JP4238832B2 - Abrasion-resistant steel plate and method for producing the same - Google Patents

Description

  The present invention relates to a wear-resistant steel plate used for industrial machines, transportation equipment, and the like, and a method for manufacturing the same.

  In recent years, in particular, due to weight reduction of trucks and other transportation equipment, civil engineering, and mining machines, steel sheets for construction machinery have been required to have higher strength and higher wear resistance than ever before. In particular, industrial machinery, parts, and transportation equipment used in the fields of construction, civil engineering, mining, etc. (for example, excavators, bulldozers, hoppers, buckets, etc.) have high wear resistance in order to ensure their life. Excellent steel is used. In order to improve the wear resistance, it is necessary to improve the hardness of the steel sheet surface, and it is preferable to have a Brinell difficulty of about 360 or more. Further, a member used in a particularly severe wear environment may require a surface hardness of about Brinell hardness of about 400 or more.

  However, when the hardness is increased, the material becomes brittle or the amount of C is increased, so that there is a problem that low temperature toughness deteriorates and low temperature weld cracking properties deteriorate. Considering work in a low temperature range of about −40 ° C., if the wear resistance is good but the low temperature toughness is low, brittle fracture occurs and the work is seriously hindered. For this reason, a wear-resistant steel sheet having a Brinell hardness of about 360 or more and excellent in low temperature toughness has been desired.

Several methods have been examined for such a requirement. For example, Japanese Patent Laid-Open No. 60-243250 proposes a wear-resistant steel plate having excellent weldability. In this technology, the P content is specified to be 0.010% or less to improve weldability. Further, in JP-A-63-307249, welding abrasion steel plate has been proposed. In this technique, the carbon equivalent is defined as 0.35 to 0.65% to improve weldability. Japanese Patent Laid-Open No. 63-169359 proposes a wear-resistant steel plate with excellent weldability that can withstand use in cold regions. In this technique, the C content is set to 0.1 to 0.2% to ensure weldability.

  In the technique described in Patent Document 1, the C content is as high as 0.3 to 0.5%, and no consideration is given to toughness. Also, because of this, the carbon equivalent is considerably high (> 0.5%), so it can be said that this steel cannot be expected in terms of weldability.

  In the technique described in Patent Document 2, although the carbon equivalent is defined as 0.35 to 0.65%, the C content is set to a very high value of 0.2 to 0.4%, and the toughness at -40 ° C is insufficient. .

  In the technique described in Patent Document 3, the C content is set to 0.1 to 0.2% in order to ensure weldability. However, it is necessary to limit the nitrogen content to 0.0025% or less, which may increase the cost. In addition, since hardenability is not taken into consideration, there is a problem that a Brinell hardness of about 360 or more cannot be stably secured in the case of a steel plate having a thickness of about 20 mm or more as described below.

  That is, when the plate thickness increases, the hardness may decrease from the surface layer portion to the center portion of the plate thickness, and the life as a wear-resistant member cannot be ensured. In order to improve the life of the wear-resistant member, it is effective to make the hardness in the plate thickness direction uniform. However, in the field of wear-resistant steel, there is no example from this viewpoint.

  As described above, when considering use in a low temperature range of about −40 ° C., it is desirable to maintain not only high strength and wear resistance but also low temperature toughness. In the prior art, it is difficult to improve the low temperature toughness and the low temperature weld cracking property while stably ensuring high strength and wear resistance.

  An object of the present invention is to solve these problems and provide a wear-resistant steel sheet excellent in low-temperature toughness and low-temperature weld cracking properties and a method for producing the same while ensuring strength and wear resistance stably.

  Another object of the present invention is to provide a wear-resistant steel sheet having a small difference in hardness in the thickness direction and a method for producing the same.

