JP5821260B2 - High-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property, and method for producing the same - Google Patents

Description

  The present invention relates to a high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property suitable for use as a steel sheet for automobiles, and a method for producing the same.

  In recent years, improving the fuel efficiency of automobiles has become an important issue from the viewpoint of conservation of the global environment. For this reason, efforts are being made to reduce the thickness by increasing the strength of the vehicle body material and to improve the fuel efficiency by reducing the weight of the vehicle body itself. Steel sheets that are formed into products by pressing or bending, such as automobile parts, are required to have formability that can withstand processing while maintaining high strength. In Patent Document 1, both high strength and high workability are realized by utilizing tempered martensite and retained austenite. However, generally, as the strength of the steel sheet increases, the spring back after processing increases, and there is a problem that the shape freezing property decreases. In Patent Document 1, the shape freezing property is not studied and there is room for improvement. On the other hand, Patent Document 2 uses a structure composed of ferrite, bainite, and austenite having a low C concentration to obtain a steel sheet having a low YR and excellent shape freezeability. However, stretch flangeability has not been evaluated, and it is difficult to say that it has sufficient workability. In Patent Document 3, high strength and high ductility are made compatible by utilizing tempered martensite, bainite, and retained austenite, but no mention is made regarding shape freezeability. Further, the stretch flangeability is not necessarily high in absolute value, and there is room for improvement.

JP 2009-209450 JP JP 2010-126808 A JP 2010-90475 A

  The present invention advantageously solves the above-mentioned problems of the prior art and is suitable as a material for automobile parts. Tensile strength (TS): 1180 MPa or more, total elongation (EL): 14% or more, hole expansion rate (λ ): 30% or more and yield ratio (YR): 70% or less It is an object to provide a high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property, and a method for producing the same. The yield ratio (YR) is the ratio of the yield strength (YS) to the tensile strength (TS) and is expressed as YR (%) = (YS / TS) × 100.

  In order to achieve the above-mentioned problems and to produce a high-strength hot-dip galvanized steel sheet that is excellent in formability and shape freezing property, the present inventors have conducted earnest research from the viewpoint of the component composition and microstructure of the steel sheet. I found out.

  After appropriately adjusting the alloy elements, the area ratio is 0-5% polygonal ferrite, 5% or more bainitic ferrite, 5-20% martensite, 30-60% tempered martensite, 5 When the structure contains -20% retained austenite and the average particle size of prior austenite is 15 μm or less, both high strength, high formability, and high shape freezing property can be achieved.

  The reason why the shape freezing property is improved by dispersing martensite in the tempered martensite main structure is not necessarily clear, but austenite in contact with the tempered martensite after cooling after plating or plating alloying is martensite. This may be because YR is reduced by introducing mobile dislocations in the tempered martensite after transformation. The reason why λ is improved by making the prior austenite grains fine is not clear, but the fine grain of the prior austenite grains decreases the average grain size of the microstructure after annealing, and crack propagation during stretch flange processing This is probably because the number of paths increases and the crack connection is suppressed.

During annealing, these microstructures were heated from 500 ° C. to Ac ₁ point at an average heating rate of 5 ° C./s or more to Ac ₃ point −20 to 1000 ° C. and held for 10 to 1000 seconds, and then from 750 ° C. to 15 ° C. After cooling to a temperature range of Ms point −80 ° C. to Ms point −30 ° C. at an average cooling rate of at least ° C./s, it is obtained by heating to 350 to 500 ° C. and holding for 10 to 600 seconds.

  The present invention has been made based on such findings, and provides the following inventions.

  (1) In mass%, C: 0.10 to 0.35%, Si: 0.5 to 3.0%, Mn: 1.5 to 4.0%, P: 0.100% or less, S: 0.02% or less, Al: 0.010 to 0.5%, the balance Has a composition composed of Fe and inevitable impurities, and the microstructure is 0-5% polygonal ferrite, 5% bainitic ferrite, 5-20% martensite, 30-30 High-strength hot-dip galvanizing with excellent formability and shape-freezing properties, comprising 60% tempered martensite and 5-20% retained austenite, and the average grain size of prior austenite is 15 μm or less steel sheet.

  (2) Further, at least one element selected from Cr: 0.005-2.00%, Mo: 0.005-2.00%, V: 0.005-2.00%, Ni: 0.005-2.00%, Cu: 0.005-2.00% in mass%. The high-strength hot-dip galvanized steel sheet having excellent formability and shape freezing property as described in (1).

