KR102579428B1 - Clad steel with controlled hardness change - Google Patents

Clad steel with controlled hardness change Download PDF

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KR102579428B1
KR102579428B1 KR1020210047129A KR20210047129A KR102579428B1 KR 102579428 B1 KR102579428 B1 KR 102579428B1 KR 1020210047129 A KR1020210047129 A KR 1020210047129A KR 20210047129 A KR20210047129 A KR 20210047129A KR 102579428 B1 KR102579428 B1 KR 102579428B1
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weight
less
clad
base material
steel
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KR20220141056A (en
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심호섭
조수철
김기혁
성준호
박병규
김지탁
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동국제강 주식회사
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
    • B21B45/04—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing
    • B21B45/06—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing of strip material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
    • B23K20/04—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating by means of a rolling mill
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/38—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling sheets of limited length, e.g. folded sheets, superimposed sheets, pack rolling
    • B21B2001/383—Cladded or coated products

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Pressure Welding/Diffusion-Bonding (AREA)

Abstract

탄소강인 모재와 스테인레스강인 클래딩재를 포함하는 클래드 강으로, 상기 모재와 상기 클래드재 간 계면층에서의 경도 증가율은 20 내지 50%이며, 상기 계면층에서의 경도 변화율은 15% 이하인 것을 특징으로 하는 클래드 강이 제공된다.It is a clad steel containing a base material that is carbon steel and a cladding material that is stainless steel, and the hardness increase rate in the interface layer between the base material and the clad material is 20 to 50%, and the hardness change rate in the interface layer is 15% or less. Clad steel is provided.

Description

경도 변화가 제어된 클래드 강{Clad steel with controlled hardness change}Clad steel with controlled hardness change}

본 발명은 경도 변화가 제어된 클래드 강에 관한 것으로, 보다 상세하게는 모재와 클래딩재간 계면층에서 경도를 제어하여 모재와 클래딩재 사이의 과도하게 큰 경도 변화에 따른 문제를 해결할 수 있는, 경도 변화가 제어된 클래드 강에 관한 것이다. The present invention relates to a clad steel with controlled hardness change. More specifically, the hardness change in the interface layer between the base material and the cladding material can be controlled to solve problems caused by excessively large hardness changes between the base material and the cladding material. relates to controlled clad steels.

일반적으로, 복합재료의 일종인 클래드 접합재는 한 금속의 전면을 다른 금속으로 피복하여 구성되는 것으로, 성질이 다른 금속을 접합함으로써 단일 금속에서는 얻기 어려운 효과(강도 등)를 발휘시키는 재료이다.In general, a clad bonding material, a type of composite material, is composed of covering the entire surface of one metal with another metal, and is a material that exhibits effects (strength, etc.) that are difficult to obtain with a single metal by bonding metals with different properties.

상기 클래드 접합재에서는 통상적으로 피복하는 금속을 클래드재, 피복되는 금속을 모재라고 칭하고 있으며, 특히, 강재를 모재로 하는 클래드 접합재의 경우에는 클래드강(clad steel)이라 부르고 있다.In the above clad bonding material, the covering metal is generally called a clad material, and the covered metal is called a base material. In particular, in the case of a clad bonding material using steel as a base material, it is called clad steel.

이러한 클래드강은 제조 비용면에서 상대적으로 경제성이 있으면서도 단일 재료에 비해 높은 물성을 가질 수 있어, 화학 플랜트, 압력용기류, 가전제품, 전자부품, 건축용 자재 등에서 많이 이용되고 있다.Such clad steel is relatively economical in terms of manufacturing cost and can have higher physical properties than single materials, so it is widely used in chemical plants, pressure vessels, home appliances, electronic components, and building materials.

한편, 상술한 클래드강을 선박의 선체외판에 적용하고자 하는 시도도 많이 이루어지고 있다. 클래드강은 일반적으로 모재로 강재(주로 탄소강)를 사용하고 클래드재로 스테인리스강을 사용하고 있는데, 선체외판에 적용됨에 있어 강도와 내식성의 문제가 주로 연구되고 있다. Meanwhile, many attempts are being made to apply the above-described clad steel to the hull shell of ships. Clad steel generally uses steel (mainly carbon steel) as the base material and stainless steel as the clad material, and the issues of strength and corrosion resistance are mainly studied when applied to hull shell plating.

