JP5213307B2 - Method for producing high ductility and high strength alloyed hot-dip galvanized steel sheet with excellent surface properties - Google Patents

Description

The present invention relates to a method of manufacturing a high-ductility and high strength galvannealed steel sheet excellent in surface properties for use in applications as automotive steel sheets.

  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, a movement to reduce the thickness of the vehicle body by increasing the strength of the vehicle body material and to reduce the weight of the vehicle body has become active. However, increasing the strength of a steel sheet causes a decrease in ductility, that is, a decrease in forming processability, and therefore development of a material having both high strength and high processability is desired.

  In response to such demands, various composite structure steels such as ferrite, martensite duplex steel (Dual-Phase steel) and TRIP steel utilizing transformation-induced plasticity of retained austenite have been developed so far.

  These steel plates may be plated on the surface for the purpose of improving rust prevention during actual use, but as a plated steel plate, heat treatment is performed after hot dip galvanization from the viewpoint of ensuring pressability, spot weldability, and paint adhesion. An alloyed hot-dip galvanized steel sheet in which Fe of the steel sheet is diffused in the plated layer is widely used, and various proposals have been made in connection therewith.

  For example, Patent Document 1 proposes an alloyed hot-dip galvanized steel sheet having excellent workability that ensures residual ductility by adding a large amount of Si and achieves high ductility. However, since Si deteriorates the plateability, in order to plate such high Si steel, pre-plating of Ni or application of a special agent is performed, or the oxide layer on the steel sheet surface is reduced, and the oxide film A complicated process such as appropriately controlling the thickness is required.

  Further, Patent Document 2 proposes an alloyed hot-dip galvanized steel sheet having excellent ductility and improved plating wettability and powdering properties by adding Al, which has a small adverse effect on plating properties, instead of Si. Yes. However, in high Al steel, N and Al in the steel become AlN during continuous casting and precipitate in large amounts at the austenite grain boundaries, and the grain boundaries become brittle. In normal continuous casting, since bending correction from the vertical direction to the horizontal direction is performed, if the grain boundary becomes brittle, a slab crack is likely to occur in the correction portion. If a cracked slab is rolled as it is, the crack remains in the final product and the surface properties are significantly deteriorated. Therefore, it is necessary to take care of removing the crack of the slab with a grinder or the like, resulting in a significant cost increase.

  Patent Document 3 proposes a method for avoiding slab cracking by adding Ti and fixing N as TiN in order to avoid such slab cracking. However, in practice, precipitation of AlN starts at a temperature higher than the temperature at which N is completely fixed as TiN, and it is difficult to completely avoid slab cracking.

For further Al is to increase the are A ₃ transformation point a powerful ferrite stabilizing element, by its transformation point rises, the temperature drop is likely to occur slab corner until exiting the furnace during hot rolling performed a width reduction of the slab It becomes easy to generate ferrite in the part. As a result, local strain concentration occurs at the corner portion when the width is reduced, and surface defects such as baldness are likely to occur.
Japanese Patent Application Laid-Open No. 11-296991 JP 2002-030403 A Japanese Patent No. 3596316

The present invention has been made in view of such circumstances, and can obtain good alloyed hot dip galvanizing properties without going through complicated steps, and suppresses slab cracking during continuous casting and surface defects during hot rolling. An object of the present invention is to provide a method for producing a high ductility, high-strength galvannealed steel sheet having excellent surface properties of the final product after plating.

  In order to obtain a high ductility, high-strength galvanized steel sheet having excellent surface properties, the present inventors have conducted intensive research from the viewpoints of the composition and microstructure of the steel sheet. As a result, in order to achieve high ductility and high strength, residual austenite is utilized, and N: less than 0.005% and N ≦ 0.007% − (0.003 × Al)% by mass%. It was found that slab cracking during continuous casting can be suppressed. That is, when the amount of N is less than 0.005% by mass, the amount of precipitated AlN is reduced and effectively works to suppress slab cracking. It has been found that it is not sufficient to suppress the content to less than 0.005% by mass, and it is necessary to satisfy N ≦ 0.007% − (0.003 × Al)%, which is a relational expression between N and Al. . Although the details of the reason are not necessarily clear, it is considered that when the amount of Al is increased, precipitation of AlN occurs from a high temperature, and the precipitate is likely to be coarsened, and the adverse effect of AlN on slab cracking is increased.

