JP6245220B2 - Abrasion resistant steel plate with excellent low temperature toughness and corrosion wear resistance - Google Patents

Description

  The present invention relates to a wear-resistant steel plate suitable for parts such as industrial machines and transportation equipment, and in particular, improved resistance to wear (corrosion wear resistance) due to contact with moisture-containing earth and sand, and improved low-temperature toughness. About.

  Conventionally, for example, construction of power shovels, bulldozers, hoppers, buckets, dump trucks, etc., and parts such as industrial machines and transport equipment used on site such as civil engineering and mining are worn by contact with earth and sand. For this reason, steel materials excellent in wear resistance are used as steel materials for parts such as industrial machines and transportation equipment for the purpose of extending the life of parts and the like. Various conditions such as dryness and wetness are assumed for earth and sand in the actual use environment. In particular, since earth and sand in a wet state often contains a corrosive substance, wear due to the earth and sand in a wet state becomes wear in an environment containing a corrosive substance, so-called corrosive wear. Corrosion wear is known to be very severe as a wear environment, and a steel material having excellent corrosion wear resistance has been desired.

  In addition, these industrial machines, transportation devices, and the like are assumed to be used in a low temperature range of 0 ° C. or lower. For this reason, it is desired that steel materials used for parts such as these industrial machines and transportation equipment have excellent low-temperature toughness in addition to wear resistance and corrosion wear resistance.

  In response to such a request, for example, in Patent Document 1, in mass%, C: 0.30 to 0.45%, Si: 0.10 to 0.50%, Mn: 0.30 to 1.20%, Cr: 0.50 to 1.40%, Mo: 0.15 -0.55%, B: 0.0005-0.0050%, sol.Al: 0.015-0.060%, Nb: 0.02-0.05% and / or Ti: 0.01-0.03%, the balance being high toughness substantially consisting of Fe Abrasion resistant steel is described. According to the technique described in Patent Document 1, a high-strength, high-toughness, relatively inexpensive, high-toughness wear-resistant steel is obtained by the synergistic action effect of addition of B, Al and Nb and / or Ti.

  Patent Document 2 includes, in mass%, C: 0.18 to 0.25%, Si: 0.10 to 0.30%, Mn: 0.03 to 0.10%, Cr: 1.00 to 2.00%, Mo: more than 0.50 to 0.80%, Nb: 0.007 to 0.020%, B: 0.0003 to 0.0012%, sol.Al: 0.020 to 0.080%, N: 0.0010 to 0.0050%, the balance being Fe and unavoidable impurities after water quenching and tempering treatment A wear-resistant steel sheet having excellent toughness and delayed fracture resistance is described. In the technique described in Patent Document 2, the Mn content is suppressed to 0.10% or less, the toughness and delayed fracture resistance are improved, the Mo content is increased, and Cr, B, sol.Al, N, etc. By adjusting the content of, it is said that it is possible to ensure sufficient hardness as wear-resistant steel. In the technique described in Patent Document 2, low temperature toughness is further improved by performing tempering treatment.

In Patent Document 3, the mass percentage is C: 0.30 to 0.50%, Si: 0.40 to 1.50%, Mn: 0.40 to 1.50%, Cr: 0.10 to 0.50%, Mo: 0.05 to 1.00%, Ti: 0.005. Steel strips containing ~ 0.050%, Nb: 0.005 ~ 0.050%, B: 0.0005 ~ 0.0030%, sol.Al: 0.01 ~ 0.10%, N: 0.0010 ~ 0.0060% are heated to 1000 ~ 1250 ° C and hot rolled after performs quenching process for cooling the a ₃ transformation point or above the temperature to a temperature of 100 ° C. or less at 10 ° C. / s or more cooling rate, followed tempering treatment at a temperature of 150 to 450 ° C., the excellent low temperature toughness A method for producing a high hardness wear resistant steel is described. According to the technique described in Patent Document 3, it is said that by adding Si and Nb in combination, temper embrittlement and temper softening can be suppressed at the same time, and a high-strength wear resistant steel of HB500 or more excellent in low-temperature toughness can be produced.

Further, in Patent Document 4, in mass%, C: 0.05 to 0.40%, Si: 0.1 to 0.8%, Mn: 0.5 to 2.0%, Cr: 0.1 to 2.0%, Ti: 0.005 to 0.5%, B: 0.0005 After hot rolling a steel having a composition containing up to 0.005%, Al: 0.005 to 0.10%, and N: 0.005% or less in an austenite non-recrystallized region at 900 ° C. or less at a cumulative reduction ratio of 50% or more, Ar ₃ points A method for producing wear-resistant steel that is quenched from the above and then tempered at _one point of 300 to Ac is described. In addition to the above composition, Cu, Ni, Mo, and V may be further included as optional components. In the technique described in Patent Document 4, the low temperature toughness is remarkably improved by directly quenching and tempering the structure in which the austenite grains are expanded to obtain a tempered martensite structure in which the prior austenite grains are expanded. Yes.

  Patent Document 5 includes, in mass%, C: 0.10 to 0.30%, Si: 0.05 to 1.0%, Mn: 0.1 to 2.0%, W: 0.10 to 1.40%, B: 0.0003 to 0.0020%, A wear-resistant steel sheet having a composition containing Ti: 0.005-0.1% and / or Al: 0.035-0.1% and excellent in low-temperature toughness is described. In the technique described in Patent Document 5, one or more of Nb and / or Cu, Ni, Cr, and V, and / or one of Ca and REM, or Two types may be contained. According to the technique described in Patent Document 5, a wear-resistant steel sheet having high surface hardness, excellent wear resistance, and excellent low-temperature toughness can be easily manufactured without accompanying process difficulties. I can do it.

