High-strength bridge structural steel q500qenh steel plate and production method thereof

Abstract

The application provides a high-strength bridge structure steel Q500qENH steel plate and a production method thereof, the composition of the steel plate comprises the following components: C: 0.07-0.11%, Si: 0.20-0.40%, Mn: 1.35-1.65%, P: ≤0.015%, S: ≤0.005%, Alt: 0.010-0.040%, Nb: 0.030-0.050%, Ni: 0.30-0.40%, Cr: 0.40-0.50%, Cu: 0.25-0.35%, Ti: 0.010-0.020%, Mo: 0.13-0.20%, B: ≤0.0005%, the rest is Fe and residual elements, Pcm: ≤0.22, I: ≥6.5, and Cr equivalent / Ni equivalent: 0.12-0.25. The production process and parameters are controlled, and the obtained weather-resistant bridge steel has high strength and excellent low-temperature toughness, and meets the engineering technical requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a high-strength bridge structure steel Q500qENH steel plate and a production method thereof. BACKGROUND

[0002] The Q500qENH steel plate is mainly used for weather-resistant steel plates (atmospheric corrosion-resistant steel) for large bridges under special weather conditions. The corrosion resistance is between that of ordinary steel and stainless steel, and the atmospheric corrosion resistance is 2-8 times that of ordinary steel of the same grade. The corrosion behavior of the produced high-strength weather-resistant bridge steel Q500qENH and the traditional weather-resistant steel 09CuPCrNi and Q420qENH in a simulated industrial atmospheric environment was compared and studied through a cyclic immersion corrosion test, and the corrosion behavior was analyzed by means of corrosion morphology observation and electrochemical test. The results show that the microstructure and chemical composition have a certain influence on the corrosion resistance of the steel matrix. After the formation of the protective rust layer, the corrosion resistance mainly depends on the protective effect of the rust layer. The results of the cyclic immersion corrosion test and the electrochemical impedance spectroscopy and linear polarization curve analysis of the rust test show that the industrial atmospheric corrosion resistance of the Q500qENH steel is better than that of the 09CuPCrNi steel.

[0003] The patent with publication number CN 115094324 A disclosed on September 23, 2022 discloses a production method for a series of high-grade E-grade weather-resistant bridge steel from a single billet, the composition of the steel material is as follows: C: 0.05-0.07%, Si: 0.25-0.45%, Mn: 1.25-1.50%, P: 0.009-0.014%, S: ≤0.003%, Nb: 0.02-0.03%, Ti: 0.008-0.018%, Cu: 0.25-0.35%, Ni: 0.25-0.35%, Cr: 0.45-0.55%, Mo: 0.05-0.15%, Alt: 0.020-0.045%, and the balance is Fe and impurities; the production method includes the steps of casting billet heating, one-stage rolling, two-stage rolling, and heat treatment, etc. A set of component design is used to realize the production of a single billet with multiple steel grades, which is beneficial to save time and simplify the production process. However, the highest yield strength of the produced steel is 573 MPa, the highest tensile strength is 686 MPa, and the elongation is about 20%, which cannot meet the current requirements for processing performance and strength.

[0004] Therefore, it is necessary to develop a high-strength weather-resistant bridge steel Q500qENH steel plate under the premise of ensuring good processing performance of the steel plate. SUMMARY

[0005] The purpose of this invention is to provide a high-strength bridge structural steel Q500qENH steel plate and its production method. Through composition design, the high-strength bridge structural steel Q500qENH steel plate has a yield strength Rp0.2≥530MPa, tensile strength Rm≥720MPa, elongation A≥29%, yield strength ratio≤0.75, and longitudinal impact energy at 1 / 2 thickness at -40℃≥220J. Under the premise of ensuring good processing performance of the steel plate, it has high strength and meets increasingly higher performance requirements.

[0006] The specific technical solution of this invention is as follows:

[0007] A high-strength bridge structural steel Q500qENH plate comprises the following chemical composition by weight percentage:

[0008] C: 0.07–0.11%, Si: 0.20–0.40%, Mn: 1.35–1.65%, P ≤ 0.015%, S ≤ 0.005%, Alt: 0.010–0.040%, Nb: 0.030–0.050%, Ni: 0.30–0.40%, Cr: 0.40–0.50%, Cu: 0.25–0.35%, Ti: 0.010–0.020%, Mo: 0.13–0.20%, B ≤ 0.0005%, with the remainder being Fe and residual elements.

[0009] The composition of the high-strength bridge structural steel Q500qENH steel plate also meets the following requirement: ensuring that the welding crack sensitivity index Pcm ≤ 0.22;

[0010] Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5 × B, where Pcm% is the mass fraction of the chemical composition.

[0011] The composition of the high-strength bridge structural steel Q500qENH steel plate also meets the following requirements: atmospheric corrosion resistance index I ≥ 6.5; I = 26.01 × (% Cu) + 3.88 × (% Ni) + 1.20 × (% Cr) + 1.49 × (% Si) + 17.28 ×

[0012] (%P)-7.29×(%Cu)×(%Ni)-9.10×(%Ni)×(%P)-33.39×(%Cu)×(%Cu); The higher the index, the better the corrosion resistance of the steel.

[0013] The composition of the high-strength bridge structural steel Q500qENH steel plate also meets the following requirements: the Cr equivalent / Ni equivalent is maintained within the range of 0.12 to 0.25;

[0014] Nickel equivalent Nieq = Ni + 35 × C + 20 × N + 0.25 × Cu;

[0015] Chromium equivalent Creq = Cr + Mo + 0.7 × Nb;

[0016] The thickness of the high-strength bridge structural steel Q500qENH steel plate is 10-100mm, and the width is 2500-3500mm;

[0017] The high-strength bridge structural steel Q500qENH steel plate has a microstructure of granular sorbite and ferrite at half its thickness, with an average grain size of 50-200 nanometers.

