JP4339612B2 - Rolling roll for galvanized steel sheet excellent in spalling resistance and steel material for the rolling roll - Google Patents

Description

【００５２】
【表２】

【００５３】
表２や図２〜３から次の様に考察できる。No.1〜5は本発明で規定する何れかの要件を満足しない例である。No.1はＴｉ等の元素を含有していない例、No.2はＴｉ含量が本発明で規定する範囲より少ない例であり、侵入水素量が多く、耐スポーリング性を改善できていない。No.3はＴｉ含量が本発明で規定する範囲より多い例であり、侵入水素量は低減できているものの、粗大なＴｉ窒化物が析出し、機械的特性が劣化するので耐スポーリング性は改善できていない。No.4はＴｉ等の元素を含有していない例であり、耐スポーリング性を改善できていない。No.5はＮ含量が本発明で規定する範囲より多い例であり、粗大な窒化物や炭窒化物を形成してスポーリングが発生し易くなる。一方、No.6〜18は本発明で規定する要件を満足する例であり、侵入水素量が少なく、耐スポーリング性を改善できている。
【００５４】
実施例２
上記表１に示した化学成分組成の鋼材Ｇを用いて作製した試験片について、熱処理の条件を変更して表面硬度の異なる試験片を作製した。即ち、上記実施例１における空冷後の丸棒に対して、100〜200℃で2時間焼戻して表面硬度の異なる試験片を得た。
【００５５】
得られた試験片を用いて、上記実施例１と同様にＳＳＲＴ試験機で伸びを測定し、上記（１）式より算出したスポーリング感受性の値に基づいて耐スポーリング性を評価した。スポーリング感受性の算出値と評価結果を下記表３に示す。また、上記実施例１と同様に試験片の表面硬度を測定し、結果を下記表３に示す。
【００５６】
次に、得られた熱処理後の試験片を用いて、ヘイドン１軸式摩耗試験機で摩耗試験を行った。摩耗試験の相手材には直径：10ｍｍのアルミナを用い、荷重：9.8Ｎをかけながら1ｃｍ×1万回往復させた後の摩耗減量を測定して耐摩耗性を評価した。耐摩耗性の評価基準は次の通りであり、評価結果を下記表３に併せて示す。
【００５７】
＜耐摩耗性の評価基準＞
○：摩耗量が10ｍｇ未満であり、耐摩耗性に優れる
△：摩耗量が10〜20ｍｇ未満
×：摩耗量が20ｍｇ以上であり、耐摩耗性に劣る
また、総合評価は、耐スポーリング性と耐摩耗性に基づいて下記基準で判断した。
【００５８】
＜総合評価の基準＞
○：耐スポーリング性の評価が◎又は○で、且つ、耐摩耗性の評価が○
×：上記○以外の組み合わせ全て
【００５９】
【表３】

【００６０】
表３から次の様に考察できる。No.19は本発明で規定する要件を満足する例であり、耐スポーリング性も耐摩耗性も良好である。これに対して、No.20とNo.21は表面硬度が小さいので、耐摩耗性が不充分である。No.22は表面硬度が大きいので、スポーリングを発生し易くなる。
【００６１】
【発明の効果】
本発明によれば、圧延ロールにクロムめっき等を施していないので、ロール原単位を高めることなくロール表面損傷の発生を防止できる耐スポーリング性に優れた亜鉛めっき鋼板用圧延ロールを提供することができる。また、本発明によれば、前記圧延ロールの製造に有用な鋼材を提供することができる。
【図面の簡単な説明】
【図１】 ＳＳＲＴ試験機の概略説明図である。
【図２】 各試験片のスポーリング感受性をプロットしたグラフである。
【図３】 侵入水素量とスポーリング感受性の関係をプロットしたグラフである。
【符号の説明】
１ 試験片
２ ＳＳＲＴ試験機
３ ＳＳＲＴ試験機内の雰囲気[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rolling roll for galvanized steel sheet excellent in spalling resistance and a steel material useful as a material for producing the roll.
