JPH036330A - Manufacture of cold rolled steel sheet for enameling by hot direct rolling - Google Patents

Abstract

PURPOSE:To improve the porcelain enameling characteristics, deep drawability and weldability of the steel sheet by subjecting a slab of a steel having regulated amounts of N and contg. Ti particularly in the specified relationship with C and N to hot direct rolling, subjecting it to finishing and coiling at a specified temp. and thereafter executing cold rolling and recrystallization annealing. CONSTITUTION:A steel contg. <=0.010% C, <=0.50% Mn, <=0.03% P, 0.010 to 0.040% S, 0.005 to 0.10% sol.Al, <=0.0050% N, 4XC%+3.42N% to 0.12% Ti and 0.0002 to 0.0020% B is subjected to continuous casting. As it is or after subjected to auxiliary heating, the slab is subjected to hot direct rolling, is finished at >=800 deg.C and is coiled at <=750 deg.C. After that, the steel is cold-rolled at >=60% rolling reduction and is subjected to recrystallization annealing. In this way, the cold rolled steel sheet for enameling having excellent porcelain enameling characteristics and deep drawability can be obtd. in a process of which continuous casting and hot rolling are directly connected without executing the addition of REM or that of large amounts of N.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a cold rolled steel sheet for enameling which has excellent deep drawability and enameling properties.

(Prior Art) Cold-rolled steel sheets for enameling are used for various purposes, but especially when used for bathtubs, kettles, etc., excellent deep drawing properties are required in addition to enameling properties. In addition, since the material is often processed and formed and then welded, it is important that the product has excellent weldability. Conventional cold-rolled steel sheets for enameling with excellent waxability and deep drawability are disclosed, for example, in JP-A-58197254 and JP-A-58-136747.
As in the publication, a method is disclosed in which Ti or a combination of Ti and Nb is added to ultra-low carbon All-guild steel, and REM is further added. Also, JP-A-62-16193
9 and JP-A-83-420, in ultra-low carbon Aρ-killed steels to which Ti or Ti and Nb are added, the N content in the steel is 0.012 to 0. A method of containing extremely large amounts of up to 4% is also disclosed.

(Problem to be solved by the invention) However, when REM is added in a mold, it requires blooming, which increases manufacturing costs, and when it is added in a wire during continuous casting, REM is added in a mold. A wire-based addition device and its operating personnel are required, which complicates continuous casting operations. However, the most problematic thing is that R
When EM is added, welding defects such as spatter and bead meandering occur when molded products are arc welded, making it impractical for arc welding. On the other hand, due to the recent remarkable progress in low nitrogen melting technology, equipment is now available to stably obtain Nm of about 0.0050% or less. Processing is required, and a large amount of Ti is required to fix N, which significantly increases manufacturing costs.

An object of the present invention is to solve the problems of the above-mentioned prior art and to provide a cold-rolled steel plate for enameling that has excellent waxability, deep drawability, and weldability.

(Means for Solving the Problems) The present invention has been made as a result of various studies to achieve the above object, and has the following configuration.

That is, the gist is that C:O, [1,0% or more, Mo
: 0.50% or less, P: 0.03% or less, S: 0
．． 010-0.040%, son, A, Q: 0.00
5-0.10%, N: 0.0050% or less, Ti:
4×C (%) +3.42×N (%) or more 0.12%
Hereinafter, after steel containing B: 0.0020 to 0.0002% is made into a slab by continuous casting, it is directly hot-rolled as it is or with auxiliary heating, and then g o o
After finishing at 0c or higher and winding at 750℃ or lower, 60%
A method for producing a cold rolled steel sheet for enameling by direct rolling, characterized by cold rolling at the above rolling reduction ratio and recrystallization annealing.

The present invention will be explained in detail below.

First, the reason for limiting the components in the present invention will be described.

The upper limit of C is set to 0.01096 in order to ensure excellent deep drawability and enameling property by applying direct hot rolling. In order to obtain deep drawability, it is preferably 0.0040% or more.

Mn forms sulfides and improves the resistance to flaking, but
Since it reduces deep drawability, the upper limit is set at 0.50%.

Although P is advantageous for enamel adhesion, it causes brittle cracking during secondary processing, so the upper limit is set at 0.03%.

The lower limit of S is set to 0.010% in order to form sulfides and ensure flaking resistance. However, if the content is too large, deep drawability and weldability will deteriorate, so the upper limit is set at 0.040%.

