JPH08143953A - Production of aging resisting hot rolled steel plate of baking hardening type - Google Patents

Abstract

PURPOSE: To produce an aging resisting hot rolled steel plate of baking hardening type, which has aging resistance capable of holding softness till at the time of forming and can be increased in strength at the time of baking finish after forming. CONSTITUTION: The aging resisting hot rolled steel plate of baking hardening type can be produced by subjecting a slab of a steel, which has a composition consisting of, by weight, 0.003-0.08% C, <=0.25% Si, 0.05-1.5% Mn, <=0.1% P, <=0.02% S, 0.004-0.035% Al, 0.001-0.006% N, and the balance iron with inevitable impurities and containing, if necessary, 0.05-1.0% Cu and <=1.0% Ni, to hot rolling at 830-940 deg.C hot rolling finishing temp. and 525-675 deg.C coiling temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing technology of a hot rolled steel sheet for automobiles used as a reinforcing member or an underbody member of an automobile, and to produce a hot rolled steel sheet having aging resistance and bake hardenability. It is about the method.

[0002]

2. Description of the Related Art Hot rolled steel sheets, which are widely used as reinforcing members and underbody members for automobiles, are manufactured by JIS G3113 SPH.
C, SPHD, SPHE and SPA of JISG3131
The mainstream was a soft hot-rolled sheet such as H310 which was inexpensive and had good formability and was soft. However, from the viewpoint of improving fuel efficiency of automobiles, weight reduction of car bodies is aimed, and use of high-strength hot-rolled steel sheets is increasing.

Since these high-strength hot-rolled steel sheets are used for chassis, members, wheels, etc., not only the strength but also the formability such as drawability, overhanging property, shape fixability and weldability are good. In addition, it was necessary to control the variation in strength within a very narrow range. In order to meet these demands, development of high strength hot rolled steel sheets for automobiles with good formability has been focused on,
Research has been conducted for practical use such as improvement of material properties and relationship between material properties and car body molding. Through these efforts, the formability of high-strength hot-rolled steel sheets strengthened by solid solution strengthening and precipitation strengthening was improved, and composite structure type steel sheets, retained austenite type steel sheets, and bainite type steel sheets were developed. There are numerous proposals for these high strength hot rolled steel sheets.

For example, regarding a composite microstructure hot rolled steel sheet having a low yield stress and good ductility, iron and steel, 58 (197)
4) A method for obtaining a composite structure by controlled cooling is proposed in 4, S220, J. Metals, 30 (1978)
4, p6: iron and steel, 64 (1978) 4, S257: iron and steel, 64 (1978) 4, S257 with Mn-Si-C
A manufacturing method for obtaining a composite structure with an r-Mo steel plate has been proposed,
Further, JP-A-59-140332 and JP-A-62-9
Many technologies similar to this are disclosed in Japanese Patent Publication Nos. 3001 to 93005 and the like.

Regarding a retained austenitic steel sheet having a better ductility than the composite structure hot rolled steel sheet, JP-A-60-
Many techniques are disclosed, such as Japanese Patent Laid-Open No. 43425, Japanese Patent Laid-Open No. 60-165320 and Japanese Patent Laid-Open No. 63-4017. With respect to a bainite type steel sheet having a good stretch flangeability, many techniques have been disclosed such as JP-A-57-145965 and JP-A-2-179847.

These are techniques for obtaining not only the strength of a steel sheet but also a steel sheet having excellent formability, and are intended to achieve thinning, that is, weight reduction of an automobile steel sheet. However, although the strength of steel sheets is increased, although great effort is being made to obtain formability comparable to that of soft steel sheets by selecting strengthening elements, reducing impurities, adjusting and controlling the metal structure, etc. Deterioration in formability cannot be denied, and weldability, surface texture, chemical conversion treatment, etc. also generally deteriorate. Furthermore, a large amount of alloying elements are required, and the productivity is inferior, so the manufacturing cost is inevitably high.

Recently, cost reduction of automobiles has become a major issue. However, if a soft steel plate is simply used for cost reduction, the amount of steel used increases and the vehicle body weight increases. Make fuel consumption worse. Therefore, there is a strong demand for hot-rolled steel sheets that have good formability, high strength, and low cost.

From this point of view, a bake-hardening type in which the softest possible state is maintained at the time of molding and curing (strengthening) is performed by utilizing the baking temperature (around 160 to 180 ° C.) at the time of baking coating after molding. Various high strength hot rolled steel sheets have been proposed. For example, Japanese Patent Application Laid-Open No. 62-180021 proposes a method of quenching steel having a specific chemical composition containing N after hot rolling. In this method, a ferrite and bainite structure is obtained by hot-rolling and then quenching to increase the strength, and bake hardening is obtained by utilizing the strain aging of solid solution N.