  Patent Document 6 describes a wear-resistant steel plate having excellent bending workability. The wear-resistant steel sheet described in Patent Document 6 contains C: 0.05 to 0.30% and Ti: 0.1 to 1.2% in mass%, and is composed of the remainder Fe and inevitable impurities, and the amount of dissolved C is 0.03% or less. It is a steel plate having a composition in which a ferrite phase is a base phase and a hard phase is dispersed in the base phase. Furthermore, one or two of Nb and V, one or two of Mo and W, one or more of Si, Mn and Cu, one of Ni and B Alternatively, two types and Cr may be contained. As a result, both wear resistance and bending workability against earth and sand wear are drastically improved without a significant increase in hardness.

  As described above, each technology described in Patent Documents 1 to 5 has excellent low temperature toughness, and the technology described in Patent Document 6 has excellent wear resistance that maintains excellent bending workability along with excellent wear resistance. The purpose is to provide steel sheets. In addition, in the technique described in patent document 5, W is contained essential and there exists a problem which manufacturing cost increases. Further, the technique described in Patent Document 6 has a problem that the main phase is ferrite, the surface hardness is low, and the wear resistance is not sufficient. In addition, in each technique described in Patent Documents 1 to 6, there is no special examination on wear in an environment containing a corrosive substance such as wet earth and sand, that is, corrosion wear. Abrasion remains unclear. For these reasons, there has been a demand for a wear-resistant steel plate having excellent corrosion wear resistance.

  In response to such a request, for example, Patent Document 7 includes C: 0.23-0.35%, Si: 0.05-1.00%, Mn: 0.1-2.0%, Al: 0.005-0.100%, Cr: 0.03-2.0%, Mo: has a composition containing 0.03 to 1.0% so that DI * satisfies 45 or more, has a structure in which the martensite phase is the main phase as quenched and the prior austenite grain size is 30 μm or less, and the surface hardness A wear-resistant steel sheet having a Brinell hardness of HBW 10/3000 and 450 or higher and excellent in low temperature toughness and corrosion wear resistance is described. According to the technique described in Patent Document 7, a wear-resistant steel sheet that contains Cr and Mo in combination, is excellent in corrosion wear resistance particularly in a wet earth and sand wear environment, and is also excellent in low-temperature toughness. It is said that it can be produced without a decrease in surface hardness.

  Patent Document 8 includes C: 0.10 to 0.20%, Si: 0.05 to 1.00%, Mn: 0.1 to 2.0%, Al: 0.005 to 0.100%, and Cr: 0.05 to 2.0%, Mo: 0.05. -1% or 2 types selected from 1.0%, and solid solution Cr content in steel (Crsol) and solid solution Mo content in steel (Mosol) satisfy 0.05 ≦ (Crsol + 2.5Mosol) ≦ 2.0 And having a composition comprising the balance Fe and inevitable impurities, a martensite phase as quenched and having a structure with a prior austenite grain size of 30 μm or less, and a surface hardness of Brinell hardness HBW10 / A wear-resistant steel sheet having excellent low temperature toughness and corrosion wear resistance of 3000 or more is proposed. According to the technique described in Patent Document 8, a wear-resistant steel sheet having excellent corrosion wear resistance particularly in a wet earth and sand wear environment and excellent in low temperature toughness can be produced without reducing surface hardness. I can do it.

JP-A-61-166954 Japanese Patent Laid-Open No. 02-179842 Japanese Patent Laid-Open No. 08-41535 Japanese Patent Laid-Open No. 2002-20837 JP 2007-92155 A JP 2007-197813 A WO 2014/045552 Publication WO 2014/045553 Publication

  However, in the technique described in Patent Document 7, by increasing the C content to 0.23% or more, the steel has a Brinell hardness HBW10 / 3000 and a high surface hardness of 450 or more. There is a problem that it has not yet reached a wear-resistant steel sheet having sufficient corrosion and wear resistance commensurate with the amount and surface hardness. In the technique described in Patent Document 8, the C content is relatively low at 0.20% or less, and the surface hardness is as low as about 485 at the maximum. Therefore, it has excellent corrosion wear resistance at a higher surface hardness level. The problem of not having excellent low temperature toughness was left.

  The present invention solves the problems of the prior art, has a Brinell hardness HBW10 / 3000 and a surface hardness as high as 500 or more, has excellent wear resistance, excellent low temperature toughness, excellent corrosion wear resistance, It aims at providing the wear-resistant steel plate which combines.

  In order to achieve the above-mentioned object, the present inventors made extensive research on various factors affecting low temperature toughness and corrosion wear resistance after having high surface hardness and excellent wear resistance. It was. As a result, it was first found that by making the C content more than 0.20%, a high surface hardness of 500 or more was stably obtained with a Brinell hardness HBW10 / 3000, and excellent wear resistance was obtained. . And with such a component system, we have eagerly investigated measures to achieve both excellent low temperature toughness and excellent corrosion wear resistance, and contain an appropriate amount of Cr and / or Mo, and the amount of solute Cr In addition, the inventors have sought to ensure that the amount of solute Mo is within an appropriate range to make the component system capable of suppressing corrosion wear to some extent, and to further contain Sb and B in an essential manner. According to the study by the present inventors, Sb has a function of remarkably improving the corrosion wear resistance particularly in a high C system exceeding 0.20% by mass. However, when Sb is added in a high C system exceeding 0.20% by mass, the toughness deteriorates remarkably. Therefore, the present inventors have newly found that the inclusion of B in combination with Sb can suppress a decrease in toughness due to the inclusion of Sb, and have come to think that B is included in combination with Sb.

