JPH0873933A - Production of autoobile hot rolled steel sheet excellent in corrosion resistance - Google Patents

Abstract

PURPOSE: To provide a method for producing a hot rolled steel sheet excellent in corrosion resistance in an environment contg. chlorides and furthermore good in workability. CONSTITUTION: A steel contg. 0.0001 to 0.18% C, 0.30 to 1.5% Si, 0.10 to 2.O% Mn, 0.020 to O.12% P,<=0.020% S, 0.10 to 0.80% Cu, 0.01 to 0.50% Ni, 0.10 to 0.60% sol.Al, <=0.0040% N and 0 to 0.0050% B, furthermore contg., at need, one or more kinds among 0.0002 to 0.01% Ca, 0.01 to 0.10% Zr, 0.002 to 0.10% rare earth elements, 0.01 to 1.20% Cr, 0.003 to 0.10% Ti, 0.003 to 0.10% Nb and 0.003 to 0.10% V, and the balance Fe with ineyitable impurities is subjected to continuous casting. Directly after that or after being reheated to >=1150 deg.C, it is subjected to hot rolling. The hot rolling is completed at >=800 deg.C, and it is coiled at <=500 deg.C. Thus, the hot rolled steel sheet usable without being applied with galvanizing as a corrosion resistant material for automobiles or the like can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a steel sheet for high-strength members for automobiles or industrial machines, which is excellent in corrosion resistance in an environment containing chloride and has good workability. The present invention relates to a method for manufacturing a rolled steel sheet.

[0002]

2. Description of the Related Art In order to improve the performance and cost efficiency of automobiles, it is always required to achieve both performance and cost even for thin steel sheets for automobiles, but the present invention also requires steel sheets with excellent corrosion resistance at low cost. The present invention relates to a manufacturing method. With the increasing use of road antifreeze materials such as salt and calcium chloride in cold regions, and the increasing demand to prevent the rapid corrosion progress of automobile parts in harsh environments such as beach areas, rust-proof steel sheets have been Usage is expanding. In automobiles where appearance is important, stainless steel and zinc-based plated steel sheets are often used in places visible from the outside to prevent even slight rusting during a long service period. Further, since the steel plate used as the outer plate is thin, galvanization or the like is used as a countermeasure against perforation due to the progress of corrosion from the inside due to the environment containing salt and the like.

[0003] Zinc-based plated steel sheets generally have sufficient rust preventive power during the service life of automobiles, but steel sheets having a relatively large thickness used for strength members such as suspension parts are usually visible from the outside. If there is no problem and there is no problem in use, it is considered that there is no problem even if rust occurs on the surface. Further, these parts are often assembled by arc welding after press forming. Weldability is not a problem for general unplated steel sheets, but when zinc-based plated steel sheets are arc-welded, blowholes, etc. due to evaporation of Zn in the plating film on the lap fillet welds. However, there was a problem that the reliability of the joint was impaired and sufficient component strength could not be obtained, such as the occurrence of welding defects in No. 2 and a decrease in fatigue strength.

Further, when the plate thickness is thin, even if a bare part without plating appears on the cut end face, the anticorrosion effect due to zinc plating on the plate surface can be expected, but if the thickness is thick like hot rolled steel plate, the effect tends to disappear. In addition, plating thick plates is expensive. Therefore, it is desired that the steel sheet itself has corrosion resistance and the cost is low.

As a steel plate having good corrosion resistance to which an alloy component is added, there is stainless steel. However, it has a durability far exceeding the service life of automobiles for use in undercarriage, etc.
Moreover, it is expensive and practically unthinkable. On the other hand, the corrosion resistance is inferior to the zinc-based plated steel sheet and rust occurs on the surface, but the corrosion resistance is far better than the normal hot-rolled high-strength steel sheet, which is sufficient for the life of the automobile. There is a demand for steel plates that have corrosion resistance and are cheaper than plated steel plates.
Corresponding steel sheets are being studied.

