KR101500048B1 - Method for manufacturing steel sheet having superior resistance to corrosion by sulfuric acid - Google Patents

Abstract

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains 0.01 to 0.07% of C, 1.0% or less of Si, 0.2 to 1.2% of Mn, 0.2 to 1.0% of Cu, 0.05 to 0.5% of Cr, 0.1% 0.001-0.1% of N, 0.001-0.12% of Na, 0.2% or less of Ca, the balance of iron (Fe) and other unavoidable impurities, 0.001-0.1% Ti, 0.001-0.1% Nb, : 0.001 to 0.1%, Sb: 0.3% or less, and Co: 0.2% or less; Continuously casting the steel material at a casting speed of 4.0 mpm or more to produce a slab; Subjecting the slab to rough rolling to 950 to 1100 占 폚; Reheating and heating to 1000 to 1150 占 폚; Finishing rolling at an Ar3 transformation point or more; And coiling at 500 to 700 占 폚 after the continuous cooling, thereby producing a steel material excellent in sulfuric acid corrosion resistance.
According to the present invention, it is possible to produce sulfuric acid-resistant corrosion resistant steel which has no surface defects due to cracking and can improve the corrosion resistance by the thin slab method (hereinafter referred to as "high mill").

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a steel sheet having excellent sulfuric acid corrosion resistance,

The present invention relates to a method for producing a steel sheet excellent in sulfuric acid corrosion resistance.

Generating facilities usually produce sulfuric acid and hydrochloric acid by reacting with exhaust water containing sulfur dioxide and chlorine gas generated by combustion of fossil fuel such as coal or petroleum in sulfuric acid or sulfuric acid-hydrochloric acid complex atmosphere, It has a serious effect on corrosion. Generally, sulfuric acid resistant steels have been known to add a large amount of Cu in steel to delay the corrosion rate in general in sulfuric acid and hydrochloric acid atmospheres.

Cu has a superior effect of delaying the sulfuric acid corrosion rate compared to other additive elements. However, since Cu added steel has a relatively low amount of Cu having a relatively low melting point, cracks are generated at the corners of the slab at the time of hot rolling, There is a problem that it is corroded earlier than other parts. In order to solve such problems, Ni is added but it is not a fundamental solution, and Ni is a problem of raising the manufacturing cost by an expensive alloy element.

The method for producing sulfuric acid corrosion resistant steel in conventional blast furnace processes as disclosed in Patent Documents 1 and 2 is a method in which a slab is cracked at the edge due to Cu liquefaction during high temperature (1200 ° C) reheating in a conventional hot rolling process In addition, it is difficult to avoid the problem that the material deviation in the width direction and the length direction is very large.

Japanese Patent Application Laid-Open No. 10-110237 Korean Unexamined Patent Publication No. 2007-0138183

An aspect of the present invention is to provide a steel sheet excellent in corrosion resistance to sulfuric acid which has no surface defects due to cracking and can improve corrosion resistance even though the cost of adding alloys is reduced, and a manufacturing method thereof.

However, the problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, one aspect of the present invention provides a method of manufacturing a semiconductor device, comprising: 0.01 to 0.07% of C, 1.0% or less of Si, 0.2 to 1.2% of Mn, 0.2 to 1.0% of Cu, (Excluding 0%), S: not more than 0.02%, N: not more than 0.02%, sol.Al: 0.005-0.12%, Ca: not more than 0.2% (Fe) and other unavoidable impurities, and contains at least one of 0.001 to 0.1% of Ti, 0.001 to 0.1% of Nb, 0.001 to 0.1% of V, 0.3% or less of Sb and 0.2% or less of Co Further comprising the steps of: Continuously casting the steel at a casting speed of 4.0 mpm or more to produce a slab; Subjecting the slab to rough rolling to 950 to 1100 占 폚; Reheating and heating to 1000 to 1150 占 폚; Finishing rolling at an Ar3 transformation point or more; And a step of cooling the steel sheet at 500 to 700 DEG C after the continuous cooling, thereby producing a steel sheet excellent in sulfuric acid corrosion resistance.