Further, by controlling the ^{Al ≦ (1.25 × C 0.5 -0.57Si} + 0.625Mn)%, it found that the occurrence of scab at the time of hot rolling is suppressed. This is a balance between an increase in the Ar ₃ transformation point due to the addition of Al and Si and a decrease in the transformation point due to the addition of C and Mn. By setting the component within the above range, ferrite is generated at the slab corner before the width reduction. Is considered to be suppressed.

  Furthermore, it discovered that ductility improved further by controlling so that the metal structure of a steel plate may contain a retained austenite in a fixed range.

This invention is completed based on the said knowledge, and provides the following (1)-( 7 ).

(1) By mass%, C: 0.05 to 0.25%, Si: 0.30% to 0.5%, Mn: 1 to 3%, P: 0.1% or less, S: 0.00. 01% or less, Al: 0.1 to 2%, N: less than 0.005%, and Si + Al ≧ 0.6%, N ≦ 0.007% − (0.003 × Al)%, Al ≦ ( meets ^{1.25 × C 0.5 -0.57Si + 0.625Mn)} %, Cr: 1% or less, V: further contain one or two elements selected from 1% or less, and the balance Fe and unavoidable Steel made of mechanical impurities is melted, cast, hot rolled, and cold rolled, and then annealed in a temperature range of 730 to 900 ° C., and the annealing temperature is 20 ° C./s to 50 ° C./s or less. After cooling to a temperature range of 350 to 600 ° C. at a cooling rate, holding in that temperature range for 30 to 250 seconds, and then galvanizing, 470 to 6 Alloying is performed at 00 ° C., and an alloyed hot-dip galvanized steel sheet having a metal structure having the above component composition and containing a retained austenite phase of 3 to 20% by volume is produced. Manufacturing method of hot dip galvanized steel sheet.

(2) By mass%, C: 0.05 to 0.25%, Si: 0.30% to 0.5%, Mn: 1 to 3%, P: 0.1% or less, S: 0.00. 01% or less, Al: 0.1 to 2%, N: less than 0.005%, and Si + Al ≧ 0.6%, N ≦ 0.007% − (0.003 × Al)%, Al ≦ ( 1.25 × C ^0.5 -0.57Si + 0.625Mn)%, Nb: further containing 0.1% or less, the balance Fe and unavoidable impurities are melted, cast, hot After performing rolling and cold rolling, annealing is performed at a temperature range of 730 to 900 ° C., and cooling is performed from the annealing temperature to a temperature range of 350 to 600 ° C. at a cooling rate of more than 20 ° C./s and 50 ° C./s or less. Hold for 30 to 250 seconds in the temperature range, then galvanize, alloy at 470 to 600 ° C., and have the above component composition And method for producing a galvannealed steel sheet characterized by producing a galvannealed steel sheet having a metal structure containing 3-20% of residual austenite phase by volume.

(3) By mass%, C: 0.05 to 0.25%, Si: 0.30% to 0.5%, Mn: 1 to 3%, P: 0.1% or less, S: 0.00. 01% or less, Al: 0.1 to 2%, N: less than 0.005%, and Si + Al ≧ 0.6%, N ≦ 0.007% − (0.003 × Al)%, Al ≦ ( 1.25 × C ^0.5 −0.57 Si + 0.625 Mn)%, B: further containing one or two elements selected from 0.005% or less, Ni: 1% or less, the balance Fe and Steel made of inevitable impurities is melted, cast, hot rolled, and cold rolled, then annealed in the temperature range of 730 to 900 ° C., and from the annealing temperature to 20 ° C./s over 50 ° C./s. After cooling to a temperature range of 350 to 600 ° C. at that cooling rate, holding in that temperature range for 30 to 250 seconds, and then galvanizing, 4 Alloying is performed at 0 to 600 ° C., and an alloyed hot-dip galvanized steel sheet having the above component composition and having a metal structure containing a residual austenite phase of 3 to 20% by volume is produced. A method for producing a galvannealed steel sheet.

