KR20210000844A - Pressure vessel steel sheet excellent in pwhthresistance and menufacturing mwthod thereof - Google Patents

Abstract

According to one perspective of the present invention, a manufacturing method of a steel sheet having excellent strength and toughness even if a post-weld heat treatment (PWHT) is performed comprises: a step of reheating a steel slab comprising 0.12-0.17 wt% of carbon (C), 0.4-0.6 wt% of silicon (Si), 0.45-0.65 wt% of manganese (Mn), 0-0.01 wt% (excluding 0 wt%) of phosphorus (P), 0-0.03 wt% (excluding 0 wt%) of sulfur (S), 0.001-0.02 wt% of soluble aluminum (S_Al), 1-1.2 wt% of chromium (Cr), 0.25-0.35 wt% of nickel (Ni), 0-0.01 wt% (excluding 0 wt%) of titanium (Ti), 0.1-0.15 wt% of copper (Cu), 0.01-0.02 wt% of niobium (Nb), 0.4-0.6 wt% of molybdenum (Mo), 0-0.02 wt% (excluding 0 wt%) of vanadium (V), and the remainder consisting of iron (Fe) and other inevitable impurities to a temperature range of 1,100-1,200°C; a step of hot-rolling the reheated steel slab; a step of performing a normalizing heat treatment on the hot-rolled steel sheet in a temperature range of 910-940°C; and a step of cooling the heat-treated steel sheet and performing a tempering heat treatment on the cooled steel sheet in a temperature range of 690-720°C.

Description

Pressure vessel steel plate with excellent PWHT resistance and its manufacturing method {PRESSURE VESSEL STEEL SHEET EXCELLENT IN PWHTHRESISTANCE AND MENUFACTURING MWTHOD THEREOF}

The present invention relates to a high-temperature pressure vessel steel sheet, and more particularly, to a steel sheet excellent in strength and toughness even after a long-time welding heat treatment (PWHT, Post Weld Heat Treatment), and a manufacturing method thereof.

In recent years, due to the shortage of oil and high oil prices, oil fields in poor environments are being actively developed, and steel materials for refining and storage of crude oil are being thickened. In addition to the thickening of these steel materials, post-welding heat treatment (PWHT, Post Weld Heat) for the purpose of preventing the deformation of the structure after welding and stabilizing the shape and dimensions when the steel materials are welded, in order to remove the stress generated during welding, Treatment).

However, the steel sheet subjected to the PWHT process for a long time has a problem that the tensile strength of the steel sheet decreases due to the coarsening of the structure. That is, after a long PWHT, strength and toughness are simultaneously deteriorated due to softening of the matrix and grain boundaries, grain growth, and coarsening of carbides.

As a related technology, there is Korean Patent Publication No. 10-0797326 (registered on January 16, 2008, deep-sea riser pipe steel for guaranteeing properties of PWHT and a manufacturing method thereof).

An object of the present invention is to provide a steel sheet having excellent strength and toughness even after performing heat treatment (PWHT) after welding for a long time, and a method of manufacturing the same.

According to an aspect of the present invention, a method of manufacturing a steel sheet having excellent strength and toughness even after performing a long-term heat treatment (PWHT) after welding according to an aspect of the present invention includes, in weight%, carbon (C); 0.12 to 0.17%, silicon (Si): 0.40 to 0.60%, manganese (Mn): 0.45 to 0.65%, phosphorus (P): more than 0 0.010%, sulfur (S): more than 0 0.030%, soluble aluminum ( S_Al): 0.001 to 0.020%, chromium (Cr): 1.00 to 1.20%, nickel (Ni): 0.25 to 0.35%, titanium (Ti): greater than 0 and not more than 0.010%, copper (Cu); 0.10 to 0.15%, niobium (Nb): 0.01 to 0.02%, molybdenum (Mo); 0.40 to 0.60%, vanadium (V): more than 0 and 0.02% or less, reheating the steel slab containing residual iron (Fe) and other inevitable impurities to a temperature range of 1,100 to 1200°C; Hot rolling the reheated steel slab; Subjecting the hot-rolled hot-rolled steel sheet to a normalizing heat treatment in a temperature range of 910 to 940°C; And cooling the heat-treated steel sheet and tempering heat treatment at a temperature range of 690 to 720°C.

In the present invention, the step of normalizing heat treatment may be performed for 1 hour + (15 to 30 minutes).

