JP2020105547A - Structure member and method for manufacturing the same - Google Patents
Structure member and method for manufacturing the same Download PDFInfo
- Publication number
- JP2020105547A JP2020105547A JP2018243060A JP2018243060A JP2020105547A JP 2020105547 A JP2020105547 A JP 2020105547A JP 2018243060 A JP2018243060 A JP 2018243060A JP 2018243060 A JP2018243060 A JP 2018243060A JP 2020105547 A JP2020105547 A JP 2020105547A
- Authority
- JP
- Japan
- Prior art keywords
- grain size
- structural member
- crystal grain
- nitriding
- manufacturing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Images
Landscapes
- Heat Treatment Of Articles (AREA)
- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
Abstract
Description
本発明は、熱処理を経て与えられる疲労特性に優れた構造用部材及びその製造方法に関し、特に、比較的低廉な合金からなるとともに寸法及び形状制限の少ない構造用部材及びその製造方法に関する。 TECHNICAL FIELD The present invention relates to a structural member which is excellent in fatigue characteristics given through heat treatment and a manufacturing method thereof, and more particularly to a structural member which is made of a relatively inexpensive alloy and has few size and shape restrictions and a manufacturing method thereof.
構造用部材、特に継ぎ手やボルトのような締結部材などにあっては、静的な荷重に対する強度とともに、繰り返し荷重に対する強度が求められる。かかる疲労特性に優れる構造用部材は、ＮｉやＭｏなどの合金元素を添加した合金鋼などが用いられ、一般的には、焼入れ焼戻しの熱処理を経て提供される。 Structural members, particularly fastening members such as joints and bolts, require strength against static loads as well as strength against repeated loads. As the structural member having excellent fatigue characteristics, alloy steel added with an alloying element such as Ni or Mo is used, and is generally provided through heat treatment such as quenching and tempering.
例えば、特許文献１では、焼入れ焼戻し後に時効処理することで、ボルトの疲労強度を向上させる方法を開示している。ここでは、ＪＩＳ規格ＳＣＭ４３５相当のいわゆるクロムモリブテン合金鋼を用いたボルトの例について述べている。ボルト形状に機械加工された被処理材を８００〜９５０℃に加熱して水または油中に焼入れ、続いて、４００〜５５０℃で３０〜１２０分間保持して焼き戻し、更に、２０〜３００℃で１０分〜７３５日間保持する時効処理をするとしている。かかる熱処理により、疲労強度を高めることができるとしている。 For example, Patent Document 1 discloses a method of improving the fatigue strength of bolts by aging treatment after quenching and tempering. Here, an example of a bolt using so-called chrome molybdenum alloy steel equivalent to JIS SCM435 is described. The material to be processed which has been machined into a bolt shape is heated to 800 to 950° C. and quenched in water or oil, subsequently held at 400 to 550° C. for 30 to 120 minutes and tempered, and further 20 to 300° C. The aging treatment is said to be held for 10 minutes to 735 days. It is said that such heat treatment can increase the fatigue strength.
一方、ＮｉやＭｏなどの合金元素を抑制し又はこれを含まず、比較的に低廉な成分組成の鋼又は合金鋼を用いて、窒化や浸炭などの表面拡散処理を施すことにより、疲労特性を高めた構造用部材及び製造方法も広く知られている。 On the other hand, steel or alloy steel that suppresses or does not contain alloying elements such as Ni and Mo and that has a relatively low component composition is subjected to surface diffusion treatment such as nitriding or carburizing to improve fatigue characteristics. Enhanced structural members and manufacturing methods are also widely known.
例えば、特許文献２では、上記したようにＮｉやＭｏなどを含まない比較的に低廉な成分組成の合金鋼であって、浸炭処理しつつ結晶粒径を制御することで疲労特性を高めた構造部材を開示している。質量％で、Ｃ：０．１０〜０．４０％，Ｓｉ：０．０５〜２．００％，Ｍｎ：０．３０〜２．００％，Ｃｒ：０．３０〜３．００％，Ｎ：０．０２５％以下とした合金に、Ａｌ：０．０２０〜０．１００％，Ｎｂ：０．０１〜０．２０％，Ｔｉ：０．００５〜０．２０％のうちの１種若しくは２種以上を含有させて、ピン止め粒子を生成させて窒化による結晶粒径の制御をするとともに、更に、浸炭処理をして疲労強度を高めるとしている。表面から３ｍｍ以上の内部の結晶粒度番号が５番以下の粗粒である一方、浸炭処理により、表面から５０μｍ以内の表層では結晶粒度番号で５番よりも大きな細粒になる。かかる結晶粒径の傾斜により、疲労強度を高めることができるとしている。 For example, in Patent Document 2, as described above, it is an alloy steel having a relatively low component composition that does not contain Ni, Mo, etc., and has a structure in which fatigue characteristics are enhanced by controlling the crystal grain size while carburizing. A member is disclosed. % By mass, C: 0.10 to 0.40%, Si: 0.05 to 2.00%, Mn: 0.30 to 2.00%, Cr: 0.30 to 3.00%, N: One or two of Al: 0.020 to 0.100%, Nb: 0.01 to 0.20%, Ti: 0.005 to 0.20% in an alloy of 0.025% or less. By adding the above, pinning particles are generated to control the crystal grain size by nitriding, and further, carburizing treatment is performed to increase fatigue strength. The inside of the grain size number of 3 mm or more is a coarse grain with a grain size number of 5 or less, while the carburizing treatment results in fine grains having a grain size number of 5 or larger in the surface layer within 50 μm from the surface. It is said that the fatigue strength can be increased by the inclination of the crystal grain size.
