MX2013000031A

MX2013000031A - Abrasion-resistant steel plate or sheet with excellent weld toughness and delayed fracture resistance.

Info

Publication number: MX2013000031A
Application number: MX2013000031A
Authority: MX
Inventors: Shinichi Suzuki; Keiji Ueda
Original assignee: Jfe Steel Corp
Priority date: 2010-06-30
Filing date: 2011-06-29
Publication date: 2013-02-01
Also published as: EP2589676A4; MX354630B; JP2012031510A; CA2801703A1; EP2589676B1; EP2589676A1; KR20130045900A; WO2012002567A1; JP5866820B2; RU2013103814A; US20130216422A1; AU2011272188B2; CN102959113A; CA2801703C; RU2550985C2; AU2011272188C1

Abstract

Provided is an abrasion-resistant steel plate or sheet which exhibits excellent weld toughness and excellent delayed fracture resistance and is thus suitable for construction machines, industrial machines, and so on. Specifically provided is a steel plate or sheet which contains, in mass%, 0.20 to 0.30% of C, 0.05 to 1.0% of Si, 0.40 to 1.2% of Mn, 0.010% or less of P, 0.005% or less of S, 0.40 to 1.5% of Cr, 0.005 to 0.025% of Nb, 0.005 to 0.03% of Ti, 0.1% or less of Al, 0.01% or less of N, and, as necessary, one or more of Mo, W, B, Cu, Ni, V, REM, Ca and Mg, and has a DI* of 45 to 180 while satisfying the relationship: C+Mn/4-Cr/3+10Pà 0.47, and which has a microstructure that comprises martensite as the matrix phase. DI*=33.85Ã (0.1Ã C)<sup>0.5</sup>Ã (0.7Ã Si+1)Ã (3.33Ã Mn+1)Ã ( 0.35Ã Cu+1)Ã (0.36Ã Ni+1)Ã (2.16Ã Cr+1)Ã (3Ã Mo+1)Ã (1.75Ã V+1)Ã (1.5Ã W+1).

Description

ABRASION-RESISTANT STEEL PLATE OR PLATE WITH EXCELLENT WELDING STRENGTH AND DELAYED FRACTURE RESISTANCE TECHNICAL FIELD The present invention relates to an abrasion-resistant steel plate or steel plate having a plate thickness of 4 mm or more preferably used in construction machines, industrial machines, shipbuilding, steel pipe, civil engineering, architecture or the like, and more particularly with an abrasion-resistant steel plate or steel plate showing excellent welding tenacity and excellent resistance to delayed fracture.

ANTECEDENTS OF THE TECHNIQUE When a hot-rolled steel plate is used to manufacture steel structural products, machines, devices or the like, construction machines, industrial machines, shipbuilding, steel pipes, civil engineering, architecture or the like, there may be a case where requires that the steel plates have a property resistant to abrasion. Conventionally, to impart an excellent abrasion-resistant property to a steel material, the hardness in general is increased, and the hardness of the steel material can be markedly improved by obtaining the steel material in the microstructure of the simple phase of the steel. martensite. The increase of a quantity of carbon in solid solution is also effective to improve the hardness of the martensite microstructure as such.

Accordingly, the abrasion-resistant steel plate shows a high susceptibility to cold cracking so that the steel plate shows a lower toughness than welding in general, so when the steel plate resistant to abrasion is used to obtain The welded steel structure, in general, the abrasion-resistant steel plate is laminated to a surface of a steel member which is brought into contact with the rock, soil and sand or the like as a coating. For example, with respect to a container of a cushioned engine truck, a case has been known where the container is assembled by welding using mild steel and, after this, an abrasion-resistant steel plate is laminated on only one surface front of the container which is put in contact with the earth and the sand.

However, in the manufacturing method in which the abrasion-resistant steel plate is laminated to the welded steel structure after the welded steel structure has been assembled, the labor for manufacturing and the cost of Manufacturing increases. Accordingly, there has been a demand for an abrasion resistant steel plate that can be used as a strength member of the welded steel structure.

Patent document 1 relates to an abrasion-resistant steel plate that exhibits excellent resistance to delayed fracture and a method for manufacturing the abrasion-resistant steel plate. In the patent document 1, the description says that, in order to improve the resistance to delayed fracture, the steel further contains one, two or more component types selected from a group consisting of Cu, V, Ti, B and Ca in the composition of a type containing low Si content, low P content, low S, Cr, Mo and Nb content undergoes direct quenching (after this also referred to as DQ), and is tempered when necessary .

Patent document 2 relates to a plate having a high abrasion resistant property and a method for manufacturing a steel product. In the patent document 2, steel is described which has the composition composed of a system of 0.24 to 0.3C-N, Cr, Mo, B, complies with a formula parameter consisting of contents of these elements, and includes martensite which it contains from 5 to 15% by volume of austenite or martensite structure and bainite structure in this way improving the abrasion-resistant property. Patent document 2 also discloses that the steel having the aforementioned components is cooled to a cooling rate of 1 ° C / sec or more at a temperature between an austenite temperature and 450 ° C.

The patent document 3 is ·. It relates to an abrasion-resistant steel material that exhibits excellent toughness and excellent resistance to delayed fracture and a method to manufacture the abrasion-resistant steel material. In the patent document 3, a steel material having the composition containing Cr, Ti and B as indispensable components is described, wherein a surface layer is formed of tempered martensite, an internal part is formed of tempered martensite and structure with a low content of tempered bainite, and an aspect ratio of pre-austenite grain diameter between the direction of wall thickness and the direction of rolling, is defined. The patent document 3 also discloses that the steel having the content composition is subjected to hot rolling at a temperature of 900 ° C or less and in a cumulative reduction ratio of 50% or more and, after that, Cool directly and temper.

