KR102491305B1 - Non-magnetic steel having excellent High strength property and manufacturing method thereof - Google Patents

Abstract

In the present invention, C: 0.2 to 0.25%, Si: 2.5 to 3.5%, Mn: 4.5% or less, Cr: 19.0 to 23.0%, Ni: 5.5 to 8.5%, Cu: 0.8 to 2.5%, N: 0.1 to 0.4%, the balance being Fe and other unavoidable impurities.

Description

Non-magnetic austenitic stainless steel having improved strength and manufacturing method thereof {Non-magnetic steel having excellent High strength property and manufacturing method thereof}

The present invention relates to a non-magnetic austenitic stainless steel with improved strength and a method for manufacturing the same, more preferably a non-magnetic and high-strength austenitic stainless steel having a permeability (μ) of 1.02 or less and a yield strength of 1,550 MPa or more, and It's about the manufacturing method.

Materials such as materials for smart devices, structural steel for automobiles and bicycles, and construction materials, which are in increasing demand in recent years, have characteristics that require high strength and non-magnetic properties at the same time. In particular, when materials for smart devices have magnetism, they may cause malfunctions of the device, and there is a concern that efficiency may be reduced by interfering with the flow of electricity or radio waves.

In order to meet this, austenitic stainless steel having a non-magnetic austenite phase is widely used in existing ferrite-based materials having magnetism.

However, in austenitic stainless steel, martensitic transformation in which some austenite phase is transformed into martensite phase may occur during the work hardening process. The martensite phase has excellent mechanical characteristics compared to the austenite phase and can enhance the strength of the material, but has the disadvantage of weakening the non-magnetic properties of the non-magnetic austenitic stainless steel.

Accordingly, there is a demand for a technique for securing sufficient strength while suppressing the formation of the martensite phase.

1. Japanese Patent Laid-Open No. 2015/190422 (published on December 17, 2015) 2. Japanese Registered Patent No. 04606113 (registered on April 27, 2006) 3. Japanese Registered Patent No. 02668113 (registered on July 4, 1997)

An object of the present invention is to provide a non-magnetic austenitic stainless steel having a magnetic permeability of 1.02 or less at a reduction ratio of more than 0 and less than 80% by controlling Md30 to at least -200 ° C or less.

In addition, another technical problem to be achieved by the present invention is to control the stacking fault energy (SFE) to 15 mJ / ㎡ or less to suppress martensitic phase transformation and at the same time to provide high-strength stainless steel having a yield strength of 1,550 MPa or more. There is a purpose.

Furthermore, an object of the present invention is to provide an austenitic stainless steel in which N-pore formation is prevented by controlling the N content to 0.25% or less.

Objects of the embodiments of the present invention are not limited to the above-mentioned purposes, and other objects not mentioned above will be clearly understood by those skilled in the art from the description below. .

One aspect of the present invention for achieving the above object is C: 0.2 to 0.25%, Si: 2.5 to 3.5%, Mn: 4.5% or less, Cr: 19.0 to 23.0%, Ni: 5.5 to 8.5%, Cu : 1.0 to 2.5% N: 0.1 to 0.4%, the balance relates to a high-strength non-magnetic austenitic stainless steel characterized by consisting of Fe and other unavoidable impurities.

In the above aspect, the non-magnetic austenitic stainless steel may satisfy the following relational expression 1.

[Relationship 1]

551-462(C+N)-9.2Si-8.1Mn-13.7Cr-29(Ni+Cu)-18.5Mo ≤ -200

(In the above relational expression 1, C, N, Si, Mn, Cr, Ni, Cu, and Mo are weight percent of each element, and when Mn is not contained, 0 is substituted for Mn in the formula.)

In the above aspect, the non-magnetic austenitic stainless steel may satisfy the following relational expression 2.

[Relationship 2]

28.87+1.64Ni-1.1Cr+0.21Mn-4.45Si+36.5N ≤ 15

(In the above relational expression 2, Ni, Cr, Mn, Si, and N are the weight% of each element, and when Mn is not contained, 0 is substituted for Mn in the formula.)

