JP5099660B2 - High strength tapping screw - Google Patents
High strength tapping screw Download PDFInfo
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- JP5099660B2 JP5099660B2 JP2005185796A JP2005185796A JP5099660B2 JP 5099660 B2 JP5099660 B2 JP 5099660B2 JP 2005185796 A JP2005185796 A JP 2005185796A JP 2005185796 A JP2005185796 A JP 2005185796A JP 5099660 B2 JP5099660 B2 JP 5099660B2
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
- C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
- C23C28/322—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
- C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
- C23C28/34—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates
- C23C28/345—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer
- C23C28/3455—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one inorganic non-metallic material layer, e.g. metal carbide, nitride, boride, silicide layer and their mixtures, enamels, phosphates and sulphates with at least one oxide layer with a refractory ceramic layer, e.g. refractory metal oxide, ZrO2, rare earth oxides or a thermal barrier system comprising at least one refractory oxide layer
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
- F16B25/00—Screws that cut thread in the body into which they are screwed, e.g. wood screws
- F16B25/001—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by the material of the body into which the screw is screwed
- F16B25/0021—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by the material of the body into which the screw is screwed the material being metal, e.g. sheet-metal or aluminium
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
- F16B33/00—Features common to bolt and nut
- F16B33/06—Surface treatment of parts furnished with screw-thread, e.g. for preventing seizure or fretting
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Ceramic Engineering (AREA)
- Heat Treatment Of Steel (AREA)
- Metal Rolling (AREA)
- Other Surface Treatments For Metallic Materials (AREA)
Description
本発明は、金属材料のワークに予め形成されているねじ込み用の下穴に、ねじ自身でめねじを形成しながらねじ込む高強度タッピンねじに関するものである。 The present invention relates to a high-strength tapping screw that is screwed into a prepared screw hole formed in advance on a metal material workpiece while forming a female screw with the screw itself.
タッピンねじの性能特性として要求される重要なものは、一般に金属板状のワークにタッピンねじをねじ込む場合、このタッピンねじの表面硬度をワークの硬度以上に高くすることにより、ワークの下穴にこれをねじ込む際に、タッピンねじの脚部に形成されているおねじが潰れないようにしてねじ込み性を確保すると共に、タッピンねじ本体の硬さを必要以上に高めないようにして靭性を確保することにより、締結部品としてタッピンねじを下穴にねじ込んだときのトルク負荷に十分に耐えることができるようにしてねじり強さを確保し、更にねじ込み後のタッピンねじが耐遅れ破壊特性にも優れていることである。 An important requirement of the tapping screw performance characteristics is that when a tapping screw is generally screwed into a metal plate workpiece, the surface hardness of the tapping screw is made higher than the workpiece hardness, so that When screwing the screw, ensure that the male screw formed on the leg of the tapping screw is not crushed and secure the screwing property, and that the toughness is ensured by not increasing the hardness of the tapping screw body more than necessary. Therefore, the torsional strength is ensured by sufficiently withstanding the torque load when the tapping screw is screwed into the pilot hole as a fastening part, and the tapping screw after screwing is also excellent in delayed fracture resistance. That is.
そのため、鋼製タッピンねじの製造においては、通常、低炭素鋼鋼線を素材として用い、冷間圧造及び転造で成形されたねじに浸炭焼入れ・焼戻し処理を施しておねじの表面硬度を高くしたものが使用されている。例えばJIS B 1122 十字穴付きタッピンねじには、JIS G 3539 冷間圧造用炭素鋼線のSWCH12A〜22A(アルミキルド鋼)又はSWCH12K〜22K(シリコンキルド鋼)が素材として用いられ、転造等によってネジ部を成形し、浸炭焼入れ・焼戻しの調質処理によって製造されてきている。このようなタッピンねじの機械的性質は、例えばJIS B 1055 によれば、表面硬さはビッカース硬さHVで450以上、心部硬さはHVで270〜390と規定されており、靭性及び耐遅れ破壊の確保と同時に、靭性と相反する傾向を示す硬さ・強さ特性も同時に確保しなければならないとされている。 For this reason, in the manufacture of steel tapping screws, low-carbon steel wires are usually used as raw materials, and the screws formed by cold forging and rolling are carburized and tempered to increase the surface hardness of the screws. Is used. For example, JIS G 3539 carbon steel wire for cold heading, SWCH12A-22A (aluminum killed steel) or SWCH12K-22K (silicon killed steel), is used as the material for the JIS B 1122 cross-tapped tapping screw. The part has been molded and manufactured by tempering treatment of carburizing quenching and tempering. The mechanical properties of such a tapping screw are, for example, according to JIS B 1055, the surface hardness is defined as 450 or more in terms of Vickers hardness HV, and the core hardness is defined as 270 to 390 in terms of HV. In addition to ensuring delayed fracture, it is also necessary to ensure hardness and strength properties that tend to conflict with toughness.
上記の如きタッピンねじが具備すべき特性の内、靭性と硬さ・強さとの両立を図るための手段として、特開2001−247937号公報(特許文献1)には、素材の鋼の化学成分組成を低炭素鋼系の適切な組成範囲内に制限すると共に、タッピンねじの成形体本体の適切な浸炭焼入れ処理条件と低温焼戻し処理条件との組合せ作用・効果により、表面硬さHVを550〜700に高め、硬化深さを0.05〜0.7mmの範囲内に制御すると同時に、心部硬さHVを200〜320の範囲内に制御するという技術が開示されている。 As a means for achieving both toughness and hardness / strength among the characteristics to be possessed by the tapping screw as described above, Japanese Patent Application Laid-Open No. 2001-247937 (Patent Document 1) describes the chemical composition of the material steel. The surface hardness HV is reduced from 550 to 550 by limiting the composition within an appropriate composition range of the low carbon steel system, and combining and effecting appropriate carburizing and quenching treatment conditions and low-temperature tempering treatment conditions for the body of the tapping screw. A technique is disclosed in which the core hardness HV is controlled within the range of 200 to 320 while the curing depth is controlled within the range of 0.05 to 0.7 mm.
一方、ワークの硬さが高水準である場合にも、タッピンねじのねじ込み性(ねじ切り機能)の向上を図るための手段として、特開2003−130024号公報(特許文献2)には、タッピンねじの成形体本体の表面には、融点が高く硬性で且つ成形体本体に対する接着度の高い本体保護膜(例えばNiめっきやCrめっき等の皮膜)を設け、更にこの本体保護膜の表面に融点が低く軟性で、且つ本体保護膜からの剥離が容易である焼付き防止膜(例えばZn系やSn系めっき等の皮膜)を設けることにより、下穴を塑性変形させる際の摩擦高熱により所謂焼付き現象を生じさせないようにし、適正なめねじを形成させることにより強固な締結力を得るという技術が開示されている。
上記の通りの特許文献1又は2のいずれの発明によってもタッピンねじをねじ込んだときに、おねじが潰れないようなねじ込み性と、トルク負荷に十分に耐え得るねじり強さと
が確保できるとされている。しかしながら、いずれの発明においても、タッピンねじ本体の心部の靭性を確保し、表層部のみを硬化させるために、浸炭焼入れ・焼戻しの調質処理を施すことが前提条件となっている。例えば特許文献2の発明においては、最表層部に所要の焼付き防止膜を形成させており、しかもその実施の形態の段落番号0022に記載されているように、ねじ部の表面硬さをビッカース硬さHVで500〜750に設定した浸炭焼入れ処理を施すものとしている。
According to either invention of Patent Document 1 or 2 as described above, when a tapping screw is screwed in, it is possible to secure a screwing property so that the male screw is not crushed and a torsional strength that can sufficiently withstand a torque load. Yes. However, in any of the inventions, in order to ensure the toughness of the center portion of the tapping screw main body and harden only the surface layer portion, it is a precondition that the tempering treatment of carburizing quenching and tempering is performed. For example, in the invention of Patent Document 2, a required anti-seizure film is formed on the outermost layer portion, and the surface hardness of the screw portion is set to Vickers as described in paragraph No. 0022 of the embodiment. Carburizing and quenching treatment set to 500 to 750 in hardness HV is performed.
だが、以下のとおりの問題点は解消できないのが実情である。 However, in reality, the following problems cannot be resolved.
1)HV≧400では、遅れ破壊による頭とびの危険があり、また、靭性の低下も免れ得ない。一方、ねじ込み性は表面硬さがHV≧500であることが望ましい。 1) When HV ≧ 400, there is a risk of head skipping due to delayed fracture, and a decrease in toughness cannot be avoided. On the other hand, it is desirable that the surface hardness of the screwability is HV ≧ 500.
2)上記表面硬化処理としての浸炭焼入れ・焼戻し処理は、処理条件の制御や工程管理に手数がかかり、エネルギー消費も大きいという問題がある。また浸炭焼入れ・焼戻し処理では遅れ破壊を100%は回避することができない。 2) The carburizing quenching and tempering treatment as the surface hardening treatment has problems that control of treatment conditions and process management are troublesome and energy consumption is large. Moreover, 100% delayed fracture cannot be avoided by carburizing and tempering.
そこで、本発明は、上記問題点を解決して、浸炭焼入れ・焼戻し処理を施すことのない、ねじ込み性及びねじり強さのいずれにも優れた新しい高強度タッピンねじを提供することを課題としている。
Then, this invention makes it a subject to solve the said problem and to provide the new high intensity | strength tapping screw excellent in both the screwing property and torsion strength which does not perform a carburizing quenching and tempering process. .
上記課題を解決するために本発明者等は鋭意検討を行ない、その過程において下記の知見を得てきている。 In order to solve the above problems, the present inventors have conducted intensive studies and have obtained the following knowledge in the process.
まず、本発明者等は、C含有量が0.45質量%以下の炭素鋼成分系の鋼塊、鋳片、鋼片又は鋼材に対して、圧延温度が350〜800℃の範囲内において、所要のひずみを導入する温間でのカリバー圧延を行なうことにより、圧延方向に垂直な断面の平均粒径が2μm以下の超微細フェライト組織を主相とする鋼が得られ、この温間圧延ままの材料は、その機械的性質として引張強さが600MPa以上で絞りが65%以上を有し、更には引張強さが800MPa以上で絞りが70%以上を有するという冷間圧造性に優れ、且つ高強度を有する線材あるいは鋼線となることを見出した(特願2003−435980)。 First, for the steel ingot, cast slab, steel slab or steel material of carbon steel component system having a C content of 0.45% by mass or less, the present inventors have a rolling temperature in the range of 350 to 800 ° C. By performing caliber rolling in a warm state to introduce the required strain, a steel having an ultrafine ferrite structure whose main grain size is 2 μm or less in the cross section perpendicular to the rolling direction is obtained. The material has excellent cold forging properties such as a tensile strength of 600 MPa or more and a drawing of 65% or more as a mechanical property, and further a tensile strength of 800 MPa or more and a drawing of 70% or more, and It has been found that the wire or steel wire has high strength (Japanese Patent Application No. 2003-435980).
