JPH08277442A - High strength and high toughness 9% nickel shape steel and its production - Google Patents

Abstract

PURPOSE: To produce a 9% Ni shape steel excellent in strength and toughness. CONSTITUTION: A shape steel having a compsn. contg., by weight, 0.04 to 0.12% C, 0.05 to 0.40% Si, 0.40 to 0.90% Mn, 8.50 to 9.50% Ni, 0.05 to 0.15% Cr, and the balance iron with inevitable impurities and satisfying C(%)+1/6Mn(%)+1/5Cr(%) >=0.185 is normalized at the Ac3 or above, is furthermore normalized at the Ac3 or above once more and is then subjected to tempering treatment of heating to the temp. range of 550 to 600 deg.C and thereafter executing air-blast cooling to an ordinary temp. so as to regulate the cooling rate to 400 deg.C to 0.5 to 5 deg.C/S.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a 9% Ni shaped steel excellent in strength and toughness which constitutes equipment and pressure vessel for manufacturing, transporting and storing products at extremely low temperature such as liquid nitrogen and liquefied natural gas, and The present invention relates to a manufacturing method thereof.

[0002]

2. Description of the Related Art Extremely low temperature (for example, -196 for liquid nitrogen)
℃, liquefied natural gas is -162 ℃) As a steel material that constitutes equipment and pressure vessels that handle products, Ni-containing steel having excellent toughness and high strength at extremely low temperatures, especially 9% Ni steel, has been developed. It has been put to practical use. It is well known that the strength and toughness of this 9% Ni steel are determined by the component composition and heat treatment, and the 9% Ni steel sheet is standardized. However, the composition of 9% Ni shaped steel and the heat treatment method have not been standardized.

Means conventionally used for imparting serviceability to 9% Ni-section steel is JIS G shown in Table 1.
3127 (SL9N520) and ASTM-A353
It depends on the chemical composition and heat treatment specified in. In particular, in the case of shaped steel, it is extremely difficult to perform quenching-tempering without deformation and bending due to the complexity of the shape, so a double-tempering-tempering type heat treatment is adopted. There is.

[0004]

[Table 1]

[0005]

However, in the proper production with the chemical components and the heat treatment which are standardized as described above, the strength may be slightly above or below the lower limit of the standard in some cases. Also, the V-notch Charpy absorbed energy at -196 ° C (hereinafter abbreviated as absorbed energy) was found to be slightly higher than the lower limit of the standard, especially for thick materials. An intermediate heat treatment was also attempted to improve the toughness (details will be described later), but although the absorbed energy at -196 ° C is improved to a sufficient level, the yield point is remarkably lowered due to the increase in precipitated austenite, and It was off. In recent years, the absorbed energy at -196 ° C is 100.
The need for high quality 9% Ni shaped steel called J has emerged. For this reason, the strength of the above standard and -196 are stable.
There is a demand for a method for manufacturing 9% Ni-shaped steel that satisfies the absorbed energy at ° C.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to such problems, that is, 9% Ni-shaped steel, specifically tensile strength, that sufficiently satisfies the mechanical properties specified in JIS G3127 (SL9N520) and ASTM A353-82. Is a 9% Ni shaped steel having an average value of 725 N / mm ² or more and an absorbed energy at -196 ° C. of 100 J or more, and a manufacturing method thereof, and the gist is as follows.

(1) C: 0.04 to 0.12 in% by weight
%, Si: 0.05 to 0.40%, Mn: 0.40
0.90%, Ni: 8.50 to 9.50%, Cr: 0.
05-0.15%, the balance consisting of iron and inevitable impurities, and C (%) + 1 / 6Mn (%) + 1 / 5Cr
Steel having a composition satisfying (%) ≧ 0.185,
Tensile strength of 5 N / mm ² or more and 100 J or more of -196 ° C
9% Ni shaped steel having high strength and high toughness, which has Charpy impact absorption energy in

(2) C by weight%: 0.04 to 0.12
%, Si: 0.05 to 0.40%, Mn: 0.40
0.90%, Ni: 8.50 to 9.50%, Cr: 0.
05-0.15%, the balance consisting of iron and inevitable impurities, and C (%) + 1 / 6Mn (%) + 1 / 5Cr
(%) ≧ 0.185, a shaped steel having a composition satisfying Ac
Normalizing fired at ₃ temperatures above once again Ac normalizing fired at _three or more temperature and then cooling rate to 400 ° C. After heating to a temperature range of 550 to 600 ° C. is 0.5 to 5 ° C. / S
A high strength and high toughness 9% Ni shaped steel manufacturing method, characterized by performing a tempering treatment in which a blast cooling such that

