JPS58185752A - Cold rolled dead soft steel plate for deep drawing with superior surface prorerty - Google Patents

Abstract

PURPOSE:To enhance the surface properties and deep drawability of the resulting cold rolled steel plate by using a dead soft steel having a specified composition contg. Si, Mn, Cr, Ti, P, S, Al, N, O and Ca. CONSTITUTION:This cold rolled dear soft steel plate has a composition consisting of 0.002-0.02% C, <=0.1% Si, <=0.4% Mn, 0.05-0.35% Cr, 0.02-0.15% Ti, 0.01-0.04% P, <=0.02% S, 0.01-0.06% Al, <=0.006% N, <=0.01% O, <=0.01% Ca and the balance essentially Fe and satisfying relation represented by (Ti+Ca)/ (C+N+S)=0.5-2.0 (atomic concn. ratio). The steel plate has superior surface properties and deep drawability. The surface properties relate to the surface defect causing rate, the amount of a phosphate film to be stuck and the nonplating rate.

Description

[Detailed description of the invention] Regarding cold rolled steel sheets.

Cold-open rolled steel sheets and hot-dip galvanized steel sheets are used in a wide variety of applications, including automobiles and electrical equipment. The deep drawing method is used to process this steel plate into the desired shape.
- is widely practiced, but recently it has become difficult to add complex shapes...
Alternatively, from the viewpoint of simplification of addition, etc., there is a strong demand for the development of steel sheets that have lost their deep drawability.

Conventionally, as a manufacturing method for cold rolled steel sheets with good deep drawability and J1 aging properties, banona annealing of l\1 quilt steel or de-human annealing using 5L per order/coil has been carried out. However, both of them are extremely economical and have a manufacturing cost of about 1".
3. In recent years, continuous annealing lines have been used to produce cold I8 threads for deep drawing. uJ1 can also produce rolled steel plates at low cost.
However, in terms of ultra-deep drawability and aging properties, it is difficult to obtain sufficient leakage resistance. ■Mackerel 5 and 7/Nomer type molten zinc menkirai/ cannot be subjected to over-aging treatment such as /lZ, and the annealing and soaking time for J1 is always short, so A1 quilt steel is used. Lii Melt 111 for ultra-deep drawing with aging properties and low yield stress! It is almost 4-11f capacity to obtain lead agate steel plate. In order to improve drawability and aging properties in a continuous line where such rapid heating short-time annealing is performed and L does not include an overaging treatment zone, it is necessary to use an alloy T.
It is known that the addition of titanium ('i) is effective as LA, and with the advent of vacuum desaturation, demand for titanium-containing low carbon steels as cold-rolled steel sheets for deep drawing is increasing.
There is one. However, due to the following 11 circumstances, a satisfactory solution has not yet been found regarding the material properties of titanium-containing low-carbon cold-rolled steel sheets, especially the tensile strength.

In other words, titanium-containing ultra-low carbon steel is produced by subjecting molten steel refined in a steelmaking furnace such as a converter to a vacuum dehydration treatment to reduce C and oxygen in the steel to a predetermined limit. of titanium (1
The amount of oxygen in the molten steel is still quite large even after the vacuum degassing treatment described in 2). In this state, i' has an extremely strong affinity for oxygen.
Since i is added, some of it is consumed by oxidation and becomes expensive ′
In addition to lowering the yield of 1"1, the generated non-metallic inclusions remain in the steel and deteriorate the material quality. This causes a decrease in product yield.As a means of removing the alignment caused by oxygen in the steel, aluminum (A1), which has a strong oxidizing power, is poured into the molten steel prior to the addition of titanium for forced deoxidation. For example, +
+J Soluble aluminum (sol・A I ) is at least 0.01% 1. A method has been proposed in which AI is added as much as possible (Japanese Patent Publication No. 41531, 1973).

When A1 deoxidation is carried out, many A1 particles are present in the steel.
．． 0. [2] remains and causes slipper flaws, which deteriorate the surface quality.

On the other hand, it is reported in Japanese Patent Publication No. 46-20563 that when 0.05% or 0.5% of 1-1 is contained, the adhesion of the plating layer is improved and a galvanealed steel sheet with good formability can be obtained. It is described in.

In particular, when containing Ti/C
When the ratio is between 4 and 1-, the effect of improving the properties of the steel becomes remarkable, but when this l' i-containing steel is processed in a continuous molten metal plating line such as the Sennmier type, it becomes cold-open rolled sheet. 1, 1, which requires surface cleaning, is reduced after being weakly oxidized in the so-called gas cleaning stage.In steel containing a large number of easily oxidized alloy logs such as 1, 1, the reduction is light. This is not done in the 5th round, resulting in 111 yuan and 4 feet, which causes a problem of frequent failures.

Therefore, even if we expect the effect of improving deep drawability by adding T1, when continuous hot-dip plating is applied, there is a major obstacle that the addition of Ti increases the defective rate of non-plated products, and the true effect cannot be obtained. I can't do it.

