KR101997733B1 - Step plate - Google Patents

Abstract

A step plate according to an embodiment of the present invention is a step plate in which a height adjustment surface facing a rolling roller is formed in a multi-stage so as to adjust a gap between rolling rollers, the step plate comprising: a multi- And a second layer disposed on top of the layer.

Description

STEP PLATE {STEP PLATE}

The present invention relates to a step plate. More specifically, the present inventors have developed a material having excellent strength and hardness, abrasion resistance, impact resistance and corrosion resistance of the surface, and formed a multi-layered metal material having different characteristics, thereby being generated in the micron- The present invention relates to a step plate of a hot plate rolling process for preventing a phenomenon in which a hardened layer is peeled, corroded or abraded due to repetitive action due to high depressing force and impact and the service life is remarkably reduced.

Carbon steel containing carbon (C) in steel plate of step plate is superior in machinability, durability, formability and environment-friendly characteristics. Carbon steel is used in steel industry, automobile, ship, industrial material, It is widely used for industrial materials such as construction materials, home appliances, parts materials, and electrical products.

Generally, the material of the steel plate with the characteristics of ferritic metal structure containing carbon (C) is SNCM 447 or its similar material and its strength and hardness are comparatively high. However, the hot plate for producing hot rolled sheet In the rolling process, the width is varied in step form to control the width according to the width of the plate. When the plate passes through the rolling apparatus, the rolling force is transmitted to the rolling roll, ), But the surface of the step plate is easily worn and corroded due to heavy load, impact, abrasion, surface peeling, and corrosion repeatedly transmitted in the rolling process. 탆), the oxynitrided surface hardening portion is dropped off

At this time, the step plate apparatus supports the hot rolling rolled steel sheet by supporting the pressing force transmitted to the rolling apparatus when the hot rolled steel sheet reaches the binding point between the upper and lower rolls of the rolling apparatus by rolling, It is continuously rolled to a desired thickness and guided to the next process.

Plate Mill Plate Stand consists of various facilities. Most equipment repeats movement according to the material during rolling, but the step plate equipment is a facility to set the optimum rolling pass line by calculating the interlocking with back up roll dia when new work roll is pulled in roll replacement .

The finish rolling (FM) step plate is, for example, from step 1 to step 9, and each step has a deviation of 15 mm. The main function is to compensate the gap under the back up roll (BUR) to prevent the abrupt change of the position of the AGC cylinder when the roll back (B, U, R-Back Up Roll) Is a key facility to perform.

However, due to the roll force of 10,000 Ton / Set or more, which is applied to the material during rolling, the surface of the step plate which is in contact with the back up roll choke is damaged, so that the obstacle controlling the gap of the rolling roll And when the size of the gap becomes 5 mm or more, the driving of the rolling device is stopped by the position control sensor and the quality of the hot rolled plate is significantly deteriorated.

FIG. 1 is an image showing a conventional step plate, and FIG. 2 is an enlarged view of FIG.

1 and 2, the step plate 10 is made of high carbon steel (C: 0.44 to 0.50) and is made of NI-Cr-Mo steel, Si: 0.15- 0.35% of Mn, 0.80-1.2% of Mn, 0.03% or less of P, 0.03% or less of S, 1.60-2.00% of Ni, 0.6-1.0% of Cr and 0.15-0.30% There is a characteristic of a steel material in which the surface hardened layer by the oxynitriding treatment of one surface of the step plate apparatus is easily peeled off by corrosion, wear and abrasion due to repeated load, high heat, moisture and impact load.

The step plate 10 has higher toughness and strength than the rolled steel material for general structure but the oxynitriding treatment and the titanium (Ti) coating layer coated on the surface 11 are in the order of microns The coating layer is peeled off due to the repeated load at high load and the impact due to the peeling, and the fine metal structure thus peeled is secondarily pressed onto the surface 11 of the step plate and at the same time, the wear (A) (A).

