JP4146271B2 - High strength PC steel wire with excellent delayed fracture resistance and method for producing the same - Google Patents

Description

【００３８】
【表２】

【００３９】
【発明の効果】
本発明は伸線パーライト鋼よりなるＰＣ鋼線において、板状セメンタイトのアスペクト比を制御することによって、引張強さが１６５０ＭＰａ以上の高強度ＰＣ鋼線の遅れ破壊特性を大幅に向上させることを可能にするとともに、鋼の化学成分、伸線減面率、ブルーイング条件を最適に選択することによって、その製造方法を確立したものであり、産業上の効果は極めて顕著なものがある。
【図面の簡単な説明】
【図１】ブルーイング温度がＦＩＰ試験破断時間に及ぼす影響を示す図である。
【図２】ブルーイング温度・時間がＦＩＰ結果に及ぼす影響を示す図である。
【図３】（ａ）は３５０℃ブルーイング材、（ｂ）は５００℃ブルーイング材のセメンタイト形状を示す図である。
【図４】セメンタイトのアスペクト比がＦＩＰ破断時間に及ぼす影響を示す図である。
【図５】ブルーイング温度がセメンタイトのアスペクト比に及ぼす影響を示す図である。
【図６】ブルーイング温度が昇温水素分析における水素放出曲線に及ぼす影響を示す図。
【図７】ブルーイング温度が昇温分析の２５０〜５００℃の温度で放出される水素量に及ぼす影響を示す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a PC steel wire widely used as a reinforcing material for prestressed concrete structures such as poles, piles, buildings, bridges, and the like. The present invention relates to a PC steel wire and a manufacturing method thereof.
[0002]
[Prior art]
PC steel materials widely used as reinforcing materials for prestressed concrete structures such as poles, piles, buildings, bridges, etc. PC steel bars are used. The material used for the PC steel wire is a piano wire material conforming to JIS G 3502, and is manufactured by performing a drawing process after a patenting treatment.
[0003]
On the other hand, PC steel bars are manufactured by quenching and tempering using medium carbon steel having a C content of 0.25 to 0.35%, as described in Patent Document 1, for example. As described in Non-Patent Document 1 as a characteristic of PC steel rods, high strength PC steel rods with strength exceeding 1275 MPa (130 kgf / mm ² ) have inferior fracture fracture characteristics compared to PC steel wires. Yes. Therefore, many proposals have been made in the past to improve the delayed fracture characteristics of PC steel bars. For example, Patent Document 2 proposes that reducing the P and S contents is effective. Patent Document 1 proposes that the Si and Mn contents are regulated and that bending or drawing is performed in the tempering process after quenching. On the other hand, regarding the PC steel wire, since the delayed fracture resistance was originally superior to that of the PC steel rod, there has been almost no invention in terms of improving the delayed fracture resistance. However, in recent years, PC steel wires are also required to have high strength or external cables, and at the present time, those having high strength of 1650 MPa class are required. As is well known (for example, “Delayed Fracture” by Keisaku Matsuyama / Nikkan Kogyo Shimbun) Steel materials become more resistant to hydrogen embrittlement as the strength increases or the usage environment becomes severe. There is a need for high strength PC steel wires with improved delayed fracture properties. For example, Patent Document 3 proposes to improve delayed fracture characteristics by maintaining a predetermined temperature and a predetermined time after wire drawing. However, this is intended to remove hydrogen in the steel simply by heating without changing the steel structure and mechanical properties, and it cannot suppress the destruction caused by hydrogen that has entered during use. This is not a fundamental measure to improve the characteristics. The same applies to Patent Document 4 and Patent Document 5.
[0004]
[Patent Document 1]
Japanese Patent Publication No. 5-41684 [Patent Document 2]
Japanese Patent Publication No. 5-59967 [Patent Document 3]
Japanese Patent Laid-Open No. 10-259425 [Patent Document 4]
JP-A-8-337844 [Patent Document 5]
JP-A-8-337845 [Non-Patent Document 1]
“Prestressed concrete design and construction standards / comments” (edited by Architectural Institute of Japan, pages 43-45 of Maruzen)
[0005]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object of the present invention is to realize a high strength PC steel wire having a good strength of delayed fracture characteristics of 1650 MPa or more and to provide a manufacturing method thereof. is there.
