Q960e steel plate and heat treatment method and production method thereof

Abstract

The application discloses a Q960E steel plate and a heat treatment method and a production method thereof, the Q960E steel plate comprises the following chemical components in percentage by weight: C: 0.15-0.19%, Si: 0.30-0.40%, Mn: 1.30-1.50%, Cr: 0.30-0.40%, Alt: 0.060-0.070%, Nb: 0.015-0.030%, B: 0.0015-0.0025%; by controlling rolling + intercritical quenching, the low-cost Q960E steel plate with a thickness of 6-25 mm is produced, the transverse impact value at-40 DEG C is greater than 30J, the yield strength is 1000-1050MPa, the tensile strength is 1050-1150MPa, the elongation is greater than 14%, the CEV is less than or equal to 0.50%, and the Q960E steel plate has excellent welding performance.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, specifically relating to a Q960E steel plate and its heat treatment and production methods. Background Technology

[0002] With the rapid development of the equipment manufacturing industry towards high performance, large size, and reduced weight, the market demand for engineering machinery steel with a yield strength of 960MPa or higher is increasing. Q960E conforms to the national standard GB / T16270, and its typical performance characteristics are high strength and poor toughness. The standard requires a yield strength ≥960MPa, tensile strength 980-1150MPa, elongation ≥10%, and longitudinal impact value ≥27J at -40℃.

[0003] With intensifying competition in the construction machinery industry, improving the cost-effectiveness of products has become a key challenge for steel companies and workers. Steel plates not only need to meet customers' mechanical performance requirements, but also need to be inexpensive, have short production cycles, be easy to weld, and possess excellent straightness.

[0004] Currently, the production of 960MPa high-strength steel generally adopts the heat treatment method of quenching and tempering (offline quenching + high-temperature tempering), combined with high content of alloying elements such as Mn, Cr, Mo, Ni, Nb, and V in the steel to achieve the goal of high strength. This method has high production costs and will inevitably lead to the consumption of mineral resources and energy.

[0005] Chinese patent CN 114134419 A discloses a high-strength steel plate with a yield strength of 960MPa and its manufacturing method. Its shortcomings are that it simultaneously adds alloying elements such as 0.1% to 0.4% Cr and 0.3% to 0.6% Ni and Nb, resulting in relatively high alloy costs. In addition, it adopts an online quenching + tempering at 150 to 300℃ heat treatment method, which increases heat treatment costs and energy consumption. The steel plate thickness is 10 to 30 mm.

[0006] Chinese patent CN 114752851 A discloses a low crack sensitivity steel plate with a yield strength of 960MPa and its manufacturing method. Its drawback is that it also adds 1.15% to 1.35% Cr alloying element, which increases the alloy cost. In addition, it adopts an online quenching + tempering at 450 to 600℃ heat treatment method, which increases the heat treatment cost and energy consumption. The steel plate thickness is less than 20mm and the CEV is less than 0.54%. Summary of the Invention

[0007] This invention provides a Q960E steel plate and its heat treatment and production methods. It employs appropriate amounts of carbon, silicon, and manganese, with suitable additions of chromium and boron (hardenability-enhancing elements), and a small amount of niobium (grain-refining element) to leverage the grain-refining and hardenability-improving effects of aluminum. Through controlled rolling and sub-temperature quenching, Q960E steel plates with a thickness of 6–25 mm are produced. These plates meet the following requirements: transverse impact value greater than 30 J at -40℃, yield strength of 1000–1050 MPa, tensile strength of 1050–1150 MPa, elongation greater than 14%, CEV ≤ 0.50%, and excellent weldability.

[0008] The functions and control of each component in the Q960E steel plate provided by this invention are as follows:

[0009] Carbon: The most effective element for increasing the strength of steel, forming chromium carbides to ensure the strength of the steel plate. However, the higher the carbon content, the lower the weldability, impact toughness, and elongation. Therefore, this steel grade is selected with a carbon content of 0.15% to 0.19%.

[0010] Manganese: In the steel, it improves hardenability, promotes martensitic transformation, and increases strength. However, Mn is a major segregating element; excessive content can cause MnS to form in the center of the continuously cast billet, which adversely affects the fracture toughness, resistance to lamellar tearing, and weldability of the steel plate. Therefore, the content is selected to be 1.30–1.50% in this steel grade.

