KR20110000424A - Hot-rolled steel sheet having excellent galvanized coating quality and the method for manufacturing the same - Google Patents

Abstract

The present invention is P: 0.02 ~ 0.1wt% B: 0.0003 ~ 0.001wt% in the component system based on C: 0.001 ~ 0.04wt%, Si: greater than 0 and 0.05wt%, Mn: greater than 0 and 0.5wt% Slabs containing the alloy composition of the remaining Fe and other unavoidable impurities are reheated at a temperature of 1180 ~ 1250 ° C, and hot rolled the reheated slabs and wound at a temperature of 580 ~ 700 ° C.

According to the present invention, there is an advantage that a hot-dip galvanized hot-rolled steel sheet having excellent surface quality can be manufactured because the over-plating phenomenon is prevented during hot dip galvanizing and powdering is improved even during processing.

Hot Rolled Steel, Hot Dip Galvanized

Description

Hot-rolled steel sheet having excellent galvanized coating quality and the method for manufacturing the same}

The present invention relates to a hot-rolled steel sheet and a method for manufacturing the same, and more particularly, to a hot-rolled steel sheet excellent in hot-dip galvanizing properties to improve the hot-dip galvanizing properties by increasing the amount of P component generated during the steelmaking process, and a method of manufacturing the same. It is about.

Steel sheets used as materials for automobiles, construction materials, and home appliances are subjected to hot dip galvanizing to improve corrosion resistance.

Hot dip galvanizing process to improve the corrosion resistance of hot rolled steel sheet is largely degreasing process to remove foreign substances in steel sheet, pickling and washing process to remove hot roll scale, flux pretreatment and drying process to prevent oxidation, hot dip galvanizing It is divided into zinc bath immersion process immersed in the bath, and after the hot dip galvanizing process is subjected to a chromate treatment of chromium as a main component on the hot-dip galvanized hot-rolled steel sheet to secure additional corrosion resistance and drying process.

However, such a prior art has the following problems.

In an electric furnace process using scrap as a main raw material, impurity elements such as Cu, Ni, Sn, As, Cr, Mo, and Pb, which are not removed during a general steel production process, remain in the steel.

Such an impurity element is not a component added by the purpose, and it remains unnecessarily in steel and deteriorates the quality of a steel plate.

In addition, Si, Cu, Sn and the like remaining unnecessarily in the steel is concentrated on the surface of the steel sheet during hot dip galvanizing to accelerate or delay the reaction between the Fn-Zn to reduce the plating quality.

Degradation of the plating quality deteriorates the powdering resistance and makes it difficult to form a uniform coating layer during the subsequent chromate treatment, which causes a decrease in the appearance quality of the steel sheet.

The present invention is to solve the conventional problems as described above, the object of the present invention is to increase the amount of P component generated during the steelmaking process, the appearance damage and powdering resistance caused by overplating by Si, Cu, Sn, etc. To provide a hot-rolled steel sheet excellent in hot-dip galvanizing properties to prevent deterioration in advance, and a manufacturing method thereof.

According to a feature of the present invention for achieving the above object, the present invention is P in the component system based on C: 0.001 ~ 0.04wt%, Si: more than 0 and 0.05wt%, Mn: more than 0 and 0.5wt% or less : 0.02 ~ 0.1wt% B: It contains 0.0003 ~ 0.001wt% and has alloy composition of remaining Fe and other unavoidable impurities.

The impurities include S: more than 0 and 0.01 wt% or less, Cu: 0 and more and 0.20 wt% or less and Sn: 0 and more and 0.03 wt% or less.

C: 0.001 to 0.04 wt%, Si: greater than 0 and 0.05 wt% or less, Mn: greater than 0 and 0.5 wt% or less P: 0.02 to 0.1 wt% B: 0.0003 to 0.001 wt% Slabs with alloys of Fe and other unavoidable impurities

Reheat at a temperature of 1180 ~ 1250 ℃, hot roll the reheated slab and wind up at a temperature of 580 ~ 700 ℃.

After the winding, pickling and immersion in a plating bath are performed to perform a hot dip galvanizing process. The temperature of the hot rolled steel sheet drawn into the plating bath is 400 to 450 ° C.

Al is added to the plating bath to prevent a rapid reaction between Fe and Zn.