예를 들어 대한민국 공개특허 10-2013-0053706호는 선박용 클래드강 제조방법을 개시하고 있으며, 대한민국 공개특허 공개특허 10-2019-0102029호는 시그마상, 탄화물의 석출을 억제하고, 내식성이 우수한 2상 스테인리스 클래드강에 관한 특허를 개시하고 있다. For example, Republic of Korea Patent Publication No. 10-2013-0053706 discloses a method for manufacturing clad steel for ships, and Republic of Korea Patent Publication No. 10-2019-0102029 discloses a two-phase sigma phase, which suppresses precipitation of carbides and has excellent corrosion resistance. Patents related to stainless clad steel are disclosed.

하지만, 상이한 경도(hardness)의 두 금속재를 접합함에 있어서, 모재인 탄소강과 클래드재인 스테인레스강 사이의 경도 변화가 과도하게 큰 경우 클래드재가 가지게 되는 변형이나 외부 충격에 대한 취약함 등의 문제를 해결하는 기술은 개시되지 못하는 상황이다.However, when joining two metal materials of different hardness, if the change in hardness between the carbon steel as the base material and the stainless steel as the clad material is excessively large, it is difficult to solve problems such as deformation of the clad material or vulnerability to external shock. The technology cannot be launched.

KRKR 10-2013-005370610-2013-0053706 A1A1 KRKR 10-2019-010202910-2019-0102029 A1A1

따라서, 본 발명이 해결하고자 하는 과제는 모재와 클래드재 사이의 계면층에서 경도 변화율이 일정 수준 이하로 조절되어 상술한 문제가 해결된 클래드 강 및 그 제조방법을 제공하는 것이다. Therefore, the problem to be solved by the present invention is to provide a clad steel and a manufacturing method thereof that solve the above-mentioned problems by controlling the hardness change rate in the interface layer between the base material and the clad material below a certain level.

본 발명은 탄소강인 모재와 스테인레스강인 클래딩재를 포함하는 클래드 강으로, 상기 모재와 상기 클래드재 간 계면층에서의 경도 증가율은 20 내지 50%이며, 상기 계면층에서의 경도 변화율은 15% 이하인 클래드 강을 제공한다.The present invention is a clad steel comprising a base material that is carbon steel and a cladding material that is stainless steel, and the hardness increase rate in the interface layer between the base material and the clad material is 20 to 50%, and the hardness change rate in the interface layer is 15% or less. Provides a river.

본 발명의 일 구현예로 상기 계면층은 상기 모재와 상기 클래딩재 사이의 계면으로부터 상기 모재와 상기 클래딩재 양 방향으로 10 내지 50 μm일 수 있다.In one embodiment of the present invention, the interfacial layer may be 10 to 50 μm in both directions between the base material and the cladding material from the interface between the base material and the cladding material.

본 발명의 일 구현예로 상기 모재는 C 0.07 중량% 이하, Si 0.45 중량% 이하, Mn 1.6 중량% 이하, P 0.025 중량% 이하, S 0.015 중량% 이하, V 0.1 중량% 이하, Nb 0.1 중량% 이하, Ti 0.1 중량% 이하와 잔부의 철로 구성되며, 상기 클래딩재는 C 0.03 중량% 이하, Cr 16.0 내지 18.0 중량%, Mo 2.0 내지 3.0 중량%, Ni 10.0 내지 14.0 중량%, Mn 2.0 중량% 이하, P 0.045 중량% 이하, S 0.03 중량% 이하, N 0.10 중량% 이하와 잔부의 철로 구성되며, 상기 클래드 강의 접합계면 전단강도는 350 MPa 이상일 수 있다.In one embodiment of the present invention, the base material contains 0.07% by weight or less of C, 0.45% by weight or less of Si, 1.6% by weight or less of Mn, 0.025% by weight or less of P, 0.015% by weight or less of S, 0.1% by weight or less of V, and 0.1% by weight of Nb. Hereinafter, it is composed of 0.1% by weight or less of Ti and the balance of iron, and the cladding material contains 0.03% by weight or less of C, 16.0 to 18.0% by weight of Cr, 2.0 to 3.0% by weight of Mo, 10.0 to 14.0% by weight of Ni, and 2.0% by weight or less of Mn. It is composed of P 0.045% by weight or less, S 0.03% by weight or less, N 0.10% by weight or less, and the balance is iron, and the joint interface shear strength of the clad steel may be 350 MPa or more.