そして、この超微細フェライト組織及び機械的性質を有する温間圧延材料に所定の冷間加工を施すことにより、フェライトの結晶粒は圧延方向に垂直な断面の平均粒径で更に微細化され、その結果一層の著しい高強度鋼を得ることが可能となり、しかもこの著しい強度上昇にもかかわらず絞りの低下は極めて小さく抑えられることを見出した(特願2005−114033、特願2005−114030)。 Then, by subjecting the warm-rolled material having the ultrafine ferrite structure and mechanical properties to predetermined cold working, the ferrite crystal grains are further refined to have an average grain size in a cross section perpendicular to the rolling direction. As a result, it has become possible to obtain steel with a significantly higher strength, and it has been found that the reduction in the drawing can be suppressed to an extremely small level despite this remarkable increase in strength (Japanese Patent Application Nos. 2005-111403 and 2005-11040).
これらの知見を踏まえてさらに検討を進め、本発明者は下記の知見を得て本発明を完成した。 Based on these findings, further investigations were made, and the inventor obtained the following findings and completed the present invention.
すなわち、上記温間圧延、又は温間圧延と冷間圧延との組合せにより得られた材料を素材として用いれば、これに球状化焼なましを施して材料を軟化さなくても、通常の冷間圧造と冷間転造等によりねじに成形加工することができ、こうして調製されたねじの成形体本体は焼入・焼戻し処理を施さなくても、高強度を有するタッピンねじの成形体本体が得られること、そして、これに金属めっき皮膜、クロメート処理皮膜、及び電着塗装皮膜といった通常の表面皮膜の形成処理方法により、適宜表面皮膜を形成させた結果、得られたタッピンねじは、ねじ込み性及びねじり強度の両方に優れた特性を有する高強度のタッピンねじが得られることがわかった。 That is, if a material obtained by the above warm rolling or a combination of warm rolling and cold rolling is used as a raw material, normal cold cooling can be performed without subjecting the material to spheroidizing annealing and softening the material. It can be formed into a screw by cold rolling and cold rolling, etc., and the molded body of the screw thus prepared can be a high-strength tapping screw molded body without being subjected to quenching and tempering treatment. As a result of appropriately forming a surface film by a normal surface film forming treatment method such as a metal plating film, a chromate treatment film, and an electrodeposition coating film, the obtained tapping screw has screwability It was found that a high-strength tapping screw having excellent characteristics in both torsional strength can be obtained.
本願発明は、上記知見に基づくものであって、本発明が提供する高強度タッピンねじの特徴は以下の通りである。 The present invention is based on the above findings, and the features of the high-strength tapping screw provided by the present invention are as follows.
本願の第1の発明に係る高強度タッピンねじは、その成形体本体の結晶組織として、この成形体本体の任意方向断面における少なくとも1断面における平均粒径が200nm以下の超微細粒フェライト組織を有し、前記成形体本体の表層部には硬化処理による硬化層が形成されず、且つ、この成形体本体の表面には、下記3種の表面処理皮膜の内の1種、即ち金属めっき皮膜、クロメート処理皮膜、及び電着塗装皮膜の3種から選ばれた1種以上が形成されていることに特徴を有するものである。
The high-strength tapping screw according to the first invention of the present application has, as a crystal structure of the molded body, an ultrafine-grained ferrite structure having an average grain size of 200 nm or less in at least one cross section in an arbitrary direction of the molded body. In the surface layer portion of the molded body, a cured layer is not formed by the curing treatment, and on the surface of the molded body, one of the following three types of surface treatment films, that is, a metal plating film, It is characterized in that at least one selected from a chromate-treated film and an electrodeposition coating film is formed.
本願の第2の発明に係る高強度タッピンねじは、上記第1の発明に係るタッピンねじにおいて、ねじ成形体本体の化学成分組成が下記の通りであることに特徴を有するものである。即ち、
C :0.60質量%以下、
Si:1.50質量%以下、
Mn:0.15〜1.80質量%、
P :0.015質量%以下、
S :0.015質量%以下、及び、
Al:0.080質量%以下
で、残部はFe及び不可避不純物からなることに特徴を有するものである。
The high-strength tapping screw according to the second invention of the present application is characterized in that, in the tapping screw according to the first invention , the chemical component composition of the screw molded body is as follows. That is,
C: 0.60 mass% or less,
Si: 1.50 mass% or less,
Mn: 0.15 to 1.80% by mass,
P: 0.015 mass% or less,
S: 0.015 mass% or less, and
Al: 0.080% by mass or less, with the balance being made of Fe and inevitable impurities.
本願の第3の発明に係る高強度タッピンねじは、第2の発明に係るタッピンねじにおいて、ねじ成形体本体の化学成分組成として、更にCr、Mo、Ni、Cu、Ti、Nb、V及びBの内、少なくとも1元素が含有されていることに特徴を有するものである。
The high-strength tapping screw according to the third invention of the present application is the tapping screw according to the second invention, wherein the chemical component composition of the screw molded body is further Cr, Mo, Ni, Cu, Ti, Nb, V and B. Among these, it is characterized by containing at least one element.
以上の通り、この出願の発明によれば、タッピンねじの素材である鋼線又は棒鋼は、その圧延方向に垂直な断面における平均フェライト粒径が超微細組織を呈しているので、強度と延性とのバランスに優れているため、これに従来実施されている球状化焼なましを施すことなくねじの成形体本体に成形加工することができる。そして、従来技術によるタッピンねじのように、成形体本体の表層部に浸炭焼入・焼戻し乃至浸炭窒化焼入・焼戻しに代表される硬化処理を施す必要もなく、この成形体本体に金属めっき皮膜、クロメート処理皮膜、又は電着塗装皮膜といった表面処理皮膜を形成させるだけで、ねじ込み性及びねじり強度に優れ、しかも遅れ破壊フリーのタッピンねじを得ることができる。 As described above, according to the invention of this application, the steel wire or the steel bar, which is the material of the tapping screw, exhibits an ultrafine structure in the average ferrite grain size in the cross section perpendicular to the rolling direction. Therefore, the thread body can be molded without subjecting it to conventional spheroidizing annealing. And, unlike the conventional tapping screw, it is not necessary to subject the surface layer portion of the molded body to a hardening treatment typified by carburizing quenching / tempering or carbonitriding / quenching / tempering. By simply forming a surface treatment film such as a chromate treatment film or an electrodeposition coating film, it is possible to obtain a tapping screw which is excellent in screwing property and torsional strength and free from delayed fracture.
本願発明は上記通りの構成とこれに関して以下の特徴を有するものである。以下、本願発明の実施形態について詳細に説明する。 The present invention has the following configuration and the following features. Hereinafter, embodiments of the present invention will be described in detail.
(1)本願タッピンねじの素材の調製方法と素材のフェライト粒径及び機械的性質の特
徴
本願発明に係るタッピンねじの特徴の一つは、その製造過程において、素材である鋼線又は棒鋼をタッピンねじの成形体本体に成形加工するに先立って、当該鋼線又は棒鋼に対して軟化のために球状化焼なましを施す必要がないこと、しかも、成形後の本体の強度を向上させるために焼入・焼戻しを施す必要もないことにある。このような特性を備えた鋼線又は棒鋼が得られる理由は、本願発明の方法により鋼線又は棒鋼を調製することにより、C方向断面において平均粒径が2μm以下、更には500nm以下乃至200nm以下のフェライト主体の鋼が得られるからである。これは、鋼線又は棒鋼を調製する工程において、鋼材の高強度化を実現する方法として相変態による強化機構を利用せずに、結晶粒の微細化を図る方法を採ることにしたこと、そして、この際、粒径の微細化につれて引張強さが増加し、引張強さの増加にもかかわらず絞りの低下量は小さく、強度と延性バランスに優れた材料が得られるからである。
(1) Features of the tapping screw material preparation method and the ferrite particle size and mechanical properties of the material One of the features of the tapping screw according to the invention is that the steel wire or steel bar as the material is used in the manufacturing process. In order to improve the strength of the main body after molding, it is not necessary to subject the steel wire or steel bar to spheroidizing annealing prior to forming the formed body of the tapping screw. There is no need to quench and temper the steel. The reason why a steel wire or steel bar having such characteristics is obtained is that the average particle size in the cross section in the C direction is 2 μm or less, further 500 nm or less to 200 nm or less by preparing the steel wire or steel bar by the method of the present invention. This is because a ferrite-based steel is obtained. This is because, in the process of preparing the steel wire or the steel bar, the method of achieving the refinement of the crystal grains without using the strengthening mechanism by the phase transformation is adopted as a method for realizing the high strength of the steel material, and In this case, the tensile strength increases as the particle size becomes finer, and the amount of reduction in drawing is small despite the increase in tensile strength, and a material excellent in the balance between strength and ductility can be obtained.
以下、平均粒径が2μm以下のフェライトを有するタッピンねじの素材(鋼線又は棒鋼)の調製方法を、熱間加工鋼材を温間加工のみで得る方法と、熱間加工と冷間加工とで得る方法とに分けて述べると共に、得られる素材の特徴について述べる。
(1−1)温間加工のみにより素材を調製する場合
所定の鋼線又は棒鋼の調製を、鋼塊、鋳片、鋼片又は線材若しくは棒材等半成品のいずれかを被加工材として、カリバーロール圧延による多パスの温間加工をすることにより行なう。ここで、鋼片又は線材若しくは棒材等半成品とは、鋼塊又は鋳片を従来技術による熱間圧延又は熱間鍛造により調製した熱間加工材を指す。これは本明細書において全て同じである。なお、被加工材の化学成分組成は、後述の第(3)項で述べる通りの炭素鋼及び機械構造用合金鋼の範囲内であれば特に規定する必要はない。鋼線又は棒鋼の調製条件は、その加工温度を350〜800℃の範囲内とし、更に、その際に臨界ひずみよりも大きなひずみを材料内へ導入することにより、このひずみによる結晶粒のミクロ的な局所方位差が微細結晶粒の起源となり、加工中あるいは加工後に起きる回復過程において、粒内の転位密度が低下すると同時に結晶粒界が形成されて、微細粒組織を形成することを利用するものである。
In the following, a method for preparing a tapping screw material (steel wire or steel bar) having ferrite having an average particle diameter of 2 μm or less is obtained by a method of obtaining hot-worked steel only by warm working, and hot working and cold working. It is divided into the method of obtaining and the characteristics of the obtained material are described.
