JP4158593B2 - High-tensile hot-dip galvanized steel sheet with excellent secondary work brittleness resistance and method for producing the same - Google Patents

Description

【００４８】
【表２】

【００４９】
【表３】

【００５０】
【表４】

【００５１】
【発明の効果】
本発明によれば、非常に優れた耐二次加工脆性を有し、しかも自動車部品に代表される成形品素材として好適な引張強さが980MPa級の高張力亜鉛めっき鋼板を得ることができ、産業上格段の効果を奏する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-tensile hot-dip galvanized steel sheet, particularly a high-tensile hot-dip galvanized steel sheet having a tensile strength of 980 MPa, which is manufactured in a continuous hot-dip galvanizing line, and a method for producing the same. It relates to the improvement of secondary work brittleness.
[0002]
[Prior art]
Automotive parts are required to have high corrosion resistance depending on the application site. A hot-dip galvanized steel sheet is suitable as a material for a part applied to a portion where high corrosion resistance is required. For example, Patent Documents 1 and 2 disclose high-tensile hot-dip galvanized steel sheets imparted with excellent ductility and stretch flangeability by adjusting the steel components and the steel structure.
[0003]
On the other hand, there has been a strong demand for improving the fuel efficiency of automobiles from the viewpoint of conservation of the global environment in recent years. In addition, in order to protect passengers in the event of a collision, the strengthening of automobile bodies is being actively promoted. It is said that it is effective to increase the material strength of parts in order to satisfy the weight reduction and strengthening of the car body at the same time. Yes.
[0004]
[Patent Document 1]
JP 2001-207221 A [Patent Document 2]
Japanese Patent Laid-Open No. 2001-207235
[Problems to be solved by the invention]
Development of a high-tensile hot-dip galvanized steel sheet having a tensile strength of 980 MPa or more is desired because of the demand for high tension. For example, the hot-dip zinc disclosed in Patent Document 1 and Patent Document 2 described above is desired. The high tension so far has not been realized in the plated steel sheet. In addition, when hot-dip galvanized steel sheets are subjected to hot dip galvanization, the surface of the hot dip galvanized steel sheet has a relatively large sliding resistance, so that strain is likely to accumulate in the soft phase during forming, and it is more resistant than cold-rolled steel sheets. We are anxious about being inferior to secondary processing brittleness.
[0006]
That is, in order to further promote weight reduction and strengthening of an automobile body, a high-tensile hot-dip galvanized steel sheet that has excellent corrosion resistance and excellent secondary work brittleness resistance is an indispensable material.
Accordingly, the present invention is intended to provide a high-tensile hot-dip galvanized steel sheet that is excellent in corrosion resistance and excellent in secondary work brittleness resistance.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors conducted extensive research on the influence of the component composition and the microstructure on the properties of the steel sheet. As a result, the microstructure of the high-tensile hot-dip galvanized steel sheet having a predetermined chemical composition was obtained. In addition, a composite structure consisting of ferrite, martensite, and other second phases is used, and by setting the average crystal grain size of ferrite and the volume ratio of martensite within a predetermined range, the steel sheet has excellent tensile strength of 980 MPa or more. It has been found that it is possible to simultaneously provide secondary work brittleness resistance.
[0008]
Furthermore, the inventors have applied the heat treatment and plating treatment under a predetermined condition to a steel sheet whose chemical composition is adjusted to a predetermined range, so that the structure of the steel sheet becomes the above-mentioned composite structure, and resistance to secondary work brittleness. It has also been found that it is possible to produce a high-tensile hot-dip galvanized steel sheet that is excellent in resistance.
[0009]
The present invention has been made based on the above-described findings, and the gist thereof is as follows.
