JPS62151546A - Hot-rolled steel plate for vitreous enameling having high strength after baking and excellent in fishscale resistance and its production - Google Patents

Abstract

PURPOSE:To obtain the titled steel plate having high strength after baking and excellent in fishscale resistance, by incorporating specific amounts of C, Mn, N, and Ti to a hot-rolled steel for vitreous enameling and by allowing specific relations to hold among Ti, C, N, and S included in inevitable impurities. CONSTITUTION:The steel has a composition consisting of, by weight, 0.005-0.05% C, 1.5-3% Mn, 0.003-0.015% N, 0.05-0.2% Ti, and the balance Fe with inevitable impurity elements. Further, relations in a inequality hold among Ti, C, N, and an inevitable impurity element. This steel is hot-rolled, wound up at 500-700 deg.C, and allowed to form a hardened structure at the time of cooling, so that hot-rolled steel plate for vitreous enameling can be obtained.

Description

Detailed Description of the Invention "Object of the Invention" The present invention relates to a heat-treated plate for enamel that has high strength after firing and excellent resistance to nail chipping, and a method for manufacturing the same, and relates to a heat-treated plate for enamel that has high strength after firing and excellent resistance to chipping, and a method for producing the same. Another object of the present invention is to provide a heat-treated piece of enamel that exhibits little strength loss due to enamel firing and has improved nail chipping resistance, and to obtain a preferable method for producing the same.

Industrial applications: A heat-treated enamel plate with excellent resistance to chipping and its manufacturing method.

Conventional technology There are cold-rolled steel sheets and hot-rolled steel sheets as thin steel sheets used for enameled products, but large-sized enameled products such as enameled silos, hot water boilers, and water storage tanks are
Since the plate must have strength, hot rolled steel plate is suitable. However, conventional hot-rolled G-sheets have the disadvantage that "nail skipping" is apt to occur, in which a single layer of enamel peels off in a half-moon shape after enamel firing. For this reason, hot-rolled steel sheets were used only as single-sided enameled materials, and the occurrence of nail skipping was suppressed by letting the hydrogen in the steel, which is the cause of nail skipping, escape from the non-enameled surface.

Therefore, the development of hot-rolled steel sheets for double-sided enameling, which improved the chipping resistance of this hot-rolled steel sheet, was progressed, and hot-rolled steel sheets for enameling with added Ti came to be used (Japanese Patent Laid-Open Publication No. 1983-1999-1). 169727, Special Publication Showa 58-1170. Special Publication Showa 5
B-3666, Special Publication Showa 5!116894, etc.). However, Ti-added hot-rolled steel sheets have the disadvantage that their strength is significantly reduced by enameling, making them unsuitable as enameled materials that require strength. For example, C,
Method of increasing the content of Si, Mn, etc.
36666), and these methods attempt to ensure the strength after firing by increasing the strength of the hot-rolled original sheet before enamel firing.

Another possible method is to partially precipitate TiC during enamel firing to suppress ferrite grain growth during firing to avoid a decrease in strength.

Problems to be Solved by the Invention The conventional techniques described above still have their own problems. In other words, a method in which the content of C, SilMn, etc. is increased is not a preferable method because the moldability of the material is difficult.

In addition, a method in which TiC is partially precipitated during enamel firing and suppresses ferrite grain growth during firing has a temperature of 850°C.
Even if it can withstand firing for about 5 minutes, if it is fired at a higher temperature for a longer time, or if the number of firings is increased, a decrease in strength cannot be avoided.

