JP3374644B2 - High-strength hot-rolled steel sheet, high-strength galvanized steel sheet excellent in pitting corrosion resistance and workability, and methods for producing them - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a high-strength hot-rolled steel sheet which is excellent in perforation corrosion resistance, has a low yield ratio (yield stress / tensile strength), and exhibits excellent workability, and the hot-rolled steel sheet. High-strength zinc-based plating whose base material is various electrogalvanized, hot-dip galvanized, or alloyed hot-dip galvanized (hereinafter collectively referred to as “zinc-based plating”) The present invention relates to a steel sheet and a manufacturing method thereof, and is widely used in industrial fields such as automobile parts, which need to have excellent perforation corrosion resistance and workability and require high strength. The present invention relates to a hot-rolled steel sheet, a high-strength zinc-plated steel sheet having the surface of the hot-rolled steel sheet as a base material and various zinc-based plating, and a useful method for producing them.

[0002]

2. Description of the Related Art Iron is corrosive even in the atmosphere. Therefore, when steel sheets are used industrially, it is necessary to prevent corrosion and to exhibit sufficient characteristics even if corrosion occurs. The reality is that they are consuming costs. Specifically, various kinds of zinc-based plating and the like are carried out.

By the way, automobiles are used in a very severe corrosive environment such as a large temperature change, peeling of paint due to flying stones, snow melting agents in cold regions, etc. on the other hand,
In recent years, there has been a strong demand for protection of the global environment and thinning of automobiles to improve fuel efficiency. Especially in applications such as automobile outer panels and floor materials, it is excellent in deep drawability and
It is necessary that the so-called puncture resistance, in which no holes are formed due to corrosion, is good. Similarly, the member material that serves as the skeleton of the vehicle body, the bumper that serves as the reinforcing member, the door guard, and the like are also required to have good perforation corrosion resistance.

In order to reduce the thickness of parts, it is necessary to secure at least rust prevention ability. Also, from the viewpoint of high quality and high quality, it is required to use a steel sheet which is less likely to cause rust and has excellent perforation corrosion resistance. In particular, as in North America and Northern Europe, spray antifreeze agents on roads in winter,
In areas where gravel is spread to prevent slipping, the coating may be destroyed by the collision of incoming gravel, and Cl ^- ions derived from salts such as NaCl, KCl, and MgCl contained in the antifreezing agent may be generated. Corrosion is promoted by its presence, and since it is in a dry and wet environment, a particularly excellent rust preventive ability is required.

For these reasons, various zinc-based plated steel sheets have been used, but in order to improve the perforation corrosion resistance, it is necessary to first increase the corrosion resistance of the base material. From such a point of view, techniques such as Japanese Patent Laid-Open No. 22224/1990 have been proposed. This technique improves the perforation corrosion resistance of a steel sheet by adding P or Cu alone or in combination. This technique discloses that the formation of a dense rust layer of P or Cu is effective in improving the perforation corrosion resistance. However, the addition of at least Cu is apt to cause defects such as bald spots and deteriorates the surface quality of the steel sheet. In order to avoid such defects, it is necessary to add a relatively large amount of Ni, and as a result, there is a problem that the cost becomes high. On the other hand, the addition of P does not cause the above-mentioned defects, but it has a problem that the perforation corrosion resistance deteriorates rather than the case of the composite addition.

[0006]

SUMMARY OF THE INVENTION The present invention has been made by paying attention to the above-mentioned problems, and its object is excellent in corrosion resistance against perforation without causing the problems as in the prior art. The present invention provides a hot-rolled steel sheet having a low yield ratio and excellent workability, a high-strength zinc-based plated steel sheet using the hot-rolled steel sheet as a base material, and a useful method for producing them. .

[0007]

The hot-rolled steel sheet of the present invention which has been able to achieve the above object has a C content of 0.05 to 0.25.
%, Mn: 1.0 to 3.0%, P: 0.01 to 0.12
%, Ti: 0.02-0.5%, Al: 0.01-0.
1% each, S: 0.01% or less and N: 0.01% or less, respectively, with the balance being a chemical composition of Fe and inevitable impurities, and the amount of solid solution Ti. Is 0.001 to 0.25% and 16 to 70
It consists of volume% ferrite and the balance of one or more of low temperature transformation structures of martensite, tempered martensite and bainite, and has a tensile strength of 5
The gist is that it is 00 N / mm ² or more.