Al concentration is 0.10 ~ 0.12wt% relative to the total plating solution in the plating bath.

The impurities include S: more than 0 and 0.01 wt% or less, Cu: 0 and more and 0.20 wt% or less and Sn: 0 and more and 0.03 wt% or less.

According to the present invention, the pickling property is improved by further containing P and B in a component system containing inevitable impurities such as P, S, Cu, and Sn by an electric furnace process. This imparts uniform plating conditions to the entire steel sheet during hot dip galvanizing to form a uniform plating layer.

In the present invention, Al is further added to the zinc plating bath to perform hot dip galvanizing. Al added to the plating bath prevents rapid plating between Fe-Zn to prevent overplating.

Therefore, there is an effect that can be produced hot-dip galvanized hot-rolled steel sheet having excellent surface quality and improved powdering resistance during processing.

Hereinafter, the preferred embodiment of the hot-rolled steel sheet excellent in the hot-dip galvanizing properties according to the present invention and its manufacturing method will be described in detail.

In order to obtain the excellent plating property, this invention contains P which is an impurity element at 0.02-0.1 wt%, and also adds B in order to prevent secondary work brittleness by P addition. And Al is further added to the zinc plating bath in order to give uniform plating conditions to a steel plate before plating bath deposition.

Al added to the plating bath forms a FeAl ₅ reaction suppression layer during the formation of the intermetallic compound between Fe-Zn to prevent rapid reaction between Fe-Zn.

Specific alloy composition of the present invention is C: 0.001 ~ 0.04wt%, Si: more than 0 and 0.05wt% or less, Mn: more than 0 and 0.5wt% or less as a basic composition, P: 0.02 ~ 0.1wt%, S as an impurity element : More than 0 wt% and less than 0.01 wt%, Cu: more than 0 wt% and less than 0.20 wt% and less than Sn: more than 0 wt% and less than 0.03 wt%, further comprising B: 0.0003 to 0.001 wt% and remaining Fe.

Hereinafter, the function and content of the alloying elements of the present invention will be described in detail.

C: 0.001-0.04wt%

C is for strength. If carbon is added in a small amount, it is difficult to secure strength, and thus, a solid solution element must be added, and thus, the production cost increases, and if it is added excessively, pickling becomes difficult, weldability decreases, and ductility and stretch-flange property decreases as strength increases. Here, the upper limit of C is set based on the ultra low carbon steel because the present invention is applied to both general carbon steel and ultra low carbon steel.

Si: more than 0 and 0.05wt% or less

Si is a solid solution hardening element, which contributes to the steel cleaning. When added to the steel to which the appropriate Mn is added, Si improves the fluidity of the molten metal during welding, thereby reducing the inclusions in the weld as much as possible and improving the strength without disturbing the yield ratio and the balance between strength and ductility.

However, when a large amount of Si is added, a hard compound such as FeSiO ₄ is formed on the surface during hot rolling, making it difficult to pickle and deteriorating plating adhesion during hot dip galvanizing, thereby causing problems such as unplating and plating peeling. Therefore, the content of Si is limited to 0.05 wt% or less.

Mn: more than 0 and less than 0.5wt%

Mn precipitates S in the steel as MnS to prevent red brittleness by solid-solution sulfur and to refine crystal grains without ductile damage.

In addition, by lowering the transformation temperature between austenite ferrite to form a fine ferrite also serves to improve the strength.

If the Mn exceeds 0.5wt%, the machinability is poor and the manganese band develops at the center of the thickness during slab casting, which decreases the bending workability and makes it difficult to pickle. Limited to

In addition to the basic alloy components described above, depending on the required mechanical properties, elements such as Nb, Ti, Cr may be further contained.

P, S, Cu, Sn is an impurity concept is an element remaining in the steel more than a certain amount in the case of an electric furnace. Among them, Cu, Sn, etc. are concentrated on the surface of the steel sheet during the hot dip galvanizing process to accelerate or delay the reaction between Fe-Zn, thereby reducing the plating quality.

P: 0.02 ~ 0.1wt%

P is added for the purpose of improving pickling. P removes the concentration of impurity elements on the surface of the base material during pickling.

If P is more than 0.02wt%, pickling property is improved and plating quality is improved, but if it exceeds 0.1wt%, secondary processing brittleness may occur due to P segregation, so the content is limited to 0.02 ~ 0.1wt%.