[0002]
[Prior art]
In the hot dip galvanizing line, in order to improve the mechanical properties of the plated steel sheet, skin pass rolling is applied to the steel sheet after plating. Further, skin pass rolling may be performed on the exit side of the electrogalvanizing line in order to adjust the flatness and surface properties of the plated steel sheet. Skin pass rolling refers to rolling in which a steel plate immediately after plating is lightly reduced with a rolling roll, and is generally performed in a water-lubricated environment in order to prevent zinc from adhering to the surface of the rolling roll and to improve lubricity. is there.
[0003]
A rolling roll used for skin pass rolling is manufactured through steps of melting, heating, forging, annealing, tempering, (surface) quenching, finishing, and the like, and further subjected to dull processing as necessary. It is known that when this rolling roll is continuously used in a water-lubricated environment, fine blisters are formed on the roll surface, and further, the surface of the blisters is peeled off to generate fine pit flaws. When these wrinkles occur on the roll surface, the wrinkles are transferred to the plated steel sheet and cause quality deterioration. Further, these wrinkles generated on the roll surface become the starting point of fatigue cracks, and when the cracks progress into the roll, a brittle fracture phenomenon called spalling finally occurs.
[0004]
Therefore, various techniques have been proposed to reduce spalling generated on the surface of the rolling roll. For example, Patent Document 1 proposes a technique for preventing a spalling phenomenon by applying chromium plating to a rolling roll for a zinc-based plated steel sheet and limiting the plating thickness and the hydrogen content in the plating film. However, in the technique of plating on the roll surface, (1) since hydrogen easily penetrates into the steel during plating, spalling is likely to occur, and it is necessary to perform a dehydrogenation treatment in order to adjust the hydrogen content in the steel. (2) There is a possibility of damaging the steel sheet because of the high hardness of the plating film. (3) When the plating film is peeled off, the film is hard and may damage the steel sheet. (4) The plating treatment is expensive. (5) In particular, there is a problem that the roll unit is increased. (5) In particular, since the Cr plating film has low smoothness, the plating surface must be polished, resulting in high costs. On the other hand, in Patent Document 2, there is a work roll for galvanized steel sheet skin pass rolling that regulates the composition of the roll and the surface hardness and suppresses the occurrence of roll surface damage (spoling) by specifying the tempering temperature condition. Proposed. However, as a result of studies by the present inventors, this technique is not satisfactory from the viewpoint of preventing the occurrence of spalling, and there remains room for improvement.
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2-30309 (see “Claims”, page 3, lower left column, etc.)
[Patent Document 2]
JP-A-6-17196 (see [Claims], [0033], [0049], etc.)
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and its purpose is for a galvanized steel sheet having excellent spalling resistance that can prevent the occurrence of roll surface damage without increasing the basic unit as a roll material. An object of the present invention is to provide a rolling roll and a steel material suitable for manufacturing the rolling roll.
[0007]
[Means for Solving the Problems]
The steel material for a galvanized steel sheet rolling roll excellent in spalling resistance according to the present invention that has solved the above problems is C: 0.6 to 1.2% (meaning “mass%”; the same applies hereinafter). , Si: 0.3 to 1.5%, Mn: 1% or less (excluding 0%), Ni: 1% or less (including 0%), Cr: 2 to 6%, Mo: 1% or less ( In the steel materials for galvanized steel sheet rolling rolls, each containing 1% or more selected from the group consisting of Ti, Zr, Hf and Nb, 0.01 to 0.30% in total At the same time, N is suppressed to 0.02% or less (including 0%), and the gist is that the balance is made of Fe and inevitable impurities. In the steel material of this invention, it is preferable to contain V: 0.01-0.5% as another element further.
[0008]
Moreover, the rolling roll for galvanized steel sheets excellent in spalling resistance according to the present invention that has solved the above-mentioned problems is a rolling roll manufactured using a steel material having the above-described composition, and the rolling roll The surface layer part is a structure mainly composed of martensite and has a gist in that the surface hardness of the roll satisfies 80 to 100 (HS).
