JP3254108B2 - Ultra-high-strength steel sheet excellent in hydrogen embrittlement resistance and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-high-strength steel sheet having excellent tensile strength of 1180 MPa or more and excellent in hydrogen embrittlement resistance and a method for producing the same. Such ultra-high-strength steel sheets according to the present invention, in particular, thin steel sheets are, for example, as pipe applications, for applications requiring light weight and strength, such as reinforcing members for automobile doors, and for Zn, Cd, Sn, Al, Cr, Ni,
Plating treatment such as Pb, chemical conversion treatment such as chromate treatment and phosphate treatment, and further, anticorrosion surface treatment by organic coating can be performed, and it can be suitably used for various applications in severe corrosive environment.

[0002]

2. Description of the Related Art Recently, from the viewpoint of environmental protection of the earth, there is a strong demand for improving fuel efficiency of automobiles. Therefore, in order to reduce the weight of the vehicle body, the need for ultra-high-strength steel sheets having a tensile strength of 1180 MPa or more has been increasing for various reinforcing members of automobiles such as bumpers and door impact beams. But,
Bolts made of ultra-high-strength steel having a strength of 1180 MPa or more are susceptible to cracking due to hydrogen embrittlement, so-called delayed fracture, as described in, for example, JP-A-60-155644.
It is already known as described in Japanese Patent Publication No.
Therefore, even in various members using an ultra-high strength thin steel sheet, hydrogen generated by a corrosion reaction in an atmospheric environment may enter the steel sheet and be suddenly broken during use.

[0003] As for prevention of hydrogen embrittlement of ultra-high strength thin steel sheet, as described in JP-A-4-268053, Si is added to steel to control penetration of hydrogen atoms into the steel sheet. Thus, a method for preventing the occurrence of hydrogen embrittlement has been proposed. However, the state of rust changes depending on the corrosive environment. Therefore, it is not always possible to sufficiently control penetration of hydrogen atoms into a steel sheet by adding Si to prevent hydrogen embrittlement. Also, Japanese Patent Application Laid-Open No. 4-2
Japanese Patent No. 80940 describes improvement of water cracking resistance of spot welds, but it is not practical because it requires addition of 3% or more of Ni and causes an increase in cost. Nothing is mentioned about the water cracking resistance of the base material.

Further, Japanese Patent Application Laid-Open No. Hei 5-295481 discloses that, by adding Ca to steel and changing MnS extended in the rolling direction to spherical CaS, the bonding force at austenite crystal grain boundaries is strengthened, and hydrogen embrittlement resistance is reduced. It has been proposed to improve the oxidation characteristics, but the effect of Ca cannot be obtained unless Si is added in an amount of 1.0 to 2.0%. However, when a large amount of Si is added, there is a problem that the delayed fracture resistance of the steel sheet is reduced.

[0005]

An object of the present invention is to solve the above-described problem of hydrogen embrittlement in an ultra-high-strength steel sheet having a tensile strength of 1180 MPa or more. It is an object of the present invention to provide an excellent ultra-high strength steel sheet, particularly a thin steel sheet, and a method for producing the same.

[0006]

The ultrahigh-strength steel sheet having excellent hydrogen embrittlement resistance according to the present invention has the following properties.
0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.
0%, P 0.020% or less, S 0.010% or less,
And 0.001-0.010% of Ca, and (b) C
r At least one element selected from the group consisting of 0.10 to 5.00%, Ni 0.10 to 4.00%, and Cu 0.05 to 3.00%, with the balance being iron and unavoidable impurities And at least one of martensite, tempered martensite and bainite structure in a volume ratio of 40% or more and a strength of 1180 MPa or more.

Further, according to the present invention, there is provided an ultra-high strength steel sheet having excellent hydrogen embrittlement resistance as follows.

(2) In terms of% by weight, (a) C 0.08 to 0.30
%, Si less than 1.0%, Mn 1.5-3.0%, P 0.
020% or less, S 0.010% or less, and Ca 0.0
0.01 to 0.010%, and (b) Al 0.05 to 2.
00%, W 0.05 to 1.00%, and Co 0.10
At least one element selected from the group consisting of 5.00%, the balance being iron and unavoidable impurities, and at least one of martensite, tempered martensite and bainite structure at least 40% by volume Including, strength 1
Ultra-high-strength steel sheet of 180 MPa or more.

