn, and rolling problems such as slipping occur. Easy to occur.

On the other hand, if rolling can be done in a relatively high temperature range of 300°C or higher and 800°C or lower (so-called warm range), and particularly good workability can be obtained, the above problems can be eliminated and there are great manufacturing advantages. You could say that.

However, there are major problems with manufacturing by warm rolling. That is Rising.

Ridging is a defect in surface irregularities that occurs during the processing of products, and is a fatal defect for this type of steel sheet, which is mainly used on the outermost side of processed products.

In terms of metallurgy, ridging is caused by crystallographically oriented grain groups (e.g. (100) oriented grains) that are not easily divided even after undergoing the annealing recrystallization process and remain stretched in the rolling direction. , generally like warm rolling, ferrite (
This tends to occur when processing is carried out at relatively high temperatures in the α) region, and is particularly noticeable when the reduction rate in the warm region is high (i.e., when manufacturing thin steel sheets).

Recently, as processed products have become more complex and sophisticated, these processed steel plates are often subjected to severe processing, and excellent ridging resistance is required.

Incidentally, the manufacturing process of steel materials has changed significantly in recent years, and the case of thin steel sheets for processing is no exception.

That is, the molten steel is made into a steel billet with a thickness of about 250 mm by ingot-making and blooming rolling, then heated and soaked in a heating furnace, processed into a sheet bar with a thickness of about 3011II11 by a rough hot rolling process, and then processed into a sheet bar with a thickness of about 3011II11 by a finishing hot rolling process. In contrast to the conventional practice of hot-rolled steel strips, the introduction of continuous casting processes in recent years has made it possible to omit the blooming process, and in order to improve material quality and save energy, the heating temperature of steel slabs has been reduced from the conventional 1200 mm.
There is a tendency for the temperature to decrease from around 1100°C to around 1100°C or lower.

On the other hand, a new process is being put into practical use that allows the heat treatment and rough rolling process of hot rolling to be omitted by immediately producing a steel strip with a thickness of 50III11 or less from molten steel.

However, these new manufacturing processes are disadvantageous in that they destroy the structure formed by solidifying molten steel (cast structure). and (formed upon solidification to (100)
It is extremely difficult to destroy the strong casting texture whose main orientation is (uvw>).

As a result, the final thin steel sheet tends to suffer from gluing, and the warm rolling process particularly promotes this.

(Prior Art) Several methods for manufacturing deep drawing steel sheets by warm rolling have been disclosed, such as Japanese Patent Publication No. 47-30809 and Japanese Patent Application Laid-open No. 49/1989.
-86214, JP-A No. 59-93835, JP-A-Sho 5
9-133325, JP 59-136425, JP 59-185729, and JP 59-226
No. 149 and No. 8 is an example. Both methods are characterized by recrystallization treatment immediately after rolling in the warm region, and are innovative technologies that can omit the cold rolling step.

However, these known techniques do not give any consideration to improving the above-mentioned ridging resistance.
In this respect, warm rolling is generally more disadvantageous than cold rolling when it comes to the ridging resistance of thin steel sheets.

(Problems to be Solved by the Invention) It is an object of the present invention to provide a method for producing a thin steel sheet that has excellent ridging resistance, workability, and hot-dip metal plating adhesion by eliminating the need for a cold rolling process. .

(Means for Solving the Problems) The present invention provides at least one pass in the process of warm rolling low carbon steel to a predetermined thickness in a temperature range of 300 to 800°C at a strain rate ('t) of 300 s - For processing with excellent ridging resistance and plating adhesion, characterized by finishing at a coiling temperature of 400°C or less, followed by recrystallization and plating in an annealing-type continuous hot-dip metal plating line within the line. This is a method for manufacturing a hot-dip metal plated thin copper plate.

First, the results that form the basis of this invention will be explained.

The test materials were two types of hot-rolled low carbon aluminum killed steel sheets shown in Table 1. The test materials are both (A) and (B) 600
It was heated and soaked at a temperature of 0.degree. C. and rolled for one pass at a rolling reduction of 30%.

