JPS59190331A - Continuous casting steel plate of extralow carbon and extralow nitrogen for enamel - Google Patents

Abstract

PURPOSE:To provide a titled steel plate which has excellent press formability and is obtd. at a low cost by rolling a continuous casting slab of extralow carbon and extralow nitrogen which is melted in a converter and is subjected to a vacuum decarburization treatment then subjecting the rolled plate to annealing at a specific temp. and further to temper rolling. CONSTITUTION:A continuous casting slab which is produced by melting in a converter and is subjected to a vacuum decarburization treatment and has the component compsn. contg. <=30ppm C, <=30ppm C+N, 300ppm <0<700ppm, and the balance Fe and unavoidable impurities is hot rolled and is then cold-rolled at >=60%, more preferably 75-90% cold rolling draft. The cold-rolled steel plate is subjected to Ni plating at 0.1-2.0g/cm<2> on the surface according to need and is then annealed in a range of recrystallization temp.- Ac3 transformation point and further the steel plate is subjected to temper rolling, by which the inexpensive steel plate for enamel having excellent press formability as well as excellent fishscaling resistance and adhesion to enamel is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultra-low carbon, ultra-low nitrogen continuous casting steel sheet with excellent press formability.

Conventionally, as a steel plate for soldering, a steel plate in which capped steel or rimmed steel is cast into an ingot, hot-rolled and cold-rolled, and then decarburized by an oven coil annealing method has been widely used. The reason why capped steel and the like are used is that the oxygen content in the steel is higher than that of killed steel, so that it is possible to effectively prevent tripping, which is a crawling defect. Floating is a phenomenon in which the hydrogen stored in the steel plate during the formation of the enamel aggregates at the interface between the steel plate and the enamel when the enamel layer solidifies after firing, destroying the tI enamel layer. When the oxygen content in the steel is high, voids are formed around the oxide during cold rolling,
Since hydrogen is transported into these gaps, the amount of hydrogen that aggregates at the porosity interface of the steel plate is reduced, and the occurrence of splatter can be prevented. However, as the conventional method requires blooming rolling and oven coil dulling,
It had the disadvantage that the manufacturing cost was extremely high.

Therefore, in order to reduce the cost of enamel steel plates for press forming, many methods have been proposed for manufacturing enamel plates using continuous casting slabs (hereinafter referred to as continuous casting slabs). For example, the special public Sho 5ti-3 ogog issue and the special public Sho 1&
-11OA! ; A method of adding B or Ti to prevent the occurrence of skipping as in No. 3, or Tokukosho! ;7-'190
A method is known in which high oxygen steel is cast by continuous casting after being subjected to vacuum degassing treatment, such as No. G9. but,
Adding elements such as B and Ti inevitably increases costs, and nitrides such as BN and TiN are formed in the steel. Oxidation produces coarse bubbles in the enamel layer, making it impossible to obtain a beautiful enamel surface. To compensate for these shortcomings, Tokukai Sho! ;/-1
No. 33// discloses a method of adding TI in the form of a wire during continuous casting to reduce the TI content of the surface layer of the first plate. Although this method is useful for improving the surface properties, a significant increase in cost is unavoidable due to the addition of Ti wire, and the drawback remains that the uniformity of the chipping resistance is low.

On the other hand, steel sheets obtained by continuously casting high oxygen steel have good flaking resistance, and since oxides do not react during enameling firing, they have good surface properties and excellent enameling properties. . However, the press formability is significantly inferior to steel sheets manufactured using conventional capped steel, as well as Ti-added steel and B-added steel, so it cannot be applied at all to applications where it is press-formed. It has the disadvantage of being

The present invention overcomes the above-mentioned drawbacks of the conventional enameling steel sheets as well as the drawbacks of the enameling steel sheets according to the various prior art techniques, and provides continuous cast slabs with good press formability, sagging resistance, and creeping resistance. The object of the present invention is to provide an inexpensive steel plate for enameling with excellent adhesion, and the object of the present invention can be achieved by providing the steel plate described in the claims.

The present inventors have come up with the idea that in order to overcome the various drawbacks of conventional copper plates as described above, the objective can be achieved by controlling the amounts of C and N in high oxygen steel to extremely low levels. However, as a result of various prototype research, the present invention was completed.

The steel plate for enameling of the present invention is produced by melting in a converter and subjected to vacuum treatment. 0pprn, 'C+N<,
? Oppm.

