Martensitic stainless steel and manufacturing method therefor

Abstract

A martensitic stainless steel according to one embodiment of the present invention comprises, by wt%, 0.40-0.55% of C, 0.01-0.50% of N, 0.10-0.80% of Si, 0.20-0.80% of Mn, 13.0-15.5% of Cr, 0.01-0.50% of Ni, 0.001-0.020% of Ti, and the balance of Fe and inevitable impurities, and satisfies relation (1), wherein the number of pores inside a cold annealed material is in the range of 1*104 to 50*104 ea / mm2. Relation (1) 80 ≤ 3[Cr]+17[Si]+100[C]-400[Ti] ≤ 105 (Here, [Cr], [Si], [C] and [Ti] represent the amount of each element.)

Description

Martensitic stainless steel and its manufacturing method

[0001] The present invention relates to martensitic stainless steel and a method for manufacturing the same.

[0002] As living standards improve, the application of martensitic stainless steels, which boast high hardness, strength, and corrosion resistance, is increasing in applications such as household kitchen knives and industrial band saws. These applications require high hardness, high strength, and corrosion resistance, and to achieve these properties, tempered martensite, created through strengthening heat treatment and tempering, is utilized.

[0003] Conventionally, methods have been proposed to remove primary carbides formed in martensitic steels by heat-treating the material within an equilibrium temperature range where primary carbides do not form. This approach aims to improve mechanical properties by controlling coarse carbides, but suffers from poor polishing efficiency.

[0004] The purpose of the present invention to solve the above-described problem is to provide a martensitic stainless steel and a method for manufacturing the same, which improves polishability by appropriately controlling the number of pores through an alloy composition and a manufacturing method.

[0005] The problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0006] According to an example of the present invention, a martensitic stainless steel contains, in wt%, C: 0.40 to 0.55%, N: 0.01 to 0.05%, Si: 0.10 to 0.80%, Mn: 0.20 to 0.80%, Cr: 13.0 to 15.5%, Ni: 0.01 to 0.50%, and Ti: 0.001 to 0.020%, the remainder being Fe and unavoidable impurities, and satisfies the following formula (1), and the number of pores inside the cold-rolled annealed material is 1*104 50*10 4 ea / mm 2 It exists in a range.

[0007] Equation (1) 80 ≤ 3[Cr]+17[Si]+100[C]-400[Ti] ≤ 105

[0008] (Here, [Cr], [Si], [C], and [Ti] represent the content of each element)

[0009] In addition, the martensitic stainless steel according to an example of the present invention may further include one or more of Mo: 0.01 to 0.80% and V: 0.01 to 0.20%.

[0010] In addition, the martensitic stainless steel according to an example of the present invention may not cause cracks during polishing.

[0011] Additionally, the martensitic stainless steel according to one example of the present invention may have a polishing time of less than 60 seconds.

[0012] In addition, the martensitic stainless steel according to an example of the present invention may have a thickness of 0.5 mm to 4.0 mm.

[0013] A method for manufacturing a martensitic stainless steel according to an example of the present invention comprises the steps of: casting and pressing a slab containing, in wt%, C: 0.40% to 0.55%, N: 0.01% to 0.05%, Si: 0.10% to 0.80%, Mn: 0.20% to 0.80%, Cr: 13.0% to 15.5%, Ni: 0.01% to 0.50%, and Ti: 0.001 to 0.020%, the remainder being Fe and unavoidable impurities; preparing a cast steel sheet by reheating the cast steel sheet at 1200°C to 1300°C; hot-rolling the reheated cast steel sheet at 1000°C to 1200°C; coiling the hot-rolled steel sheet at a temperature of 700°C or higher; A step of hot rolling annealing by maintaining at 800°C to 900°C for 3 to 10 hours and then maintaining at 700°C to 790°C for 5 to 15 hours; and a step of cold rolling annealing at 800°C to 1000°C.

[0014] Equation (1) 80 ≤ 3[Cr]+17[Si]+100[C]-400[Ti] ≤ 105

[0015] (Here, [Cr], [Si], [C], and [Ti] represent the content of each element)

[0016] In addition, a method for manufacturing martensitic stainless steel according to an example of the present invention may further include a step of hot rolling pickling and cold rolling after the hot rolling annealing and before the cold rolling annealing.

