HIGH-STRENGTH AND HIGH-FATIGUE-LIFE STEEL FOR CABLE, AND WIRE ROD AND PREPARATION METHOD THEREFOR

Abstract

A high-strength and high-fatigue-life steel for a cable, which comprises, in addition to Fe, the following chemical elements in percentages by mass: 0.90-1.00% of C; 0.90-1.50% of Si; 0.25-0.58% of Mn; 0.20-1.00% of Cr; 0.03-0.12% of V; and 0.0008-0.0025% of Ca. In addition, further provided are a wire rod made of the high-strength and high-fatigue-life steel for a cable and a preparation method for the wire rod.

Claims

1. A high-strength and high-fatigue-life cable steel, comprising the following chemical elements in mass percentages besides Fe: C: 0.90-1.00%; Si: 0.90-1.50%; Mn: 0.25-0.58%; Cr: 0.20-1.00%; V: 0.03-0.12%; Ca: 0.0008-0.0025%.

2. The high-strength and high-fatigue-life cable steel according to claim 1, wherein the chemical elements have the following mass percentages: C: 0.90-1.00%; Si: 0.90-1.50%; Mn: 0.25-0.58%; Cr: 0.20-1.00%; V: 0.03-0.12%; Ca: 0.0008-0.0025%; a balance of Fe and other unavoidable impurities.

3. The high-strength and high-fatigue-life cable steel according to claim 1, wherein the mass percentages of the chemical elements satisfy at least one of the following: Si: 1.0-1.4%; Cr: 0.2-0.7%.

4. The high-strength and high-fatigue-life cable steel according to claim 2, wherein a total content of the other unavoidable impurities is ≤0.10%, wherein contents of the impurities satisfy at least one of the following: Cu≤0.05%; Al≤0.004%; Ti≤0.003%; P≤0.015%; S≤0.010%; O≤0.0025%; N≤0.0045%.

5. The high-strength and high-fatigue-life cable steel according to claim 1, further comprising at least one of the following chemical elements: Mo: 0.10-0.80%; B: 0.0008-0.0012%; Re: 0.0005-0.008%.

6. The high-strength and high-fatigue-life cable steel according to claim 1, wherein its microstructure is dominated by refined sorbite structure, wherein a phase proportion of sorbite is ≥95%, and a phase proportion of reticular cementite at grains boundaries and martensite structure is ≤0.5%; and/or the microstructure further comprises precipitate of carbonitride(s) of V having a size of 5-50 nm; and/or inclusions in the microstructure have a size of <35 um and an aspect ratio of >2.

7. The high-strength and high-fatigue-life cable steel according to claim 6, wherein a carbon segregation index in its core is lower than 1.08.

8. The high-strength and high-fatigue-life cable steel according to claim 1, wherein the high-strength and high-fatigue-life cable steel has a tensile strength of ≥1430 MPa.

9. A wire rod made of the high-strength and high-fatigue-life cable steel according to claim 1.

10. A steel wire made by drawing, galvanizing and stabilizing the wire rod according to claim 9.

11. A manufacturing method for the wire rod according to claim 9, comprising the following steps: (1) Smelting and casting; (2) Rough rolling; (3) High-speed wire rolling; (4) Stelmor controlled cooling; (5) Isothermal treatment: austenite heating temperature: 890-1050° C.; holding time: 6-20 min; isothermal treatment temperature: 530-600° C.

12. The manufacturing method according to claim 11, wherein in step (1), a vacuum degassing time is controlled to be >20 min during the smelting; and a carbon segregation index in a billet core is controlled to be less than 1.08 during the casting.

13. The manufacturing method according to claim 11, wherein in step (2), a twice-heating rolling process is used to cog down a continuously cast bloom at a temperature of 1100-1250° C. into a 150-250 mm square billet, and then the square billet is heated in a heating furnace, wherein a heating temperature is controlled at 960-1150° C., and a hold time is controlled at 1.5-2.5 h.

