JP5741454B2 - Ni-added steel sheet excellent in toughness and productivity in which Charpy test value at −196 ° C. is 100 J or more for both base metal and welded joint, and manufacturing method thereof - Google Patents

Description

  The present invention relates to a Ni-added steel plate excellent in toughness and a method for producing the same. Steel plates produced by this method can be used for general welding structures such as shipbuilding, bridges, buildings, marine structures, pressure vessels, tanks, line pipes, etc., especially at extremely low temperatures of about -160 ° C to -196 ° C. It is effective when used in an LNG tank that requires high toughness. In addition, the toughness in this invention refers to the resistance with respect to brittle fracture occurrence, and an object site | part is both the base material part of a steel plate, and a welded joint part. The required strength of the steel sheet in the present invention is that the yield stress is 590 MPa or more and the tensile strength is 690 MPa or more.

As a steel type used for the inner tank of a liquefied natural gas (LNG) storage tank, a so-called 9% Ni steel (Ni is contained in an amount of about 8.5 to 9.5% by mass, and is mainly composed of tempered martensite. In particular, a low temperature toughness, for example, a steel material excellent in Charpy impact absorption energy at −196 ° C.). Various inventions for improving the toughness of 9% Ni steel have been disclosed so far. For example, Patent Document 1, Patent Document 2, and Patent Document 3 disclose an invention in which P that causes a decrease in toughness due to grain boundary embrittlement is disclosed. In addition, Patent Document 4, Patent Document 5, and Patent Document 6 disclose an invention that improves the toughness by reducing the temper embrittlement susceptibility by the two-phase region heat treatment. In addition, Patent Document 7, Patent Document 8, and Patent Document 9 disclose an invention that significantly improves toughness by adding Mo capable of increasing strength without increasing temper embrittlement sensitivity. Further, Patent Document 4, Patent Document 8, and Patent Document 10 disclose inventions that improve the toughness by reducing the amount of Si that increases the temper embrittlement sensitivity.
Against the backdrop of the recent increase in demand for natural gas, further improvement in tank toughness is required in order to cope with the increase in size of LNG tanks. The methods of Patent Documents 1 to 10 are extremely effective in improving toughness, but increase the cost and decrease the productivity. Therefore, there is a large limit to use it in the LNG tank as it is.

JP-A-7-278734 JP-A-6-179909 JP-A-63-130245 JP-A-9-143557 JP-A-4-107219 JP 56-156715 A JP 2002-129280 A JP-A-4-371520 Japanese Patent Application Laid-Open No. 61-13312 JP 7-316654 A

  The problem to be solved is to provide a steel sheet of 9% Ni-added steel that is remarkably excellent in toughness at about −160 ° C. to −196 ° C. and also excellent in productivity, and a method for producing the same.