(3) In weight% (a) C 0.08 to 0.30
%, Si less than 1.0%, Mn 1.5-3.0%, P 0.
020% or less, S 0.010% or less, and Ca 0.0
01-0.010%, and (b) La 0.001-
0.10%, and at least one element selected from the group consisting of 0.001% to 0.100% of Ce, the balance being iron and unavoidable impurities, and any of martensite, tempered martensite or bainite structure An ultra-high-strength steel sheet containing at least one kind in a volume ratio of 40% or more and having a strength of 1180 MPa or more.

(4) By weight% (a) C 0.08 to 0.30
%, Si less than 1.0%, Mn 1.5-3.0%, P 0.
020% or less, S 0.010% or less, and Ca 0.0
0.1-0.010%, and (b) Cr 0.10-5.
00%, Ni 0.10 to 4.00%, and Cu 0.05 to
At least one element selected from the group consisting of 3.00%, (c) Al 0.05 to 2.00%, and W 0.05 to 1.0.
0% and at least one element selected from the group consisting of Co 0.10 to 5.00%, the balance being iron and unavoidable impurities, and one of martensite, tempered martensite and bainite structure. An ultra-high-strength steel sheet containing at least 40% by volume of at least seeds and having a strength of 1180 MPa or more.

(5) By weight percent (a) C 0.08 to 0.30
%, Si less than 1.0%, Mn 1.5-3.0%, P 0.
020% or less, S 0.010% or less, and Ca 0.0
0.1-0.010%, and (b) Cr 0.10-5.
00%, Ni 0.10 to 4.00%, and Cu 0.05 to
At least one element selected from the group consisting of 3.00%, (c) La 0.001 to 0.100%, and Ce 0.0
At least one selected from the group consisting of 01 to 0.100%
Ultra-high strength containing at least 40% by volume of at least one of martensite, tempered martensite, and bainite structure, and the strength is 1180 MPa or more. steel sheet.

(6) By weight% (a) C 0.08 to 0.30
%, Si less than 1.0%, Mn 1.5-3.0%, P 0.
020% or less, S 0.010% or less, and Ca 0.0
0.01 to 0.010%, and (b) Al 0.05 to 2.
00%, W 0.05 to 1.00%, and Co 0.10
At least one element selected from the group consisting of 5.00%, (c) La 0.001 to 0.100%, and Ce 0.0
At least one selected from the group consisting of 01 to 0.100%
Ultra-high strength containing at least 40% by volume of at least one of martensite, tempered martensite, and bainite structure, and the strength is 1180 MPa or more. steel sheet.

(7) By weight% (a) C 0.08 to 0.30
%, Si less than 1.0%, Mn 1.5-3.0%, P 0.
020% or less, S 0.010% or less, and Ca 0.0
0.1-0.010%, and (b) Cr 0.10-5.
00%, Ni 0.10 to 4.00%, and Cu 0.05 to
At least one element selected from the group consisting of 3.00%, (c) Al 0.05 to 2.00%, and W 0.05 to 1.0.
0%, and at least one element selected from the group consisting of Co 0.10 to 5.00%, and (d) La 0.001 to 0.005%.
100%, and at least one element selected from the group consisting of 0.001 to 0.100% of Ce, the balance being iron and unavoidable impurities, and one of martensite, tempered martensite, and bainite structure. An ultra-high-strength steel sheet containing at least 40% by volume of at least seeds and having a strength of 1180 MPa or more.

Further, according to the present invention, each ultra-high-strength steel sheet having excellent hydrogen embrittlement resistance as described above has a steel slab containing each of the above elements and having a balance of iron and inevitable impurities of 1100 ° C. or more. Heat to temperature, 600
After hot rolling at a temperature of ℃ or less, pickling,
After removing the scale and performing cold rolling, and then performing continuous annealing, after soaking at a temperature in the range of 800 ° C. or more and 1000 ° C. or less, 800-650 at a cooling rate of 30 ° C./sec or less. C. and slowly cooled to a temperature in the range of 40.degree.
Cool to a temperature of 0 ° C. or less and then reheat, or as it is, at a temperature in the range of 150 to 400 ° C. for 1 to 20
It can be obtained by performing a tempering treatment of heating for minutes.

