JPS5884929A - Production of cold-rolled steel plate for deep drawing having excellent nonaging property and curing performance for baked paint - Google Patents

Abstract

PURPOSE:To obtain a steel plate having excellent nonaging property and curing performance for baked paint by subjecting an Al killed steel ingot contg. prescribed ratios of C, Mn, N, B, etc. to prescribed hot working. CONSTITUTION:Al killed steel contg. <=0.01% C, <=0.6% Mn, 0.005-0.07% solAl., <=0.008% N, 0.5-1.6 B/N and 0.5-4 Nb/C is melted. The Al killed steel ingot obtd. by casting the molten metal thereof is hot rolled at <=1,200 deg.C and is coiled at <=680 deg.C. Thereafter, the steel plate is cold-rolled and is annealed continuously at temps. higher than the recrystallization temp. and lower than the Ac3 point. Thus, the steel plate having excellent nonaging property and curing performance for baked paint is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a cold rolled steel sheet for deep drawing, which is non-aging and has excellent paint bake hardenability, by continuous annealing.

Cold-rolled steel sheets for automotive L-less forming are especially suitable for doors.

Excellent deep drawing properties, stretchability, formability, and non-aging properties are required for the outer panels of roofs and quarter-nell capes. IIIF for the purpose of preventing panel buckling due to
In the car manufacturing process, there is a further demand for a property (paint baking hardenability) in which the yield point is significantly increased by the heat of paint baking.

To promote sales of cold-rolled steel with such paint-baking hardening properties, for example, as proposed in Japanese Patent Publication No. 54-107419, Mushikild steel is hot-rolled and then box annealed after cold rolling. Soak to a temperature of 5 points and %30-20
Cool at a cooling rate of about 0°C/hour, or reduce the amount of C to 0.
Mushi 11 reduced to about 01-? It is possible to increase the amount of solid solution C in the steel by performing tight coil annealing using the same box annealing method using cold steel. Still not enough to achieve 6! In addition, such a box annealing method involves slow heating, long soaking, and slow cooling, which requires a long time for manufacturing, which is a problem in terms of productivity.

On the other hand, several methods have been disclosed for producing cold-rolled steel for deep drawing by adopting a continuous annealing method, which is very advantageous in terms of high productivity and imparting paint-bake hardening ability. 〉
In order to improve the properties, high-temperature winding is performed during hot rolling, and during continuous annealing after cold rolling, rapid heating is performed, and after soaking, the temperature is reduced to several ils at around 0400'C. Alternatively, after rapid heating and soaking, water cooling to room temperature and further reheating to around 250 to 400 °C and tempering treatment II.
There is a method to carry out (overage treatment). Walking is also O.

That is, the supersaturated solid solution [C
) Requires over-aging treatment for rounding to improve ductility and aging properties by reducing t-t, so there is a limit to the shortening of the cycle. In addition, in order to ensure deep drawability, it is necessary to heat the hot rolling to IIk at a high temperature of approximately 680°C or higher, but high-temperature coiling greatly reduces the efficiency of pickling, which poses an operational problem. Hold it back - ゐ・ Severe deep squeeze) 4! In order to increase the amount of gold in the coal, efforts are being made to reduce the C content to produce extremely low coal, and to add Ti+N, etc. to fix the CAM. According to this, a cold-rolled steel sheet with excellent deep drawing properties and no aging resistance can be produced by continuous annealing, but a cold-rolled steel sheet with a zero hardening property has low paint baking hardenability.
There is a point to be improved in that the increase in yield point O is not sacrificed during paint baking.In view of this situation, the present invention is non-aging at room temperature and also has gelatinization properties for IUI hooking. In order to manufacture cold-rolled steel sheets for deep drawing and processing by applying continuous annealing, we investigated the steel composition and manufacturing conditions. As a result, it was found that the relationship between the reduction of the C content O and the ON content in ml steel at a weight ratio of 1A was also reduced, and that Nb was simply included, but the C content and the weight ratio Nb/l were not reduced. : If we also include the relation t as
It has been found that due to the synergistic effect, excellent deep drawing properties, non-aging properties, and coating hardenability can be obtained. moreover.

If cold is included, the problem arises that the value 7, which indicates deep drawability, is generally low when the hot-rolled coiling temperature is low, but by regulating the hot-rolled slab heating temperature to 1200 C or less. It has also been found that good deep drawing properties can be obtained even at low temperatures.

