JP3475560B2 - High tensile alloyed hot-dip galvanized steel sheet excellent in plating characteristics and secondary work brittleness resistance and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength hot-dip galvanized steel sheet suitable for use in applications such as bending, press forming, drawing, etc., mainly for automobile bodies and the like, and a method for producing the same. Regarding In recent years, environmental problems have been clamoring loudly, and the exhaust gas regulations of automobiles are being tightened due to this. Further, from the viewpoint of energy saving, it is required to improve the fuel efficiency of automobiles. The weight reduction of the vehicle body is effective for these measures. Furthermore, the increase in the number of fatalities due to car accidents has become a problem, and improving the safety of cars has become an important issue. In order to reduce the weight of the vehicle body and improve passive safety, it is one of the advantageous means to use a steel plate having a higher tensile strength of about 400 MPa or more.

On the other hand, cold-rolled steel sheets including hot-dip galvanized steel sheets generally deteriorate in press formability (represented by average r value and strength-ductility (TS-El) balance) as the tensile strength increases. Moreover, the surface treatment characteristics such as plating characteristics tend to deteriorate. Further, so-called secondary working brittleness, which is embrittled by an impact applied after forming into a predetermined shape, is easily caused. Therefore, in order to apply the hot-dip galvanized steel sheet to the application of automobile bodies, it is important not only to increase the tensile strength but also to improve the press forming property and the secondary processing brittleness as well as the plating property. Is.

[0003]

2. Description of the Related Art Up to now, various measures have been proposed in order to improve press formability associated with higher tension. For example, in a high-strength cold-rolled steel sheet having excellent formability disclosed in Japanese Patent Laid-Open No. 63-100158, an ultra-low carbon steel with reduced C is used as a base for improving workability and aging. It is disclosed that Ti, Nb, etc., which are nitride forming components, are added, and that Si, Mn, P, which does not impair the workability, is mainly added in order to increase the tensile strength. Among them, Si is r
It is considered to be an advantageous component capable of increasing the tensile strength without deteriorating the workability represented by the value and elongation. However, when a large amount of Si is added, it is unavoidable that the surface treatment characteristics are deteriorated, and in particular, the plating characteristics are significantly deteriorated.

Therefore, in order to increase the tensile strength of the hot-dip galvanized steel sheet, as disclosed in JP-A-5-255807, the Si content is limited to 0.03% or less, and P and Mn are mainly used as strengthening components. However, there is a problem that addition of a large amount of P delays the alloying of the hot-dip galvanizing and easily causes secondary work embrittlement particularly in an extremely low carbon steel. In addition, although Mn has little effect on the plating characteristics, if the Si content is limited to 0.1% as described later, the plating characteristics will also start to deteriorate with an Mn content of 1% or more, and a large amount will also occur. However, there is also a problem in that when added to the alloy, the transformation point is lowered and the hot-rolled sheet is hardened or does not recrystallize during annealing, leading to deterioration of the material. Therefore, there is a limit to achieving high strength while maintaining workability and plating characteristics only with Mn and P, and a measure for obtaining a hot-dip galvanized steel sheet having higher strength has been desired.

[0005]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems. In order to use it for automobile bodies and the like, the present invention has not only plating characteristics but also workability such as press molding and secondary processing resistance. It is an object of the present invention to propose an alloyed hot-dip galvanized steel sheet having excellent heat resistance and higher tensile strength together with its advantageous manufacturing method. That is, the tensile strength
400 MPa or more, TS × El is 16000 MPa ·% or more, and the brittle transition temperature in the drop weight test described later is −45 ° C. or less,
Moreover, it is an object of the present invention to propose a method for producing a steel sheet having good hot-dip galvanizing property.

[0006]

[Means for Solving the Problems] As a result of repeated research and study, the inventors have found that by appropriately containing Si in the balance with Mn, it is possible to improve the strength without deteriorating the plating characteristics. It has been found that it is possible to obtain a high-strength galvannealed steel sheet having a tensile strength of 400 MPa or more while having good plating characteristics and press formability. It was also found that the above characteristics can be advantageously obtained by limiting the manufacturing conditions.
The present invention is based on the above findings.

