KR20160078845A - Steel sheet having excellent resistance and excellent low temperature toughness to hydrogen induced cracking, and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a thick steel sheet having excellent low temperature toughness and excellent resistance to hydrogen induced cracking, and a method for manufacturing the same, wherein the thick steel sheet comprises: 0.12-0.20 wt% of C; 0.1-0.5 wt% of Si; 1.0-2.0 wt% of Mn; an amount equal to or less than 0.03 wt% of P; an amount equal to or less than 0.003 wt% of S; an amount equal to or less than 0.06 wt% of Al; an amount equal to or less than 0.01 wt% of N; 0.05-0.5 wt% of Cr; 0.05-0.4 wt% of Mo; an amount equal to or less than 0.02 wt% of Nb; an amount equal to or less than 0.02 wt% of Ti; 0.005-0.04 wt% of V; and the remainder consisting of Fe and inevitable impurities.

Description

TECHNICAL FIELD [0001] The present invention relates to a steel plate having excellent low-temperature toughness and hydrogen-induced cracking resistance, and a method of manufacturing the same.

The present invention relates to a steel plate having excellent low-temperature toughness and hydrogen organic cracking resistance, and a method for producing the same.

Plate steel for guaranteeing hydrogen organic cracking according to API (American Petroleum Institute) standards is used for line pipes and process pipes, and the required properties of steel are determined according to the material to be stored in the container and the environment of use. Therefore, in many cases, low-temperature toughness is required when the material to be treated by the steel material is low in temperature or when it is used in cold regions. In addition, when applied to a process pipe of a refinery, most of the cases are used at a high temperature, so that a heat-treated pipe having little change in physical properties even at a high temperature is applied. In recent years, there has been an increasing demand for steel materials required for crude oil refining facilities due to the development of the energy industry. In view of the environment in which each facility is used, a steel material Demand is increasing.

Generally, the steel toughness of the steel is lowered as the use temperature is lowered, and cracks are easily generated even in a weak impact, and the steel has a great influence on the stability of the material. Therefore, a steel having a low operating temperature controls components and microstructure so that the toughness is not lowered even at a low temperature. As a typical method for increasing the low-temperature toughness, a method of minimizing the addition of impurities such as sulfur and phosphorus and appropriately adding an amount of alloying elements such as Ni, which helps improve the low-temperature toughness, is used.

The following Patent Document 1 proposes a technique for a steel material for a pressure vessel having a tensile strength of 600 MPa and excellent in toughness containing Ti and Ni.

Korean Patent Laid-Open Publication No. 2004-0021117

An object of the present invention is to provide a steel plate having excellent low temperature toughness and hydrogen organic cracking resistance and a method for producing the same.

A steel plate having excellent low-temperature toughness and hydrogen-organic cracking resistance according to an embodiment of the present invention is composed of 0.12 to 0.20 wt% of C, 0.1 to 0.5 wt% of Si, 1.0 to 2.0 wt% of Mn, 0.03 wt% 0.003 wt% or less of S, 0.06 wt% or less of Al, 0.01 wt% or less of N, 0.05 to 0.5 wt% of Cr, 0.05 to 0.4 wt% of Mo, 0.02 wt% or less of Nb, , V: 0.005 to 0.04% by weight, the balance Fe and unavoidable impurities.

A method for producing a steel plate having excellent low-temperature toughness and hydrogen-organic cracking resistance according to an embodiment of the present invention comprises the steps of: C: 0.12 to 0.20 wt%; Si: 0.1 to 0.5 wt%; Mn: 1.0 to 2.0 wt% 0.003 wt% or less of Al, 0.06 wt% or less of Al, 0.01 wt% or less of N, 0.05 to 0.5 wt% of Cr, 0.05 to 0.4 wt% of Mo, 0.02 wt% or less of Nb, 0.02% by weight or less, V: 0.005 to 0.04% by weight, the balance Fe and unavoidable impurities, heating the slab to a temperature of 1100 to 1300 ° C, heating the slab to a finish rolling temperature 950 캜 or higher and a cumulative rolling reduction of 40% or higher, secondarily heating the hot-rolled steel sheet at a temperature of Ac 3 to Ac 3 + 80 캜, heating the secondarily heated steel sheet at a cooling rate 20,000 / (thickness of the steel sheet) ² to 60000 / (thickness of steel) a step of cooling the ^second quenching treatment and the quenching the treated steel sheet And a step of tempering at a temperature of 580 ~ 700 ℃.