[0006]
[Means for Solving the Problems]
The present inventors first analyzed delayed fracture behavior in detail using PC steel wires of various strength levels manufactured by patenting, wire drawing, and brewing. The delayed fracture characteristics of PC steel wires were evaluated by a widely used FIP test. This is a method of measuring the breaking time by applying a load of 70% of the breaking load in the atmosphere to a PC steel wire in a solution obtained by heating a 20 mass% ammonium thiocyanate aqueous solution to 50 ° C. At this time, the amount of the test solution per 1 cm ² of the surface area in contact with the test solution of the PC steel wire (hereinafter referred to as the specific liquid amount) was 55 cc / cm ² . Moreover, the hydrogen storage behavior of the PC steel wire in the FIP test was measured with a temperature rising gas chromatograph.
[0007]
By conducting the above tests, in order to increase the FIP fracture time of high-strength PC steel wires, that is, to increase delayed fracture characteristics, the effects of steel materials, austenite heating temperature, wire drawing conditions, bluing heat treatment conditions, etc. are examined. Piled up. As a result, blueing was performed at a high temperature of 700-100 × log (t) ≧ T ≧ 450 ° C. in the range of 300 ≧ t ≧ 1 (s), and the lamellar cementite in pearlite was If a structure having an average aspect ratio of 30 or less, which is the ratio of length to width, is formed, the f ₅₀ value of the FIP test break time (break time when the cumulative breakage rate is 50%) even in a high strength region of 1650 MPa or more. Was found to be over 30 hours. In the following the specific liquid volume is 55 cc / cm ^2, if the rupture time over 30 hours, is very small possibility of delayed fracture in actual use. In order to achieve 1650 MPa or higher at a bluing temperature of 500 ° C. or higher, it is necessary to appropriately select the steel material component and the wire drawing area reduction rate.
[0008]
Based on the above examination results, it was concluded that the steel material component, the wire drawing condition, and the bluing condition were optimally selected to achieve a high-strength PC steel bar with excellent delayed fracture characteristics. is there.
[0009]
The present invention has been made on the basis of the above findings, and the gist thereof is as follows.
(1) By mass%, C: 0.6-1.1%, Si: 0.12-2.0%, Mn: 0.3-1.0%, P: 0.025% or less, S: 0.025% or less, consisting of the remainder Fe and inevitable impurities, mainly composed of pearlite structure (which is a layered structure of ferrite and cementite), and the average aspect ratio of plate-like cementite in pearlite is 30 or less A high-strength PC steel wire excellent in delayed fracture resistance, characterized by having a tensile strength of 1650 MPa or more.
(2) Furthermore, by mass%, Al: 0.005-0.1%, Cr: 0.05-2.0%, Mo: 0.05-1.0%, Ni: 0.05-3. 0%, Cu: 0.05 to 1.0%, V: 0.05 to 0.3%, Nb: 0.005 to 0.1%, W: 0.05 to 0.5%, Ti: 0 .High strength PC steel wire with excellent delayed fracture resistance as described in (1) above, comprising 0.005% to 0.05% and B: 0.0003% to 0.005% .
(3) By mass%, C: 0.6-1.1%, Si: 0.12-2.0%, Mn: 0.3-1.0%, P: 0.025% or less, S: 10% or more in an ammonium thiocyanate solution at 50 ° C. and 20% by weight, containing 0.025% or less, consisting of the remainder Fe and inevitable impurities, mainly composed of a pearlite structure (which is a layered structure of ferrite and cementite) When immersed and heated at a rate of 100 ° C./h, the total amount of hydrogen released in the temperature range of 250 ° C. to 500 ° C. is 0.2 mass ppm or less and the tensile strength is 1650 MPa or more. High strength PC steel wire with excellent delayed fracture resistance.