According to the present invention, it is possible to produce a sulfuric acid corrosion resistant steel which is free from surface defects due to cracking and can improve the corrosion resistance by the thin slab playing method (hereinafter referred to as high mill).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process drawing showing a process for producing a steel sheet having excellent sulfuric acid corrosion resistance according to an embodiment of the present invention. FIG.
2 is a SEM photograph of a surface of a steel sheet according to one embodiment of the present invention and one comparative example.

Hereinafter, a method of manufacturing a steel sheet having excellent sulfuric acid corrosion resistance according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The present invention relates to a method for producing a low alloy steel sheet excellent in corrosion resistance in a sulfuric acid atmosphere and a hot rolled steel sheet capable of improving corrosion resistance so as to be suitable for piping of a desulfurization and denitration facility of a thermal power plant with severe sulfuric acid corrosion, Lt; / RTI >

In the high mill process for producing a plate by a so-called thin slab process (hereinafter referred to as "high mill process"), a new steel process that has recently attracted attention, the temperature deviation in the width direction longitudinal direction of the strip is small, And the possibility of occurrence of cracks is very small because a high temperature hot rolling reheating process is not required. Therefore, it is a very beneficial process for manufacturing Cu-added corrosion resistant steel.

In addition, while Ni is essentially added in order to prevent cracking by Cu, the present invention is important to develop a steel which does not cause cracking even when expensive Ni is not added in continuous thin slab continuous rolling. In addition, it is possible to contribute to the improvement of the corrosion resistance by spheroidizing a trace amount of Ca-based oxide which is unevaporated by Ca addition. We also propose a sulfuric acid corrosion resistant steelmaking technology that has superior properties in the conventional blast furnace process, using the characteristics of the high - mill process.

As shown in Fig. 1, the process for producing a steel sheet excellent in sulfuric acid corrosion resistance according to the present invention is roughly performed in the order of continuous casting, rough rolling, reheating, finish rolling, cooling on a runout table, and winding.

For this purpose, the steel sheet preferably contains 0.01 to 0.07% of C, 1.0 to 1.0% of Si, 0.2 to 1.2% of Mn, 0.2 to 1.0% of Cu, 0.05 to 0.5% of Cr, (Excluding 0%), the balance iron (Fe) and other unavoidable impurities, and the content of Ti (Ti) is not more than 0.02%, N: not more than 0.02%, sol.Al: 0.005-0.12% 0.001 to 0.1% of Nb, 0.001 to 0.1% of V, 0.001 to 0.1% of V, 0.3% or less of Sb and 0.2% of Co or less.

The reason for limiting the numerical values of the above components will be described as follows. Hereinafter, it is necessary to pay attention that the content unit of each component is weight% unless otherwise stated.

C: 0.01% to 0.07%

C is an element added to secure the strength of the steel sheet. When the addition amount is less than 0.01%, the strength is too low to be used as a hot-rolled steel sheet for sulfuric acid steel, and the lower limit is set to 0.01%. In the case of 0.07% And the content thereof is limited.

Si: 1.0% or less (excluding 0%)

Si is an element to be added mainly for improving the strength and is added within the range of no scaling problem. If it exceeds 1.0%, the occurrence of surface defects and scaling due to the formation of silicon oxide is not easy, so the upper limit value is limited to 1.0%.

Mn : 0.2 to 1.2%

Mn is usually added to precipitate solid sulfur in manganese sulfide as a manganese sulfide to prevent hot shortness due to solid solution sulfur. When the Mn content is less than 0.2%, the strength is too low to be used as a hot-rolled steel sheet. When the Mn content is less than 0.2%, the Mn content is lower than the Mn content. In particular, if it exceeds 1.2%, there is a high possibility that problems such as weldability and hot rolling property are likely to occur. Therefore, the content of Mn is preferably limited to 0.2 to 1.2%.