[0017] In addition, in the method for manufacturing martensitic stainless steel according to an example of the present invention, the cold rolling may have a total reduction ratio of 40% to 80% for all passes.

[0018] In addition, in the method for manufacturing martensitic stainless steel according to an example of the present invention, the cold rolling annealing time may be 50 to 80 seconds.

[0019] In addition, the method for manufacturing martensitic stainless steel according to an example of the present invention may further include at least one of Mo: 0.01 to 0.80% and V: 0.01 to 0.20%.

[0020] According to an example of the present invention, the number of pores generated inside the cold-rolled annealed martensitic stainless steel and between the carbide and the matrix is ​​1*10 4 50*10 4 ea / mm 2 By controlling the range, cracks can be prevented during polishing.

[0021] FIG. 1 is a photograph taken using a scanning electron microscope (SEM) of the number of pores generated inside the carbide and between the carbide and the matrix of Invention Example 4 according to an example of the present invention.

[0022] Preferred embodiments of the present invention are described below. However, the embodiments of the present invention may be modified in various ways, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more fully explain the present invention to those of ordinary skill in the art.

[0023] The terminology used in this application is solely for the purpose of describing specific examples. Therefore, for example, singular expressions include plural expressions unless the context clearly dictates otherwise. Additionally, it should be noted that terms such as "comprise" or "have" used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the presence of other features, steps, functions, components, or combinations thereof.

[0024] Meanwhile, unless otherwise defined, all terms used herein should be considered to have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Therefore, unless explicitly defined herein, specific terms should not be interpreted in an overly idealistic or formal sense. For example, singular expressions herein include plural expressions unless the context clearly indicates otherwise.

[0025] In addition, the terms "about", "substantially", etc. in this specification are used in the sense of or close to the numerical value when manufacturing and material tolerances inherent to the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly using the disclosure contents in which exact or absolute numerical values ​​are mentioned to aid in the understanding of the present invention.

[0026] According to an example of the present invention, a martensitic stainless steel contains, in wt%, C: 0.40% to 0.55%, N: 0.01% to 0.05%, Si: 0.10% to 0.80%, Mn: 0.20% to 0.80%, Cr: 13.0% to 15.5%, Ni: 0.01% to 0.50%, and Ti: 0.001% to 0.020%, the remainder being Fe and unavoidable impurities, and satisfies the following formula (1), and the number of pores inside the cold-rolled annealed material is 1*10 4 50*10 4 ea / mm 2 It exists in a range.

[0027] Equation (1) 80 ≤ 3[Cr]+17[Si]+100[C]-400[Ti] ≤ 105

[0028] (Here, [Cr], [Si], [C], and [Ti] represent the content of each element)

[0029] Below, the reasons for limiting the composition range of each alloy element are explained. Unless otherwise specified, the unit is weight percent.

[0030] The content of C may be 0.40 to 0.55 wt%.

[0031] Carbon (C) is an essential element for improving the hardness of steel, and must be added appropriately to secure hardness after quenching and tempering heat treatment. Considering this, C may be added in an amount of 0.40% or more to satisfy the purposes of the present invention. However, if the content is excessive, the toughness of the steel sheet may deteriorate. Considering this, the upper limit of the C content may be limited to 0.55%. Preferably, the C content may be 0.43% or more and 0.53% or less.

[0032] The content of N may be 0.01 to 0.05 wt%.

[0033] Nitrogen, like C, is an effective element for improving the hardness of steel. Considering this, N may be added in an amount of 0.01% or more. However, if the content of N is excessive, chromium nitride, which is a low-temperature precipitation phase, is formed, and the γ phase remains, which may result in insufficient strength after strengthening heat treatment. Therefore, if the content of N is excessive, fatigue resistance may be deteriorated. Considering this, the upper limit of the N content may be limited to 0.05%. Preferably, the content of N may be 0.02% to 0.04% or less.

[0034] The content of Si may be 0.10 to 0.80 wt%.

[0035] Silicon (Si) is added to deoxidize steel. Furthermore, Si is an effective element for securing strength through solid solution strengthening. Considering this, Si may be added in amounts of 0.10% or more. However, if the Si content is excessive, scale may form on the steel surface during hot rolling, degrading surface quality. Considering this, the upper limit of the Si content may be limited to 0.80%. Preferably, the Si content may be 0.12% to 0.70% or less.

