JPH0247217A - Production of steel having excellent toughness - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention involves casting and solidifying molten steel, and while the steel is above the Ars point temperature, the lower limit temperature (hereinafter referred to as T) at which austenite (hereinafter referred to as T) can be recrystallized is determined. MnS is precipitated by holding at a temperature of Tp and Sakaki for 5 minutes or more and 1300°C or less,
Subsequently, in the recrystallization zone, strong reduction with a one-pass rolling reduction rate of 10% or more is performed one or more times, and due to the synergistic effect of these, the solidified coarse γ is made fine with a small number of passes even in the relatively low temperature side of the recrystallization zone, making it economical. The present invention relates to a method for manufacturing steel materials with excellent toughness.

(Prior Art) In the hot rolling process, in recent years, a method of directly hot rolling (hereinafter referred to as DR) a continuously cast slab immediately after casting has been put into practical use because of its high energy saving effect.

On the other hand, the thickness of the continuously cast slab is 50m+, which is close to the product thickness.
Continuous casting methods that extract m~100I@11 are being put into practical use, and various manufacturing processes are being studied in which slabs cast by this continuous casting method are made into steel plates by OR.

In this case, OR is a coarse 1 at the time of solidification, which is several tens to several tens of sum.
Rolling starts from the grain, and the conventional thickness is 250 to 300 mm.
1 to 2, which is much smaller than the reduction ratio applied to the slab of I*Im.
It is desired to stably and smoothly provide the desired shape and material, even if only to a certain extent.

In order to meet this demand, for example, Japanese Patent Application Laid-open No. 60-213322 discloses a method in which a slab containing a finely dispersed Ti oxide precipitated in large amounts without rolling recrystallization is used during the subsequent cooling process. After rolling to the final thickness at a temperature of 900°C or higher, accelerated cooling is performed to form a fine Widmanstellaten-like ferrite plate structure, that is, a fine bainite structure (hereinafter referred to as fine bainite structure). A method of manufacturing a strong steel plate is shown.

■Japanese Patent Application No. 61-146072 discloses that high-temperature slabs obtained by continuous casting from steel containing Ti are rolled directly or after heat retention and heating to the extent that the surface temperature is the same as the center temperature. A method for producing a strong thick steel plate is disclosed, which is characterized in that hot rolling is started at a reduction ratio of 4 or more, a recrystallization zone rolling rate of 50% or more, and an Ar point of 3 or more.

■Unexamined Japanese Patent Publication No. 60-75518 discloses that slabs obtained by continuous casting are charged into a heating furnace either directly or before the transformation is completed, and are subjected to a reduction of 5% or more three times or more at a temperature above the recrystallization temperature to coarsen the slab. γ is refined by partial recrystallization, and then 10
Hot rolling that is effective in improving low-temperature toughness, characterized by applying a reduction of 15% or more three times or more at a temperature below 50°C or above the recrystallization temperature, and refining γ by large reduction rolling on the low-temperature side of the recrystallization zone. The rolling method is shown.

<Problems to be Solved by the Invention> However, in order to ensure the toughness of the steel sheet, the method (2) described above requires T/α (ferrite) transformation from Ti oxides dispersed and precipitated in large amounts in the slab. The means to achieve this is to secure a fine bainite structure, and therefore accelerated cooling is required, resulting in problems such as a decrease in rolling efficiency due to accelerated cooling and an increase in cost due to the introduction of accelerated cooling equipment.

In addition, method (2) sets constraints on the rolling reduction ratio, recrystallization zone rolling rate, and finishing temperature in order to ensure the toughness of the steel plate, but as shown in the example, vTrs≦-60°C is stable. In particular, steel materials with strict requirements for low-temperature toughness such as shipbuilding E grade have the problem of deterioration of low-temperature toughness, and furthermore, there is the problem that toughness cannot be ensured when the reduction ratio is 1 to 4.

