A method for producing a 80kg grade steel plate for hydroelectric power

Abstract

A kind of production method of 80kg grade steel plate for hydroelectricity, the thickness of steel plate is 20~50mm, and the chemical composition of steel is as follows: C≤0.1%, Si≤0.15%, P≤0.015%, S≤0.003%, Mn=1.2%~1.4%; Cr=0.4%~0.5%, Nb=0.015%~0.025%, V=0.03%~0.05%, Ti≤0.02%, Alt=0.02%~0.06%; Ni=0.5%~0.8%, Mo=0.2%~0.4%; B=0.001%~0.002%, Ceq≤0.52%, Pcm≤0.25%, the rest is Fe and inevitable impurities. Through controlled rolling and controlled cooling, off-line tempering technology, produce 80kg grade steel plate for hydroelectricity, the maximum thickness reaches 50mm, yield strength ≥700MPa, tensile strength ≥800MPa, elongation ≥15%, transverse impact at-40 ℃ ≥100J, fully meet the technical requirements of 80kg grade steel plate for hydroelectricity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel production and relates to a production method of 80kg-grade steel plate for hydropower. BACKGROUND

[0002] The development and utilization of clean energy enter a high-speed development stage, and large high-HD (water head height H x steel bifurcated pipe diameter D) hydropower stations all need to use high-strength grade steel plates for hydropower. The 80kg-grade steel for hydropower is widely used due to high technical maturity and excellent comprehensive performance. However, the 80kg-grade steel for hydropower has high performance requirements, a relatively complex production process, and a large amount of addition of valuable elements, which causes low production efficiency and high production cost of the steel plate.

[0003] Optimizing the production process and composition of the 80kg-grade steel plate for hydropower with a thickness of 20-50mm and a large use amount meets the needs of the development of the steel industry and has important significance for reducing enterprise cost and promoting industrial upgrading. SUMMARY

[0004] The technical problem to be solved by the application is to provide a production method of 80kg-grade steel plate for hydropower with high efficiency and low cost. While ensuring that the yield strength, tensile strength, elongation, impact, aging strain impact, and cold bending performance of the 80kg-grade steel plate for hydropower with a thickness of 20-50mm meet relevant standards, the production method realizes the reduction of enterprise production cost and the improvement of production efficiency by appropriately reducing the content of part of valuable alloy, canceling the slab cooling process to realize slab warm charging, and canceling the offline quenching process.

[0005] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0006] A production method of 80kg-grade steel plate for hydropower, the thickness of the steel plate is 20-50mm, and the chemical composition of the steel is as follows: C≤0.1%, Si≤0.15%, P≤0.015%, S≤0.003%, Mn=1.2%-1.4%; Cr=0.4%-0.5%, Nb=0.015%-0.025%, V=0.03%-0.05%, Ti≤0.02%, Alt=0.02%-0.06%; Ni=0.5%-0.8%, Mo=0.2%-0.4%; B=0.001%-0.002%, Ceq≤0.52%, Pcm≤0.25%, and the rest is Fe and inevitable impurities; the metallographic structure of the steel plate is tempered bainite+tempered martensite; the yield strength of the steel plate is ≥700MPa, the tensile strength is ≥800MPa, the elongation is ≥15%, and the transverse impact at-40℃ is ≥100J; the process flow is converter smelting-LF-RH / VD-continuous casting-slab heating-rolling-online cooling-slitting-heat treatment, and the key process steps include:

[0007] 1) continuous casting: the overheat degree of the tundish is controlled at 10-20 DEG C, and the billet is sprayed with water for 200s after two cutting;

[0008] 2) slab heating: the billet is directly heated with temperature after being sprayed with water, the billet time in the furnace is controlled according to the heating coefficient of 8-12min / cm, the hearth temperature is 1200-1250 DEG C, and the uniformity of the billet heating is ensured;

[0009] 3) rolling: two-stage controlled rolling process is adopted, the first stage guarantees 2 passes of 18% or more pass reduction rate, the second stage is opened at a temperature of 820-850 DEG C, the final rolling temperature is 800-830 DEG C, and the second stage cumulative reduction rate is more than 50%;

[0010] 4) on-line cooling: the steel plate is directly sent to the on-line cooling equipment after rolling, the water inlet temperature is 780-810 DEG C, the cooling speed is 15-20 DEG C / s, and the final cooling temperature is less than or equal to 350 DEG C;

[0011] 5) cutting: the large plate is cut into sub-plates according to the order length, and the low temperature zone of 100-200mm needs to be cut off at the head and tail of the large plate;

[0012] 6) heat treatment: the controlled rolling and controlled cooling steel plate is subjected to offline tempering heat treatment, the tempering temperature is 630-660 DEG C, the time in the furnace is 2.3-3.0min / mm, and the steel plate is air cooled to room temperature after being taken out of the furnace.