[0009]
DETAILED DESCRIPTION OF THE INVENTION
As described above, it is known that blisters are likely to occur on the surface of a rolling roll for galvanized steel sheet used in a water-lubricated environment, and this wrinkle is finally developed into spalling. The reason is considered as follows.
[0010]
That is, in the rolling process of the galvanized steel sheet, the surface of the rolling roll is exposed to a special environment where zinc and water coexist. In this environment, hydrogen is likely to be generated, and the generated hydrogen diffuses and penetrates from the roll surface to the inside to induce fine cracks. After the cracks develop into fine blisters, the surface of the blisters further peels off. It is thought to be a fine pit trap. When the pits are further separated, a brittle fracture phenomenon appears.
[0011]
Accordingly, the present inventors have studied from various angles in order to suppress the occurrence of spalling by paying attention to a rolling roll for galvanized steel sheet used in a special environment in which zinc and water coexist. As a result, the inventors have found that the above problems can be solved brilliantly by producing a rolling roll using a steel material containing one or more selected from the group consisting of Ti, Zr, Hf and Nb, and the present invention has been completed. Hereinafter, the function and effect of the present invention will be described.
[0012]
First, the steel material used when manufacturing the rolling roll for galvanized steel sheets of this invention is demonstrated. In the present invention, spalling refers to surface texture defects such as fine blisters, pit wrinkles, cracks, and peeling that occur on the surface of the rolling roll. Therefore, spalling resistance is unlikely to cause these surface texture defects. Means a characteristic.
[0013]
The steel materials for rolling rolls for galvanized steel sheets according to the present invention include, as basic components, C: 0.6 to 1.2%, Si: 0.3 to 1.5%, Mn: 1% or less (excluding 0%), Ni: 1% or less ( 0% is included), Cr: 2 to 6%, Mo: 1% or less (not including 0%). The reasons for determining the contents of these constituent elements are as follows.
[0014]
C: 0.6 ~ 1.2 %
C is an element that combines with alloy elements such as Fe, Cr, and Mo to form a hard carbide, increases the surface hardness of the roll, and improves the wear resistance. Further, as will be described later, it combines with Ti, Zr, Hf and Nb to form a carbide or carbonitride, which contributes to an improvement in spalling resistance. In order to exhibit these effects effectively, it should be contained at least 0.6%, preferably 0.75% or more. However, if the C content exceeds 1.2%, the carbides and carbonitrides become coarse and become agglomerates, or network-like eutectic carbides form and cause toughness deterioration. is there. Preferably, it should be suppressed to 1.0% or less.
[0015]
The C content defined in the present invention refers to the total amount of C contained in the steel material, for example, the amount of C in carbides or carbonitrides present in a bonded state with the alloy elements contained in the steel material, steel material. It is the total amount such as the amount of C dissolved in the solution.
[0016]
Si: 0.3 ~ 1.5 %
Si is a useful element contributing to the improvement of hardenability and the increase of temper softening resistance as well as exhibiting a solid solution hardening effect by dissolving in a steel material. In order to exhibit these effects effectively, it is necessary to contain 0.3% or more, preferably 0.4% or more. However, if the Si content exceeds 1.5%, not only the forgeability when processing into a rolled roll is lowered, but also the crack resistance and toughness of the roll itself are significantly reduced, so the Si content must be suppressed to 1.5% or less. There is. Preferably 1.0% or less is recommended.
[0017]
Mn: 1 %Less than( 0 % Not included)
Mn dissolves in the steel material in the same way as Si and contributes to solid solution hardening, hardenability improvement and temper softening resistance improvement. In order to effectively exhibit such an action, it is recommended to contain 0.2% or more (more preferably 0.25% or more). However, if the content exceeds 1%, crack resistance particularly as a rolling roll is remarkably deteriorated, so the Mn content must be suppressed to 1% or less.
