JPS5932202B2 - Reikanseikeiyouusukouhanno Seizouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a thin steel sheet with excellent cold workability by controlling a hot rolling method.

Various methods have been proposed in the past to produce steel sheets with excellent cold workability, but these can be roughly divided into: a) identifying the ingredients; c) identifying the hot rolling conditions; and c) determining the cold rolling annealing conditions. It can be divided into specific.

The present invention specifies the hot rolling conditions, whereas most of the hot rolling conditions were determined by the hot rolling temperature (heating, finishing, winding temperature). By specifying the total rolling reduction rate, finish finishing temperature, and rolling reduction distribution in finishing rolling, it is possible to manufacture a new steel plate that has not been previously available.

The main components of the present invention are c4o, 1s%, and Mn40.60.
When hot rolling steel containing zinc by a continuous finishing rolling mill group consisting of n units, the total finishing reduction rate (Zn h ,
o ) is 1.9 or more [ho is the finished board thickness (mi), h
n is the finished plate thickness at the exit side (m→), the finishing temperature is Ar3 or higher, and a) the rolling reduction ratio α1 of the first rolling mill (Fl) and the rolling mill (Fn-1) before the final rolling mill (Fn). ) rolling reduction ratio (αn
During -1), the relational force of α1-αn-1=8 is established.The rolling reduction rate of the final rolling mill (Fn) in-rise ≧01L is the rolling mill (Fn-1) in the previous stage of the final rolling mill. The gist of this invention is a method for producing thin steel sheets for cold-open forming, characterized by a rolling reduction ratio of .

The effects of the present invention are b) Deep drawability represented by r value is important.

The effect is particularly great in cold-rolled steel sheets that are cold-rolled and annealed using the hot-rolled coil obtained by the present invention as a raw material.

A further effect of the present invention is that abnormally coarse grains do not occur in the surface layer of the hot rolled sheet even if the winding temperature after hot rolling is set to a high temperature (for example, 680° C. or higher).

Conventionally, when high-temperature winding of 680°C or higher is performed, abnormally coarse grains on the order of several hundred micrometers occur on the surface of the hot-rolled sheet, and this is particularly noticeable in low-carbon rimmed and Cambuton steels, but even in killed steels, the winding temperature This occurs when the temperature becomes higher, and even after cold working, although it is not as noticeable as in hot-rolled sheets, it can still become a problem as a roughening or ridging phenomenon.

c) Therefore, according to the present invention, even if high-temperature winding is performed at 680°C or higher, there is no occurrence of surface roughness due to abnormally coarse grains, so not only can a softer steel plate be manufactured, but also the temperature at 680°C due to the conventional material. The effects of the present invention are maximized in low-carbon hot steel sheets and cold-rolled steel sheets that require the above-mentioned high-temperature winding.

The present invention will be explained in detail below.

First, the present invention uses c4o as the main component, 1s%, Mn≦0.
Steel containing 60%? This applies.

The upper limit of this component was determined from the viewpoint of cold workability.

That is, above the above upper limit, the steel becomes hard and not only unsuitable as a steel plate for cold working, but also it becomes impossible to expect an improvement in the r value, which is one of the main effects of the present invention.

The main components are Cry, 10%, Mn≦0.40
%, the effects of the present invention will be maximized.

The above-mentioned steel may be produced by any method such as rimmed, campbutted, core-killed, or killed steel, which is commonly used for low carbon steels.

In addition, in order to improve stretch flangeability and ultimate deformability, Zr and Ti control the morphology of cured product inclusions.
, Ca, REM, etc. may be added, and Cr sNit Cu etc. may be added as appropriate to improve weather resistance and corrosion resistance.

Further, in order to improve deep drawability, Ti, Nb, P, Zr, etc. may be added as appropriate.

Next, the above-mentioned steel is hot-rolled to a predetermined thickness and then coiled by a coiler. However, in the present invention, it is necessary to specify the hot-rolling conditions, particularly the finish-rolling conditions.

In other words, continuous hot rolling equipment usually has a group of 6 to 7 finishing rolling stands, but in the present invention, the distribution of the rolling reduction among the finishing rolling mills as well as the finishing total rolling reduction and finishing molten metal are extremely important. This is a configuration requirement.

That is, in the present invention, (a) the reduction distribution in finish rolling is specified by the reduction distribution index (I).

(1) and the rolling reduction ratio of the final rolling mill (Fn) and the rolling mill (Fn-1) in the preceding stage of the final rolling mill.