The real truth is based on this knowledge), so O1
! That is, C: 0.01s or less, Mn: 0.6- or less, a
Soluble AA: 0.005-a, -07%, N: 0.0
08% or less, B:N weight % ratio B/N is 0.5 or more 1
．． 6 or less, Nb:C weight-ratio Nb/C is 0.5
A U-killed steel piece containing 4 or less of the above is soaked at 1200°C or lower, hot-rolled, then rolled at 680°C or lower after hot rolling, then cold-rolled at 3-point temperature higher than the recrystallization temperature. The following describes a method for producing a cold-sharpened steel sheet for deep drawing, which is continuously annealed at O temperature, is non-aging, and has excellent paint hardenability.

Furthermore, as for the summary of Honjitsu WAO and others, the above-mentioned steel composition o
p1 An AA killed steel billet containing one or more of Cm *Cr eZr eV O in a total amount of 1.051 or less is heated to a temperature of 1200 ° C. or less and hot rolled,
After hot pressing, it is rolled up at 680C or less, cold rolled, and then continuously annealed at a temperature above the recrystallization temperature and below the AeB point, resulting in a ζ roll.

The present invention will be explained in detail below.

If C exceeds 0.01911YC, it becomes hard due to the precipitation of a large amount of NbC, and the deep drawability deteriorates, so the upper limit is set to 0.0.
1%! is o, 0Q5s or less is good - *SIIA.

If Mm exceeds 0.61, the deep drawing properties will deteriorate, so the upper limit is set to 0.6-.

Mut is essential as a deoxidizing agent, and in order to perform sufficient deoxidation, an acid-capable #IAA of 0.005 or more is required.
On the other hand, in order to reduce the harmful effect of suppressing the reaction between 1 and N, which will be described later, if the amount is too large, the upper limit of Aj is set to 0.07'4 as acidic @Aj.

Since N is a special component because it deteriorates deep drawing properties and is one of the causes of aging, in the present invention it is fixed with 1 and its harmful effects are eliminated, but if there is too much of it, B
Let the upper limit to,oos* be ``increase the content of ``. Preferably it is 0.004S or less.

No. 1 is Nt-fixed to form BNI, which improves deep drawing resistance and has a non-aging effect. In order to exhibit this effect, it is important to add N to the weight ratio of N to the steel φ, and B/N is required to be 0.5 or more. However, if the content is too large, the deep drawability will deteriorate again, so the BA ratio is set to 1.6 or less, so the preferable range of the Blki ratio is 0.7 to 1.0.

Although Wb is non-aging at room temperature, it is an important component for imparting paint-baking hardenability to the steel sheet. t) In order to impart M properties, the weight ratio to the C content in the steel is important. Nb/
It is essential to include C in a relationship. N
If b/C is small, aging will occur, so it is set to 0.5 or more with cold A. In addition, if the Nb/C content increases, the Ik scissors hook hardenability deteriorates, so it is set to 4 or less.

Recently, in cold regions such as North America and Scandinavia, severe corrosion of automobile bodies due to salt sprayed on roads to prevent freezing has become a problem, and steel plates with surface treatment or cold weather with good corrosion resistance have become a problem. Demand for rolled steel sheets has become stronger. In response to such a demand, the present invention has Kanaru O corrosion resistance, but in order to further improve the corrosion resistance, sCu*Crm
Although it is possible to contain one or more of ZtaV, the upper limit is 1.011 because O impairs ductility if the total amount exceeds 1.0. Furthermore, when one of the above-mentioned elemental gold is contained in 9F12 or more, the paint bake hardenability is improved to some extent.

Other P, 8. For the Bl group, P is unavoidably contained in O, Oa- or less, 8 is 0.02- or less, and 81 is 0.1- or less, but it is preferable to have as little as possible.

Steel with composition within the above-mentioned limited range is melted through a normal converter-vacuum degassing process, and is continuously cast or ingot-formed.
It is made into a steel billet by Jll. The steel billet is then hot-rolled, and when the hot billet is sent to a hot press grinder, it is desirable that the temperature of the hot billet is below the ArB point or O temperature.

In hot rolling, in particular, the heating temperature of the steel billet is set to 1200℃ or less,
Regulate the winding temperature to 680°C or less.

jllllfl, C: 0.004 s, 81:0
．． 015GsMm: 0.131G, P: 0.008%,
8:0.0101G, 11tj-Al o, o 30
fN: 0.00241%B: 0, GOolg,
IIA: 0.92, Nb: 0.01411%Nb/C
: A steel piece consisting of 3.5 is soaked at a temperature of 1000 to 130.
After finishing rolling, winding at 600°C,
%O indicates the relationship between the Rank Four r value (r value) of a steel plate continuously annealed at 800° C. after cooling and the heating temperature of the steel slab.