(4) Furthermore, in mass%, Al: 0.005-0.1%, Cr: 0.05-2.0%, Mo: 0.05-1.0%, Ni: 0.05-3. 0%, Cu: 0.05 to 1.0%, V: 0.05 to 0.3%, Nb: 0.005 to 0.1%, W: 0.05 to 0.5%, Ti: 0 A high strength PC steel wire having excellent delayed fracture resistance according to the above (3), characterized in that it contains one or more of 0.005 to 0.05% and B: 0.0003 to 0.005% .
(5) By mass%, C: 0.6-1.1%, Si: 0.12-2.0%, Mn: 0.3-1.0%, P: 0.025% or less, S: After performing patenting on steel composed of the balance Fe and unavoidable impurities, including 0.025% or less, after cold drawing, to obtain a layered structure of ferrite and cementite, in the final step, The tensile strength is set to 1650 MPa or more by performing blueing at a high temperature of 700-100 × log (t) ≧ T ≧ 450 ° C. in a time range of 300 ≧ t ≧ 20 (s). A method for manufacturing high-strength PC steel wires with excellent delayed fracture resistance.
(6) Furthermore, by mass%, Al: 0.005-0.1%, Cr: 0.05-2.0%, Mo: 0.05-1.0%, Ni: 0.05-3. 0%, Cu: 0.05 to 1.0%, V: 0.05 to 0.3%, Nb: 0.005 to 0.1%, W: 0.05 to 0.5%, Ti: 0 .High strength PC steel wire having excellent delayed fracture resistance according to (5) above, characterized in that it contains one or more of 0.005 to 0.05% and B: 0.0003 to 0.005% Manufacturing method.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
First, the reasons for limiting the components of steel to be the subject of the present invention will be described. Hereinafter, the unit is mass%.
[0011]
C: C is an essential element for securing the strength of the PC steel wire. However, if it is less than 0.6%, the amount of pro-eutectoid ferrite increases during patenting, and the required strength cannot be obtained. If it exceeds 1%, the amount of pro-eutectoid cementite increases and the wire drawing characteristics are remarkably deteriorated. Therefore, the content is limited to the range of 0.6 to 1.1%.
[0012]
Si: Si has the effect of improving relaxation properties and increasing strength by solid solution hardening. If the content is less than 0.12%, the above-mentioned action cannot be exhibited. On the other hand, if the content exceeds 2%, the effect is saturated, so the content is limited to the range of 0.12 to 2.0%.
[0013]
Mn: Mn is not only necessary for deoxidation and desulfurization, but also has the effect of increasing the strength of the patenting material. However, if the content is less than 0.3%, the above effect cannot be obtained. Segregation at the time became prominent, and micromartensite that deteriorates the wire drawing characteristics at the time of patenting was generated, so the content was limited to a range of 0.3 to 1.0%.
[0014]
P: P co-segregates with Mn, and remarkably enhances the hardenability. Therefore, in order to promote the formation of micromartensite at the time of patenting, the content was made 0.025% or less.
[0015]
S: S is precipitated as MnS and deteriorates the wire drawing characteristics, so the content was made 0.025% or less.
[0016]
The above are the basic components of the steel that is the subject of the present invention. In the present invention, the steel further has a weight percentage of Al: 0.005-0.1%, Cr: 0.05-2.0%. , Mo: 0.05-1.0%, Ni: 0.05-3.0%, Cu: 0.05-1.0%, V: 0.05-0.3%, Nb: 0.005 ~ 0.1%, W: 0.05-0.5%, Ti: 0.005-0.05%, B: 0.0003-0.0050% may be included alone or in combination it can.
[0017]
Al: Al has the effect of preventing the coarsening of austenite grains and suppressing the deterioration of toughness by forming AlN during deoxidation and heat treatment, and securing solid solution B effective for fixing delayed N and improving delayed fracture characteristics However, if less than 0.005%, these effects are not exhibited, and even if it exceeds 0.1%, the effect is saturated, so the content is limited to a range of 0.005 to 0.1%.