On the other hand, there is a strong demand for improvement of corrosion resistance such as perforation corrosion resistance in steel sheets used for underbody members and reinforcing members of automobiles. Since these members are exposed to corrosion by, for example, sea salt particles in coastal areas and salts sprayed for road surface freeze prevention or snow melting in cold regions, higher corrosion resistance is required.

As a typical method for improving the corrosion resistance of a steel sheet, there is a Zn plating method, and from this background, many hot-dip Zn-plated steel sheets having excellent corrosion resistance have been developed. For example, Japanese Unexamined Patent Publication No. 2-310354 discloses a method for producing a hot-dip Zn-plated steel sheet having excellent workability.
However, most of the undercarriage members and reinforcing members of automobiles are manufactured by arc-welding individual parts, and those using Zn-plated steel sheet are prone to defects such as blowholes during welding, and sound welding There is a problem that it is difficult to get a copy. This problem can be solved to some extent by using a Zn coating having a light weight, for example, JP-A-2-22416.
In the publication, an alloyed hot dip galvanized steel sheet having excellent corrosion resistance even with a light weight is introduced. However, it is difficult to completely avoid the occurrence of defects during welding because the Zn plating layer exists on the surface of the steel sheet even though the weight is light.

Therefore, a steel plate that can be used without being used as the underbody member or the reinforcing member is required, but a high strength steel plate having a thin plate for high strength is required in order to reduce the weight of the vehicle body. However, the reduction in plate thickness associated with higher strength has a disadvantageous effect on pitting corrosion.

From such a background, the inventors of the present invention have disclosed in JP-A-5-195144 and JP-A-5-195145 a high strength that can be used as an underbody member or a reinforcing member of an automobile without being used. A hot-rolled steel sheet and its manufacturing method are proposed. However, these hot-rolled steel sheets require a large amount of alloying elements to increase the strength of the steel sheet, and in order to improve workability, it is necessary to reduce impurities and control the metallographic structure. In terms of cost, it cannot be denied that the cost will increase.

[0013]

The conventional bake hardening type hot rolled steel sheet utilizes the strain aging of solute N. However, since solute N generally precipitates to dislocations even at room temperature, it can be kept at room temperature. If kept, the hot rolled steel sheet hardens due to room temperature aging and the ductility deteriorates. For this reason, there are problems that the press formability may already be deteriorated at the time of press forming and the plate shape may be deteriorated.

In view of such an actual situation, the present invention makes the strength of the hot-rolled steel sheet material as low as possible, and has the aging resistance capable of maintaining the state for a long time. In preparation, a hot rolled steel sheet that can be hardened at the time of bake coating after press forming and has high strength is an issue.

In addition to solving such problems,
The object is to develop a hot-rolled steel sheet that has excellent corrosion resistance such that bare materials can be used as underbody members and reinforcing members for automobiles.

[0016]

According to the present invention, the weight percent is
Then, C: 0.003 to 0.08%, Si: 0.25% or less, Mn: 0.05 to 1.5%, P: 0.1% or less, S:
0.02% or less, Al: 0.004 to 0.035%, N:
0.001 to 0.006%, and in some cases, (1) a total of one or two of W and Mo: 0.005 to 0.005.
1% (2) Total of one or more of Ti, Nb and V: 0.0.
04 or less, where (Ti + Nb + V) / (C + N):
4 or less, (3) B: 0.0003 to 0.003%, containing these singly or in combination, with the balance being iron and unavoidable impurities, the steel slab is hot rolled at a finishing temperature of 830 to 830. 940 ° C, winding temperature: 525-675 ° C
Provided is a method for producing an age-resistant, bake-hardening hot-rolled steel sheet, which comprises hot-rolling with.

Furthermore, according to the invention, in% by weight, C:
0.003 to 0.08%, Si: 1.5% or less, Mn: 0.0
05-1.5%, P: 0.01-0.1%, S: 0.02%
Hereinafter, Cu: 0.05 to 1.0%, Al: 0.004 to 0.0.
035%, N: 0.001 to 0.006%, and if necessary, Ni: 1.0% or less, depending on the case, (1) One or two of W and Mo. Total species: 0.005-0.
1% (2) Total of one or more of Ti, Nb and V: 0.0.
04 or less, where (Ti + Nb + V) / (C + N):
4 or less, (3) B: 0.0003 to 0.003%, containing these singly or in combination, with the balance being iron and unavoidable impurities, the steel slab is hot rolled at a finishing temperature of 830 to 830. 940 ° C, winding temperature: 525-675 ° C
Provided is a method for manufacturing a corrosion-resistant, aging-resistant, bake-hardened hot-rolled steel sheet, which comprises hot rolling.