A continuous casting slab having a composition of 300 ppm (oxygen), the balance iron and unavoidable impurities is hot rolled, and the cold rolling reduction rate is Aθ% or more, preferably 5 to 95%.
After cold-rolling within the range of An ultra-low carbon, ultra-low carbon material with excellent press formability, made by applying Ni plating of / ~ 0 /rrL2, then annealing within the range of recrystallization temperature to AC3 transformation point humidity, and then temper rolling. The present invention relates to steel sheets produced by continuous casting with low nitrogen.

Next, the reason for limiting the components of the steel sheet of the present invention and the processing conditions such as hot rolling and cold rolling will be explained in detail.

C: When continuously casting high-oxygen steel, C reacts with oxygen present in molten steel and generates CO or CO2 gas, which causes slab defects. Furthermore, since the oxygen content □ in steel is approximately inversely proportional to Cm, controlling the C content is also important in order to control the oxygen content.

On the other hand, from the viewpoint of waxiness, it is preferable that the amount of C in the steel is as low as possible, since firing distortion, bubbles, etc. cause waxiness defects. Therefore, the amount of C is set to 30 pp'rrV or less.

C + N: As mentioned above, the amount of C is limited to prevent defects in continuous casting slabs, but on the other hand, from the point of view of press formability, C and N
It is necessary that the total of the above is less than 3θppm. C1N is less than goppm, oxygen content is 30θ to left θOpp
Ultra-low carbon manufactured by continuous casting of m.

An ultra-low nitrogen slab is hot-rolled in a conventional manner, and 3.lf
vun hot-rolled coil, then pickled, cold rolled for 0.7 seconds, continuous annealed for 40 seconds, and then subjected to 0.5% temper rolling, and the mechanical properties were investigated. . Figures 1, 2, and 3 show the relationship between the amount of C+N and Et, and the relationship between the amount of C+N and r, respectively.

This is a graph showing the relationship between C+N f( and AI. As shown in FIGS. 7 to 3, when the amount of C+N exceeds ?opm, the Et and r values deteriorate, and the AI is also high. (3
0 to so C), the mechanical properties deteriorate significantly over time, so it is necessary to satisfy C0N < joppm.

Oxygen: The reason why the oxygen content must exceed 300 ppm is for two reasons: to prevent the occurrence of flakes and to prevent the occurrence of rough skin. That is, when oxygen is less than 300 ppm, the storage capacity for hydrogen that has diffused into the steel sheet during floating firing becomes small, and spalling occurs.

However, in ultra-low carbon and ultra-low nitrogen steels such as the steel of the present invention, the grain growth during annealing is too large, so oxygen
Below prn, since there is nothing to inhibit grain boundary movement, the crystal grain size becomes abnormally large and roughness occurs. Oxygen) to prevent this? Must be set to OOppm.

On the other hand, if the oxygen content exceeds 700 ppm, coarse oxides will form in the steel, which will increase the number of cracks caused by inclusions during press forming, and cause enamel defects such as porcupine heads, so the oxygen content should be 300 ppm. over 70
It is necessary to specify less than 0 ppm.

Hot rolling conditions: This component of copper is A because it is an ultra-low carbon steel.
The rB transformation point is high, the α+γ region is very thin, and the l'-
Since there is no precipitation of AN, it is suitable for various hot rolling methods. For example, there is a method in which a continuously cast slab is directly hot rolled without passing it through a slab heating furnace (CC-DR method), and a method in which the slab is heated to a temperature between deOOC and t/soC, and the slab is heated at a lower temperature than normal. Or normal /2θθ~/300
It is suitable for various hot rolling methods, such as a heating method of about C.

Cold rolling conditions: The cold rolling rate must be within the range of 60 to 95%, and the reason for this is to obtain good press formability as well as the hot rolling finishing temperature.

However, in order to reduce the in-plane anisotropy of ductility and Lankford value, it is preferable to set the cold rolling reduction to % or more.

That is, when the cold rolling reduction is 60% or less, the rolling direction (L direction), the direction perpendicular to the rolling direction (C direction), and the rolling direction by 3°
The elongation in the direction (0 direction) and the Lankford value are small, making it impossible to obtain good press formability, and the cold rolling reduction is 60%.
Within the range of % to 2%, the Lankford value of ductility in the C direction is improved and the average value increases, but the Lankford value of ductility in the D direction is not improved. For this reason, it is necessary to place restrictions on the direction of blanking during pressing. D
In order to improve the directional ductility and Lankford value and obtain good isotropic press formability, the cold rolling reduction should be 7S%.
It is preferable to set it as above. ``Also, the cold rolling reduction rate is 9j%
When the value exceeds , the Lankford value decreases again.

Phosphate conditions: Recrystallization annealing may be performed within the temperature range of recrystallization temperature to Ac3 transformation point temperature, and any of the continuous annealing method, the two-box annealing method, and the open annealing method may be used.