[0018] The high-strength bridge structural steel Q500qENH steel plate has a yield strength Rp 0.2 ≥530MPa, tensile strength R m ≥720MPa, elongation A≥29%; yield strength ≤0.75, longitudinal impact energy at 1 / 2 thickness at -40℃ ≥220J.

[0019] The present invention provides a method for producing high-strength bridge structural steel Q500qENH steel plate, comprising: a heating process, a rolling process, and a post-rolling cooling process.

[0020] The heating process includes: the billet preheating section temperature is ≤890℃, the first heating section temperature is ≤1140℃, the second heating section temperature is 1190℃~1255℃, the soaking section temperature is 1200~1235℃, the total heating time is ≥1.12×H minutes, the billet thickness is H, and the unit is mm; when H is 300, the total heating time is ≥336 minutes.

[0021] The rolling process includes a two-stage controlled rolling process: differential temperature rolling in the recrystallization zone and rolling in the non-recrystallization zone.

[0022] The differential temperature rolling in the recrystallization zone specifically involves: In the first stage, differential temperature rolling is used, with an initial rolling temperature ≥1050℃ and a final rolling temperature >950℃. In the first and third passes, a pre-machine cooling device is used to surface-cool the steel plate, with a cooling water flow rate of 1300-1500 L / min and a cooling rate of 6.5-7.5℃ / s, ensuring that the temperature difference between the surface and core of the steel plate reaches F... A After cooling, the reduction rate of each of the first to fourth rolling passes is 9% to 16%, and the final rolling temperature is F. B ℃;

[0023] F A It is the temperature difference between the surface and the core after cooling during the rough rolling stage, F A =150 + 20 × C + 34 × Mn + 26 × Cr;

[0024] F Bis the finish rolling temperature of the rough rolling stage, F B =850+20xC+34xMn+26xCr+35xNi+120xMo+95xCu

[0025] The non-recrystallization zone rolling includes: open rolling temperature 800-880℃, finish rolling temperature F C ℃, cumulative reduction ratio 45%-60%, single pass reduction amount 16-29mm

[0026] F C is the finish rolling temperature of the finish rolling stage; F C =735+20xC+34xMn+26xCr+26xMo+130xNi

[0027] The post-rolling cooling process includes: using interval cooling, and the interval cooling is specifically as follows: the water entry temperature of the steel plate after rolling is greater than or equal to 826℃, interval ACC nozzle groups 1-3, 6-8, 11-13, 16-18 and 20-21 are opened in total 14 groups, water quantity: 500-550m 3 / h for the first three groups, 440-470m 3 / h for the sixth to eighth groups, 240-260m 3 / h for the eleventh to thirteenth groups and the sixteenth to eighteenth groups, and 150-170m 3 / h for the twentieth to twenty-first groups, cooling roller speed 1.0-1.2m / s, cooling speed control at 15-25℃ / s, and the red temperature F D ℃ after cooling, and the steel plate is discharged and stack cooled for 24-48 hours at 200-300℃ after cooling is completed

[0028] F D is the cooling red temperature in the cooling stage; F D =532+20xC+34xMn+26xCr+88xMo+139xNi

[0029] F A The design idea is that: in the high temperature state of 900-1200℃, the temperature field between the surface and the core of the steel plate and the composition of the steel plate changes subtly in the air, and the temperature difference of the heat conduction of the surface and the core is calculated.

[0030] F B The design idea is that: in the medium temperature state of 700-1000℃, the temperature of the steel plate and the microstructure and dynamic recrystallization of the steel plate have an inherent relationship, and the temperature driving energy required for recrystallization rolling is obtained from the driving energy of dynamic recrystallization and the temperature field change.

[0031] F CThe design idea is that under the condition of medium temperature 700-1000 DEG C, the internal relationship between the temperature of the steel plate and the microstructure and dynamic recrystallization of the steel plate is obtained by the driving energy of dynamic recrystallization and the change of temperature field, and the temperature driving energy required for rolling without recrystallization.

[0032] F D The design idea is that under the condition of low temperature 400-800 DEG C, the internal relationship between the temperature of the steel plate and the microstructure and static recrystallization and recovery of the steel plate is obtained by the driving energy of static recrystallization and recovery and the change of temperature field, and the temperature driving energy required for rolling and cooling to obtain uniform microstructure (granular sorbite and ferrite composite structure).

[0033] Compared with the prior art, the present application improves the strength and toughness of the steel plate by low-carbon component design, simultaneously adding elements such as Cr, Cu, Ni, Nb and Mo to control the microstructure, refine the grain and increase the hardenability of the steel plate, the combination of Mo and Nb can delay the ferrite and pearlite phase change, reduce the critical cooling speed for obtaining acicular ferrite and expand the cooling speed range for forming acicular ferrite. In combination with a suitable controlled rolling and controlled cooling process, coarse rolling is carried out in the austenite recrystallization zone, a large deformation amount is given to obtain fine and uniform austenite grains, the reduction rate of the first to fourth rolling passes is 9% to 16%; then fine rolling is carried out at a temperature interval below the recrystallization zone temperature and above the Ar3 temperature, a large cumulative deformation amount is given as much as possible in the fine rolling stage, and the final rolling temperature is controlled at about F C ℃, and then rapid cooling is carried out, when the cooling speed is 15-25 DEG C / s, ideal microstructure mainly composed of fine and uniform AF and dispersed M / A (martensite-austenite) islands can be obtained; the final cooling temperature has a significant effect on the phase composition, with the decrease of the final cooling temperature, the M / A island size becomes smaller, the number increases, and the structure gradually refines. The cooling speed is controlled at 15-25 DEG C / s, the red temperature after cooling is F D ℃, the ferrite transformation is inhibited, the structure is promoted to ultra-low carbon bainite transformation, the granular sorbite and ferrite composite structure is obtained, and the average grain size can reach 50-200 nanometers. And by controlling the process temperature in the production process, the weather-resistant bridge steel obtained has high strength and excellent low-temperature toughness, meets the engineering technical requirements, and is successfully applied to the Sichuan-Tibet railway and large highway bridges in Tibet and other major bridge projects. Under the premise of ensuring good processability of the steel plate, the present application develops a high-strength weather-resistant bridge steel Q500qENH steel plate to effectively obtain stable performance, better adapts to the demand of the structural steel market, and has important social and economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The metallographic structure photo at the surface of the steel plate produced in Example 1;