First, in the present invention, the ranges of the chemical components of the steel sheet and the reasons thereof are as follows.

C is an essential element for forming a required low-temperature transformation structure such as martensite in the steel sheet and increasing the strength of the steel sheet. In particular, according to the present invention, C is 1180 MPa.
In order to obtain the above tensile strength, it is necessary to add at least 0.08%. However, when the addition amount exceeds 0.30%, the workability may be reduced, or the deterioration of the hydrogen embrittlement resistance may be accelerated due to the deterioration of the corrosion resistance or the like. In particular, in the present invention, from the viewpoint of the strength and corrosion resistance of the steel sheet, the C content is more preferably in the range of 0.12 to 0.20%.

Si is an element effective for solid solution strengthening of steel without deteriorating ductility. However, when the addition amount is 1.0% or more, not only the effect is saturated, but also the paintability decreases. Therefore, in the present invention,
The Si content is less than 1.0%. Mn is an element that enhances the hardenability of steel. In order to stably generate martensite in continuous annealing equipment, Mn must be added in an amount of 1.5% or more. However, when the content exceeds 3.0%, not only the effect is saturated, but also segregation increases, the structure becomes non-uniform, and the workability deteriorates. Therefore, the upper limit of the addition amount is 3.0%.

P is an element effective for strengthening the steel and increasing the ductility, but on the other hand, it tends to segregate at the grain boundaries and lowers the grain boundary behavior. S is M
Since inclusions are formed together with n and the like to become a starting point of corrosion generation and to deteriorate bending workability and the like, the content is restricted to 0.010% or less. Particularly preferably, it is 0.005% or less.

In general, Ca has the effect of spheroidizing and dispersing inclusions such as MnS to improve the toughness of steel. Furthermore, when Ca forms a solid solution in the matrix, it has the effect of preventing grain boundary fracture and suppressing hydrogen embrittlement.
Further, like La and Ce described later, Ca also has an effect of improving corrosion resistance. In order to exhibit these effects effectively, it is necessary to add at least 0.001%, and particularly preferably 0.003% or more. However, when Ca is added excessively, it generates coarse Ca-based inclusions and lowers the workability. Therefore, the upper limit of the addition amount is set to 0.010%.

[0020] Cr improves the hardenability of the steel and improves the corrosion resistance of the steel by densifying the formed rust. In order to effectively obtain such effects, it is necessary to add at least 0.10%. However, when excessively added, it causes a decrease in toughness after quenching and tempering, and further promotes localization of corrosion form (pitting corrosion) and easily forms a starting point of hydrogen embrittlement. The upper limit is
5.00%. Particularly, from the viewpoint of corrosion resistance and toughness, in the present invention, the amount of addition is preferably in the range of 1.0 to 3.5%.

Ni, by adding 0.10% or more, has an effect of improving the corrosion resistance of steel by densifying the generated rust. However, an excessive addition causes a decrease in tensile strength due to an increase in retained austenite, so the upper limit is made 4.00%. Further, Ni is an expensive metal, and a more preferable addition range is 2.00% or less from the viewpoint of economy.

Since Cu is electrochemically more noble than iron, Cu has the effect of densifying the formed rust, improving corrosion resistance, particularly weather resistance, and improving pitting corrosion resistance. To obtain these effects effectively, at least 0.05
% Addition is required. However, even if it is added in excess of 3.00%, the above effect is saturated, and there is a possibility of causing embrittlement during hot rolling. Therefore, the upper limit of the addition amount is set to 3.0.
00%. From a practical viewpoint, in particular, 0.20 to 1.0
A range of 0% is preferred.

Al has the effect of improving the corrosion resistance of steel. In order to effectively obtain this effect, 0.05% or more of addition is necessary. On the other hand, if it is added excessively, it causes deterioration of the surface state and lowers the workability of the steel. The upper limit is 2.00%. In particular, according to the present invention, the addition amount is preferably 0.15 to 1.00%.

