WO2024136135A1 - Ferritic stainless steel with improved impact toughness, and manufacturing method thereof - Google Patents

Abstract

The disclosed invention relates to a ferritic stainless steel with an improved impact toughness, and a manufacturing method thereof. A ferritic stainless steel with an improved impact toughness according to one embodiment has, in weight%: C: 0.005% to 0.015%; N: 0.005% to 0.015%; Si: 0.01% to 0.60%; Mn: 0.2% to 0.9%; Cr: 10.5% to 13.0%; Ni: 0.6% to 1.1%; Ti: 0.05% to 0.30%; B: 0.0005% to 0.0070%; P: 0.04% or less; S: 0.01% or less; and the remaining Fe and inevitable impurities, wherein the ferritic stainless steel can have an impact toughness of over 100J at -20℃.

Description

Ferritic stainless steel with improved impact toughness and manufacturing method thereof

The present invention relates to a ferritic stainless steel with improved impact toughness and a method of manufacturing the same.

In general, stainless steel can be classified according to its chemical composition or metal structure. According to metal structure, stainless steel can be classified into austenitic, ferritic, martensitic, and dual phase.

Ferritic stainless steel has excellent corrosion resistance while adding a small amount of expensive alloy elements, so it is more price competitive than austenitic stainless steel. In particular, low-Cr ferritic stainless steel containing 10.5 to 14% Cr has excellent price competitiveness even among ferritic stainless steels, and is widely used as automobile exhaust system flanges and architectural structural materials.

For automobile exhaust system flanges and structural structural materials for construction, thick hot-rolled annealed materials with a thickness of 3 mm or more are mainly used.

In the manufacturing process of the thick hot-rolled annealed material parts, processing defects may occur due to brittle fracture during stamping. In addition, brittle fracture may occur due to vibration during actual use in automobiles, buildings, etc.

Therefore, in order to suppress brittle fracture during processing and actual use, it is very important to improve the impact toughness properties of ferritic stainless steel.

The purpose of the disclosed invention to solve the above-described problems is to provide a ferritic stainless steel and a manufacturing method thereof that improve impact toughness and suppress brittle fracture by controlling alloy components and manufacturing methods.

The present invention can provide ferritic stainless steel with improved impact toughness.

Ferritic stainless steel with improved impact toughness according to one embodiment has, in weight percent, C: 0.005 to 0.015%, N: 0.005 to 0.015%, Si: 0.01 to 0.60%, Mn: 0.2 to 0.9%, Cr: 10.5 to 13.0%, Ni: 0.6 to 1.1%, Ti: 0.05 to 0.30%, B: 0.0005 to 0.0070%, P: 0.04% or less, S: 0.01% or less, including the remaining Fe and inevitable impurities, -20°C shock Toughness may be 100J or more.

In the ferritic stainless steel with improved impact toughness according to one embodiment, the value of equation (1) below may be 4 to 60.

Equation (1): 10000 B - 100 (C + N) / Ti

In formula (1), B, C, N and Ti mean the content (% by weight) of each element.

Ferritic stainless steel with improved impact toughness according to one embodiment may have an impact toughness of 120J or more at 20°C.

Ferritic stainless steel with improved impact toughness according to one embodiment may have an average grain diameter of 65㎛ or less.

Ferritic stainless steel with improved impact toughness according to one embodiment may have a thickness of 3 to 15 mm.

The present invention provides a method for manufacturing the ferritic stainless steel with improved impact toughness described above.

A method for manufacturing ferritic stainless steel with improved impact toughness according to an embodiment includes, in weight percent, C: 0.005 to 0.015%, N: 0.005 to 0.015%, Si: 0.01 to 0.60%, Mn: 0.2 to 0.9%, Cr. : 10.5 to 13.0%, Ni: 0.6 to 1.1%, Ti: 0.05 to 0.30%, B: 0.0005 to 0.0070%, P: 0.04% or less, S: 0.01% or less, producing a slab containing the remaining Fe and inevitable impurities. steps; Reheating the slab and then hot rolling and rough rolling to produce a hot rolled material; And it may include the step of cooling the hot rolled material after winding it at 700 to 900°C.