In the above aspect, the yield strength of the non-magnetic austenitic stainless steel may be 1,550 MPa or more.

In the above aspect, the sum of the C and the N may be 0.4 to 0.5% by weight.

In the above aspect, the N may be 0.2 to 0.25% by weight.

In the above aspect, the non-magnetic austenitic stainless steel may have a martensite phase fraction of less than 0.01% by volume.

In the above aspect, the non-magnetic austenitic stainless steel may have permeability (μ) of 1.02 or less at a reduction ratio of more than 0 and 80% or less.

According to another aspect of the present invention, by weight % C: 0.2 to 0.25%, Si: 2.5 to 3.5%, Mn: 4.0% or less, Cr: 19.0 to 23.0%, Ni: 5.5 to 8.0%, Cu: 1.0 to preparing a hot-rolled steel sheet by hot-rolling a slab containing 2.0% N: 0.1 to 0.4%, the remainder Fe and other unavoidable impurities; maintaining the hot-rolled steel sheet at 1100 to 1200° C. for 1 to 10 minutes and then performing water cooling; and cold-rolling the water-cooled hot-rolled steel sheet at a reduction ratio of greater than 0 and less than or equal to 80%.

In the above aspect, the slab may satisfy the following relational expression 1.

[Relationship 1]

551-462(C+N)-9.2Si-8.1Mn-13.7Cr-29(Ni+Cu)-18.5Mo ≤ -200

(In the above relational expression 1, C, N, Si, Mn, Cr, Ni, Cu, and Mo are weight percent of each element, and when Mn is not contained, 0 is substituted for Mn in the formula.)

In the above aspect, the slab may satisfy the following relational expression 2.

[Relationship 2]

28.87+1.64Ni-1.1Cr+0.21Mn-4.45Si+36.5N ≤ 15

(In the above relational expression 2, Ni, Cr, Mn, Si, and N are the weight% of each element, and when Mn is not contained, 0 is substituted for Mn in the formula.)

In the above aspect, the N may include 0.2 to 0.25% by weight.

The non-magnetic austenitic stainless steel having improved strength according to an embodiment of the present invention adjusts the content of each element so that the Md30 and the stacking fault energy (SFE) are -200 ° C or less and 15 mJ / m 2 or less, respectively. It has the advantage of having high strength and high strength at the same time.

Through this, it can be used for materials such as smart device materials that require high non-magnetic properties and high strength, structural steel materials for automobiles and bicycles, and building materials. In particular, high-strength structures for smart device materials that require high non-magnetic properties can be used as a material.

1 is a graph for explaining the concept of a steel material manufactured according to an embodiment of the present invention.
2 is a graph for comparing true stress-true strain curves of steel materials manufactured according to Examples and Comparative Examples of the present invention.
3 is a diagram showing the correlation between magnetic permeability, yield strength and Md30 of steels manufactured according to an embodiment of the present invention.

Characteristics of the embodiments of the present invention, and methods for achieving them will become clear with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only these embodiments make the disclosure of the present invention complete, and common knowledge in the art to which the present invention belongs. It is provided to completely inform the person who has the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numbers designate like elements throughout the specification.

In describing the embodiments of the present invention, if it is determined that a detailed description of a known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description will be omitted. In addition, terms to be described later are terms defined in consideration of functions in the embodiment of the present invention, which may vary according to the intention or custom of a user or operator. Therefore, the definition should be made based on the contents throughout this specification.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

A feature of the present invention is to suppress the occurrence of martensitic phase transformation during work hardening by controlling the mixing amount of components that affect the stability of austenite in the present invention. Through this, an austenitic stainless steel having the permeability (μ) of 1.02 or less was manufactured.

According to one embodiment of the present invention, the non-magnetic austenitic stainless steel contains C: 0.2 to 0.25%, Si: 2.5 to 3.5%, Mn: 4.5% or less, Cr: 19.0 to 23.0%, Ni: 5.5 to 8.5%, Cu: 1.0 to 2.5%, N: 0.1 to 0.4%, the rest Fe and other unavoidable impurities.

