JP2009256769A - Method for producing steel material for carburizing - Google Patents
Method for producing steel material for carburizing Download PDFInfo
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- JP2009256769A JP2009256769A JP2008222315A JP2008222315A JP2009256769A JP 2009256769 A JP2009256769 A JP 2009256769A JP 2008222315 A JP2008222315 A JP 2008222315A JP 2008222315 A JP2008222315 A JP 2008222315A JP 2009256769 A JP2009256769 A JP 2009256769A
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 32
- 239000010959 steel Substances 0.000 title claims abstract description 32
- 238000005255 carburizing Methods 0.000 title claims description 25
- 239000000463 material Substances 0.000 title claims description 24
- 238000004519 manufacturing process Methods 0.000 title claims description 10
- 238000001816 cooling Methods 0.000 claims abstract description 17
- 238000005098 hot rolling Methods 0.000 claims abstract description 9
- 239000012535 impurity Substances 0.000 claims abstract description 5
- 238000005096 rolling process Methods 0.000 claims abstract description 5
- 230000009467 reduction Effects 0.000 claims description 5
- 238000000034 method Methods 0.000 abstract description 7
- 229910052799 carbon Inorganic materials 0.000 abstract description 6
- 238000010438 heat treatment Methods 0.000 abstract description 6
- 229910052748 manganese Inorganic materials 0.000 abstract description 3
- 229910052710 silicon Inorganic materials 0.000 abstract description 3
- 229910052804 chromium Inorganic materials 0.000 abstract description 2
- 229910052750 molybdenum Inorganic materials 0.000 abstract description 2
- 229910052757 nitrogen Inorganic materials 0.000 abstract description 2
- 229910052760 oxygen Inorganic materials 0.000 abstract 1
- 229910052698 phosphorus Inorganic materials 0.000 abstract 1
- 229910052717 sulfur Inorganic materials 0.000 abstract 1
- 230000003647 oxidation Effects 0.000 description 10
- 238000007254 oxidation reaction Methods 0.000 description 10
- 230000000694 effects Effects 0.000 description 7
- 238000005242 forging Methods 0.000 description 6
- 238000005496 tempering Methods 0.000 description 6
- 229910001566 austenite Inorganic materials 0.000 description 5
- 229910000859 α-Fe Inorganic materials 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 239000013078 crystal Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000010791 quenching Methods 0.000 description 4
- 230000000171 quenching effect Effects 0.000 description 4
- 230000006872 improvement Effects 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 230000002159 abnormal effect Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000007711 solidification Methods 0.000 description 2
- 230000008023 solidification Effects 0.000 description 2
- 230000000087 stabilizing effect Effects 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 230000000007 visual effect Effects 0.000 description 2
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910001567 cementite Inorganic materials 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000001627 detrimental effect Effects 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
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- Heat Treatment Of Steel (AREA)
Abstract
Description
本発明は、熱間鍛造にて製造された浸炭部品の素材となる浸炭用鋼材の製造方法に関するものである。 The present invention relates to a method for manufacturing a carburized steel material which is a material of a carburized part manufactured by hot forging.
従来、ガス浸炭焼入れ−焼戻し処理される浸炭部品、例えば歯車類における、疲労強度や耐久寿命の向上に関して、特許文献1には、粒界酸化や不完全焼入層を低減することを目的として、Feより酸化され易い元素であるSi、MnおよびCr等を低減させ、Feより酸化されにくいNiおよびMo等にて、焼入れ性や機械的性質を調整することが記載されている。 Conventionally, regarding the improvement of fatigue strength and durability life in carburized parts subjected to gas carburizing and tempering treatment, for example, gears, Patent Document 1 describes the purpose of reducing grain boundary oxidation and incomplete quenching layers. It describes that Si, Mn, Cr, etc., which are more easily oxidized than Fe, are reduced, and that hardenability and mechanical properties are adjusted with Ni, Mo, etc., which are less easily oxidized than Fe.