The above problems are solved by the following invention.
(A) Mass% as a chemical component, C: 0.15-0.30%, Si: 0.1-1.0%, Mn: 0.1-2.0%, Nb: 0.005-0.1%, P: 0.02% or less, S: 0.005% or less And the balance is steel composed of iron and inevitable impurities , the hardenability index H represented by the formula (1) is 1.2 or more, the carbon equivalent Ceq represented by the formula (2) is 0.50% or less, and Thickness characterized by Brinell hardness HB 400 or more, Vickers hardness difference ΔHV between steel plate surface layer and plate thickness center part 50 or less, Charpy absorbed energy vE-40 at -40 ° C is 27 J or more Wear-resistant steel plate of 30mm or more.

H = C × (1 + 0.5Si) × (1 + 3Mn) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + 1.5V) × (1 + 5Nb) × (1 + 300B) (1)
Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (2)
However, the element symbol represents the content (mass%) of each element.
(B) In the wear-resistant steel sheet described in (a), the chemical component is mass% in addition to the described chemical component, Cu: 0.1 to 2.0%, Ni: 0.1 to 2.0%, Cr: 0.1 to 1.5% , Mo: 0.08 to 2.0%, V: 0.01 to 0.5%, Ti: 0.005 to 0.05%, B: 0.0005 to 0.0025%.
(C) Mass% as a chemical component, C: 0.15-0.30%, Si: 0.1-1.0%, Mn: 0.1-2.0%, Nb: 0.005-0.1%, P: 0.02% or less, S: 0.005% or less And the balance is steel composed of iron and inevitable impurities , the hardenability index H represented by the formula (1) is 1.2 or more, the carbon equivalent Ceq represented by the formula (2) is 0.50% or less, and Sheet thickness characterized by Brinell hardness HB of 400 or more, Vickers hardness difference ΔHV of steel sheet surface layer part and sheet thickness center part 14 or less, Charpy absorbed energy vE-40 at -40 ° C is 27 J or more Wear-resistant steel sheet of less than 30mm.

H = C × (1 + 0.5Si) × (1 + 3Mn) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + 1.5V) × (1 + 5Nb) × (1 + 300B) (1)
Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (2)
However, the element symbol represents the content (mass%) of each element.
(D) In the wear-resistant steel sheet described in (c), the chemical component is mass% in addition to the described chemical component, Cu: 0.1 to 2.0%, Ni: 0.1 to 2.0%, Cr: 0.1 ~1 .5%, Mo: 0 .08~ 2.0%, V: 0.01~0.5%, Ti: 0.005~0.05%, B: 0.0005~0.0025% leaf you characterized by containing one or more of Wear- resistant steel sheet with a thickness of less than 30mm .
(E) Heating the steel having the chemical composition described in (a) or (b) to 950 to 1250 ° C, hot rolling the steel at a temperature of 900 ° C or less at 30% or more, and quenching. difference Vickers hardness of the steel sheet surface layer part and mid-thickness portion you characterized ΔHV is 50 or less, and method for producing a wear-resistant steel plate is the plate thickness 30mm or more.
Heating the steel having the chemical composition described in (f), (c) or (d) to 950 to 1250 ° C., hot rolling the steel at a temperature of 900 ° C. or less at 30% or more, and quenching. the difference ΔHV Vickers hardness of the steel sheet surface layer part and mid-thickness portion you wherein is 14 or less, and method for producing a wear-resistant steel plate is less than the thickness 30 mm.

  The present invention suppresses the carbon equivalent Ceq of the wear-resistant steel sheet to a low level and adjusts the hardenability index H, which is related to the structure after quenching, to a predetermined value. In addition to ensuring the thickness, the low temperature toughness and the low temperature weld cracking property can be improved. In addition, it is possible to obtain a wear-resistant steel plate having a small difference in hardness in the thickness direction. As a result, steel materials such as thick steel plates that have excellent wear resistance, low-temperature toughness, and weld crack resistance, and that can withstand use in low-temperature regions, can be obtained. is there.