14. The manufacturing method according to claim 11, wherein in step (3), a rolling speed is controlled at 20-60 m/s; preferably in step (3), an inlet temperature of a finishing rolling unit is controlled at 920-990° C., an inlet temperature of a reducing and sizing unit is 920-990 ° C., and a spinning temperature is 880-950° C.

15. The manufacturing method according to claim 11, wherein in step (4), air volumes of 14 fans on a Stelmor line are adjusted in the following ranges: fans Fl -F8 have an air volume of 80-100%, fans F9-F12 have an air volume of 75-100%, and fans F13-F14 have an air volume of 0-45%.

16. The high-strength and high-fatigue-life cable steel according to claim 6, wherein an average interlamellar spacing of the sorbite structure is 40-260 nm.

17. The high-strength and high-fatigue-life cable steel according to claim 2, further comprising at least one of the following chemical elements: Mo: 0.10-0.80%; B: 0.0008-0.0012%; Re: 0.0005-0.008%.

18. The wire rod made of the high-strength and high-fatigue-life cable steel according to claim 9, wherein performances of the wire rod satisfy at least one of the following: tensile strength: ≥1430 MPa; area reduction rate: >30%; tensile strength of a steel wire made of the wire rod by drawing and galvanization: ≥2000 MPa; torsion value of the steel wire: >8 cycles; fatigue life of the steel wire: >2.4 million cycles.

19. The steel wire made by drawing, galvanizing and stabilizing the wire rod according to claim 10, wherein the steel wire has a tensile strength of ≥2000 MPa; a torsion value of >8 cycles as measured on a 100D gauge sample, and a fatigue life of >2.4 million cycles under a maximum stress of 0.45 σ.sub.b.

20. The steel wire made by drawing, galvanizing and stabilizing the wire rod according to claim 10, wherein the steel wire has a tensile strength of 2020-2100 MPa; a torsion value of 12-24 cycles as measured on a 100 D gauge sample, and a fatigue life of 2.49-4.20 million cycles under a maximum stress of 0.45 σ.sub.b.

Description

DETAILED DESCRIPTION

[0078] The high-strength and high-fatigue-life cable steel, the wire rod and the preparation method therefor will be further explained and illustrated with reference to the specific examples. Nonetheless, the explanation and illustration are not intended to unduly limit the technical solution of the disclosure.

Examples 1-11 and Comparative Examples 1-3

[0079] The wire rods of Examples 1-11 were all made using the following steps:

[0080] (1) Smelting and casting were performed with the use of the chemical compositions shown in Table 1: after smelting in an electric furnace or a converter, refining was performed outside the furnace. An LF furnace plus a VD or RH degassing treatment process was used for the refining outside the furnace. The composition and amount of synthetic slag added during the smelting process were adjusted. The vacuum degassing time was controlled to be >20 min during the smelting process. A bloom continuous casting machine was used to cast a bloom. During the casting, the drawing speed, cooling and terminal soft reduction parameters were adjusted in the continuous casting to control the carbon segregation index in the core of the bloom to be lower than 1.08.

[0081] (2) Rough rolling: a twice-heating rolling process was used to cog down the continuously cast bloom at a temperature of 1100-1250° C. into a 150-250 mm square billet. After ultrasonic flaw detection, magnetic powder flaw detection, grinding wheel polishing, supplemental magnetic particle flaw detection and polishing, the square billet was heated in a heating furnace. The heating temperature was controlled at 960-1150° C., and the hold time was controlled at 1.5-2.5 h.

[0082] (3) High-speed wire rolling: the rolling speed was controlled at 20-60 m/s; the inlet temperature of the finishing rolling unit was controlled at 920-990° C.; the inlet temperature of the reducing and sizing mill was controlled at 920-990° C.; and the spinning temperature was controlled at 880-950° C.