In addition, prior to the above-mentioned continuous phosphate formation, 0.0% of metallic Ni is applied to the surface of the cold-rolled sheet in advance. / 9/m2~s, o 97m2
By plating to a certain thickness, it is possible to obtain an enameled product with good adhesion even without pre-enameling treatment such as pickling or Ni dipping. In this respect, conventional steel plates for enameling,
Before waxing, pretreatments such as degreasing, pickling, water washing, and Ni flushing were required. In short, pickling is performed to activate the surface of the copper plate and improve the adhesion between the wax layer and the steel plate, and Ni flashing is performed to improve adhesion and prevent H2 from entering during enamel firing. be.

However, if N1 plating is applied to the surface of the steel plate before annealing as in the present invention, good adhesion can be achieved by simply dry-baking at the waxing stage without such pre-treatment. We found that it is possible to obtain Particularly for the purpose of degreasing, extremely excellent adhesion can be obtained by heating a cold-rolled sheet to a temperature of 0-soo C to burn off fats and oils adhering to the surface of the steel sheet and to generate a thin scale. The Ni plating effect cannot be obtained if the Ni plating is less than 0.197m2, and if the plating amount is more than 2,097m2, it is necessary to install large plating equipment on the entrance side of the continuous annealing furnace, which is not economical. Not. For the above reasons, the amount of N1 plating to be applied in advance during annealing was set to o, i-2, Og/m2.

Next, the present invention will be explained with reference to examples.

Example I Molten steel having a composition within the range for the present invention as shown in Table 1 was made into a continuously cast slab, hot rolled to a thickness of 9.0 to 500, and heated to a hot rolling coiling temperature of ggo C. I wound it up.

Then cold rolled to θ, gtnm, then glo (:
'X IIO seconds of continuous annealing was performed. 0.7% after annealing
Skin bath rolling was performed. The mechanical properties were investigated at O'(L), l/, t°(D), q(7°(
JIS No. 5 test specimens were prepared in the three directions of C), and the yield strength and tensile strength are shown in Table 2. In addition, as an aging test, JIS & No. test pieces in the L direction were tested.
Stress (σW) after 7.3% prestrain and then /θOCX
After aging for 30 minutes, the falling point (“A”) was measured, and (FA-6w was determined as AI (Aging Inde).
x).

For each sample, ■ Degreasing,
Pickling in 09%H2SO4・70C for 20 seconds, (■ indicates rinsing, 0g30CX +J-min baking, ■//, OCX
/xhr jumping promotion treatment was performed, and the presence or absence of the occurrence of jumping was investigated. × marks are samples with skipping, ◎
indicates a sample in which no skipping occurred.

For the skin roughness test, an Erichsen test was conducted, and samples with good rough skin were evaluated as ○, and samples with poor skin roughness were evaluated as X.

Example ■ A cold-rolled coil of the invention steel A shown in Table 1 was cold-rolled to Q, gem, and then the surface of the steel plate was coated with 0, d/m before continuous annealing.
Coils were made with Ni plating in step 2 and recrystallization annealing for g da OC x da θ seconds, and coils without Ni plating. oo
Bake for 7 minutes at C, and after directly rinsing, G3
0 CX '1. After decoration was performed for j minutes, the adhesion index (P, E, I) was examined using a PEI tester.

The results are shown in Table 3.

Table 3 As explained above, since the steel plate for enameling of the present invention is rolled from a continuous cast slab, the manufacturing cost is extremely economical, and the quality is resistant to sagging.

It has excellent performance in wax adhesion and deep drawability.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between C+Nkk and elongation.
The figure shows a graph showing the relationship between C+NR and T value, and FIG. 3 shows a graph showing the relationship between C+Ng and aging index. Patent applicant Kawasaki Steel Co., Ltd. Agent Patent attorney Mura 1) Politics Figure 1 100 (L, C, D, for a while)

Claims (1)

[Claims] 1. C<30 after melting in a converter and vacuum decarburization treatment
ppm, C+N<30ppm, 300ppm<oxygen<7
A continuous @ manufactured slab having a composition of 0 θ ppm + balance iron and unavoidable impurities was hot rolled, and the cold rolling reduction rate was AO%.
After cold rolling, preferably within the range of 73 to 95%, 0.0% is applied to the surface of the cold rolled steel sheet. /-yu, 0
9/m2 Ni plating, then recrystallization temperature ~ Ac
An ultra-low carbon, ultra-low nitrogen continuous casting copper plate with excellent press formability, which is annealed within the range of 3 transformation temperatures and then temper rolled.