(3) C by weight%: 0.04 to 0.12
%, Si: 0.05 to 0.40%, Mn: 0.40
0.90%, Ni: 8.50 to 9.50%, Cr: 0.
05-0.15%, the balance consisting of iron and inevitable impurities, and C (%) + 1 / 6Mn (%) + 1 / 5Cr
(%) ≧ 0.185, a shaped steel having a composition satisfying Ac
Normalizing fired at ₃ temperatures above once more cooling rate until heated to Ac ₃ temperature above 400 ° C. is 0.7 to 5 ° C. / S
High strength and high toughness 9% Ni, characterized by performing normalizing by blast cooling to room temperature, and then performing tempering treatment in the temperature range of 550 to 600 ° C.
Shaped steel manufacturing method.

(4) C by weight%: 0.04 to 0.12
%, Si: 0.05 to 0.40%, Mn: 0.40
0.90%, Ni: 8.50 to 9.50%, Cr: 0.
05-0.15%, the balance consisting of iron and inevitable impurities, and C (%) + 1 / 6Mn (%) + 1 / 5Cr
(%) ≧ 0.185, a shaped steel having a composition satisfying Ac
Normalizing fired at ₃ temperatures above once more cooling rate until heated to Ac ₃ temperature above 400 ° C. is 0.7 to 5 ° C. / S
Blast cooling to room temperature, then 550-
High-strength and high-toughness characterized by performing a tempering treatment in which wind-cooling is performed up to room temperature such that the cooling rate up to 400 ° C is 0.5 to 5 ° C / S after heating in the temperature range of 600 ° C 9 % Ni shaped steel manufacturing method.

The reasons for limiting the components of the present invention and the heat treatment conditions will be described in detail below. C increases the hardenability to improve the strength, but if it is less than 0.04%, JIS G3127
(SL9N520) and ASTM A353-82, the lower limit is set to 0 because the strength is not stably satisfied.
The upper limit was made 0.14% because the presence of excessive C increases the amount of solid solution in the phyllite and reduces the toughness.

Si is necessary as a deoxidizing component and is usually 0.05
% Or more. Further, if the content is 0.40% or more, the toughness tends to decrease. Therefore, it is limited to 0.05 to 0.40%. Ni is a useful element indispensable for improving toughness and strength, and is diffused and absorbed in austenite during tempering to stabilize precipitated austenite at a low temperature. However, if the content is too large, it becomes expensive, so the content was limited to 8.50 to 9.50%.

Mn improves the hardenability of steel and stabilizes the ultrafine austenite precipitated during tempering to enhance the toughness and strength of the ferrite body. However, if too much, 0.4 is added to promote temper brittleness.
It was limited to 0 to 0.90%. Cr improves hardenability and strength. However, a large amount is not preferable because it stabilizes the carbide to a high temperature and increases the temper susceptibility to brittleness. Therefore, it is limited to 0.05 to 0.15%.

In order to obtain stable tensile strength (725 N / mm ² ) as well as excellent toughness, the present invention not only has the above-mentioned effects and range limits of each element, but also C (%) + 1 / 6Mn.
The range of additional elements is limited so that (%) + 1 / 5Cr (%) ≧ 0.185.

FIG. 1 shows JIS G3127 (SL9N52).
0) and ASTM A353-82, the steel ingots of more than 20 kinds of composition are rolled into three types of equilateral angle steel, and then the first normalizing (heating temperature 890 ° C, natural air cooling) → 2 times normalizing (heating temperature 790 ° C, natural cooling) → tempering (575 ° C, natural cooling), though (C (%) + 1 / 6Mn (%) + 1 / 5Cr)
(%)) And the tensile strength are shown, but both have a very good correlation.

Further, FIG. 2 shows that C (%) + 1 / 6Mn (%)
+ 1 / 5Cr (%) = 0.180 and a steel ingot having a composition of 0.167 were rolled into unequal thickness unequal thick angle steel, and then the heat treatment of the present invention, that is, the first normalizing (heating temperature 890
℃, natural air cooling → 2nd normalizing (heating temperature 790 ℃,
Wind cooling) → Tempering (heating temperature 575 ° C, natural air cooling)
Although the above heat treatment is performed, the relationship between the cooling rate during the second normalization and the absorbed energy at −196 ° C. is shown. In the range of the cooling rate of the present invention, excellent absorbed energy exceeding 100 J that is the target is obtained. To be Table 2 shows the chemical composition of materials A and B in FIG.