That is, according to the present invention, C: 0.0005 to 0.0050 mass%, Si: 0.1 to 2.5 mass%, Mn: 0.1 to 2.5 mass%, Ni: 0.05 to 2. 0 mass%, B: 0.0010 to 0.0100 mass%, Cu: 0.1 to 2.5 mass%, Al: 0.005 to 0.10 mass%, P: 0.040 to 0.18 mass% and N: 0. 0.0003 to 0.0060 mass% per content expressed in mass% (% Si), (%
Mn), (% Ni) and (% Cu) represented by the following formulas (1), (2) and (3), and Ti: 0.003 to 0.10 mass% and Nb: The total of Ti and Nb is one or two selected from 0.003 to 0.10 mass%.
It is contained in the range of 0.03 mass% or more, and the balance is 9% on the surface of the steel sheet consisting of Fe and unavoidable impurities.
A high-strength galvannealed steel sheet (first invention) having an alloying hot-dip galvanized layer of up to 12% and being excellent in plating characteristics and secondary work brittleness resistance. Note 1.5 (% Mn) -2 ≦ (% Si) ≦ 2 (% Mn)
――― (1) 2 (% Cu) ≧ (% Mn) ――
-(2) (% Cu) ≤ 3 (% Ni)-
-(3)

Further, the present invention is C: 0.0005 to 0.0050 mass%, Si: 0.1 to 2.5 mass%, Mn: 0.1 to 2.5 mass%, Ni: 0.05 to 2. 0 mass%, B: 0.0010 to 0.0100 mass%, Cu: 0.1 to 2.5 mass%, Al: 0.005 to 0.10 mass%, P: 0.040 to 0.18 mass% and N: 0. 0.0003 to 0.0060 mass% per content expressed in mass% (% Si), (%
Mn), (% Ni) and (% Cu) represented by the following formulas (1), (2) and (3), and Ti: 0.003 to 0.10 mass% and Nb: One or two selected from 0.003 to 0.10 mass% and one or two selected from W: 0.01 to 1.0 mass% and Mo: 0.01 to 1.0 mass%. Is the sum of Ti and Nb
It is contained in the range of 0.03 mass% or more, and the balance is 9% on the surface of the steel sheet consisting of Fe and unavoidable impurities.
A high-strength hot-dip galvanized steel sheet (second invention) having an alloying hot-dip galvanized layer of up to 12% and having excellent plating characteristics and secondary processing brittleness resistance. Note 1.5 (% Mn) -2 ≦ (% Si) ≦ 2 (% Mn)
――― (1) 2 (% Cu) ≧ (% Mn) ――
-(2) (% Cu) ≤ 3 (% Ni)-
-(3)

Further, according to the present invention, a steel slab having the same composition as that of the first invention is used as a material, and the material is hot-rolled and finish-rolled at a temperature in the range of 1000 ° C or lower and 750 ° C or higher. After completion, the product is wound up at a temperature in the range of 650 ° C or lower and 550 ° C or higher, then pickled, and then cold-rolled at a rolling reduction of 60 to 95%.
Recrystallization annealing was performed in the temperature range of 0 to 950 ℃, and then 53
After quenching to a temperature in the range below 0 ℃ and above 380 ℃, Al
Containing 0.12% to 0.145% in a hot dip galvanizing bath in the temperature range of 450 to 490 ℃ in the temperature range above the bath temperature and below the bath temperature +10 ℃ to perform the plating treatment, and then in the temperature range between 450 and 550 ℃. For 14 seconds or more and 28 seconds or less to perform alloying treatment, and a method for producing a high-strength galvannealed steel sheet having excellent plating characteristics and secondary work brittleness resistance (third invention) ).

Furthermore, the present invention is characterized in that a steel slab having the same composition as the second invention is used as a raw material, and this material is subjected to the same manufacturing process as that of the third invention. It is a method for manufacturing a high-strength alloyed hot-dip galvanized steel sheet (fourth invention) which is excellent in subsequent working brittleness.

[0011]

First, the experimental results which are the basis of the present invention will be described. C: 0.002 mass%, Ni: 0.4 mass%, Cu: 0.4 mass%,
P: 0.10 mass%, Al: 0.04 mass%, N: 0.002 mass%,
B: 0.0040 mass%, Ti: 0.04 mass% and Nb: 0.03 mass%
, And further Si and Mn, the sheet bar formed by adding various contents thereof, hot rolling at a finishing temperature of 820 ~ 910 ℃, followed by pickling, reduction ratio 75 ~ 85 % Cold-rolled to a thickness of 0.75 mm, then further annealed at 780 to 890 ℃ in the hot dip galvanizing line, and then rapidly cooled to 450 to 500 ℃, and then molten zinc containing 0.13% Al. After soaking in the plating bath and performing the plating treatment, 45
Alloying treatment (Fe content in the plating layer: about 10%) was performed in the temperature range of 0 to 550 ° C to obtain a galvannealed steel sheet.