In the hot rolled steel sheet of the present invention, (a) Si: 0.01 to 2.0% and Nb:
0.005-0.05%, V: 0.005-0.05
%, Zr: 0.005 to 0.05%, Mo: 0.1
1.0% and W: one or more elements selected from the group consisting of 0.01 to 2.0%, (b) Cr: 0.1 to 2.0
%, (C) Cu: 0.05 to 1.0%, (d) especially Cu
When Ni is included, Ni: 0.05 to 1.0%, (e)
B: 0.0003 to 0.0060%, (f) Ca: 0.
0004 to 0.010% and / or rare earth elements:
It is also effective to contain 0.0004 to 0.010% or the like.

Further, the high-strength zinc-based plated steel sheet of the present invention which has been able to achieve the above-mentioned object uses the above-mentioned various high-strength hot-rolled steel sheets as a base material and has (a) an electrogalvanized plated layer on the surface thereof. Formed, and if necessary subjected to chromate treatment and organic film treatment on the surface of the zinc-plated steel sheet,
(B) A hot-dip galvanized layer is formed, and if necessary, the hot-dip galvanized layer is further alloyed to form an alloyed hot-dip galvanized layer, and the like.

On the other hand, in producing the hot-rolled steel sheet of the present invention, the steel materials having various chemical composition are
Hot-rolled at a finishing temperature of 0 ° C or higher, average cooling rate: 5
It may be cooled to 650 ° C or lower at ~ 30 ° C / sec and wound up.

In producing the high-strength zinc-based plated steel sheet of the present invention, steel materials having various chemical composition described above are hot-rolled at a finishing temperature of 800 ° C. or higher, and an average cooling rate: 5 to 30 ° C. After cooling at 650 ° C./sec or less and winding, (a) forming an electrogalvanized plating layer on the surface, and subjecting the surface of the galvanized steel sheet to chromate treatment and organic film treatment, if necessary, ( b) After heating to 420 to 650 ° C. in a continuous hot dip galvanizing annealing furnace, performing hot dip galvanizing at 420 to 500 ° C., and if necessary, performing hot dip galvanizing at 500 to 700 ° C. The molten zinc-based plating layer may be alloyed by heating at a temperature of 10 seconds to 2 minutes, and subsequently cooled at an average cooling rate of 5 ° C./sec or more and 450 ° C. or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied from various angles in order to achieve the above object. As a result, if the chemical composition of the hot-rolled steel sheet is made appropriate and the manufacturing conditions are made appropriate and the amount of solid solution Ti in the hot-rolled steel sheet and its structure are adjusted as described above, the yield ratio is reduced and the Of the hot-rolled steel sheet exhibiting excellent corrosion resistance in the presence of Cl ⁻ ions that promote corrosion of the steel sheet and even in a corrosive environment in which dryness and humidity are repeated, It is possible to realize a zinc-based plated steel sheet that exhibits desired properties if the hot-rolled steel sheet is used as a base material and various types of zinc-based plating are applied to the surface of the base material while appropriately adjusting the continuous annealing conditions for hot dip galvanizing. The inventors have found out and completed the present invention. First, the reason for defining the chemical composition of the hot rolled steel sheet in the present invention is as follows.

C: 0.05 to 0.25% C is an essential element for ensuring the required strength, and for that purpose it is necessary to contain 0.05% or more. However, even if it is contained excessively, the strength becomes too high and the workability deteriorates, so it is necessary to make it 0.25% or less.

Mn: 1.0 to 3.0% Mn is an element effective for obtaining a low temperature transformation structure such as martensite and bainite, and for that purpose, it is necessary to contain 1.0% or more. . However, even if added excessively, segregation causes deterioration of workability, so 3.0%
Is the upper limit.

P: 0.01 to 0.12% P is an element effective in increasing the strength of the steel sheet, and for this purpose, it is necessary to contain 0.01% or more. However, if the content exceeds 0.12%, the steel sheet becomes brittle.