[0011] Silicon plays a role in solid solution strengthening in the steel. However, excessively high Si content will deteriorate the toughness of martensitic high-strength steel, increase the susceptibility to weld cracking, and also lead to a decrease in the surface quality of the steel plate. Therefore, the Si content is selected at 0.30–0.40% for this steel grade.

[0012] Chromium: Improves the hardenability of steel, inhibits the formation of polygonal ferrite and pearlite, promotes the transformation of bainite or martensite in low-temperature structures, and enhances the strength and corrosion resistance of steel. However, excessive chromium content will affect the toughness of the steel and reduce the weldability of the steel plate. Therefore, the chromium content for this steel grade is selected at 0.30-0.40%.

[0013] Aluminum: A strong deoxidizing element, and it also has a strong affinity for nitrogen (N), which can eliminate the aging sensitivity caused by N. The precipitation of nitrogen compounds refines the austenite grains and protects the hardenability of boron (B). Excessive content can easily lead to inclusions such as Al2O3, reducing the ductility and toughness of the steel plate. Therefore, the content is selected at 0.060–0.070% for this steel grade.

[0014] Niobium: It can delay austenite recrystallization, lower the phase transformation temperature, significantly refine grains, and improve low-temperature toughness. During tempering, precipitation strengthening increases the strength of the steel. Therefore, this steel grade is selected with a content of 0.015-0.030%.

[0015] Boron improves the hardenability of steel plates, thereby reducing the amount of other precious metals required and lowering costs. However, boron levels exceeding 0.0050% easily lead to segregation, forming borides that severely deteriorate the toughness and reduce hardenability of the steel plate. Therefore, this steel grade uses a boron content of 0.0015–0.0025%.

[0016] S is a harmful impurity element in steel that is difficult to avoid. Impurity elements such as S and P in steel tend to segregate at grain boundaries, forming network or lamellar compounds, which reduces grain boundary strength. In order to minimize the temper brittleness of steel, this steel grade selects P ≤ 0.015% and S ≤ 0.005%.

[0017] The technical solution adopted in this invention is as follows:

[0018] A Q960E steel plate comprises the following chemical composition by weight percentage: C: 0.15-0.19%, Si: 0.30-0.40%, Mn: 1.30-1.50%, P: ≤0.015%, S≤0.005%, Cr: 0.30-0.40%, Alt: 0.060-0.070%, Nb: 0.015-0.030%, B: 0.0015-0.0025%, with the balance being Fe and unavoidable impurities.

[0019] The metallographic structure of the Q960E steel plate after heat treatment is martensite and bainite.

[0020] The thickness of the Q960E steel plate is 6-25mm; its -40℃ transverse impact value is greater than 30J, yield strength is 1000-1050MPa, tensile strength is 1050-1150MPa, elongation is greater than 14%, and CEV≤0.50%.

[0021] The present invention also provides a heat treatment method for the Q960E steel plate, the heat treatment method comprising sub-temperature quenching and tempering;

[0022] In the sub-temperature quenching step, the holding temperature is 870±10℃ and the water cooling rate is ≥10℃ / s; if the quenching temperature is too high, it will be detrimental to impact resistance; if the quenching temperature is too low, the strength will be unqualified.

[0023] In the tempering step, the holding temperature is 465±15℃, which, combined with the sub-temperature quenching step, yields a steel plate with the target strength and toughness requirements.

[0024] The parameters of the quenching machine, the amount of quenching water, and the water ratio used for steel plates of different thicknesses in the sub-temperature quenching step are shown in Table 1.

[0025] Table 1

[0026]

[0027] In Table 1, the unit for water volume is m.3 / h; water pressure 0.83±0.2MPa; water temperature 18~26℃.

[0028] In the sub-temperature quenching step, the furnace time is 4.0 H minutes for steel plates with a thickness of less than 14 mm, and 2.5 H minutes for steel plates with a thickness of 14–25 mm, where H is the thickness of the steel plate in mm. Setting different holding times according to different plate thicknesses is beneficial for uniform temperature distribution in the steel plate and facilitates uniform diffusion of elements.

