JP4349732B2 - Spring wire and steel wire with excellent weldability and workability - Google Patents

Description

【００３３】
【表２】

【００３４】
【表３】

【００３５】
更に、溶接部の強度を確認するため、各鋼種を代表する試料Ｎｏ．の鋼線（φ４．５ｍｍ）を選択し、十字形に点溶接を実施し、剪断強度および剥離強度を測定した。この結果を表４に示す。なお、溶接時の加圧力は、３００Ｎ、溶接２次側電流は、２．０ＫＶＡ、通電時間は、０．１２ｓｅｃであった。なお、剪断強度は、図３に示す治具を、そして、剥離強度は、図４に示す治具を用いてそれぞれ測定した。
【００３６】
【表４】

【００３７】
表２および表３から、以下のことが明らかになった。
【００３８】
本発明例Ｎｏ．１、２、４、５、７、８、１０、１２、１３、１４、１６、１７は、線材および鋼線共に高強度および高靭性を示し、曲げ加工性も良好である。
【００３９】
化学成分は、本発明範囲内であるが、冷却速度が本発明範囲を外れて低い比較例Ｎｏ．３、６、９、１１、１５は、線材および鋼線共に、本発明例に比べて強度および延性共に低く、曲げ加工性も劣る。
【００４０】
Ｎｏ．１８の比較例は、線材および鋼線共に、延性は本発明例レベルに近似し、曲げ加工性も良好であったが、本発明例に比べて強度が低いので、ばね用鋼線には適さない。
【００４１】
Ｎｏ．１９の比較例は、線材および鋼線共に、強度および延性は、本発明例レベルに近似し、曲げ加工性も良好であるが、後述のように、溶接後の強度が低い。
【００４２】
Ｎｏ．２０の比較例は、Ｔｉ含有量が本発明範囲を外れて大きいので、線材および鋼線共に、延性が本発明例に比べて低く、曲げ加工性も劣る。
【００４３】
Ｎｏ．２１の比較例は、ＴｉおよびＢが添加されていないため、線材および鋼線共に、本発明例に比べて強度および延性が低く、曲げ加工性も劣る。
【００４４】
Ｎｏ．２２の比較例は、Ｎｂが添加されていないために、線材および鋼線共に、本発明例に比べて延性が低く、曲げ加工性も劣る。
【００４５】
表４から、以下のことが明らかになった。
【００４６】
本発明例Ｎｏ．１、４、７、１０、１３、１４、１６、１７は、何れも、比較例に比べて、剪断強度および剥離強度の何れも高い値を示している。
【００４７】
従来ばね用鋼線として使用されていた比較例Ｎｏ．１９は、溶接部分にマルテンサイトを生じるため、剪断強度および剥離強度の何れも低い値を示し、溶接加工を用いる工法に不向きであることを示している。
【００４８】
【発明の効果】
以上説明したように、この発明によれば、Ｃ、Ｓｉ、Ｍｎの基本成分に、Ｃｒ、Ｎｂ、Ａｌ、Ｂ、Ｔｉ、Ｎを各々所定範囲内に含有させ、また、必要に応じて、前記成分に更に、Ｎｉ、Ｍｏ、Ｖの内の少なくとも１種を含有させ、鋼の熱間圧延完了後に５〜５０℃／ｓｅｃの制御冷却を行って、組織全体をベイナイトとすることにより、従来のばね用鋼に比べＣ含有量が低いにもかかわらず、高強度で加工性に優れ且つ溶接性に優れた特性を有するばね用線材および鋼線を得ることができる。
【００４９】
従って、この発明によれば、圧延ままで伸線加工が可能で、鋼線の加工途中で強度を付与するための特別な熱処理を必要とせず、溶接性に優れていることから、生産性の低い、従来のかしめ等の接合方法から溶接への工法変更が可能となるために、生産性、歩留まりの向上、および、省資源、省エネルギーが強く唱えられている昨今の社会的趨勢に答えられ、自動車用シートの枠線、インサートワイヤー等の緩衝構造材の素材として有効に活用することができるといった有用な効果がもたらされる。
【図面の簡単な説明】
【図１】鋼中のＢ含有量と線材の引張り強さおよび絞りとの関係を示すグラフである。
【図２】線材の組織を示す顕微鏡写真である。
【図３】剪断強度を測定するための治具を示す図であり、（ａ）は、正面図、（ｂ）は、断面図、（ｃ）は、平面図である。
【図４】剥離強度を測定するための治具を示す概略斜視図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a spring wire and a steel wire excellent in weldability and workability, in particular, a spring wire and a steel wire excellent in weldability and workability required as a buffer structure material such as a frame wire of an automobile seat and an insert wire. It is about.
[0002]
[Prior art]
As the steel wire for spring, a hard steel wire defined mainly in JIS G 3521 is adopted. That is, this type of spring is generally manufactured by patenting a hot-rolled wire and then drawing it cold to prepare a spring material, followed by cutting and bending. The core structure of the buffer is assembled by joining by caulking.
[0003]
However, in recent social trends where productivity, yield, resource saving, and energy saving are strongly advocated, it is difficult to use a hard steel wire for the above-mentioned spring structure and use a caulking joining method. Due to the disadvantage, there is an increasing demand for a steel wire that has the same strength as a hard steel wire but has the same workability as a mild steel wire and can be processed by a welding method. Techniques related to weldable steel wires are disclosed in Technology 1), Japanese Patent Application Laid-Open No. 8-176636 (Conventional Technology 2), Japanese Patent Application Laid-Open No. 10-195600 (Conventional Technology 3) and Japanese Patent Application Laid-Open No. 10-53814 (Conventional Technology 4). Yes.
[0004]
[Problems to be solved by the invention]
However, prior art 1 requires quenching in the processing step after completion of rolling, and prior art 2 requires controlled cooling and tempering or tempering from the austenitizing temperature in the processing step after completion of rolling. Since No. 3 requires aging treatment with heating and a lead bath in the processing step after the completion of rolling, both have problems from the viewpoint of productivity improvement and resource / energy saving.
[0005]
Furthermore, in the prior art 4, since the area ratio of (bainite + pearlite) after the completion of rolling is 10 to 95% and the balance is composed of at least one of ferrite, martensite and retained austenite, the steel wire is drawn. Further, when processing the spring, voids due to the difference in workability between the structure constituting the remaining part and (bainite + pearlite) are easily formed, so that problems remain in workability such as bending.