  Furthermore, the present inventors contain an appropriate amount of Cr and / or Mo, further contain a composite of Sb and B, and further contain an appropriate amount of C, Si, Mn, P, S, Al, etc. As a composition with improved hardenability, a quenching treatment is performed, and the structure is a low temperature transformation phase (martensite, tempered martensite, lower bainite) having a prior austenite (γ) particle size of 30 μm or less and a volume ratio of 95% or more. It has been found that a wear-resistant steel sheet having excellent low-temperature toughness can be obtained by making the structure having a main phase of).

The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.
(1) By mass%, C: more than 0.20% and 0.35% or less, Si: 0.02 to 1.00%, Mn: 0.1 to 2.0%, P: 0.020% or less, S: 0.005% or less, Al: 0.005 to 0.100%, Sb : 0.005 to 0.20%, B: 0.0003 to 0.0030%, Cr: 0.05 to 2.0%, Mo: 0.05 to 1.0% selected from one or two, and solute Cr in steel The amount of solute Mo in steel
0.05 ≤ (Crsol + 2.5 Mosol) ≤ 2.0 ... (1)
(Here, Crsol: amount of solute Cr in steel (mass%), Mosol: amount of solute Mo in steel (mass%))
And a composition composed of the balance Fe and unavoidable impurities, and a structure in which the prior austenite (γ) grain size is 30 μm or less and the volume ratio of the low-temperature transformation phase is 95% or more at the 1/4 thickness position, A wear-resistant steel sheet having excellent low-temperature toughness and corrosion wear resistance, characterized by having a surface hardness of 500 or more with a Brinell hardness HBW10 / 3000.
(2) In (1), in addition to the above composition, in addition to mass, one or two selected from Nb: 0.005 to 0.1%, Ti: 0.005 to 0.1%, and V: 0.005 to 0.1% A wear-resistant steel sheet comprising the above.
(3) The wear-resistant steel sheet according to (1) or (2), further containing Sn: 0.005 to 0.2% by mass% in addition to the above composition.
(4) In any one of (1) to (3), in addition to the above composition, one or two selected from Cu: 0.03 to 1.0% and Ni: 0.03 to 2.0% by mass% A wear-resistant steel sheet comprising:
(5) In any one of (1) to (4), in addition to the above-described composition, in addition to mass, REM: 0.0005 to 0.008%, Ca: 0.0005 to 0.005%, Mg: 0.0005 to 0.005% A wear-resistant steel sheet comprising one or more of the above-mentioned.

  According to the present invention, it stably has excellent wear resistance without reducing surface hardness, and also has excellent low-temperature toughness, particularly excellent corrosion wear resistance in a wet earth and sand wear environment. A wear-resistant steel plate can be manufactured easily and stably, and has a remarkable industrial effect.

  First, the reasons for limiting the composition of the wear resistant steel sheet of the present invention will be described. Hereinafter, unless otherwise specified, mass% is simply expressed as%.

C: More than 0.20% and 0.35% or less C is an important element for increasing the hardness of the steel sheet and improving the wear resistance. In the present invention, in order to ensure the surface hardness of the steel sheet to be 500 or more with HBW 10/3000, the content needs to exceed 0.20%. If C is 0.20% or less, the desired surface hardness cannot be obtained. On the other hand, when it contains more than 0.35%, weldability, low temperature toughness and workability deteriorate. For this reason, C was limited to the range of more than 0.20% and not more than 0.35%. In addition, Preferably it is 0.21 to 0.34%.

Si: 0.02 to 1.00%
Si is an effective element that acts as a deoxidizer for molten steel. Si is an element that contributes effectively to improving the strength of the steel sheet by solid solution strengthening. In order to obtain such an effect, a content of 0.02% or more is required. If Si is less than 0.02%, sufficient deoxidation effect cannot be obtained. On the other hand, when it contains exceeding 1.00%, ductility and toughness will fall, and the amount of inclusions in a steel plate will increase. For this reason, Si was limited to the range of 0.02 to 1.00%. In addition, Preferably it is 0.2 to 0.50%.

Mn: 0.1-2.0%
Mn is an effective element that has the effect of improving hardenability and increasing the hardness of the steel sheet. In order to obtain such an effect, a content of 0.1% or more is required. On the other hand, if the content exceeds 2.0%, the weldability decreases. For this reason, Mn was limited to the range of 0.1 to 2.0%. In addition, Preferably it is 0.4 to 1.6%, More preferably, it is 0.7 to 1.4%.

P: 0.020% or less When P is contained in a large amount in steel, the low temperature toughness is lowered. For this reason, it is desirable to reduce P as much as possible, but it is acceptable up to 0.020%. For this reason, P was limited to 0.020% or less. In addition, since excessive reduction causes the refining cost to rise, it is desirable that P is 0.005% or more.

S: 0.005% or less When S is contained in a large amount in steel, it precipitates as MnS and causes a decrease in ductility and toughness. In particular, in high-strength steel sheets, MnS becomes a starting point for fracture occurrence and causes a decrease in toughness. Therefore, in the present invention, it is desirable to reduce S as much as possible, but up to 0.005% is acceptable. For these reasons, S is limited to 0.005% or less. In addition, since excessive reduction leads to an increase in refining cost, S is desirably 0.0005% or more.