Note that the rolling distribution index here is the rolling ratio of the first rolling mill (Fl) -α1 and the rolling mill in the previous stage of the final rolling mill (Fn, )
The rolling reduction ratio (α.

=1) and means ■-α1-αn-1.

In addition, the rolling reduction ratio is defined as hi, hi are the thicknesses of the inlet and outlet sides of the i-th finishing mill (F'i), respectively, and ho is the inlet plate of the first rolling mill (Fl). Thickness, hn is the final rolling mill (F
Indicates the exit side plate thickness of n).

In other words, the rolling reduction ratio αi indicates the ratio of the rolling reduction of the i-th rolling mill to the total rolling reduction of the finishing rolling mill group.

In the present invention, in order to specify the reduction distribution, the reduction rate is expressed as a logarithmic strain used in the theoretical formula, but the logarithmic strain (ε
) and the normally used nominal rolling reduction rate (r (%)), the following relational expression holds true, so the nominal rolling reduction rate is also shown hereafter. Figure 1 is a conceptual diagram explaining the specific rolling reduction ratio distribution of the present invention. However, the broken line in the figure is the conventional method, and the solid line is the method of the present invention.

In the conventional rolling distribution, as shown by the broken line A in FIG. 1, the rolling reduction ratio decreases as the stage progresses, and ■=α1-α.

-1 was at least 10%, usually 15-20%.

Also, the rolling reduction in the latter stage of the finishing mill is small, for example, hn-2.
.

The rolling reduction ratio in The rolling reduction ratio was approximately 10%).

Such reduction distribution has conventionally been determined empirically from the viewpoints of motor power, threadability, and shape during finish rolling.

On the other hand, in the present invention, as shown by broken line B in Fig. 1, the rolling reduction in the first half of the finishing mill is significantly lower than that in the conventional method, and the rolling reduction in the latter half is significantly increased. It is a characteristic.

Furthermore, as shown in the broken line, the rolling reduction ratio in the latter half may be thicker than in the first half, or it may be distributed as shown in the broken line C.

In general, the characteristics of the present invention are that the rolling reduction ratio in the first half of finish rolling is made as low as possible and the rolling reduction ratio in the latter half is increased. It has been found that the squeezing property is improved.

As a result of more detailed experiments, we found that not only does the r value stably improve when the following conditions are met (particularly in cold-rolled steel sheets), but even when hot-rolled steel sheets are rolled at a high temperature of 680℃ or higher, Abnormal coarse grains do not occur on the surface, so even when hot-rolled sheets are cold processed, roughness (orange peel) does not occur.
It has also been found that even cold-rolled steel sheets do not suffer from surface roughening or writhing even when cold-worked.

That is, in a group of n finishing rolling mills, the total finishing rolling reduction tn ho is 1.9 or more (nominal rolling reduction is 85.
0% or higher), and the rolling is finished at a temperature of Ar3 or higher, and a) as parameters expressing the rolling reduction distribution, the rolling reduction ratio α1 of the first rolling mill (Fl) and the rolling mill immediately before the final rolling mill (Fn- 1) The difference in the rolling reduction ratio (α'n,) is defined as the rolling reduction distribution index 1, and ■=α1-α1l-1≦8% hn-1°) Simultaneously'' final 1 rolling mill (F,) (7) E-power tn
h.

≧0.11 (nominal rolling reduction 10.4%), rolling reduction of the rolling mill (Fn-1) immediately before the final rolling mill tn'2F! −E−≧
n-1 0.25 (nominal rolling reduction rate: 22.1%).

To explain in more detail, the feature of the present invention is to increase the rolling reduction in the latter stage of finish rolling to further improve the r value and to produce a steel plate that does not cause surface roughness even when rolled at high temperatures. However, in order to do so, the finish rolling mill group tn, jQ must be 169 or higher (nominal rolling reduction of 85
% or more) [preferably 2.0 or more (nominal rolling reduction: 86.
5% or more)].

On the other hand, in terms of equipment and operation, normal rolling has a finishing total reduction of 2.
Although it is 0 or more (nominal rolling reduction ratio of 86.5 ratio or more), it is necessary to ensure at least the above-mentioned total rolling reduction ratio.

The finish rolling end temperature is A r
Must score 3 points or more.

As is well known, cold workability deteriorates when the rolling end temperature is below Ar3 point.