[0006]
Accordingly, the present invention has been made by paying attention to the above-mentioned circumstances, and it is possible to draw a steel wire as it is rolled, and a special heat treatment is required for imparting strength during the processing step. However, the object is to provide a spring wire and a steel wire that have excellent weldability and workability while having the same strength as a hard steel wire.
[0007]
[Means for Solving the Problems]
The inventors of the present application have made extensive studies to solve the above-described problems. As a result, the following findings were obtained.
{Circle around (1)} In a steel having a predetermined chemical composition, when a wire having a bainite structure as a whole is drawn, a spring steel wire having excellent strength and ductility, and excellent weldability and workability can be obtained.
{Circle around (2)} In particular, B dissolved in steel refines the bainite structure and contributes to increasing the strength and toughness of the steel.
(3) In order to refine and homogenize the steel structure and obtain sufficient strength and ductility as a spring material, after hot rolling, for example, 5-50 ° C. by controlled cooling using a combination of mist and blast. It is effective to cool the wire at a cooling rate of / sec.
[0008]
The present invention has been made on the basis of the above-described knowledge, and is characterized by the following.
[0009]
The invention according to claim 1 includes: C: 0.05 to 0.20, Si: 0.35 to 1.50, Mn: 1.00 to 3.00, Cr: 0.10 to 1.50, Nb: 0.01 to 0.10, Al: 0.005 to 0.080, B: 0.0005 to 0.0050, Ti: 0.02 to 0.06, N: 0.003 to 0.015 (or more , Mass%), balance: Fe and Fe unavoidable impurities are hot-rolled, and after the completion of rolling, controlled cooling at 5 to 50 ° C./sec is performed to make the structure bainite.
[0010]
The invention according to claim 2 further includes, as steel components, Ni: 1.0 or less (not including 0), Mo: 1.0 or less (not including 0), V: 0.05 to 0.30 ( As described above, it is characterized by containing at least one selected from the group consisting of mass%).
[0011]
The invention described in claim 3 is characterized in that the wire rod described in claim 1 or 2 is drawn.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Next, the reason for limiting the component composition in this invention will be described.
[0013]
(1) C: 0.05-0.20 mass%
C is important as a steel strengthening element and a hardenability improving element, but if it is less than 0.05 mass%, the strengthening action and the hardenability improving action are insufficient, and sufficient strength cannot be obtained. On the other hand, if it exceeds 0.20 mass%, the weldability and workability of the present invention will be deteriorated. Therefore, the C content is limited to a range of 0.05 to 0.20 mass%.
[0014]
(2) Si: 0.35 to 1.50 mass%
Si is important as a deoxidizer at the time of melting steel and welding after being processed into a steel wire. In addition to contributing to strengthening ferrite as a solid solution strengthening element, it is an important element for improving sag resistance as a spring. In order to exhibit these effects, it is necessary to contain 0.35 mass% or more. On the other hand, when it exceeds 1.50 mass%, ductility will fall and workability will deteriorate. Therefore, the Si content is limited to the range of 0.35 to 1.50 mass%.
[0015]
(3) Mn: 1.00 to 3.00 mass%
Mn, like Si, acts as a deoxidizer during steel melting and steel wire welding, and also has the effect of fixing S, which inhibits ductility, as MnS, mitigating the damage, and hardenability. It acts as an improving element, and effectively works to improve ductility by making the base structure finer. In order to obtain these actions appropriately, it is necessary to contain 1.00 mass% or more, but when it exceeds 3.00 mass%, the effect is saturated. Therefore, the Mn content is limited to the range of 1.00 to 3.00 mass%.
