JPS6280250A - Warm-rolled sheet steel for working excellent in ridging resistance and its production - Google Patents

Abstract

PURPOSE:To obtain a sheet steel combining superior workability with excellent ridging resistance even if cold rolling or cold rolling-recrystallization annealing stage is omitted, by allowing C, N, Al and O content in steel to satisfy specific relations, respectively. CONSTITUTION:A steel stock has a composition which consists of, by weight, <0.1% C, <0.1% Si, <0.5% Mn, <0.1% P, 0.002-0.1% Al, <0.01% N, <0.003% O and the balance Fe with inevitable impurities and in which C(wt%)+0.02N(wt%)=0.001-0.1(wt%) is satisfied. This steel stock is subjected to warm rolling at 200-800 deg.C by at least one pass and successively to annealing at 400-950 deg.C to be formed into a rolled sheet steel.

Description

Detailed Description of the Invention (Industrial Field of Application) This specification describes a cold rolling process or cold rolling and annealing process in relation to a working warm rolled thin steel sheet with excellent ridging resistance and a method for manufacturing the same. This article describes the results of research and development that advantageously avoids process complications and eliminates the occurrence of ringing after press working.

Processing thin steel sheets with a thickness of approximately 2 ms+ or less that are used for applications such as building materials, automobile body materials, can stock, and various surface-treated original sheets are required to have the following properties.

(1) Mechanical properties In order to obtain good bending workability, stretchability and drawing workability, high ductility and high Lankford value (r value) are mainly required.

(2) Surface properties Since these materials are mainly used on the outermost side of the final product, not only the shape and surface beauty of the material but also various surface treatments are important.

The general manufacturing method for these thin steel sheets is as follows.

First, we mainly use low carbon steel as the steel material, and after making copper pieces into copper pieces with a thickness of about 200 mm by ingot-forming and blooming rolling, we heated and soaked them in a heating furnace, and then performed a rough hot rolling process to thicken the plates. Approximately 30
After forming a sheet bar into a hot-rolled steel strip with a predetermined thickness in a final hot rolling process at a finishing temperature of Ar3 transformation point or higher, the strip is then pickled and cold-rolled to a predetermined thickness (2 mm). , 0 mrr1 or less), and further subjected to recrystallization annealing to obtain a final product.

The biggest drawback of this practice is the extremely long process required to reach the final product. As a result, not only does the amount of energy, personnel and time required to produce the product increase, but there are additional disadvantages during these long steps which can cause problems with the quality of the product, particularly its surface properties.

As mentioned above, it has been essential for the manufacturing procedure of thin steel sheets for processing to include a cold rolling process (rolling temperature of less than 200° C.).

This cold rolling process not only aims to reduce the desired thickness, but also utilizes the plastic strain introduced by cold working to produce crystals with (111) orientation, which is advantageous for deep drawability, in the final annealing process. Helps promote grain growth.

However, in cold working, the deformation resistance of the steel strip is significantly higher than in hot working, so the energy required for rolling is also significant, the rolling rolls are severely worn, and rolling problems such as slipping occur. Easy to occur.

On the other hand, if rolling can be performed at a relatively high temperature range of 200°C or higher and lower than the Arl transformation point (so-called warm range), and particularly good workability can be obtained, the above problems can be eliminated and the manufacturing merits will be You could say it's big.

In addition, as a method for manufacturing thin steel sheets for processing, a method of producing the final product through a hot rolling process is also considered.

According to this method, cold rolling and recrystallization annealing steps can be omitted, which is a great advantage.

However, the mechanical properties of the three steel sheets obtained as hot-rolled are far inferior to those that have undergone a cold-rolling-annealing process. In particular, press-formed materials used for automobile bodies require excellent deep drawability, but hot-rolled steel sheets have a low r value of around 1.0, so their processing applications are extremely limited. Become something. This is because in the conventional hot rolling method, the finishing temperature is Ar, which is higher than the transformation point, so the texture becomes random during the T→α transformation.