Al: 0.005-0.100%
Al is an effective element that acts as a deoxidizer for molten steel. Moreover, Al contributes effectively to the improvement of low temperature toughness by refining crystal grains. In order to acquire such an effect, 0.005% or more of content is required. If Al is less than 0.005%, the above-described effects cannot be obtained sufficiently. On the other hand, if Al is contained in a large amount exceeding 0.100%, the weldability is lowered. For this reason, Al was limited to the range of 0.005 to 0.100%. In addition, Preferably it is 0.015 to 0.050%.

Sb: 0.005-0.20%
Sb is an element that improves the corrosion wear resistance, and is an important element in the present invention. Sb suppresses the anode reaction of the steel sheet and also suppresses the hydrogen generation reaction that is a cathode reaction. Thereby, corrosion of a steel plate can be suppressed and corrosion wear resistance can be improved. In the present invention, in addition to the adjustment of the solid solution Cr amount and the solid solution Mo amount, excellent corrosion wear resistance can be obtained by further containing Sb. Furthermore, Sb can suppress decarburization during reheating for hot rolling and heat treatment after hot rolling, and can suppress a decrease in hardness of the steel sheet surface. In order to sufficiently obtain such an effect, Sb needs to be contained in an amount of 0.005% or more. On the other hand, a content exceeding 0.20% causes a decrease in toughness. For this reason, Sb was limited to 0.005 to 0.20% of range. In addition, Preferably it is 0.010 to 0.1%.

B: 0.0003-0.0030%
B is an effective element that improves hardenability when contained in a small amount. Further, B is a useful element that can reduce a decrease in toughness due to Sb content. The reason why such an effect is obtained is not necessarily clear, but the present inventors consider as follows.

  When Sb is contained in the ultrahigh hardness wear-resistant steel as in the present invention, Sb segregates at the old γ grain boundary and the toughness decreases. However, it is considered that when B is contained together with Sb, segregation of Sb to the grain boundary can be suppressed by preferentially segregating B to the grain boundary.

Further, in a wear-resistant steel having a hardness of 500 or higher in HBW 10/3000, excellent corrosion and wear resistance can be obtained by combining B and Sb. In order to acquire such an effect, B needs to contain 0.0003% or more. On the other hand, when it contains exceeding 0.0030%, conversely, toughness falls. For this reason, B was limited to the range of 0.0003 to 0.0030%. In addition, B is preferably limited to a range of 0.0003 to 0.0015% from the viewpoint of suppressing low-temperature cracking in a low heat input weld such as CO ₂ welding generally used for welding of wear-resistant steel plates.

One or two selected from Cr: 0.05-2.0%, Mo: 0.05-1.0%
Both Cr and Mo are effective elements that have the effect of suppressing corrosion wear and improve the resistance to corrosion wear. In the present invention, one of the important elements is selected as one or two kinds. contains.

  Cr is eluted as Cr acid ions by an anodic reaction in a corrosive wear environment where contact with wet earth and sand becomes a problem, and corrosion resistance is improved by inhibiting corrosion by an inhibitor effect. Cr also has the effect of improving the low temperature toughness by increasing the hardenability and making the martensite phase fine. In order to acquire such an effect, 0.05% or more of content is required. If Cr is less than 0.05%, such an effect cannot be exhibited sufficiently. On the other hand, if the content exceeds 2.0%, the weldability is lowered and the production cost is increased. For this reason, when it contained, Cr was limited to 0.05 to 2.0% of range. In addition, Preferably, it is 0.07 to 1.20%.

  Mo, like Cr, elutes as Mo acid ions by the anodic reaction in a corrosive wear environment where contact with wet earth and sand becomes a problem. Improve sexiness. Mo also has the effect of improving the low temperature toughness by increasing the hardenability and refining the martensite phase. In order to acquire such an effect, Mo needs to contain 0.05% or more. If Mo is less than 0.05%, such an effect cannot be sufficiently exhibited. On the other hand, if the content exceeds 1.0%, the weldability is lowered and the production cost is increased. For this reason, when it contained, Mo was limited to 0.05 to 1.0% of range. In addition, Preferably, it is 0.10 to 0.50%.

  In addition, by containing Cr and Mo in combination, an improvement in corrosion wear resistance can be expected. This is presumed to be because the pH range in which Cr and Mo can exist as oxyacids is different and corrosive wear due to wet earth and sand having a wide pH range can be suppressed.

Further, in order to improve corrosion wear resistance, the present invention contains Cr and Mo in the above-mentioned ranges, and further, the amount of solute Cr in steel and the amount of solute Mo in steel are expressed by the following formula (1)
0.05 ≦ (Crsol + 2.5 Mosol) ≦ 2.0 …… (1)
(Here, Crsol: amount of solute Cr in steel (mass%), Mosol: amount of solute Mo in steel (mass%))
Make adjustments to satisfy When Cr, Mo forms carbides, etc., and precipitates as precipitates, the amount of solid solution Cr and solid solution Mo decreases around the precipitate, so the above inhibitor effect is reduced and corrosion wear resistance is reduced. . For this reason, in the present invention, the amount of solute Cr in steel (Crsol) and the amount of solute Mo in steel (Mosol) are adjusted so as to satisfy the above-described formula (1).

  When (Crsol + 2.5 Mosol) is less than 0.05, the above inhibitor effect cannot be sufficiently ensured. For this reason, in the present invention, (Crsol + 2.5 Mosol) needs to be 0.05 or more. On the other hand, when (Crsol + 2.5 Mosol) exceeds 2.0, the effect is saturated and the manufacturing cost increases. In addition, Preferably (Crsol + 2.5 Mosol) is 0.10-1.0.

