JPH1088230A - Production of high tensile strength steel material excellent in toughness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high tensile strength steel material excellent in strength and toughness while obviating the necessity of the addition of large amounts of expensive elements by subjecting a steel stock, in which the contents of V and N and the value of Ceq are respectively specified, to hot rolling at respectively specified temp. and draft and then to air cooling. SOLUTION: A steel, having a composition which consists of, by weight, 0.05-0.18% C, 0.10-0.60% Si, 0.80-1.80% Mn, <=0.030% P, <=0.015% S, 0.005-0.050% Al, 0.04-0.15% V, 0.0050-0.0150% N, and the balance Fe with inevitable impurities and in which V/N is regulated to 4.0-12.0 and also the value of Ceq defined by equation I is regulated to 0.34-0.48%, is used. This stock is heated to 1050-1350 deg.C and then hot worked while regulating the cumulative draft, in the temp. range between the temp. Tps ( deg.C) defined by equation II and 830 deg.C, to >=30% and also regulating hot working finishing temp. to a temp. between the Ar3 point ( deg.C) defined by equation III and 900 deg.C. Subsequently, air cooling is performed down to room temp. Moreover, in the course of hot working, accelerated cooling can be applied once or twice or more times at a cooling velocity not lower than air cooling velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-tensile steel material, and more particularly to a high-tensile steel material having excellent toughness and a tensile strength of 490 MPa or more.

[0002]

2. Description of the Related Art As a method for securing strength and toughness in a well-balanced manner in a thick steel plate, TMCP (Thermo Mechanical) is used.
2. Description of the Related Art A method of manufacturing a thick steel plate by a control process is known. For example, Japanese Unexamined Patent Publication No. 3-223419 discloses that a steel material containing Nb is reduced by 30% in a recrystallization temperature range of (Ar ₃ + 150 ° C.) or higher.
After subjected to more pressure it has been proposed a manufacturing method of a steel plate adding (Ar ₃ +150 ℃) reduction of 50% or more in a temperature range of to Ar _3. In this method, a deformation zone is introduced by applying a strong pressure in a non-recrystallized region to make the structure finer. Japanese Patent Application Laid-Open No. 2-25968 discloses that a steel slab containing Ca, Ti and Nb or V is heated to 900 to 1100 ° C., and the rolling reduction is 900 ° C. or less.
A method of manufacturing a high-strength high-strength steel has been proposed in which hot rolling is performed at a rolling finish temperature of 680 to 860 ° C at a temperature of 30% or more, and then cooled to 500 ° C or less at a cooling rate of 3 to 10 ° C / sec. ing.

However, in order to sufficiently exert the effect of the rolling in the non-recrystallization temperature range as described above, it is necessary to apply a high pressure at a lower temperature, and a great load is applied to the rolling mill, so that a great load is applied. In addition to consuming energy, in the case of a thick steel plate, there have been problems such as an increase in waiting time for temperature control and a reduction in rolling efficiency. In addition, when high pressure under low temperature cannot be ensured as in the case of an extremely thick steel sheet, the introduction of the deformation zone is insufficient, ferrite nuclei are reduced, and the structure cannot be refined.On the other hand, in the case of a thin steel sheet, However, there are problems such as the anisotropy of sound due to the formation of texture, and the increase in residual stress and residual strain due to cooling to a low temperature of 500 ° C. or less.

On the other hand, unlike the above-mentioned method, a high-strength steel using VN to refine the structure and improve the strength toughness as rolled has been conventionally known (for example, iron and steel). , Vol.77 (1991) No.1, p171.). Also, JP-A-5-18
No. 6848 discloses that TiN-MnS-VN
There is disclosed a technique for dispersing the composite precipitates of the above and effectively acting a ferrite generating function to improve the HAZ toughness.
However, in these techniques, particularly in the case of an extremely thick steel plate, the effect of VN is not always efficiently exhibited, and there is a problem that the properties of the base material as-rolled are insufficient.