[0018]
Ni: 1 %Less than( 0 %including)
If the Ni content exceeds 1%, the spalling sensitivity of the roll is increased and spalling is likely to occur, so the Ni content should be suppressed to 1% or less (more preferably 0.80% or less). However, since Ni acts as an element that improves the hardenability by solid solution in the steel material and enhances the toughness of the roll itself, it may be preferable to contain it depending on the steel type. In order to exert these effects effectively, it is recommended to contain 0.30 %% or more (more preferably 0.40% or more) and 0.60% or less.
[0019]
Cr: 2 ~ 6 %
Cr combines with Fe and C (Cr, Fe)_{twenty three}C₆Ya (Fe, Cr)_ThreeIt is an element that forms a composite carbide such as C and contributes to precipitation hardening. Moreover, a part of Cr is dissolved in the steel material and contributes to improvement of hardenability. In order to exert these effects, the content should be 2% or more, preferably 2.3% or more. However, if the Cr content exceeds 6%, the toughness of the roll is significantly deteriorated, so it is necessary to keep it to 6% or less. It is recommended that the content be 5.5% or less.
[0020]
Mo: 1 %Less than( 0 % Not included)
Mo is an element that dissolves in steel and improves the hardenability of the roll. It is recommended to contain 0.1% or more (more preferably 0.2% or more) to effectively exhibit this effect. However, if it exceeds 1%, Mo₆Since carbides such as C-type are formed and the crack resistance and toughness of the roll are lowered, the Mo content must be suppressed to 1% or less. Preferably it is 0.9% or less.
[0021]
In addition to the above basic components, the steel material for rolling rolls for galvanized steel sheets according to the present invention contains 0.01 to 0.30% in total of at least one selected from the group consisting of Ti, Zr, Hf and Nb, and also has an N content. Is suppressed to 0.02% or less. The reasons for determining the contents of these constituent elements are as follows.
[0022]
One or more selected from the group consisting of Ti, Zr, Hf and Nb: 0.01 ~ 0.30 %
Ti, Zr, Hf, and Nb (hereinafter sometimes referred to as “Ti etc.”) combine with C and N to form a carbide, nitride, carbonitride (hereinafter sometimes referred to as “carbide etc.”). Is an important element for improving the spalling resistance of the roll. The reason why the spalling resistance is improved by these elements is not necessarily clarified, but is considered as follows.
[0023]
That is, in an environment where zinc and water coexist, while zinc is ionized (Zn → Zn²⁺+ 2e^-), Some of the generated adsorbed hydrogen atoms are recombined (H + H → H₂) And released as hydrogen molecules to the outside of the steel material, but some are thought to penetrate into the steel material. The hydrogen that penetrates into the steel material diffuses from the steel material surface to the inside, and becomes a major cause of spalling. However, if carbides such as Ti are present on the surface of the rolling roll, the recombination of adsorbed hydrogen atoms is promoted to increase hydrogen release to the outside of the steel material. As a result, hydrogen intrusion into the steel material can be suppressed, and spalling can be reduced. Even if hydrogen diffuses and penetrates into the roll, the carbides such as Ti function as suitable hydrogen trap sites and make the hydrogen harmless, so it is considered that the spalling resistance is drastically improved. . Moreover, since the carbides and the like are very hard, the wear resistance of the roll is also greatly improved.
[0024]
In the present invention, the carbide or the like is a carbide, nitride, or carbonitride in which at least one element selected from the group consisting of Ti, Zr, Hf, and Nb is bonded to carbon and / or nitrogen. That is, the compound contains at least one element selected from the group consisting of Ti, Zr, Hf and Nb and at least one carbon or nitrogen in one compound. Therefore, a single compound may be a carbide, nitride, or carbonitride containing two or more elements selected from the group consisting of Ti, Zr, Hf, and Nb.
