JPH07103463B2 - Method for producing alloyed zinc plated steel sheet with excellent deep drawability - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an alloyed vapor-deposited galvanized steel sheet which is excellent in deep drawability and powdering resistance.

[Prior Art] Al-killed steel and Ti-killed steel are generally known as deep-drawing steel plates. By the way, an alloyed vapor-deposited galvanized steel sheet based on Ti killed steel has a problem that flaking of a plated layer is likely to occur during processing when alloyed under the same conditions as Al killed steel. It is considered that this is because the iron in the Ti-killed steel is more likely to diffuse into the plating layer than the Al-killed steel and the average concentration in the plating layer becomes excessive.
FIG. 1 shows an example of the concentration gradient of iron in the zinc-plated layer when Ti-killed steel and Al-killed steel are vapor-deposited by galvanizing and then alloyed up to the surface of the plated layer. In the illustrated Al-killed steel, the iron concentration is about 5 to 6.5% from the plating surface to the deep portion of the plating layer, and the iron concentration gradient sharply rises from the deep portion of the plating layer to the interface with the steel sheet.
On the other hand, in the Ti killed steel, the iron concentration in the vicinity of the surface layer is 5 to 6%, which is the same as that in the Al killed steel, but the iron concentration from the middle portion to the deep portion of the plating layer is higher than that of the Al killed steel. Thus, it can be seen that Ti-killed steel has an alloyed plating layer with a higher iron concentration than Al-killed steel. Therefore, when alloying treatment of vapor-deposited zinc-plated Ti-killed steel under the same conditions as Al-killed steel, alloying proceeds excessively, and the average iron concentration in the plating layer is 1.5-1.5% higher than that of Al-killed steel. As a result of 2.0% increase and the average iron concentration becoming excessive, there is a problem that the powdering resistance is lowered and the plating layer is likely to be peeled and damaged during processing.

[Discovery of Problem Solving] The inventors of the present invention have found that, when alloyed vapor deposition zinc plating is performed on Ti killed steel as described above, alloying proceeds excessively when alloying treatment is performed under the same conditions as Al killed steel. We found that there is a problem that the powdering resistance is reduced, and as a method to solve this problem, for low carbon Ti killed steel, keep the substrate temperature immediately before vapor deposition plating as low as possible, and alloying temperature and time. If the average Fe temperature in the alloy layer (also called the average Fe content ratio) is controlled to 8.0 to 12.0 wt% by limiting the content to a predetermined range, the alloyed zinc-plated Ti-killed steel with good powdering resistance can be obtained. The knowledge that can obtain

According to the present invention, C ≦ 0.010 wt%, Si <0.15 wt%, Mn:
When vapor-depositing a low carbon titanium killed steel sheet containing 0.15 to 0.85% by weight and Ti: 0.05 to 0.30% by weight, the temperature of the steel sheet immediately before the plating was set to 180 to 280 ° C, and then in the batch annealing furnace. Alloying is carried out in a non-oxidizing atmosphere with a heating temperature of 220 to 320 ° C. and a heating time of 1 to 50 hours, and the relationship between the temperature and time is the range surrounded by the shaded area in FIG. Provided is a method for producing an alloyed galvanized steel sheet having excellent deep drawability, which is characterized by performing a treatment.

Here, the range surrounded by the shaded area in FIG. 3 is the horizontal axis (X
When the axis is the logarithmic scale of the heating time (hr) and the vertical axis (Y-axis) is the standard scale of the heating temperature (° C), points A, B, C, and
It is a range of a polygon formed by connecting D, E and F with a straight line. The coordinates of these points are as shown in the figure.
(1hr, 320 ℃), B (2hr, 320 ℃), C (50hr, 270 ℃), D (50
hr, 220 ° C), E (15 hr, 220 ° C), F (1 hr, 280 ° C).

In the present invention, a low carbon having the following composition (% by weight)
Ti killed steel is used.