[0029] In the tempering step, the furnace time is 1.5 × H + 30 minutes, where H is the steel plate thickness in mm. If the holding time is too short, the steel plate will have high strength but low impact toughness; if the holding time is too long, the steel plate will have low strength.

[0030] The present invention also provides a method for producing the Q960E steel plate, the method comprising the following steps: steelmaking, billet heating, rolling and heat treatment; the heat treatment adopts the heat treatment method described in the present invention.

[0031] The steelmaking process includes the following steps: converter smelting, LF refining, RH vacuum refining, continuous casting, and billet cleaning.

[0032] In the converter smelting process, slag is blocked by a sliding plate and a slag plug. The P content should be ≤0.012% when the steel is tapped. When the steel is 1 / 4 tapped, it should be added in the order of "aluminum blocks - medium silicon manganese". Ferrosilicon, medium carbon ferrochrome, ferroniobium and ferroboron are added in the refining process.

[0033] In the LF refining process, the heating and slag-forming time is 40-50 minutes, and the [S] content is controlled to be ≤0.005%. After the composition is uniform, 100-150 meters of seamless calcium wire is fed, and the soft blowing time is ≥10 minutes.

[0034] During the casting process, the superheat is controlled within the range of 10-30℃. A casting machine with a thickness of 226mm is used, the casting speed is 1.0m / min, the secondary cooling water ratio is 0.8L / kg, and the liquid level fluctuation in the crystallizer is within the range of ±3mm, in order to obtain a cast billet with high surface and internal quality.

[0035] In the billet heating step, the billet temperature upon entering the furnace is 350–550℃; the preheating section temperature is 700–900℃, the first heating section temperature is 1100–1200℃, the second heating section temperature is 1200–1250℃, and the soaking temperature is 1200–1240℃. The furnace time is (0.85–1.10) × h (minutes), where h is the billet thickness in mm. This invention uses low-temperature heating to extend the furnace time of the billet, resulting in uniform composition and grain size.

[0036] The rolling process is carried out in one stage; the roughing temperature is greater than 1000℃, the roll speed is ≤2.5m / s, and the reduction rate per pass is 10-12%; the final rolling temperature is 850-880℃, and the rolling is followed by air cooling or weak cooling.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The Q960E steel plate provided by this invention does not contain expensive alloys such as nickel and molybdenum, and the alloy cost is only about 200 yuan / ton. The recrystallization temperature of the steel is 850℃. By controlling the final rolling temperature to 850~880℃, not only are the austenite grains refined, but strain-induced precipitation is also facilitated. The rolled steel plate obtains a certain amount of ferrite. The small amount of ferrite in the steel improves the low-temperature toughness of the steel, and the process flow is short. Through sub-critical quenching and medium-temperature tempering, a balance of strength and toughness is achieved in Q960E, with a yield strength greater than 1000MPa, tensile strength of 1050~1150MPa, elongation greater than 12%, longitudinal impact value at -40℃ greater than 40J, and flatness of the steel plate less than 3mm / m. Attached Figure Description

[0039] Figure 1 The metallographic structure of the Q960E steel plate in the hot-rolled state in Example 3;

[0040] Figure 2 The metallographic structure of the Q960E steel plate after heat treatment in Example 3;

[0041] Figure 3 The phase transformation law during quenching and cooling of Q960E steel plate in Example 3 is shown. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the embodiments.

[0043] This invention provides a Q960E steel plate comprising the following chemical composition by weight percentage: C: 0.15-0.19%, Si: 0.30-0.40%, Mn: 1.30-1.50%, P: ≤0.015%, S≤0.005%, Cr: 0.30-0.40%, Alt: 0.060-0.070%, Nb: 0.015-0.030%, B: 0.0015-0.0025%, with the balance being Fe and unavoidable impurities.

[0044] The production method of the Q960E steel plate includes the following steps: steelmaking, billet heating, rolling and heat treatment.

[0045] The steelmaking process includes the following steps: converter smelting, LF refining, RH vacuum refining, continuous casting, and billet cleaning.

[0046] In the converter smelting process, slag is blocked by a sliding plate and a slag plug. The P content should be ≤0.012% when the steel is tapped. When the steel is 1 / 4 tapped, it should be added in the order of "aluminum blocks - medium silicon manganese". Ferrosilicon, medium carbon ferrochrome, ferroniobium and ferroboron are added in the refining process.

