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

Abstract

The present invention provides a ferritic stainless steel having improved corrosion resistance and magnetic properties through optimization of alloy components and manufacturing processes, and a manufacturing method thereof. [Solution] The ferritic stainless steel of the present invention with improved corrosion resistance and magnetic properties consists, by weight, of C: 0.0005% or more and 0.035% or less, N: 0.005% or more and 0.05% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.1% or more and 0.5% or less, Cr: 16.0% or more and 20.0% or less, Mo: more than 0% and 0.5% or less, Nb: more than 0% and 0.5% or less, Ti: 0.005% or more and 0.30% or less, with the balance being Fe and unavoidable impurities, and is characterized by the value of the following formula (1) being 20 or more. Formula (1): Cr+(3*Mo+10*N+Si+Nb+Ti) / Mn (In the above formula (1), Cr, Mo, N, Si, Nb, Ti, and Mn represent the weight percentage of each element).

Description

[Technical Field]

[0001] The present invention relates to a ferritic stainless steel having improved corrosion resistance and magnetic properties and a method for manufacturing the same, and more particularly to a ferritic stainless steel having improved corrosion resistance and magnetic properties by optimizing alloy components and manufacturing processes, and a method for manufacturing the same. [Background technology]

[0002] Recently, with the development of technology fields such as smartphones and semi-autonomous vehicles, the use of various electronic devices has led to a rapid increase in the use of electromagnetic waves. This has led to an increase in electromagnetic interference between electronic devices. Electromagnetic interference can cause devices to malfunction or make precise control of devices difficult. To prevent electronic devices from malfunctioning due to electromagnetic interference, important components must be surrounded by materials that can block magnetic fields. On the other hand, ferritic stainless steel has a relatively high magnetic permeability and is corrosion-resistant, making it a versatile material that can be used in a variety of applications where both corrosion resistance and shielding are required. However, until now, there have not been many technologies that can simultaneously achieve high corrosion resistance and high magnetic permeability.

[0003] Patent Document 1 attempts to provide a ferritic stainless steel with improved corrosion resistance by controlling the contents of Si, Ti, Nb, and Al. However, it was not possible to ensure high magnetic permeability for use in electronic devices. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Korean Patent No. 10-2302386 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made to solve the above problems, and its object is to provide a ferritic stainless steel having improved corrosion resistance and magnetic properties by optimizing the alloy components and manufacturing process, and a manufacturing method thereof. [Means for solving the problem]

[0006] The ferritic stainless steel of the present invention with improved corrosion resistance and magnetic properties is characterized by having, by weight%, C: 0.0005% to 0.035%, N: 0.005% to 0.05%, Si: 0.1% to 2.0%, Mn: 0.1% to 0.5%, Cr: 16.0% to 20.0%, Mo: more than 0% to 0.5%, Nb: more than 0% to 0.5%, Ti: 0.005% to 0.30%, with the remainder being Fe and unavoidable impurities, and having a value of 20 or more for the following formula (1): Formula (1): Cr+(3*Mo+10*N+Si+Nb+Ti) / Mn In the formula (1), Cr, Mo, N, Si, Nb, Ti, and Mn represent the weight percentage of each element.

[0007] The ferritic stainless steel of the present invention preferably has a maximum magnetic permeability value of 1,000 or more in a 50 Hz frequency band. The ferritic stainless steel of the present invention may have a pitting potential of 200 mV or more. The ferritic stainless steel of the present invention preferably has a surface crystal grain size of 30 μm or more.

[0008] The present invention provides a method for producing a ferritic stainless steel having improved corrosion resistance and magnetic properties, the method comprising the steps of: producing a slab containing, by weight, C: 0.0005% to 0.035%, N: 0.005% to 0.05%, Si: 0.1% to 2.0%, Mn: 0.1% to 0.5%, Cr: 16.0% to 20.0%, Mo: more than 0% to 0.5%, Nb: more than 0% to 0.5%, Ti: 0.005% to 0.30%, and the remainder being Fe and unavoidable impurities, and having a value of 20 or more in the following formula (1): reheating the slab at 1100 to 1300°C; hot-rolling the reheated slab and hot-annealing it to produce a hot-rolled steel sheet; and cold-rolling the hot-rolled steel sheet, cold-annealing it, and pickling it to produce a cold-rolled steel sheet. Formula (1): Cr+(3*Mo+10*N+Si+Nb+Ti) / Mn In the formula (1), Cr, Mo, N, Si, Nb, Ti, and Mn represent the weight percentage of each element.