(1) A hot-dip galvanized steel sheet having a hot-dip galvanized layer on the surface of the steel sheet,
C: 0.05-0.2 mass%,
Si: 0.05 mass% or more and less than 0.3 mass%
Mn: 1.0-3.0mass%,
P: 0.03 mass% or less,
S: 0.003 mass% or less and
Al: containing 0.1 mass% or less, having a component composition consisting of the balance Fe and inevitable impurities, and having an average crystal grain size of 10 μm or less, 50 vol % or more of ferrite and 20 vol% or more of martensite, bainite, pearlite, and A high-tensile hot-dip galvanized steel sheet having a secondary work brittleness resistance having a composite structure composed of 5 to 20 vol % of any one of tempered martensite or other phases and other second phases.
It goes without saying that an alloyed hot-dip galvanized layer is included as the hot-dip galvanized layer.
[0010]
(2) In the above (1), as a component of the steel sheet, it further contains one group or two or more groups selected from the following groups (a) to (d), and is a high tensile melt excellent in secondary work brittleness resistance. Galvanized steel sheet.
(A) 0.05 to 1.0 mass% in total of any one or two of Cr and Mo
(B) B: 0.003 mass% or less (c) 0.05 to 1.0 mass% in total of any one or more of Ti, Nb and V
(D) A total of 0.01 mass% or less of either one or two of Ca and REM.
(3)
C: 0.05-0.2 mass%,
Si: 0.05 mass% or more and less than 0.3 mass%
Mn: 1.0-3.0mass%,
P: 0.03 mass% or less,
S: 0.003 mass% or less and
Al: A steel plate containing 0.1 mass% or less and having a component composition consisting of remaining Fe and inevitable impurities is held at a temperature of (Ac ₃ transformation point −50 ° C.) to Ac ₃ transformation point for 5 to 120 seconds, and then 5 ° C. Cools to a temperature of 500 ° C. or less at a rate of at least / s, then forms a hot-dip galvanized layer on the surface of the steel sheet, and then cools to 300 ° C. at a rate of at least 5 ° C./s. Manufacturing method of high-tensile hot-dip galvanized steel sheet.
[0012]
(4)
C: 0.05-0.2 mass%,
Si: 0.05 mass% or more and less than 0.3 mass%
Mn: 1.0-3.0mass%,
P: 0.03 mass% or less,
S: 0.003 mass% or less and
Al: A steel sheet containing 0.1 mass% or less and having a composition composed of the balance Fe and inevitable impurities is heated and held at a temperature of Ac ₁ transformation point to ( Ac ₃ transformation point −50 ° C.) for 120 s or less. ° C. / s at speeds above is cooled to a temperature below Ms point, further after holding 5~120s a temperature of (Ac ₃ transformation point -50 ° C.) to Ac ₃ transformation point, at 5 ° C. / s or faster 500 A high-tensile hot-dip galvanized steel sheet with excellent secondary work brittleness resistance, which is cooled to a temperature of ℃ or less and then cooled to 300 ℃ at a rate of 5 ℃ / s after forming a galvanized layer on the surface of the steel sheet. Production method.
[0013]
(5) In the above (3) or (4), after forming a hot-dip galvanized layer on the surface of the steel sheet, the steel sheet is further reheated to a temperature range of 450 to 550 ° C. and subjected to alloying treatment of the hot-dip galvanized layer. A method for producing a high-tensile hot-dip galvanized steel sheet having excellent secondary work brittleness resistance, which is cooled to 300 ° C. at a rate of 5 ° C./s or higher after the alloying treatment.
[0014]
(6) In the above (3), (4), or (5), as a component of the steel plate, further containing one group or two or more groups selected from the following groups (a) to (d): A method for producing a high-tensile hot-dip galvanized steel sheet that is excellent in secondary processing brittleness.
(A) 0.05 to 1.0 mass% in total of any one or two of Cr and Mo
(B) B: 0.003 mass% or less (c) 0.05 to 1.0 mass% in total of any one or more of Ti, Nb and V
(D) Any one or two of Ca and REM in total 0.01 mass% or less
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, each constituent requirement of the present invention will be described in detail.
First, the reasons for limiting the component composition of the steel sheet used in the present invention will be described.