  (3) The moldability according to (1) or (2), further comprising at least one element selected from Ti: 0.01 to 0.20% and Nb: 0.01 to 0.20% by mass%. High-strength hot-dip galvanized steel sheet with excellent shape freezing properties.

  (4) The high-strength hot-dip galvanizing excellent in formability and shape freezing property according to any one of (1) to (3), further comprising B: 0.0005 to 0.0050% by mass% steel sheet.

  (5) The composition according to any one of (1) to (4), further comprising at least one element selected from Ca: 0.001 to 0.005% and REM: 0.001 to 0.005% by mass%. High-strength hot-dip galvanized steel sheet with excellent formability and shape freezing properties.

  (6) The high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property according to any one of (1) to (5), wherein the galvanizing is alloyed galvanizing.

(7) When the slab having the component composition according to any one of (1) to (5) is hot-rolled or further cold-rolled, and then subjected to continuous annealing, 500 ° C. to Ac ₁ point. Ac ₃ point at an average heating rate of 5 ° C / s or more-After heating to a temperature range of 20 ° C to 1000 ° C and holding for 10 to 1000 seconds, Ms point at an average cooling rate of 750 ° C to 15 ° C / s or more- After cooling to a temperature range of 80 ° C to Ms point -30 ° C, after heating to 350 ° C to 500 ° C and holding for 10 to 600 seconds, hot dip galvanizing is performed, or further plating alloying treatment is performed. A method for producing a high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing.

  According to the present invention, the tensile strength (TS) is 1180 MPa or more, the total elongation (EL) is 14% or more, the hole expansion rate (λ) is 30% or more, and the yield ratio (YR) is 70% or less. In addition, a high-strength hot-dip galvanized steel sheet excellent in shape freezing property can be obtained.

  Details of the present invention will be described below. Note that “%” representing the content of component elements means “% by mass” unless otherwise specified.

1) Component composition
C: 0.10 to 0.35%
C is an element necessary for increasing TS by generating a low temperature transformation phase such as martensite and tempered martensite. If the amount of C is less than 0.10%, it is difficult to secure tempered martensite in an area ratio of 30% or more and martensite of 5% or more. On the other hand, when the C content exceeds 0.35%, EL and spot weldability deteriorate. Therefore, the C content is 0.10 to 0.35%, preferably 0.15 to 0.3%.

Si: 0.5-3.0%
Si is an element effective for improving the TS-EL balance by solid solution strengthening of steel and generating retained austenite. In order to obtain such effects, the Si amount needs to be 0.5% or more. On the other hand, if Si exceeds 3.0%, the EL is lowered and the surface properties and weldability are deteriorated. Therefore, the Si content is 0.5 to 3.0%, preferably 0.9 to 2.0%.

Mn: 1.5-4.0%
Mn is an element that is effective in strengthening steel and promotes the generation of low-temperature transformation phases such as martensite. In order to obtain such an effect, the Mn content needs to be 1.5% or more. On the other hand, if the amount of Mn exceeds 4.0%, the EL deteriorates significantly and the workability decreases. Therefore, the Mn content is 1.5 to 4.0%, preferably 2.0 to 3.5%.

P: 0.100% or less
P deteriorates steel by grain boundary segregation and deteriorates weldability. Therefore, it is desirable to reduce the amount of P as much as possible. However, the amount of P is 0.100% or less from the viewpoint of manufacturing cost.

S: 0.02% or less
Since S exists as inclusions such as MnS and degrades weldability, the amount is preferably reduced as much as possible. However, the amount of S is 0.02% or less from the viewpoint of manufacturing cost.

Al: 0.010 to 0.5%
Al acts as a deoxidizer and is preferably added in the deoxidation step. In order to obtain such an effect, the Al content needs to be 0.010% or more. On the other hand, if the Al content exceeds 0.5%, the risk of slab cracking during continuous casting increases. Therefore, the Al content is 0.010 to 0.5%.

  The balance is Fe and inevitable impurities, but one or more of the following elements can be appropriately contained as necessary.

Cr: 0.005-2.00%, Mo: 0.005-2.00%, V: 0.005-2.00%, Ni: 0.005-2.00%, Cu: 0.005-2.00%
Cr, Mo, V, Ni, and Cu are effective elements for generating a low-temperature transformation phase such as martensite. In order to obtain such an effect, the content of at least one element selected from Cr, Mo, V, Ni, and Cu needs to be 0.005%. On the other hand, if the content of each of Cr, Mo, V, Ni, and Cu exceeds 2.00%, the effect is saturated and the cost is increased. Therefore, the contents of Cr, Mo, V, Ni, and Cu are each 0.005 to 2.00%.

