KR101115801B1 - Zn-plated steel sheet for hot pressed parts and method for manufacturing hot pressed parts having excellent corrosion resistance and electro-painting properties - Google Patents

Abstract

PURPOSE: A Zn-plated steel sheet for hot pressing and a method for manufacturing a hot pressed part with excellent corrosion resistance and electro-painting properties are provided to enhance corrosion resistance and surface characteristics since when a plating member using Zn-plating is hot-pressed, the deterioration or loss of a Zn-plated layer is prevented. CONSTITUTION: A Zn-plated steel sheet for hot pressing comprises a steel sheet, metal, an Al-enriched layer, and a Zn-plated layer. The metal and the Al-enriched layer are less than Cr in the absolute value of the reduced amount of Gibb's free energy per Oxygen 1M when oxidation is made on the steel sheet. The Zn-plated layer is formed on the enriched layer. The enriched layer comprises Al of 30weight% ~ 100weight%. The metal less than the Cr in the absolute value of the reduced amount of Gibb's free energy per Oxygen 1M when oxidation is made is contained in the enriched layer by greater than 70weight%.

Description

Zn-PLATED STEEL SHEET FOR HOT PRESSED PARTS AND METHOD FOR MANUFACTURING HOT PRESSED PARTS HAVING EXCELLENT CORROSION RESISTANCE AND ELECTRO-PAINTING PROPERTIES }

The present invention relates to a method for manufacturing a hot-rolled galvanized steel sheet and a hot press molded part having excellent corrosion resistance and electrodeposition coating property using the same, and more particularly, by preventing the deterioration of the plating layer during the hot press process to secure a stable plating layer. The present invention provides a method of manufacturing a hot press molded galvanized steel sheet having excellent corrosion resistance and a continuous coating formed on the surface of a plating layer to improve electrodeposition coating properties, and excellent corrosion resistance and electrodeposition coating property using the same.

Recently, the demand for high strength steel sheet is rapidly increasing in order to reduce fuel consumption of automobiles due to environmental regulations. As automobile steel sheet is strengthened, wear, fracture, etc. occur easily during press molding, and complicated product molding is difficult. Therefore, in order to solve this problem, the production of products by the hot press process of forming a steel sheet in a hot state by heating the steel sheet has been greatly increased.

Hot press steel sheet is usually subjected to press working in a state heated to 800 ~ 900 ℃, when heating the surface of the steel sheet is oxidized to generate a scale. Therefore, a separate process such as a short blast to remove the scale after forming the product is required, and the corrosion resistance of the product is also inferior to the plating material.

Therefore, in order to solve this problem, as Al-based plating is applied to the surface of the steel sheet as in US Pat. Increasing products have been developed and commercialized.

However, the Al plating material is excellent in heat resistance at high temperature but inferior in corrosion resistance compared to the sacrificial anode type Zn plating has a disadvantage in that the manufacturing cost increases.

However, in the case of Zn, the Zn plated steel sheet manufactured by the conventional method is inferior to Al in heat resistance at a high temperature, and the plating layer is nonuniformly formed by alloying and high temperature oxidation of the Zn layer at a high temperature of 800 to 900 ° C. The ratio of is lowered to less than 30% there is a problem that the function as a plating material is reduced in terms of corrosion resistance.

One side of the present invention is excellent in corrosion resistance by preventing deterioration or loss of the zinc plated layer during hot press molding of the plated material using zinc plating, hot-dip galvanized steel sheet for hot press molding that can form a continuous coating on the surface of the plating layer And it provides a method for producing a hot press molded part excellent in corrosion resistance and electrodeposition coating using the same.

One side of the present invention is a steel sheet; A thickening layer of Al and a metal having an absolute value of the Gibbs free energy reduction amount per mole of oxygen during the oxidation reaction formed on the base steel sheet smaller than Cr; Including a galvanized layer formed on the thickening layer,

The thickening layer contains at least 30% by weight of Al, and the metal having an absolute value of Gibbs free energy reduction per mole of oxygen during the oxidation reaction is smaller than Cr is contained in the thickening layer of the thickening layer and the entire plating layer by 70% by weight or more. It provides a galvanized steel sheet for hot press forming.

At this time, the thickness of the concentrated layer is preferably 0.1 ~ 1㎛.