본 발명에 따르면, 모재와 클래딩재간 계면층에서 경도를 제어하여 모재와 클래딩재 사이의 과도하게 큰 경도 변화에 따른 문제를 해결할 수 있다. According to the present invention, the problem caused by an excessively large change in hardness between the base material and the cladding material can be solved by controlling the hardness at the interface layer between the base material and the cladding material.

도 1은 본 발명의 일 실시예에 따른 클래드강 제조방법의 모식도이다.
도 2는 본 발명의 일 실시예에 따라 제조된 클래드강의 단면 조직 사진이고, 도 3은 본 발명의 일 실시예와 달리 모재로 A516-70N, 클래드재로 STS-316L을 사용하여 공냉시킨 경우의 클래드강의 단면 조직사진이다.
도 4 및 5는 각각 도 2 및 도 3의 클래드강에 대한 마이크로 비커스 경도 측정 결과이다. Figure 1 is a schematic diagram of a clad steel manufacturing method according to an embodiment of the present invention.
Figure 2 is a cross-sectional photo of the clad steel manufactured according to an embodiment of the present invention, and Figure 3 is a photo of the cross-sectional structure of the clad steel manufactured according to an embodiment of the present invention, and Figure 3 is a photograph of the case of air cooling using A516-70N as a base material and STS-316L as a clad material, unlike an embodiment of the present invention. This is a cross-sectional tissue photo of the clad steel.
Figures 4 and 5 are micro Vickers hardness measurement results for the clad steel of Figures 2 and 3, respectively.

본 발명은 다양한 변경을 가할 수 있고 여러 가지 실시예를 가질 수 있는 바, 특정 실시예들을 도면에 예시하고 상세한 설명에 상세하게 설명하고자 한다.Since the present invention can make various changes and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description.

그러나, 이는 본 발명을 특정한 실시 형태에 대해 한정하려는 것이 아니며, 본 발명의 사상 및 기술 범위에 포함되는 모든 변경, 균등물 내지 대체물을 포함하는 것으로 이해되어야 한다. 본 발명을 설명함에 있어서 관련된 공지 기술에 대한 구체적인 설명이 본 발명의 요지를 흐릴 수 있다고 판단되는 경우 그 상세한 설명을 생략한다.However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention. In describing the present invention, if it is determined that a detailed description of related known technologies may obscure the gist of the present invention, the detailed description will be omitted.

본 출원에서 사용한 용어는 단지 특정한 실시예를 설명하기 위해 사용된 것으로, 본 발명을 한정하려는 의도가 아니다. 단수의 표현은 문맥상 명백하게 다르게 뜻하지 않는 한, 복수의 표현을 포함한다.The terms used in this application are only used to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

본 발명에서, "포함한다" 또는 "가지다" 등의 용어는 명세서상에 기재된 특징, 숫자, 단계, 동작, 구성요소, 부품 또는 이들을 조합한 것이 존재함을 지정하려는 것이지, 하나 또는 그 이상의 다른 특징들이나 숫자, 단계, 동작, 구성 요소, 부품 또는 이들을 조합한 것들의 존재 또는 부가 가능성을 미리 배제하지 않는 것으로 이해되어야 한다.In the present invention, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that it does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

