JPH07145448A - Hot tool steel excellent in fatigue fracture property - Google Patents
Hot tool steel excellent in fatigue fracture propertyInfo
- Publication number
- JPH07145448A JPH07145448A JP29201693A JP29201693A JPH07145448A JP H07145448 A JPH07145448 A JP H07145448A JP 29201693 A JP29201693 A JP 29201693A JP 29201693 A JP29201693 A JP 29201693A JP H07145448 A JPH07145448 A JP H07145448A
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- Prior art keywords
- tool steel
- fatigue fracture
- toughness
- steel
- fatigue
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、熱間工具鋼、主として
熱間鍛造用金型材として、あるいは継目無鋼管製造用の
マンドレルバー等の材料として適用できる優れた高温硬
度特性を有し、かつ疲労破壊特性に優れている長寿命な
熱間工具鋼に関するものである。FIELD OF THE INVENTION The present invention has excellent high temperature hardness characteristics applicable to hot tool steel, mainly as a die material for hot forging, or as a material for mandrel bars for producing seamless steel pipes, and the like. The present invention relates to a long-life hot work tool steel having excellent fatigue fracture characteristics.
【０００２】[0002]
【従来の技術】熱間鍛造用金型材として、また製管用マ
ンドレルバー材として使用されている熱間工具鋼の寿命
は、高温硬度、靱性、ヒートチェック、疲労破壊特性等
により決定される。2. Description of the Related Art The life of hot work tool steel used as a hot forging die material and a pipe manufacturing mandrel bar material is determined by high temperature hardness, toughness, heat check, fatigue fracture characteristics and the like.
【０００３】しかしながら、従来の熱間工具鋼では疲労
特性が十分でないため、高温の被加工材との繰り返し接
触により導入された熱亀裂を起点として疲労亀裂が進展
し大割れなどの工具破損を生じることがあった。寿命を
のばすためには、使用時の高温硬度を維持し疲労による
亀裂の進展を防ぐことのできる高い靱性を持つ材質が要
求される。However, since the fatigue properties of conventional hot work tool steels are not sufficient, fatigue cracks develop from thermal cracks introduced by repeated contact with a high-temperature work material, and tool damage such as large cracks occurs. There was an occasion. In order to extend the life, a material having high toughness that can maintain the high temperature hardness during use and prevent the development of cracks due to fatigue is required.
【０００４】ところで、現在主に使用されている熱間工
具鋼としては、JIS −Ｇ4404に規定の熱間金型用鋼なら
びに特開昭53−80318 号公報および特開昭54−50421 号
公報に見られるような鋼があるが、年々製品の多様化と
高精度化および製造スピードの高速化など熱間工具鋼の
使用環境が厳しくなってきており、そのような今日的状
況下からは、十分な疲労破壊特性を持っているとは言え
ない。By the way, as hot work tool steels that are mainly used at present, hot die steels specified in JIS-G4404 and Japanese Patent Laid-Open Nos. 53-80318 and 54-50421 are disclosed. Although there are steels that can be seen, the environment in which hot work tool steels are used has become more severe due to diversification of products, higher precision, and higher production speeds every year. It cannot be said that it has excellent fatigue fracture characteristics.
【０００５】例えば、特開昭53−80318 号公報に開示す
る鋼組成は高温強度を改善することで工具寿命を向上さ
せることを目的にしているが、靱性が十分でない。組成
的にはNiがを含有していない。特開昭54−50421 号公報
に開示する発明もＶ:0.85 〜1.50％含有しており、靱性
の点で十分でない。これらはいずれも疲労亀裂特性につ
いては何ら言及していない。For example, the steel composition disclosed in Japanese Patent Application Laid-Open No. 53-80318 aims at improving the tool life by improving the high temperature strength, but the toughness is not sufficient. Compositionally, it does not contain Ni. The invention disclosed in Japanese Patent Application Laid-Open No. 54-50421 also contains V: 0.85 to 1.50% and is not sufficient in terms of toughness. None of them mentions fatigue crack properties.