[0083] (4) Stelmor controlled cooling: the size of the rolled wire rod was Φ10-15 mm After the wire rod was rolled, the structure transformation of the wire rod was controlled by adjusting the air volumes of fan components of the Stelmor line to optimize the structure of the wire rod. The air volumes of 14 fans on the Stelmor line were adjusted in the following ranges: fans F1-F8 had an air volume of 80-100%, fans F9-F12 had an air volume of 75-100%, and fans F13-F14 had an air volume of 0-45%.

[0084] (5) Isothermal treatment: isothermal treatment was performed on the wire rod in a lead bath or a salt bath, wherein the austenite heating temperature was 890-1050° C.; the hold time was 6-20 min; and the isothermal treatment temperature was 530-600° C.

[0085] It should be noted that the wire rods of Examples 1-11 according to the present disclosure were prepared using the above steps. The chemical compositions and related process parameters in these Examples all met the control requirements of the design specification according to the present disclosure. The comparative wire rods of Comparative Examples 1-3 were also made using the process including smelting and casting, rough rolling, high-speed wire rolling, Stelmor controlled cooling and isothermal treatment, but their chemical compositions and related process parameters did not all meet the design requirements according to the present disclosure.

[0086] In addition, it should be noted that the wire rods of Examples 1-11 were all made of the high-strength and high-fatigue-life cable steel according to the present disclosure.

[0087] Correspondingly, the wire rods of Comparative Examples 1-3 were made of the corresponding comparative steel. Table 1 lists the mass percentages of the chemical elements in the high-strength and high-fatigue-life cable steel in each of Examples 1-11 and in the comparative steel in each of Comparative Examples 1-3.

TABLE-US-00001 TABLE 1 (wt %, the balance is Fe and other unavoidable impurities except for Cu, Al, Ti, P, S, O and N) Chemical elements No. C Si Mn Cr Cu Al Ca Ti P V S O N Mo B Re Ex. 1 0.95 0.92 0.58 0.4  0.03  0.004  0.0008 0.001  0.007 0.03 0.005  0.0017 0.0041 — — — Ex. 2 0.90 1.1  0.43 0.35 0.01  0.001  0.0019 0.002  0.015 0.05 0.002  0.002  0.0045 — — — Ex. 3 0.96 1.45 0.25 0.7  0.005 0.0005 0.0021 0.0025 0.006 0.12 0.009  0.0019 0.0032 — — — Ex. 4 0.98 1.00 0.37 0.9  0.04  0.001  0.0025 0.003  0.006 0.03 0.010  0.0025 0.0035 — — — Ex. 5 0.95 1.05 0.44 1.0  0.01  0.0002 0.0008 0.0005 0.014 0.07 0.008  0.0002 0.0005 — — — Ex. 6 1.00 0.90 0.25 0.9  0.03  0.003  0.0009 0.003  0.011 0.09 0.0009 0.0008 0.0015 — — — Ex. 7 0.96 0.96 0.39 0.65 0.05  0.001  0.0010 0.0015 0.012 0.10 0.0005 0.0021 0.0045 — — 0.0005 Ex. 8 0.90 0.94 0.45 0.74 0.04  0.0017 0.0009 0.0025 0.002 0.05 0.002  0.0009 0.0023 — 0.0008 — Ex. 9 0.93 1.50 0.58 0.89 0.015 0.0001 0.001  0.002  0.001 0.06 0.009  0.0017 0.0015 0.10 — 0.0080 Ex. 10 0.92 1.02 0.50 0.20 0.025 0.0009 0.0008 0.001  0.009 0.03 0.010  0.0019 0.0030 0.80 — 0.0015 Ex. 11 0.96 0.91 0.39 0.38 0.035 0.003  0.0015 0.001  0.013 0.06 0.005  0.0024 0.0041 — 0.0012 — Comp. 0.95 0.9  0.001  0.0010 0.003  0.010 0.009  0.0023 — — — Ex. 1 Comp. 0.96 0.45 0.8 0.10 0.010 0.0015 0.0045 — — — Ex. 2 Comp. 0.4 0.04 0.06 0.007 0.0040 — — — Ex. 3

[0088] Table 2 lists the specific process parameters in the above steps for the wire rods of Examples 1-11 and the comparative wire rods of Comparative Examples 1-3.