The plating characteristics of these galvannealed steel sheets were investigated. The plating characteristics were evaluated by visual judgment of appearance (presence or absence of non-plating) and judgment of powdering resistance by 90 ° bending test. The plating characteristics of the steel sheet are summarized in Table 1 in relation to the Si content and Mn content of the steel sheet.

[0013]

[Table 1]

From Table 1, when the relationship between the Si content and the Mn content is within the range of 1.5 (% Mn) -2≤ (% Si) ≤2 (% Mn), the plating appearance and powder resistance It was revealed that the ring property was good. On the other hand, if either Si or Mn is large and the relationship between the Si content and the Mn content is out of the above range, the plating characteristics deteriorate. The reason for this is not clear in detail, but the oxide film formed on the surface of the steel sheet becomes SiO ₂ when Si alone is added, and MnO when Mn alone is added. Whereas the wettability is poor, Si and Mn are added in combination within the range satisfying the above relational expression, in the annealing step prior to the hot dip galvanizing treatment step, MnSiO having a structure advantageous for plating characteristics. _It is considered that the oxide film mainly composed of ₃ is formed on the surface of the steel sheet, and the wettability with molten zinc is improved.

Next, C: 0.002 mass%, B: 0.0040 mass
%, P: 0.10mass%, Al: 0.04mass%, N: 0.002mass
%, Ti: 0.04 mass% and Nb: 0.03 mass%, and
Sheet bars containing various contents of Si, Mn, Ni, and Cu were hot-rolled at a finishing temperature of 820 to 910 ° C, followed by pickling, and a reduction ratio of 75 to 85%. After cold rolling to a plate thickness of 0.75 mm, it was further annealed at 780 to 890 ° C in the hot dip galvanizing line, and then 450
After quenching to ~ 500 ° C, dipping in a hot dip galvanizing bath containing 0.13% Al for plating treatment, then 450 ~ 55
Alloying treatment in the temperature range of 0 ℃ (Fe content in the plating layer
10%) to obtain a galvannealed steel sheet.

Secondary galvanizing resistance of these alloyed hot-dip galvanized steel sheets was investigated. Here, the evaluation of the secondary processing brittleness is as follows. After punching a 50φ test piece from a steel plate, this test piece is squeezed out with a 24φ ball head punch, and the obtained cup is placed at a depth of 21 mm. After cutting, put it sideways and weigh 5 kg against this cup, drop height 80 cm
The maximum temperature at which cracking occurred was evaluated as the brittle transition temperature. The pass / fail judgment was evaluated as ○ (OK) when the transition temperature was −45 ° C. or lower, and × (NG) when the transition temperature exceeded −45 ° C. Regarding the secondary work brittleness resistance of such steel sheet,
Table 2 shows the relationship between the content, Mn content, Ni content and Cu.

[0017]

[Table 2]

As can be seen from Table 2, steel A having a small total amount of Si content, Mn content, Ni content and Cu content has good secondary work embrittlement resistance, but tensile strength (TS ) Was less than the target 400-700 MPa of this invention. Also,
In steels B and E having a Cu content less than one half of the Mn content, the secondary work brittleness resistance is poor, and conversely, a C steel having a Cu content of one half or more of the Mn content. , D steel, F steel, and G steel were found to have improved secondary work brittleness resistance. That is, although the detailed mechanism is not clear, it is half of the Mn content.
It has been clarified that the secondary working brittleness resistance is remarkably improved by adding the above Cu.

Regarding the effects of the present invention as described above, in order to improve the strength, one or two of Mo and W is used.
Even when the seed was added in the range of 1 mass% or less, it was not damaged at all.

Next, the reasons for limiting the composition range of each component in the present invention will be described. C: 0.0005 to 0.0050 mass% C is an extremely low carbon steel in order to obtain a steel sheet having good workability, particularly good TS-El balance, so the upper limit is made 0.0050 mass%. . Preferably 0.0040ma
ss% or less, more preferably 0.0030 mass% or less. However, in the case where a large amount of P is added to improve the strength, if C is less than 0.0005 mass%, the secondary working brittleness resistance deteriorates. Therefore, the C content is 0.0005 to 0.
0050 mass% only. Preferably 0.0005 to 0.0040 mass
%, And more preferably 0.0005 to 0.0030 mass%.