On the other hand, in the process of using the step plate 10, when the cross section of the surface 11 of the step plate 10 is reduced due to wear and corrosion, Gaps lose the original function of the step plate which keeps the gap set by the control rolling uniformly, causing the thickness deviation of the hot-rolled steel sheet, resulting in poor quality of the hot rolled sheet There was a key problem.

Also, there is a problem in frequent replacement of step plates due to damage and cost increase due to an increase in production cost due to purchase.

The present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a method of manufacturing a step plate, which comprises a step plate having a surface made of chromium (Cr), nickel (Ni), manganese (Mn) Cr-Mo steel with SNCM 447 or similar materials that constitute a weld material having an age hardening property, an excellent ductility, an impact resistance, an abrasion resistance and a corrosion resistance among Austenite type weld materials, a first buttering welding method (C), silicon (Si), molybdenum (Si), and silicon carbide are formed on the surface of a step plate, which is formed by forming a corrosion prevention layer, (Second layer) with Austenite welding material whose hardness is largely improved by using mainly Mo, Cr, Ni and Mn as a main component, , The corrosion resistance is maximized, and a step plate The impact on one surface of the step plate and the detachment of the surface hardened layer due to repetitive high load are suppressed under repeated impact and pressing action on the surface, (BUR-Back) due to the decrease in the thickness of the step plate due to heat, moisture, oil, etc., due to the phenomenon that the surface is left on the surface and repetitive pressing force is prevented, Up Roll It is a high performance step plate which can prevent the defect from being compensated at the bottom and prevent the frequent replacement due to the decrease of the lifetime of the step plate and the increase of the cost accordingly. ).

The problems to be solved by the embodiments are not limited to the above-mentioned problems, and other problems not mentioned here can be clearly understood by those skilled in the art from the following description.

A step plate according to an embodiment of the present invention is a step plate in which a height adjustment surface facing a rolling roller is formed in a multi-stage so as to adjust a gap between rolling rollers, the step plate comprising: a body formed in a multi- Layer and a second layer disposed over the first layer.

Wherein the body comprises, by weight, 0.44 to 0.50% of C, 0.15 to 0.35% of Si, 0.80 to 1.2% of Mn, 0.03% or less of P, 0.03% or less of S, 1.60 to 2.00% To 1.0% and Mo: 0.15 to 0.30%.

Wherein the first layer contains 0.1% of C, 0.69% of Si, 6.0% of Mn, 8.9% of Ni, and 19.5% of Cr, the balance being austenite, the balance being Fe and other impurities It may be an age-hardening material.

At least one or all of Mo, V, W, Co, Nb, N, Ti and B may be added in a small amount to the other impurities in the first layer.

Wherein the second layer contains 0.13% of C, 0.72% of Si, 1.2% of Mn, 9.2% of Ni, 19.3% of Cr and 0.9% of Mo and the balance of iron (Fe) And may be an austenitic age-hardening material made of an impurity.

The other impurities of the second layer may be added in trace amounts to at least one or all of V, W, Co, Nb, N, Ti and B.

The second layer may have a Rockwell hardness of at least 50 HRc or higher.

The thickness of the first layer may be 10 to 15 mm.

The thickness of the second layer may be 10 to 15 mm.

The thickness of the second layer may be 0.6 to 1.5 times the thickness of the first layer.

The first layer may have an elongation of at least 38%.

An impact toughness of at least be equal to or greater than 55 (J / cm ^2).

According to the embodiment of the present invention, the step plate is austenitic based on manganese, chromium, and nickel as a main material to be applied to one surface of the step plate, and the material of the step plate is SNCM447 (NI- (10,000 ~ 13,000Ton) and high tensile strength (tensile strength, tensile strength, tensile strength, tensile strength, tensile strength, etc.) Repeated action of impact load and improved shock resistance, toughness and elongation even under conditions of use accompanied by high temperature, limiting the surface of the step plate to peeling or partial corrosion and abrasion even with repetitive pressing force and impact load , The welded structure changes into martensite structure due to rapid quenching after buttering welding, and the welded structure is hardened to prevent cracks from falling out in the form of chips It said, there is an effect that it is possible to prevent the iron oxide produced by the rapid oxidation of the surface of the step plate (Step Plate).