[0018]

The above problems have been solved by the composition design of steel and regulation of hot rolling conditions according to the present invention. That is, the hot-rolled steel sheet obtained by the method of the present invention has low strength and high elongation as it is as a raw material and its state is maintained for a long time at room temperature (aging resistance Shows sex)
Therefore, it has the characteristics of good moldability and a large amount of bake hardening during paint baking after molding. Further, the hot-rolled steel sheet according to the present invention to which Cu and P are added in combination has excellent corrosion resistance.

Such characteristics are obtained by controlling both the component design and the hot rolling conditions. First, the action of the steel components of the hot rolled steel sheet and the reason for the content regulation will be explained individually. To do.

C is an element effective for improving the strength, and also acts effectively for achieving both the aging resistance and the bake hardenability. If C is less than 0.003%, sufficient bake hardenability cannot be obtained. On the other hand, if it exceeds 0.08%, the precipitation of solid solution C is promoted by the presence of carbides, so the amount of solid solution C decreases, and as a result, high bake hardenability cannot be obtained. Therefore, C is set to 0.003 to 0.008%.

Si is a preferable element for improving the strength of steel without impairing the workability, and also improves the corrosion resistance. However, if it exceeds 1.5%, the ferrite grains become large, which makes it difficult to obtain high bake hardenability and also deteriorates the surface texture. Therefore, the upper limit of the Si amount is set to 1.5%, and the upper limit of the Si amount is set to 0.25% when corrosion resistance is not particularly considered.

Mn effectively acts to prevent hot embrittlement due to S, and for this purpose, at least 0.05% or more is necessary. It is also a preferable element for improving the strength of steel, but if it exceeds 1.5%, the ductility and bake hardenability deteriorate, so the lower limit of Mn content is 0.05%, and the upper limit is 1.5%.
%.

P is an element preferable for improving the strength of the hot-rolled steel sheet, and the content of P has the effect of increasing the amount of solute C, which improves the bake hardenability. In addition, P significantly improves the corrosion resistance of steel by the combined addition of Cu. However, if the P content exceeds 0.1%, the ductility deteriorates and the effect of improving corrosion resistance is saturated. Therefore, the upper limit of P content is 0.1%. When corrosion resistance is not taken into consideration, the lower limit of P content is not particularly limited,
When corrosion resistance is required, the composite addition of Cu-P is indispensable, and for this purpose, P must be contained at least 0.01% or more.

S is an element that is essentially harmful to the steel of the present invention, and the smaller the amount, the more preferable.
Since up to 02% is acceptable, it should be 0.02% or less.

Cu, combined with P, remarkably improves the corrosion resistance of steel. For this, Cu is at least 0.05
% Or more is required. However, if it exceeds 1.0%, not only the effect of improving the corrosion resistance is saturated, but also the ductility is deteriorated. Therefore, Cu is 0.05 to 1.0%, preferably 0.15 to
It is contained in the range of 0.35%.

Ni prevents hot brittleness due to Cu,
It has the effect of suppressing the occurrence of hot cracking during hot rolling. In order to prevent hot embrittlement due to Cu, when the Cu content exceeds about 0.15%, it is necessary to add Ni, and the Ni content is required to be half the Cu content to the same level.
For this reason, the upper limit of the Ni content is set to 1.0%.

Al needs to be 0.004% or more in order to function as a deoxidizing agent. Also, Al is N
It has a function of fixing as N, and if the Al content is less than 0.004%, the room temperature aging due to the solid solution N becomes large, and 0.035
If it exceeds%, the bake hardenability decreases. Therefore, the lower limit of the amount of Al is 0.004% and the upper limit is 0.35%. Further, Al is preferably added so that the N / Al ratio becomes 0.5 or less.

N is an element that is generally harmful to steel, but it has the function of improving the bake hardenability. N amount is 0.
If it is less than 001%, the effect of improving the bake hardenability is small, while if it exceeds 0.006%, the room temperature aging progresses rapidly and becomes large, and the ductility deteriorates and the press formability deteriorates. For this reason, the lower limit of N amount is 0.001% and the upper limit is 0.00.
It was set to 006%. Furthermore, N is preferably added so that the N / Al ratio is 0.5 or less.