In the present invention, it is preferable that the normalizing heat treatment and the tempering heat treatment are performed in the same facility.

In the present invention, the steel sheet may have a yield strength (YP) of 310 MPa or more and a tensile strength (TS) of 500 MPa or more, and a Charpy impact toughness value of 200 J or more at -20°C.

Another aspect of the present invention is a steel sheet having excellent strength and toughness even after performing a heat treatment (PWHT) after welding for a long time, in wt%, carbon (C); 0.12 to 0.17%, silicon (Si): 0.40 to 0.60%, manganese (Mn): 0.45 to 0.65%, phosphorus (P): more than 0 0.010%, sulfur (S): more than 0 0.030%, soluble aluminum ( S_Al): 0.001 to 0.020%, chromium (Cr): 1.00 to 1.20%, nickel (Ni): 0.25 to 0.35%, titanium (Ti): greater than 0 and not more than 0.010%, copper (Cu); 0.10 to 0.15%, niobium (Nb): 0.01 to 0.02%, molybdenum (Mo); 0.40~0.60%, vanadium (V): greater than 0 and less than 0.02%, contains residual iron (Fe) and other inevitable impurities, has a yield strength (YP) of 310 MPa or more and a tensile strength (TS) of 500 MPa or more, -20℃ It relates to a steel plate having a Charpy impact toughness value of 200J or more.

According to the present invention, according to the present invention, by increasing the normalizing temperature and time, the generation of fine pearlite that suppresses cementite decomposition is promoted to suppress grain growth and cementite growth, and normalizing and tempering processes are performed in the same facility. By proceeding, the problem due to the increase of the process variable is blocked, and the growth of crystal grains is suppressed by controlling the tempering temperature, thereby securing optimum strength and toughness.

1 is a micrograph of an austenite structure before phase transformation of a conventional steel and a developed steel.
FIG. 2 is a photomicrograph of observing microstructure changes of conventional steels and developed steels according to changes in normalizing (NOR) temperature after hot rolling.
3 is a photomicrograph observing a change in the pearlite layer spacing between a conventional steel and a developed steel according to a change in normalizing (NOR) temperature after hot rolling.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. The present invention may be implemented in a number of different forms, and is not limited to the embodiments described herein. The same reference numerals are assigned to the same or similar components throughout the present specification. In addition, detailed descriptions of known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

The present invention relates to a high-temperature pressure vessel steel plate used as a structural steel in power generation and plant industries, and a manufacturing method thereof. Post-weld heat treatment performed to minimize residual stress generated by welding during manufacturing; It relates to a high-temperature pressure vessel steel sheet and a manufacturing method thereof, which greatly improves resistance to deterioration of the strength and toughness of the steel sheet even after performing PWHT) for a long time.

The high-temperature pressure vessel steel plate of the present invention is more preferably used for high-temperature pressure vessel steel plates of 350 to 600°C, such as boilers and pressure vessels of power plants with excellent PWHT resistance, which does not deteriorate strength and toughness even after performing PWHT for a long time. Can be applied.

Even after long-time welding heat treatment (PWHT) of the present invention, the high-temperature pressure vessel steel sheet excellent in strength and toughness, in weight%, includes carbon (C); 0.12 to 0.17%, silicon (Si): 0.40 to 0.60%, manganese (Mn): 0.45 to 0.65%, phosphorus (P): more than 0 0.010%, sulfur (S): more than 0 0.030%, soluble aluminum ( S_Al): 0.001 to 0.020%, chromium (Cr): 1.00 to 1.20%, nickel (Ni): 0.25 to 0.35%, titanium (Ti): greater than 0 and not more than 0.010%, copper (Cu); 0.10 to 0.15%, niobium (Nb): 0.01 to 0.02%, molybdenum (Mo); 0.40~0.60%, vanadium (V): greater than 0 and less than 0.02%, including the remaining iron (Fe) and other unavoidable impurity elements.

First, the composition range of the present invention will be described in detail (hereinafter,% by weight).

Carbon (C); 0.12~0.17%

Carbon (C) is the most effective element for strengthening and strengthening, but when added in a large amount, it is preferable to be added in consideration of this because it lowers weldability and low-temperature toughness. If the carbon (C) content of steel is less than 0.12%, it is uneconomical because a large amount of other expensive alternative alloying elements such as nickel (Ni) must be added to achieve the target strength, and the carbon (C) content exceeds 0.17%. In this case, since weldability and low-temperature toughness deteriorate, it is not preferable.