  The present invention has been made on the basis of knowledge obtained through extensive studies to provide a wear-resistant steel sheet having both weldability and toughness. It is said that adjusting the hardenability index H to a predetermined value instead of keeping the carbon equivalent Ceq low is effective in achieving both weldability and toughness while ensuring hardness and wear resistance. Is.

  Hereinafter, the reasons for limiting the chemical components of the present invention will be described. In the following description, all units indicated by% are mass%.

C: 0.10 ~ 0.30%
C is an important element for increasing the hardness of steel, and is required to be 0.10% or more in order to ensure hardenability. However, when C is added in a large amount exceeding 0.30%, weldability, toughness, and workability deteriorate. Therefore, the C content is defined as 0.10 to 0.30%. When the Brinell hardness HB is 400 or more, C is preferably 0.15% or more.

Si: 0.1-1.0%
Si is an effective element as a deoxidizing element and needs to be added in an amount of 0.1% or more. Further, although it is an element effective for solid solution strengthening, when it is added in an amount exceeding 1.0%, problems such as a decrease in ductility and toughness and an increase in inclusions occur. Therefore, the Si content is defined as 0.1 to 1.0%.

Mn: 0.1-2.0%
Mn is an effective element from the viewpoint of ensuring hardenability, and it is necessary to add 0.1% or more. On the other hand, when it exceeds 2.0%, weldability deteriorates. For this reason, the amount of Mn was specified as 0.1 to 2.0%.

P: 0.02% or less
P is preferably a small impurity element, and if contained in a large amount exceeding 0.02%, toughness is deteriorated. Therefore, the P content is specified to be 0.02% or less.

S: 0.005% or less
S is preferably a small amount of impurity elements, and if contained in a large amount exceeding 0.005%, toughness is deteriorated. Therefore, the S content is specified to be 0.005% or less.

  Hereinafter, in the present invention, one or more of the following elements may be contained as required. Hereinafter, the reasons for limiting those additive elements will be described.

Cu: 0.1-2.0%
Cu is an element that enhances hardenability, but if it is less than 0.1%, this effect cannot be exhibited. On the other hand, addition over 2.0% reduces hot workability and increases alloy costs. Therefore, when adding Cu, it is taken as 0.1 to 2.0% of range.

Ni: 0.1-2.0%
Ni is an element that enhances hardenability and improves low-temperature toughness, but if it is less than 0.1%, this effect cannot be exhibited. On the other hand, when the content exceeds 2.0%, the alloy cost increases. Therefore, when adding Ni, it is set as 0.1 to 2.0% of range.

Cr: 0.1-1.5%
Cr is an element that enhances hardenability, but if it is less than 0.1%, this effect cannot be exhibited. On the other hand, addition exceeding 1.5% degrades weldability and increases alloy costs. Therefore, when adding Cr, it is made 0.1 to 1.5% of range.

Mo: 0.08-2.0 %
Mo is an element that enhances hardenability, but if it is less than 0.08% , this effect cannot be exhibited. On the other hand, addition over 2.0% degrades weldability and increases alloy costs. Therefore, when adding Mo, it is made into the range of 0.08 to 2.0%. Particularly preferably, the content is 0.1 to 1.0%.

V: 0.01-0.5%
V is an element effective for precipitation hardening and has the effect of increasing the hardness of steel. This effect is not exhibited when the content is less than 0.01%, and weldability deteriorates when the content exceeds 0.5%. Therefore, when V is added, the content is made 0.01 to 0.5%.

Nb: 0.005-0.1%
Nb is an element effective for precipitation strengthening, has an effect of increasing the hardness of steel, and also has an effect of improving toughness by refinement of the structure. These effects are not exhibited when the content is less than 0.005%, and when the content exceeds 0.1%, the weldability deteriorates. For this reason, Nb is added in a range of 0.005 to 0.1%.