Mo and W, when contained in appropriate amounts, have the effect of improving bake hardenability. The reason for this is not clear, but it may be because the amount of dissolved C increases. To obtain this effect, the total amount of one or two of Mo and W is 0.005%.
The above is necessary. On the other hand, Mo and W react with C to react with Mo.
It has a function of forming carbides such as C and WC, and a large amount of it reduces bake hardenability. Since it is an expensive element, the total amount of one or two of Mo and W should be 0.1% or less.

Ti, Nb and V are effective elements for refining the metal structure of the hot rolled steel sheet, but C, N and TiC, Ti
It has a function to make compounds such as N, NbC, VC, VN,
Therefore, the bake hardenability is lowered. If Ti, Nb, and V are added in excess of the total amount of C and N that can be fixed, bake hardenability cannot be obtained. Therefore, the total amount of one or more of Ti, Nb, and V is limited to 0.04% or less, and more specifically, the ratio of (Ti + Nb + V) / (C + N) is 4 or less. .

B effectively acts to improve embrittlement during secondary processing. For that purpose, it is necessary to contain B of 0.0003% or more. On the other hand, the effect is saturated even if the content exceeds 0.003%. Therefore, the addition amount of B is 0.000.
It is set to 3 to 0.003%.

In the present invention, a slab of steel having such a composition is hot-rolled to form a hot rolled steel sheet (steel strip). In order to obtain an age-resistant bake hardening hot rolled steel sheet, It is necessary to properly control hot rolling conditions, especially hot rolling finishing temperature and winding temperature.

First, the hot rolling finish temperature (the temperature of the material leaving the final pass of the rolling mill) is basically just above the Ar ₃ transformation point of the steel, but if it exceeds 940 ° C., it will be rolled in the high temperature γ region and the metal structure will change. On the other hand, if the temperature is less than 830 ° C., it will be low-temperature rolling in the α + γ range, and the metal structure will also become rough, and it will not be possible to obtain a hot-rolled steel sheet in which the strength-ductility balance is narrow. Therefore, the hot rolling finishing temperature is 830-94.
It must be in the range of 0 ° C.

The coiling temperature of the hot rolled steel strip has an important influence on the aging resistance and the bake hardenability of the hot rolled steel strip. AlN is not formed under the condition that the winding temperature is lower than 525 ° C.
For this reason, the amount of solid solution N becomes too large, and the deterioration of elongation due to room temperature aging becomes remarkable, and the aging resistance is not exhibited. On the other hand, if the coiling temperature exceeds 675 ° C, the precipitation of carbides (Fe ₃ C) increases, the amount of solid solution C decreases, and the bake hardenability deteriorates. In addition, the pickling property also becomes poor. Therefore, the hot rolling coiling temperature of the steel of the present invention is limited to 525 ° C to 675 ° C.
Desirably, it is 575-625 degreeC.

[0035]

【Example】

[Example 1] Steel slabs having the chemical composition values (% by weight) shown in Table 1 were produced, and each slab was hot-rolled with a plate thickness of 3.2 mm under the conditions of finishing temperature and winding temperature shown in Table 2. A steel strip was used. Each hot-rolled steel strip was then skin-pass rolled with an elongation of 1% and pickled. Test pieces were taken from each of the obtained hot-rolled steel strips and subjected to a tensile test, a bake hardenability test, and an aging resistance test. The results are also shown in Table 2.

The tensile test was carried out according to JISZ2241 using a No. 5 test piece of JISZ2202.

The bake hardenability test was conducted in accordance with the JIS B3135 Appendix Bake hardenability test method, and a pre-strain of 2% was applied in the tensile test and 170 ° C equivalent to paint bake.
After the heat treatment for 20 minutes, the tensile test was performed again. In this test, the difference between the stress when a prestrain of 2% was applied and the yield stress after the heat treatment was taken as the bake hardening amount (BH), and if this bake hardening amount was 30 N / mm ² or more, it was considered good.

The aging resistance was evaluated by the difference in elongation before and after the room temperature aging treatment, which was maintained at 20 ° C. for 3 months. If this difference in elongation (deterioration) was 2% or less, the aging resistance was considered good.

[0039]

[Table 1]

[0040]

[Table 2]

As can be seen from the results in Table 2, the hot-rolled steel sheet manufactured using the comparative steel No. 1 having a larger amount of C and a larger amount of Al than those specified in the present invention has a tensile strength (TS ) Is relatively high and the elongation deterioration after room temperature aging is small, but the bake hardening amount (BH) is low.