Therefore, even in normal rolling, the temperature at the end of rolling is controlled to be equal to or higher than the Ar3 point.

One of the features of the present invention is that cold workability is improved by increasing the rolling reduction in the latter stage of finish rolling, but in order to take full advantage of this, even in the present invention, finish rolling is carried out at Ar3 It is necessary to finish with a score or higher.

Next, in the present invention, rolling distribution is specified as a specific rolling method for increasing the rolling reduction ratio in the latter stage. Various methods can be considered to express the rolling reduction distribution, but if I were to add an additional comment about the reason for introducing the above parameter, it would be best to Instead of α1, PL±a, , a1+a2+a is used to express the rolling reduction rate.
3 etc. are also possible, but 3. In normal rolling operations, α1 can sufficiently represent the rolling reduction distribution in the first half, and the idea of increasing the rolling reduction ratio in the latter half as much as possible is expressed in relation to the parameter α1-αn-1. This is because it is simple and convenient.

Also, α the reduction distribution in the second half. The reason why it is represented by −1 is that r
In order to improve the value and prevent abnormally coarse grains on the surface of the hot-rolled sheet after high-temperature rolling and the occurrence of rolling of the cold-rolled annealed sheet caused by this, Fn-1 is better than increasing the rolling reduction ratio of Fn-2 and Fn-3.
This is because the effect is greater when the rolling reduction ratio is increased.

Figure 2 shows a hot strip mill consisting of a group of seven finishing mills using steel type A in Table 1, with a finishing inlet thickness of 29 mm and a finished plate thickness of 3.5 mm (finishing total rolling reduction rate of 2.115 (nominal strain (87.9%)], and the final rolling mill reduction rate was 0.1.
1 to 0.12 (nominal strain: 10.4 to 11.3%), and the rolling reduction just before the final rolling mill to 0.25 to 0.26 (nominal strain: 2
2.1 to 22.9%) and variously varied the rolling distribution index 1.

The hot rolling finishing temperature is 890-900℃, and the winding temperature is 7.
50℃, plate thickness after cold rolling is 0.8 ytrtc, annealing is 8
Continuous annealing was performed at 00°C for 1 minute.

Roughness of the skin was determined by observing the surface after the Erichsen test.

As is clear from FIG. 2, when the reduction distribution index becomes 8% or less, the 7 value sharply increases, and it is also seen that no roughening occurs at all despite high-temperature winding.

In this way, the reduction distribution of 148% is a necessary condition of the present invention, but furthermore, in the present invention, in addition to specifying the reduction distribution in F1 to Fn-1 by the reduction rate ratio, F ns F n
It is necessary to make the rolling reduction ratio at -1 as large as possible.

In order to exhibit the effects of the present invention, the above α1-αl-1-
In connection with a reduction distribution of 1≦8%, the final rolling mill (F
) rolling reduction ratio t-5・-” of 0.11 or more
hn (nominal rolling reduction of 10.4% or more), rolling mill (Fn-1) immediately before the final rolling mill (Fn-1) rolling reduction in''- of 0.25n-1 or more (nominal rolling reduction of 22.1% or more) It is necessary to do so.

If the rolling reduction ratio is less than this, the effects of the present invention cannot be stably exhibited.

Of course, it goes without saying that it is preferable to increase the rolling reduction as close to the exit side of the finishing rolling mill as possible. 13.1% at nominal rolling reduction), 7nQ・-'≧0.27 (23.7% at nominal rolling reduction)h
n-1, the effect of the present invention is further improved.3Additionally, regarding workability, the rolling area An of the final rolling mill is
If the knee is 0.22 (nominal rolling reduction: hn 19.7%), there will be almost no problems especially with respect to shape, threadability, etc.

However, if the rolling reduction is higher than this, it is preferable to actively use a roll bender or the like.

There is no need to particularly limit other hot rolling conditions, and the sheet is cooled to a predetermined temperature and rolled up as is usually done.

I would like to add that the number of finishing rolling mills is usually 6.
~7 units, but in the present invention, n units of a finishing rolling mill group consisting of n units does not mean the number of installed rolling mills, but the number of rolling mills actually used for rolling. There is no need to specifically limit n as long as the rolling conditions are satisfied, and in some cases, a part of the installed rolling mill may not be used for rolling in order to stably satisfy the above specific conditions.

Industrially, it is appropriate for n to be 5 to 8.

The hot coil manufactured in this manner is used as a hot-rolled steel sheet as it is, or is descaled and then cold-rolled and annealed to be made into a cold-rolled steel sheet.