In addition, in the method (2) above, in order to make the coarse solidified T grains fine, a reduction of 5% or more is applied in one pass three or more times at a temperature higher than the recrystallization temperature, partially recrystallizes the coarse solidified γ, and then continues to form the recrystallized region. On the low temperature side, specifically, as shown in the example, one pass 15 in the temperature range of 1050°C or lower and 900°C or higher for Nb-added steel.
The means to achieve this is to apply forceful pressure of % or more,
Rolling must be performed at least 6 times in total,
There is a problem in that rolling efficiency decreases as the number of passes increases.

In addition, only Jib-added steel is shown in the examples,
51-Mn steel, which is considered to have a lower Tp than Nb tone (Hiroshi Sekine, Tadakatsu Maruyama: Tetsu to Hagane 5B (1972) lp72),
Or Ti, which is considered to have a higher Tp than 51-Mn 8
Steel (Kurihara Hisa et al.: Tetsu to Hagane 73 (1987), 51399
) are not shown in the examples, and 5i-rI
There is a problem in that the specific method for increasing the toughness of n steel and Ti steel is unknown.

The present invention has the above-mentioned prior art problems: 1. Decrease in rolling efficiency due to accelerated cooling and increase in cost due to increase in equipment costs.

■Deterioration of low-temperature toughness, which is required for shipbuilding grade E, etc., and toughness at Trs≦-60°C cannot be stably obtained.

■Deterioration of toughness when the reduction ratio is 1 to 4.

■Decrease in rolling efficiency as the number of passes increases.

■Unestablished method to ensure toughness of 51-Mn@, Ti steel, etc.

We have solved these problems using a manufacturing method based on new knowledge that was not known with conventional rolling technology, and we have created blooms, billets, slabs, steel plates, and shaped steel that have materials equivalent to or better than the steel materials obtained with each of the above proposals. The present invention provides a method for manufacturing steel materials such as steel materials with good thermoeconomic efficiency and high productivity.

Means for Solving the Problems> In order to achieve the above-mentioned objects, the present invention aims to achieve the above object by heating the steel to 1300° C. above Tp while the steel is at Ar3 point temperature or above after casting molten steel.
MnS is precipitated by holding at the following temperature for 5 minutes or more, and then in the recrystallization area, the reduction rate is 10% in one pass.
The basic method is to carry out the above rolling process one or more times, and furthermore: ■ End the rolling at an Ar point of 2 or more and below +100°C; ■ Carry out rolling at a total reduction ratio of 2 or more at a temperature of Ars point or higher; Either of these methods is used, or they are combined synergistically to further enhance the action and effect and further improve toughness.Specifically, it is characterized by using the following methods.

(1) After casting and solidifying molten steel, while the temperature of the cough steel is above the Ar3 point temperature, the minimum temperature at which austenite can be recrystallized is 130°C.
After holding at a temperature of 0℃ or less for 5 minutes or more, one pass reduction rate of 10% at a temperature of at least the minimum temperature at which austenite can be recrystallized.
The first method is to carry out the above rolling at least once, (2) C: 0.005-0.20% S: 0.001-0.00% by weight.
0250%Si: 0.01~0.80% AI=≦
After casting and solidifying molten steel containing 0.1% Mn: 0.20 to 2.00% and the balance iron and unavoidable components, the steel is heated at 800°C or above 1 while the steel is at a temperature above the Ar1 point.
The second method is to hold the temperature at 300°C or lower for 5 minutes or more and then roll it at least once in a temperature range of 800°C or higher with a one-pass reduction rate of 10% or more, and (3) C: 0 in weight%. .005~0.20% S: o, oot~0
．． 0250%Si: 0.01~0.80% AI=
50.1% Mn: 0.20-2.00% Nb: 0.
After casting and solidifying molten steel containing 0.002 to 0.1% and the balance consisting of iron and unavoidable components, the steel is held at a temperature of 900°C or more and 1300°C or less for 5 minutes or more while it is above the Ars point temperature, and then heated to 900°C. The third means is to perform rolling at least once at a one-pass reduction rate of 10% or more in the above temperature range, (4)
C in weight%: 0.005-0.20% S: o, oot~
0.0250%Si: 0.01-0.80% AI:
50.1%Mn: 0.20-2.00% Tf: 0
．． After casting and solidifying molten steel containing 0.002 to 0.1% and the balance consisting of iron and unavoidable components, the steel is held at a temperature of 950°C or more and 1300°C or less for 5 minutes or more while the steel is at Ar, boiling temperature or higher. 1 pass reduction rate of 10% in the temperature range of 950℃ or higher
The fourth method is to perform the above rolling one or more times, (5
) C in weight%: 0.005-0.20% 41850.1%Si
:0.01~0.80% Ti:0.002~0.1
%An: o, 20~2.00% Nb: 0.002~
After casting and solidifying molten steel containing 0.1% S: O, 001 to 0.0250% and the remainder iron and unavoidable components, the steel is heated to 950°C or higher while it is on Arz boiling water.
The fifth means is to hold the temperature at 300° C. or lower for 5 minutes or more and then perform rolling at a temperature range of 950° C. or higher at a one-pass reduction rate of 10% or more once or more, and (6) Cu in weight%: 51% Zr: 50.1% Ni: 51
0% Ca: 50.008% Cr: 51%
B=≦0.006%Mo: 51%R
EM: ≦0.01% C: ≦0.2% Adding one or more of the following to any of the first to fifth means is the sixth to tenth means, (7 ) After starting rolling by any of the first to tenth means, the eleventh to twentyth means are to end the rolling at a temperature of 3 Ar points or more and 3 Ar points + 100°C or less; (8) Items 1 to 10. After starting rolling by any of the means described in Item 10, the 21st to 30th means include rolling with a reduction ratio of 2 or more, including said rolling, at a boiling temperature of 1 or more, and (9) 1st. After starting rolling by any of the tenth means, rolling with a reduction ratio of 2 or more including said rolling is carried out.