[0005]

SUMMARY OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and does not require the addition of a large amount of expensive elements and does not apply a high-temperature low-temperature, and has a low tensile strength.
An object of the present invention is to propose a method for producing a high-tensile steel material having a strength of 490 MPa or more and excellent toughness.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above object, and have obtained the following findings. By controlling the amounts of V and N and dispersing an appropriate amount of VN precipitates in austenite, these precipitates act as ferrite nuclei to form a fine ferrite + pearlite structure. Furthermore, the tissue refining effect of this VN is enhanced by adjusting Ceq to a range of 0.34 to 0.48%.

[0007] After the ferrite transformation, VN is finely precipitated in a large amount in ferrite, and thus greatly contributes to an increase in strength. Further, since VN is finely precipitated in a large amount even with relatively slow cooling, it is possible to suppress variations in strength and toughness in the cross section of the steel sheet and occurrence of residual stress and residual strain. In addition to controlling the amount of V and N of the material, the rolling of the material in a specific temperature range related to the amount of V and N is 30% or more in cumulative rolling reduction, and the hot working end temperature is Ar ₃ points (° C). Less than 900
By performing hot working at a temperature of not less than ° C., precipitation of VN having a size of 10 nm or more, which can be a ferrite precipitation nucleus, is promoted, and the structure can be further refined.

The present invention has been completed based on the above findings. That is, in the present invention, C: 0.
05 ~ 0.18%, Si: 0.10 ~ 0.60%, Mn: 0.80 ~ 1.80%,
P: 0.030% or less, S: 0.015% or less, Al: 0.005-0.
050%, V: 0.04 to 0.15%, N: 0.0050 to 0.0150%, and V / N: 4.0 to 12.0 are satisfied, and the following equation (1) is used: Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 A material consisting of the balance of Fe and unavoidable impurities, with Ceq defined by (1) being 0.34 to 0.48%, is heated to 1050 to 1350 ° C., and the following equation (2) Tps = ｛ V (N−0.292Ti) × 10 ⁵ +397 mm / 0.480 ……………………………………………………………………………………………………………………………………………………………………………………… (2) Is subjected to hot working in which Ar ₃ = 910-273 C + 25Si-74Mn-56Ni-16Cr-9Mo-5Cu-1620Nb defined by the following equation (3): not less than Ar ₃ points (° C) and not more than 900 ° C. After that, it is a method for producing a high-tensile steel material excellent in toughness, characterized by air-cooling to room temperature.

Further, in the present invention, accelerated cooling may be performed once or twice or more at a cooling rate higher than air cooling during the hot working. Further, in the present invention, instead of the air cooling to the room temperature, the cooling may be performed at a cooling rate of not less than air cooling and not more than 30 ° C./sec to a temperature not more than (Ar ₃ −60 ° C.) and not less than 600 ° C. Further, in the present invention, the above-mentioned raw material is expressed as C: 0.
05 ~ 0.18%, Si: 0.10 ~ 0.60%, Mn: 0.80 ~ 1.80%,
P: 0.030% or less, S: 0.015% or less, Al: 0.005-0.
050%, V: 0.04-0.15%, N: 0.0050-0.0150%, Nb: 0.003-0.030%, Ti: 0.005-0.03%
% Or one or two selected from
(V + Ti) / N: 4.0 to 12.0 was satisfied, and the Ceq was 0.34.
It is preferable to use a material containing the balance of Fe and unavoidable impurities with a content of about 0.48%.

[0010] In the present invention, the material may be used in an amount of
And C: 0.05-0.18%, Si: 0.10-0.60%, Mn: 0.80-
1.80%, P: 0.030% or less, S: 0.015% or less, Al: 0.
005 to 0.050%, V: 0.04 to 0.15%, N: 0.0050 to 0.01
Including 50%, Cu: 0.05-0.50%, Ni: 0.05-0.50%, C
r: 0.05 to 0.50%, Mo: 0.02 to 0.20%, one or more selected from among them, and V / N: 4.0 to
12.0 was satisfied, and the Ceq was 0.34 to 0.48%.
Alternatively, the material may be made of unavoidable impurities.