[0025]
In order to exert such an effect effectively, it is necessary to contain one element selected from the group consisting of Ti, Zr, Hf and Nb alone, and a combination of two or more elements arbitrarily selected from this group is contained. Of course, it does not matter. In particular, Ti carbide is most preferable because it has the highest bonding strength with hydrogen.
[0026]
Ti or the like contained in the steel material needs to be contained in a total of 0.01% or more in order to exhibit the above effects. The content is preferably 0.02% or more, more preferably 0.03% or more. However, if it exceeds 0.30% in total, it will combine with C and N contained in the steel material, and coarse carbides, nitrides and carbonitrides will precipitate and degrade the mechanical properties, so the upper limit is It should be 0.30%. Preferably it is 0.1% or less.
[0027]
N: 0.02 %Less than( 0 %including)
N is an element that combines with the elements such as Ti to form nitrides or carbonitrides and contributes to the improvement of spalling resistance. However, when the N content exceeds 0.02%, coarse nitrides and N-content should be suppressed to 0.02% or less (more preferably 0.01% or less) because carbonitride is formed to deteriorate mechanical properties and spalling properties are likely to occur.
[0028]
In addition, the steel material itself containing Ti etc. is conventionally known. However, since carbides and the like formed by combining elements such as Ti and C or N are very hard, it is considered that if included in the steel material for rolling rolls, the grindability is significantly deteriorated. The steel material which contains etc. positively was not used as a raw material for rolling rolls. However, when the present inventors studied, while strictly specifying the content of Ti and the like, and also specifying the C content and the N content, a steel material containing Ti and the like was adopted as the material for the rolling roll. However, it has been found that the above-described effects of Ti and the like are remarkably exhibited without causing the conventional problems. Therefore, it is considered that the use of a steel material containing Ti or the like as a steel material for a rolling roll for a galvanized steel sheet is a new finding.
[0029]
The remaining component other than the above basic components in the steel material of the present invention is substantially Fe, but may contain trace components other than these. Examples of such a trace component include impurities, particularly unavoidable impurities such as P and S, and these unavoidable impurities are allowed as long as the effects of the present invention are not impaired (for example, several tens of ppm).
[0030]
It is also effective for the steel material of the present invention to contain V in an amount of 0.01 to 0.5% as another element as required. The reason for determining the preferred range is as follows.
[0031]
V: 0.01 ~ 0.5 %
V is an element that combines with C to form a very hard carbide (VC) and improves the wear resistance of the roll. Further, when V is added in combination with one or more selected from the group consisting of Ti, Zr, Hf and Nb, carbides such as Ti and Zr are refined by V, so the interface between the carbide and the base material increases. This will increase the number of hydrogen trap sites. For this reason, hydrogen which has penetrated into the steel material can be reliably trapped, and the spalling resistance is further improved. In order to effectively exhibit these effects, it is preferable to contain 0.01% or more. More preferably 0.05% or more is recommended. However, since the machinability deteriorates when the V content exceeds 0.5%, the V content is preferably suppressed to 0.5% or less. More preferably, it is recommended to be 0.30% or less.
[0032]
In addition, when V is added alone to the steel material, V also combines with C and N to form carbides and the like, as with Ti and the like, but V carbides and the like are sufficiently effective in promoting recombination of adsorbed hydrogen atoms. The present inventors have confirmed that this is not the case. V carbides also have a hydrogen trapping effect, but the trapping power is smaller than that of Ti carbides and the like, and it is considered that once trapped hydrogen is easily released in an actual machine environment where repeated stress is applied. It is done. Therefore, the present inventors consider that the spalling resistance cannot be improved by adding V alone to the steel material.
[0033]
Next, the rolling roll for galvanization of this invention is demonstrated.
[0034]
The rolling roll for galvanized steel sheet according to the present invention is manufactured using a steel material having the above component composition, and in particular, spalling resistance is improved by generating carbides such as Ti in the roll.