  Further, at least one selected from Ti: 0.01 to 0.20% and Nb: 0.01 to 0.20% can be contained.

  Ti and Nb are effective elements for forming carbonitrides and increasing the strength of steel by precipitation strengthening. In order to obtain such effects, the Ti and Nb contents must be 0.01% or more. On the other hand, when the content of Ti and Nb exceeds 0.20%, the effect of increasing the strength is saturated and the EL decreases. Therefore, the content of Ti and Nb is set to 0.01 to 0.20%.

  Further, B: 0.0005 to 0.0050% can be contained.

  B is an element effective in suppressing the formation of ferrite from the austenite grain boundary and generating a low-temperature transformation phase. In order to obtain such an effect, the B amount needs to be 0.0005% or more. On the other hand, when the amount of B exceeds 0.0050%, the effect is saturated and the cost is increased. Therefore, the B amount is 0.0005 to 0.0050%.

  Further, it may further contain at least one selected from Ca: 0.001 to 0.005% and REM: 0.001 to 0.005%.

  Ca and REM are both effective elements for improving workability by controlling the morphology of sulfides. In order to obtain such an effect, the content of at least one element selected from Ca and REM needs to be 0.001% or more. On the other hand, if the content of each of Ca and REM exceeds 0.005%, the cleanliness of the steel is adversely affected and desired characteristics may not be obtained. Therefore, the content of Ca and REM is set to 0.001 to 0.005%.

2) Microstructure Area ratio of polygonal ferrite: 0 to 5%
If the area ratio of polygonal ferrite exceeds 5%, it becomes difficult to achieve both TS1180MPa or more and hole expansion ratio of 30% or more. Therefore, the area ratio of polygonal ferrite is set to 0 to 5%.

Bainitic ferrite area ratio: 5% or more The bainite transformation is effective in securing retained austenite effective for increasing EL by concentrating C in austenite and stabilizing austenite. In order to obtain this effect, the area ratio of bainitic ferrite needs to be 5% or more. Therefore, the area ratio of bainitic ferrite is set to 5% or more.

Martensite area ratio: 5-20%
Martensite is effective in improving TS. It is also effective in reducing YR.
In order to obtain such an effect, the area ratio of martensite is required to be 5% or more. On the other hand, when it exceeds 20%, the decrease in EL and hole expansion rate becomes remarkable. Therefore, the area ratio of martensite is 5 to 20%.

Tempered martensite area ratio: 30-60%
If the area ratio of tempered martensite is less than 30%, it becomes difficult to achieve both TS1180MPa or more and hole expansion ratio of 30% or more. On the other hand, if the area ratio exceeds 60%, the increase in YR becomes remarkable and the shape freezing property decreases. Therefore, the area ratio of tempered martensite is 30 to 60%.

Residual austenite area ratio: 5-20%
Residual austenite is effective in improving EL. In order to obtain such an effect, the area ratio of retained austenite needs to be 5% or more. However, when the area ratio exceeds 20%, the hole expansion rate is significantly reduced. Therefore, the area ratio of retained austenite is 5 to 20%.

The average grain size of prior austenite is 15 μm or less Refinement of prior austenite grains is effective in improving λ. In order to obtain such an effect, it is necessary to make the average grain size of prior austenite 15 μm or less. Therefore, the average particle size of the prior austenite is set to 15 μm or less.

  In addition, pearlite may be included as a phase other than polygonal ferrite, bainitic ferrite, martensite, tempered martensite, and retained austenite, but the object of the present invention is achieved as long as the above microstructure conditions are satisfied. Is done.