(1-1) When preparing a raw material only by warm working Preparation of a predetermined steel wire or steel bar is performed using a steel ingot, slab, steel slab, or a semi-finished product such as a wire or a bar as a work material. It is performed by warm processing of multiple passes by roll rolling. Here, a steel slab or a semi-finished product such as a wire rod or a bar refers to a hot-worked material prepared by hot rolling or hot forging of a steel ingot or cast slab according to a conventional technique. This is all the same in this specification. The chemical component composition of the workpiece need not be specified as long as it is within the range of carbon steel and alloy steel for machine structure as described in the item (3) below. The preparation conditions of the steel wire or steel bar are such that the processing temperature is in the range of 350 to 800 ° C., and a strain larger than the critical strain is introduced into the material at that time. The local orientation difference is the origin of fine grains, and in the recovery process that occurs during or after processing, the dislocation density in the grains decreases and at the same time the grain boundaries are formed, forming a fine grain structure It is.
上記温間加工において、総減面率Rが50%以上で且つ平均塑性ひずみεが2.0以上となるように、カリバーロールによる圧延を行なうことにより、C方向断面における平均粒径が2μm以下のフェライトを有する鋼線又は棒鋼が得られる。このような温間加工条件により相変態による強化機構を実質的に利用せず、フェライトの平均粒径を2μm以下に微細化することにより、鋼の高強度化を実現し、しかも絞りを所定の水準以上にすることができる。その結果、上述したタッピンねじの成形体本体を成形する前に、素材(鋼線又は棒鋼)を軟化のための球状化焼なまし、及び成形後の強度向上のための焼入・焼戻しを施す必要がなくなる。 In the warm working, rolling with a caliber roll is performed so that the total area reduction ratio R is 50% or more and the average plastic strain ε is 2.0 or more, so that the average particle diameter in the cross section in the C direction is 2 μm or less. A steel wire or steel bar having the following ferrite is obtained. Under such warm working conditions, the strengthening mechanism by phase transformation is not substantially utilized, and the average grain size of ferrite is refined to 2 μm or less, thereby realizing high strength of the steel and further reducing the drawing to a predetermined range. It can be above the standard. As a result, before forming the above-described body of the tapping screw, the material (steel wire or bar) is subjected to spheroidizing annealing for softening and quenching / tempering for strength improvement after forming. There is no need.
ここで、鋼の化学成分組成をSi−Mn系炭素鋼(但し、標準組織がbccの場合である)で種々変化させたとき、本発明の範囲内のカリバーロールによる温間圧延により大ひずみ導入の多方向・多パス圧延をした場合、フェライトの平均粒径dと引張強さTSとの関係は、平均粒径dの減少につれて引張強さTSが増加する。圧延方向に垂直な断面(C方向断面)組織の平均粒径を2μm以下のフェライト組織を主相とする材料を得るために、この温間圧延による材料の総減面率Rを50%以上とし、且つ3次元有限要素法で計算される平均塑性ひずみεが2.0以上となるようにする。そうすれば、前述したとおり、引張強さTSは600MPa以上が得られ、更に総減面率及び平均塑性ひずみを大きくすれば、平均粒径は微細化して引張強さTSは800MPa以上となり、しかも絞りRAも高く、RA=70%程度の強度と延性バランスに優れた鋼線が得られる。一方、更に圧延温度を380〜450℃の範囲内まで低くすると、更に平均粒径が小さくなり、例えば、d=500nmで、TS=960MPa、RA=72%が得られる。 Here, when the chemical composition of the steel is variously changed with Si-Mn carbon steel (where the standard structure is bcc), large strain is introduced by warm rolling with a caliber roll within the scope of the present invention. When the multi-direction and multi-pass rolling is performed, the relationship between the average grain diameter d of ferrite and the tensile strength TS increases as the average grain diameter d decreases. In order to obtain a material whose main phase is a ferrite structure in which the average grain size of the cross section perpendicular to the rolling direction (C direction cross section) is 2 μm or less, the total area reduction ratio R of the material by this warm rolling is set to 50% or more. The average plastic strain ε calculated by the three-dimensional finite element method is set to 2.0 or more. Then, as described above, the tensile strength TS is 600 MPa or more, and if the total area reduction ratio and the average plastic strain are further increased, the average particle size becomes finer and the tensile strength TS becomes 800 MPa or more. The aperture RA is also high, and a steel wire excellent in strength and ductility balance of RA = 70% can be obtained. On the other hand, when the rolling temperature is further lowered to the range of 380 to 450 ° C., the average particle size is further reduced. For example, TS = 960 MPa and RA = 72% are obtained at d = 500 nm.
また、JIS SWCH15Aの化学成分組成の80mm角熱間加工材に、本発明の範囲内における温間圧延を施して、18mm角の温間圧延材に加工する。温間圧延におけるパススケジュールとしては、スクウェア型及びバイヤモンド型ロールを用い、多パスの圧延を行なう。更に望ましくは、オーバル型に次いでスクウェア型ロールによる圧延を行なうパススケジュールを取り入れることにより、材料内部に導入される所謂平均塑性ひずみεを一層大きくすることができるので、高強度且つ高延性バランスを備えた材料の調製に効果的である。なお、この温間圧延における材料の総減面率Rは、R=95.0%であり、平均塑性ひずみεは、3.0以上となることが推定される。これにより、C方向断面の平均粒径dが0.7μmで、引張強さTSが702MPa、絞りRAが78.6%の強度と延性とのバランスに優れた棒鋼が得られた。 In addition, an 80 mm square hot-worked material having a chemical composition of JIS SWCH15A is subjected to warm rolling within the scope of the present invention to be processed into an 18 mm square hot-rolled material. As a pass schedule in the warm rolling, a square type and a Baymond type roll are used to perform multi-pass rolling. More desirably, a so-called average plastic strain ε introduced into the material can be further increased by adopting a pass schedule for rolling by a square type roll after the oval type, so that a high strength and high ductility balance is provided. It is effective for the preparation of the material. The total area reduction R of the material in this warm rolling is R = 95.0%, and the average plastic strain ε is estimated to be 3.0 or more. As a result, a steel bar having an excellent balance between strength and ductility was obtained in which the average particle diameter d of the cross section in the C direction was 0.7 μm, the tensile strength TS was 702 MPa, and the drawing RA was 78.6%.
(1−2)温間加工後に冷間加工をして素材を調製した場合
上記タッピンねじの素材としての鋼線又は棒鋼の調製工程としては、カリバーロール圧延による温間圧延により得られた材料を被加工材(通常は線材又は棒材に相当する)として、更に圧延又は伸線により冷間加工を施してもよい。
(1-2) When a raw material is prepared by cold working after warm working As a preparation step of the steel wire or steel bar as the material of the tapping screw, a material obtained by warm rolling by caliber roll rolling is used. As a workpiece (usually corresponding to a wire or a bar), cold working may be further performed by rolling or wire drawing.
先ず、温間加工は、上記(1−1)項における条件に準じて行い、同じ原理に基づき細粒化を図る。但し、材料内へ導入すべき臨界ひずみとして、(1−1)項における条件を若干緩和して、総減面率Rが50%以上で且つ平均塑性ひずみεが0.7以上となるように、カリバーロールによる圧延を行なってもよい。この段階においては、本願発明に必要な十分な粒径の微細化はされていないが、引き続き冷間加工を施して、細粒化を図るので問題は無い。 First, warm working is performed according to the conditions in the above section (1-1), and fine graining is attempted based on the same principle. However, as the critical strain to be introduced into the material, the conditions in the item (1-1) are slightly relaxed so that the total area reduction ratio R is 50% or more and the average plastic strain ε is 0.7 or more. Rolling with a caliber roll may be performed. At this stage, the sufficient particle size required for the present invention has not been refined, but there is no problem because it is subsequently subjected to cold working to achieve finer grain.
次いで更に、上記温間加工で得られた材料(線材又は棒材)に冷間加工を施す。加工温度は、350℃未満において、総減面率(%):R’={(S0’−S’)/S0’}×100が、5%以上となるように冷間加工する。ここで、S0’:冷間加工開始前の材料の
C方向断面積、S’:冷間加工終了後のC方向断面積である。なお、冷間加工法としては、公知の冷間伸線及び冷間圧延のいずれを採用してもよく、また、冷間伸線と冷間圧延を組み合わせてもよい。なお、切削又は表面研磨等に伴う減面率は、上記総減面率の算定から除外する。
Next, the material (wire or rod) obtained by the warm processing is further subjected to cold processing. When the processing temperature is less than 350 ° C., cold processing is performed so that the total area reduction ratio (%): R ′ = {(S 0 ′ −S ′) / S 0 ′} × 100 is 5% or more. Here, S 0 ′: C direction sectional area of the material before the start of cold working, and S ′: C direction sectional area after the end of cold working. As the cold working method, any of known cold wire drawing and cold rolling may be adopted, or cold wire drawing and cold rolling may be combined. Note that the reduction in area due to cutting or surface polishing is excluded from the calculation of the total reduction in area.
こうして冷間加工により調製された鋼線又は棒鋼のC方向断面のフェライトは、結晶粒が冷間加工方向に延伸した所謂バンブーストラクチャーの形態を呈するが、結晶粒が成長することはなく、C方向断面のフェライト平均粒径は更に微細化し、平均粒径は2μm以下、あるいは500nm以下、更には200nm以下に微細化する。その結果、引張強さTSは更に著しく上昇し、それにもかかわらず絞りRAの低下は小さく抑制されて、強度と延性のバランスに優れたものが得られる。 The ferrite in the C direction cross section of the steel wire or steel bar thus prepared by cold working exhibits a so-called bamboo structure form in which the crystal grains are stretched in the cold working direction, but the crystal grains do not grow and is in the C direction. The average ferrite grain size in the cross section is further refined, and the average grain size is refined to 2 μm or less, 500 nm or less, and further 200 nm or less. As a result, the tensile strength TS further increases remarkably, and nevertheless, the reduction of the aperture RA is suppressed to a small level, and an excellent balance between strength and ductility is obtained.
