JPH02305926A - Production of hot rolled steel sheet for enamel - Google Patents

Abstract

PURPOSE:To easily and inexpensively produce the hot rolled steel sheet which is excellent in enamel property and is free from degradation in strength after enamel firing by continuously casting a steel consisting of C, Mn, Al, N, B, and Fe and subjecting the ingot to a specific hot rolling and coiling. CONSTITUTION:The steel consisting of 0.010 to 0.080% C, 0.10 to 0.80% Mn, 0.03 to 0.08% Al, 0.050 to 0.0150% N, and >=0.0025% B as N-14/11.B, and further 0.010 to 0.050% Cu at need and the balance Fe and unavoidable impurities is continuously cast. The resulted ingot is hot rolled as it is or after the ingot is heated by auxiliary heating means, such as gas edge heaters at need so as to prevent the surface temp. from falling to <=800 deg.C for >=20 minutes. This hot rolled sheet is coiled at about >=600 deg.C, more preferably 650 to 700 deg.C. The hot rolled steel sheet for enamel which has excellent fishscale resistance and is free from the degradation in the strength after the enamel firing while saving energy is obtd. in this way by executing a direct rolling without adding costly alloy components, such as Ti at a high rate.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a hot-rolled steel sheet for enameling, and in particular, a method for manufacturing a hot-rolled steel sheet for enameling that has excellent enameling properties and does not reduce strength due to enameling firing. It is related to.

(Prior Art) Several hot-rolled steel sheets with excellent enamel properties have been proposed so far.1 However, in applications where they are press-formed and subjected to enamel firing, such as in water heaters, for example, in addition to the enamel properties, the strength due to enamel calcination ( It is required that no significant decrease in yield point) occurs. Therefore, as a manufacturing method for hot-rolled steel sheets for enamel that satisfy these characteristics, for example,
No. 1-40285 discloses a method of adding a very large amount of Ti to ordinary low carbon steel and winding the steel at a low temperature.

(Problem to be Solved by the Invention) In order to reduce the decrease in strength after enamel firing, it is necessary to avoid coarsening of carbonitrides in the hot-rolled sheet and allow fine precipitation. On the other hand, in order to ensure porosity on a low-temperature coiling basis, it is also necessary to generate a large amount of precipitates and inclusions, and from this point of view, it is not necessary to add a large amount of Ti as in the above patent publication. This results in a significant increase in manufacturing costs and also causes the problem of surface defects.

(Means for Solving the Problems) The object of the present invention is to easily and inexpensively obtain a hot-rolled steel sheet that has excellent enameling properties and does not lose strength after enameling, without adding large amounts of expensive elements. do. And the gist is C: 0.010-0.080%, Mn:
0.10-0.80%, ^9. :0.03~0.08%
, N: 0.0050-0.0150%, B:
Continuously casting steel containing N-"-, 0.0025% or more as B, and further containing Cu:o, oio~o, oso% if necessary, the remainder consisting of iron and inevitable impurities,
It is characterized in that the surface temperature of the slab is not lowered for more than 20 minutes at 800°C or lower, hot rolled as it is or after auxiliary heating, and then coiled at 600°C or higher.

The present invention will be explained in detail below.

C is required at least 0.010% to obtain strength, but
If it is too large, workability will be reduced and hollow defects will be more likely to occur, so the content should be 0.080% or less.

Mn is set to 0.10% or more to prevent hot embrittlement due to S. However, if it is too large, the workability will deteriorate, so the content should be 0.80% or less.

An content of 0.03% or more is required for deoxidation and to prevent a decrease in strength after enamel firing.

On the other hand, if it is contained in a large amount, the effect of suppressing the decrease in strength after firing will be reduced, so the content should be 0.08% or less.

N is necessary to prevent chipping and to eliminate a decrease in strength after enamel firing, and should be 0.0050% or more. On the other hand, if the amount is too high, the above effects will be saturated, so 0.0
150% or less. N content of around 0.0100 to 0.0120% is preferable.

B is added to prevent skipping, and in relation to the N content, B is added to prevent strength loss after enamel firing.
--・B ≧Q, 0Q25% must be satisfied.