"Structure of the invention" Means for solving the problem C: 0.005 to 0.05 W t%, Mn: 1
．． 5-3.0wt%, N: 0. OO3~0.015wt%, Ti:o,
05 to 0.2 wt%, the remainder consists of Fe and unavoidable impurity elements, and the following relationship is established between Ti, C, N and S. It has high strength after firing. A hot-rolled steel plate for enamel having excellent nail-flying resistance, and C: 0. QO5-0.05 wt%, Mn: 1.5-3.0 wt%, N: 0.003
~0.015wt%, Ti: 0.05~0. 2 wt%, with the remainder consisting of Fe and unavoidable impurity elements, including Ti, C,
, N, and S are hot-rolled and coiled at a temperature of 500 to 706°C, and Ti precipitates are present in the hot-rolled sheet. This is a method for producing a hot-rolled steel sheet for enameling, which has high strength after firing and has good nail chipping resistance, by forming a hardened structure during cooling after firing, thereby preventing a decrease in strength after firing.

The action C is 0.005 wt% or more, and the N is 0.003W.
[% or more, and by setting Ti to 0.05 wL% or more, good nail-flying resistance can be obtained.

C is o, 05 W t% or less, and Mn is 3. O
Hardening of the hot-rolled original sheet is avoided by setting it to less than wt%. Furthermore, Mn was set to 1,5 wt% or more to optimize the formation of hardened structure during cooling after firing, and Nl was set to 0.015 wt% or more.
By setting the amount of wj% or less, nail-flying resistance can be achieved without increasing the amount of Ti added, and Ti is 0. 2w
A preferable hardened structure can be obtained at t% or less.

By setting the coiling temperature to 500°C or higher during manufacturing, deterioration in workability due to the increase in strength of the hot-rolled original sheet can be avoided, and
By winding at a temperature of 0° C. or lower, the coarsening of the ferrite structure is prevented, thereby eliminating the decrease in strength due to enamel annealing.

EXAMPLE To further explain the present invention as described above, the present invention has high strength even after enameling by making Ti (C, N) precipitates and quenched structure coexist in the steel sheet after enameling. This is based on the new knowledge that it has excellent resistance to chipping, and that the conventional hot-rolled steel sheet for enameling with Ti added has no T, i (C) precipitated in the steel.
, N) to ensure strength, but due to enamel firing, Ti (C, N) particles grow and the strengthening ability is lost.
Furthermore, as the ferrite grains become coarser, the strength decreases. However, since Ti (C, N) in the steel acts as a trap site for hydrogen in the steel, which causes nail chipping, the nail chipping resistance is improved. In addition, a quenched structure is used to ensure strength after enamel firing. This hardened structure is formed during cooling after enamel firing, and 1'i (C, N) is formed during hot rolling.

The reason for limiting the component composition of the product according to the present invention using wt% (hereinafter simply referred to as %) is as follows.

C: 0.005-0.05%.

If C is less than 0.005%, the amount of TiC precipitated will be small and the number of trap sites for hydrogen in the steel will be reduced, resulting in poor nail chipping resistance. Moreover, if it exceeds 0.05%, the material of the hot-rolled original sheet becomes hard and difficult to process, so this is set as the upper limit.

Mn: 1.5-3.0%.

If Mn is less than 1.5%, it will be difficult to form a hardened structure during cooling after firing, and if it exceeds 3.0%, the material of the hot rolled sheet will become hard and difficult to process, so this should be set as the upper limit. It is something to do.

N: 0.003-0.015%.

N is 0. If the OO is less than 3%, the amount of TiN precipitated will be small and the nail chipping resistance will be poor. In order to obtain good nail-flying resistance, 3% or more of O, OO is required. However, if the amount of N is large, it is necessary to increase the amount of Ti added, which increases the cost, so 0.
The upper limit was set at 0.015%.

'l' i: 0.05-0.2%.

Ti is an essential element for improving nail-flying resistance, and 0
．． If it is less than 0.05%, sufficient nail fly resistance cannot be obtained, so it is 0.0%.
．． 05% or more. On the other hand, if the amount of Ti is too large, all of the C will precipitate as TiC, making it difficult to form a hardened structure, so the upper limit was set at 0.2%.

It is necessary that the following relationships hold between Ti and C, N, and S. If this relationship does not hold, a hardened structure will not be formed and the strength will be significantly reduced by firing.

Further, the coiling temperature after hot rolling is preferably 500 to 700°C.