[0018]
Cr: Cr is an effective element for reducing the spacing of the pearlite lamella and increasing the strength of the patenting material. However, if it is less than 0.05%, the effect cannot be fully exerted, whereas it exceeds 2.0%. In order to saturate the effect, it was limited to 0.05 to 2.0%.
[0019]
Mo: Mo is an effective element for increasing the strength of the patenting material in order to make the pearlite lamella spacing as fine as Cr. However, if it is less than 0.05%, the effect cannot be fully exerted. If it exceeds 0.0%, the progress of pearlite transformation is delayed, so the content was limited to 0.05 to 1.0%.
[0020]
Ni: Ni has an effect of suppressing the intrusion of hydrogen. However, if it is less than 0.05%, the effect cannot be exhibited. On the other hand, if it exceeds 3.0%, the effect corresponding to the added amount cannot be exhibited. Limited to -3.0% range.
[0021]
Cu: Cu also has an effect of suppressing the penetration of hydrogen, but if it is less than 0.05%, the effect cannot be exhibited, and if it exceeds 1.0%, the hot workability deteriorates, so 0.05 to 1.0 %.
[0022]
V: V is an effective element for refining austenite grains by producing carbonitride. Further, it precipitates as carbides during patenting and functions as a hydrogen trap site, so that it has an effect of improving delayed fracture resistance. However, if it is less than 0.05%, the above effect cannot be obtained. Even if it exceeds%, the effect is saturated, so it was limited to 0.05 to 1.0%.
[0023]
Nb: Nb is also an element effective for reducing the austenite grains and improving ductility and toughness by producing carbonitrides in the same manner as V. If it is less than 0.005%, the above effect is insufficient. On the other hand, if it exceeds 0.1%, this effect is saturated, so the content is limited to 0.005 to 0.1%.
[0024]
W: W, like V, is an element effective for improving the delayed fracture characteristics of a high-strength PC steel wire. However, if it is less than 0.05%, the above effect cannot be exhibited, while 0.5% Even if it is added over the range, the effect is saturated, so the content is limited to 0.05 to 0.5%.
[0025]
Ti: Ti has the effect of preventing the coarsening of austenite grains by forming deoxidation and TiN, and has the effect of fixing N and ensuring effective solute B for improving delayed fracture characteristics. If it is less than 0.005%, these effects are not exhibited, and even if it exceeds 0.05%, the effect is saturated, so the content is limited to a range of 0.005 to 0.05%.
[0026]
B: B has an effect of improving delayed fracture characteristics. However, if B is less than 0.0003%, the above effect is not exhibited, and even if it exceeds 0.0050%, the effect is saturated. Limited to 0050%.
[0027]
N: N has an effect of refining austenite grains by forming nitrides of Al, V, Nb, and Ti, and can contribute to improvement of ductility and toughness, so 0.003 to 0.015% is preferable range It is.
[0028]
Next, the reasons for limiting the microstructure of the PC steel wire and the bluing temperature, which are the most important points for improving the delayed fracture characteristics of the high strength PC steel wire intended in the present invention, will be described.
[0029]
FIG. 1 shows an example in which the influence of the bluing temperature on the average rupture time by the FIP test is analyzed. The FIP test is a result of a specific liquid amount of 55 cc / cm ² , a load load of 1200 MPa, and 12 steels for each steel type. As is apparent from the figure, the f ₅₀ fracture time in the FIP test is increased as the brewing temperature is increased, indicating that the delayed fracture resistance is improved. A preferable bluing temperature is 500 ° C. or higher. The relationship between bluing temperature and bluing time is shown in FIG. In the figure, ● indicates that the FIP test f ₅₀ rupture time is 30 h or more, and x indicates that the time is less than 30 h, or less than 1650 MPa. The effect is recognized when the bluing time is in the range of 300 ≧ t ≧ 1 (s) and the bluing temperature is in the range of 700-100 × log (t) ≧ T ≧ 450 ° C.