[0009] In the method for producing a ferritic stainless steel of the present invention, it is preferable that the value of the following formula (2) is 50 or more. Formula (2): [Hot rolling annealing temperature (℃) * Hot rolling annealing time (min) + 1.1 * (Cold rolling annealing temperature (℃) * Cold rolling annealing time (min))] / Cold rolling reduction rate (%). In the method for producing a ferritic stainless steel of the present invention, the hot rolling annealing can be carried out at 950 to 1150°C for 1.5 to 2.5 minutes.

[0010] In the method for producing a ferritic stainless steel of the present invention, the cold rolling annealing is preferably carried out at 1000 to 1200° C. for 1 to 2 minutes. In the method for producing ferritic stainless steel of the present invention, cold rolling It is advisable to carry out the rolling reduction at a rate of 60 to 75%. [Effects of the Invention]

[0011] According to one embodiment of the present invention, it is possible to provide a ferritic stainless steel having improved corrosion resistance and magnetic properties by optimizing the alloy components and manufacturing process, and a manufacturing method thereof. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the change in pitting potential according to formula (1). [Figure 2] 10 is a graph showing the change in maximum magnetic permeability according to formula (2). DETAILED DESCRIPTION OF THE INVENTION

[0013] A ferritic stainless steel with improved corrosion resistance and magnetic properties according to one embodiment of the present invention is characterized by having, in weight percent, C: 0.0005% to 0.035%, N: 0.005% to 0.05%, Si: 0.1% to 2.0%, Mn: 0.1% to 0.5%, Cr: 16.0% to 20.0%, Mo: more than 0% to 0.5%, Nb: more than 0% to 0.5%, Ti: 0.005% to 0.30%, with the remainder being Fe and unavoidable impurities, and having a value of 20 or more for the following formula (1): Formula (1): Cr+(3*Mo+10*N+Si+Nb+Ti) / Mn In the formula (1), Cr, Mo, N, Si, Nb, Ti, and Mn represent the weight percentage 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 presented to fully convey the concept of the present invention to those skilled in the art. The present invention is not limited to the embodiments presented herein and may be embodied in other forms. In the drawings, parts not relevant to the description may be omitted to clarify the present invention, and the sizes of components may be somewhat exaggerated to facilitate understanding.

[0015] Throughout the specification, when any part is said to "comprise" a certain element, this does not mean that it excludes other elements, but that it may further include other elements, unless specifically stated to the contrary. Any expression in the singular includes a plural expression unless the context clearly indicates otherwise. The reasons for limiting the numerical values ​​of the alloy component contents in the embodiments of the present invention will be explained below. Unless otherwise specified, the units are % by weight.

[0016] The ferritic stainless steel with improved corrosion resistance and magnetic properties according to one embodiment of the present invention contains, in weight percent, C: 0.0005% to 0.035%, N: 0.005% to 0.05%, Si: 0.1% to 2.0%, Mn: 0.1% to 0.5%, Cr: 16.0% to 20.0%, Mo: more than 0% to 0.5%, Nb: more than 0% to 0.5%, Ti: 0.005% to 0.30%, and the remainder being Fe and unavoidable impurities.

[0017] The C (carbon) content is 0.0005% or more and 0.035% or less. As the C content increases, the amount of impurities increases, so the C content needs to be reduced. However, if the C content is too low, refining costs will increase. Taking this into consideration, C can be added up to 0.0005% or more. However, if the C content is excessive, the elongation rate will decrease, the Ductile-Brittle Transition Temperature (DBTT) will increase, and impact properties will deteriorate. Taking this into consideration, the upper limit of the C content should be 0.035%.

[0018] The N (nitrogen) content is 0.005% or more and 0.05% or less. If the N content is too low, TiN crystallization will be reduced, resulting in a low equiaxed crystal ratio in the slab. Taking this into consideration, it is preferable to add 0.005% or more of N. However, if the N content is excessive, the elongation rate will decrease and the impact properties will deteriorate. Taking this into consideration, the upper limit of the N content should be 0.05%.

[0019] The Si (silicon) content is 0.1% or more and 2.0% or less. Si is a ferrite phase forming element and can increase hardness. Taking this into consideration, it is preferable to add Si in an amount of 0.1% or more. However, if the Si content is excessive, the elongation rate may decrease, Si-based inclusions may increase, and workability may decrease. Taking this into consideration, it is preferable to limit the Si content to an upper limit of 2.0%.

[0020] The Mn (manganese) content is 0.1% or more and 0.5% or less. If the Mn content is too low, fine MnS precipitates are formed, which leads to grain refinement and weakened magnetic properties. Taking this into consideration, it is recommended that Mn be added in an amount of 0.1% or more. However, if the Mn content is excessive, the proportion of precipitates increases, which may actually reduce magnetic properties. Taking this into consideration, it is preferable to limit the Mn content to an upper limit of 0.5%.