Further, in the present invention, the material may be contained in a
And C: 0.05-0.18%, Si: 0.10-0.60%, Mn: 0.80-
1.80%, P: 0.030% or less, S: 0.015% or less, Al: 0.
005 to 0.050%, V: 0.04 to 0.15%, N: 0.0050 to 0.01
Including 50%, Cu: 0.05-0.50%, Ni: 0.05-0.50%, C
r: 0.05 to 0.50%, Mo: 0.02 to 0.20%, one or more selected from the group consisting of: Nb: 0.003 to 0.030
%, Ti: 0.005 to 0.03%, and one or two selected from the group consisting of: (V + Ti) / N: 4.0 to 12.0, and the Ceq being 0.34 to 0.48%. It may be a material composed of Fe and inevitable impurities.

In the present invention, in addition to the above-mentioned material composition, the material has a composition of B: 0.0003 to 0.0020% and REM: 0.0010 to 0.
010%, Ca: 0.0010 to 0.010%, may contain one or more kinds selected from them.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The steel material referred to in the present invention means a steel material including a thick steel plate, a hot-rolled steel plate, a steel pipe, a shape steel, and a steel bar. In the present invention, the chemical composition of a suitable material will be described. C: 0.05 to 0.18% C is an element that increases the strength of steel, and it is necessary to add 0.05% or more to secure the strength. However, if added in excess of 0.18%, the base material toughness, weld cracking resistance, and weld heat affected zone (HAZ) toughness deteriorate, so that C is 0.05 to 0.18%.
% Range. In addition, it is preferably in the range of 0.08 to 0.16%.

Si: 0.10 to 0.60% Si is an element that acts as a deoxidizing agent and further increases the strength of steel by solid solution strengthening. To get this effect,
It is necessary to add 0.10% or more, but if it exceeds 0.60%,
Significantly degrades HAZ toughness. For this reason, Si is 0.10 ~
The range was 0.60%. In addition, it is preferably 0.20 to 0.45%.

Mn: 0.80 to 1.80% Mn is an element that increases the strength of steel, and it is necessary to add 0.80% or more to secure the strength. However, if the content exceeds 1.80%, the structure becomes a structure mainly composed of low-temperature products such as bainite from ferrite + pearlite, and the base material toughness deteriorates. Therefore, Mn is set in the range of 0.80 to 1.80%. In addition, it is preferably 1.00 to 1.70%.

P: not more than 0.030% P segregates at the grain boundaries and lowers toughness. For this reason, it is reduced as much as possible, but up to 0.030% is acceptable. In addition,
The content is preferably set to 0.015% or less. S: 0.015% or less Since S forms nonmetallic inclusions and deteriorates ductility and toughness, it is limited to 0.015% or less. Incidentally, preferably 0.010
% Or less.

Al: 0.005 to 0.050% Al acts as a deoxidizing agent, but when added in a large amount, nonmetallic inclusions increase, the cleanliness decreases, and the toughness deteriorates.
In addition, Al easily bonds with N to form AlN, and inhibits stable deposition of VN. Therefore, the content of Al is set in the range of 0.005 to 0.050%. Incidentally, the content is preferably 0.010 to 0.040%.

V: 0.04 to 0.15% V is an important element in the present invention, and combines with N to form VN, which precipitates in austenite during cooling after rolling. This VN acts as a ferrite precipitation nucleus, refines crystal grains and improves toughness. Further, after the ferrite transformation, fine precipitates are also formed in the ferrite, whereby the strength of the base material can be increased without strengthening the cooling, and the uniformity of the properties within the thickness of the steel sheet, the residual stress and the residual strain can be reduced. To achieve these effects, 0.04% or more is required, but 0.15%
If added in excess of, the base metal toughness and weldability deteriorate. For this reason, V is limited to the range of 0.04 to 0.15%. In addition, it is preferably 0.04 to 0.12%.

N: 0.0050 to 0.0150% N combines with V and / or Ti to form a nitride, suppresses the growth of austenite grains during heating, acts as a ferrite precipitation nucleus, refines crystal grains, and reduces toughness. Has the effect of improving If it is less than 0.0050%, the required amount of nitride is insufficient. On the other hand, if it exceeds 0.0150%,
The amount of solute N increases, deteriorating the base metal toughness and the HAZ toughness. For this reason, N was limited to the range of 0.0050 to 0.0150%. The preferred range is 0.0060 to 0.0120%.