In order to further improve the enamel properties, it is effective to include Cu, but if it is less than 0.010%, it is difficult to obtain the effect of improving the enamel adhesion, and if it is too much, it will become saturated.
．． 050% or less.

Steel with the above composition was continuously cast, and the surface temperature of the slab was raised to 8.
Hot rolling is carried out at 00° C. or below without lowering the temperature for 20 minutes or more or with supplementary heating. This is because if the surface temperature of the slab drops below 800°C for more than 20 minutes, it becomes difficult to obtain good sagging resistance when it is rolled up at a low temperature during hot rolling, and the effect of suppressing strength loss after enamel firing also decreases. It is from. It is presumed that the effect of the so-called direct rolling method of the present invention on improving the sagging resistance is due to the fact that sulfide-containing precipitates are extremely finely dispersed and precipitated, and these act effectively as hydrogen storage sites. It is presumed that the effect of eliminating strength loss after firing is also deeply related to the fine precipitation of sulfides, but the details are unknown.

After continuous casting, the slab can be heated as is, or if necessary, it can be auxiliary heated by using a gas edge heater or hot rolling reheating furnace until the surface temperature reaches 800℃ or less.
It is hot-rolled without falling for more than a minute. There is no need to specify the finishing temperature of hot rolling, and it is usually 850~850°C.
900°C is sufficient. In the present invention, the winding temperature after finishing is set at 500°C.
℃ or more, because if the temperature is less than 600°C, the strength will be significantly reduced after enamel firing.

On the other hand, if the temperature is too high, the strength after enamel firing will drop significantly and the pickling efficiency will also drop, so the temperature should be set to 750°C or less. 6
Winding at a temperature of about 50 to 700°C is preferred.

(Example) Steels with the components shown in Table 1 were melted and hot-rolled using a conventional reheat rolling method (reheating temperature: 1150° C.) and a direct rolling method. The finishing temperature was 890°C, the plate thickness was 2.3 mm, and the winding temperature was varied. After pickling, cut out a tensile test piece, add 20% pre-strain equivalent to press processing, and then heat at 870°C x 7
Enamel firing was performed for several minutes, and the amount of change in yield point from the base metal was investigated. In addition, a sample of 100 mm x 100 mm was cut out, enameled, and the occurrence of skipping was investigated.

Table 2 shows the manufacturing conditions and investigation results. As is clear from Table 2, by directly rolling the component steel of the present invention, excellent stubble resistance can be obtained even at low temperature coiling, and the strength after enamel firing is considerably higher than that of the base material. On the other hand, even if the slab is directly rolled, the surface of the slab has been kept at a low temperature for a long time or the composition is outside the range, and the yield point is lowered by enamel firing.

(Effects of the invention) According to the method of the present invention, by performing direct rolling without adding a large amount of expensive elements such as Ti,
It is possible to produce hot-rolled steel sheets for enameling that have excellent tear resistance even when rolled at low temperatures and whose strength does not decrease (on the contrary, increases) after enamel firing. Furthermore, it also has the additional effect of energy saving due to direct delivery, and technology The effect is significant.

4 others

Claims (1)

[Claims] 1 C: 0.010-0.080%, Mn: 0.10-0.80%, Al: 0.03-0.08%, N: 0.0050-0.0150% , B:N-(14/11)・B is 0.0025% or more, the balance is iron and unavoidable impurities, and the surface temperature of the slab is lowered to 800℃ or less for 20 minutes or more. Method 2 for producing a hot rolled steel sheet for enamel, characterized by hot rolling as it is or after auxiliary heating, and winding at 500°C or higher C: 0.010 to 0.080%, Mn: 0 .10 to 0.80%, Al: 0.03 to 0.08%, N: 0.0050 to 0.0150%, B: 0.0025% or more as N-(14/11)・B, Cu: Steel consisting of 0.010 to 0.050%, the balance being iron and unavoidable impurities is continuously cast, and the surface temperature of the slab is kept at 800℃ or less without dropping for more than 20 minutes, either as it is or with auxiliary heating. A method for producing a hot-rolled steel sheet for enameling, which is then hot-rolled and coiled at 600°C or higher.