Si: 0.1 to 2.5 mass% Si has the effect of reducing the deterioration of workability and strengthening the steel, so its content must be 0.1 mass% or more. However, if it exceeds 2.5 mass%, the secondary processing brittleness resistance is deteriorated, so the Si content is limited to 0.1 to 2.5 mass%. However, in view of the gist of the present invention of strengthening steel while maintaining workability by utilizing Si, the Si content in the case of a steel sheet of 400 MPa class or higher is preferably 0.2 to 2.5 mass.
%, And more preferably 0.3 to 2.5 mass%.

Further, in the present invention, the amount of Si is set within a range satisfying 1.5 (% Mn) −2 ≦ (% Si) ≦ 2 (% Mn) depending on the Mn content. If the value is out of the range of the above formula, an oxide film having a structure advantageous for the plating property is not formed on the surface of the steel sheet in the annealing process prior to the plating process, and thus the plating property cannot be improved.

Mn: 0.1 to 2.5 mass% It is desirable to reduce the Mn content from the viewpoints of workability and resistance to secondary working brittleness, but when it is less than 0.1 mass%, it is sufficient as a material for automobiles. No strengthening effect can be obtained.
Further, when a large amount of Si having an action of increasing the transformation point during hot rolling is added, it becomes difficult to carry out normal hot rolling in the austenite region, so that the transformation point is lowered.
Is preferably 0.2 mass% or more, more preferably 0.4 mass%
% Or more to adjust the transformation point to an appropriate temperature range. On the other hand, if it exceeds 2.5 mass%, it becomes difficult to improve the secondary work brittleness resistance, and the steel is significantly hardened to make cold rolling difficult. Therefore, the Mn content is 0.1 to 2.5 mass.
%, But preferably 0.2 to 2.5 mass%, more preferably 0.4 to 2.5 mass%.

Ni: 0.05 to 2.0 mass% Ni is an effective component for improving the strength of the steel without impairing the workability and suppressing the brittleness.
If it is less than 0.05 mass%, a sufficient effect cannot be obtained. Also, if a large amount of Si, which has the effect of raising the transformation point during hot rolling, is added, it becomes difficult to carry out normal hot rolling in the austenite region, so the transformation point is lowered.
Ni is preferably 0.1 mass% or more, more preferably 0.2 ma
It is desirable to add ss% or more to adjust the transformation point to an appropriate temperature range. On the other hand, if Ni is added in an amount of more than 2.0 mass%, the cost will be significantly increased. Therefore, the Ni content is limited to 0.05 to 2.0 mass%. Preferably 0.1 to 2.
It is 0 mass%, more preferably 0.2 to 2.0 mass%.

B: 0.0010 to 0.0100 mass% B segregates at the grain boundaries and exhibits a remarkable effect in preventing secondary processing brittleness, but if less than 0.0010 mass%, the effect is small,
On the other hand, even if added in excess of 0.0100mass%, not only the effect is saturated, but also workability deteriorates due to increase in yield strength, decrease in elongation, etc., so it is limited to 0.00010 to 0.0100mass%. However, since the workability is slightly deteriorated by the addition, it is preferably 0.00010 to 0.0050 mass%, more preferably 0.0010 to 0.0030 mass%, except for the case of containing P of 0.15 mass% or more.

Cu: 0.1 to 2.5 mass% Cu is an important component in the present invention. By adding it in the range of 2 (% Cu) ≧ (% Mn) in the ratio with Mn, secondary processing resistance is obtained. It is possible to significantly improve the sex. Further, Cu is a component effective in increasing the strength of steel by forming a solid solution or precipitation in the steel, and in order to obtain that effect, 0.1 ma is required.
Requires more than ss%. Also, raise the transformation point during hot rolling
When a large amount of Si is added, it becomes difficult to carry out normal hot rolling in the austenite region, so Cu having a function of lowering the transformation point is preferably 0.2 mass% or more,
More preferably, 0.4 mass% or more is added to adjust the transformation point to an appropriate temperature range. But Cu to 2.5 ma
If it is added in excess of ss%, the spot weldability is significantly deteriorated. Therefore, the Cu content is 0.1-2.5 mass%
Limited to It is preferably 0.2 to 2.5 mass%, more preferably 0.4 to 2.5 mass%. Further, if the Cu content exceeds 3 times the Ni content, the hot workability deteriorates, so the upper limit is specified within the above range from the relationship with the Ni content.