上記したように、比較的低廉な合金でありながら、熱処理により疲労特性を向上させた構造用部材が提案されている。一方で、熱処理を経るため、寸法及び形状に制限が生じる。すなわち、大型部材や複雑形状の部材では、焼入れ時に中心部と表面部とで温度差が生じることから、得られる金属組織にも差が生じて、結果として、所定の疲労特性を得られないことがある。 As described above, there has been proposed a structural member having a fatigue property improved by heat treatment while being a relatively inexpensive alloy. On the other hand, since heat treatment is performed, the size and shape are limited. That is, in the case of a large member or a member having a complicated shape, a temperature difference occurs between the central portion and the surface portion during quenching, so that a difference also occurs in the obtained metallographic structure, and as a result, the predetermined fatigue characteristics cannot be obtained. There is.
本発明は、以上のような状況に鑑みてなされたものであって、その目的とするところは、比較的低廉な合金からなるとともに、寸法及び形状制限の少ない疲労特性に優れた構造用部材及びその製造方法を提供することにある。 The present invention has been made in view of the above circumstances, and an object thereof is a structural member which is made of a relatively inexpensive alloy and has excellent fatigue characteristics with small size and shape restrictions. It is to provide the manufacturing method.
本発明による構造用部材は、部材形状に加工後に浸窒処理されて窒化層を有する構造用部材であって、質量％で、Ｃ：０．１３〜０．４３％、Ｓｉ：０．０５〜０．３５％、Ｍｎ：０．６０〜０．９０％、Ｃｒ：０．８０〜１．２５％、Ｎ：０．０１５％以下、Ａｌ：０．０２０〜０．１００％、を含み、残部Ｆｅ及び不可避的不純物からなる成分組成の鋼からなり、オーステナイト結晶粒度で、表面から３ｍｍ以上の内部の結晶粒径を５．０番よりも小さな粗粒としつつ、表面から５０μｍ以内の前記窒化層の結晶粒径を８．０番よりも大きな細粒に維持した組織を有することを特徴とする。 The structural member according to the present invention is a structural member having a nitrided layer that has been nitrided after being processed into a member shape and has a mass% of C: 0.13 to 0.43% and Si: 0.05 to. 0.35%, Mn: 0.60 to 0.90%, Cr: 0.80 to 1.25%, N: 0.015% or less, Al: 0.020 to 0.100%, and the balance The nitride layer, which is made of steel having a composition of Fe and inevitable impurities, has an austenite grain size of 3 mm or more from the surface and has a coarse grain size of less than 5.0, while having a grain size of less than 5.0 μm from the surface. Is characterized by having a structure in which the crystal grain size of is maintained at a fine grain larger than 8.0.
かかる発明によれば、比較的低廉な成分組成の合金からなるとともに、表層の窒化層と内部との結晶粒径に傾斜を与えて疲労特性に優れた構造用部材とし得るのである。 According to such an invention, it is possible to obtain a structural member which is made of an alloy having a relatively inexpensive component composition and which has a graded crystal grain size between the surface nitrided layer and the inside thereof and is excellent in fatigue characteristics.
上記した発明において、前記内部は焼き入れ焼き戻し組織を有することを特徴としてもよい。かかる発明によれば、構造用部材として必要とされる靭性を含む機械的性質に優れた構造用部材とし得るのである。 In the above invention, the inside may have a quenching and tempering structure. According to this invention, a structural member having excellent mechanical properties including toughness required as a structural member can be obtained.
また、本発明による構造用部材の製造方法は、質量％で、Ｃ：０．１３〜０．４３％、Ｓｉ：０．０５〜０．３５％、Ｍｎ：０．６０〜０．９０％、Ｃｒ：０．８０〜１．２５％、Ｎ：０．０１５％以下、Ａｌ：０．０２０〜０．１００％、を含み、残部Ｆｅ及び不可避的不純物からなる成分組成を有する鋼を部品形状に加工し、この被処理材を浸窒性ガスにて浸窒処理後に焼き入れ焼き戻しする窒化層を有する構造用部材の製造方法であって、前記浸窒処理において、オーステナイト結晶粒度で、結晶粒径を８．０番よりも大とした前記被処理材を浸窒処理炉内に設置し、Ａ３点以上の保持温度に加熱して保持し、表面から５０μｍ以内の前記窒化層の結晶粒径を８．０番よりも大の細粒に維持させつつ、表面から３ｍｍ以上の内部の結晶粒径を５．０番よりも小の粗粒となるようにするにあたって、前記保持温度をＴ（℃）として保持時間をｔ（ｈ）とすると、２４０００＜５０１６＋２０Ｔ＋１５２ｔ＜２５５００とすることを特徴とする。 Moreover, the manufacturing method of the structural member by this invention is C:0.13-0.43%, Si:0.05-0.35%, Mn:0.60-0.90% by mass %, A steel containing Cr: 0.80 to 1.25%, N: 0.015% or less, Al: 0.020 to 0.100%, and a balance of Fe and unavoidable impurities has a component shape. A method for manufacturing a structural member having a nitrided layer, which is processed and quenched and tempered after a nitriding treatment of this material with a nitriding gas, wherein in the nitriding treatment, the austenite crystal grain size is a crystal grain. and installing the workpiece that is larger than the diameter 8.0 No. to carbonitriding treatment furnace, and held by heating to the holding temperature of the three or more points a, from the surface of the nitride layer within 50μm grain The holding temperature is set to T in order to maintain the diameter of fine grains larger than No. 8.0 and the crystal grain size of 3 mm or more from the surface into coarse grains smaller than No. 5.0. When the holding time is (° C.) and t(h), 24000<5016+20T+152t<25500.
かかる発明によれば、比較的低廉な合金を用いて、表層の窒化層と内部との結晶粒径に傾斜を有する疲労特性に優れた構造用部材を寸法及び形状制限を受けることなく与え得るのである。 According to this invention, it is possible to provide a structural member excellent in fatigue characteristics having a grain size gradient between the surface nitrided layer and the inside without using size and shape restrictions, using a relatively inexpensive alloy. is there.
上記した発明において、前記浸窒処理は、前記浸窒性ガスの窒素の分圧を０．１気圧以上とすることを特徴としてもよい。かかる発明によれば、構造用部材として必要とされる靭性を含む機械的性質を劣化させずに、表層の窒化層と結晶粒径の傾斜を確実に与え得るのである。 In the above invention, the nitrogen treatment may be performed by setting the partial pressure of nitrogen in the nitrogen gas to be 0.1 atm or more. According to this invention, it is possible to surely give the surface nitride layer and the gradient of the crystal grain size without deteriorating the mechanical properties including the toughness required as the structural member.