The present invention provides a 9% Ni steel sheet having excellent toughness at about −160 ° C. to −196 ° C. and excellent productivity, and a method for producing the same. It is as follows.
(1) Steel is mass%, C: 0.04% to 0.10%, Si: 0.02% to 0.15%, Mn: 0.30% to 1.00%, P : 0.0010% or more and 0.0100% or less, S: 0.0001% or more and 0.0035% or less, Ni: more than 7.5% and 10.0% or less, Al: 0.01% or more and 0.08% or less , N: 0.0001% or more and 0.0070% or less, TO: 0.0001% or more and 0.0050% or less, and the balance is a steel composition composed of Fe and inevitable impurities. The Charpy test value at −196 ° C. is characterized in that the interfacial segregation concentration of P in the portion where only ¼ of the thickness of the steel sheet enters in the thickness direction is mass% and 0.100% or less. A Ni-added steel sheet with excellent toughness and productivity that is 100 J or more for both welded joints.
(2) Further, by mass%, Cr: 0.01% to 1.5%, Mo: 0.01% to 0.4%, Cu: 0.01% to 1.0%, Nb: 0 0.001% to 0.05%, Ti: 0.001% to 0.05%, V: 0.001% to 0.05%, B: 0.0002% to 0.05%, Ca : 0.0003% or more and 0.0040% or less, Mg: 0.0003% or more and 0.0040% or less, REM: 0.0003% or more and 0.0040% or less, and the balance is Fe The Ni-added steel sheet having excellent toughness and productivity in which the Charpy test value at −196 ° C. at −196 ° C. is 100 J or more for both the base material and the welded joint, which is a steel composition comprising unavoidable impurities and .
(3) By mass%, C: 0.04% to 0.10%, Si: 0.02% to 0.15%, Mn: 0.30% to 1.0%, P: 0.00. 0010% to 0.0100%, S: 0.0001% to 0.0035%, Ni: more than 7.5% to 10.0%, Al: 0.01% to 0.08%, N: 0.0001% or more and 0.0070% or less,
T-O: steel composition containing 0.0001% or more and 0.0050% or less, the balance being Fe and inevitable impurities, and heating the steel slab after continuous casting at 1250 ° C or more and 1380 ° C or less for 10 hours or more After that, the first hot rolling was performed at a rolling ratio of 1.1 to 10 and the temperature before the final one pass of rolling was 800 ° C. to 1200 ° C., and after cooling to 300 ° C., 900 ° C. After heating to 1280 ° C or lower, second hot rolling is performed with a reduction ratio of 3.0 to 50 and a temperature before the final one pass of rolling of 650 ° C to 950 ° C, and subsequently heated if necessary. 750 ° C. or more and 900 ° C. or less, followed by water-cooling or air-cooling quenching, followed by heating to 500 ° C. or more and 650 ° C. or less, followed by water-cooling or air-cooling tempering, Charpy test values preform at 196 ° C., a manufacturing method excellent Ni added steel sheet productivity and toughness is 100J or more welded joints both.
(4) Further, in mass%, Cr: 0.01% to 1.5%, Mo: 0.01% to 0.4%, Cu: 0.01% to 1.0%, Nb: 0 0.001% to 0.05%, Ti: 0.001% to 0.05%, V: 0.001% to 0.05%, B: 0.0002% to 0.05%, Ca : 0.0003% or more and 0.0040% or less, Mg: 0.0003% or more and 0.0040% or less, REM: 0.0003% or more and 0.0040% or less, and the balance is Fe The Ni-added steel sheet having excellent toughness and productivity in which the Charpy test value at −196 ° C. at −196 ° C. is 100 J or more for both the base metal and the welded joint. Manufacturing method.

  According to the present invention, the base material toughness and weld joint toughness of 9% Ni steel can be greatly improved, and the productivity can be improved. That is, it is possible to provide a Ni-added steel sheet having a higher level of brittle fracture resistance than before and a method for producing the same, and it can be said that the invention has high industrial value.

It is a graph which shows the relationship between the interface segregation density | concentration of P, and the Charpy impact absorption energy which is a parameter | index of base material toughness. It is a graph which shows the influence which the heating holding temperature and holding time in 1st hot rolling have on the interface segregation density | concentration of P.

The present invention will be described in detail.
The inventors diligently studied the conditions for significantly improving the toughness of 9% Ni steel and improving the productivity. As a result, it has been found that even when the amount of P is increased by shortening the P removal step that significantly reduces productivity, the interface segregation concentration of P can be reduced, thereby improving toughness. That is, in order to reduce the P segregation concentration of P, it is effective to apply a manufacturing method in which the amount of Si is greatly reduced and the slab after casting is hot-rolled in two stages. FIG. 1 shows the relationship between the P segregation concentration of P and the Charpy impact absorption energy, which is an index of base material toughness. As described above, in order to obtain excellent toughness, the P segregation concentration of P needs to be 0.100% or less in mass%. The interfacial segregation concentration of P in the part containing only 4 is defined as 0.100 % or less. In addition, the part where the interface segregation concentration of P is measured is a part where only ¼ of the steel sheet thickness is entered from the steel sheet surface to the steel sheet thickness direction. This part generally evaluates the material such as strength and toughness. This is because it is a part to be implemented, that is, it is often handled as a material representative part of a steel material. Note that when the P interface segregation amount is 0.05% or less, the toughness is remarkably improved. Therefore, the P interface segregation amount is desirably 0.05% or less.
The interface segregation concentration of P can be measured by observation with a transmission electron microscope and EDS analysis. In the present invention, a thin film is prepared by collecting a sample from a part of the steel sheet that is within ¼ of the thickness of the steel sheet, and the prior austenite grain boundaries, packet grain boundaries, block grain boundaries are obtained with a transmission electron microscope. The interface of any of the above is observed 50 times at 100,000 times, and the average value of the measured amount of interface segregation P is defined as the amount of interface segregation P.