C: 0.05-0.2mass%
C is an essential element for increasing the strength of steel and is essential for the formation of martensite. However, if the C content is less than 0.05 mass%, the desired high strength cannot be obtained. On the other hand, if the C content exceeds 0.2 mass%, the weldability of the steel decreases. For this reason, content of C is limited to the range of 0.05-0.2 mass%.
[0016]
Si: 0.05 mass% or more and less than 0.3 mass%
Si is an element having an effect of strengthening steel by solid solution strengthening, and in order to obtain this effect, it is necessary to contain 0.05 mass% or more. However, when the Si content is 0.3 mass% or more, the plating property is remarkably deteriorated. For this reason, Si content is limited to the range of 0.05 mass% or more and less than 0.3 mass%.
[0017]
Mn: 1.0-3.0mass%
Mn strengthens the steel by solid solution strengthening, improves the hardenability of the steel, and promotes the formation of martensite. Such an effect is recognized when the Mn content is 1.0 mass% or more. On the other hand, even if it contains exceeding 3.0 mass%, an effect will be saturated and the effect commensurate with content will no longer be expected, leading to an increase in manufacturing cost. For this reason, content of Mn is limited to the range of 1.0-3.0 mass%.
[0018]
P: 0.03 mass% or less P is an impurity element that segregates at the grain boundaries and lowers the toughness of the steel sheet, and adversely affects weldability. Therefore, the P content is limited to a range of 0.03 mass% or less.
[0019]
S: 0.003 mass% or less S is an impurity element that forms inclusions in the steel and lowers the toughness and workability of the steel sheet, and adversely affects weldability. Therefore, the S content is limited to a range of 0.003 mass% or less.
[0020]
Al: 0.1 mass% or less
Al is an element useful for deoxidation of steel, and can be contained preferably at 0.01 mass% or more depending on the necessity. However, when the content exceeds 0.1 mass%, not only the effect on deoxidation is saturated, but also an adverse effect due to an increase in inclusions in the steel tends to occur. Therefore, the Al content is limited to a range of 0.1 mass% or less.
[0021]
Furthermore, in the steel plate of this invention, in addition to the above-mentioned chemical component, it is possible to contain one group or two or more groups of the following groups (a) to (d) as necessary.
(A) 0.05 to 1.0 mass% in total of any one or two of Cr and Mo
(B) B: 0.003 mass% or less (c) 0.05 to 1.0 mass% in total of any one or more of Ti, Nb and V
(D) A total of 0.01 mass% or less of either one or two of Ca and REM.
(A) 0.05 to 1.0 mass% in total of any one or two of Cr and Mo
Cr and Mo are elements having an effect of improving the hardenability of steel and promoting the formation of martensite phase. Such an action is recognized by containing 0.05 mass% or more of one or two of Cr and Mo in total. On the other hand, even if it contains exceeding 1.0 mass% in total, an effect will be saturated and the effect corresponding to content cannot be expected, but it becomes economically disadvantageous. For this reason, 1 type or 2 types in Cr and Mo is limited to the range of 0.05-1.0 mass% in total. A more preferable range is 0.05 to 0.5 mass% in total of one or two of Cr and Mo.
[0023]
(B) B: 0.003 mass% or less B is an element having an effect of improving the hardenability of steel, and can be contained as necessary. However, if the B content exceeds 0.003 mass%, the effect is saturated, and therefore B is preferably limited to 0.003 mass% or less. A more desirable range is 0.001 to 0.002 mass%.
[0024]
(C) A total of 0.05 to 1.0 mass% of any one or more of Ti, Nb and V Ti, Nb and V form carbonitrides in the steel, and strengthen the steel by precipitation strengthening In addition to the effect of this, it also has the effect of refining the crystal grain size and can be contained if necessary. Such an effect is recognized by adding any one or more selected from Ti, Nb and V in a total of 0.05 mass% or more. On the other hand, even if any one type or two or more types are contained exceeding 1.0 mass% in total, the effect is saturated, and an effect commensurate with the content cannot be expected, which is economically disadvantageous. For this reason, the total content of any one or more of Ti, Nb and V is limited to a range of 0.05 to 1.0 mass%. A more preferable range is 0.05 to 0.2 mass%.