In other words, the hot-rolling coiling temperature, together with the chemical components mentioned above, does not affect the strength of the hot-rolled steel sheet. At coiling temperatures exceeding 700°C, the ferrite structure may become coarser, and the The upper limit is set to 7 as the strength may decrease.
If the coiling temperature is low, the strength of the hot-rolled original sheet will reach an upper limit and the workability will be impaired, so the lower limit is set to 500°C.
It is preferable to set it to °C.

A specific manufacturing example of the product according to the present invention will be described below.

That is, the composition of the test steel used by the present inventors is as shown in Table 1 below.

Each of the steel slabs in Table 1 described above is a hot-rolled steel plate that has been hot-rolled to a thickness of 4.5 mm at a finishing temperature of 900°C, coiled at 580°C, cooled, and then pickled to remove scale. did. The mechanical test values of these hot-rolled steel sheets before firing (original sheet) and after firing six types under different temperature conditions and firing times are as shown in Table 2 below.

Further, the amount of scratches generated by these products is as shown in Table 3 below, and all of them are free of scratches.

Table 3 For the items in Table 3, the pre-glazing treatment was only degreasing, and a commercially available glaze was applied on both sides, and after drying, it was fired in an atmosphere with a dew point of 30°C. It is expressed as the number of nail marks generated per hit.

That is, items 1 to 6 in these tables are steel plates according to the present invention, and as is clear from Table 2 above, no significant decrease in strength is observed even when the number of firings is increased. In addition, it has excellent resistance to nail marks, even though the firing conditions are such that nail marks are relatively likely to occur.

The NaO steel is a comparative steel, but the difference from the steels of the present invention in Nos. 1 to 6 is that M n 14 is 0.27%. In other words, this steel has excellent scratch resistance due to its high Ti content, but because the Mnfi content is low and the Ti content is high, the C in the steel combines with Ti, so a hardened structure is not formed. . As a result, the strength is significantly reduced by firing.

A graph showing changes in mechanical test values after the six types of firing for the above-mentioned invention steels (Nos. 1 to 6) and comparative m (NaO) is shown in the attached drawings.
According to this figure, the difference in strength between the steel according to the present invention and the comparative steel is clearly recognized.

"Effects of the Invention" According to the present invention as described above, it is possible to accurately provide a hot-rolled steel sheet for enameling which has a small decrease in strength due to enameling firing and has excellent scratch resistance, and also provides a preferable manufacturing method thereof. This is an invention that is highly effective in terms of industry.

[Brief explanation of drawings]

The drawing shows the technical content of the present invention, and is a chart summarizing changes in mechanical test values before and after firing for the steel of the present invention and comparative steel. Patent applicant Nippon Kokan Co., Ltd. Inventor Akihiko Nishimoto

Claims (1)

[Claims] 1. C: 0.005 to 0.05 wt%, Mn: 1.5 to 3.0 wt%, N: 0.003 to 0.015 wt%, Ti: 0.05 to 0.2 wt% %, the remainder consists of Fe and unavoidable impurity elements, and between Ti, C, N and S, Ti^*=Ti-
(48/12)C-(48/14)N-(48/32)
A hot-rolled steel sheet for enameling which has high strength after firing and excellent nail-flying resistance, and is characterized by the relationship S<O. 2. Contains C: 0.005 to 0.05 wt%, Mn: 1.5 to 3.0 wt%, N: 0.003 to 0.015 wt%, Ti: 0.05 to 0.2 wt%, and the remainder is composed of Fe and unavoidable impurity elements, and between Ti, C, N and S, Ti^*=Ti-
(48/12)C-(48/14)N-(48/32)
Hot-rolled steel with the relationship S<O is 500-7
After firing, the hot-rolled sheet is rolled at a temperature of 00°C and Ti precipitates are present in the hot-rolled sheet, and furthermore, a hardened structure is formed during cooling after enamel firing to prevent strength loss after firing. A method for producing a hot rolled steel plate for enamel which has high strength and excellent resistance to nail flying.