The steel plate according to one embodiment of the present invention is excellent in low temperature toughness and hydrogen organic cracking resistance.

1 is a graph showing the Charpy impact toughness according to the test temperature of a steel material according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are also provided to more fully describe the present invention to those skilled in the art.

A steel plate having excellent low-temperature toughness and hydrogen-organic cracking resistance according to an embodiment of the present invention is composed of 0.12 to 0.20 wt% of C, 0.1 to 0.5 wt% of Si, 1.0 to 2.0 wt% of Mn, 0.03 wt% 0.003 wt% or less of S, 0.06 wt% or less of Al, 0.01 wt% or less of N, 0.05 to 0.5 wt% of Cr, 0.05 to 0.4 wt% of Mo, 0.02 wt% or less of Nb, , V: 0.005 to 0.04% by weight, the balance Fe and unavoidable impurities.

The steel plate having excellent low-temperature toughness and hydrogen-organic cracking resistance may have tempered bainite or tempered martensite phase as a base and the area fraction of ferrite may be less than 10%.

In addition, at least one of Ti-based, Nb-based and Ti-Nb composite-based carbonitrides may be present within the upper and lower portions of 5 mm from the center of the thickness of the steel, and the Ti-, Nb- and Ti- The length of the longest side of the carbonitride may be 10 탆 or less.

Further, it may have a thickness of 30 mm or more and a tensile strength of 500 MPa or more.

Component  And composition range

Hereinafter, the composition of the steel plate and the range of the composition of the steel plate excellent in cold toughness and hydrogen organic cracking resistance according to the embodiment of the present invention will be described.

C (carbon): 0.12-0.20 wt%

C plays a role in increasing the strength by being dissolved in the steel or forming a precipitation phase.

If the C content is less than 0.12% by weight, it is difficult to ensure the strength and the weld heat affected zone is softened more than necessary. If the C content exceeds 0.20% by weight, there is a problem that the low temperature impact toughness of the steel sheet is deteriorated and the weldability is lowered. Therefore, the content of C is preferably 0.12 to 0.20% by weight.

Si (Silicon): 0.1 to 0.5 wt%

Si not only acts as a deoxidizer in the steelmaking process but also enhances the strength of the steel.

If the Si content is less than 0.1 wt%, the manufacturing cost increases. If the Si content exceeds 0.5 wt%, the impact toughness of the material deteriorates, and the weldability is deteriorated, causing scale peeling at the time of rolling. Therefore, the content of Si is preferably 0.1 to 0.5% by weight.

Mn (Manganese): 1.0 to 2.0 wt%

Mn is an element which improves the incombustibility of the steel without impairing impact toughness.

It is preferable that 1.0 wt% or more of Mn is added in order to sufficiently exhibit the property of improving the incombustibility of the steel without impairing impact toughness. When the content of Mn exceeds 2.0 wt%, center segregation occurs and impact toughness is lowered, and the hardenability of the steel is increased and the weldability is deteriorated. In addition, Mn-centered segregation is also a factor causing hydrogen-organic cracking. Therefore, the content of Mn is preferably 1.0 to 2.0% by weight.

P (phosphorus): not more than 0.03% by weight

P is an impurity element.

When the content of P exceeds 0.03% by weight, the weldability remarkably decreases and the impact toughness deteriorates. Therefore, the content of P is preferably limited to 0.03 wt% or less. In particular, from the viewpoint of low-temperature impact toughness, 0.01 wt% or less is more preferable.

S (sulfur): not more than 0.003 wt%

S is an impurity element.

If the content of S exceeds 0.003% by weight, there is a problem that the ductility, impact toughness and weldability of the steel are deteriorated. Therefore, it is preferable to limit the content of S to 0.03% by weight or less. Particularly, S is combined with Mn to form MnS inclusions to lower the impact resistance at low temperatures of the steel, and therefore, it is more preferably 0.002 wt% or less.