Ti: 0.005-0.05%
Ti is effective for improving hardenability as well as improving toughness by fixing solute N harmful to toughness as TiN. This effect is not exhibited when the content is less than 0.005%, and when it exceeds 0.05%, the toughness deteriorates. Therefore, when adding Ti, it is set as 0.005 to 0.05% of range.

B: 0.0005-0.0025%
B is an element that enhances hardenability by adding a small amount, but if less than 0.0005%, this effect cannot be exhibited. On the other hand, if it exceeds 0.0025%, the toughness decreases. Therefore, when adding B, it is set as 0.0005 to 0.0025% of range.

  With the chemical component in the above range, the hardenability index is defined in the following range.

Hardenability index H: 1.0 or more The hardenability index H is expressed by the following formula (1) and is related to the structure after quenching, and as a result, it has a great influence on the hardness of the steel. When the hardenability index H is less than 1.0, even if the structure is not completely hardened, or even if the surface structure is completely hardened, it must be completely hardened from the surface layer to the center of the plate thickness. However, the hardness decreases to a Brinell hardness of less than 360. Therefore, the hardenability index H is specified to be 1.0 or more. When the Brinell hardness is 400 or more, the hardenability index H is preferably specified to be 1.2 or more.

H = C × (1 + 0.5Si) × (1 + 3Mn) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + 1.5V) × (1 + 5Nb) × (1 + 300B) ...... (1)
Carbon equivalent Ceq: 0.50% or less The carbon equivalent Ceq is expressed by the following equation (2) and has a great influence on toughness and weldability. When the carbon equivalent Ceq exceeds 0.50%, the predetermined low temperature toughness cannot be obtained and the weldability is also deteriorated. Therefore, the carbon equivalent Ceq is specified to be 0.50% or less.

Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 …… (2)
In carrying out the invention, the chemical components may be adjusted as described above. However, the characteristics of some chemical components can be improved by the following.

  As for C, when the addition amount is too large, the upper limit of Ceq is approached, and other alloy elements such as Mn cannot be sufficiently added. Therefore, C is preferably set to 0.25% or less.

  With regard to Nb, when the addition amount is large, the effect of refining the structure becomes small, and the improvement of toughness may not be expected. Therefore, the Nb addition amount is preferably 0.05% or less.

  For Cu, Ni, Cr, Mo, V, when added, 0.5%, 1.0%, 1.0%, 0.5%, 0.1%, respectively, in order to avoid the increase in alloy costs while ensuring hardenability The following is preferable.

  Figure 1 shows the effect of carbon equivalent Ceq on toughness. As shown in Figure 1, when the carbon equivalent Ceq exceeds 0.45%, the absorbed energy vE-40 at -40 ° C decreases significantly, and when Ceq exceeds 0.50%, vE-40≥27J is stabilized. It cannot be secured. From this, the carbon equivalent Ceq needs to be at least 0.50% or less, but in order to stably secure vE-40 ≧ 27J and obtain higher toughness, the carbon equivalent Ceq is preferably 0.45% or less. .

  Further, the weldability was judged by a y-type weld cracking test in covering arc welding in accordance with JIS standard Z 3153. As a result, it was also found that when the carbon equivalent Ceq exceeds 0.50%, weld cracking is likely to occur.

  As for the hardenability index H, the influence on the hardness after quenching is shown in FIG. As shown in FIG. 2, when the hardenability index H is 1.0 or more, the surface hardness (Brinell hardness) is 360 or more, and when the hardenability index H is 1.2 or more, the surface hardness (Brinell hardness) is 400. As described above, when H is less than 1.0, the structure is not a completely quenched structure, and the hardness is greatly reduced. On the other hand, when the plate thickness is 30 mm or more, the hardenability index H is less than 1.5, and even if the hardness of the steel plate surface is HB360 or more, the structure at the center of the plate thickness is not a completely quenched structure, May be greatly reduced. Therefore, when the plate thickness is 30 mm or more, the hardenability index H is preferably 1.5 or more. When the plate thickness is 30 mm or more and the hardness of the steel plate surface is HB400 or more, in order to obtain a completely quenched structure up to the structure at the center of the plate thickness, H is preferably set to 2.0 or more. The case of a plate thickness of 30 mm or more will be described later because it relates to the rolling reduction during the production of the steel plate.