なお、加工温度を350℃未満とすることが望ましい。これは加工発熱により、冷間加工中にこれよりも高い温度に達すると、引張強さの上昇度合いが低下して望ましくないからである。 It is desirable that the processing temperature be less than 350 ° C. This is because if the temperature reaches higher during cold working due to heat generated by the work, the degree of increase in tensile strength decreases, which is undesirable.
具体例として、C含有量=0.03質量%の低炭素アルミキルドの場合、13mmφの熱間圧延線材を上記のような本発明の範囲内のカリバーロール圧延による温間圧延により6mmφに調製された線材では、C方向断面のフェライト平均粒径dが0.8μmで、引張強さTSが817MPa、絞りRAが75%の材料が得られた。この温間圧延による総減面率Rは、R=78.7%であり、平均塑性ひずみεは、3次元有限要素法解析計算の結果、2.0以上であることが確認されている。 As a specific example, in the case of a low carbon aluminum kill having a C content of 0.03% by mass, a 13 mmφ hot-rolled wire was prepared to 6 mmφ by warm rolling by caliber roll rolling within the scope of the present invention as described above. As the wire, a material having a ferrite average particle diameter d of 0.8 μm in the cross section in the C direction, a tensile strength TS of 817 MPa, and a drawing RA of 75% was obtained. The total area reduction R by this warm rolling is R = 78.7%, and the average plastic strain ε is confirmed to be 2.0 or more as a result of the three-dimensional finite element method analysis calculation.
上記で調製された温間圧延線材を、本発明の範囲内の冷間圧延により1.8mmφの鋼線とした。このとき、冷間圧延総減面率R’は91.0%であり、C方向断面のフェライト平均粒径dは240nmで、引張強さTSが1140MPa、絞りRAが72.3%の材料が得られた。更に1.3mmφの鋼線としたとき(即ち、冷間圧延総減面率R’=95.3%、平均塑性ひずみε≧3.1のとき)には、C方向断面のフェライト平均粒径dは186nmで、引張強さTSは1202MPa、絞りRA=70.2%、ビッカース硬さHV=310の材料が得られた。 The warm-rolled wire prepared above was made into a 1.8 mmφ steel wire by cold rolling within the scope of the present invention. At this time, the cold rolling total area reduction ratio R ′ is 91.0%, the ferrite average particle diameter d in the cross section in the C direction is 240 nm, the tensile strength TS is 1140 MPa, and the drawing RA is 72.3%. Obtained. Further, when the steel wire has a diameter of 1.3 mmφ (that is, when the cold rolling total area reduction ratio R ′ = 95.3% and the average plastic strain ε ≧ 3.1), the ferrite average grain size in the C-direction cross section A material having d of 186 nm, tensile strength TS of 1202 MPa, drawing RA = 70.2%, and Vickers hardness HV = 310 was obtained.
上述したように、素材(鋼線又は棒鋼)の機械的性質は上記温間加工、又は温間加工と冷間加工とにより、上述したような機械的性質の優れたものとなり、タッピンねじの成形体本体の成形性に寄与し、この素材(鋼線又は棒鋼)に対しては球状化焼なましによる軟化処理を行わなくても、冷間圧造、転造あるいは切削加工により成形加工ができ、しかも得られた成形体本体に焼入・焼戻し処理を施さなくても、素材に準じた水準の引張強さと絞りとが具備され、また相当する硬さが具備される。しかも、焼入・焼戻しがなされていないので、耐遅れ破壊特性に優れた成形体本体が得られる。そして、上記成形加工により結晶粒が素材での状態よりも成長することはない。それどころか、いわゆる2段打ちヘッ
ダー(ダブルヘッダー)で本体の頭部を成形し、十字穴リセスを形成させてねじを成形したところ、係合溝の部分が等軸状の超微細組織に変化していることが断面のTEM観察からわかった。またこの部分の硬さは成形体軸部よりも著しく上昇していることもわかった。従って、係合部の材質特性の異方性も大幅に改善されたことが推定される。
As described above, the mechanical properties of the material (steel wire or steel bar) are excellent in the mechanical properties as described above by the warm processing, or the warm processing and the cold processing, and forming the tapping screw. Contributes to the formability of the body, and this material (steel wire or bar) can be molded by cold forging, rolling or cutting without softening by spheroidizing annealing, Moreover, even if the obtained molded body is not subjected to quenching and tempering treatment, it has a tensile strength and a drawing of the same level as the material and has a corresponding hardness. In addition, since it has not been quenched and tempered, a molded body having excellent delayed fracture resistance can be obtained. And the crystal grain does not grow more than the state in a raw material by the said shaping | molding process. On the contrary, when the head of the main body is formed with a so-called double-stepped header (double header), a cross hole recess is formed and a screw is formed, the engagement groove changes into an equiaxed ultra-fine structure. It was found from cross-sectional TEM observation. It was also found that the hardness of this part was significantly higher than that of the molded body shaft. Therefore, it is estimated that the material property anisotropy of the engaging portion is also greatly improved.
なお、上記工程において、更に、タッピンねじの成形体本体の成形工程の前において、上記素材(鋼線又は棒鋼)に対して低温焼なましを施すことにより、その成形性が一層向上するので、延性が高度に要求されるタッピンねじの成形体本体の調製時には成形性向上効果が発揮される。ここで、焼なまし温度としては550℃以下であれば、結晶粒の成長もなく、問題はない。なお、低温焼なましは、望ましくは製造ライン設計の観点から、冷間加工ライン上において、冷間加工の直前で連続的に行なうと一層望ましい。 In addition, in the above process, further, the moldability is further improved by performing low temperature annealing on the material (steel wire or steel bar) before the forming process of the formed body of the tapping screw. When preparing a molded body of a tapping screw that requires a high degree of ductility, the effect of improving moldability is exhibited. Here, if the annealing temperature is 550 ° C. or less, there is no problem because there is no growth of crystal grains. It should be noted that low-temperature annealing is more desirably performed continuously immediately before the cold working on the cold working line, preferably from the viewpoint of production line design.
上記理由により、本発明のタッピンねじ本体の結晶組織は、上記の通りの超微細粒フェライト組織を有するものと規定した。ここで、超微細粒フェライト組織を有するとは、主相がフェライト組織であることを意味し、主相(第1相)がフェライト粒からなる複相組織又はフェライト単相組織からなるものである。 For the above reasons, the crystal structure of the tapping screw main body of the present invention is defined as having the ultrafine grain ferrite structure as described above. Here, having an ultrafine grained ferrite structure means that the main phase is a ferrite structure, and the main phase (first phase) is composed of a multiphase structure or a ferrite single phase structure composed of ferrite grains. .
ここで、フェライトの平均粒径の観察面として、任意方向断面の内少なくとも1観察面と規定したのは、成形体本体の素材として本発明で供される鋼材である鋼線又は棒鋼の圧延加工、伸線加工又は鍛造加工ままにおける結晶粒は、当該鋼材の長手方向に延伸した形状となっており、従ってヘッダー加工及び転造を施された成形体本体におけるメタルフローは複雑な形状を呈しているから、一義的に結晶粒径の測定断面を規定すべきでないからである。 Here, as the observation surface of the average grain diameter of ferrite, it is defined that at least one observation surface of the cross section in an arbitrary direction is a rolling process of a steel wire or a steel bar which is a steel material provided in the present invention as a material of a formed body. The crystal grains in the wire drawing or forging process are in a shape that extends in the longitudinal direction of the steel material, and therefore the metal flow in the formed body subjected to header processing and rolling exhibits a complicated shape. This is because the measurement cross section of the crystal grain size should not be defined uniquely.
(2)本願タッピンねじの成形体本体の硬さ
本願発明に係るタッピンねじは、その成形体本体が上記(1)項で述べた超微細粒フェライト組織を有する代わりに、任意方向断面での硬さが、少なくとも1測定断面においてビッカース硬さHVで250以上360以下であるフェライト組織を有するものであってもよい。更に望ましくは、ビッカース硬さHVで250以上330以下とする。ビッカース硬さで250以上とするのは、強度を確保するためであり、一方360以下とするのは成形体本体の成形性確保、及び遅れ破壊防止の観点から上限を設ける。更に、耐遅れ破壊を改善するために、330以下とする。
(2) Hardness of the molded body of the present tapping screw The tapping screw according to the present invention has a hardness in a cross section in an arbitrary direction, instead of the molded body having the ultrafine-grained ferrite structure described in the above section (1). However, it may have a ferrite structure having a Vickers hardness HV of 250 or more and 360 or less in at least one measurement cross section. More preferably, the Vickers hardness HV is 250 to 330. The reason why the Vickers hardness is 250 or more is to secure the strength, while the value of 360 or less provides an upper limit from the viewpoint of securing the moldability of the molded body and preventing delayed fracture. Furthermore, in order to improve delayed fracture resistance, it is set to 330 or less.
このように、タッピンねじの成形体本体の強度特性を、フェライトの結晶粒径により規定する代わりに、硬さにより規定した場合の条件である。この場合、本願発明に係るタッピンねじの引張強さTSは凡そ800から1400MPaに相当する。浸炭焼入・焼戻しを施された従来技術によるタッピンねじの場合は、表面硬さがHVで500〜600程度、心部が300〜400程度である。従って、本発明のタッピンねじは、遅れ破壊の防止にも効果的である。 As described above, the strength characteristics of the main body of the tapping screw are defined by the hardness instead of the crystal grain size of the ferrite. In this case, the tensile strength TS of the tapping screw according to the present invention corresponds to approximately 800 to 1400 MPa. In the case of a conventional tapping screw subjected to carburizing and tempering, the surface hardness is about 500 to 600 in terms of HV, and the core is about 300 to 400. Therefore, the tapping screw of the present invention is also effective in preventing delayed fracture.
(3)化学成分組成
本願発明に係るタッピンねじの化学成分組成は、本願発明の範囲内にある温間圧延で得られる材料の金属結晶組織の主相がフェライトであるか、フェライト単相であればよい。具体的には、上記温間圧延条件にも依存するが、炭素鋼成分系であればC含有量が0.60質量%以下を指す。なお、C含有量の下限値は、主相が実質的にセメンタイトフリーとなる場合でもよい。例えば、C含有量がAe1点におけるフェライト相の炭素の固溶限以
下でもよく、具体的にはC含有量が0.010質量%以下であってもよい。そして、いかなるC含有量に決定するかは、その他の成分元素含有量を与えた場合に、タッピンねじの素材である鋼線又は棒鋼で所望される引張強さTSと絞りRAとのバランスに応じて設計する。
(3) Chemical component composition The chemical component composition of the tapping screw according to the present invention is that the main phase of the metal crystal structure of the material obtained by warm rolling within the scope of the present invention is ferrite or a ferrite single phase. That's fine. Specifically, although depending on the warm rolling conditions, the carbon content is 0.60% by mass or less in the case of a carbon steel component system. The lower limit of the C content may be a case where the main phase is substantially cementite-free. For example, the C content may be not more than the solid solubility limit of carbon of the ferrite phase at the Ae 1 point, and specifically, the C content may be 0.010% by mass or less. The C content to be determined depends on the balance between the tensile strength TS and the restriction RA desired for the steel wire or bar steel that is the material of the tapping screw when other component element contents are given. Design.