[0016]
(4) Cr: 0.10 to 1.50 mass%
Cr has the effect of improving hardenability like the above-described Si and Mn, and has the effect of suppressing softening due to heat applied during welding. In order to exert such an action, it is necessary to contain 0.10 mass% or more, but if it exceeds 1.50 mass%, the action is saturated and economically useless. Therefore, the Cr content is limited to the range of 0.10 to 1.50 mass%.
[0017]
(5) B: 0.0005 to 0.0050 mass%
B has the effect of improving hardenability like Si, Mn, and Cr described above, but unlike other elements, when a certain amount or more is incorporated in the steel, it is constant regardless of its content. It has the characteristic of maintaining the hardenability improving effect. For this reason, if the wire after completion of rolling is cooled under appropriate conditions, the bainite transformation is promoted without being affected by the content, and the structure is stabilized and refined. In order to exhibit such an action, it is necessary to contain 0.0005 mass% or more, but even if it exceeds 0.0050 mass%, the effect is saturated. Therefore, the B content is limited to a range of 0.0005 to 0.0050 mass%.
[0018]
(6) Nb: 0.01 to 0.10 mass%, Al: 0.005 to 0.080 mass%, Ti: 0.02 to 0.06 mass%, N: 0.003 to 0.015 mass%,
Al acts as a deoxidizer during melting. Further, Al forms nitrides, and Nb and Ti form carbonitrides, preventing austenite crystal grains from coarsening, refining the crystal grains after rolling, and increasing the strength and toughness of steel. Works. In particular, Nb has the effect of increasing the yield strength ratio and improving sag resistance. The content that makes the effect of addition of each of these elements effective is set as the lower limit, and the content that becomes saturated when the effect is saturated and exceeds it is made the upper limit. Accordingly, the Nb content is 0.01 to 0.10 mass%, the Al content is 0.005 to 0.080 mass%, the Ti content is 0.02 to 0.06 mass%, and the N content is 0. It was limited within the range of 0.003 to 0.015 mass%.
[0019]
(7) Ni: 1.0 mass% or less (not including 0), Mo: 1.0 mass% or less (not including 0), V: 0.05 to 0.30 mass%
Ni and Mo increase the hardenability of steel and contribute to high strength. Moreover, Mo has the effect | action which suppresses the softening by the heat added in the case of welding. In order to make these addition effects effective, it is preferably 0.05% by mass or more. V improves the hardenability, forms carbonitrides like Nb and Ti, prevents coarsening of the austenite crystal grains, refines the crystal grains after rolling, and increases the strength of the steel. Although the effect | action which raises toughness is carried out, in order to make an addition effect effective, it is required to contain 0.05 mass% or more. The upper limit of each element was a content that was wasted even if the effect was saturated and exceeded. Therefore, the Ni and Mo contents are limited to 1.0 mass% or less, and the V content is limited to a range of 0.05 to 0.30 mass%.
[0020]
In general, a wire rod is cooled with water immediately after completion of hot rolling, and then wound on a reel, placed in a ring shape on a conveyor, and cooled by blast on a moving conveyor. Manufactured. The steel wire for springs excellent in weldability and workability according to the present invention has a cooling rate after hot rolling of the steel having the above chemical components adjusted within a range of 5 to 50 ° C./sec, and the whole has a bainite structure. Can be obtained.
[0021]
The process and conditions from the heating prior to rolling of the spring steel wire rod according to the present invention to the cooling after hot rolling will be described below.
[0022]