The 31st requirement is to finish at a temperature higher than the Arz point and lower than the Arz point +100°C.
This is the fortieth means.

The reason for limiting the amount of each element added in each of the above methods will be described below.

C, Si, and Mn are all good from the viewpoint of toughness and weldability in addition to strength! is limited to the above range from the viewpoint of economy, and S is limited to the above range from the viewpoint of the formation of MnS peculiar to the present invention and toughness in order to refine the solidified coarse T together with Mn. be.

In addition, Nb is added to increase strength, and Ti is added to improve strength, toughness, and joint toughness. However, when Ti is added, in addition to the above-mentioned MnS due to retention, 0.1
Fine Ti (CN) of μm or less is precipitated, and this precipitate further contributes to the refinement of the solidified coarse particles γ, thereby improving the toughness.

Also, since Cu prevents hot cracking of weld metal, Ni,
From the point of view of ensuring economic efficiency, Ti is Cr, Mo, V
, Nb prevents deterioration of toughness in the heat affected zone, B improves hardenability and prevents hot cracking during the transformation process, Zr and C improve ductility and notch toughness.
A is limited to the above range from the viewpoint of preventing surface defects and maintaining cleanliness, and REM is limited to the above range for the same reason as Ca.

The purpose of addition of each element and its effects are within the range of the purpose of addition and the expected effects commonly used in this field of application.

<Function> As a result of repeated experiments and studies in order to solve the above-mentioned problems and establish a method for manufacturing high-toughness steel materials that exhibit excellent thermoeconomic efficiency and high practicality, the present inventors have developed the first method. As shown in the figure, prior to rolling of 10% or more per pass in a temperature range of Tp or higher, solidification and coarsening of several NUW to several tens of mm is achieved by holding at a temperature of 11,300°C or lower for 5 minutes or more after IP. T recrystallizes into regular grains of 180μm or less after rolling, and there is no need to repeat large reduction rolling on the low temperature side of the recrystallization zone (Tp = Tp + 150℃ or less), and the toughness of vTrs≦-40℃ can be maintained smoothly and stably. I found out what I could get.

In addition, as shown in Fig. 2, after holding at a temperature below Tp of 11,300°C for 5 minutes or more, rolling is performed at least once with a one-pass reduction rate of 10% or more in a temperature range above Tp, resulting in a reduction of several mm.
Coagulation coarse γ of ~ several tens of μm can be more easily reduced to 180 μm
It recrystallizes into the following fine grains, and the low temperature side of the recrystallization region (Tp-Tp
They have found that the toughness of Trs≦-40°C can be obtained extremely smoothly and stably without the need to repeat large reduction rolling at temperatures below +150°C.

