JP3464611B2 - High-strength hot-dip galvanized steel sheet excellent in formability and corrosion resistance and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a high-strength hot-dip galvanized hot-rolled steel sheet and a method for producing the same, and more specifically, it has a low yield ratio and a tensile strength of 590 MPa or more excellent in formability (hole expandability) and corrosion resistance. The present invention relates to a high-strength hot-dip galvanized hot-rolled steel sheet having a composite structure and a method for producing the same.

[0002]

2. Description of the Related Art From the viewpoint of protecting the global environment and ensuring collision safety, automobile manufacturers are increasingly promoting the weight reduction of vehicle bodies by expanding the use of high-strength steel plates. The target parts are structural members such as members such as inner and outer panels, steel plates for panels, arm cans, and underbody members,
Expansion of target parts is expected. Among these members, especially the suspension member, there is a concern that the corrosion resistance may be deteriorated as the plate thickness decreases. Therefore, adoption of high strength hot-dip galvanized galvanized steel sheet has also been considered for this member. For example, Japanese Patent Application Laid-Open No. 56-16625 discloses a method for producing a hot-rolled high-strength galvanized steel sheet which contains ferrite and a low temperature transformation phase and is excellent in workability. Further, Japanese Patent Laid-Open No. 4-297527 discloses a method for producing a high-strength hot-dip galvanized hot-rolled steel sheet having an excellent strength-ductility balance consisting of bainite and martensite of 95% or more. In addition,
Japanese Patent No. 5-247586 discloses a high-strength, high-ductility hot-dip galvanized steel sheet containing retained austenite.

[0003]

However, among the high-strength hot-dip galvanized hot-rolled steel sheets intended for the above-mentioned suspension member, those disclosed in JP-A-6-306533 have a low yield ratio. Although a method for obtaining excellent formability and weldability is disclosed, the heat treatment temperature range in the hot dip plating step is completely different, and the obtained microstructure is different. Therefore, the level of hole expandability obtained also differs.
Further, Japanese Patent Laid-Open No. 4-297527 discloses a manufacturing method in which the amount of Mn is increased and the diffusion of Mn is used during heating in a hot dip galvanizing process to obtain retained austenite stably.
Although it exhibits excellent ductility, there is no mention of hole expansibility, and when applied to a member targeted by the present invention,
There is concern about cracks during burring. Further, since the amount of Mn is high, there is concern that weldability may deteriorate. On the other hand, Japanese Patent Laid-Open No. 5-2475
Although Japanese Patent No. 86 discloses an example of adding Mo, the object is not only a cold-rolled steel sheet but also contains retained austenite, which is structurally different from the present invention. Also, the method of plating treatment is completely different from the present invention.

Therefore, an object of the present invention is to provide a high-strength hot-dip galvanized hot-rolled steel sheet which secures the hole expandability required for the underbody member and has improved corrosion resistance, and a method for producing the same.

[0005]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present inventors have melted steel in which C, Mn and Mo are changed at various levels by vacuum melting. Arrange these steels into billets
Finish rolling was completed in the temperature range of ₃ transformation points or higher to obtain a hot rolled sheet of 2.6 mm. Then, after cooling to 550 ° C. at a cooling rate of 50 ° C./s, winding treatment was carried out at that temperature. About the obtained hot rolled sheet, after pickling, Ni was plated on the surface layer by electroplating at a basis weight of 0.5 g / m ² , and subsequently heated to 460 ° C.,
Immediately, 60 g / m ² of pure zinc was plated. The plated material thus obtained was examined for tensile properties, hole expandability and corrosion resistance. For hole expandability, let the diameter of the hole as punched be d ₀ ,
A hole expansion test was carried out with a 60 ° conical punch with the burr on the outside, and evaluation was made by d / d ₀ where d is the diameter of the hole when a crack penetrating the plate thickness occurs. Regarding the corrosion resistance, the salt spray test described in JIS Z 4371 was carried out, and it was determined that no red rust was generated after 48 hours of the test. as a result,
The following points were found.

(1) It was found that the target strength in the present invention can be obtained by setting the component range as shown in FIG. That is, in the relational expression between C and Mn and Mo, C ≧ −0.
In the region where 049 × (Mn + 1.7Mo) +0.15 is satisfied, a strength of 590 MPa or more is obtained. In addition, as a result of detailed investigation of the transformation behavior, it was found that the addition of Mo delayed the bainite transformation. This is considered to be advantageous for microstructure control in a region where the cooling rate is relatively low, such as the hot dip galvanizing process.