In rolling, in order to precipitate carbonitride by Nb, Ti, V and increase the strength, it is necessary to dissolve the precipitate by heating before rolling, but if the heating temperature is too high, However, it is preferable to set the heating temperature during rolling to a temperature range of 1000 to 1230 ° C. In particular, the coiling temperature is preferably in a temperature range of 750 to 900 ° C. in order to prevent coarsening of the crystal grains after the coiling and not to deteriorate the ductility.
[0023]
In addition, when ferrite and bainite coexist in the wire after controlled cooling, not only the strength sufficient as a spring material cannot be obtained, but also in the tensile test after wire and steel wire processing or when bending steel wire, As a result, cracks are likely to occur from the interface between bainite and bainite, and the ductility is insufficient, resulting in insufficient workability.
[0024]
In order to prevent such a thing and to obtain sufficient ductility and workability, it is necessary to adjust the cooling rate after being placed on the conveyor within a range of 5 to 50 ° C./sec and to make the whole a bainite structure. is there. In particular, adjusting the cooling rate at the initial stage of cooling from the coiling temperature to 450 ° C. to 10 ° C. or more effectively works to prevent precipitation of pro-eutectoid ferrite. Thus, it is preferable to perform controlled cooling with enhanced cooling capacity of the cooling medium.
[0025]
【Example】
Next, the present invention will be further described with reference to examples. Needless to say, the present invention is not limited to these examples, and can be appropriately modified according to the gist of the present invention described above.
[0026]
FIG. 1 is a graph showing the results of examining the influence of the B content in steel on the tensile strength and drawing of the steel after rolling. The chemical components other than B are 0.12% C-0.80% Si-1.45% Mn-0.55% Cr-0.030% Ti-0.030% Nb satisfying the present invention. Steel whose B content was changed in the range of 0.0001 to 0.0030% was melted, rolled into a wire of φ7 mm by hot rolling, placed on a winding conveyor at 850 ° C., and up to 450 ° C. The mist was cooled at about 15 ° C./sec by using a mist and a gust of wind, wound around a coil, and then a sample was taken from the coil and subjected to a tensile test. The test piece was a JIS Z 2201 No. 2 test piece.
[0027]
As is clear from FIG. 1, both the tensile test and the drawing increase with an increase in the B content, and when the B content exceeds 0.0005%, a substantially constant value (high strength / high ductility) is exhibited. I understand.
[0028]
FIG. 2 shows the microstructure of the steel having a B content of 0.0010% with the tensile strength and drawing stabilized in FIG. As is clear from FIG. 2, the entire structure exhibits uniform bainite. Similar structures were observed for other samples having a B content of 0.0005% or more, which showed substantially the same tensile strength and drawing value.
[0029]
Next, 8 kinds of steels of the present invention (A to H) and 5 kinds of comparative steels (I to M) shown in Table 1 are melted, and the heating and cooling conditions are changed, rolled and cooled, and φ7 mm And the wire rod of (phi) 9mm (sample No. 1-22) was manufactured, and the tensile test of the wire rod was implemented. Table 2 shows the heating conditions, cooling conditions, and tensile test values of the wire.
[0030]
Further, a φ7 mm wire was drawn to φ4.5 mm, and a φ9 mm wire was drawn to a φ5.5 mm steel wire, and a tensile test and a bending test were performed. These results are shown in Table 3.
[0031]
The tensile test was a JIS Z 2201 No. 2 test piece for the wire, and a steel wire No. 9B test piece for JIS Z 2201. Further, the bending test was performed by the V block method of JIS Z 2248, the bending angle was 90 degrees, and the inner radius was a steel wire size.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
[Table 3]