また、特許文献2には、高濃度浸炭と呼ばれ、浸炭時のカーボンポテンシャルを高める手法によって、表面に微細な球状炭化物を析出させ、表面硬さを向上させる技術が提案されている。
しかしながら、これらの改善技術はいずれも、歯車が使用される前の特性に関するものであり、歯車が実際に使用され、噛み合っている状態を考慮したものではない。とりわけ、歯車の駆動面と被駆動面が高面圧で接している状態では、使用前の特性のみでは対応できない面疲労現象が生じてくる。特に、最近の歯車における損傷形態では、エンジンの高出力化、歯車の小型化に対する要望と相俟って、面疲労がより支配的となっている。すなわち、歯車が使用され、噛み合っている状態では、すべりを含む接触圧による摩擦によって、歯の接触面の温度は200〜300℃に上昇していることが推定されている。そのような高温に晒された場合、浸炭層の硬さは使用前より低下することが認められている。浸炭層の硬さの維持は、面疲労に対する因子のなかでも最も重要なものであるが、前述した改善技術によって使用前の浸炭層の硬さを向上させても、使用中における摩擦熱によって生じる浸炭層の硬さ低下が原因となって、面疲労が発生してしまうといった問題があった。 However, all of these improvement techniques relate to characteristics before the gear is used, and do not consider the state in which the gear is actually used and meshed. In particular, when the driving surface and the driven surface of the gear are in contact with each other at a high surface pressure, a surface fatigue phenomenon that cannot be dealt with only by the characteristics before use occurs. In particular, in recent damage forms in gears, surface fatigue is more dominant due to the demand for higher engine output and smaller gears. That is, when the gear is used and meshed, it is estimated that the temperature of the tooth contact surface is increased to 200 to 300 ° C. due to friction caused by contact pressure including slip. It has been observed that when exposed to such high temperatures, the hardness of the carburized layer is lower than before use. Maintaining the hardness of the carburized layer is the most important factor for surface fatigue. However, even if the hardness of the carburized layer before use is improved by the above-described improvement technology, it is caused by frictional heat during use. There has been a problem that surface fatigue occurs due to a decrease in the hardness of the carburized layer.
そこで、本発明は、以上の問題点を安価に解決するために、浸炭部品の焼戻し軟化抵抗の増加を達成する方途について提案することを目的とするものである。 In view of this, the present invention aims to propose a way to achieve an increase in the temper softening resistance of carburized parts in order to solve the above problems at low cost.
さて、発明者らは、上記の目的を達成すべく、特に浸炭部品の焼戻し軟化抵抗を増加するための条件を模索したところ、以下に述べる知見を得るに到った。まず、焼戻し軟化抵抗に有効な元素として知られる、Siを活用することである。すなわち、Siはセメンタイトの析出を抑制することを通して軟化を抑制する作用がある。一方で、Siは、フェライト安定化元素であるため、鋼の変態開始温度を上げ、浸炭後の焼入れにおいて、炭素含有量の少ない心部組織にフェライトを発生する問題がある。フェライトの発生は、ミクロ組織を強度的に不均一にし、靭性並びに疲労強度の低下に結びつき易く、望ましく無い。また、Si添加により熱間鍛造ままでの硬さが増加し、鍛造後の機械加工において、被削性を低下させる原因になる。さらに、Siは浸炭時の粒界酸化を発生しやすい元素であるという、最大の問題点もある。 Now, in order to achieve the above object, the inventors have sought conditions for increasing the temper softening resistance of carburized parts, and have obtained the following knowledge. The first is to use Si, which is known as an effective element for temper softening resistance. That is, Si has an action of suppressing softening through suppressing precipitation of cementite. On the other hand, since Si is a ferrite stabilizing element, there is a problem of raising the transformation start temperature of steel and generating ferrite in a core structure having a low carbon content in quenching after carburizing. The generation of ferrite is undesirable because it makes the microstructure non-uniform in strength and easily leads to a decrease in toughness and fatigue strength. Further, the addition of Si increases the hardness in hot forging, which causes a reduction in machinability in machining after forging. Furthermore, Si has the biggest problem that it is an element that easily generates grain boundary oxidation during carburizing.