[0030]
In the drawn pearlite structure, the cementite elongated in a plate shape is dissolved and divided by bluing at a high temperature as shown in FIG. FIG. 4 shows the result of analyzing the influence of the bluing temperature on the ratio of the length and thickness (aspect ratio) of plate-like cementite. Measurements were taken with a scanning electron microscope (SEM) after etching the specimen with a saturated picral solution, and three arbitrary locations where the cementite was linear were photographed at a magnification of 5000 times, and the visual field was measured to determine the average aspect ratio by image analysis. Asked. From the figure, it is shown that the cementite is divided and spheroidized as the bluing temperature increases.
[0031]
FIG. 5 shows the effect of cementite aspect ratio on FIP rupture time. As the aspect ratio of cementite decreases, the FIP fracture time increases. A remarkable effect is recognized when the aspect ratio is 30 or less, and more preferably 20 or less. This is presumably because when the aspect ratio of cementite is small, stress relaxation at the crack tip becomes easy, and the FIP fracture time becomes long.
[0032]
In addition, as a simple method for confirming such a tissue state, a method of specifying by measuring the amount of hydrogen released in a temperature range of 250 ° C. to 500 ° C. by hydrogen temperature rising analysis was devised. FIG. 6 shows a hydrogen release curve when the PC steel wire having the pearlite structure shown in FIG. 3 is taken out after carrying out the FIP test for 10 hours and subjected to hydrogen analysis at a heating rate of 100 ° C./h. The 350 ° C. blueing material has hydrogen release peaks at 100 ° C. and around 350 ° C. It is considered that the peak at 100 ° C. is the amount of diffusible hydrogen, and the peak at 350 ° C. is hydrogen trapped by the working dislocation piled up in the vicinity of the cementite / ferrite interface. Cementite is spheroidized by high temperature bluing, and interfacial dislocation is reduced, so that the amount of trapped hydrogen is also reduced. Therefore, in FIG. 6, the peak at 350 ° C. is not detected for the 500 ° C. bluing material. FIG. 7 shows the relationship between the bluing temperature and the amount of hydrogen at the 350 ° C. peak (the amount of released hydrogen from 250 ° C. to 500 ° C.). As shown in the figure, there is a close relationship between the blueing temperature and the 350 ° C peak hydrogen. If the blueing temperature is 450 ° C or higher, the amount of hydrogen released from 250 ° C to 500 ° C is 0.2 ppm by mass or lower. .
[0033]
【Example】
After rolling the test material having the chemical composition shown in Table 1 under normal hot rolling conditions, patenting and drawing are performed in various temperature ranges, and brewing is performed at different temperatures to produce PC steel wire did. The brewing time was 30 s. Table 2 shows the results of evaluating the mechanical properties, structure morphology, and delayed fracture characteristics using the above PC steel wires. Delayed fracture characteristics were carried out at a load stress of 1200 MPa in the FIP test. Evaluation was performed by taking the f ₅₀ of rupture time of 12 in FIP test.
[0034]
In Tables 1 and 2, A to T are examples of the present invention, and the others are comparative examples. As can be seen from the table, all of the examples of the present invention have a blueing temperature of 450 ° C. or higher and a tensile strength of 1650 MPa or higher. F ₅₀ rupture time in FIP test is 30 hours or more.
[0035]
U, which is a comparative example, is an example in which 1650 MPa could not be achieved by bluing at 450 ° C. or higher because the steel material component and the wire drawing area reduction ratio were not appropriate.
[0036]
V to Z which are comparative examples are all manufactured by a conventional manufacturing method. That is, an example in which blueing is performed at 400 ° C. or less and 1650 MPa or more is achieved, but the cementite aspect ratio is greater than 30, the FIP test has a fracture time of 30 hours or less, and delayed fracture characteristics are poor It is.
[0037]
[Table 1]

[0038]
[Table 2]

[0039]
【The invention's effect】
By controlling the aspect ratio of plate-like cementite in PC steel wire made of drawn pearlitic steel, the present invention can greatly improve delayed fracture characteristics of high-strength PC steel wire with a tensile strength of 1650 MPa or more. In addition, the manufacturing method has been established by optimally selecting the chemical composition, the drawing area reduction ratio, and the bluing condition of the steel, and the industrial effects are extremely remarkable.