The present invention has been made in view of the various problems of conventional cold-open rolled steel sheets explained in Section F. Namely, the present inventor has developed ultra-low carbon aluminum killed steel into a 4-layered steel with ingredients that affect press formability. As a result of detailed research on the influence of component ratios, we found that the deoxidation and desulfurization treatment using Ca, the identification of the ratio of C and N content to the T1 content, and the composite content of Cr, reduced the Ti content. We have discovered that the effect of Ti content can be maximized by using this method, and have completed an ultra-low carbon cold-open rolled steel sheet for deep drawing with excellent surface properties.

゛ The features of the ultra-low carbon cold rolled steel sheet for deep drawing with excellent surface properties according to the present invention are CO,002-0,
02%, Si 0.1% or less, Mn 0.4% or less, Cr
O, 05・0. :(5%, Ti 0.02-0.15
%, 110.01~0.04%, So, 02% or more, A
I OJI+-0,06%, N (more than 1,006% °
, 00.01% or more, Ca (1-Of% or more 1・゛, and ('I'i+Ca),'(C+N+5J=0
．． 5-2.0 (atomic concentration ratio) is at a point where the remainder F(·).

The ultra-low carbon cold rolled steel sheet for deep drawing with excellent surface properties according to the present invention (in the following description, the steel sheet according to the present invention will be referred to as the steel sheet 1) will be explained in detail.

First, the A/J component and the proportion thereof in the steel sheet according to the present invention will be explained.

If the C content is less than 0.002%, it becomes difficult to melt the steel in an industrial-scale steelmaking furnace, and furthermore, formability deteriorates due to the rapidly increasing oxygen concentration in the steel. Moreover, if the content exceeds 0.02%, the growth of austenite grains will be suppressed, the amount of TiC precipitation will increase, and the +li crystal temperature will increase, resulting in low temperature, Improved formability through short-time continuous annealing! j is i:n(ability). Therefore, the C content is (1,002 to 0.02%).

Si is an element that contributes to the surface texture, and by reducing the A1 content by containing S1 in aluminum killed steel, the effect of improving the surface texture can be obtained, but if Si is contained in an amount exceeding 0.1%. This effect does not exist. Therefore, the 81 content is set to 0.1% or less. In addition, by setting the 81 content to 0.1% or more, it is possible to reduce the occurrence of surface defects in continuously cast material slabs and product steel sheets, which are particularly prone to surface quality problems.

Mn is an element that prevents hot embrittlement caused by S content, but if the content exceeds 0.4%, it will lead to deterioration of formability, especially when molded with low C content. In the steel sheet according to the invention, the disadvantage is slight, but it is not preferable because it increases the recrystallization temperature.

Therefore, the Mn content is set to 0.4% or more.

By containing Cr in combination with Ti, the deep drawability is further improved compared to the case where T1 is included alone, but this is because the TiC precipitated particles tend to become coarser due to the inclusion of Cr. , Cr not only improves the deep drawability, but also improves the solid solute C that is not bonded as Ti(C,N) (two causes of V
It also has the effect of making it difficult for aging to occur, and the content is 0.05
If the CI is less than %, the - effect cannot be sufficiently exhibited, and in the steel sheet according to the present invention with a small TI-containing armpit, the CI is +
It is not necessary to contain more than 1.35%. Therefore, (
The content of 2R should be 0.05 to 0.35%.7]1 is an element that improves deep drawability due to its complex content with C. The higher the content, the higher the deep drawability. By fixing C1 and N in the steel completely as carbonitrides (C, NJ), deep drawability becomes extremely good, but when the I content increases, production The cost is 1
- Since it also increases the amount of 0.15%
It should not exceed 0.02% or less than 1#i.
Since the above effect cannot be expected, the i' i content is 0.0.
2 to 0.15% 7. The content of 'I'1 is the original f concentration ratio 1'1i (C 10N) I 0.5-2
．． By specifying 0, as shown in Figure 1, the surface quality is excellent, and furthermore, it is possible to maximize the effect of containing '1゛1 and sufficiently improve deep drawability. be. If the ratio of the contained components is deviated from, even if the content ratio is less than 0.02%, aging is likely to occur when the overaging treatment is omitted.

In this way, the inclusion of 1'i sufficiently fixes C1 and N in the steel, making it difficult for aging to occur, and improving the overhang properties at the same time.Furthermore, since T1 has a strong effect of fixing N, There is no need for special treatments such as high-temperature winding as in the case of all-aluminum alloys.

Next, C00007%, Si0.01%, Mno, 2o
%, AI (sol) 0.030%, Cr 0.2%, and steels with various T1 contents were subjected to alloying plating using a Sendzimir-type continuous melting Menki line, and the γ value and the failure due to non-plating were Figure 2 shows the relationship between the incidence of cracks. That is, an increase in the γ value is achieved by increasing the Ti content, but as the Ti content increases, the unplating rate also increases. Therefore, even if the effect of improving deep drawing density is expected by containing 'l'1, it is not effective when hot-dip plating is carried out because it is compounded by the content of 'r;.