  Here, the area ratio of polygonal ferrite, bainitic ferrite, martensite, and tempered martensite is the ratio of the area of each phase in the observed area. Polygonal ferrite, martensite, bainitic ferrite, The area ratio of tempered martensite was determined by the method shown below. After the plate thickness section of the steel plate was polished, it was corroded with 3% nital, and the 1/4 position of the plate thickness was photographed with SEM (scanning electron microscope) at a magnification of 1500 times, and this was image-produced by Media Cybernetics. The target tissue of each visual field was painted using Pro, the area ratio of the target tissue in the visual field was determined, and the average of the area ratios of each visual field was defined as the area ratio of the target tissue. As for the area ratio of retained austenite, the surface of the steel plate was polished to a thickness of 1/4 position and then further polished by 0.1 mm by chemical polishing. Measure the integrated strength of the (200), (220), (311) plane and the (200), (211), (220) plane of bcc iron, determine the percentage of retained austenite from this, and use this ratio as the area ratio of retained austenite It was. The average grain size of the prior austenite was corroded with 3% nital after polishing the thickness section of the steel sheet, and the 1/4 position of the thickness was observed with a scanning electron microscope (SEM) at a magnification of 1500 times. The total area of the structures surrounded by the prior austenite grain boundaries in the field of view was divided by the number to determine the average area, and the 1/2 power was taken as the average grain size.

3) Manufacturing conditions The high-strength hot-dip galvanized steel sheet of the present invention is hot-rolled, pickled, or further cold-rolled to a slab having the above component composition, and then subjected to continuous annealing at 500 ° C to Heat up to Ac ₁ point at an average heating rate of 5 ° C / s or higher and hold at Ac ₃ point –20 ° C to 1000 ° C for 10 to 1000 seconds, then average cooling from 750 ° C to 15 ° C / s or higher After cooling to a temperature range of Ms point -80 ° C to Ms point -30 ° C at a speed, heat to 350 ° C to 500 ° C and hold for 10 to 600 seconds, then apply hot dip galvanizing or further alloying treatment To make. This will be described in detail below.

  Steel having the above composition is melted to form a slab, the slab is hot-rolled, and then cooled and wound. When the coiling temperature after hot rolling exceeds 650 ° C., black spots are generated and the plating property is lowered. On the other hand, when the coiling temperature after hot rolling is less than 400 ° C., the shape of the hot rolled sheet deteriorates. Therefore, the coiling temperature after hot rolling is preferably 400 to 650 ° C.

  Next, the hot-rolled sheet is preferably pickled to remove the scale of the hot-rolled sheet surface layer. The pickling step is not particularly limited, and may be a conventional method. If necessary, the hot-rolled sheet after pickling is cold-rolled. A cold rolling process is not specifically limited, A conventional method may be sufficient. The hot-rolled sheet after pickling or the cold-rolled sheet after cold rolling is continuously annealed under the following conditions.

Average heating rate from 500 ℃ to Ac ₁ point: 5 ℃ / s or more
If the average heating rate from 500 ° C. to Ac ₁ point is less than 5 ° C./s, the austenite is coarsened by recrystallization, and the microstructure of the present invention cannot be obtained. Therefore, the average heating rate from 500 ° C. to Ac ₁ point is set to 5 ° C./s or more.

Heating in the temperature range of Ac ₃ point -20 ° C to 1000 ° C and keeping soaking for 10 to 1000 seconds If the soaking temperature is less than Ac ₃ point -20 ° C, austenite formation is insufficient and the microstructure of the present invention is obtained. I can't. On the other hand, when the soaking temperature exceeds 1000 ° C., austenite becomes coarse, and the constituent phase after annealing becomes coarse to reduce toughness and the like. Therefore, the soaking temperature is set to Ac ₃ point −20 ° C. to 1000 ° C. If the soaking time is less than 10 seconds, austenite is not sufficiently generated, and the microstructure of the present invention cannot be obtained. In addition, if the soaking time exceeds 1000 seconds, the cost increases. Therefore, the soaking time is 10 to 1000 seconds.

Cooling from 750 ° C to an average cooling rate of 15 ° C / s or higher to a temperature range of Ms point –80 ° C to Ms point –30 ° C
If the average cooling rate from 750 ° C. to the temperature range from Ms point −80 ° C. to Ms point −30 ° C. is less than 15 ° C./s, a large amount of ferrite is generated during cooling, and the microstructure of the present invention cannot be obtained. Accordingly, the average cooling rate is set to 15 ° C./s or more.

Cooling stop temperature: Ms point –80 ° C to Ms point –30 ° C
When cooled to the cooling temperature, a part of austenite is transformed into martensite, and during subsequent reheating or plating alloying process, martensite becomes tempered martensite and untransformed austenite becomes residual austenite or martensite or bainite. Become. At this time, when the temperature reached by cooling exceeds the Ms point −30 ° C., the amount of tempered martensite becomes insufficient. When the Ms point is less than −80 ° C., untransformed austenite is remarkably reduced, and tempered martensite is increased. A microstructure cannot be obtained. Accordingly, the cooling arrival temperature is set to Ms point −80 ° C. to Ms point −30 ° C.

