500MPa-grade bridge steel and manufacturing method thereof

Abstract

The bridge steel comprises the following chemical components in percentage by weight: 0.07 to 0.11 percent of C, 0.10 to 0.40 percent of Si, 1.55 to 1.70 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.0005 percent of B, less than or equal to 0.008 percent of N, 0.10 to 0.20 percent of Mo, 0.035 to 0.045 percent of Nb, 0.040 to 0.050 percent of V, 0.01 to 0.02 percent of Ti, 0.015 to 0.060 percent of Als and the balance of Fe and inevitable impurities, wherein Pcm is less than or equal to 0.23 percent; the bridge steel is low in alloy cost, simple in process control, small in residual stress and excellent in comprehensive performance, the straightness of the steel plate can be guaranteed without cold straightening or flattening, and the requirement for machining and manufacturing of a large bridge steel structure can be better met.

Description

Technical Field

[0001] The invention belongs to the technical field of bridge steel, and specifically relates to a 500MPa-grade bridge steel and a manufacturing method thereof. Background Art

[0002] With the rapid development of bridge construction, the construction of dual-use bridges for highways and railways and large-span bridges is increasing day by day, and the requirements for the safety and reliability of bridge structures are becoming higher and higher. Therefore, the performance requirements for steel used in bridge structures are also becoming higher and higher. Not only are bridge structure steels required to have high strength, high toughness and good welding performance, but they are also required to have a low yield strength ratio to meet the conditions of lightweight bridge structures and large spans and heavy loads, thereby improving the safety and service life of steel bridge structures. In addition, in order to facilitate the processing and production of bridge steel structures, high requirements are also placed on the straightness of steel plates. For example, the standard for structural steel for railway bridges (TB3556-2020) requires that the straightness of steel plates should not exceed 5mm / m.

[0003] The manufacturing methods disclosed in patents CN 114182165 A, CN 108624744 B, CN 111057945 B, CN 111455287 A, CN111155032A, CN 107326304A, and CN 105063509B all require the addition of three or more precious alloy elements of Cr, Ni, Cu, Mo, and Ce, resulting in high alloy costs. They all adopt TMCP or TMCP+tempering process for production, and the post-rolling controlled cooling process window is narrow, the red return temperature is required to be in the range of 300 to 650°C, and the laminar cooling equipment has high precision requirements. The steel plate has poor flatness and often requires cold straightening or flattening to ensure flatness. In addition, the steel plate has large residual stress, which is not conducive to the processing and manufacturing of bridge steel structures.

[0004] Therefore, it is of great significance to develop a low yield ratio, high flatness 500MPa grade bridge steel and its manufacturing method, which has a chemical composition that only requires a small amount of a precious alloy element to be added, has simple process control, good plate shape, and does not require cold straightening or flattening to ensure flatness. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a 500MPa grade bridge steel and a manufacturing method thereof. The bridge steel has low alloy cost and simple process control. It does not need cold straightening or flattening to ensure the straightness of the steel plate. The steel plate has small residual stress and excellent comprehensive performance, which can better meet the processing and manufacturing of large-scale bridge steel structures.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A 500MPa grade bridge steel, comprising the following chemical components in weight percentage: C: 0.07-0.11%, Si: 0.10-0.40%, Mn1.55-1.70%, P≤0.015%, S≤0.005%, B≤0.0005%, N≤0.008%, Mo: 0.10-0.20%, Nb: 0.035-0.045%, V: 0.040-0.050%, Ti: 0.01-0.02%, Als: 0.015-0.060%, and the rest are Fe and unavoidable impurities; the welding crack sensitivity coefficient Pcm of the bridge steel is ≤0.23%.

[0008] The calculation formula of Pcm welding crack sensitivity coefficient is as follows:

[0009] Pcm(%)=C+Si / 30+Mn / 20+Cu / 20+Cr / 20+Ni / 60+Mo / 15+V / 10+5B.

[0010] Furthermore, the composition of the bridge steel is Cu≤0.05%, Cr≤0.05%, and Ni≤0.05%.

[0011] The metallographic structure of the bridge steel is bainite+ferrite.

[0012] The transverse and longitudinal yield strength of the bridge steel is ≥500MPa, the tensile strength is ≥630MPa, the yield strength ratio is ≤0.86, and the elongation is ≥18%; -20℃ KV 2 ≥280J, -40℃KV 2 ≥270J.