In the ferritic stainless steel with improved impact toughness according to one embodiment, the slab may have a value of 4 to 60 in equation (1) below.

Equation (1): 10000 B - 100 (C + N) / Ti

In formula (1), B, C, N and Ti mean the content (% by weight) of each element.

The ferritic stainless steel may have an impact toughness of -20°C of 100J or more.

The ferritic stainless steel may have an impact toughness of 120J or more at 20°C.

The reheating can be performed at 1200 to 1280°C.

The finishing rolling can be performed at 900 to 1100°C.

The ferritic stainless steel may have an average grain diameter of 65㎛ or less.

According to one embodiment of the disclosed invention, a ferritic stainless steel with improved impact toughness, which suppresses brittle fracture, suppresses the rate of machining defects, and has excellent durability during actual use of parts, and a method for manufacturing the same can be provided.

Figure 1 is an image taken with an EBSD (Electron Backscatter Diffraction) of the center of a ferritic stainless steel with improved impact toughness according to an example of the disclosed invention.

Hereinafter, embodiments of the disclosed invention will be described in detail with reference to the accompanying drawings. The following examples are presented to sufficiently convey the idea of the disclosed invention to those skilled in the art in the technical field to which the disclosed invention belongs. The disclosed invention is not limited to the embodiments presented herein and may be embodied in other forms. In order to clarify the disclosed invention, the drawings may omit illustrations of parts unrelated to the description and may slightly exaggerate the sizes of components to aid understanding.

Throughout the specification, when a part is said to “include” a certain element, this means that it may further include other elements rather than excluding other elements, unless specifically stated to the contrary.

Singular expressions include plural expressions unless the context clearly makes an exception.

Hereinafter, the reason for limiting the numerical content of alloy components in the embodiments of the present invention will be explained. Hereinafter, unless otherwise specified, the unit is weight%.

Ferritic stainless steel with improved impact toughness according to one embodiment has, in weight percent, C: 0.005 to 0.015%, N: 0.005 to 0.015%, Si: 0.01 to 0.60%, Mn: 0.2 to 0.9%, Cr: 10.5 to 13.0%, Ni: 0.6 to 1.1%, Ti: 0.05 to 0.30%, B: 0.0005 to 0.0070%, P: 0.04% or less, S: 0.01% or less, and may include the remaining Fe and inevitable impurities.

The content of C (carbon) may be 0.005 to 0.015%.

C is an element effective in increasing strength through solid solution strengthening. However, in order to manage the C content to an extremely low level, price competitiveness may decrease due to an increase in steelmaking VOD process costs. Considering this, the C content may be 0.005% or more. However, if the C content is excessive, Cr ₂₃ C ₆ precipitates may be generated and corrosion resistance may be deteriorated due to local Cr depletion in the matrix. Considering this, the upper limit of C content may be 0.015%. Preferably, the C content may be 0.007 to 0.014%.

The content of N (nitrogen) may be 0.005 to 0.015%.

N is an element effective in increasing the strength of steel. However, in order to manage the N content to an extremely low level, price competitiveness may decrease due to an increase in steelmaking VOD process costs. Considering this, the N content may be 0.005% or more. However, when the N content is excessive, the solid solution N concentration reaches a limit, Cr ₂ N precipitates are generated, and corrosion resistance may be deteriorated due to local Cr depletion in the matrix. Considering this, the upper limit of N content may be 0.015%. Preferably, the N content may be 0.006 to 0.015%.

The content of Si (silicon) may be 0.01 to 0.60%.

Si is an element that can partially contribute to strength improvement through solid solution strengthening. Considering this, Si may be added in an amount of 0.01% or more. However, if the Si content is excessive, the strength of the steel may increase excessively, resulting in poor impact toughness. Considering this, the upper limit of Si content may be limited to 0.60%. Preferably, the Si content may be 0.20 to 0.40%.

The content of Mn (manganese) may be 0.2 to 0.9%.

Mn is an element that facilitates the creation of austenite phase at high temperatures and is effective in realizing structure refinement through activation of phase transformation from austenite phase to ferrite phase. Considering this, the Mn content may be 0.2% or more. However, if the Mn content is excessive, the corrosion resistance of the material may be greatly inferior. Considering this, the upper limit of Mn content may be 0.9%. Preferably, the Mn content may be 0.2 to 0.7%.