The austenitic weld material (first layer) mainly composed of manganese, chromium and nickel applied to one surface of the step plate (body 141a) has the stability of the welded portion heat affected portion structure (Body 141a) of the step plate in consideration of the use conditions of the step plate, which plays a role of preventing corrosion and securing physical properties of high hardness but requiring extreme shock resistance, Molybdenum (Mo), chromium (Cr), nickel (Ni), manganese (Mn), silicon (Si), vanadium (V), tungsten (Second layer) of Austenite welding material (W) and cobalt (Co) which have greatly improved impact resistance, hardness and abrasion resistance. Step Plate prevents the surface from being peeled, corroded, abraded or oxidized, and the first layer (141b) 141a and the second layer 141c.

In addition, excessive wear, peeling and erosion of the step plate may prevent the deterioration of the quality of the hot rolled material and the degradation of the production capacity, and it may be possible to prevent a step plate from being newly purchased or replaced Time, and cost, thereby contributing to productivity improvement and cost reduction.

The various and advantageous advantages and effects of the present invention are not limited to the above description, and can be more easily understood in the course of describing a specific embodiment of the present invention.

1 is an image showing a conventional step plate,
FIG. 2 is an enlarged view of FIG. 1,
3 is an exemplary view schematically showing a rolling apparatus including a step plate according to an embodiment of the present invention,
4 is an enlarged view of an enlarged enlarged view of the inner cut surface of the region of FIG. 3;

The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated and described in the drawings. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terms including ordinal, such as second, first, etc., may be used to describe various elements, but the elements are not limited to these terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the second component may be referred to as a first component, and similarly, the first component may also be referred to as a second component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings, wherein like or corresponding elements are denoted by the same reference numerals, and redundant description thereof will be omitted.

FIG. 3 is an exemplary view schematically showing a rolling apparatus including a step plate according to an embodiment of the present invention, and FIG. 4 is an enlarged view of an enlarged inside sectional view of the region of FIG.

First, referring to FIG. 3, a rolling apparatus including a step plate according to an embodiment will be schematically described.

The rolling apparatus 100 may include a housing part 130, a work roll 110, a backup roll 120, and a height adjusting part 140.

The housing part 130 is a member in which the backup roll 120 and the work roll 110 are rotatably installed. The housing part 130 may have an opening 131 at an inner side thereof and the backup roll 120 and the work roll 110 may be installed at the opening part 131. In addition, the housing part 130 may have a bar-like shape having an opening 131 on the inner side. The housing part 130 may include a bolt part 135 on the outer side thereof to fix the housing part 130 to the outside, for example, a supporting member of an external device, a paper surface, or the like.

The work rolls 110 can be implemented in pairs so that the pressurized strips 200 can pass between them and be rolled. The work roll 110 may be rotatably installed in the opening portion 131 of the housing portion 130 and may be connected to the housing portion 130 through the work roll chock 111 (bearing box).

The backup roll 120 may be implemented to support the outside of the work roll 110. That is, the backup roll 120 is located on the opposite side of the work roll 110 in the direction in which the workpieces 200 pass, preventing the work roll 110 from being excessively bent by the reaction force of the workpieces 200 can do. The backup roll 120 may be installed in the opening 131 of the housing part 130 as a pair on the outside of the work roll 110 so as to correspond to the pair of the work rolls 110. Also, the backup roll 120 may be rotatably installed in the housing part 130 through the backup roll chocks 121.

In addition, a height adjusting unit 140 for adjusting the height of at least one backup roll 120 to impart a desired reduction amount to the rolled material 200, and a hydraulic pusher 140 capable of minimizing variations in the rolling force during rolling Can be installed in the housing part (130).