In the case of making a cold rolled steel sheet, it is cold rolled by 30% or more as is usually done, annealed in a hot water temperature range above the recrystallization temperature and below the A3 point, and subjected to temper rolling if necessary.

Note that the annealing may be either box annealing or continuous annealing.

Examples of the present invention will be described below.

Example 1 Steel type A in Table 1 was melted in a converter, made into core-killed steel, made into a slab, and then hot-rolled according to the hot-rolling conditions in Table 2 to form a hot-rolled steel plate with a thickness of 2.5 mm. Obtained.

The number of rolling mills used for finish rolling was seven.

The mechanical properties and surface roughness of the obtained hot rolled steel sheets are also shown in Table 2.

The numbers in the table indicate 2 and 4 force body invention steels.

The roughness of the skin was determined by observing the surface after the Erichsen test.

The following can be seen from Table 2.

b) Regardless of the winding temperature, improvements in T value, elongation, and Erichsen value are observed under the finish rolling conditions specific to the present invention.

Furthermore, it is worth noting that when high-temperature winding is performed to make the material softer, the conventional method (3) causes roughness due to abnormally coarse grains on the surface, making it unusable for cold processing. It was impossible to wind up the upper and lower parts.

On the other hand, in the method (4) of the present invention, even when high-temperature winding is performed at 750° C., no rough skin occurs, and therefore, the material becomes softer and elongation is improved, and at the same time, the T-value etc., which are effects unique to the present invention, are improved.

Furthermore, the aging index is lowered and it can be practically made non-aging, so that an extremely excellent steel plate for cold working can be obtained.

Example 2 Steel type B in Table 1 was melted in a converter and then made into a capped steel L7. After being made into a slab and drawn out, it was made into a 3.0mm hot rolled coil according to the hot rolling conditions shown in Table 3, and further after pickling, it was made into a 3.0mm hot rolled coil. After cold rolling to 8 mrn, recrystallization annealing was performed by a continuous annealing method, and 1.0% temper rolling was performed.

The continuous annealing conditions were held at 700°C for 1 minute, then cooled,
Overaging treatment was performed at 50°C for 5 minutes.

Note that the number of rolling mills used for hot finish rolling was seven.

Table 3 also shows the mechanical properties, surface roughness, and presence or absence of abnormal coarse grains on the surface of the hot-rolled steel sheets.

Reference numbers 6, 8 and 9 in the table are the steels of the present invention. The roughness of the skin was determined by observing the surface after the Erichsen test.

The following can be seen from Table 3.

b) Irrespective of the degree of winding, the finish rolling conditions specific to the present invention improve workability, especially the 〒 value.

Furthermore, it can be seen that the workability is further improved in case No. 9 in which the rolling reduction ratio in the latter stage is higher than that in the former stage.

Furthermore, what is noteworthy is that in the case of continuous firing, increasing the winding temperature not only softens the material and improves elongation, but also significantly improves the 〒 value.

However, the conventional method (7) has the risk of causing rough skin.

On the other hand, in the case of code (8) under the hot rolling conditions specific to the present invention with high-temperature winding, not only does no roughness occur at all, but
Compared to the conventional method (7), the workability, especially the T value, is further improved.

Although the present invention has been described in detail above, the steel plate obtained by the present invention has excellent workability.

This effect is particularly noticeable when a soft steel plate is obtained by winding at a high temperature of 680°C or higher.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram illustrating one minute of rolling. FIG. 2 is a diagram showing the relationship between the rolling distribution index and the lower value and surface roughness of a cold-rolled steel sheet.

Claims (1)

[Claims] 1. When steel containing C<0.15% and Mn 40.60% as main components is hot rolled by a continuous finishing rolling mill group consisting of n units, the total finishing reduction rate O tn h , is 1.9 or more [ho is the finished board thickness (im
), h. is the finished exit plate thickness (mrIt)], rolling is completed at a temperature above the Arg point, and the reduction distribution is as follows: a) Reduction ratio α1 of the first rolling mill (Fl) and the front stage of the final rolling mill (Fn) The relationship of α1-α s 48% is established between the rolling reduction ratio (α. -0) of the final rolling mill (Fn-1). A method for manufacturing a thin steel sheet for cold-open forming, characterized in that the rolling reduction ratio of a rolling mill (Fn, ) in the preceding stage of a final rolling mill is set as follows.