Silicon (Si); 0.40~0.60%

Silicon (Si) is added as a deoxidizing agent during steel making, and is an element added to improve strength by solid solution strengthening. In the present invention, it is added in the range of 0.4 to 0.6% to ensure this effect. If the added amount of silicon (Si) is less than 0.4%, the deoxidation of molten steel is not sufficient and the toughness may decrease. If the amount of silicon (Si) exceeds 0.6%, the red color due to silicon (Si) during hot rolling. Scale is formed, the shape of the steel plate surface becomes uneven, and the toughness of the weld after PWHT may decrease.

Manganese (Mn); 0.45~0.65%

Manganese (Mn) is an element effective in solid-solution strengthening of steel, and is added in the range of 0.45 to 0.65%. Manganese (Mn) must be contained in at least 0.45% to ensure the effect of increasing quenching and high strength properties.However, if the content exceeds 0.65%, the central segregation part in the center of the thickness when casting the slab in the steelmaking process is large. It is developed, and micro-segregation is developed in the thickness direction, so that low-temperature impact toughness may be deteriorated.

Phosphorus (P); More than 0 and less than 0.010%

Phosphorus (P) is an impurity element present in steel and is mainly segregated in the center of the steel sheet to reduce toughness, so it is desirable to reduce it as much as possible, so the upper limit is set to 0.01%.

Sulfur (S); More than 0 and less than 0.030%

Sulfur (S) is also an impurity element present in the steel, and it is desirable to reduce it as much as possible because it combines with Mn and the like to form non-metallic inclusions, thereby greatly reducing the toughness and strength of the steel. In particular, in order to secure brittle fracture stopping properties at cryogenic temperatures, the upper limit is preferably limited to 0.03%.

Soluble aluminum (S_Al); 0.001~0.020%

Aluminum (Al) is added as a deoxidizing agent along with silicon (Si) during steelmaking, and has a solid solution strengthening effect. However, if it is added in excess of 0.02%, the impact toughness may be inhibited, and if it is added in less than 0.001%, the deoxidation effect is insufficient and the toughness is lowered.

Chrome (Cr): 1.00~1.20%

Since chromium (Cr) is an element that increases high-temperature strength, it must be added at least 1.00% for the strength increase effect, but since it is an expensive element, adding more than 1.20% causes an increase in manufacturing cost, so it is managed to be less than 1.20%. It is desirable to do.

Nickel (Ni): 0.25~0.35%

Nickel (Ni) is the most effective element for improving low-temperature toughness, and the above effect can be obtained only when its content is added at 0.25% or more, but it is preferably added at 0.35% or less since it is an expensive element and causes an increase in manufacturing cost.

Titanium (Ti): greater than 0 and less than 0.010%

Titanium (Ti) improves the toughness of the steel by forming TiN precipitates during the solidification process of the steel, suppressing the austenite grains in the slab heating and hot rolling process, and minimizing the final structure grain size. If the content of titanium (Ti) exceeds 0.01%, the content of titanium (Ti) is limited to 0.01% or less because TiN may not be helpful for finer particle size due to coarse precipitation of TiN when heating the slab due to the excessive presence of solute Ti. do.

Copper (Cu); 0.10~0.15%

Copper (Cu) is an element effective in increasing the strength of steel materials. Therefore, it is possible to achieve the effect of increasing the strength when 0.1% or more is added, but it is preferable to add 0.15% or less because of the high cost.

Niobium (Nb): 0.01~0.02%

Niobium (Nb) is a very useful element for refining grains, and at the same time, it plays a role of greatly improving the strength of steel by promoting the formation of acicular ferrite or bainite, which is a high-strength structure. Furthermore, it is preferable to add at least 0.01% or more because it is present in the steel as a precipitate after PWHT to prevent a decrease in strength that may occur after heat treatment. However, if it is added in excess of 0.02%, the weldability may deteriorate, so the content of niobium (Nb) is limited to 0.01 to 0.02%.

Molybdenum (Mo); 0.40~0.60%

Like chromium (Cr), molybdenum (Mo) is not only an element effective in increasing high-temperature strength, but also an element that prevents cracking due to sulfides. For the above effect, 0.4% or more should be added, but since molybdenum (Mo) is also an expensive element and causes an increase in manufacturing cost, it is preferable to limit it to 0.6% or less.