  The addition amount of P is important for lowering the P segregation concentration of P. When the P addition amount exceeds 0.0100%, the P segregation concentration of P exceeds 0.1%. On the other hand, if it is less than 0.0010%, the productivity is greatly reduced due to an increase in the refining load. Therefore, the addition amount of P is defined as 0.0010% or more and 0.0100% or less.

  Since Si has a repulsive interaction with P, increasing the amount of addition increases the P segregation concentration of P. As a result of investigating the relationship between the P segregation concentration of P and the Si addition amount, the inventor has found that the addition amount is 0.15% or less in order to make the P interface segregation concentration 0.1% or less. . On the other hand, if it is less than 0.02%, the productivity is greatly reduced due to an increase in the refining load. Therefore, the addition amount of Si is defined as 0.02% or more and 0.15% or less. Note that when the Si addition amount is 0.10% or less, the toughness is further improved, so the Si addition amount is desirably 0.10% or less. If the Si addition amount is 0.06% or less, the toughness is further improved. Therefore, the Si addition amount is more preferably 0.06% or less.

Since Mn has a repulsive interaction with P, increasing the amount added increases the P segregation concentration of P. As a result of investigating the relationship between the amount of interface segregation of P and the amount of Mn added, the inventor has found that the amount of addition is made 1.00% or less in order to make the interface segregation concentration of P or less 0.1% or less. . On the other hand, if it is less than 0.30% , the tensile strength decreases. Therefore, the amount of Mn added is defined as 0.30% or more and 1.00% or less . In addition, since the toughness is further improved when the Mn addition amount is 0.9% or less, the Mn addition amount is desirably 0.9% or less. When the amount of Mn added is 0.8% or less, the toughness is further improved. Therefore, the amount of Mn added is more preferably 0.8% or less.
The range of other alloy elements is specified below.

Since C is an element essential for ensuring the strength, its addition amount is set to 0.04% or more. However, on the other hand, an increase in the amount of C causes a decrease in base material toughness, weldability, and tensile strength due to the formation of coarse precipitates. Therefore, S with an upper limit of 0.10% is 0.0001%. If the ratio is less than 0.0035%, the productivity is greatly reduced due to an increase in the refining load, and if it exceeds 0.0035%, the toughness is reduced. Therefore, the addition amount of S is defined as 0.0001% or more and 0.0035% or less.

  Ni is an element effective for improving the brittle fracture resistance. If it is 7.5% or less, the margin for improving the brittle fracture resistance is small, and if it exceeds 10.0%, the production cost increases. Therefore, the addition amount of Ni is specified to be more than 7.5% and 10.0% or less.

  Al is an element that is effective as a deoxidizing material. If less than 0.01% is added, deoxidation is insufficient and the toughness of the base metal decreases, and if added over 0.08%, the toughness of the welded joint decreases. Invite. Therefore, the addition amount of Al is defined as 0.01% or more and 0.08% or less.

  When N is less than 0.0001%, productivity decreases due to an increase in the refining load, and when it exceeds 0.007%, the base metal toughness and weld joint toughness decrease. Therefore, the addition amount of N is defined as 0.0001% or more and 0.007% or less.

If T-O is less than 0.0001%, the refining load is very high and the productivity decreases, and if it exceeds 0.0050%, the toughness decreases. Therefore, the T—O amount is regulated to be 0.0001% or more and 0.0050% or less. Note that when the amount of T-O is 0.0015% or less, the toughness is remarkably improved. Therefore, the amount of T-O is desirably 0.0001% or more and 0.0015% or less.
In the present invention, the following elements are further added.

  Cr is an element effective for increasing the strength, and at least 0.01% of addition is necessary, but if added over 1.5%, the weld joint toughness decreases. Therefore, the addition amount of Cr is defined as 0.01% or more and 1.5% or less.

  Mo is an element effective for increasing strength without increasing susceptibility to temper embrittlement. If the addition amount is less than 0.01%, the effect of increasing the strength is small, and if it exceeds 0.4%, the manufacturing cost increases and the welded joint toughness decreases. Therefore, the addition amount of Mo is defined as 0.01% or more and 0.4% or less.