( 4 ) By mass%, C: 0.05 to 0.25%, Si: 0.30% or more and 0.5% or less, Mn: 1 to 3%, P: 0.1% or less, S: 0.00. 01% or less, Al: 0.1 to 2%, N: less than 0.005%, and Si + Al ≧ 0.6%, N ≦ 0.007% − (0.003 × Al)%, Al ≦ ( 1.25 × C ^0.5 −0.57 Si + 0.625 Mn)%, steel further containing a total of 0.01% or less of one or two of Ca and REM, the balance being Fe and inevitable impurities After melting, casting, hot rolling, and cold rolling, annealing is performed in a temperature range of 730 to 900 ° C., and 350 to 350 ° C. at a cooling rate of 20 ° C./s or more and 50 ° C./s or less from the annealing temperature. After cooling to a temperature range of 600 ° C., holding in that temperature range for 30 to 250 seconds, and then galvanizing, 470 to 600 Alloyed hot dip galvanized steel, characterized by producing an alloyed hot dip galvanized steel sheet having a metal structure containing the above component composition and containing 3-20% residual austenite phase by volume Manufacturing method of plated steel sheet.

(5) The method for producing an galvannealed steel sheet according to (1), wherein the steel further contains, by mass%, Nb: 0.1% or less.
(6) In the above (1), (2) or (5), the steel further contains one or two elements selected from B: 0.005% or less and Ni: 1% or less in mass%. A method for producing an alloyed hot-dip galvanized steel sheet, comprising:

(7) In any one of the above (1), (2), (3), (5) or (6), the steel is in% by mass, and one or two of Ca and REM are combined in a total of 0.00. The manufacturing method of the galvannealed steel plate characterized by further containing 01% or less.

  According to the present invention, it is possible to obtain good alloying hot dip galvanizing properties without going through complicated steps, and by suppressing surface defects during slab cracking and hot rolling during continuous casting, A highly ductile and high-strength galvannealed steel sheet having excellent surface properties of the final product can be obtained.

Hereinafter, the present invention will be specifically described.
First, the reasons for limiting the composition of the galvannealed steel sheet of the present invention will be described. In the following,% means mass%.

C: 0.05-0.25%
C is an element that stabilizes austenite, and is an element necessary for securing the amount of martensite and for retaining residual austenite at room temperature. If the amount of C is less than 0.05%, it is difficult to secure the strength of the steel sheet and at the same time secure the amount of retained austenite and achieve high ductility. On the other hand, if the amount of C exceeds 0.25%, the welded part and the heat-affected zone are markedly cured, and the weldability deteriorates. For this reason, C amount is made into the range of 0.05 to 0.25%.

Si: 0.5% or less Si is an element effective for strengthening steel. Further, it is a ferrite-forming element and promotes the formation of retained austenite because it promotes the concentration of C in austenite and suppresses the formation of carbides. However, if the amount of Si exceeds 0.5%, the plating property is deteriorated, and plating becomes difficult in a normal hot dip galvanizing process. Therefore, the Si content is 0.5% or less. Preferably it is 0.03% or less. When Si is 0.03% or less, the occurrence of red scale in hot rolling is suppressed, the final plating appearance is improved, and application to an automobile outer plate material is also possible.