Vanadium (V): greater than 0 and less than 0.02%

Vanadium (V), like niobium (Nb), is a very useful element for refining crystal grains. At the same time, it promotes the formation of needle-like ferrite or bainite, which is a high-strength structure, greatly improving the strength of steel, and is present in the steel as a precipitate after PWHT. Thus, it is possible to prevent a decrease in strength that may occur after heat treatment. However, if vanadium (V) is added in excess of 0.02%, the weldability may be deteriorated, so the upper limit thereof is limited to 0.02% or less.

The rest is made of iron (Fe) and unavoidable impurities.

Hereinafter, a method of manufacturing a high-temperature pressure vessel steel sheet having excellent strength and toughness even after long-time welding heat treatment (PWHT) of the present invention will be described in detail.

The change in physical properties of the steel plate for the high temperature pressure vessel has a great effect on the phase transformation microstructure and the microstructure after heat treatment. As a result of repeated research, the inventors of the present invention (1) promote the production of fine pearlite that inhibits cementite decomposition through an increase in normalizing temperature and time, thereby inhibiting grain growth and cementite growth, and (2) normalizing and Tempering or accelerated cooling and tempering process are performed in the same facility to block problems due to the increase of process variables. (3) By controlling the tempering temperature at 690 ~ 720℃, the growth of crystal grains is suppressed to provide optimum strength and toughness. We present a way to secure it.

First, the present invention, by weight, carbon (C); 0.12 to 0.17%, silicon (Si): 0.40 to 0.60%, manganese (Mn): 0.45 to 0.65%, phosphorus (P): more than 0 0.010%, sulfur (S): more than 0 0.030%, soluble aluminum ( S_Al): 0.001 to 0.020%, chromium (Cr): 1.00 to 1.20%, nickel (Ni): 0.25 to 0.35%, titanium (Ti): greater than 0 and not more than 0.010%, copper (Cu); 0.10 to 0.15%, niobium (Nb): 0.01 to 0.02%, molybdenum (Mo); 0.40~0.60%, vanadium (V): greater than 0 and less than 0.02%, and the steel slab containing the remaining iron (Fe) and other inevitable impurity elements is reheated to a temperature range of 1,150~1,200℃. Through this slab reheating process, re-use of segregated components during casting and re-use of precipitates may occur. In this case, the slab may be a slab plate manufactured by a continuous casting process.

If the slab reheating temperature is less than 1,150°C, the heating temperature is not sufficient, so that the rolling load increases. In addition, there is a problem in that the austenite crystal grains rapidly coarsen because the Nb-based precipitates do not reach the solid solution temperature and are not re-precipitated as fine precipitates during hot rolling, and thus the growth of austenite grains cannot be suppressed. Conversely, when the reheating temperature exceeds 1,200°C, austenite grains rapidly coarsen or decarburization occurs, making it difficult to secure strength and low-temperature toughness of the steel produced.

After the slab is heated, the heated slab is subjected to a process of hot rolling.In order for the steel sheet to have toughness, austenite grains must exist in a fine size, which is possible by controlling the rolling temperature and the rolling reduction rate. The rolling step is preferably performed at a temperature Tnr or higher at which recrystallization of austenite stops. It has the effect of destroying the cast structure such as dendrite formed during casting by rolling, and reducing crystal grains through austenite recrystallization. Such grain refinement has an important effect on improving the strength and toughness of the steel sheet. The rolling step of the present invention proceeds with 1,000 to 1,150°C as the rolling end temperature.

Normalizing to heat-treat the rolled hot-rolled steel sheet is performed. The heat treatment is performed at a temperature range of 910 to 940°C for about 1 hour and maintained for 15 to 30 minutes. When the normalizing heat treatment temperature is less than 910°C, it is difficult to re-use solid solution solute elements, making it difficult to secure strength. On the other hand, when the heat treatment temperature exceeds 940°C, crystal grain growth occurs, resulting in low-temperature toughness. In addition, if the heat treatment holding time is less than 15 minutes, homogenization of the tissue is difficult, and if it exceeds 30 minutes, productivity may be impaired.