[0036] The content of Mn may be 0.20 to 0.80 wt%.

[0037] Manganese (Mn) is a very effective element for improving hardenability and forming a substitutional solid solution within the matrix, thereby exerting a solid solution strengthening effect. Furthermore, if the Mn content is low, it may not sufficiently combine with the sulfur (S) introduced as impurities in the steel, which may cause cracks during casting. Considering this, Mn may be added in an amount of 0.20% or more. However, if the Mn content is excessive, the toughness of the steel may deteriorate. Considering this, the upper limit of the Mn content may be limited to 0.80%. Preferably, the Mn content may be 0.33% to 0.70% or less.

[0038] The Cr content may be 13.0 to 15.5 wt%.

[0039] Cr is an effective element for improving corrosion resistance and enhancing hardness and wear resistance by forming chromium carbides. Considering this, Cr may be added in amounts of 13.0% or more. However, excessive Cr content may unnecessarily increase hardenability and increase manufacturing costs. Considering this, the upper limit of the Cr content may be limited to 15.5%. Preferably, the Cr content may be 13.5% to 15.3% or less.

[0040] The content of Ni may be 0.01 to 0.50 wt%.

[0041] Ni is an essential element added to martensitic stainless steels to transform the metal structure into an austenite structure during hot working. Furthermore, Ni, when added in small amounts, improves corrosion resistance and hardenability. Considering this, Ni may be added in an amount of 0.01% or more. However, if the Ni content is excessive, workability may deteriorate, excessive austenite may remain after strengthening heat treatment, making it difficult to secure the hardness of the product and increasing the manufacturing cost. Considering this, the upper limit of the Ni content may be limited to 0.50%. Preferably, the Ni content may be 0.11% to 0.40% or less.

[0042] The content of Ti may be 0.001 to 0.020 wt%.

[0043] Ti is typically an element added to ferritic general-purpose steels such as 409L and 439, and even when there is no Ti component in the raw materials when manufacturing martensitic steel at the same steel mill, a small amount may be present as it flows in from the ladle and mold. Ti may be included in an amount of 0.001% or more to prevent intergranular corrosion. However, Ti may combine with C to form TiC precipitates, which may lower the strength of martensite. Therefore, Ti is controlled to be 0.020% or less. Preferably, the Ti content may be 0.010% to less than 0.020%.

[0044] A martensitic stainless steel slab according to an example of the present invention may further include at least one of Mo: 0.01% to 0.8% and V: 0.01% to 0.2%.

[0045] The content of Mo can be 0.01 to 0.8 wt%.

[0046] Mo is an element that is effective in improving corrosion resistance and hardenability, and thus may be optionally included in the present invention. Furthermore, Mo, together with V, is an element that suppresses the refinement and growth of carbides. Considering this, Mo may be added in an amount of 0.01% or more. However, excessive Mo content may increase manufacturing costs. Considering this, the upper limit of the Mo content may be limited to 0.8%.

[0047] The content of V may be 0.01% to 0.2% by weight.

[0048] Since V is an element that effectively forms carbides and suppresses the coarsening of chromium carbides, it may be optionally further included in the present invention. Furthermore, V is an element that is effective in preventing grain coarsening during heat treatment and improving wear resistance. However, if the V content is excessive, it may form more carbides than necessary, which may lower the toughness of the steel and increase the manufacturing cost. Considering this, the upper limit of the V content may be limited to 0.2%.

[0049] Meanwhile, the above Mo and V can be added in a composite manner during steel manufacturing.

[0050] The remaining component of the present invention is iron (Fe). However, during the typical manufacturing process, unintended impurities from raw materials or the surrounding environment may inevitably be mixed in, and thus cannot be excluded. Since these impurities are readily apparent to anyone skilled in the art of typical manufacturing, their full details are not specifically discussed in this specification.

[0051] A martensitic stainless steel according to an example of the present invention can satisfy the following formula (1), and the number of pores generated inside the carbide and between the carbide and the matrix within the cold-rolled annealed material is 1*10 4 50*10 4 ea / mm 2 It can exist in a range.