Strain rate (λ) at this time and after annealing (soaking temperature 800
FIG. 1 shows the relationship between the r value (°C) and the ridging index.

r value and ridging resistance strongly depend on strain rate, 6
By setting the strain rate to a high strain rate of 300 s-' or more at a rolling temperature of 00°C, the r value and ridging resistance were significantly improved.

Next, steel (C) having the composition shown in Table 2 was continuously cast and rough hot rolled into a sheet bar with a thickness of 25 mm, and then rolled at a high strain rate (562 s -1) in the 6th stand of a finishing mill consisting of 6 rows. I did it. The finishing temperature is 670°C, and the plate thickness is 1.2 mm.

This steel strip was wound up at various winding temperatures, annealed at a soaking temperature of 810° C. on a continuous hot-dip galvanizing line without pickling, and then continuously galvanized. Figure 2 shows the results of the zinc plating adhesion test for this steel plate.

This bending test is performed from close contact (bending radius OT) bending to
Those that were bent to a double bending radius (4T) were judged based on the separation limit value. In addition, the peeling limit value during swing-out processing was also investigated using an Erichsen tester.

From FIG. 2, it can be seen that by setting the winding temperature to 400° C. or lower, extremely excellent adhesion and Erichsen values are obtained.

As a result of repeated research based on this basic data, the inventors confirmed that a thin steel sheet with excellent plating adhesion and ridging resistance can be manufactured by regulating the manufacturing conditions as described below.

(1) Steel composition The effects of high strain rate rolling do not essentially depend on the steel composition. However, in order to ensure workability above a certain level, the interstitial solid solution elements C and N should be 0.10% and 0.1%, respectively.
It is preferable that it is 0.01% or less.

Furthermore, reducing the content of zero in steel by adding Al is advantageous for improving the material quality, especially the ductility.

Furthermore, in order to obtain even better workability, special elements that can precipitate and fix C and N as stable carbonitrides, such as Tt+N, are used.
Addition of b+Zr, B, etc. is also effective.

Further, in order to obtain high strength, P, Si, Mn, etc. can be added depending on the strength.

(2) Manufacturing method of rolled material Steel slabs obtained by conventional methods, ie, ingot-blowing rolling or continuous casting methods, can naturally be applied.

The heating temperature of the steel piece is suitably 800 to 1250°C, and preferably less than 1100°C from the viewpoint of energy saving.

Of course, the so-called CC-DR (continuous casting-direct rolling) method, in which rolling of a steel billet from continuous casting is started without reheating, is also applicable.

On the other hand, the methods of directly casting rolled materials of approximately 50 cranes or less from molten steel (sheet bar caster method and strip caster method) are also particularly advantageous as methods for manufacturing rolled materials because they have great economic effects from the viewpoint of energy saving and process saving. .

(3) Warm rolling This process is the most important, and in the process of warm rolling low carbon steel to a predetermined thickness, at least one pass is
It is essential to finish at a temperature range of 0 to 300°C, a strain rate of 300 g-' or higher, and a winding temperature of 400°C or lower.

Regarding the rolling temperature, it is difficult to obtain good workability and ridging resistance by controlling the strain rate when rolling at a high temperature of over 800℃, while a temperature lower than 300℃ results in a significant increase in deformation resistance, which is unique to the cold rolling method. Since the same problems as mentioned above are involved, temperatures of 800 to 300℃, especially 700 to
400°C is particularly suitable.

The target material quality cannot be secured unless the strain rate is 300 s-' or higher.

This strain rate range is particularly from 500 to 2500 s-'
is suitable.

Excellent plating adhesion cannot be obtained unless the winding temperature is 400° C. or lower.

The number of rolling passes and the distribution of the rolling reduction ratio may be arbitrary as long as the above conditions are satisfied.

The arrangement, structure, roll diameter, tension, presence or absence of lubrication of the rolling mill, etc. have no essential influence.