[0013] The present invention also provides a method for manufacturing the 500MPa grade bridge steel, which comprises the following steps: smelting, continuous casting, heating, rolling, cooling, hot straightening, sub-temperature quenching, and tempering.

[0014] In the heating step, the heating temperature is 1200-1240° C., the total heating time is 270-310 min, and the soaking time is ≥60 min.

[0015] In the rolling step, two-stage rolling is adopted, the starting temperature of rough rolling is ≥1050°C, the starting temperature of finishing rolling is 850-920°C, the thickness of the intermediate billet at warm temperature is not less than twice the thickness of the finished product; and the final rolling temperature is 780-840°C.

[0016] In the cooling step, the steel is air-cooled to above 720° C. after rolling for hot straightening.

[0017] In the heat straightening step, heat straightening is performed for 1 to 3 times.

[0018] In the sub-temperature quenching step, the quenching temperature is 815-880°C, and the time in the furnace is plate thickness mm×2.5 min / mm.

[0019] In the sub-temperature quenching step, the quenching machine roller speed is 0.08-0.28 m / s, and the total water volume in the high-pressure section is 3700-4664 m 3 / min, the ratio of water volume under the gap in the high-pressure section to that on the upper side is 1.15-1.20, the ratio of water volume under the high-density water in the high-pressure section to that on the upper side is 1.00-1.25; the total water volume in the low-pressure section is 2625m 3 / min, the ratio of water volume between the lower and upper reaches of the low-pressure section is 1.50.

[0020] In the tempering step, the tempering temperature is 490-590° C., the time in the furnace is plate thickness mm×1.5min / mm+60min, and the plate is air-cooled after being taken out of the furnace.

[0021] The thickness specification of the 500MPa bridge steel plate provided by the present invention is 10 to 80mm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1) The present invention adopts a composition design of low C, Nb+V+Ti composite microalloying and adding only a small amount of Mo, and adopts a controlled rolling+sub-temperature quenching+tempering process to obtain a steel plate with a thickness of 10 to 80 mm, and obtains a microstructure dominated by bainite+ferrite, thereby achieving the good characteristics of low alloy cost, high strength and toughness, low yield ratio and high flatness of the steel plate;

[0024] 2) The present invention performs hot straightening by air cooling to above 720°C after rolling, so that the steel plate has low deformation resistance and the straightness of the steel plate after hot straightening is ≤1mm / m, which provides a good plate shape for subsequent heat treatment. The process is simple to execute, and there is no requirement for the accuracy of laminar cooling equipment, and the requirements for the power parameters of the hot straightening machine are also greatly reduced;

[0025] 3) The present invention adopts different sub-temperature quenching and tempering holding times for steel plates in different thickness ranges, which not only ensures good strength-toughness matching of the steel plates, but also effectively ensures a low yield strength ratio of the steel plates;

[0026] 4) The present invention ensures the uniformity of upper and lower surface temperatures of the steel plate during the sub-temperature quenching process by controlling the water ratio of the upper and lower manifolds, the water volume of the high and low pressure sections and the roller speed; after quenching, the steel plate does not need cold straightening and flattening treatment to meet the control requirement of plate flatness below 3mm / 1m, and the steel plate does not deform after cutting.

[0027] 5) The bridge steel provided by the present invention has excellent comprehensive properties, with transverse and longitudinal yield strength ≥500MPa, tensile strength ≥630MPa, yield strength ratio ≤0.86, and elongation ≥18%; -20℃ KV2 ≥280J, -40℃KV 2 ≥270J; and has a low welding crack sensitivity coefficient, good welding performance, can be better applied to large bridge construction, and has high social value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the metallographic structure diagram of the bridge steel at 1 / 4 of the thickness in Example 6. DETAILED DESCRIPTION

[0029] The present invention provides a 500MPa grade bridge steel, which includes the following chemical components in weight percentage: C: 0.07-0.11%, Si: 0.10-0.40%, Mn1.55-1.70%, P≤0.015%, S≤0.005%, Cu≤0.05%, Cr≤0.05%, Ni≤0.05%, B≤0.0005%, N≤0.008%, Mo: 0.10-0.20%, Nb: 0.035-0.045%, V: 0.040-0.050%, Ti: 0.01-0.02%, Als: 0.015-0.060%, and the rest are Fe and unavoidable impurities; the welding crack sensitivity coefficient Pcm of the bridge steel is ≤0.23%.