According to the same concept as that of weather resistant steel, a small amount of elements such as P, Cu and Cr are added to the steel sheet to change products such as rust generated by corrosion into a dense film, and It is intended to restrain the progress of. It is necessary to examine the type and amount of the additive element depending on the corrosion environment and the like. For example, in Japanese Patent Laid-Open No. 54-9113, in the corrosion of the automobile body by the road deicing inhibitor for the steel plate without plating,
In particular, for the purpose of preventing pitting corrosion, the addition of Cr was stopped, Cu,
A corrosion-resistant steel plate to which the three elements of P and Ni are added is presented.

Hot-rolled steel sheets used for underbody parts of automobiles and the like are often formed into a required shape by press working, and bending is mainly performed, but depending on the shape, elongation and hole expandability are required. It is preferable that these have good processability. At present, it is hard to say that a steel sheet that is sufficiently satisfactory is provided at present in response to the demand for a low-cost hot-rolled steel sheet having excellent corrosion resistance, good workability, and low cost.

[0008]

Means for Solving the Problems The present inventors have obtained the following findings as a result of repeated studies to achieve the above object.

First, from the experience in conventional weathering steel,
After adjusting to the required strength level with C, Mn, and Si,
After investigating the corrosion resistance of a hot rolled steel sheet to which a small amount of Cu, P and Ni were added, the effects of changing the amount and adding other elements were investigated. In this case, assuming a corrosive environment containing chlorides inside the automobile body, "salt water spray (0.5%
A dry-wet repeated test was carried out with one cycle of "saline, 35 ° C x 7h hold)-> dry (70 ° C x 5h hold)-> wet (humidity: 85%, 50 ° C x 12h hold)". From those results,
It was found that the corrosion resistance is remarkably improved by increasing the amount of Si and adding Al in addition to Cu, P and Ni.

An example comparing the effects of these additional elements is shown in FIG.
Shown in In this case, C: 0.14%, Si: 0.05% and M
Based on steel containing n: 1.30%, steel with almost no impurity element added, nothing added, steel added with Cu: 0.35%, Ni: 0.15% and P: 0.045%, and these components Then, steel ingots with Si: 0.56% and Al: 0.37% were vacuum-melted in a laboratory, heated to 1200 ° C, finished at 880 ° C, and hot-rolled under conditions equivalent to winding at 500 ° C. As a result, a hot rolled steel sheet with a thickness of 2.5 mm was used. From these hot rolled steel sheets
Cut out a 2.0 mm thick × 70 mm wide × 150 mm long test piece,
After exposing to the above corrosive environment, the corrosion resistance of the steel sheet was evaluated by the method of measuring the maximum corrosion depth of the test piece. From this figure, C
It can be seen that the addition of u, P and Ni has better corrosion resistance than mild steel, and that the combined addition of Si and Al further improves the corrosion resistance.

Furthermore, the corrosion resistance of this steel sheet was also influenced by the hot rolling conditions, and the heating temperature and finishing temperature of the material before rolling were sufficiently high, and the coiling temperature was low. The reason for this is not clear, but Al and N in the steel do not precipitate as AlN in the hot-rolled steel sheet, and the hot-rolling conditions in which they are in a substantially solid solution state and the conditions for improving corrosion resistance match, It is considered that if AlN is deposited, it promotes the local cell reaction and deteriorates the corrosion resistance.

The present invention has been completed on the basis of the above-mentioned findings and the like, and the steel of (1), (2), (3) or (4) shown below is used to directly cast a raw billet directly after continuous casting. , Or reheat to 1150 ℃ or higher, and then finish hot rolling at 800 ℃ or higher,
A method for producing a hot-rolled high-strength steel sheet having excellent corrosion resistance, which comprises winding at a temperature of 500 ° C or lower.

(1) C: 0.0001 to 0.18% by weight,
Si: 0.30 to 1.50%, Mn: 0.10 to 2.00%, P: 0.02 to
0.12%, S: 0.02% or less, Cu: 0.10 to 0.80%, Ni:
0.01 to 0.50%, sol.Al: 0.10 to 0.60%, N: 0.0040%
Below and B: Steel containing 0 to 0.0050% with the balance Fe and unavoidable impurities.