  Summarizing these findings, it is necessary to provide at least carbon equivalent Ceq of 0.50% or less and hardenability index H of 1.0 or more in order to provide a wear-resistant steel sheet with excellent weldability and toughness as-quenched. Further, in order to stably secure the characteristics of Brinell hardness of 400 or more, it is desirable that the carbon equivalent Ceq is 0.45% or less and the hardenability index H is 2.0 or more.

  A wear-resistant steel sheet is produced using steel having the above chemical components.

  In the present invention, the steel having the above chemical components is hot-rolled to refine the coarse structure as cast and improve toughness. The hot rolling may be performed under normal manufacturing conditions, and the steel slab may be heated to a temperature at which rolling can be performed and rolled to a target plate thickness.

  If the steel plate after rolling is a chemical component of the present invention, the hardness and low temperature toughness can be adjusted within the target ranges by quenching.

  For hot rolling, if the heating temperature is too high, the texture grains become coarse and the toughness deteriorates, and wrinkles may occur on the surface of the steel sheet. Therefore, the heating temperature is preferably 1250 ° C. or lower. On the other hand, if the heating temperature is too low, in the case of direct quenching, the quenching start temperature may decrease and the desired performance may not be obtained, so the temperature setting should be such that quenching can be started at least from the Ar3 point or higher There is a need to. Further, if the heating temperature is low, the structure grains may be mixed and the toughness may be deteriorated.

  In hot rolling, hardness and toughness can be increased from the steel sheet surface layer to the plate thickness central part by applying effective reduction near the recrystallization temperature of austenite. In order to obtain the effect, it is desirable to perform hot rolling at a temperature of 900 ° C. or less so that the reduction rate is 15% or more.

  For quenching, after the hot rolling is finished, the steel sheet may be quenched from the temperature above the Ar3 point without allowing to cool, or the steel plate cooled to a temperature below the Ar1 point is reheated to a temperature above the Ar3 point. It can be hardened. When quenching after reheating, if the reheating temperature is too high, the structure of the steel sheet becomes coarse and the toughness may be deteriorated. Therefore, the reheating temperature is preferably 1150 ° C. or less. If necessary, cooling can be stopped at a temperature below the Ar3 point during quenching. The cooled structure is preferably mainly composed of martensite.

  For example, a steel having the above chemical components, a hardenability index H represented by the formula (1) of 1.2 or more, and a carbon equivalent Ceq represented by the formula (2) of 0.50% or less is hot-rolled, Then, by quenching, a wear-resistant steel plate having a Brinell hardness HB of 400 or more and a Charpy absorbed energy vE-40 at −40 ° C. of 27 J or more can be produced.

  Next, the case where a steel plate having a thick plate thickness that causes hardenability is a problem will be described. Fig. 3 shows the reduction ratio and the firing rate when the wear-resistant steel of the present invention is heated to 1200 ° C and hot-rolled at a reduction rate of 900 ° C or less to 0 to 45% to produce a steel plate with a thickness of 30 mm or more. The relationship between Brinell hardness HB and ΔHV (difference in Vickers hardness between the steel sheet surface layer portion and the plate thickness center portion) with respect to the insertion index H is shown. The wear-resistant steel sheet of the present invention can be produced using the above-mentioned method without any particular problem up to a plate thickness of about 20 mm. Is difficult to enter, and the difference in hardness between the steel plate surface and the central portion of the steel plate thickness increases. When the rolling reduction at 900 ° C. or lower is high, the martensitic transformation in the central portion of the sheet thickness is promoted by strain due to the rolling, and the difference in hardness between the steel plate surface and the central portion of the thickness of the steel sheet is reduced.