[0030] The manufacturing method of the bridge steel is as follows:

[0031] 1) Smelt and continuously cast the required 250mm thick billet according to the chemical composition;

[0032] 2) Heating: Send the continuous casting billet to the heating furnace, the heating temperature is 1200-1240℃, the total heating time is controlled at 270-310min, and the soaking time is ≥60min;

[0033] 3) Rolling: Two-stage rolling is adopted, the starting temperature of rough rolling is ≥1050℃, the starting temperature of finishing rolling is 850~920℃, the intermediate billet strip temperature thickness is not less than 2 times the thickness of the finished product; the final rolling temperature is 780~840℃;

[0034] 4) After rolling, air cool to above 720℃ and perform hot straightening for 1-3 passes;

[0035] 5) Sub-temperature quenching: quenching temperature 815~880℃, furnace time plate thickness mm×2.5min / mm; quenching machine roller speed 0.08~0.28m / s, total water volume in high pressure section 3700~4664m 3 / min, the gap water ratio of the high-pressure section is 1.15~1.20, the high-density water ratio of the high-pressure section is 1.00~1.25; the total water volume of the low-pressure section is 2625m 3 / min, water ratio in low pressure section is 1.50.

[0036] 6) Tempering: Tempering temperature is 490~590℃, the time in the furnace is plate thickness mm×1.5min / mm+60min, and air cooling is performed after leaving the furnace;

[0037] The present invention is described in detail below with reference to the embodiments.

[0038] The chemical composition, process parameters and properties of the bridge steel in each embodiment are shown in Table 1, Table 2 and Table 3 respectively.

[0039] Table 1 Chemical composition mass percentage (wt%)

[0040] C Mn Si S P Nb V Ti Example 1 0.08 1.62 0.38 0.002 0.01 0.036 0.046 0.013 Example 2 0.09 1.57 0.30 0.003 0.013 0.035 0.041 0.012 Example 3 0.11 1.55 0.25 0.004 0.012 0.038 0.040 0.014 Example 4 0.09 1.58 0.25 0.004 0.010 0.037 0.043 0.014 Example 5 0.09 1.68 0.31 0.002 0.015 0.039 0.044 0.017 Example 6 0.09 1.60 0.29 0.002 0.009 0.040 0.043 0.014 Example 7 0.10 1.65 0.24 0.002 0.014 0.044 0.043 0.014 Mo Als Cr Ni Cu B N Pc Example 1 0.165 0.030 0.03 0.02 0.04 0.0001 0.0043 0.194 Example 2 0.146 0.021 0.05 0.02 0.05 0.0002 0.0042 0.199 Example 3 0.155 0.023 0.04 0.02 0.04 0.0001 0.0048 0.215 Example 4 0.146 0.027 0.04 0.02 0.03 0.0001 0.0045 0.196 Example 5 0.143 0.027 0.04 0.02 0.04 0.0001 0.0045 0.203 Example 6 0.151 0.027 0.04 0.02 0.03 0.0001 0.0033 0.198 Example 7 0.165 0.032 0.04 0.02 0.03 0.0001 0.0033 0.210

[0041] Table 2 Process parameters

[0042]

[0043] Table 3 Performance and flatness of Examples 1-7

[0044]

[0045]

[0046] The chemical composition, process parameters and properties of the bridge steel in each comparative example are shown in Table 4, Table 5 and Table 6 respectively.

[0047] Table 4 Chemical composition mass percentage (wt%)

[0048] Comparative Example C Mn Si S P Nb V Ti 1 0.06 1.53 0.38 0.006 0.016 0.030 0.035 0.013 2 0.06 1.51 0.25 0.004 0.012 0.046 0.052 0.014 3 0.06 1.54 0.31 0.002 0.015 0.030 0.054 0.017 4 0.06 1.50 0.24 0.002 0.014 0.046 0.038 0.014 Comparative Example Mo Als Cr Ni Cu B N Pc 1 0.08 0.030 0.03 0.02 0.04 0.0001 0.0043 0.162 2 0.08 0.023 0.04 0.02 0.04 0.0001 0.0048 0.159 3 0.21 0.027 0.04 0.02 0.04 0.0001 0.0045 0.172 4 0.21 0.032 0.04 0.02 0.03 0.0001 0.0033 0.165

[0049] Table 5 Process parameters

[0050]

[0051]

[0052] Table 6 Performance and straightness

[0053]

[0054] Figure 1 This is the metallographic structure diagram of the bridge steel plate at 1 / 4 of the thickness in Example 6, and its microstructure is bainite and ferrite.