[0017]

[Table 2]

However, in FIG. 3 which similarly shows the relationship between the cooling rate and the tensile strength at the time of the second normalizing, although the yield point increases even in the cooling rate range of the present invention, the tensile strength does not increase so much and the standard It is slightly above the lower limit. This is the chemical composition of the angle steel C + 1 / 6Mn + 1 / 5Cr ≦ 0.18.
5 is caused. Based on the above results, in the present invention, in order to obtain a stable tensile strength (725 Nmm ² ), C (%) + 1 / 6Mn (%) + 1 / 5Cr (%) ≧ 0.
185. Table 3 shows the chemical composition of materials A and B in FIG.

[0019]

[Table 3]

Next, the heat treatment conditions of the present invention will be described.
FIG. 4 shows C (%) + 1 / 6Mn in the composition range of the present invention.
(%) + 1 / 5Cr (%) = 0.203 steel ingot is rolled into equilateral angle steel (150mm × 150mm × 10mm), then 1st normalizing (heating temperature 890 ° C, natural air cooling) → 2nd Tensile strength at the time of heat treatment of tempering (heating temperature 790 ° C, natural air cooling and wind cooling) → tempering (heating temperature 575 ° C, natural air cooling) and cooling rate at the time of second tempering Shows the relationship with.

FIG. 5 also shows the relationship between the absorbed energy at −196 ° C. and the cooling rate during the second normalizing. The tensile strength shows a slight decrease as the cooling rate in the ^second normalizing becomes faster, but by adjusting the component composition, 725 N / mm ² or more can be secured within the cooling rate range of the present invention.

The absorbed energy at −196 ° C. of the test piece taken from the rolling direction (L direction) increases up to the cooling rate of 2 ° C./S during the second normalizing, but above that, it is stable at a high level. To do. On the other hand, the absorbed energy at −196 ° C. of the sample taken from the direction perpendicular to the rolling direction (C direction) becomes higher as the cooling rate becomes faster.

The improvement of the absorbed energy at -196 ° C. is to increase the amount of fine martensite after tempering by increasing the cooling rate during the second normalizing.
Refining and uniform dispersion of carbides, refinement and homogenization of precipitated austenite, stabilization of precipitated austenite (-19
It is stable even at an extremely low temperature of 6 ° C.).

FIG. 6 shows the equine angle steel having the above-described composition and size, the first normalizing (heating temperature 890 ° C., natural air cooling) → the second normalizing (heating temperature 790 ° C., natural air cooling)
→ The relationship between the cooling rate after tempering and the tensile strength when heat treatment of tempering (heating temperature 575 ° C., natural air cooling and wind cooling) is shown, and FIG. 7 also shows the cooling rate after tempering and − The relationship of the absorbed energy at 196 ° C is shown.

As is clear from the figure, the tensile strength in the case of tempering the section steel which was naturally air-cooled after the second normalization was slightly lowered when the cooling rate after tempering was increased, but was set as a target. 725 N / mm ² is sufficiently satisfied, and the absorbed energy at −196 ° C. is remarkably improved in proportion to the cooling rate after tempering.

The improvement of the absorbed energy at -196 ° C. is due to the relaxation of temper embrittlement, that is, the suppression of grain boundary precipitation / aggregation of carbides by blast cooling, and the increase of precipitated austenite which is stable even at an extremely low temperature. I knew it was.

FIG. 8 shows the first normalizing of equilateral angle steel having the above-described composition and size (heating temperature 890 ° C., natural air cooling).
→ 2nd normalizing (heating temperature 790 ° C, air cooling) → tempering (heating temperature 575 ° C, natural air cooling and air cooling)
FIG. 9 shows the relationship between the cooling rate after tempering and the tensile strength when the above heat treatment was performed, and FIG. 9 shows the relationship between the cooling rate after tempering and the absorbed energy at −196 ° C.

After the second tempering, the tensile strength in the case of temper tempered shaped steel that has been cooled by blast does not depend much on the cooling rate after tempering, and the target value is sufficient in the composition range of the present invention. To be satisfied with. Also sampled from the rolling direction -196 ° C
The absorbed energy of 1 shows high stability without depending on the cooling rate, but the absorbed energy at -196 ° C of the sample taken at a right angle to the rolling direction improves in proportion to the cooling rate. Such an improvement in low temperature toughness is a result of the fact that tempering brittleness is relaxed by the blast cooling during tempering, in addition to the effect of blast cooling after the second tempering described above. .

