JPS6240353A - Production of alloyed zinc plated steel sheet - Google Patents

Abstract

PURPOSE:To easily form a Zn-Fe alloy plating film by immersing a steel sheet in a Zn hot dipping bath under specific temp. conditions then subjecting the same to a heat treatment including heating and holding in the stage of forming Zn alloy plating with the hot dipping bath which contains Al at a high ratio and is inadequate for Zn alloy plating. CONSTITUTION:The Ti-added steel sheet contg., by weight %, 0.002-0.05% C, <0.6% Si, 0.6-1.6% Mn, <0.025% P, <0.12% sol Al and 0.02-0.5% Ti is subjected to recrystallization annealing by heating the same to 780-900 deg.C in a continuous Zn hot dipping line. The steel sheet is immersed at 460-550 deg.C in an ordinary Zn hot dipping bath which contains >=0.15% Al and is kept at 450-490 deg.C in the process for cooling the same. The steel sheet is heated and held for >=10sec to and at 475-550 deg.C in succession thereto to alloy Zn and Fe and to form the Fe-Zn alloy plating layer. The Fe-Zn alloy plating film is formed with the ordinary Zn hot dipping bath without changing over the bath to a Zn hot dipping bath contg. <0.15% Al for alloying.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for producing an alloyed galvanized steel sheet, particularly a hot-dip galvanizing bath having a bath temperature of 450 to 490°C and an Al'lH degree of 0.15% or more. The present invention relates to a method for producing an alloyed galvanized steel sheet by immersing a steel strip in water.

(Prior art) Conventionally, in the continuous furnace heat cycle in continuous hot-dip galvanizing, a steel strip is heated to about 700°C in a heating soaking zone, and then gradually cooled through a primary cooling zone, a low-temperature holding zone, and a secondary cooling zone. After reaching the same temperature as the hot-dip galvanizing bath, it enters the plating bath and is plated.

In that case, the hot-dip galvanizing bath is operated with slightly different bath components depending on the product. In other words, among the component elements added to the zinc plating bath, Al suppresses alloying of Zn and Fe, so it is commonly used in plating materials (hereinafter referred to as "Gl
In order to ensure plating adhesion, the alloyed material (hereinafter referred to as "GA material") is operated at a higher Al p3 degree and heated after plating to achieve alloying.
In the case of Al? in a hot-dip galvanizing bath? We are operating at a lower M degree.

Based on my experience, AC in GL material! /Zn (weight%) is 0
．． 15 or more is required, and it has been considered desirable for GA materials to be less than 0.15.

That is, when a continuous hot-dip galvanizing line is used to manufacture GI materials and GA materials, the hot-dip galvanizing bath composition in each case is usually 0.16% and 0.16%, respectively. 0.
It is adjusted to be 12%. In this way, when producing a Grl material, since alloying is suppressed, the Al stars in the bath are lower than when producing a GI material. Therefore, when the manufacturing material is changed from GI material to GA material during operation, or vice versa, this is usually done by changing the Al content of the mixed zinc added to the bath, but this requires complicated operations. Not only that, but it is also not possible to change the amount of Al in the bath quickly, so during the transition period, alloy formation in the GA material may be insufficient, or the adhesion of the plating layer on the GI material may be poor. The occurrence of defects is unavoidable.

(Problems to be Solved by the Invention) Thus, an object of the present invention is to provide a method for easily switching between GI material and GA material. Another object of the present invention is to provide a method for easily switching between GI material and GA material. During production, by making it possible to operate without reducing the Al concentration in the bath, G
It is an object of the present invention to provide a method that facilitates switching between I material and GA material.

(Means for Solving the Problems) In order to achieve the above-mentioned objective, the present inventors have made various studies and found that the steel to be treated, which is so-called Ti-added steel, is By increasing the temperature of the strip, the alloying reaction between zinc and iron proceeds rapidly,
Focusing on the fact that even the presence of 0.15% or more Al does not cause any problems, we continued our research and development, and found that in the case of Ti-added steel, Al fHHO was formed at a bath temperature of 450-490°C
The present invention was completed based on the knowledge that GA material can be effectively produced by dipping at a temperature of 460 to 550° C. when the GA material is 215% or more, and the object of the present invention can be achieved.

