JPS58197254A - Steel plate for enamel with superior secondary workability and deep drawability - Google Patents

Abstract

PURPOSE:To obtain a steel plate for enamel with superior secondary workability and deep drawability, by adding specified amounts of C, Mn, P, S, acid sol. Al, N, Ti and B to steel and by specifying the total amount of REM. CONSTITUTION:The composition of a steel plate for enamel is composed of, by weight, <0.02% C, <0.5% Mn, <0.03% P, 0.015-0.05% S, 0.01-0.15% acid sol. Al, 0.02-0.5% Ti [Ti/(C+N)>4], 0.0005-0.008% B, 0.01-0.15% in total of REM and the balance Fe with inevitable impurities. To obtain the composition, Ti, REM and S are added to low carbon Al killed steel, and the strength of the grain boundaries is increased by further adding B.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a steel plate for enameling in which nail skipping occurs, r<<, deep drawability, and does not cause brittle fractures such as vertical cracks during secondary processing. In the present invention, a clear plate for enameling refers to a cold-rolled steel plate that is an original plate before being subjected to enameling treatment.

In general, enameled steel sheets are used for a wide range of applications such as housing and household goods. Nail skipping, which is a defect when a steel plate is enameled, often occurs several days to several months after the enameling is fired, so once it occurs, it costs a lot of money to treat it. Furthermore, when enameled steel sheets are used for bathtubs and the like, a processing method is adopted in which the final product is obtained by performing severe deep drawing press processing to form the material, and then performing secondary processing such as seven-lunge bending. For this reason, steel sheets for enameling are required not only to be free from nail skipping but also to be excellent in the ability to undergo severe deep drawing and subsequent secondary workability.

Various studies have been carried out on steel plates for enameling, and methods have been proposed to improve the resistance to nail chipping. For example, (a) by increasing the zero content in the steel, a large amount of oxide inclusions are generated in the steel, increasing the hydrogen storage capacity and improving the nail-skipping resistance. (Example) During hot rolling, high-temperature rolling is performed to form large-sized carbides and sulfides, and after cold rolling, decarburization annealing is performed to remove the carbides, and this and sulfides absorb hydrogen. capacity and improve load resistance. e38'i-, B to steel with lower kL content
is added to form a B oxide, which increases the hydrogen storage capacity and improves the load resistance. etc.

According to these methods, the load resistance is improved to some extent, but relatively large inclusions are formed, which impairs workability, and the crystal orientation that is advantageous for deep drawing cannot be obtained. For this reason, there is a problem when it comes to parts that undergo severe press processing.
The scope of application is limited to enameled steel plates that undergo relatively light processing.

On the other hand, several proposals have been made regarding steel plates for enameling that have deep drawability in addition to weight resistance. for example,
) Ti and REM are added to steel that has undergone vacuum degassing treatment to reduce 0.
is added, the Ti fixes O and N as a compound, makes it non-aging, and gives deep drawability, and furthermore, this Ti
and REM ensure load resistance. Also, the r
T i −RE for steel with reduced 0 such as −=4o
In addition to the addition of M, some also add S, thereby further improving the weight jump resistance while maintaining deep drawability.

According to these materials, they have high resistance to heavy lifting and have improved deep drawability, and can withstand extremely severe deep drawing with a drawing ratio of 2.4 or more, but after this deep drawing, e.g. When performing secondary processing such as flange bending, brittle fractures (vertical cracks) called secondary processing cracks are occasionally observed, so there is still room for improvement.

Under these circumstances, the present inventors conducted various studies with the aim of developing a steel plate for deep drawing and enameling that has excellent secondary workability. As a result, TI-RE is applied to low carbon At-killed steel.
By adding M-8 and further adding B, in addition to improving secondary workability, which is thought to be due to the effect of increasing the strength of grain boundaries due to B, the weight resistance is improved due to the combined addition of S and B. It was found that the jumpability was further improved.

It also has deep drawability due to the effect of TI.

The present invention is based on the above findings, and the gist thereof is as follows:
0.02% or less, Mn: Q-59' or less, P: 0.
03 or less, s: 0.015 to 0,050, acid-soluble At: 0.010 to 0.15, N: 0. ．． 00
Less than 80 inches.

Ti: 0.02-0.50% Ti/(C+N)〉
4. B: 0.0005 to 0.0080, total amount of HLEM: 0.010 to 0.15, and the balance is iron and inevitable impurities. A steel plate for deep drawing enameling with excellent secondary workability. be.

The reasons for limiting the chemical composition of the steel of the present invention will be described below.
When d: 0.020% or more, the amount of TiO, which is a compound of Ti and C, increases, resulting in hardening. Also, since the value (rank for r value) also deteriorates, the deep drawability that is a feature of the present invention cannot be obtained. Preferably 0.010%
The following is good. Mn is a component that suppresses hot brittleness,
If there is too much A1, the steel plate will become hard, so the upper limit should be set to 0.50.
%, preferably 0.30% or less.

Too much P not only hardens the steel sheet, but also tends to segregate at grain boundaries, which has a negative effect on secondary workability, so the upper limit should be set at 0.
030 person in charge. Preferably it is 0.020 inch or less.

SI/'iT i-REM and B to form sulfide or sulfide and to ensure load resistance, the lower limit is set to 0.0.
Let's say 15. Also, if the content is too large, problems such as hot embrittlement may occur, so the upper limit is set at 0.050%. Preferably 0.020
~0.030chi is good.

It is a necessary component for AJJ deoxidation, and in order to avoid surface defects on steel sheets due to Ti formation, acid-soluble At of 0.010 or more is required, but if it is too large, defects caused by At will become a problem. Therefore, the upper limit of acid-soluble At is set at 0.150. Preferably it is in the range of 0.020 to 0.080.

