JPS581170B2 - Manufacturing method for hot-rolled steel sheets with excellent enameling properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a hot rolled steel sheet with excellent enameling properties.

Conventionally, hot-rolled steel sheets have not been widely used for enameled products.

The reason for this is that hot-rolled steel sheets have a higher enameling property than cold-rolled steel sheets.
This is particularly because the resistance to flaking is poor.

Therefore, hot-rolled steel plates are used for pressure vessels and the like that require strength, but currently they are only used with enameling on one side, which is less likely to cause chipping.

However, single-sided enameling has a problem in terms of corrosion resistance compared to double-sided enameling, and this has hindered its use in chemical industrial equipment, etc., which require not only strength but also high corrosion resistance.

Recently, even in pressure vessels such as water heaters, stronger hot-rolled steel plates have been used to increase the strength of the product, while maintaining the same strength as before and reducing the plate thickness, improving workability. There is a movement to do so.

The present invention has been established in line with the above-mentioned points, and specifically, it suppresses the sagging in double-sided enameling, which is a drawback of hot-rolled steel sheets for enameling, and also suppresses sagging in double-sided enameling. The present invention provides a hot-rolled steel sheet with excellent enameling properties and strength suitable for use in.

That is, in the method of the present invention, C0.02 to 0.10%, Mn
0.05-0.40% and Ti0.05-0.30
%, the remainder being substantially Fe, is hot rolled, and after the hot rolling is finished, it is cooled at a rate of 50°C/sec or more to
It is characterized by being wound up at 0 to 650°C.

The present invention will be sequentially explained below.

First, C0.02-0.10%, Mn 0.05-0.
A steel material containing 40% Ti and 0.05 to 0.30% Ti, with the remainder substantially consisting of Fe, is melted and hot rolled. The reason for limiting the chemical composition is as follows. .

C: 0.02 to 0.10% C is required to be at least 0.02% in order to ensure the specified strength, and degassing treatment is necessary to produce a steel plate with a C content of 0.02% or less. This requires special processes such as, etc., which increases the price.

On the other hand, if the C content is less than 0.02%, as shown in FIG. 1 below, the amount of precipitates that are effective in improving the resistance to flaking decreases, which is not preferable.

Although the strength increases with an increase in the amount of C, it is necessary to ensure a certain degree of formability and weldability even if it is a hot-rolled steel sheet.

Furthermore, in terms of enamelability, a large amount of C not only causes defects such as bubbles, but also reduces chipping resistance, although the mechanism is unknown.

Taking these things into consideration, the upper limit of C was limited to 0.10%.

Mn: 0.05-0.40% Mn is also necessary to obtain a predetermined strength, and if it is less than 0.05%, hot brittleness will occur, so it is necessary to ensure a minimum of 0.05%.

The deoxidizing effect of Mn also promotes the effective use of Ti.

However, as the amount of Mn increases, the strain during enamel firing increases and the sagging resistance deteriorates.
impairs adhesion in enamel.

In order to prevent the occurrence of strain (sagging) during firing, special attention was paid to the upper limit of Mn in the steel sheet manufactured by the method of the present invention, and the upper limit value was limited to 0.40%.

Ti: 0.05 to 0.30% In the present invention, high tensile strength and excellent enameling properties, particularly stent resistance, are obtained in a hot rolled steel sheet.

For this purpose, Ti is an absolutely necessary element.

The reason why Ti improves the chipping resistance is not clear, but it is thought that the presence of fine TiC precipitated in the steel is effective.

In addition, since Ti fixes C as TiC, it has the effect of preventing the generation of bubbles during firing, and also improves formability.
Ti-added steel is preferable because stretch flangeability and bendability are improved.

In this regard, 0.02-0.10% C and 0.02-0.10% C.
Ti is added to molten steel containing 0.05 to 0.40%, the steel ingot is cooled at 50°C/sec or more after hot pressing, and then the relationship between the amount of fine precipitates and the Ti content is determined. The results were as shown in Figure 1.

Moreover, when the relationship between the tensile strength and the Ti content at this time was determined, it was as shown in FIG.

As shown in FIG. 1, as the amount of C increases, the amount of precipitates effective for preventing skipping increases, but when Ti<0.05%, the amount of precipitates is small, so this value was set as the lower limit.

Furthermore, as the Ti content increases, the strength also increases;
It can be seen that when i is 0.30% or more, the tensile strength reaches a saturated state and there is no need to add any more.

(See Figure 2). Furthermore, if the amount of Ti is too large, the surface quality of the steel sheet will deteriorate, and bubbles, pristle, etc. will be likely to occur during enamel firing. Therefore, the upper limit of Ti was limited to 0.30%.

In addition, when adding Ti as described above, it is preferable to add Ti after adding aluminum or silicon as a deoxidizing agent, since Ti can be used more effectively.