(V + Ti) / N: 4.0 to 12.0 In the present invention, when no Ti is added, (V + Ti) / N becomes
Calculate as V / N. V and N are set in the above ranges, and the V and N amounts are adjusted so that V / N is in the range of 4.0 to 12.0. When adding Ti, the calculation is performed using (V + Ti) / N instead of V / N, and the amounts of V, Ti, and N are similarly adjusted to be in the range of 4.0 to 12.0. If V / N or (V + Ti) / N is less than 4.0, the amount of solute N increases, causing strain aging and further reducing the HAZ toughness. On the other hand, if V / N or (V + Ti) / N exceeds 12.0, V or V and Ti combine with C to lower the base material toughness. Therefore, V / N or (V + Ti) / N is set to 4.
The range was 0 to 12.0. Preferably, 5.0 to 10.0
It is.

Ceq: 0.34 to 0.48% Ceq is defined by the following equation (1). Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 (1) Ceq is obtained by adjusting the chemical composition and limiting it to the range of 0.34 to 0.48%. , Steel hardenability,
The transformation point is adjusted, VN precipitation is promoted, and high strength, good toughness and weldability can be secured. If the Ceq is less than 0.34%, it is difficult to secure the strength of the base metal and the softened portion of the HAZ, and if it exceeds 0.48%, the susceptibility to weld cracking increases and the toughness of the HAZ deteriorates.

Nb: 0.003 to 0.030%, Ti: 0.005 to 0.03
% Or two kinds of Nb have the effect of lowering the Ar ₃ point and accelerating the precipitation of VN in austenite, and have the effect of precipitation of Nb compounds and refinement of crystal grains. , Improve both toughness. To obtain this effect, the addition of 0.003% or more is required, but if it exceeds 0.030%, the toughness and weldability of the HAZ deteriorate. Therefore, Nb is limited to the range of 0.003 to 0.030%. Preferably, the content is 0.005 to 0.025%.

Ti combines with N to form TiN, which suppresses the growth of austenite grains during heating, and has the effect of remaining or precipitating in austenite to promote the precipitation of VN in austenite. To obtain this effect, it is necessary to add 0.005% or more.
If the content exceeds 0%, the cleanliness of the steel is reduced and VN
To suppress precipitation and degrade the toughness of the base material. For this reason,
Ti was set in the range of 0.005 to 0.050%. Preferably,
0.010 to 0.025%.

Cu: 0.05-0.50%, Ni: 0.05-0.50%, C
r: 0.05 to 0.50%, Mo: 0.02 to 0.20% One or more selected from Cu, Ni, Cr and Mo all have the effect of improving hardenability and increasing strength. And one or more kinds can be added. In order to obtain such effects, Cu, Ni, Cr,
Mo must be added in an amount of 0.05%, 0.05%, 0.05%, 0.02% or more, respectively. However, even if Cu and Ni are added in excess of 0.50%, the effect is saturated and the cost becomes high economically. Therefore, both Cu and Ni are limited to the range of 0.05 to 0.50%.
Cr and Mo exceed 0.50% and 0.20% respectively, weldability,
Base material toughness deteriorates. Therefore, Cr is 0.05-0.50%, Mo
Was limited to the range of 0.02 to 0.20%.

B: 0.0003-0.0020%, REM: 0.0010-0.
010%, Ca: one or more kinds selected from 0.0010 to 0.010% B, REM, and Ca all have an effect of contributing to the refinement of ferrite grains. Two or more can be added. B segregates at the grain boundaries, suppresses the precipitation of coarse grain boundary ferrite, and contributes to the refinement of ferrite grains. In order to obtain such an effect, 0.0003% or more of addition is required. However, if it exceeds 0.0020%, toughness is reduced. For this reason, B is limited to the range of 0.0003 to 0.0020%.

REM and Ca form stable oxides even at high temperatures and are finely dispersed in the steel to suppress the growth of austenite grains and to refine the ferrite grains after rolling. Also,
It also has the effect of refining the structure of the HAZ portion and improving the toughness of the HAZ portion. Less than 0.0010% has little effect, while adding more than 0.010% increases the amount of oxides,
In addition, because of coarsening, cleanliness is reduced and toughness is deteriorated. For this reason, REM and Ca are limited to the range of 0.0010 to 0.010%.