Hereinafter, the reason for limiting the numerical value of the alloying element content in the embodiments of the present invention will be described. Hereinafter, unless otherwise specified, units are % by weight.

C is added in an amount of 0.2 to 0.25% by weight.

C is one of the austenite phase stabilizing elements and is an effective element for increasing material strength by solid solution strengthening. In addition, since it greatly contributes to the phase stabilization effect during processing, it may be added in an amount of 0.2% by weight or more to suppress martensitic phase transformation at a reduction ratio of more than 0 and less than 80%.

On the other hand, if the C exceeds 0.25% by weight, segregation and coarse carbides may be formed in the center during the material manufacturing process, and adversely affect the subsequent hot rolling-annealing-cold rolling-cold rolling annealing process. . In addition, the C may be easily combined with carbide-forming elements such as Cr, which will be described later, to lower the Cr content around grain boundaries, thereby reducing corrosion resistance. Accordingly, the C is preferably added in an amount of 0.2 to 0.25% by weight, and more preferably in an amount of 0.2 to 0.22% by weight.

Si is added in an amount of 2.5 to 3.5% by weight.

The Si is an element effective in reducing stacking fault energy (SFE) together with Cr, which will be described later, and is preferably added in an amount of 2.5% by weight or more. On the other hand, when the Si content exceeds 3.5% by weight, slag fluidity is reduced during steelmaking, and corrosion resistance may be reduced by combining with oxygen to form inclusions. Accordingly, the Si is preferably added in an amount of 2.5 to 3.5% by weight, more preferably 2.9 to 3.1% by weight.

Mn is added at 4.5% by weight or less.

Mn is an austenite stabilizing element together with C and Ni, which will be described later. Since Mn increases the solubility of N in the stainless steel, it can consequently improve the strength of the non-magnetic austenitic stainless steel. On the other hand, when the amount of Mn exceeds 4.5% by weight, MnS may be formed by combining with S contained in the stainless steel. This can reduce the corrosion resistance of the stainless steel and weaken the hot workability. Therefore, the Mn is preferably added in an amount of 4.5% by weight or less.

Cr is added in an amount of 19.0 to 23.0% by weight.

Cr is an element added to ensure corrosion resistance of the stainless steel. In addition, it is possible to effectively reduce the stacking fault energy (SFE) of the stainless steel. Accordingly, the Cr is preferably added in an amount of 19.0% by weight or more. However, when the Cr content exceeds 23% by weight, a ferrite phase is formed during the solidification of the stainless steel, and thus magnetic properties may be exhibited. Therefore, in order to control the stacking fault energy (SFE) and reduce the magnetic properties, the Cr content is preferably added in an amount of 19.0 to 23.0% by weight, more preferably 20 to 22.1% by weight.

Ni is added in an amount of 5.5 to 8.5% by weight.

The Ni is an element contributing to stabilization of austenite together with the Mn and N to be described later. Accordingly, when the Ni content is less than 5.5% by weight, the stability of the austenite phase may decrease, and the martensite phase may be formed during the rolling process. On the other hand, when the amount of Ni exceeds 8.5% by weight, the stacking fault energy (SFE) of the stainless steel is increased, making it difficult to secure strength. Accordingly, the Ni is preferably added in an amount of 5.5 to 8.5% by weight.

Cu is added in an amount of 1.0 to 2.5% by weight.

Similar to Ni, Cu may be added for the purpose of stabilizing the austenite phase. As described above for the Ni, when the content of Cu is less than 1.0% by weight, the stability of the austenite phase may be reduced and the martensite phase may be formed during the rolling process. On the other hand, if the Cu content exceeds 2.5% by weight, the stacking fault energy (SFE) of the stainless steel is increased, making it difficult to secure strength. Accordingly, the Cu is preferably added in an amount of 1.0 to 2.5% by weight.