(2) C: 0.0001 to 0.18% by weight,
Si: 0.30 to 1.50%, Mn: 0.10 to 2.00%, P: 0.02 to
0.12%, S: 0.02% or less, Cu: 0.10 to 0.80%, N
i: 0.01 to 0.50%, sol.Al: 0.10 to 0.60%, N: 0.00
40% or less and B: 0 to 0.0050%, and further C
a: 0.0002 to 0.01%, Zr: 0.01 to 0.10% and rare earth element: 0.002 to 0.10%, and the balance is F
Steel consisting of e and inevitable impurities.

(3) C: 0.0001 to 0.18% by weight,
Si: 0.30 to 1.50%, Mn: 0.10 to 2.00%, P: 0.02 to
0.12%, S: 0.02% or less, Cu: 0.10 to 0.80%, N
i: 0.01 to 0.50%, sol.Al: 0.10 to 0.60%, N: 0.00
40% or less and B: 0 to 0.0050%, and further C
r: 0.01 to 1.20%, Ti: 0.003 to 0.10%, Nb: 0.00
Steel containing at least one of 3 to 0.10% and V: 0.003 to 0.10%, with the balance being Fe and inevitable impurities.

(4) C: 0.0001 to 0.18% by weight,
Si: 0.30 to 1.50%, Mn: 0.10 to 2.00%, P: 0.02 to
0.12%, S: 0.02% or less, Cu: 0.10 to 0.80%, N
i: 0.01 to 0.50%, sol.Al: 0.10 to 0.60%, N: 0.00
40% or less and B: 0 to 0.0050%, and further C
a: 0.0002 to 0.01%, Zr: 0.01 to 0.10% and rare earth element: 0.002 to 0.10%, and C
r: 0.01 to 1.20%, Ti: 0.003 to 0.10%, Nb: 0.00
Steel containing at least one of 3 to 0.10% and V: 0.003 to 0.10%, the balance being Fe and inevitable impurities.

In the following, the reason why the component composition of the raw steel billet and the manufacturing conditions of the hot rolled steel sheet are limited as described above in the present invention will be explained together with its action.

[0018]

[Action]

A) Component ratio of raw steel slab (1) C: 0.0001 to 0.18% C is an element that can inexpensively increase the strength of steel sheet, but when the content increases, hard second phases such as cementite particles and pearlite phase increase. However, since the workability of the obtained hot rolled steel sheet is deteriorated and the weldability is deteriorated, it is set to 0.18% or less. Regarding the strength, since P and Si, which have a large effect of solid solution strengthening, are added, they should be kept to the necessary minimum. Further, an increase in the cementite particles and the pearlite phase increases the electrochemical non-uniformity, promotes the local corrosion reaction, and lowers the corrosion resistance. Therefore, it is preferable that the C content be small. If the strength and the cost of reducing C are allowed, reducing it to 0.02% or less will further improve the corrosion resistance and improve the workability, but reducing it to less than 0.0001% is practical in terms of cost. is not.

(2) Si: 0.30 to 1.50% Si, particularly when added in combination with Al, has the effect of significantly improving the corrosion resistance of the steel sheet. Although the mechanism by which Si enhances the corrosion resistance is unknown, in the steels with Cu and P added, a dense α-FeOOH phase is generated at the interface between the base iron and the rust layer, which has the effect of suppressing the formation of rust. Al is α-
It seems to have an effect of increasing the stability of the FeOOH phase against chlorine ions. Since Si has a large solid solution strengthening effect and the deterioration of elongation due to the increase in strength is relatively small,
It is convenient to obtain a high-strength steel plate with good workability. However, caution is required because the surface properties are deteriorated by the formation of oxides. If the Si content is less than 0.30%, its corrosion resistance improving effect is small, and if it exceeds 1.50%, it is hardened too much to lower the workability or deteriorate the surface property, so the Si content is 0.30 to 1.50. Defined as%.