【０００６】[0006]
【発明が解決しようとする課題】このように、上記のJI
S 規格鋼等では、現在の熱間工具鋼に求められている工
具寿命を実現できる疲労破壊特性を十分に満足するもの
であると言えなくなってきている。[Problems to be Solved by the Invention]
It has become difficult to say that S-standard steels and the like sufficiently satisfy the fatigue fracture characteristics required to achieve the tool life required for current hot work tool steels.
【０００７】ここに、本発明の目的は、上述のような厳
しい使用環境下でも十分な疲労破壊特性を備えた熱間工
具鋼を提供することである。より具体的には、本発明の
目的は、熱間工具鋼使用時の疲労亀裂の進展速度を抑
え、大割損の原因となる負荷応力の臨界値を向上させ工
具寿命を延ばすことのできる熱間工具鋼を提供すること
である。It is an object of the present invention to provide a hot work tool steel having sufficient fatigue fracture characteristics even under the severe operating environment as described above. More specifically, the object of the present invention is to suppress the progress rate of fatigue cracks during the use of hot tool steel, improve the critical value of the load stress that causes major fracture, and increase the tool life. Is to provide inter-tool steel.
【０００８】さらに具体的には、本発明の目的は、熱間
型鍛造金型である場合、その金型の最も薄肉部分におけ
る肉厚中央部の温度が 100〜200 ℃であり、型表面に作
用する面圧が80 kgf/mm2以下の条件下で使用して、その
工具寿命を40％以上延長可能とする熱間工具鋼を提供す
ることである。More specifically, the object of the present invention is, in the case of a hot die forging die, that the temperature of the central portion of the thickness of the die at the thinnest portion is 100 to 200 ° C. It is intended to provide a hot work tool steel capable of extending the tool life by 40% or more when used under the condition that the acting surface pressure is 80 kgf / mm 2 or less.
【０００９】[0009]
【課題を解決するための手段】本発明者らは、かかる課
題を解決すべく種々検討を重ねた結果、工具鋼使用中の
温度である200 ℃における疲労亀裂進展速度 (da/dn)(d
a ：亀裂長さ、dn：荷重負荷回数) の値を小さくするこ
とと、疲労亀裂進展速度が急速に早くなる応力拡大係数
範囲 (ΔＫ) を向上させることによって工具寿命を伸ば
すことに着目した。Means for Solving the Problems As a result of various studies to solve the problems, the present inventors have found that the fatigue crack growth rate (da / dn) (d
We focused on prolonging the tool life by decreasing the values of a: crack length, dn: number of times of load application, and improving the stress intensity factor range (ΔK) where the fatigue crack growth rate rapidly increases.
【００１０】第１図には、その検討過程で行った疲労亀
裂進展試験(ASTM E647−88) において、得られる亀裂進
展速度 (da/dn)と応力拡大係数範囲 (ΔＫ) の関係を模
式的に示す。FIG. 1 schematically shows the relationship between the crack growth rate (da / dn) and the stress intensity factor range (ΔK) obtained in the fatigue crack growth test (ASTM E647-88) conducted in the examination process. Shown in.
【００１１】このときの試験片形状および供試材の組成
は次の通りであった。 供試材 : JIS G 4404 SKD61相当(C: 0.38、Si: 0.95、
Mn: 0.39、Cr: 5.04、Mo: 1.10、V: 0.81) 試験片 : コンパクト引張り (CT) 試験片。The shape of the test piece and the composition of the test material at this time were as follows. Specimen: JIS G 4404 SKD61 equivalent (C: 0.38, Si: 0.95,
Mn: 0.39, Cr: 5.04, Mo: 1.10, V: 0.81) Specimen: Compact tensile (CT) specimen.