W dissolves in an aqueous solution, and has an excellent effect of improving pitting corrosion resistance due to the adsorption of tungstate ions generated by dissolution. To obtain this effect effectively, it is necessary to add at least 0.05%. However, 1.00%
If the amount is too large, the effect is only saturated, so the upper limit is made 1.00%.

Co is a solid solution strengthening element, has the property of not deteriorating the toughness, and has the effect of increasing the corrosion resistance. To obtain these effects effectively, 0.
Addition of 10% or more is necessary, and addition of 1.0% or more is particularly preferable. However, since Co is an expensive element, the upper limit of the addition amount is set to 5.00%, preferably 3.00%.
%.

Both La and Ce dissolve in the aqueous solution when the steel is corroded, and form alkaline hydroxides. Thus, like Ca, they dissolve iron ions on the corroded surface. It has the effect of neutralizing and suppressing the accompanying acidification, thereby improving the corrosion resistance. The addition of these elements reduces the average rate of corrosion, since local acidification by corrosion reactions not only promotes corrosion, but also promotes the formation of pitting, which is a source of stress concentration. In addition, it also has the effect of improving pitting corrosion resistance.

In order to effectively exhibit such an effect of improving corrosion resistance, it is necessary to add 0.001% or more of each of these elements. Increasing inclusions, reducing workability, and during steelmaking, may cause erosion of the furnace wall,
The upper limit is 0.100% for any of the elements.
And In particular, according to the present invention, the added amount of La and Ce is preferably in the range of 0.005 to 0.020% for any element.

Hydrogen embrittlement of high-strength steel is phenomena-wise, in that diffusible hydrogen infiltrated into steel is locally concentrated at a certain point according to a tensile stress gradient, and at that point, the steel undergoes hydrogen embrittlement cracking. Seems to wake up. Although various mechanisms have been proposed for hydrogen embrittlement cracking, such as the theory of surface pressure and the theory of reduced cohesive force between iron atoms, they have not yet been elucidated yet, but they have a tendency to absorb hydrogen and diffuse hydrogen. It is understood that the three factors of easiness and the susceptibility of the steel itself to hydrogen embrittlement are interconnected phenomena.

Therefore, as a countermeasure against hydrogen embrittlement, from the raw material side, (1) blocking the hydrogen entry path, (2) suppressing the diffusion of hydrogen in the steel and the concentration in the tensile stress portion,
(3) It is considered that three measures for reducing the hydrogen embrittlement susceptibility of the steel itself are effective. Conventionally, there are many measures against hydrogen embrittlement according to (2) and (3), but the present invention focuses on the measure (1) in addition to (2) and (3).

That is, the hydrogen absorption of steel in a normal use environment is caused by the fact that hydrogen generated by the cathode reaction enters the steel without being gasified when the steel is corroded.
According to the present invention, the measure (1) can be implemented by improving the corrosion resistance of the steel and preventing hydrogen storage.

As described above, according to the present invention, as a result of intensive studies on the additional elements for improving the hydrogen embrittlement resistance of ultra-high-strength steel, the tensile strength of 1180 MPa or more was obtained by using the above-mentioned predetermined elements. However, the present invention succeeded in obtaining an ultra-high-strength steel sheet having excellent hydrogen embrittlement resistance.

Next, a method of manufacturing an ultra-high strength steel sheet having excellent hydrogen embrittlement resistance according to the present invention will be described.

According to the method of the present invention, first, a steel slab having the above-mentioned chemical composition is subjected to hot rolling according to a conventional method at a heating temperature of 1100 ° C. or more and a winding temperature of 600 ° C. or less. In the slab heating, in a high-strength steel as in the present invention, since the rolling load during hot rolling tends to be high, it is preferable that the rolling temperature is not excessively low. Temperature 110
0 ° C or higher. In this case, the heating method is not particularly limited, such as direct rolling of the continuous cast piece as it is, light heating, and a method of reheating after cooling the slab. However, setting the heating temperature to a temperature exceeding 1300 ° C. requires only heat energy costs, and has no particular advantage. The hot rolling of the steel slab may be performed by a conventional method, and the finish rolling may be performed at a temperature of 800 ° C. or more.