本発明による１つの実施例としての構造用部材及びその製造方法について、図１及び図２を用いて説明する。 A structural member and a method for manufacturing the same according to one embodiment of the present invention will be described with reference to FIGS. 1 and 2.
図１を参照すると、まず、所定の成分組成を有する鋼を部材形状に加工し、被処理材とする（Ｓ１）。ここでは、鍛造加工や機械加工などによって、得ようとする構造用部材の形状に素材を成形する。部材形状は、後述するように浸窒処理によって得られた窒化層を残存させるため、部材としての最終形状に近い形状である。例えば、窒化層を十分残存させられる場合において、部材形状から表面研磨等の加工をして最終形状としてもよい。なお、被処理材は、その金属組織において、その結晶粒径をオーステナイト結晶粒度で８．０番よりも大きな細粒のものとする。これについては後述する。 Referring to FIG. 1, first, steel having a predetermined component composition is processed into a member shape to obtain a material to be processed (S1). Here, the material is formed into the shape of the structural member to be obtained by forging or machining. The shape of the member is a shape close to the final shape of the member because the nitrided layer obtained by the nitriding treatment remains as described later. For example, when the nitrided layer can be left sufficiently, the final shape may be obtained by subjecting the member shape to processing such as surface polishing. The material to be treated has a fine grain size of austenite grain size larger than 8.0 in its metal structure. This will be described later.
上記した所定の成分組成は、質量％で、Ｃ：０．１３〜０．４３％、Ｓｉ：０．０５〜０．３５％、Ｍｎ：０．６０〜０．９０％、Ｃｒ：０．８０〜１．２５％、Ｎ：０．０１５％以下、Ａｌ：０．０２０〜０．１００％、を含むものである。ＮｉやＭｏなどの原材料として高価な合金元素を添加するものではなく、比較的低廉な合金の成分組成である。図２の実施例１〜７にその代表な成分組成を示した。 The above-mentioned predetermined composition is% by mass, C: 0.13 to 0.43%, Si: 0.05 to 0.35%, Mn: 0.60 to 0.90%, Cr: 0.80. Up to 1.25%, N: 0.015% or less, and Al: 0.020 to 0.100%. It does not add an expensive alloying element as a raw material such as Ni or Mo, but has a relatively inexpensive alloy composition. Typical component compositions are shown in Examples 1 to 7 of FIG.
次いで、被処理材は、処理炉内において焼入れに併せて浸窒処理される（Ｓ２）。すなわち、処理炉内を真空引きして減圧雰囲気とした上で、オーステナイト相の安定領域となるＡ３点以上の保持温度Ｔ（℃）まで加熱するとともに窒素ガス等をパージして浸窒性ガス雰囲気下で保持時間ｔ（ｈ）の保持を行い、浸窒させる。保持後、部材を急冷し、焼入れを完了させる。ここで、浸窒処理による窒化層を確実に与えるために、浸窒性ガスは窒素の分圧を０．１気圧以上とされることが好ましい。 Next, the material to be treated is subjected to the nitriding treatment in the treatment furnace along with the quenching (S2). That is, the inside of the processing furnace is evacuated to create a decompressed atmosphere, and then heated to a holding temperature T (° C.) of A 3 or higher, which is a stable region of the austenite phase, and nitrogen gas or the like is purged to remove the nitriding gas Holding is carried out for a holding time t (h) under an atmosphere and nitrification is performed. After holding, the member is rapidly cooled to complete quenching. Here, it is preferable that the nitrogen partial pressure of the nitriding gas is 0.1 atm or more in order to surely give a nitrided layer by the nitriding treatment.
浸窒条件としては、表面近傍に窒化層を形成するとともに、表面から深さ３．０ｍｍ以上の内部において結晶粒をオーステナイト結晶粒度で５．０番よりも小さな粗粒とし、且つ、表面から５０μｍ以内の表層部において結晶粒を同じく結晶粒度で８．０番よりも大きな微細粒とするように定める。 As the nitriding conditions, a nitride layer is formed in the vicinity of the surface, and the crystal grains inside the depth of 3.0 mm or more from the surface are coarse grains with an austenite grain size smaller than No. 5.0 and 50 μm from the surface. In the surface layer portion within, the crystal grains are determined so as to be fine grains having a grain size larger than No. 8.0.
特に、浸窒条件として、保持温度Ｔ（℃）と保持時間ｔ（ｈ）とを用いた以下の式１の値を２４０００よりも大きく２５５００よりも小さい範囲内となるようにすることが好ましい。
５０１６＋２０Ｔ＋１５２ｔ … （式１）
式１の値を２４０００よりも大きくすることで素材を良好に焼入れ可能とするとともに、ピン止め粒子の少ない内部を十分に粗粒化させる。このような浸窒に伴い内部の結晶粒は成長する。他方、式１の値を２５５００よりも小さくすることで、表面から侵入する窒素による窒化物を形成させて結晶粒の粗大化を抑制して、特に、表面から深さ５０μｍ以内の表層部の結晶粒を微細に維持する。つまり、保持温度を低く、保持時間を短くする傾向とすることで結晶粒の過剰な成長を抑制し、表層の窒化物からなるピン止め粒子によるピン止め効果を十分得るのである。すなわち、このように式１の値を上記した範囲内に納めるような浸窒条件とすることで、得られる構造用部材の表層部と内部とに上記したような結晶粒径の傾斜を与えることが容易になる。
In particular, as the nitriding condition, it is preferable that the value of Expression 1 below, which uses the holding temperature T (° C.) and the holding time t (h), be set within the range of more than 24000 and less than 25500.