[0035]
However, the rolling roll for galvanized steel sheet of the present invention needs to have a surface hardness of 80 to 100 (HS). In order to improve the spalling property of the rolling roll, it is desirable that the surface hardness is as low as possible. However, if the surface hardness is less than 80 (HS), the surface of the roll is likely to be rough, and the wear resistance is also deteriorated. It is important that the surface hardness is 80 (HS) or more. More preferably, 85 (HS) or more is desirable. However, if the surface hardness exceeds 100 (HS), spalling is likely to occur, so the surface hardness needs to be 100 (HS) or less.
[0036]
Here, the roll surface refers to a region having a depth of about 100 mm from the outermost surface of the roll, and the rolling roll for galvanized steel sheet according to the present invention may have a hardness in this region within the above range. In addition, a Shore hardness meter may be used for the measurement of the surface hardness, the measurement points are at least five, and the average value of the obtained measurement results is defined as the surface hardness.
[0037]
In the rolling roll of the present invention, the hardness inside the roll surface (that is, inside the roll) is not particularly limited, but in order to ensure sufficient strength for transmitting rolling torque, the hardness inside the roll is 25 (HS ) Or more is desirable. However, if the hardness inside the roll exceeds 45 (HS), the cracking susceptibility tends to increase, so it is desirable that the hardness be 45 (HS) or less. The inside of the roll refers to a region inside the roll surface.
[0038]
In order to satisfy the above-mentioned preferable range of roll surface hardness, it is important that the structure of the roll surface layer is mainly composed of martensite. This is because martensite is a hardened structure. In addition, a roll surface layer part points out the area | region to at least 100 mm in depth from a roll outermost surface. In addition, the martensite main body means that the average area ratio of the martensite structure calculated by observing at least 10 visual fields of the roll surface layer portion at 200 to 1000 times using an optical microscope is 80% or more, and several% If so, it is acceptable to include a structure such as retained austenite.
[0039]
The method for producing the rolling roll for galvanized steel sheet according to the present invention is not particularly limited. For example, the roll material is subjected to induction quenching or medium frequency quenching and then tempered at 100 to 200 ° C. A rolling roll that satisfies the requirements is obtained. In particular, in order to make the roll surface layer part a structure mainly composed of martensite and to secure a surface hardness of 80 to 100 (HS), it is desirable to perform medium frequency quenching for deep quenching.
[0040]
The rolling roll of this invention can be used suitably as a roll used when performing skin pass rolling to the steel plate after plating.
[0041]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.
[0042]
Test pieces simulating actual galvanized steel sheet rolling rolls were prepared, and an embrittlement test simulating the actual environment was performed to evaluate the spalling resistance and wear resistance.
[0043]
Example 1
Steel materials having the chemical composition shown in Table 1 below were melted in a 50 kg vacuum melting furnace, cast to produce an ingot, and then cooled. This ingot was hot forged to produce a round bar having a diameter of 12 mm. The round bar was heated at 930 ° C. for 2 hours to austenite, and then air-cooled. The obtained round bar was tempered at 110 to 150 ° C. for 2 hours in order to adjust the surface hardness to about 90 (HS) to obtain a test piece. Using this specimen, the spalling resistance of the rolling roll in an environment where zinc and water coexist was experimentally evaluated.
[0044]
The test piece has a dumbbell shape, and the length is 150 mm and the distance between marked lines is 10 mm. The grip part at both ends has a circular shape with a cross section of 8 mm in diameter, and the thin part at the center has a circular shape with a cross section of 4 mm in diameter. Threaded portions having a length of about 15 mm are formed at both ends of the test piece. The portion except the central thin portion and the screw portions at both ends is galvanized. The thin-walled portion not subjected to galvanization shows an artificial defect portion, and reproduces a portion where zinc powder does not adhere to the surface of the rolling roll used in the actual machine. On the other hand, the galvanized part reproduces the part where the zinc powder adheres to the rolling roll surface used in the actual machine.