본 발명은 상술한 문제를 해결하기 위하여 C 0.07 중량% 이하, Si 0.45 중량% 이하, Mn 1.6 중량% 이하, P 0.025 중량% 이하, S 0.015 중량% 이하, V 0.1 중량% 이하, Nb 0.1 중량% 이하, Ti 0.1 중량% 이하와 잔부의 철로 구성된 모재와, C 0.03 중량% 이하, Cr 16.0 내지 18.0 중량%, Mo 2.0 내지 3.0 중량%, Ni 10.0 내지 14.0 중량%, Mn 2.0 중량% 이하, P 0.045 중량% 이하, S 0.03 중량% 이하, N 0.10 중량% 이하와 잔부의 철로 구성된 클래드재로 이루어진 클래드강을 제공한다.In order to solve the above-mentioned problem, the present invention contains 0.07% by weight or less of C, 0.45% by weight of Si, 1.6% by weight or less of Mn, 0.025% by weight or less of P, 0.015% by weight of S or less, 0.1% by weight of V or less, and 0.1% by weight of Nb. Hereinafter, a base material composed of Ti 0.1% by weight or less and the balance iron, C 0.03% by weight or less, Cr 16.0 to 18.0% by weight, Mo 2.0 to 3.0% by weight, Ni 10.0 to 14.0% by weight, Mn 2.0% by weight or less, P 0.045% Provides a clad steel composed of a clad material composed of 0.03% by weight or less of S, 0.10% by weight or less of N, and the balance of iron.

상기 모재에 포함된 C는 다른 합금 원소에 비해 높은 확산 속도를 가지므로 모재로부터 클래드재 방향으로 확산되어 계면층에 다량의 탄화물이 존재하는 구간에 해당하는 Severely Carburized Layer(이하 SCL)을 형성할 수 있다. SCL 내 다량의 탄화물은 내식성을 저해할 뿐만 아니라 모재와 클래드재 사이의 과도한 경도 변화를 초래하여 클래드강의 인성 저하 등의 문제를 야기한다. 따라서, 다량의 탄소 함유는 피해야 하며, 탄소의 확산과 과도한 SCL의 형성을 억제하여 계면층 내 탄소가 집중되는 문제를 방지하기 위해 C 량은 0.07 중량% 이하로 한다.Since C contained in the base material has a higher diffusion rate than other alloy elements, it can diffuse from the base material toward the clad material to form a Severely Carburized Layer (hereinafter referred to as SCL) corresponding to the section where a large amount of carbide exists in the interface layer. there is. A large amount of carbides in SCL not only impairs corrosion resistance but also causes excessive hardness changes between the base material and the clad material, causing problems such as a decrease in the toughness of the clad steel. Therefore, the inclusion of a large amount of carbon should be avoided, and the amount of C should be 0.07% by weight or less to prevent the problem of carbon concentration in the interface layer by suppressing the diffusion of carbon and the formation of excessive SCL.

상기 모재에 포함된 V, Nb, Ti는 모재 내 탄소와 탄화물을 형성하여 모재로부터 클래드재 방향으로 확산되는 탄소량을 감소시켜 SCL의 형성을 억제하며, V+Nb+Ti≤0.15 중량%를 만족한다. 상기 범위에서 탄화물의 형성에 따른 탄소의 확산이 억제되어 과도한 SCL의 형성과 계면층 내 탄소의 집중 현상을 방지할 수 있다.V, Nb, and Ti contained in the base material form carbon and carbide in the base material, reducing the amount of carbon diffusing from the base material toward the clad material to suppress the formation of SCL, and satisfy V+Nb+Ti≤0.15% by weight. do. In the above range, diffusion of carbon due to the formation of carbides is suppressed, thereby preventing excessive formation of SCL and concentration of carbon in the interface layer.

본 발명에서 계면층은 상기 모재와 상기 클래딩재 사이의 계면으로부터 상기 모재와 상기 클래딩재 양 방향으로 10 내지 50 μm로 정의하지만, 적어도 모재와 클래드재 단독의 조성과 달라지는 임의의 범위가 모두 본 발명에 속한다.In the present invention, the interfacial layer is defined as 10 to 50 μm in both directions from the interface between the base material and the cladding material, but any range that differs from the composition of the base material and the cladding material alone is at least within the scope of the present invention. belongs to

이하, 본 발명의 경도 변화가 제어된 클래드 강의 제조방법에 대하여 설명한다.Hereinafter, the method for manufacturing clad steel with controlled hardness change according to the present invention will be described.

본 발명의 클래드 강은 상기 조성 범위의 모재와 클래드재를 결합하여 클래드 압연용 조립 슬래브를 제조하고 클래드 압연 이후 수냉과 공냉을 거쳐 제조된다.The clad steel of the present invention is manufactured by combining a base material and a clad material within the above composition range to manufacture a assembled slab for clad rolling, followed by water cooling and air cooling after clad rolling.