Cu : 0.2 to 1.0%

Cu is an element which must be added in consideration of the sulfuric acid corrosion property. When the content is more than 0.2%, the effect of the corrosion resistance is remarkable. If it exceeds 1.0%, the corrosion resistance is less effective than the increase of the addition amount. There is a high possibility of cracking due to Cu liquefaction, and it is preferable to set the upper limit to 1.0%.

Cr : 0.05 to 0.5%

In case of Cr, it is an element that greatly improves the sulfuric acid corrosion property when added with Cu. When the content is less than 0.05%, the effect of the corrosion resistance is greatly deteriorated. When the content exceeds 0.5%, the effect of improving the corrosion resistance is less than the increase of the addition amount, and it is not only economical but also the Cr-based carbide is formed in the crystal grain. And it is economically disadvantageous because the cost of ferroalloy is high, so that the upper limit is preferably set at 0.5%.

P: 0.1% or less (excluding 0%)

The P component is a very effective element mainly used for securing strength. In the high-mill process, the P component is usually controlled to be 0.02% or less at the level of the tramp element. It is effective to prevent cracking by keeping the P content as low as possible. However, in order to secure the strength, the component range that minimizes the risk of cracking Setting is important. When the content exceeds 0.1%, the possibility of cracking due to crystal grain boundary P segregation increases greatly, so it is desirable to control the content to 0.1% or less.

S: not more than 0.02%

The S and N components are impurity elements managed by the tramp element in the present invention. The lower the content, the better the surface quality. However, when the content exceeds 0.02%, the content is limited because the surface quality deteriorates sharply.

N: 0.02% or less

The S and N components are impurity elements managed by the tramp element in the present invention. The lower the content, the better the surface quality. However, when the content exceeds 0.02%, the content is limited because the surface quality deteriorates sharply.

left . Al : 0.005-0.12%

sol.Al is an effective component that combines with oxygen in steel to conduct deoxidation. If the content is less than 0.005%, the above effects can not be secured. On the other hand, when the content exceeds 0.12%, the effect is saturated and the production cost is increased. Therefore, the content of the soluble Al is limited to 0.005 to 0.12% desirable.

Ca: 0.2% or less (excluding 0%)

Ca has a very high affinity with oxygen (O) in the steel and exists in the form of oxides or emulsions. It controls the form and distribution of nonmetal inclusions and contributes to spheroidization of inclusions, thereby being effective in preventing cracks and forming Cr- It is an element to improve. In the present invention, Ca is effective even in the case of adding a trace amount of Ca, but when it exceeds 0.2%, Ca acts as an impurity element and is disadvantageous from an economical point of view.

0.001 to 0.1% of Nb, 0.001 to 0.1% of V, 0.3% or less of Sb, and 0.2% or less of Co is further added to the steel to be formed as described above .

Ti : 0.001 to 0.1%, Nb : 0.001 to 0.1%, V: 0.001 to 0.1%

Ti, Nb and V are effective elements for increasing the strength and grain size of the steel sheet. When the content of the above elements is less than 0.001%, it is difficult to secure such effect. When the content exceeds 0.1%, ferrite ductility may be deteriorated due to an increase in production cost and excessive precipitates. Therefore, the content thereof is preferably limited to 0.001 to 0.1%.

Sb : Not more than 0.3%

Sb is an element improving the corrosion resistance of the Cu-Cr system. Normally, the Cu-Cr composite system also exhibits excellent corrosion resistance. However, in a steel grade requiring higher corrosion resistance, the maximum content is limited to 0.3% because the corrosion resistance is improved when Sb is added within a range in which cost rise is permitted.

Co : Not more than 0.2%

Co is also an element that helps improve corrosion resistance, so the maximum content is limited to 0.2% in order to further improve the corrosion resistance

The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.