5016+20T+152t (Equation 1)
By setting the value of Expression 1 to be larger than 24000, the material can be satisfactorily quenched, and the inside with few pinning particles is sufficiently coarsened. With such nitriding, internal crystal grains grow. On the other hand, by setting the value of Expression 1 to be smaller than 25500, a nitride due to nitrogen penetrating from the surface is formed to suppress coarsening of crystal grains, and in particular, a crystal of a surface layer portion within a depth of 50 μm from the surface is formed. Keep the grains fine. That is, by making the holding temperature low and making the holding time short, the excessive growth of crystal grains is suppressed, and the pinning effect of the pinning particles made of the nitride of the surface layer is sufficiently obtained. That is, by providing the nitriding conditions such that the value of Equation 1 is within the above range, the above-described inclination of the crystal grain size is given to the surface layer portion and the inside of the obtained structural member. Will be easier.
最後に、必要に応じて焼戻し処理して、焼入れ焼き戻し組織を与えて構造用部材としての機械的性質を調整する（Ｓ３）。上記したように式１の値を所定の範囲内に納めたことで、かかる焼き戻し処理の後に構造用部材として必要とされる靭性や引張強度などの機械的性質を確実に与えることができる。 Finally, if necessary, a tempering process is performed to give a quenching and tempering structure to adjust the mechanical properties of the structural member (S3). By setting the value of Expression 1 within the predetermined range as described above, it is possible to reliably provide mechanical properties such as toughness and tensile strength required for the structural member after the tempering treatment.
上記した浸窒処理により、表層の結晶粒の成長を抑制して微細に維持する。特に、焼戻し後において、表面から深さ３．０ｍｍ以上の内部では、粒度番号を５．０番よりも小さくする粒径の粗大な結晶粒に成長するが、表面から深さ５０μｍ以内の表層部では、粒度番号を８．０番よりも大きな細かい結晶粒径を有する細粒を維持させるのである。すなわち、浸窒処理される被処理材は浸窒処理前において、オーステナイト結晶粒度で粒度番号を８．０番より大きな粒径の微細な結晶粒を有するものとする必要がある。 By the above-mentioned nitriding treatment, the growth of the surface crystal grains is suppressed and finely maintained. In particular, after tempering, inside the depth of 3.0 mm or more from the surface, coarse crystal grains having a grain size that makes the grain size number smaller than 5.0 grow, but the surface layer portion within a depth of 50 μm from the surface. Then, fine grains having a fine grain size larger than the grain size number of 8.0 are maintained. That is, the material to be subjected to the nitriding treatment needs to have fine crystal grains with a grain size number larger than 8.0 in austenite grain size before the nitriding treatment.
ここで、特許文献２でも述べられているように、結晶粒について部材の表層を細粒にして内部を粗粒にすることで疲労強度を高くできる。よって、本実施例においても上記したように、表層部を微細な結晶粒に維持したまま、内部を粗大な結晶粒に成長させたことで高い疲労強度を得ることができる。これにより、大型部材や複雑形状の部材のように焼入れ時に中心部と表面部とで温度差が生じるような部材であっても、所定の疲労特性を得ることが容易となる。つまり、寸法及び形状制限を受けることなく疲労特性に優れた構造用部材を得ることができる。 Here, as described in Patent Document 2, the fatigue strength can be increased by making the surface layer of the member fine with respect to the crystal grain and making the inside coarse. Therefore, also in the present embodiment, as described above, high fatigue strength can be obtained by growing the inside of the crystal grains to be coarse while maintaining the fine crystal grains in the surface layer portion. This makes it easy to obtain a predetermined fatigue characteristic even for a member such as a large member or a member having a complicated shape that causes a temperature difference between the central portion and the surface portion during quenching. That is, it is possible to obtain a structural member having excellent fatigue characteristics without being restricted in size and shape.
本実施例による構造部材は、表層を細粒にしたことで、さらに耐遅れ破壊性にも優れる。遅れ破壊は、水素の拡散に起因するが、例えば、０．１規定の塩酸を滴下する曲げ遅れ破壊試験において、３０ｈ破断強度を静曲げ試験の破断強度に対する比（遅れ破壊強度比）で０．６以上とすることができる。よって、例えば、耐遅れ破壊性を要求される継ぎ手やボルトのような締結部材などにも適用し得る。細粒とすることで結晶粒全体としての表面積が増え、結晶粒界に偏析する不純物の面積あたりの濃度を低下させるため、粒界強度が上昇し耐遅れ破壊性を向上させ得るものと考えられる。 The structural member according to this example is further excellent in delayed fracture resistance because the surface layer is made fine. Delayed fracture is caused by the diffusion of hydrogen. For example, in a bending delayed fracture test in which 0.1N hydrochloric acid is dropped, the 30 h fracture strength is a ratio of the fracture strength of the static bending test (delayed fracture strength ratio) to 0. It can be 6 or more. Therefore, for example, the present invention can be applied to a joint member or a fastening member such as a bolt that requires delayed fracture resistance. It is considered that the fine grain increases the surface area of the entire crystal grain and reduces the concentration per unit area of the impurities segregated at the grain boundary, so that the grain boundary strength is increased and the delayed fracture resistance can be improved. ..
［製造試験］
上記した製造方法により構造部材としての試験材を製造し、結晶粒度、引張強度、遅れ破壊強度比を測定した結果について、図２及び図３を用いて説明する。
[Manufacturing test]
A test material as a structural member is manufactured by the above-described manufacturing method, and the results of measuring the grain size, the tensile strength, and the delayed fracture strength ratio will be described with reference to FIGS. 2 and 3.
図２に示すように、実施例１〜７及び比較例１〜５の成分組成による合金を用いて試験材を製造した。すなわち、これらの合金からなる素材について、上記した部材形状として試験片形状に加工した後、浸窒処理した。 As shown in FIG. 2, test materials were manufactured using the alloys having the component compositions of Examples 1 to 7 and Comparative Examples 1 to 5. That is, the raw materials made of these alloys were processed into the shape of the test piece as the above-mentioned member shape, and then subjected to the nitriding treatment.