Ti: 0.02 to 0.5% Ti is an element effective for refining crystal grains and improving workability. However, by appropriately setting the manufacturing conditions, the puncture resistance of the steel sheet can be improved. It also works effectively to improve corrosion resistance. The mechanism of the effect of improving the perforation corrosion resistance by the addition of Ti can be considered as follows. Rust steel sheet, Fe is eluted in Fe ²⁺ (or Fe ³⁺⁾ ions, but in which was then changed to hydroxide or oxide of iron, the inclusion of Ti, Fe is Fe ² It is considered that the solid solution element of Ti elutes with iron at the same time as ⁺ (Fe ³⁺ ) ions are eluted, and the presence of this solid solution Ti improves the perforation corrosion resistance. That is, the addition of Ti significantly enhances the passivation, improves the structure and morphology of iron oxyhydroxide by Ti ions, specifically stabilizes the generated rust, and prevents the formation of a dense rust layer such as TiO ₂ . It is believed that the formation improves the perforation corrosion resistance. In order to exert these effects, the amount of solid solution Ti is set to 0.00 as described later.
1 to 0.25% is necessary, but in the present invention, the Ti content is 0.02 to 0.02 in consideration of the amounts of C, S, N and the like.
It was defined as 0.5%.

Al: 0.01 to 0.1% Al is added as a deoxidizing element, but its content is 0.1.
If it is less than 01%, sufficient deoxidation cannot be achieved, and the oxygen (O) content in the steel cannot be sufficiently reduced. However, even if added excessively, the effect is saturated, so 0.1% is made the upper limit.

S: 0.01% or less Sulfide-based inclusions generate a potential difference with the metal and become the starting point of corrosion, so the S content should be as low as possible. In particular, when the S content exceeds 0.01%, the corrosivity is extremely reduced due to an increase in the amount of sulfide inclusions, so the content is suppressed to 0.01% or less. There is a need.

N: 0.01% or less When the amount of N increases, aging occurs, and a part of N binds to Ti to form TiN to reduce formability and further reduce the amount of solid solution Ti. By doing so, the perforation corrosion resistance is lowered, so it is necessary to suppress it to 0.01% or less.

The basic components of the steel material targeted by the present invention are as described above, and the balance is Fe and unavoidable impurities. However, as other elements, Si,
Nb, V, Zr, Mo, W, Cr, Cu, Ni, B, C
It is also effective to contain an appropriate amount of a, a rare earth element or the like.
The reasons for limiting the component ranges when adding these elements are as follows.

Si: 0.01 to 2.0%, Nb: 0.0
05-0.05%, V: 0.005-0.05%, Z
r: 0.005-0.05%, Mo: 0.1-1.0%
And W: one or more element Si selected from the group consisting of 0.01 to 2.0% is an extremely effective element for improving the workability of steel, and if less than 0.01%, that effect is obtained. Although it cannot be exhibited, an excessive content of more than 2.0% increases the deformation resistance during hot rolling.

Like Si, Nb is an element that is extremely effective in improving the workability of steel, and is an element that is effective in improving the resistance to perforation corrosion by increasing the amount of solid solution Ti by adding Nb. . In order to exert these effects,
It is necessary to contain 0.005% or more, but 0.05%
If added in excess, the ductility will decrease.

V is also an extremely effective element for improving the workability of steel, and if it is less than 0.005%, its effect cannot be exerted, and if it exceeds 0.05%, it is excessively contained. However, the effect is saturated.

Zr is also an element effective for improving the workability of steel, and if it is less than 0.005%, its effect cannot be exhibited, and if it exceeds 0.05%, it is contained excessively. Not only is the effect saturated, but the steel becomes brittle and expensive.

Mo is an element effective for improving the workability by refining the structure of steel, and if it is less than 0.1%, the effect cannot be exhibited, and 1.0
Even if it is contained excessively in excess of%, not only the effect is saturated but also it becomes expensive.

W is also an element effective for improving the workability of steel. If it is less than 0.01%, its effect cannot be exhibited, and if it exceeds 2.0%, it is contained excessively. The effect is not only saturated, but also expensive.

Cr: 0.1 to 2.0% Cr is an element effective for obtaining a transformation structure necessary for strengthening steel and enhancing corrosion resistance, and 0.1 is required for exerting the effect. % Or more is necessary, but if added in excess, not only will the effect be saturated, but the coatability will decrease, so 2.0% is the upper limit.

Cu: 0.05 to 1.0% Cu is an element effective in densifying the generated rust and improving the perforation corrosion resistance, and in order to exert its effect, 0.05 % Or more must be contained. However, even if it is contained in excess of 1.0%, not only the effect is saturated but also the workability is deteriorated.