On the other hand, another side of the present invention is the step of annealing the steel sheet holding; After the annealing heat treatment, Al is immersed in a zinc plating bath composed of 0.05 to 0.5% by weight of Al, 0.01 to 0.5% by weight of metal having an absolute value of Gibbs free energy reduction per mole of oxygen during oxidation, and less than Cr, balance Zn and other unavoidable impurities. Galvanizing step; Heating the galvanized steel sheet to an oxidizing atmosphere at a heating rate of 2 to 10 ° C./sec to 750 to 950 ° C. and then maintaining the galvanized steel sheet for 10 minutes or less; And it provides a method of producing a hot press molded part excellent in corrosion resistance and electrodeposition coating comprising the step of pressing the steel sheet maintained after the heating at a temperature range of 600 ~ 900 ℃.

At this time, the annealing heat treatment is preferably carried out at a temperature range of 700 ~ 900 ℃ or less.

The zinc plating may be performed by using one or more selected from the group consisting of Ni, Fe, Co, Cu, Sn, and Sb as metals in which the absolute value of Gibbs free energy reduction per mole of oxygen is less than Cr during the oxidation reaction. It is more preferable to do.

In addition, the zinc plating step is preferably performed by immersing in a plating bath having a temperature range of 430 ~ 500 ℃.

On the other hand, after the step of galvanizing may further comprise the step of performing an alloying heat treatment in a temperature range of less than 600 ℃.

In addition, the annealing heat treatment step is carried out for the base steel sheet consisting of C: 0.1 ~ 0.4%, Si: 2.0% or less (excluding 0%), Mn: 0.1 ~ 4.0%, the balance Fe and other unavoidable impurities in weight% It is preferable.

At this time, the annealing step is N: 0.001 ~ 0.02%, B: 0.0001 ~ 0.01%, Ti: 0.001 ~ 0.1%, Nb: 0.001 ~ 0.1%, V: 0.001 ~ 0.1%, Cr: 0.001 ~ 1.0%, It is more preferable to carry out with respect to the steel plate further containing 1 or more types chosen from the group which consists of Mo: 0.001-1.0%, Sb: 0.001-0.1%, and W: 0.001-0.3%.

According to an aspect of the present invention, the corrosion resistance and surface properties can be improved by preventing deterioration or loss of the zinc plated layer during hot press molding of the plated material using zinc plating, and electrodeposition by forming a continuous oxide film on the plated layer. A hot press molded part having improved paintability can be obtained.

Hereinafter, the galvanized steel sheet for hot press forming of this invention is demonstrated.

One side of the present invention is a steel sheet; A thickening layer of Al and a metal having an absolute value of the Gibbs free energy reduction amount per mole of oxygen during the oxidation reaction formed on the base steel sheet smaller than Cr; Including a galvanized layer formed on the thickening layer,

The thickening layer contains at least 30% by weight of Al, and the metal having an absolute value of Gibbs free energy reduction per mole of oxygen during the oxidation reaction is smaller than Cr is contained in the thickening layer of the thickening layer and the entire plating layer by 70% by weight or more. It provides a galvanized steel sheet for hot press forming.

As described above, it is very important to prevent the deterioration of the galvanized layer having a structure in which the absolute value of the Gibbs free energy reduction amount per mole of oxygen is less than Cr and the Al is concentrated at the interface between the base steel sheet and the galvanized layer. It is advantageous. That is, during the oxidation reaction concentrated at the interface, the metal whose absolute value of Gibbs free energy reduction per mole of oxygen is less than Cr enters into the plating layer during hot press heating and is dissolved in Zn-Fe to suppress zinc from diffusing into the base steel sheet. Al concentrated at the interface diffuses into the surface layer of the plating layer during hot press heating to continuously form an Al ₂ O ₃ oxide film to protect the zinc plating layer.

Therefore, it is preferable that the thickening layer is 30 wt% or more of Al, so that the oxide film is easily generated, and the metal having the absolute value of the Gibbs free energy reduction amount per mole of oxygen less than Cr during the oxidation reaction is the thickening layer and the plating layer. Containing at least 70% by weight of the concentrated layer in total is advantageous for forming a ternary phase to prevent zinc diffusion in the plating layer. Particularly, since the metal having a smaller absolute value of Gibbs free energy reduction per mole of oxygen during the oxidation reaction is less than Cr, the reactivity with Al is strong, and as the amount is increased at the interface, an Al ₂ O ₃ oxide film is formed during hot press heating. It will concentrate more Al to the interface.