[0047] In the LF refining process, the heating and slag-forming time is 40-50 minutes, and the [S] content is controlled to be ≤0.005%. After the composition is uniform, 100-150 meters of seamless calcium wire is fed, and the soft blowing time is ≥10 minutes.

[0048] During the casting process, the superheat is controlled within the range of 10-30℃. A casting machine with a cross section of 226mm thickness is used, the casting speed is 1.0m / min, the secondary cooling water ratio is 0.8L / kg, and the liquid level fluctuation in the crystallizer is within the range of ±3mm.

[0049] In the billet heating step, the billet temperature entering the heating furnace is 350-550℃; the preheating section temperature is 700-900℃, the first heating section temperature is 1100-1200℃, the second heating section temperature is 1200-1250℃, the soaking temperature is 1200-1240℃, and the furnace time is (0.85-1.10) × h minutes, where h is the billet thickness in mm.

[0050] The rolling process is carried out in one stage; the roughing temperature is greater than 1000℃, the roll speed is ≤2.5m / s, and the reduction rate per pass is 10-12%; the final rolling temperature is 850-880℃, and the rolling is followed by air cooling or weak cooling.

[0051] The heat treatment includes sub-temperature quenching and tempering;

[0052] In the sub-temperature quenching step, the holding temperature is 870±10℃. For steel plates with a thickness of less than 14mm, the furnace time is 4.0H minutes, and for steel plates with a thickness of 14~25mm, the furnace time is 2.5H minutes, where H is the thickness of the steel plate in mm; the water cooling rate is ≥10℃ / s.

[0053] In the tempering step, the holding temperature is 465±15℃, and the furnace time is 1.5×H+30 minutes, where H is the thickness of the steel plate in mm.

[0054] The parameters of the quenching machine, the amount of quenching water, and the water ratio used for steel plates of different thicknesses in the sub-temperature quenching step are shown in Table 1.

[0055] The present invention will now be described in detail with reference to the embodiments.

[0056] Example 1

[0057] A Q960E steel plate, the chemical composition and weight percentage of which are shown in Example 1 in Table 1, with the remainder being Fe and unavoidable impurities.

[0058] The production method of the Q960E steel plate includes the following processes:

[0059] 1) Steelmaking process: The process flow is converter smelting - LF refining - RH vacuum degassing - continuous casting; the P content of the converter tapping steel is 0.010%, the heating and slag making time is 45 minutes, and the S content is 0.003%; 120 meters of seamless calcium wire is fed, and the soft blowing time is 12 minutes; the superheat is 23℃, the drawing speed is 1.0m / min, the secondary cooling water ratio is 0.8L / kg, the liquid level fluctuation in the crystallizer is 2mm, and there are no defects on the slab surface.

[0060] 2) Billet heating process: The temperature of the 226mm thick billet entering the furnace is 380℃, the temperature of the preheating section is 750-850℃, the first heating section is 1165℃, the second heating section is 1235℃, the soaking temperature is 1230℃, the furnace time is 200 minutes, and rolling is carried out after reaching the temperature.

[0061] 3) Rolling process: One-stage rolling is adopted. The roughing rolling temperature is 1058℃. High temperature, low speed and large reduction rolling is adopted. The roll speed is ≤2.5m / s, the reduction rate per pass is 10%, the final rolling temperature is 856℃, and the thickness is rolled to 6mm; air cooling is performed after rolling.

[0062] 4) Heat treatment process: The steel plate is quenched and held at 870℃ for 24 minutes, then water-cooled after being taken out of the furnace at a cooling rate of 23℃ / s; and tempered at 460℃ for 39 minutes.

[0063] Example 2

[0064] A Q960E steel plate, the chemical composition and weight percentage of which are shown in Example 2 in Table 1, with the remainder being Fe and unavoidable impurities.

[0065] The production method of the Q960E steel plate includes the following processes:

[0066] 1) Steelmaking process: The process flow is converter smelting - LF refining - RH vacuum degassing - continuous casting; the P content of the converter tapping steel is 0.014%, the heating and slag forming time is 45 minutes, and the S content is 0.001%; ​​120 meters of seamless calcium wire is fed, and the soft blowing time is 12 minutes; the superheat is 23℃, the drawing speed is 1.0m / min, the secondary cooling water ratio is 0.8L / kg, the liquid level fluctuation in the crystallizer is 2mm, and there are no defects on the slab surface.