N is added in an amount of 0.1 to 0.4% by weight.

Like C, N is an austenite phase forming element and is effective in improving the strength of a material by solid solution strengthening. At the same time, the N may greatly contribute to suppressing the transformation of the austenite phase into the martensite phase during the heat treatment process. However, when N is added in an amount exceeding 0.4% by weight, N-pores may be formed, and surface cracks may occur due to the N-pores. Accordingly, the N is preferably added in an amount of 0.1 to 0.4% by weight, and more preferably in an amount of 0.2 to 0.25% by weight.

According to an embodiment, strength of the non-magnetic austenitic stainless steel may be improved by adding interstitial elements such as C and N. However, excessive addition of C and N may reduce corrosion resistance and increase the stacking fault energy (SFE) by generating carbides or carbonitrides by combining with the Cr or the like as described above. Accordingly, it is preferable that the sum of C and N is 0.4 to 0.5% by weight, and more preferably 0.4 to 0.5% by weight.

The remainder of stainless steel, excluding the aforementioned alloying elements, consists of Fe and other unavoidable impurities.

In general, when steel is heated to a temperature above the A2 transformation point, it undergoes magnetic transformation and loses magnetism and transforms into a non-magnetic body, in other words, a paramagnetic body. Thereafter, when heated to a temperature higher than the A3 transformation point, the ferrite phase in the steel may transform into an austenite phase. Austenitic stainless steel is a steel material manufactured to maintain the austenite phase even at room temperature, and can maintain a metastable austenite phase even at room temperature by rapidly cooling after heat treatment at a temperature of 1,000 ° C. or higher. The retained austenite phase inherits the characteristics of the existing austenite and does not have magnetism, but may transform into a martensite phase when plastic deformation such as cold rolling occurs.

The martensite phase can enhance the mechanical properties of the non-magnetic austenitic stainless steel, but due to the presence of magnetism, it is difficult to use it in fields requiring a high level of non-magnetism, such as smart device materials, structural steel materials for automobiles and bicycles, and building materials. there is

Therefore, in the present invention, the transformation of the austenite phase to the martensite phase is suppressed even under the condition of a reduction ratio of more than 0 and less than 80%, and the magnetic permeability (μ) is maintained at 1.02 or less at a reduction ratio of more than 0 and less than 80%. Austenitic stainless steels can be produced.

The permeability (μ) means that an induced magnetic field is formed inside when a magnetic field is applied from the outside, and the degree to which the induced magnetic field is formed. The degree of magnetic properties can be quantified based on the magnetic permeability. In general, a steel whose permeability (μ) is maintained at 1.02 or less even when the use environment changes can be defined as non-magnetic steel. If the magnetic permeability (μ) exceeds 1.02, non-magnetic properties may be deteriorated, resulting in loss of current and radio waves, and noise may be generated.

In order to suppress the transformation of the austenite phase into the martensite phase, the austenite stabilization temperature (Md30) was evaluated in the present invention. The Md30 means a relational expression predicting the temperature at which the martensite phase is formed by 50% when a 30% true strain is applied to the austenite phase, and can usually be defined as follows.

Md30 = 551-462(C+N)-9.2Si-8.1Mn-13.7Cr-29(Ni+Cu)-18.5Mo

(The above C, N, Si, Mn, Cr, Ni, Cu, and Mo are weight percent of each element, and when Mn is not contained, 0 is substituted for Mn in the formula.)

According to the embodiment, the smaller the value of Md30 is, the higher the stability of the austenite phase is, and the transformation of the austenite phase into the martensite phase can be suppressed. That is, the Md30 may be used as a criterion for evaluating the stability of austenite.

According to an embodiment, in the non-magnetic austenitic stainless steel of the present invention, the stability of the austenite phase can be secured by adjusting the content of each element such that Md30 is -200 ° C or less. Preferably, the content of each element in the non-magnetic austenitic stainless steel may be adjusted to satisfy the following relational expression 1.