Al: 0.005 to 0.10 mass% Al is added in a necessary amount for deoxidation and precipitation fixation of N in steel, but if the content is less than 0.005 mass%, inclusions increase and good working is performed. I can not get sex. On the other hand, if the Al content is too large, not only the workability is deteriorated but also the surface properties are deteriorated, so the Al content is limited to 0.005 to 0.10 mass%. However, it is preferably 0.005 to 0.06 mass%, more preferably 0.01 to 0.06 mass% from the viewpoint of optimizing workability by the above mechanism.

P: 0.040 to 0.18 mass% Although the detailed mechanism is not clear, P has the effects of strengthening steel and improving workability, especially the average r value, and is added depending on the desired strength. The effect becomes remarkable when 0.040 mass% or more is added. On the other hand, when P is added in excess of 0.18 mass%, alloying of the plating is significantly delayed and the material deteriorates due to solidification segregation during casting. . When the amount of C is reduced for the purpose of improving the material quality, the secondary workability starts to deteriorate with the addition of 0.12 mass% or more, and a large amount of B needs to be added with the addition of 0.15 mass% or more. Therefore, P
The content is specified to be 0.040 to 0.18 mass%. Preferably 0.
040-0.15mass%, more preferably 0.040-0.12mass%
Is.

N: 0.0003 to 0.0060 mass% It is preferable that the N content is low, but if it is less than 0.0003 mass%, the production cost will remarkably increase, so this is the lower limit. On the other hand, if it is too much, a large amount of N is made to be harmless.
Since it is necessary to add Ti and Al, the upper limit is 0.0060 mass%. However, from the viewpoint of workability, it is preferably 0.0003 to 0.
0040 mass%, more preferably 0.0003 to 0.0030 mass%.

1 selected from Ti: 0.003 to 0.10 mass% and Nb: 0.003 to 0.10 mass%
The total of Ti and Nb is 0.03 mass%
In the above range , (Ti + Nb) ≧ 0.03 mass%
In the range of Ti and Nb are both carbide forming components, Ti is a part or all of N, C and S, and Nb.
Is effective in securing the workability and non-aging property of the ultra-low carbon steel because it fixes part or all of C. However, in all cases, if less than 0.003 mass%, the effect is not obtained, so this is made the lower limit. On the other hand, both are 0.10 m
On the other hand, if it exceeds ass%, the workability is deteriorated, so this is made the upper limit. However, from the viewpoint of workability, Ti, total Nb is the least 0.03 mass%. Preferably 0.03 to 0.10 mass%, more preferably 0.0.
It is 3 to 0.08 mass%.

S: 0.0005 to 0.015 mass% In the present invention, S is an impurity, and it is preferable that the S content is low, but if it is less than 0.0005 mass%, the manufacturing cost will remarkably increase. On the other hand, if it exceeds 0.015 mass%, a large amount of MnS is precipitated and the workability deteriorates, so this is made the upper limit. However, from the viewpoint of workability, it is preferably 0.0005 to 0.
It is 010 mass%, more preferably 0.0005 to 0.008 mass%.

W: 0.01 to 1.0 mass% and Mo: 0.01 to 1.0
1 type or 2 types selected from mass% In the second invention and the fourth invention, in addition to the above components, W
And 1 or 2 kinds of Mo are contained. Both W and Mo are effective components for increasing the strength without deteriorating the workability and the secondary work embrittlement resistance, and are effective when added in an amount of 0.01 mass% or more. In addition, these components can increase the strength without deteriorating the plating characteristics, and therefore preferably have a content of 0.05 ma in order to reduce the components degrading the plating characteristics.
Add ss% or more, more preferably 0.1 mass% or more. On the other hand, excessive addition causes the recrystallization temperature of steel to extremely rise, deteriorating the workability and increasing the cost. Therefore, the W and Mo contents are both 0.01 to 1.0 mass%, preferably 0.05 to 1.0 mass%, and more preferably 0.1 to 1.0 ma.
ss%.

Next, the limitation of manufacturing conditions in the present invention will be described. First, a steel slab having a predetermined composition is manufactured through a steel making process and a casting process. Next, during hot rolling, the finishing temperature must be at least 750 ° C in order to improve workability after cold rolling and annealing. Finishing at a temperature of less than 750 ° C. makes the rolling structure remarkably remain in the hot-rolled sheet, which is disadvantageous in forming a texture structure favorable to press formability. On the other hand, when rolling is completed at a temperature exceeding 1000 ° C., the structure of the hot-rolled sheet is coarsened, and the texture advantageous for press formability cannot be obtained. Therefore, the hot rolling finish temperature is
It is preferably 750 ° C or higher and 1000 ° C or lower.