TABLE-US-00002 TABLE 2 Step (1) Step (3) Vacuum Carbon Inlet Inlet degassing time precipitation temperature temperature Austenite controlled index at of of heating Isothermal during bloom core Rolling finishing reducing Spinning temper- Hold treatment smelting during speed rolling and sizing temperature ature time temperature No. (min) casting (m/s) unit (° C.) mill (° C.) (° C.) (° C.) (min) (° C.) Ex. 1 25 1.05 20 920 920 880  890  6 540 Ex. 2 22 1.01 25 950 940 890  900 10 530 Ex. 3 30 1.05 35 990 990 950 1000 12 550 Ex. 4 26 1.06 60 930 920 880  890 18 560 Ex. 5 25 1.06 49 920 920 890 1050 16 570 Ex. 6 25 1.06 20 950 940 890 1000 20 550 Ex. 7 21 1.07 30 970 950 900  900  8 540 Ex. 8 27 1.02 24 970 960 920  910  6 550 Ex. 9 30 1.04 55 950 950 920  915  9 588 Ex. 10 22 1.04 35 980 980 950  920 15 600 Ex. 11 25 1.05 30 920 920 950  950 16 560 Comp. Ex. 40 990 980  900 10 550 1 Comp. Ex. 30 950 880   15 580 2 Comp. Ex. 1.05 25 950 900 560 3

[0089] The wire rods of Examples 1-11 and the comparative wire rods of Comparative Example 1-3 obtained were sampled, observed, analyzed and subjected to relevant performance tests. The observation results and performance test results obtained are listed in Table 3 and Table 4 respectively.

[0090] Table 3 lists the observation results of the wire rods of Examples 1-11 and the comparative wire rods of Comparative Examples 1-3.

TABLE-US-00003 TABLE 3 Interlamellar Wire rod Sorbitizing spacing of sorbite Inclusion dimension rate structure size No. (mm) (%) (nm) (um) Ex. 1 11 95 50 30 Ex. 2 13 97 90 34 Ex. 3 15 95 260 34 Ex. 4 10 97 40 28 Ex. 5 13 99 210 19 Ex. 6 13.5 98 95 34 Ex. 7 14 97 220 15 Ex. 8 15 99 130 33 Ex. 9 11.5 95 50 14 Ex. 10 14 98 109 16 Ex. 11 13 99 203 20 Comp. Ex. 1 12 95 45 34 Comp. Ex. 2 13 92 150 50 Comp. Ex. 3 15 97 200 45

[0091] As shown by Table 3, it should be noted that the wire rods according to the present disclosure were all made of the high-strength and high-fatigue-life cable steel described in the present disclosure. Accordingly, in Examples 1-11, the microstructure of the high-strength and high-fatigue-life cable steel from which the wire rods of Examples 1-11 were made is dominated by the refined sorbite structure, and the phase proportion of sorbite is ≥95%. There is no obvious reticular cementite at grain boundaries or martensite structure in the microstructure. In addition, in Examples 1-11 according to the present disclosure, the lamellar spacing of the sorbite structure is 40-260 nm, and the carbon segregation index in the core is lower than 1.08.

[0092] In addition, it should be noted that in the high-strength and high-fatigue-life cable steel of each of Examples 1-11 according to the present disclosure, the microstructure further comprises precipitate of carbonitride(s) of V having a size of 5-50 nm.

[0093] Further, in the high-strength and high-fatigue-life cable steel of each of Examples 1-11 according to the present disclosure, the inclusions in the steel have a size of <35 um, and the inclusions have an aspect ratio of >2.

[0094] Table 4 lists the performance test results of the wire rods of Examples 1-11 and the comparative wire rods of Comparative Example 1-3, wherein the test method for tensile strength and area reduction rate is: GB/T 228.1-2010 Metallic Materials Tensile Testing Method of Test at Room Temperature.