[0025]
(D) A total of 0.01 mass% or less of either one or two of Ca and REM
Ca and REM have an effect of controlling the form of the sulfide inclusions, thereby improving the stretch flangeability of the steel sheet. Such an effect is saturated when the total of any one or two selected from Ca and REM exceeds 0.01 mass%. For this reason, any one or two of Ca and REM are limited to 0.01 mass% or less in total. A more preferable range is 0.001 to 0.005 mass%.
In the steel sheet of the present invention, the balance other than the chemical components described above consists of Fe and inevitable impurities.
[0026]
Furthermore, it is important that the steel sheet of the present invention has a composite structure composed of ferrite, martensite and other second phases together with the above-described component composition.
[Ferrite]
Ferrite is a soft phase that does not contain iron carbide, has high deformability, and has an effect of improving the workability of the steel sheet. The steel sheet of the present invention has this ferrite as the main phase. Specifically, more than 50vol% is Ru ferrite der.
[0027]
And the finer the average crystal grain size of the ferrite, the better the secondary work brittleness resistance of the steel sheet, and in particular, this effect is prominent when the average crystal grain size is 10 μm or less. The particle size is limited to 10 μm or less. It should be noted that the phase other than ferrite usually has a particle size equal to or smaller than that of the main phase ferrite, and is not particularly limited here.
[0028]
[Martensite]
Martensite is a very hard phase and a phase that contributes to increasing the strength of the steel sheet. However, in order to set the tensile strength of the steel sheet to 980 MPa or more, it is necessary to use a steel sheet having a microstructure containing martensite of 20 vol% or more. For this reason, the amount of martensite in the composite structure in the present invention is limited to 20 vol% or more. In addition, in order to avoid the workability fall of a steel plate, it is preferable to set it as 40 vol% or less.
[0029]
[Other phase 2]
In the present invention, “other second phase” refers to any of bainite, pearlite, tempered martensite, or a plurality of phases thereof. Such a second phase is not as hard as martensite and has a small hardness difference from ferrite as the main phase, and is therefore an advantageous phase for improving the workability of the steel sheet while increasing the strength of the steel sheet. to ~20vol%. The tempered martensite is a phase obtained after heating lath-like martensite to a temperature range of (Ac ₁ transformation point to Ac ₃ transformation point) for a short time, and martensite or carbide is present in the ferrite ground. It refers to a phase formed in a layered form taking over the lath-like form.
[0030]
The high-tensile hot-dip galvanized steel sheet of the present invention is obtained by forming a hot-dip galvanized layer or an alloyed hot-dip galvanized layer on the surface layer of a steel sheet having the above-described chemical composition and the above-described composite structure. Here, the basis weight of the plating layer may be appropriately selected depending on the corrosion resistance requirement depending on the use site, and there is no particular limitation. Incidentally, in the steel plate used for automobile parts, the basis weight of the plating layer is preferably 30 to 120 g / m ² per one side of the steel plate.
[0031]
Next, a method for producing the high-tensile hot-dip galvanized steel sheet according to the present invention will be described.
First, a steel piece having a chemical composition within the above-described limited range is melted and cast and then hot-rolled or further cold-rolled to obtain a steel plate according to the generality of this type of steel plate. Moreover, processes, such as pickling or annealing, can be added as needed.
[0032]
Next, the steel sheet having the composition according to the present invention is held at a temperature of (Ac ₃ transformation point −50 ° C.) or higher for 5 to 120 seconds, and then cooled to a temperature of 500 ° C. or lower at a rate of 5 ° C./s or higher. At this time, if the holding temperature is less than (Ac ₃ transformation point −50) ° C. or the holding time is less than 5 s, the amount of martensite obtained after cooling is insufficient. On the other hand, if the holding time exceeds 120 s, the crystal grains become coarse and ferrite having a desired particle diameter cannot be obtained. When the cooling rate is less than 5 ° C./s, most of the second phase becomes pearlite or bainite, and a structure containing a desired amount of martensite cannot be obtained. In addition, in order to keep the shape of a steel plate favorable, it is desirable for a cooling rate to be 100 degrees C / s or less. Furthermore, it is preferable that the holding temperature is not higher than the Ac ₃ transformation point.