The coiling temperature after hot rolling is 550 ° C or higher, 65
0 ° C or less is desirable. If the coiling temperature is lower than 550 ° C, the hot-rolled sheet is likely to be hard and the cold rolling property is deteriorated. Therefore, the lower limit was set to 550 ° C. On the other hand, the winding temperature is 650 ℃
If it exceeds, the phosphorus compound will be generated and coarse particles will be generated, which will lead to material deterioration, so the upper limit was made 650 ° C.

In cold rolling, sufficient workability cannot be obtained unless the cold rolling reduction rate is 60% or more, so the lower limit of the reduction rate is preferably 60% or more. More preferably, a cold rolling reduction of 70% or more is advantageous. On the other hand, if the cold rolling reduction ratio is 95% or more, the workability is rather deteriorated, so the upper limit is preferably 95%.

The plating treatment is carried out in a continuous hot dip galvanizing facility. The recrystallization annealing temperature after cold rolling may be in the range of 700 ° C to 950 ° C from the viewpoint of sufficient recrystallization and not forming austenite, but preferably 800 ° C or more. Is good.

After the recrystallization annealing, it is rapidly cooled to a temperature in the range of 530 ° C or lower and 380 ° C or higher. When the quenching stop temperature is lower than 380 ° C, non-plating occurs, while when quenching is stopped at a temperature higher than 530 ° C, unevenness occurs on the plating surface, which is not preferable.

After the rapid cooling, the content of Al is 0.12 to 0.145%.
The plating treatment is performed by immersing in the hot dip galvanizing bath containing it. At this time, if the Al content in the bath is less than 0.12%, alloying will proceed too much and the plating adhesion (powdering property) will deteriorate, while if the Al content exceeds 0.145%, non-plating will occur. Limit the Al content in the bath to the range of 0.12 to 0.145%. The temperature of the galvanizing bath is 450-490.
The temperature of the plate to be immersed in the bath should be above the bath temperature, and the bath temperature +
The temperature shall be within 10 ℃. If the bath temperature is lower than 450 ° C or the plate temperature during immersion is lower than the bath temperature, the solidification of zinc is promoted and it becomes difficult to adjust the coating amount. On the other hand, if the bath temperature exceeds 490 ° C or the plate temperature during immersion exceeds + 10 ° C, the elution of iron from the steel plate into the bath is promoted to form dross, which easily causes surface defects.

By the alloying treatment following this plating treatment,
Although an alloyed hot-dip galvanized steel sheet is obtained, this alloying treatment is a treatment for heating so that the Fe content in the plated layer is 9 to 12%. That is, heating is performed for 14 seconds to 28 seconds in the temperature range of 450 to 550 ° C to form an alloy. If the heating temperature is less than 450 ° C. or the heating time is less than 14 seconds, alloying is not sufficiently performed and the Fe content becomes less than 9%, resulting in deterioration of flaking resistance. On the other hand, if the heating temperature exceeds 550 ° C or the heating time exceeds 28 seconds, alloying proceeds excessively and the Fe content exceeds 12%, so that the powdering resistance deteriorates.

The hot-dip galvanized steel sheet of the present invention is
Even if the press-formability, weldability, or corrosion resistance is further improved by subjecting the surface to a special treatment such as applying a lubricant, the characteristics of the present invention remain unchanged. In addition, even if the steel sheet of the present invention (or the steel sheet of the present invention having the surface subjected to the above-mentioned special treatment) is temper-rolled within a normal range for the purpose of shape correction or the like, the characteristics of the present invention can be obtained. There is no change.

[0041]

Example A steel slab having the composition shown in Tables 3 and 4 prepared by melting in a converter was prepared. In Tables 3 and 4, Steel Nos. 25 to 32 are comparative examples, and in Steel Nos. 25 to 29, the relationship between the Si content and the Mn content is 1.5 (% Mn) -2 ≦ (% This is an example in which Si) ≦ 2 (% Mn) is not satisfied, and Steel Nos. 30 to 32 are examples in which the relationship between the amount of Mn and the amount of Cu does not satisfy 2 (% Cu) ≧ (% Mn). is there.