図３に示すように、浸窒処理については、実施例１〜７、比較例１〜５のそれぞれについての「浸窒条件」に従った。すなわち、それぞれの実施例及び比較例において、示された窒素分圧、保持温度Ｔ（℃）、保持時間ｔ（ｈ）による浸窒処理をし、油冷により焼入れした。このとき、上記した式１：５０１６＋２０Ｔ＋１５２ｔの値をそれぞれ示した。さらに、焼戻し処理として、５００℃で１ｈ保持し、空冷した。 As shown in FIG. 3, the nitrification treatment was performed in accordance with the “nitrification conditions” for each of Examples 1 to 7 and Comparative Examples 1 to 5. That is, in each of the Examples and Comparative Examples, the nitrogen partial pressure, the holding temperature T (° C.), and the holding time t (h) shown in the examples were used for nitrification treatment, and quenching was performed by oil cooling. At this time, the values of the above formula 1:5016+20T+152t are shown. Further, as a tempering treatment, it was held at 500° C. for 1 hour and air-cooled.
得られた試験片を用いて、結晶粒度、引張強度、遅れ破壊強度比、それぞれについての測定を行った。結晶粒度については、表面からの深さ５０μｍの位置及び３ｍｍの位置で測定してそれぞれ表層結晶粒度及び内部結晶粒度とした。引張試験はＪＩＳ Ｚ２２４１に従った。また、遅れ破壊強度比については、曲げ遅れ破壊試験によって測定した。静曲げ強度を測定した上で、０．１規定の塩酸を滴下しつつ静曲げ強度の０．８〜０．２倍の応力を負荷し、遅れ破壊の破断時間を求めた上で、３０ｈ破断強度と静曲げ強度との比をとって遅れ破壊強度比とした。 The obtained test pieces were used to measure the grain size, the tensile strength, and the delayed fracture strength ratio. The crystal grain size was measured at a position at a depth of 50 μm from the surface and at a position of 3 mm to obtain the surface layer grain size and the internal grain size, respectively. The tensile test was in accordance with JIS Z2241. The delayed fracture strength ratio was measured by a bending delayed fracture test. After the static bending strength was measured, a stress of 0.8 to 0.2 times the static bending strength was applied while dropping 0.1 N hydrochloric acid, and the fracture time for delayed fracture was calculated, and then the fracture was performed for 30 hours. The delayed fracture strength ratio was obtained by taking the ratio between the strength and the static bending strength.
実施例１〜７は、いずれも、式１の値を２４０００超及び２５５００未満の範囲内としている。表層部の窒化層内では微細な結晶粒径を維持しており、結晶粒度番号で最低９．２番、少なくとも、結晶粒度番号で８．０番よりも大きな微細な結晶粒となっていた。また、内部では、結晶粒度番号で最大４．９番であり、少なくとも、結晶粒度番号で５．０番よりも小さい粗大な結晶粒となっていた。上記した通り、表層の窒化層を微細粒に維持しつつ、内部において粗粒となるような浸窒処理であり、これにより疲労強度を高く且つ引張強度を１１８０〜１２４６ＭＰａとできて、遅れ破壊強度比をいずれも０．６０以上とできるのである。つまり、耐遅れ破壊性にも優れる。 In each of Examples 1 to 7, the value of the formula 1 is set within the range of more than 24000 and less than 25500. A fine crystal grain size was maintained in the nitride layer in the surface layer portion, and the crystal grain size number was at least 9.2, and at least the crystal grain size was greater than 8.0. In addition, inside the grains, the maximum grain size was 4.9, and the coarse grains were at least smaller than the grain size 5.0. As described above, the nitriding treatment is performed so as to form coarse particles inside while maintaining the fine particles in the surface nitrided layer, whereby the fatigue strength is high and the tensile strength can be 1180 to 1246 MPa, and the delayed fracture strength is All the ratios can be 0.60 or more. That is, the delayed fracture resistance is also excellent.
一方、比較例１では、式１の値が２４０００に満たず、内部でも結晶粒径が細かく、結晶粒度番号で１１．０であった。つまり、内部でも、結晶粒度番号を５．０番よりも小とするような粗大な結晶粒は得られず、疲労強度の観点で劣っていた。また、引張強度も他に比べて低く、１０５０ＭＰａであった。 On the other hand, in Comparative Example 1, the value of Formula 1 was less than 24000, and the crystal grain size was fine inside, and the crystal grain size number was 11.0. That is, even inside, a coarse crystal grain having a crystal grain size number smaller than 5.0 was not obtained, which was inferior in terms of fatigue strength. In addition, the tensile strength was lower than the others and was 1050 MPa.
比較例２では、式１の値が２５５００以上となり、表層部でも結晶粒径が大きく、結晶粒度番号で７．２番であった。つまり、表層部でも、結晶粒度番号を８．０番よりも大とするような微細な結晶粒は得られず、疲労強度の観点で劣っていた。また、遅れ破壊強度比を０．６未満として耐遅れ破壊性に乏しい。 In Comparative Example 2, the value of Formula 1 was 25500 or more, the crystal grain size was large even in the surface layer portion, and the grain size number was 7.2. That is, even in the surface layer portion, fine crystal grains having a grain size number larger than 8.0 were not obtained, which was inferior in terms of fatigue strength. Further, the delayed fracture strength ratio is less than 0.6, and the delayed fracture resistance is poor.
比較例３では、式１の値を２４０００よりも大きく２５５００よりも小さい範囲内としたものの、表層部でも結晶粒径が大きく、結晶粒度番号で７．１番であった。つまり、表層部でも結晶粒度番号を８．０番よりも大とする微細な結晶粒は得られず、疲労強度の観点で劣っていた。また、遅れ破壊強度比を０．６未満として耐遅れ破壊性にも乏しい。これはＡｌの含有量が少なかったために、窒化層のうち特に表層部にピン止め粒子を十分に形成できなかったものと考えられる。 In Comparative Example 3, although the value of Formula 1 was set in the range of larger than 24000 and smaller than 25500, the crystal grain size was large even in the surface layer portion, and the crystal grain size number was 7.1. That is, even in the surface layer, fine crystal grains having a grain size number larger than 8.0 were not obtained, which was inferior in terms of fatigue strength. Further, the delayed fracture strength ratio is less than 0.6, and the delayed fracture resistance is also poor. It is considered that this is because the pinning particles could not be formed sufficiently in the surface layer portion of the nitride layer because the content of Al was small.