클래드 압연용 조립 슬래브 제조시 모재와 클래드재간의 접합성을 향상시키기 위해 슬라브 패킹 진공도는 10-3torr로 하며, 가열 시 클래드재를 충분히 용체화하기 위해 슬라브 가열은 1050~1150℃ 범위에서 실시한다.In order to improve the adhesion between the base material and the clad material when manufacturing assembled slabs for clad rolling, the slab packing vacuum degree is set to 10 -3 torr, and the slab heating is performed in the range of 1050~1150℃ to sufficiently solutionize the clad material during heating.

이후, 모재의 강도, 인성을 확보하고 모재와 클래드재간의 접합성의 열화를 방지하기 위해 압하비 2~3, 누적 압하율 50% 이상, 압연온도 820℃ 이상에서 압연을 실시한다.Afterwards, in order to secure the strength and toughness of the base material and prevent deterioration of the bond between the base material and the clad material, rolling is performed at a reduction ratio of 2 to 3, a cumulative reduction ratio of 50% or more, and a rolling temperature of 820°C or more.

특히 본 발명은 압연 이후 수냉을 통해 모재로부터 클래드재 방향으로의 탄소 확산을 제어하여 SCL의 형성을 억제함으로써 탄소가 계면층으로 집중되는 문제를 해결하여 경도 변화율을 제어한다. 즉, 압연 이후 수냉을 거치지 않고 공냉과 열처리를 통해 제조되는 클래드강과 달리 본 발명은 탄소의 확산속도를 낮춰 탄소 확산과 SCL 형성을 억제하기 위해 800℃ 범위에서 수냉을 실시하며, 바람직하게는 550℃까지 수냉을 실시한다.In particular, the present invention suppresses the formation of SCL by controlling the diffusion of carbon from the base material to the clad material through water cooling after rolling, thereby solving the problem of carbon being concentrated in the interface layer and controlling the hardness change rate. That is, unlike clad steel, which is manufactured through air cooling and heat treatment without water cooling after rolling, the present invention performs water cooling in the range of 800°C, preferably at 550°C, to suppress carbon diffusion and SCL formation by lowering the diffusion rate of carbon. Carry out water cooling until.

이하 본 발명의 일 실시예와, 실시예에 따라 제조된 클래드재에 대한 실험예를 통하여 본 발명을 보다 상세히 설명한다. 하지만, 이하 실시예와 실험예에 따라 본 발명의 범위는 제한되지 않는다.Hereinafter, the present invention will be described in more detail through an example of the present invention and an experimental example of a clad material manufactured according to the example. However, the scope of the present invention is not limited to the following examples and experimental examples.

실시예Example

도 1은 본 발명의 일 실시예에 따른 클래드강 제조방법의 모식도이다. Figure 1 is a schematic diagram of a clad steel manufacturing method according to an embodiment of the present invention.

도 1을 참조하면, 상술한 탄소강 모재에 클래드강을 패킹한 후, 하기의 공정 조건에 따라 클래드강을 제조하였다.Referring to Figure 1, after packing the clad steel into the carbon steel base material described above, the clad steel was manufactured according to the following process conditions.

패킹된 슬라브는 압연 전, 모재와 클래드재간의 접합성을 향상시키기 위해 슬라브 패킹 진공도는 10-3torr로 하였다. 슬라브 가열온도는 클래드재를 충분히 용체화하기 위해 1050~1150℃ 범위에서 실시하였다. 가열온도가 낮으면 고온역에서 충분한 압연량을 확보할 수 없어 접합성이 열화된다. 따라서 모재와 클래드재 간의 접합성 확보 측면에서 가열온도는 1050~1150℃ 범위로 하였다. 한편, 압연온도는 1000℃ 이상에서 압하비 2~3, 누적압하율 50% 이상을 적용하였으며, 최종 압연종료온도는 820℃이다. 이후 550℃까지 수냉한 후 상온까지 공냉하여 베이나이트 및 페라이트로 이루어지는 복합조직의 클래드강을 제조하였다. 수냉 시 냉각속도는 5℃/sec 이상으로 하였다.Before rolling of the packed slab, the slab packing vacuum degree was set to 10 -3 torr to improve the adhesion between the base material and the clad material. The slab heating temperature was carried out in the range of 1050~1150℃ to sufficiently solutionize the clad material. If the heating temperature is low, sufficient rolling amount cannot be secured in the high temperature range, and the jointability deteriorates. Therefore, in terms of ensuring adhesion between the base material and the clad material, the heating temperature was set in the range of 1050 to 1150°C. Meanwhile, the rolling temperature was applied at over 1000℃, with a reduction ratio of 2~3 and a cumulative reduction ratio of over 50%, and the final rolling end temperature was 820℃. Afterwards, it was water cooled to 550°C and then air cooled to room temperature to produce a clad steel with a composite structure made of bainite and ferrite. The cooling rate during water cooling was 5°C/sec or more.