[0035] Figure 2 Microstructure photograph of the steel plate produced for Example 1 at the thickness 1 / 2;

[0036] Figure 3 Microstructure photograph of the steel plate produced for Example 1 at the thickness 1 / 2;

[0037] Figure 4 Tensile test parameters of the steel plate produced for Example 1;

[0038] Figure 5 Photograph obtained by surface detector for the steel plate produced for Comparative Example 2;

[0039] Figure 6 Photograph of tensile delamination of the steel plate produced for Comparative Example 2;

[0040] Figure 7 Photograph of cold acid macrograph of the steel plate produced for Comparative Example 2;

[0041] Figure 8 Microstructure photograph of the steel plate produced for Comparative Example 3 at the surface;

[0042] Figure 9 Microstructure photograph of the steel plate produced for Comparative Example 3 at the thickness 1 / 4;

[0043] Figure 10 Microstructure photograph of the steel plate produced for Comparative Example 3 at the thickness 1 / 2;

[0044] Figure 11 Microstructure photograph of the fracture at the impact low of the steel plate produced for Comparative Example 3. DETAILED DESCRIPTION

[0045] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0046] The present application provides a high-strength bridge structural steel Q500qENH steel plate, comprising the following mass percentage chemical components:

[0047] C: 0.07-0.11%, Si: 0.20-0.40%, Mn: 1.35-1.65%, P≤0.015%, S≤0.005%, Alt: 0.010-0.040%, Nb: 0.030-0.050%, Ni: 0.30-0.40%, Cr: 0.40-0.50%, Cu: 0.25-0.35%, Ti: 0.010-0.020%, Mo: 0.13-0.20%, B≤0.0005%, and the balance being Fe and residual elements.

[0048] The high-strength bridge structural steel Q500qENH steel plate has a C content of 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, etc., a Si content of 0.20%, 0.30%, 0.40%, etc., a Mn content of 1.35%, 1.38%, 1.40%, 1.42%, 1.45%, 1.48%, 1.52%, 1.56%, 1.65%, P≤0.015%, S≤0.005%, etc., an Alt content of 0.010%, 0.020%, 0.030%, 0.040%, etc., a Nb content of 0.030%, 0.040%, 0.050%, etc., a Ni content of 0.30%, 0.32%, 0.34%, 0.35%, 0.36%, 0.38%, 0.40%, etc., a Cr content of 0.40%, 0.41%, 0.43%, 0.44%, 0.45%, 0.46%, 0.47%, 0.50%, etc., a Cu content of 0.25%, 0.27%, 0.28%, 0.29%, 0.30%, 0.32%, 0.33%, 0.35%, etc., a Ti content of 0.011%, 0.013%, 0.015%, 0.016%, 0.018%, 0.019%, 0.020%, etc., and a Mo content of 0.13%, 0.15%, 0.16%, 0.18%, 0.20%.

[0049] The composition of the high-strength bridge structural steel Q500qENH steel plate also satisfies: guaranteeing a welding crack sensitivity index Pcm≤0.22.

[0050] Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5×B, the welding crack sensitivity index, Pcm%, wherein C, Si, Mn, Cu, Ni, Cr, Mo, V, and B are mass fractions of chemical components, %.

[0051] The composition of the high-strength bridge structural steel Q500qENH steel plate also satisfies: guaranteeing an atmospheric corrosion resistance index I≥6.5.

[0052] I = 26.01 x (%Cu) + 3.88 x (%Ni) + 1.20 x (%Cr) + 1.49 x (%Si) + 17.28 x

[0053] (%P) - 7.29 x (%Cu) x (%Ni) - 9.10 x (%Ni) x (%P) - 33.39 x (%Cu) x (%Cu) ; the greater the index, the better the corrosion resistance of the steel.

[0054] The composition of the high-strength bridge structure steel Q500qENH steel plate also satisfies that the Cr equivalent / Ni equivalent is kept in the range of 0.12-0.25;

[0055] The nickel equivalent Nieq = Ni + 35 x C + 20 x N + 0.25 x Cu;

[0056] The chromium equivalent Creq = Cr + Mo + 0.7 x Nb;

[0057] The high-strength bridge structure steel Q500qENH steel plate has a thickness of 10-100 mm and a width of 2500-3500 mm;

[0058] The microstructure at the thickness 1 / 2 of the high-strength bridge structure steel Q500qENH steel plate is a granular sorbite and ferrite composite structure, and the average grain size can reach 50-200 nm.

[0059] The yield strength Rp 0.2 of the high-strength bridge structure steel Q500qENH steel plate is ≥530 MPa, the tensile strength R m is ≥720 MPa, the elongation A is ≥29%, the yield strength ratio is ≤0.75, and the longitudinal impact energy at the thickness 1 / 2 at -40 DEG C is ≥220 J.