Mn: 1-3%
Mn is an element effective for strengthening steel. Further, it is an element that stabilizes austenite, and is an element that is necessary for increasing retained austenite. However, when the amount of Mn is less than 1%, it is difficult to obtain such an effect. On the other hand, when the amount exceeds 3%, the increase in strength becomes significant due to an excessive increase in the second phase fraction and the increase in the amount of solid solution strengthening, and the ductility Incurs a decline. Therefore, the Mn content is in the range of 1 to 3%.

P: 0.1% or less P is an element effective for strengthening steel, but if it exceeds 0.1%, it causes embrittlement due to segregation at the grain boundaries and deteriorates impact characteristics. Therefore, the P content is 0.1% or less.

S: 0.01% or less S is an inclusion such as MnS, which causes deterioration in impact resistance and cracks along the metal flow of the weld. 0.01% or less.

Al: 0.1 to 2%
Si + Al ≧ 0.6%
Al, like Si, is a ferrite-forming element and promotes the formation of retained austenite because it promotes the concentration of C in austenite and suppresses the formation of carbides. Such effects are insufficient if the total amount of Al and Si added is less than 0.6%, and sufficient ductility cannot be obtained. If Al is less than 0.1%, the Si + Al content is less than 0.6% even if Si is added up to the upper limit. On the other hand, if the Al content exceeds 2%, the inclusions in the steel sheet increase and the ductility deteriorates. Therefore, the Al content is in the range of 0.1 to 2%, and Si + Al ≧ 0.6%.

Al ≦ (1.25 × C ^0.5 −0.57 Si + 0.625 Mn)%
When the Al content exceeds (1.25 × C ^0.5 −0.57 Si + 0.625 Mn)%, the occurrence of shave during hot rolling is likely to occur. Therefore, the Al content is Al ≦ (1.25 × C ^0.5 −0.57 Si + 0.625 Mn)%.

N: Less than 0.005% N ≦ 0.007% − (0.003 × Al)%
N is an important element in the present invention, and slab cracking during continuous casting is likely to occur due to an increase in the precipitation amount of AlN accompanying an increase in the N content. In order to avoid such slab cracking, the N amount is limited to less than 0.005%, and further, N ≦ 0.007% − (0.003 × Al)%, which is a relational expression between N and Al. To be satisfied. Preferably, 0.006 × Al ≦ N ≦ 0.0058− (0.0026 × Al).

Cr, V: 1% or less respectively Cr, V has an action of suppressing the formation of pearlite during cooling from the annealing temperature, and can be added as necessary. However, if each exceeds 1%, there is a concern about a decrease in ductility and a deterioration in plating properties due to an excessive increase in strength. Therefore, when Cr and V are added, these amounts are each 1% or less.

Nb: 0.1% or less
N b can be optionally added because they are effective in precipitation strengthening of steel. However, if it exceeds 0.1%, the workability and the shape freezing property decrease. Therefore , when Nb is added, the amount is reduced to 0 . 1% or less.

B: 0.005% or less Since B works effectively for strengthening steel, it can be added as necessary. However, if it exceeds 0.005%, the strength increases excessively and the workability decreases. Therefore, when adding B, the amount is made 0.005% or less.

Ni: 1% or less Ni is an austenite stabilizing element, and austenite remains and is effective in increasing the strength, so it can be added as necessary. However, if it exceeds 1%, the ductility of the steel sheet is lowered. Therefore, when adding Ni, the amount is made 1% or less.

Ca or REM: 0.01% or less in total of 1 type or 2 types Ca and REM have the effect of controlling the form of sulfide-type inclusions, thereby improving the stretch flangeability of the steel sheet. It can be added as necessary. Such an effect is saturated when the total of these effects exceeds 0.01%. Therefore, when adding Ca and REM, these 1 type or 2 types shall be 0.01% or less in total.

  In addition to the above elements and the remaining Fe, various impurity elements and trace addition elements essential in the manufacturing process are inevitably mixed in the manufacturing process. Such inevitable impurities are particularly effective for the effects of the present invention. It does not affect and is allowed.