[0033]
In the present invention, the heat treatment step for heating and cooling described above can be replaced by a heat treatment combining a primary step and a secondary step described below. In this case, tempered martensite is included in the microstructure of the steel sheet after the hot dip galvanizing treatment.
[Primary process]
In the primary process, the steel sheet is heated and held at a temperature equal to or higher than the Ac ₁ transformation, and then rapidly cooled to a temperature equal to or lower than the Ms point at a rate of 10 ° C./s or higher. By this primary process, lath-shaped martensite is generated in the steel sheet. When the heating and holding temperature at this time is less than the Ac ₁ transformation point, martensite is not generated. Further, when the cooling rate is less than 10 ° C./s, lath-like martensite cannot be obtained. In order to make it easy to obtain a desired microstructure after the hot dip galvanizing step, it is desirable that the heating temperature is (Ac ₃ transformation point −50 ° C.) or less and the holding time is 120 s or less.
[0034]
[Secondary process]
Next, in the second step, the steel sheet to produce a lath martensite in the primary process, (Ac ₃ transformation point -50 ° C.) to Ac ₃ was 5~120s maintained at a temperature of transformation point, 500 ° C. or less To a temperature of 5 ° C./s or more. At this time, if the holding temperature is less than (Ac ₃ transformation point −50) ° C. or the holding time is less than 5 s, the amount of martensite newly generated after cooling is insufficient. On the other hand, if the holding time exceeds 120 s, the crystal grains become coarse and ferrite having a desired particle diameter cannot be obtained. Further, when the cooling rate is less than 5 ° C./s, a structure containing a desired amount of martensite cannot be obtained after cooling.
In addition, in order to keep the shape of a steel plate favorable, it is desirable for a cooling rate to be 100 degrees C / s or less. Further, the holding temperature is preferably not more than the Ac ₃ transformation point.
[0035]
In the subsequent hot dip galvanizing treatment, hot dip galvanizing is applied to the steel sheet and cooled to 300 ° C. at a cooling rate of 5 ° C./s or more. The hot dip galvanizing treatment is usually performed under the same conditions as those performed in a continuous hot dip galvanizing line, and is not particularly limited. However, if the plating process is performed in an extremely high temperature range, it becomes difficult to secure the necessary amount of martensite. For this reason, it is preferable to set it as the plating process at 500 degrees C or less. Moreover, it becomes difficult to secure the necessary amount of martensite even when the cooling rate after the plating treatment is extremely small. For this reason, the cooling rate in the temperature range from after plating to 300 ° C. is limited to 5 ° C./s or more. More preferably, it is 50 ° C./s or less.
Needless to say, wiping for adjusting the basis weight may be performed as necessary after the plating treatment.
[0036]
Moreover, you may perform the alloying process of a plating layer after the hot dip galvanization process. In this alloying treatment, the hot-dip galvanized steel plate is reheated to a temperature range of 450 to 550 ° C. to alloy the hot-dip galvanized layer. After the alloying treatment, it is cooled to 300 ° C. at a cooling rate of 5 ° C./s or more. Alloying at a high temperature makes it difficult to secure the necessary amount of martensite, and the ductility of the steel sheet decreases. For this reason, the upper limit of the alloying temperature is limited to 550 ° C. On the other hand, when the alloying temperature is less than 450 ° C., the alloying progresses slowly and the productivity decreases. For this reason, the lower limit of the alloying temperature is 450 ° C.
[0037]
In addition, when the cooling rate after the alloying process is extremely small, it is difficult to secure necessary martensite. For this reason, the cooling rate in the temperature range up to 300 ° C. after the alloying treatment is limited to 5 ° C./s or more.