[0060] The production method of the high-strength bridge structure steel Q500qENH steel plate provided by the application comprises the following steps: converter smelting, LF furnace refining, RH vacuum treatment, continuous casting, heating, rolling, post-rolling cooling, and heat treatment.

[0061] The converter smelting step comprises: end-point composition control C: ≥0.080%, P ≤0.010%, S ≤0.025%; ladle tapping temperature 1580-1610 DEG C, and tapping slag blocking.

[0062] The LF furnace refining step comprises: adding refining agent 420-530 kg, lime 650-820 kg, submerged arc slag 230-270 kg, fluorite 100-160 kg, LF furnace power-on slagging for 5-7 minutes, temperature measurement and sampling, feeding of aluminum wire to form white slag, and white slag holding time 11-15 minutes.

[0063] The RH vacuum treatment process includes: ensuring vacuum degree ≤100 Pa, vacuum time ≥15 min, pure degassing time ≥11 min, hydrogen is determined when leaving the station, and ensuring that [H] ≤2 ppm when leaving the station; after breaking the vacuum, boron iron is added, then pure calcium wire 220-270 m is fed, soft argon blowing is performed for 10-15 min after the treatment is completed, the soft argon blowing flow is controlled, and the soft blowing effect is ensured (liquid surface peristalsis is available).

[0064] The continuous casting process includes: good protection casting is performed during the casting process, and the impact area cannot be bright red. The overheating is ensured to be 12-28 ℃, the continuous casting blank must be timely put into the pit for slow cooling for 30-48 hours, the blank temperature when entering the pit should be higher than 550 ℃, after the blank is taken out of the pit, it should be far away from the hot blank, and at the same time, it should not be stacked on the tuyere, and it must be stacked between other cold blanks.

[0065] The heating process includes: the heating temperature of the billet preheating section is ≤890 ℃, the first heating section temperature is ≤1140 ℃, the second heating section temperature is 1190-1255 ℃, the soaking section temperature is 1200-1235 ℃, and the total heating time is ≥1.12×H minutes, wherein H is the thickness of the casting blank, and the unit is mm; when H is 300, the total heating time is ≥336 minutes.

[0066] The rolling process includes: two-stage control rolling process of differential temperature rolling in the recrystallization zone and rolling in the unrecrystallization zone.

[0067] The first stage adopts differential temperature rolling, the opening rolling temperature is ≥1050 ℃, the final rolling temperature is >950 ℃, the first pass and the third pass use the pre-cooling device to cool the surface of the steel plate, the cooling water amount is 1350-1550 L / min, the cooling speed is 6.5-7.5 ℃ / s, the temperature difference between the surface of the steel plate after cooling and the core reaches F A ℃, the reduction rate of each pass of the first to fourth rolling passes after cooling is 9%-16%, and the final rolling temperature is F B ℃; the second stage adopts unrecrystallization rolling, the opening rolling temperature is 800-880 ℃, the final rolling temperature is F C ℃, the cumulative reduction rate is 45%-60%, and the single pass reduction amount is 16-29 mm.

[0068] Since the temperature of the surface of the steel plate has been reduced to 940-980 ℃, but the temperature of the core of the steel plate is still higher than 1050 ℃, there is a temperature difference between the surface and the core, at this time, the deformation of the rolling process width is better penetrated into the core through differential temperature rolling, the core deformation is increased, the welding probability of the core organization defects is increased, the core nucleation capacity is improved, and the core organization is more refined.

[0069] The post-rolling cooling process includes: using interval cooling, specifically: the water entry temperature after the steel plate rolling is completed is ≥826℃, interval ACC nozzle groups 1-3, 6-8, 11-13, 16-18, 20-21 in total 14 groups are opened, water quantity: 500-550m 3 / h for the first three groups, 440-470m 3 / h for the sixth to eighth groups, 240-260m 3 / h for the eleventh to eighteenth groups, and 150-170m 3 / h for the twentieth to twenty-first groups, the cooling roller speed is 1.0-1.2m / s, the cooling speed is controlled at 15-25℃ / s, the red temperature F D after cooling is ℃, and after the cooling is completed, the steel plate is discharged at 200-300℃ and is stacked and cooled for 24-48 hours.

[0070] Wherein F A , F B , F C and F D are the temperature difference between the surface and the core after the surface cooling in the rough rolling stage, the finish rolling temperature in the rough rolling stage, the finish rolling temperature in the fine rolling stage and the red temperature after the cooling in the cooling stage, and the calculation formula is as follows:

[0071] F A = 150+20×C+34×Mn+26×Cr;

[0072] F B = 850+20×C+34×Mn+26×Cr+35×Ni+120×Mo+95×Cu;

[0073] F C = 735+20×C+34×Mn+26×Cr+26×Mo+130×Ni;

[0074] F D = 532+20×C+34×Mn+26×Cr+88×Mo+139×Ni;

[0075] The embodiment of the application increases the deformation of the core of the steel plate by adopting differential temperature rolling in the rough rolling stage, and the combination of Mo and Nb can delay the phase transition of ferrite and pearlite, reduce the critical cooling speed for obtaining acicular ferrite, and expand the cooling speed range for forming acicular ferrite. In combination with a suitable controlled rolling and controlled cooling process, rough rolling is performed in the austenite recrystallization zone, a large deformation amount is given to obtain fine and uniform austenite grains, then finish rolling is performed in the temperature range below the recrystallization temperature and above the Ar3 temperature, a large cumulative deformation amount is given as much as possible in the finish rolling stage, and finish rolling is performed at about Ar3, and then rapid cooling is performed with the cooling speed controlled at 15-30 ℃ / s to inhibit the ferrite transformation, promote the transformation of the structure to ultra-low carbon bainite, and be beneficial to obtaining granular sorbite and ferrite composite structure, and the average grain size can reach 50-200 nm.