If the holding time at a temperature below Tp is less than 11300°C for less than 5 minutes, or if the holding temperature exceeds 1'300°C, the solidified coarse T will be sufficiently fine even if rolling is performed with an l-pass reduction rate of 10% or more. No granulation occurred, γ grains of 180 pm or less were not obtained, and vT
Toughness of rs≦−40°C cannot be obtained.

In addition, if the l-pass rolling reduction rate is less than 10%, Tp or more 130
Even if the temperature is maintained at a temperature below 0°C for more than 5 minutes, the solidified coarse γ shows partial recrystallization or non-recrystallization, and the grains do not become fine and vTr
Toughness of s≦-40°C cannot be obtained.

Furthermore, as shown in Fig. 3, after holding at a temperature of Tp or higher and 1300°C or lower for 5 minutes or more, one pass was applied in a temperature range of Tp or higher.
If rolling is performed at least once at 0% or more, and rolling is completed in a temperature range from Art point to Arz point + 100°C, or if rolling is performed at a cumulative reduction ratio of 2 or more, T after rolling is 90 μm.
The toughness is further improved and vTrs is ≦-60℃.
If the level of is stably satisfied, and rolling with a cumulative reduction ratio of 2 or more is completed in a temperature range of 3 Ar points or more and Ars point + 100°C or less, γ will be 45 μm or less, and vTrs will be ≦-
It was discovered that the toughness level of 80° C. can be stably satisfied and the desired purpose can be achieved.

If the finishing temperature exceeds the Arz point +100°C, or if the rolling reduction ratio is less than 2, T will not become fine enough and vTrs≦-6.
0°C cannot be stably obtained.

In other words, if rolling is performed at least once in a temperature range of 11 or more at a rate of 10% or more per pass after holding at a temperature below 11,300°C for 5 minutes or more, the solidification coarse T
is refined to 180 μm or less, exhibits a toughness level of vTrs≦-40°C, and is further rolled with a cumulative reduction ratio of 2 or more, or when rolling is completed at a total of 5 points or more and Ar3 points + 100°C or less, T becomes 90 μm. The toughness is reduced by refining the grains to below
≦-60℃ level, and after the intended rolling in the recrystallization zone, rolling with a reduction ratio of 2 or more including said rolling is performed at Ar3 points or more A
When the process is completed at the r3 point +100°C or lower, T becomes finer to 45 m or less, and a toughness level of vTrs≦-80°C can be stably obtained.

All of the steel materials obtained in this way are in the condition range shown by diagonal lines in FIGS. 1 to 3, and the vTrs of the obtained steel materials are below -40°C, -60°C or below, and below 80°C, respectively. Ta.

The present invention has been made based on the above knowledge, and by implementing the present invention, DR and HCR that are inevitably performed
The purpose of this project is to reform the manufacturing method of steel products, thereby dramatically improving the practicality of manufacturing this type of steel products in terms of thermo-economic efficiency, productivity, etc.

<Example> (Example 1) Tables 1 to 4 show the chemical compositions of the test steels used in the invention examples 1 to 10 and their comparative examples, and Tables 5 to 8 and Tables 9 to 12 show the manufacturing conditions for each steel plate and the obtained materials.

As is clear from the table, all of the inventive perfumes 1 to 136 exhibited vTrs of -40°C or less, and steel materials having the desired material properties were obtained.

Comparative examples of fragrances 138, 141, 144 whose 1-pass rolling reduction ratio does not satisfy the range of the invention compared to these examples of the invention.
, 145, 148.152-154.158.159.
164°165, 169.172.175.178.1
79.182.186-188.192゜193, 19
8.199.203,206,209,212,213
,216.220~222.226,227,232,
233,237240.243,246,247,25
0°254~256,260,261,266.267
．． 271 has vT because the coarse T does not recrystallize and does not become fine grained.
rs did not reach -40°C.