As described above, C (%) + 1 / 6Mn (%) + 1 / 5Cr of the present invention obtained by hot rolling a steel ingot produced by the steel ingot method or a slab produced by the continuous casting method.
(%) In the form steel composition of ≧ 0.185, normalizing baked by a heat treatment i.e. Ac ₃ temperatures above the present invention, normalizing baked at once more Ac ₃ or higher, and then 550 to 600
After being heated in the temperature range of ℃, heat treatment is performed to cool the air flow to 400 ℃ is 0.5 to 5 ℃ / S, and the heat treatment is performed to room temperature, the high strength and excellent low temperature toughness 9 % Ni shaped steel can be manufactured.

Further, the present invention is the same as the above hot rolled steel
Normalizing fired at ₃ temperatures above once more cooling rate until heated to Ac ₃ temperature above 400 ° C. is 0.7 to 5 ° C. / S
Blast cooling to room temperature, then 550-
A heat treatment for performing a tempering process of heating within a temperature range of 600 ° C. is performed.

Further, in the present invention, the hot-rolled shaped steel is the same as Ac ₃
Normalize at the above temperature, heat it again to a temperature of Ac ₃ or higher, and cool it to 400 ° C with a blast cooling of 0.7 to 5 ° C / S to room temperature, then 550 to 6
After being heated to a temperature range of 00 ° C., heat treatment is performed to cool it to room temperature by blast cooling so that the cooling rate up to 400 ° C. is 0.5 to 5 ° C./S.

If the cooling rate after the second normalizing and after the tempering exceeds 5 ° C./S, the large bending of the product will be JI.
Since it was clarified that it did not fall within the allowable range of the S standard, the upper limit of the cooling rate was set to 5 ° C / S. If the cooling rate at the time of the second normalizing is less than 0.7 ° C / S, the absorbed energy at -196 ° C may be less than the target 100J, so 0.7 ° C / S is set as the lower limit of the cooling rate, The lower limit of the cooling rate during tempering was set to 0.5 ° C./S for the same reason.

[0033]

[Example] The steel ingots of the five components shown in Table 4 are one type of unequal side unequal thick angle steel {250 mm × 90 mm × 15 mm × (flange thickness) × 10 mm (web thickness)}, three types of equilateral angle steel { Two
50mm x 250mm x 25mm, 200mm x 200mm x 20
mm, 150 mm × 150 mm × 10 mm} and then cut into lengths of 10 m, and heat-treated at trial numbers 1 to 18 in a heat treatment furnace of a factory.

In the term of the cooling rate of the heat treatment conditions, the mark * is kept at a predetermined temperature (30 minutes for non-equal unequal thick angle steel, 45 minutes for equilateral angle 200 mm x 200 mm x 20 mm, 250
mm x 250 mm x 25 mm for 60 minutes, 150 mm x 150 mm
(× 10 mm for 30 minutes), and after being extracted from the heating furnace, it was naturally air-cooled.

Those not marked with * are those subjected to blast cooling while extracting from the heating furnace and oscillating the shaped steel in the cooling floor with large air blowers arranged at appropriate intervals on both sides.

A tensile test piece and a 2 mm V-notch Charpy impact test piece (full size) were taken in parallel with the rolling direction from the position of the ½ flange at the center in the length direction of each heat-treated shaped steel and mechanically sampled. The nature was investigated. The results are summarized in Table 4.

[Table 4]

[0037]

[Table 5]

In Table 4, trial numbers 1 to 3 are C (%) + 1 / 6M
It shows the relationship between the heat treatment conditions and the mechanical properties of the shaped steel having the conventional composition of n (%) + 1 / 5Cr (%) = 0.167 which is out of the present invention. That is, in the trial number 1, the cooling rate of the ^second normalizing and tempering is slower than the cooling rate of the present invention (natural air cooling), and the tensile strength thereof is 686 N / mm ^{2 according} to JIS.
G3127 / SL9N520 standard (hereinafter abbreviated as standard)
And the absorbed energy at -196 ° C is also low.

Test No. 2 is one in which the cooling rate of the second normalizing and tempering is increased to the range of the present invention.
Although a remarkable increase in absorbed energy at 196 ° C. was recognized, the tensile strength was only slightly improved and was below the target value (725 N / mm ² ) just within the lower limit of the standard. Trial number 3 is second
A so-called intermediate heat treatment is applied instead of the normalizing, but in this case, the yield point is remarkably lowered and the result is out of the specification.