[0052] Equation (1) 80 ≤ 3[Cr]+17[Si]+100[C]-400[Ti] ≤ 105

[0053] (Here, [Cr], [Si], [C], and [Ti] represent the content of each element)

[0054] The above equation (1) is correlated with the number of pores within the cold-rolled annealed martensitic steel. The number of pores refers to the number of pores that occur within the carbide and between the carbide and the matrix.

[0055] If equation (1) is less than 80, the number of pores is 1*10 4 When the grinding property is less than 10, the grinding property is significantly reduced after the strengthening heat treatment, and when it exceeds 105, it was confirmed that cracks occur during polishing after the strengthening heat treatment. Accordingly, the range of the above formula (1) is preferably 80 to 105. Cr and C facilitate the formation of carbides, and the addition of Si can harden the matrix and promote the formation of pores. In the case of Ti, the formation of carbides composed of Cr and C can be inhibited, and as a result, the formation of pores within the carbides or between the carbides and the matrix can be suppressed. The pores existing within the carbides or between the carbides and the matrix can shorten the polishing time by making the polishing easier, but the number of pores is 50*10 4 ea / mm 2 If it is excessive, it may act as a crack source and cause cracks during polishing. The number of pores is preferably 2*10 4 48*10 inland 4 ea / mm 2 It could be.

[0056] According to another example of the present invention, the martensitic stainless steel may preferably have a value of the above formula (1) of 84 to 105, more preferably 90 to 105, and even more preferably 95 to 104. Within this range, not only will polishing cracks not occur, but the effect of shortening the polishing time can be further improved. In this case, the effect of further improving the polishing properties and durability can be achieved.

[0057] According to another example of the present invention, the number of pores in the martensitic stainless steel is preferably 5*10 4 ea / mm 2 50*10 4 ea / mm 2 , more preferably 10*10 4 ea / mm 2 50*10 4 ea / mm 2 , more preferably 20*10 4 ea / mm 2 50*10 4 ea / mm 2 Within the above range, not only can polishing cracks not occur, but the effect of shortening the polishing time can be further enhanced. In this case, the effect of further improving polishing properties and durability can be realized.

[0058] In addition, the martensitic stainless steel according to an example of the present invention may not generate cracks during polishing. That is, the martensitic stainless steel according to an example of the present invention may have crack-free characteristics.

[0059] Additionally, the martensitic stainless steel according to one embodiment of the present invention may have a polishing time of less than 60 seconds. In this case, the polishing performance may be evaluated as excellent by conventional standards. Preferably, the polishing time may be less than 50 seconds. More preferably, it may be less than 30 seconds.

[0060] The above polishing conditions were as follows: cutting to a size of 100 mm x 100 mm, lapping polishing using a #240 roughness grinding stone, and measuring the time required for polishing to a thickness of 0.5 mm. At this time, if no cracks occur and the polishing time is less than 60 seconds, it indicates excellent polishing performance, and if it is more than 60 seconds, it indicates poor polishing performance.

[0061] In addition, the martensitic stainless steel according to an example of the present invention may have a thickness of 0.5 mm to 4.0 mm. The thickness may refer to a thickness measured after cold rolling annealing. Hereinafter, a method for manufacturing a martensitic stainless steel according to an example of the present invention having the above-described alloy composition will be described. The description of the martensitic stainless steel at this time is as described above.

[0062] A method for manufacturing a martensitic stainless steel according to an example of the present invention comprises the steps of: casting and pressing a slab containing, in wt%, C: 0.40% to 0.55%, N: 0.01% to 0.05%, Si: 0.10% to 0.80%, Mn: 0.20% to 0.80%, Cr: 13.0% to 15.5%, Ni: 0.01% to 0.50%, and Ti: 0.001% to 0.020%, the remainder being Fe and unavoidable impurities; preparing a cast steel sheet by reheating the cast steel sheet at 1200°C to 1300°C; hot-rolling the reheated cast steel sheet at 1000°C to 1200°C; coiling the hot-rolled steel sheet at a temperature of 700°C or higher; A step of hot rolling annealing by maintaining at 800°C to 900°C for 3 to 10 hours and then maintaining at 700°C to 790°C for 5 to 15 hours; and a step of cold rolling annealing at 800°C to 1000°C.