  Cu is an element effective for securing strength. If the addition is less than 0.01%, the effect is small, and if it exceeds 1.0%, the weld joint toughness is reduced. Therefore, the addition amount of Cu is defined as 0.01% or more and 1.0% or less.

  Nb is an element effective for securing strength. If the addition is less than 0.001%, the effect is small, and if it exceeds 0.05%, the weld joint toughness is lowered. Therefore, the addition amount of Nb is defined as 0.001% or more and 0.05% or less.

  Ti is an element effective for improving toughness. If the addition is less than 0.001%, the effect is small, and if it exceeds 0.05%, the weld joint toughness is lowered. Therefore, the addition amount of Ti is defined as 0.001% or more and 0.05% or less.

  V is an element effective for ensuring the strength. If the addition is less than 0.001%, the effect is small, and if it exceeds 0.05%, the weld joint toughness is lowered. Therefore, the addition amount of V is defined as 0.001% or more and 0.05% or less.

  B is an element effective for securing the strength. If the addition is less than 0.0002%, the effect is small, and if it exceeds 0.05%, the toughness of the base material is lowered. Therefore, the addition amount of B is defined as 0.0002% or more and 0.05% or less.

  Ca is an element effective for preventing nozzle clogging. If the addition is less than 0.0003%, the effect is small, and if the addition exceeds 0.0040%, the toughness is reduced. Therefore, the addition amount of Ca is defined as 0.0003% or more and 0.0040% or less.

  Mg is an element effective for improving toughness. If the addition is less than 0.0003%, the effect is small, and if the addition exceeds 0.0040%, the toughness is reduced. Therefore, the addition amount of Ca is defined as 0.0003% or more and 0.0040% or less.

REM is an element effective for preventing nozzle clogging. If the addition is less than 0.0003%, the effect is small, and if the addition exceeds 0.0040%, the toughness is reduced. Therefore, the amount of REM added is specified to be 0.0003% or more and 0.0040% or less.
In addition, Zn, Sn, Sb, Zr, etc., which can be mixed as raw materials including additive alloys or inevitable impurities eluted from furnace materials during melting when the steel of the present invention is melted, are 0.002 If it is less than%, the effect of the present invention is not impaired.

Next, the manufacturing method of this invention is demonstrated.
The first hot rolling in which hot rolling is performed after the cast slab is heated at a high temperature for a long time is also important for reducing the P segregation concentration of P. As a result of investigating the influence of the heating holding temperature and holding time on the interface segregation concentration of P in the first hot rolling, the inventor found that the P segregation concentration of P is 0.100 % or less as shown in FIG. It was found that it is necessary to set the heating and holding temperature to 1250 ° C. or more and the holding time to 10 hours or more. P interface segregation is reduced by heating at a high temperature, and as a result, the final P grain boundary segregation concentration is lowered. On the other hand, when the heating and holding temperature exceeds 1380 ° C. and the holding time exceeds 50 hours, the productivity is significantly reduced. Therefore, the heating and holding temperature is set to 1250 ° C. to 1380 ° C., and the holding time is set to 10 hours to 50 hours. Is preferred. Note that when the heating and holding temperature is 1300 ° C. or more and the holding time is 20 hours or more, the grain boundary segregation concentration of P is significantly reduced. Therefore, the heating and holding temperature in the first hot rolling is desirably 1300 to 1380 ° C. Hereinafter, the holding time is 20 hours or more and 50 hours or less. It is important to perform hot rolling after heating and holding. When processing strain is introduced by hot rolling, the diffusion of P becomes easy and the final grain boundary segregation concentration of P decreases. If the temperature measured on the surface before the first pass of hot rolling exceeds 1200 ° C, the effect of reducing the amount of P grain boundary segregation is small due to recovery of processing strain, and if it falls below 800 ° C, the productivity is greatly reduced. Therefore, the temperature before the first pass in the first hot rolling is set to 800 ° C. or more and 1200 ° C. or less. The reduction ratio is also important. If the reduction ratio is less than 1.1, the processing strain is small, and the effect of reducing the P grain boundary segregation concentration is small. If the reduction ratio is more than 10, the productivity is significantly reduced. Therefore, the reduction ratio in the first hot rolling is set to 1.1 or more and 10 or less. Here, the temperature before one pass means the temperature measured on the surface of the steel slab immediately before the final pass of the first hot rolling, and can be measured with a radiation thermometer or the like. Here, the reduction ratio is a value obtained by dividing the steel slab thickness before the start of rolling in the first hot rolling by the steel slab thickness after the end of rolling.