Hereinafter, a method of manufacturing the steel sheet of the present invention will be described.

The manufacturing process of the present invention is a high mill process in which rough rolling is performed immediately after the end of the performance stage, and then the strip is uniformly heated and finished in an induction heater.

Specifically, the steel constituted by the above components is continuously cast at a casting speed of 4.0 mpm or more to produce a slab. (The peripheral speed means mpm is m / min)

The reasons for limiting the casting speed to 4.0 mpm or more in continuous casting of the steel into slabs are as follows. That is, in the case of the thin slab performance and continuous continuous rolling process, there is a risk that segregation may occur from the casting as the casting speed is slower because the tramp elements are larger than the blast furnace. If the segregation occurs, Because of this size, the speed was limited to over 4.0mpm. On the other hand, the higher the rate, the higher the productivity.

Subsequently, the cast thin slab is roughly rolled in a roughing mill so that the roughly rolled bar is at 950 to 1100 ° C. However, in the present invention, the slab temperature at the inlet side of the rough rolling mill is controlled at 1100 ° C or less, thereby preventing Cu liquefaction It is advantageous that Ni is not added. If the surface temperature of the roughly rolled bar is less than 950 DEG C, a large rolling load occurs during finish rolling, and if the temperature exceeds 1100 DEG C, not only the energy cost for temperature increase is increased but also the surface scale defect Is increased, it is preferable to limit the temperature to the range of 950 to 1100 占 폚.

Subsequently, reheating and boiling are carried out at 1000 to 1150 占 폚.

The reason for reheating and heat treatment is that when the temperature is lowered at rolling, the rolling load becomes higher, so reheating is required at a temperature of at least 1000 ° C., and when the temperature exceeds 1150 ° C., energy consumption during heating is large and productivity is deteriorated. do

The bar is then rolled in a tandem-type rolling machine at an Ar3 transformation point or higher to minimize the deviation of the material in the coil by rolling in a single phase rather than a composite phase. When the finishing rolling temperature is lower than the Ar3 transformation point, the possibility that the ferrite structure is mixed is increased and the hole determinability is lowered. Therefore, the temperature is limited to the Ar3 transformation point or higher.

The rolled strip is rolled at 500 to 700 DEG C after continuous cooling in a run-out table. When the temperature is less than 500 ° C, the shape is poor due to the rapid cooling and the material deviation in the width direction is large. When the temperature exceeds 700 ° C, pearlite is formed and cracks and material deviation increase. Respectively.

Hereinafter, the present invention will be described in detail with reference to Examples. However, the following examples are only for illustrating the present invention in more detail and do not limit the scope of the present invention.

[ Example ]

A steel having the composition shown in Table 1 was prepared.

Table 2 shows the yield strength, the occurrence of surface cracks, and the corrosion resistance of each of the above steels after manufacturing the hot-rolled sheets by the thin slab method under the process conditions shown in Table 2.

Steel grade Playing speed
(mpm) After rough rolling
Temperature (℃) Reheating /
Supplementary heat temperature
(° C) Finish rolling
Temperature (℃) Yield strength
(MPa) Surface crack
Length (mm) Corrosion loss
(mg) Remarks One 5.5 993 1063 885 401 0 32 Inventory 1 2 5.7 985 1065 882 399 0 35 Inventory 2 3.5 987 1075 889 401 0.1 34 Comparative Example 1 3 5.8 965 1083 887 411 0 28 Inventory 3 4 5.5 1003 1092 891 423 0 29 Honorable 4 7.1 963 1075 889 421 0 31 Inventory 5 5 6.8 987 1088 895 456 0 18 Inventory 6 7.2 985 1079 896 449 0 28 Honorable 7 6 6.4 976 1088 876 451 0 35 Honors 8 7 6.2 987 1035 865 365 0 35 Proposition 9 8 6.3 985 1056 861 374 0 28 Inventory 10 9 6.1 968 1029 856 472 0 33 Exhibit 11 10 5.8 993 1085 875 462 0.5 104 Comparative Example 2 11 7.1 961 1096 872 461 0.3 98 Comparative Example 3

In the present invention, the higher the yield strength, the more advantageous it is. However, in the present patent, if it is maintained at 350 MPa or more, it can meet customer's demand.