In addition, in the steel ingot having the above composition, in addition to C, Mn, and Ti, Nb, V, Mo, Si, Cu, N1, etc. can be added singly or in combination within a total amount of 1% or less. In this case, the strength can be increased, and the above-mentioned excellent enameling properties are not impaired in any way.

Furthermore, in order to improve formation, REM, Zr, Ca, etc. can be added, and in this case, the enameling property is not inhibited, so it is possible to add these elements as necessary. is preferred.

Next, the steel material having the composition as described above is hot-rolled, then cooled at a cooling rate of 50° C./sec or more, and wound at 500 to 650° C. to produce a hot-rolled steel sheet.

That is, even if the steel material has the above composition, if the steel sheet is slowly cooled and wound up after hot rolling, the strength will deteriorate and the stiffness resistance will be impaired.

On the other hand, when hot rolling is cooled at a rate of 50°C/second or higher and rolled at 500 to 650°C, TiC precipitates in a fine and uniformly dispersed manner, resulting in high strength and stumbling resistance. .

As described above, in the present invention, a steel material melted to the above chemical composition is hot rolled at a finishing temperature of 800 to 900°C, and after the rolling is finished, it is cooled at a rate of 50°C/second or more, and then heated to 500°C. A steel plate is produced by winding at ~650°C.

Moreover, the steel material as a starting material can be manufactured by either a normal ingot-forming method or a continuous casting method.

Next, examples will be described.

Example 1 Steel ingots (sample Nos. 1 to 6) having compositions as shown in Table 1 were melted, and these six types of steel ingots were heated to a hot rolling finish temperature of 850°C,
Hot rolling was carried out at a cooling rate of 50° C./sec or higher and a winding temperature of 550° C. to give a plate thickness of 4 mm.

Thereafter, pickling and 1% temper rolling were performed to obtain a product.

The tensile strength of these hot rolled sheets is as shown in Table 1.

Next, after shot blasting these steel plates for ≠100, high-temperature firing frits are applied to both sides and 820
Firing was performed for 8 minutes at ℃.

The adhesion was good in all cases, and the sample after firing was
It was kept in a constant temperature bath at 0° C. for 12 hours, and after cooling, the enamel surface was observed.

The results are shown in Table 1, and sample No. without Ti addition. In contrast to sample No. 6, a large number of jumps occurred on the entire surface. Nos. 1 to 5 had no flaking, and no bubbles or blisters were observed, indicating that they had excellent enameling properties.

In addition, in Table 1, the case where no tripping occurs is indicated by ○.
The cases where a large number of skips occurred are shown with an X mark.

Example 2 Sample 45 in Table 1 was hot-rolled at a finishing temperature of 850°C, a cooling rate of 3 stages: 10, 30, and 60°C/sec, and wound at a winding temperature of 550°C to obtain a sheet with a thickness of 4 mm. A hot-rolled sheet was made.

These three types of hot-rolled sheets were subjected to a tensile test and enamel fired in the same manner as in Example 1. After that, they were kept in a constant temperature bath at 160°C for 12 hours and then cooled, and then the enamel surface was Observed.

The results are shown in Table 2.

As is clear from Table 2, the cooling rate is 10℃/sec and 30℃
In the case of 50° C./second, occurrence of skipping was observed on the entire surface, and the tensile strength was lower than that of Example 1 at 50° C./second.

On the other hand, the sample cooled at 60° C./second did not have any blockage, and its tensile strength was slightly higher than that of Example 1.

As explained in detail above, in the method of the present invention, C0.02 to 0.10% and Mn 0.05 to 0.4% by weight.
A steel material containing 0% Ti and 0.05 to 0.30% Ti with the remainder substantially consisting of Fe is hot rolled, and after the hot rolling is finished, it is cooled at a rate of 50°C/second or more to 500°C to 650°C.
The steel is rolled up to produce hot-rolled steel sheets.

Therefore, this hot-rolled steel sheet has high tensile strength and excellent enameling properties, and can be enameled on both sides.Also, a steel sheet enameled on both sides has excellent corrosion resistance even though it is a hot-rolled steel sheet, and is suitable for use in pressure vessels. It can be used for chemical industry equipment, etc. Furthermore, since the plate thickness can be reduced, weight reduction of pressure vessels, etc. can also be achieved, and workability can be improved.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the Ti and C contents and the area ratio of precipitates in the method of the present invention, and FIG. 2 is a graph showing the relationship between the Ti content and tensile strength in the method of the present invention.

Claims (1)

[Claims] 1 C0.02-0.10%, Mn0.05-0.40
% and 0.05 to 0.30% of Ti, with the remainder substantially consisting of Fe, and after the hot rolling is finished, the steel material is cooled at 50°C/sec or more and wound at 500 to 650°C. A method for producing hot-rolled steel sheets with excellent enameling properties.