Reheating temperature: 350-500 ° C
After cooling to the temperature at which cooling is achieved, when reheated to a temperature range of 350 to 500 ° C., the martensite generated during cooling is tempered to become tempered martensite, and C enrichment proceeds to untransformed austenite, resulting in residual austenite. As stabilized. In addition, bainite transformation proceeds, C diffuses from bainitic ferrite and further stabilizes untransformed austenite. If the reheating temperature is less than 350 ° C., the bainite transformation that progresses becomes bainite containing carbide, so that C does not concentrate much in the untransformed austenite, and the stability as retained austenite becomes insufficient. On the other hand, if it exceeds 500 ° C., untransformed austenite tends to form carbides or pearlite, and the microstructure of the present invention cannot be obtained. Therefore, the reheating temperature is set to 350 to 500 ° C. Preferably it is 380-480 degreeC.

Holding time at reheating temperature: 10 to 600 seconds If the holding time is less than 10 seconds, the formation of bainite becomes insufficient, and if it exceeds 600 seconds, untransformed austenite tends to generate carbide or pearlite, The microstructure of the present invention cannot be obtained. Therefore, the holding time is 10 to 600 seconds.

  The hot dip galvanizing treatment is preferably performed by immersing the steel plate obtained as described above in a galvanizing bath at 440 ° C. or higher and 500 ° C. or lower, and then adjusting the plating adhesion amount by gas wiping or the like. Further, when alloying the galvanizing, it is preferable to keep the alloy in the temperature range of 460 ° C. to 550 ° C. for 1 second to 40 seconds. For galvanization, it is preferable to use a galvanizing bath having an Al content of 0.08 to 0.18%.

  The steel sheet after the hot dip galvanizing alloying treatment can be subjected to temper rolling for the purpose of shape correction, adjustment of surface roughness, and the like. Moreover, various coating processes, such as resin and oil-fat coating, can also be given.

  The conditions for other production methods are not particularly limited, but the following conditions are preferable.

  The slab is preferably produced by a continuous casting method in order to prevent macro segregation, but can also be produced by an ingot-making method or a thin slab casting method. To hot-roll the slab, the slab may be cooled to room temperature and then re-heated for hot rolling, or the slab may be charged in a heating furnace without being cooled to room temperature. Can also be done. Alternatively, an energy saving process in which hot rolling is performed immediately after performing a slight heat retention can also be applied. When heating the slab, it is preferable to heat to 1100 ° C. or higher in order to dissolve carbides and prevent an increase in rolling load. In order to prevent an increase in scale loss, the heating temperature of the slab is preferably 1300 ° C. or lower.

When hot rolling a slab, the rough bar after rough rolling can be heated from the viewpoint of preventing troubles during rolling even if the heating temperature of the slab is lowered. Moreover, what is called a continuous rolling process which joins rough bars and performs finish rolling continuously can be applied. Since finish rolling may increase anisotropy and reduce workability after cold rolling / annealing, it is preferably performed at a finishing temperature equal to or higher than the Ar ₃ transformation point. Further, in order to reduce the rolling load and make the shape and material uniform, it is preferable to perform lubrication rolling with a friction coefficient of 0.10 to 0.25 in all passes or a part of the finish rolling.

  The steel sheet after winding is removed by pickling or the like, and then the hot-rolled sheet is annealed under the above-mentioned conditions, or the hot-rolled sheet is cold-rolled and then annealed under the above-mentioned conditions. Applied. When performing cold rolling, it is preferable that the cold rolling reduction be 40% or more. Moreover, in order to reduce the rolling load at the time of cold rolling, the steel plate after winding can also be hot-rolled sheet annealed.