Al (Aluminum): not more than 0.06% by weight

Al acts as a deoxidizer to remove oxygen by reacting with oxygen present in molten steel. It is added to ensure sufficient deoxidizing power in steel.

When the content of Al exceeds 0.06% by weight, oxide-based inclusions are formed in a large amount and the impact toughness of the material is deteriorated. Therefore, the content of Al is preferably 0.06% by weight or less.

N (nitrogen): not more than 0.01% by weight

N is difficult to completely remove industrially from the steel, so the upper limit is 0.01 wt%, which is an allowable range in the manufacturing process. N forms nitrides with Al, Ti, Nb, V and the like to interfere with the growth of austenite grains to improve toughness and improve strength. When the content exceeds 0.01% by weight, N in the solid state is present and low temperature toughness There is a problem that it gets worse. Therefore, it is preferable to limit it to 0.01% by weight.

Cr (Chrome): 0.05 to 0.5 wt%

Cr is dissolved in the austenite during the process of reheating the slab, thereby increasing the incombustibility of the steel.

It is preferable that Cr is added in an amount of 0.05 wt% or more in order to sufficiently exhibit the effect of increasing the entrapping property of the steel material. If the content of Cr exceeds 0.5% by weight, the weldability is deteriorated. Therefore, the content of Cr is preferably limited to 0.05 to 0.5% by weight.

Mo (Molybdenum): 0.05 to 0.4 wt%

Mo plays a role in increasing the incombustibility of the steel.

It is preferable that Mo is added in an amount of 0.05% by weight in order to sufficiently exhibit the increasing effect of the ingot property of the steel material. If the content of Mo exceeds 0.4% by weight, impact toughness forms a structure for heating, deteriorates weldability, and causes a problem of brittleness of the template. Therefore, the content of Mo is preferably 0.05 to 0.4% by weight.

Nb (Niobium): not more than 0.02% by weight

Nb is dissolved during the reheating of the slab and inhibits the growth of austenite grains during hot rolling and then precipitates to improve the strength of the steel.

If the content of Nb exceeds 0.02% by weight, the austenite grains are refined and the ingot of the steel is lowered. Therefore, the content of Nb is preferably 0.02 wt% or less. From the viewpoint of low-temperature toughness, it is more preferable to add 0.01% by weight or less.

Ti (Titanium): 0.02% by weight or less

Ti reacts with N during reheating of the slab to inhibit the growth of austenite grains in the form of TiN.

If the content of Ti exceeds 0.02% by weight, the low-temperature impact toughness of the heat-treated material deteriorates. Therefore, the content of Ti is preferably 0.02% by weight. From the viewpoint of low-temperature toughness, it is more preferable to add 0.01% by weight or less.

V (vanadium): 0.005 to 0.04 wt%

V increases the incombustibility of the steel material and precipitates during reheating of the heat treatment material to prevent the strength from dropping.

V is added in an amount of 0.005% by weight or more in order to sufficiently exhibit the effect of preventing the increase of the incombustibility and the decrease in strength. If the content of V is more than 0.04% by weight, hydrogen organic cracking is caused and deterioration of low temperature impact toughness and hydrogen organic cracking resistance is caused. Therefore, the content of V is preferably 0.005 to 0.04% by weight.

According to the description of the component system and the composition range, according to the embodiment of the present invention, it is possible to provide a thick plate steel excellent in low temperature toughness and hydrogen organic cracking resistance without containing commonly used Ni.

Further, the steel plate having excellent resistance to hydrogen organic cracking according to the embodiment of the present invention has at least one of tempered bainite and tempered martensite phase as its base structure, and may contain less than 10% of ferrite in an area fraction have.

If the base structure is composed of ferrite and pearlite, there is a problem that not only the strength is low but also the hydrogen organic cracking resistance and low temperature toughness are deteriorated. Therefore, the steel material according to the embodiment of the present invention has tempered bainite (including acicular ferrite) And a single phase or a composite phase on tempered martensite.

