TWI399444B - High strength and low temperature toughness, and a method for manufacturing the same - Google Patents

Description

Steel for welding structure excellent in high temperature strength and low temperature toughness and method for producing same Field of invention

In the present invention, fire-resistant steel for building structure is mainly used for the purpose of maintaining the strength of the high-temperature stress at the time of high temperature, but it is not limited to the use of the building, and is also applicable to marine structures, ships, bridges, and various storage tank containers. Steel for welding structures for a wide range of applications. Moreover, the level of the steel plate strength of the main object is 235 to 475 MPa, and the tensile strength is 400 to 640 MPa, which is a so-called 40 kg and 50 kg steel grade.

Background of the invention

A so-called fire-resistant steel for use in construction for the purpose of ensuring the high-temperature-reducing strength has been disclosed in Japanese Laid-Open Patent Publication No. Hei 2-77523. But almost all of them contain molybdenum products. Although molybdenum is an extremely effective element for the high temperature drop strength of steel, it is also a high-priced element.

However, the steel for general structure normalized by the Japanese Industrial Standards (JIS) has an allowable temperature of about 350 ° C due to a decrease in strength from about 350 ° C. In other words, when buildings such as buildings, office buildings, houses, and three-dimensional parking lots use the above-mentioned steel materials, in order to ensure safety during fires, they are required to fully implement fire-resistance obligations; various laws and regulations related to construction in Japan In the event of fire, the steel temperature cannot reach above 350 °C. The lowering strength of the steel material at about 350 ° C is about 2/3 of the normal temperature, and is lower than the necessary strength. Therefore, when general steel materials are used for construction materials, it is necessary to carry out fire-resistance coating so that the steel temperature during the fire is prevented from reaching 350 °C.

In order to omit or reduce the refractory coating, the high temperature drop strength at the high temperature tensile test of 600 ° C (hereinafter, unless otherwise specified, the high temperature means 600 ° C, the high temperature strength is the high temperature drop strength), the fire resistant steel is generally The ground is used.

Generally, fire resistant steel is added with molybdenum for the purpose of maintaining high temperature strength. However, the market for molybdenum has changed greatly, and because of the added amount, the price is higher than that of the fire-resistant coating. Therefore, development and practical use of a fire-resistant steel in which molybdenum is added to a mother must be expected.

Summary of invention

An object of the present invention is to obtain a steel for fusion-bonding structure which is excellent in low-temperature toughness and which is excellent in high-temperature strength and which is excellent in high-temperature strength and which is one of the basic properties of steel. Therefore, by limiting the steel composition to a specific range and further limiting the production method, it is possible to provide a method of industrially maintaining a stable and low-cost fire-resistant steel which is excellent in high-temperature strength and which suppresses weld crack sensitivity and ensures low-temperature toughness.

According to the present invention, the steel for welding structure having sufficient sufficient strength to be exposed to a high temperature environment such as a fire can be supplied in a large amount and at low cost, and the safety of the welded steel structure for improving various kinds of applications can be improved. Help.

The gist of the present invention is to ensure the stability of the high temperature strength at 600 ° C, by adding a relatively small amount of carbon and chromium, and replacing the high-priced molybdenum with the use of metamorphic tissue strengthening with precipitates of chromium or strontium. (carbonitride) to enhance precipitation.

That is, when molybdenum is not contained, it is found to contain an appropriate amount by addition. Chromium increases the hardenability of steel and lowers the metamorphic temperature, and the hard structure containing ferritic carbon iron becomes a toughened body.

Therefore, while the normal temperature and the high temperature strength are increased, since the matrix becomes a fine tough structure at a relatively low temperature, the chromium and the lanthanum are added at a high temperature to separate the chrome and the ruthenium. Since the carbonitride material is extremely finely precipitated in the substrate, it has been found that the present invention can be completed while maintaining high temperature strength and maintaining a high level.

For example, the fire-resistant steel not contained in molybdenum is extremely epoch-making, and since it does not contain molybdenum, it can be used as a basic property (strength, toughness) of the steel for welding structure, and also with welding or gas cutting. Sexual improvement is related.

In the present invention, not only chromium, antimony, but also carbon, antimony, and manganese are specified as the first various elements, and the fusion cracking sensitivity composition P _{CM is} defined, and the manufacturing conditions are limited, so that not only high-priced molybdenum is required Excellent high-temperature strength and low-temperature toughness, and ensure various performance properties of steel used as a welded structure. The gist of the following is as follows.