More N and P than specified in the present invention Al
The hot-rolled steel sheet manufactured using a comparatively small No. 2 comparative steel has a relatively high tensile strength (TS) and a large amount of bake hardening (BH), but the deterioration of elongation after room temperature aging is extremely high. It is extremely poor in aging resistance.

When the amount of C is smaller than that specified in the present invention, Ti
The hot-rolled steel sheet manufactured using the comparatively high No. 3 comparative steel is
The tensile strength (TS) is low, the elongation (El) is large, and the elongation does not deteriorate after room temperature aging, which is good, but the bake hardening amount (BH) is very low.

The amount of Mn is larger than that specified in the present invention, and Al
A hot-rolled steel sheet manufactured using a comparatively small No. 4 comparative steel has a high tensile strength (TS) and a small elongation (El), and thus is inferior in formability. Although the bake-hardening amount (BH) is high, the deterioration of elongation after room temperature aging is very large and the aging resistance is poor.

On the other hand, hot-rolled steel sheets manufactured using steel Nos. 5 to 14 having a composition within the range specified in the present invention may have relatively low or high tensile strength (TS). Elongation (El) is good and moldability is good. It can be seen that all of them have a high bake hardening amount (BH) and have good aging resistance.

Example 2 Steel slabs having the chemical composition values (% by weight) shown in Table 3 were hot-rolled under the conditions shown in Table 4 to obtain hot-rolled sheets having a plate thickness of 3.2 mm and an elongation of 1 % Skin pass rolling and pickling. Test pieces were taken from each of the obtained hot-rolled sheets and subjected to the same tensile test, bake hardenability and aging resistance test as in Example 1. In addition, 70 mm x from each hot rolled sheet
A 150 mm test piece for corrosion test was sampled, and only the end face and the back face were sealed with a polyester tape and subjected to a complex corrosion test. This composite corrosion test was repeated for 240 times consecutively, with a total of 8 hours of "JISZ2271 salt spray test 2 hours" → "70 ° C hot air drying 4 hours" → "wet test 2 hours" as one cycle. Then, the maximum erosion depth due to the corrosion generated on the surface of the test piece was measured. The test results are also shown in Table 2.

[0047]

[Table 3]

[0048]

[Table 4]

As can be seen from the results in Table 4, the hot rolled steel sheets No. 6 to No. 15 of the present invention all have a very small maximum erosion depth due to corrosion and have good corrosion resistance.
And those of No. 6 to No. 15 have both good bake hardenability and aging resistance.

On the other hand, Comparative Examples Nos. 1 to 5 all had maximum corrosion depths due to corrosion of Example No. 6 of the present invention.
It is larger than that of ~ 15 and the corrosion resistance is not sufficient.

Further, the amount of C is larger than that specified in the present invention.
The hot-rolled steel sheet of No. 1 containing a large amount of 1 has a relatively high tensile strength and good aging resistance, but the bake hardening amount is low and the bake hardening property is poor. More N and P than specified in the present invention Al
The No. 2 hot-rolled steel sheet with a small amount has a relatively high tensile strength and a good bake hardenability, but has a poor aging resistance. No. 3 hot rolled steel sheet with a small amount of C and a large amount of Ti has good aging resistance, but does not show bake hardening performance and has low tensile strength. The hot-rolled steel sheet of No. 4 having a large amount of Mn and a small amount of Al has high tensile strength and good bake hardenability, but has poor aging resistance and low elongation. The hot rolled steel sheet of No. 5 containing less Cu than specified in the present invention has good bake hardenability and aging resistance, but is inferior in corrosion resistance.

[0052]

As described above, according to the present invention, the raw material has good aging resistance that maintains a soft state even after a long period of time. Therefore, the moldability is good, In addition, a bake hardening type hot rolled steel sheet can be obtained which can favorably have high strength during coating baking after forming. In addition, a corrosion-ageing, age-resistant, bake-hardened hot-rolled steel sheet with good corrosion resistance even when bare can be obtained. This hot-rolled steel sheet is particularly useful as a reinforcing member and an underbody member for automobiles, and can greatly contribute to the weight reduction of the vehicle body and the material cost reduction.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikio Soge 11-1 Showa-cho, Kure-shi, Hiroshima Prefecture Steel Research Laboratory, Nisshin Steel Co., Ltd. (72) Seiichi Hamanaka 11-Showa-cho, Kure-shi, Hiroshima No. 1 Inside Steel Research Laboratory, Nisshin Steel Co., Ltd. (72) Inventor Teruo Tanaka 11-11 Showa-cho, Kure City, Hiroshima Prefecture Inside Steel Research Laboratory, Nisshin Steel Co., Ltd.