【００１２】図示の結果からは、試験片にかかる応力が
大きくなるに従い亀裂進展速度は上昇し、あるΔＫ値
(ΔＫcr) を境に亀裂が急速に進展し破断を迎えること
がわかる。この破断を押さえるため、すなわち工具鋼の
寿命となる急速な疲労亀裂進展を阻止するためには次の
２点が有効であると考えられる。From the results shown in the figure, the crack growth rate increases as the stress applied to the test piece increases, and a certain ΔK value is obtained.
It can be seen that the crack progresses rapidly at the boundary of (ΔK cr ) and reaches the fracture. The following two points are considered to be effective for suppressing this fracture, that is, for preventing rapid fatigue crack growth, which is the life of the tool steel.
【００１３】ΔＫcrを大きくする。 すなわち、図１において急速な疲労亀裂進展が急速に進
行するΔＫcrの値をΔＫ1 からΔＫ2 に移すことができ
れば、従来より高応力 (ここではΔＫ1 からΔＫ2 まで
の範囲) をかけても急速な疲労亀裂の進展が起こらず工
具寿命を伸ばすことができる。Increase ΔK cr . That is, in FIG. 1, if the value of ΔK cr at which rapid fatigue crack growth progresses rapidly can be shifted from ΔK 1 to ΔK 2 , a higher stress (here, a range from ΔK 1 to ΔK 2 ) is applied than before. The tool life can be extended without rapid fatigue crack growth.
【００１４】da/dn を小さくする。 すなわち、図１において実線の速度から点線の速度へ亀
裂進展速度を下げることができれば、従来と同じ応力を
かけても亀裂の進展が押さえられ工具寿命を伸ばすこと
ができる。Make da / dn small. That is, if the crack growth rate can be reduced from the solid line speed to the dotted line speed in FIG. 1, even if the same stress as in the conventional case is applied, the crack growth is suppressed and the tool life can be extended.
【００１５】ここに、本発明者らは、da/dn を小さく
し、ΔＫcrを増大させることができる鋼組成として、前
述のSKD61 相当に比較してNi: 0.50〜2.5 ％を配合する
とともに、特にＣ:0.25 〜0.35％、Cr:3.00 〜5.00％と
比較的低目に規定し、一方Si:0.05 〜0.35％、Ｖ:0.40
〜0.80％と規定するのが有効であることを知り、本発明
を完成した。Here, the present inventors have added Ni: 0.50 to 2.5% as a steel composition capable of decreasing da / dn and increasing ΔK cr , as compared with the above-mentioned SKD61 equivalent, and In particular, C: 0.25 to 0.35% and Cr: 3.00 to 5.00% are relatively low, while Si: 0.05 to 0.35% and V: 0.40.
The present invention has been completed, knowing that it is effective to define the ratio to be 0.80%.
【００１６】よって、本発明の要旨とするところは、質
量％で、 Ｃ：0.25 〜 0.35 ％、 Si：0.05 〜 0.35 ％ Mn：0.30 〜 0.80 ％、 Cr：3.00 〜 5.00 ％ Mo：1.00 〜 1.80 ％、 Ｖ：0.40 〜 0.80 ％ Ni：0.50 〜 2.50 ％、残部Feおよび不可避的不純物か
ら成る鋼組成を有する疲労破壊特性に優れた熱間工具鋼
である。Therefore, the gist of the present invention is, in mass%, C: 0.25 to 0.35%, Si: 0.05 to 0.35% Mn: 0.30 to 0.80%, Cr: 3.00 to 5.00% Mo: 1.00 to 1.80% , V: 0.40 to 0.80% Ni: 0.50 to 2.50%, with a steel composition consisting of the balance Fe and inevitable impurities, a hot work tool steel excellent in fatigue fracture characteristics.
【００１７】[0017]
【作用】本発明のような鋼組成成分を採用することによ
り、da/dn を小さくし、ΔＫcrを増大させることが可能
で工具寿命を伸ばすことができる。その理由は以下のと
おりである。By using the steel composition components as in the present invention, da / dn can be reduced, ΔK cr can be increased, and the tool life can be extended. The reason is as follows.