Next, the metal structure of the steel plate will be described.
Residual austenite phase: 3 to 20% by volume
In the present invention, the retained austenite phase is essential for obtaining high ductility by effectively utilizing strain-induced transformation, and the control of the volume ratio is extremely important. In the present invention, from the viewpoint of ensuring high ductility, the retained austenite phase is preferably at least 3% or more. On the other hand, when the retained austenite phase exceeds 20%, a large amount of martensite is formed after molding, the brittleness becomes large, and it is difficult to suppress the brittleness within an allowable range. Therefore, the retained austenite phase should be 20% or less. Is preferred. The metal structure of the steel sheet of the present invention comprises a second phase including a ferrite phase as a main phase and a retained austenite phase. The volume fraction of the ferrite phase is preferably 40 to 90% from the viewpoint of ensuring high ductility. Moreover, as a 2nd phase other than a retained austenite phase, it is preferable that the volume ratio of a bainite phase, a martensite phase, and a pearlite phase is 7 to 50% in total.

Next, the manufacturing conditions of the galvannealed steel sheet according to the present invention will be described.
In the present invention, steel having the above-described composition is melted, made into a slab by continuous casting, hot-rolled, and cold-rolled, but these conditions are not particularly limited. Then, after annealing at a temperature range of 730 to 900 ° C. in a continuous hot dipping line, cooling at 3 to 100 ° C./s, holding at a temperature range of 350 to 600 ° C. for 30 to 250 seconds, and then galvanizing, Alloying is performed at 470 to 600 ° C.

Annealing temperature: 730-900 ° C
In the present invention, annealing is performed in an austenite single phase or a two-phase region of an austenite phase and a ferrite phase. When the annealing temperature is less than 730 ° C., the carbide in the steel sheet is not sufficiently dissolved, and the ferrite Since the crystal is incomplete, the target characteristics may not be obtained. On the other hand, when the annealing temperature exceeds 900 ° C., the growth of austenite grains is remarkable, which may cause a decrease in ferrite nucleation sites from the second phase caused by subsequent cooling. Therefore, annealing temperature shall be 730-900 degreeC.

Cooling rate: 3-100 ° C / s
When the cooling rate is less than 3 ° C./s, a large amount of pearlite is precipitated, and the amount of solid solution C in the untransformed austenite is significantly reduced, so that the target structure may not be obtained. Further, when the cooling rate exceeds 100 ° C./s, the growth of ferrite is suppressed and the volume fraction of ferrite is remarkably reduced, so that sufficient ductility may not be ensured. Therefore, the cooling rate shall be the 3 to 100 ° C. / s. Good Mashiku is, 1 0 ° C. / s or higher, still more preferably greater than 20 ° C. / s.

Holding temperature: 350-600 ° C
When the holding temperature exceeds 600 ° C., carbide precipitates from untransformed austenite, and conversely, when it is less than 350 ° C., carbide precipitates in bainitic ferrite due to lower bainite transformation, Stable retained austenite cannot be obtained sufficiently. Accordingly, the holding temperature is set to 350 to 600 ° C. In order to stably generate retained austenite, 500 ° C. or lower is preferable.

Holding time: 30 to 250 seconds The holding time plays a very important role in controlling the retained austenite. That is, when the holding time is less than 30 seconds, the stabilization of untransformed austenite does not proceed and the amount of retained austenite cannot be ensured, so that desired characteristics cannot be obtained. On the other hand, when the holding time exceeds 250 seconds, in the CGL line where the austempering process cannot be performed for a long time, it is necessary to extremely reduce the sheet passing speed, and the productivity is lowered. Accordingly, the holding time is set to 30 to 250 seconds. From the viewpoint of mass productivity, 200 seconds or less is preferable.