The winding is performed at a temperature of 600 ° C. or less in consideration of the removability of scale on the surface. However, when the temperature is too low, the cold rolling property is reduced, so that the lower limit of the winding temperature is preferably 300 ° C. The hot-rolled steel sheet obtained in this manner is subjected to pickling, grinding, shot blasting or other means according to a conventional method to remove the scale of the surface, cold-rolled, and then continuously annealed.

According to the present invention, a part or the whole is transformed into austenite during heating by continuous annealing, and these are transformed into martensite by cooling thereafter.
According to the present invention, a desired strength can be obtained by the amount of the martensite and the amount of the alloying element.

Accordingly, in the present invention, the heating temperature in the continuous annealing is set to 800 ° C. or more and 1000 ° C. or less. In order to obtain a structure such as martensite, tempered martensite or bainite by a cooling treatment after continuous annealing, it is necessary to precipitate austenite during heating, and the heating temperature is set to 800 ° C. or higher. However, even if the temperature exceeds 1000 ° C., there is no particular advantage, and only the energy cost increases.

After such continuous annealing, the temperature is gradually cooled (primary cooling) to a temperature in the range of 800 to 650 ° C. at a cooling rate of 30 ° C./second or less, and then quenched from this temperature (secondary cooling). I do. When the slow cooling temperature is higher than 30 ° C./sec, ferrite is not easily generated, and a predetermined strength cannot be stably obtained. The cooling rate during the rapid cooling is 70 ° C. in order to cause low-temperature transformation of martensite and the like.
/ Sec or more is required, and at such a cooling rate, 400
Cooling to below ℃ causes transformation such as martensite. When the quenching start temperature is lower than 650 ° C., the transformation of austenite to ferrite proceeds before the start of quenching, and it is difficult to obtain a required low-temperature transformed structure such as martensite having a volume ratio of 40% or more. On the other hand, when the quenching start temperature is higher than 800 ° C., the shape of the obtained steel sheet deteriorates, which is not preferable. Although the quenching rate is not particularly limited, the cooling rate by water quenching (1000 to 2000 ° C./second) is usually the upper limit industrially.

The steel sheet according to the present invention has a low-temperature transformation structure of at least one of martensite, tempered martensite and bainite structure in a volume fraction of 40% or more, and all structures are low-temperature transformation products. You may. When the low-temperature transformation structure is less than 40%, the amount of alloying elements necessary to obtain a desired strength increases, and the production cost increases.

Next, when the quenched structure is martensite, it is reheated after continuous annealing as described above so as to improve its workability and to easily work, for example, on pipes and the like. Alternatively, tempering is performed at a temperature in the range of 150 to 400 ° C. as it is from continuous annealing. Performing the tempering treatment at a temperature of 400 ° C. or higher not only increases the production cost due to reheating, but also cannot obtain particularly useful effects.

[0040]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited by these examples.

Example 1 The steels shown in Tables 1 to 3 were heated to 1230 ° C., hot-rolled to a thickness of 3.0 mm at a finishing temperature of 800 ° C., and wound at 480 ° C. This was pickled and then cold rolled to a thickness of 1.8 mm. Thereafter, the temperature was maintained at 850 ° C. for 2 minutes, the air was forcedly cooled to 750 ° C., water quenching was performed from this temperature, and tempering was performed. Tempering conditions were as follows: a steel sheet having a tensile strength of 1180 MPa or more was obtained at a temperature of 180 to 400 ° C. and a heating time of 12 minutes. In the table, in the column of low-temperature transformation product, M
Indicates martensite, Mt indicates tempered martensite, B indicates bainite, and P indicates pearlite.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

The steel sheet thus obtained was examined for its resistance to hydrogen embrittlement as follows. That is, a steel sheet is cut out to a width of 20 mm and a length of 100 mm by machining, and this sample is subjected to a U-shaped bending process with a radius of curvature of 10 mm at the center in the longitudinal direction of the plate, and bolted near the end of the plate to bend a certain amount. A test piece to which stress was applied was used. Here, the bolt was covered with a Teflon tube and insulated to avoid galvanic corrosion between the bolt and the test piece. Also,
Bare materials were used for all test pieces.