  According to FIG. 3, if the rolling reduction during hot rolling is 30% or more, the wear index is H1.0 or more and Brinell hardness 360 or more, and the quenching index H is 1.2 or more and Brinell hardness 400 or more wear resistance. A steel plate can be obtained. Moreover, (DELTA) HV which is a difference of the Vickers hardness of a steel plate surface layer part and plate | board thickness center part is 50 or less, and hardness is ensured stably to the plate | board thickness center part. Therefore, the steel having the chemical component of the present invention is heated to 950 to 1250 ° C., hot-rolled at a reduction rate of 900 ° C. or less at 30% or more, and quenched, regardless of the plate thickness. It can be seen that a worn steel plate can be produced.

  Further, according to FIG. 3, when the rolling reduction during hot rolling is less than 30%, even if the hardenability index H is 1.0 or more, ΔHV exceeds 50, and the hardness of the central portion of the plate thickness decreases. May end up. However, even when the rolling reduction during hot rolling is less than 30%, if the quenching index H is 1.5 or more, the Brinell hardness HB is 360 or more and ΔHV is 50 or less, and if the quenching index H is 2.0 or more, the Brinell hardness It can be seen that a wear-resistant steel sheet having a thickness of 400 or more and ΔHV of 50 or less can be obtained. Therefore, a steel having the chemical component of the present invention and a hardenability index H of 1.5 or more is heated to 950 to 1250 ° C. and heated to a thickness of 30 mm or more with a reduction rate of less than 30% at 900 ° C. or less. By rolling and quenching, a wear-resistant steel plate with a uniform thickness direction hardness of Brinell hardness of 360 or more, and a steel with a hardenability index H of 2.0 or more are heated to 950-1250 ° C, 900 It is possible to produce a wear-resistant steel sheet with a uniform thickness direction hardness of Brinell hardness of 400 or more by hot rolling to a thickness of 30 mm or more with a reduction rate of less than 30% below ℃ and quenching. .

  Therefore, when the hardenability index H ≧ 1.5, HB ≧ 360 regardless of the rolling reduction, and the sheet thickness direction hardness can be made uniform. Further, when the hardenability index H ≧ 2.0, HB ≧ 400 regardless of the rolling reduction, and the sheet thickness direction hardness can be made uniform. However, a higher rolling reduction is preferable in that the difference in hardness between the central portion of the plate thickness and the surface layer portion is small, and even when the plate thickness is less than 30 mm, if the rolling reduction at 900 ° C. or less is 30% or more, It is more preferable because the difference in hardness between the center portion of the plate thickness and the surface layer portion becomes small.

Steel slabs of steels A to Q having the composition shown in Table 1 are heated to 1150 ° C. and hot-rolled to a sheet thickness of 9 to 50 mm with a reduction rate of 900 ° C. or less as 20%, and then directly quenched or After standing to cool, it was reheated and quenched. Steels C, E, H and K are invention steels, and steels L to Q are comparative steels.

About the obtained steel plate, hardness, low temperature toughness, and weldability were investigated as characteristic values. The surface hardness was based on JIS standard Z2243, and an average value of 5 points randomly selected and measured on the steel sheet surface from which the black skin was removed was used , and H B400 or more was set as a particularly preferable range. The thickness direction hardness was evaluated by Vickers hardness HV according to JIS standard Z2244. Using the average value of Vickers hardness HV of the 5 points measured at the steel sheet surface under 2mm and mid-thickness portion, the difference Delta] HV ≦ 50 hardness of the front layer and the plate thickness central portion in the plate thickness 30mm or more, the plate the thickness less than 30mm the difference Delta] HV ≦ 14 hardness of the surface layer and mid-thickness portion was evaluated as a small steel plate difference in hardness at the plate thickness direction.