Patent document 4 relates to an abrasion-resistant steel material which exhibits excellent toughness and excellent resistance to delayed fracture and a method for manufacturing the abrasion-resistant steel material. In the patent document 4, a steel material having the composition containing Cr, Ti and B as an indispensable component is described, wherein a surface layer is formed of martensite and an internal part is formed of the mixed structure of martensite and the structure with low bainite content or low-bainite single-phase structure, and an elongation ratio of the previous austenite grains expressed by an aspect ratio between the pre-austenite grain diameter and a central portion of Plate thickness and pre-austenite grain diameter in the rolling direction is defined. The document of 4 also discloses that the steel having the composition is subjected to hot rolling at a temperature of 900 ° C or less and in a cumulative reduction ratio of 50% or more and, after that, it is suddenly cooled off. direct way Patent document 5 relates to abrasion-resistant steel which exhibits excellent welding capacity, excellent abrasion-resistant property and excellent corrosion resistance, and a method for manufacturing abrasion-resistant steel. Patent document 5 discloses a steel containing from 4 to 9% by mass of Cr as an indispensable element, containing one or two types of Cu and Ni and complying with a formula parameter consisting of content of specific components. The patent document 5 also discloses that the steel having the composition is subjected to hot rolling at a temperature of 950 ° C or less and at a cumulative reduction ratio of 30% or more and, after this, the steel is reheated at a temperature of Ac3 or more and it cools sharply.

LITERATURE OF THE PREVIOUS TECHNIQUE [Patent Document] [Patent Document 1] JP-A-5-51691 [Patent Document 2] JP-A-8-295990 [Patent Document 3] JP-A-2002-115024 [Patent Document 4] JP-A-2002-80930 [Patent Document 5] JP-A-2004-162120 THE INVENTION [Task to be Resolved by Invention] The most serious problem with respect to the reduction of tenacity when welding a steel material is the deterioration of toughness in a bond area of a fusion line. In abrasion resistant steel having a martensite structure in an abruptly cooled state, the deterioration of toughness which is termed as brittleness by tempering at low temperature also arises as a problem in an area affected by welding heat (after this also denominated as HAZ) reheated to a temperature around 300 ° C that is far from the fusion line. It is thought that the brittleness by tempering at low temperature is carried out by a synergistic action between a change of carbide morphology in the martensite and the intergranular segregation of impure or similar elements.

In a region in which it is reheated to a temperature of brittleness by tempering at low temperature, the hydrogen that invades a weld from a protective gas at the time of welding and a residual stress generated by heat from the weld overlap each other so that delayed fracture is possible (cracks that occur in welding are called cracks due to low temperature in general) and, particularly, it is possible that delayed fracture occurs in an abrasion resistant steel that has high strength.

Therefore, when applying an abrasion-resistant steel plate to a strength member of a welded structure, it is necessary to improve the toughness of the bonding area and the affected area by heat of welded overheated at a temperature around 300 ° C which It is far from a fusion line. However, in the conventional abrasion resistant steel plate, the susceptibility to cold cracking of the weld is high and therefore, to avoid cold cracks, it is necessary to discharge the hydrogen into the steel plate and reduce a stress Residual on the plate when performing treatments such as preheating and post-heating before and after welding.

Patent documents 1 and 2 do not describe the improvement of welding toughness in the. abrasion-resistant steel plate, and patent documents 3 and 4 also do not define the microstructure that has as its objective the improvement of tenacity of a base material. Although the patent document 5 studies the welding capacity and the abrasion-resistant property of a weld, the study is not aimed at improving the welding toughness. That is, the abrasion resistant steels proposed in patent documents 1 to 5 and the like are less than optimal with respect to the improvement in welding toughness and resistance to delayed fracture.

Accordingly, it is an object of the present invention to provide an abrasion-resistant steel plate that exhibits excellent welding toughness and excellent resistance to delayed fracture without inducing reduction of productivity at a manufacturing cost. In the present invention, the welding tenacity means toughness of a zone affected by welding heat, and the excellent welding toughness means in particular that the toughness is excellent in a bonding area and an area of brittleness temperature by tempering at low temperature .

MEANS TO SOLVE THE PROBLEM.

To achieve the aforementioned objective, the invention has made complete studies on several factors that determine the chemical components of a steel plate, a method for manufacturing the steel plate and the microstructure of the steel plate to ensure a welding toughness and resistance to delayed fracture with respect to abrasion-resistant steel plate, and has made the following findings. 1. To ensure an excellent property resistant to abrasion, it is indispensable to form the base microstructure or the main microstructure of the steel plate in martensite. For this purpose, it is important to strictly control the chemical composition of the steel plate thereby ensuring the property of abrupt cooling. 2. In order to achieve excellent welding toughness, it is necessary to prevent grain particles from becoming thick in the bonding area, and for this purpose, it is effective to make use of a rotating effect by dispersing the fine precipitates in the steel plate. 3. To ensure excellent toughness and to suppress the delayed fracture in an area of brittleness temperature by tempering at low temperature of the affected area by welded heat, it is important to adequately control the amounts of alloying elements such as C, Mn, Cr, P .

The present invention has been made by further studying the aforementioned findings. That is, the present invention is directed to: 1. A. abrasion-resistant steel plate that has excellent welding tenacity and excellent resistance to delayed fracture, and has a composition containing% by mass 0.20 to 0.30% C, 0.05 to 1.0% Si, 0.40 to 1.2% of Mn, 0.010% or less of P, 0.005% or less of S, 0.40 to 1.5% of Cr, 0.005 to 0.025% of Nb, 0.005 to 0.03% of Ti, 0.1% or less of Al, 0.01% or less of N, and Fe and the rest of unavoidable impurities where the index of hardening DI * (1) is 45 or more, and a base phase of the microstructure is formed of martensite.