Claims (8)

[Claims] 1. C: 0.003 to 0.08% by weight,
Si: 0.25% or less, Mn: 0.05 to 1.5%, P:
0.1% or less, S: 0.02% or less, Al: 0.004 to
0.035%, N: 0.001 to 0.006%,
A steel slab whose balance consists of iron and unavoidable impurities
Hot rolling finishing temperature: 830 to 940 ° C, winding temperature: 525
A method for producing an age-resistant, bake-hardening, hot-rolled steel sheet comprising hot rolling at 675 ° C. 2. C: 0.003 to 0.08% by weight,
Si: 0.25% or less, Mn: 0.05 to 1.5%, P:
0.1% or less, S: 0.02% or less, Al: 0.004 to
0.035%, N: 0.001 to 0.006%, W and Mo
1 or 2 in total: 0.005-0.1%, and the balance is steel slab consisting of iron and inevitable impurities, hot rolling finishing temperature: 830-940 ° C, coiling temperature: 52
A method for producing an age-resistant, bake-hardening, hot-rolled steel sheet comprising hot rolling at 5 to 675 ° C. 3. C: 0.003 to 0.08% by weight,
Si: 0.25% or less, Mn: 0.05 to 1.5%, P:
0.1% or less, S: 0.02% or less, Al: 0.004 to
0.035%, N: 0.001 to 0.006% Total of one kind or two or more kinds of Ti, Nb and V: 0.04
Below, however, a steel slab containing (Ti + Nb + V) / (C + N): 4 or less, with the balance being iron and inevitable impurities, hot rolling finishing temperature: 830-940 ° C, coiling temperature: 525-675 A method for producing an age-resistant, bake-hardening, hot-rolled steel sheet comprising hot rolling at ℃. 4. The steel slab has a B content of 0.0003 to 0.0.
The method for producing an age-resistant, bake-hardening, hot-rolled steel sheet according to claim 1, further comprising 03%. 5. C .: 0.003 to 0.08% by weight,
Si: 1.5% or less, Mn: 0.05 to 1.5%, P: 0.0.
01-0.1%, S: 0.02% or less, Cu: 0.05-
1.0%, Al: 0.004 to 0.035%, N: 0.00
A steel slab containing 1 to 0.006% and the balance of iron and unavoidable impurities was hot rolled to a finish temperature of 830 to 9
A method for producing a corrosion-resistant, aging-resistant, bake-hardened, hot-rolled steel sheet comprising hot rolling at 40 ° C and a winding temperature of 525 to 675 ° C. 6. C. 0.003 to 0.08% by weight,
Si: 1.5% or less, Mn: 0.05 to 1.5%, P: 0.0.
01-0.1%, S: 0.02% or less, Cu: 0.05-
1.0%, Ni: 1.0% or less, Al: 0.004 to 0.0
35%, N: 0.001 to 0.006% Total of one or two of W and Mo: 0.005 to 0.1%
Corrosion-resistant aging baking consisting of hot-rolling a slab of steel containing iron and the balance iron and unavoidable impurities at a hot rolling finishing temperature of 830 to 940 ° C and a winding temperature of 525 to 675 ° C. Manufacturing method of hardening type hot rolled steel sheet. 7. C: 0.003 to 0.08% by weight,
Si: 1.5% or less, Mn: 0.05 to 1.5%, P: 0.0.
01-0.1%, S: 0.02% or less, Cu: 0.05-
1.0%, Ni: 1.0% or less, Al: 0.004 to 0.0
35%, N: 0.001 to 0.006% Total of one or two kinds of W and Mo: 0.005 to 0.1% Total of one or more kinds of Ti, Nb and V: 0.0 04
Below, however, a steel slab containing (Ti + Nb + V) / (C + N): 4 or less, with the balance being iron and inevitable impurities, hot rolling finishing temperature: 830-940 ° C, coiling temperature: 525-675 A method for producing a corrosion-resistant, age-resistant, bake-hardened hot-rolled steel sheet, which comprises hot rolling at ℃. 8. The steel slab has a B content of 0.0003 to 0.0.
The method for producing an age-resistant, bake-hardening, hot-rolled steel sheet according to claim 5, 6 or 7, further containing 03%.