실험예Experiment example

조직group

도 2는 본 발명의 일 실시예에 따라 제조된 클래드강의 단면 조직 사진이고, 도 3은 본 발명의 일 실시예와 달리 모재로 A516-70N, 클래드재로 STS-316L을 사용하여 수냉없이 공냉 방식으로 냉각시킨 비교예에 따른 클래드강의 단면 조직사진이다. Figure 2 is a cross-sectional structure photograph of a clad steel manufactured according to an embodiment of the present invention, and Figure 3 is an air cooling method without water cooling using A516-70N as a base material and STS-316L as a clad material, unlike an embodiment of the present invention. This is a cross-sectional photo of the clad steel according to the comparative example cooled.

도 2 및 3을 참조하면, 본 발명의 일 실시예에 따라 제조된 단면은 계면 부근의 클래드재에 모재로부터 확산된 탄화물이 형성된 것을 알 수 있으나, 도 3과 달리 과도하게 많은 탄화물이 침착된 계면층(도 3의 30μm 두께층), 즉 SCL이 형성되지 않은 것을 알 수 있다. 이는 페라이트 및 펄라이트의 미세조직을 갖는 비교예와 달리 본 발명의 일 실시예에 따라 제조된 클래드강은 수냉에 따른 베이나이트와 페라이트의 미세조직을 갖게 되어 탄소의 확산이 억제된 것으로 판단된다.Referring to Figures 2 and 3, it can be seen that the cross section manufactured according to an embodiment of the present invention has carbide diffused from the base material formed in the clad material near the interface. However, unlike Figure 3, the interface has an excessive amount of carbide deposited. It can be seen that the layer (30 μm thick layer in Figure 3), that is, the SCL, was not formed. Unlike the comparative example, which has a microstructure of ferrite and pearlite, the clad steel manufactured according to an embodiment of the present invention has a microstructure of bainite and ferrite due to water cooling, and it is believed that diffusion of carbon is suppressed.

경도 측정Hardness measurement

도 4 및 5는 각각 도 2 및 도 3의 클래드강에 대한 마이크로 비커스 경도 측정 결과이다. Figures 4 and 5 are micro Vickers hardness measurement results for the clad steel of Figures 2 and 3, respectively.

도 4를 참조하면, 본 발명에 따라 제조된 클래드강의 경우, 모재와 클래드재 사이의 계면영역에서의 경도 변화는 모재에서 클래드재 방향으로 15% 이하로 증가하는 것을 알 수 있다. 이것은 탄소 확산이 억제됨에 따라 모재와 클래드재 사이의 경도 변화가 급격하게 증가하지 않고 낮아진 결과로 예상된다.Referring to Figure 4, in the case of the clad steel manufactured according to the present invention, it can be seen that the change in hardness in the interface area between the base material and the clad material increases by 15% or less in the direction from the base material to the clad material. This is expected to be the result of the hardness change between the base material and the clad material lowering rather than rapidly increasing as carbon diffusion is suppressed.

또한, 이러한 급격한 경도 변화를 억제함에 따라 과도한 경도 차이에 의한 계면에서의 균열 발생을 억제하여 계면 파단 위험성을 낮출 수 있으며, 클래드강의 인성 저하 등의 문제를 해결할 수 있다.In addition, by suppressing this rapid change in hardness, the occurrence of cracks at the interface due to excessive hardness differences can be suppressed, lowering the risk of interface fracture, and solving problems such as lowering the toughness of clad steel.