(3) Mn: 0.1 to 2.0% Mn is not directly related to the corrosion resistance, but has the function of increasing the strength of the hot rolled steel sheet through solid solution strengthening and transformation strengthening. However, if the content exceeds 2.0%, hard martensite and the like are likely to occur, and workability and weldability are greatly deteriorated. If strength is not particularly required, 1.2% or less is preferable. Also, a minimum of 0.1% is necessary to prevent hot embrittlement due to S mixed as an unavoidable impurity. For these reasons, the component amount range is 0.1-2.0%.

(4) Cu: 0.10 to 0.80% Cu is a main component for improving the corrosion resistance,
Improves corrosion resistance through the formation of a dense corrosion film. It also has the effect of increasing the strength of the steel sheet through solid solution strengthening. If the content is less than 0.10%, the desired effect due to the above-mentioned action cannot be obtained, while if it exceeds 0.80%, not only the above-mentioned action is saturated but also Cu
It is necessary to increase the amount of Ni added in order to prevent hot work cracking due to addition, and this impairs economic efficiency. From this, the Cu content is 0.
It was set at 10 to 0.80%.

(5) Ni: 0.01 to 0.50% Ni has an effect of preventing deterioration of hot workability due to addition of Cu and an effect of improving corrosion resistance, but its content is 0.01%. If it is less than 0.5%, the desired effect due to the above action cannot be obtained, while if it exceeds 0.50%, the economical efficiency is impaired. Therefore, the Ni content is set to 0.01 to 0.50%.

(6) P: 0.02 to 0.12% P enhances corrosion resistance through the formation of a dense corrosion film, but has a large effect of solid solution strengthening. If its content is less than 0.02%, the effect of improving corrosion resistance cannot be obtained, while on the other hand, it is 0.
If the content exceeds 12%, the toughness and hole expandability of the base material deteriorate, so the content was made 0.02 to 0.12%.

(7) S: 0.02% or less In most cases, S reacts with Mn in steel to form MnS, but since it deteriorates properties such as corrosion resistance, workability and toughness, the smaller the content, the better. However, the reduction of S leads to an increase in cost, and is 0.02 as a limit that does not impair the effects of the present invention.
% Or less, but preferably 0.008% or less.

(8) sol.Al: 0.10 to 0.60% Al is usually added as a deoxidizing agent for ensuring the soundness of the slab. In the present invention, however, the addition of Si in combination greatly increases the corrosion resistance of the steel sheet. Has the effect of improving.

The action is considered to be similar to that of Si, and sol.
If the content as l is less than 0.10%, the desired effect due to the above-mentioned action cannot be obtained, while if the content exceeds 0.60%, the above action is saturated, so the sol.Al content is 0.10%. It was set at ~ 0.60%.

(9) N: 0.0040% or less N is one of the unavoidable impurities and usually reacts with Al in steel to form AlN. It is considered that when a large amount of AlN particles are generated, the local cell reaction is promoted and the corrosion resistance is deteriorated. As described below, precipitation can be prevented by selecting hot rolling conditions such as increasing the slab heating temperature in hot rolling and decreasing the winding temperature. However, when a large amount of Al is contained as in the present invention, it becomes difficult to prevent precipitation when the amount of N is large, so the content is limited to 0.0040% or less. From the viewpoint of preventing the generation of AlN particles, the N content is preferably 0.0020% or less.

(10) B: 0 to 0.0050% B segregates at the grain boundaries and strengthens the crystal grain boundaries of the steel. In the corrosion-resistant steel sheet of the present invention, since P that promotes grain boundary embrittlement is added, when the C content is particularly low, the origin of cracks may show secondary work brittleness at grain boundaries. Therefore, B is added if necessary. However, the B content is 0.
If less than 0003%, the effect is not sufficient, so if adding
0.0003% or more is desirable. On the other hand, if the content exceeds 0.0050%, not only the above effects are saturated but also the ductility and hole expandability of the steel sheet are deteriorated.

