JPS623223B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-strength hot-rolled steel sheet for double-sided enameling, which can be enameled on both sides without causing nail-skipping defects. Currently, steel plates for enameling with excellent enameling properties are manufactured and marketed, but all of them are cold-rolled steel plates, and due to constraints in the manufacturing process, the thickness that can be manufactured is approximately 0.5 to 2.0 mm. is limited to. For this reason, 2.0 mm is used as the base plate for enamel.
If a greater thickness is required, hot-rolled steel plates are used. For example, in the field of enameling for chemical industry containers, large airtight silos, water tanks, hot water boilers, etc., steel plates are required to have a certain strength, so the plate thickness is
A thick steel plate of 2.0 mm or more is required, and hot-rolled steel plate is used. However, conventional hot-rolled steel sheets have the disadvantage that they tend to have nail skipping defects, which is one of the enamel surface defects. Here, the nail skipping defect is a phenomenon in which hydrogen that accumulates locally at the boundary between the enamel layer and the steel plate after enamel processing forms a high-pressure atmosphere and explodes the enamel layer, making it almost impossible to repair. For some reason, this is one of the fatal flaws in enamel products. Therefore, in the field of enameling, where hot-rolled steel sheets with a thickness of 2.0 mm or more have to be used, enameling is performed on only one side, and hydrogen escapes from the back side to prevent the occurrence of nail skipping defects. but,
It is necessary to take measures to prevent corrosion on the back side, and the current situation is to rely on anti-corrosion methods other than enamel, such as painting. This increases the product cost and may also cause problems in terms of anti-corrosion effect, putting it at a disadvantage in competition with other materials. Furthermore, regarding the strength of steel sheets, due to the scale of the product to which they are applied, strength problems may become an obstacle with normal strength hot rolled steel sheets, and in the future high strength hot rolled steel sheets with a tensile strength of 40 kg/mm2 ^or higher There is a tendency for it to be used more and more. Therefore, steel sheets for enameling have been known that improve the workability of the steel sheet, improve the enameled appearance, and reduce firing distortion by adding an appropriate amount of Ti to ordinary steel and fixing the C in the steel as TiC. However, the present inventors have previously developed a high-strength heat-rolled steel sheet for double-sided enameling, which is characterized by adding appropriate amounts of Ti and S, to provide even better nail-skipping resistance and to create a high-strength hot-rolled steel sheet. We proposed rolled steel plate. However, in the proposed steel sheet, since S is added at a relatively high level of 0.02 to 0.05%, S segregation is likely to occur in the normal ingot forming method, and therefore, the position of the steel sheet after hot rolling causes S segregation.
It was found that the amount was less than the required lower limit, and the nail-skipping resistance of this part became unstable. Therefore, the present inventors conducted various studies on chemical composition systems that can stably impart excellent nail-skipping resistance to the entire steel plate even by ordinary ingot-forming methods, and found that Ti and S, as well as It has been discovered that by adding an appropriate amount of rare earth elements, a steel plate that meets the above objectives can be obtained. Based on this knowledge, the present invention has developed a high-strength hot rolled steel sheet for double-sided enameling that can be enameled on both sides without causing nail skipping defects even though it is a hot-rolled steel sheet, and has a tensile strength of 40 kg/mm ² or more. It provides steel plates. That is, in the present invention, C 0.03 to 0.10%, Si 0.1% or more 1.0%
Below, Mn0.3~1.5%, Ti over 0.20% and 0.30% or less,
High-strength hot rolling for double-sided enameling characterized by containing 0.01 to 0.04% S, 0.1% or less Al, and 0.01 to 0.10% rare earth elements (hereinafter referred to as Rem), with the balance consisting of iron and unavoidable impurities. The gist is steel plates. The present invention will be explained in detail below. The reasons for adding elements and limiting the range in the present invention are as follows. C is necessary to ensure the required strength, and should be at least 0.03% so that it can be melted using normal steel manufacturing methods. 0.10% as a range not to
is the limit. Si needs to be added because it has a deoxidizing effect and a reinforcing effect, but in the present invention, it is necessary to exceed 0.1% in order to stabilize the effect of Ti addition, which will be described later. Since it deteriorates the toughness and toughness, the content is preferably 1% or less. Mn is important for ensuring the specified strength,