The Ti-killed steel used as a deep-drawing steel plate is an ultra-low carbon steel, and usually C ≦ 0.010% by weight is used. Further, Si is preferably Si <0.15% by weight. If the Si content is more than 0.15, the plating adhesion will decrease. To improve this adhesion, it is necessary to raise the substrate temperature, but in the case of Ti-killed steel, if the diffusion of Fe is rapid and the substrate temperature is raised, a fragile alloy layer occurs at the interface between the plating layer and the steel sheet. Occurs. Therefore, the Si content of Ti killed steel is preferably 0.05 wt% or less. Mn is a component that mainly increases the strength, and is preferably 0.15 to 0.85% by weight. If it is less than 0.05% by weight, sufficient strength cannot be maintained. On the other hand, if it exceeds 0.85%, plating adhesion and other quality problems do not occur, but if it contains 0.85% by weight or more of Mn, You can't expect the strength of to increase.

Ti is 0.05 to 0.30% by weight. This is a normal deep drawing Ti
The content is similar to that of killed steel. Generally, as a deep-drawing steel plate, a content of about 4 times the content of C is usually required to fix C in Ti steel, and the content is determined in consideration of the amount of nitrogen as an impurity in the steel. .

In addition, as inevitable impurities, P ≦ 0.020% by weight, S
≦ 0.020 wt%, solAl ≦ 0.050 wt% are included. These are the same as the impurity levels of ordinary steel.

For the above Ti killed steel, the steel plate temperature immediately before plating is set to 180
Set to 280 ℃ and apply evaporated zinc plating. Generally, in vapor deposition zinc plating, if the substrate temperature during plating is too low, the adhesion of the zinc plating layer becomes poor, so the substrate temperature is usually kept at 180 ° C or higher. Since it condenses to form a plating layer, the temperature of the substrate rises due to the heat of condensation of zinc. Other,
Heat transfer from the winding rolls in the vapor deposition chamber also contributes to raising the substrate temperature. Therefore, if the substrate temperature immediately before plating is unnecessarily high, the substrate temperature further rises due to the condensation heat and heat transfer, and as a result, a fragile alloy layer develops near the interface between the plating layer and the steel sheet, and the plating layer Causes a problem of impairing the adhesiveness. In one example, when the steel strip temperature after plating is around 360 ° C, an alloy layer of 0.1 to 1.0μ develops after about 35 seconds, and when the steel strip temperature rises to 410 ° C or more, the alloy layer having the above layer thickness is formed in 5 seconds or less. Develop. For this reason, in order to prevent the development of the alloy layer, the substrate temperature of the steel strip immediately before plating is set to 180 to 280 ° C in the case of thick weighting and to 180 to 300 ° C in the case of thin weighting in consideration of the temperature rise. I am adjusting. In the present invention, as compared with Ti killed steel Al killed steel, because it is easier to alloy, it is lower than the normal substrate temperature, 180 to 260 ℃ in the case of thick basis weight and adjusted to 180 to 280 ℃ in the case of light weight To minimize the diffusion of iron into the plating layer.

An alloying treatment is applied after the vapor deposition plating.

Generally, as the alloying treatment by batch annealing, heat treatment is performed in a non-oxidizing atmosphere in order to prevent oxidation of the steel sheet. The coil shape may be either a tight coil or an open coil. The processing temperature and time can be changed depending on the plating deposition amount and the target Fe content rate. The heat cycle of the alloying treatment of FIG. 2 is shown, and the alloying range is shown in FIG. The heat cycle in Fig. 2 shows the case where after the alloying treatment, the inside of the furnace was cooled to 100 ° C or less in a non-oxidizing atmosphere. The non-oxidizing atmosphere in the furnace was based on N ₂ and H ₂ was added to it. 3-75
It consists of a gas with a composition of% contained. CO in gas,
The CO ₂ concentration is 0 to 10% in all cases.