Steel having the component composition shown in Table 1 was melted by a converter and made into a steel slab by continuous casting (in Table 1, N is an unavoidable impurity). These steel slabs were heated to 1200 ° C., followed by rough rolling and finish rolling, and the steel slab was wound at a winding temperature of 400 to 650 ° C. to obtain a hot-rolled sheet having a thickness of 2.3 mm. Next, softening was performed by partial batch processing under the conditions of an ultimate temperature of 600 ° C. and a heat treatment time of 5 hours, pickling, and cold rolling to a thickness of 1.4 mm to produce a cold-rolled steel plate, which was subjected to annealing. A part of the steel sheet hot-rolled to a thickness of 2.3 mm and pickled was subjected to annealing as it was. Annealing is performed by a continuous hot dip galvanizing line under the conditions shown in Tables 2 and 3 and immersed in a plating bath at 460 ° C. to form a plating with an adhesion amount of 35 to 45 g / m ² at a cooling rate of 10 ° C./s. It cooled and produced the hot-dip galvanized steel plates 1-29. Further, after partially plating, a plating alloying treatment was further performed at 525 ° C., and cooling was performed at a cooling rate of 10 ° C./s to prepare an alloyed hot-dip galvanized steel sheet. And about the obtained plated steel plate, the area ratio of polygonal ferrite, bainitic ferrite, martensite, tempered martensite, the area ratio of retained austenite, and the average particle diameter of prior austenite were measured by the above-described methods. In addition, a JIS No. 5 tensile test piece was taken in a direction perpendicular to the rolling direction, and a tensile test was performed at a strain rate of 10 ⁻³ . In addition, a 150mm x 150mm test piece was taken and the hole expansion test was performed three times in accordance with JFST 1001 (Japan Iron and Steel Federation Standard, 2008) to obtain the average hole expansion rate (%), and stretch flangeability was determined. evaluated. The results are shown in Tables 4 and 5.

  In the present invention, YR was 70% or less, and it was confirmed to have high shape freezing property. In addition, TS was 1180 MPa or more, EL was 14% or more, and λ was 30% or more, and it was confirmed that it had high strength and moldability. Therefore, according to the example of the present invention, a hot-dip galvanized steel sheet having excellent shape freezing property is obtained, which contributes to reducing the weight of the automobile and greatly improving the performance of the automobile body.

  According to the present invention, the tensile strength (TS) is 1180 MPa or more, the total elongation (EL) is 14% or more, the hole expansion rate (λ) is 30% or more, and the yield ratio (YR) is 70% or less. In addition, a high-strength hot-dip galvanized steel sheet excellent in shape freezing property can be obtained. When the high-strength hot-dip galvanized steel sheet of the present invention is used for automotive parts, it contributes to reducing the weight of an automobile and greatly contributes to improving the performance of an automobile body.

Claims (7)

In mass%, C: 0.11 to 0.35%, Si: 0.5 to 3.0%, Mn: 1.5 to 4.0%, P: 0.100% or less, S: 0.02% or less, Al: 0.010 to 0.5%, the balance being Fe and It has a component composition consisting of inevitable impurities, and the microstructure is 0 to 5% polygonal ferrite, 5% or more bainitic ferrite, 5 to 20% martensite, and 30 to 60% by area ratio. Tempered martensite, containing 5-20% retained austenite, the average grain size of prior austenite is 15 μm or less , and tensile strength (TS): 1180 MPa or more High strength hot-dip galvanized steel sheet. Furthermore, it contains at least one element selected from Cr: 0.005-2.00%, Mo: 0.005-2.00%, V: 0.005-2.00%, Ni: 0.005-2.00%, Cu: 0.005-2.00% by mass%. The high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property according to claim 1. Furthermore, it contains at least one element selected from Ti: 0.01-0.20% and Nb: 0.01-0.20% by mass%, and has excellent formability and shape freezing property according to claim 1 or 2. High strength hot dip galvanized steel sheet. The high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property according to any one of claims 1 to 3, further comprising B: 0.0005 to 0.0050% by mass%. Furthermore, it contains at least one element selected from Ca: 0.001 to 0.005% and REM: 0.001 to 0.005% by mass%, and the formability and shape freezing according to any one of claims 1 to 4 High strength hot-dip galvanized steel sheet with excellent properties. The high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing property according to any one of claims 1 to 5, wherein the galvanizing is alloyed galvanizing. A process for producing a high-strength galvanized steel sheet according to any one of claims 1 to 5, when a slab, hot-rolled or further cold rolling, subjected to subsequent continuous annealing, 500 ° C. to Ac ₁ After heating up to the point at an average heating rate of 5 ° C / s or higher and holding the Ac ₃ point in the temperature range of -20 ° C to 1000 ° C for 10 to 1000 seconds, the average cooling rate from 750 ° C to 15 ° C / s or higher After cooling to a temperature range from Ms point -80 ° C to Ms point -30 ° C, heating to 350 ° C to 500 ° C and holding for 10 to 600 seconds, then hot dip galvanizing or further plating alloying treatment A method for producing a high-strength hot-dip galvanized steel sheet excellent in formability and shape freezing characteristics.