  The low temperature toughness was based on JIS standard Z2242, measured Charpy impact absorption energy at -40 ° C., and passed vE-40 ≧ 27J. Weldability was evaluated based on the presence or absence of cracks in a y-type weld cracking test in accordance with JIS standard Z3157 and a preheating temperature of 125 ° C. The obtained characteristic values are shown in Table 2 together with the production method.

  As shown in Table 2, the steel according to the present invention has sufficient low-temperature toughness and good weld cracking properties as well as high surface hardness and thickness center hardness effective as a wear-resistant steel plate.

  On the other hand, the comparative steel L has a C content outside the range of the present invention, and good weld cracking properties are not obtained. The comparative steel N has a carbon equivalent Ceq outside the range of the present invention, and sufficient low temperature toughness and good weld cracking properties are not obtained. Comparative steels P and Q have P and S amounts exceeding the range of the present invention, respectively, and sufficient low temperature toughness is not obtained.

Comparative Steel O is outside the scope of the chemical components present invention, although Brinell hardness HB is 400 or more, the hardenability index H relative thickness 30mm is less than 1.5, the hardness in the plate thickness central portion And ΔHV> 50. Therefore, when the plate thickness is large, it is preferable to adjust the hardenability index H to 1.5 or more in order to obtain sufficient hardness in the central portion of the plate thickness.

Steel pieces A to Q having the composition shown in Table 3 were hot-rolled to a thickness of 9 to 50 mm using the manufacturing method shown in Table 4, and then directly quenched to obtain No. 1 to 17 steel plates. Manufactured. Steels F and K are steels of the present invention, and steels A, B, and L to Q are comparative steels.

About the obtained steel plate, hardness, low temperature toughness, and weldability were investigated as characteristic values. Surface hardness, according to JIS standard Z2243, using an average value of 5 points measured at randomly selected in the removed surface of the steel sheet black skin, was passed over H B 400. The thickness direction hardness was evaluated by Vickers hardness HV according to JIS standard Z2244. Using the average value of Vickers hardness HV of the 5 points measured at the steel sheet surface under 2mm and mid-thickness portion, the difference Delta] HV ≦ 50 hardness of the front layer and the plate thickness central portion in the plate thickness 30mm or more, the plate the thickness less than 30mm and rated the difference Delta] HV ≦ 14 hardness of the surface layer and mid-thickness portion as small steel sheet hardness difference in the thickness direction.

  The low temperature toughness was based on JIS standard Z2242, measured Charpy impact absorption energy at -40 ° C., and passed vE-40 ≧ 27J. Weldability was evaluated by welding cold cracking resistance, and evaluated by the presence or absence of cracking in a y-type weld cracking test in accordance with JIS standard Z3157 and a preheating temperature of 125 ° C. The obtained characteristic values are also shown in Table 4.

As shown in Table 4, the steel sheets of the present invention No. 5 and 11 have high surface hardness effective as wear-resistant steel sheets, uniform thickness direction hardness, sufficient low temperature toughness, and good Has weld cracking properties.

  On the other hand, the heating temperature of the No. 6 steel plate is over 1250 ° C., and the low temperature toughness deteriorates due to the coarsening of the grains. The comparative steel L has a C content outside the range of the present invention, and the No. 12 steel sheet does not have good low temperature toughness and weld cracking properties. The comparative steel M has a low C content, and the No. 13 steel sheet does not have a hardness higher than HB360. The comparative steel N has a carbon equivalent Ceq outside the range of the present invention, and the No. 14 steel sheet does not have sufficient low temperature toughness. The comparative steels P and Q have P and S amounts exceeding the range of the present invention, respectively, and the steel plates No. 16 and 17 do not have sufficient low temperature toughness.

  In the comparative steel O, H is less than 1.0 and the chemical composition is outside the scope of the present invention. The No. 15 steel sheet had a Brinell hardness HB of 360 or more, but the hardenability was low, so the hardness decreased at the center of the sheet thickness and ΔHV> 50.