In the prior art, Ni is added in an amount of 50% based on the amount of Cu in order to prevent cracking due to Cu liquefaction. In the present invention, as can be seen from Table 1, cracks are not generated without adding expensive Ni Component-based design. Such cracking due to Cu liquefaction usually occurs when the Cu-based oxide is liquefied and penetrates into the grain boundary of the steel during reheating at 1200 ° C during hot rolling of the blast furnace, thereby causing cracks. However, in the thin slab continuous casting, rolling is continuously performed after casting, so that high-temperature reheating is not required and the tendency of crack occurrence is reduced. In addition to the advantages of the thin slab, it is possible to produce a steel free from cracks by controlling a trace amount of components such as Ca even without adding an expensive Ni component.

In Comparative Example 1 of Table 2, the possibility of cracking was confirmed by changing the thin slab circumferential speed, and steel type 2 belonging to the steel material component range of the present invention was examined. However, cracks were observed by a scanning electron microscope because the strain was too low. Table 2 shows the temperature after the rough rolling (RDT), the induction heater / boiling temperature, and the finish rolling temperature. The corrosion loss was measured and cracks were observed for each condition.

The corrosion rate was measured by immersing in a 50 vol% sulfuric acid solution at 70 ° C for 1 hour. The lower the amount of corrosion loss, the better. Crack observations were averaged using a scanning electron microscope (SEM) to determine the depth of crack penetration from the surface into the interior.

In Table 2, it can be seen that Comparative Example 2 and Comparative Example 3 using the comparative steels were in the case where Cr or Ca was not added and the corrosion characteristics were very favorable.

Fig. 2 is a SEM image of the surface of the sample. As a result of observing Inventive Example 1 (Fig. 2 (a)), no crack was observed, but Comparative Example 2 (Fig. 2 (b)) shows cracks.

2 (a)). In Comparative Example 2 (Fig. 2 (b)), cracks were observed in the inside of the base iron. However, Is generated. It is considered that this is due to the coarse spheroidization of the oxide during the Ca addition, and the crack propagation due to the Cu liquid phase was effectively reduced. In the photograph of FIG. 2, the lower part is a photograph of the surface image, and the upper part shows the component distribution of the image. In FIG. 2 (b) It is understood that it provides.

Claims (2)

The steel sheet according to any one of the above items (1) to (3), wherein the steel sheet contains 0.01 to 0.07% of C, 1.0% or less of Si (excluding 0%), 0.2 to 1.2% of Mn, 0.2 to 1.0% of Cu, 0.05 to 0.5% (Excluding 0%), S: not more than 0.02%, N: not more than 0.02%, sol.Al: 0.005-0.12%, Ca: not more than 0.2% (excluding 0%), the balance iron (Fe) Preparing a steel further comprising at least one of 0.001 to 0.1% of Ti, 0.001 to 0.1% of Nb, 0.001 to 0.1% of V, 0.3% or less of Sb and 0.2% of Co or less;
Continuously casting the steel at a casting speed of 4.0 mpm or more to produce a slab;
Subjecting the slab to rough rolling to 950 to 1100 占 폚;
Reheating and heating to 1000 to 1150 占 폚;
Finishing rolling at an Ar3 transformation point or more; And
And then winding the steel sheet at 500 to 700 占 폚 after the continuous cooling, thereby producing a steel sheet excellent in sulfuric acid corrosion resistance. The method according to claim 1,
Wherein the thickness of the slab is 30 to 150 mm.

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