S: greater than 0 and less than 0.01wt%

S may be included as an unavoidable impurity. S is a red brittle occurs when remaining in the steel, and increases the size of the MnS precipitates to limit the content to less than 0.008wt%.

Cu: more than 0 and less than 0.20wt%

Cu is present as an impurity that cannot be removed in a steelmaking process using scrap as a raw material. Cu mainly has a side effect as an element to increase strength, but it is preferable to regulate the content to 0.20 wt% or less because it lowers elongation, r value and surface quality of steel.

Sn: more than 0 and less than 0.03wt%

Sn, like Cu, exists as an impurity that cannot be removed in a steelmaking process using scrap as a raw material. Sn plays a decisive role in lowering the mechanical properties of steel, unlike other impurity elements. Therefore, the content of Sn is limited to 0.03wt% or less.

B: 0.0003 to 0.001 wt%

B is added to prevent intergranular segregation caused by P addition. B is an invasive element that prevents P from grain boundary segregation due to a site competition effect with P. In addition, B present in the steel is combined with solid solution N in the steel to precipitate as BN, thereby contributing to the improvement of workability.

If boron (B) is added less than 0.0003wt% has no effect, if it is added exceeding 0.001wt% difficult to control the steelmaking process, the material deviation of the steel sheet after hot rolling and heat treatment becomes large. Therefore, the content of B is controlled to 0.0003 to 0.001 wt%.

Ni may be added as an additional element. When Ni is added in the range of more than 0 wt% and 0.05 wt%, it forms a uniform alloying to give uniform plating conditions during hot dip galvanizing.

In addition to the above-described alloy components, it may contain trace amounts of inevitable impurities as elements contained according to the situation of raw materials, materials, manufacturing facilities, and the like.

 Detailed process conditions are as follows.

[Reheating, Hot Rolling Process]

To re-use segregated components during casting, it is carried out in the temperature range of 1180 ~ 1250 ℃. After reheating, hot rolling is finished under normal conditions to produce a hot rolled steel sheet, and wound and cooled in a temperature range of 700 ° C. or lower to prevent grain boundary segregation of P. Cooling can be performed by water or air cooling depending on the desired tissue properties.

If the reheating temperature is lower than 1180 ° C., uniform austenite grains may not be obtained and may be mixed, resulting in degradation of surface quality due to intragranular and grain boundary segregation caused by P. If the reheating temperature is higher than 1250 ° C, the material softens with abnormal grain growth and the manufacturing cost increases due to high temperature heating.

The hot rolled finishing temperature can be carried out directly above or below the Ar3 temperature, depending on the required tissue properties.

As for winding temperature, 580-700 degreeC is preferable. If the coiling temperature is lower than 580 ℃, elongation is reduced and material degradation occurs, and if higher than 700 ℃, the particle quality, grain boundary segregation by P occurs, resulting in surface quality degradation.

[Molten zinc plating process]

The wound hot rolled steel sheet is immersed in 8% to 12% HCl solution for 10 to 25 seconds to remove the hot rolled oxide layer and then washed, and is subjected to flux pretreatment and drying to prevent oxidation. Thereafter, the steel sheet is immersed in a plating bath to perform hot dip galvanizing.

It is preferable that the steel plate temperature drawn into a plating bath is 400-450 degreeC. Here, the steel sheet temperature introduced into the plating bath is the steel sheet temperature immediately before entering the plating bath.

If the plating temperature is less than 400 ℃ surface quality of the steel sheet may be deteriorated, if it exceeds 450 ℃ the adhesion of the plating layer itself may be deteriorated due to the increase in the coating amount.

Al is added to the plating bath to prevent rapid reaction between Fe and Zn. The Al concentration of the plating solution in the plating bath is preferably 0.12 to 0.20 wt%.

If the Al concentration in the plating bath is less than 0.12wt%, FeAl ₅ reaction suppression layer formation is insufficient, and if it exceeds 0.12wt%, Fe and Zn alloying reaction may be suppressed due to excessive FeAl ₅ reaction suppression layer formation.

After the hot dip galvanizing process, chromate coating may be further performed to secure additional corrosion resistance.

Hereinafter, a method of manufacturing a hot rolled steel sheet having excellent hot dip galvanizing characteristics will be described with reference to examples.