Ni: 0.05 to 1.0% In steel having a high Cu content, as described above, bald spots are likely to occur on the surface, but addition of Ni prevents such bald spots from occurring. And is an element effective for improving the surface properties. Ni is also an effective element in improving the perforation corrosion resistance. To bring out these effects, 0.05
%, But if added in excess, it causes an increase in cost due to expensive Ni.
It should be 0% or less. From the viewpoint of improving the surface properties, when the Cu content exceeds 0.2%, the addition amount of Ni is preferably about half or the same as the addition amount of Cu.

B: 0.0003 to 0.0060% B is an element effective in enhancing the hardenability of steel, and in order to exert its effect, 0.0003% or more must be contained. However, if B is added excessively, the steel becomes brittle, so 0.0060% or less is necessary.

Ca: 0.0004 to 0.010% and / or rare earth element: 0.0004 to 0.010% At the stage where the corrosion of the steel sheet is progressing, the following formula (1) and (2 ) Reaction occurs and the inside of pitting corrosion is acidified, so that the corrosion of steel is further promoted.
When a is present, Ca dissolves at the same time as iron and this Ca is an alkali metal, so that the inside of the pitting corrosion is made basic and exerts an action of suppressing the progress of pitting corrosion. Fe → Fe ²⁺ + 2e ⁻ (1) Fe ²⁺ + 2H ₂ O → Fe (OH) ₂ + 2H ⁺ (2) In order to exert such effect of Ca, 0.000
It is necessary to contain 4% or more, but even if added excessively, the effect is saturated, so it is necessary to make it 0.010% or less.

Similar to Ca, the rare earth element is also an element effective in basifying the inside of the pitting corrosion and suppressing the progress of the pitting corrosion. In order to exert such an effect, 0.0004
% Or more, but the effect is saturated even if added excessively, so it is necessary to make it 0.010% or less. As is well known, the rare earth element means Sc, Y and lanthanoid series rare earth elements.

The chemical composition of the hot-rolled steel sheet of the present invention is as described above, but the amount of solid solution Ti in the hot-rolled steel sheet needs to be 0.001 to 0.25% as described above. That is,
As described above, the effect of improving the corrosion resistance against perforation due to the addition of Ti is mainly due to the solid solution Ti in the hot rolled steel sheet.
In order to exert such effects by i, the amount needs to be 0.001% or more. However, if the amount of solid solution Ti is excessive, the Ti-based inclusions become coarse and rather deteriorate the workability, so the content should be 0.25% or less. From this point of view, the preferable range of the amount of solid solution Ti is about 0.003 to 0.10%. Solid solution Ti
Regarding the method of measuring the amount, it is difficult to directly quantify it, but in the present invention, TiC, Ti
A value excluding the amount of Ti existing as S and TiN was used.

The microstructure of the hot-rolled steel sheet of the present invention is composed of 16 to 70% by volume of ferrite, and the balance of any one or more of the low temperature transformation structures of martensite, tempered martensite and bainite. However, if the volume ratio of ferrite is less than 16%, the ductility of the steel sheet, particularly the elongation, is reduced and the drawability is deteriorated. The volume ratio is 70
If it exceeds%, the desired strength cannot be obtained. And the hot rolled steel sheet having the above structure has a tensile strength of 500 N / m.
It has a high strength of m ² or more.

Next, manufacturing conditions for manufacturing the hot-rolled steel sheet of the present invention will be described. First, a steel material having the above chemical composition is melted and cast into a slab by an ordinary method, and then hot rolled. The slab heating temperature at the time of performing this hot rolling is not particularly limited, but it is preferably 1200 ° C. or higher in order to increase the amount of solid solution Ti. The finishing temperature during hot rolling must be 800 ° C or higher, and the average cooling rate up to 650 ° C or lower must be 5 to 30 ° C / sec. The finishing temperature during hot rolling is 800 ° C. or higher, and the average cooling rate up to 650 ° C. is 5 ° C./sec or higher. This is because the amount of molten Ti is increased to ensure perforation corrosion resistance. That is, if the specified requirements are not satisfied, the amount of Ti carbon / nitride increases, the structure becomes non-uniform, and the amount of solid solution Ti decreases, so that the object of the present invention cannot be achieved. The average cooling rate is 30 ° C
If it exceeds / sec, the generation of ferrite becomes insufficient, and it becomes difficult to secure the volume ratio of 16 vol% or more. The upper limit of the finishing temperature of hot rolling is not particularly specified, but it is preferably 1000 ° C. or lower, and if it is higher than this, the slab heating temperature becomes too high, scale loss increases, yield and surface quality, etc. Is reduced.