[0076] The test method of the application is as follows:

[0077] Chemical composition - sampling method (GB / T20066) - test method (GB / T223, GB / T4336, GB / T20123-20125)

[0078] Tensile test - sampling method (GB / T 2975) - test method (GB / T 228.1)

[0079] Impact test - sampling method (GB / T 2975) - test method (GB / T 229) The specific implementation is as follows:

[0080] Embodiment 1

[0081] A high-strength bridge structure steel Q500qENH steel plate with a thickness of 60 mm and a width of 2800 mm comprises the following mass percentage chemical components:

[0082] C: 0.08%, Si: 0.28%, Mn: 1.45%, P: 0.012%, S: 0.003%, Alt: 0.026%, Nb: 0.045%, Ni: 0.35%, Cr: 0.46%, Cu: 0.32%, Ti: 0.016%, Mo: 0.17%, B: 0.0003%, and the rest is Fe and residual elements. The Pcm calculated according to the formula is 0.22, the weathering index I is 6.58, and the Cr equivalent / Ni equivalent is 0.20.

[0083] The production method of the high-strength bridge structure steel Q500qENH steel plate in Embodiment 1 comprises a heating process, a rolling process, a post-rolling cooling process, and a heat treatment process, and the specific parameters are as follows:

[0084] Heating process: the steel billet containing the above smelting components is transported into a heating furnace which has reached a set furnace temperature, the steel billet has an end face size of 295 mm, the preheating section temperature is 855℃, the first adding section temperature is 1140℃, the second adding section temperature is 1242℃, the soaking temperature is 1235℃, and the total heating time is 352 minutes.

[0085] Rolling process: the first stage rolling open rolling temperature is 1058℃, the first pass and the third pass are rolled by using a cooling device to cool the steel billet, the cooling water amount is 1360L / min, the cooling speed is 7.12℃ / s, the roller speed is set to 1.0m / s during cooling, after cooling, the surface cooling and the core temperature difference is F A =212.9℃, the first four passes of rolling reduction amounts are 32mm, 30mm, 29mm and 30mm, the reduction rates are 10.85%, 11.41%, 12.45% and 14.71% respectively, the finish rolling temperature is F B =975.9℃, the second stage rolling open rolling temperature is 862℃, the finish rolling temperature is F C =847.8℃, the cumulative reduction rate is 41.01%.

[0086] Post-rolling cooling process: interval cooling is adopted, the steel plate enters the water at a temperature of 826℃ after rolling, the first-3rd, 6th-8th, 11th-13th, 16th-18th and 20th-21st groups of ACC nozzles are opened in intervals, a total of 14 groups, the water amount is 535m 3 / h for the first-3rd group, 453m 3 / h for the 6th-8th group, 255m 3 / h for the 11th-13th and 16th-18th groups, and 158m 3 / h for the 20th-21st group, the cooling roller speed is 1.15m / s, the cooling speed is 21.65℃ / s, the re-red temperature after cooling is F D =658.5℃, and the steel plate is cooled at a temperature of 290℃ for 29 hours after cooling.

[0087] The microstructure of the steel plate provided in the embodiment is shown in Figures 1-4 , and the mechanical properties of the steel plate are shown in Table 1.

[0088] Table 1: Mechanical property results of the 2800mm wide and 60mm thick Q500qENH steel plate of Example 1

[0089]

[0090] It can be seen from Table 1 and Figures 1-4 that the mechanical properties at the 1 / 4 thickness and the 1 / 2 thickness of the 60mm Q500qENH steel plate are good, Figures 1-3, the microstructure of the surface, 1 / 4 thickness and 1 / 2 thickness of the steel plate of Example 1 are all complex structure of granular sorbite and a small amount of ferrite, and the structure is uniform. The microstructure of the 1 / 4 thickness and 1 / 2 thickness is complex structure of granular sorbite + ferrite, and the average grain size is 107 nm, Figure 4 The tensile test parameters of the steel plate of Example 1 fully meet the requirements of the corresponding standards, and have good strength and toughness matching.

[0091] Example 2

[0092] A high-strength bridge structural steel Q500qENH steel plate with a thickness of 20 mm and a width of 3000 mm, comprising the following mass percentage chemical components:

[0093] C: 0.09%, Si: 0.32%, Mn: 1.45%, P: 0.012%, S: 0.002%, Alt: 0.032%, Nb: 0.044%, Ni: 0.33%, Cr: 0.47%, Cu: 0.33%, Ti: 0.018%, Mo: 0.17%, B: 0.0003%, and the rest is Fe and residual elements. The Pcm calculated according to the formula is 0.23, the weathering index I is 6.65, and the Cr equivalent / Ni equivalent is 0.19.

[0094] The production method of the high-strength bridge structural steel Q500qENH steel plate of Example 2, comprising: a heating process, a rolling process, a post-rolling cooling process and a heat treatment process, and the specific parameters are as follows:

[0095] The heating process: the steel billet containing the above smelting components is transported into the heating furnace which has reached the set furnace temperature, the steel billet adopts an end face size of 230 mm, the preheating section temperature is 852℃, the first adding section temperature is 1140℃, the second adding section temperature is 1248℃, the soaking temperature is 1235℃, and the total heating time is 276 minutes.