[0067] 2) Billet heating process: The temperature of the 226mm thick billet entering the furnace is 380℃, the temperature of the preheating section is 750-850℃, the first heating section is 1180℃, the second heating section is 1230℃, the soaking temperature is 1220℃, the furnace time is 200 minutes, and rolling is carried out after reaching the temperature.

[0068] 3) Rolling process: One-stage rolling is adopted. The roughing rolling temperature is 1058℃. High temperature, low speed and large reduction rolling is adopted. The roll speed is ≤2.5m / s, the reduction rate per pass is 11%, the final rolling temperature is 856℃, and the thickness is rolled to 10mm; air cooling is performed after rolling.

[0069] 4) Heat treatment process: The steel plate is quenched and held at 870℃ for 10 minutes, then water-cooled after being taken out of the furnace at a cooling rate of 21℃ / s; and tempered at 465℃ for 45 minutes.

[0070] Example 3

[0071] A Q960E steel plate, the chemical composition and weight percentage of which are shown in Example 3 in Table 1, with the remainder being Fe and unavoidable impurities.

[0072] The production method of the Q960E steel plate includes the following processes:

[0073] 1) Steelmaking process: The process flow is converter smelting - LF refining - RH vacuum degassing - continuous casting; the P content of the converter tapping steel is 0.009%, the heating and slag forming time is 45 minutes, and the S content is 0.002%; 120 meters of seamless calcium wire is fed, and the soft blowing time is 12 minutes; the superheat is 23℃, the drawing speed is 1.0m / min, the secondary cooling water ratio is 0.8L / kg, the liquid level fluctuation in the crystallizer is 2mm, and there are no defects on the slab surface.

[0074] 2) Billet heating process: The temperature of the 226mm thick billet entering the furnace is 380℃, the temperature of the preheating section is 750-850℃, the first heating section is 1169℃, the second heating section is 1240℃, the soaking temperature is 1231℃, the furnace time is 200 minutes, and rolling is carried out after reaching the temperature.

[0075] 3) Rolling process: One-stage rolling is adopted. The roughing rolling temperature is 1058℃. High temperature, low speed and large reduction rolling is adopted. The roll speed is ≤2.5m / s, the reduction rate per pass is 12%, the final rolling temperature is 856℃, and the rolling thickness is 16mm. After rolling, air cooling is performed.

[0076] 4) Heat treatment process: The steel plate is quenched and held at 870℃ for 40 minutes, then water-cooled after being taken out of the furnace at a cooling rate of 16℃ / s; tempered at 463℃ for 54 minutes.

[0077] Example 4

[0078] A Q960E steel plate, the chemical composition and weight percentage of which are shown in Example 4 of Table 1, with the remainder being Fe and unavoidable impurities.

[0079] The production method of the Q960E steel plate includes the following processes:

[0080] 1) Steelmaking process: The process flow is converter smelting - LF refining - RH vacuum degassing - continuous casting; the P content of the converter tapping steel is 0.013%, the heating and slag forming time is 45 minutes, and the S content is 0.001%; ​​120 meters of seamless calcium wire is fed, and the soft blowing time is 12 minutes; the superheat is 23℃, the drawing speed is 1.0m / min, the secondary cooling water ratio is 0.8L / kg, the liquid level fluctuation in the crystallizer is 2mm, and there are no defects on the slab surface.

[0081] 2) Billet heating process: The temperature of the 226mm thick billet entering the furnace is 380℃, the temperature of the preheating section is 750-850℃, the first heating section is 1185℃, the second heating section is 1245℃, the soaking temperature is 1237℃, the furnace time is 200 minutes, and rolling is carried out after reaching the temperature.

[0082] 3) Rolling process: One-stage rolling is adopted. The roughing rolling temperature is 1058℃. High temperature, low speed and large reduction rolling is adopted. The roll speed is ≤2.5m / s, the reduction rate per pass is 11%, the final rolling temperature is 856℃, and the rolling thickness is 20mm. After rolling, air cooling is performed.