The steel sheet maintained under the above temperature and time conditions is cooled at a cooling rate of 25°C to 30/sec based on the central cooling rate. If the cooling rate is 25°C/sec or less, coarse ferrite grains may be generated during cooling, and if it exceeds 30°C/sec, excessive cooling equipment is disadvantageous in terms of economic efficiency.

A tempering heat treatment step of maintaining the heat treated and cooled steel sheet in a temperature range of 690 to 720°C is performed. When the temperature of the tempering heat treatment is less than 690°C, it is difficult to secure the strength due to the difficulty in precipitation of fine precipitates. On the other hand, when the heat treatment temperature exceeds 720°C, the growth of the precipitate occurs, thereby impairing the strength and low-temperature toughness. The normalizing heat treatment, cooling, and tempering heat treatment steps are continuously performed in the same facility to prevent a decrease in productivity due to an increase in process variables.

When manufacturing a pressure vessel using the steel sheet of the present invention manufactured through a tempering heat treatment process that cools the heat-treated steel sheet at a cooling rate of 25°C to 30/sec and maintains it in a temperature range of 600 to 720°C for a certain time, PWHT treatment can be performed to remove residual stress added by the welding process.

In general, deterioration of strength and toughness occurs after a long PWHT heat treatment, and the steel sheet manufactured by the present invention can be welded without a significant decrease in strength and toughness even if it is carried out for a long time at 690 to 720°C, which is a typical PWHT temperature condition. It has the advantage of being possible. The steel sheet of a preferred example of the present invention has a tensile strength of 500 MPa or more even after 50 hours of PWHT, and a Charpy impact energy value at -20° C. satisfies 250 J or more, thereby having excellent strength and toughness.

Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited to the following examples.

Example

Table 1 and Table 2 below show the chemical composition of the conventional steel and the invention steel, respectively.

division
Ingredient (% by weight) C Si Mn P S S_Al Cr Ni Ti Conventional
River Comparative Example 1 0.123 0.52 0.49 0.007 0.001 0.020 1.15 0.29 0.001 Comparative Example 2 0.123 0.55 0.50 0.007 0.001 0.015 1.12 0.28 0.001 Comparative Example 3 0.121 0.55 0.51 0.007 0.001 0.013 1.15 0.28 0.001 Development
River Example 1 0.120 0.55 0.51 0.008 0.001 0.011 1.14 0.26 0.001 Example 2 0.122 0.52 0.51 0.008 0.001 0.020 1.16 0.26 0.001 Example 3 0.123 0.55 0.51 0.007 0.001 0.015 1.16 0.29 0.001

division Ingredient (% by weight) Process conditions Cu Nb Mo V SRT(℃) NOR(℃) NT(℃) Conventional
River Comparative Example 1 0.12 0.017 0.46 0.017 1200 902 720 Comparative Example 2 0.12 0.018 0.45 0.018 1200 899 719 Comparative Example 3 0.12 0.018 0.47 0.016 1191 903 720 Development
River Example 1 0.12 0.017 0.45 0.016 1194 931 719 Example 2 0.12 0.016 0.45 0.018 1200 930 720 Example 3 0.12 0.019 0.45 0.017 1193 930 720

The steel slabs having the alloy composition of Tables 1 and 2 were reheated at the temperature (SRT) shown in Table 2 and then hot-rolled to prepare a hot-rolled steel sheet. The hot-rolled steel sheet was subjected to normalizing heat treatment by maintaining the temperature (NOR) in Table 2, and then tempering heat treatment was performed at the temperature (NT) shown in Table 2, respectively.

Next, for the manufactured steel sheet, the yield strength (YP), tensile strength (TS), and elongation (EL) were measured, and the results are shown in Table 3, 18°C, 0°C, -20°C, -40°C And Charpy shock absorption energy (CVN) at -60°C was measured, and the results are shown in Table 4. In Table 4, the low-temperature toughness was evaluated by the Charpy impact energy value obtained by performing a Charpy impact test on a specimen having a V notch at each temperature.

division YP(MPa) TS(MPa) EL(%) Conventional steel Comparative Example 1 291 485 33 Comparative Example 2 292 485 33 Comparative Example 3 286 491 32 Development river Example 1 321 515 30 Example 2 320 511 31 Example 3 311 507 30

division CVN (J), test temperature 18℃ 0℃ -20℃ -40℃ -60℃ Conventional steel Comparative Example 1 267 161 143 87 22 Comparative Example 2 272 154 141 83 18 Development river Example 1 386 375 265 150 30 Example 2 379 369 257 144 45

In the results of Tables 3 and 4, the developed steel that satisfies the alloy composition and manufacturing process conditions of the present invention exhibited a yield strength (YP) of 310 MPa or more and a tensile strength (TS) of 500 MPa or more, showing a larger value than the conventional steel. , In the case of the impact toughness value according to temperature, it can be seen that the developed steel of the present invention exhibited a significantly higher value than that of the conventional steel.