  In addition, the amount of solid solution Cr and the amount of solid solution MO shall be calculated by the following methods.

  A test piece for electrolytic collection is collected from the steel plate, the test piece is subjected to electrolytic extraction in a 10% acetylacetone-based electrolytic solution, and the obtained extraction residue (precipitate) is analyzed by ICP emission spectroscopy. As the amount of Cr contained in the extraction residue, and as the amount of Mo contained in the extraction residue as a precipitate. Here, the amount of Cr contained in the extraction residue is the amount of precipitated Cr, the amount of Mo contained in the extraction residue is the amount of precipitated Mo, and subtracted from the total Cr amount and the total Mo amount, respectively, the solid solution Cr amount and the solid solution Mo amount Ask for.

  Further, in order to satisfy the above-described expression (1) in the amount of solid solution Cr and the amount of solid solution Mo, it is necessary to suppress precipitation of carbides as much as possible. For this purpose, it is necessary to adjust the heat history and control the Nb amount and Ti amount. Specifically, for example, Nb and Ti that can form carbides more easily than Cr and MO, for example, shortening the time that is maintained in the temperature range (500 to 800 ° C.) in which Cr and Mo carbides are precipitated are as short as possible. It is desirable to contain.

  The above component is a basic component, but in addition to the basic composition, Nb: 0.005-0.1%, Ti: 0.005-0.1%, V: 0.005-0.1% Or two or more, and / or Sn: 0.005 to 0.2%, and / or Cu: 0.03 to 1.0%, Ni: 0.03 to 2.0%, and / or REM : 0.0005-0.008%, Ca: 0.0005-0.005%, Mg: One or more selected from 0.0005-0.005% may be selected and contained as necessary.

One or more selected from Nb: 0.005-0.1%, Ti: 0.005-0.1%, V: 0.005-0.1%
Nb, Ti and V are all elements that precipitate as precipitates such as carbonitrides and improve toughness through refinement of the structure. 1 type or 2 types or more selected from.

  Nb is an element that precipitates as carbonitride and contributes effectively to improving toughness through refinement of the structure. In order to ensure such an effect, it is preferable to contain 0.005% or more. On the other hand, when it contains more than 0.1%, weldability will fall. For this reason, when it contains, it is preferable to limit Nb to 0.005 to 0.1% of range. In addition, from a viewpoint of refinement | miniaturization of a structure, it is more preferable to set it as 0.012 to 0.03% of range.

  Ti is an element that precipitates as TiN and contributes to improvement of toughness through fixation of solute N. In order to acquire such an effect, it is preferable to contain Ti 0.005% or more. On the other hand, when it contains more than 0.1%, coarse carbonitride precipitates and toughness decreases. For this reason, when it contains, it is preferable to limit Ti to 0.005 to 0.1% of range. In addition, from a viewpoint of cost reduction, it is more preferable to set it as 0.005 to 0.03% of range.

  V is an element that precipitates as carbonitride and contributes to improvement of toughness through the effect of refining the structure. In order to acquire such an effect, it is preferable to contain V 0.005% or more. On the other hand, when it contains more than 0.1%, weldability will fall. For this reason, when it contains, it is preferable to set V as 0.005 to 0.1% of range. In addition, it is more preferable to set it as the range of 0.01 to 0.06% from a viewpoint of structure refinement | miniaturization and weldability.

Sn: 0.005-0.2%
Sn is an element that improves the corrosion wear resistance and can be contained as necessary in the present invention. Sn elutes as Sn ions by the anode reaction and suppresses corrosion by the inhibitor effect, thereby improving the corrosion wear resistance of the steel sheet. Sn also forms an oxide film containing Sn on the surface of the steel sheet, and suppresses the anode reaction and cathode reaction of the steel sheet, thereby improving the corrosion wear resistance of the steel sheet. In order to acquire such an effect, it is preferable to contain Sn 0.005% or more. On the other hand, if the content exceeds 0.2%, the ductility and toughness of the steel sheet are lowered. For this reason, when it contains, it is preferable to limit Sn to 0.005 to 0.2% of range. In addition, it is more preferable to set it as 0.005-0.1% from a viewpoint of reduction of a playing element.

One or two selected from Cu: 0.03-1.0%, Ni: 0.03-2.0%
Both Cu and Ni are elements that improve the hardenability and contribute to the increase in hardness, and can be selected and contained as necessary. In order to obtain such an effect, it is preferable to contain Cu: 0.03% or more and Ni: 0.03% or more. On the other hand, when Cu exceeds 1.0%, the hot workability is lowered and the manufacturing cost is also increased. Further, if Ni is contained in excess of 2.0%, the production cost increases. Therefore, when contained, Cu is preferably limited to a range of 0.03 to 1.0%, and Ni is preferably limited to a range of 0.03 to 2.0%. From the viewpoint of further cost reduction, it is more preferable to limit Cu to a range of 0.03-0.5% and Ni to a range of 0.03-0.5%.

REM: 0.0005 to 0.008%, Ca: 0.0005 to 0.005%, Mg: One or more selected from 0.0005 to 0.005%
REM, Ca, and Mg are all elements that combine with S to form spherical sulfide inclusions, and are elements that are selected and included as necessary to suppress the formation of MnS.