そこで、発明者らは、このようなSiに関する問題を解決し、その軟化抵抗に寄与する効果を著しく発揮する浸炭用鋼の製造方法について究明したところ、浸炭素材の化学成分調整と熱間圧延および熱間加工条件とを適正化することが有効であるとの知見を得て、本発明を完成するに到った。 Therefore, the inventors have solved the problem related to Si and investigated a manufacturing method of carburizing steel that exhibits the effect of contributing to its softening resistance. Obtaining knowledge that it is effective to optimize the hot working conditions, the present invention has been completed.
本発明の要旨構成は、次にとおりである。
(1)C:0.1〜0.35mass%、
Si:0.3〜1.1mass%、
Mn:0.2〜1.0mass%、
Mo:0.1〜1.0mass%、
Cr:0.2〜2.0mass%、
Al:0.01〜0.05mass%、
P:0.02mass%以下、
N:0.005〜0.02mass%、
S:0.03mass%以下、
O:0.0015mass%以下および
Sb:0.002〜0.02mass%
を含有し、残部Feおよび不可避的不純物からなる鋼素材に、1150℃以上の温度域に加熱して熱間圧延を施し、800〜950℃の温度域で減面率30〜50%の仕上圧延を施し、次いで0.5℃/s以下で冷却した後、1150℃以下で熱間加工を施し、その後2℃/s以下の冷却速度にて冷却することを特徴とする浸炭用鋼材の製造方法。
The gist configuration of the present invention is as follows.
(1) C: 0.1 to 0.35 mass%,
Si: 0.3-1.1mass%,
Mn: 0.2-1.0mass%,
Mo: 0.1-1.0mass%,
Cr: 0.2 to 2.0 mass%
Al: 0.01-0.05 mass%,
P: 0.02 mass% or less,
N: 0.005-0.02 mass%,
S: 0.03 mass% or less,
O: 0.0015 mass% or less and
Sb: 0.002 to 0.02 mass%
The steel material containing the balance Fe and unavoidable impurities is heated to a temperature range of 1150 ° C or higher and subjected to hot rolling, and finish rolling with a reduction in area of 30 to 50% in the temperature range of 800 to 950 ° C. And then cooling at 0.5 ° C./s or less, then hot working at 1150 ° C. or less, and then cooling at a cooling rate of 2 ° C./s or less.
(2)前記鋼素材は、さらに
Ni:0.1〜2.0mass%および
Cu:0.1〜2.0mass%
の1種または2種を含有することを特徴とする前記(1)に記載の浸炭用鋼材の製造方法。
(2) The steel material further
Ni: 0.1-2.0mass% and
Cu: 0.1-2.0mass%
1 or 2 types of these are contained, The manufacturing method of the steel material for carburizing as described in said (1) characterized by the above-mentioned.
(3)前記鋼素材は、さらに
V:0.03〜0.3mass%
を含有することを特徴とする前記(1)または(2)に記載の浸炭用鋼材の製造方法。
(3) The steel material is further V: 0.03-0.3 mass%
The method for producing a carburizing steel material according to (1) or (2), characterized in that
(4)前記鋼素材は、さらに
Nb:0.005〜0.05mass%
を含有することを特徴とする前記(1)、(2)または(3)に記載の浸炭用鋼材の製造方法。
(4) The steel material further includes
Nb: 0.005-0.05mass%
The method for producing a carburized steel material according to (1), (2) or (3), characterized in that
本発明の製造方法にて得られた浸炭用鋼材を用いれば、浸炭後の浸炭部品における焼戻し軟化抵抗を増加することができる。 If the carburizing steel obtained by the production method of the present invention is used, the temper softening resistance in the carburized parts after carburizing can be increased.
以下、本発明を具体的に説明する。
まず、本発明の浸炭用鋼の素材について、その成分組成を詳しく説明する。
[成分組成]
C:0.1〜0.35mass%
Cは、浸炭処理後の焼入れにより浸炭部品中心部の硬度を高めるために0.1mass%以上は必要であり、一方、多量に含有すると心部の靭性を低下させるため、上限を0.35mass%とする。
The present invention will be specifically described below.
First, the component composition of the material for carburizing steel of the present invention will be described in detail.
[Ingredient composition]
C: 0.1 ~ 0.35mass%
C is required to be 0.1 mass% or more in order to increase the hardness of the carburized part center by quenching after carburizing treatment. On the other hand, if contained in a large amount, the toughness of the core is reduced, so the upper limit is 0.35 mass%. .