After the first hot rolling described above, the second hot rolling is performed. The conditions for hot rolling are arbitrary, but standard conditions are described here. After the first hot rolling, the temperature is raised again after cooling to 300 ° C. or lower, heated to 900 ° C. or higher and 1280 ° C. or lower, and then rolled at a reduction ratio of 3.0 or higher and 50 or lower. The final one-pass temperature of rolling is set to 650 ° C. or higher and 950 ° C. or lower, and then cooled. After hot rolling, quenching is performed. When the heating temperature at the time of quenching is lower than 750 ° C. or exceeds 900 ° C., an embrittled structure or a coarse structure is generated and the toughness is lowered. Therefore, the heating temperature at the time of quenching is defined as 750 ° C. or higher and 900 ° C. or lower. Upon a 650 ° C. or higher 950 ° C. or less of the second hot rolling final pass temperature range, below 900 ° C. 750 ° C. or higher temperature range quenching is because the ranges overlap, to a temperature range of hardening, it required any Heat to the quenching temperature range. In addition, after heating at the time of quenching, after holding, it is cooled with water. Following quenching, tempering is performed. When the heating temperature for tempering is less than 500 ° C. or exceeds 650 ° C., the toughness is lowered. Therefore, the heating temperature at the time of tempering is defined as 500 ° C. or more and 650 ° C. or less. After the tempering heating, after holding, it is cooled with water or air.

  For steel plates with a thickness of 6 to 50 mm manufactured under various chemical components and manufacturing conditions, the yield stress and tensile strength of the base material, the C direction Charpy test of the base material, the thickness of the Charpy test steel plate of the welded joint, the chemical composition, Tables 1 and 2 show the interface segregation concentration and production method of P, and Table 3 shows the evaluation results of the characteristics.

  Yield stress and tensile strength were measured by a metal material tensile test method described in JIS Z 2241. The test piece is a metal material tensile test piece as described in JIS Z 2201, No. 5 test piece from a steel plate with a plate thickness of 20 mm or less, and No. 10 test taken from a 1/4 t portion from the steel plate surface from a steel plate with a plate thickness of 40 mm or more. A piece was used. The test piece was collected so that the longitudinal direction was perpendicular to the rolling direction. The yield stress was 0.2% proof stress calculated by the offset method. Two tests were performed at room temperature, and an average value was adopted. The yield stress was 590 MPa or more, and the tensile strength was 690 MPa or more.

  The toughness of the base metal and the welded joint was evaluated by a Charpy test. The test piece used was a full-size test piece having a cross section of 10 × 10 mm for a plate thickness of 12 mm or more, and a sub-size test piece having a cross section of 10 × 5 mm for a plate thickness of 6 mm. For the base material, the C direction in which the longitudinal direction of the test piece was perpendicular to the rolling direction was evaluated. In the evaluation of weld joint toughness, test pieces were collected so that the notch tips correspond to weld bonds. The test temperature was −196 ° C., and the lowest value obtained by performing three tests was adopted. In the Charpy test, 100 J or more was accepted and less than 100 J was rejected.

  In addition, the welded joint used for the Charpy test of the welded joint was produced by SMAW. The conditions for SMAW are heat input of 3.5 to 4.0 kJ / cm, vertical welding, preheating, and interpass temperature of 100 ° C. or less.

  Invention Example 1 is a steel sheet having a thickness of 6 mm, which is excellent in base metal toughness and weld joint toughness. On the other hand, although Comparative Example 1 is a production method similar to Invention Example 1, since the C content is outside the scope of the present invention, it is inferior in the base metal toughness and weld joint toughness regardless of the P segregation concentration of P. .

  Invention Example 2 is a steel sheet having a thickness of 12 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although the comparative example 2 is a manufacturing method similar to the invention example 2, since Si amount is outside the scope of the present invention, it is inferior to the base metal toughness and the welded joint toughness.

  Invention Example 3 is a steel sheet having a thickness of 20 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although the comparative example 3 is a component similar to the invention example 3, since the rolling reduction ratio of the first hot rolling is out of the range of the present invention, it is inferior to the base metal toughness and the welded joint toughness.