[0038]
In addition, you may add the temper rolling for adjustment of shape correction, surface roughness, etc. to the steel plate after a plating process or an alloying process. Moreover, there is no inconvenience even if treatments such as resin or oil coating, various paintings or electroplating are performed.
[0039]
【Example】
Steel having the components shown in Table 1 and the balance consisting of Fe and unavoidable impurities was melted in a converter and made into a slab by a continuous casting method. The obtained slab was hot-rolled to a thickness of 2.6 mm, pickled, and then finished into a steel plate having a thickness of 1.4 mm by cold rolling. The balance other than the chemical components shown in Table 1 is Fe and inevitable impurities.
[0040]
Next, these cold-rolled steel sheets were subjected to heat treatment and hot dip galvanizing treatment by heating and cooling under the conditions shown in Tables 2 and 3. In addition, some of the galvanized layers were further alloyed.
[0041]
Here, the hot dip galvanizing treatment is performed by immersing the steel plate in a plating bath with a bath temperature of 475 ° C., and after pulling up the immersed steel plate, gas wiping is performed so that the basis weight per side is 50 g / m ^2. The basis weight was adjusted. In the case of alloying the galvanized layer, after the wiping treatment, the temperature was raised to 500 ° C. at a heating rate of 10 ° C./s to perform the alloying treatment. The holding time during the alloying treatment was adjusted so that the iron content in the plating layer was 9 to 11 mass%.
[0042]
The hot-dip galvanized steel sheet thus obtained was examined for its microstructure, tensile properties and secondary work brittleness resistance.
That is, the microstructure of the steel sheet was examined by observing a cross section in the rolling direction of the steel sheet with an optical microscope or a scanning electron microscope. And the ferrite grain size measured the crystal grain size of the ferrite based on the prescription | regulation of JISZO552 , and converted it into the average crystal grain size. The martensite volume ratio in the steel sheet is obtained by image analysis to determine the occupied area ratio of the martensite phase existing in the arbitrarily set square region using a cross-sectional structure photograph with a magnification of 1000 to 5000 times. The volume ratio was used. The volume fraction of ferrite was determined in the same manner, and the remainder was set as the other second phase.
[0043]
In addition, the tensile properties (TS) and elongation at break (El) according to JIS Z 2241 were measured for the tensile properties of the steel sheet using JIS Z 2204 No. 5 test piece taken in the direction perpendicular to the rolling direction from the steel sheet. It was measured.
[0044]
The secondary work brittleness resistance of the steel sheet was investigated by the following method.
First, a 50 mmφ test piece is taken from a steel plate and cup-formed in two stages using a 33 mmφ and 27 mmφ cylindrical punch. After cutting the edge of the cup at a position where the depth of the cup is 25 mm, hold it at various temperatures for 10 minutes or more and place it sideways on the test table. A weight of 5 kg is placed on it. Drop from height. At this time, the lowest temperature at which cracks did not occur even when the weight was dropped was taken as the brittle transition temperature, and the level of this temperature was taken as an indicator of secondary work brittleness resistance.
[0045]
The above survey results are shown in Table 4. From Table 4, the hot-dip galvanized steel sheet suitable for the present invention has a tensile strength (TS) of 980 MPa or higher and a brittle transition temperature of −80 ° C. or lower, which has excellent secondary work brittleness resistance. It can be seen that this is a high-tensile hot-dip galvanized steel sheet of 980 MPa class.
[0046]
On the other hand, in the case of a comparative example that is outside the scope of the present invention, none of the tensile strength (TS) of 980 MPa or more and a brittle transition temperature of −80 ° C. or less are compatible, and tensile strength excellent in secondary work brittleness resistance. However, a 980 MPa class high-tensile hot-dip galvanized steel sheet has not been obtained.
[0047]
[Table 1]

[0048]
[Table 2]

[0049]
[Table 3]

[0050]
[Table 4]

[0051]
【The invention's effect】
According to the present invention, it is possible to obtain a high-tensile galvanized steel sheet having an excellent secondary work brittleness resistance and having a tensile strength suitable as a molded article material typified by automobile parts of 980 MPa class, There are remarkable effects in the industry.