In addition, it is extremely difficult to manufacture thin steel sheets with a thickness of 2.0 mm or less using only a hot rolling process. Moreover, in addition to the problem of dimensional accuracy, the decrease in steel plate temperature due to thinning makes it necessary to roll the low carbon steel below the Ar and transformation point, and the material (
ductility, drawability). Again analogy A
Even if the quality of the material can be secured by rolling below the r+ transformation point, a new problem arises in that the steel plate rolled in the ferrite region is more likely to suffer from cringing.

Here, ridging is a defect of surface irregularities that occurs during processing of a product, and is a fatal defect for this type of steel plate, which is mainly used on the outermost side of processed products.

In terms of metallurgy, ridging is caused by crystal orientation groups (for example, (100) oriented grain groups) that are not easily divided even after undergoing the annealing recrystallization process and remain stretched in the rolling direction. , generally tends to occur when processing is performed at a relatively high temperature in the ferrite (α) region, and this tendency is particularly strong when the reduction rate in the ferrite region is high, that is, when manufacturing thin steel sheets.

Recently, these thin steel sheets for processing have become more complex,
As materials become more sophisticated, they are often subject to more severe processing, and excellent ridging resistance is now required.

Incidentally, the manufacturing process of steel materials has changed significantly in recent years, and the case of thin steel sheets for processing is no exception.

In other words, in recent years, the introduction of a continuous casting process has made it possible to omit the blooming process, and the heating temperature of steel slabs has tended to be lowered from the conventional 1200°C to around 1100°C or lower in order to improve material quality and save energy. It is in. Furthermore, a process is being put into practical use that can omit the heat treatment and rough rolling steps of hot rolling by immediately producing a strip with a thickness of 50 mm or less from molten steel.

However, all of these new manufacturing processes are disadvantageous in that they destroy the structure (casting microstructure) formed when molten steel solidifies. especially formed during solidification (100)
It is extremely difficult to destroy the strong casting texture whose main orientation is <uvw>.

As a result, the final thin steel sheet was prone to the aforementioned jinging.

(Prior Art) Several warm-rolled thin steel sheets for processing with controlled steel compositions have been disclosed. For example, Japanese Patent Application Laid-Open No. 58-9932 discloses that the solid solution (C1N) is 13 to 142 ppm in a tort at 200°C.
It has been shown that (110) [001) strength is increased by recrystallization annealing after rolling at a reduction rate of 2o% or more in a temperature range of ~500°C. Also, JP-A-59-22614
In Publication No. 9, C: 0.002wt%, N: 0.
0018-0.0021 value 0.0011-0.00
It is disclosed that a thin plate with excellent formability can be produced by rolling a steel having a composition in the range of 22 wtχ to 76 to 95% while applying lubricating oil at 500 to 900°C, and then annealing or omitting annealing.

In addition, some methods for manufacturing deep drawing ropes by warm rolling that omit the cold rolling process have been disclosed, for example,
No. 0809, JP-A-49-86214, JP-A-59-
No. 93835, JP-A-59-133325, JP-A-5
No. 9-185729, and JP-A-59-226149.
An example of this is the number of publications. Both methods are characterized by recrystallization treatment immediately after rolling in the warm region, and are innovative technologies that can omit the cold rolling step.

Furthermore, several methods have been proposed for manufacturing thin steel sheets for processing, which are formed into a thin steel sheet of a predetermined thickness in a relatively low temperature range below Ar=transformation point, and then are not subjected to cold rolling or recrystallization annealing steps.

For example, in Japanese Patent Application Laid-Open No. 48-4329, low carbon rimmed steel is rolled to 4 m1 by 90% rolling at a temperature below the transformation point in Ar.
Yield point: 26.1 kg/
mm2□Tensile strength 37.3kg/mm2. Elongation 49.7
%, a production example is shown which yields a property of r=1.29.

On the other hand, in JP-A-52-44718, low carbon rimmed steel is hot-rolled to a thickness of 2.0 mm at a finishing temperature of 800 to 860°C (below the Ar3 transformation point) and rolled at a coiling temperature of 600 to 730°C.
A method of manufacturing a low yield point steel plate with a yield point of 20 kir/mm2 or less by using ``C'' has been shown, but the conical cup value, which is an index of drawability, is 60.60~60.
It is about 62.18n+m, which is 60.5 in the conventional example.
Compared to 8 to 60.61, the drawability is the same or lower, and as disclosed in JP-A-53-22850, low carbon rimmed steel is hot-rolled at a finishing temperature of 1.8 to 2.
A method for manufacturing a low carbon hot rolled steel sheet is disclosed in which the sheet thickness is 3 mm and the coiling temperature is 530 to 600°C, and the conical cup value of the product obtained by this method is disclosed in JP-A No. 52-44718 listed above. As in the case of the publication, the drawing performance is higher than that of the conventional example and is inferior.