また、本願発明においては、材料の強度向上のために、合金元素を添加することは必ずしも必要ではないが、焼入れ性向上を促進させる元素、例えばCr、Mo及びB、固溶強化元素であるCuやNi、並びに分散析出強化元素としてのTi、Nb及びV等の有価元素の添加は必要に応じて適宜添加してもよい。なお、上記合金元素は製造コスト低減上からも添加せずに済ます方が望ましい。 In the present invention, it is not always necessary to add an alloy element to improve the strength of the material, but elements that promote the improvement of hardenability, such as Cr, Mo and B, and Cu, which is a solid solution strengthening element, are used. Ni, and valuable elements such as Ti, Nb and V as dispersion precipitation strengthening elements may be added as necessary. It is desirable that the alloy elements are not added from the viewpoint of manufacturing cost reduction.
一方、脱酸剤としてのSi、Mn及びAlの含有量は、製鋼法及び精錬法に応じた従来の精錬、鋳造技術水準に基づき、非金属介在物の清浄性を確保可能な範囲内に適宜決定する。具体的には、Si:1.50質量%以下、Mn:0.15〜1.80質量%、Al:0.080質量%以下とする。更に、CaやREMの含有量は特に規定しないが、適宜添加しても差し支えない。 On the other hand, the contents of Si, Mn and Al as deoxidizers are appropriately set within a range that can ensure the cleanliness of non-metallic inclusions based on the level of conventional refining and casting techniques according to steelmaking and refining methods. decide. Specifically, Si: 1.50 mass% or less, Mn: 0.15 to 1.80 mass%, Al: 0.080 mass% or less. Furthermore, the content of Ca or REM is not particularly specified, but may be added as appropriate.
通常は有害不純物元素として扱われるP、S及びN等については、それらの含有量を特に規定しないが、従来の精錬、鋳造技術上から不可避的に混入する含有量の水準に制限すべきである。但し、特に超低含有量に制限する必要はない。これにて、本願発明は、その課題を十分に解決し得るからである。 For P, S, N, etc., which are usually treated as harmful impurity elements, their content is not specified, but should be limited to the level of content inevitably mixed from the conventional refining and casting techniques . However, it is not necessary to limit to an extremely low content. This is because the present invention can sufficiently solve the problem.
以上により、低コストにて本願発明を実施する際の望ましい化学成分組成範囲として、C:0.60質量%以下、Si:1.50質量%以下、Mn:0.15〜1.80質量%、P:0.015質量%以下、S:0.015質量%以下、及び、Al:0.080質量%以下であって、残部はFe及び不可避不純物であるものとする。 From the above, as a desirable chemical component composition range when carrying out the present invention at low cost, C: 0.60 mass% or less, Si: 1.50 mass% or less, Mn: 0.15-1.80 mass% , P: 0.015 mass% or less, S: 0.015 mass% or less, and Al: 0.080 mass% or less, with the balance being Fe and inevitable impurities.
(4)表面皮膜
本願発明のタッピンねじの成形体本体の表面には、金属めっき皮膜、クロメート処理皮膜、及び電着塗装皮膜からなる3種の皮膜の内の1種以上が形成されていることを要する。この表面処理皮膜の種類としては、電気Znめっき皮膜のような金属めっき皮膜、電気Znめっき皮膜の上にクロメート皮膜が形成された複層皮膜、又はカチオン電着若しくはアニオン電着塗装皮膜であればよい。このような表面皮膜が存在すると、タッピンねじのねじ込み性に優れているのは、この表面皮膜がタッピンねじのワークへのねじ込み時に潤滑剤に類似した作用により摩擦係数が低下すると共に、いわゆる焼きつきによる両者の材料間での損傷が防止されるからである。
(4) Surface coating One or more of three coatings consisting of a metal plating coating, a chromate coating coating, and an electrodeposition coating coating are formed on the surface of the molded body of the tapping screw of the present invention. Cost. The surface treatment film may be a metal plating film such as an electric Zn plating film, a multilayer film in which a chromate film is formed on the electric Zn plating film, or a cationic electrodeposition or anion electrodeposition coating film. Good. When such a surface coating exists, the screwing performance of the tapping screw is excellent because the friction coefficient decreases due to the action similar to the lubricant when the surface coating is screwed into the workpiece, and so-called seizure occurs. This is because damage between the two materials is prevented.
(4−1)本願発明のタッピンねじにおける金属めっき皮膜としては、公知の従来技術の方法によりタッピンねじの表面に形成させる金属皮膜をさし、その通常の目的は耐食性を目的として形成される皮膜を指す。例えば、JIS B 1122の十字穴付きタッピンねじにおいては、付属書において必ずしも表面処理を施す必要はないが、電気めっきを施す場合には、JIS B 1044に規定する締結用部品の電気めっきを適用するものとしている。本願発明における電気めっき皮膜の有効性は潤滑剤的機能にあると推定されるところから、金属種としてはワークの材質に対して相対的に軟質であることが望ましいので、ZnやSnが好適である。また、皮膜の厚さは過度に厚くないことが必要であり、タッピング時のめねじの塑性加工量に依存して増加させることが望ましい。具体的には、ねじの呼び径の増大、従ってねじのピッチの増大により、2〜20μm程度が好適であり、更にはねじ部の一定の寸法・諸元に対しては均一の厚さであることが望ましい。 (4-1) The metal plating film on the tapping screw of the present invention is a metal film formed on the surface of the tapping screw by a known prior art method, and its normal purpose is a film formed for the purpose of corrosion resistance. Point to. For example, a cross-tapped tapping screw of JIS B 1122 does not necessarily have to be subjected to surface treatment in the appendix. However, when electroplating is applied, electroplating of fastening parts specified in JIS B 1044 is applied. It is supposed to be. Since it is presumed that the effectiveness of the electroplating film in the present invention is in the function of a lubricant, it is desirable that the metal species is relatively soft with respect to the material of the workpiece, so Zn or Sn is preferable. is there. Further, the thickness of the film needs to be not excessively thick, and is desirably increased depending on the amount of plastic processing of the internal thread at the time of tapping. Specifically, about 2 to 20 μm is preferable due to an increase in the nominal diameter of the screw, and hence an increase in the pitch of the screw. Furthermore, the thickness is uniform for a certain dimension and specifications of the threaded portion. It is desirable.
(4−2)本願発明のタッピンねじにおけるクロメート処理皮膜としては、公知の従来技術の方法によりタッピンねじの表面に形成させる皮膜を指す。即ち、化成処理の1種で、通常は6価Crを主成分とする処理液中に成形体本体を浸漬して、6価Crと3価Crを主成分とするゲル状の複合水和酸化物皮膜(XCr2O3・YCr2O3・ZH2O)をそ
の表面に形成させる。但し、6価Crの有害性の故に、3価クロメート処理が一層望まし
い。通常、3価クロメート処理はZnめっき後の後処理として行なわれる。なお、Znめっきはめっきしたままの状態では比較的変色や腐食しやすいので、この上にクロメート処理を施すことが望ましい。
(4-2) The chromate-treated film in the tapping screw of the present invention refers to a film formed on the surface of the tapping screw by a known prior art method. That is, it is a kind of chemical conversion treatment, and usually the molded body is immersed in a treatment liquid mainly composed of hexavalent Cr to form a gel-like composite hydrated oxidation mainly composed of hexavalent Cr and trivalent Cr. things coating the (XCr 2 O 3 · YCr 2 O 3 · ZH 2 O) is formed on the surface thereof. However, trivalent chromate treatment is more desirable because of the harmfulness of hexavalent Cr. Usually, trivalent chromate treatment is performed as a post-treatment after Zn plating. In addition, since Zn plating is relatively easy to discolor or corrode in the as-plated state, it is desirable to perform chromate treatment thereon.
(4−3)本願発明のタッピンねじにおける電着塗装皮膜としては、公知の従来技術の方法によりタッピンねじの表面に形成させる皮膜を指す。即ち、タッピンねじの成形体本体を水溶性塗料溶液又は水分散性樹脂溶液に浸漬し、被塗物である成形体本体を陰極、対極を陽極としてこの間に直流電流を流し、正に荷電した塗膜形成成分を電気泳動により成形体本体の表面に電着させて皮膜を形成する(カチオン電着塗装)。なお、成形体本体を陽極とし、負に荷電した塗膜形成成分を電着させて皮膜を形成してもよい(アニオン電着塗装)。樹脂種の例としてはカチオン型電着ではアミノ基をもつ樹脂やオニウム塩基をもつ樹脂を、アニオン型電着ではカルボキシル基をもつ樹脂を用いればよい。そして、皮膜厚さは金属めっき皮膜における場合と同じ考え方により、5〜15μm程度の範囲内で適宜設定するのが好ましい。なお、電着塗装皮膜は下地のZnめっきの上に形成させてもよい。 (4-3) The electrodeposition coating film on the tapping screw of the present invention refers to a film formed on the surface of the tapping screw by a known conventional method. In other words, the molded body of the tapping screw is immersed in a water-soluble paint solution or a water-dispersible resin solution, and the molded body that is the object to be coated is a cathode and the counter electrode is an anode. A film forming component is electrodeposited on the surface of the molded body by electrophoresis to form a film (cation electrodeposition coating). In addition, you may form a membrane | film | coat by making a molded object main body into an anode and electrodepositing the negatively charged coating-film formation component (anion electrodeposition coating). As examples of the resin species, a resin having an amino group or an onium base may be used for cationic electrodeposition, and a resin having a carboxyl group may be used for anionic electrodeposition. And it is preferable to set suitably the film thickness within the range of about 5-15 micrometers by the same view as the case in a metal plating film. The electrodeposition coating film may be formed on the underlying Zn plating.