Si:0.3〜1.1mass%
Siは、本発明鋼において最も重要な元素である。Siは、歯車等が転動中に到達すると予想される200〜300℃の温度域における軟化抵抗を高める元素であり、そのためには0.3mass%以上の添加が必要である。好ましくは、0.5mass%以上で添加する。しかし、Siはフェライト安定化元素であり、その過剰な添加はAc3変態点を上昇し、通常の焼入れ温度範囲で炭素の含有量の低い心部でフェライトの出現が生じ易くなり、強度の低下を招く。また、浸炭前の鋼材が硬くなり過ぎると、切削性を劣化させる。これを回避するために、上限は1.1mass%とする。
Si: 0.3-1.1mass%
Si is the most important element in the steel of the present invention. Si is an element that increases the softening resistance in the temperature range of 200 to 300 ° C., which is expected to reach during rolling of gears and the like, and for that purpose, addition of 0.3 mass% or more is necessary. Preferably, it is added at 0.5 mass% or more. However, Si is a ferrite stabilizing element, and its excessive addition raises the Ac 3 transformation point, and it is easy for ferrite to appear at the core with a low carbon content in the normal quenching temperature range, resulting in a decrease in strength. Invite. Moreover, when the steel material before carburizing becomes too hard, machinability will deteriorate. In order to avoid this, the upper limit is 1.1 mass%.
Mn:0.2〜1.0mass%
Mnは、焼入れ性に有効な元素であり、少なくとも0.2mass%の添加は必要である。しかし、浸炭異常層を形成し易く、これを低減するために、上限は1.0mass%とする。
Mn: 0.2-1.0mass%
Mn is an element effective for hardenability, and it is necessary to add at least 0.2 mass%. However, it is easy to form a carburized abnormal layer, and in order to reduce this, the upper limit is 1.0 mass%.
Mo:0.1〜1.0mass%
Moは、焼入れ性に有効な元素であり、また浸炭層および心部の靭性を向上させる元素であると同時に、SiやMn等の浸炭異常層を低減する効果もある。そのためには、0.1mass%以上の添加が必要である。しかし、過剰の添加は熱間鍛造後の硬さが硬くなり過ぎ、靭性並びに被削性を劣化させるため、上限を1.0mass%とする。
Mo: 0.1-1.0mass%
Mo is an element effective for hardenability, and is an element that improves the toughness of the carburized layer and the core, and at the same time, has an effect of reducing abnormal carburized layers such as Si and Mn. For that purpose, addition of 0.1 mass% or more is necessary. However, excessive addition makes the hardness after hot forging too hard and deteriorates toughness and machinability, so the upper limit is made 1.0 mass%.
Cr:0.2〜2.0mass%
Crは、焼入れ性に有効な元素であり、そのためには、0.2mass%以上で添加することが好ましい。一方で過剰に添加すると、粒界酸化を招き易い。これを低減するために、上限は2.0mass%とする。
Cr: 0.2-2.0mass%
Cr is an element effective for hardenability, and for that purpose, it is preferably added at 0.2 mass% or more. On the other hand, excessive addition tends to cause grain boundary oxidation. In order to reduce this, the upper limit is set to 2.0 mass%.
Al:0.01〜0.05mass%
Alは、Nと結合してAlNを形成し、オーステナイト結晶粒の微細化に寄与する元素である。そのためには、0.01mass%以上の添加が必要である。しかし、過剰な添加は、疲労強度に対して有害なAl203介在物の生成を助長する。これを回避するために、上限は0.05mass%とする。
Al: 0.01-0.05mass%
Al is an element that combines with N to form AlN and contributes to the refinement of austenite crystal grains. For that purpose, addition of 0.01 mass% or more is necessary. However, excessive addition promotes the formation of Al 2 0 3 inclusions that are detrimental to fatigue strength. In order to avoid this, the upper limit is set to 0.05 mass%.
P:0.02mass%以下
Pは、結晶粒界に偏析し、浸炭層および心部の靭性を低下させる元素であり、低いほど望ましいが、0.02mass%までは許容される。
P: 0.02 mass% or less P is an element that segregates at the grain boundary and lowers the toughness of the carburized layer and the core, and is preferably as low as possible, but is acceptable up to 0.02 mass%.