[0063] Equation (1) 80 ≤ 3[Cr]+17[Si]+100[C]-400[Ti] ≤ 105

[0064] (Here, [Cr], [Si], [C], and [Ti] represent the content of each element)

[0065] According to a method for manufacturing martensitic stainless steel according to an example of the present invention, a cast steel having a thickness of 250 mm to 320 mm can be hot rolled at a reduction ratio of 90% to 98% to secure a thickness of martensitic stainless steel of 0.5 to 4.0 mm.

[0066] The method for manufacturing martensitic stainless steel of the present invention may include a coiling step after hot rolling; and a hot rolling annealing step. The coiling step may be performed at a temperature of 700°C or higher. The hot rolling annealing step may be a step of charging the steel into a hot rolling annealing furnace at a temperature of 600°C or higher, then maintaining it at 800 to 900°C for 3 to 10 hours, and then maintaining it at 700°C to 790°C for 5 to 15 hours to perform hot rolling annealing.

[0067] When the temperature is lower than 800℃ or the time is lower than 50 seconds during cold rolling annealing, the recrystallization growth rate is slow, resulting in excessively high hardness and low mechanical properties. In addition, the number of pores generated within the annealed material and between the carbide and the matrix is ​​50*10 4 ea / mm 2 It may exceed. When the temperature exceeds 1000℃ or the cold annealing time exceeds 80 seconds during cold rolling annealing, it is difficult to secure strength due to the formation of non-uniform grains due to the increase in grain size, and the number of pores is also 1*10 4 ea / mm 2 It may be less than.

[0068] In addition, a method for manufacturing martensitic stainless steel according to an example of the present invention may further include a step of hot rolling pickling and cold rolling after the hot rolling annealing and before the cold rolling annealing.

[0069] In addition, in the method for manufacturing martensitic stainless steel according to an example of the present invention, the cold rolling may have a total reduction ratio of 40 to 80% for all passes.

[0070] In addition, in the method for manufacturing martensitic stainless steel according to an example of the present invention, the cold rolling annealing time may be 50 to 80 seconds.

[0071] In addition, the method for manufacturing martensitic stainless steel according to an example of the present invention may further include at least one of Mo: 0.01 to 0.80% and V: 0.01 to 0.20%.

[0072] {Example}

[0073] A 200 mm thick slab having an alloy composition according to Table 1 below was reduced by 0 to 6% using an inline roller before the cast steel was completely solidified. The cast steel was reheated at 1250°C for approximately 3 hours, hot-rolled at 1050°C to a final thickness of 5 mm, and the resulting hot-rolled steel sheet was coiled at 700°C. The coiled coil was charged into a hot-rolling annealing furnace at 600°C, maintained at 850°C for 10 hours, and then maintained at 750°C for 10 hours to perform hot-rolling annealing. Afterwards, it was pickled and cold-rolled from 5 mm to 2.5 mm at a total reduction ratio of 50%, and the sum of the reduction ratios of the first and second passes was 15%. Afterwards, cold rolling annealing heat treatment was performed at 900°C for 60 seconds to manufacture specimens of comparative examples and invention examples described below.

[0074] Classification CSiMnCrNiTiNMoVComparative Example 10.780.510.5415.40.280.0100.03--Comparative Example 20.540.790.3317.40.220.0100.02--Comparative Example 30.610.590.3114.30.250.0100.04--Comparative Example 40.550.810.4415.50.270.0100.03--Comparative Example 50.430.200.4013.50.150.0200.02--Comparative Example 60.420.210.5512.40.160.0100.03--Comparative Example 70.400.110.3813.50.160.0100.04--Comparative Example 80.300.230.4713.80.260.0100.03--Inventive Example 10.530.530.3315.30.190.0100.02--Inventive Example 20.470.550.3915.00.230.0100.04--Inventive Example 30.490.410.4114.80.210.0100.040.650.15Inventive Example 40.440.220.4013.50.110.0100.03--Inventive Example 50.430.120.3313.60.180.0100.03--

[0075] [Physical property evaluation]

[0076] Measuring the number of voids

[0077] The cross-sections of the cold-rolled annealed specimens manufactured previously were observed using a scanning electron microscope (SEM) to measure the number of pores generated within the carbide and between the carbide and the matrix, and the results are shown in Table 2.