Further, ferrite having an area fraction of less than 10% may be included. If the area fraction of ferrite exceeds 10%, there is a problem that the strength of the steel decreases. Therefore, the ferrite area fraction is preferably 10 percent by area or less.

Due to the above-described structure characteristics, the steel plate according to the embodiment of the present invention is excellent in low-temperature toughness and hydrogen organic cracking resistance, and can have a high tensile strength of 500 MPa or more at a thickness of 30 mm or more.

In addition, at least one of Ti-based, Nb-based and Ti-Nb composite-based carbonitrides may exist within 5 mm from the center of the thickness of the steel plate according to the embodiment of the present invention, And the length of the longest side of the Ti-Nb composite carbonitride can be 10 m or less.

The Ti-based, Nb-based and Ti-Nb complex-based carbonitrides are formed of Ti or Nb elements contained in the steelmaking process. The Ti-based, Nb-based, and Ti-Nb composite-based carbonitrides are precipitates which deteriorate the low-temperature impact toughness at the center of the after-treatment material.

Manufacturing method

Hereinafter, a method for producing a steel plate having excellent low temperature toughness and hydrogen organic cracking resistance according to an embodiment of the present invention will be described.

A method for producing a steel plate having excellent low-temperature toughness and hydrogen-organic cracking resistance according to an embodiment of the present invention comprises the steps of: C: 0.12 to 0.20 wt%; Si: 0.1 to 0.5 wt%; Mn: 1.0 to 2.0 wt% 0.003 wt% or less of Al, 0.06 wt% or less of Al, 0.01 wt% or less of N, 0.05 to 0.5 wt% of Cr, 0.05 to 0.4 wt% of Mo, 0.02 wt% or less of Nb, 0.02% by weight or less, V: 0.005 to 0.04% by weight, the balance Fe and unavoidable impurities, heating the slab to a temperature of 1100 to 1300 ° C, heating the slab to a finish rolling temperature 950 캜 or higher and a cumulative rolling reduction of 40% or higher, secondarily heating the hot-rolled steel sheet at a temperature of Ac 3 to Ac 3 + 80 캜, cooling the reheated steel sheet at a cooling rate of 20000 / (thickness of the steel sheet) ² to 60000 / (thickness of the steel sheet) cooling the ^second and the cooled steel sheet at a temperature of 580 ~ 700 ℃ And a step of tempering treatment.

The first heating step

The primary heating step is a step of heating the steel slab to a high temperature for hot rolling.

When the heating temperature exceeds 1300 ° C, the austenite grains are coarsened and the low-temperature impact toughness of the steel is lowered. If the heating temperature is lower than 1100 ° C, there is a problem that the alloy element availability ratio is lowered. Therefore, the heating temperature is preferably 1100 to 1300 ° C. In terms of low temperature impact toughness, it is preferably 1100 to 1180 占 폚.

Hot rolling step

The slab subjected to the heating process is subjected to a hot rolling step of finishing rolling at 950 DEG C or higher.

However, if the austenite grains are refined, the ingotability of the steel is lowered. Therefore, it is necessary to add an additional alloying element to improve the strength of the steel. When the finishing rolling temperature is lower than 950 占 폚, it is difficult to secure the ingotability of the steel material and it is difficult to secure the strength of the steel material having a thickness of 30 mm or more. Therefore, the finishing rolling temperature is preferably 950 DEG C or higher. The diameter of the austenite grains can be controlled to 30 탆 or more.

On the other hand, the cumulative rolling reduction during rolling may be 40% or more. When the cumulative rolling reduction is 40% or less, recrystallization by rolling does not occur at the central portion of the steel sheet, thereby deteriorating the low temperature toughness of the center portion of the steel sheet. Therefore, the cumulative rolling reduction is preferably 40% or more.

Cooling step

The hot-rolled steel sheet is air-cooled. When water-cooling a steel sheet at a high temperature by hot rolling, there is a problem of shape deformation and productivity resistance of the steel sheet.