The hot-rolled steel sheet as described above is used as a base material, and various zinc-based plating such as electrogalvanizing, hot-dip galvanizing or alloying hot-dip galvanizing is applied to the surface of the base material to obtain a desired zinc-based plated steel sheet. However, all of these zinc-based plated steel sheets have high tensile strength of 500 N / mm ² or more, reflecting the characteristics of the hot-rolled steel sheet as the base material.

Of the above zinc-based plating, the type of electrozinc-based plating is not particularly limited, and Z
n, Zn-Ni, Zn-Fe, Zn-Mn, Zn-Cr
And the like, and these may be formed by an ordinary method. The preferred component composition of these various electrogalvanized plating layers is as follows. That is, Zn-
The Ni content in the Ni plating layer is about 5 to 20%, and the Fe content in the Zn-Fe plating layer is 5 to 20%.
About 40%, in the Zn-Mn plating layer, the Mn content is about 5-30%, and in the Zn-Cr plating layer,
It is preferable that the Cr content is about 5 to 40% from the viewpoint of corrosion resistance. After performing these electrozinc plating, if necessary, a chromate treatment of about 30 to 100 mg / m ² and an organic film treatment of about 0.3 to 2.0 μm (for example, polyester) are performed.

On the other hand, in order to manufacture the hot-dip galvanized steel sheet of the present invention, the following procedure and manufacturing conditions may be followed.
First, after hot rolling and winding according to the procedure for producing the above hot-rolled steel sheet, it is heated in an annealing furnace for continuous hot-dip galvanizing. If the heating temperature at this time is lower than 420 ° C, Hot-dip galvanization becomes impossible. If the heating temperature is higher than 650 ° C, the strength of the steel sheet will be reduced. The heating time at this time is preferably about 10 seconds to 10 minutes, and if it is shorter than 10 seconds, the plating becomes uneven in the coil, and if it is longer than 10 minutes, the effect is saturated and the equipment is Be too large.

Subsequently, hot dip galvanizing is performed, and the temperature at this time (that is, the plating bath temperature) is 420 to 50.
It needs to be 0 ° C. If this temperature is less than 420 ° C,
As in the above case, hot dip galvanizing becomes impossible. Further, if this temperature exceeds 500 ° C., for example, partial alloying proceeds and the quality of the plating layer becomes non-uniform.

When the alloy is reheated after hot-dip galvanizing to form an alloy, the lower limit temperature is set to 500 ° C. because a lower temperature lowers the alloying time and the equipment becomes too large. The upper limit temperature at this time is set to 700 ° C., because at a temperature higher than this, the structure adjusted in the hot rolling process is tempered, and the strength and workability are lowered. The upper limit temperature is preferably about 650 ° C. If the alloying time is shorter than 10 seconds, the alloying will be insufficient and a non-uniform plating layer will be formed, and if it exceeds 2 minutes, the Fe concentration in the alloyed hot-dip galvanized layer will be high, and press molding Powdering will occur.

After the hot dip galvanizing or alloying hot dip galvanizing, it is necessary to cool to 450 ° C. or lower at a cooling rate of 5 ° C./sec or more. At this time, if the temperature is higher than 450 ° C, the martensite and bainite structures cannot be sufficiently obtained. Even at a cooling rate lower than 5 ° C./sec, sufficient martensite and bainite structure cannot be obtained, and the bainite structure becomes coarse and ductility decreases.

Next, examples of the present invention will be shown. However, the present invention is not limited to the following examples, and
It is of course possible to make appropriate modifications and implement them within a range that is compatible with the gist of the preceding and following statements, and all of them are included in the technical scope of the present invention.