The height adjusting unit 140 may include a step plate 141 and a moving unit 145 for moving the step plate 141.

The step plate 141 may include a plurality of step surfaces 143 connecting the support regions 142 and the plurality of support regions 142 having different heights. Here, the step plate 141 may have the same shape as a step, for example, and may have a plurality of horizontal support areas 142 and a vertical stepped surface 143 connecting them.

At this time, the backup roll 120 may be directly supported in any one of the plurality of support areas 142 on the step plate 141, or may be supported via a separate pressure block 150. [ Hereinafter, the backup roll chock 121 of the backup roll 120 will be described as being supported in the support region 142 through the pressure block 150 for convenience of explanation, but the present invention is not limited thereto. The backup roll chocks 121 may be provided on both sides of the backup roll 120 and may be supported through a pair of pressure blocks 150. In this case, the step rollers 141 are also provided in pairs Each pressure block 150 can be supported.

Since the step plate 141 has a plurality of support regions 142 having different heights from each other, the height of the backup roll 120 varies depending on which support region 142 the backup roll chocks 121 are supported . For example, when the backup roll chock 121 is supported in the low support region 142a as shown in FIG. 2, the height of the backup roll 120 may be relatively low and the backup roll chock 121 may be supported in the high support region 142b, the height of the backup roll 120 may be relatively high. At this time, if the height of the backup roll 120 is adjusted, the height of the work roll 110 in contact with the backup roll 120 may be changed. Therefore, even if the rolling apparatus 100 is continuously used at the initial position and the work roll 110 is worn and the diameter becomes small as shown in FIG. 3, the step plate 141 is moved to the moving unit 145 to the position shown in FIG. So that the height of the backup roll 120 can be adjusted so that the pair of work rolls 110 come close to each other. Therefore, the width of the pass line, which is the space between the work rolls 110 through which the pressurized sheet 200 passes, can be easily maintained through a relatively simple structure.

At this time, for example, a motor or the like may be used as the moving unit 145. In this case, the pair of step plates 141 are connected to one moving part 145, but the present invention is not limited to this, and the independent moving parts 145 may be connected to the respective step plates 141 It will be possible.

The height adjustment unit 140 may be installed on only one side of the backup roll 120 so as to adjust the height of the backup roll 120 or may be provided on both sides to adjust the height of the pair of backup rolls 120 It is possible. In this case, when the height adjusting units 140 are implemented as a pair, pass line adjustment of the rolling apparatus 100 is performed by applying a value obtained by dividing the difference between the initial maximum diameter and the present maximum diameter of the work roll 110 by 2, The support area 142 in which the pressure block 150 is supported may be changed.

4, the step plate according to an embodiment of the present invention includes a body 141a, a first layer 141b, a second layer 141c, and a second layer 141c, which is an outermost layer, Directly accept impact, high load, friction, high temperature and corrosive environment during hot rolling.

The body 141a contains, by weight%, 0.44 to 0.50% of C, 0.15 to 0.35% of Si, 0.80 to 1.2% of Mn, 0.03% or less of P, 0.03% or less of S, 1.60 to 2.00% : A backup roll of a back-up roll which is composed of carbon steel containing 0.6 to 1.0% and Mo: 0.15 to 0.30%, and which is assembled and driven in a hot plate rolling stand and supports a rolling roll; And is connected to a choke (Back Up Roll Chock). Depending on the width of the hot-rolled plate, left and right portions of the plate are coupled to the connecting shaft of the control device. The width of the step plate is controlled by hydraulic, Rolled steel sheet joined together vertically to the rolling direction of the steel sheet and operating organically according to the set width of the hot-rolled steel sheet.

At this time, the body 141a heightens the height of the step plate 141 composed of a stepped plate.