  REM has the effect of fixing S and suppressing the generation of MnS that causes a decrease in toughness. In order to acquire such an effect, it is preferable to contain 0.0005% or more. On the other hand, if the content exceeds 0.008%, the amount of inclusions in the steel increases, leading to a decrease in toughness. For this reason, when it contains, it is preferable to limit REM to 0.0005 to 0.008% of range. In addition, More preferably, it is 0.0005 to 0.0020%.

  Ca has an action of fixing S and suppressing the generation of MnS that causes a decrease in toughness. In order to acquire such an effect, it is preferable to contain 0.0005% or more. On the other hand, if the content exceeds 0.005%, the amount of inclusions in the steel increases, leading to a decrease in toughness. For this reason, when it contains, it is preferable to limit Ca to 0.0005 to 0.005% of range. In addition, 0.0005 to 0.0030% is more preferable.

  Mg fixes S and suppresses the generation of MNS that causes a decrease in toughness. In order to acquire such an effect, it is preferable to contain 0.0005% or more. On the other hand, if the content exceeds 0.005%, the amount of inclusions in the steel increases, leading to a decrease in toughness. For this reason, when it contains, it is preferable to limit Mg to the range of 0.0005 to 0.005%. In addition, More preferably, it is 0.0005 to 0.0040%.

  The balance other than the components described above consists of Fe and inevitable impurities.

  Next, the reason for limiting the structure of the wear-resistant steel sheet of the present invention will be described.

  The wear-resistant steel sheet according to the present invention has the above-described composition, and has a structure in which the prior austenite (γ) grain size is 30 μm or less and the main phase is a low-temperature transformation phase at a thickness of 1/4. The “main phase” as used herein refers to a phase occupying 95% or more in terms of volume ratio relative to the entire structure. In addition, plate | board thickness 1/4 position is a position which shows the average structure of a steel plate, and was used as a position which represents a steel plate structure.

Main phase: Low-temperature transformation phase The term "low-temperature transformation phase" refers to the self-tempered martensite phase in which carbides are generated during the cooling process after martensite transformation in addition to the as-quenched martensite phase, toughness and workability. In order to improve, a phase including a low-temperature tempered martensite phase intentionally tempered at 300 ° C. or lower and a lower bainite phase in which fine carbides are precipitated in bainitic ferrite is used. In addition, when intentionally tempering, if the tempering temperature exceeds 300 ° C, Cr and Mo form carbides with Fe when cementite is produced by tempering, and the amount of solute Cr effective in ensuring corrosion resistance In addition, the amount of dissolved Mo decreases and the corrosion resistance decreases. For this reason, the tempered martensite here is low-temperature tempered martensite tempered at 300 ° C. or lower.

  If the low-temperature transformation phase as the main phase is less than 95% by volume, the desired hardness cannot be ensured, the wear resistance is lowered, and the desired wear resistance cannot be ensured. In addition to the low-temperature transformation phase, the upper bainite phase in which carbides are generated between bainitic ferrite, pearlite, and ferrite phase are produced in large amounts, and the low-temperature transformation phase that is the main phase is less than 95% by volume. Not only is the strength reduced significantly, but the toughness is significantly reduced. For this reason, the low temperature transformation phase which is the main phase is limited to 95% or more in volume ratio. In addition, Preferably it is 98% or more.

Old γ particle size: 30 μm or less Even if the low temperature transformation phase can secure 95% or more by volume ratio, if the old γ particle size exceeds 30 μm and becomes coarse, the low temperature toughness is also lowered. The old γ particle diameter is a value obtained by observing the structure corroded with picric acid corrosive solution with an optical microscope (magnification: 400 times) in accordance with the provisions of JIS G 0551.

  The wear-resistant steel sheet of the present invention has the composition and structure described above, and has a surface hardness of 500 or more with a Brinell hardness HBW10 / 3000. “Surface hardness” here refers to a value (Brinell hardness) measured in accordance with JIS Z 2243 (2008) at a position 0.5 mm from the surface in the thickness direction.

Surface hardness: 500 or more with Brinell hardness HBW10 / 3000 If the surface hardness is less than 500 with HBW10 / 3000, the surface hardness is too low, the wear environment is severe, and higher wear resistance is required. The desired wear life cannot be ensured. For this reason, in the wear-resistant steel sheet of the present invention, the surface hardness is limited to 500 or more with the Brinell hardness HBW10 / 3000. Brinell hardness shall be measured in accordance with JIS Z 2243 (2008).

  Next, a preferred method for producing the wear-resistant steel sheet of the present invention will be described.

  A steel material having the above composition is used as a starting material.

  The starting material (steel material) is heated to a predetermined heating temperature and then hot-rolled to obtain a steel plate having a desired size and shape. In addition, when the starting material is maintaining a predetermined temperature, there is no problem even with a steel plate having a desired dimension and shape as it is without being cooled or after being subjected to a slight heating and hot rolling. Absent.

  In addition, the manufacturing method of the steel material is not particularly limited, but the molten steel having the above composition is melted by a conventional melting method such as a converter and an electric furnace, and a conventional casting method such as a continuous casting method is used. It is preferable to use a slab of a predetermined size (slab or the like: steel material). Needless to say, the steel material may be a piece of steel produced by the ingot-bundling rolling method.

Heating temperature: 950-1250 ° C
If the heating temperature is less than 950 ° C., the deformation resistance becomes high, the rolling load becomes too large, and hot rolling may not be possible. On the other hand, at a high temperature exceeding 1250 ° C., the coarsening of crystal grains becomes remarkable, and the desired high toughness cannot be ensured. For this reason, heating temperature was limited to the range of 950-1250 degreeC.