[0043]

【Example】

Example 1 A steel material shown in Table 1 below was melted and cast by a usual method, and then hot-rolled and wound under the conditions shown in Table 2 below to produce a hot-rolled steel sheet. investigated.
At this time, for corrosiveness, the hot rolled steel sheet is subjected to a phosphate treatment, followed by cationic electrodeposition coating, and then a cross cut reaching the base steel sheet is applied to the coating film, and the following steps (1) to (3) are performed. A cycle corrosion promotion test was carried out for 100 cycles, and the maximum perforation depth due to corrosion of the cross-cut portion after film removal was measured. Table 3 shows the corrosion test results together with mechanical properties.
And shown in Table 4. (1) Spray with salt water for 16 hours at 50 ° C → (2) 4 at 70 ° C
Dry in time → (3) Wet at 50 ° C (humidity 85%) for 4 hours

[0044]

[Table 1]

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

[Table 4]

From these results, the following can be considered.
No. In Nos. 3 and 4, the manufacturing conditions deviate from the requirements specified in the present invention. Nos. 4 to 8 and 10 to 13 have a chemical composition that is out of the requirements specified in the present invention, and any one of tensile strength, perforation corrosion resistance and workability is deteriorated. I understand. On the other hand, No. Nos. 1, 2, 9 and 14 to 27 are examples satisfying all the requirements specified in the present invention, and all have a high tensile strength of 500 N / mm ² or more and are resistant to perforation corrosion. It can be seen that the workability and workability are also excellent.

Example 2 No. 1 in Table 2 above. The hot-rolled steel sheet manufactured under the conditions shown in 1 was used as a base material, and these were subjected to hot dip galvanizing under the conditions shown in Table 5 below to obtain a zinc-based plated steel sheet (Table 5
1-1 to 1-3). The conditions in Table 5 show the conditions in the continuous hot dip galvanizing annealing furnace. Further, No. The hot-rolled steel sheet base materials produced under the conditions shown in Nos. 2 and 3 were subjected to hot dip galvanizing, and then subjected to alloying treatment. 2-1 to 2-3 and No. The alloying conditions are shown as No. 3.

[0050]

[Table 5]

The corrosiveness of these zinc-based plated steel sheets was investigated in the same manner as in Example 1. However, the corrosion acceleration test at this time was performed for 150 cycles. The powdering property was also investigated in the bent part of the galvanized steel sheet. Corrosion test results and powdering properties are shown in Table 6 below together with mechanical properties.

[0052]

[Table 6]

As is clear from these results, in the examples satisfying all the requirements specified in the present invention, the mechanical properties, the corrosiveness and the processability reflecting the properties of the base material were obtained. I understand.

Example 3 In Table 2, No. Hot-rolled steel sheets manufactured under the conditions shown in 4 to 27 were used as base materials, and various electrolytic zinc-based plating was applied to these to obtain zinc-based plated steel sheets. Corrosion and powdering properties of these zinc-based plated steel sheets were investigated in the same manner as in Example 2. Corrosion test results and powdering properties are shown in Table 7 below together with mechanical properties.

[0055]

[Table 7]

As is clear from these results, in the examples satisfying all the requirements specified in the present invention, the mechanical properties, the corrosiveness and the processability reflecting the properties of the base material were obtained. I understand.

[0057]

EFFECTS OF THE INVENTION The present invention is constituted as described above, and a hot-rolled steel sheet excellent in perforation corrosion resistance and workability and a zinc-based plated steel sheet using the hot-rolled steel sheet as a base material can be easily obtained. Not only for automobiles, but also for construction, shipbuilding, etc., it is most suitable as a material applied in the industrial field where corrosion of steel is a problem.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C23C 2/06 C23C 2/06 (56) Reference JP-A-7-75756 (JP, A) JP-A-7-18373 (JP , A) JP 6-336641 (JP, A) JP 6-336640 (JP, A) JP 57-104650 (JP, A) JP 5-179396 (JP, A) JP 6-306533 (JP, A) JP-A-5-112832 (JP, A) JP-A-8-60304 (JP, A) JP-A-9-125194 (JP, A) JP-A-9-111396 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 8/00-8/04 C21D 9/46-9/48

Claims (16)