[Example]

 Slab containing C, Si, Mn as basic composition, containing P, S, Cu, Sn as an impurity element, and optionally containing B, was heated at 1120 ℃ for 2 hours, and hot rolled under Ar3 point. It was wound up at ° C.

Thereafter, hot dip galvanizing was performed at 440 ° C. and 460 ° C., and plating characteristics were measured. At this time, 0.12wt% Al was added to the plating bath to prevent rapid reaction between Fe and Zn.

Table 1 below shows chemical composition ratios, process conditions, and plating properties accordingly.

division
Composition (wt%) Process conditions Plating characteristics
Remarks C Si Mn P S Cu Sn B Plating temperature Powder ring Adhesion
(g / m ² ) Surface defects One 0.04 0.01 0.2 0.01 0.01 0.01 0.01 460 ℃ Grade 2 55-65 Not Occurred Comparative steel 2 0.04 0.04 0.2 0.01 0.01 0.01 0.01 460 ℃ Grade 3 80-90 Occur Comparative steel 3 0.04 0.01 0.2 0.01 0.01 0.20 0.01 460 ℃ Grade 2 70-80 Not Occurred Comparative steel 4 0.04 0.01 0.2 0.01 0.01 0.01 0.03 460 ℃ Grade 3 75-85 Occur Comparative steel 5 0.04 0.04 0.2 0.01 0.01 0.20 0.03 460 ℃ Grade 4 140-150 Occur Comparative steel 6 0.04 0.04 0.2 0.01 0.01 0.20 0.03 440 ℃ Grade 6 90-130 Occur Comparative steel 7 0.04 0.04 0.2 0.02 0.01 0.20 0.03 0.0005 460 ℃ Grade 3 85-95 Occur Comparative steel 8 0.04 0.04 0.2 0.04 0.01 0.20 0.03 0.0005 460 ℃ Grade 3 70-80 Not Occurred Invention steel 9 0.04 0.04 0.2 0.06 0.01 0.20 0.03 0.0005 460 ℃ Grade 2 55-65 Not Occurred Invention steel 10 0.04 0.04 0.2 0.02 0.01 0.20 0.03 0.0005 440 ℃ Grade 2 70-80 Not Occurred Invention steel 11 0.04 0.04 0.2 0.04 0.01 0.20 0.03 0.0005 440 ℃ Grade 2 60-70 Not Occurred Invention steel 12 0.04 0.04 0.2 0.06 0.01 0.20 0.03 0.0005 440 ℃ Grade 2 45-55 Not Occurred Invention steel

40-65 is suitable for plating adhesion amount, since the plating adhesion amount is less than 40, corrosion resistance is inadequate, and when it exceeds 65, the plating layer becomes excessively thick, the adhesiveness of the plating layer itself deteriorates, and appearance deteriorates.

Powdering is to determine whether the plating layer is cracked during processing and peeled off in a powder state.

Looking at Table 1 and Table 2, as in the case of Comparative Steel 1, when the impurities such as Si, P, S, Cu, Sn and the like contained less than 0.01wt%, the adhesion amount is good, and no surface defects occurred, Powdering property was also good. However, in an electric furnace process using scrap as a main raw material, Si, P, S, Cu, and Sn are difficult to control in the range of Comparative Steel 1, and even if controlled, it is not preferable because it causes an increase in steelmaking cost.

In the case of Comparative Steels 2 to 7, the plating properties decreased as the content of any one of Si, P, S, Cu, and Sn increased. From this, it can be seen that the impurity element of the electric furnace process causes the plating adhesion amount to increase after plating bath deposition.

In the case of Comparative Steel 2, overplating occurred as the Si content increased, and the surface defect occurred according to the increase of the Si content. In the case of Comparative Steel 3, the overplating occurred as the Cu content increased. As a result of over plating, surface defects were also generated.

Comparing Comparative Steel 5 and Comparative Steel 6, overplating occurs as the content of Cu and Sn increases, but the degree of overplating is further increased when the plating temperature of the steel sheet is high.

On the other hand, in the invention steel 8 to invention steel 12, even if the content of any one or more of Si, P, S, Cu, Sn increased the plating properties by the addition of P and B. However, in the case of Comparative Steel 7, even if P and B were added, when the P content was low, the coating temperature was increased due to the high plating temperature, and thus surface defects occurred.