[Brief description of the drawings]
FIG. 1 is a graph showing the effect of bluing temperature on FIP test break time.
FIG. 2 is a diagram showing the influence of bluing temperature and time on FIP results.
3A is a view showing a cementite shape of a 350 ° C. bluing material, and FIG. 3B is a view showing a cementite shape of a 500 ° C. bluing material.
FIG. 4 is a diagram showing the influence of the aspect ratio of cementite on FIP fracture time.
FIG. 5 is a diagram showing the influence of bluing temperature on the aspect ratio of cementite.
FIG. 6 is a graph showing the influence of bluing temperature on a hydrogen release curve in a temperature rising hydrogen analysis.
FIG. 7 is a diagram showing the influence of bluing temperature on the amount of hydrogen released at a temperature of 250 to 500 ° C. in temperature rising analysis.

Claims (6)

  In mass%, C: 0.6-1.1%, Si: 0.12-2.0%, Mn: 0.3-1.0%, P: 0.025% or less, S: 0.025 %, And the balance is composed of Fe and inevitable impurities, is mainly composed of a pearlite structure (which is a layered structure of ferrite and cementite), and the average aspect ratio of the plate-like cementite in the pearlite is 30 or less. A high-strength PC steel wire excellent in delayed fracture resistance, characterized by having a thickness of 1650 MPa or more.   Furthermore, in mass%, Al: 0.005-0.1%, Cr: 0.05-2.0%, Mo: 0.05-1.0%, Ni: 0.05-3.0%, Cu: 0.05-1.0%, V: 0.05-0.3%, Nb: 0.005-0.1%, W: 0.05-0.5%, Ti: 0.005- The high strength PC steel wire excellent in delayed fracture resistance according to claim 1, comprising 0.05%, B: 0.0003 to 0.005%, or one or more.   In mass%, C: 0.6-1.1%, Si: 0.12-2.0%, Mn: 0.3-1.0%, P: 0.025% or less, S: 0.025 %, And the balance is composed of Fe and inevitable impurities, mainly composed of a pearlite structure (which is a layered structure of ferrite and cementite), and immersed in a 20 wt% ammonium thiocyanate solution for 10 hours or more, When the temperature is raised at a rate of 100 ° C./h, the total amount of hydrogen released in a temperature range of 250 ° C. or more and 500 ° C. or less is 0.2 mass ppm or less, and the tensile strength is 1650 MPa or more. High strength PC steel wire with excellent delayed fracture resistance.   Furthermore, in mass%, Al: 0.005-0.1%, Cr: 0.05-2.0%, Mo: 0.05-1.0%, Ni: 0.05-3.0%, Cu: 0.05-1.0%, V: 0.05-0.3%, Nb: 0.005-0.1%, W: 0.05-0.5%, Ti: 0.005- The high-strength PC steel wire having excellent delayed fracture resistance according to claim 3, characterized by containing one or more of 0.05% and B: 0.0003 to 0.005%.   In mass%, C: 0.6-1.1%, Si: 0.12-2.0%, Mn: 0.3-1.0%, P: 0.025% or less, S: 0.025 %, And the steel composed of the remaining Fe and inevitable impurities is subjected to patenting, followed by cold drawing to obtain a layered structure of ferrite and cementite. Delayed fracture resistance characterized by a tensile strength of 1650 MPa or more by performing bluing at a high temperature of 700-100 × log (t) ≧ T ≧ 450 ° C. within a range of ≧ t ≧ 20 (s) Manufacturing method of high strength PC steel wire with excellent properties.   Further, by mass%, Al: 0.005-0.1%, Cr: 0.05-2.0%, Mo: 0.05-1.0%, Ni: 0.05-3.0%, Cu : 0.05-1.0%, V: 0.05-0.3%, Nb: 0.005-0.1%, W: 0.05-0.5%, Ti: 0.005-0 The method for producing a high-strength PC steel wire having excellent delayed fracture resistance according to claim 5, comprising 0.05%, B: 0.0003 to 0.005%.

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