[0083] 4) Heat treatment process: The steel plate is quenched and held at 870℃ for 50 minutes, then water-cooled after being taken out of the furnace at a cooling rate of 12℃ / s; and tempered at 470℃ for 60 minutes.

[0084] Example 5

[0085] A Q960E steel plate, the chemical composition and weight percentage of which are shown in Example 5 of Table 1, with the remainder being Fe and unavoidable impurities.

[0086] The production method of the Q960E steel plate includes the following processes:

[0087] 1) Steelmaking process: The process flow is converter smelting - LF refining - RH vacuum degassing - continuous casting; the P content of the converter tapping steel is 0.015%, the heating and slag forming time is 45 minutes, and the S content is 0.003%; 120 meters of seamless calcium wire is fed, and the soft blowing time is 12 minutes; the superheat is 23℃, the drawing speed is 1.0m / min, the secondary cooling water ratio is 0.8L / kg, the liquid level fluctuation in the crystallizer is 2mm, and there are no defects on the slab surface.

[0088] 2) Billet heating process: The temperature of the 226mm thick billet entering the furnace is 380℃, the temperature of the preheating section is 750-850℃, the first heating section is 1165℃, the second heating section is 1243℃, the soaking temperature is 1238℃, the furnace time is 200 minutes, and rolling is carried out after reaching the temperature.

[0089] 3) Rolling process: One-stage rolling is adopted. The roughing rolling temperature is 1058℃. High temperature, low speed and large reduction rolling is adopted. The roll speed is ≤2.5m / s, the reduction rate per pass is 10%, the final rolling temperature is 856℃, and the rolling thickness is 25mm. After rolling, air cooling is performed.

[0090] 4) Heat treatment process: The steel plate is quenched and held at 870℃ for 62 minutes, then water-cooled after being taken out of the furnace at a cooling rate of 11℃ / s; and tempered at 465℃ for 68 minutes.

[0091] Comparative Example 1

[0092] A Q960E steel plate, the chemical composition and weight percentage of which are shown in Comparative Example 1 in Table 1, with the remainder being Fe and unavoidable impurities.

[0093] The production method of the Q960E steel plate includes the following processes:

[0094] 1) Steelmaking process: The process flow is converter smelting - LF refining - RH vacuum degassing - continuous casting; the P content of the converter tapping steel is 0.011%, the heating and slag forming time is 44 minutes, and the S content is 0.002%; 121 meters of seamless calcium wire is fed, and the soft blowing time is 12 minutes; the superheat is 22℃, the drawing speed is 1.0m / min, the secondary cooling water ratio is 0.8L / kg, the liquid level fluctuation in the crystallizer is 2mm, and there are no defects on the slab surface.

[0095] 2) Billet heating process: The temperature of the 226mm thick billet entering the furnace is 380℃, the temperature of the preheating section is 750-850℃, the temperature of the first heating section is 1150-1200℃, the temperature of the second heating section is 1230-1250℃, the temperature of the soaking is 1225℃, the time in the furnace is 205 minutes, and the rolling is carried out after reaching the temperature.

[0096] 3) Rolling process: One-stage rolling is adopted. The roughing rolling temperature is 1055℃. High temperature, low speed and large reduction rolling is adopted. The roll speed is ≤2.5m / s, the reduction rate per pass is 11%, the final rolling temperature is 855℃, and the rolling thickness is 25mm. After rolling, air cooling is performed.

[0097] 4) Heat treatment process: The steel plate is quenched and held at 870℃ for 62 minutes, then water-cooled after being taken out of the furnace at a cooling rate of 13℃ / s; and tempered at 465℃ for 68 minutes.

[0098] Comparative Example 2

[0099] A Q960E steel plate, the chemical composition and weight percentage of which are shown in Comparative Example 2 in Table 1, with the remainder being Fe and unavoidable impurities.

[0100] The production method of the Q960E steel plate includes the following processes:

[0101] 1) Steelmaking process: The process flow is converter smelting - LF refining - RH vacuum degassing - continuous casting; the P content of the converter tapping steel is 0.012%, the heating and slag forming time is 44 minutes, and the S content is 0.001%; ​​125 meters of seamless calcium wire is fed, and the soft blowing time is 12 minutes; the superheat is 21℃, the drawing speed is 1.0m / min, the secondary cooling water ratio is 0.8L / kg, the liquid level fluctuation in the crystallizer is 1mm, and there are no defects on the slab surface.