At this time, the thickness of the concentrated layer is preferably 0.1 ~ 1㎛. If the thickness is less than 0.1 μm, the amount of metal and Al that is less than Cr in the absolute value of Gibbs free energy reduction per mole of oxygen during the oxidation reaction is not sufficient. If the thickness is more than 1 μm, the oxide layer is formed too thick on the plating layer during hot press heating, thereby degrading the weldability. Therefore, the thickness is preferably limited to 0.1 to 1 μm.

Hereinafter, the manufacturing method of the hot press molding part of this invention is demonstrated.

One side of the present invention comprises the steps of annealing the steel sheet holding; After the annealing heat treatment, Al is immersed in a zinc plating bath composed of 0.05 to 0.5% by weight of Al, 0.01 to 0.5% by weight of metal having an absolute value of Gibbs free energy reduction per mole of oxygen during oxidation, and less than Cr, balance Zn and other unavoidable impurities. Galvanizing step; Heating the galvanized steel sheet to an oxidizing atmosphere at a heating rate of 2 to 10 ° C./sec to 750 to 950 ° C. and then maintaining the galvanized steel sheet for 10 minutes or less; And it provides a method of producing a hot press molded part excellent in corrosion resistance and electrodeposition coating comprising the step of pressing the steel sheet maintained after the heating at a temperature range of 600 ~ 900 ℃.

First, when the plating bath composition is examined, it is preferable that Al is contained in the plating bath at 0.05 to 0.5% by weight. If Al is included in the plating bath, Al is concentrated at the interface of the base steel plate and the plating layer alone or in an alloy state during hot dip plating, and the Al concentrated at this interface diffuses to the surface of the plating layer during hot press heating to form an oxide on the plating layer. Done. At this time, the oxide formed is mainly composed of Al ₂ O ₃ , the form of the continuous film form, this film plays an important role in preventing Zn deterioration in the plating layer.

At this time, the Al ₂ O ₃ layer formed on the surface of the plating layer should be continuously formed on the surface of the plating layer, the average thickness is preferably 10 ~ 300nm. Even when the Al ₂ O ₃ oxide film is discontinuously formed or continuous, if the average thickness is 10 nm or less, the oxide film which acts as a surface protection during the hot press heating process may be damaged to rapidly promote the development of Zn oxide in the plating layer. Since there is a concern, it becomes difficult to have sufficient heat resistance. In addition, when the average thickness of the Al ₂ O ₃ oxide film is 300 nm or more, the welding properties may be deteriorated due to the oxide. Therefore, the average thickness of the oxide film formed on the surface of the plating layer is limited to 10 to 300 nm.

At this time, an oxide made of ZnO, MnO and other impurities is further formed on the continuous oxide film made of Al ₂ O ₃ , and thus the total average thickness of the oxide layer formed on the plating layer is 0.01 to 5 μm. desirable. When the thickness of the oxide layer exceeds 5 μm, the oxide tends to be brittle and growth stress is concentrated and the oxide is easily peeled off from the surface, so that the product cannot be used in the presence of the oxide. There is a problem that a process for removing oxides on the surface, such as a test process, is required separately. In addition, when the thickness of the oxide layer is less than 0.01 μm, the deterioration prevention effect of the galvanized layer is insignificant, so that the thickness of the oxide layer is preferably 0.01 to 5 μm.

In particular, Al ₂ O ₃ as described above When oxide is continuously formed, coating property is very excellent at the time of electrodeposition coating process after that, and it can greatly contribute to improving the adhesiveness of the formed coating film. Therefore, even if the separate phosphate treatment is omitted, since the same level of coating film formation as that of the phosphate treatment is possible, it can be very efficient in terms of economy and productivity. In addition, Al in the plating bath contributes to the improvement of the plating property by forming an activation layer at the interface between the base steel sheet and the plating layer during plating.

Therefore, in order for Al to perform the above-mentioned role in the plating bath, Al should be included in the plating bath at least 0.05% by weight or more, but if it exceeds 0.5% by weight, the activation layer is excessively formed at the interface. Since the alloying is excessively suppressed and the melting point increase effect in the galvanized layer is insignificant, a problem may easily occur. Therefore, the Al content in the plating bath is preferably controlled to 0.05 to 0.5% by weight.