Furthermore, in order to prevent red heat embrittlement caused by the addition of S, which will be described later, it is necessary to add at least 0.3% or more. The upper limit of Mn is 1.5% as long as it does not harm firing strain, weldability, and toughness. As mentioned above, Ti improves the appearance of the enameled finish,
It is effective in reducing firing distortion, but in the present invention, it is important for improving the nail-skipping resistance due to its combined effect with S and Rem, which will be described later. In the range of S and Rem described later, if Ti is less than 0.20%, the effect of preventing nail skipping defects is insufficient, and if Ti is less than 0.30%
Exceeding this is not preferable because the effect of preventing nail skipping defects is saturated, the surface properties and toughness of the steel sheet deteriorate, and the strength of the steel sheet becomes unstable. As mentioned above, S is an essential element for improving the nail chip resistance due to its combined effect with Ti and Rem. It is necessary to add 0.01% or more of S in a Ti range of more than 0.20% and 0.30% or less and Rem as described below, and if it is less than this, a practical effect of preventing nail skipping defects cannot be expected. The upper limit of 0.04% is set to prevent red heat brittleness. Rem is a particularly important element in the present invention, as it has been confirmed that it acts in combination with Ti and S to contribute to improving the nail-skipping resistance.
It is necessary to add Rem in order to ensure stable nail-skipping resistance against fluctuations in . Ti over 0.20%
0.30% or less, in the range of S0.01~0.040%,
Regarding Rem, it is necessary to add 0.01% or more.
If it is less than this, the nail-skipping resistance becomes unstable. upper limit
The limit is set at 0.10% because if it exceeds this, the effect will be saturated and the cost will increase. Note that Rem here is a general term for various elements ranging from La with atomic number 57 to Lu with atomic number 71, represented by La and Ce. Al is added for deoxidation, but in the present invention, in order to stabilize the effect of adding Ti and Rem, it must be added before adding these elements, and the amount added depends on the appearance of the enameled finish, 0.1% as a range that does not harm the surface properties of the steel plate
It is necessary to do the following. The configuration of the present invention has been described above, and the effects of the present invention will be explained in more detail below using Examples. Example Steel having the chemical composition shown in the attached table is melted by a normal steel manufacturing method and hot rolled at a hot rolling finishing temperature of 850 to 880°C and a hot rolling winding temperature of 600 to 630°C. A rolled steel plate was manufactured. A to D shown in the charge column of the same table
is the steel plate of the present invention, E is the Ti amount, F is the S amount,
And G is a steel plate whose Rem amount is less than the range of the present invention. H is normal SS41 material. A 150mm x 200mm test piece is cut out from these steel plates, shot blasted to descale it, and then sprayed with a commercially available regular enamel underglaze flip to make the enamel thickness 170 to 200μ on one side after firing. Both sides are glazed so that the temperature inside the furnace
840℃, steam in the furnace

[Table] 10 to 11 in an electric furnace set at Dew point 30℃
Bake for a minute. After firing, the test pieces were allowed to cool naturally, and 48 hours after firing, they were observed for the occurrence of nail skipping defects. The results are shown in the same table, and while steel plates E to G, which are outside the scope of the present invention, and H, which is a normal SS41 material, are found to have skipping defects, steel plates A to D of the present invention No nail skipping defects occurred at all. Regarding strength, the steel plate of the present invention has a sufficient tensile strength of 40 kg/mm ² or more. As detailed above, by using the steel plate of the present invention, it is possible to secure a tensile strength of 40 kg/mm ² or more, and it is possible to enamel both sides without causing nail skipping defects, thereby improving product quality and reducing costs. There are some extremely notable contributions to the enamel processing industry, such as the reduction of CO2 emissions and the expansion of product application fields.

Claims (1)

[Claims] 1 C0.03~0.10%, Si over 0.1% and 1.0% or less, Mn0.3
~1.5%, Ti over 0.20% 0.30% or less, S0.01~0.04
%, Al 0.1% or less, and rare earth elements 0.01 to 0.10
%, with the remainder consisting of iron and unavoidable impurities.