N:0.005〜0.02mass%
Nは、AlおよびNbと結合し、AlN、Nb(CN)を形成し、オーステナイト結晶粒の微細化に寄与する元素である。従って、適正添加量は、AlおよびNbとの量的バランスで決まるが、その効果を発揮するためには0.005mass%以上の添加が必要である。しかし、過剰に添加すると、凝固時の鋼塊に気泡の発生や鍛造性の劣化を招くため、上限を0.02mass%とする。
N: 0.005-0.02 mass%
N is an element that combines with Al and Nb to form AlN and Nb (CN) and contributes to the refinement of austenite crystal grains. Therefore, the appropriate addition amount is determined by a quantitative balance with Al and Nb, but 0.005 mass% or more is necessary to exert the effect. However, if excessively added, bubbles are generated in the steel ingot during solidification and deterioration of forgeability is caused, so the upper limit is made 0.02 mass%.
S:0.03mass%以下
Sは、硫化物系介在物として存在し、被削性の向上に有効な元素である。そのためには、0.005mass%以上で添加することが好ましい。しかし、過剰な添加は、疲労強度の低下を招く要因となるため、上限を0.03mass%とする。
S: 0.03 mass% or less S is an element that exists as sulfide inclusions and is effective in improving machinability. For that purpose, it is preferable to add at 0.005 mass% or more. However, excessive addition causes a decrease in fatigue strength, so the upper limit is made 0.03 mass%.
O:0.0015mass%以下
Oは、鋼中において酸化物系介在物として存在し、疲労強度を損う元素である。含有量は低いほど望ましいが、0.0015mass%までは許容される。
O: 0.0015 mass% or less O is an element that exists as an oxide inclusion in steel and impairs fatigue strength. The lower the content, the better, but up to 0.0015 mass% is acceptable.
Sb:0.002〜0.02mass%
Sbは、粒界酸化を低減する効果がある。そのためには、少なくとも0.002mass%は必要であるが、0.02mass%を超えて含有しても効果が飽和するため、0.002〜0.02mass%とする。好ましくは、0.005〜0.02mass%とする。
Sb: 0.002 to 0.02 mass%
Sb has the effect of reducing grain boundary oxidation. For that purpose, at least 0.002 mass% is necessary, but even if it exceeds 0.02 mass%, the effect is saturated, so 0.002 to 0.02 mass%. Preferably, it is 0.005 to 0.02 mass%.
さらに、本発明では、以下に述べる元素を適宜含有させることができる。
Ni:0.1〜2.0mass%
Niは、焼入れ性に有効な元素であり、そのためには、0.1mass%以上で添加することが好ましい。一方、過剰な添加は経済的な観点から好ましくないばかりか、浸炭層の残留オーステナイトの形成を促進し、硬さを低下させる場合もあることから、上限は2.0mass%とする。
Furthermore, in the present invention, the following elements can be appropriately contained.
Ni: 0.1-2.0mass%
Ni is an element effective for hardenability, and for that purpose, it is preferable to add at 0.1 mass% or more. On the other hand, excessive addition is not preferable from an economical point of view, but also promotes formation of retained austenite in the carburized layer and may reduce hardness, so the upper limit is set to 2.0 mass%.
Cu:0.1〜2.0mass%
Cuは、焼入れ性に有効な元素であり、そのためには、0.1mass%以上で添加することが好ましい。一方、過剰な添加は熱間鍛造性を劣化させるために、上限は2.0mass%とする。
Cu: 0.1-2.0mass%
Cu is an element effective for hardenability, and for that purpose, it is preferably added at 0.1 mass% or more. On the other hand, excessive addition deteriorates hot forgeability, so the upper limit is made 2.0 mass%.
V:0.03〜0.3mass%
Vは、浸炭温度近傍の低温域で炭化物を形成して硬さを向上する効果を有し、そのためには0.03mass%以上で添加する。一方、過剰な添加は靭性を劣化させるため、上限は0.3mass%とする。
V: 0.03-0.3 mass%
V has an effect of improving the hardness by forming carbide in a low temperature region near the carburizing temperature, and for that purpose, V is added at 0.03 mass% or more. On the other hand, since excessive addition degrades toughness, the upper limit is made 0.3 mass%.