Secondary heating stage

The steel sheet is secondarily heated to a temperature of Ac 3 to Ac 3 + 80 ° C. The steel sheet that has been cooled after the hot rolling is secondarily heated to austenite region in the range of Ac3 to Ac3 + 80 占 폚. The secondary heating is performed for the quenching treatment of the steel sheet.

When the reheating temperature is lower than Ac3, ferrite and pearlite formed during air cooling do not undergo complete transformation to the austenite phase. When the secondary heating temperature exceeds Ac3 + 80 占 폚, the austenite grains are coarsened, . Therefore, the secondary heating temperature is preferably Ac3 to Ac3 + 80 占 폚.

Submission  Processing step

The secondary heated steel sheet is cooled at a cooling rate of 20000 / (thickness of the steel sheet) ² to 60000 / (thickness of the steel sheet) ² , and quenched.

If the quenching cooling rate is less than 20000 / (steel sheet thickness) ² (mm ² ), it is difficult to secure sufficient strength. If the quenching cooling rate exceeds 60000 / (steel sheet thickness) ² (mm ² ), it will cause shape deformation and productivity resistance of the steel sheet. Therefore, the quenching cooling rate is preferably 20000 / (steel sheet thickness) ² to 60000 / (steel sheet thickness) ² .

Stage processing step

The steel sheet thus quenched is sintered at a temperature of 580 to 700 ° C. The bake treatment is a heat treatment method for recovering low-temperature toughness by reheating the steel sheet cured by the quenching treatment to a certain temperature range and air-cooling it.

If the annealing temperature is lower than 580 占 폚, low-temperature toughness deteriorates. If the annealing temperature exceeds 700 ° C, there is a problem that the phase transformation occurs to the anomaly of the ferrite-austenite and the strength is reduced. Therefore, the bake temperature is preferably 580 to 700 ° C. Further, in order to ensure the optimum combination of low temperature toughness and strength, it is more preferable to set the blanket temperature to 600 to 680 캜. The sanded steel sheet is then preferably air-cooled.

Example

The slabs having the composition shown in Table 1 were heated, hot-rolled and reheated to prepare steel sheets. In the following Tables 1 to 3, the inventive steels are in conformity with the composition, manufacturing conditions and the tissue conditions of the present invention, and the comparative steels are out of at least one of the composition, the manufacturing conditions and the tissue conditions of the present invention.

The inventive steels and comparative steels of Table 1 below were prepared by the same process except that the compositions were according to the composition of Table 1 and the manufacturing process conditions of Table 2. [ Specifically, the inner steel sheet of the invention steels and the comparative steels were hot rolled at a rolling temperature of the following Table 2 after heating the slab having the composition shown in the following Table 1 at the primary heating temperature of Table 2, followed by air cooling.

The air-cooled steel sheet was heated to the secondary heating temperature shown in Table 2 below, cooled to the quenching cooling rate shown in Table 2, and quenched.

Crack type opening sensitivity (CLR) and hydrogen organic cracking sensitivity (CTR) were measured for the steel sheets prepared as described above with respect to the maximum length of carbonitride, pearlite area fraction, distance between Al-Ca inclusions, tensile strength, low temperature impact toughness, CTOD Length Ratio) was measured, and the results are shown in Table 3 below.

The longest length of the carbonitride was determined by cutting the specimen and observing the cut surface to examine the longest sides of the Ti-based, Nb-based and Ti-Nb-based carbonitrides present within the upper and lower 5 mm from the center of the specimen, The area fraction and the distance between the Al-Ca inclusions were obtained by observing the microstructure of the steel sheet. The Hydrogen Organic Cracking Sensitivity (CLR) is obtained by calculating the percentage ratio of the length of hydrogen organic cracking to the total length of the specimen after testing in accordance with NACE (National Association of Corrosion Engineers). The CTOD is a characterization at -10 ° C.

The values listed in Table 1 below refer to weight percent. The comparative steels 1 to 3 are comparative examples in which the maximum length of the carbonitride in Table 3 is out of the range of Examples of the present invention and Comparative steels 2 to 8 are comparative examples in which the composition shown in Table 1 is out of the examples of the present invention, To 12 are comparative examples in which the process conditions described in Table 2 are out of the range of Examples of the present invention.