  Invention Example 4 is a steel sheet having a thickness of 32 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 4 is a production method similar to Invention Example 4, since the total rolling reduction and P amount are out of the scope of the present invention, the base material toughness and welded joint are independent of the P segregation concentration of P. Inferior toughness.

  Invention Example 5 is a steel sheet having a thickness of 40 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 5 is a production method similar to Invention Example 5, since the amount of S is outside the range of the present invention, the base metal toughness and weld joint toughness are inferior regardless of the P segregation concentration of P.

  Invention Example 6 is a steel sheet having a thickness of 40 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 6 is a manufacturing method similar to Invention Example 6, since the amount of Ni is outside the scope of the present invention, the base metal toughness and weld joint toughness are inferior regardless of the interface segregation concentration of P.

  Invention Example 7 is a steel sheet having a thickness of 6 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 7 is a production method similar to Invention Example 7, since the Al content is outside the range of the present invention, the base material toughness and weld joint toughness are inferior regardless of the P segregation concentration of P.

  Invention Example 8 is a steel sheet having a thickness of 12 mm, and is excellent in base metal toughness and weld joint toughness. On the other hand, although the comparative example 8 is a component similar to the invention example 8, since the amount of Al is outside the range of the present invention, the base metal toughness and the welded joint toughness are inferior regardless of the interface segregation concentration of P.

  Invention Example 9 is a steel sheet having a thickness of 20 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 9 is a production method similar to Invention Example 9, since the N amount is outside the scope of the present invention, the base metal toughness and weld joint toughness are inferior regardless of the P segregation concentration of P.

  Invention Example 10 is a steel sheet having a thickness of 40 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 10 is a component similar to Invention Example 10, the heating temperature and the amount of interfacial segregation P in the first hot rolling are out of the scope of the present invention. Inferior to

  Invention Example 11 is a steel sheet having a thickness of 40 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 11 is a component similar to Invention Example 11, the final one pass temperature and interface segregation P amount in the first hot rolling are out of the scope of the present invention. Inferior to weld joint toughness.

  Invention Example 12 is a steel sheet having a thickness of 6 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although the comparative example 12 is a component similar to the invention example 12, since the temperature before 1 last pass and the amount of interface segregation P are outside the scope of the present invention, the base material toughness and the welded joint toughness are inferior.

  Invention Example 13 is a steel sheet having a thickness of 12 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 13 is a component similar to Invention Example 13, since the quenching heating temperature is outside the range of the present invention, the base material toughness and the weld heat affected zone toughness regardless of the P segregation concentration of P. Inferior to

  Invention Example 14 is a steel sheet having a thickness of 20 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 14 is a component similar to Invention Example 14, the quenching heating temperature is out of the range of the present invention, so that the base metal toughness and weld joint toughness are inferior regardless of the interface segregation concentration of P. .

  Invention Example 15 is a steel sheet having a thickness of 32 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 15 is a component similar to Invention Example 15, the interfacial segregation concentration of P and the tempering heating temperature are out of the scope of the present invention, so that the base metal toughness and the welded joint toughness are inferior.

  Invention Example 16 is a steel sheet having a thickness of 40 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although Comparative Example 16 is a component similar to Invention Example 16, since the tempering heating temperature is out of the range of the present invention, the base metal toughness and weld joint toughness are inferior regardless of the interface segregation concentration of P. .

  Invention Example 17 is a steel sheet having a thickness of 40 mm, and is excellent in base metal toughness and weld joint toughness. On the other hand, although Comparative Example 17 is a component similar to Invention Example 17, the interface segregation concentration of P and the holding time in the first hot rolling are out of the scope of the present invention. Inferior toughness.

  Invention Example 18 is a steel sheet having a thickness of 20 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although the comparative example 18 is a manufacturing method similar to the invention example 18, since the amount of Mn is outside the range of this invention, it is inferior to weld joint toughness.

  Invention Example 19 is a steel sheet having a thickness of 40 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although the comparative example 19 is a manufacturing method similar to the invention example 19, since the amount of C is outside the scope of the present invention, the strength is low.

  Invention Example 20 is a steel sheet having a thickness of 40 mm, and is excellent in base metal toughness and welded joint toughness. On the other hand, although the comparative example 20 is a manufacturing method similar to the invention example 20, since the amount of Mn is outside the scope of the present invention, the strength is low.