Further, the trial compositions Nos. 4 and 5 are component compositions (C + 1 / 6Mn + 1 / 5Cr =) having higher hardenability than the trial Nos. 1 to 3.
0.180), but the cooling rate of the second normalizing and tempering is lower than that of the present invention (natural air cooling), the tensile strength of the test No. 4 is 698 N / mm ² , which is slightly lower than the lower limit of the specification. It exceeds the level, and the absorbed energy at -196 ° C is 68J.
Is lower than the target value (100J).

Test No. 5 has a cooling rate for the second normalizing and tempering increased to the range of the present invention, and is -196 ° C.
Although the absorbed energy of is remarkably improved, the tensile strength is just below the lower limit of the standard.

On the other hand, trial Nos. 6 to 18 show the relationship between the heat treatment conditions and the mechanical properties of the shaped steels having the composition within the range of the present invention. Trial Nos. 6 to 10 are C + 1 / 6Mn + 1 / 5Cr =
In the case of a 25 mm equilateral angle steel having a composition of 0.204, the cooling rate of the second normalizing and tempering is smaller than the range of the present invention (natural air cooling), the tensile strength of trial No. 6 Satisfies the standard and exceeds the target value,
Absorbed energy at -196 ° C is not much different from trial number 1 50J
Met.

However, trial number 7 in which the cooling rate for tempering was increased to 0.62 ° C./S within the range of the present invention, and trial number in which the cooling rate for the second normalizing was also increased to 0.86 ° C./S 8 and second
Both of the trial numbers 9 in which the cooling rates of both the normalizing and the tempering were increased within the scope of the present invention, the tensile strength (725 N / mm ² ) and the target tensile strength (725 N / mm ² ) which exceeded the standard were satisfied. Satisfies the absorbed energy (100 J).

Also, in the trial No. 10 in which the tempering temperature was set to 600 ° C. and the cooling rates of the second normalizing and the tempering were within the scope of the present invention, the tempering temperature was 575 ° C. and the cooling condition was trial No. 10. The same mechanical property as that of trial No. 9 was exhibited.

Test Nos. 11 to 14 are C (%) + 1/6 Mn
(%) + 1 / 5Cr (%) = 0.203 shows the relationship between heat treatment conditions and mechanical properties of equilateral angle steel with a thickness of 10 mm, which is the same as trial number 6-10. Showed a trend. That is, although trial number 11 with a low cooling rate for the second normalizing and tempering (natural air cooling) has a high tensile strength, the absorbed energy at −196 ° C. is below the target value, but it is at the lower limit level.

On the other hand, the cooling rate for tempering is 1.01 ° C./S.
No. 12 increased to 1, the second normalizing cooling rate was also increased to 1.60 ° C./S, and the second cooling rate for both normalizing and tempering is within the range of the present invention. The tensile strength of each of the raised test Nos. 14 sufficiently satisfies the standard and exceeds the target value. Further, the absorbed energy at −196 ° C. is improved in all of the trial numbers 12 to 14 to more than twice that of the trial number 11 which is naturally air cooled after the second normalizing and tempering.

Test Nos. 15 to 18 are C (%) + 1/6 Mn
(%) + 1 / 5Cr (%) = 0.192, the tempering temperature of the equilateral angle steel with a thickness of 20 mm is 550
The relationship between heat treatment conditions and mechanical properties when the temperature is set to ° C is shown. Even if the tempering temperature reaches 550 ° C., the cooling rate for the second tempering and tempering is within the range of the present invention, trial number 1.
Each of Nos. 6, 17 and 18 has a value of −19 as compared with Test No. 15 in which the cooling rate of the second normalizing and the tempering is small.
The absorbed energy at 6 ° C. is improved by about 1.5 to 2 times.

[0048]

EFFECTS OF THE INVENTION By defining the component composition or the component composition and the cooling rate of the second normalizing and tempering, the conventional component composition and heat treatment method (the second normalizing and tempering are naturally air cooled). It has a tensile strength of 7
A high-strength, high-toughness 9% Ni shaped steel having an absorbed energy of 25 N / mm ² or more and an absorption energy of -196 ° C of 100 J can be manufactured.

[Brief description of drawings]

FIG. 1 C (%) + 1/6 Mn (%) + 1 / 5Cr
The chart which shows the relationship between the value of (%) and tensile strength (TS).

FIG. 2 is a chart showing the relationship between the cooling rate between 760 and 400 ° C. and the absorbed energy at −196 ° C. during the second normalizing.