The test environment was a salt spray test (JIS Z).
2371) is carried out for 12 hours and then left for 12 hours as a cycle test and a 0.1 N hydrochloric acid immersion test (30 ° C.). The hydrogen embrittlement resistance of the steel was evaluated by measuring the number and cracking time. As shown in FIG. 1, in the steel according to the present invention, it was understood that the time until cracking occurred was significantly long in any of the tests, and that the steel of the present invention was excellent in hydrogen embrittlement resistance. Is done.

Example 2 A high-strength steel sheet was manufactured using steel having the chemical components shown in Table 4 under the conditions shown in Tables 4 and 5. Table 5 shows the strength and hydrogen embrittlement resistance of the obtained steel sheet. Evaluation of the hydrogen embrittlement resistance was performed in the same manner as in Example 1.

[0048]

[Table 4]

[0049]

[Table 5]

[0050]

As described above, the ultra-high strength steel sheet according to the present invention has a tensile strength of 1180 MPa or more, and at the same time, has excellent resistance to hydrogen embrittlement. For example, it can be suitably used for reducing the weight of a reinforcing member for a bumper or a door of an automobile.

[Brief description of the drawings]

FIG. 1 is a graph showing the hydrogen embrittlement resistance characteristics of a high-strength steel sheet according to the present invention and a steel sheet as a comparative example. In the figure, the appended numbers indicate steel type numbers.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C22C 38/58 C22C 38/58 (72) Inventor Haruo Tomari 1 Kanazawacho, Kakogawa City, Hyogo Prefecture Kobe Steel, Ltd. Kakogawa Works (72) Inventor Gohiro Nakajima 1 Kanazawacho, Kakogawa City, Hyogo Prefecture Kobe Steel, Ltd.Kakogawa Works (72) Inventor Fukuta Tanaka 1 Kanazawacho, Kakogawa City, Hyogo Prefecture Kobe Steel Works, Kakogawa Works (56 References JP-A-8-134589 (JP, A) JP-A-58-157948 (JP, A) JP-A-53-106318 (JP, A) JP-A-61-96059 (JP, A) 6-306543 (JP, A) JP-A-58-133351 (JP, A) JP-A-57-107064 (JP, A) JP-A-4-333524 (JP, A) JP-A-7-102341 (JP, A) A) (58) Minutes surveyed Field (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 8/02 C21D 9/46

Claims (14)