At this time, the body 141a is made of NI-Cr-Mo steel, which is a carbon steel having a carbon content of 0.44-0.50% and is made of carbon steel composed of chemical components of Si, Mn, P, S, Ni, Cr, have.

Carbon (C) is preferably limited to 0.44% to 0.50% or less in order to suppress compound formation due to a chemical reaction and to maintain a constant hardness of the buttering welding layer.

The body 141a is an SNCM 447 (NI-Cr-Mo steel) having a carbon content of 0.44 to 0.50% and a high carbon steel content of 0.15-0.35% Si, 0.80% Of carbon, 0.1-2.0% of P, 0.03% or less of S, 0.03% or less of S, 1.60-2.00% of Ni, 0.6-1.0% of Cr and 0.15-0.30% of Mo.

The first layer 141b may be disposed to cover the upper surface or the entire surface of the upper portion of the body 141a.

The first layer 141b contains 0.10% by weight of carbon (C), 0.69% by weight of silicon (Si), 6.0% by weight of manganese (Mn), 19.5% by weight of chromium (Cr) A small amount of boron (B) in PPM is added in an amount of 8.9 wt%, molybdenum (Mo), vanadium (V), tungsten (W), cobalt (Co), niobium (Nb) And may be an austenitic age-hardening material containing iron (Fe) as a base material.

That is, the first layer 141b is positioned between the body 141a and the second layer 141c and is formed to surround the surface of the body 141a.

The first layer 141b stabilizes the structure of the buttering weld portion with the metal structure of the body 141a to absorb the high load and impact load transmitted to the buttering weld layer of the second layer 141c, As shown in Fig.

The first layer 141b serves as an intermediate material of the buttering welding material. The first layer 141b has a thickness (T1) of the buttering layer of at least a minimum value such that corrosion, abrasion, and local peeling do not occur even with repetitive impact, thermal stress, friction, Preferably 8 to 10 mm or more, and is preferably formed in a range of 10 mm to 15 mm, and is preferably made of a material having corrosion resistance, high ductility, and age hardenability.

The first layer 141b of high toughness, high impact absorbing property and high ductility is welded to the surface of the step plate of the body 141a during buttering welding for surface hardening of the step plate, (HAZ) of the second layer 141c are hardened and a portion of the buttering layer changes into a martensite structure during use to generate cracks and peel off in the form of a piece to serve as secondary quality and facility defects .

The second layer 141c may be arranged to cover the upper surface or the entire surface at the upper portion of the first layer 141b.

The second layer 141c includes 0.13% by weight of carbon (C), 1.2% by weight of manganese (Mn), 0.72% by weight of silicon (Si), 19.30% by weight of chromium (Cr) (V), tungsten (W), cobalt (Co), niobium (Nb) + nitrogen (N) + titanium (Ti) in an amount of 9-20% by weight, molybdenum It may be an austenitic age-hardening material containing iron (Fe) added as a base material in PPM units.

That is, the second layer 141c is located outside the first layer 141b and is formed to surround the surface of the first layer 141b.

The second layer 141c stabilizes the structure of the buttering weld portion with the metal structure of the first layer 141b and the first layer 141b has a hardness gradient between the body 141a and the first layer 141b and the second layer 141c, The layer 141b, the body 141a, and the second layer 141c are formed in this order so as to maximize the impact resistance and the abrasion resistance.

The second layer 141c has a role of greatly increasing the hardness (HRC 50 to HRC 53), and the step plate surface is peeled off or abraded due to repetitive pressing load, impact, thermal stress, friction, It is preferable that it is made of a material having corrosion resistance, hardness and age hardening property so as not to be abraded or corroded.

The second layer 141c having a high hardness is formed on the surface 142 of the step plate of the first layer 141b and the surface 142 of the first layer 141b during the buttering welding for surface hardening of the step plate, (HAZ) is hardened and a portion of the buttering layer is changed into a martensite structure during use, so that cracks are generated, T2 is formed to be at least 8 to 10 mm or more, and is preferably formed in the range of 10 to 15 mm.

