JPH049859B2 - - Google Patents

Description

[Detailed description of the invention]

``Object of the Invention'' The present invention relates to a thin hot-rolled steel sheet for enamel that has excellent resistance to nail chipping and high strength after firing, and a method for producing the same. It is an object of the present invention to provide a heat-treated plate for enamel which has excellent properties and has little strength loss due to enamel firing and is suitable for being processed and used as a thin plate material, and also to obtain a preferable manufacturing method thereof. Industrial application: Excellent nail chipping resistance and high strength after firing.
Furthermore, a heat-treated plate for enamel suitable for processing and use as a thin plate material and a method for manufacturing the same. Conventional technology There are cold-rolled steel sheets and hot-rolled steel sheets as thin steel sheets used for enamel products, but large-sized enamel products such as enamel silos, hot water boilers, and water storage tanks require strength from the steel sheets. A hot rolled steel stomach is suitable. However, conventional hot-rolled steel sheets have the disadvantage that the enamel layer peels off in a half-moon shape after enamel firing, which tends to cause "nail skipping."
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, we improved the nail-flying resistance of this hot-rolled steel sheet.
The development of hot-rolled steel sheets for double-sided enameling is progressing, and Ti
Hot-rolled steel sheets for enamel added with
1170, Special Publication 58-3666, Special Publication 59-6894, 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. There are methods to improve this drawback, such as increasing the content of C, Si, Mn, etc. (Japanese Patent Publication No. 58-36666). These methods increase the strength of the hot-rolled original sheet before enamel firing. This is to ensure the strength that will be achieved later. Another possible method is to partially precipitate TiC during enamel firing to suppress the growth of ferrite grains during firing to avoid a decrease in strength. In addition, in the present applicant, in Japanese Patent Publication No. 49-79311 as glass lining steel, C: 0.05 to 0.20
%, Si: 0.05-0.03%, Mn: 0.20-1.50%, Ti/
C: 8.5 or less, N: 0.0060-0.0150%, sol.Al:
We propose a steel containing 0.030% or less of iron, with the remainder consisting of iron and unavoidable impurities. Problems to be Solved by the Invention The conventional techniques described above still have their own problems. That is, the method of increasing the content of C, Si, Mn, etc. is not a preferable method because it involves difficulties in forming the material. Furthermore, even if TiC is partially precipitated during enamel firing and suppresses ferrite grain growth during firing, it can withstand firing at 850°C for about 5 minutes.
Furthermore, if the firing is performed at a high temperature for a long time, or if the number of firings is increased, a decrease in strength cannot be avoided. In the above-mentioned Japanese Patent Application Publication No. 49-79311,
Intended for special cases where glass lining is performed several times, for thick steel plates with large thickness, and for thin steel plates with small thickness (6 mm or less), and when this thin steel plate is processed in various ways. cannot be adopted. In particular, when the material is fired many times, its strength inevitably decreases, making it impossible to obtain sufficient strength. "Structure of the invention" Means for solving problem C: 0.005 wt% to less than 0.05 wt% Mn: More than 1.6 wt% 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) S
A hot-rolled steel plate for enamel having high strength after firing and excellent resistance to nail chipping, which is characterized by the following relationship: C: 0.005wt% to less than 0.05wt%, Mn: 1.6wt% Contains N: 0.003 to 0.015 wt%, Ti: 0.05 to 0.2 wt%, the remainder is Fe and unavoidable impurity elements, and between Ti, C, N and S, Ti ^* =Ti-(48/12)C-(48/14)N-(48/32)S
Hot-rolled steel with the relationship <O at 500-700℃
It is characterized by the presence of Ti precipitates in the hot-rolled sheet, which is rolled at a temperature of This is a method for producing a hot-rolled steel plate for enamel that has high strength and excellent resistance to chipping. Effect Good nail-fly resistance can be obtained by setting C to 0.005wt% or more, N to 0.003wt% or more, and Ti to 0.05wt% or more. Hardening of the hot rolled original sheet is avoided by setting C to less than 0.05wt% and Mn to 3.0wt% or less. Furthermore, by setting Mn in excess of 1.5 wt%, the formation of a hardened structure during cooling after firing is optimized, and strength after repeated firing is effectively obtained. In addition, by setting the N content to 0.015wt% or less, nail chipping resistance can be achieved without particularly increasing the amount of Ti added, and in combination with setting the C content to less than 0.05 as described above, it is possible to achieve thinness. Ensure workability as a plate material. When Ti is 0.2wt% or less, a preferable hardened structure can be obtained as described above. During manufacturing, the coiling temperature is set at 500℃ or higher to avoid deterioration in workability due to the increase in strength of the hot-rolled original sheet, and by coiling at 700℃ or lower, the coarsening of the ferrite structure is prevented. Eliminates strength loss after enameling. EXAMPLE To further explain the present invention as described above, the present invention provides a method for forming a steel plate after enamel firing.
It has high strength even after enamel firing due to the coexistence of Ti (C, N) precipitates and hardened structure.
Moreover, it is based on the new knowledge that it has excellent nail chipping resistance. Conventional Ti-added hot-rolled steel sheets for enameling use precipitated Ti (C, N) in the steel to ensure strength. By enamel firing
The Ti (C, N) particles grow and the strengthening ability is lost, and the ferrite grains become coarser, resulting in a decrease in strength. However, Ti(C,
Since N) acts as a trap for hydrogen in the steel, which causes nail skipping, the nail skipping 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 Ti(C,N)
is formed during hot rolling. The reason for limiting the composition of the product according to the present invention using wt% (hereinafter simply referred to as %) is as follows. C: 0.005 to less than 0.05% If C is less than 0.005%, the amount of TiC precipitated will be small, and the hydrogen trap sites in the steel will be reduced, resulting in poor nail chipping resistance. Furthermore, if it is less than 0.05%, the material of the hot-rolled original sheet becomes hard and difficult to process into a thin sheet material, so this is set as the upper limit. Mn: over 1.5% up to 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%, even if C is less than 0.05% as mentioned above, the material of the hot rolled sheet will become hard and difficult to process. Therefore, this is the upper limit. N: 0.003 to 0.015% If N is less than 0.003%, the amount of TiN precipitated will be small and the nail chipping resistance will be poor. 0.003% or more is required to obtain good nail fly resistance. However, if the amount of N is large, it is necessary to increase the amount of Ti added.
Due to the high cost, the upper limit was set at 0.015%. Ti: 0.05~0.2%. Ti is an indispensable element for improving nail chip resistance, and if it is less than 0.05%, sufficient nail chip resistance cannot be obtained, so it is set at 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%. Note that between Ti, C, N, and S, Ti ^* = Ti − (48/12) C − (48/14) N − (48/32) S
It is necessary that the relationship <O 2 be satisfied; 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 winding temperature, along with the above chemical components, influences the strength of the hot-rolled steel sheet.
If the coiling temperature exceeds 700℃, the ferrite structure may become coarse and the strength after enameling may decrease, so the upper limit is set at 700℃. It is preferable to set the lower limit to 500°C because the strength increases and the workability is impaired. 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.