(1) A method for producing a steel for welding structure excellent in high-temperature strength and low-temperature toughness, wherein the steel material is heated at a temperature of 1000 to 1300 ° C, and the steel is cooled at a temperature of 800 ° C or higher, and the composition of the steel is mass-treated. %, including: carbon: 0.003~0.05%; 矽: 0.60% or less; manganese: 0.6~2.0%; phosphorus: 0.020% or less; sulfur: 0.010% or less; chromium: 0.20~1.5%; 铌: 0.005~0.05 %; aluminum: 0.060% or less; and nitrogen: 0.001 to 0.006%; and molybdenum as an impurity is limited to 0.03% or less, the remainder is composed of iron and unavoidable impurities, and P _CM = C + Si / 30 + Mn / The susceptibility of the fusion crack defined by 20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B has a P _CM value of 0.22% or less.

(2) The method for producing a steel for welded structure excellent in high-temperature strength and low-temperature toughness according to Item (1), wherein after the completion of the hot rolling, the cooling is accelerated from a temperature of 750 ° C or higher, and the temperature is stopped at a temperature of 550 ° C or lower. Accelerate cooling.

(3) The method for producing a steel for welding structure excellent in high-temperature strength and low-temperature toughness according to item (1) or (2), in addition to mass%, more preferably: vanadium: 0.01 to 0.10%; titanium: 0.005 to 0.025% Nickel: 0.05~0.50%; copper: 0.05~0.50%; boron: 0.0002~0.003%; magnesium: 0.0002~0.005%; calcium: 0.0005~0.004%; REM: 0.0005~0.008% of any one or 2 More than one species.

(4) A steel for welding structure having excellent high-temperature strength and low-temperature toughness, which is obtained by heating a steel material at a temperature of 1000 to 1300 ° C, cooling at a temperature of 800 ° C or higher, and cooling the steel, and the composition of the steel is in mass%. Calculated, including: carbon: 0.003~0.05%; 矽: 0.60% or less; manganese: 0.6~2.0%; phosphorus: 0.020% or less; sulfur: 0.010% or less; chromium: 0.20~1.5%; 铌: 0.005~0.05% Aluminum: 0.060% or less; and nitrogen: 0.001 to 0.006%; and molybdenum as an impurity is limited to 0.03% or less, the remainder is composed of iron and unavoidable impurities, and P _CM = C + Si / 30 + Mn / 20 The fusion susceptibility sensitivity composition defined by +Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B has a P _CM value of 0.22% or less.

Detailed description of the preferred embodiment

The range of addition of each alloying element specified by the present invention will be described.

Carbon: 0.003~0.05%

Carbon is limited to very low levels as high tensile steel. It is closely related to other ingredients and to manufacturing methods. Among the steel components, carbon has the greatest influence on the characteristics of steel. The lower limit of 0.003% is a heat-affected portion that secures strength or causes welding, and is maintained at a minimum value that does not cause a softening or more.

When the amount of carbon is too large, the quenching property is increased as necessary, and the balance between the strength and the toughness of the steel material and the weldability are adversely affected. Further, as will be described later, there has been a case where the accelerated cooling is stopped at a lower temperature by the thickness or strength of the object. In this case, in order to suppress extreme hardening in the vicinity of the steel sheet surface or material variation in the thickness direction, The upper limit was taken as 0.05%.

In order to avoid a decrease in strength due to work variation or balance with other components, the lower limit is preferably 0.005%, and the lower limit is preferably 0.01%. Further, in order to avoid excessive quench hardening or material variation, the upper limit is preferably 0.04%, and more preferably 0.03%.

矽: 0.60% or less

Although the element contained in steel is deacidified, the weldability and HAZ toughness are deteriorated due to the addition of a large amount. Therefore, the upper limit is 0.60%, and the deacidification of steel is also due to the balance of the elements with aluminum and titanium. Decide on the content. However, from the viewpoint of HAZ toughness and hardenability, the lower the better, the more it is not added. Therefore, the upper limit is not limited to 0.40%, 0.20%, and 0.10%. Further, when steel is produced in a steelmaking plant, when deuterium is not added by adding titanium or aluminum, it is usually contained in an amount of 0.01% or more.