Others are Fe and inevitable impurities. For elements other than the elements specified above, O: 0.010%
Below, Zr: 0.02% or less, Mg: 0.02% or less is acceptable. Next, the reasons for limiting the manufacturing method will be described.
For the smelting of the steel having the above-mentioned composition, any commonly known smelting method such as a converter and an electric furnace can be applied, and there is no particular limitation. The smelted molten steel is solidified by a continuous casting method or an ingot-making method to be a working material.

The material of the present invention can be formed into a thick steel plate, a hot-rolled steel plate, a steel pipe, a shape steel, a steel bar or the like by hot rolling. The heating temperature for hot rolling is 1050 to 1350 ° C. If the heating temperature is lower than 1050 ° C., precipitates such as V and Nb do not sufficiently form a solid solution, making it difficult to sufficiently exert the effects of these precipitation strengthening elements. It is difficult to secure the rolling reduction. On the other hand, if it exceeds 1350 ° C,
In addition to deteriorating the heating furnace basic unit, it causes an increase in scale loss and an increase in the number of times of furnace repair. For this reason, the heating temperature of the material was set in the range of 1050 to 1350 ° C.

After the material is heated, the temperature is 830 ° C. below the Tps temperature (° C.) defined by the following equation (2): Tps = {V (N−0.292Ti) × 10 ⁵ +397} /0.480 (2) the cumulative rolling reduction of 30% or more in the temperature range described above, is defined hot working finishing temperature by the following equation (3) _{Ar 3 = 910 -273 C + 25Si} -74Mn-56Ni-16Cr-9Mo -5Cu -1620Nb ... (3) The hot working is performed at a temperature between ₃ Ar (° C) and 900 ° C.

The strain induced by the hot working promotes the strain-induced precipitation of VN, and the VN serves as a nucleus to generate intragranular ferrite and refine the structure. In order to promote the strain-induced precipitation of VN, the cumulative rolling reduction of hot working needs to be 30% or more. However, processing at a temperature exceeding the Tps temperature defined by the equation (2) cannot expect the effect of promoting VN strain-induced precipitation due to the introduced strain. On the other hand, when processing at a temperature lower than 830 ° C., the size of VN precipitated by strain-induced precipitation is as small as 10 nm or less, and hardly becomes a core of intragranular ferrite. Therefore, the cumulative rolling reduction in the temperature range from Tps temperature (° C) to 830 ° C is specified as 30% or more. Note that V, N, and Ti used in the equation (2) are% by weight.

As the hot working end temperature decreases,
In addition to the grain refinement effect by VN, the structure is further refined by the effect of the non-recrystallization temperature range processing, and the toughness is improved. In order to obtain the effect of this non-recrystallization temperature range processing, the hot working end temperature is set to 900 ° C or less, but if the hot working conditions for promoting VN precipitation are satisfied, the microstructure can be sufficiently refined. It is not necessary to set the hot working end temperature to an unnecessarily low temperature, and the hot working end temperature was set to _three or more Ar points. When the hot working end temperature is as low as less than the Ar ₃ point, a texture is formed and adverse effects such as deterioration of toughness occur.

In the present invention, accelerated cooling may be performed once or twice or more at a cooling rate higher than air cooling during the hot working. During the hot working, the working is interrupted, and cooling is performed at a cooling rate of at least air cooling, preferably at least 1 ° C./sec.
Cooling is performed at about 50-150 ° C each time.
Prevents N from being fixed as AlN, NbN, etc. before VN is deposited, effectively deposits VN, and increases the number of VN deposited particles.

After the completion of the rolling, the air is cooled to room temperature. By applying slow cooling such as air cooling, variation in strength and toughness,
Residual stress and residual strain can be reduced. In the present invention, instead of air cooling to the room temperature, cooling may be performed at a cooling rate of not less than air cooling and not more than 30 ° C./sec to a temperature of not more than (Ar ₃ −60 ° C.) and not less than 600 ° C. By accelerated cooling at a cooling rate of air cooling to 30 ° C / sec or less, the generation of grain boundary ferrite is suppressed, austenite is supercooled, and the structure refinement effect due to the generation of intragranular ferrite with VN as a nucleus is remarkable. Become. However, when the cooling rate exceeds 30 ° C./sec, the temperature difference in the thickness direction becomes remarkable, and the strength and toughness vary, and the occurrence of residual stress and residual strain becomes remarkable.