[0078] Evaluation of abrasiveness and crack occurrence

[0079] For the previously manufactured specimens, a strengthening heat treatment was performed by holding the cold-rolled annealed material at 1050℃ for 300 seconds and then rapidly cooling. The strengthened heat-treated stainless steel was cut into 100mm*100mm sizes and lapping polished using a #240 roughness grinding wheel, and the time required to polish to a thickness of 0.5mm was measured.

[0080] If the polishing time was 90 seconds or longer or the measurement failed due to cracking, the polishing performance was evaluated as Х, which means poor polishing performance. If the polishing time was less than 90 seconds or more than 60 seconds, the polishing performance was evaluated as ○, which means good polishing performance. If the polishing time was less than 60 seconds, the polishing performance was evaluated as ◎, which means excellent polishing performance.

[0081] If a crack occurs during polishing, the evaluation is stopped, and whether or not a crack occurs is shown in Table 2 below.

[0082] Classification formula (1) Number of carbide pores (10^4 / mm) 2 ) Polishing time (sec) Polishing evaluation Evaluation of crack occurrence Comparative example 1128.993 Measurement failure × Crack occurrence Comparative example 2115.684 Measurement failure × Crack occurrence Comparative example 3109.972 Measurement failure × Crack occurrence Comparative example 4111.356 Measurement failure × Crack occurrence Comparative example 578.90.890 × No crack occurrence Comparative example 678.80.6100 × No crack occurrence Comparative example 778.40.3120 × No crack occurrence Comparative example 871.30.1160 × No crack occurrence Invention example 1103.94832◎ No crack occurrence Invention example 297.43437◎ No crack occurrence Invention example 396.42942◎ No crack occurrence Invention example 484.2647◎ Crack Non-occurring invention example 581.8256◎Crack-free

[0083] Referring to Table 2 above, it can be confirmed that invention examples 1 to 5 according to the present invention satisfy the value of the following equation (1). Equation (1) 80 ≤ 3[Cr]+17[Si]+100[C]-400[Ti] ≤ 105

[0084] Through this, the number of carbide pores is 1*10 4 50*10 4 ea / mm 2 , and accordingly, it was confirmed that the polishing time was drastically shortened to less than 90 seconds, especially less than 60 seconds, and at the same time, crack occurrence during polishing was suppressed.

[0085] In particular, Fig. 1 is a photograph taken using a scanning electron microscope (SEM) of the number of pores generated inside the carbide and between the carbide and the matrix of Invention Example 4 according to the present invention. The width is 24 ㎛, the height is 18 ㎛, and the area is 432 ㎛. 2 Since the number of pores is 26, the number of pores per unit area is 6*10 4 ea / mm 2 Accordingly, it can be confirmed that no cracks occur during polishing and the polishing time is 47 seconds, indicating excellent polishing properties.

[0086] On the other hand, in Comparative Examples 1 to 4, when Equation (1) exceeds 105, the number of carbide pores is 50*10 4 ea / mm 2 In this case, it was confirmed that cracks occurred during polishing.

[0087] In addition, Comparative Examples 5 to 8 have a value of formula (1) according to the present invention of less than 80, so the number of carbide pores is 1*10 4 ea / mm 2 It was confirmed that the polishability could not be measured due to cracks occurring during polishing under controlled conditions, or the polishing time was very long, resulting in poor polishability.

[0088] In particular, it was found that Comparative Examples 5 and 7, although satisfying the range of the alloy composition according to the present invention, did not satisfy Equation (1), and thus exhibited poor polishability depending on the number of pores in the carbide.

[0089] In addition, based on the composition and manufacturing method of the above invention example 1, the number of carbide pores (unit: 1*10) of the final stainless steel manufactured by the temperature and time of cold rolling annealing in Table 3 below 4 / mm 2 ), the polishing performance according to polishing time and the occurrence of cracks during polishing are shown in Table 3 below.