[0055] As can be seen from Table 3, the 500Mpa bridge steel produced by the present invention has excellent transverse and longitudinal tensile and impact properties, yield strength 510-580MPa, tensile strength 630-680MPa, yield strength ratio ≤0.85, elongation 24-37%; -20℃ longitudinal impact energy KV 2 280~310J, -40℃ longitudinal impact energy KV2 270~290J, steel plate straightness ≤3mm / m.

[0056] It can be seen from Table 6 that if the production of 500Mpa grade bridge steel is not carried out according to the solution provided by the present invention, the comprehensive performance of the bridge steel will not be well controlled.

[0057] The detailed description of a 500MPa grade bridge steel and its manufacturing method with reference to the above-mentioned embodiments is illustrative rather than restrictive, and several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A 500MPa grade bridge steel, characterized in that: The bridge steel includes the following chemical components in weight percentage: C: 0.07-0.11%, Si: 0.10-0.40%, Mn1.55-1.70%, P≤0.015%, S≤0.005%, B≤0.0005%, N≤0.008%, Mo: 0.10-0.20%, Nb: 0.035-0.045%, V: 0.040-0.050%, Ti: 0.01-0.02%, Als: 0.015-0.060%, and the rest are Fe and unavoidable impurities; the welding crack sensitivity coefficient Pcm of the bridge steel is ≤0.23%.

2. The 500MPa grade bridge steel according to claim 1, characterized in that: The components of the bridge steel include Cu≤0.05%, Cr≤0.0.05%, and Ni≤0.05%.

3. The 500MPa grade bridge steel according to claim 1, characterized in that: The metallographic structure of the bridge steel is bainite+ferrite.

4. The 500MPa grade bridge steel according to any one of claims 1 to 3, characterized in that: The transverse and longitudinal yield strengths of the bridge steel are ≥500MPa, the tensile strength is ≥630MPa, the yield strength ratio is ≤0.86, and the elongation is ≥18%; -20℃ KV2 is ≥280J, -40℃ KV2 is ≥270J.

5. The method for manufacturing 500MPa grade bridge steel according to any one of claims 1 to 4, characterized in that: The manufacturing method comprises the following steps: smelting, continuous casting, heating, rolling, cooling, hot straightening, sub-temperature quenching and tempering.

6. The manufacturing method according to claim 5, characterized in that: In the heating step, the heating temperature is 1200-1240° C., the total heating time is 270-310 min, and the soaking time is ≥60 min.

7. The manufacturing method according to claim 5, characterized in that: In the rolling step, two-stage rolling is adopted, the starting temperature of rough rolling is ≥1050°C, the starting temperature of finishing rolling is 850-920°C, the thickness of the intermediate billet at warm temperature is not less than twice the thickness of the finished product; and the final rolling temperature is 780-840°C.

8. The manufacturing method according to claim 5, characterized in that: In the cooling step, the steel is air-cooled to above 720° C. after rolling for hot straightening.

9. The manufacturing method according to claim 5, characterized in that: In the sub-temperature quenching step, the quenching temperature is 815-880°C, the furnace time is plate thickness mm×2.5min / mm; the quenching machine roller speed is 0.08-0.28m / s, and the total water volume in the high-pressure section is 3700-4664m 3 / min, the ratio of water volume under the gap in the high-pressure section to that on the upper side is 1.15-1.20, the ratio of water volume under the high-density water in the high-pressure section to that on the upper side is 1.00-1.25; the total water volume in the low-pressure section is 2625m 3 / min, the ratio of water volume between the lower and upper reaches of the low-pressure section is 1.

50.

10. The manufacturing method according to claim 5, characterized in that: In the tempering step, the tempering temperature is 490-590° C., the time in the furnace is plate thickness mm×1.5min / mm+60min, and the plate is air-cooled after being taken out of the furnace.

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