[0021] The Cr (chromium) content is 16.0% or more and 20.0% or less. Cr, together with Si, is a ferrite phase stabilizer, and not only plays a major role in securing the ferrite phase, but is also an essential element added to improve corrosion resistance. Taking this into consideration, it is recommended that Cr be added in an amount of 16.0% or more. However, excessive Cr content may promote the formation of delta (δ) ferrite in the slab, reducing elongation and impact toughness and potentially causing hot rolling sticking defects. Taking this into consideration, it is preferable to limit the Cr content to an upper limit of 20.0%.

[0022] The Mo (molybdenum) content is more than 0% and not more than 0.5%. Mo, together with Cr, is an element that stabilizes ferrite and is effective in improving corrosion resistance. However, Mo can cause grain refinement, weakening magnetic properties. In consideration of this, it is preferable to limit the Mo content to an upper limit of 0.5%.

[0023] The Nb (niobium) content is more than 0% and not more than 0.5%. If the Nb content is excessive, the Nb-based precipitates increase excessively, and the grain size may not be large enough. Therefore, if the Nb content is excessive, there is a risk of a problem of a decrease in magnetic permeability. In consideration of this, it is advisable to limit the upper limit of the Nb content to 0.5% or less.

[0024] The content of Ti (titanium) is 0.005% or more and 0.30% or less. Ti is an element that is effective in improving strength by causing precipitation. In consideration of this, Ti can be 0.005% or more. However, if the Ti content is excessive, it may induce a decrease in magnetic permeability due to the refinement of crystal grains. In consideration of this, it is preferable to limit the Ti content to an upper limit of 0.30%.

[0025] The remaining component of the present invention is iron (Fe). However, in a normal manufacturing process, unintentional impurities may be inevitably mixed in from the raw materials or the surrounding environment, and this cannot be excluded. Since these impurities are known to anyone skilled in normal manufacturing processes, the contents of all of them will not be specifically mentioned in this specification.

[0026] In the ferritic stainless steel having improved corrosion resistance and magnetic properties according to one embodiment of the present invention, the value of the following formula (1) is 20 or more. Formula (1): Cr+(3*Mo+10*N+Si+Nb+Ti) / Mn In the formula (1), Cr, Mo, N, Si, Nb, Ti, and Mn represent the weight percentage of each element.

[0027] FIG. 1 is a graph showing the change in pitting potential according to formula (1). 1, it can be seen that the larger the value of formula (1), the higher the pitting potential. In particular, to maintain the pitting potential value at 200 mV or higher to ensure high corrosion resistance, it is recommended to control the range of alloy components so that the value of formula (1) is 20 or higher.

[0028] The ferritic stainless steel with improved corrosion resistance and magnetic properties according to one embodiment of the present invention has a maximum magnetic permeability value of 1,000 or more in the 50 Hz frequency band. As will be described later, by controlling the main process factors that affect the magnetic properties of stainless steel, namely the hot rolling annealing temperature, hot rolling annealing time, cold rolling reduction, cold rolling annealing temperature, and cold rolling annealing time, it is possible to ensure a maximum magnetic permeability value of 1,000 or more.

[0029] The ferritic stainless steel with improved corrosion resistance and magnetic properties according to one embodiment of the present invention has a surface crystal grain size of 30 μm or more. The finer the surface crystal grain size, the more likely it is that the magnetic properties will be poor. Therefore, the present invention improves the magnetic properties by optimizing the contents of Mn, Mo, Nb, Ti, etc. to control the surface crystal grain size to 30 μm or more.

[0030] Next, a method for producing a ferritic stainless steel having improved corrosion resistance and magnetic properties according to the present invention will be described. According to one embodiment of the present invention, a method for producing a ferritic stainless steel having improved corrosion resistance and magnetic properties comprises, in weight percent, C: 0.0005% to 0.035%, N: 0.005% to 0.05%, Si: 0.1% to 2.0%, Mn: 0.1% to 0.5%, Cr: 16.0% to 20.0%, Mo: more than 0% to 0.5%, Nb: more than 0% to 0.5%, Ti: The method preferably includes the steps of: producing a slab having a content of 0.005% or more and 0.30% or less, the remainder being Fe and unavoidable impurities, and having a value of 20 or more in the following formula (1); reheating the slab at 1100 to 1300°C; hot-rolling the reheated slab and hot-rolling annealing it to produce a hot-rolled steel sheet; and cold-rolling the hot-rolled steel sheet, cold-rolling it, annealing it, and then pickling it to produce a cold-rolled steel sheet. Formula (1): Cr+(3*Mo+10*N+Si+Nb+Ti) / Mn In the formula (1), Cr, Mo, N, Si, Nb, Ti, and Mn represent the weight percentage of each element.