1 to 3 are electron microscopy (SEM) photographs observing the microstructure of the conventional steel and the developed steel of the present invention.

Specifically, FIG. 1 is a micrograph of austenite structure before phase transformation of a conventional steel and a developed steel. The average size of austenite grains of the conventional steel is 39.9 μm, and the average size of the austenite grains of the developed steel is 36.1 μm. It showed a finer or similar level.

2 and 3 are micrographs showing changes in microstructure and pearlite layer spacing between conventional and developed steels according to changes in normalizing (NOR) temperature after hot rolling.

As shown in Fig. 2, the structure of the developed steel normalized at 930°C is more uniform than the conventional steel normalized at 900°C after hot rolling, and the pearlite layer spacing of the developed steel is also finer as shown in Fig.3. And uniform.

As described above, according to the present invention, by increasing the normalizing temperature and time, the generation of fine pearlite that suppresses cementite decomposition is promoted to inhibit grain growth and cementite growth, and normalizing and tempering processes are performed in the same facility. By proceeding, it is possible to block problems due to an increase in process parameters, and to control the tempering temperature to suppress the growth of crystal grains, thereby securing optimum strength and toughness. The high-temperature pressure vessel steel plate of the present invention is more preferably used for high-temperature pressure vessel steel plates of 350 to 600°C, such as boilers and pressure vessels of power plants with excellent PWHT resistance, which does not deteriorate strength and toughness even after performing PWHT for a long time. Can be applied.

In the above, the embodiments of the present invention have been described mainly, but various changes or modifications may be made at the level of those skilled in the art. Such changes and modifications can be said to belong to the present invention as long as they do not depart from the scope of the present invention. Therefore, the scope of the present invention should be determined by the claims set forth below.

Claims (5)

In weight percent, carbon (C); 0.12 to 0.17%, silicon (Si): 0.40 to 0.60%, manganese (Mn): 0.45 to 0.65%, phosphorus (P): more than 0 0.010%, sulfur (S): more than 0 0.030%, soluble aluminum ( S_Al): 0.001 to 0.020%, chromium (Cr): 1.00 to 1.20%, nickel (Ni): 0.25 to 0.35%, titanium (Ti): greater than 0 and not more than 0.010%, copper (Cu); 0.10 to 0.15%, niobium (Nb): 0.01 to 0.02%, molybdenum (Mo); 0.40 to 0.60%, vanadium (V): more than 0 and 0.02% or less, reheating the steel slab containing residual iron (Fe) and other inevitable impurities to a temperature range of 1,100 to 1200°C;
Hot rolling the reheated steel slab;
Normalizing heat treatment of the hot-rolled hot-rolled steel sheet at a temperature range of 910 to 940°C; And
Comprising the step of cooling the heat-treated steel sheet and tempering heat treatment at a temperature range of 690 to 720°C,
A method of manufacturing a pressure vessel steel plate with excellent PWHT resistance.
The method of claim 1,
The normalizing heat treatment step is performed for 1 hour + (15 to 30 minutes),
A method of manufacturing a pressure vessel steel plate with excellent PWHT resistance.
The method of claim 1,
The normalizing heat treatment and the tempering heat treatment are performed in the same facility,
A method of manufacturing a pressure vessel steel plate with excellent PWHT resistance.
The method of claim 1,
The steel sheet has a yield strength (YP) of 310 MPa or more and a tensile strength (TS) of 500 MPa or more, and a Charpy impact toughness value of 200 J or more at -20°C,
A method of manufacturing a pressure vessel steel plate with excellent PWHT resistance.
As a steel sheet manufactured by the method of any one of claims 1 to 4,
It has a yield strength (YP) of 310 MPa or more and a tensile strength (TS) of 500 MPa or more, and a Charpy impact toughness value of 200 J or more at -20°C,
Pressure vessel steel plate with excellent PWHT resistance.

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