本願発明のタッピンねじは、成形体本体の結晶形態がフェライト主体の組織であって任意方向断面の少なくとも1断面における平均粒径が2μm以下、あるいは500nm以下、更に望ましくは200nm以下である故に、従来技術によるタッピンねじのように本体表層部に浸炭焼入・焼戻し処理による硬化層が形成されている必要はない。かかる表面硬化層が形成されていなくても、上述した表面皮膜が形成されていれば、ねじ込み時にねじ山がワークに焼付いておねじが破壊されるようなことはないからである。このときの成形体本体の引張強さTSは800MPa程度以上であり、またねじ部表層硬さは転造によりHV=250程度以上となっている。そして、心部の絞りRAは65%以上を有する材質水準が確保されているからである。但し、成形体本体の引張強さTSが600MPa程度以上ではあるが、締結されるワークの機械的性質、特にその引張強さTSの水準(従って硬さの水準)が高くなるにつれて、成形体本体の引張強さTSの水準を高めた材料とする必要がある。そのためには、上記フェライトの平均粒径を微細領域とすることが必要である。 The tapping screw of the present invention has a structure in which the crystal form of the molded body is mainly composed of ferrite, and the average grain size in at least one cross section in an arbitrary direction is 2 μm or less, or 500 nm or less, more preferably 200 nm or less. It is not necessary to form a hardened layer by carburizing quenching / tempering treatment on the surface layer of the main body like a tapping screw by technology. This is because even if such a surface hardened layer is not formed, if the above-described surface film is formed, the screw thread is not baked on the workpiece during screwing and the screw is not destroyed. The tensile strength TS of the molded body at this time is about 800 MPa or more, and the surface hardness of the threaded portion is about HV = 250 or more by rolling. This is because a material level of 65% or more is secured for the central aperture RA. However, although the tensile strength TS of the molded body is about 600 MPa or more, as the mechanical properties of the workpiece to be fastened, especially the level of the tensile strength TS (and hence the level of hardness) becomes higher, the molded body main body. It is necessary to use a material with an increased level of tensile strength TS. For that purpose, it is necessary to make the average grain diameter of the ferrite into a fine region.
このように、本願発明においては、タッピンねじの心部の機械的性質は、成形体本体を構成する化学成分組成の影響も受けるが、フェライトの結晶粒径による影響が支配的である。その状況について前記第(1)項で述べたが、成形体本体の機械的性質は、その素材である鋼線又は棒鋼のそれに依存する。 As described above, in the present invention, the mechanical properties of the core portion of the tapping screw are influenced by the chemical composition of the molded body, but the influence of the ferrite crystal grain size is dominant. Although the situation was described in the above item (1), the mechanical properties of the molded body depend on that of the steel wire or steel bar which is the material.
以下、本願発明を実施例により更に詳しく説明する。本願発明の範囲内にあるタッピンねじである実施例1及び実施例2、並びに本願発明の範囲外にあるタッピンねじである比較例1、比較例2及び比較例3の調製方法について説明し、次いで各タッピンねじの性能試験結果について説明する。 Hereinafter, the present invention will be described in more detail with reference to examples. Example 1 and Example 2, which are tapping screws within the scope of the present invention, and Comparative Example 1, Comparative Example 2 and Comparative Example 3, which are tapping screws outside the scope of the present invention, are described, and then The performance test result of each tapping screw will be described.
[I]タッピンねじの調製
[I−1] 実施例1、2
実施例1及び実施例2のタッピンねじは、所定成分の鋼塊を熱間加工により12mmφ材料に加工し、この熱間加工材を温間加工により6mmφとし、次いで更に冷間加工により2.12mmφの鋼線とし、これをタッピンねじの形状に加工して成形体本体を調製し、そして表面硬化処理を施すことなく、表面皮膜の形成処理を施すことにより調製した。その詳細は次の通りである。
[I] Preparation of tapping screw [I-1] Examples 1 and 2
The tapping screws of Example 1 and Example 2 were obtained by processing a steel ingot having a predetermined component into a 12 mmφ material by hot working. The hot-worked material was warmed to 6 mmφ, and then further cold worked to 2.12 mmφ. The steel body was processed into a tapping screw shape to prepare a compact body, and a surface film was formed without applying a surface hardening treatment. The details are as follows.
(1)実施例1、2の温間圧延線材の調製
表1に示す成分No.1の化学成分組成を有する鋼を真空溶解炉で溶製し、鋳造して試験鋼塊を調製し、これを熱間鍛造して直径12mmφの棒材に調製した(以後、「12mmφ熱間鍛造棒材」という)。次いでこれを圧延温度450〜530℃の範囲内において、スクウェア型、ダイヤモンド型、丸型及びオーバル型カリバーロールを組合せた多パスのカリバー圧延による温間圧延工程で6mmφの線材に加工した(表2参照)。この温間圧延による材料の総減面率Rは75%であり(Rは前記(1)式による)、また平均塑性ひずみεは、3次元有限要素法による計算で2.0以上であることを確認している。
(1) Preparation of warm-rolled wire rod of Examples 1 and 2 Component No. 1 shown in Table 1 Steel having a chemical composition of 1 was melted in a vacuum melting furnace and cast to prepare a test steel ingot, which was hot forged to prepare a bar with a diameter of 12 mmφ (hereinafter, “12 mmφ hot forging” Bar ”). Next, this was processed into a 6 mmφ wire in a rolling temperature range of 450 to 530 ° C. in a warm rolling process by multi-pass caliber rolling in which square type, diamond type, round type and oval type caliber rolls were combined (Table 2). reference). The total area reduction ratio R of the material by this warm rolling is 75% (R is the above equation (1)), and the average plastic strain ε is 2.0 or more as calculated by the three-dimensional finite element method. Have confirmed.
約1.4以上となる。上記の通り調製された線材を以後、「6mmφ温間圧延線材」という。 It becomes about 1.4 or more. The wire prepared as described above is hereinafter referred to as “6 mmφ warm rolled wire”.
得られた6mmφ温間圧延線材のミクロ組織はフェライト主体であって長手方向に垂直な断面(C方向断面)における平均結晶粒径は0.6μmであって、引張強さTSは817MPa、絞りRAは72.0%であり、C方向断面における硬さはビッカース硬さHVで259であった(表3参照)。 The microstructure of the obtained 6 mmφ warm-rolled wire is mainly composed of ferrite, the average grain size in the cross section perpendicular to the longitudinal direction (C direction cross section) is 0.6 μm, the tensile strength TS is 817 MPa, and the drawing RA. The hardness in the cross section in the C direction was 259 in terms of Vickers hardness HV (see Table 3).
(2)実施例1、2の冷間伸線鋼線の調製
上記6mmφ温間圧延線材を冷間伸線工程で2.12mmφの鋼線に加工した。この伸線工程においては、球状化焼なましその他の軟化処理を施すことなく鋼線を伸線することができた。この伸線による材料の総減面率R’は87.5%である(R’は前記(2)式による)。上記の通り調製された鋼線を以後、「2.12mmφ冷間伸線鋼線」という)
得られた2.12mmφ冷間伸線鋼線のミクロ組織はフェライト主体であってC方向断面における平均結晶粒径は200nmであり、伸線方向に延伸したバンブー状組織を呈し、引張強さTSは1100MPa、絞りRAは61.1%であり、C方向断面における硬さはビッカース硬さHVで295であった。
(2) Preparation of cold-drawn steel wire of Examples 1 and 2 The 6 mmφ warm-rolled wire was processed into a 2.12 mmφ steel wire in the cold drawing process. In this wire drawing step, the steel wire could be drawn without performing spheroidizing annealing or other softening treatment. The total area reduction ratio R ′ of the material by this wire drawing is 87.5% (R ′ is according to the above formula (2)). The steel wire prepared as described above is hereinafter referred to as “2.12 mmφ cold-drawn steel wire”)
The microstructure of the obtained 2.12 mmφ cold-drawn steel wire is mainly composed of ferrite, the average grain size in the cross section in the C direction is 200 nm, exhibits a bamboo-like structure drawn in the drawing direction, and has a tensile strength TS. Was 1100 MPa, the aperture RA was 61.1%, and the hardness in the cross section in the C direction was 295 in terms of Vickers hardness HV.
(3)実施例1、2の成形体本体及びタッピンねじの調製
上記実施例1、2における2.12mmφ冷間伸線鋼線を素材として、冷間圧造による頭部成形及び転造によるねじ部成形により、JIS B1123 「六角タッピンねじ」に類似したタッピンねじの成形体本体を調製した。ねじの呼び径が2.6mm、呼び長さが12mmの成形体本体を調製した。この成形体本体に対しては、従来のタッピンねじにおいては通常行なわれている表面硬化処理としての浸炭焼入・焼戻しを施してはいない。そして、この成形体本体に、実施例1では3価クロメート処理による表面皮膜を形成させ、実施例2ではカチオン電着塗装による表面皮膜を形成させてタッピンねじに調製した。(表4を参照)。
(3) Preparation of molded body body and tapping screw of Examples 1 and 2 Using the 2.12 mmφ cold-drawn steel wire in Examples 1 and 2 as a raw material, head forming by cold heading and screw part by rolling A molded body of a tapping screw similar to JIS B1123 “Hexagon Tapping Screw” was prepared by molding. A molded body having a nominal screw diameter of 2.6 mm and a nominal length of 12 mm was prepared. The molded body is not subjected to carburizing / quenching / tempering as a surface hardening treatment that is usually performed in conventional tapping screws. And in this Example 1, the surface film by trivalent chromate treatment was formed in Example 1, and the surface film by cationic electrodeposition coating was formed in Example 2 to prepare a tapping screw. (See Table 4).
[I−2] 比較例1
比較例1のタッピンねじの調製方法は、鋼の溶製工程からねじの成形体本体の成形工程までは、前記実施例1及び実施例2のタッピンねじの調製方法及び条件と同じである。
[I-2] Comparative Example 1
The preparation method of the tapping screw of Comparative Example 1 is the same as the preparation method and conditions of the tapping screw of Example 1 and Example 2 from the steel melting step to the forming step of the screw body.