(11) Ca: 0.0002 to 0.01%, Zr: 0.01
.About.0.10% and rare earth element: 0.002 to 0.10% Ca, Zr, and rare earth element (REM) all have the effect of improving the workability and toughness of the hot-rolled steel sheet. Two or more kinds are added.

That is, Ca, Zr and rare earth elements all change the properties and morphology of inclusions in the steel to make them difficult to spread during hot rolling and prevent deterioration of workability and toughness. If the content is small, the desired effect cannot be obtained, and if it is too large, the workability and toughness are deteriorated. Therefore, the content range of each element is 0.0002 for Ca.
~ 0.01%, Zr 0.01 ~ 0.10%, and rare earth elements
0.002 to 0.10%

(12) Cr: 0.01 to 1.20%, Ti: 0.003
.About.0.10%, Nb: 0.003 to 0.10% and V: 0.003 to 0.
10% Cr, Ti, Nb, and V are all effective elements for strengthening the steel sheet, so one or more kinds of them are added as necessary.

In particular, Cr has the effects of enhancing the strength of the steel sheet by transformation strengthening and, at the same time as Cu and P, changing the corrosion products on the surface into a dense film and improving the corrosion resistance. But,
In a corrosive environment containing chloride, pitting corrosion tends to be accelerated, and although the average corrosion weight loss decreases, the maximum corrosion depth tends to increase. For this reason, conventionally, the addition of Cr has been avoided in addition to the addition of Cu and P. However, Si and A
When the amount of 1 is increased, this promotion of pitting corrosion is suppressed and Cr can be added. Unlike Mn, the addition of Cr does not cause center segregation, so that it has the effect of preventing the formation of a band-like structure in the second phase such as bainite and improving the hole expandability. Therefore, it is added if necessary, but if it is less than 0.01%, there is no effect of addition, and if it exceeds 1.2%, there is a risk of pitting corrosion, so the Cr content is made 0.01 to 1.2%.

Ti, Nb and V all form fine precipitates of TiC, NbC, VC, etc. in the cooling process after hot rolling, and the strength can be easily increased. Therefore, it is added as needed to improve the strength. If the content of any element is 0.003% or less, no effect will appear,
If it exceeds 0.10%, the workability will deteriorate. Therefore, the content of Ti is 0.003 to 0.10%, and the content of Nb is 0.003 to 0.10.
%, And V was also set to 0.003 to 0.10%.

B) Manufacturing Conditions As the steel piece to be subjected to hot rolling, either a continuously cast slab or a slab of slabs may be used. The slab obtained by continuous casting may be directly rolled, or the slab once cooled may be reheated and used. However, when the slab is reheated, the reheating temperature is set to 1150 ° C. or higher in order to sufficiently re-dissolve the nitride such as AlN.

Further, it is desirable that the hot rolling finishing temperature is a temperature sufficiently higher than the A ₃ point in consideration of the precipitation behavior of AlN. This Upon completion of hot working at a temperature below directly above or A ₃ points ₃ points A, AlN by ferrite transformation
Is rapidly deposited. A ₃ points is C amount, S
It greatly changes depending on the amount of i and the amount of Mn, and is strongly affected by the working degree of hot working and the working temperature. Therefore, although it was decided here that hot rolling should be terminated at 800 ° C or higher, rather than being regulated uniformly at a fixed limit temperature,
It is preferable to set the temperature at which the precipitation of AlN does not accelerate in the actually applied steel.

The coiling temperature in the hot rolling step is 500 ° C. or less because the corrosion resistance deteriorates as the coiling temperature increases. It is considered that this is because when the temperature exceeds 500 ° C, AlN is generated during the slow cooling after winding. Further, when the Si content is high like the steel of the present invention, the descaling property at the time of pickling is not good, but when the winding temperature is lowered, the oxide film formed on the surface of the steel sheet becomes thin and the descaling property is improved. It Although the lower limit of the coiling temperature is not particularly set, it is naturally determined by the mechanical properties and shape required for the product steel sheet.

The effects of the present invention will be described more specifically by way of examples.