In addition, Comparative Example Perfume 139, 142.146.149.150.155.1 whose rolling start temperature does not satisfy the range of the present invention
56.160~162.166°167, 170.17
3.176, 180.183.184.189.190
．． 194-196, 200.201, 204, 20
7.210.214, 215.217.218.22
3°224, 228-230,234,235,23
8.241,242,244,248°249.251
, 252, 257, 258, 262-264, 268,
In No. 269 and No. 272, vTrs did not reach -40° C. because the coarse γ did not recrystallize and did not become fine grained.

Comparative perfumes 137 and 140.143.147.151.157.1 whose retention temperature or retention time do not satisfy the range of the present invention
63.168.171 , 174.177°181 ,
185.191, 197.202.205.208.
211, 215.219.225゜231.236,
239,242,245,249.253,259.2
65.270 is v because coarse γ does not recrystallize and does not become fine grained.
Trs did not reach -40'C.

(Example 2) Tables 1 to 4 show the chemical compositions of the test steels used in the 11th to 20th invention examples and their comparative examples, and Tables 13 to 16 and 17 to Table 20 shows the manufacturing conditions of each steel plate and the obtained material.

As is clear from the table, all of the inventive perfumes 273 to 408 exhibited vTrs of -60°C or less, and steel materials having the desired material properties were obtained.

In contrast to these inventive examples, Comparative Examples 409 and 413.416.425.426.428.4 whose finishing temperature does not satisfy the range of the present invention
32.436.439.441, 443°450, 4
55.460.464, 466, 467, 470.
477, 484, 490.492°496, 500.
504.510.511, 518.524, 526
．． 529.534, 538°544 has a coarse T of 90μ
Since the grains were not refined below m, vTrs did not reach -60°C.

In addition, although the finishing temperature satisfies the range of the present invention,
Perfumes 410, 411, 414, 417, 418, 420-4 whose rolling start temperature or 1-pass rolling reduction ratio does not satisfy the range of the present invention
22,424,427,430°431,433.4
34.437.438.442.444.445.44
7.448.451.

452.454,456,458,459,461,4
62,465,468,471-473,475.47
6, 478.479.481.482.485.486
．． 488, 489°493-495,498,499
,501,502,505-507,509,5125
13, 515, 516.519.520.522.52
3.527.528.530.532゜533.535
, 536, 539-541, 543 have coarse T of 90μ
The vTrs did not reach -60°C because the grains were not refined to below 100°C.

In addition, perfumery 412, 415.41 whose finishing temperature, rolling start temperature, and 1-pass rolling reduction rate satisfy the range of the present invention, but whose holding temperature or holding time does not satisfy the range of the present invention.
9.423.429.435.440.446.449
．． 453.457°463, 469.474, 480
．． 483.487.491, 497.50.3.50
8.514゜517.521,525,531,537
, 542 is v because the coarse T does not become finer than 90μ.
Trs did not reach -60°C.

(Example 3) Tables 1 to 4 show the chemical compositions of the test steels used in each of the 21st to 30th invention examples and their respective comparative examples. Table 28 shows the manufacturing conditions of each steel plate and the obtained material.

As is clear from the table, all of the inventive perfumes 545 to 680 exhibited vTrs of -60°C or less, and steel materials having the desired material properties were obtained.

Compared to these inventive examples, comparative examples 682, 688.693, 696.700, 704 whose reduction ratio does not satisfy the range of the present invention
．． 711, 716.722.727, 730°73
4, 738.745.750.756.761, 76
4, 768.772.779.784°790.79
5,798,802,806,813 has a coarse T of 9oI
Because it does not become finer than IIm, vTrs is -60”C
did not reach.

In addition, although the rolling ratio satisfies the range of the present invention, the rolling start temperature or the 1-pass rolling reduction ratio does not satisfy the range of the present invention.
94.697～699.702゜703.705,70
6,708-710,713,714,717,719
,720723.724,726,728,731-7
33,736,737,739,740°742~74
4,747,748,751,753,754,757
,758,760°762.765~767.770,
771,773,774,776-778,781゜7
82.785-788,791,792,794,79
6,799～801,804゜805.807,808
, 810-812, 815, 816 are 0. coarse r is 90
The vTrs did not reach -60°C because the grains did not become finer than μlin.