[0031] The component ranges of each alloy composition and the reasons for limiting the numerical values ​​in formula (1) are as described above, and each production step will be described in more detail below. First, a slab satisfying the above alloy composition and formula (1) can be produced, and then subjected to a series of steps including reheating, hot rolling, hot rolling annealing, cold rolling annealing, and pickling. Next, the produced slab is preferably reheated at 1100 to 1300°C. If the reheating temperature is low, it may be difficult to redissolve the coarse precipitates formed during slab casting. Taking this into consideration, the reheating temperature should be 1100°C or higher. However, if the reheating temperature is too high, the internal crystal grains may become too coarse. Taking this into consideration, the upper limit of the reheating temperature is limited to 1300°C.

[0032] In the method for producing ferritic stainless steel with improved corrosion resistance and magnetic properties according to one embodiment of the present invention, the value of the following formula (2) is preferably 50 or greater. Formula (2): [Hot rolling annealing temperature (℃) * Hot rolling annealing time (min) + 1.1 * (Cold rolling annealing temperature (℃) * Cold rolling annealing time (min))] / Cold rolling reduction (%)

[0033] FIG. 2 is a graph showing the change in maximum magnetic permeability according to formula (2). 2, it can be seen that the greater the value of equation (2), the greater the maximum magnetic permeability. Therefore, by controlling the value of equation (2), which includes the main process factors that affect the magnetic properties, namely, the hot rolling annealing temperature, hot rolling annealing time, cold rolling reduction, cold rolling annealing temperature, and cold rolling annealing time, to 50 or more, the magnetic properties of stainless steel can be improved.

[0034] On the other hand, the hot rolling annealing can be carried out at 950 to 1150°C for 1.5 to 2.5 minutes. If the hot rolling annealing temperature is low or the annealing time is short, the crystal grains may not grow large enough, which may adversely affect the magnetic properties. However, if the hot rolling annealing temperature is too high or the annealing time is too long, the crystal grains may become coarse, which may result in a decrease in strength. In consideration of this, the hot rolling annealing is preferably performed at 950 to 1150°C for 1.5 to 2.5 minutes, and more preferably at 1000 to 1100°C for 2 to 2.5 minutes.

[0035] The cold rolling annealing can be carried out at 1000 to 1200° C. for 1 to 2 minutes. If the cold rolling annealing temperature is low or the annealing time is short, the crystal grains may not grow large enough, which may adversely affect the magnetic properties and reduce the elongation. However, if the cold rolling annealing temperature is too high or the annealing time is too long, the crystal grains may become coarse, which may reduce the strength. In consideration of this, the cold rolling annealing is preferably performed at 1000 to 1200°C for 1 to 2 minutes, and more preferably at 1100 to 1200°C for 1.5 to 2 minutes.

[0036] On the other hand, cold rolling The rolling reduction can be 60 to 75%. If the rolling reduction rate is reduced, the crystal grain size becomes larger, which is advantageous from the viewpoint of magnetic properties, but if the rolling reduction rate is too small, it may be disadvantageous from the viewpoint of workability. cold rolling The rolling reduction is preferably 60 to 75%.

[0037] The present invention will be described in more detail below through examples. However, it should be noted that the following examples are intended to illustrate and embody the present invention, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom. {Example}

[0038] Slabs having various alloy composition ranges shown in Table 1 below were produced in a melting furnace. The produced slabs were reheated at 1250°C, and then cold-rolled steel sheets were produced by applying the conditions of hot-rolling annealing temperature, hot-rolling annealing time, cold-rolling annealing temperature, cold-rolling annealing time, and cold-rolling reduction shown in Table 2 below.

[0039] [Table 1]

[0040] [Table 2]

[0041] Table 3 below shows the values ​​of formula (1), formula (2), pitting potential, and maximum magnetic permeability. The value of formula (1) was calculated using the following formula (1). Formula (1): Cr+(3*Mo+10*N+Si+Nb+Ti) / Mn In the formula (1), Cr, Mo, N, Si, Nb, Ti, and Mn represent the weight percentage of each element. The value of formula (2) was calculated using the following formula (2). Formula (2): [Hot rolling annealing temperature (℃) * Hot rolling annealing time (min) + 1.1 * (Cold rolling annealing temperature (℃) * Cold rolling annealing time (min))] / Cold rolling reduction (%)

[0042] The pitting potential was measured using a potentiostat. The stainless steel was immersed in a NaCl solution, and a voltage of 20 mV / min was applied. The pitting potential was measured at which the current reached 100 μA. The temperature of the NaCl solution was 30°C, and the concentration was 3.5%. A higher pitting potential indicates better corrosion resistance. The maximum magnetic permeability was measured using a Single Sheet Tester manufactured by Brockhaus Co. Inc. It can be evaluated that the higher the maximum magnetic permeability, the more excellent the magnetic properties.