(57) [Claims] 1. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, And 0.001 to 0.010% of Ca, and (b) 0.10 to 5.00% of Cr, 0.10 to 4.00% of Ni, and 0.05 to 3.00 of Cu. % At least one element selected from the group consisting of
The balance consists of iron and unavoidable impurities, martensite,
One of tempered martensite or bainite structure
Contains 40% or more by volume of at least seeds and has a strength of 1180M
Ultra-high strength steel sheet with excellent hydrogen embrittlement resistance of Pa or more. 2. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, 0.001 to 0.010% of Ca, and (b) 0.05 to 2.00% of Al, 0.05 to 1.00% of W, and 0.10 to 5.00 of Co. % Ultra-high strength steel sheet containing at least one element selected from the group consisting of: 3. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 % Or less, and 0.001 to 0.010% of Ca, and (b) at least one selected from the group consisting of 0.001 to 0.100% of La and 0.001 to 0.100% of Ce High strength steel sheet containing the following elements. 4. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, And 0.001 to 0.010% of Ca, and (b) 0.10 to 5.00% of Cr, 0.10 to 4.00% of Ni, and 0.05 to 3.00 of Cu. % And at least one element selected from the group consisting of: (c) Al 0.05 to 2.00%, W 0.05 to 1.00%, and Co 0.10 to 5.00%. An ultra-high strength steel sheet containing at least one element selected from the group consisting of: 5. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, And 0.001 to 0.010% of Ca, and (b) 0.10 to 5.00% of Cr, 0.10 to 4.00% of Ni, and 0.05 to 3.00 of Cu. % And at least one element selected from the group consisting of (c) La 0.001 to 0.100% and Ce 0.001 to 0.100%. Including ultra-high strength steel sheet. 6. In% by weight, (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, 0.001 to 0.010% of Ca, and (b) 0.05 to 2.00% of Al, 0.05 to 1.00% of W, and 0.10 to 5.00 of Co. % Of at least one element selected from the group consisting of: (c) La 0.001 to 0.100%, and Ce 0.001%.
An ultra-high-strength steel sheet containing at least one element selected from the group consisting of -0.100%. 7. In% by weight, (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, And 0.001 to 0.010% of Ca, and (b) 0.10 to 5.00% of Cr, 0.10 to 4.00% of Ni, and 0.05 to 3.00 of Cu. % And at least one element selected from the group consisting of: (c) Al 0.05 to 2.00%, W 0.05 to 1.00%, and Co 0.10 to 5.00%. And (d) at least one element selected from the group consisting of 0.001 to 0.100% La and 0.001 to 0.100% La. steel sheet. 8. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, And 0.001 to 0.010% of Ca, and (b) 0.10 to 5.00% of Cr, 0.10 to 4.00% of Ni, and 0.05 to 3.00 of Cu. % At least one element selected from the group consisting of
1100 steel slab consisting of iron and unavoidable impurities
After performing hot rolling at a temperature of 600 ° C. or higher and winding at a temperature of 600 ° C. or lower, pickling, removing scale, performing cold rolling, and then performing continuous annealing,
After soaking at a temperature in the range of 0 ° C. or more and 1000 ° C. or less, 800-650 ° C. at a cooling rate of 30 ° C./sec or less.
Slowly cooled to a temperature in the range of
At a cooling rate of at least 400 g / s to a temperature of 400 ° C. or less, and then reheat, or
A tempering treatment in which heating is performed at a temperature in the range of 00 ° C. for 1 to 20 minutes, wherein the martensite structure is 40% or more by volume and has a strength of 1180 MPa or more. Manufacturing method of high strength steel sheet. 9. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, 0.001 to 0.010% of Ca, and (b) 0.05 to 2.00% of Al, 0.05 to 1.00% of W, and 0.10 to 5.00 of Co. % At least one element selected from the group consisting of
1100 steel slab consisting of iron and unavoidable impurities
After performing hot rolling at a temperature of 600 ° C. or higher and winding at a temperature of 600 ° C. or lower, pickling, removing scale, performing cold rolling, and then performing continuous annealing,
After soaking at a temperature in the range of 0 ° C. or more and 1000 ° C. or less, 800-650 ° C. at a cooling rate of 30 ° C./sec or less.
Slowly cooled to a temperature in the range of
At a cooling rate of at least 400 g / s to a temperature of 400 ° C. or less, and then reheat, or
A tempering treatment in which heating is performed at a temperature in the range of 00 ° C. for 1 to 20 minutes, wherein the martensite structure is 40% or more by volume and has a strength of 1180 MPa or more. Manufacturing method of high strength steel sheet. 10. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 % Or less, and 0.001 to 0.010% of Ca, and (b) at least one selected from the group consisting of 0.001 to 0.100% of La and 0.001 to 0.100% of Ce Containing the elements of
1100 steel slab consisting of iron and unavoidable impurities
After performing hot rolling at a temperature of 600 ° C. or higher and winding at a temperature of 600 ° C. or lower, pickling, removing scale, performing cold rolling, and then performing continuous annealing,
After soaking at a temperature in the range of 0 ° C. or more and 1000 ° C. or less, 800-650 ° C. at a cooling rate of 30 ° C./sec or less.