【００１８】(i) 適量のMo、Ｖの複合添加によりγ粒を
微細化し亀裂の粒界進展を防止することにより、ΔＫcr
の増大を可能にする。[0018] (i) a suitable amount of Mo, by refining the γ grains by the combined addition of V to prevent intergranular crack propagation, [Delta] K cr
It enables the increase of
【００１９】(ii)Si量低減、低Ｃ化によりマトリックス
の靱性を上げるとともに、Mo、Ｖの微細炭化物分散によ
り亀裂進展を押さえることを可能にする。(Ii) It is possible to increase the toughness of the matrix by reducing the amount of Si and lowering the carbon content, and suppress crack growth by dispersing fine carbides of Mo and V.
【００２０】次に、本発明において鋼組成を上述のよう
に規定した理由にについて述べる。なお、本明細書にお
いて特にことわりがないかぎり、「％」は重量％であ
る。Next, the reason why the steel composition is defined as described above in the present invention will be described. In this specification, "%" is% by weight unless otherwise specified.
【００２１】Ｃ：0.25〜0.35％ Ｃは焼入れ性向上と常温および高温硬度を確保するため
に必要である。また、ＣはMo、Ｖとともに合金炭化物を
形成し、高温での軟化抵抗を向上させる。Ｃを0.35％を
超えて過剰添加すると、靱性に悪影響を及ぼすことから
上限を0.35％と定める。しかし、Ｃが添加不足となる
と、合金炭化物が十分に形成されず硬度低下を招くため
下限を0.25％とした。 C: 0.25 to 0.35% C is necessary for improving the hardenability and ensuring the hardness at normal temperature and high temperature. Further, C forms an alloy carbide with Mo and V, and improves the softening resistance at high temperature. If C is added in excess of 0.35%, the toughness is adversely affected, so the upper limit is set to 0.35%. However, if C is insufficiently added, alloy carbide is not sufficiently formed and hardness is lowered, so the lower limit was made 0.25%.
【００２２】Si：0.05〜0.35％ Siが添加不足となると脱酸不足となり鋼の清浄度が劣化
するため下限を0.05％とした。また、Siが過剰添加され
ると靱性低下を招くため上限を0.35％とした。 Si: 0.05 to 0.35% If the addition of Si is insufficient, deoxidation becomes insufficient and the cleanliness of the steel deteriorates, so the lower limit was made 0.05%. Further, if Si is excessively added, the toughness is lowered, so the upper limit was made 0.35%.
【００２３】Mn：0.30〜0.80％ Mnは焼入れ性向上のために必要であるが、過剰添加する
とMn偏析を起こし材質特性に悪影響を及ぼすため上限を
0.80％とした。また、Mnが添加不足となると十分な焼入
れ性が得られなくなるため下限を0.30％とした。 Mn: 0.30 to 0.80% Mn is necessary for improving the hardenability, but if it is added excessively, Mn segregation occurs and the material properties are adversely affected, so the upper limit is set.
It was 0.80%. Further, if the addition of Mn is insufficient, sufficient hardenability cannot be obtained, so the lower limit was made 0.30%.
【００２４】Cr：3.00〜5.00％ Crは焼入れ性向上および耐摩耗性に有用である。しか
し、Crを過剰添加するとCr炭化物が生成して切削性に問
題を生じるため上限を5.00％とした。また、Crが添加不
足になると十分な焼入れ性が得られなくなるため下限を
3.00％とした。 Cr: 3.00 to 5.00% Cr is useful for improving hardenability and wear resistance. However, if Cr is excessively added, Cr carbides are generated and a problem occurs in machinability, so the upper limit was made 5.00%. Also, if Cr is insufficiently added, sufficient hardenability cannot be obtained, so the lower limit is set.