Next, it is preferable to add 0.01 to 0.5% by weight of a metal whose absolute value of the Gibbs free energy reduction per mole of oxygen during the oxidation reaction in the plating bath is smaller than Cr. In the oxidation reaction, metals having an absolute decrease in the amount of Gibbs free energy per mole of oxygen less than Cr are concentrated at the interface between the base steel plate and the plating layer during hot dip galvanizing. Thus, the concentrated metal diffuses into the plating layer during hot press heating, and Zn , Fe meets with each other to form a ternary phase. The ternary phase serves to suppress diffusion of components such as Fe, Mn, etc. of the steel sheet into the plating layer, and at the same time serves to prevent the Zn in the plating layer from being lost to the steel sheet. In addition, metals having an absolute reduction in the amount of Gibbs free energy reduction per mole of oxygen during the oxidation reaction have a high reactivity with Al, and thus absolute values of the Gibbs free energy reduction per mole of oxygen during the oxidation reaction during the hot dip zinc plating are smaller than Cr. An Al thickening layer containing more Al is formed on the metal thickening layer.

Therefore, in order to ensure the heat resistance of the metal whose absolute value of Gibbs free energy reduction amount per mole of oxygen is less than Cr in the oxidation reaction, at least 0.01 wt% or more in the plating bath should be included, and if the amount is 0.5 wt% If exceeding, dross is generated in the plating bath, so that the plating quality may be degraded. The addition amount is preferably controlled to 0.01 to 0.5% by weight.

In the oxidation reaction, the metal of which the absolute value of the Gibbs free energy reduction amount per mole of oxygen is less than Cr is dissolved in the Zn-Fe phase during press heating. Even at a high temperature of 750 ° C. or higher, Zn of the galvanized layer can be prevented from being diffused into the steel sheet and the zinc plated layer can be stably maintained.

At this time, the annealing heat treatment is preferably carried out at a temperature range of 700 ~ 900 ℃ or less. When the annealing heat treatment temperature is less than 700 ℃ annealing temperature is too low to secure the material properties of the steel, when the temperature exceeds 900 ℃, the growth rate of the oxide is faster between the steel sheet and the hot dip galvanized layer in the present invention It becomes difficult to form a thin oxide film.

The dew point temperature of the annealing atmosphere is preferably -10 ° C or lower. The mixed gas is a hydrogen (H ₂ ) gas is a ratio of 3 to 15% by volume, the balance is a nitrogen (N ₂ ) gas is preferably a mixed gas. If the ratio of H ₂ is less than 3%, the reducing power of the atmosphere gas is reduced, and the production of oxides is easy. If the ratio of H ₂ is more than 15%, the reducing power is improved, but it is too much due to the increase in manufacturing cost, compared to the increase in reducing power. It is economically disadvantageous.

The zinc plating may be performed by using one or more selected from the group consisting of Ni, Fe, Co, Cu, Sn, and Sb as metals in which the absolute value of Gibbs free energy reduction per mole of oxygen is less than Cr during the oxidation reaction. It is more preferable to. If the absolute value of the Gibbs free energy reduction amount is greater than Cr, the coated metal itself is oxidized and there is no effect of improving heat resistance. Ni and Fe are typically applied as the metal. In addition, Co, Cu, Sn, Sb and the like may be applied, and may be applied in a mixed or alloyed state of these, Fe is more preferably applied in the alloy state.

In addition, the zinc plating step is preferably performed by immersing in a plating bath having a temperature range of 430 ~ 500 ℃. If the plating bath temperature is less than 430 ℃ the plating bath does not have sufficient fluidity, on the contrary, if the plating bath temperature exceeds 500 ℃ dross occurs frequently in the plating bath to reduce the production efficiency, the plating bath temperature is 430 It is preferable to control to -500 degreeC. More preferably, when the temperature is 460 ° C. or more, it is more effective to sufficiently concentrate Al and a metal having a less oxidizing property than Mn at the interface between the plating layer and the base steel sheet.

The hot dip galvanizing is performed so as to have a thickness of 5 to 30 µm. If the thickness of the hot-dip galvanized layer is less than 5㎛ the alloy in the plating layer in the hot press heating furnace is excessive, the amount of Zn in the plating layer after the hot press working significantly falls, when the thickness of the plating layer exceeds 30㎛, hot press heating furnace In this case, the alloying of the plating layer is delayed, so that the oxide grows rapidly on the surface of the plating layer, and it is also disadvantageous in terms of manufacturing cost.