한편 도 5를 참조하면, 모재와 클래드재간 계면층에서 급격한 경도 변화가 관찰되는 것을 알 수 있다. 이것은 본 발명에 따라 제조된 클래드강의 특성과는 명확히 구분된다. Meanwhile, referring to Figure 5, it can be seen that a rapid change in hardness is observed in the interface layer between the base material and the clad material. This is clearly distinct from the properties of the clad steel manufactured according to the present invention.

전단 강도 측정Shear strength measurements

클래드재와 모재의 접합성 평가는 ASTM A264 전단 강도 시험에 의하였다. 전단 강도 시험은 클래드재를 모재로부터 접합면과 평행하게 박리하고, 그 박리에 필요하였던 최대 전단 강도로부터 접합성을 평가하는 방법이다. 평가 기준은 전단 응력이 350 MPa 이상인 것을 접합성이 양호한 것으로 판단하였다.The adhesion between the clad material and the base material was evaluated using the ASTM A264 shear strength test. The shear strength test is a method of peeling the clad material from the base material parallel to the joint surface and evaluating the jointability based on the maximum shear strength required for the peeling. The evaluation standard was that shear stress of 350 MPa or more was judged to have good bonding properties.

도 6을 참조하면, 상기 평가에 의한 본 발명에 따른 클래드 강의 접합계면 전단강도는 350 MPa 이상임을 확인할 수 있었다.Referring to Figure 6, it was confirmed that the joint interface shear strength of the clad steel according to the present invention based on the above evaluation was 350 MPa or more.

Claims (3)

탄소강인 모재와 스테인레스강인 클래딩재를 포함하는 클래드 강으로,
상기 모재와 상기 클래드재 간 계면층에서의 경도 증가율은 20 내지 50%이며,
상기 계면층에서의 경도 변화율은 15% 이하이며,
상기 모재는 C 0.07 중량% 이하, Si 0.45 중량% 이하, Mn 1.6 중량% 이하, P 0.025 중량% 이하, S 0.015 중량% 이하, V 0.1 중량% 이하, Nb 0.1 중량% 이하, Ti 0.1 중량% 이하와 잔부의 철로 구성되며,
상기 클래딩재는 C 0.03 중량% 이하, Cr 16.0 내지 18.0 중량%, Mo 2.0 내지 3.0 중량%, Ni 10.0 내지 14.0 중량, Mn 2.0 중량% 이하, P 0.045 중량% 이하, S 0.03 중량% 이하, N 0.1 중량% 이하와 잔부의 철로 구성되며,
상기 계면층은 상기 모재와 상기 클래딩재 사이의 계면으로부터 상기 모재와 상기 클래딩재 양 방향으로 10 내지 30 μm이며,
상기 모재는 V+Nb+Ti≤0.15 중량%를 가지며,
압하비 2~3, 누적 압하율 50% 이상, 압연온도 820℃ 이상에서 압연을 실시한 후, 550℃까지 수냉을 실시하여 제조된 것을 특징으로 하는 클래드 강.It is a clad steel containing a base material of carbon steel and a cladding material of stainless steel,
The hardness increase rate at the interface layer between the base material and the clad material is 20 to 50%,
The hardness change rate in the interface layer is 15% or less,
The base material contains C 0.07% by weight or less, Si 0.45% by weight or less, Mn 1.6% by weight or less, P 0.025% by weight or less, S 0.015% by weight or less, V 0.1% by weight or less, Nb 0.1% by weight or less, and Ti 0.1% by weight or less. and the remainder is made up of iron,
The cladding material contains 0.03% by weight or less of C, 16.0 to 18.0% by weight of Cr, 2.0 to 3.0% by weight of Mo, 10.0 to 14.0% by weight of Ni, 2.0% by weight or less of Mn, 0.045% by weight or less of P, 0.03% by weight or less of S, and 0.1% by weight of N. It consists of less than % and the balance of iron,
The interfacial layer is 10 to 30 μm in both directions between the base material and the cladding material from the interface between the base material and the cladding material,
The base material has V+Nb+Ti≤0.15% by weight,
Clad steel characterized by being manufactured by rolling at a reduction ratio of 2 to 3, a cumulative reduction ratio of 50% or more, and a rolling temperature of 820 ℃ or higher, followed by water cooling to 550 ℃. 삭제delete 삭제delete
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