It was set to 3.00%.
【００２５】Mo：1.00〜1.80％ Moは焼入れ性向上と合金炭化物形成のために必要であ
る。Mo炭化物は高温硬度向上および軟化抵抗向上に有用
であるが、過剰添加すると靱性低下を招くため上限を1.
80％とした。また、Moが添加不足となるとMo炭化物の生
成量が減少して上記の効果が十分に得られないため下限
を1.00％とした。 Mo: 1.00 to 1.80% Mo is necessary for improving hardenability and forming alloy carbide. Mo carbide is useful for improving high-temperature hardness and softening resistance, but if added excessively, it causes toughness deterioration, so the upper limit is 1.
80%. Further, if the addition of Mo becomes insufficient, the amount of Mo carbide generated decreases and the above effect cannot be sufficiently obtained, so the lower limit was made 1.00%.
【００２６】Ｖ：0.40 〜0.80％ ＶはＶ炭化物を分散析出させ、高温硬度向上および高温
での軟化抵抗向上に有用である。Ｖを過剰添加すると靱
性低下をもたらすため、上限を0.80％とした。また、Ｖ
が添加不足になると、高温硬度向上および軟化抵抗向上
に効果を示す十分な量のＶ炭化物が生成しないため下限
を0.40％とした。 V: 0.40 to 0.80% V is useful for improving the high temperature hardness and the softening resistance at high temperature by dispersing and precipitating V carbide. If V is excessively added, the toughness is lowered, so the upper limit was made 0.80%. Also, V
If the addition amount is insufficient, a sufficient amount of V-carbide that is effective in improving the high temperature hardness and the softening resistance will not be formed, so the lower limit was made 0.40%.
【００２７】Ni：0.50 〜2.50％ Niは大型の熱間鍛造金型の焼入れ性および靱性の向上に
不可欠であり、疲労破壊特性を大幅に改善するが、コス
トの面から上限を2.50％とした。また、Niが添加不足と
なると十分な靱性が得られなくなるため下限を0.50％し
た。 Ni: 0.50 to 2.50% Ni is indispensable for improving the hardenability and toughness of a large-sized hot forging die and significantly improves the fatigue fracture characteristics, but the upper limit was 2.50% from the viewpoint of cost. . Further, if the addition of Ni is insufficient, sufficient toughness cannot be obtained, so the lower limit was made 0.50%.
【００２８】その他、不純物としてＳ、Ｐ等が不可避的
に混入してくるが、それぞれ0.005％以下、0.02％以下
であれば問題はない。次に、実施例によって本発明の作
用についてさらに具体的に説明する。In addition, S, P, etc. are inevitably mixed as impurities, but there is no problem if they are 0.005% or less and 0.02% or less, respectively. Next, the operation of the present invention will be described more specifically with reference to Examples.
【００２９】[0029]
【実施例】本例で使用した従来鋼、比較鋼および本発明
鋼の化学組成を表１に示す。表１中の鋼は、150 kg真空
溶解により溶製し、900 ℃以上で厚さ50mmまで鍛造後、
950 ℃×２hr空冷の焼入れ、および650 ℃×４hr空冷の
焼戻しを行なった。EXAMPLES Table 1 shows the chemical compositions of the conventional steel, comparative steel and steel of the present invention used in this example. The steels in Table 1 were melted by vacuum melting at 150 kg, forged to a thickness of 50 mm at 900 ℃ or more,
Air-cooled quenching was performed at 950 ° C. for 2 hours, and tempering was performed at 650 ° C. for 4 hours.