On the other hand, after the zinc plating step may further comprise the step of performing an alloying heat treatment in a temperature range of less than 600 ℃. When performing the alloying heat treatment after the plating, the temperature of the alloying heat treatment is limited to 600 ° C or less. If the temperature exceeds 600 ° C, alloying of the plating layer proceeds to increase the heat resistance in the hot press heating furnace, but the alloying heat treatment temperature may be increased because cracking may occur due to embrittlement of the plating layer and scale growth increases on the surface of the plating layer in the heating furnace. By limiting to less than 600 ℃, preferably less than 500 ℃ by suppressing the Fe in the plating layer to 5% by weight or less, it is possible to effectively prevent the occurrence of fine cracks in the plating layer, if the temperature is suppressed to 450 ℃ or less It is more preferable to suppress the occurrence of fine cracks.

In addition, the annealing heat treatment step is carried out for the base steel sheet consisting of C: 0.1 ~ 0.4%, Si: 2.0% or less (excluding 0%), Mn: 0.1 ~ 4.0%, the balance Fe and other unavoidable impurities in weight% It is preferable.

C: 0.1 ~ 0.4%

C is a key element for increasing the strength of steel sheet, and produces a hard phase of austenite and martensite. In the case where the content of C is less than 0.1%, even if hot pressing is performed in the austenitic single-phase zone, it is difficult to secure the target strength, and therefore, it is preferable to add the content of C at least 0.1%. If the content of C exceeds 0.4%, the likelihood of deterioration of toughness and weldability is increased, and the strength is excessively high, so that there is a disadvantage in the manufacturing process, such as impairing the flowability in the annealing and plating process, so the upper limit of C is 0.4% or less. Limited to

Mn: 0.1 ~ 4.0%

Mn, as a solid solution strengthening element, not only contributes greatly to the strength increase, but also plays an important role in delaying the transformation from austenite to ferrite. If the Mn content is less than 0.1%, the ferrite transformation temperature (Ae3) is increased in austenite, so that a high heat treatment temperature is required to press-process the steel sheet on the austenite single phase. On the other hand, when the content of Mn exceeds 4.0%, weldability, hot rolling property and the like may deteriorate, which is not preferable. At this time, the content of Mn is more preferably 0.5% or more in order to sufficiently reduce the ferrite transformation temperature (Ae3) and hardenability due to Mn.

Si: 2% or less (except 0%)

Si is a component added for the purpose of deoxidation. If the content of Si exceeds 2%, it is difficult to pickle the hot rolled sheet, which may cause scale surface defects due to hot pickled sheet and unpickled oxide. Since SiO ₂ oxide may be generated on the steel surface and unplating may occur, the upper limit of Si is preferably limited to 2%.

At this time, the annealing step is N: 0.001 ~ 0.02%, B: 0.0001 ~ 0.01%, Ti: 0.001 ~ 0.1%, Nb: 0.001 ~ 0.1%, V: 0.001 ~ 0.1%, Cr: 0.001 ~ 1.0%, It is more preferable to carry out with respect to the steel plate further containing 1 or more types chosen from the group which consists of Mo: 0.001-1.0%, Sb: 0.001-0.1%, and W: 0.001-0.3%.

N: 0.001-0.02%

If the N is less than 0.001%, the manufacturing cost for controlling N in the steelmaking process can significantly increase, so the lower limit is set to 0.001%. When the N content is more than 0.02%, it is difficult to dissolve and perform the steel sheet in the manufacturing process, so that the manufacturing cost may increase, and slab cracking due to AlN is likely to occur, so the upper limit thereof is made 0.02%.

B: 0.0001-0.01%

B is an element that delays ferrite transformation in austenite, and its content is difficult to achieve sufficiently when the content is less than 0.0001%, and when the content of B is more than 0.01%, the effect is not only saturated but also degrades hot workability. It is preferable to limit the upper limit to 0.01%.

Ti, Nb or V: 0.001 to 0.1%

Ti, Nb and V are effective elements for increasing the strength of the steel sheet, miniaturizing the grain size and improving heat treatment properties. If the content is less than 0.001%, the above effect cannot be sufficiently obtained. If the content exceeds 0.1%, the effect of the desired strength and yield strength increase cannot be expected due to an increase in manufacturing cost and excessive carbon and nitride production. Therefore, the upper limit is limited to 0.1%. desirable.