Alloying temperature: 470-600 ° C
After the holding treatment, the alloying treatment temperature after further hot dip galvanizing needs to be equal to or higher than the plating bath temperature, and therefore 470 ° C. is the lower limit. Further, when the alloying temperature exceeds 600 ° C., as in the case where the holding temperature exceeds 600 ° C., carbides are precipitated from untransformed austenite, and stable retained austenite cannot be obtained. Therefore, the alloying treatment temperature is set to 470 to 600 ° C.

In addition, if the annealing temperature, holding temperature, and alloying treatment temperature prescribed | regulated in the manufacturing conditions of this invention are in said range, holding temperature does not need to be constant. Moreover, about plating conditions, what is necessary is just to be in a normal operation range, What is necessary is just to set the weight per unit area to 20-70 g / m < ² > and the amount of Fe in a plating layer to about 6-15%.

Examples of the present invention will be described below.
Steel having the composition shown in Table 1 was melted in a converter and cast into a slab by continuous casting. The presence or absence of cracking of the slab at that time is also shown in Table 1. The occurrence of cracking was determined by color check in addition to visual determination after cooling the slab to room temperature.

  The obtained slab was heated to 1250 ° C. and then hot-rolled at a finish rolling temperature of 900 ° C. to obtain a hot-rolled steel plate having a thickness of 3.0 mm. Generation | occurrence | production of the shaving in the hot-rolled steel plate manufactured in this way was determined visually. Table 1 also shows the presence or absence of baldness.

After hot rolling, pickling and cold rolling were performed to obtain a cold-rolled steel sheet having a thickness of 1.2 mm. Thereafter, after heat treatment under the conditions shown in Table 2 in a continuous hot dip galvanizing line, 50/50 g / m ² plating was performed, and an alloying treatment was performed so that the amount of Fe in the plating layer was 9%.

  The obtained steel sheet was subjected to temper rolling of 0.5%, and the mechanical properties were investigated. As mechanical properties, tensile strength TS and elongation EL were measured using a JIS No. 5 tensile test specimen taken from the steel sheet in the direction perpendicular to the rolling direction. These measured values and TS × EL values are shown together in Table 2.

As shown in Table 2, No. 1 is a steel of the present invention that satisfies the composition and production conditions of the present invention. In Nos. 11 , 12, 17 , 18 , and 22 , neither slab cracking nor hot-rolled plate dents occurred, and the strength and elongation were sufficient. On the other hand, N amount, N ≦ 0.007% − (0.003 × Al)%, Al ≦ (1.25 × C ^0.5 −0.57Si + 0.625Mn)% or the production conditions of the present invention are satisfied No., which is a comparative steel plate that is not In Nos. 2 to 4, 9, 10, 13, 14, 21, 23 to 34, at least one of slab cracking and hot-rolled sheet shaving occurred. Further, No. with a large amount of Mn As shown in Table 2, No. 33 had a significant increase in strength and insufficient elongation. Furthermore, no. 34, as shown in Table 2, the elongation was low for the strength, and the value of TS × EL was low.

Claims (7)