【００３０】この後、１インチサイズの破壊靱性試験片
(CT型) を作製し前述の場合と同様にしてASTM、E399−
78に準じて破壊靱性特性を測定した。この破壊靱性試験
の結果を表２に示す。ここで、従来材 (No.1) を基準と
して寿命評価を行なった。また、疲労亀裂進展特性に密
接な関係のある破壊靱性値と常温硬度について表３に示
す。Thereafter, a 1-inch size fracture toughness test piece
(CT type) was prepared and ASTM, E399-
Fracture toughness characteristics were measured according to 78. The results of this fracture toughness test are shown in Table 2. Here, the life was evaluated based on the conventional material (No. 1). Table 3 shows fracture toughness values and room temperature hardness, which are closely related to fatigue crack growth characteristics.
【００３１】本例では、従来の工具鋼と比較して寿命で
1.4 倍以上、硬度370 (Hv 500g) 以上、破壊靱性値300
kgf/mm1.5 以上を合格とした。これらの試験結果から
は、本発明にかかる鋼は靱性に優れ、十分な高度を保有
し、疲労破壊特性に優れていることが分かる。In this example, the life is longer than that of the conventional tool steel.
1.4 times or more, hardness 370 (Hv 500g) or more, fracture toughness value 300
A kgf / mm of 1.5 or more was passed. From these test results, it is understood that the steel according to the present invention has excellent toughness, possesses a sufficient altitude, and has excellent fatigue fracture properties.
【００３２】[0032]
【表１】 [Table 1]
【００３３】[0033]
【表２】 [Table 2]
【００３４】[0034]
【表３】 [Table 3]
【００３５】[0035]
【発明の効果】以上説明したように、本発明にかる熱間
工具鋼を用いることにより、200 ℃における da/dn を
低下させ、ΔＫcrを増大させることができる。これによ
り、工具の寿命を約50％向上させることが可能となる。As described above, by using the hot work tool steel according to the present invention, da / dn at 200 ° C. can be lowered and ΔK cr can be increased. This makes it possible to improve the tool life by about 50%.
【図１】応力拡大係数範囲と亀裂進展速度の関係を示す
模式的図であり、予備試験の結果得られたグラフであ
る。FIG. 1 is a schematic diagram showing a relationship between a stress intensity factor range and a crack growth rate, and is a graph obtained as a result of a preliminary test.
Claims (1)
労破壊特性に優れた熱間工具鋼。1. In mass%, C: 0.25 to 0.35%, Si: 0.05 to 0.35% Mn: 0.30 to 0.80%, Cr: 3.00 to 5.00% Mo: 1.00 to 1.80%, V: 0.40 to 0.80% Ni: A hot work tool steel with excellent fatigue fracture characteristics having a steel composition of 0.50 to 2.50%, balance Fe and inevitable impurities.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5292016A JP3021256B2 (en) | 1993-11-22 | 1993-11-22 | Hot tool steel with excellent fatigue fracture properties |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5292016A JP3021256B2 (en) | 1993-11-22 | 1993-11-22 | Hot tool steel with excellent fatigue fracture properties |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH07145448A true JPH07145448A (en) | 1995-06-06 |
| JP3021256B2 JP3021256B2 (en) | 2000-03-15 |
Family
ID=17776440
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP5292016A Expired - Lifetime JP3021256B2 (en) | 1993-11-22 | 1993-11-22 | Hot tool steel with excellent fatigue fracture properties |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3021256B2 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0756018A1 (en) * | 1995-07-26 | 1997-01-29 | National-Oilwell, L.P. | Alloy steel for roll caster shell |
| JP2011195917A (en) * | 2010-03-23 | 2011-10-06 | Sanyo Special Steel Co Ltd | Hot work tool steel excellent in toughness |
-
1993
- 1993-11-22 JP JP5292016A patent/JP3021256B2/en not_active Expired - Lifetime
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0756018A1 (en) * | 1995-07-26 | 1997-01-29 | National-Oilwell, L.P. | Alloy steel for roll caster shell |
| JP2011195917A (en) * | 2010-03-23 | 2011-10-06 | Sanyo Special Steel Co Ltd | Hot work tool steel excellent in toughness |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3021256B2 (en) | 2000-03-15 |
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