[0035]
Furthermore, in order to confirm the strength of the welded portion, sample No. Steel wire (φ4.5 mm) was selected, spot welding was performed in a cross shape, and shear strength and peel strength were measured. The results are shown in Table 4. The welding pressure was 300 N, the welding secondary current was 2.0 KVA, and the energization time was 0.12 sec. The shear strength was measured using the jig shown in FIG. 3, and the peel strength was measured using the jig shown in FIG.
[0036]
[Table 4]

[0037]
From Table 2 and Table 3, the following became clear.
[0038]
Invention Example No. 1, 2, 4, 5, 7, 8, 10, 12, 13, 14, 16, and 17 show high strength and high toughness for both the wire and the steel wire, and have good bending workability.
[0039]
Although the chemical component is within the scope of the present invention, the comparative example No. 3, 6, 9, 11, and 15 are both low in strength and ductility and inferior in bending workability for both the wire and the steel wire as compared with the examples of the present invention.
[0040]
No. In the 18 comparative examples, both the wire and the steel wire had ductility similar to the level of the present invention example, and the bending workability was good, but the strength was lower than that of the present invention example, so it was suitable for the spring steel wire. Absent.
[0041]
No. In 19 comparative examples, the strength and ductility of both the wire and the steel wire are similar to those of the present invention and the bending workability is good, but the strength after welding is low as described later.
[0042]
No. In the comparative example of 20, the Ti content is large outside the range of the present invention, so both the wire and the steel wire have lower ductility than the present invention example and have poor bending workability.
[0043]
No. In Comparative Example 21, since Ti and B are not added, both the wire and the steel wire have lower strength and ductility than the examples of the present invention, and are inferior in bending workability.
[0044]
No. In Comparative Example 22, since Nb is not added, both the wire and the steel wire have lower ductility and inferior bending workability than the inventive example.
[0045]
From Table 4, the following became clear.
[0046]
Invention Example No. 1, 4, 7, 10, 13, 14, 16, and 17 all show higher values of shear strength and peel strength than the comparative example.
[0047]
Comparative Example No. used conventionally as a steel wire for springs No. 19 shows martensite in the welded portion, so that both the shear strength and the peel strength are low, indicating that it is not suitable for a method using welding.
[0048]
【The invention's effect】
As described above, according to the present invention, the basic components of C, Si, and Mn contain Cr, Nb, Al, B, Ti, and N, respectively, within a predetermined range. The composition further contains at least one of Ni, Mo, and V, and after the hot rolling of the steel is completed, the controlled cooling of 5 to 50 ° C./sec is performed to make the entire structure bainite. Although the C content is lower than that of spring steel, it is possible to obtain a spring wire and a steel wire having high strength, excellent workability, and excellent weldability.
[0049]
Therefore, according to the present invention, wire drawing can be performed as it is rolled, no special heat treatment is required for imparting strength during the processing of the steel wire, and the weldability is excellent. Because it is possible to change the construction method from low, conventional caulking etc. to welding, it is possible to answer the recent social trends that are strongly advocated for productivity, yield improvement, resource saving and energy saving, A useful effect is brought about in that it can be effectively used as a material for a cushion structure material such as a frame line of an automobile seat or an insert wire.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the B content in steel and the tensile strength and drawing of a wire.
FIG. 2 is a photomicrograph showing the structure of a wire.
3A and 3B are diagrams showing a jig for measuring shear strength, where FIG. 3A is a front view, FIG. 3B is a cross-sectional view, and FIG. 3C is a plan view.
FIG. 4 is a schematic perspective view showing a jig for measuring peel strength.

Claims (3)

C: 0.05-0.20,
Si: 0.35 to 1.50,
Mn: 1.00 to 3.00,
Cr: 0.10 to 1.50,
Nb: 0.01-0.10,
Al: 0.005 · 0.080,
B: 0.0005 to 0.0050,
Ti: 0.02-0.06,
N: 0.003 to 0.015 (more than mass%),
The remainder: a spring excellent in weldability and workability, characterized in that the steel comprising Fe and inevitable impurities is hot-rolled and controlled to 5 to 50 ° C./sec after completion of rolling to form a bainite structure. Wire rod. Furthermore, as a steel component,
Ni: 1.0 or less (excluding 0),
Mo: 1.0 or less (excluding 0),
V: 0.05-0.30 (above, mass%)
The spring wire according to claim 1, comprising at least one selected from the group consisting of: 3. A spring steel wire, wherein the spring wire according to claim 1 is drawn.

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