(57) [Claims] 1. C: 0.05 to 0.25% (meaning mass%; the same applies hereinafter), Mn: 1.0 to 3.0%, P: 0.0
1 to 0.12%, Ti: 0.02 to 0.5%, Al:
0.01 to 0.1% respectively, and S: 0.0
1% or less and N: 0.01% or less, respectively, the balance has a chemical composition of Fe and inevitable impurities, and the amount of solid solution Ti is 0.001 to 0.25%. 16 to 70% by volume of ferrite, and the balance consisting of one or more structures selected from the low-temperature transformation structures of martensite, tempered martensite, and bainite, and having a tensile strength of 500 N / mm ² or more. A high-strength hot-rolled steel sheet with excellent hole-corrosion resistance and workability. 2. As another component, Si: 0.01-
2.0%, Nb: 0.005 to 0.05%, V: 0.0
05-0.05%, Zr: 0.005-0.05%, M
The high-strength hot-rolled steel sheet according to claim 1, which contains one or more elements selected from the group consisting of o: 0.1 to 1.0% and W: 0.01 to 2.0%. 3. As another component, Cr: 0.1 to 0.1
The high-strength hot-rolled steel sheet according to claim 1 or 2, which contains 2.0%. 4. As another component, Cu: 0.05 to
The high-strength hot-rolled steel sheet according to any one of claims 1 to 3, which contains 1.0%. 5. As another component, Ni: 0.05-
The high-strength hot-rolled steel sheet according to claim 4, which contains 1.0%. 6. As another component, B: 0.0003
The high-strength hot-rolled steel sheet according to any one of claims 1 to 5, which contains ˜0.0060%. 7. As another component, Ca: 0.000
4 to 0.010% and / or rare earth element: 0.00
The high-strength hot-rolled steel sheet according to any one of claims 1 to 6, which contains 04 to 0.010%. 8. A high strength hot rolled steel sheet according to any one of claims 1 to 7 as a base material, and an electrogalvanized plating layer formed on the surface of the base material. And high-strength galvanized steel sheet with excellent workability. 9. A high-strength zinc-based plated steel sheet obtained by subjecting the surface of the zinc-based plated steel sheet according to claim 8 to chromate treatment and organic film treatment. 10. A high-strength hot-rolled steel sheet according to any one of claims 1 to 7 as a base material, and a hot-dip galvanized layer formed on the surface of the base material. High strength galvanized steel sheet with excellent workability. 11. The hot dip galvanized layer is further alloyed to form an alloyed hot dip galvanized layer.
The high-strength zinc-based plated steel sheet according to 0. 12. When producing the high-strength hot-rolled steel sheet according to any one of claims 1 to 7, a steel material having the chemical composition according to any one of claims 1 to 7 is finished at 800 ° C. or higher. Hot rolling at temperature, average cooling rate: 5-30 ° C /
A method for producing a high-strength hot-rolled steel sheet having excellent perforation corrosion resistance and workability, which comprises cooling to 650 ° C or less per second and winding. 13. When producing the high-strength galvanized steel sheet according to claim 8, a steel material having the chemical composition according to any one of claims 1 to 7 is hot-worked at a finishing temperature of 800 ° C. or higher. Rolled, average cooling rate: 5-30 ° C / sec 6
Manufacture of high-strength galvanized steel sheet excellent in perforation corrosion resistance and workability, which is characterized by forming a hot-rolled steel sheet by cooling to 50 ° C or less and winding it into a hot-rolled steel sheet. Method. 14. The method according to claim 13, wherein after forming the electrogalvanized layer, the surface of the galvanized steel sheet is subjected to a chromate treatment and an organic film treatment to produce the galvanized steel sheet according to claim 9. Method. 15. In producing the high-strength zinc-based plated steel sheet according to claim 10, a steel material having the chemical composition according to claim 1 is hot-worked at a finishing temperature of 800 ° C. or higher. After rolling, cooling to an average cooling rate of 5 to 30 ° C./sec to 650 ° C. or less and winding, and then heating to 420 to 650 ° C. in a continuous hot dip galvanizing annealing furnace, 4
A high-strength galvanized steel sheet excellent in perforation corrosion resistance and workability, characterized by being subjected to hot dip galvanizing at 20 to 500 ° C., and subsequently being cooled to an average cooling rate of 5 ° C./sec or more and 450 ° C. or less. Manufacturing method. 16. After hot-dip galvanizing, 500 to
The hot dip galvanized layer is alloyed by heating at a temperature of 700 ° C. for 10 seconds to 2 minutes, and then an average cooling rate: 5 ° C.
The manufacturing method according to claim 15, wherein the zinc-based plated steel sheet according to claim 11 is manufactured by cooling to 450 ° C or lower at a speed of not less than / sec.