Production method of steel Q490R for hydroelectric pressure pipeline

Abstract

The invention discloses a production method of steel Q490R for a hydroelectric pressure pipeline. The steel comprises the following chemical components in percentage by mass: 0.05 to 0.07 percent of C, 0.25 to 0.35 percent of Si, 1.50 to 1.60 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.022 to 0.050 percent of Alt, 0.020 to 0.025 percent of Nb, 0.18 to 0.22 percent of Cr, 0.10 to 0.15 percent of Mo, 0.10 to 0.20 percent of Ni and the balance of Fe and residual elements. The structure of the steel plate is ferrite and bainite, the welding crack sensitivity coefficient Pcm is smaller than or equal to 0.18, the yield strength is larger than or equal to 490 MPa, the tensile strength is 610-730 MPa, the ductility is larger than or equal to 17%, the transverse impact energy at the temperature of-40 DEG C is larger than or equal to 100 J, and the transverse impact energy at the temperature of-40 DEG C is larger than or equal to 100 J through 5% strain aging. On-line cooling and off-line tempering are adopted, a conventional quenching and tempering process is replaced, the whole technological process is shortened, the production cost is reduced, and the same effect after heat treatment is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and heat treatment, and relates to a production method of steel Q490R for hydroelectric pressure pipelines. Background Art

[0002] Q490R steel is widely used in industries such as petroleum, hydroelectric pressure pipelines, etc. It is mainly used to make spherical tanks, cryogenic storage tanks, pressure pipelines and other equipment. This type of steel has many advantages due to its low carbon equivalent and low Pcm: it can meet the requirements of field welding without preheating, and has excellent low-temperature toughness and high strength. With the development of social economy, more and more pumped storage hydropower stations are being put into construction, and the demand for Q490R steel is increasing, mainly concentrated in steel plates with a thickness of 25~60mm.

[0003] Chinese patent CN106222557A discloses a high-efficiency and low-cost 610MPa hydroelectric steel and its production method, the chemical composition mass percentage of which is: C: 0.07-0.09%, Si: 0.15-0.35%, Mn: 1.40-1.60%, P≤0.15%, S≤0.08%, Nb: 0.015-0.035%, V: 0.030-0.050%, Ti: 0.008-0.030%, Ni: 0.10-0.30%, Mo: 0.10-0.30%, the rest is Fe and impurities. Its composition design is suitable for the production of thinner steel plates, mainly steel plates with a thickness of only 38mm, but there is a significant gap in the requirements for -20℃ impact performance and rolling process. Summary of the invention

[0004] The purpose of the present invention is to provide a production method of Q490R steel for hydroelectric pressure pipelines, which adopts a comprehensive production process to ensure that the yield strength of the steel plate is ≥490MPa, the tensile strength is 610~730Mpa, the elongation is ≥17%, and the impact value at -40℃ is ≥100J.

[0005] The technical solution of the present invention: A production method of Q490R steel for water and electricity pressure pipelines, wherein the chemical composition mass percentage (wt%) of the steel is: C=0.05-0.07, Si=0.25-0.35, Mn=1.50-1.60, P≤0.015, S≤0.005, Alt=0.022-0.050, Nb=0.020-0.025, Cr=0.18-0.22, Mo=0.10-0.15, Ni=0.10-0.20, and the others are Fe and residual elements; the structure of the steel plate is ferrite+bainite, the welding crack sensitivity coefficient Pcm≤0.18, the yield strength is ≥490MPa, the tensile strength is 610-730MPa, the elongation is ≥17%, the -40℃ transverse impact energy is ≥100J, and the 5% strain aging -40℃ transverse impact energy is ≥100J; the method comprises the following key process steps: 1) Rolling: CR rolling is adopted, the first stage rolling temperature is greater than 1100℃, the first stage final rolling temperature is greater than 950℃, and the last two passes reduction rate is ≥18%; the second stage rolling temperature is 900~940℃, the thickness of the rolling intermediate billet is ≥1.8 times the thickness of the finished product, and the final rolling temperature is greater than 800℃; 2) Cooling: After rolling, directly cool in water, the water temperature is 790~830℃, the water volume in zone A is 110 / 140~200, the water volume in zone BCD is 400 / 480, the roller speed is 0.45~1.0m / s, and the final cooling temperature is ≤300℃; 3) Tempering heat treatment: After online cooling and cooling of the steel plate stack, tempering heat treatment is carried out at a temperature of 640±10℃, a holding time of 25~50min, and air cooling after exiting the furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 This is an optical microscopic metallographic photograph of the metallographic structure of the steel plate prepared in Example 1 at the 1 / 4 thickness position (500 times).