[0042]

[Table 3]

[0043]

[Table 4]

The finishing temperature of these steel slabs is 800 to 920 ° C.
Hot rolling, winding at 580 ~ 630 ℃, pickling,
Then, after rolling to a plate thickness of 0.8 mm by cold rolling with a reduction rate of 80%, recrystallization annealing in a continuous hot dip galvanizing line, plating treatment (plating bath temperature 460 to 490 ° C, plate temperature during immersion is bath temperature or higher, A bath temperature of + 10 ° C or less, a basis weight of 45 g / m ^{2 on} one side) and an alloying treatment (treatment temperature of 500 ° C, treatment time of 15 seconds) were performed. The recrystallization annealing temperature, the quenching stop temperature, the Al content in the plating bath and the Fe content in the plated layer after alloying at that time are shown in Table 5 and Table 6.
Shown in.

The steel sheet thus obtained was examined for tensile properties and secondary work brittleness resistance. This tensile property is JIS
The No. 5 test piece was used for the measurement, and the plating characteristics and the secondary processing brittleness resistance were tested and evaluated in the same manner as in the above experiment. The survey results are also shown in Tables 5 and 6. In Tables 5 and 6, Steel Nos. 4 to 7 are comparative examples, and
No. 4 has a low quench stop temperature, Steel No. 5 has a high quench stop temperature, Steel No. 6 has a low Al content in the plating bath, and Steel No. 7 has an Al content in the plating bath. This is an example with a high content rate.

[0046]

[Table 5]

[0047]

[Table 6]

From Tables 5 and 6, all the conforming examples of the present invention have excellent TS and El balances represented by TS × El, and at the same time have excellent plating characteristics and secondary processing brittleness resistance. I understand.

[0049]

The high-strength alloyed hot-dip galvanized steel sheet of the present invention has excellent plating characteristics by limiting the balance of Si and Mn in ultra-low carbon steel, and also has characteristics suitable for press forming. It can greatly contribute to the weight reduction and safety improvement of the automobile.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shigeru Unno 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture, Kawasaki Steel Works, Ltd. Technical Research Institute (72) Chiaki Kato 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Technical Research Institute Co., Ltd. (56) Reference JP-A-4-173925 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 9/46 C23C 2/28

Claims (4)