The figure which shows the influence of the carbon equivalent Ceq on toughness. The figure which shows the influence of the hardenability parameter | index H which acts on the hardness after hardening. The graph which shows the relationship between HB and (DELTA) HV with respect to a rolling reduction and the hardenability parameter | index H.

Claims (6)

It contains mass% as a chemical component, C: 0.15-0.30%, Si: 0.1-1.0%, Mn: 0.1-2.0%, Nb: 0.005-0.1%, P: 0.02% or less, S: 0.005% or less, The balance is steel consisting of iron and inevitable impurities , the hardenability index H shown by formula (1) is 1.2 or more, the carbon equivalent Ceq shown by formula (2) is 0.50% or less, and the Brinell hardness HB Is not less than 400, the difference in Vickers hardness between the surface layer of the steel sheet and the center of the sheet thickness is 50 or less, and Charpy absorbed energy vE-40 at -40 ° C is 27 J or more. Wear steel plate.
H = C × (1 + 0.5Si) × (1 + 3Mn) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + 1.5V) × (1 + 5Nb) × (1 + 300B) (1)
Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (2)
However, the element symbol represents the content (mass%) of each element. In the wear steel according to claim 1 Symbol placement, chemical composition, in mass% in addition to the chemical components described, Cu:. 0.1 ~2 0% , Ni: 0.1~2.0%, Cr: 0.1~1 .5 %, Mo: 0 .08~ 2.0% , V: 0.01~0.5%, Ti: 0.005~0.05%, B: 0.0005~0.0025% of the above features and to RuitaAtsu 30mm that contain one or more Wear- resistant steel plate. It contains mass% as a chemical component, C: 0.15-0.30%, Si: 0.1-1.0%, Mn: 0.1-2.0%, Nb: 0.005-0.1%, P: 0.02% or less, S: 0.005% or less, The balance is steel consisting of iron and inevitable impurities , the hardenability index H shown by formula (1) is 1.2 or more, the carbon equivalent Ceq shown by formula (2) is 0.50% or less, and the Brinell hardness HB Is not less than 400 mm, the difference in Vickers hardness ΔHV between the steel sheet surface layer part and the sheet thickness center part is 14 or less, and Charpy absorbed energy vE-40 at −40 ° C. is 27 J or more. Wear steel plate.
H = C × (1 + 0.5Si) × (1 + 3Mn) × (1 + 0.3Cu) × (1 + 0.5Ni) × (1 + 2Cr) × (1 + 3Mo) × (1 + 1.5V) × (1 + 5Nb) × (1 + 300B) (1)
Ceq = C + Mn / 6 + (Cu + Ni) / 15 + (Cr + Mo + V) / 5 (2)
However, the element symbol represents the content (mass%) of each element. The wear-resistant steel sheet according to claim 3, wherein the chemical component is in mass% in addition to the described chemical component, Cu: 0.1 to 2.0%, Ni: 0.1 to 2.0%, Cr: 0.1 to 1.5% , Mo: 0 .08~ 2.0%, V: 0.01~0.5%, Ti: 0.005~0.05%, B: 0.0005~0.0025% of resistance below features and to RuitaAtsu 30mm that contain one or more Wear steel plate. The steel having the chemical composition according to claim 1 or claim 2, heated to: 950 ° C., hot rolled at a reduction rate of at 900 ° C. or less as 30% or more, characterized in that quenching A method for producing a wear- resistant steel plate, wherein the difference ΔHV in Vickers hardness between the steel sheet surface layer portion and the plate thickness center portion is 50 or less and the plate thickness is 30 mm or more . The steel having the chemical components described in claim 3 or claim 4, heated to: 950 ° C., hot rolled at a reduction rate of at 900 ° C. or less as 30% or more, characterized in that quenching A method for producing a wear- resistant steel sheet, wherein a difference ΔHV in Vickers hardness between a steel sheet surface layer part and a sheet thickness center part is 14 or less and a sheet thickness is less than 30 mm .

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