  The heated steel material is then subjected to hot rolling. The hot rolling conditions need not be particularly limited. It is preferable to perform direct quenching (DQ) immediately after the hot rolling. In addition, when performing a direct quenching process after completion | finish of hot rolling, it is preferable to make hot rolling completion | finish temperature into the temperature more than Ar3 transformation point. In addition, after the hot rolling is finished, after air cooling, a reheating quenching process (RQ) in which reheating and quenching may be performed.

  In the direct quenching process, after the hot rolling is finished at a temperature in the range of 800 to 950 ° C., which is the temperature above the Ar3 transformation point, immediately after the quenching start temperature above the Ar3 transformation point, water cooling or the like, preferably a martensitic phase It is preferable that the cooling is performed to a cooling stop temperature below the Ms transformation point at a cooling rate (a cooling rate equal to or higher than a martensite generation critical cooling rate). The cooling stop temperature below the Ms transformation point is 300 ° C. or lower, more preferably 200 ° C. or lower.

  Moreover, it replaces with a direct quenching process, and after completion | finish of hot rolling, after air-cooling, you may give the reheating quenching process (RQ) which reheats and quenches.

  In addition, in order to form the structure | tissue which has a low-temperature transformation phase as a main phase after hardening, it is desirable for the quenching temperature (heating temperature) of a reheating quenching process to be 850-950 degreeC used as an austenite single phase area | region. Also, the quenching cooling rate after reheating is higher than the cooling rate at which the martensite phase is formed (cooling rate above the martensite formation critical cooling rate), such as water cooling, and is cooled to the cooling stop temperature below the Ms transformation point It is preferable to set it as the process to perform. The cooling stop temperature below the Ms transformation point is preferably set to 300 ° C. or lower in order to prevent the martensite phase from being self-tempered as it is quenched and to suppress a decrease in strength. In addition, More preferably, it is 200 degrees C or less.

  In addition, for the purpose of improving workability and toughness, a tempering treatment may be performed by heating to a tempering temperature of 300 ° C. or less after the direct quenching treatment or after the reheating quenching treatment. When the tempering temperature exceeds 300 ° C., Cr and Mo form carbides together with Fe when cementite is formed by tempering, and solid solution Cr and solid solution Mo effective for ensuring corrosion resistance decrease. The temperature is more preferably 200 ° C. or lower.

  Hereinafter, the present invention will be further described based on examples.

  Molten steel having the composition shown in Table 1 was melted in a vacuum melting furnace and cast into a mold to obtain a 150 kgf steel ingot (steel material). These steel materials are heated to the heating temperature shown in Table 2, hot-rolled under the hot rolling conditions shown in Table 2, and then water-cooled immediately after the hot rolling is finished, and cooled to the cooling stop temperature shown in Table 2. Direct quenching (DQ) was performed. In some cases, after the hot rolling was completed, air-cooled and then reheated to the heating temperature shown in Table 2 and then water-cooled and reheated and quenched (RQ) for cooling to the cooling stop temperature shown in Table 2. . Some steel plates were tempered by heating to the tempering temperatures shown in Table 2 and tempering.

Specimens were collected from the obtained steel sheet and subjected to structure observation, solid solution Cr and Mo content measurement, surface hardness test, Charpy impact test, and corrosion wear resistance test. The test method was as follows.
(1) Structure observation A specimen for structure observation was sampled from the position of the plate thickness ¼ of the obtained steel sheet so that the observation surface had a cross section perpendicular to the rolling direction. After polishing the observation surface of the obtained structure observation specimen and corroding with picric acid corrosion solution to reveal the former γ grain boundary, it was observed and imaged using an optical microscope (magnification: 400 times). . From the obtained structure photograph, the area of the old γ grains was measured by image analysis, and the equivalent circle diameter of each old γ grain was determined. The measured old γ grains were 100 or more. The circle equivalent diameters of the obtained prior γ grains were arithmetically averaged, and the average value was defined as the average grain diameter of the prior γ grains of the steel sheet.