[Relationship 1]

551-462(C+N)-9.2Si-8.1Mn-13.7Cr-29(Ni+Cu)-18.5Mo ≤ -200

(In the above relational expression 1, C, N, Si, Mn, Cr, Ni, Cu, and Mo are weight percent of each element, and when Mn is not contained, 0 is substituted for Mn in the formula.)

For example, in the present invention, the Md30 can be calculated as -200 ° C, which means that the austenitic stainless steel of the present invention is martensitic at a temperature of -200 ° C or less when a 30% true strain is applied. 50% damage can occur. This means that the stability of the austenite phase formed according to the embodiment of the present invention is high, and the formation of martensite is suppressed, so that it can have non-magnetic characteristics even after cold working.

On the other hand, when the Md30 is fixed at -200 ° C or less, the transformation into the martensite phase is suppressed, and the strength of the non-magnetic austenitic stainless steel can be reduced. Therefore, the present invention can maximize the formation of twins by controlling the stacking fault energy (SFE) of the non-magnetic austenitic stainless steel to enhance strength. At this time, the stacking fault energy (SFE) can be defined as follows.

SFE = 28.87+1.64Ni-1.1Cr+0.21Mn-4.45Si+36.5N

(Ni, Cr, Mn, Si, and N are the weight percent of each element, and when Mn is not contained, 0 is substituted for Mn in the formula.)

The twin refers to a phenomenon in which the crystal structure has a symmetrical structure around the grain boundary, and the strength can be enhanced by interfering with the movement of dislocations in the material. The twins can be divided into mechanical twins and annealing twins according to the generation mechanism. In the present specification, twin means an annealing twin, but is not limited thereto.

According to an embodiment, the content of each element of the non-magnetic austenitic stainless steel may be adjusted to satisfy the following relational expression 2.

[Relationship 2]

28.87+1.64Ni-1.1Cr+0.21Mn-4.45Si+36.5N ≤ 15

(In the above relational expression 2, Ni, Cr, Mn, Si, and N are the weight% of each element, and when Mn is not contained, 0 is substituted for Mn in the formula.)

When the stacking fault energy (SFE) exceeds 15, twin deformation does not proceed, and plastic deformation behavior slips, resulting in a decrease in strength. For this reason, it is preferable that the stacking fault energy (SFE) is 15 or less. On the other hand, if the stacking fault energy (SFE) is too low, the degree of formation of the plasticity induced martensite phase in the austenite phase may increase. For this reason, it is preferable that the stacking fault energy (SFE) is 0 or more, but is not limited thereto.

The non-magnetic austenitic stainless steel having improved strength according to an embodiment of the present invention has been described above. Hereinafter, a method for manufacturing non-magnetic austenitic stainless steel having improved strength according to an embodiment of the present invention will be described.

According to one embodiment, the method for producing a non-magnetic austenitic stainless steel with improved strength according to the present invention contains C: 0.2 to 0.25%, Si: 2.5 to 3.5%, Mn: 4.5% or less, Cr: 19.0 to 0.25% by weight. 23.0%, Ni: 5.5 to 8.5%, Cu: 1.0 to 2.5% N: 0.1 to 0.4%, preparing a hot-rolled steel sheet by hot-rolling a slab containing Fe and other unavoidable impurities; Maintaining the hot-rolled steel sheet at 1100 to 1200 for 1 to 10 minutes and then performing water cooling; and cold-rolling the water-cooled hot-rolled steel sheet at a reduction ratio greater than 0 and less than or equal to 80%. It may include any one or more steps of, through which non-magnetic austenitic stainless steel having a magnetic permeability (μ) of 1.02 or less can be manufactured.

The manufacturing method of non-magnetic austenitic stainless steel with improved strength according to an embodiment of the present invention can be manufactured through a general hot rolling process - water cooling process - cold rolling process. At this time, the reduction ratio during the cold rolling is preferably greater than 0 and 80% or less. If the reduction ratio is 0%, it means that cold rolling is not performed, and if the reduction ratio exceeds 80%, the load of the rolling mill is increased. Productivity may decrease as a result of excessive rolling, and surface quality may deteriorate due to excessive rolling. For this reason, the reduction ratio is preferably greater than 0 and less than 80%, more preferably 67 to 73%.