FIG. 3 shows a range of alloying treatment conditions including an average Fe content rate of 8 to 12%. In the figure, a range within a solid line a is an Al-killed steel base, and a dotted region surrounded by a broken line cd is a Ti-killed steel. The case of the base is shown. The reason why the alloying treatment time was set to 1 hour or more was that the furnace temperature did not decrease in the soaking time that was experimentally shorter than that, and the reason that it was set to 50 hours or less was that productivity was not improved above that time. This is because.

[Examples and Comparative Examples] Ti was produced using the continuous vacuum evaporation zinc plating apparatus shown in FIG.
Galvanized killed steel. In the figure, 1 is a steel plate,
2 is a pretreatment furnace, 3a and 3b are vacuum seal roll chambers, 4a and 4 are vacuum deposition chambers, and 5 is a cooling chamber. The operating conditions are shown in the following table.

When performing single-sided plating, it is sufficient to perform vacuum vapor deposition Zn plating on only one of the first vacuum vapor deposition plating chamber 4a and the second vacuum vapor deposition plating chamber 4b.

These vacuum-deposited Zn-plated steel sheets were heated in a batch annealing furnace and alloyed to produce alloyed Zn-plated steel sheets. The alloying treatment conditions are shown in the following table.

The results of examining the combination of the adhesion amount, the substrate temperature, the heating temperature, the heating time (that is, the holding time at the heating temperature), the surface appearance of the manufactured steel sheet, and the workability (powdering resistance) are first.
Shown in the table. The powdering resistance was evaluated based on the occurrence of powdering on the inner side after bending back for 6 tons and 180 °. That is, after the tape was bent at 6t, 180 °, and after bending back, cellophane tape was attached and peeled off, and the amount of the plating layer adhering to the cellophane tape was observed. “Poor” was defined as “poor”, and those with a small amount of adhesion were defined as “good”. "Surface appearance" is an evaluation of the appearance change before and after alloying by visual judgment. If the appearance as plated remains after alloying, "Zn remains", and alloying is completed uniformly. The thing was made into "good."
Next, for comparison, the substrate temperature during vapor deposition, the heating temperature during alloying, and the holding time were set to the conditions shown in Table 2, and the galvanizing alloying treatment was performed in the same manner as in the other examples. The results are shown in Table 2.

As is clear from the above results, all of the galvannealed steel sheets of this example have a good surface appearance and workability, but the comparative examples have zinc remaining in the alloy layer, or workability. Inferior to.

[Effects of the Invention] According to the production method of the present invention, an alloyed layer having an optimum iron content rate can be formed when alloying zinc-plated titanium killed steel, and the surface appearance, deep drawability, and powder resistance. It is possible to obtain an alloyed galvanized steel sheet having excellent ringability.

[Brief description of drawings]

FIG. 1 is a graph showing the iron concentration in the alloy layer for titanium killed steel and aluminum killed steel, FIG. 2 is a graph showing the heat cycle of alloy treatment, and FIG. 3 is a graph showing the relationship between alloying time and treatment temperature. FIG. 4 is a schematic view showing an example of a continuous vacuum vapor deposition plating apparatus. In the drawing 1-steel plate, 2-pretreatment furnace, 3a, 3b-vacuum seal roll chamber, 4a, 4b-vacuum deposition chamber, 5-cooling chamber

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C22C 38/14

Claims (2)

[Claims] 1. C ≦ 0.010% by weight, Si <0.15% by weight, Mn: 0.15
〜0.85wt%, Ti: 0.05〜0.30wt%, low carbon titanium killed steel sheet is vapor-deposited by galvanizing. The heating temperature is 22 in an oxidizing atmosphere.
The alloying treatment is performed under the conditions that the temperature is 0 to 320 ° C., the heating time is 1 to 50 hours, and the relationship between the temperature and time is the range surrounded by the shaded area in FIG. A method for producing an alloyed galvanized steel sheet having excellent drawability. 2. The alloyed galvanized layer has an average iron concentration of 8.0.
The manufacturing method according to claim 1, wherein the amount is ˜12.0% by weight.