C Si Mn P S Al N Cr Mo Nb Ti V Ni Inventive Steel 1 0.14 0.21 1.44 0.008 0.001 0.035 0.005 0.31 0.21 0.007 0.004 0.03 0 Invention river 2 0.13 0.32 1.55 0.008 0.001 0.029 0.007 0.25 0.15 0.006 0.01 0.02 0 Comparative River 1 0.14 0.25 1.44 0.008 0.0008 0.041 0.005 0.19 0.14 0.006 0.008 0.02 0 Comparative River 2 0.22 0.22 1.2 0.008 0.0008 0.041 0.005 0.27 0.22 0.014 0.013 0.012 0 Comparative Steel 3 0.15 0.25 2.21 0.008 0.0009 0.033 0.005 0.18 0.09 0.013 0.01 0.015 0 Comparative Steel 4 0.16 0.24 1.43 0.008 0.0008 0.029 0.007 0.27 0.12 0.005 0.03 0.22 0.25 Comparative Steel 5 0.14 0.22 1.65 0.007 0.001 0.038 0.007 0.55 0.22 0.004 0.013 0.23 0 Comparative Steel 6 0.14 0.25 1.44 0.008 0.0008 0.041 0.005 0.19 0 0.008 0.011 0.25 0 Comparative Steel 7 0.14 0.18 1.25 0.008 0.0009 0.025 0.005 0.2 0.16 0.045 0.009 0.33 0.19 Comparative Steel 8 0.16 0.22 1.36 0.009 0.0008 0.018 0.004 0.22 0.17 0.014 0.01 0.49 0 Comparative Steel 9 0.15 0.21 1.65 0.008 0.001 0.035 0.005 0.31 0.12 0.012 0.011 0.022 0 Comparative Steel 10 0.15 0.21 1.65 0.008 0.001 0.035 0.005 0.31 0.12 0.012 0.011 0.022 0 Comparative Steel 11 0.15 0.21 1.65 0.008 0.001 0.035 0.005 0.31 0.12 0.012 0.011 0.022 0 Comparative Steel 12 0.15 0.21 1.65 0.008 0.001 0.035 0.005 0.31 0.12 0.012 0.011 0.022 0

thickness
(mm) Primary heating temperature
(° C) Finishing rolling temperature
(° C) Ac3
(° C) Second heating temperature
(° C) Quenching cooling rate
(° C / sec) Sorrow temperature
(° C) Inventive Steel 1 85.00 1170 1010 842 900 5 620 Invention river 2 43.00 1165 985 845 909 19 613 Comparative River 1 70.00 1165 990 842 915 7 615 Comparative River 2 40.00 1152 998 825 885 22 596 Comparative Steel 3 55.00 1145 982 824 884 12 635 Comparative Steel 4 53.00 1144 975 840 900 12 672 Comparative Steel 5 60.00 1133 995 848 908 10 660 Comparative Steel 6 83.00 1121 996 848 908 5 655 Comparative Steel 7 65.00 1137 985 853 913 8 630 Comparative Steel 8 70.00 1122 970 857 917 7 633 Comparative Steel 9 73.00 1220 850 833 893 7 679 Comparative Steel 10 77.00 1122 1020 833 983 6 680 Comparative Steel 11 62.00 1122 996 833 895 4 645 Comparative Steel 12 44.00 1125 955 833 887 18 564

The longest length of carbonitride
(μm) Ferrite area fraction
(%) The tensile strength
(Mpa) Low temperature impact toughness
@ -80 ℃
(J) CTOD @ -10 ° C
(mm) Hydrogen organic crack
Sensitivity (CLR)
(%) Inventive Steel 1 0.6 1.2 575 251 3.5 0 Invention river 2 1.2 1.5 645 201 3.4 0 Comparative River 1 12.4 2.1 612 34 1.3 0 Comparative River 2 1.1 0.3 690 81 One 0 Comparative Steel 3 1.22 0.5 701 104 1.3 14 Comparative Steel 4 6.8 0.8 625 77 0.8 0 Comparative Steel 5 2.3 1.3 679 111 1.4 0 Comparative Steel 6 2.1 15.5 495 184 3.1 0 Comparative Steel 7 3.1 20.3 488 172 3 0 Comparative Steel 8 0.25 5.3 618 45 0.6 7.2 Comparative Steel 9 0.75 12.3 470 206 2.9 0 Comparative Steel 10 0.69 5.3 684 88 1.2 0 Comparative Steel 11 1.25 18.5 485 202 2.8 0 Comparative Steel 12 2.54 1.1 712 65 0.9 0