In the non-magnetic austenitic stainless steel having improved strength, the austenite phase can be stabilized by adjusting the content of each element to satisfy that the Md30 is -200 ° C or less, and the stacking fault energy (SFE) is 15 mJ / m 2 Twins can be formed to the maximum by adjusting the content of each element to satisfy the following. Through this, a yield strength of 1,550 MPa is realized at a reduction ratio of more than 0 and 80% or less, and at the same time, non-magnetic austenitic stainless steel having the magnetic permeability (μ) of 1.02 or less can be manufactured.

Hereinafter, preferred embodiments according to the present invention will be described in more detail.

Example

Steel having the alloy composition shown in Table 1 was cast into a slab having a thickness of 200 mm through a continuous casting process. After heating the slab at 1,250 ° C. for 2 hours, hot rolling was performed to a thickness of 2 mm to prepare a hot-rolled steel sheet.

Thereafter, the hot-rolled steel sheet was maintained at 1,150 ° C. for 8 minutes, cooled with water at the cooling rate shown in Table 1, and then cold-rolled at a reduction rate of 70%.

Accordingly, the martensite fraction (%), magnetic permeability (μ), and yield strength (MPa) of the cold-rolled steel sheets manufactured on the basis of a reduction ratio greater than 0 and less than 80% were measured and shown in Table 2 below.

Referring to FIG. 1 , the austenitic stainless steel according to an embodiment of the present invention means a steel material having the characteristics of the Md30 of -200°C or less and the stacking fault energy (SFE) of 15 mJ/m2 or less.

As can be seen in Table 2, it was confirmed that the austenitic stainless steels prepared in Examples 1 to 4 had a permeability of 1.02μ or less, more preferably an average of 1.014μ at a reduction ratio of more than 0 and 80% or less. did At the same time, it was confirmed that the yield strength was 1,550 MPa or more, more preferably an average of 1,621 MPa. Through this, it can be confirmed that the austenitic stainless steel having both non-magnetic and high strength was manufactured.

Referring back to FIG. 1, Comparative Examples 1 to 4 are steels having compositions corresponding to existing STS 301 and STS 304.

Referring to Table 2, Comparative Examples 1 to 3 were confirmed to have a yield strength of 1,550 MPa or more, as in Examples 1 to 4, but the magnetic permeability increased to 2.0 or more. This is because the magnetic properties are increased by including 15 to 55% of the martensitic phase fraction in the steel.

On the other hand, in Comparative Example 4 in which the value of Md30 was lowered, since the martensitic phase fraction was limited to 0.01 vol% or less, it could be confirmed that the yield strength was 1,285 MPa and did not reach 1,550 MPa.

In fact, referring to FIG. 2 comparing the true stress-true strain curves of the steels manufactured in Comparative Example 1, Comparative Example 4, and Example 1, Comparative Example 1 and Example 1 It can be seen that the yield strength of the steel made of 1 is 1,550 MPa or more, whereas the steel made of Comparative Example 4 is less than 1,550 MPa and is broken.

The reason for the high yield strength of Comparative Example 1 is that 41% by volume of the martensite phase in the steel was included. On the other hand, in the examples, it can be seen that the yield strength is improved despite the fact that 0.02 vol% of the martensite phase is included. This is because, as described above, the formation of the twins in the steel material is maximized to prevent the movement of dislocations, so the yield strength is improved.

Comparative Example 4 contained 0.02% by volume of the martensite phase, so the strength was lower than that of Comparative Example 1, and the stacking fault energy (SFE) also exceeded 15 mJ/m2, so the Twin in the steel was not maximized. Therefore, it can be confirmed that, unlike Comparative Example 1 and Example 1, the yield strength is 1,285 MPa, which is less than 1,550 MPa.