[0013] Wherein Ceq=C+Mn / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14,

[0014] Pcm=V+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B≤0.25%.

[0015] Compared with the prior art, the beneficial effects of the present application are:

[0016] (1) The application cancels Cu element and reduces the content of precious alloy Mo element, so that the alloy cost is reduced by more than 500 yuan / ton while the strength and toughness are ensured; (2) The application cancels the slab cooling and the steel plate offline quenching process, so that the process flow is shortened, the billet can be loaded into the furnace with temperature, and the consumption of cast slab heating gas is saved. The high-efficiency, short-flow and low-cost production of the steel plate greatly improves the profit level of the production plant; (3) The steel plate can be used for low preheating welding due to the welding crack sensitivity coefficient Pcm≤0.23, so that the welding efficiency of the construction site of a large-scale hydropower project is improved; (4) The application develops an 80kg-grade steel plate for hydropower by controlling rolling and cooling and offline tempering, the maximum thickness of the steel plate is 50mm, the yield strength is greater than or equal to 700MPa, the tensile strength is greater than or equal to 800MPa, the elongation is greater than or equal to 15%, and the transverse impact at-40℃ is greater than or equal to 100J, so that the steel plate fully meets the technical requirements of the 80kg-grade steel plate for hydropower. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a 200 times microscopic structure photo of 1 / 4 thickness of the steel plate of Example 1.

[0018] Figure 2 It is a 500 times microscopic structure photo of 1 / 4 thickness of the steel plate of Example 1. DETAILED DESCRIPTION Example 1

[0019] A production method of an 80kg-grade steel plate for hydropower with high efficiency and low cost, the thickness of the steel plate is 36mm, and the content of the chemical components of the steel is as follows: C=0.093%, Si=0.13%, Mn=1.28%, P=0.013%, S=0.002%, Alt=0.035%, Cr=0.42%, Nb=0.018%, V=0.035%, Ti=0.015%, Ni=0.71%, Mo=0.23%, B=0.0015%, and the rest is Fe and inevitable impurities. The process steps are as follows:

[0020] 1) Continuous casting: dynamic soft reduction is adopted, the overheat degree of the tundish is 15℃, a 260mm*2270mm section continuous casting slab is poured, the center segregation of the slab is C1.5 level, and the water is sprayed for 190s after the second cutting of the slab;

[0021] 2) Slab heating: the billet loading temperature is 530℃, the furnace time is 235min, and the discharging temperature is 1188℃;

[0022] 3) Rolling: two-stage controlled rolling process is adopted, the total reduction rate of the first stage is 61.5%, and the reduction rate of more than 18% is kept in the second pass; the intermediate billet is 100mm, the rough rolling temperature is 830℃, and the finish rolling temperature is 816℃;

[0023] 4) on-line cooling: the steel plate is directly put into mulpic on-line fast cooling after rolling, the water inlet temperature is 798℃, the cooling speed is 18℃ / s, and the final cooling temperature is 310℃;

[0024] 5) slitting: the large plate is cut into two sub-plates according to the order length, and 150mm of waste is cut off at the head and tail of the large plate;

[0025] 6) heat treatment: the cut steel plate is heat treated in an offline tempering furnace, the tempering temperature is 652℃, the furnace time is 92min, and the steel plate is air cooled to room temperature after tempering.