TABLE-US-00004 TABLE 4 Tensile strength Area reduction rate No. (MPa) (%) Ex. 1 1520 37 Ex. 2 1450 32 Ex. 3 1490 36 Ex. 4 1500 36 Ex. 5 1480 33 Ex. 6 1570 33 Ex. 7 1536 32 Ex. 8 1445 33 Ex. 9 1526 35 Ex. 10 1519 40 Ex. 11 1560 34 Comp. Ex. 1 1370 35 Comp. Ex. 2 1382 33 Comp. Ex. 3 1510 29

[0095] It should be noted that the wire rods of Examples 1-11 and the comparative wire rods of Comparative Examples 1-3 that were sampled above can be subjected to 6-9 passes of drawing, steel wire galvanization and stabilization, and steel wires having better performances and quality can be obtained. The steel wires obtained from Examples 1-11 and the comparative steel wires obtained from Comparative Examples 1-3 were tested for various performances. The performance test results obtained are listed in Table 5.

[0096] Table 5 lists the performance test results of the steel wires obtained from Examples 1-11 and the comparative steel wires obtained from Comparative Examples 1-3, wherein the test method for tensile strength is: GB/T 228.1-2010 Metallic Materials Tensile Testing Method of Test At Room Temperature; the test method for torsion value is: GB/T239.1-2012 Metallic Materials Wire Part 1: Simple Torsion Test; the method for fatigue test is: GB/T 3075-200 Metallic Materials Fatigue Testing Axial-Force-Controlled Method.

TABLE-US-00005 TABLE 5 Tensile strength Torsion value Steel wire fatigue life No. (MPa) (cycles) (10.sup.4 cycles) Ex. 1 2098 12 249 Ex. 2 2020 24 305 Ex. 3 2056 20 298 Ex. 4 2078 19 277 Ex. 5 2051 18 314 Ex. 6 2065 18 255 Ex. 7 2030 19 419 Ex. 8 2076 22 290 Ex. 9 2034 18 287 Ex. 10 2055 24 266 Ex. 11 2100 17 381 Comp. Ex. 1 1860 20 270 Comp. Ex. 2 2010 10 233 Comp. Ex. 3 2050 3 157

[0097] As it can be seen from Table 4 and Table 5, the performances of the comparative wire rods of Comparative Examples 1-3 and the steel wires made therefrom are obviously inferior in comparison with Examples 1-11. In the present disclosure, the wire rods of Examples 1-11 all have good performances. The tensile strength is ≥1430 MPa, and the area reduction rate is >30% for all of the wire rods.

[0098] The steel wires obtained by drawing and galvanizing the above wire rods have a tensile strength of ≥2000 MPa, a torsion value of >8 cycles as measured on a 100 D gauge sample, and a fatigue life of >2.4 million cycles under a maximum stress of 0.45 σ.sub.b.They can effectively meet the production requirements of long-span and long-life bridge cables.

[0099] As it can be seen, the wire rods according to the present disclosure can be used to produce bridge cable steel wires having a strength of 2000 MPa or higher after drawing and galvanization. At present, the span of cable-stayed bridges has exceeded 1000 meters, and the span of suspension bridges is close to 2000 meters. As the bridge span increases, in order to reduce construction costs and save materials, it is necessary to use high-strength galvanized steel wire cables to increase the service life of bridges. The market prospect of the wire rod according to the present disclosure is very broad. It has good popularization and application value, and can bring huge economic benefits.

[0100] In addition, the ways in which the various technical features of the present disclosure are combined are not limited to the ways recited in the claims of the present disclosure or the ways described in the specific examples. All the technical features recited in the present disclosure may be combined or integrated freely in any manner, unless contradictions are resulted.

[0101] It should also be noted that the Examples set forth above are only specific examples according to the present disclosure. Obviously, the present disclosure is not limited to the above Examples. Similar variations or modifications made thereto can be directly derived or easily contemplated from the present disclosure by those skilled in the art. They all fall in the protection scope of the present disclosure.