That is, in Example 1, the permeability was reduced to 1.02 or less by reducing the fraction of the martensite phase to 0.02% by volume. In addition, in order to compensate for the decrease in mechanical strength due to the reduction of the martensite phase, the stacking fault energy (SFE) was also controlled to less than 15 mJ/m 2 to maximize the formation of twins in the steel. On the other hand, Comparative Example 1 secured similar strength to Example 1, but it could be confirmed that the permeability was 2.0 or more due to an increased fraction of the martensite phase in the steel. In addition, in Comparative Example 4, the fraction of the martensite phase in the steel was reduced to 0.02% by volume in the same manner as in Example 1, but it could be confirmed that the twins were not sufficiently formed and the strength was relatively reduced. Through this, it is possible to provide a steel having improved yield strength to 1,550 MPa or more while maintaining non-magnetic properties.

It can be seen that Comparative Example 5 and Comparative Examples 9 to 10 are 1,550 MPa or more, and 1,638 to 1,654 MPa. This is because the martensite phase was included in an amount of 0.1 to 1% by volume, and at the same time, the stacking fault energy (SFE) was less than 15 mJ/m 2 and the formation of twins in the steel was maximized to improve the yield strength.

However, it can be seen that Comparative Example 5 and Comparative Examples 9 to 10 have magnetic permeability of 1.05 to 1.2 μ. This is because a part of the austenite phase is transformed into the martensite phase and the fraction of the martensite phase increases to 0.1 to 1% by volume. That is, since the Md30 of Comparative Example 5 and Comparative Examples 9 to 10 exceeded -200°C to -167.6 to -190.2°C, the stability of the austenite phase decreased and the martensite phase increased. For this reason, the magnetic permeability increased to 1.05 due to poor non-magnetic properties of the steel.

On the other hand, in Comparative Examples 11 and 12, the Md30 is less than -200 ° C, more preferably -233.79 and -244.82 ° C, and as a result, the martensite phase fraction is 0.01% by volume and the magnetic permeability is 1.02 μ or less. It can be confirmed that the steel materials manufactured in Comparative Examples 11 and 12 are non-magnetic steel.

However, in Comparative Examples 11 and 12, the stacking fault energies (SFE) were 16.87 and 16.95 mJ/m2, respectively, exceeding 15 mJ/m2. It can be seen that the twin in the steel was not maximized, and for this reason, the yield strength was lowered because slip partially occurred. In fact, it can be seen that the yield strengths of Comparative Examples 11 and 12 are 1,501 and 1,490 MPa, which are all less than 1,550 MPa.

Finally, since Comparative Examples 6 to 8 also did not satisfy the condition that the Md30 was -200 ° C or less and the stacking fault energy (SFE) was 15 mJ / m 2 or less, the physical properties of any one of the magnetic permeability and the yield strength It can be confirmed that it falls short of Examples 1 to 4.

The Md30, the yield strength, and the magnetic permeability of the steels prepared in Examples 1 to 4 and Comparative Examples 1 to 12 were compared and disclosed in FIG. 3 . Referring to FIG. 3, the non-magnetic austenitic stainless steels prepared in Examples 1 to 4 improved the stability of the austenite phase by controlling Md30 to -200 ° C or less, thereby improving the martensite phase in the steel. The fraction was controlled to 0.01 to 0.02% by volume. As a result, non-magnetic characteristics having a permeability of 1.02 or less at a reduction ratio of more than 0 and less than 80% were realized.

At the same time, the formation of twins in the steel material was maximized by controlling the stacking fault energy (SFE) to 15 mJ/m 2 or less. As a result, high-strength characteristics having a yield strength of 1,550 MPa or more were implemented even when the fraction of the martensite phase was reduced. That is, the high-strength non-magnetic austenitic stainless steel according to the present invention can simultaneously implement non-magnetic characteristics having a magnetic permeability of 1.02 or less and high-strength characteristics having a yield strength of 1,550 MPa or more at a reduction ratio of more than 0 and less than 80%. can be checked once.