[0090] Cold rolling annealing temperature (℃) Cold rolling annealing time (sec) Number of carbide pores (10^4 / mm) 2)Polishing time (sec)Polishing evaluationCrack occurrence during polishingExperimental example 1920554438◎No crack occurrenceExperimental example 2950624636◎No crack occurrenceExperimental example 3980704835◎No crack occurrenceExperimental example 47805562Measurement failure×Crack occurrenceExperimental example 57606265Measurement failure×Crack occurrenceExperimental example 67405872Measurement failure×Crack occurrenceExperimental example 71050550.6113×No crack occurrenceExperimental example 81100550.7108×No crack occurrenceExperimental example 99504565Measurement failure×Crack occurrenceExperimental example 109403870Measurement failure×Crack occurrenceExperimental example 11980920.4130×No crack occurrenceExperimental example 128201100.8142×No crack occurrence

[0091] Experimental examples 1 to 3 satisfy the cold rolling annealing temperature of 800°C to 1000°C and the cold rolling annealing time of 50 to 80 seconds according to the present invention, and the number of pores generated inside the cold rolling annealed material and between the carbide and the matrix is ​​1*10 4 50*10 4 ea / mm 2 On the other hand, experimental examples 4 to 6 or experimental examples 9 and 10 had a cold rolling annealing temperature of less than 800°C or a cold rolling annealing time of less than 50 seconds, and accordingly, the number of carbide pores was 50*10 4 ea / mm 2 It can be seen that cracks occur during polishing when the amount exceeds .

[0092] In addition, in Experimental Examples 7 and 8 or Experimental Examples 11 and 12, the cold rolling annealing temperature exceeded 1000℃ or the cold rolling annealing time exceeded 80 seconds, so the number of carbide pores was 1*10 4 ea / mm 2 As the polishing time exceeds 100 seconds, it can be confirmed that the polishing performance is poor.

Claims

1. In weight %, C: 0.40% to 0.55%, N: 0.01% to 0.05%, Si: 0.10% to 0.80%, Mn: 0.20% to 0.80%, Cr: 13.0% to 15.5%, Ni: 0.01% to 0.50%, and Ti: 0.001% to 0.020%, the remainder including Fe and inevitable impurities, Satisfies the following equation (1), The number of pores inside the cold rolled annealed steel is 1*10 4 Inside 50*10 4 ea / mm 2 Martensitic stainless steels, which exist in a range of grades. Equation (1) 80 ≤ 3[Cr]+17[Si]+100[C]-400[Ti] ≤ 105 (Here, [Cr], [Si], [C], and [Ti] represent the content of each element) 2. In claim 1, Martensitic stainless steel further comprising at least one of Mo: 0.01% to 0.80% and V: 0.01% to 0.20%.

3. In claim 1, Martensitic stainless steel that does not crack when polished.

4. In claim 3, Martensitic stainless steel having a polishing time of less than 60 seconds.

5. In claim 3, A martensitic stainless steel having a thickness of 0.5 mm to 4.0 mm.

6. A step of casting and pressing a slab containing, by weight%, C: 0.40 to 0.55%, N: 0.01 to 0.05%, Si: 0.1 to 0.8%, Mn: 0.20 to 0.80%, Cr: 13.0 to 15.5%, Ni: 0.01 to 0.50%, and Ti: 0.001 to 0.020%, the remainder being Fe and unavoidable impurities, and satisfying the following formula (1) to prepare a cast steel; A step of reheating the above cast steel at 1200℃ to 1300℃; A step of hot rolling the reheated cast steel at 1000℃ to 1200℃; A step of coiling a hot-rolled steel plate at a temperature of 700℃ or higher; A step of hot rolling annealing by maintaining at 800°C to 900°C for 3 to 10 hours and then maintaining at 700 to 790°C for 5 to 15 hours; and A method for manufacturing martensitic stainless steel, comprising a step of cold rolling annealing at 800°C to 1000°C. Equation (1) 80 ≤ 3[Cr]+17[Si]+100[C]-400[Ti] ≤ 105 (Here, [Cr], [Si], [C], and [Ti] represent the content of each element) 7. In claim 6, A method for manufacturing martensitic stainless steel, further comprising the steps of hot rolling, pickling, and cold rolling after the hot rolling annealing and before the cold rolling annealing.

8. In claim 7, The above cold rolling is a method for manufacturing martensitic stainless steel, in which the total reduction ratio of the entire pass is 40% to 80%.

9. In claim 6, A method for manufacturing martensitic stainless steel, wherein the cold rolling annealing time is 50 to 80 seconds.

10. In claim 6, A method for manufacturing a martensitic stainless steel, wherein the martensitic stainless steel further contains at least one of Mo: 0.01% to 0.80% and V: 0.01% to 0.20%.

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