Invention Example 21 is a steel sheet having a thickness of 32 mm, and is excellent in base metal toughness and weld joint toughness. On the other hand, although Comparative Example 21 is a manufacturing method similar to Invention Example 21, since the T—O amount is out of the scope of the present invention, it is inferior in the base metal toughness and weld joint toughness.
From the above examples, it is clear that the steel plates of Invention Examples 1 to 21 which are thick steel plates manufactured according to the present invention are steel plates having excellent fracture resistance.

Claims (4)

Steel is mass%
C: 0.04% or more and 0.10% or less,
Si: 0.02% or more and 0.15% or less,
Mn: 0.30% or more and 1.00% or less,
P: 0.0010% or more and 0.0100% or less,
S: 0.0001% to 0.0035%,
Ni: more than 7.5% and 10.0% or less,
Al: 0.01% or more and 0.08% or less,
N: 0.0001% or more and 0.0070% or less,
TO: contains 0.0001% or more and 0.0050% or less, and the balance is a steel composition composed of Fe and inevitable impurities, and enters the steel sheet thickness direction by a quarter of the steel sheet thickness from the steel sheet surface. The interfacial segregation concentration of P in the part is mass% and 0.100% or less, and the Charpy test value at −196 ° C. is 100 J or more for both the base metal and the welded joint, and excellent in toughness and productivity. Ni-added steel sheet. In addition,
Cr: 0.01% or more and 1.5% or less,
Mo: 0.01% to 0.4%,
Cu: 0.01% or more and 1.0% or less,
Nb: 0.001% or more and 0.05% or less,
Ti: 0.001% or more and 0.05% or less,
V: 0.001% to 0.05%,
B: 0.0002% to 0.05%,
Ca: 0.0003% or more and 0.0040% or less,
Mg: 0.0003% or more and 0.0040% or less,
REM: It contains any one of 0.0003% or more and 0.0040% or less, and the balance is a steel composition composed of Fe and inevitable impurities. A Ni-added steel sheet with excellent toughness and productivity with Charpy test values of 100 J or more for both base metal and welded joint. % By mass
C: 0.04% or more and 0.10% or less,
Si: 0.02% or more and 0.15% or less,
Mn: 0.30% or more and 1.00% or less,
P: 0.0010% or more and 0.0100% or less,
S: 0.0001% to 0.0035%,
Ni: more than 7.5% and 10.0% or less,
Al: 0.01% or more and 0.08% or less,
N: 0.0001% or more and 0.0070% or less,
T-O: Steel pieces after continuous casting containing 0.0001% or more and 0.0050% or less, with the balance being Fe and inevitable impurities, for 10 hours or more at 1250 ° C or more and 1380 ° C or less After heating, the first hot rolling with a rolling ratio of 1.1 to 10 and a temperature before the final one pass of rolling of 800 ° C. to 1200 ° C. is performed, and after cooling to 300 ° C. or less, 900 ° C. After heating to 1280 ° C. or lower, the second hot rolling is performed with a reduction ratio of 3.0 to 50 and the final one-pass temperature before rolling of 650 ° C. to 950 ° C., and subsequently heated if necessary. Then, quenching is performed by water cooling or air cooling after the temperature is set to 750 ° C. or more and 900 ° C. or less, and further, tempering is performed by heating to 500 ° C. or more and 650 ° C. or less and then water cooling or air cooling. Charpy test value matrix at -196 ° C., a manufacturing method excellent Ni added steel sheet productivity and toughness is 100J or more welded joints both. In addition,
Cr: 0.01% or more and 1.5% or less,
Mo: 0.01% to 0.4%,
Cu: 0.01% or more and 1.0% or less,
Nb: 0.001% or more and 0.05% or less,
Ti: 0.001% or more and 0.05% or less,
V: 0.001% to 0.05%,
B: 0.0002% to 0.05%,
Ca: 0.0003% or more and 0.0040% or less,
Mg: 0.0003% or more and 0.0040% or less,
REM: It contains any one of 0.0003% or more and 0.0040% or less, and the balance is a steel composition composed of Fe and unavoidable impurities at −196 ° C. A method for producing a Ni-added steel sheet having excellent toughness and productivity, with Charpy test values of 100 J or more for both the base metal and the welded joint.