In the above description, various embodiments of the present invention have been presented and described, but the present invention is not necessarily limited thereto. It will be readily apparent that branch substitutions, modifications and alterations are possible.

Claims (12)

C: 0.2 to 0.25%, Si: 2.5 to 3.5%, Mn: 4.5% or less, Cr: 19.0 to 23.0%, Ni: 5.5 to 8.5%, Cu: 1.0 to 2.5% N: 0.1 to 0.4%, consisting of the remainder Fe and other unavoidable impurities,
A high-strength, non-magnetic austenitic stainless steel characterized by a yield strength of 1,550 MPa or more. According to claim 1,
The non-magnetic austenitic stainless steel is a high-strength non-magnetic austenitic stainless steel, characterized in that it satisfies the following relational expression 1.
[Relationship 1]
551-462(C+N)-9.2Si-8.1Mn-13.7Cr-29(Ni+Cu)-18.5Mo ≤ -200
(In the above relational expression 1, C, N, Si, Mn, Cr, Ni, Cu, and Mo are weight percent of each element, and 0 is substituted for Mn when Mn is not contained.) According to claim 2,
The non-magnetic austenitic stainless steel is a high-strength non-magnetic austenitic stainless steel, characterized in that it satisfies the following relational expression 2.
[Relationship 2]
28.87+1.64Ni-1.1Cr+0.21Mn-4.45Si+36.5N ≤ 15
(In the above relational expression 2, Ni, Cr, Mn, Si, and N are the weight% of each element, and 0 is substituted for Mn when Mn is not contained.) delete According to claim 1,
A high-strength non-magnetic austenitic stainless steel that satisfies that the sum of C and N is 0.4 to 0.5% by weight. According to claim 5,
The N is characterized in that 0.2 to 0.25% by weight, high-strength non-magnetic austenitic stainless steel. According to claim 1,
The non-magnetic austenitic stainless steel is characterized in that the fraction of martensite phase is less than 0.01% by volume, high-strength non-magnetic austenitic stainless steel. According to any one of claims 1 to 7,
The non-magnetic austenitic stainless steel is characterized in that the permeability (μ) is 1.02 or less at a reduction ratio of 80% or less, high-strength non-magnetic austenitic stainless steel. C: 0.2 to 0.25%, Si: 2.5 to 3.5%, Mn: 4.5% or less, Cr: 19.0 to 23.0%, Ni: 5.5 to 8.5%, Cu: 1.0 to 2.5% N: 0.1 to 0.4%, preparing a hot-rolled steel sheet by hot-rolling a slab containing the remaining Fe and other unavoidable impurities;
maintaining the hot-rolled steel sheet at 1100 to 1200° C. for 1 to 10 minutes and then performing water cooling; and
Including; cold rolling the water-cooled hot-rolled steel sheet at a reduction ratio of 80% or less;
A method for producing high-strength non-magnetic austenitic stainless steel having a yield strength of 1,550 MPa or more. According to claim 9,
The slab is a method for producing a high-strength non-magnetic austenitic stainless steel that satisfies the following relational expression 1.
[Relationship 1]
551-462(C+N)-9.2Si-8.1Mn-13.7Cr-29(Ni+Cu)-18.5Mo ≤ -200
(In the above relational expression 1, C, N, Si, Mn, Cr, Ni, Cu, and Mo are weight percent of each element, and when Mn is not contained, 0 is substituted for Mn in the formula.) According to claim 10,
The slab is a method for producing a high-strength non-magnetic austenitic stainless steel that satisfies the following relational expression 2.
[Relationship 2]
28.87+1.64Ni-1.1Cr+0.21Mn-4.45Si+36.5N ≤ 15
(In the above relational expression 2, Ni, Cr, Mn, Si, and N are the weight% of each element, and when Mn is not contained, 0 is substituted for Mn in the formula.) According to claim 9,
The N is a method for producing a high-strength non-magnetic austenitic stainless steel comprising 0.2 to 0.25% by weight.

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