Manganese: 0.6~2.0%

Manganese is an element that is indispensable for strength and toughness at room temperature, and the lower limit is 0.6%. It is preferably 0.8% or more or 1.0% or more. However, when the amount of manganese is too large, the hardenability increases, which not only deteriorates the weldability and the HAZ toughness, but also contributes to the center segregation of the continuous cast sheet, so the upper limit is 2.0%. It is preferably 1.8% or less, more preferably 1.6% or less or 1.4% or less.

Phosphorus: 0.020% or less

The smaller the amount of phosphorus, the less the tendency to reduce the grain boundary damage in the HAZ, so the less the better. When the content is large, the low temperature toughness of the base material and the welded portion is deteriorated, so the upper limit is made 0.020%. It is preferably made 0.015% or less, 0.010% or less, or 0.008% or less. Of course, you can't add it.

Sulfur: 0.010% or less

From the point of view of the low temperature toughness of the base metal, the less sulfur is better. When the content is too large, the low temperature toughness of the base material and the welded portion is deteriorated, so the upper limit is made 0.010%. It is preferably made at 0.008% or less, 0.006%, and 0004%. Of course, you can't add it.

Chromium: 0.20~1.5%

Chromium is one of the most important elements in the invention. To ensure high temperature strength, it is necessary to add antimony and chromium. The tempering effect of chrome improves the metamorphic temperature, and since the hard structure containing ferritic carbon iron becomes a toughened body, the strength at normal temperature and high temperature is improved, and at higher temperatures, it can be utilized as precipitation by chrome. Precipitation strengthening of the substance (carbonitride).

In order to achieve these effects, the chromium content must be at least 0.20%. It is preferably 0.35% or more, and more preferably 0.50% or more, 0.8% or more. However, if the amount of addition is too large, the toughness and weldability of the base material and the welded portion are deteriorated to impair the economy, so the upper limit is 1.5%. It should be 1.3% or less.

铌: 0.005~0.05%

Both bismuth and chromium are the most important elements of the invention. In the same manner as chromium, in order to secure high-temperature strength, it can be used as precipitation strengthening by precipitation of niobium (carbonitride).

Therefore, it must be at least 0.005% or more. It is preferably 0.010% or more. However, if the amount of addition is too large, the toughness of the welded portion is deteriorated, so the upper limit is made 0.05%. It is preferably 0.045% or less, and more preferably 0.030% or less. In addition, the addition of 铌 沃 沃 沃 沃 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦 瓦

By the combined addition of the above-mentioned chromium and antimony, molybdenum does not exist, and high temperature strength can be ensured. Therefore, in the present invention, the intentional addition of molybdenum is not implemented. Further, when the molybdenum which is an impurity is not intentionally mixed, it is also limited to 0.03% or less.

Aluminum: 0.060% or less

Generally, aluminum is used for deacidification and is contained in steel. Due to deacidification It is carried out by barium or titanium and can be balanced with these elements to determine the amount. However, when the amount of aluminum is large, not only the deterioration of the steel is deteriorated, but also the toughness of the welded metal is deteriorated, so the upper limit is made 0.060%. It is preferably 0.040% or less. The smaller the amount, the better, and it may not be added. Moreover, when steel is produced in a steelmaking plant, it is usually contained in an amount of 0.001% or more of aluminum when it is not deacidified by aluminum.

Nitrogen: 0.001~0.006%

Nitrogen is contained in steel as an unavoidable impurity, and combines with niobium to form a carbonitride to increase strength. Further, niobium nitride is formed to improve the properties of steel as described above. Therefore, the minimum amount of nitrogen must be 0.001%. It is preferably 0.0015% or more. However, the increase in the amount of nitrogen impairs the toughness and weldability of the welded heat affected zone, and the upper limit of the steel of the present invention is 0.006%. It is preferably 0.0045% or less.

Next, the reasons for adding vanadium and titanium as needed should be explained.

Vanadium: 0.01~0.10%

The vanadium system has almost the same effect as the bismuth, and in the present invention, the action of vanadium is only a deficiency of the enthalpy. However, the effect of vanadium is less than that of bismuth, and it also affects the hardenability, so the upper and lower limits are limited. The lower limit is that the minimum amount of vanadium addition effect is 0.01%. It is preferably 0.025% or less. The upper limit is also considered to be 0.10% in consideration of the influence of the fusion cracking sensitivity composition P _CM described later. It is preferably 0.08% or less, more preferably 0.05% or less.