Nb:0.005〜0.05mass%
Nbは、CおよびNと結合してAl(CN)を形成し、オーステナイト結晶粒の微細化に寄与する元素である。そのためには、0.01mass%以上の添加は必要である。しかし、過剰な添加は靭性を劣化させるため、上限は0.05mass%とする。
Nb: 0.005-0.05mass%
Nb is an element that combines with C and N to form Al (CN) and contributes to the refinement of austenite crystal grains. For that purpose, addition of 0.01 mass% or more is necessary. However, excessive addition degrades toughness, so the upper limit is made 0.05 mass%.
[熱間圧延条件]
加熱温度
浸炭時の結晶粒微細化に有効な、微細な析出物を得るためには、凝固時に生成した粗大な晶出物および析出物を一度、完全に固溶させる必要がある。そのためには、熱間圧延時の加熱温度を1150℃以上とする必要がある。
[Hot rolling conditions]
Heating temperature In order to obtain fine precipitates effective for refining crystal grains during carburizing, it is necessary to completely dissolve once the coarse crystallized products and precipitates generated during solidification. For this purpose, the heating temperature during hot rolling needs to be 1150 ° C. or higher.
800〜950℃の温度域での減面率
後述の熱間加工後に軟質な組織を得るためには、前組織を微細にする必要がある。そのため、低温、すなわち、800〜950℃の温度域にて、30〜50%の減面率の仕上圧延が必要である。
Area reduction ratio in a temperature range of 800 to 950 ° C. In order to obtain a soft structure after hot working described later, it is necessary to make the previous structure fine. Therefore, finish rolling with a reduction in area of 30 to 50% is required at a low temperature, that is, in a temperature range of 800 to 950 ° C.
冷却速度
後述の熱間加工後に軟質な組織を得るためには、微細な析出物を生成させる必要があり、冷却速度が速すぎると、十分に析出が生じないため、0.5℃/s以下の冷却速度とする。
Cooling rate In order to obtain a soft structure after hot working described later, it is necessary to generate fine precipitates. If the cooling rate is too high, precipitation does not occur sufficiently, so cooling at 0.5 ° C / s or less Speed.
冷却後は、熱間加工に供する。この熱間加工とは、熱間鍛造や再度の熱間圧延を意味する。 After cooling, it is subjected to hot working. This hot working means hot forging or re-hot rolling.
[熱間加工条件]
加熱温度
熱間圧延で得られた微細折出物の固溶を防ぐために、1150℃以下の加熱とする。下限については、オーステナイト域であるAc3点以上で加熱することが好ましい。熱間加工の仕上げは、900℃以上で行うことが好ましい。
[Hot working conditions]
Heating temperature In order to prevent dissolution of fine breakouts obtained by hot rolling, heating is performed at 1150 ° C or lower. The lower limit, it is preferable to heat at Ac 3 point or more is the austenite region. The hot working finish is preferably performed at 900 ° C. or higher.
冷却速度
冷却速度が速いと硬さが増加して被削性が劣化するため、800〜500℃の温度域での平均冷却速度を2℃/s以下にする必要がある。
Cooling rate If the cooling rate is high, the hardness increases and the machinability deteriorates. Therefore, the average cooling rate in the temperature range of 800 to 500 ° C needs to be 2 ° C / s or less.
表1に示す成分組成を有し、残部Feおよび不可避的不純物からなる鋼素材に、表2に示す条件に従って、熱間圧延、次いで熱間加工を施し、その後冷却することによって、浸炭用鋼材を作製した。この鋼材から直径30mmおよび長さ150mmの丸棒並びにローラピッチング試験片を切り出した。かくして得られた丸棒について、粒界酸化および被削性を調査するとともに、浸炭処理後、180℃および300℃焼戻しを行った後の硬さ(焼戻し軟化抵抗性)を調査した。そして、ローラピッチング試験片を用いて、ローラピッチング寿命(焼戻し軟化抵抗性)を調査した。その結果を、表3に示す。 According to the conditions shown in Table 2, the steel material having the component composition shown in Table 1 and the balance Fe and inevitable impurities is subjected to hot rolling, then hot working, and then cooled to obtain a carburizing steel material. Produced. A round bar having a diameter of 30 mm and a length of 150 mm and a roller pitching test piece were cut out from this steel material. The round bar thus obtained was examined for grain boundary oxidation and machinability, and after the carburizing treatment, the hardness after tempering at 180 ° C. and 300 ° C. (tempering softening resistance) was investigated. And the roller pitching life (tempering softening resistance) was investigated using the roller pitching test piece. The results are shown in Table 3.