[0096] The rolling process: the first stage rolling open rolling temperature is 1058℃, the steel billet is cooled by using a cooling device before the first pass and the third pass rolling, the cooling water amount is 1360L / min, the cooling speed is 7.15℃ / s, the roller speed is set to 1.0m / s during cooling, and the surface cooling and the core temperature difference after cooling is F A =213.3℃, the reduction amount of the first four passes is 25mm, 24mm, 23mm and 23mm respectively, and the reduction rate is 10.87%, 11.71%, 12.71% and 14.56% respectively, the finish rolling temperature is F B =976.6℃, the second stage rolling open rolling temperature is 862℃, and the finish rolling temperature is F C =845.6℃, and the cumulative reduction rate is 41.30%.

[0097] Cooling process: using interval cooling, the water temperature of the steel plate after rolling is 826℃, the first-3, 6-8, 11-13, 16-18, 20-21 groups of ACC nozzles are opened, a total of 14 groups, water quantity: the first-3 groups is 535m 3 / h, the 6-8 groups is 453m 3 / h, the 11-13, 16-18 groups is 255m 3 / h, the 20-21 groups is 158m 3 / h, the cooling roll speed is 1.15m / s, the cooling speed is 18.23℃ / s, the red temperature after cooling F D = 656.2℃, after cooling, the steel plate is discharged at 290℃ and is stacked for 29 hours.

[0098] The mechanical properties of the steel plate are shown in Table 2.

[0099] Table 2 Mechanical property results of the 3000mm wide and 20mm thick Q500qENH steel plate of Example 2

[0100]

[0101] Comparative Example 1

[0102] A high-strength bridge structure steel Q500qENH steel plate with a width of 2500mm and a thickness of 60mm, which has the same composition as Example 1, and the production method is performed according to the parameters of Example 1, the only difference is that: Without Mo Comparative Example 1 without Mo, the surface structure of the steel plate is ferrite + pearlite, there is a certain amount of bainite at the thickness 1 / 2 in addition to the ferrite + pearlite structure, no granular sorbite is formed, and there is a certain difference between the core and the surface structure, the average grain size is 356nm, and the longitudinal impact performance at the thickness 1 / 2 at-40℃ is low, there is a difference between the surface and the core, the mechanical properties of the steel plate are shown in Table 3.

[0103] Table 3 Mechanical property results of the 2500mm wide and 60mm thick Q500qENH steel plate without Mo of Comparative Example 1

[0104]

[0105] Comparative Example 2

[0106] A high-strength weather-resistant Q500qENH steel plate with a thickness of 60mm, the chemical composition and mass percentage of the steel plate are: C: 0.08%, Si: 0.28%, Mn: 1.45%, P: 0.012%, S: 0.003%, Alt: 0.026%, Nb: 0.045%, Ni: 0.35%, Cr: 0.46%, Cu: 0.32%, Ti: 0.016%, Mo: 0.17%,La: 0.0045%, Ce: 0.0050% B: 0.0003%, the rest is Fe and residual elements. Pcm calculated according to the formula = 0.22, weathering index I = 6.58, Cr equivalent / Ni equivalent = 0.20. The production of Comparative Example 2 is carried out according to the process and parameters of Example 1.

[0107] Compared with Example 1, the amount of rare earth elements is added, and the results are: a large number of longitudinal cracks appear on the surface of the steel plate, as shown in Figure 5 , and mechanical testing appears tensile delamination, see Figure 6 , cracks also appear in the low-magnification intermediate of the steel plate, as shown in Figure 7 . The main reason is that the addition of rare earth elements changes the activity and fluidity of the steel liquid, causing problems such as nozzle clogging, and cracks occur during casting. In addition, rare earth elements in steel usually exist in three forms: solid solution and non-metallic inclusions or intermetallic compounds. And the rare earth in the steel basically exists in the inclusions, and when the rare earth in the steel exceeds the solid concentration, a small amount of rare earth intermetallic compounds (such as Fe17Ce2, etc.) can be observed along the grain boundary. When rare earth elements are added to the steel, rare earth elements can replace the corresponding metal elements in the original silicate, alumina, aluminum salt acid and sulfide in the steel, forming rare earth compounds with higher melting points. These large amounts of inclusions are segregated in the center, causing tensile delamination.

[0108] Comparative Example 3

[0109] A high-strength weathering Q500qENH steel plate, the composition is controlled according to Example 1, compared with Example 1, only the rolling process is changed: the first stage rolling opening temperature is 1059°C, the first four rolling reduction amounts are 20mm, 18mm, 16mm and 15mm, and the reduction rates are 6.78％、6.55％、6.23％、6.22％ , the finish rolling temperature F B =975.9°C, the second stage rolling opening temperature is 862°C, and the finish rolling temperature is F C =847.8°C, and the cumulative reduction rate is 23.38％ .The reduction rate of each pass and the total reduction rate are relatively low.

[0110] The microstructure of the steel plate of Comparative Example 3 is shown in Figure 8 , Figure 9 , Figure 10 , and the mechanical properties of the steel plate are shown in Table 4.

[0111] Table 4 Mechanical property results of Q500qENH steel plate with width 2500mm and thickness 60mm of Comparative Example 3

[0112]

[0113] From the performance test results of Table 4, it can be seen that the -40℃ longitudinal impact performance at the thickness 1 / 2 of the 60mm Q500qENH steel plate, the surface and the core performance have differences.

[0114] The metallographic structure photo of the microstructure map of the steel plate provided by Comparative Example 3 is shown in Figures 8-11 It can be seen that the surface structure of the steel plate is ferrite + pearlite, and there is a certain amount of bainite at the thickness 1 / 2 in addition to the ferrite + pearlite structure, and there is a certain difference between the core and the surface structure.