In addition, steel numbers 681 and 684.68 have rolling reduction ratios, rolling start temperatures, and l-pass rolling ratios that meet the ranges of the present invention, but holding temperatures or holding times that do not meet the ranges of the present invention.
7.691.695.701.707.712.715
．． 718.721.

725.729.735.741, 746.749.
752.755.759.763, 769°775.
780.783.789,793,797,803.8
In 09.814, vTrs did not reach -60°C because the coarse T did not become finer than 90μ.

(Example 4) Tables 1 to 4 show the chemical compositions of the test steels used in each of the 31st to 40th invention examples and their respective comparative examples, and Tables 29 to 32 and 33 to Table 36 shows the manufacturing conditions of each steel plate and the obtained material.

As is clear from the table, all of the inventive perfumes 817 to 952 exhibited vTrs of 180°C or less, and steel materials having the desired material properties were obtained.

Compared to these examples of the present invention, perfumes 953 and 954 are comparative examples whose finishing temperature or rolling reduction ratio does not satisfy the range of the present invention.
, 960.961 , 965.968, 969.97
2.974.976, 978°983, 986, 9
87.988.994, 995.999.1002
, 1003.1006.

1010, 101? , 1020.1021 , 102
2.1026.1028.1031 , 1033103
4, 1036.1038.1040.1044.104
6.1051, 1053.10551056, 106
2.1064, 1067, 1068.1070.10
71, 1074, 10781080, 1083.1
Since coarse γ of 085.1088 was not refined to 45 μm or less, vTrs did not reach -80°C.

In addition, although the finishing temperature and rolling ratio satisfy the range of the present invention, the rolling start temperature or the 1-pass rolling ratio does not satisfy the range of the present invention. ,9
70.971, 975.977, 980-982.9
85.989.991, 992.996.998.1
000.1004, 10051008, 1009.1
012.1014~1016.10!9.1023.1
025°1029, 1030.1032.1037.1
039.1042.1043.1045.1048~1
050.1054.1057.1059.1060.1
063.1065.106610?2.1073.10
76, 1077, 1079.1082.1084.10
87 is vTr because the coarse γ does not become finer than 45 μ-
s did not reach -80°C.

Furthermore, although the finishing temperature, rolling reduction ratio, rolling start temperature, and 1-pass rolling reduction ratio satisfy the range of the present invention, the holding temperature,
Perfume 956, 959.963.967, 973.979 whose retention time does not meet the scope of the present invention
, 984 , 990.993.997 , 100110
0? , 1013.1018.1024.1027.1
031.1035.1041.10471052, 10
58.1061, 1065.1069.1075.1
In the case of 081.1086, vTrs did not reach -80°C because the coarse T was not refined to less than 45μ.

<Effects of the Invention> As described above, the present invention provides coarse γ of molten steel after casting and solidification by Tp
19 after being held for more than 5 minutes at a temperature of over 1300℃ or less
Rolling with a one-pass reduction rate of 10% or more in the above temperature range is performed one or more times to refine the grain and improve toughness, and further finish rolling is carried out at a temperature above the Ar point temperature or above at Ar3 point + 10
Toughness can be further improved by performing the process at a low temperature of 0'C or less, by increasing the total reduction ratio to 2 or more, or by combining these synergistically to increase the effect. Dl to roll? In addition, in the case of HCH, in which the steel billet is reheated from the point at which it is in a temperature range of 8 or more points and then subjected to rolling, the steel products manufactured by each of them with excellent toughness are produced with good thermoeconomic efficiency and high productivity. The effects brought about in this field are great, such as making it possible to manufacture products at lower speeds.