Therefore, the idea of the present invention is that, in weight %, C:
0.002-0.05%, Si: 0.6% or less, M
n: 0.6 to 1.6%, P: 0.025% or less, s
ol, A(2: 0.12% or less, Ti: 0.02
~0.5%, with the remainder consisting of Fe and unavoidable impurities, on a continuous hot-dip galvanizing line.
Recrystallization annealing at a temperature within the temperature range of 80 to 900 °C,
In the cooling process after the annealing, a bath of 7 m was heated at a temperature of 450 to 490°C.
7! 46 in a molten zinc bath with an Al tM degree of 0.15% or more
Soaking at a temperature of 0-550°C, followed by 475-55°C
This is a method for manufacturing an alloyed galvanized steel sheet, characterized in that alloying treatment is performed under conditions of heating and holding at a temperature of 0° C. for 10 seconds or more.

Needless to say, when manufacturing GI materials, it is possible to continue operation under the above conditions by simply omitting the alloying treatment, and there is no need to change the Al concentration when manufacturing GA materials again. Simply adding the alloying process described above is sufficient.

Therefore, according to the present invention, the production of GA material and GI material can be switched extremely easily.

(Function) In the present invention, the steel types are limited, but this is due to the discovery that there is an optimum treatment temperature for each steel type, and the steel types specified above are the so-called Ti-added steels. That's it. Therefore, the present invention is applicable to Ti-added steel in general, and there are no particular limitations to that extent, but if necessary, the reasons for limiting each composition ratio are as follows.

C: It is preferable that the C component is low in order to exhibit the effect of adding Ti, which will be described later. In other words, when the amount of C is large, the amount of TiC produced increases, inhibiting the growth of crystal grains and lowering the r value.
Reduces the effect of adding 1. On the other hand, significantly lowering Cl not only impedes productivity in the steelmaking process, but also causes an increase in oxygen in the steel (accompanied by the addition of oxide inclusions), which is undesirable. Therefore, CI is 0.002~0
．． 05%.

Si: In order to form a good Fe-Zn alloy layer through alloying treatment and to impart good slow aging properties to the steel sheet, it is better to keep the Si content as low as possible, and to ensure these good properties. The allowable upper limit is 0.6%. On the other hand, since the Si component has the property of improving the strength of the steel sheet, it is possible to improve the strength without impairing the above properties by including Si in a range of 0.6% or less.

Mn: In order for the steel plate to have slow aging properties and appropriate bake hardenability only on a continuous line, it is necessary to control the Mn content to 0.6% to 1.6%. If the content is less than .6%, the desired slow aging properties and bake hardenability cannot be ensured, whereas if the content exceeds 1.6%, ? This not only makes it difficult to manufacture 8, but also causes an increase in cost, and furthermore, r(l!!) decreases and moldability deteriorates.

P: The P component is normally contained as an unavoidable impurity, and when emphasis is placed on the formability of the steel plate, it should be 0.025% or less.

Sol, Al Al is necessary to reduce oxide inclusions and is an essential component to obtain sound steel, but if added in large quantities, it will cause A! Since the increase in 22031 is undesirable, the allowable upper limit was set at 0.12%.

T1: By adding Ti in an amount necessary to fix C and N in the steel, it imparts anti-aging properties and dramatically improves deep drawing properties. For this reason, it is added in an amount of 0.02 to 0.5%. The specific addition amount is determined by the Cl etc. at that time within the range, but if it exceeds 0.5% Ti, the Ti
1 is saturated, and the effect of further addition is small.

The invention will now be further described in connection with the accompanying drawings.

The attached drawing is a diagram schematically illustrating a continuous hot-dip galvanizing line, in which the steel strip from the uncoiler 10 is
After passing through the shear 11 and welder 12, it is sent to a pretreatment zone consisting of a non-oxidizing heating furnace 13, a recrystallization annealing furnace 14, and a cooling furnace 15, where material quality and plating surface adjustment are performed. In the present invention, recrystallization annealing is performed at a temperature in the range of 780 to 900°C, but if the temperature is lower than 780°C, sufficient recrystallization will not occur, while if it exceeds 900°C, excessive softening will occur. I end up. The temperature leaving the cooling furnace 15, that is, the temperature entering the hot dip galvanizing bath 20, is set to 460~
The temperature is limited to 550°C, but if this temperature is lower than 460"C, alloying will not proceed sufficiently when producing GA material, and on the other hand,
If the temperature exceeds 50°C, plating fading will become significant when producing GI materials. Preferably 500-53
It is 0°C.