[0038]

【Example】

[Example 1] Hot rolling high tensile strength steel plates with a plate thickness of 2.6 mm were obtained by hot rolling the slabs whose chemical composition was indicated by A to V in Table 1 under the conditions shown in Table 2. It was

[0039]

[Table 1]

[0040]

[Table 2]

Next, a JIS No. 5 tensile test piece was taken from each of the obtained hot rolled steel sheets, and the tensile properties were investigated. In addition, 2
A steel piece having a width of 50 mm and a length of 250 mm was sampled, a hole having a diameter of 30 mm was punched out, and then a hole expanding test was performed with a conical punch having an apex angle of 60 °.

After grinding the surface of each of the above hot rolled steel sheets,
A 2.0 mm thick × 70 mm wide × 150 mm long test piece was cut out, and a dry / wet repeated test under the same conditions as the corrosion test obtained in the result of FIG. 1 was conducted to examine the change in the maximum corrosion depth.

As is clear from the results shown in Table 2, the hot-rolled high-tensile steel sheet manufactured under the conditions specified in the present invention has excellent corrosion resistance and good workability such as elongation and hole expansion. I understand.

That is, the test number 22 in Table 2 is the normal 5
Although P and Cu are added to the 0 kg class steel, it can be seen that the steels of the present invention have excellent corrosion resistance in comparison with this.

From the comparison with Test Nos. 1, 2, 3 and 19, or Test Nos. 4 and 20, even if the components are within the scope of the present invention, sufficient corrosion resistance can be obtained if the hot rolling temperature is high. You can see that you cannot get it. If the finishing temperature is too low, not only the corrosion resistance is poor as shown in Test No. 21, but also the workability is deteriorated. In the test numbers 23 and 24 in which the amounts of Al, P and Cu were out of the lower limits of the present invention,
Sufficient corrosion resistance is not obtained. Even if the amounts of Si and Al are sufficient as in Test No. 25, if the amount of N and Cr is too large, the corrosion resistance does not improve. Test No. 26 has Si and Al in the range of the present invention and is excellent in corrosion resistance, but Ti
Is too high, resulting in poor workability. Test number 27 is also Si
Although the effect of improving corrosion resistance by Al and Al is recognized to some extent,
C, Nb and V are too high and the workability is insufficient.

[Example 2] A case of an ultra-low carbon steel is shown for an application requiring workability rather than high tension.

The chemical composition is a to o and q to u in Table 3.
The slab shown in Table 1 was hot-rolled under the conditions shown in Table 4 and wound to obtain a hot-rolled steel sheet having a plate thickness of 2.6 mm.

[0048]

[Table 3]

[0049]

[Table 4]

Then, test pieces were sampled from the obtained hot-rolled steel sheet in the same manner as in Example 1, and the tensile properties, hole expandability and corrosion resistance were examined. The results of these tests are also shown in Table 4.

As is clear from the results shown in Table 4, the hot-rolled steel sheet manufactured under the conditions specified in the present invention has excellent corrosion resistance and at the same time has good elongation and hole expandability. I understand.

On the other hand, in the test numbers 44 and 45 in which the winding temperature was out of the upper limit of the specified value of the present invention, good corrosion resistance was not obtained. Further, although the finishing temperature is within the specified value of the present invention, in the test number 46 in which it is considered that the finishing temperature on the component has fallen below the A ₃ transformation point, not only the corrosion resistance is not good, but also the hole expandability is poor. There is. Also, Si, A
In Test Nos. 47 to 49 in which the amounts of 1, P and Cu were out of the lower limits of the present invention, the corrosion resistance was not improved and Si or Mn
In the test numbers 50 and 51 in which the amount exceeds the upper limit of the specified value of the present invention, the corrosion resistance is good, but the workability is deteriorated.

[0053]

As described above, according to the present invention, it is possible to inexpensively improve the corrosion resistance required for a member used in an environment containing chloride, and the structure for automobiles or industrial machines can be obtained. Industrially extremely useful effects such as stable mass production of hot-rolled steel sheets suitable as members become possible.