Referring to Tables 1 to 3, inventive steels 1 and 2 satisfy the following conditions of composition, range of composition, process conditions, and texture conditions according to the embodiment of the present invention, and have a tensile strength of 500 MPa or more, (CLR) is 0%, which indicates excellent hydrogen organic cracking resistance. In addition, it can be seen that the low-temperature impact toughness is 200 J or more and excellent low-temperature toughness.

On the other hand, comparative steels 1 to 8, which deviate from any of the component systems, component ranges and process conditions of the present invention, have tensile strengths less than 500 MPa, poor hydrogen organic cracking sensitivity (CLR) .

Meanwhile, FIG. 1 shows the results of the low-temperature impact toughness test of inventive steels 1 and 2, and shows the Charpy impact toughness according to the test temperature.

It can be seen from the Tables 1 to 3 and FIG. 1 that a steel sheet having excellent low temperature toughness and hydrogen organic cracking resistance can be obtained by manufacturing steel sheets according to the embodiment of the present invention.

Claims (6)

0.1 to 0.5 wt% of Si, 1.0 to 2.0 wt% of Mn, 0.03 wt% or less of P, 0.003 wt% or less of S, 0.06 wt% or less of Al, 0.01 wt% or less of N, And a low temperature toughness including 0.05 to 0.5 wt% of Cr, 0.05 to 0.4 wt% of Mo, 0.02 wt% or less of Nb, 0.02 wt% or less of Ti, 0.005 to 0.04 wt% of V and the balance Fe and unavoidable impurities And a plate steel material excellent in hydrogen organic cracking resistance.
The method according to claim 1,
Plate steel material having a tempered bainite or tempered martensite phase as a base and excellent in low temperature toughness and hydrogen organic cracking resistance with an area fraction of ferrite of less than 10%.
The method according to claim 1,
A thick plate steel excellent in low-temperature toughness and hydrogen organic cracking resistance having a maximum length of 10 탆 or less among Ti-based, Nb-based or Ti-Nb composite carbonitrides existing within the upper and lower portions of 5 mm from the center of the thickness of the steel.
The method according to claim 1,
Thick plate steel with a thickness of 30 mm or more and a tensile strength of 500 MPa or more with excellent low temperature toughness and hydrogen organic cracking resistance.
0.1 to 0.5 wt% of Si, 1.0 to 2.0 wt% of Mn, 0.03 wt% or less of P, 0.003 wt% or less of S, 0.06 wt% or less of Al, 0.01 wt% or less of N, 0.05 to 0.5 wt% of Cr, 0.05 to 0.4 wt% of Mo, 0.02 wt% or less of Nb, 0.02 wt% or less of Ti, 0.005 to 0.04 wt% of V and the balance Fe and unavoidable impurities, Preparing;
Firstly heating the slab to 1100 to 1300 占 폚;
Hot rolling the heated slab at a finishing rolling temperature of 950 DEG C or higher and a cumulative rolling reduction of 40% or higher;
Secondarily heating the hot-rolled steel sheet at a temperature of Ac 3 to Ac 3 + 80 ° C;
Cooling the secondary heated steel sheet at a cooling rate of 20000 / (steel sheet thickness) ² to 60000 / (steel sheet thickness) ² ; And
And sintering the cooled steel sheet at a temperature of 580 to 700 ° C.
6. The method of claim 5,
Wherein the tempered steel sheet has a tempered bainite or tempered martensite phase as a base structure and is excellent in low temperature toughness and hydrogen organic cracking resistance that the area fraction of ferrite is less than 10%.

Images