即ち、(1)温間圧延線材の調製では、表1に示した成分No.1の化学成分組成を有する真空溶解炉製の試験鋼塊から、先ず「12mmφ熱間鍛造棒材」を調製し、次いでこれに圧延温度450〜530℃の範囲内において、スクウェア型、ダイヤモンド型、丸型及びオーバル型カリバーロールを組合せたオーバル型カリバーロールを組合せた多パスのカリバー圧延による温間圧延工程で、総減面率Rが75%の温間圧延加工を施して、「6
mmφ温間圧延線材」に加工した(表2参照)。総減面率Rは75%であり、平均塑性ひずみεは約2.0以上である。
That is, in the preparation of (1) warm rolled wire rod, the component No. First, a “12 mmφ hot forged bar” was prepared from a test steel ingot made of a vacuum melting furnace having a chemical composition of 1, and then in a range of a rolling temperature of 450 to 530 ° C., a square type, a diamond type, In a warm rolling process by multi-pass caliber rolling in which oval caliber rolls are combined with round and oval caliber rolls, a total rolling reduction R of 75% is applied, and a “6
mmφ warm-rolled wire "(see Table 2). The total area reduction ratio R is 75%, and the average plastic strain ε is about 2.0 or more.
次に(2)冷間伸線鋼線の調製として、この6mmφ温間圧延線材に対して、球状化焼なまし等の軟化処理を途中で施すことなく総減面率R’が87.5%の冷間伸線加工を施して、「2.12mmφ冷間伸線鋼線」を調製した(表2及び表3を参照)。 Next, (2) as a cold-drawn steel wire, the total area reduction ratio R ′ is 87.5 without subjecting this 6 mmφ warm-rolled wire to softening treatment such as spheroidizing annealing. % Cold drawing was performed to prepare “2.12 mmφ cold drawn steel wire” (see Table 2 and Table 3).
なお、比較例1における「6mmφ温間圧延線材」及び「2.12mmφ冷間伸線鋼線」のミクロ組織並びに引張強さTS、絞りRA及び硬さ等の材質特性は、上記調製工程から明らかなように、実施例1及び2のそれらと同じである(表3を参照)。 The microstructures of “6 mmφ warm-rolled wire” and “2.12 mmφ cold-drawn steel wire” in Comparative Example 1 and material properties such as tensile strength TS, drawing RA, and hardness are apparent from the above preparation process. As is the case with Examples 1 and 2 (see Table 3).
そして(3)この鋼線を素材として、実施例1及び2と同様に、ねじの呼び径が2.6mm、呼び長さが12mmの成形体本体を冷間圧造及び転造により調製した。これに対しても、実施例1及び実施例2と同様、浸炭焼入・焼戻しを施してはいない。比較例1のタッピンねじの調製はこれで終了である。即ち、所謂「生」のねじであって、しかも表面皮膜が形成されていないタッピンねじである(表4を参照)。 (3) Using this steel wire as a raw material, a molded body having a nominal diameter of 2.6 mm and a nominal length of 12 mm was prepared by cold heading and rolling in the same manner as in Examples 1 and 2. Again, as in Example 1 and Example 2, carburizing quenching / tempering is not performed. This completes the preparation of the tapping screw of Comparative Example 1. That is, it is a so-called “raw” screw and a tapping screw without a surface coating (see Table 4).
[I−3] 比較例2、3
比較例2及び比較例3のタッピンねじは、従来技術により製造された浸炭焼入・焼戻し処理が施された低炭素鋼成分のタッピンねじである。その製造方法は次の通りである。
(1)比較例2、3の熱間圧延線材の準備
市販のJIS 3507に規定された冷間圧造用炭素鋼線材であって、化学成分はその種類記号がSWCH16Aに属するものであり、熱間圧延法により製造された直径6mmφの線材を準備した。なお、熱間圧延法における圧延温度は通常、オーステナイト領域の温度範囲で行なわれる。この線材の化学成分組成を、表1の成分No.2に示す。この6mmφの熱間圧延線材のフェライト粒径は、C方向断面において15μm、引張強さTSは455MPa、絞りRAは75.0%であり、C方向断面における硬さはビッカース硬さHVで141であった(表3を参照)。以後、この線材を「6mmφ熱間圧延線材」という。
[I-3] Comparative Examples 2 and 3
The tapping screws of Comparative Example 2 and Comparative Example 3 are low-carbon steel component tapping screws that have been subjected to carburizing quenching and tempering treatments manufactured by conventional techniques. The manufacturing method is as follows.
(1) Preparation of hot-rolled wire rods of Comparative Examples 2 and 3 Commercially available carbon steel wire rod for cold heading specified in JIS 3507, the chemical component of which belongs to SWCH16A, A wire having a diameter of 6 mmφ manufactured by a rolling method was prepared. The rolling temperature in the hot rolling method is usually performed in the temperature range of the austenite region. The chemical component composition of this wire is shown in Table 1. It is shown in 2. This 6 mmφ hot-rolled wire has a ferrite grain size of 15 μm in the cross section in the C direction, a tensile strength TS of 455 MPa, a drawing RA of 75.0%, and a hardness in the cross section in the C direction of 141 in terms of Vickers hardness HV. (See Table 3). Hereinafter, this wire is referred to as “6 mmφ hot rolled wire”.
(2)比較例2、3の冷間伸線鋼線の調製
上記6mmφ熱間圧延線材を、冷間伸線工程において適宜セメンタイトの球状化焼なましを行ない、2.12mmφの鋼線に加工した。伸線による材料の総減面率R’は、実施例1及び実施例2並びに比較例1と同じく87.5%である(表2及び表3を参照)。
(2) Preparation of cold-drawn steel wires of Comparative Examples 2 and 3 The 6 mmφ hot-rolled wire was subjected to spheroidizing annealing of cementite as appropriate in the cold-drawing process, and processed into a 2.12 mmφ steel wire. did. The total area reduction ratio R ′ of the material by wire drawing is 87.5% as in Examples 1, 2 and Comparative Example 1 (see Tables 2 and 3).
次に、ねじの成形体への加工を可能とするために、上記冷間伸線鋼線に球状化焼なまし処理を施して軟化させた。この球状化焼なまし鋼線のミクロ組織はフェライト主体であってC方向断面における平均結晶粒径は18μmで、引張強さTSは520MPa、絞りRAは81.0%であり、C方向断面における硬さはビッカース硬さHVで167であった(表3を参照)。 Next, in order to enable the processing of the screw into a molded body, the cold-drawn steel wire was softened by spheroidizing annealing. The microstructure of the spheroidized annealed steel wire is mainly ferrite, the average grain size in the C direction cross section is 18 μm, the tensile strength TS is 520 MPa, the drawing RA is 81.0%, and in the C direction cross section. The hardness was 167 in terms of Vickers hardness HV (see Table 3).
(3−1)比較例2の成形体本体及びタッピンねじの調製
比較例2では、上記で得られた球状化焼なまし後の2.12mmφ鋼線を素材として、冷間圧造による頭部成形及び転造によるねじ部成形によりタッピンねじの成形体本体を調製した。成形体本体の調製方法は、実施例1、2及び比較例1と同じであり、ねじの呼び径は2.6mm、呼び長さが12mmである。
(3-1) Preparation of molded body and tapping screw of Comparative Example 2 In Comparative Example 2, the head was formed by cold heading using the 2.12 mmφ steel wire after spheroidizing annealing obtained above. Then, a formed body of a tapping screw was prepared by forming a thread part by rolling. The method for preparing the molded body is the same as in Examples 1 and 2 and Comparative Example 1. The nominal diameter of the screw is 2.6 mm and the nominal length is 12 mm.
次いで、このねじの成形体本体の表面硬化処理として浸炭焼入・焼戻しを施した。こうして得られた比較例2のタッピンねじは、その心部硬さはHVで334、表面硬さはねじ山のHVで535であった。比較例2では、クロメート処理その他の表面皮膜の形成処理
は行なっていない。
Subsequently, carburizing quenching and tempering were performed as a surface hardening treatment of the molded body of the screw. The tapping screw of Comparative Example 2 thus obtained had a core hardness of 334 in HV and a surface hardness of 535 in the thread HV. In Comparative Example 2, the chromate treatment and other surface coating formation treatments are not performed.
(3−2)比較例2の成形体本体及びタッピンねじの調製
比較例3では、比較例2と同じ方法で、同じ呼び径及び呼び長さの成形体本体を調製し、次いで比較例2と同じように浸炭焼入・焼戻しを施した。但し、比較例3においては、更に3価クロメート処理による表面皮膜を形成させた。
(3-2) Preparation of molded body and tapping screw of Comparative Example 2 In Comparative Example 3, a molded body having the same nominal diameter and nominal length was prepared by the same method as Comparative Example 2, and then Comparative Example 2 and Carburizing quenching and tempering were performed in the same way. However, in Comparative Example 3, a surface film was further formed by trivalent chromate treatment.
[II]実施例及び比較例のタッピンねじの評価
上記の通り調製された実施例1及び実施例2並びに比較例1及び比較例2のタッピンねじにつき、
A:ねじ込み性を評価するための「ねじ込み試験」と、
B:ねじり強度を評価するための「ねじり試験」
とを行なった。
[II] Evaluation of Tapping Screws of Examples and Comparative Examples Regarding the tapping screws of Examples 1 and 2 and Comparative Examples 1 and 2 prepared as described above,
A: “Screw-in test” for evaluating screwability;
B: "Torsion test" for evaluating torsional strength
And performed.
[II−A] ねじ込み試験
[試験方法]
これは被締結体にタッピンねじをねじ込んでそれを締め付けたときに、タッピンねじのねじ山が変形乃至破壊することなく、被締結材にめねじを成形することができる性能を評価するものであって、JIS B 1055 「タッピンねじ−機械的性質」の6.2.1「ねじ込み試験」で規定された方法に準じて行なった。
[II-A] Screw-in test [Test method]
This is to evaluate the ability to form a female screw on a material to be fastened without screwing the screw thread of the tapping screw deformed or broken when the screw is screwed into the fastened body. In accordance with the method defined in 6.2.1 “Screw-in test” of JIS B 1055 “Tapping screw—mechanical properties”.
被締結試験用鋼板として、板厚が1.2mm及び2.0mmのSS400の冷間圧延鋼板を供し、このそれぞれに穴径2.20mmφ又は2.30mmφの加工穴をリーマー加工により成形し、ねじの軸方向荷重:30N、回転速度:600rpmでねじ込み試験を行なった。 SS400 cold-rolled steel sheets with thicknesses of 1.2 mm and 2.0 mm are used as the steel sheets to be fastened, and processed holes with a hole diameter of 2.20 mmφ or 2.30 mmφ are formed by reaming, respectively. A screw-in test was performed at an axial load of 30 N and a rotational speed of 600 rpm.
但し、この試験においては、タッピンねじの被締結試験用鋼板へのねじ込みの前進を途中で停止させることなく、タッピンねじの座面(頭部フランジの下面)で停止させられるまで、又は途中で自動的に前進が停止するまでねじ込みを継続させた。 However, in this test, the screwing of the tapping screw into the steel plate to be fastened is not stopped halfway, but automatically stopped until it is stopped on the tapping screw seat (the lower surface of the head flange). The screwing was continued until the forward movement stopped.