Although this causes a big problem of increasing the cracked yield rate, the T1 content can be increased by Ca treatment (described later), so the reject rate can be reduced even when obtaining the same γ value. .

A1 is an element that plays the role of a deoxidizing agent during steel production, and is also effective in fixing and rendering N harmless as ^IN, and this effect is small when the content is less than 0.01%. Moreover, if the content exceeds 0.06%, not only the effect will be saturated, but also the surface quality will deteriorate due to an increase in nonmetallic inclusions, or the recrystallized grains will become finer. Therefore, the A1 content is set to 0.01% to 0.06%.

Ca is a deoxidizing and desulfurizing agent. Cold rolling Jl: The formability of rolled steel sheets has been improved by reducing the amount of solute carbon.
In order to obtain better moldability, Ti is added.
It is effective to fix and remove solid solute carbon as carbide, but since Ti has a strong affinity with both 0 and S, liO: and 'lis are generated before IIC is generated!
and consumes T1. However, by performing the clI treatment, the content of 0 and S can be reduced, and the amount of effective Ti that can fix solute carbon is large, so the amount of Ti that inhibits phosphate film treatment and hot-dip galvanizing properties can be reduced. content can be lowered. In addition, the generated Ca-based inclusions quickly float away from the molten steel and are useful for improving surface defects.

As mentioned above, Ca has an auxiliary effect on improving the formability of Ti through its deoxidizing and desulfurizing effects, so it is not used alone, but in the form of a composite metal with Ti.
Its content is 0.01% or less to achieve each of the above effects, and (Ti+Ca)/(C+N+5)=0
．． It is necessary to satisfy each condition of 5-2.0 (atomic concentration ratio).
This is because it no longer has an auxiliary effect on the effect of i.

For both S and (), the lower the content, the better the yield of Ti and the better the moldability, so the S content is 0.02% or less, and the content is 0.

Next, examples of ultra-low carbon steel sheets for deep drawing with excellent surface properties according to the present invention will be described together with comparative steels.

It was melted by a normal melting method so as to have the ingredients and proportions shown in Example 1, deoxidized and desulfurized with Ca, then cast, and cold-rolled in accordance with a conventional method. I did it.

Table 2 shows the results of investigating various properties of this cold rolled steel sheet.

As is clear from Table 2, the mechanical properties of the steel sheet according to the present invention are as good as those of the comparative steel, and furthermore, the incidence of surface defects is lower than that of the steel sheet according to the present invention. Steel plate is much better.

Furthermore, it can be seen that the steel sheet according to the present invention is superior to the comparative steel in terms of the amount of phosphoric acid film deposited and the unplated rate.

As explained above, since the ultra-low carbon cold rolled steel sheet for deep drawing with excellent surface properties according to the present invention has the above-mentioned configuration, it can be used as a steel sheet for hot-dip galvanizing due to non-scaling. The defective rate can be significantly reduced, and by containing Ca, Al2O, TiO2 in steel
It can reduce non-metallic inclusions that cause surface defects such as Therefore, the formability can be dramatically improved, the Ti content can be lowered, and the defect rate due to non-plating can be reduced.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between Ti content, γ value, and surface defect incidence rate, and FIG. 2 is a graph showing the relationship between Te value and hot-dip galvanizing failure rate. Figure 1 - rr ('/,) Figure 2 1,') i, C) 2. ')f'Shibori Supplement 11 Fortune Telling (Spontaneous) Showa 1)'n jFebruary z211 Showa 575t'++iJ乍蹍数 (l E: !)
4 () 6. Name of the invention: 1 degree carbon cold-opening with excellent surface f1 shape for drawing [Rolled steel sheet: 3. Relationship with the person who wears the sleeve 11゛ 4th eye (Special d'I appearance!
God] Iyama Chuo-ku Waki lJ [Town 1111: 4-18 Name
(November! Month Stock λ′ Hand 1 God J・VWJ Office Representative
, +'i+ Hashiko, '11, Acting], 11 locations Tokyo is also former 1 Higashi-ku Minamisuna Z1'lB No. 15 Fujiwazuka Yocho Co-op! j, fl 1 〒1:56 Phone (646) () 1! No 4
5. Supplement 11 - IJ of life 1 (spontaneous) 6. Number of inventions that increase the number of auxiliary mortar rolls (none)゛1. Subject of Supplement 1F- (1) Detailed description of the invention in the specification (2) Amend the specification No. 13, Figure 1, Figure 1, to Table 1.

Claims (1)

[Claims] -0.02% to CO,002, Si0.1% or less, Mn
O, 4% or more F, Cr O, 05-0, 35%, Ti
0.020.15%, Po, 01~0.04%, So
, 02% or less＼ 8l 0.01-0.06%, N
O,006% or more F, OO,01% or less, Ca 0001
% or less, and (Ti+Ca),'(C+N+5
)=0.5-2.0<atomic concentration ratio), the remainder is substantially Fe
An ultra-low carbon cold rolled steel sheet for deep drawing with excellent surface properties.