Titanium: 0.005~0.025%

Titanium is desirably added to improve the toughness of the base material and the heat affected zone. When titanium is used in a small amount of aluminum (for example, 0.003% or less), a precipitate containing titanium oxide as a main component is formed by combining oxygen, and it becomes a core of intragranular metamorphic ferrite iron formation, and is improved. Welding the heat affected zone toughness.

Further, titanium is combined with nitrogen to form titanium nitride, which is finely precipitated in the steel material, suppresses coarsening of the r particles during heating, and is effective for fine graining of the rolled structure. Further, the fine titanium nitride which is present in the steel material refines the microstructure of the heat affected portion during welding to improve the toughness. In order to achieve these effects, titanium must be at least 0.005%. However, if titanium carbide is formed too much, the upper limit is made 0.025% because the low temperature toughness or the weldability is deteriorated. It is preferably 0.020% or less.

Next, the reasons for the addition of nickel, copper, boron, and magnesium will be explained.

Among the basic components, the main purpose of adding these elements is to improve the properties such as strength and toughness without impairing the excellent characteristics of the steel of the present invention. Therefore, the amount added is from the nature that should be limited.

Nickel: 0.05~0.50%

When the amount of nickel added is not excessive, the weldability and the toughness of the heat-affected zone are not impaired, and the strength and toughness of the base material are improved. In order to exert such effects, at least 0.05% or more must be added.

On the other hand, excessive addition is not only expensive but also poor in weldability. Also, it is pointed out that the excessive addition of nickel causes the possibility of stress corrosion cracking (SCC) in liquid ammonia. According to research by the inventors and the like, the deterioration of the SCC added to 1.0% of the weldability or in the liquid ammonia is not large, and the effect of improving the strength and the toughness is large, but the economy is preferred, and the upper limit is made 0.50%. . When economic priority is given, it can also be limited to 0.35%.

Copper: 0.05%~0.50%

The copper system and the nickel almost show the same effect and phenomenon, and the 0.50% upper limit of the weldability is deteriorated, and copper-cracking occurs during hot rolling due to excessive addition. It is difficult to be restricted. The minimum amount for which the lower limit is obtained is 0.05%. When economy is a priority, the upper limit can be limited to 0.30%.

Boron: 0.0002~0.003%

The boron system causes the Wostian iron to segregate at the grain boundary, which inhibits the formation of ferrite iron, improves the hardenability, and contributes to the strength improvement. In order to obtain this effect, it must be at least 0.0002%.

However, the addition of too much not only saturates the effect of improving the hardenability, but also forms a boron precipitate which is harmful to toughness, so the upper limit is made 0.003%. It is better to declare that it is 0.002% or less. also. For example, in the case of steel for barrel corrosion, in the case of stress corrosion cracking, the hardness reduction of the base material and the heat affected zone is often the case. For example, to prevent sulfide stress corrosion cracking (SCC), Rockwell The hardness must be HRC ≦ 22 (HV ≦ 248). In such cases, it is not advisable to add boron which increases the hardenability. Further, although boron has an effect of improving the strength of the above-described type, boron is added to cause deterioration of the material such as toughness of the heat-affected zone. Therefore, in order to avoid such problems, it is desirable to limit boron to 0.0003% or less or to add it.

Magnesium: 0.0002~0.005%

Magnesium is used in the heat-affected zone to suppress the growth of Worthite iron particles and has a function of fine granulation, so that the weld portion can be strengthened and toughened. In order to obtain such effects, magnesium must be 0.0002% or more. On the other hand, the increase in the amount of addition is reduced by the effect of the amount of addition, and the cost is not the best, so the upper limit is 0.005%. It is preferably 0.0035% or less.

Next, explain the reasons for adding calcium or REM.

Calcium: 0.0005~0.004%

REM: 0.0005~0.008%

Calcium and REM control the form of manganese sulfide, in addition to improving the low temperature toughness of the base metal, reducing the hydrogen induced crack (HIC, SSC, SOHIC) sensitivity in the wet hydrogen sulfide environment. In order to play the effects of these effects, a minimum of 0.0005% is required.

However, if the amount of addition is too much, the purity of the steel is deteriorated. Because of the sensitivity of the base material toughness or hydrogen-induced cracking (HIC, SSC, SOHIC) in the hydrogen sulfide environment, the upper limit of the amount of calcium is limited by calcium and REM. At 0.004%, 0.008%. Preferably, it is preferably 0.003% or less and 0.006% or less. Further, in order to achieve almost the same effect of calcium and REM, any one of them may be added to the above range, and both may be added.