  In mass%, C: 0.05 to 0.25%, Si: 0.30% to 0.5%, Mn: 1 to 3%, P: 0.1% or less, S: 0.01% or less , Al: 0.1 to 2%, N: less than 0.005%, and Si + Al ≧ 0.6%, N ≦ 0.007% − (0.003 × Al)%, Al ≦ (1.25 × C ^0.5 -0.57Si + 0.625Mn)%, further containing one or two elements selected from Cr: 1% or less, V: 1% or less, and the remainder comprising Fe and inevitable impurities. Then, after casting, hot rolling, and cold rolling, annealing is performed in a temperature range of 730 to 900 ° C., and a temperature of 350 to 600 ° C. at a cooling rate of 20 ° C./s to 50 ° C./s or less from the annealing temperature. After cooling to the temperature range, holding at that temperature range for 30 to 250 seconds, and then galvanizing, alloying is performed at 470 to 600 ° C., the above composition is included, and the retained austenite having a volume ratio of 3 to 20% A method for producing an alloyed hot-dip galvanized steel sheet having a metal structure containing a phase.   In mass%, C: 0.05 to 0.25%, Si: 0.30% to 0.5%, Mn: 1 to 3%, P: 0.1% or less, S: 0.01% or less , Al: 0.1 to 2%, N: less than 0.005%, and Si + Al ≧ 0.6%, N ≦ 0.007% − (0.003 × Al)%, Al ≦ (1.25 × C ^0.5 −0.57Si + 0.625Mn)%, further containing Nb: 0.1% or less, and the balance Fe and unavoidable impurities were melted and cast, hot rolled, and cold rolled. Then, it anneals in the temperature range of 730-900 degreeC, it cools to the temperature range of 350-600 degreeC with the cooling rate of 20 degreeC / s more than 50 degreeC / s from annealing temperature, and hold | maintains for 30 to 250 second in the temperature range Then, after galvanizing, alloying is performed at 470 to 600 ° C., and the alloyed hot-dip galvanized steel sheet having the above component composition and having a metal structure containing 3-20% residual austenite phase by volume ratio. The manufacturing method of the galvannealed steel plate characterized by manufacturing this.   In mass%, C: 0.05 to 0.25%, Si: 0.30% to 0.5%, Mn: 1 to 3%, P: 0.1% or less, S: 0.01% or less , Al: 0.1 to 2%, N: less than 0.005%, and Si + Al ≧ 0.6%, N ≦ 0.007% − (0.003 × Al)%, Al ≦ (1.25 × C ^0.5 -0.57Si + 0.625Mn)%, B: 0.005% or less, Ni: further containing one or two elements selected from 1% or less, the balance Fe and inevitable impurities steel, After melting, casting, hot rolling, and cold rolling, annealing is performed at a temperature range of 730 to 900 ° C., and 350 to 600 ° C. at a cooling rate of 20 ° C./s to 50 ° C./s or less from the annealing temperature. After cooling to the temperature range of 30 to 250 seconds and then galvanizing, alloying is performed at 470 to 600 ° C., the composition is as described above, and the volume ratio is 3 to 20%. A method for producing an alloyed hot-dip galvanized steel sheet, comprising producing an alloyed hot-dip galvanized steel sheet having a metal structure containing a retained austenite phase.   In mass%, C: 0.05 to 0.25%, Si: 0.30% to 0.5%, Mn: 1 to 3%, P: 0.1% or less, S: 0.01% or less , Al: 0.1 to 2%, N: less than 0.005%, and Si + Al ≧ 0.6%, N ≦ 0.007% − (0.003 × Al)%, Al ≦ (1.25 × C ^0.5 -0.57Si + 0.625Mn)%, and further containing a total of 0.01% or less of one or two of Ca and REM, and the balance Fe and unavoidable impurities are melted, cast, After performing hot rolling and cold rolling, annealing is performed in a temperature range of 730 to 900 ° C., and cooling is performed from the annealing temperature to a temperature range of 350 to 600 ° C. at a cooling rate of more than 20 ° C./s and 50 ° C./s or less. , Held for 30 to 250 seconds in that temperature range, and then galvanized, then alloyed at 470 to 600 ° C., having the above component composition, and containing 3-20% residual austenite phase by volume ratio A method for producing an galvannealed steel sheet, characterized by producing an galvannealed steel sheet having a metal structure.   The said steel is the mass%, and further contains Nb: 0.1% or less, The manufacturing method of the galvannealed steel plate of Claim 1 characterized by the above-mentioned.   The steel further contains one or two elements selected from B: 0.005% or less and Ni: 1% or less by mass%. Item 6. A method for producing the galvannealed steel sheet according to Item 5.   The said steel further contains 0.01% or less in total of 1 type or 2 types of Ca and REM by the mass%, The claim 1, 2, 3, 5, Or the manufacturing method of the galvannealed steel plate of any one of Claim 6.