Di * = 33.85 x (O.lxC) 0-5 x (0.7xSi + l) x (3.33xMn + l) x (0.35xCu + l) x (0.36xNi + l) x (2.16xCr + l) x ( 3xMo + l) x (1.75xV + l) x 1.5xW + l) (1), wherein the respective element symbols are contained (% by mass) of the elements. 2. The abrasion-resistant steel plate having excellent weld tenacity and excellent resistance to delayed fracture described in 1, wherein the steel composition additionally contains% by mass one, two or more types of components selected from a group that It consists of 0.05 to 1.0% of Mo, 0.05 to 1.0% of W, and 0.0003% to 0.0030% of B. 3. The abrasion-resistant steel plate having excellent weld tenacity and excellent resistance to delayed fracture described in 1 or 2, wherein the steel composition additionally contains in mass% one, two or more types of components selected from a group consisting of 1.5% or less of Cu, 2.0% or less of Ni, and 0.1% or less of V.

. The abrasion-resistant steel plate having excellent welding tenacity and excellent resistance to delayed fracture described in any of 1 to 3, wherein the steel composition also contains% by mass, one, two or more types of selected components of a group consisting of 0.008% or less of REM, 0.005% or less of Ca, and 0.005% or less of Mg. 5. The abrasion-resistant steel plate having excellent weld tenacity and excellent resistance to delayed fracture described in any of 1 to 4, wherein the hardness of the surface of the steel plate is 400 HBW10 / 3000 or more in Brinell hardness. 6. The abrasion-resistant steel plate having excellent welding tenacity and excellent resistance to delayed fracture described in any of 1 to 5, wherein the index of hardening DI * is 180 or less. 7. The abrasion-resistant steel plate having excellent welding tenacity and excellent resistance to delayed fracture described in any of 1 to 6, wherein the steel plate complies with the following formula (2), C + Mn / 4-Cr / 3 + 10P < 0.47 (2), wherein the respective element symbols are contained (% by mass) of the elements.

Advantage of the Invention According to the present invention, it is possible to acquire the abrasion-resistant steel plate having excellent welding toughness and excellent resistance to delayed fracture. The present invention contributes greatly to the improvement of manufacturing efficiency and safety at the time of manufacturing a steel structure which acquires an industrially remarkable effect in this way.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a view to explain a cracking test by T-shaped angle welding.

Figure 2 is a view showing a position where a Charpy impact test piece is taken from a weld.

MODE FOR CARRYING OUT THE INVENTION The present invention defines the composition and the microstructure.

Composition In the explanation given above,% indicates% by mass. C: 0.20 to 0.30%.

C is an important element to increase the hardness of the martensite and to allow the steel plate to secure property. resistant to abrasion. It is necessary that the steel plate contains 0.20% or more of C to acquire such effects. On the other hand, when the C content exceeds 0.30%, not only the welding capacity deteriorates but also the tenacity of a bond area and toughness of a tempered region at low temperature deteriorate. Therefore, the content of C is limited to a value which falls within a range of 0.20 to 0.30%. The C content of preference is limited to a value that falls within a range of 0.20 to 0.28%.

Yes: 0.05 to 1.0% If it acts as a deoxidizing agent, and not only if it is necessary for the manufacture of steel but also if it has an effect of increasing the hardness of a steel plate by a reinforcement by solid solution where Si is present in the steel in a state of solid solution. In addition, if it has an effect of suppressing the deterioration of the tenacity in an area of fragility by tempering of a zone affected by heat of welding. It is necessary that the steel plate contains 0.05% or more of Si to acquire such effect. On the other hand, when the content of Si exceeds 1.0%, the tenacity of the area affected by welding heat deteriorates markedly. Therefore, the content of Si is limited to a value that falls within a range of 0.05% to 1.0%. The content of Si is preferably limited to a value that falls within a range of 0.07 to 0.5%.

Mn: 0.40. to 1.2% Mn has an effect of increasing the hardness of the steel, and it is necessary that the steel plate contains 0.40% or more of Mn to ensure hardness of a base material. On the other hand, when the Mn content exceeds 1.2%, not only the tenacity, ductility and welding capacity of the base material deteriorate, but also an intergranular segregation of P accelerates in this way accelerating the generation of delayed fracture. Therefore, the content of Mn is limited to a value that falls within a range of 0.40 to 1.2%. The Mn content is preferably limited to a value that falls within a range of 0.40 to 1.1% P: 0.010% or less When the content of P exceeds 0.010%, P is segregated in a grain limit, segregated P becomes a point of beginning of delayed fracture, and deteriorates the tenacity of a zone affected by welding heat. Therefore, an upper limit of the content of P is set at 0.010% and it is desirable that the content of P be set as little as possible. Since the excessive reduction of P raises the retention cost and becomes economically disadvantageous, the content of P is desirably set at 0.002% or more.

S: 0.005% or less S deteriorates the toughness at low temperature and the ductility of a base material and therefore, the content of S is desirably set to little with an allowable upper limit of 0.005%.

Cr: 0.40 to 1.5% Cr is an important alloying element in the present invention, and has an effect of increasing the hardness of the steel and also has an effect of suppressing the deterioration of the toughness in the brittleness area by tempering the affected area by welding heat. This is because the inclusion of Cr delays the diffusion of C in the steel plate and therefore, when the steel plate overheats in a region of temperature where fragility occurs by tempering at low temperature, the change in the morphology of the carbide in martensite can be suppressed. It is necessary that the steel plate contains 0.40% or more of Cr to acquire such effect. On the other hand, when the steel content exceeds 1.5%, the effect is saturated so that not only becomes economically disadvantageous but also the welding capacity is reduced. Therefore, the Cr content is limited to a value that falls within a range of 0.40 to 1.5%. The content of Cr is preferably limited to a value that falls within a range of 0.40 to 1.2%.

Nb: 0.005% to 0.025% Nb is an important element that has an effect of improving the tenacity of the area affected by welding heat and an effect of suppressing the appearance of delayed fracture by thinning the microstructure of the base material and the area affected by heat of welding. cause precipitation of the carbonitride and also when fixing the solid solution N. It is necessary that the steel plate contains 0.0050% or more of Nb to acquire such effects. On the other hand, when the Nb content exceeds 0.025% coarser carbonitride precipitates and there may be a case where thick carbonitride becomes a point of fracture initiation. Therefore, the content of Nb is limited to a value that falls within a range of 0.005% to 0.025%. The Nb content of preference is limited to a value that falls within a range of 0.007 to 0.023%.