A, Il) is 5 oil for deoxidation, All is 0.
0.005% or more is necessary, but if it is too much, the cost will increase, so the upper limit is set at 0.10%.

N, as TiN, is effective in improving resistance to flaking, but the nitriding process is costly, and a large amount of T1 is required to fix N as TiN, increasing costs. upper limit to 0.0050%
shall be.

Ti is 4× to fix C and N and ensure deep drawability.
C (%) +3.42×N (%) or more is required, but in order to improve the splintering resistance due to -Ti sulfide, 4×C (%) → −3,42×N (%) )+1.5Xs(
%) or more is valid. However, if the amount is too high, bubble defects and enamel density problems may occur, so the upper limit is set at 0.12%.

B is required to be 0.0002% or more in order to prevent secondary work embrittlement cracking, which is characteristic of ultra-low carbon steels with fixed C and N, but if it is too large, deep drawability deteriorates, so 0.0020% or more is required.
The upper limit is %.

In the present invention, after continuous casting of steel made of the above components,
Hot rolling is carried out directly or with supplementary heating. By so-called direct rolling of a slab having the above-mentioned composition range, excellent enameling properties can be ensured without adding large amounts of REM or N as in the conventional method. The reason why excellent enameling properties can be obtained by performing direct rolling is not necessarily clear, but the α
It is presumed that this is closely related to the fact that -γ metamorphosis does not occur.

In addition, if the temperature of the slab drops too much or the time is too long during direct rolling, the effect of the present invention will be lost.
The slab may be cut at 900°C or higher and then supplementary heating may be performed using an edge heater or reheating furnace as a heat retention furnace, but hot rolling must be performed within 60 minutes. is preferred.

After hot rolling, the finish rolling temperature is set at a lower limit of 800°C since too low a temperature will cause zinc.

The upper limit does not need to be metallurgically regulated. The higher the winding temperature is, the better it is in order to ensure enameling properties and deep drawability.
If the temperature is too high, the pickling properties will be significantly inhibited, so the upper limit should be set at 750℃.
shall be.

In cold rolling, the rolling reduction is set to 60% or more to ensure excellent deep drawability and enameling properties. However, if the rolling reduction rate is too high, both properties will deteriorate, so the upper limit should be 85%.

Recrystallization annealing may be continuous annealing or box annealing, but 2
Continuous annealing is preferable to prevent subsequent processing embrittlement cracking. After annealing, skin pass rolling of about 1% is usually performed.

(Example) Steels with the components shown in Table 1 were melted and made into slabs by continuous casting, and then hot rolled by a direct rolling method and a conventional reheated rolling method.

The conditions for direct rolling were that the slab was cut at 930 to 980°C, and after 10 to 15 minutes, supplementary heating was performed for about 5 minutes using a gas edge heater.

The heating temperature during rolling after reheating was 1150°C.

In hot rolling, finish rolling is performed at approximately 900℃, and the temperature is 620 to 680℃.
℃ coiling, then pickling, cold rolling in order from plate thickness 4.0'++un to 1.0, and continuous annealing at 800℃ to 0.8
% temper rolling was performed.

The mechanical properties, melting properties, and arc weldability of the obtained steel sheets were investigated. The results are shown in Table 2, and the steel sheet 1.2.3 according to the present invention has the same enameling properties as the conventional steel sheet 6 which was reheated and rolled after adding REM, and has no bubble defects or deep drawability. There is no problem with arc weldability. Comparative material 7 is the result of direct charging into a reheating furnace, but 1. ．． 2.3 has poor resistance to slippage.

(Effects of the Invention) According to the method of the present invention, a cold rolled steel sheet for enameling with excellent enameling properties and deep drawability can be produced by continuous casting and hot rolling without adding REM or adding a large amount of N. Since it can be manufactured through a directly connected process, it has major benefits such as simplifying steelmaking work and manufacturing at low cost.

sub-agent

Claims (1)

[Claims] (1) C: 0.010% or less, Mn: 0.50% or less,
P: 0.03% or less, S: 0.010 to 0.040%,
sol. Al: 0.005-0.10%, N: 0.00
50% or less, Ti: 4 x C (%) + 3.42 x N (%)
0.12% or more, B: 0.0002 to 0.0020
%, is made into a slab by continuous casting, and then directly hot-rolled as it is or with auxiliary heating.
A method for producing a cold-rolled steel sheet for enameling by direct rolling, characterized by finishing at 0° C. or higher, winding at 750° C. or lower, cold rolling at a rolling reduction of 60% or higher, and recrystallizing annealing.