Figures 'e and o show that if the heating temperature of the steel billet is 1200°C or less, an r value of 1.8 or more, which is necessary for deep drawing, can be obtained. Therefore, the heating temperature of the steel piece shall be 1200°C or less. In order to manufacture cold-rolled steel ATM with excellent deep drawing properties using conventional island-added steel using the continuous annealing method, it is necessary to increase the hot-rolling temperature 1.
It was necessary to set the temperature to 680°C or higher. However, setting the coiling temperature to a high temperature of 680°C or higher requires a long pickling time for descaling, resulting in a significant drop in efficiency.Therefore, in the present invention, the coiling temperature is set to 680°C or lower. However, in the present invention, by regulating the heating temperature of the steel billet to a low level, it is equal to or higher than the conventional one. The r value is obtained.

In cold rolling, the cold rolling rate should be set to 75 to improve deep drawability.
% or more.

The next continuous annealing is performed by soaking in a temperature range from the recrystallization temperature to the Ac3 point temperature. The soaking temperature is determined by rounding K1l1 to ensure deep drawability.6 In the present invention, depending on the combination of steel composition and hot rolling conditions, the O solid solution in the steel is maintained at room temperature to the limit that shows non-aging properties9. Because the amount is controlled, over-aging after soaking #! &
The altar is a necessary table.

After annealing, it is temper-rolled if necessary and used as a product. The present invention will be explained below based on Examples.

Example A primary steel sheet with the composition shown in Table 1 was melted, hot-rolled to a thickness of 4.0 mm under the hot arc conditions shown in the same table, and cold-rolled to a thickness of 0.7 ms after pickling. After soaking for 1 minute at 800℃ using continuous annealing method, cooling to 4oo'c at an average rate of 10℃/lee, followed by air cooling, followed by skin pass rolling at a rolling reduction of 0.8-0, followed by material testing. I did it. The results are also shown in Table 1.

1! [fi is the yield stress when applying 25110 prestrain (
Evaluation was made based on the difference (#B--m) between σA) and the O yield stress (#B) when a baking equivalent treatment of 1701:x20 minutes was subsequently performed.

Aging property was evaluated by the degree of elongation at yield point caused by artificial aging at 38° C. for 14 days.

As is clear from Table 1, steels A~ produced by the method of the present invention do not exhibit yield point elongation due to aging, and have a BH content of about 3 to 6 to 9/-, making them excellent for deep drawing. It is a steel plate.

As is clear from the above examples, according to the present invention, cold-rolled pots and plates for deep drawing that are non-aging at room temperature and have excellent BH properties can be produced continuously by hot rolling and low-temperature winding without over-aging treatment. It can also be easily manufactured using an annealing method.

Note that the present invention applies not only to cold-rolled steel sheets but also to zinc, tin, aluminum
It is also the most suitable method for producing peripheral surface-treated steel sheets (deep drawing for plating metal, chromium, tin-lead alloys, etc.).

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the heating temperature of an expanded steel piece and the r value of a continuously annealed round steel plate. ttX;oyI00r2oo y300 Steel Agency Nona1
Moku 3rd generation)

Claims (1)

[Claims] (1) C: 0.01- or less, Mn: 0.6- or less, acid-soluble AJ: 0.005-0.07%, N
: 0.008- or less. The weight ratio B/N of l to N is 0.5 to 1.6. Nbt-C
At-killed steel billet containing Nb/C in a weight ratio of 0.5 to 4. Hot rolled by heating to a heating temperature of 1200°C or lower, coiled at a temperature of 680°C or lower after hot rolling, and then cold rolled,
A method for producing a cold-rolled steel sheet for deep drawing which is non-aging and has excellent paint bake hardenability, which is characterized by continuous annealing at a temperature above the recrystallization temperature and below Ac5 point. 1) C: 0.01- or less, Mn: 0.6% or less,
Acid soluble Aj: 0.005-0.07%, N: 0.008
- Below. It contains Nb in a weight ratio B/N of 0.5 to 1.6 with respect to ltN, and 9.5 to 4'i in a weight ratio Nb/l with C, and further contains Cm and Cr. The total amount of one or more of Zr*V() is 1.0-
An At-killed steel piece containing the following is heated to a heating source temperature of 1200°C or less and hot rolled, then cold rolled at a temperature of 680°C or less after hot rolling, and then cold rolled to a temperature higher than the recrystallization temperature. Cold-rolled steel 1 [O production method] for deep drawing, which is characterized by continuous annealing at a temperature below 100 mL and is non-aging and has excellent paint bake hardenability.