[Brief description of drawings]

FIG. 1 shows Cu, Ni, P and additionally Si, A.
It is a graph comparing the corrosion resistance (maximum corrosion depth) of the corrosion resistant steel containing 1 with that of ordinary steel.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location C22C 38/54 (72) Inventor Akito Sakoda 4-53, Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metals Industrial Co., Ltd. (72) Inventor Shigeru Wakano 4-53 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd.

Claims (4)

[Claims] 1. A weight ratio of C: 0.0001 to 0.18%, S
i: 0.30 to 1.50%, Mn: 0.10 to 2.00%, P: 0.02 to 0.
12%, S: 0.02% or less, Cu: 0.10 to 0.80%, Ni: 0.
Steel containing 01 to 0.50%, sol.Al: 0.10 to 0.60%, N: 0.0040% or less and B: 0 to 0.0050%, with the balance Fe and inevitable impurities, directly after continuous casting or
A method for producing a hot-rolled steel sheet having excellent corrosion resistance, which comprises reheating to 1150 ° C or higher, hot rolling, completing hot rolling at 800 ° C or higher, and winding at a temperature of 500 ° C or lower. 2. By weight ratio, C: 0.0001 to 0.18%, S
i: 0.30 to 1.50%, Mn: 0.10 to 2.00%, P: 0.02 to 0.
12%, S: 0.02% or less, Cu: 0.10 to 0.80%, Ni:
0.01 to 0.50%, sol.Al: 0.10 to 0.60%, N: 0.0040%
The following and B: 0 to 0.0050%, and Ca: 0.
0002 to 0.01%, Zr: 0.01 to 0.10% and rare earth elements:
Steel containing at least one of 0.002 to 0.10% and the balance being Fe and unavoidable impurities is directly cast or reheated to 1150 ° C or higher after continuous casting, then hot-rolled and hot-rolled at 800 ° C or higher. A method for producing a hot-rolled steel sheet excellent in corrosion resistance, which comprises rolling at a temperature of 500 ° C or less after completion of rolling. 3. A weight ratio of C: 0.0001 to 0.18%, S
i: 0.30 to 1.50%, Mn: 0.10 to 2.00%, P: 0.02 to 0.
12%, S: 0.02% or less, Cu: 0.10 to 0.80%, Ni:
0.01 to 0.50%, sol.Al: 0.10 to 0.60%, N: 0.0040%
Or less and B: 0 to 0.0050%, and further Cr: 0.
01 to 1.20%, Ti: 0.003 to 0.10%, Nb: 0.003 to 0.
10% and V: 0.003 to 0.10%, and at least one of
Steel with the balance Fe and unavoidable impurities is directly cast or reheated to 1150 ℃ or higher after continuous casting, then hot rolled, completed hot rolling at 800 ℃ or higher, and wound at a temperature of 500 ℃ or lower. A method for producing a hot-rolled steel sheet having excellent corrosion resistance, which is characterized by the following. 4. By weight ratio, C: 0.0001 to 0.18%, S
i: 0.30 to 1.50%, Mn: 0.10 to 2.00%, P: 0.02 to 0.
12%, S: 0.02% or less, Cu: 0.10 to 0.80%, Ni:
0.01 to 0.50%, sol.Al: 0.10 to 0.60%, N: 0.0040%
The following and B: 0 to 0.0050%, and Ca: 0.
0002 to 0.01%, Zr: 0.01 to 0.10% and rare earth elements:
Contains at least one of 0.002 to 0.10%, and Cr: 0.0
1-1.20%, Ti: 0.003-0.10%, Nb: 0.003-0.1
0% and V: 0.003 to 0.10%, including one or more of
Steel with the balance Fe and unavoidable impurities is directly cast or reheated to 1150 ℃ or higher after continuous casting, then hot rolled, completed hot rolling at 800 ℃ or higher, and wound at a temperature of 500 ℃ or lower. A method for producing a hot-rolled steel sheet having excellent corrosion resistance, which is characterized by the following.