Ti: 0.005 to 0.03% Ti has an effect of preventing the grains in the bonding area from becoming thick when forming TiN due to the fixation of the solid solution N and also having an effect of preventing the deterioration of the toughness and the appearance of the delayed fracture in the Temperature region by tempering at low temperature due to the decrease of the solid solution N. It is necessary that the steel plate contains 0.005% or more Ti to acquire such effects. On the other hand, when the content of Ti exceeds 0.03%, TiC is precipitated so that the tenacity of the base material deteriorates. Therefore, the content of Ti is limited to a value that falls within a range of 0.005 to 0.03%. The content of Ti is preferably limited to a value that falls within a range of 0.007 to 0.025%.

Al: 0.1% or less Al acts as a deoxidizing agent and is used more particularly in a process of deoxidation of molten steel from a steel plate. In addition, by forming A1N by fixing the solid solution N in steel, Al has an effect of preventing the grains in a bonding area from becoming thick and an effect of preventing the deterioration of toughness and the appearance of delayed fracture in a region of tempering temperature at low temperature due to the reduction of solid solution N. On the other hand, when the content of Al exceeds 0.1%, Al is mixed in welding metal at the time of welding in this way deteriorating the tenacity of the weld metal. Therefore, the content of Al is limited to 0.1% or less. The content of Al is preferably limited to a value that falls within a range of 0.01 to 0.07%.

N: 0.01% or less N forms a nitride with Nb or Ti, and has an effect that prevents the grains of the area affected by welding heat from becoming thick. However, when the content of N exceeds 0.01%, the tenacity of a base material and the weld tenacity is markedly reduced and therefore, the N content is limited to 0.01% or less. The content of N of preference is limited to a value that falls within a range of 0.0010 to 0.0070%. The rest is Faith and unavoidable impurities.

In accordance with the present invention, in order to further improve the properties of the steel plate, in addition to the aforementioned basic component system, the steel plate may contain one, two or more types of components selected from a group consisting of Mo, W, B, Cu, Ni, V, REM, Ca and Mg.

Mo: 0.05 to 1.0% Mo is an effective element to markedly increase the hardness in this way by increasing the hardness of a base material. The content of Mo preferably can be 0.05% or more to acquire such an effect. However, when the Mo content exceeds 1.0%, Mo adversely influences the toughness, ductility and crack resistance of base material. Therefore, the content of Mo is set at 1.0% or less.

W: 0.05 to 1.0% W is an effective element for remarkably increasing the hardness in this way by increasing the hardness of a base material. The content of W preferably can be 0.05% or more to acquire such an effect. However, when the content of W exceeds 1.0%, W adversely influences the toughness, ductility and resistance to weld cracking of the base material. Therefore, the content of W is set at 1.0% or less.

B: 0.0003 to 0.0030% B is an effective element for remarkably increasing the hardness with the addition of a small amount of B in this way by increasing the hardness of a base material. The content of B preferably can be 0.0003% or more to acquire such an effect. However, when the content of B exceeds 0.0030%, B adversely influences the tenacity, ductility and resistance to weld cracking of the base material. Therefore, the content of B is set at 0.0030% or less.

Cu, Ni and V all are elements that contribute to the improvement of steel strength, and the steel plate can contain adequate amounts of Cu, Ni and V depending on the strength required by the steel plate.

Cu: 1.5% or less Cu is an effective element for increasing the hardness of the base material in this way, the content of Cu can preferably be 0.1% or more to acquire such effect. However, when the content of Cu exceeds 1.5%, the effect becomes saturated and Cu causes deterioration by heat thereby deteriorating the property of the surface of a steel plate. Therefore, the Cu content is set at 1.5% or less.

Ni: 2.0% or less Neither is an effective element to increase the hardness in this way by increasing the hardness of the base material, the Ni content can preferably be 0.1% or more to acquire such an effect. However, when the Ni content exceeds 2.0%, the effect becomes saturated in a way that becomes economically disadvantageous. Accordingly, the content of Ni is set at 2.0% or less.

V: 0.1% or less V is an effective element for increasing the hardness in this way by increasing the hardness of the base material, the content of V may preferably be 0.01% or more to acquire such an effect. However, when the content of V exceeds 0.1%, the tenacity and ductility of the base material deteriorates. Therefore, the content of V is set at 0.1% or less.

REM, Ca and g all contribute to the improvement of tenacity, and these elements are selectively added corresponding to the properties desired by the steel plate. When REM is added, the REM content may preferably be 0.002% or more. On the other hand, when the REM content exceeds 0.008%, the effect becomes saturated. Therefore, an upper limit of REM is set at 0.008%.

When Ca is added, the content of Ca may preferably be 0.0005% or more. On the other hand, when the content of Ca exceeds 0.005%, the effect becomes saturated. Therefore, an upper limit of Ca is set at 0.005%.

When Mg is added, the Mg content may preferably be 0.001% or more. On the other hand, when the Mg content exceeds 0.005%, the effect becomes saturated. Therefore, an upper limit of Mg is set at 0.005%. DI * = 33.85 x (O.lxC) 0-5 x (0.7xSi + l) x (3.33xMn + l) x (0.35xCu + l) x (0.36xNi + l) x (2.16xCr + l) x 3xMo + l) x 1.75xV + l) x (1.5xW + l) (1) wherein the respective element symbols are contained (% by mass) of the elements.

This parameter: DI * (hardening index) is defined to form the base structure of the martensite base material in this way imparting an excellent abrasion resistant property to the base structure within the range of the aforementioned composition, and a value of parameter is set to 45 or more. When the value of the parameter is set to less than 45, a depth of abrupt cooling of a surface layer in the thickness direction of the plate becomes less than 10 mm and therefore, a duration of the steel plate as the plate abrasion-resistant steel is shortened.

When the value DI * of the parameter exceeds 180, the base structure of the base material is martensite and therefore, the base structure shows a property resistant to favorable abrasion. However, the property of low temperature cracking at the time of welding and the low temperature welding toughness deteriorate. Accordingly, the value of the parameter DI * of preference is set to 180 or less. The value of the most preferred parameter DI * is set to a value that falls within a range of 50 to 160.