[0045]
The obtained test piece was immersed in water for 14 days and mounted on an SSRT test (Slow Strain Rate Technique) machine shown in FIG. 1 to measure elongation. In FIG. 1, 1 indicates a test piece, 2 indicates an SSRT tester, and 3 indicates an atmosphere in the SSRT tester. The test piece 1 is pulled in the direction of the arrow shown in the figure, and the elongation is measured. At this time, the atmosphere in the SSRT tester is water, and the elongation measured in water is El.₁And Crosshead speed is 2 × 10^-3mm / min. The reason for measuring the elongation in water is that this test takes a long time to measure, so that the actual machine environment in which zinc and water coexist during the elongation measurement is simulated. That is, the presence of the zinc-plated part and the non-plated part in water simulates an environment in which zinc is ionized while the generated adsorbed hydrogen atoms enter the thin-walled part.
[0046]
In addition, the same test piece as used above (not immersed in water for 14 days) was directly attached to an SSRT tester to measure elongation. At this time, the atmosphere in the SSRT tester is air, and the elongation measured in the air is El.₀And Crosshead speed is 2 × 10^-3mm / min. The reason for measuring the elongation in the atmosphere is to evaluate the characteristics of the test piece itself.
[0047]
Measured El₀And El₁The spalling sensitivity was calculated from the following equation (1), and the spalling resistance was evaluated based on the calculated value based on the following evaluation criteria. The calculated values and evaluation results of the spalling sensitivity according to the following formula (1) are shown in the following Table 2, and a graph plotting the calculated values of the spalling sensitivity is shown in FIG.
Spalling sensitivity = 1-El₁/ El₀    ... (1)
[0048]
<Evaluation criteria for spalling resistance>
A: The calculated value of the spalling sensitivity is less than 0.3, and the spalling resistance is extremely excellent.
○: Calculated value of spalling sensitivity is less than 0.3 to 0.6, and has excellent spalling resistance
X: The calculated value of spalling sensitivity is 0.6 or more, and is inferior in spalling resistance
[0049]
Next, for the test piece after being immersed in water for 14 days, the thin part (parallel part: φ4 mm × 10 mm) at the center of the test piece was cut, and the amount of hydrogen that had entered the test piece was measured by hydrogen temperature analysis. . In the hydrogen temperature rising analysis, heating was performed in a vacuum at a temperature rising rate of 12 ° C./min, and the hydrogen release peak appearing in the temperature range of 50 to 600 ° C. was integrated to calculate the amount of invading hydrogen. The calculation results are also shown in Table 2 below. A graph plotting the relationship between the amount of invading hydrogen and the spalling sensitivity is shown in FIG. In FIG. 3, ● represents the results of Nos. 1 to 5, and ○ represents the results of Nos. 6 to 18, respectively.
[0050]
Next, the surface hardness of the obtained test piece was measured with a Vickers hardness tester. The measurement position was the thin part at the center of the test piece, the load was 196 N (20 kgf), and the load retention time was 10 seconds. The measured Vickers hardness is converted to Shore hardness, and the results are also shown in Table 2 below. In addition, when the surface layer part of each test piece was observed by 10 visual fields at 200 to 1000 times using an optical microscope, it was a structure mainly composed of martensite.
[0051]
[Table 1]

[0052]
[Table 2]

[0053]
The following can be considered from Table 2 and FIGS. Nos. 1 to 5 are examples that do not satisfy any of the requirements defined in the present invention. No. 1 is an example that does not contain an element such as Ti, and No. 2 is an example in which the Ti content is less than the range defined in the present invention, and the amount of invading hydrogen is large and the spalling resistance cannot be improved. No. 3 is an example in which the Ti content is greater than the range specified in the present invention, and although the amount of invading hydrogen can be reduced, coarse Ti nitride precipitates and the mechanical properties deteriorate, so the spalling resistance is It has not improved. No. 4 is an example not containing an element such as Ti, and the spalling resistance cannot be improved. No. 5 is an example in which the N content is larger than the range specified in the present invention, and spalling is likely to occur by forming coarse nitrides or carbonitrides. On the other hand, Nos. 6 to 18 are examples that satisfy the requirements defined in the present invention, and the amount of intrusion hydrogen is small and the spalling resistance can be improved.