Although the various components of steel are limited, but the composition is not appropriate, excellent characteristics cannot be obtained. In the present invention, the value of the weld crack sensitivity composition P _CM defined by the following formula is limited to 0.22% or less from the content (% by mass) of each element.

P _CM =C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B

P _CM is an indicator of weldability, and the lower the weldability, the better. JIS G 3106 "rolled steel for welding structure" varies depending on the strength level or thickness, and is most limited to 0.24% or less.

According to the inventors of the present invention, various weld crack tests were carried out on a wide range of steel grades, and P _{CM was} limited to 0.22% or less under conditions of more severe restrictions and environmental conditions as a condition for preventing weld cold cracks. Further, although the lower limit is not particularly limited, it is possible to limit itself from the limited range of each component.

Then, the manufacturing conditions are explained.

Before the hot rolling, the heating temperature is limited to 1000 to 1300 ° C, and the Worthite iron particles are kept in small particles to refine the rolled structure. When the 1300 °C is heated, the upper limit temperature of the extreme coarsening does not occur. When the heating temperature exceeds, the iron particles of the Worthfield coarse and coarse, and the microstructure after the metamorphosis is coarsened, so the toughness of the steel is remarkable. Deterioration.

On the other hand, when the heating temperature is too low, it is difficult to ensure the rolling end temperature to be described later, and the unrecrystallized temperature of the Worthite iron is increased. Therefore, the viewpoint of the melt strengthening of the precipitation strengthening is found. , the lower limit is taken as 1000 °C. The optimum heating temperature range is 1050~1250 °C.

The steel material heated under the above conditions is cooled after the hot rolling at 800 ° C or higher. The cooling method is not particularly limited. Although it can be placed in the atmosphere for cooling, it is possible to accelerate the cooling to a temperature of 550 ° C or lower from a temperature of 750 ° C or higher, thereby improving the characteristics of the steel.

When the rolling end temperature is lower than 800 ° C, the steel of the present invention having a small amount of carbon causes the ferrite and iron to be metamorphosed and must be processed (rolled) by the ferrite, so that it is not good to ensure low temperature toughness. . Therefore, the rolling end temperature is limited to 800 ° C or more. It is preferably 820 ° C or more.

After the hot rolling at 800 °C or higher, the so-called 40 kg grade steel (for example, JIS-size SM400 and SN400 steel) having a lower strength can satisfy the predetermined strength even when it is cooled in the atmosphere.

However, 50 kg of grade steel (for example, JIS-size SM490, SN490 steel) or 40 kg of steel is also cooled by the thickness of the plate, so that the stability of strength is difficult to ensure, so it is expected to be above 800 °C. After the hot rolling is finished, the cooling is accelerated from a temperature of 750 ° C or higher. Accelerated cooling after rolling However, it is necessary to improve the characteristics of the steel without impairing the excellent features of the present invention.

Accelerated cooling was originally intended to precede the cold rate of the metamorphic range and to make the microstructure finer, while at the same time improving strength and toughness. Therefore, it does not make any sense if it does not start before the beginning of metamorphosis or at least before the end of metamorphosis. Therefore, the accelerated cooling start temperature is limited to 750 ° C or higher. In order to obtain its effect, the accelerated cooling must be cooled to a temperature below 550 °C. At a temperature exceeding 550 ° C, the deformation at the time of accelerated cooling is not sufficiently performed, and the microstructure cannot be sufficiently refined. Therefore, the temperature at which the accelerated cooling is started is preferably 760 ° C or higher, and the temperature at which the accelerated cooling is stopped is preferably 520 ° C or lower and 300 ° C or higher.

In addition, the cooling rate at the time of accelerated cooling varies depending on the steel component, the intended strength, or the low-temperature toughness level, and it is desirable to carry out the accelerated cooling start temperature to 550 ° C in the thickness direction from the surface to the thickness of 1⁄4. The average cooling rate is 3 ° C / sec or more.

Further, the rolled material after cooling is subjected to tempering treatment at a temperature equal to or lower than Ac1, and the excellent characteristics of the present invention are not impaired. In order to improve the uniformity of the material in the board, it is better to eliminate the unevenness of cooling.

Example

In the converter-continuous casting-thickness step, steel sheets (thicknesses of 19 to 100 mm) of various steel compositions were produced, and the materials thereof were investigated.