When accelerated cooling is stopped at a temperature exceeding (Ar ₃ -60 ° C.), the effect of accelerated cooling is not recognized. On the other hand, when accelerated cooling is performed to a temperature lower than 600 ° C., a large amount of low-temperature transformation products such as bainite are generated, and toughness is deteriorated. The temperature and cooling rate specified in the present invention are values at the center of the steel sheet in the thickness.

[0035]

EXAMPLES Steel having the composition shown in Table 1 was melted in a converter and slabs having a thickness of 240 to 310 mm were produced by continuous casting. Next, these slabs were heated to the temperatures shown in Table 2, and were made into thick steel plates under the hot rolling conditions shown in Table 2. Immediately after the completion of the rolling, cooling was performed at a cooling rate shown in Table 2. Using these thick steel plates, the tensile properties, toughness, and weld HAZ toughness of the base metal were investigated. Table 2 shows the results.

[0036]

[Table 1]

[0037]

[Table 2]

The methods for testing the tensile properties, toughness, and toughness of the heat affected zone of the base metal are as follows. (1) Tensile test of base metal JI in the direction perpendicular to the rolling direction from the 1/2 T thickness of the above product sheet
A No. 4 test piece specified in SZ2201 was sampled, and the yield point (YP) and tensile strength (TS) were determined in accordance with JIS Z2241. (2) Toughness test of base metal From the T 1/2 part of the above product sheet, JI was applied in the direction perpendicular to the rolling direction.
A No. 4 test piece specified in SZ2202 was sampled and subjected to a test in accordance with JIS Z 2242 to determine a fracture surface transition temperature (vTrs). (3) Toughness test of heat affected zone Welded specimens were taken from the 1/2 T section of the above product sheet in the direction perpendicular to the rolling direction, and were subjected to submerged arc welding with a heat input of 50 kJ / cm using a high frequency heating device. HAZ part of grain area (maximum heating temperature 14
JIS Z 2202
No. 4 test piece specified taken, in conformity with JIS Z 2242, the Charpy absorbed energy at -20 ° C. _(V E
_-20 ).

As can be seen from Table 2, in the example of the present invention, a high strength of 500 MPa or more in TS and a high toughness of vTrs of −70 ° C. or less are obtained, and the strength and toughness of the base material are excellent, and the toughness of the HAZ portion is high. Also
vE _{-2 0} is obtained than with high toughness 87 J, it can be seen that excellent HAZ zone toughness. In Comparative Examples No. 17, No. 18, No. 19 and No. 20 in which the chemical composition is out of the range of the present invention, the strength, base material toughness and HAZ part toughness are reduced.

Further, in Comparative Example No. 3 in which the cumulative draft was out of the range of the present invention, the strength and toughness of the base material were deteriorated, and in Comparative Example No. 4 in which the accelerated cooling stop temperature was low, the toughness of the base material was deteriorated. And
Comparative Example No. 7, in which the hot rolling end temperature is out of the range of the present invention,
In No.15, the toughness of the base metal was deteriorated. In Comparative Examples No. 10 and No. 12 in which the heating temperature was out of the range of the present invention, the toughness of the base material was deteriorated.

[0041]

According to the present invention, a high-tensile steel material having excellent tensile strength of 490 MPa or more in both strength and toughness can be produced without adding a large amount of expensive elements and without subjecting it to low-temperature strong pressure reduction. A steel material that can be easily manufactured industrially and has a small variation in strength and toughness in the plate thickness direction can be easily manufactured, and has a great industrial effect.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kenji Ooi 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Prefecture (without address) Inside the Mizushima Works, Kawasaki Steel Corporation (72) Inventor Fumimaru Kawabata, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama 1-chome (without address) Inside Mizushima Steel Works, Kawasaki Steel Corp. (72) Inventor Kenichi Amano 1-chome, with Kawasaki-dori Mizushima, Kurashiki City, Okayama Prefecture (without address) Inside Mizushima Works, Kawasaki Steel Corporation