Further, the polished specimen for woven observation was corroded with a nital solution, and the structure was observed and imaged using a scanning electron microscope (magnification: 2000 to 5000 times). In addition, the observation was performed for each 10 fields or more. The tissue was identified from the obtained tissue photograph, the area of each phase was measured by image analysis, the ratio (area ratio) with respect to the whole structure was obtained, and the volume fraction was converted into the tissue fraction of the phase. In the present invention, the martensite phase, the tempered martensite phase, and the lower bainite phase are collectively referred to as a low temperature transformation phase. The tempered martensite phase is a self-tempered martensite in which carbides are formed in the lath during cooling after the martensitic transformation, and a low-temperature tempering intentionally tempered at 300 ° C or lower to improve toughness and workability. Includes return martensite. The lower bainite phase refers to a phase in which fine carbides are precipitated in bainitic ferrite, and the martensite phase refers to as-quenched martensite in which no carbide is generated.
(2) Measurement of solid solution Cr and Mo amount From the obtained steel sheet, a test piece for electrolytic extraction was collected and electrolyzed in 10% AA electrolyte (10% acetylacetone-1% tetramethylammonium chloride-methyl alcohol electrolyte). And the residue was extracted. About the obtained extraction residue, the amount of Cr and Mo contained in the extraction residue was analyzed using ICP emission spectroscopy, and the amount of Cr as a precipitate and the amount of Mo as a precipitate were determined. The amount of Cr obtained as a precipitate was subtracted from the total amount of Cr to calculate the amount of solid solution Cr (Crsol). Further, the amount of Mo as a precipitate was subtracted from the total amount of Mo to calculate the amount of solid solution Mo (Mosol).
(3) Surface hardness test Surface hardness measurement test specimens were collected so that the measurement surface was 0.5 mm from the surface of the obtained steel sheet, and surface hardness was measured in accordance with JIS Z 2243 (2008). HBW10 / 3000 was measured. Hardness measurement was performed using a tungsten hard ball of 10 mm and a load of 3000 kgf. Note that five or more points were measured at a position 0.5 mm from the surface, the arithmetic average of the obtained measured values was obtained, and the average value was defined as the surface hardness of the steel sheet.
(4) Charpy impact test A V-notch test piece was sampled so that the length direction of the test piece was a direction perpendicular to the rolling direction (C direction) from the position of the plate thickness ¼ of the obtained steel plate. A Charpy impact test was performed in accordance with JIS Z 2242 (2005). The test temperature was −40 ° C., and the absorbed energy vE ₋₄₀ (J) was determined. Note that the number of test pieces was three each, and the arithmetic average was the absorbed energy vE- _{40 of the} steel sheet. A steel sheet having a vE- ₄₀ of 30 J or more was evaluated as a steel sheet excellent in “base metal low temperature toughness”.
(5) Corrosion-resistant wear test Wear test piece (size: 10mm thickness x 25mm width x 75mm length) so that the test surface (wear surface) is 0.5mm from the surface in the plate thickness direction. Sa) was collected. These test pieces were mounted on an abrasion tester and subjected to an abrasion test.

  Abrasion test piece is mounted so that the surface of the test machine rotor is perpendicular to the rotation axis of the test machine rotor and the surface of 25 mm x 75 mm is in the circumferential tangent direction of the rotation circle. Wear material was introduced inside. The wear material used was a mixture of cinnabar sand having an average particle size of 0.65 mm and an aqueous NaCl solution prepared to a concentration of 15000 mass ppm so that the weight ratio of the cinnabar sand to the NaCl aqueous solution was 3: 2.

  The test conditions were as follows: rotor: 600 times / min and outer tank: 45 times / min. After rotating the rotor until the total number of rotations reached 10800 times, the test was terminated. After completion of the test, the weight of each test piece was measured. Then, the difference between the post-test weight and the initial weight (= weight reduction amount) was calculated. In addition, as a conventional example, a wear test was similarly performed on a wear test piece collected from a rolled steel SS400 (JIS G3101) having a tensile strength of 400 MPa class general structure, and the weight loss amount of the test piece was obtained.

  The weight reduction amount of the obtained test piece was calculated based on the wear resistance ratio (= (reference value) / (weight reduction amount of the test piece)) using the test piece weight reduction amount of the conventional example as a reference value. A case where the wear resistance ratio was 2.60 or more was evaluated as “excellent in corrosion wear resistance”.

  The obtained results are shown in Table 3.

Each of the inventive examples has a surface hardness of HBW 10/3000 and a surface hardness of 500 or more, an excellent low temperature toughness of vE- ₄₀ : 30J or more, and an excellent corrosion wear resistance ratio of 2.60 or more. It has sex. On the other hand, the comparative examples out of the scope of the present invention have a surface hardness of HBW10 / 3000 as low as less than 500, a low temperature toughness as low as vE- ₄₀ : 30J or a corrosion wear resistance as a wear resistance ratio: It is reduced to less than 2.60, or two or more of surface hardness, low temperature toughness and corrosion wear resistance are reduced.

Claims (5)

% By mass
C: 0.20% to 0.35% or less, Si: 0.02 to 1.00%,
Mn: 0.1 to 2.0%, P: 0.020% or less,
S: 0.005% or less, Al: 0.005-0.100%,
Sb: 0.005-0.20%, B: 0.0003-0.0030%
In addition, one or two selected from Cr: 0.05 to 2.0% and Mo: 0.05 to 1.0% are included, and the solute Cr amount in the steel and the solute Mo amount in the steel are the following (1 ) Satisfying the formula, the composition consisting of the balance Fe and inevitable impurities,
Having a structure in which the prior austenite (γ) grain size is 30 μm or less and the volume ratio of the low-temperature transformation phase is 95% or more at a thickness of 1/4 position,
Furthermore, a wear-resistant steel sheet having excellent low-temperature toughness and corrosion wear resistance, characterized in that the surface hardness is 500 or more with Brinell hardness HBW10 / 3000.
Record
0.05 ≦ (Crsol + 2.5 Mosol) ≦ 2.0 …… (1)
Here, Crsol: amount of solute Cr in steel (% by mass), Mosol: amount of solute Mo in steel (% by mass)   In addition to the above composition, the composition further contains one or more selected from Nb: 0.005 to 0.1%, Ti: 0.005 to 0.1%, and V: 0.005 to 0.1% by mass%. The wear-resistant steel plate according to claim 1.   The wear-resistant steel sheet according to claim 1 or 2, further comprising Sn: 0.005 to 0.2% by mass% in addition to the composition.   4. The composition according to claim 1, further comprising one or two selected from Cu: 0.03-1.0% and Ni: 0.03-2.0% by mass% in addition to the composition. Abrasion-resistant steel sheet according to the above.   In addition to the above composition, the composition further comprises one or more selected from REM: 0.0005 to 0.008%, Ca: 0.0005 to 0.005%, and Mg: 0.0005 to 0.005% by mass%. The wear-resistant steel sheet according to any one of claims 1 to 4.