なお、浸炭処理は930℃で7時間、カーボンポテンシャル0.8%の条件で浸炭を実施した。ローラピッチング寿命は180℃×1時間加熱の焼戻し処理を実施したものを用いて評価した。
また、粒界酸化は浸炭処理後の試験片の表面を光学顕微鏡で観察し、粒界酸化深さを測定した。光学顕微鏡観察は、400倍で行い、各視野での最大粒界酸化深さを求め、10視野の平均値を粒界酸化深さとした。
被削性は、熱間加工後の硬さで評価した。浸炭処理後の硬さは、表面から50μmの深さの浸炭層深さを180℃焼戻しと300℃×1時間再加熱処理後で測定した。
ローラピッチング試験は、最大ヘルツ面圧3400MPa、すべり率40%、油温80℃の条件で行い、ピッチングが発生する寿命で評価した。
The carburizing process was carried out at 930 ° C. for 7 hours under the condition of a carbon potential of 0.8%. The roller pitting life was evaluated using a roller tempered by heating at 180 ° C. for 1 hour.
Moreover, the grain boundary oxidation observed the surface of the test piece after a carburizing process with the optical microscope, and measured the grain boundary oxidation depth. Observation with an optical microscope was performed at a magnification of 400 times, the maximum grain boundary oxidation depth in each visual field was determined, and the average value of 10 visual fields was defined as the grain boundary oxidation depth.
The machinability was evaluated by the hardness after hot working. The hardness after the carburizing treatment was measured after the carburized layer depth of 50 μm from the surface was tempered at 180 ° C. and reheated at 300 ° C. for 1 hour.
The roller pitching test was conducted under the conditions that the maximum hertz surface pressure was 3400 MPa, the slip rate was 40%, and the oil temperature was 80 ° C.
表に示すように、Si量が本発明範囲から外れて少なくなりすぎると、焼き戻し軟化抵抗が低下し、ローラピッチング寿命が低下する。一方、Si量が本発明範囲から外れて多くなりすぎると、熱間鍛造後の硬さが高すぎて、その後の加工に悪影響を及ぼす、おそれがある。
また、Sbは本発明範囲から外れて少なくなりすぎると、粒界酸化層が厚くなる結果、ローラピッチング寿命が低下する。なお、Sbの添加量が0.02%を超えると、その効果は飽和している。
As shown in the table, when the amount of Si deviates from the scope of the present invention and becomes too small, the temper softening resistance is lowered and the roller pitching life is lowered. On the other hand, if the amount of Si is too large outside the scope of the present invention, the hardness after hot forging is too high, which may adversely affect the subsequent processing.
On the other hand, if Sb falls outside the scope of the present invention and becomes too small, the grain boundary oxide layer becomes thick and as a result, the roller pitching life is reduced. Note that when the amount of Sb added exceeds 0.02%, the effect is saturated.