Further, in JP-A-54-109022, low carbon aluminum killed steel is hot-rolled to a thickness of 1.6 mm at a finishing temperature of 760 to 820°C, and a coiling temperature of 65°C is disclosed.
Yield point: 14.9-18 at 0-690°C
．． 8kg/mm2 tensile strength 27.7-29.8 kg
An example of manufacturing a low-strength mild steel sheet having a property of / mm '' + elongation of 39.0 to 44.8% is disclosed.

However, none of the above-mentioned known techniques give any consideration to improving the above-mentioned ridging resistance.

(Problems to be Solved by the Invention) The inventors previously disclosed in Japanese Patent Application No. 60-043981 that recrystallization is performed after rolling at a temperature range of 800 to 300°C for at least one pass at a strain rate of 300 s-' or more. It was disclosed that a thin steel sheet with excellent ridging resistance and workability can be obtained by annealing. Also, patent application No. 60-043971
As shown in the specification, excellent ridging resistance and workability can be achieved by rolling at least one pass in the temperature range from the Ar3 transformation point to 500°C, at a strain rate of 300 s-' or more, and at a reduction rate of 35% or more. We have discovered a method for manufacturing azu-rolled thin steel sheets with the following properties.

These manufacturing methods are revolutionary methods that make it possible to manufacture thin steel sheets with excellent ridging resistance and workability, but all of them require the strain rate to be increased to 300 s-' or higher.
It is unavoidable that the rolling technique involves some difficulties.

As a result of repeated experiments, the inventors discovered that by regulating the steel composition, it was possible to produce thin steel sheets with excellent ridging resistance and workability without the strain rate exceeding 300 s-'. .

In other words, by developing a new process that does not involve a cold rolling process or a cold rolling-recrystallization annealing process, and which overcomes the constraints on strain rate during rolling, we are able to produce thin steel sheets with excellent ridging resistance and workability. It is an object of this invention to provide a manufacturing method.

(Means for Solving the Problems) The above object can be advantageously achieved by a configuration based on the following points.

C: 0.01wt% or less, Si: 0.10wt% or less, Mn: 0.5wt"1 or less, P: 0.1wt% or less, Al: 0.002 ~ 0.10wt!　　.

N: 0.01 wt% or less, 0: 0.003 ht% or less, and C content and N content are 0.001 (wtX) ≦C (WtX) + 0.0
2. A warm-rolled thin steel sheet for processing with excellent ridging resistance, which satisfies the relationship of ≦0.010 (WtX) and has a composition of unavoidable impurities and Fe as the remainder (first invention) .

C: 0.01at% or less, Si: 0.10wt% or less, Mn: 0.5WtX or less, P: Q, lWtX or less, Al F 0.002 ~ 0°10WtX, N:
0.01t% or less, 0: 0.003wt% or less, the value of C(wtX) +0.02・N(WtX) is within the range of 0.001 to 0.010(wtX) 2oo to 8o for steel material.

A method for producing a warm-rolled thin steel sheet for processing with excellent ridging resistance, characterized by performing at least one pass of warm rolling in the temperature range of 2 invention).

C: 0.01wt% or less, Si: 0.10wt% or less, Mn: 0.511t% or less, P: 0.1% or less, AI: 0.002 to 0.10wt1, N: 0.
01 Tsuba t% or less, 0: Q, 00awt% or less, Nite C (WtX) + 0.02 ・N (wt
%) is within the range of 0.001 to 0.010 (wt A method for producing an as-rolled warm-rolled thin steel sheet for processing having excellent ridging resistance (third invention).

Now, I will start by explaining the research results that formed the basis of this invention.