比較例４では、式１の値を上記した範囲内としたものの、表層部でも結晶粒径が大きく、結晶粒度番号で６．６番であった。つまり、表層部でも結晶粒度番号を８．０番よりも大とする微細な結晶粒を得られず、疲労強度の観点で劣っていた。また、遅れ破壊強度比を０．６未満として耐遅れ破壊性にも乏しい。これは、窒素分圧が０．１気圧よりも低かったために、表層部にピン止め粒子を十分に形成できるような浸窒性ガス雰囲気を得られていなかったためと考えられる。 In Comparative Example 4, although the value of Formula 1 was within the above range, the crystal grain size was large even in the surface layer portion, and the crystal grain size number was 6.6. That is, even in the surface layer portion, it was not possible to obtain fine crystal grains having a grain size number larger than 8.0, which was inferior in terms of fatigue strength. Further, the delayed fracture strength ratio is less than 0.6, and the delayed fracture resistance is also poor. It is considered that this is because the nitrogen partial pressure was lower than 0.1 atm, and therefore the nitriding gas atmosphere capable of sufficiently forming the pinned particles in the surface layer portion was not obtained.
比較例５では、合金にＭｏを添加された成分組成を有することで浸窒条件の同じ比較例１に比べて高い引張強度を得ており、高い焼入れ性を有すると考えられる。しかし、比較例１と同様に式１の値を２４０００以下とした結果、内部でも結晶粒径が小さく、結晶粒度番号で１０．７番であった。このように、結晶粒度番号を５．０番よりも小とする粗大な結晶粒を得られていないが、遅れ破壊強度比は高く、耐遅れ破壊性には優れる。なお、上記した実施例１〜７のＭｏは不可避的不純物（０．０５％以下）として含有したものである（図２参照）。 Comparative Example 5 has a higher tensile strength than Comparative Example 1 under the same nitriding conditions because it has a component composition in which Mo is added to the alloy, and is considered to have high hardenability. However, as in Comparative Example 1, the value of Formula 1 was set to 24000 or less, and as a result, the crystal grain size was small inside, and the grain size number was 10.7. Thus, although coarse crystal grains having a grain size number smaller than 5.0 have not been obtained, the delayed fracture strength ratio is high and the delayed fracture resistance is excellent. In addition, Mo of Examples 1 to 7 described above is contained as an unavoidable impurity (0.05% or less) (see FIG. 2 ).
以上の結果からわかるように、実施例１〜７においては、結晶粒に関して部材の表層部で微細粒を得るとともに内部で粗粒を得て、上記したように疲労強度の観点から優れるとともに、耐遅れ破壊性にも優れる。他方、比較例によれば、表層部の結晶粒を粗大にしたり内部の結晶粒を微小にしたりして、いずれも疲労強度の観点で劣っていた。また、比較例２〜４においては耐遅れ破壊性においても劣った。 As can be seen from the above results, in Examples 1 to 7, fine grains were obtained in the surface layer portion of the member with respect to the crystal grains and coarse grains were obtained inside, and as described above, it was excellent from the viewpoint of fatigue strength and Excellent delayed fracture property. On the other hand, according to the comparative example, the crystal grains in the surface layer were made coarse and the crystal grains in the interior were made fine, which were all inferior in terms of fatigue strength. Further, in Comparative Examples 2 to 4, the delayed fracture resistance was also inferior.
ところで、上記した実施例を含む合金とほぼ同等の結晶粒度を部材の表層部及び内部で得てほぼ同等の疲労強度及び耐遅れ破壊性を得ることのできる合金の組成範囲は以下のように定められる。 By the way, the composition range of the alloy that can obtain substantially the same grain size as the alloy including the above-described examples in the surface layer portion and the inside of the member to obtain substantially the same fatigue strength and delayed fracture resistance is defined as follows. To be
Ｃは、機械強度を確保するために必要である。一方、過剰に含有させると靭性を低下させてしまう。これらを考慮して、Ｃは、質量％で０．１３〜０．４３％の範囲内である。 C is necessary to secure mechanical strength. On the other hand, if contained too much, the toughness will be reduced. Considering these, C is in the range of 0.13 to 0.43% by mass.
Ｓｉは、脱酸剤として必要である。一方、過剰に含有させると熱間鍛造などの塑性加工において割れの発生を助長する。これらを考慮して、Ｓｉは、質量％で、０．０５〜０．３５％の範囲内である。 Si is necessary as a deoxidizing agent. On the other hand, an excessive content promotes the occurrence of cracks in plastic working such as hot forging. Considering these, Si is in the range of 0.05 to 0.35% in mass %.
Ｍｎは、焼入れ性を確保するために必要である。一方、過剰に含有させると冷間や熱間での塑性加工性や被削性などの機械加工性を劣化させる。これらを考慮して、Ｍｎは、質量％で、０．６０〜０．９０％の範囲内である。 Mn is necessary to secure hardenability. On the other hand, if contained excessively, the machinability such as plastic workability and machinability in cold or hot is deteriorated. Considering these, Mn is in the range of 0.60 to 0.90% in mass %.
Ｃｒは、引張強度及び靭性を向上させるために必要である。一方、過剰に含有させると加工性の劣化を招く。これらを考慮して、Ｃｒは、質量％で、０．８０〜１．２５％の範囲内である。 Cr is necessary to improve tensile strength and toughness. On the other hand, if it is contained excessively, workability is deteriorated. Taking these into consideration, Cr is in the range of 0.80 to 1.25% in mass %.