Slowly cooled to a temperature in the range of
At a cooling rate of at least 400 g / s to a temperature of 400 ° C. or less, and then reheat, or
A tempering treatment in which heating is performed at a temperature in the range of 00 ° C. for 1 to 20 minutes, wherein the martensite structure is 40% or more by volume and has a strength of 1180 MPa or more. Manufacturing method of high strength steel sheet. 11. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, And 0.001 to 0.010% of Ca, and (b) 0.10 to 5.00% of Cr, 0.10 to 4.00% of Ni, and 0.05 to 3.00 of Cu. % And at least one element selected from the group consisting of: (c) Al 0.05 to 2.00%, W 0.05 to 1.00%, and Co 0.10 to 5.00%. A steel slab containing at least one element selected from the group consisting of
After heating to a temperature of 00 ° C. or higher and performing hot rolling at a temperature of 600 ° C. or lower, pickling, removing the scale, performing cold rolling, and then performing continuous annealing,
After soaking at a temperature in the range of 800 ° C. or more and 1000 ° C. or less, 800-650 at a cooling rate of 30 ° C./sec or less.
Slowly cooled to a temperature in the range of
At a cooling rate of not less than 400 ° C./sec, it is cooled to a temperature of not more than 400 ° C. and then reheated, or
A tempering treatment in which heating is performed at a temperature in the range of 400 ° C. for 1 to 20 minutes, wherein the martensite structure contains 40% or more by volume and has a strength of 1180 MPa or more. Manufacturing method of high strength steel sheet. 12. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, And 0.001 to 0.010% of Ca, and (b) 0.10 to 5.00% of Cr, 0.10 to 4.00% of Ni, and 0.05 to 3.00 of Cu. % And at least one element selected from the group consisting of (c) La 0.001 to 0.100% and Ce 0.001 to 0.100%. 11 steel slabs containing iron and unavoidable impurities
After heating to a temperature of 00 ° C. or higher and performing hot rolling at a temperature of 600 ° C. or lower, pickling, removing the scale, performing cold rolling, and then performing continuous annealing,
After soaking at a temperature in the range of 800 ° C. or more and 1000 ° C. or less, 800-650 at a cooling rate of 30 ° C./sec or less.
Slowly cooled to a temperature in the range of
At a cooling rate of not less than 400 ° C./sec, it is cooled to a temperature of not more than 400 ° C. and then reheated, or
A tempering treatment in which heating is performed at a temperature in the range of 400 ° C. for 1 to 20 minutes, wherein the martensite structure contains 40% or more by volume and has a strength of 1180 MPa or more. Manufacturing method of high strength steel sheet. 13. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, 0.001 to 0.010% of Ca, and (b) 0.05 to 2.00% of Al, 0.05 to 1.00% of W, and 0.10 to 5.00 of Co. % And at least one element selected from the group consisting of (c) La 0.001 to 0.100% and Ce 0.001 to 0.100%. 11 steel slabs containing iron and unavoidable impurities
After heating to a temperature of 00 ° C. or higher and performing hot rolling at a temperature of 600 ° C. or lower, pickling, removing the scale, performing cold rolling, and then performing continuous annealing,
After soaking at a temperature in the range of 800 ° C. or more and 1000 ° C. or less, 800-650 at a cooling rate of 30 ° C./sec or less.
Slowly cooled to a temperature in the range of
At a cooling rate of not less than 400 ° C./sec, it is cooled to a temperature of not more than 400 ° C. and then reheated, or
An ultrahigh temperament comprising a martensitic structure of 40% or more by volume and having a strength of 1180 MPa or more and excellent in hydrogen embrittlement resistance, characterized by performing a tempering treatment at a temperature in the range of 400 ° C. for 1 to 20 minutes. Manufacturing method of high strength steel sheet. 14. In% by weight: (a) C 0.08 to 0.30%, Si less than 1.0%, Mn 1.5 to 3.0%, P 0.020% or less, S 0.010 %, And 0.001 to 0.010% of Ca, and (b) 0.10 to 5.00% of Cr, 0.10 to 4.00% of Ni, and 0.05 to 3.00 of Cu. % And at least one element selected from the group consisting of: (c) Al 0.05 to 2.00%, W 0.05 to 1.00%, and Co 0.10 to 5.00%. And at least one element selected from the group consisting of (d) La 0.001 to 0.100% and Ce 0.001 to 0.100%, with the balance being iron And steel slabs consisting of unavoidable impurities
After heating to a temperature of 00 ° C. or higher and performing hot rolling at a temperature of 600 ° C. or lower, pickling, removing the scale, performing cold rolling, and then performing continuous annealing,
After soaking at a temperature in the range of 800 ° C. or more and 1000 ° C. or less, 800-650 at a cooling rate of 30 ° C./sec or less.
Slowly cooled to a temperature in the range of
At a cooling rate of not less than 400 ° C./sec, it is cooled to a temperature of not more than 400 ° C. and then reheated, or
A tempering treatment in which heating is performed at a temperature in the range of 400 ° C. for 1 to 20 minutes, wherein the martensite structure contains 40% or more by volume and has a strength of 1180 MPa or more. Manufacturing method of high strength steel sheet.