C + Mn / 4-Cr / 3 + 10P < 0.47 (2), where the respective element symbols are contained (% by mass of the elements).

When the basic structure of the base material of the steel plate is formed of martensite and has the composition showing excellent tenacity in the bonding area and the brittleness area by tempering at low temperature when welding is performed, a value of the parameter: C + Mn / 4-Cr / 3 + 10P is set to 0.47 or less within a range of the aforementioned composition. Although the base structure of the base material is maintained in the martensite and exhibits a favorable abrasion-resistant property even when the value of the parameter exceeds 0.47, the weldability deteriorates markedly. The value of the preference parameter can be 0.45 or less.

Microstructure According to the present invention, to improve the abrasion-resistant property, a base phase or a main phase of the microstructure of a steel plate is defined as martensite. The structure such as bainite or ferrite other than martensite reduces the abrasion resistant property and therefore, it is preferable not to mix such a martensite structure as much as possible. However, when a total area ratio of these structures is less than 10%, the influence exerted by these structures can be ignored. In addition, when the surface hardness of the steel plate is less than 400 HBW10 / 3000 in Brinell hardness, a steel plate durability such as abrasion resistant steel shortens. Accordingly, it is desirable to establish the hardness of the surface at 400 HB 10/3000 or more in Brinell hardness.

The microstructure of the bonding area is the mixed structure of martensite and bainite. The structure such as ferrite other than martensite and bainite reduces the abrasion resistant property and therefore, it is preferable not to mix such a structure as much as possible. However, when a total area ratio of these structures is less than 20%, the influence exerted by these structures can be ignored.

In addition, to ensure tenacity of the binding area, it is preferable that the N and Ti carbonitride particles having an average particle size of 1 μ? or less are present in a proportion of 1000 pieces / mm2 or more, an average particle size of prior austenite is less than 200 μp ?, and an average particle size of lower microstructure surrounded by a grain boundary of great inclination that has a radial retention of 15 ° or more is less than 70 μp ?.

The abrasion resistant steel according to the present invention can be manufactured under the following manufacturing conditions. In the explanation given hereinafter, the indication "° C" in relation to temperature means temperature 1/2 position of a plate thickness. It is preferred that a molten steel having the aforementioned composition is produced by a known molten steel production method, and the molten steel is formed into a steel raw material such as a slab having a predetermined size by a coating process. continuous or an ingot / wear method.

Then, the steel raw material obtained is immediately subjected to hot rolling without cooling or subjected to hot rolling after heating to a temperature of 950 to 1250 ° C after cooling, thus forming a steel plate having a desired plate thickness. Immediately after hot rolling, water cooling is performed or abrupt cooling is carried out after reheating. Subsequently, when necessary, the tempering is carried out at a temperature of 300 CC or below.

Modality 1 The steel slabs which were prepared with various compositions shown in Table 1 by means of an acre converter, ladle refining and a continuous casting method were heated to a temperature of 1000 to 1250 ° C and, subsequently, the slabs of steel were subjected to hot rolling under manufacturing conditions shown in Table 2. Water cooling (quenching (QD)) was applied on some steel plates after rolling. With respect to other steel plates, air cooling was performed after rolling, and water cooling (quenching (RQ)) was performed after reheating.

In the steel plates obtained, the measurement of surface hardness, the evaluation of property of resistance to abrasion, the measurement of tenacity of the base material, a test of cracking of welding in angle in the form of T (evaluation of resistance property to the delayed fracture), a synthetic heat affected zone test and a tenacity test of an existing steel joint weld were carried out according to the following forms. The acquired result was shown in Table 3.

Surface hardness 1 Surface hardness measurement was carried out on each steel plate in accordance with the stipulation of JIS Z 2243 (1998) to measure the surface hardness below a surface layer (hardness of a surface measured after the removal scales). in the superficial layer). In the measurement, rigid tungsten balls having a diameter of 10 mm are used, and set at a load of 3000 kgf.

Tenacity of the Base Material 1 A sample of a notch test specimen V was taken from each steel plate in the direction perpendicular to the rolling direction at a position away from a surface of the steel plate by 1/4 of a plate thickness in accordance with the stipulation of JIS Z 2202 (1998), and a Charpy impact test was carried out at three respective temperatures with respect to each steel plate in accordance with the JIS Z 2242 (1998) stipulation, and absorbed energies were obtained in a test temperature of 0 ° C, and the tenacity of the base material is evaluated. The 0 ° C test temperature was selected by taking into account the use of the steel plate in a warm area under consideration.

The steel plate where an average of the three absorbed energies (also referred to as vE0) at the 0 ° C test temperature was 30 J or more was determined as the steel plate having excellent tenacity of the base material (within the scope of the present invention).

Property of Resistance to Abrasion 1 With respect to the property of abrasion resistance, a rubber wheel abrasion test was carried out on each steel plate in accordance with the stipulation of ASTM G65. The test was carried out by using each of the specimens having a size of 10 mmt (t: plate thickness) x 75 mmw (w: width) x 20 mmL (L: length) (t (plate thickness) x 75 mmw x 20 mmL when the plate thickness is less than 10 mm), and when using abrasive sand made of 100% S1O2 as an abrasive material.

A weight of the specimen was measured before and after the test, and the wear of the specimen was measured. The test result was evaluated based on the proportion of abrasion resistance: (wear of the mild steel plate) / (wear of each steel plate) using the wear of the mild steel plate (SS400) as reference ( 1.0). This means that the higher the abrasion resistance ratio, the more excellent the abrasion resistance property will become, and with respect to the scope of the present invention, the steel plate that showed the abrasion resistance ratio of 4.0 or more was determined excellent.

Delayed Fracture 1 In the T-shaped angle weld cracking test, the restriction weld was carried out on each of the specimens which were assembled into a T-shape as shown in Figure 1 by electric arc welding. protected metal and, subsequently, test welding was carried out at room temperature (25 ° C x 60% humidity) or after preheating at 100 ° C.