(2) Regarding the hole expandability (d / d ₀ ), as shown in FIG. 2, when C is added in an amount of more than 0.1 mass%, the amount of precipitation of carbides increases, so that sufficient hole expansion is achieved. It was found that sex could not be obtained. Further, it can be seen that the relationship between the fraction of bainite and pearlite of 1 or 2 and the hole expandability is as shown in Fig. 3, that is, the fraction of the second phase exceeds 30% and It has been found that d / d ₀ exceeding 2.3 cannot be obtained at higher values. The bainite referred to here also includes bainitic ferrite.

(3) As a result of evaluating the corrosion resistance of the obtained steel sheet by the above-mentioned test method, it was confirmed that no red rust was generated. As a comparison, red rust was generated on the entire surface of the non-plated product.

Based on the above findings, a high-strength hot-dip galvanized hot-rolled steel sheet excellent in formability and corrosion resistance and a method for producing the same were established.

The gist of the present invention is that (1) an alloy layer containing 0.04 to 5 μm of Ni in the surface layer of a steel plate, 0.1 to 10% of Al, 0.05 to 5% of Mg, and the balance being unavoidable. High-strength hot-dip galvanized hot-rolled steel sheet with a tensile strength of 590 MPa or more and excellent corrosion resistance consisting of a zinc alloy layer of 100 μm or less containing mechanical impurities. (2) one or more of bainite and pearlite as the second phase, consisting of a composite structure containing 1% or more and 30% or less in area ratio,
A high-strength hot-dip galvanized hot-rolled steel sheet having a yield ratio of 0.75 or less and having a tensile strength of 590 MPa or more as described in (1) and excellent in corrosion resistance. (3)% by weight, C: 0.001 to 0.1%, Si: 0.01 to 2%, Mn: 1.0
~ 3.5%, P: 0.001-0.1%, S: 0.001-0.015%, Ti: 4x
[N] to 0.05%, Nb: 0.005 to 0.05%, Mo: 0.2 to 0.8%, Al:
Included in the range of 0.01 to 0.1%, N: 0.005% or less, and satisfy the following formula, the balance Fe and unavoidable impurities (1) or (2) described above formability having a tensile strength of 590 MPa or more And high strength hot dip galvanized steel sheet with excellent corrosion resistance. C ≧ −0.049 ([Mn] +1.7 [Mo]) + 0.15 (4) Ca: 0.001 to 0.01%, REM: 0.005 to 0.05% One or more of (1) to (3) A high-strength hot-dip galvanized hot-rolled steel sheet having a tensile strength of 590 MPa or more and excellent formability and corrosion resistance. (5) B: 0.0005 to 0.005% containing 59 according to (3) or (4)
A high-strength hot-dip galvanized hot-rolled steel sheet having a tensile strength of 0 MPa or more and excellent in formability and corrosion resistance. (6) Cu: 0.05 to 0.5%, Ni: 0.02 to 0.3% (3) to (5)
A hot-rolled hot-dip galvanized steel sheet having a tensile strength of 590 MPa or more and excellent formability and corrosion resistance. (7) After forming a slab by continuous casting, finish rolling at a temperature of Ar ₃ transformation point or higher immediately after reheating or casting,
After air-cooling until the ferrite fraction exceeds 70%, 5 to 150
Cooled at a cooling rate of ℃ / sec, wound in the temperature range of 350 ~ 650 ℃, pickled the hot-rolled steel thus obtained, electroplated with Ni on the surface layer, followed by continuous molten zinc By heating the plate temperature to less than 550 ° C on the plating line and immersing it in the plating bath as it is, it has excellent formability and corrosion resistance with a tensile strength of 590 MPa or more according to any of (3) to (6). Method for producing high strength hot-dip galvanized hot rolled steel sheet. (8) Finishing rough rolling, characterized in that the sheet bar is once wound into a coil (7) high-strength hot-dip galvanized hot-rolled steel sheet excellent in formability and corrosion resistance having a tensile strength of 590 MPa or more according to Manufacturing method. (9) A high-strength melt excellent in formability and corrosion resistance having a tensile strength of 590 MPa or more according to (7) or (8), which is characterized by performing rough rolling immediately after casting into a slab of 100 mm or less. Manufacturing method of galvanized hot rolled steel sheet. It is in.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below.