[0026] The mechanical property detection of the 36mm specification 80kg grade steel plate for water and electricity produced in example 1 is: yield strength 789MPa, tensile strength 832MPa, elongation 18.5%, transverse impact energy at 1 / 4 position of plate thickness-40℃ 157J, 154J, 152J, surface transverse-20℃ aging strain impact energy 190J, 191J, 179J. As shown in Figure 1 the steel plate has a microstructure of tempered bainite + tempered martensite, and no cracks are found at the root and surface after the steel plate is welded after preheating to 80℃. Example 2

[0027] A high-efficiency and low-cost production method of 80kg grade steel plate for water and electricity, the thickness of the produced steel plate is 50mm, and the weight percentage content of the steel chemical composition is: C=0.089%, Si=0.11%, Mn=1.26%, P=0.011%, S=0.0015%, Alt=0.042%, Cr=0.43%, Nb=0.02%, V=0.033%, Ti=0.017%, Ni=0.51%, Mo=0.22%, B=0.0013%, and the rest is Fe and inevitable impurities. The process steps are as follows:

[0028] 1) continuous casting: dynamic soft reduction is adopted, the tundish superheat is 13℃, and 300mm×2270mm section continuous casting slab is cast, the center segregation of the casting blank is C1.0 level, and the casting blank is watered for 220s after two cutting;

[0029] 2) slab heating: the blank inlet temperature is 516℃, the in-furnace time is 273min, and the outlet temperature is 1176℃;

[0030] 3) rolling: two-stage controlled rolling process is adopted, the first stage total reduction is 60%, and more than 18% is kept to this reduction rate; the intermediate blank is 120mm, the rough rolling temperature is 828℃, and the finish rolling temperature is 816℃;

[0031] 4) on-line cooling: the steel plate is directly put into mulpic on-line fast cooling after rolling, the water inlet temperature is 802℃, the cooling speed is 16℃ / s, and the final cooling temperature is 326℃;

[0032] 5) slitting: the rolled large plate is cut into two sub-plates according to the order length, and 150mm of waste is cut off at the head and tail of the large plate;

[0033] 6) heat treatment: the cut rolled steel plate is heat treated in an offline tempering furnace, the tempering temperature is 643℃, the furnace time is 136min, and the steel plate is air cooled to room temperature after tempering.

[0034] The mechanical property test results of the 50mm specification 80kg grade steel plate produced in Example 2 are: yield strength 802MPa, tensile strength 843MPa, elongation 19%, -40℃ transverse impact energy at 1 / 4 plate thickness 184J, 184J, 191J, and surface transverse -20℃ aging strain impact energy 116J, 123J, 141J. The steel plate is welded after preheating to 80℃, and no cracks are found at the root and surface.

Claims

1. A method of producing a steel plate for hydroelectric power generation of 80 kg grade, the thickness of the steel plate being 20 to 50 mm, characterized by: The chemical composition of the steel is as follows: C≤0.1%, Si≤0.15%, P≤0.015%, S≤0.003%, Mn=1.2%~1.4%; Cr=0.4%~0.5%, Nb=0.015%~0.025%, V=0.03%~0.05%, Ti≤0.02%, Alt=0.02%~0.06%; Ni=0.5%~0.8%, Mo=0.2%~0.4%; B=0.001%~0.002%, Ceq≤0.52%, Pcm≤0.25%, the rest being Fe and inevitable impurities; the metallographic structure of the steel plate is tempered bainite + tempered martensite; the yield strength of the steel plate is ≥700 MPa, the tensile strength is ≥800 MPa, the elongation is ≥15%, and the transverse impact at -40℃ is ≥100 J; the process flow is converter smelting-LF-RH / VD-continuous casting-slab heating-rolling-online cooling-cutting-heat treatment, and the key process steps include: 1) continuous casting: the tundish superheat is controlled at 10~20℃, and the billet is watered for 200s after the second cutting; 2) slab heating: the billet is directly loaded into the furnace after watering, the billet time in the furnace is controlled according to the heating coefficient of 8~12min / cm, the furnace temperature is 1200~1250℃, and the uniformity of the billet heating is ensured; 3) rolling: two-stage controlled rolling process is adopted, the first stage ensures more than 18% pass reduction rate of 2 passes; the second stage is rolled at a temperature of 820~850℃, and the final rolling temperature is 800~830℃, and the cumulative reduction rate in the second stage is >50%; 4) online cooling: the steel plate is directly sent to the online cooling equipment after rolling, the water inlet temperature is 780~810℃, the cooling speed is 15~20℃ / s, and the final cooling temperature is ≤350℃; 5) cutting: the large plate is cut into sub-plates according to the order length, and the head and tail of the large plate need to be cut off 100~200mm of low temperature zone; 6) heat treatment: the controlled rolling and controlled cooling steel plate is subjected to offline tempering heat treatment, the tempering temperature is 630~660℃, the time in the furnace is 2.3~3.0min / mm, and the steel plate is air cooled to room temperature after being taken out of the furnace.

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