(57) [Claims] 1. C: 0.0005 to 0.0050 mas
s%, Si: 0.1 to 2.5 mass%, Mn: 0.1 to 2.5 mass%, Ni: 0.05 to 2.0 mass%, B: 0.0010 to 0.0100 mass%, Cu: 0 1 to 2.5 mass%, Al: 0.005 to 0.10 mass%, P: 0.040 to 0.18 mass% and N: 0.0003 to 0.0060 mass% per content represented by mass% (% Si), (%
Mn), (% Ni) and (% Cu) represented by the following formulas (1), (2) and (3), and Ti: 0.003 to 0.10 mass% and Nb: The total of Ti and Nb is one or two selected from 0.003 to 0.10 mass%.
It is contained in the range of 0.03 mass% or more, and the balance is 9% on the surface of the steel sheet consisting of Fe and unavoidable impurities.
A high-strength galvannealed steel sheet having an alloying hot-dip galvanized layer of up to 12% and being excellent in plating characteristics and secondary work brittleness resistance. Note 1.5 (% Mn) -2 ≦ (% Si) ≦ 2 (% Mn)
――― (1) 2 (% Cu) ≧ (% Mn) ――
-(2) (% Cu) ≤ 3 (% Ni)-
-(3) 2. C: 0.0005 to 0.0050 mas
s%, Si: 0.1 to 2.5 mass%, Mn: 0.1 to 2.5 mass%, Ni: 0.05 to 2.0 mass%, B: 0.0010 to 0.0100 mass%, Cu: 0 1 to 2.5 mass%, Al: 0.005 to 0.10 mass%, P: 0.040 to 0.18 mass% and N: 0.0003 to 0.0060 mass% per content represented by mass% (% Si), (%
Mn), (% Ni) and (% Cu) represented by the following formulas (1), (2) and (3), and Ti: 0.003 to 0.10 mass% and Nb: One or two selected from 0.003 to 0.10 mass% and one or two selected from W: 0.01 to 1.0 mass% and Mo: 0.01 to 1.0 mass%. Is the sum of Ti and Nb
It is contained in the range of 0.03 mass% or more, and the balance is 9% on the surface of the steel sheet consisting of Fe and unavoidable impurities.
A high-strength galvannealed steel sheet having an alloying hot-dip galvanized layer of up to 12% and being excellent in plating characteristics and secondary work brittleness resistance. Note 1.5 (% Mn) -2 ≦ (% Si) ≦ 2 (% Mn)
――― (1) 2 (% Cu) ≧ (% Mn) ――
-(2) (% Cu) ≤ 3 (% Ni)-
-(3) 3. C: 0.0005 to 0.0050 mas
s%, Si: 0.1 to 2.5 mass%, Mn: 0.1 to 2.5 mass%, Ni: 0.05 to 2.0 mass%, B: 0.0010 to 0.0100 mass%, Cu: 0 1 to 2.5 mass%, Al: 0.005 to 0.10 mass%, P: 0.040 to 0.18 mass% and N: 0.0003 to 0.0060 mass% per content represented by mass% (% Si), (%
Mn), (% Ni) and (% Cu) represented by the following formulas (1), (2) and (3), and Ti: 0.003 to 0.10 mass% and Nb: The total of Ti and Nb is one or two selected from 0.003 to 0.10 mass%.
A steel slab containing 0.03 mass% or more and the balance being Fe and unavoidable impurities is used as a material, and this material is hot-rolled and finish-rolled at a temperature in the range of 1000 ° C or lower and 750 ° C or higher. Finished, 650 ℃ or below, 55
After winding at a temperature in the range of 0 ° C. or higher, pickling, and then cold rolling at a rolling reduction of 60 to 95%, followed by recrystallization in a temperature range of 700 to 950 ° C. in a continuous hot dip galvanizing facility. After performing annealing and then rapidly cooling to a temperature in the range of 530 ° C. or lower and 380 ° C. or higher, Al is 0.12 to 0.12.
45% contained in a hot dip galvanizing bath in the temperature range of 450 to 490 ° C. in a temperature range of not less than bath temperature and not more than + 10 ° C. to perform plating treatment, and then in the temperature range of 450 to 550 ° C. for 14 seconds. As described above, the method for producing a high-strength hot-dip galvanized steel sheet having excellent plating characteristics and secondary work brittleness resistance, which comprises heating for 28 seconds or less to perform alloying treatment. Note 1.5 (% Mn) -2 ≦ (% Si) ≦ 2 (% Mn)
――― (1) 2 (% Cu) ≧ (% Mn) ――
-(2) (% Cu) ≤ 3 (% Ni)-
-(3) 4. C: 0.0005-0.0050mas
s%, Si: 0.1 to 2.5 mass%, Mn: 0.1 to 2.5 mass%, Ni: 0.05 to 2.0 mass%, B: 0.0010 to 0.0100 mass%, Cu: 0 1 to 2.5 mass%, Al: 0.005 to 0.10 mass%, P: 0.040 to 0.18 mass% and N: 0.0003 to 0.0060 mass% per content represented by mass% (% Si), (%
Mn), (% Ni) and (% Cu) represented by the following formulas (1), (2) and (3), and Ti: 0.003 to 0.10 mass% and Nb: One or two selected from 0.003 to 0.10 mass% and one or two selected from W: 0.01 to 1.0 mass% and Mo: 0.01 to 1.0 mass%. Is the sum of Ti and Nb
A steel slab containing 0.03 mass% or more and the balance being Fe and unavoidable impurities is used as a material, and this material is hot-rolled and finish-rolled at a temperature in the range of 1000 ° C or lower and 750 ° C or higher. Finished, 650 ℃ or below, 55
After winding at a temperature in the range of 0 ° C. or higher, pickling, and then cold rolling at a rolling reduction of 60 to 95%, followed by recrystallization in a temperature range of 700 to 950 ° C. in a continuous hot dip galvanizing facility. After performing annealing and then rapidly cooling to a temperature in the range of 530 ° C. or lower and 380 ° C. or higher, Al is 0.12 to 0.12.
45% contained in a hot dip galvanizing bath in the temperature range of 450 to 490 ° C. in a temperature range of not less than bath temperature and not more than + 10 ° C. to perform plating treatment, and then in the temperature range of 450 to 550 ° C. for 14 seconds. As described above, the method for producing a high-strength hot-dip galvanized steel sheet having excellent plating characteristics and secondary work brittleness resistance, which comprises heating for 28 seconds or less to perform alloying treatment. Note 1.5 (% Mn) -2 ≦ (% Si) ≦ 2 (% Mn)
――― (1) 2 (% Cu) ≧ (% Mn) ――
-(2) (% Cu) ≤ 3 (% Ni)-
-(3)