On the other hand, Figure 1 is a schematic diagram showing the intermetallic compound formation reaction between Fe, Zn according to the addition of Al to P, B and the plating bath.

Figure 1 (a) is a schematic diagram corresponding to Comparative Steel 5 of Table 1, P and B were not added to the scope of the present invention, the overplating and impurity segregation occurred.

1 (b) shows that P and B are added within the scope of the present invention, so that the pickling property is good, but Al is not added to the plating bath to cause overplating. In this case, it can be said that overplating occurred due to the rapid reaction between Fe and Zn.

1 (c) illustrates that Al is added to the plating bath, but impurity elements are concentrated on the surface of the hot-rolled steel sheet due to the non-addition of P and B to form a non-uniform condition of the Fe-Al reaction, thereby causing overplating and segregation. .

Figure 2 (d) is a schematic diagram corresponding to the invention steel 8 to invention steel 12 of Table 1, P improves pickling properties to give uniform plating conditions to the entire steel sheet, B prevents P segregation, plating Al added to the bath forms a FeAl ₅ reaction inhibiting layer to prevent overplating.

As can be seen in Figure 2, P, B is added, it can be seen that the appearance surface of the hot-rolled steel sheet after hot-dip galvanizing (c) in which Al is added to the plating bath. Here, (a) of FIG. 2 is the surface photograph which showed the comparative steel 1 of Table 1, (b) is the surface photograph which shows the comparative steel 5 of Table 1, (c) is the surface which showed invention steel 12 of Table 1 It is a photograph.

From the above test results, it can be seen that hot rolled steel sheet with excellent hot-dip galvanizing properties can be manufactured by adding P and B, controlling the plating temperature, and adding Al to the plating bath even if the electric furnace process using scrap as a main raw material is applied. Can be.

It is to be understood that the invention is not limited to the disclosed embodiments, but is capable of many modifications and alterations, all of which are within the scope of the appended claims. It is self-evident.

1 is a schematic diagram showing the intermetallic compound formation reaction between Fe, Zn according to the addition of Al to P, B and the plating bath.

Figure 2 is a photograph showing the surface after hot-dip galvanizing of the comparative steel and the inventive steel of Table 1.

Claims (7)

C: 0.001 to 0.04 wt%, Si: greater than 0 and 0.05 wt% or less, Mn: greater than 0 and 0.5 wt% or less P: 0.02 to 0.1 wt% B: 0.0003 to 0.001 wt% Hot rolled steel sheet having excellent hot-dip galvanizing characteristics, characterized by having an alloy composition of Fe and other unavoidable impurities. The method according to claim 1, The impurity is a hot rolled steel sheet having excellent hot-dip galvanizing properties, including S: greater than 0% 0.01wt%, Cu: greater than 0% and 0.20wt% or less, Sn: greater than 0% and 0.03wt% or less. C: 0.001 to 0.04 wt%, Si: greater than 0 and 0.05 wt% or less, Mn: greater than 0 and 0.5 wt% or less P: 0.02 to 0.1 wt% B: 0.0003 to 0.001 wt% Slabs with alloys of Fe and other unavoidable impurities Reheating at a temperature of 1180 ~ 1250 ℃, hot rolling the reheated slab and then wound at a temperature of 580 ~ 700 ℃ characterized in that the hot-rolled steel sheet excellent production method. The method according to claim 3, After the winding, the process of pickling and immersing in a plating bath to perform hot dip galvanizing, and the temperature of the hot rolled steel sheet drawn into the plating bath is 400 to 450 ° C. Manufacturing method. The method according to claim 4, The method of manufacturing a hot rolled steel sheet having excellent plating characteristics, characterized in that Al is added to the plating bath to prevent a rapid reaction between Fe-Zn. The method according to claim 5, Al concentration relative to the total plating solution in the plating bath is 0.10 ~ 0.12wt% method for producing a hot rolled steel sheet having excellent plating characteristics, characterized in that. The method according to any one of claims 3 to 6, The impurity is S: more than 0% 0.01wt%, Cu: 0% and more than 0.20wt%, Sn: more than 0% and 0.03wt% or less, the method of producing a hot rolled steel sheet excellent in hot-dip galvanizing properties.

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