Note that the strain rate (-) is calculated according to the following formula.

n; Roll rotation speed (rpm) r: Reduction rate (%) / 100 R: Roll radius (fin) Ho: Plate thickness before rolling (4) Annealing The rolled copper strip needs to be recrystallized and annealed.

The annealing method is to perform recrystallization and plating on an in-line annealing continuous hot-dip metal plating line.

The annealing heating temperature is suitably in the range from the recrystallization temperature to 950°C. For steel plates with a carbon content of 0.01 ivt% or more, it is advantageous to perform an overaging treatment after soaking to improve the material quality.

The scale on the surface of the steel strip is thin and easily removed because the rolling temperature is much lower than in conventional hot rolling. Therefore, descaling can be performed not only by conventional acid removal but also mechanically or by controlling the annealing atmosphere in a continuous hot-dip metal plating line.

The copper strip after annealing may be subjected to temper rolling of 10% or less for adjustment such as shape correction.

(Function) Regarding the behavior of high strain rate warm rolling according to the present invention,
The mechanism that brings about the ridging resistance and workability is not necessarily clear, but it is thought to have a close relationship with changes in the texture and processing strain of the rolled material.

(Example) Steel slabs having the chemical composition shown in Table 3 were manufactured by a converter-continuous casting method and a converter-sheet bar caster method. In the converter continuous casting method, a sheet bar having a thickness of 20 to 30 m was obtained by heating and soaking at 1100 to 950°C and then rough rolling.

These sheet bars were rolled at a high strain rate at the 6th stand of a finishing mill consisting of 6 rows and wound up. Continuous molten metals (Zn, Aρ, Pb) without subsequent pickling
) Annealed on plating line (soaking temperature 700-850℃)
Then, continuous hot-dip plating was applied.

Table 4 shows the rolling conditions and the material properties and plating adhesion test results after 0.5 to 1.2% skin pass rolling.

The ridging property is determined by removing the plating layer through chemical research.
A No. 1 tensile test piece was taken from the rolling direction and evaluated visually after deformation at 15% strain (1 (good) to 5 (poor)).

No evaluation criteria have been established for this evaluation since no ridging actually appeared when using the conventional manufacturing method of low carbon cold rolled steel sheets. Therefore, in the present invention, the conventional index evaluation criteria based on the visual method for stainless steel was used as the standard.

Judgment 1.2 indicates ridging property that poses no problem in practical use.

The plating adhesion was determined based on the method described above, and each unmarked example in the table shows excellent workability, ridging resistance, and plating adhesion.

(Effects of the Invention) According to the present invention, a thin steel sheet that exhibits high ductility and r value through high strain rate warm rolling, as well as excellent plating adhesion and ridging resistance, can be obtained, and the conventional cold rolling process is omitted. Not only is this possible, but it is also compatible with the sheet bar caster method, strip caster method, etc. for rolled materials, and it is possible to simplify the manufacturing process of hot-dip metal-plated thin steel sheets for processing.

[Brief explanation of drawings]

FIG. 1 is a graph showing the influence of rolling strain rate on r value and ridging property. FIG. 2 is a graph showing the influence of winding temperature on plating adhesion. Figure 2 lack = *Gentleness ('c) Procedural amendment March 1, 1986 Michibe Uga, Commissioner of the Patent Office 1, Indication of the case Patent application No. 43983 of 1985 2, Invention Name: Method for producing hot-dip metal-plated thin steel sheets for processing with excellent ridging resistance and plating adhesion 3. Relationship with the amended case Patent applicant (125) Kawasaki Steel Corporation 4, Agent

Claims (1)

[Claims] 1. In the step of warm rolling low carbon steel to a predetermined thickness, at least one pass is performed at a temperature range of 300 to 800°C, at a strain rate (■) of 300 s^-^1 or more, and at a rolling rate of 300 s^-^1 or more. temperature 40
Manufacture of hot-dip metal-plated thin steel sheets for processing with excellent ridging resistance and plating adhesion, which are finished at 0°C or lower and then recrystallized and plated on an in-line annealing continuous hot-dip metal plating line. Method.