Ｎは、Ａｌと結合してピン止め粒子としての窒化物粒子を形成し、浸窒処理によって表層の結晶粒成長を抑制するが、内部の結晶粒を粗大化させるために予め鋼中に含有させる量を少なくしておくことが好ましい。そこで、Ｎは、質量％で、０．０１５％以下の範囲内である。 N combines with Al to form nitride particles as pinning particles, and suppresses the growth of crystal grains in the surface layer by the nitriding treatment, but N is contained in steel in advance in order to coarsen the crystal grains. It is preferable to keep the amount small. Therefore, N is in the range of 0.015% or less by mass %.
Ａｌは、Ｎと結合してピン止め粒子としての窒化物粒子を形成し、浸窒処理によって表層の結晶粒成長を抑制するために必要である。一方、過剰に含有させると加工性を劣化させたり、粗大な窒化物を生成したりする。これらを考慮して、Ａｌは、質量％で、０．０２０〜０．１００％の範囲内である。 Al is necessary to combine with N to form nitride particles as pinning particles and to suppress the crystal grain growth of the surface layer by the nitriding treatment. On the other hand, if contained excessively, the workability is deteriorated and coarse nitrides are generated. Taking these into consideration, Al is in the range of 0.020 to 0.100% in mass %.
以上、本発明の代表的な実施例を説明したが、本発明は必ずしもこれらに限定されるものではなく、当業者であれば、本発明の主旨又は添付した特許請求の範囲を逸脱することなく、種々の代替実施例及び改変例を見出すことができるであろう。
Although the typical embodiments of the present invention have been described above, the present invention is not necessarily limited to these, and a person skilled in the art can deviate from the gist of the present invention or the scope of the appended claims. , Various alternatives and modifications may be found.
Claims (4)
質量％で、
Ｃ：０．１３〜０．４３％、
Ｓｉ：０．０５〜０．３５％、
Ｍｎ：０．６０〜０．９０％、
Ｃｒ：０．８０〜１．２５％、
Ｎ：０．０１５％以下、
Ａｌ：０．０２０〜０．１００％、
を含み、残部Ｆｅ及び不可避的不純物からなる成分組成の鋼からなり、
オーステナイト結晶粒度で、表面から３ｍｍ以上の内部の結晶粒径を５．０番よりも小さな粗粒としつつ、表面から５０μｍ以内の前記窒化層の結晶粒径を８．０番よりも大きな細粒に維持した組織を有することを特徴とする構造用部材。 A structural member having a nitrided layer that has been subjected to surface nitriding treatment after being processed into a member shape,
In mass %,
C: 0.13 to 0.43%,
Si: 0.05 to 0.35%,
Mn: 0.60 to 0.90%,
Cr: 0.80 to 1.25%,
N: 0.015% or less,
Al: 0.020 to 0.100%,
And a balance of Fe and unavoidable impurities.
With austenite grain size, the inner grain size of 3 mm or more from the surface is a coarse grain smaller than No. 5.0, while the grain size of the nitride layer within 50 μm from the surface is a fine grain greater than No. 8.0. A structural member having a structure maintained at.
Ｃ：０．１３〜０．４３％、
Ｓｉ：０．０５〜０．３５％、
Ｍｎ：０．６０〜０．９０％、
Ｃｒ：０．８０〜１．２５％、
Ｎ：０．０１５％以下、
Ａｌ：０．０２０〜０．１００％、
を含み、残部Ｆｅ及び不可避的不純物からなる成分組成を有する鋼を部品形状に加工し、この被処理材を浸窒性ガスにて浸窒処理後に焼き入れ焼き戻しする窒化層を有する構造用部材の製造方法であって、
前記浸窒処理において、オーステナイト結晶粒度で、結晶粒径を８．０番よりも大きな細粒の前記被処理材を浸窒処理炉内に設置し、Ａ３点以上の保持温度に加熱して保持し、表面から５０μｍ以内の前記窒化層の結晶粒径を８．０番よりも大きな細粒に維持させつつ、表面から３ｍｍ以上の内部の結晶粒径を５．０番よりも小さな粗粒となるようにするにあたって、
前記保持温度をＴ（℃）として保持時間をｔ（ｈ）とすると、
２４０００＜５０１６＋２０Ｔ＋１５２ｔ＜２５５００
とすることを特徴とする構造用部材の製造方法。 In mass %,
C: 0.13 to 0.43%,
Si: 0.05 to 0.35%,
Mn: 0.60 to 0.90%,
Cr: 0.80 to 1.25%,
N: 0.015% or less,
Al: 0.020 to 0.100%,
And a structural member having a nitride layer in which a steel having a component composition containing the balance Fe and unavoidable impurities is processed into a component shape, and the material to be treated is quenched and tempered after a nitriding treatment with a nitriding gas. The manufacturing method of
In the nitriding treatment, austenitic grain size, the grain size the material to be treated larger granules than 8.0 No. installed in nitriding treatment furnace and heated to a holding temperature of three or more points A While maintaining and maintaining the crystal grain size of the nitride layer within 50 μm from the surface to a fine grain larger than No. 8.0, the crystal grain size of the inside of 3 mm or more from the surface is a coarse grain smaller than No. 5.0. In order to be
When the holding temperature is T (° C.) and the holding time is t (h),
24000<5016+20T+152t<25500
And a method for manufacturing a structural member.