[0054]
Example 2
About the test piece produced using the steel material G of the chemical component composition shown in the said Table 1, the conditions of heat processing were changed and the test piece from which surface hardness differs was produced. That is, the air-cooled round bar in Example 1 was tempered at 100 to 200 ° C. for 2 hours to obtain test pieces having different surface hardness.
[0055]
Using the obtained test piece, the elongation was measured with an SSRT tester in the same manner as in Example 1, and the spalling resistance was evaluated based on the value of the spalling sensitivity calculated from the above equation (1). The calculated values and evaluation results of spalling sensitivity are shown in Table 3 below. Further, the surface hardness of the test piece was measured in the same manner as in Example 1, and the results are shown in Table 3 below.
[0056]
Next, using the obtained heat-treated test piece, a wear test was performed with a Haydon uniaxial wear tester. Alumina having a diameter of 10 mm was used as a counterpart material for the wear test, and wear resistance was evaluated by measuring wear loss after reciprocating 1 cm × 10,000 times while applying a load of 9.8 N. The evaluation criteria for wear resistance are as follows, and the evaluation results are also shown in Table 3 below.
[0057]
<Evaluation criteria for wear resistance>
○: Wear amount is less than 10 mg, and wear resistance is excellent
Δ: Wear amount is less than 10 to 20 mg
X: Wear amount is 20 mg or more and inferior in wear resistance
Moreover, comprehensive evaluation was judged on the following reference | standard based on spalling resistance and abrasion resistance.
[0058]
<Comprehensive evaluation criteria>
○: Evaluation of spalling resistance is ◎ or ○, and evaluation of wear resistance is ○
×: All combinations other than the above ○
[0059]
[Table 3]

[0060]
From Table 3, it can be considered as follows. No. 19 is an example that satisfies the requirements defined in the present invention, and has good spalling resistance and wear resistance. On the other hand, No. 20 and No. 21 have insufficient wear resistance due to their low surface hardness. No. 22 has a large surface hardness, so it tends to generate spalling.
[0061]
【The invention's effect】
According to the present invention, since the rolling roll is not subjected to chrome plating or the like, a rolling roll for galvanized steel sheet excellent in spalling resistance capable of preventing the occurrence of roll surface damage without increasing the roll basic unit is provided. Can do. Moreover, according to this invention, the steel material useful for manufacture of the said rolling roll can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory diagram of an SSRT testing machine.
FIG. 2 is a graph plotting the spalling sensitivity of each test piece.
FIG. 3 is a graph plotting the relationship between the amount of invading hydrogen and the spalling sensitivity.
[Explanation of symbols]
1 Test piece
2 SSRT testing machine
3 Atmosphere in SSRT testing machine

Claims (3)

% By mass
C: 0.6-1.2%
Si: 0.3 to 1.5%,
Mn: 1% or less (excluding 0%),
Ni: 1% or less (including 0%),
Cr: 2-6%
In steel materials for galvanized steel sheet rolling rolls, each containing Mo: 1% or less (excluding 0%),
Containing one or more selected from the group consisting of Ti, Zr, Hf and Nb in a total of 0.01 to 0.30%,
A steel material for a galvanized steel sheet rolling roll excellent in spalling resistance, characterized in that N is suppressed to 0.02% or less (including 0%), and the balance is made of Fe and inevitable impurities.   Furthermore, the steel material of Claim 1 which contains V: 0.01-0.5% as another element. A rolling roll manufactured using the steel material according to claim 1,
Area to a depth of 100mm from the outermost surface is a surface portion of said rolling roll, the average area ratio of martensite is 80% or more of the tissue, and the surface hardness of the roll satisfies the 80 to 100 (HS) A rolling roll for galvanized steel sheet having excellent spalling resistance.

Images