Claims (6)

A hot-dip galvanized steel sheet having a hot-dip galvanized layer on the surface of the steel sheet,
C: 0.05-0.2 mass%,
Si: 0.05 mass% or more and less than 0.3 mass%
Mn: 1.0-3.0mass%,
P: 0.03 mass% or less,
S: 0.003 mass% or less and
Al: containing 0.1 mass% or less, having a component composition consisting of the balance Fe and inevitable impurities, and having an average crystal grain size of 10 μm or less, 50 vol % or more of ferrite and 20 vol% or more of martensite, bainite, pearlite, and A high-tensile hot-dip galvanized steel sheet having a secondary work brittleness resistance having a composite structure composed of 5 to 20 vol % of any one of tempered martensite or other phases and other second phases. The high-tensile hot-dip galvanized steel sheet excellent in secondary work brittleness resistance according to claim 1, further comprising one group or two or more groups selected from the following groups (a) to (d) as components of the steel sheet.
(A) 0.05 to 1.0 mass% in total of any one or two of Cr and Mo
(B) B: 0.003 mass% or less (c) 0.05 to 1.0 mass% in total of any one or more of Ti, Nb and V
(D) A total of 0.01 mass% or less of either one or two of Ca and REM C: 0.05-0.2 mass%,
Si: 0.05 mass% or more and less than 0.3 mass%
Mn: 1.0-3.0mass%,
P: 0.03 mass% or less,
S: 0.003 mass% or less and
Al: A steel plate containing 0.1 mass% or less and having a component composition consisting of remaining Fe and inevitable impurities is held at a temperature of (Ac ₃ transformation point −50 ° C.) to Ac ₃ transformation point for 5 to 120 seconds, and then 5 ° C. Cools to a temperature of 500 ° C. or less at a rate of at least / s, then forms a hot-dip galvanized layer on the surface of the steel sheet, and then cools to 300 ° C. at a rate of at least 5 ° C./s. Manufacturing method of high-tensile hot-dip galvanized steel sheet. C: 0.05-0.2 mass%,
Si: 0.05 mass% or more and less than 0.3 mass%
Mn: 1.0-3.0mass%,
P: 0.03 mass% or less,
S: 0.003 mass% or less and
Al: A steel sheet containing 0.1 mass% or less and having a composition composed of the balance Fe and inevitable impurities is heated and held at a temperature of Ac ₁ transformation point to ( Ac ₃ transformation point −50 ° C.) for 120 s or less. ° C. / s at speeds above is cooled to a temperature below Ms point, further after holding 5~120s a temperature of (Ac ₃ transformation point -50 ° C.) to Ac ₃ transformation point, at 5 ° C. / s or faster 500 A high-tensile hot-dip galvanized steel sheet with excellent secondary work brittleness resistance, which is cooled to a temperature of ℃ or less and then cooled to 300 ℃ at a rate of 5 ℃ / s after forming a galvanized layer on the surface of the steel sheet. Production method.   In Claim 3 or 4, after forming the hot dip galvanized layer on the surface of the steel sheet, the steel sheet is further reheated to a temperature range of 450 to 550 ° C and subjected to alloying treatment of the hot dip galvanized layer. A method for producing a high-tensile hot-dip galvanized steel sheet having excellent secondary work brittleness resistance, which is cooled to 300 ° C. at a rate of 5 ° C./s or more. 6. The high-tensile melt excellent in secondary work brittleness resistance according to claim 3, 4 or 5, further comprising one group or two or more groups selected from the following groups (a) to (d) as components of the steel sheet. Manufacturing method of galvanized steel sheet.
(A) 0.05 to 1.0 mass% in total of any one or two of Cr and Mo
(B) B: 0.003 mass% or less (c) 0.05 to 1.0 mass% in total of any one or more of Ti, Nb and V
(D) A total of 0.01 mass% or less of either one or two of Ca and REM