[0007] Figure 2 This is an optical microscopic metallographic photograph of the metallographic structure of the steel plate prepared in Example 2 at the 1 / 4 thickness position (500 times). DETAILED DESCRIPTION Example 1

[0008] Produce 25mm thick Q490R steel plate. The chemical composition of the steel is as follows (in wt%): C: 0.05-0.07, Si: 0.25-0.35, Mn: 1.50-1.60, P≤0.015, S≤0.005, Alt: 0.022-0.050, Nb: 0.020-0.025, Cr: 0.18-0.22, Mo: 0.10-0.15, Ni: 0.10-0.20, and the rest are Fe and residual elements.

[0009] Process steps: 1) Rolling: The first stage rolling temperature is 1160℃, the last two passes have reduction rates of 19% and 22% respectively, the final rolling temperature is 1121℃, and the intermediate billet thickness is 80mm. The second stage rolling temperature is 940℃, the final rolling temperature is about 820℃, and the rolled product thickness is 25mm.

[0010] 2) Cooling: After rolling, the steel is directly cooled in water, the water temperature is 790-815℃, the water volume in zone A is 110 / 140, the water volume in zone BCD is 400 / 480, the roller speed is 1.0m / s, and the final cooling temperature is 220-246℃.

[0011] 3) Tempering: After rolling, the steel plate is subjected to tempering heat treatment at a tempering temperature of 640° C. and a holding time of 30 min, followed by air cooling to obtain the steel plate.

[0012] The metallographic structure of the 25 mm thick Q490R steel at 1 / 4 of the thickness is shown in FIG. Figure 1 ,Depend on Figure 1 It can be seen that the structure is bainite and a small amount of ferrite. Finally, the steel plate is obtained, and its properties are shown in Table 1 and Table 2. The strain aging impact is the surface. Example 2

[0013] Produce 58mm thick Q490R steel plate. The chemical composition of the steel is as follows (in wt%): C: 0.05-0.07, Si: 0.25-0.35, Mn: 1.50-1.60, P≤0.015, S≤0.005, Alt: 0.022-0.050, Nb: 0.020-0.025, Cr: 0.18-0.22, Mo: 0.10-0.15, Ni: 0.10-0.20, and the rest are Fe and residual elements.

[0014] 1) Rolling: The first stage rolling temperature is 1178℃, the last two passes have reduction rates of 19% and 21% respectively, the final rolling temperature is 1131℃, and the intermediate billet thickness is 118mm. The second stage rolling temperature is 900℃, the final rolling temperature is about 820℃, and the thickness of the rolled product is 58mm.

[0015] 2) Cooling: After rolling, the steel is directly cooled in water, the water temperature is 780-811℃, the water volume in zone A is 110 / 200, the water volume in zones BCD is 400 / 480, the roller speed is 0.45m / s, and the final cooling temperature is 260-286℃.

[0016] 3) Tempering: After rolling, the steel plate is subjected to tempering heat treatment at a tempering temperature of 640° C. for a holding time of 35 min and then air-cooled after being taken out of the furnace to obtain the steel plate.

[0017] The metallographic structure of the 58 mm thick Q490R steel at 1 / 4 of the thickness is shown in FIG. Figure 2 ,Depend on Figure 2 It can be seen that the structure is bainite and a small amount of ferrite. Finally, the steel plate is obtained, and its properties are shown in Table 1 and Table 2. The strain aging impact is the surface.

[0018] Table 1 Tensile properties test results .

[0019] Table 2 Impact performance test results .

Claims

1. A production method of steel Q490R for hydropower pressure pipelines, characterized in that: The chemical composition mass percentage of the steel is C=0.05-0.07, Si=0.25~0.35, Mn=1.50~1.60, P≤0.015, S≤0.005, Alt=0.022~0.050, Nb=0.020~0.025, Cr=0.18~0.22, Mo=0.10~0.15, Ni=0.10~0.20, and the others are Fe and residual elements; the structure of the steel plate is ferrite + bainite, the welding crack sensitivity coefficient Pcm≤0.18, the yield strength ≥490MPa, the tensile strength 610~730MPa, the elongation ≥17%, the -40℃ transverse impact energy ≥100J, and the 5% strain aging -40℃ transverse impact energy ≥100J; the following key process steps are included: (1) Rolling: CR rolling is adopted, the first stage rolling temperature is greater than 1100℃, the first stage final rolling temperature is greater than 950℃, and the last two passes reduction ratio is ≥18%; the second stage rolling temperature is 900~940℃, the rolling intermediate billet thickness is ≥1.8 times the finished product thickness, and the final rolling temperature is greater than 800℃; (2) Cooling: After rolling, directly cool in water, the water temperature is 790~830℃, the water volume in zone A is 110 / 140~200, the water volume in zone BCD is 400 / 480, the roller speed is 0.45~1.0m / s, and the final cooling temperature is ≤300℃; (3) Tempering heat treatment: After online cooling and cooling of the steel plate stack, the steel plate is subjected to tempering heat treatment at a temperature of 640±10℃ for 25~50min of holding time and then air-cooled after being taken out of the furnace.

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