[Brief explanation of the drawing]

Figure 1 shows the holding temperature, holding time, rolling start temperature, and vTrs of steel materials that have been rolled at least once with an l-pass reduction rate of 10% or more.
FIG. 2 is a diagram showing the relationship between vTrs and the 1-pass rolling reduction rate and rolling start temperature of steel materials that have been rolled for one or more passes. FIG. Finishing temperature, rolling ratio and vTr of steel materials that have been rolled at least once at a temperature of 19 or higher and a one-pass rolling reduction of 10% or more.
It is a figure showing the relationship of s. Patent applicant: Nippon Steel Corporation Agent: Masu Tebori (and 2 others)

Claims (9)

[Claims] (1) After casting and solidifying molten steel, while the steel is at a temperature of Ar_3 or higher, the minimum temperature at which austenite can be recrystallized is 13
After holding at a temperature of 00℃ or less for 5 minutes or more, one pass reduction rate of 10 at a temperature of at least the minimum temperature at which austenite can be recrystallized.
1. A method for producing a steel material with excellent toughness, which comprises rolling a steel material at least once. (2) C: 0.005-0.20% S: 0.001-0.02 in weight%
50%Si: 0.01~0.80%Al:≦0.1%M
After casting and solidifying molten steel containing n: 0.20 to 2.00% and the balance consisting of iron and unavoidable components, the steel is held at a temperature of 800°C or higher and 1300°C or lower for 5 minutes or more while the steel is at Ar_3 point temperature or higher. 800℃ after
A method for producing a steel material with excellent toughness, which comprises rolling at a temperature above 10% or more in one pass at a reduction rate of 10% or more. (3) C: 0.005-0.20% S: 0.001-0.02 in weight%
50%Si: 0.01~0.80%Al:≦0.1%M
n: 0.20-2.00% Nb: 0.002-0.1%
After casting and solidifying molten steel containing iron and other unavoidable components, the steel is held at a temperature of 900°C or more and 1300°C or less for 5 minutes or more while it is at Ar_3 point temperature or higher, and then heated to 900°C.
A method for manufacturing a steel material with excellent toughness, which comprises rolling at least once at a one-pass reduction rate of 10% or more in the above temperature range. (4) C: 0.005-0.20% S: 0.001-0.02 in weight%
50%Si: 0.01~0.80%Al:≦0.1%M
n: 0.20-2.00% Ti: 0.002-0.1%
After casting and solidifying molten steel containing iron and other unavoidable components, the steel is held at a temperature of 950°C or higher and 1300°C or lower for 5 minutes or more while the steel is at Ar_3 point temperature or higher, and then heated to 950°C.
A method for manufacturing a steel material with excellent toughness, which comprises rolling at least once at a one-pass reduction rate of 10% or more in the above temperature range. (5) C in weight%: 0.005-0.20% Al: ≦0.1% Si: 0
．． 01-0.80%Ti: 0.002-0.1%Mn:
0.20-2.00% Nb: 0.002-0.1% S:
After casting and solidifying molten steel containing 0.001 to 0.0250% with the balance iron and unavoidable components, after holding the steel at a temperature of 950°C or higher and 1300°C or lower for 5 minutes or more while the steel is at Ar_3 point temperature or higher. 950℃
A method for manufacturing a steel material with excellent toughness, which comprises rolling at least once at a one-pass reduction rate of 10% or more in the above temperature range. (6) In weight% Cu: ≦1% Zr: ≦0.1% Ni: ≦10% Ca: ≦0.008% Cr: ≦1% B: ≦0.006% Mo: ≦1% REM: ≦ 0.01% V:≦0.2% A method for producing a steel material with excellent toughness according to any one of claims 1 to 5, characterized in that the V:≦0.2% is contained. (7) After starting rolling by the method according to any one of claims 1 to 6, the temperature at Ar_3 point or higher is Ar_3.
A method for producing a steel material with excellent toughness, characterized in that rolling is completed at a temperature of +100°C or lower. (8) After starting rolling by the method described in any one of claims 1 to 6, the rolling including said rolling at a reduction ratio of 2 or more is completed at a temperature of Ar_3 point or more. A method for producing steel with excellent toughness. (9) After starting rolling by the method described in any one of claims 1 to 6, rolling including said rolling with a reduction ratio of 2 or more is finished at a temperature of Ar_3 point or higher and Ar_3 point + 100°C or lower. A method for manufacturing steel materials with excellent toughness.