The content of Cr (chromium) may be 10.5 to 13.0%.

Cr is an essential element added to form a passive film that suppresses oxidation of steel. Additionally, Cr is an element effective in suppressing high temperature oxidation. Considering this, the Cr content may be added at 10.5% or more. However, if the Cr content is excessive, the formation of austenite phase can be suppressed at high temperatures, thereby limiting structure refinement through phase transformation activation. Considering this, the upper limit of Cr content may be limited to 13.0%. Preferably, the Cr content may be 11.3 to 12.5%.

The content of Ni (nickel) may be 0.6 to 1.1%.

Ni is an element that facilitates the creation of austenite phase at high temperatures and is effective in realizing structure refinement through phase transformation activation. Considering this, Ni may be added in an amount of 0.6% or more. However, if the Ni content is excessive, price competitiveness may decrease due to increased raw material costs. Considering this, the upper limit of Ni content may be 1.1%.

The content of Ti (titanium) may be 0.05 to 0.30%.

Ti can improve weldability by combining with C and N and suppressing the formation of Cr carbonitride. Considering this, Ti may be added in an amount of 0.05% or more. However, since Ti is an expensive element, if the Ti content is excessive, price competitiveness may decrease. Considering this, the upper limit of Ti content may be limited to 0.30%. Preferably, the Ti content may be 0.16 to 0.27%.

The content of B (boron) may be 0.0005 to 0.0070%.

B is an element that concentrates at grain boundaries and is an effective element in improving impact toughness by suppressing the propagation of microcracks. Considering this, B may be added in an amount of 0.0005% or more. However, if the content of B is excessive, impact toughness may be deteriorated by combining with N and forming a BN precipitated phase. Considering this, the upper limit of B content can be limited to 0.0070%. That is, if the B content exceeds 0.0070%, room temperature impact toughness and/or low temperature impact toughness may decrease. In this case, it is difficult to achieve the effect of suppressing brittle fracture. Preferably, the content of B may be 0.0011 to 0.0065%.

The P (phosphorus) content may be 0.04% or less.

P is an unavoidable impurity contained in steel and is an element that causes intergranular corrosion or impairs hot workability during pickling during the steel manufacturing process. Considering this, the upper limit of P content can be limited to 0.04%. Preferably, the upper limit of P content may be limited to 0.02%.

The S (sulfur) content may be 0.01% or less.

S is an unavoidable impurity contained in steel and is an element that segregates at grain boundaries and impairs hot workability. Considering this, the upper limit of S content may be limited to 0.01%. Preferably, the upper limit of S content may be limited to 0.007%.

The remaining component of the disclosed invention is iron (Fe). However, in the normal manufacturing process, unintended impurities from raw materials or the surrounding environment may inevitably be mixed, so this cannot be ruled out. Since these impurities are known to anyone skilled in the ordinary manufacturing process, all of them are not specifically mentioned in this specification.

The ferritic stainless steel with improved impact toughness according to the above embodiment may have a ferrite structure fraction of 98 volume% or more, specifically 99 volume% or more. Such ferritic stainless steel has a relatively low thermal expansion coefficient and excellent corrosion resistance compared to steel types with other structures. In this case, for example, the strength, corrosion resistance, and processability are suitable for application as exhaust system parts for internal combustion engine vehicles, home appliance parts, kitchen items, interior and exterior construction items with excellent corrosion resistance, and hydrogen fuel cell parts for hydrogen vehicles. It can be implemented.

As a result of various studies on ferritic stainless steels with improved impact toughness, the present inventors were able to obtain the following findings.

In general, ferritic stainless steels with a BCC (Body Centered Cubic) crystal structure have very low impact toughness compared to austenitic stainless steels with an FCC (Face Centered Cubic) crystal structure. Additionally, in the case of Ti-stabilized ferritic stainless steel, since there is no phase transformation process during the steelmaking-continuous-casting-hot rolling process, it is difficult to implement grain refinement, which may further deteriorate impact toughness.

Conventionally, to improve the impact toughness of Ti-stabilized ferritic stainless steel, large amounts of Mn and Ni elements, which are austenite stabilizing elements, were added. Through this, we attempted to realize grain refinement by activating the phase transformation from the austenite phase to the ferrite phase during the manufacturing process of the Ti-stabilized ferritic stainless steel. However, the effect of improving impact toughness due to the addition of a large amount of austenite stabilizing elements was not significant, and there was a problem of poor price competitiveness.

Ferritic stainless steel with improved impact toughness according to one embodiment may satisfy low-temperature impact toughness of -20°C of 100J or more. If the low-temperature impact toughness of ferritic stainless steel at -20°C is less than 100J, the resistance to brittle fracture in a low-temperature environment may be poor. For example, when processing for use as exhaust system flange parts, it is difficult to suppress brittle fracture. At this time, the processing may include stamping processing, milling processing, etc.

Additionally, specifically, the low-temperature impact toughness at -20°C may be 110J or more, more specifically 120J or more, and more specifically 130J or more. In this case, when the ferritic stainless steel with improved impact toughness according to an embodiment of the present invention is applied to, for example, exhaust system flange parts, these parts become brittle at low temperatures due to the characteristic of being exposed to a low temperature environment of around -20°C for a long time. Since resistance to heat is very important, more advantageous physical properties can be realized in harsh environments.

Ferritic stainless steel with improved impact toughness according to one embodiment may have an impact toughness of 120 J or more at room temperature at 20°C. If the impact toughness of ferritic stainless steel at room temperature at 20°C is less than 120J, it is difficult to suppress brittle fracture, for example, when processing to apply it to exhaust system flange parts. At this time, the processing may include stamping processing, milling processing, etc.

In the ferritic stainless steel with improved impact toughness according to an embodiment, the value of equation (1) below may be 4 to 60, specifically 5 to 55, and more specifically 10 to 40.

Equation (1): 10000 B - 100 (C + N) / Ti

In formula (1), B, C, N and Ti mean the content (% by weight) of each element.

The present inventors manufactured various hot-rolled steel sheets having the composition range and microstructure of the disclosed invention and analyzed the impact toughness at room temperature and low temperature, and derived the above equation (1).

Equation (1) refers to the degree to which B is concentrated at the grain boundaries. C and N, like B, can be concentrated at grain boundaries and thus may prevent B from being enriched. Therefore, by adding Ti to form a Ti(C,N) precipitate phase, grain boundary enrichment of C and N can be suppressed. Through this, impact toughness can be improved by facilitating B thickening and preventing the propagation of fine cracks inside the crystal grains.

In the disclosed invention, it is intended to improve impact toughness through B enrichment by controlling the value of equation (1) from 4 to 60. If the value of equation (1) is less than 4, the concentrated B content may be too small and the effect of improving impact toughness may be small. On the other hand, if the value of equation (1) exceeds 60, B is concentrated too much and combines with elements such as Ti, C, N, etc. to form a precipitated phase, so impact toughness, specifically impact toughness at -20°C low temperature, decreases. It can become inferior.

In one example, the value of equation (1) may preferably be 4.0 to 59.0, more preferably 4.1 to 58.8, and even more preferably 5 to 55, 5.4 to 55, or 5.4 to 53.8. there is. Within the above range, the ferritic stainless steel with improved impact toughness according to an embodiment of the present invention can further improve the impact toughness at 20°C at room temperature and at low temperature at -20°C, and the effect of suppressing brittle fracture is improved to a higher efficiency. It can be.

Ferritic stainless steel with improved impact toughness according to an embodiment may additionally have an average grain diameter of 65 ㎛ or less at the center of the steel, preferably 50 ㎛ or less. In this case, by implementing grain refinement through phase transformation activation, impact toughness values, specifically impact toughness at room temperature at 20°C and low temperature at -20°C, can be further improved.

In one example, the value of equation (1) may be preferably 10 to 40, and more preferably 11.5 to 37.8. At the same time, the average grain diameter at the center of the steel can be controlled to 65㎛ or less. In this case, the ferritic stainless steel with improved impact toughness according to an embodiment of the present invention can realize impact toughness at room temperature at 20°C above 150J and at low temperature at -20°C at above 130J, thereby realizing better impact toughness. .

Here, the average means the average of the measured values measured at five arbitrary locations. In addition, the center of the steel refers to a point between 1/4t and 3/4t when the steel thickness is t.

Figure 1 is an image taken with an EBSD (Electron Backscatter Diffraction) of the center of a ferritic stainless steel with improved impact toughness according to an example of the disclosed invention.

Referring to Figure 1, it can be seen that the average grain diameter of the ferritic stainless steel according to an example is 32㎛. In other words, it can be confirmed that the ferritic stainless steel with improved impact toughness according to an example has grain refinement.

The ferritic stainless steel with improved impact toughness according to an example of the disclosed invention is a ferritic stainless steel with improved impact toughness at -20°C of 100 J or more, especially low-temperature impact toughness, by controlling the alloy composition, equation (1), and manufacturing method. Stainless steel can be provided. In addition, the ferritic stainless steel with improved impact toughness according to an embodiment can provide ferritic stainless steel with improved impact toughness at 20°C of 120J or more, particularly impact toughness at room temperature. That is, according to an example of the disclosed invention, by improving impact toughness even though it is a ferritic stainless steel, it is possible to suppress the processing defect rate and ensure durability in actual use.

Ferritic stainless steel with improved impact toughness according to one embodiment may have a thickness of 3 to 15 mm in a hot-rolled state. However, it is not limited to this, and the thickness can be adjusted depending on the purpose and function.

Next, a method for manufacturing ferritic stainless steel with improved impact toughness according to another aspect of the disclosed invention will be described.

A method for manufacturing ferritic stainless steel with improved impact toughness according to an embodiment includes, in weight percent, C: 0.005 to 0.015%, N: 0.005 to 0.015%, Si: 0.01 to 0.60%, Mn: 0.2 to 0.9%, Cr. : 10.5 to 13.0%, Ni: 0.6 to 1.1%, Ti: 0.05 to 0.30%, B: 0.0005 to 0.0070%, P: 0.04% or less, S: 0.01% or less, producing a slab containing the remaining Fe and inevitable impurities. steps; Reheating the slab and then hot rolling and rough rolling to produce a hot rolled material; And it may include the step of cooling the hot rolled material after winding it at 700 to 900°C.

In the ferritic stainless steel with improved impact toughness according to one embodiment, the slab may have a value of equation (1) below of 4 to 60, specifically 5 to 55, and more specifically 10 to 40.

Equation (1): 10000 B - 100 (C + N) / Ti

In formula (1), B, C, N and Ti mean the content (% by weight) of each element.

The range of components of each alloy composition and the reason for limiting the values in equation (1) are as described above, and each manufacturing step will be described in more detail below.

After manufacturing a slab that satisfies the alloy composition and equation (1), it can be subjected to a series of reheating, hot rolling, rough rolling, finishing rolling, winding, and cooling processes.

Meanwhile, in order to suppress grain growth of the material after rolling, additional annealing can be omitted and only pickling can be performed.

The reheating can be performed at 1200 to 1280°C.

By controlling the reheating temperature to 1200 to 1280°C, coarse precipitates generated during slab manufacturing can be sufficiently re-decomposed. Additionally, by controlling the reheating temperature to 1200 to 1280°C, the average grain diameter can be prevented from increasing and surface defects due to surface oxidation can be suppressed.

The finishing rolling can be performed at 900 to 1100°C.

By controlling the finishing rolling temperature to 900 to 1100°C, cracks that may occur on the surface of the steel material during rolling can be prevented, and the structure can be made uniform to improve toughness and strength. In addition, by controlling the finishing rolling temperature to 900 to 1100°C, coarsening of austenite grains can be prevented and sufficient refinement of ferrite grains after transformation can be achieved.

The hot rolled material can be wound at 700 to 900°C.

By controlling the coiling temperature to 700 to 900°C, the shape and surface quality can be improved. Additionally, by controlling the coiling temperature to 700 to 900°C, the formation of martensite phase during the cooling process can be suppressed.

The cooling can be performed through air cooling.

Hereinafter, the present invention will be described in more detail through examples. However, the description of these examples is only for illustrating the implementation of the present invention, and the present invention is not limited by the description of these examples. This is because the scope of rights of the present invention is determined by matters stated in the patent claims and matters reasonably inferred therefrom.

{Example}

(Preparation of Examples 1 to 5, 7 to 9 and Comparative Examples 1 to 6)

For the various alloy composition ranges shown in Table 1 below, slabs were manufactured by melting them in a vacuum melting furnace. At this time, the components were controlled so that P was 0.04% or less and S was 0.01% or less. The slab was reheated at 1250°C, and then hot rolled, rough rolled, and finished rolled to produce a hot rolled material. The finishing rolling was performed at 1000°C. The hot rolled material was wound at 800°C and then air-cooled to prepare a specimen with a thickness of 8 mm.

(Preparation of Example 6)

An 8 mm thick specimen was manufactured in the same manner as in Example 5 described above, except that the coiling temperature was changed to 900°C.

(weight%)	C	N	Si	Mn	Cr	Ni	Ti	B
Example 1	0.013	0.014	0.50	0.3	12.2	0.6	0.21	0.0017
Example 2	0.010	0.007	0.60	0.7	12.5	0.9	0.27	0.0011
Example 3	0.008	0.009	0.20	0.7	12.0	0.8	0.16	0.0016
Example 4	0.011	0.009	0.30	0.4	11.8	0.7	0.21	0.0021
Example 5	0.007	0.006	0.30	0.4	11.9	0.7	0.23	0.0025
Example 6	0.007	0.006	0.30	0.4	11.9	0.7	0.23	0.0025
Example 7	0.012	0.013	0.40	0.2	11.6	0.6	0.19	0.0051
Example 8	0.014	0.015	0.30	0.4	11.3	1.1	0.26	0.0065
Example 9	0.007	0.006	0.30	0.6	11.2	0.8	0.25	0.0064
Comparative Example 1	0.010	0.009	0.20	0.8	12.6	0.7	0.23	0.0005
Comparative Example 2	0.007	0.006	0.10	0.4	11.4	0.8	0.22	0.0006
Comparative Example 3	0.011	0.012	0.40	0.5	12.8	1.0	0.18	0.0015
Comparative Example 4	0.007	0.008	0.20	0.5	11.0	0.9	0.29	0.0069
Comparative Example 5	0.006	0.011	0.50	0.7	10.6	0.7	0.25	0.0085
Comparative Example 6	0.013	0.014	0.20	0.5	10.7	0.9	0.11	0.0077

Table 2 below shows equation (1) values, average grain diameter, 20°C impact toughness, and -20°C impact toughness.

The value of equation (1) was expressed by calculating equation (1) below.

Equation (1): 10000 B - 100 (C + N) / Ti

In formula (1), B, C, N and Ti mean the content (% by weight) of each element.

The average grain diameter was expressed by measuring the center of the specimen with EBSD (Electron Backscatter Diffraction).

Here, the average means the average of the measured values measured at five arbitrary locations. In addition, the center of the steel refers to a point between 1/4t and 3/4t when the steel thickness is t.

Impact toughness was measured by performing a Charpy-V notch impact test at temperatures of 20℃ and -20℃ using an impact tester from Zwick Roell. In addition, if the measured impact toughness at -20°C was 100J or more, the brittle fracture inhibition ability was evaluated as “excellent,” and if the measured impact toughness value at -20°C was less than 100J, the brittle fracture inhibition ability was evaluated as “poor,” and the results are listed in Table 2.

(weight%)	Equation (1)	Grain size (㎛)	20℃ impact toughness (J)	-20℃ impact toughness (J)	Brittle fracture inhibition ability
Example 1	4.1	32	122	101	Great
Example 2	4.7	36	125	107	Great
Example 3	5.4	33	147	128	Great
Example 4	11.5	31	151	131	Great
Example 5	19.3	36	155	130	Great
Example 6	19.3	65	121	104	Great
Example 7	37.8	29	153	133	Great
Example 8	53.8	28	146	125	Great
Example 9	58.8	37	128	104	Great
Comparative Example 1	-3.3	34	117	95	error
Comparative Example 2	0.1	32	121	98	error
Comparative Example 3	2.2	37	123	99	error
Comparative Example 4	63.8	28	119	93	error
Comparative Example 5	78.2	33	96	83	error
Comparative Example 6	52.5	35	103	88	error

As can be seen from Tables 1 and 2, in Examples 1 to 9 according to the present invention, low-temperature impact toughness, especially -20°C impact toughness, was achieved at 100J or more. In this case, it has excellent resistance to low-temperature embrittlement even when exposed to a low-temperature environment for a long time, and, for example, has an excellent ability to suppress brittle fracture during stamping for application as exhaust system flange parts.

In the case of Example 5 according to the present invention, it was manufactured in the same manner as Example 6, except that the coiling temperature was performed differently to additionally control the grain size. Through the physical property measurement results of Examples 5 and 6, it can be confirmed that there is an additional improvement in impact toughness when the grain size is controlled to 65㎛ or less.

According to an example of the disclosed invention, it is possible to provide a ferritic stainless steel with improved impact toughness and a manufacturing method thereof, which suppresses the rate of machining defects and has excellent durability during actual use of parts.

Claims (12)

1. In weight percent, C: 0.005 to 0.015%, N: 0.005 to 0.015%, Si: 0.01 to 0.60%, Mn: 0.2 to 0.9%, Cr: 10.5 to 13.0%, Ni: 0.6 to 1.1%, Ti: 0.05 to 0.05% 0.30%, B: 0.0005 to 0.0070%, P: 0.04% or less, S: 0.01% or less, including the remaining Fe and inevitable impurities,

   Ferritic stainless steel with improved impact toughness, with an impact toughness of over 100J at -20℃.
2. In claim 1,

   A ferritic stainless steel with improved impact toughness where the value of equation (1) below is 4 to 60.

   Equation (1): 10000 B - 100 (C + N) / Ti

   (In equation (1), B, C, N and Ti mean the content (% by weight) of each element)
3. In claim 1,

   Ferritic stainless steel with improved impact toughness, with an impact toughness of 120J or more at 20°C.
4. In claim 1,

   Ferritic stainless steel with improved impact toughness with an average grain diameter of 65㎛ or less.
5. In claim 1,

   Ferritic stainless steel with improved impact toughness, with an average thickness of 3 to 15 mm.
6. In weight percent, C: 0.005 to 0.015%, N: 0.005 to 0.015%, Si: 0.01 to 0.60%, Mn: 0.2 to 0.9%, Cr: 10.5 to 13.0%, Ni: 0.6 to 1.1%, Ti: 0.05 to 0.05% Preparing a slab containing 0.30%, B: 0.0005 to 0.0070%, P: 0.04% or less, S: 0.01% or less, the remaining Fe and inevitable impurities;

   Reheating the slab and then hot rolling and rough rolling to produce a hot rolled material; and

   A method of manufacturing ferritic stainless steel with improved impact toughness, comprising the step of winding the hot rolled material at 700 to 900 ° C and then cooling it.
7. In claim 6,

   The slab is a method of manufacturing ferritic stainless steel with improved impact toughness, wherein the value of equation (1) below is 4 to 60.

   Equation (1): 10000 B - 100 (C + N) / Ti

   (In equation (1), B, C, N and Ti mean the content (% by weight) of each element)
8. In claim 6,

   A method of manufacturing ferritic stainless steel with improved impact toughness, wherein the ferritic stainless steel has an impact toughness of 100J or more at -20°C.
9. In claim 6,

   A method of manufacturing ferritic stainless steel with improved impact toughness, wherein the ferritic stainless steel has an impact toughness of 120J or more at 20°C.
10. In claim 6,

    The reheating is performed at 1200 to 1280°C. A method of manufacturing ferritic stainless steel with improved impact toughness.
11. In claim 6,

    A method of manufacturing ferritic stainless steel with improved impact toughness, wherein the finishing rolling is performed at 900 to 1100°C.
12. In claim 6,

    A method of manufacturing ferritic stainless steel with improved impact toughness, wherein the ferritic stainless steel has an average grain diameter of 65㎛ or less.

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