First, in order to achieve both formability and corrosion resistance, the plating layer applied to the surface of the steel sheet must consist of an alloy layer containing Ni and a zinc alloy layer containing Al and Mg above it. . If there is no alloy layer containing Ni, in the steel with a high Si content targeted by the present invention, Al and
Adhesion between the zinc alloy layer containing Mg and the base steel cannot be secured.
Therefore, the thickness of the Ni-containing alloy layer is required to be 0.04 μm or more in order to secure the adhesion between the base iron and the zinc alloy layer containing Al and Mg. However, the effect saturates at 5 μm,
This is the upper limit. In this case, Ni is applied by electroplating. Subsequently, a zinc alloy layer containing Al and Mg is plated by hot dipping, and the thickness thereof is preferably 100 μm or less from the viewpoint of uniformity of appearance. The amount of Al added is required to be 0.1% or more in order to secure the adhesion to the base material, but if it exceeds 10%, the effect of improving the corrosion resistance is small, so this is the upper limit. On the other hand, with respect to the amount of addition of Mg as well, from the viewpoint of corrosion resistance, the effect is saturated even if added in excess of 5%, so this is the upper limit. If it is less than 0.05%, the effect cannot be obtained.

On the other hand, it is necessary that the structure is mainly composed of ferrite and that the second phase is contained from the viewpoint of ensuring strength. However, the second phase having a large hardness difference from that of ferrite is not preferable because it deteriorates the hole expandability. Therefore, it is necessary to form bainite or pearlite as the type of the second phase. At this time, formation of bainitic ferrite without precipitation of cementite is also included in the present invention. It is better that the fraction of this second phase is as small as possible, 2.
In order to secure a hole expandability of more than 3, it must be 30% or less. Further, if it is less than 1%, it is insufficient to secure the strength, so this is made the lower limit.

Next, the reasons for limiting the component composition in the present invention will be described.

C must be 0.1 mass% or less.
If it is added in excess of this amount, the amount of cementite precipitated in the hot-rolled sheet increases, not only the hole expandability is greatly reduced, but also the ductility is reduced, so that the workability is greatly deteriorated. On the other hand, if the amount is less than 0.001 mass%, the decarburization time will be prolonged in the steelmaking stage and the characteristics can be expected to be improved, but the amount of alloying elements added to secure the strength will be large. Therefore, decarburization cost and alloy cost increase, which is not preferable.

Mn is an element that forms a predetermined composite structure in combination with Mo, and plays an important role in securing the strength together with the amount of strengthening increase by solid solution strengthening. In order to obtain the desired strength in the present invention, it is necessary to add 1 mass% or more. On the other hand, if excessively added, the strength becomes too high and workability cannot be ensured, so 3.5 mass% was made the upper limit.

Mo is an element that plays an important role in the present invention together with Mn. That is, it is added for the purpose of forming bainite and pearlite and strengthening precipitation by carbide. In the hot-dip galvanizing step, the cooling rate is relatively slow, so in order to obtain the tensile strength specified in the present invention, it is necessary to secure the strength by controlling the structure of bainite or pearlite. Therefore, it is necessary to add 0.2% or more, but from the above experimental results, C ≧ −0.049 ([Mn] +1.7
[Mo]) + 0.15 is required to be a combination of C, Mn and Mo. Further, excessive addition causes a significant increase in cost, so the upper limit is 0.8%.

Si is added to strengthen the solid solution of ferrite and secure the strength. Therefore, it is added when necessary, but if it is not necessary, it is reduced to the extent that it does not increase the cost, and 0.01% is made the lower limit. Note that excessive addition deteriorates the weldability, so the upper limit was made 2.0 mass%.

P is an element that is added mainly for the purpose of increasing the strength, but if it is contained in excess, it not only lowers the ductility but also embrittles the grain boundaries, so the upper limit is 0.1 mass.
s% In addition, 0.001% is the lower limit because excessive reduction will significantly increase dephosphorization cost.

If S is excessively added, not only hot cracking occurs, but also many sulfides are formed, which causes cracking during processing. Therefore, 0.015 mass% is set as the upper limit. In addition, 0.001% is set as the lower limit because excessive reduction leads to a large increase in desulfurization cost.

Since Al is also an element added for deoxidation, it does not contribute to the achievement of the object of the present invention. However, if 0.005% or less, the intended effect is not exhibited. On the other hand, if more than 0.1% is added, not only the oxide remains in the steel but also the cost rises, so the upper limit is set.