Cr or Mo: 0.001-1.0%

Since Cr and Mo not only increase the hardenability but also increase the toughness of the heat-treated steel sheet, the effect is greater when added to a steel sheet that requires high impact energy characteristics, and the effect is lower when the content is less than 0.001%. It is preferable to limit the upper limit to 1.0% because it cannot be sufficiently obtained and the effect is saturated not only in 1.0% but also the manufacturing cost increases.

Sb: 0.001-0.1%

Sb is an element which plays a role of making the generation of scale uniform by suppressing selective oxidation of grain boundaries during hot rolling and improving pickling properties of hot rolled materials. If the Sb content is less than 0.001%, the effect is difficult to achieve, and if the Sb content is more than 0.1%, the effect is not only saturated, but the manufacturing cost may be increased and brittleness may occur during hot working, so the upper limit is limited to 0.1%. desirable.

W: 0.001-0.3%

W is an element that improves the heat treatment hardenability of the steel sheet and at the same time, W-containing precipitates are advantageous for securing strength, and when the content is less than 0.001%, the above effect cannot be sufficiently obtained, and the content is 0.3%. When exceeded, the effect is not only saturated, but also increases the manufacturing cost, the content is preferably limited to 0.001 ~ 0.3%.

After the hot-dip galvanized steel sheet is manufactured, the hot pressing process is performed. First, the hot-dip galvanized steel sheet is subjected to a heat treatment process. The heat treatment step is preferably heated to 750 ~ 950 ℃ in an oxidizing atmosphere at a temperature rising rate of 2 ~ 10 ℃ / second and maintained for 10 minutes or less. When the temperature increase rate is less than 2 ℃ / sec, the plating time is easy to deteriorate due to excessive time in the heating furnace, and when the temperature increase rate exceeds 10 ℃ / second, the galvanized layer is not sufficiently alloyed This is because there is a risk that the galvanized layer deteriorates due to excessive temperature rise.

When heating, the maximum temperature is 750 ~ 950 ℃ and the holding time at the maximum temperature is preferably within 10 minutes. When the maximum temperature is less than 750 ° C, the steel microstructure is not sufficiently transformed into the austenite region, and thus it is not easy to secure the strength. In addition, when the holding time at the above temperature is too long, the surface quality of the plating may be lowered. Therefore, it should not exceed 30 minutes, and more preferably within 10 minutes is effective.

In particular, when heated to 750 ~ 950 ℃ in an oxidizing atmosphere to form an Al ₂ O ₃ layer on the surface of the steel sheet to act as a protective layer to suppress the volatilization of Zn of the plating layer, in order to form such a protective layer continuously It is advantageous that the oxygen partial pressure in the heating atmosphere is 10 ^-40 atm or more, and more preferably, the protective layer can be more smoothly formed in the case of 10 ^-5 atm or more.

After the heat treatment, press molding is performed at a temperature range of 600 to 900 ° C. to manufacture hot press molded parts. When the temperature is less than 600 ℃, it is difficult to secure sufficient strength even if the austenite is transformed to ferrite to perform a hot press, it is preferable to limit the upper limit to 900 ℃ in terms of economics.

Hereinafter, the present invention will be described in detail by way of examples, which are intended for a more complete description of the present invention, and the scope of the present invention is not limited by the following individual examples.

( Example )

First, the steel plate which cold-rolled the steel material which has a composition of Table 1 was tested.

Category (% by weight) C Si Mn P S Al thickness River 1 0.17 0.25 1.4 0.01 0.001 0.02 1.2 mm River 2 0.24 0.04 2.3 0.008 0.0015 0.025 1.5mm River 3 0.22 1.0 1.7 0.01 0.001 0.04 1.8mm

The steel sheet was immersed in a plating bath having the composition shown in Table 2 to perform hot dip galvanizing, and then the thickness of the plated layer was measured. Then, after performing a hot press process under the conditions shown in Table 2, the thickness of the plated layer was measured again. In this case, the thickness of the plating layer was measured by indicating the length from the surface layer of the plating layer to the point where the Zn content is 30% by weight or more in the vertical direction.