表4に示す成分組成を有し、残部Feおよび不可避的不純物からなる鋼素材に、表2のNo.2に示した条件に従って、熱間圧延、次いで熱間加工を施し、その後冷却することによって、実施例1と同様に浸炭用鋼材を作製した。この鋼材から直径30mmおよび長さ150mmの丸棒並びにローラピッチング試験片を切り出した。かくして得られた丸棒について、粒界酸化および被削性を調査するとともに、浸炭処理後、180℃および300℃焼戻した後の硬さ(焼戻し軟化抵抗性)を、実施例1と同様に調査した。そして、ローラピッチング試験片を用いて、ローラピッチング寿命(焼戻し軟化抵抗性)を実施例1と同様に調査した。
さらに、丸棒の芯部の靭性を評価するために、該丸棒の中心部から、10mm角で長さ55mmのUノッチシャルピー試験片を切り出し、この靭性を評価した。
その結果を、表5に示す。
No. 1 in Table 2 is added to a steel material having the component composition shown in Table 4 and the balance Fe and inevitable impurities. According to the conditions shown in No. 2, carburizing steel was produced in the same manner as in Example 1 by performing hot rolling, then hot working, and then cooling. A round bar having a diameter of 30 mm and a length of 150 mm and a roller pitching test piece were cut out from this steel material. The round bars thus obtained were investigated for grain boundary oxidation and machinability, and after carburizing, the hardness after tempering at 180 ° C. and 300 ° C. (tempering softening resistance) was investigated in the same manner as in Example 1. did. And the roller pitching life (temper softening resistance) was investigated similarly to Example 1 using the roller pitching test piece.
Further, in order to evaluate the toughness of the core of the round bar, a U-notch Charpy test piece having a 10 mm square and a length of 55 mm was cut out from the center of the round bar, and this toughness was evaluated.
The results are shown in Table 5.
Claims (4)
Si:0.3〜1.1mass%、
Mn:0.2〜1.0mass%、
Mo:0.1〜1.0mass%、
Cr:0.2〜2.0mass%、
Al:0.01〜0.05mass%、
P:0.02mass%以下、
N:0.005〜0.02mass%、
S:0.03mass%以下、
O:0.0015mass%以下および
Sb:0.002〜0.02mass%
を含有し、残部Feおよび不可避的不純物からなる鋼素材に、1150℃以上の温度域に加熱して熱間圧延を施し、800〜950℃の温度域で減面率30〜50%の仕上圧延を施し、次いで0.5℃/s以下で冷却した後、1150℃以下で熱間加工を施し、その後2℃/s以下の冷却速度にて冷却することを特徴とする浸炭用鋼材の製造方法。 C: 0.1-0.35 mass%
Si: 0.3-1.1mass%,
Mn: 0.2-1.0mass%,
Mo: 0.1-1.0mass%,
Cr: 0.2 to 2.0 mass%
Al: 0.01-0.05 mass%,
P: 0.02 mass% or less,
N: 0.005-0.02 mass%,
S: 0.03 mass% or less,
O: 0.0015 mass% or less and
Sb: 0.002 to 0.02 mass%
The steel material containing the balance Fe and unavoidable impurities is heated to a temperature range of 1150 ° C or higher and subjected to hot rolling, and finish rolling with a reduction in area of 30 to 50% in the temperature range of 800 to 950 ° C. And then cooling at 0.5 ° C./s or less, then hot working at 1150 ° C. or less, and then cooling at a cooling rate of 2 ° C./s or less.
Ni:0.1〜2.0mass%および
Cu:0.1〜2.0mass%
の1種または2種を含有することを特徴とする請求項1に記載の浸炭用鋼材の製造方法。 The steel material is further
Ni: 0.1-2.0mass% and
Cu: 0.1-2.0mass%
1 or 2 types of these are contained, The manufacturing method of the steel material for carburizing of Claim 1 characterized by the above-mentioned.
V:0.03〜0.3mass%
を含有することを特徴とする請求項1または2に記載の浸炭用鋼材の製造方法。 The steel material is further V: 0.03-0.3 mass%
The method for producing a carburizing steel material according to claim 1 or 2, characterized by comprising:
Nb:0.005〜0.05mass%
を含有することを特徴とする請求項1、2または3に記載の浸炭用鋼材の製造方法。 The steel material is further
Nb: 0.005-0.05mass%
The method for producing a carburizing steel material according to claim 1, 2, or 3.
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CN115369322A (en) * | 2022-08-26 | 2022-11-22 | 包头钢铁(集团)有限责任公司 | Production method of 900 MPa-grade high-strength sucker rod round steel containing rare earth |
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JP2011074467A (en) * | 2009-09-30 | 2011-04-14 | Jfe Steel Corp | Steel for carburization |
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CN115369322A (en) * | 2022-08-26 | 2022-11-22 | 包头钢铁(集团)有限责任公司 | Production method of 900 MPa-grade high-strength sucker rod round steel containing rare earth |
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