When the N content increases, press formability deteriorates, and a large amount of Ti is required to fix the glass as TIN, which increases manufacturing costs.
o s o chi. Preferably it is 0J)050% or less.

Reacts with TiriO,N, 0.8, etc., but 0 and N
If 0 is limited as above and removed with At or old, it will combine with S liREM and become sulfide. Therefore, in order to ensure deep drawability, T1 must be 0.02% or more and TI/
(0+N) > 4 is required. Furthermore, the enameling property is also improved by adding REM in combination. On the other hand, if the coefficient is 0.50 or more, the manufacturing cost will only increase. Good luck 0.
A range of 0.05 to 0.20 is preferable.

Bf'i is required to be 000005% or more in order to improve secondary workability and ensure load resistance. If the gap is too large, the deep drawability will deteriorate and cracks will occur in the steel billet, so the upper limit is set at 0.0080%. Preferably 00001
A value between 0 and 0.0050 is good.

If the total amount of RTCM exceeds 0.15 q6, it will harden the steel, reduce press formability, increase manufacturing costs, and
If the content is less than 010, no effect of improving the slip resistance can be expected, so the content is set in the range of 00010 to 0.15%.

Steel with the above-mentioned composition is melted in a regular steelmaking furnace such as an electric furnace or a converter, combined with vacuum degassing treatment, and made into steel slabs by a continuous casting method or a normal ingot-forming method. Hot rolling - pickling - cold rolling - electric cleaning - annealing (continuous annealing, box annealing) -
It is manufactured through the usual manufacturing process of temper rolling if necessary.

In order to ensure deep drawability (high r value), it is desirable for the steel of the present invention to have a large cold rolling reduction, and cold rolling of 70% or more is preferable. The finishing temperature of hot rolling does not necessarily require a temperature of Ar3 or higher, and a temperature in the a+γ range is sufficient.

The annealing method may be continuous annealing or box annealing, but it is said to prevent grain boundary segregation of element P, which is harmful to secondary workability, and to preserve voids near inclusions in order to improve load resistance. In this sense, continuous annealing characterized by rapid heating, short-time soaking, and rapid cooling is preferable.

Examples of the present invention are shown below.

The composition steel of the present invention steel and conventional steel as shown in No.
After melting with a combination of vacuum degassing treatment and continuous casting to form a steel billet, hot rolling with a finishing temperature of 900°C and a winding temperature of 600°C to form a hot-rolled coil with a plate thickness of 6.0°C, followed by pickling. It was cold rolled to a plate thickness of 1.5 inches at a post-cold rolling reduction of 75 inches. Next, continuous annealing was performed at 800° C. for 2 minutes. Temper rolling was carried out using a rolling force of 8 inches.

Table 2 shows the mechanical properties, Table 3 shows the evaluation results of secondary workability,
The rate of occurrence of nail skipping and hydrogen permeation time are shown in Table 4. For secondary workability, a disc-shaped blank is taken from a steel plate, and a two-step cylindrical drawing process is used to prototype the primary processed product with different drawing ratios. Next, after cooling the drawn product to 0° C., a load was applied to the cup head, and evaluation was repeated three times to determine whether brittle cracks had occurred or distortion had occurred in the side wall of the cup. In Table 3, "No" indicates that brittle cracking did not occur, and "Presence" indicates that brittle cracking occurred.

The occurrence rate of nail skipping is the rate of occurrence of nail skipping when a glaze that is particularly likely to cause nail skipping is applied once to these steel plates and fired with enamel. Hydrogen permeation time is the quotient of the time it takes for hydrogen penetrated through electrolysis from one surface of a steel sheet under certain conditions to diffuse to the other surface and be released, divided by the square of the sheet thickness. It is known that the larger the value, the less the tendency for nail skipping to occur.

From Tables 2 and 3, it can be seen that the mechanical properties of the steel sheet of the present invention are extremely excellent, and the secondary workability has reached a level where there is no need to worry about it in practical use.Table 4 shows that conventional steel does not collapse. In contrast, in the case of the steel ABC of the present invention, there is no occurrence of pit jumps, whereas jumps are observed here and there. In addition, the hydrogen permeation time of the steel of the present invention is at a higher level than that of the conventional steel.

As described above, as shown in the Examples, the steel sheet of the present invention has deep drawability, secondary workability, and load resistance necessary for a steel sheet for filling.

Table 1 [Table 2 Table 3' Table 4 Patent attorney Masaaki Akizawa Mitsugai 2 June 22, 1981 Commissioner of the Japan Patent Office Lord 3. Person making the amendment Relationship with the case Applicant's address (Residence) 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name (665) Nippon Steel Corporation 4.
Address: Taiyo Building 5, 12-1 Nihonbashi Kabutocho, Chuo-ku, Tokyo
, correction command ++iMf4J! ltljm'm'm! Showa era
On page 9, line 5 of the amended statement of contents for year, month, date (shipping), "...distortion" is corrected to "...not".

Claims (1)

[Claims] (1) C: 0.02% or less, Mn: Q, 5% or less, P: 0.03% or less, S: 0.015% to 0.050
%, acid soluble type A: 0.010-0.15%, N: o
,oos. % or less, Ti: 0.02 to 0.50%, Ti/(C ten N
)〉4, Contains B: 0.0005-0, ooso%, total amount of RIM: 0.01-0.15%, and the balance is iron and unavoidable impurities. Excellent secondary workability and deep drawability. Steel plate for enamel.