[0115] Comparative Example 4

[0116] A high-strength weathering Q500qENH steel plate, the composition is controlled according to Example 2, compared with Example 2, only the heating process is changed: the steel billet containing the above smelting composition is conveyed into the heating furnace which has reached the set furnace temperature, the steel billet adopts the end face size of 230mm, the preheating section temperature is 852℃, First temperature increasing section: 1183°C, second temperature increasing section: 1288°C, soaking temperature 1269℃， Total heating time 206 minutes The heating temperature is increased, and the heating time is shortened.

[0117] The mechanical properties of the steel plate of Comparative Example 4 are shown in Table 5.

[0118] Table 5 Mechanical property results of the 60mm Q500qENH steel plate of Comparative Example 4 with a width of 3000mm and a thickness of 60mm

[0119]

[0120] From Table 5, it can be seen that the various properties of the Q500qENH steel plate produced by Comparative Example 4 are poor, the average grain size is in 450 nm to 600 nm , which cannot meet the requirements. The main reason is that the heating temperature is too high, the initial grain grows, the heating time is insufficient, the middle of the billet is not completely heated and burned through, and the billet temperature is not uniform.

[0121] Comparative Example 5

[0122] A high-strength weathering Q500qENH steel plate, the composition is controlled according to Example 1, compared with Example 1, only the cooling process is changed: Non-interval cooling was used, and after the steel plate was rolled, the entry water temperature was 793°C, and the ACC nozzle was directly opened for a total of 1-18 Group 18, water amount: 255 m 3 / h, cooling roll speed 1.05 m / s, cooling rate 6.12 °C / s, post-cooling reheat temperature 722 °C, cooling After the rolling was completed, the steel plate was discharged at 280°C and was stacked and cooled for 24 hours The mechanical properties of the steel plate of Comparative Example 5 are shown in Table 6.

[0123] Table 6 Mechanical property results of the 60mm Q500qENH steel plate of Comparative Example 5 with a width of 2500mm and a thickness of 60mm

[0124]

[0125] As shown in Table 6, the yield and tensile strength of the Q500qENH steel plate produced in Comparative Example 5 do not meet the requirements, and the impact is also extremely low. The main reason is that, in the cooling process, non-interval cooling is used, and there is not enough time for the steel plate to obtain fine core M / A island structure during the process of the core temperature returning to the surface, so that the strength of the core of the steel plate is low and the low-temperature toughness is poor. Therefore, the interval cooling process can not only improve the strength and low-temperature toughness of the core of the steel plate and improve the performance uniformity in the thickness direction, but also can reduce the yield strength ratio of the steel plate and improve the anti-seismic performance of the steel plate.

[0126] As shown above, the high-strength weather-resistant Q500qENH steel plate provided by the embodiment of the present application comprises the following chemical components in mass percentage: C: 0.07-0.11%, Si: 0.20-0.40%, Mn: 1.35-1.65%, P≤0.015%, S≤0.005%, Alt: 0.010-0.040%, Nb: 0.030-0.050%, Ni: 0.30-0.40%, Cr: 0.40-0.50%, Cu: 0.25-0.35%, Ti: 0.010-0.020%, Mo: 0.13-0.20%, B≤0.0005%, and the rest is Fe and residual elements. The high-strength weather-resistant Q500qENH steel plate provided by the embodiment of the present application is designed with low-carbon components, and elements such as Cr, Cu, Ni, Nb and Mo are added to control the microstructure to improve the strength and toughness of the steel plate, refine the grains and increase the hardenability of the steel plate. Through two-stage controlled rolling (first-stage temperature difference rolling and second-stage non-recrystallization rolling) and interval cooling, the cooling rate and the roll speed are controlled, the rate and proportion of ferrite and bainite phase transformation are controlled, the formation of ferrite is inhibited, the bainite phase transformation is promoted, the combination of Mo and Nb can delay the ferrite and pearlite phase transformation, reduce the critical cooling speed for obtaining acicular ferrite, and expand the cooling speed range for forming acicular ferrite. In combination with a suitable controlled rolling and controlled cooling process, coarse rolling is performed in the austenite recrystallization zone, a large deformation amount is given to obtain fine and uniform austenite grains, then finish rolling is performed below the recrystallization temperature and above the Ar3 temperature, a large cumulative deformation amount is given as much as possible in the finish rolling stage, and the final rolling is performed around Ar3, then rapid cooling is performed with the cooling speed controlled at 15-25℃ / s to inhibit the ferrite transformation and promote the transformation of the structure to ultra-low-carbon bainite, which is beneficial to obtaining acicular ferrite + ultra-fine bainite structure, and the average grain size can reach 50-200 nanometers.

[0127] The produced high-strength weather-resistant Q500qENH steel plate has the characteristics of pure steel, high density and stable quality.

[0128] The above underlined data do not meet the requirements of the present application.

[0129] The foregoing description of the examples has been presented for the purposes of illustration and description. It is apparent to a person skilled in the art that modifications and improvements can be made to the examples described without departing from the scope of the application. Therefore, the above-described examples are intended not to limit the scope of the application, and modifications and improvements made to the present disclosure by those skilled in the art without departing from the scope of the present application should be construed as falling within the scope of the present application.