The test steel was Si: 0.01-0.04wtX, Mn: 0
．． 07~0.20wtX, P:0.008~0.
017wt%, S: 0.002 ~ 0.008wtX,
AI: 0.002~0.03wt! , 0:0.001
~0.014wt%, C(wtX)+0.02 ・N(
wtX): 0.0007 to 0.030 (wt″A).

This hot-rolled steel plate was heated to 600°C, soaked, and heated in a bath for 30
It was rolled at a rolling reduction of χ.

At this time (C(wtX)+0.02・N(stχ))
FIG. 1 shows the relationship between the value of and the lower value and ridging index after annealing (soaking temperature 800° C.).

The lower value and ridging resistance are (C(w tχ) + 0.02
・It strongly depends on the value of N (wtX)) and O content, and 600
At the rolling temperature of °C, 0.001(wtX)≦C(imt
X)+0.024 N(wtX))≦0.010(wt
It can be seen that by regulating the steel composition to X) and O≦0.003 tχ, the lower value and ridging resistance are significantly improved.

In addition, a similar hot-rolled plate was heated to 700℃ and soaked, ■Pass 2
Rolling was carried out at rolling reductions of 0%, 40χ, and 60%.

At this time, (C(wtX)+0.02 ・N(wtX)
) value and the lower value and ridging index of the steel plate after rolling are shown in Figure 2.

The lower value and ridging resistance are still (C(w tχ)+0
．． 02・N (wt
X)≦(C(wtX)+0.02 ・N(wtri)
By regulating the steel composition to ≦0.010 (wt

As a result of repeated research based on these basic data, the inventors confirmed that a thin steel plate with excellent ridging resistance and workability can be manufactured by regulating the steel composition as described below.

fll steel composition In this invention, the steel composition is the most important, and C, N, AI, and O in the steel are C50, 01wt%, N
≦0.01wt%, 0.002wtX≦AI≦0.10
wt%, 0≦0.003wt? ! Big and C and N are 0.0
01(Ivtχ)≦(C(wtX)+0.02- NC
It is important to satisfy the relationship wtx))≦0.010(wtX). If the steel composition does not satisfy the above relationship,
Excellent ridging resistance and workability cannot be obtained under normal rolling conditions (strain rate of 300 s-' or less).

Of course, in order to obtain high strength, P: 0.1 wt% or less, Si: 0.1 wt% or less, and Mn: 0.5.
The content may be less than or equal to wt% depending on the desired strength.

In this invention, the unavoidable impurity mainly refers to S, and the less S there is, the more a texture is formed which is advantageous for workability, but if it is 0.01 wt% or less, there is no significant deterioration in workability.

(2) Manufacturing method of rolled material Steel slabs obtained by conventional methods, ie, ingot-blowing or continuous casting methods, can of course be applied.

The appropriate heating temperature for the steel piece is 800 to 1250°C,
From the viewpoint of energy saving, the temperature is preferably less than 1100°C.

Of course, the so-called CC-0R (continuous casting-direct rolling) method, in which rolling is started without reheating the steel billet after continuous casting, is also applicable.

On the other hand, methods of immediately casting rolled materials of 50 mm or less from molten steel (sheet bar caster method and strip caster method) also have great economic merits from the viewpoint of energy saving and process saving, and are particularly advantageous as methods for manufacturing rolled materials. .

(3) Rolling process In the process where the cold rolling process can be omitted, in the process of rolling low carbon steel to a predetermined thickness, at least one pass is
It is essential to roll in a temperature range of 800°C. In a high temperature range where the finish rolling temperature exceeds 800°C, no matter how much the steel composition is controlled, only a product with poor ridging resistance and workability can be obtained. On the other hand, the finish rolling temperature was limited to a range of 200 to 800°C since a temperature lower than 200°C would result in a significant increase in deformation resistance and cause problems specific to cold rolling.

In addition, in the process where cold rolling-recrystallization annealing can be omitted, at least one pass is performed at 300°C to 300°C in the temperature range of Ar=transformation point.
It is essential to roll with a rolling reduction of 5% or more. If this rolling temperature exceeds the Ar or transformation point, no matter how much the steel composition is controlled, there will be waxing, which is poor in ridging resistance and workability;
If the temperature is less than 00°C, recrystallization after rolling will not proceed sufficiently. Therefore, at least one pass with a rolling reduction of 35% or more is performed at 300° C. to Ar.