【table】

[Table] Each steel piece in Table 1 as described above has a finishing temperature of
After hot rolling at 900°C to a thickness of 4.5 mm, it was coiled at 580°C, cooled, and then pickled to remove scale, resulting in a hot rolled steel plate. 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.

【table】

【table】

[Table] * Invention steel range
YP, TS (Kgf/ ^mm2 )
YPEl, El(%)
Furthermore, the amount of occurrence of nail skipping for the above-mentioned products No. 0 to 6 is as shown in Table 3 below, but this state of no occurrence of nail skipping is also the same for products No. 7 to 15. .

【table】

[Table] For the items in Table 3, the only pre-glazing treatment was degreasing, both sides were coated with a commercially available glaze, and after drying, they were fired in an atmosphere with a dew point of 30°C (100mm x 100mm x 5 pieces)
It is expressed as the number of nail skipping occurrences per unit area. That is, Nos. 1 to 6 and 8 in these tables,
11 and 14 are steel plates according to the present invention, and are shown in Table 2 above.
As is clear from the above, no significant decrease in strength was observed even if the number of firings was increased. In addition, despite the firing conditions where nail flying is relatively easy to occur, it has excellent nail flying resistance. No. 0 is a comparison steel, but it differs from the invention steels of Nos. 1 to 6 in that the Mn content is 0.27%, and Ti ^* = Ti - (48/12) C - (48/14 )N-(48/32)S
= 0.019>0. In other words, this steel has a high Ti content, so it has excellent nail chipping resistance, but because the Mn content is low and the Ti content is large, the C in the steel combines with the Ti, so a hardened structure is formed. Not done. As a result, the strength is significantly reduced by firing. In addition, No. 7, 10, 12, and 13 have low Mn, and No. 9 has high Mn. Furthermore, Nos. 12 and 13 have high C, and No. 15 has N.
This is the case when Ti is high. Comparison steel No. 7, 10,
In case of No. 12, the strength decreases due to firing, which is the same as in No. 0, and in No. 15, which has high N and Ti content, it is also insufficient in terms of strength. Also with No.9
12 and 13 have low elongation. The above-mentioned invention steels (No. 1 to 6) and comparative steel (No.
A graph showing changes in mechanical test values after firing for the six types of steels mentioned above for 0) is shown in the attached drawing, and this figure shows the difference in strength between the steel according to the present invention and the comparison steel. The difference is clearly seen in ``Effects of the Invention'' As explained above, the invention according to the present invention not only has excellent nail-flying resistance, but also has a small decrease in strength due to enamel firing, and is also suitable for use as a thin sheet material. This invention is capable of accurately providing a hot-rolled steel plate for enameling with excellent workability, and also provides a preferable manufacturing method thereof, and is industrially highly effective.

[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.

Claims (1)

[Claims] 1 Contains C: 0.005wt% to less than 0.05wt%, Mn: more than 1.5wt% to 3.0wt%, N: 0.003 to 0.015wt%, Ti: 0.05 to 0.2wt%, 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) S
A hot-rolled steel sheet for enameling, which is characterized by the following relationship: <O, and which has excellent nail-flying resistance and high strength after firing. 2 C: 0.005wt% to less than 0.05wt%. Contains Mn: more than 1.5 to 3.0wt%, N: 0.003 to 0.015wt%, Ti: 0.05 to 0.2wt%, the balance consists of Fe and unavoidable impurity elements, and between Ti, C, N and S. , Ti ^* = Ti − (48/12) C − (48/14) N − (48/32) S
＜O The steel with the following relationship is hot-rolled at 500-700℃.
It is characterized by the presence of Ti precipitates in the hot-rolled sheet by winding at a temperature of A method for producing a thin hot-rolled steel sheet for enamel that has excellent properties and high strength after firing.