Claims

1. A high-strength bridge structural steel Q500qENH steel plate, characterized in that, The high-strength bridge structure steel Q500qENH steel plate comprises the following mass percentage chemical components: C: 0.07~0.11%, Si: 0.20~0.40%, Mn: 1.35~1.65%, P≤0.015%, S≤0.005%, Alt: 0.010~0.040%, Nb: 0.030~0.050%, Ni: 0.30~0.40%, Cr: 0.40~0.50%, Cu: 0.25~0.35%, Ti: 0.010~0.020%, Mo: 0.13~0.20%, B≤0.0005%, and the rest is Fe and residual elements; The production method of the high-strength bridge structure steel Q500qENH steel plate comprises a heating process, a rolling process, a post-rolling cooling process and a heat treatment process. The rolling process comprises a two-stage controlled rolling process of differential temperature rolling in a recrystallization zone and rolling in a non-recrystallization zone. The recrystallization zone differential temperature rolling includes: a first stage differential temperature rolling, a starting rolling temperature ≥ 1050℃, a final rolling temperature > 950℃, a first pass and a third pass using a front cooling device to cool the surface of the steel plate, a cooling water amount of 1300-1500L / min, a cooling speed of 6.5~7.5℃ / s, so that the temperature difference between the surface of the steel plate after cooling and the core reaches F A ℃, and the reduction rate of each pass of the first to fourth rolling passes after cooling is 9%~16%, and the final rolling temperature is F B ℃. F A = 150 + 20 x C + 34 x Mn + 26 x Cr; F B = 850 + 20 x C + 34 x Mn + 26 x Cr + 35 x Ni + 120 x Mo + 95 x Cu; The rolling process in the non-recrystallization zone includes: an initial rolling temperature of 800~880℃ and a final rolling temperature of F. C ℃, cumulative reduction rate 45%~60%, single-pass reduction 16~29mm; F C =735+20×C+34×Mn+26×Cr+26×Mo+130×Ni; The post-rolling cooling process comprises: using interval cooling, specifically: after the steel plate is rolled, the water entry temperature is greater than or equal to 826 DEG C, interval ACC nozzle groups 1-3, 6-8, 11-13, 16-18 and 20-21 are opened in total 14 groups, water quantity: 500-550 m 3 / h for the first to third groups, 440-470 m 3 / h for the sixth to eighth groups, 240-260 m 3 / h for the eleventh to thirteenth groups, 16-18 groups, 150-170 m 3 / h for the twentieth to twenty-first groups, the cooling roller speed is 1.0-1.2 m / s, the cooling speed is controlled to be 15-25 DEG C / s, the red temperature F D of the steel plate after cooling is greater than or equal to 532+20xC+34xMn+26xCr+88xMo+139xNi; and after the cooling is completed, the steel plate is discharged at 200-300 DEG C and is stacked and cooled for 24-48 hours. D =532+20xC+34xMn+26xCr+88xMo+139xNi; The microstructure at the thickness 1 / 2 of the high-strength bridge structure steel Q500qENH steel plate is a granular sorbite and ferrite composite structure, and the average grain size reaches 50~200nm. The high-strength bridge structure steel Q500qENH steel plate has yield strength Rp 0.2 ≥ 530 MPa, tensile strength R m ≥ 720 MPa, elongation A ≥ 29%; yield strength ratio ≤ 0.75, longitudinal impact energy at 1 / 2 thickness at -40 °C ≥ 220 J. 2.The high-strength bridge structural steel Q500qENH steel plate according to claim 1, characterized in that, The composition of the high-strength bridge structure steel Q500qENH steel plate also satisfies: Pcm≤0.22; the atmospheric corrosion resistance index I≥6.5, and the Cr equivalent / Ni equivalent is kept at 0.12~0.

25. Pcm=C+Si / 30+Mn / 20+Cu / 20+Ni / 60+Cr / 20+Mo / 15+V / 10+5×B, the welding crack sensitivity index, Pcm%, wherein C, Si, Mn, Cu, Ni, Cr, Mo, V and B are mass fractions of chemical components, %; I=26.01×(%Cu)+3.88×(%Ni)+1.20×(%Cr)+1.49×(%Si)+17.28×(%P)-7.29×(%Cu)×(%Ni)-9.10×(%Ni)×(%P)-33.39×(%Cu)×(%Cu); Cr equivalent=Ni+35×C+20×N+0.25×Cu; Ni equivalent=Cr+Mo+0.7×Nb. 3.The high-strength bridge structural steel Q500qENH steel plate according to claim 1 or 2, characterized in that, The high-strength bridge structure steel Q500qENH steel plate has a thickness of 10~100mm and a width of 2500~3500mm.

4. A method for producing a high-strength bridge structural steel plate Q500qENH steel plate according to any one of claims 1 to 3, characterized by, The production method comprises a heating process, a rolling process, a post-rolling cooling process and a heat treatment process.

5. The production method according to claim 4, characterized by, The heating process comprises: a billet preheating section heating temperature≤890℃, a first heating section temperature≤1140℃, a second heating section temperature of 1190℃~1255℃, a soaking section temperature of 1200~1235℃, and a total heating time:≥1.12×H minutes, wherein H is the thickness of the cast billet, in mm.

6. The production method according to claim 4, characterized by, The recrystallization zone differential temperature rolling includes: a first stage differential temperature rolling, a starting rolling temperature ≥ 1050℃, a final rolling temperature > 950℃, a first pass and a third pass using a front cooling device to cool the surface of the steel plate, a cooling water amount of 1300-1500L / min, a cooling speed of 6.5~7.5℃ / s, so that the temperature difference between the surface of the steel plate after cooling and the core reaches F A ℃, and the reduction rate of each pass of the first to fourth rolling passes after cooling is 9%~16%, and the final rolling temperature is F B ℃. F A = 150 + 20 x C + 34 x Mn + 26 x Cr; F B = 850 + 20 x C + 34 x Mn + 26 x Cr + 35 x Ni + 120 x Mo + 95 x Cu.

7. The production method according to claim 5, characterized by, The rolling process in the non-recrystallization zone includes: an initial rolling temperature of 800~880℃ and a final rolling temperature of F. C ℃, cumulative reduction rate 45%~60%, single-pass reduction 16~29mm; F C =735+20×C+34×Mn+26×Cr+26×Mo+130×Ni.

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