FIG. 3 is a chart showing the relationship between the cooling rate and the tensile strength between 760 and 400 ° C. during the second normalizing.

FIG. 4 shows the relationship between the cooling rate, tensile strength (TS) and yield point (YP) between 760 and 400 ° C. during the second normalizing of equilateral angle steel (150 × 150 × 10). Chart showing.

FIG. 5: -196 and the cooling rate between 760 and 400 ° C during the second normalizing of equilateral angle steel (150 × 150 × 10)
The chart which shows the relationship of the absorbed energy of ° C.

[Fig. 6] 560 to 40 when tempered after the second normalizing (natural air cooling) of equilateral angle steel (150 x 150 x 10)
The figure of the relationship of the cooling rate, tensile strength, and yield point between 0 degreeC.

FIG. 7: 560-40 when tempered after the second normalizing (blast cooling) of equilateral angle steel (150 × 150 × 10)
The figure of the relationship of the cooling rate, tensile strength, and yield point between 0 degreeC.

[Fig. 8] 560 to 40 when tempered after the second normalizing (natural air cooling) of equilateral angle steel (150 x 150 x 10)
The figure of the relationship between the cooling rate between 0 degreeC, and the absorbed energy of -196 degreeC.

FIG. 9: 560 to 40 when tempered after the second normalizing (blast cooling) of equilateral angle steel (150 × 150 × 10)
The figure of the relationship between the cooling rate between 0 degreeC, and the absorbed energy of -196 degreeC.

Claims (4)

[Claims] 1. C: 0.04 to 0.12% by weight, Si: 0.05 to 0.40%, Mn: 0.40 to 0.90%, Ni: 8.50 to 9.50. %, Cr: 0.05 to 0.15%, the balance being iron and inevitable impurities, and a steel having a composition satisfying C (%) + 1 / 6Mn (%) + 1 / 5Cr (%) ≧ 0.185. A high strength and high toughness 9% Ni shaped steel having a tensile strength of 725 N / mm ² or more and a Charpy impact absorption energy of 100 J or more at -196 ° C. 2. C: 0.04 to 0.12% by weight%, Si: 0.05 to 0.40%, Mn: 0.40 to 0.90%, Ni: 8.50 to 9.50. %, Cr: 0.05 to 0.15%, the balance being iron and inevitable impurities, and having a composition satisfying C (%) + 1 / 6Mn (%) + 1 / 5Cr (%) ≧ 0.185. Shaped steel is normalized at a temperature of Ac ₃ or higher, further normalized at a temperature of Ac ₃ or higher, then heated to a temperature range of 550 to 600 ° C., and then 400
A method for producing a high strength and high toughness 9% Ni-shaped steel, which comprises performing tempering treatment in which blast cooling is performed to room temperature such that the cooling rate up to ℃ becomes 0.5 to 5 ° C / S. 3. C: 0.04 to 0.12% by weight%, Si: 0.05 to 0.40%, Mn: 0.40 to 0.90%, Ni: 8.50 to 9.50. %, Cr: 0.05 to 0.15%, the balance being iron and inevitable impurities, and having a composition satisfying C (%) + 1 / 6Mn (%) + 1 / 5Cr (%) ≧ 0.185. normalizing baked shaped steel Ac ₃ temperatures above and heated to once more Ac ₃ temperatures above 400
Normalizing by blast cooling to room temperature such that the cooling rate up to ℃ becomes 0.7 to 5 ℃ / S, and then 550 to 6
A method for producing a high-strength, high-toughness 9% Ni-section steel, which comprises performing a tempering treatment by heating in a temperature range of 00 ° C. 4. C: 0.04 to 0.12% by weight, Si: 0.05 to 0.40%, Mn: 0.40 to 0.90%, Ni: 8.50 to 9.50. %, Cr: 0.05 to 0.15%, the balance being iron and inevitable impurities, and having a composition satisfying C (%) + 1 / 6Mn (%) + 1 / 5Cr (%) ≧ 0.185. normalizing baked shaped steel Ac ₃ temperatures above and heated to once more Ac ₃ temperatures above 400
Normalizing by blast cooling to room temperature such that the cooling rate up to ℃ becomes 0.7 to 5 ℃ / S, and then 550 to 6
High-strength and high-toughness characterized by performing a tempering treatment in which wind-cooling is performed up to room temperature such that the cooling rate up to 400 ° C. is 0.5 to 5 ° C./S after heating to a temperature range of 00 ° C. 9 % Ni shaped steel manufacturing method.