division Steel grade Plating bath
adding
metal Plating bath
adding
Metallic
content
(weight%) Plating bath
Al
content
(weight%) Zn plating layer thickness
(Μm) Alloying
Temperature
(℃) Hot
Press
heating
Temperature
(℃) Hot
Press
heating
time
(minute) After hot press
Plating layer thickness
(Μm) Inventive Example 1 River 1 Ni 0.08 0.12 8 - 910 6 20 Inventive Example 2 River 2 Ni 0.15 0.12 7 500 910 6 19 Inventory 3 River 2 Ni 0.3 0.12 10 - 930 5 23 Honorable 4 River 3 Ni 0.45 0.21 12 - 930 5 24 Inventory 5 River 3 Co 0.2 0.21 12 - 870 7 22 Comparative Example 1 River 2 - - 0.21 8 - 910 5 - Comparative Example 2 River 3 - - 0.21 8 - 870 6 - Comparative Example 3 River 3 - - 0.12 12 - 930 5 - Comparative Example 4 River 2 Ni 0.008 0.12 8 560 930 5 -

First, Inventive Examples 1 to 4 contain Ni or Co, which is a metal that is weaker than Cr, in 0.05 to 0.5% by weight, and Al is also included in the range of 0.1 to 0.3% by weight. It can be effectively prevented from being lost to the steel sheet or deteriorated to the outside, and as a result it can be confirmed that after the hot pressing, the plating layer thickened more than 1.5 times more stably.

On the contrary, Comparative Examples 1 to 3 contained Al in the plating bath, but did not contain any metal having a weaker oxidizing property than Mn, and Comparative Example 4 contained Ni as a oxidizing element weaker than Mn, but the amount was 0.008. At the time of hot press heating, the ternary phase which prevented the loss of Zn in the plating layer was hardly formed, and the plating layer would diffuse into the base steel sheet. It was found that it did not remain.

Claims (9)

Steel plate; A thickening layer of Al and a metal having an absolute value of the Gibbs free energy reduction amount per mole of oxygen during the oxidation reaction formed on the base steel sheet smaller than Cr; Including a galvanized layer formed on the thickening layer,
The thickening layer may contain at least 30% by weight of Al and less than 100% by weight, and the metal having an absolute value of Gibbs free energy reduction per mole of oxygen during the oxidation reaction smaller than Cr is 70% by weight of the thickening layer among the thickening layer and the whole plating layer. Galvanized steel sheet for hot press molding containing more than%.
The method according to claim 1,
The thickened layer is a galvanized steel sheet for hot press forming the thickness of 0.1 ~ 1㎛.
Annealing heat treatment of the steel sheet in the temperature range of 700 ~ 900 ℃;
Al of 0.05 to 0.5% by weight after the annealing heat treatment, 0.01 to 0.5% by weight of the metal of less than Cr, the absolute value of Gibbs free energy reduction per mole of oxygen in the oxidation reaction, the balance of 430 ~ 500 ℃ of Zn and other unavoidable impurities Galvanizing by immersing in a zinc plating bath having a temperature range;
Heating the galvanized steel sheet to 750 to 950 ° C. at an elevated temperature rate of 2 to 10 ° C./sec in an oxidizing atmosphere without performing alloying heat treatment, and then maintaining the galvanized steel sheet for 10 minutes or less; And
Method for producing a hot press molded part excellent in corrosion resistance and electrodeposition coating comprising the step of pressing the steel sheet maintained after the heating at a temperature range of 600 ~ 900 ℃.
delete The method according to claim 3,
The galvanizing step is a metal whose absolute value of Gibbs free energy reduction amount per mole of oxygen during the oxidation reaction is less than Cr, and uses at least one selected from the group consisting of Ni, Fe, Co, Cu, Sn, and Sb. And a method for producing hot press molded parts having excellent electrodeposition coating properties.
delete delete The method according to claim 3 or 5,
The annealing heat treatment may be performed by weight percent C: 0.1-0.4%, Si: 2.0% or less (excluding 0%), Mn: 0.1-4.0%, balance Fe and other inevitable impurities. Method of manufacturing hot press molded parts with excellent electrodeposition coating properties.
The method according to claim 8,
The annealing heat treatment step is N: 0.001-0.02%, B: 0.0001-0.01%, Ti: 0.001-0.1%, Nb: 0.001-0.1%, V: 0.001-0.1%, Cr: 0.001-1.0%, Mo: A method for producing a hot press molded part having excellent corrosion resistance and electrodeposition coating property on a base steel sheet further comprising at least one member selected from the group consisting of 0.001 to 1.0%, Sb: 0.001 to 0.1%, and W: 0.001 to 0.3%.