Therefore, in the embodiment of the present invention, the material of the inner surface of the step plate, the hardness and the high ductility of the surface of the step plate is formed into a plate shape, and a hole and a thread are formed at regular intervals on the surface of the step plate In case of using bolts or the like, when the bolts are broken due to repetitive action such as repeated strong impact, push-down load, high heat, friction, etc., the entire plate is dropped and collides with the rolling roll, It can serve as a factor of facility accidents.

In addition, when the step plate is stepped with a stainless steel material, which is corrosion resistant, buttering is applied to the surface of the step plate, corrosion and erosion due to impact, high load and the like are secured. The surface texture of the step plate is easily worn away due to impact and friction, and the setting gap of the hot rolling roll is abnormally separated due to the reduction of the step plate, thereby causing serious quality defects such as poor thickness of the hot rolled plate It is preferable to restrict the use of the drug.

Chromium (Cr) among the components of the weld material of the first layer 141b is an important element for strengthening the corrosion resistance. However, when added in a large amount, there is a problem that the high-temperature strength is reduced and the hot workability is impaired at a high temperature, and the elongation can be lowered. If the addition amount of chromium is less than 14%, the effect of the high-temperature oxidation characteristic is insignificant, whereas if it exceeds 20%, the high-temperature strength and elongation are decreased and the hot workability is impaired. Therefore, the addition amount of chromium in the buttering welding material of the first layer 141b is limited within a range of 16 to 20%, preferably limited to 19.5%.

On the other hand, in order to increase the strength and hardness of the weld material of the second layer 141c, chromium (Cr) is required to be about 19.3% by weight and manganese (Mn) about 7.0% by weight.

On the other hand, the carbon (C) of the welding material composition of the second layer (141c) is a first view of the welding material composition of the first layer (141b) to prevent cracking of beoteoring layer due to the formation of chromium carbide (Cr ₂₃ C ₆₎ 0.13% by weight is required.

Silicon (Si) is a very effective element for improving the high-temperature oxidation characteristics as the addition amount is increased, and also remarkably reduces high-temperature strength and phase stability (grain growth resistance). In the embodiment of the present invention, silicon is added at a level of at least about 0.4% to limit sag resistance, phase stability, high-temperature oxidation characteristics and elongation, and to suppress a sharp decrease in elongation, Is limited to 0.8%.

On the other hand, manganese (Mn) is advantageous in terms of sag resistance, high temperature oxidation resistance, and phase stability as the addition amount is increased, but it is an element that decreases the elongation and moldability when added in excess. That is, in the embodiment of the present invention, manganese is added in an amount of 6.0 to 7.0% so as to improve the age hardening property, sag resistance, high temperature oxidation resistance and phase stability, but if it exceeds 8.0% , The addition amount of manganese is limited to 4.5 to 7.5%, preferably to 7.0%.

On the other hand, manganese (Mn) in the weld material component of the second layer 141c is required to be not less than 7.0% in order to improve abrasion resistance through hardness improvement.

The weld material of the second layer 141c is preferably such that the weld material component of the first layer 141b stabilizes the metal structure of the heat affected zone of the welded portion and has a Mo content of 0.9% or more for improving impact resistance, strength, hardness, heat resistance, A small amount of niobium (Nb + N + Ti), vanadium (V), tungsten (W) and cobalt (Co) is added and boron (B) is added in PPM units.

The following Table 1 is a table showing the chemical composition of conventional comparative steels in comparison to the first layer 141b and the second layer 141c. Table 2 shows the impact toughness, abrasion resistance, hardness and elongation Table.

(Unit: wt%)

The first layer 141b contains 0.10% of carbon (C), 0.69% of silicon (Si), 6.0% of manganese (Mn), 19.5% of chromium (Cr), 8.9% of nickel (Ni) Austenitic material containing a trace amount of Mo and Nb + N + Ti and having boron (B) added in PPM units and the balance of iron (Fe) as a material of the first layer 141b It is confirmed that not only the corrosion is small, but also the high temperature, impact, hardness under impact, impact toughness, corrosion resistance and abrasion resistance are good.