The method for manufacturing a structural member according to claim 3, wherein in the nitrification treatment, the partial pressure of nitrogen in the nitrifying gas is set to 0.1 atm or more.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2018243060A JP7261385B2 (en) | 2018-12-26 | 2018-12-26 | Structural member and manufacturing method thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2018243060A JP7261385B2 (en) | 2018-12-26 | 2018-12-26 | Structural member and manufacturing method thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2020105547A true JP2020105547A (en) | 2020-07-09 |
| JP7261385B2 JP7261385B2 (en) | 2023-04-20 |
Family
ID=71449006
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2018243060A Active JP7261385B2 (en) | 2018-12-26 | 2018-12-26 | Structural member and manufacturing method thereof |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP7261385B2 (en) |
Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH08311607A (en) * | 1995-05-16 | 1996-11-26 | Sumitomo Metal Ind Ltd | Low strain carburized gear excellent in deddendum bending strength and its production |
| WO2000077265A1 (en) * | 1999-06-15 | 2000-12-21 | Skf Engineering & Research Centre B.V. | Wear-and fracture-resistant steel |
| JP2007077411A (en) * | 2005-09-09 | 2007-03-29 | Daido Steel Co Ltd | Machine structural component having excellent fatigue strength and wear property, and method for producing the same |
| WO2009054530A1 (en) * | 2007-10-24 | 2009-04-30 | Nippon Steel Corporation | Carbonitrided induction-hardened steel part with excellent rolling contact fatigue strength at high temperature and process for producing the same |
| JP2011168820A (en) * | 2010-02-17 | 2011-09-01 | Sumitomo Metal Ind Ltd | Steel product having carbo-nitrided layer and method for producing the same |
| JP2011184768A (en) * | 2010-03-10 | 2011-09-22 | Kobe Steel Ltd | High strength case hardening steel component and method for producing the same |
| JP2014208867A (en) * | 2013-03-26 | 2014-11-06 | 大同特殊鋼株式会社 | Vacuum carburization method |
| JP2014234552A (en) * | 2013-06-05 | 2014-12-15 | 大同特殊鋼株式会社 | Carburized component and method of manufacturing the same |
| JP2017171970A (en) * | 2016-03-22 | 2017-09-28 | 新日鐵住金株式会社 | Carbonitrided component |
-
2018
- 2018-12-26 JP JP2018243060A patent/JP7261385B2/en active Active
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH08311607A (en) * | 1995-05-16 | 1996-11-26 | Sumitomo Metal Ind Ltd | Low strain carburized gear excellent in deddendum bending strength and its production |
| WO2000077265A1 (en) * | 1999-06-15 | 2000-12-21 | Skf Engineering & Research Centre B.V. | Wear-and fracture-resistant steel |
| JP2007077411A (en) * | 2005-09-09 | 2007-03-29 | Daido Steel Co Ltd | Machine structural component having excellent fatigue strength and wear property, and method for producing the same |
| WO2009054530A1 (en) * | 2007-10-24 | 2009-04-30 | Nippon Steel Corporation | Carbonitrided induction-hardened steel part with excellent rolling contact fatigue strength at high temperature and process for producing the same |
| JP2011168820A (en) * | 2010-02-17 | 2011-09-01 | Sumitomo Metal Ind Ltd | Steel product having carbo-nitrided layer and method for producing the same |
| JP2011184768A (en) * | 2010-03-10 | 2011-09-22 | Kobe Steel Ltd | High strength case hardening steel component and method for producing the same |
| JP2014208867A (en) * | 2013-03-26 | 2014-11-06 | 大同特殊鋼株式会社 | Vacuum carburization method |
| JP2014234552A (en) * | 2013-06-05 | 2014-12-15 | 大同特殊鋼株式会社 | Carburized component and method of manufacturing the same |
| JP2017171970A (en) * | 2016-03-22 | 2017-09-28 | 新日鐵住金株式会社 | Carbonitrided component |
Also Published As
| Publication number | Publication date |
|---|---|
| JP7261385B2 (en) | 2023-04-20 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| KR101122840B1 (en) | Carbon steel sheet having excellent carburization properties, and method for producing same | |
| JP5328785B2 (en) | Hardened martensitic steel with low or no cobalt content, method for producing parts from the steel, and parts thus obtained | |
| US6767414B2 (en) | Maraging steel having high fatigue strength and maraging steel strip made of same | |
| JP2011528068A (en) | Hardened martensitic steel with low cobalt content, method for producing parts from the steel, and parts obtained thereby | |
| KR101726251B1 (en) | Steel for nitrocarburizing and nitrocarburized component, and methods for producing said steel for nitrocarburizing and said nitrocarburized component | |
| JP2019167630A (en) | Martensitic stainless steel member | |
| JP2020519757A (en) | Martensitic hardenable steel and its use, especially screw manufacturing | |
| US20100247368A1 (en) | Alloy and a method of making an alloy | |
| JP2010070827A (en) | Carbonitrided component made of steel | |
| JP2023002842A (en) | Machine component for automobiles made of steel material for carburization excellent in static torsional strength and torsional fatigue strength | |
| KR102554100B1 (en) | NiCrMo STEEL AND METHOD FOR MANUFACTURING NiCrMo STEEL MATERIAL | |
| JP2007063584A (en) | Oil tempered wire and manufacturing method therefor | |
| JP2005146303A (en) | Method for manufacturing curburized steel superior in grain-coarsening resistance after high temperature carburizing | |
| JP7261385B2 (en) | Structural member and manufacturing method thereof | |
| JP2020029608A (en) | Steel for carbonitriding | |
| JP2003201513A (en) | High strength case hardening steel | |
| JP3480630B2 (en) | Case-hardened steel with excellent cold workability and crystal grain coarsening properties | |
| TW200418997A (en) | High tensile strength steel having excellent fatigue strength and method of producing the same | |
| JPH08260039A (en) | Production of carburized and case hardened steel | |
| JP6721141B1 (en) | Steel for soft nitriding, soft nitriding component, and manufacturing method thereof | |
| JP3907986B2 (en) | Method for producing case-hardened steel with excellent cold workability and grain size characteristics | |
| JP6477614B2 (en) | Steel for soft nitriding and parts and method for manufacturing them | |
| JP2019026899A (en) | Carburization component and carbonitride component | |
| JP7196707B2 (en) | Forged member for nitriding and its manufacturing method, and surface hardened forged member and its manufacturing method | |
| JP7167482B2 (en) | Non-heat treated steel for nitriding and crankshaft |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20211014 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20221026 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20221028 |
|
| A601 | Written request for extension of time |
Free format text: JAPANESE INTERMEDIATE CODE: A601 Effective date: 20221216 |
|
| A521 | Request for written amendment filed |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20230119 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20230310 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20230323 |
|
| R150 | Certificate of patent or registration of utility model |
Ref document number: 7261385 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R150 |