このねじ込み試験によるタッピンねじのねじ込み性は、
(1)ねじ山の変形状態及び被締結試験用鋼板へのめねじの成形状態をみることを主体とし、更に、
(2)ねじ込み途中におけるねじ込みトルクの最大値を参考とすることにより評価した。
The screwability of the tapping screw by this screwing test is
(1) Mainly to see the deformation state of the thread and the forming state of the internal thread on the steel plate for fastening test,
(2) Evaluation was made by referring to the maximum value of the screwing torque in the middle of screwing.
[試験結果]
(1)ねじ山の変形・破壊及びめねじの成形性について
ねじ込み試験終了後の試験片の軸心を含むL方向断面組織を、20倍の光学顕微鏡で観察した。その結果、ねじ山の変形乃至破壊が認められず、しかも被締結試験用鋼板が頭部座面の至近距離までねじ込まれたものであって、被締結試験用鋼板がタッピンねじの首下不完全ねじ部直下の無変形乃至無破壊のねじ山によって座面に押し付けられている、という条件を満たすものを、ねじ込み性が「良」であると判定し、「○」印で表記した。これに対して、ねじ込み性の判定が上記「良」の条件を満たさないもののねじ込み性を「不良」と判定し、「×」印で表記した。
[Test results]
(1) Thread Deformation / Destruction and Formability of Female Thread The cross-sectional structure in the L direction including the axis of the test piece after the completion of the screwing test was observed with a 20 × optical microscope. As a result, the deformation or destruction of the screw thread is not recognized, and the steel plate for fastening test is screwed to the closest distance of the head seating surface, and the steel plate for fastening test is incomplete under the neck of the tapping screw. Those satisfying the condition that they are pressed against the bearing surface by an undeformed or non-destructive screw thread directly under the threaded portion were judged to be “good” and indicated by “◯”. On the other hand, the screwability was judged as “bad” when the screwability did not satisfy the above “good” condition, and indicated by “x”.
図1及び図2のそれぞれに、実施例1及び実施例2の上記ねじ込み試験終了後の試験片断面組織の顕微鏡写真を示し、図3、図4及び図5のそれぞれに、同じく比較例1、比較例2及び比較例3のそれらを示す。そして、表5に実施例1、2及び比較例1、2、3のタッピンねじのねじ込み性の判定結果(○又は×)を示す。 FIGS. 1 and 2 show micrographs of the cross-sectional structure of the test piece after completion of the screwing test of Example 1 and Example 2, respectively, and FIGS. Those of Comparative Example 2 and Comparative Example 3 are shown. Table 5 shows the determination results (◯ or ×) of the screwability of the tapping screws of Examples 1 and 2 and Comparative Examples 1, 2, and 3.
ここで、良(○)と判断された実施例1、2及び比較例2、3におけるめねじの成形性に関して、断面組織写真によれば、被締結試験用鋼板1に対して正常なめねじの成形がされていない。 Here, regarding the formability of the female thread in Examples 1 and 2 and Comparative Examples 2 and 3 determined to be good (◯), according to the cross-sectional structure photograph, Not molded.
上記ねじ込み試験結果によれば、本願発明の範囲内にある実施例1及び実施例2のタッピンねじはいずれも、被締結試験用鋼板に対するタッピンねじのねじ込みにおけるねじ山の変形乃至破壊は無く、ねじ込み性に優れていることがわかる。また、従来技術の比較例2及び比較例3のタッピンねじは、浸炭焼入・焼戻しにより表面硬化処理が施されているものであり、表面皮膜の形成がなされていてもいなくても、実施例1及び2と同様、ねじ
込み性に優れていることがわかる。
According to the above screwing test results, both the tapping screws of Examples 1 and 2 within the scope of the present invention have no thread deformation or breakage when tapping the tapping screw with respect to the steel plate to be fastened. It turns out that it is excellent in property. Further, the tapping screws of Comparative Example 2 and Comparative Example 3 of the prior art are subjected to surface hardening treatment by carburizing quenching and tempering, and even if the surface coating is not formed, Similar to 1 and 2, it can be seen that the screwing property is excellent.
これに対して、比較例1のタッピンねじは、実施例1又は2のタッピンねじとの相違点が、表面皮膜の形成がされていない点のみにあるが、ねじ込みによりねじが完全に破壊され、ねじ込みの進行が途中で停止した(図3を参照)。 In contrast, the tapping screw of Comparative Example 1 is different from the tapping screw of Example 1 or 2 only in that the surface film is not formed, but the screw is completely destroyed by screwing, The progress of screwing stopped halfway (see FIG. 3).
なお、前記JIS B 1055 「タッピンねじ−機械的性質」の4項「要求事項」によれば、4.2.1「ねじ込み性」として、前記6.2.1「ねじ込み試験」によって試験用鋼板にねじ込んだとき、タッピンねじのねじ山が変形することなく、めねじを試験用鋼板に成形することができることと規定されている。従って、この試験で、ねじ込み性が「○」と判定されることは重要である。 According to Section 4 “Requirements” of JIS B 1055 “Tapping Screws—Mechanical Properties”, the steel plate for testing was used as 4.2.1 “Screwability” according to 6.2.1 “Screw Test”. It is stipulated that the internal thread can be formed into the test steel plate without deformation of the thread of the tapping screw when screwed into the test plate. Therefore, in this test, it is important that the screwability is determined as “◯”.
[II−B] ねじり試験
[試験方法]
これはタッピンねじのねじり強度を測定するものであって、JIS B 1055 「タッピンねじ−機械的性質」の6.2.2「ねじり強さ試験」で規定された方法に準じて行なった。試験は同規定の図1のねじり強さ試験装置を用いて、ねじが破壊するまでトルクを加えることにより、破壊トルク値を測定した。
[II-B] Torsion test [Test method]
This was to measure the torsional strength of the tapping screw, and was carried out in accordance with the method defined in 6.2.2 “Torsional strength test” of JIS B 1055 “Tapping pin-mechanical properties”. In the test, the breaking torque value was measured by applying torque until the screw broke using the torsional strength test apparatus of FIG.
[試験結果]
(2)破壊トルク値について
各実施例及び各比較例の破壊トルク値を、表5に併記する。実施例1、2は、12.40〜13.00kgf・cmの範囲内にある。一方、従来技術による比較例2、3においては、それぞれ15.54kgf・cm、15.63kgf・cmと、各実施例を上回る破壊トルクが得られている。なお、比較例1も、実施例1、2と同じ水準にある。
[Test results]
(2) Breaking torque values The breaking torque values of the examples and comparative examples are shown in Table 5. Examples 1 and 2 are in the range of 12.40 to 13.00 kgf · cm. On the other hand, in Comparative Examples 2 and 3 according to the prior art, the breaking torque exceeding 15.54 kgf · cm and 15.63 kgf · cm, respectively, is obtained. Note that Comparative Example 1 is also at the same level as Examples 1 and 2.
一方、参考として上記JIS B 1055 JISの6.2.2「ねじり強さ試験」の項の表3によれば、ねじの呼びが2.6mmの場合には、最小ねじり強さの要求値は0.9N(9.18kgf・cm)とされている。従って、このJISによる規定値を基準とすれば、実施例1、2の破壊トルクは要求値を3〜4kgf・cm程度上回っている。 On the other hand, according to Table 3 in the section of JIS B 1055 JIS 6.2.2 “Torsional strength test”, when the nominal diameter of the screw is 2.6 mm, the required value of minimum torsional strength is 0.9 N (9.18 kgf · cm). Therefore, if this JIS standard is used as a reference, the breaking torques of Examples 1 and 2 exceed the required values by about 3 to 4 kgf · cm.
上述した所から、本願発明のタッピンねじのねじ込み性は、今回の被締結材に関する試験条件下において、従来技術による浸炭焼入・焼戻しされたタッピンねじのそれとほぼ同等であり、またタッピンねじのねじり強さについては、本願発明のタッピンねじは従来技術によるタッピンねじには及ばないが、JISに規定された要求値をかなりの程度上回っていることがわかる。 From the above, the screwability of the tapping screw of the present invention is almost the same as that of the conventional carburized and tempered tapping screw under the test conditions regarding the material to be fastened, and the tapping screw is twisted. In terms of strength, it can be seen that the tapping screw of the present invention does not reach the tapping screw according to the prior art, but significantly exceeds the required value defined in JIS.
以上の試験より、この出願の発明に係る熱処理を省略した高強度タッピンねじの産業上の有用性、並びにこれらを製造するための製造方法の産業上の有用性が確認された。 From the above tests, it was confirmed that the industrial utility of the high-strength tapping screw without the heat treatment according to the invention of this application and the industrial utility of the production method for producing them.
1 被締結試験用鋼板
2 タッピンねじの座面
1 Steel plate for fastening test 2 Seat surface of tapping screw
Claims (3)
前記成形体本体の表層部には硬化処理による硬化層が形成されず、且つ、
前記成形体本体の表面には、金属めっき皮膜、クロメート処理皮膜、及び電着塗装皮膜からなる3種の皮膜の内、少なくとも1種が形成されていることを特徴とする高強度タッピンねじ。 The formed body of the tapping screw has an ultrafine-grained ferrite structure having an average particle diameter of 200 nm or less in at least one section in the arbitrary direction section;
The surface layer portion of the molded body is not formed with a cured layer by a curing process, and
A high-strength tapping screw characterized in that at least one of three types of coatings comprising a metal plating film, a chromate-treated film, and an electrodeposition coating film is formed on the surface of the molded body.
C :0.60質量%以下、
Si:1.50質量%以下、
Mn:0.15〜1.80質量%、
P :0.015質量%以下、
S :0.015質量%以下、及び、
Al:0.080質量%以下
で、残部はFe及び不可避不純物であることを特徴とする請求項1に記載の高強度タッピンねじ。 The chemical component composition of the molded body is:
C: 0.60 mass% or less,
Si: 1.50 mass% or less,
Mn: 0.15 to 1.80% by mass,
P: 0.015 mass% or less,
S: 0.015 mass% or less, and
The high-strength tapping screw according to claim 1 , wherein Al: 0.080% by mass or less, and the balance is Fe and inevitable impurities.
3. The high strength according to claim 2 , further comprising at least one element of Cr, Mo, Ni, Cu, Ti, Nb, V, and B as a chemical component composition of the molded body. Tapping screw.
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