The welding method was the arc welding of protected metal (welding material: LB52UL (4.0 mm)), where a heat input was 17 kJ / cm, and the welding of 3 layers and 6 steps was carried out cape. After the test, the specimen was left at room temperature for 48 hours and, subsequently, samples of 5 pieces of observation samples were taken in cross section of weld (length of cord of 200 mm that is equally divided by 5) of the Sample plate, and the presence or absence of occurrence of fissures in an area affected by heat of welding was analyzed by a projector and an optical microscope. In both, the specimens were prepared without preheating and the specimens were prepared with preheating at a temperature of 100 ° C, in 5 samples in respective sampled cross section, the samples where the occurrence of fissures in the heat affected area was not found of welding were evaluated as excellent in the resistance to delayed fracture.

Welding Tenacity 1-1 In a synthetic heat affected area test, a bond area and the brittleness area by tempering at low temperature were simulated when two steps of arc welding protected with C02 gas with a heat input of welding of 17 kJ / cm are made. In the simulation of the bond area, the bond area was maintained at a temperature of 1400 ° C for 1 second and cooled at a cooling rate of 30 ° C / s from 800 to 200 ° C. On the other hand, in the simulation of the area of fragility by tempering at low temperature, the area of fragility by tempering at low temperature was maintained at a temperature of 300 ° C for 1 second and cooled to a cooling ratio of 5 ° C / s from 300 to 100 ° C.

A specimen of square bar sample sampled in the rolling direction was subjected to the aforementioned heat cycle by a high frequency induction heating device, and subsequently, a Charpy V groove impact test was carried out in accordance with the stipulation of JIS Z 2242 (1998). The Charpy V-slot impact test was carried out with respect to the three specimens for each steel plate while being set at a test temperature at 0 ° C.

The steel plate in which an average value of the three energies absorbed (vE0) in the bonding area and the brittleness area by tempering at low temperature was 30 J or more was determined as the steel plate having excellent toughness of welding (within the scope of the present invention).

Tenacity of Welding 1-2 In addition, to confirm the tenacity of an existing weld joint, a bead was applied in the plate weld to a steel plate by protected metal arc welding (heat input: 17 kJ / cm, preheat: 150 ° C, solder: LB52UL (4.0 mm (t>)) A sample of a Charpy impact specimen was taken at a position 1 mm below a surface of the steel plate, and a test was carried out of V-shaped Charpy impact according to JIS Z 2242 (1998) stipulation using a slot location as the bonding area Figure 2 shows a sample position of the Charpy impact specimen and slot location.

The Charpy V-groove impact test of the existing weld joint was carried out using all three specimens while the test temperature was set at 0 ° C. The steel plate in which an average value of three energies absorbed (vE0) is 30 J or more was determined as in the steel plate having excellent bond area tenacity (within the scope of the present invention).

Table 2 shows the manufacturing conditions in the steel plates used in the test, and Table 3 shows the results of the respective tests mentioned above. The examples of the present invention (steels No. 1 to 5) had the surface hardness of 400 HBW10 / 3000 or more, showed excellent property of abrasion resistance and tenacity of the base material of 30 J or more at 0 ° C. In addition, cracks did not occur in the T-shaped angle weld cracking test, and the examples of the present invention also had excellent tenacity with respect to the synthetic heat affected zone test and the existing weld and therefore , it was confirmed that the examples of the present invention showed excellent welding toughness.

On the other hand, with respect to the comparison examples (steels No. 6 to 14) whose compositions were outside the scope of the present invention, it was confirmed that the comparison examples could not satisfy the objective performances with respect to either one or a plurality of properties and tests between surface hardness, abrasion resistance property, T-angle weld cracking test, toughness of the base material, heat cycle Charpy impact test reproduced, Charpy impact test of the existing solder joint.

Mode 2 The steel slabs that were prepared with various compositions shown in Table 4 by means of a steel converter, steel buffing and a continuous casting method were heated to a temperature of 1000 to 1250 ° C and, after this , the steel tiles were subjected to hot rolling under manufacturing conditions shown in Table 5. Water cooling (quenching (DQ)) is applied to some steel plates immediately after rolling. With respect to other steel plates, air cooling was applied to other steel plates after rolling, and cooling with water (quenching (RQ)) was performed after reheating.

The steel plates obtained, the measurement of surface hardness, the evaluation of property resistant to abrasion, the measure of tenacity of base material, a proof of weld cracking at an angle in the form of T (evaluation of the property resistant to delayed fracture), a synthetic heat affected zone test and a tenacity test of a weld of a real weld joint were carried out in accordance with the following forms. The acquired result is shown in Table 6.

Surface Hardness 2 The surface hardness measurement was carried out in accordance with the stipulation of JIS Z 2243 (1998) in this way by measuring the surface hardness under a surface layer (hardness of a measured surface after removing the scale in the layer, Of surface) . In the measurement, hard tungsten balls having a diameter of 10 mm were used, and a load was set at 3000 kgf.

Tenacity of Base Material 2 A notch test specimen V is sampled from each steel plate in the direction perpendicular to the rolling direction in a position remote from one surface of the steel plate by a quarter of a plate thickness in accordance with the stipulation of JIS Z 2202 (1998), and a Charpy impact test was carried out at three respective temperatures with respect to each steel plate in accordance with the JIS Z 2242 (1998) stipulation, and the energy absorbed at the temperatures of Test of 0 ° C and -40 ° C were obtained, and tenacity of base material was evaluated. The 0 ° C test temperature was selected when taking the use of the steel plate in a hot region under consideration, and the test temperature of -40 ° C was selected when taking into consideration the use of the steel plate in a cold region.