N is fixed by Ti before the hot-rolled sheet stage, but if a large amount of TiN is formed, the workability deteriorates, so the upper limit is made 0.005%. N may not be contained.

Since Ti is added to fix N, the lower limit is the amount equivalent to N. However, excessive addition increases cost, so 0.005% was made the upper limit.

Nb also contributes to the strength increase through the refinement of the structure of austenite. Therefore, if less than 0.005%, the effect is not exhibited. However, if added in excess of 0.05%, the strength will increase too much, and there is concern that workability will deteriorate.

[0025] Ca and REM are added to control the morphology of sulfide, but less than 0.001% of Ca, or
The effect cannot be obtained with REM less than 0.005%. On the other hand, excessive addition not only causes inclusions to remain in the steel, but also leads to cost increase, so the upper limits are Ca: 0.01% and REM: 0.
05% Here, REM is an element such as La, Ce, Y.

B is an element that is supplementarily added to ensure hardenability. If less than 0.0005% is added, the effect does not appear. On the other hand, if added excessively, it will cause slab cracking after continuous casting, so 0.005% is made the upper limit.

Cu and Ni are added when steel is melted using scrap. The amount added is proportional to the amount of scrap used, but especially when Cu is added excessively, the amount of Ni added to avoid cracks that occur during hot working becomes too large, so 0.5% is the upper limit. did. From the viewpoint of avoiding hot cracking, the amount of Ni required is about half the amount of contained Cu, so the upper limit was made 0.3%.

Next, the manufacturing conditions will be described in detail.

A slab is made by normal continuous casting, but 100m
Even if it is manufactured by a thin slab continuous casting method of m or less, the effect of the present invention is not impaired.

After slab is formed by continuous casting, finish rolling is finished immediately after reheating or casting in the temperature range of Ar ₃ transformation point or higher. When finish rolling is performed in a temperature range lower than the Ar ₃ transformation point, the structure becomes non-uniform and the ductility deteriorates, and the workability targeted by the present invention cannot be obtained. From the viewpoint of microstructure refinement, it is better that the austenite grain size before transformation is smaller. Therefore, finish rolling is preferably completed within the range of Ar _{3 to} Ar ₃ + 20 ° C.

The cooling conditions and the winding conditions after the finish hot rolling are set so that the structure desired in the present invention is formed by the cooling rate and the winding temperature. As cooling conditions after finish rolling, it is necessary to perform air cooling until the ferrite fraction reaches 70% or more. After that, it is cooled to form the second phase, but when the cooling rate at that time is less than 5 ° C / s, the formation of pearlite increases, and as a result, the volume ratio exceeds 30%, so holes exceeding 2.3 Expandability cannot be obtained. On the other hand, 1
Cooling at a cooling rate of over 50 ° C / s not only makes temperature control difficult in actual operation, but also leads to deterioration of shape accuracy.
It is not preferable because it lowers the yield.

The winding temperature is the most important factor from the viewpoint of controlling the structure in the present invention. I.e. 350
When the temperature is lower than 0 ° C, martensite is formed, which may deteriorate the hole expansibility. On the other hand, when the winding temperature becomes higher, the fraction of the second phase exceeds 30%, and the hole expandability exceeding 2.3 cannot be obtained. Therefore, 650 ° C is set as the upper limit. Although not particularly specified in the present invention, temper rolling after winding has no influence on the characteristics in the present invention.

When performing hot dip galvanizing,
The surface of the steel sheet is heated to the same temperature as the temperature of the zinc bath and immersed in the zinc bath at that temperature. However, if the temperature is too high, the strength of the hot-rolled sheet changes due to structural change, so 550 ° C is set as the upper limit. On the other hand, if the surface temperature is too lower than that of the zinc bath, defective plating and non-uniformity of the plating layer thickness will occur, so the temperature is set to 420 ° C. or higher. Therefore, the temperature of the plating bath is also in the above-mentioned temperature range. However, especially when the bath temperature is higher than this, a large amount of fumes are generated, so this is the upper limit.