The hot-dip galvanizing bath 20 is maintained at a temperature range of 450 to 490°C and an Al concentration of 0.15% or higher, regardless of whether GI or GA materials are manufactured. However, if the bath temperature is lower than 450°C, In the present invention, the alloyed layer is not sufficiently formed during the production of the GA material, and on the other hand, if the bath temperature is too high above 490° C., corrosion by the hot-dip galvanizing bath becomes significant. Therefore, in the present invention, the temperature is limited to the above range. Preferably it is 460-480°C. A
It is also necessary to ensure a concentration of 0.15% or more when manufacturing the Gll type, and preferably it is adjusted to around 0.16%.

Thus, in the present invention, since the temperature of the steel strip to be treated is relatively high, the temperature of the plating bath tends to be correspondingly high, thus accelerating the erosion of the structural members of the plating bath. The plating bath according to the present invention is preferably equipped with a cooling means to prevent an excessive rise in bath temperature, such as the cooling device disclosed in JP-A-57-35671.

The steel strip that has left the plating bath then enters the alloying treatment furnace 21 and undergoes 475 to 55
The alloy is heated and held at 0° C. for 10 seconds or more to perform alloying treatment. When manufacturing a CR material, this step is omitted and the plating layer is simply wound around the coiler 26 after solidification, and the process is completed.

The alloying treatment conditions described above are conventional.

In this way, in the present invention, alloying is promoted and controlled by increasing the immersion temperature.
The alloying behavior at 525°C for 20 seconds at 0°C is shown in Table 1. A case where similar tests were conducted on GI materials without alloying is also shown.

Table 1: Large plating discoloration As is clear from these results, the areas where plating discoloration occurs in GI materials indicate that Fe diffusion from the m-plate is progressing even without alloying treatment. , it has been shown that when the temperature of the treated material entering the plating bath increases, the Fe-Al alloy layer in the plating layer and the steel base is destroyed and alloying of Fe-Zn is promoted.

The quality of the plating layer of the GA material obtained in the above case was investigated in terms of the plating film composition analysis and processability (powdering property), and the results are summarized in a graph and shown in FIG. 2. As is clear from the illustrated results, the workability (powderability) was good when Fe/Zn+Fe=10 to 13% in the plating film.

The powdering resistance was evaluated by performing a cylindrical drawing test on the blank of the test material, forcibly peeling it off by a taping test after molding, and evaluating the weight loss of the test material.

It is difficult to unambiguously determine the temperature of the person immersed in the plating bath due to its relationship with the plate thickness, but it should be set near the upper limit of the appropriate range for thin plates, and near the lower limit for thick plates. .

Next, the present invention will be explained in more detail using examples.

Example 1 A Ti-added steel strip (thickness: 0.8 mm) having the steel composition shown in Table 2 was continuously hot-dip galvanized and then alloyed using the apparatus shown in FIG.

The alloying treatment was performed at a furnace temperature of 1000° C. and a temperature of the treated material of 525° C. (target).

Table 2 CSi Mn P SO, 010, 0120, 150, 0140, 005 -
"-" Ldan-0,0400,00300,010,060 The treatment conditions and the properties of the obtained plated steel sheets are summarized in Table 3. Alffi in the bath was 0.16%.

Table 3 (Note) ◎ Excellent, Good Example 2 In Example 1, various experiments were conducted by setting the plating bath temperature to 463° C. and changing the plate thickness, penetration temperature, and line speed.

The processing characteristics of the plated films obtained in each case are summarized in Table 4 together with the operating conditions.

The processability was evaluated by the powdering property described above, and all results were satisfactory.

Table 4

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically explaining a continuous hot-dip galvanizing line, and FIG. 2 is a graph showing the relationship between immersion temperature and powdering property. I3: Non-oxidizing heating furnace, 14: Recrystallization annealing furnace, 15: Cooling furnace, 20: Hot-dip galvanizing bath, 21: Alloying treatment furnace tail/I2J

Claims (1)

[Claims] In weight%, C: 0.002 to 0.05%, Si: 0.6
% or less, Mn: 0.6 to 1.6%, P: 0.025% or less, sol. Al: 0.12% or less, Ti: 0.02~
0.5%, with the remainder consisting of Fe and unavoidable impurities, on a continuous hot-dip galvanizing line.
Recrystallization annealing is performed at a temperature within the temperature range of 0 to 900°C, and in the cooling process after the annealing, it is placed in a molten zinc bath with a bath temperature of 450 to 490°C and an Al concentration of 0.15% or more at a temperature of 460 to 550°C. Soaking and subsequently at a temperature of 475-550°C for 10
A method for manufacturing an alloyed galvanized steel sheet, characterized by performing alloying treatment under conditions of heating and holding for more than a second.