The first table shows comparative steel and shows the steel composition of the steel of the present invention, and the second table shows the steel sheet production conditions and various characteristics.

The steel sheets (steel of the present invention) produced according to the present invention all have good characteristics. On the other hand, it is understood that the steel sheet (comparative steel) not manufactured according to the present invention has some characteristics.

Since the comparative steel 11 system has a high carbon content, the base material and the reflow heat affected portion (HAZ) are inferior in low temperature toughness as compared with the steel of the present invention.

Since the comparative steel 12 system is not added with bismuth, the comparative steel 13 system has a low high-temperature strength because of the low chromium content.

Since the comparative steel 14 system has a low carbon content, the high temperature strength is low.

Since the comparative steel 15 system has a high amount of chromium, the base material and the HAZ are reproduced, and the toughness is poor.

Since the comparative steel 16 system has a high amount of niobium, the HAZ toughness is poor.

The components of Comparative Examples 17-1 to 3 were the same as those of the steel 5 of the present invention. However, since the comparative steel 17-1 has a low rolling end temperature, the accelerated cooling start temperature is not ensured and is lowered, so that the normal temperature and the high temperature strength are low. Comparative Steel 17-2 is low in normal temperature and high temperature because the accelerated cooling start temperature is low. Since Comparative Steel 17-3 has a high temperature at the accelerated cooling stop, the normal temperature and high temperature strength are low.

Comparative steel 18 series is within the scope of the present invention due to various elements or manufacturing methods, so normal temperature, high temperature strength or toughness conforms to the desired characteristics as 490 MPa grade, but since P _{CM is} high, weldability ( oblique y-shaped fusion) Crack test) Cracks occurred.

Industry availability

According to the present invention, it is possible to provide a steel for welding structure which is excellent in high-temperature strength and low-temperature toughness which is large and inexpensive. As a result, the refractory coating can be lightly reduced or omitted as a building structure. In addition, since it has high-strength strength in addition to basic properties such as strength and toughness, it is possible to improve the safety of the structure as a steel for welding structure that may be exposed to high temperatures.

Claims (4)

A method for producing a steel for welding structure having excellent high-temperature strength and low-temperature toughness, wherein the steel material is heated to a temperature of 1000 to 1300 ° C, and the hot rolling is finished at a temperature of 800 ° C or higher, and then cooled; and the steel is mass-treated %, the composition is as follows: carbon: 0.003~0.05%; 矽: 0.60% or less; manganese: 0.6~2.0%; phosphorus: 0.020 or less; sulfur: 0.010% or less; chromium: 0.20~1.5%; 铌: 0.005~0.05% Aluminum: 0.060% or less; and nitrogen: 0.001 to 0.006%; and, the molybdenum as an impurity is limited to 0.03% or less, and the remainder is composed of iron and unavoidable impurities; further, the steel is defined by the following formula: The sensitivity composition P _CM value is 0.22% or less: P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B. A method for producing a steel for welding structure excellent in high-temperature strength and low-temperature toughness according to the first aspect of the patent application, which is accelerated from a temperature of 750 ° C or higher after the completion of the hot rolling, and is stopped at a temperature of 550 ° C or lower. Accelerate cooling. The method for producing a steel for welding structure excellent in high-temperature strength and low-temperature toughness according to the first or second aspect of the patent application, which comprises, in mass%, more: nickel: 0.05 to 0.50%; copper: 0.05 to 0.50%; boron: 0.0002~0.003%; magnesium: 0.0002~0.005%; calcium: 0.0005~0.004%; REM: 0.0005~0.008% one or more. A steel for welding structure having excellent high-temperature strength and low-temperature toughness, which is obtained by heating a steel material to a temperature of 1000 to 1300 ° C, ending hot rolling at a temperature of 800 ° C or higher, and then cooling it; and the steel is of quality %, the composition is as follows: carbon: 0.003~0.05%; 矽: 0.60% or less; manganese: 0.6~2.0%; phosphorus: 0.020% or less; sulfur: 0.010% or less; chromium: 0.20~1.5%; 铌: 0.005~0.05 %; aluminum: 0.060% or less; and nitrogen: 0.001 to 0.006%; and, the molybdenum which is an impurity is limited to 0.03% or less, and the remainder is composed of iron and unavoidable impurities; The crack sensitivity composition P _CM value is 0.22% or less: P _CM = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B.