The steel plate where an average value of three energies absorbed (also referred to as vEo) at the test temperature of 0 ° C was 30 J or more and an average value of three energies absorbed (also referred to as vE_4o) at the temperature Testing of -40 ° C was 27 J or more was determined as the steel plate having excellent tenacity of base material (within the scope of the present invention). With respect to the steel plates having a plate thickness of less than 10 mm, the V-notch test specimens having a sub-size (5 mm x 10 mm) were sampled and subjected to a Charpy impact test. The steel plate was an average value of three energies absorbed (vE0) was 15 J and an average value of three energies absorbed (vE-4o) was 13 J or more was determined as the steel plate that has excellent tenacity of base material (within the scope of the present invention).

Abrasion Resistant Property 2 With respect to the abrasion resistant property, a rubber test abrasion test was carried out in accordance with the stipulation of ASTM G65. The test was carried out using a specimen having a size of 10 mmt (t: plate thickness) x 75 mmw (w: width) x 20 mmL (L: length) (t (plate thickness) x 75 mmw x mmL when the plate thickness was less than 10 mm), and when using the abrasive sand formed of 100% S1O2 as an abrasive material.

A weight of the specimen was measured before and after the test and the wear of the specimen was measured. The result of the test was evaluated based on a ratio of abrasion resistance: (wear of the soft steel plate) / (wear of each steel plate) using wear of the soft steel plate (SS400) as the reference (1.0 ). This means that the larger the abrasion resistance ratio, the more excellent the abrasion resistant property becomes, and with respect to the scope of the present invention, the steel plate showing the abrasion resistance ratio of 4.0 or more was determined excellent.

Delayed Fracture 2 In a T-shaped angle weld cracking test, the restriction weld was carried out on a specimen that was assembled into a T shape as shown in Figure 1 by protected metal arc welding and after this, the test weld was carried out at room temperature (25 ° C x 60% humidity) or after preheating at 100 ° C.

The welding method was protected metal arc welding (solder material: LB52UL (4.0mmO) where a heat input was 17 kJ / cm and welding of 3 layers and 6 steps was carried out. test, the specimen was left at room temperature for 48 hours and, after that, 5 pieces of weld cross-section observation samples (200 mm bead length being equally divided by 5) is sampled from a plate Test, and the presence or absence of cracks in an area affected by heat of welding was investigated by a projector and an optical microscope, in both, the specimens prepared without preheating and the specimens prepared with preheating at a temperature of 100 ° C, between 5 samples in cross section sampled respectively, the samples where the appearance of cracks in the affected area by heat of welding was not found in all, are evaluated as being e xcelentes in resistance to the delayed fracture.

Tenacity of Welding 2-1 In a synthetic heat affected area test, a bonding area and a brittleness area were simulated by tempering at low temperature when welding was carried out by electric arc protected with one-way C02 gas with a solder heat input of 17 kJ / cm. In the simulation of the bonding area, the bonding area was heated to 1400 ° C for 1 second and cooled to a cooling rate of 30 ° C / s from 800 to 200 ° C. In addition, in the simulation of the area of fragility by tempering at low temperature, the area of fragility by tempering at low temperature was heated to a temperature of 300 ° C for 1 second and was carried out at a cooling rate of 5 ° C / sec. 300 to 100 ° C.

A square bar test specimen sampled in the rolling direction was subjected to the aforementioned heat cycle by means of a high frequency induction heating device and, subsequently, a Charpy V-groove impact test was carried out according to with the stipulation of JIS Z 2242 (1998). The Charpy V-groove impact test was carried out with respect to the three specimens for each steel plate while adjusting to test temperatures at 0 ° C and -40 ° C at respective temperatures.

The steel plate in which an average value of the three energies absorbed (vE0) in the bond area and the area of fragility by tempering at low temperature was 30 J or more and an average value of three energies absorbed (?? -40) in the bonding area and the brittleness area by tempering at low temperature was 27 J or more was determined as the steel plate having excellent welding toughness (within the scope of the present invention).

With respect to steel plates that have a plate thickness of less than 10 mm, the Charpy V-groove specimens that have a sub-size (5 mm x 10 mm) samples were taken and subjected to a Charpy impact test. The steel plate in which an average value of the three energies absorbed (vEo) was 15 J or more in the bond area and the area of fragility by tempering at low temperature and an average value of three energies absorbed (vE_40) was 13 J or more in the bonding area and the brittleness area by tempering at low temperature was determined as the steel plate having excellent welding toughness (within the scope of the present invention).

Tenacity of Welding 2-2 In addition, to confirm the tenacity of an existing weld joint, a bead was applied in the plate weld to a steel plate by protected metal arc welding (heat input: 17 kJ / cm, preheat: 150 ° C, welding material: LB52UL (4.0 ??? p? F)). A sample of a Charpy impact specimen was taken from a position of 1 mm below a surface of the steel plate and a Charpy V-groove impact test was carried out in accordance with the stipulation of JIS Z 2242 (1998 ) using a slot location as the link area. Figure 2 shows a sample position of the Charpy impact specimen and slot location.

The Charpy V-groove impact test of the existing weld joint was carried out using three specimens for each test temperature while setting the test temperatures at 0 ° C and -40 ° C. The steel plate in which an average value of the three energies absorbed (vE0) is 30 J or more and an average value of three energies absorbed (vE_4o) is 27 J or more was determined as the steel plate that has excellent bond area tenacity (within the scope of the present invention).

With respect to steel plates having a plate thickness of less than 10 mm, Charpy V-groove specimens having a sub-size (5mm x 10mm) were sampled and subjected to a Charpy impact test. The steel plate in which the average value of the three energies absorbed (vEo) was 15 J or more and an average value of the three energies absorbed (vE-o) was 13 J or more was determined as the plate steel having excellent bond area tenacity (within the scope of the present invention).

Table 5 shows the manufacturing conditions of the steel plates used in the test, and Table 6 shows the results of the respective tests mentioned above. The examples of the present invention (steels No. 15 to 17 (steel No. 17 having a plate thickness of 8 mm)) had the surface hardness of 400 HBW10 / 3000 or more, showing excellent property of abrasion resistance, and had a tenacity of base material of 30 J or more at 0 ° C and tenacity of base material of 27 J or more at -40 ° C. In addition, cracks did not occur in the T-shaped angle weld cracking test, and the examples of the present invention also had excellent tenacity with respect to the test zone affected by synthetic heat and the existing solder joint and therefore, it was confirmed that the examples of the present invention showed excellent welding toughness.