It is better to keep it within the metamorphosis point range.

Regarding the strain rate, the inventors disclosed in Japanese Patent Application No. 60-0439
71, Japanese Patent Application No. 60-043981, 30 in each specification.
It is disclosed that a thin steel sheet with excellent ridging resistance and workability can be manufactured by setting the steel composition to 0s-' or more, but in this invention, simply by newly regulating the steel composition, it is possible to produce a thin steel sheet with excellent ridging resistance and workability. It has been discovered that an excellent thin steel plate can be produced, and therefore, in this invention, the strain rate may be arbitrary.

The number of rolling passes and the distribution of the rolling reduction ratio may be arbitrary as long as the above conditions are satisfied.

The arrangement and structure of the rolling mill, roll diameter and tension, presence or absence of lubrication, etc. have no essential influence.

(4) Annealing process The annealing method may be either a box annealing method or a continuous annealing method, but the latter is advantageous from the viewpoint of homogeneity and productivity.

The heating temperature is 400 to 950°C.

In principle, annealing is not required for products where the recrystallization annealing process can be omitted, but due to material requirements, heat retention is required on the runte after rolling and during the winding process.
It is not prohibited to perform soaking treatment or, if necessary, to perform some heat treatment after rolling.

(5) Pickling and temper rolling The strip obtained by the above-mentioned procedure is rolled at a lower temperature than conventional methods, so the oxidized layer is thin, and the pickling property is extremely good, so it cannot be pickled. It can also be used for a wide range of purposes. In addition to conventional acid removal, mechanical removal can also be used for descaling. Furthermore, for the purpose of shape correction, surface roughness adjustment, etc.
Temper rolling of 10% or less can be added.

(6) Surface treatment The surface treatment obtained in this way is galvanized (including alloy-based).
It has excellent surface treatment properties such as tin plating and enameling, so it can be used as a base plate for various surface treatments.

(for production) The reasons for limiting the steel composition and its effects are as follows.

First, as a result of research using the above-mentioned test steel, the inventors found that C in steel
, N in a solid solution state is 10χ and 0.2χ of their respective contents, and the rest is charcoal,
It was found that these substances are precipitated and fixed as nitrides.

Furthermore, it has been found that when approximately 1 to 10 pprn of interstitial solid solution C and N are present during warm rolling, a texture with a crystal orientation that is advantageous for ridging resistance and workability is formed due to the effect of dynamic strain aging. Ta.

And, such an effect is caused by 0.003wt% of 0 in steel.
It was found that it contributes to the effectiveness only when it contains the following: Therefore, C and N are 0.0001 (wtχ)≦0,
IC(wtχ)+0.002 ・N(wtχ)≦0.
001 (wtχ) or 0.001 (wtχ)≦(
C(wtχ)+0.02 ・N(wtχ))≦0.01
It was limited to 0 (wtχ). Although the effect of zero in steel is not clear, it is thought to have an influence on changes in processing strain.

The reasons for limiting the other steel components mentioned above are as follows.

■C≦0.01wtχ The smaller the C component, the better the workability;
If the content exceeds χ, the amount of carbide precipitated becomes too large and the workability of the final product deteriorates, so C50,
01wtχ.

■N≦0.01wtχ The smaller the N component, the better the workability;
If N≦0.
01wtχ.

■Al is added to 0.002wtχ≦81≦0.10wt to perform deoxidation, but if it is less than 0.002wtχ, sufficient deoxidation will not be performed, and according to this invention, 0≦0.0
It becomes difficult to realize 03wtχ. On the other hand, 0.10wtχ
Even if more than 0.002-tχ
．． It was set to 10wtχ.

■Si≦0.1wtχ The Si component has the effect of strengthening steel, but 0.1wtχ
Since it becomes difficult to form a texture that is advantageous for workability when the SiS content exceeds 2.1wtχ.

■Mn≦0.5ht! The Mn component has the effect of improving the toughness of the rope, but 0゜5w
If tχ is exceeded, it becomes difficult to form a texture that is advantageous for workability, so MnS was set at 2.5wtχ.