[0034]

[Example] Example 1

[0035]

[Table 1] C: 0.023%, Si: 0.02%, Mn: 2.55%, P: 0.005%, S: 0.008%, Al: 0.
Steel containing 027%, N: 0.0016%, Ti: 0.021%, Nb: 0.013, Mo: 0.038% was tapped from the converter and continuously cast into a slab. Hot rolled 12
After heating at 00 ° C., rough rolling was performed, and then finish rolling was completed at 900 ° C., which was a temperature range of the Ar ₃ transformation point or higher, to obtain a hot rolled sheet of 2.6 mm. Then, cooling and winding were performed under the conditions shown in Table 1. After pickling the obtained hot-rolled sheet, 0.08 μm thick N
The i-layer is electroplated, then the plate temperature is raised to 420 ° C by electrical heating
After heating up to, it was immersed in a zinc bath as it was. The composition of the zinc bath soaked here is Al: 0.2%, Mg: 0.5%, and the temperature of the zinc bath is 430 ° C. The obtained plated plate was temper-rolled at 1% and used for material evaluation. Material evaluation is JIS Z 2201
The sample was processed into the No. 5 test piece described and a tensile test was performed according to the test method described in JIS Z 2241. In addition, the hole expandability was investigated by using a 30-degree conical punch to spread a hole with a diameter of 10 mm (d ₀ ) and measuring the hole diameter (d) at the time when the crack penetrated the plate thickness. It was evaluated by d ₀ . The results are shown in the table. Further, regarding the corrosion resistance, a salt spray test described in JIS Z 4371 was carried out, and one in which no red rust was generated after 48 hours was passed. The characteristics of the hot-rolled sheet before plating obtained here are:
YP: 440MPa, TS: 640MPa, El: 31%, d / d 0: was 2.6.
No. 1, 2, 3, 4, 5, 6, according to the method of the present invention
In 7, 8 and 9, the fraction of the second phase is 1 to 20%, and
The tensile strength exceeds 590 MPa and the hole expandability exceeds 1.8. In Nos. 10 and 11 in which the cooling rate after finish rolling was out of the range of the present invention, the fraction of the second phase was out of the range of the present invention, and thus the hole expandability was low. Further, even if the coiling temperature is higher or lower than the range of the present invention, the fraction of the second phase becomes high, so that only low hole expandability is obtained. On the other hand, if the coiling temperature is too low as shown in No. 14, martensite will be formed, and the workability such as hole expandability will be greatly deteriorated. Further, in Nos. 12 and 13, the winding temperature is out of the range limited by the present invention. In both cases, the proportion of the respective second phase was out of proportion, and thus the hole expandability was low. The corrosion resistance was acceptable in all cases.

Example 2

[0037]

[Table 2]

[0038]

[Table 3] Steels having various compositions shown in Table 2 were taken out from the converter and continuously cast into slabs. After hot rolling at 1150 to 1250 ° C., rough rolling and finish rolling were carried out to manufacture hot rolled sheets having plate thicknesses shown in Table 3. The finish rolling was completed in the temperature range above the Ar ₃ transformation point. Furthermore, the amount of water in the cooling zone was adjusted so that the cooling rate after finish rolling was within the range of the present invention, and after cooling, winding was performed at 600 ° C. After pickling, a 0.05 μm-thick Ni layer was electroplated, and the plate temperature was heated to the temperature shown in the table by electric heating, and then immersed in a zinc bath as it was. The composition of the zinc bath soaked here is Al:
0.2%, Mg: 1%, and the temperature of the zinc bath was (plate temperature + 10 ° C). The obtained plated plate was temper-rolled at 1% and material evaluation was performed. In the same manner as in Example 1, a material evaluation by a tensile test, a hole expandability evaluation, and a corrosion resistance test were performed. The results are shown in the table. In the A, B, C, D, F, G, I, J, K, M, N, O and P steels according to the present invention, a tensile strength of more than 590 MPa and a hole expandability of more than 1.8 have been obtained. . However, with A-5 and F-4, the plate temperature during plating exceeded 600 ° C, so the strength exceeding 590 MPa was not obtained. Further, even with E, H and L steels in which Mn and Mo do not satisfy the formula, the strength exceeding 590 MPa is not obtained. Further, in the Q steel with a large amount of C, there is a large amount of carbide precipitation, so hole expandability exceeding 1.8 cannot be obtained. Since all steels were plated within the scope of the method of the present invention, they passed the corrosion resistance.

Example 3

[0040]

[Table 4] The steel B of Example 2 was heated to 420 ° C. by an electric heating method and then immersed in a zinc bath. The plating conditions at that time are as shown in Table 4. JIS Z for the obtained plated materials
The salt spray test described in 4371 was carried out to evaluate the corrosion resistance. Nos. 1,2,4,5,6,7 and 9 according to the scope of the present invention showed excellent corrosion resistance and no red rust occurred even after 48 hours. However, in No. 3 in which the thickness of the Ni plating layer on the surface of the steel sheet is lower than the range of the present invention, the adhesion of the plating is insufficient, and therefore corrosion resistance cannot be secured. Further, even in No. 8 in which Al and Mg contained in the plating layer are lower than the range of the present invention, the corrosion resistance cannot be ensured.