[0043] [Table 3]

[0044] Referring to Table 3, Examples 1 and 2 satisfied the component range of the alloy composition, formula (1), manufacturing process, and formula (2) specified in the present invention, and also satisfied the pitting potential of 200 mV or more and the maximum magnetic permeability of 1000 or more. However, Comparative Examples 1 to 4 did not satisfy the value of formula (1) of 20 or more. Therefore, Comparative Examples 1 to 4 did not satisfy the pitting potential of 200 mV or more. In other words, Comparative Examples 1 to 4 had poor corrosion resistance. Furthermore, in Comparative Examples 1 to 3 and Comparative Examples 5 to 7, the value of formula (2) did not satisfy the requirement of 50 or more. Therefore, in Comparative Examples 1 to 3 and Comparative Examples 5 to 7, the maximum magnetic permeability did not satisfy the requirement of 1000 or more. In other words, Comparative Examples 1 to 3 and Comparative Examples 5 to 7 had poor magnetic properties. [Industrial Applicability]

[0045] According to one embodiment of the present invention, it is possible to provide a ferritic stainless steel and a manufacturing method thereof in which the alloy components and manufacturing process are optimized to simultaneously improve corrosion resistance and magnetic properties, and therefore industrial applicability is recognized.

Claims

1. In mass %, C: 0.0005% or more and 0.035% or less, N: 0.005% or more and 0.05% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.1% or more and 0.5% or less, Cr: 16.0% or more and 20.0% or less, Mo: more than 0% and 0.5% or less, Nb: more than 0% and 0.5% or less, Ti: 0.005% or more and 0.30% or less, the remainder consisting of Fe and unavoidable impurities, The value of the following formula (1) is 20 or more, The maximum magnetic permeability value is 1,000 or more in the 50 Hz frequency band; A ferritic stainless steel having improved corrosion resistance and magnetic properties, characterized by a pitting potential of 200 mV or more. Formula (1): Cr+(3*Mo+10*N+Si+Nb+Ti) / Mn (In the formula (1), Cr, Mo, N, Si, Nb, Ti, and Mn represent the mass percentage of each element).

2. A method for producing ferritic stainless steel with improved corrosion resistance and magnetic properties, comprising: In mass%, C: 0.0005% or more and 0.035% or less, N: 0.005% or more and 0.05% or less, Si: 0.1% or more and 2.0% or less, Mn: 0.1% or more and 0.5% or less, Cr: 16.0% or more and 20.0% or less, Mo: more than 0% and 0.5% or less, Nb: more than 0% and 0.5% or less, Ti: 0.005% or more and 0.30% or less, and the balance being Fe and unavoidable impurities, A step of producing a slab having a value of 20 or more in the following formula (1): reheating the slab at 1100-1300°C; hot rolling the reheated slab and hot annealing it to produce a hot rolled steel sheet; and The method includes cold rolling the hot-rolled steel sheet, cold-rolling the hot-rolled steel sheet, cold-rolling annealing the hot-rolled steel sheet, and pickling the hot-rolled steel sheet; The hot rolling annealing is performed at 950 to 1150°C for 1.5 to 2.5 minutes, The cold rolling annealing is carried out at 1000 to 1200°C for 1 to 2 minutes, The manufacturing method is a manufacturing method of ferritic stainless steel having improved corrosion resistance and magnetic properties, characterized in that the value of the following formula (2) is 50 or more: Formula (1): Cr+(3*Mo+10*N+Si+Nb+Ti) / Mn (In the formula (1), Cr, Mo, N, Si, Nb, Ti, and Mn represent the mass percentage of each element). Equation (2): [hot rolling annealing temperature (°C) * hot rolling annealing time (min) + 1.1 * (cold rolling annealing temperature (°C) * cold rolling annealing time (min))] / cold rolling reduction (%).

3. 3. The method for producing ferritic stainless steel with improved corrosion resistance and magnetic properties according to claim 2, wherein the cold rolling is carried out at a reduction ratio of 60 to 75%.

Images