■P≦0.1wtχ The P component has the effect of strengthening steel, but if it exceeds O,'htχ, recrystallization becomes difficult and ductility deteriorates, so P≦0.1wtχ.

(Example) Using molten steel whose composition was adjusted to the composition shown in back 1, it was made into a sheet bar with a thickness of 30 to 40 mm by the methods shown in Tables 2 and 3, respectively. 0.8
A thin steel plate with a thickness of ~1.6 m was used.

Thereafter, material properties after recrystallization annealing (soaking temperature 600 to 820°C), pickling, and temper rolling (reduction ratio 0.5 to 1%) are shown in Table 2. Further, after rolling, recrystallization annealing is omitted, and material properties after pickling and temper rolling (reduction ratio of 0.5 to 1%) are shown in Table 3. Note that the tensile properties were determined using a JISS No. test piece.

Furthermore, the ridging property was evaluated using a JIS No. 5 test piece cut out from the rolling direction and subjected to a tensile strain of 15χ, and visually inspecting the surface unevenness on a scale of 1 (good) to 5 (poor). No evaluation criteria have been established for this evaluation because virtually no ridging appeared when using the conventional manufacturing method of low carbon cold rolled steel sheets. Therefore, in this invention, the index evaluation criteria based on the visual method for conventional stainless steels are applied as is. Ratings 1 and 2 indicate ridging properties that pose no problem in practical use.

The thin steel sheet manufactured according to the present invention exhibits better ridging resistance and workability than the comparative example.

(Effects of the Invention) According to the present invention, by simply regulating the steel composition and omitting the cold rolling process or the cold rolling-recrystallization annealing process, a thin film with good workability and excellent ridging resistance can be obtained. It is possible to obtain steel plates, and the rolled material is also compatible with the sheet bar caster method, strip caster method, etc., and the manufacturing process of thin steel plates for processing can be greatly simplified.

[Brief explanation of drawings]

Figure 1 shows (C+0.02・
FIG. 2 is a graph showing the influence of the (C+0.02·N) amount, the 0 amount, and the rolling reduction rate on the lowering index. Figure 1 C (wf%) to, 02・N (Wf%) Figure 2 C (wr%) to, 02-AI (pry%) Procedure
Amendment December 28, 1985 Michibe Uga, Commissioner of the Patent Office1, Incident Indication 1985 Patent Export No. 2199992 Title of Invention Warm rolled thin steel plate for processing with excellent ridging resistance and its manufacture Method 3: Relationship with the case of the person making the amendment Patent applicant (125) Kawasaki Steel Corporation 4, agent

Claims (1)

[Claims] 1. C: 0.01 wt% or less, Si: 0.10 wt% or less, Mn: 0.5 wt% or less, P: 0.1 wt% or less, Al: 0.002 to 0.10 wt% , N: 0.01 wt% or less, O: 0.003 wt% or less, and C content and N content are 0.001 (wt%) ≦ C (wt%) + 0.02・N (
A warm-rolled thin steel sheet for processing with excellent ridging resistance, which satisfies the relationship: wt%)≦0.010 (wt%), and has a composition of unavoidable impurities and Fe with the remainder being unavoidable impurities. 2, C: 0.01wt% or less, Si: 0.10wt% or less, Mn: 0.5wt% or less, P: 0.1wt% or less, Al: 0.002 to 0.10wt%, N: 0.01wt % or less, O: 0.003 wt% or less, 200 A method for producing a warm-rolled thin steel sheet for processing with excellent ridging resistance, characterized by performing at least one pass of warm rolling in a temperature range of ~800°C, and subsequently annealing in a range of 400-950°C. . 3. C: 0.01wt% or less, Si: 0.10wt% or less, Mn: 0.5wt% or less, P: 0.1wt% or less, Al: 0.002-0.10wt%, N: 0.01wt % or less, O: 0.003 wt% or less, 300 A method for producing an as-rolled warm-rolled thin steel sheet for processing with excellent ridging resistance, characterized by performing warm rolling at a reduction rate of 35% or more in at least one pass in the temperature range of °C to Ar_3 transformation point.