Claims (7)

[Claims] C .: 0.05 to 0.18%, Si: 0.10 to 0.60%, Mn: 0.80 to 1.80%, P: 0.030% or less, S: 0.015% or less, Al: 0.005 to 0.050%, V : 0.04 to 0.15%, N: 0.0050 to 0.0150%, and V / N: 4.0 to 12.0, and Ceq defined by the following formula (1) is 0.34 to 0.48%.
Material consisting of Fe and unavoidable impurities, 1050-1350 ℃
The cumulative reduction ratio in the temperature range of Tps temperature (℃) below 830 ° C and above defined by the following equation (2) is 30% or more, and the hot working end temperature is Ar defined by the following equation (3). _Three
After hot working to a temperature between (° C) and 900 ° C,
A method for producing a high-tensile steel material having excellent toughness, characterized by air cooling to room temperature. Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 (1) Tps = {V (N−0.292Ti) × 10 ⁵ +397} /0.480 (2) Ar ₃ = 910 -273 C + 25Si-74Mn-56Ni-16Cr-9Mo -5Cu-1620Nb ... (3) 2. The method for producing a high-tensile steel material according to claim 1, wherein accelerated cooling is performed once or twice or more at a cooling rate of air cooling or more during the hot working. 3. An air-cooling rate of not less than (Ar ₃ −60 ° C.) and not more than 600 ° C. at a cooling rate of not less than 30 ° C./sec.
The method for producing a high-tensile steel material according to claim 1 or 2, wherein the method is cooled to the above temperature. 4. The material is, by weight%, C: 0.05 to 0.18%, Si: 0.10 to 0.60%, Mn: 0.80 to 1.80%, P: 0.030% or less, S: 0.015% or less, Al: 0.005 to 0.005%. 0.050%, V: 0.04 to 0.15%, N: 0.0050 to 0.0150%, Nb: 0.003 to 0.030%, Ti: 0.005 to 0.030%, and one or two selected from the group consisting of: ,
(V + Ti) / N: 4.0 to 12.0 was satisfied, and the Ceq was 0.34.
The method for producing a high-tensile steel material having excellent toughness according to claim 1, 2 or 3, wherein the material is a material containing Fe and unavoidable impurities, the content being set to 0.48%. 5. The material is, by weight, C: 0.05 to 0.18%, Si: 0.10 to 0.60%, Mn: 0.80 to 1.80%, P: 0.030% or less, S: 0.015% or less, Al: 0.005 to 0.005%. 0.050%, V: 0.04-0.15%, N: 0.0050-0.0150%, Cu: 0.05-0.50%, Ni: 0.05-0.50%, Cr: 0.05-0.50%, Mo: 0.02-0.20% It contains one or more selected compounds, and satisfies V / N: 4.0 to 12.0, and has a Ceq of 0.34 to 0.
4. The method for producing a high-tensile steel material according to claim 1, wherein the material is 48%, the balance being Fe and a material comprising unavoidable impurities. 6. The material is, by weight, C: 0.05 to 0.18%, Si: 0.10 to 0.60%, Mn: 0.80 to 1.80%, P: 0.030% or less, S: 0.015% or less, Al: 0.005 to 0.005%. 0.050%, V: 0.04-0.15%, N: 0.0050-0.0150%, Cu: 0.05-0.50%, Ni: 0.05-0.50%, Cr: 0.05-0.50%, Mo: 0.02-0.20% One or two or more selected from Nb: 0.003 to 0.030% Ti: 0.005 to 0.03%, and
(V + Ti) / N: 4.0 to 12.0 was satisfied, and the Ceq was 0.34.
The method for producing a high-tensile steel material according to claim 1, wherein the material is a material containing Fe and unavoidable impurities, the content being set to 0.48%. 7. The method according to claim 6, wherein the material further comprises B: 0.0003 to 0.00.
20%, REM: 0.0010-0.010%, Ca: 0.0010-0.010%
The method for producing a high-tensile steel material according to any one of claims 1 to 6, comprising one or more selected from the group consisting of: