Ferritic stainless steel with improved magnetic properties and method for manufacturing the same

Abstract

The present invention provides a ferritic stainless steel having improved magnetic properties, which exhibits high magnetic permeability in response to a low externally applied magnetic field and thereby increases reactivity to electromagnetic wave shielding, and a method for producing the same. [Solution] The stainless steel of the present invention is characterized by the following components, by weight: C: more than 0% and not more than 0.02%, N: more than 0% and not more than 0.02%, Si: 0.5% to 2.0%, Mn: 0.1% to 0.3%, Cr: 16.0% to 20.1%, Mo: more than 1.0% and not more than 2.0%, Ti: 0.1% to 0.4%, with the balance being Fe (iron) and other unavoidable impurities, and the value of the following formula (1) being 130 or less. Formula (1): 30 + 2500 * ([C] + [N]) - 15 * [Si] + 2.5 * [Cr] + 22 * ​​[Mo] (In formula (1), [C], [N], [Si], [Cr], and [Mo] mean the content (weight%) of each element).

Description

Technical Field

[0001] The present invention relates to a ferrite stainless steel with improved magnetic properties and a method for manufacturing the same. More specifically, in order to enhance the responsiveness to an externally applied magnetic field, the present invention relates to a ferrite stainless steel with improved magnetic properties and a method for manufacturing the same by controlling alloy components and manufacturing processes.

Background Art

[0002] In recent years, due to the development of technical fields such as smartphones and semi-autonomous vehicles, various electronic devices have come to be used, and the use of electromagnetic waves has increased rapidly. As a result, interference caused by electromagnetic waves between electronic devices has increased. Electromagnetic wave interference causes malfunction of devices or makes precise control of devices difficult. In order to prevent malfunction of electronic devices due to electromagnetic wave interference, important elements must be isolated with a material that can shield magnetic fields.

[0003] In the case of shielding from low-frequency or magnetic fields, a material with high magnetic permeability has excellent shielding ability. In particular, there is an increasing demand for a material that exhibits high magnetic permeability with respect to a low externally applied magnetic field.

[0004] Conventionally, research has been conducted on materials that exhibit high magnetic permeability with respect to a high externally applied magnetic field, but this has the problem of being inferior in responsiveness to an externally applied magnetic field.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made to solve the above problems, and an object thereof is to provide a ferrite stainless steel with improved magnetic properties and a method for manufacturing the same, which increase the reactivity to electromagnetic wave shielding by exhibiting high magnetic permeability with respect to a low externally applied magnetic field.

Means for Solving the Problems

[0006] ​The ferritic stainless steel with improved magnetic properties of the present invention is characterized by having, in weight percent, C: more than 0% but 0.02% or less, N: more than 0% but 0.02% or less, Si: 0.5% to 2.0%, Mn: 0.1% to 0.3%, Cr: 16.0% to 20.1%, Mo: more than 1.0% but 2.0%, Ti: 0.1% to 0.4%, with the remainder being Fe (iron) and other unavoidable impurities, and the value of the following formula (1) being 130 or less. Formula (1): 30+2500*([C]+[N])-15*[Si]+2.5*[Cr]+22*[Mo] In equation (1), [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element.

[0007] Furthermore, the ferritic stainless steel with improved magnetic properties according to the present invention is preferable to have a value of 50 or less in the following formula (2). Formula (2): 18+800*([C]+[N])-6*[Si]+[Cr]+6*[Mo] In equation (2), [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element.

[0008] The ferritic stainless steel of the present invention may further contain, by weight, Nb: greater than 0% but 0.1% or less and Sn: greater than 0% but 0.1% or less. Furthermore, it is preferable that the stainless steel of the present invention has a maximum magnetic permeability of 1,000 or more in the 50 Hz frequency band. Furthermore, the stainless steel of the present invention is preferable to have an externally applied magnetic field of 130 A / m or less that exhibits maximum magnetic permeability.

[0009] The ferritic stainless steel of the present invention can have a coercivity of less than 50 A / m under conditions that exhibit maximum permeability in the 50 Hz frequency band. Furthermore, it is preferable that the stainless steel of the present invention has a pitting potential of 300 mV or higher. Furthermore, the ferritic stainless steel of the present invention is preferable to have a hardness of Hv140 or higher.

[0010] The present invention relates to a method for producing ferritic stainless steel with improved magnetic properties, characterized in that, by weight percent, C: greater than 0% but 0.02% or less, N: greater than 0% but 0.02% or less, Si: 0.5% or more but 2.0% or less, Mn: 0.1% or more but 0.3% or less, Cr: 16.0% or more but 20.1% or less, Mo: greater than 1.0% but 2.0% or less, Ti: 0.1% or more but 0.4% or less, the remainder being Fe (iron) and other unavoidable impurities, the value of formula (1) below is 130 or less, and the value of formula (2) below is 50 or less, and the method comprises the steps of: producing a slab; hot rolling the slab at a reheating temperature of 1050 to 1150°C to produce a hot-rolled material; cold rolling the hot-rolled material to produce a cold-rolled material; and final annealing the cold-rolled material at 1050 to 1150°C. Formula (1): 30+2500*([C]+[N])-15*[Si]+2.5*[Cr]+22*[Mo] Formula (2): 18+800*([C]+[N])-6*[Si]+[Cr]+6*[Mo] In equations (1) and (2), [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element.

[0011] Furthermore, in the manufacturing method of the present invention, the cold rolling is preferably carried out with a reduction ratio of 70% or more. [Effects of the Invention]

[0012] According to one embodiment of the present invention, it is possible to provide a ferritic stainless steel with improved magnetic properties and a method for manufacturing the same, which exhibits high magnetic permeability and high magnetic permeability to low externally applied magnetic fields, thereby increasing its reactivity to electromagnetic wave shielding. [Modes for carrying out the invention]

[0013] The ferritic stainless steel with improved magnetic properties according to one embodiment of the present invention consists of, by weight percent, C: more than 0% but 0.02% or less, N: more than 0% but 0.02% or less, Si: 0.5% to 2.0%, Mn: 0.1% to 0.3%, Cr: 16.0% to 20.1%, Mo: more than 1.0% but 2.0%, Ti: 0.1% to 0.4%, with the remainder being Fe (iron) and other unavoidable impurities, and the value of the following formula (1) can be 130 or less. Formula (1): 30+2500*([C]+[N])-15*[Si]+2.5*[Cr]+22*[Mo] In equation (1), [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element.

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided to fully convey the idea of ​​the present invention to those who are ordinary skill in the art to which the present invention pertains. The present invention is not limited to the embodiments presented herein and may be embodied in other forms. When, throughout the specification, a part of the specification "includes" a certain component, this means that, unless otherwise stated, it may include other components rather than excluding them. Unless otherwise stated in the context, singular expressions include plural forms.

[0015] The ferritic stainless steel with improved magnetic properties according to one embodiment of the present invention consists of, by weight percent, C: more than 0% but 0.02% or less, N: more than 0% but 0.02% or less, Si: 0.5% to 2.0%, Mn: 0.1% to 0.3%, Cr: 16.0% to 20.1%, Mo: more than 1.0% but 2.0%, Ti: 0.1% to 0.4%, with the remainder being Fe (iron) and other unavoidable impurities. The following explains the reasons for the numerical limitations on the alloy component content in the embodiments of the present invention. Unless otherwise specified, the unit is weight percent.

[0016] The carbon (C) content is greater than 0% and less than or equal to 0.02%. Since carbon (C) is an unavoidable impurity element in steel, it is preferable to reduce its content as much as possible. If the C content is excessive, a decrease in magnetic properties occurs due to carbide formation, which can result in poor magnetic permeability. Furthermore, if the C content is excessive, impurities increase, reducing the elongation rate, decreasing the work hardening index n value, and raising the ductile-to-brittle transition temperature (DBTT), thus reducing impact properties. Taking this into consideration, the upper limit of the C content is limited to 0.02%. Considering workability and mechanical properties, the upper limit of the C content is preferably 0.01% by weight.

[0017] The nitrogen (N) content is greater than 0% and less than or equal to 0.02%. If the nitrogen content is excessive, the amount of impurities in the material increases, reducing the elongation rate and raising the ductile-to-brittle transition temperature (DBTT), thus degrading the impact properties. Furthermore, excessive nitrogen content can lead to the formation of rod-shaped AlN precipitates, causing grain refinement and potentially resulting in poor iron loss. Considering this, the upper limit of the nitrogen content is restricted to 0.02%. Considering processability and mechanical properties, the upper limit of the nitrogen content is preferably 0.015% by weight.

[0018] The silicon (Si) content is between 0.5% and 2.0%. Si is an effective element for improving magnetic permeability at low externally applied magnetic fields. Considering this, it is preferable to add Si at a concentration of 0.5% or more. However, if the Si content is excessive, the elongation rate decreases, the work hardening index n value decreases, and Si-based inclusions increase, leading to reduced workability. Considering this, the upper limit of Si content is restricted to 2.0%. Taking workability into consideration, the upper limit of Si content is preferably 1.0% by weight.

[0019] The manganese (Mn) content is between 0.1% and 0.3%. When the content of Mn is low, fine MnS precipitates are formed, and the grain size is refined, thereby reducing the magnetism. Therefore, Mn is preferably added at 0.1% or more so that the MnS precipitates are formed coarsely. However, when the content of Mn is excessive, there is a risk that the magnetism will be inferior due to an increase in the MnS precipitate fraction. Considering this, the upper limit of the Mn content is restricted to 0.3%.

[0020] The content of Cr (chromium) is 16.0% or more and 20.1% or less. Cr is an element that forms a passive film in an oxidizing environment to improve corrosion resistance. Considering this, it is preferable to add Cr at 16.0% or more. However, when the content of Cr is excessive, it promotes the formation of delta (δ) ferrite in the slab, resulting in a decrease in elongation and impact toughness, and a decrease in magnetic permeability. Considering this, the upper limit of the Cr content is restricted to 20.1%.

[0021] The content of Mo (molybdenum) is more than 1.0% and 2.0% or less. Mo is an element effective in increasing the corrosion resistance of stainless steel. Considering this, it is advisable to add 1.0% or more. However, when the content of Mo is excessive, it segregates at the grain boundaries and suppresses grain growth, thereby causing grain refinement and a risk of inferior magnetism. Considering this, the upper limit of the Mo content is restricted to 2.0%.

[0022] The content of Ti (titanium) is 0.1% or more and 0.4% or less. Ti is an element effective in causing precipitation phenomena and improving strength. Considering this, it is advisable to add Ti at 0.1% or more. However, when the content of Ti is excessive, the problem of a decrease in magnetic permeability occurs because the Ti-based precipitates increase and the grain size does not become sufficiently large. Considering this, the upper limit of the Ti content is restricted to 0.4%.

[0023] The remaining component of this invention is iron (Fe). However, in the normal manufacturing process, unintended impurities from the raw materials and surrounding environment inevitably become mixed in, and these cannot be eliminated. Since these impurities are recognizable to any technician in the normal manufacturing process, not all of them are specifically mentioned herein.

[0024] Furthermore, the ferritic stainless steel with improved magnetic properties according to one embodiment of the present invention may further contain, by weight, Nb: greater than 0% but 0.1% or less and Sn: greater than 0% but 0.1% or less.

[0025] The niobium (Nb) content is greater than 0% and less than or equal to 0.1%. Nb is an element that forms a fine precipitate phase, similar to Ti. However, while Ti forms a relatively high-temperature phase and fine precipitation can be prevented by heat treatment, Nb forms a stable phase at relatively low temperatures, so it can be redissolved during hot rolling and cause fine precipitation during annealing. Therefore, if the Nb content is excessive, there is a risk of a decrease in magnetism due to fine precipitation, and it is preferable to control it as an impurity. Taking this into consideration, the upper limit of the Nb content is restricted to 0.1%.

[0026] The tin (Sn) content is greater than 0% and less than or equal to 0.1%. Sn (T), like Ti (Ti), is an element that forms a fine precipitate phase. However, while Ti forms a relatively high-temperature phase and fine precipitation can be prevented by heat treatment, Sn forms a stable phase at relatively low temperatures and can be redissolved during hot rolling, potentially causing fine precipitation during annealing. Therefore, if the Sn content is excessive, there is a risk of reduced magnetism due to fine precipitation, and it is preferable to control it as an impurity. Taking this into consideration, the upper limit of the Sn content is restricted to 0.1%.

[0027] In one embodiment of the present invention, the ferritic stainless steel with improved magnetic properties has a value of 130 or less in the following formula (1). Formula (1): 30+2500*([C]+[N])-15*[Si]+2.5*[Cr]+22*[Mo] In equation (1), [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element.

[0028] The present invention provides a ferritic stainless steel with improved magnetic properties, exhibiting high permeability to low externally applied magnetic fields, thereby increasing its reactivity to electromagnetic shielding, and a method for manufacturing the same. When the value of formula (1) exceeds 130, it exhibits a high permeability value to relatively large externally applied magnetic fields, resulting in decreased reactivity to electromagnetic shielding. Therefore, it is preferable that the value of formula (1) be 130 or less. By controlling the value of equation (1) to 130 or less, the ferritic stainless steel with improved magnetic properties according to one embodiment of the present invention can have a maximum magnetic permeability of 1,000 or more in the 50 Hz frequency band. Furthermore, the externally applied magnetic field required to exhibit the maximum magnetic permeability is 130 A / m or less.

[0029] In one embodiment of the present invention, the ferritic stainless steel with improved magnetic properties is preferably such that the value of the following formula (2) is 50 or less. Formula (2): 18+800*([C]+[N])-6*[Si]+[Cr]+6*[Mo] In equation (2), [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element.

[0030] Coercivity refers to the magnitude of the external magnetic field in the reverse direction required to return a magnetized magnetic material to an unmagnetized state. If the value of equation (2) exceeds 50, the coercivity will be high, which may result in poor shielding ability. Therefore, it is preferable that the value of equation (2) be 50 or less. By controlling equation (2) above to 50 or less, the ferritic stainless steel with improved magnetic properties according to one embodiment of the present invention can have a coercivity of less than 50 A / m under conditions that exhibit maximum permeability in the 50 Hz frequency band. Furthermore, the ferritic stainless steel with improved magnetic properties according to one embodiment of the present invention is preferable to have a pitting potential of 300 mV or higher, achieved by controlling the alloy composition and manufacturing process to improve corrosion resistance. Furthermore, the ferritic stainless steel with improved magnetic properties according to one embodiment of the present invention can have a hardness of Hv140 or higher by controlling the alloy composition and manufacturing process to improve its strength.

[0031] Next, a method for manufacturing ferritic stainless steel with improved magnetic properties according to another aspect of the present invention will be described. A method for producing ferritic stainless steel with improved magnetic properties according to one embodiment of the present invention preferably includes the steps of: producing a slab in which, by weight percent, C: greater than 0% but 0.02% or less, N: greater than 0% but 0.02% or less, Si: 0.5% or more but 2.0% or less, Mn: 0.1% or more but 0.3% or less, Cr: 16.0% or more but 20.1% or less, Mo: greater than 1.0% but 2.0% or less, Ti: 0.1% or more but 0.4%, with the remainder being Fe (iron) and other unavoidable impurities, the value of formula (1) below is 130 or less, and the value of formula (2) below is 50 or less; producing a hot-rolled material by hot-rolling the slab at a reheating temperature of 1050 to 1150°C; producing a cold-rolled material by cold-rolling the hot-rolled material; and performing a final annealing of the cold-rolled material at 1050 to 1150°C.

[0032] Formula (1): 30+2500*([C]+[N])-15*[Si]+2.5*[Cr]+22*[Mo] In equation (1), [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element. Formula (2): 18+800*([C]+[N])-6*[Si]+[Cr]+6*[Mo] In equation (2), [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element.

[0033] The reasons for the numerical limitations on the component ranges and component relationships of each alloy composition are as described above, and each manufacturing stage will be explained in more detail below. First, a slab satisfying the aforementioned alloy composition and component relationship is manufactured, followed by a series of hot rolling, cold rolling, and final annealing processes.

[0034] The slab is hot-rolled at a reheating temperature of 1050 to 1150°C. If the reheating temperature of the slab is too low, the load on the rolling rolls increases, making it difficult to re-decompose the coarse precipitates generated during slab casting and hindering the homogenization of the internal structure. Considering this, the reheating temperature of the slab should ideally be 1050°C or higher. However, if the reheating temperature is too high, the grain size of the slab may become excessively coarse, potentially resulting in reduced strength. Considering this, the upper limit of the slab reheating temperature is limited to 1150°C.

[0035] The aforementioned cold rolling should be carried out with a reduction ratio of 70% or more. If the reduction ratio is less than 70%, it is difficult to achieve the desired strength. The cold-rolled material can be annealed at 1050 to 1150°C. If the final annealing temperature is low, the required time will increase and manufacturing costs will rise. Taking this into consideration, the final annealing temperature is preferably 1050°C or higher. However, if the final annealing temperature is too high, the microstructure may become excessively coarse, potentially resulting in inferior mechanical properties. Taking this into consideration, the final annealing temperature is preferably 1150°C or lower.

[0036] The present invention will be described in more detail below through examples. However, such examples are provided to illustrate the implementation of the present invention and do not limit the present invention. The scope of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom. {Example}

[0037] Steels with various chemical compositions as shown in Table 1 below were cast into slabs, and the cast slabs were reheated to 1050°C. The reheated slabs were hot-rolled, then cold-rolled to a reduction ratio of 70%, and finally annealed at 1050°C to produce stainless steel as the final cold-rolled product.

[0038] [Table 1]

[0039] The values ​​of equations (1) and (2), maximum permeability, applied magnetic field, coercivity, pitting potential, and hardness are shown in Table 2 below. The value of equation (1) is the calculated value of 30 + 2500 * ([C] + [N]) - 15 * [Si] + 2.5 * [Cr] + 22 * ​​[Mo]. In formula (1) above, [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element. The value of equation (2) is the calculated value of 18 + 800 * ([C] + [N]) - 6 * [Si] + [Cr] + 6 * [Mo]. In formula (2) above, [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element.

[0040] For the final cold-rolled product, the magnetic properties were evaluated by measuring the magnetic field due to the magnetization of the material while gradually increasing the externally applied magnetic field in the 50 Hz frequency band. The maximum magnetic permeability was measured using a non-magnetic permeability meter with the model name Ferropro FP-5, by contacting the probe to the cross-section of a steel sample with a diameter of 20 mm or more and a thickness of 5 mm or more. The pitting potential is the value measured when pitting corrosion occurs after immersion in an NaCl solution and application of a potential. Here, the temperature of the NaCl solution was set to 30°C and the concentration to 3.5%. The hardness was measured using a Vickers hardness tester manufactured by Zwick Roell.

[0041] [Table 2]

[0042] Referring to Table 2, Examples 1 to 7 all satisfied the condition that the value of equation (1) is 130 or less and the value of equation (2) is 50 or less. Therefore, they satisfied the conditions that the maximum magnetic permeability in the 50 Hz frequency band is 1,000 or more, the externally applied magnetic field required to exhibit maximum magnetic permeability is 130 A / m or less, and the coercivity under the conditions that exhibit maximum magnetic permeability is less than 50 A / m. In other words, Examples 1 to 7 showed increased responsiveness to electromagnetic shielding and improved magnetic properties by exhibiting high magnetic permeability to low externally applied magnetic fields. Furthermore, Examples 1 to 7 satisfied the conditions that the pitting potential value is 300 mV or more and the hardness is Hv140 or more. In other words, Examples 1 to 7 had excellent corrosion resistance and strength.

[0043] Comparative Examples 1-5 did not satisfy the condition that the value of equation (1) is 130 or less. Therefore, Comparative Examples 1-5 did not satisfy the condition that the externally applied magnetic field required to exhibit maximum permeability is 130 A / m or less. In addition, Comparative Examples 1-5 did not satisfy the condition that the value of equation (2) is 50 or less. Therefore, Comparative Examples 1-5 did not satisfy the condition that the coercivity is less than 50 A / m. In other words, Comparative Examples 1-5 have relatively high externally applied magnetic fields, which indicates that they exhibit poor responsiveness to electromagnetic shielding. Furthermore, Comparative Example 4, without the addition of Mo, did not meet the requirement of a pitting potential of 300 mV or higher due to its relatively low Cr content. In other words, Comparative Example 4 had inferior corrosion resistance. [Industrial applicability]

[0044] According to one embodiment of the present invention, a ferritic stainless steel with improved magnetic properties and a method for manufacturing the same can be provided, which derives a component system exhibiting high magnetic permeability and exhibits high magnetic permeability to low externally applied magnetic fields, thereby increasing its reactivity to electromagnetic wave shielding, and thus has industrial applicability.

Claims

1. In weight percent, C: over 0% but 0.02% or less, N: over 0% but 0.02% or less, Si: 0.5% to 2.0%, Mn: 0.18% to 0.20%, Cr: 16.0% to 20.1%, Mo: over 1.0% but 2.0%, Ti: 0.1% to 0.4%, with the remainder being Fe (iron) and other unavoidable impurities. The value of the following formula (1) is 130 or less, A ferritic stainless steel with improved magnetic properties, characterized by a maximum magnetic permeability of 1,000 or more in the 50 Hz frequency band. Formula (1): 30+2500*([C]+[N])-15*[Si]+2.5*[Cr]+22*[Mo] (In formula (1), [C], [N], [Si], [Cr], and [Mo] represent the content (by weight %) of each element.)

2. The ferritic stainless steel with improved magnetic properties according to claim 1, characterized in that the value of formula (2) below is 50 or less. Formula (2): 18+800*([C]+[N])-6*[Si]+[Cr]+6*[Mo] (In formula (2), [C], [N], [Si], [Cr], and [Mo] represent the content (by weight %) of each element.)

3. The ferritic stainless steel with improved magnetic properties according to claim 1, characterized in that the externally applied magnetic field required to exhibit maximum magnetic permeability is 130 A / m or less.

4. The ferritic stainless steel with improved magnetic properties according to claim 1, characterized in that the coercivity under conditions exhibiting maximum permeability in the 50 Hz frequency band is less than 50 A / m.

5. The ferritic stainless steel with improved magnetic properties as described in claim 1, characterized in that it has a hardness of Hv140 or higher.

6. In weight percent, C: over 0% but 0.02% or less, N: over 0% but 0.02% or less, Si: 0.5% to 2.0%, Mn: 0.18% to 0.20%, Cr: 16.0% to 20.1%, Mo: over 1.0% but 2.0%, Ti: 0.1% to 0.4%, with the remainder being Fe (iron) and other unavoidable impurities. The stage of manufacturing a slab in which the value of formula (1) below is 130 or less and the value of formula (2) below is 50 or less, The process involves hot-rolling the aforementioned slab at a reheating temperature of 1050 to 1150°C to produce a hot-rolled material, The steps include: cold rolling the hot-rolled material to produce a cold-rolled material; A method for producing ferritic stainless steel with improved magnetic properties, characterized by including a step of final annealing of the cold-rolled material at 1050 to 1150°C. Formula (1): 30+2500*([C]+[N])-15*[Si]+2.5*[Cr]+22*[Mo] (In formula (1), [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element.) Formula (2): 18+800*([C]+[N])-6*[Si]+[Cr]+6*[Mo] (In formula (2), [C], [N], [Si], [Cr], and [Mo] represent the content (weight %) of each element.)

7. The method for producing ferritic stainless steel with improved magnetic properties according to claim 6, characterized in that the cold rolling is performed with a reduction ratio of 70% or more.

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