In particular, the first layer (141b) is impact toughness of at least 55 (J / cm ²⁾ or more, elongation is followed by at least 38%, the body the body (141a) between the (141a) and the second layer (141c) and And has a buffering effect according to the hardness change of the second layer 141c.

In addition, the second layer 141c is composed of 0.13% of carbon (C), a small amount of niobium (Nb + N + Ti), 7.0% of manganese (Mn), 7.2% (Fe), the remaining amount of which is iron (Fe), in which the amount of iron (Fe) is 19.30%, the content of nickel (Ni) is 9.20%, the content of vanadium It is confirmed that the impact-type toughness, the corrosion resistance, the hardness, and the wear resistance are very good as a knight-based material as a whole.

Particularly, the second layer 141c has a Rockwell hardness of at least 50 HRc or more, so that the impact on the surface of the step plate, the impact on one surface of the step plate, It is possible to suppress peeling of the surface hardened layer caused by the surface hardening layer.

On the other hand, in Comparative Example 1, 0.07% of carbon (C), 0.3% of silicon (Si), 1.9% of manganese (Mn), 21% of chromium (Cr) and 6.4% of nickel And the balance of iron (Fe) is an austenitic material having a high content of chromium, which shows good corrosion resistance but low impact resistance and abrasion resistance.

On the other hand, in Comparative Example 2, 0.14% of carbon (C), 0.2% of silicon (Si), 1.5% of manganese (Mn), 12.5% of chromium (Cr) and 5.9% of nickel (Fe), and the content of chromium is relatively low. As a result, it is confirmed that the corrosion resistance is lowered and the impact resistance, abrasion resistance and hardness are poor.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims It can be understood that

Claims (12)

A step plate having a plurality of height adjustment surfaces opposed to a rolling roller for adjusting a gap between the rolling rollers,
A body formed in multiple stages;
A first layer disposed on top of the body; And
And a second layer disposed over the first layer,
Wherein the body comprises, by weight, 0.44 to 0.50% of C, 0.15 to 0.35% of Si, 0.80 to 1.2% of Mn, 0.03% or less of P, 0.03% or less of S, 1.60 to 2.00% To 1.0% and Mo: 0.15 to 0.30%
Wherein the first layer contains 0.1% of C, 0.69% of Si, 6.0% of Mn, 8.9% of Ni, and 19.5% of Cr, the balance being austenite, the balance being Fe and other impurities Based curable material,
Wherein the second layer contains 0.13% of C, 0.72% of Si, 1.2% of Mn, 9.2% of Ni, 19.3% of Cr and 0.9% of Mo and the balance of iron (Fe) An austenitic age-hardening material comprising an impurity,
Wherein the hardness of the body, the first layer, and the second layer satisfy the following relational expression (1).
[Relation 1]
First Layer <Body <Second Layer
delete delete The method according to claim 1,
Wherein the at least one or all of Mo, V, W, Co, Nb, N, Ti and B is added in a small amount to the other impurities in the first layer.
delete The method according to claim 1,
Wherein at least any one or both of V, W, Co, Nb, N, Ti, and B is added in a small amount to the other impurities in the second layer.
The method according to claim 6,
The second layer
A Rockwell hardness of at least 50 HRc.
The method according to claim 1,
Wherein the thickness of the first layer is 10 to 15 mm.
The method according to claim 1,
And the thickness of the second layer is 10 to 15 mm.
The method according to claim 1,
Wherein the thickness of the second layer is 0.6 to 1.5 times the thickness of the first layer.
5. The method of claim 4,
The first layer
A step plate having an elongation of at least 38%.
12. The method of claim 11,
A step plate having an impact toughness of at least 55 (J / cm ² ).

Images