[0041]

Industrial Applicability The present invention clarifies a high-strength hot-dip galvanized hot-rolled steel sheet having excellent formability and corrosion resistance for a steel sheet used as an underbody member of an automobile, and a method for producing the same. According to the present invention, the applied member can be thinned and the weight of the vehicle body can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the amount of Mn, Mo and C and the tensile strength.

FIG. 2 is a diagram showing a relationship between Mn, Mo, and C amounts and hole expandability.

FIG. 3 is a diagram showing the relationship between hole expansibility and second phase fraction.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 3-24255 (JP, A) JP 4-346645 (JP, A) JP 5-255799 (JP, A) JP 4- 289126 (JP, A) JP 62-93003 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 2/00-2/40 C22C 38/00 301 C22C 38/14 C23C 28/02

Claims (9)

(57) [Claims] 1. An alloy layer containing 0.04 to 5 μm of Ni in the surface layer of a steel sheet, and a zinc alloy layer of 100 μm or less containing 0.1 to 10% of Al, 0.05 to 5% of Mg, and the balance unavoidable impurities in the upper layer. Consists of
A high-strength hot-dip galvanized steel sheet with a tensile strength of 590 MPa or more and excellent in formability and corrosion resistance. 2. A tensile strength of 590 MPa or more according to claim 1, which has a composite structure containing one or more of bainite and pearlite as an second phase in an area ratio of 1% or more and 30% or less and a yield ratio of 0.75 or less. High-strength hot-dip galvanized steel sheet with excellent formability and corrosion resistance. 3. By weight%, C: 0.001 to 0.1%, Si: 0.01 to 2
%, Mn: 1.0 to 3.5%, P: 0.001 to 0.1%, S: 0.001 to 0.015
%, Ti: 4 x [N] ~ 0.05%, Nb: 0.005 ~ 0.05%, Mo: 0.2 ~
0.8%, Al: included in the range of 0.01 to 0.1%, N: 0.005% or less, and satisfy the following formula, the tensile strength of 590 MPa or more according to claim 1 or 2 consisting of the balance Fe and unavoidable impurities A high-strength hot-dip galvanized hot rolled steel sheet with excellent formability and corrosion resistance. C ≧ −0.049 ([Mn] +1.7 [Mo]) + 0.15 4. Ca: 0.001-0.01%, REM: 0.005-0.05%
4. A high-strength hot-dip galvanized hot-rolled steel sheet having a tensile strength of 590 MPa or more and excellent in formability and corrosion resistance, containing at least one of the above. 5. A high-strength hot-dip galvanized hot-rolled steel sheet having a tensile strength of 590 MPa or more and excellent corrosion resistance, which comprises B: 0.0005 to 0.005%. 6. A high-strength molten zinc excellent in formability and corrosion resistance having a tensile strength of 590 MPa or more according to claim 3, which contains Cu: 0.05 to 0.5% and Ni: 0.02 to 0.3%. Plated hot rolled steel sheet. 7. A slab is produced by continuous casting, and after finish heating or rolling at a temperature not lower than the Ar ₃ transformation point immediately after reheating or casting, air cooling is performed until the fraction of ferrite reaches 70% or more, and then 5 Cooled at a cooling rate of ~ 150 ° C / sec, wound in the temperature range of 350-650 ° C, pickled the hot-rolled steel thus obtained, electroplated with Ni on the surface layer, and then continuously By heating the plate temperature in the hot dip galvanizing line to a temperature of less than 550 ° C and immersing it in the plating bath as it is, excellent formability and corrosion resistance having a tensile strength of 590 MPa or more according to any one of claims 3 to 6 Method for producing high strength hot-dip galvanized hot rolled steel sheet. 8. The 590 MPa according to claim 7, wherein the rough rolling is finished, and the sheet bar is once wound around a coil.
A method for producing a high-strength hot-dip galvanized hot rolled steel sheet having the above tensile strength and excellent in formability and corrosion resistance. 9. The method according to claim 7, wherein rough casting is performed immediately after casting into a slab having a diameter of 100 mm or less.
A method for producing a high-strength hot-dip galvanized steel sheet having a tensile strength of 0 MPa or more and excellent in formability and corrosion resistance.