On the other hand, it was confirmed that although steel No. 18 in which the composition falls within the scope of the present invention but DI * exceeds 180, it showed favorable results in surface hardness, property of abrasion resistance and toughness of material base, and a T-shaped angle weld cracking test, the results of a reproduced heat cycle Charpy impact test corresponding to the area of brittleness by low temperature tempering and Charpy impact test of existing weld joint were near the lower limit values of the target yield and therefore, steel No. 18 was lower than the other examples of the present invention, with respect to the low temperature welding toughness.

The steel plate No. 19 falls outside the scope of the present invention with respect to Si in the composition. Therefore, although steel No. 19 showed favorable results in the surface hardness, property of abrasion resistance and toughness of the base material, the toughness in the area of brittleness by tempering of the area affected by welding heat is deteriorated and by therefore, steel No. 19 could not satisfy the objective performances with respect to a T-shaped angle weld cracking test, a Charpy impact test of the area affected by synthetic heat that corresponds to the area of fragility by tempering at low temperature and a Charpy impact test of the existing solder joint.

Although the composition of steel No. 20 falls within the scope of the present invention, the value obtained by formula (2) exceeded 0.47. Accordingly, it was confirmed that vE40 was close to the lower yield limit of the present invention in both of a Charpy impact test of the affected area by synthetic heat and a Charpy impact test of existing weld joint so that the 20 is less than other examples of the present invention. In the description of Tables 4, 5 and 6 although steels No. 18 and 20 fall within the scope of the present invention mentioned by claim 3 in composition, the value DI * and the value of formula (2) falls outside of the scope of the present invention mentioned in claims 6 and 7 and therefore, these steels are established as the comparison examples.

Neither CP O Table 1 Note 1: Underlined values are outside the scope of the present invention Note 2: Contents of N, B, REM, Ca, Mg indicated by ppm in chemical components Note 3: DI * = 33.85 x (0.1 xC) 05 x (0.7xSi + 1) x (3.33xMn + 1) x (0.35xCu + 1) x (0.36xNi + 1) x (2.16xCr + 1) x ( 3xMo + 1) x (1.75xV + 1) x (1.5xW + 1) Note 4: P in formula (2); left side of the formula (2) = C + Mn / 4-Cr / 3 + 10P The respective element symbols are contained (% by mass) N3 P Table 2 Note: Underlined values are outside the scope of the present invention > Or in Table 3 Note: Underlined values are outside the scope of the present invention in or Table 4 Note 1: Underlined values are outside the scope of the present invention Note 2: Contents of N, B, REM, Ca, Mg indicated by ppm in chemical components Note 3: DI * = 33.85 x (O.lxC) "x (0.7xSi + l) x (3.33xMn + l) x (0.35xCu + l) x (0.36xNi + l) x (2.16xCr + l) x (3xMo + l) x (1.75xV + l) x (1.5xW + l) Note 4: Formula (2) = C + Mn / 4-Cr / 3 + 10P The respective element symbols are contained (% by mass) Table 5 Note: Underlined values are outside the scope of the present invention Table 6 Note: The underlined values are outside the scope of this nvencón

Claims

1. An abrasion-resistant steel plate characterized by excellent weld tenacity and excellent resistance to delayed fracture and having a composition containing% by mass of 0.20 to 0.30% C, 0.05 to 1.0% Si, 0.40 to 1.2 % of Mn, 0.010% or less of P, 0.005% or less of S, 0.40 to 1.5% of Cr, 0.005 to 0.025% of Nb, 0.005 to 0.03% of Ti, 0.1% or less of Al, 0.01% or less of N, and Fe the rest of unavoidable impurities, wherein the index of hardening of DI * expressed by a formula (1) is 45 or more, and a base phase of the microstructure is formed of martensite. DI * = 33.85 x (O.lxC) 0-5 x (0.7xSi + l) x (3.33xMn + l) x (0.35xCu + l) x (0.36xNi + l) x (2.16xCr + l) x ( 3x or + l) x (1.75xV + l) x (1.5xW + l) (1), wherein the respective element symbols are contained (% by mass) of the elements.

2. The abrasion-resistant steel plate having excellent weld tenacity and excellent resistance to delayed fracture according to claim 1, characterized in that the steel composition also contains% by mass of one, two or more types of components selected from the group consisting of 0.05 to 1.0% of Mo, 0.05 to 1.0% of W, and 0.0003% to 0.0030% of B.

3. The abrasion-resistant steel plate having excellent weld tenacity and excellent resistance to delayed fracture according to claim 1 or 2, characterized in that the steel composition also contains% by mass of one or two or more types of components selected from a group consisting of 1.5% or less of Cu, 2.0% or less of Ni, and 0.1% or less of V.

4. The abrasion-resistant steel plate having excellent weld tenacity and excellent resistance to delayed fracture according to any of claims 1 to 3, characterized in that the steel composition further contains% by mass of one, two or more types of components selected from a group consisting of 0.008% or less of REM, 0.005% or less of Ca, and 0.005% or less of Mg.

5. The abrasion-resistant steel plate having excellent weld tenacity and excellent resistance to delayed fracture according to any of claims 1 to 4, characterized in that the surface hardness of the steel plate is 400 HBW10 / 3000 or more in the hardness of Brinell.

6. The abrasion-resistant steel plate having excellent welding tenacity and excellent resistance to delayed fracture according to any of claims 1 to 5, characterized in that the hardening index DI * is 180 or less.

7. The abrasion-resistant steel plate having excellent weld tenacity and excellent resistance to delayed fracture according to any of claims 1 to 6, characterized in that the steel plate satisfies a formula (2). C + Mn / 4-Cr / 3 + 10P < 0.47 (2), wherein the respective element symbols are contained (% by mass) of the elements.