[0102] 2) Billet heating process: The temperature of the 226mm thick billet entering the furnace is 380℃, the temperature of the preheating section is 750-850℃, the first heating section is 1185℃, the second heating section is 1245℃, the soaking temperature is 1230℃, the furnace time is 209 minutes, and rolling is carried out after reaching the temperature.

[0103] 3) Rolling process: One-stage rolling is adopted. The roughing rolling temperature is 1058℃. High temperature, low speed and large reduction rolling is adopted. The roll speed is ≤2.5m / s, the reduction rate per pass is 10%, the final rolling temperature is 855℃, and the rolling thickness is 20mm. After rolling, air cooling is performed.

[0104] 4) Heat treatment process: The steel plate is quenched and held at 900℃ for 50 minutes, then water-cooled after being taken out of the furnace at a cooling rate of 12℃ / s; and tempered at 400℃ for 60 minutes.

[0105] Table 1. Percentage (wt%) of Q960E steel plates from Examples 1-5 and Comparative Examples

[0106]

[0107]

[0108] The mechanical properties of the Q960E steel plates described in Examples 1-5 and the comparative examples are shown in Table 2 below.

[0109] Table 2. Performance of Q960E steel plates from Examples 1-5 and Comparative Example.

[0110]

[0111] The steel plate of this invention meets the following performance requirements: tensile strength Rm: 1087-1142 MPa, yield strength Rp0.2: 1012-1036 MPa, elongation A (L0 = 200 mm): 15.5-16.5%, and average longitudinal V-shaped impact strength at -40℃ ≥ 40 J. It also meets the standard technical requirements for Q960E steel plates: yield strength greater than 960 MPa, tensile strength 1000-1150 MPa, elongation greater than 10%, and longitudinal impact energy absorption greater than 27 J at -40℃. The steel plate has moderate strength and good low-temperature impact performance, fully meeting the requirements for key load-bearing components in engineering machinery such as crane booms, crawler crane pull plates, and concrete pump trucks, where high requirements are placed on steel plate strength, fracture toughness, surface quality, straightness, and weldability.

[0112] The above detailed description of a Q960E steel plate and its heat treatment and production methods, with reference to the embodiments, is illustrative rather than limiting. Several embodiments can be listed according to the defined scope. Therefore, changes and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A Q960E steel plate, characterized in that, It is composed of the following chemical components by weight percentage: C: 0.15–0.19%, Si: 0.30–0.40%, Mn: 1.30–1.50%, P: ≤0.015%, S≤0.005%, Cr: 0.30–0.40%, Alt: 0.060–0.070%, Nb: 0.015–0.030%, B: 0.0015–0.0025%, with the balance being Fe and unavoidable impurities; The thickness of the Q960E steel plate is 6~25mm, and its metallographic structure is martensite and bainite. The production method of the Q960E steel plate includes the following steps: steelmaking, billet heating, rolling and heat treatment; In the rolling process, a one-stage rolling process is adopted; the roughing rolling temperature is greater than 1000℃, the roll speed is ≤2.5m / s, and the reduction rate per pass is 10~12%; the final rolling temperature is 850~880℃, and the rolling is followed by air cooling or weak cooling. The heat treatment method includes sub-temperature quenching and tempering; In the sub-temperature quenching step, the holding temperature is 870±10℃ and the water cooling rate is ≥10℃ / s. During the tempering process, the holding temperature is 465±15℃.

2. The Q960E steel plate according to claim 1, characterized in that, The Q960E steel plate has a transverse impact value of greater than 30J at -40℃, a yield strength of 1000-1050MPa, a tensile strength of 1050-1150MPa, an elongation of greater than 14%, and a CEV of ≤0.50%.

3. The method for producing Q960E steel plate as described in claim 1 or 2, characterized in that, The production method includes the following steps: steelmaking, billet heating, rolling, and heat treatment; the heat treatment method includes sub-temperature quenching and tempering.

4. The production method according to claim 3, characterized in that, In the sub-temperature quenching step, for steel plates with a thickness of less than 14 mm, the furnace time is 4.0 H minutes, and for steel plates with a thickness of 14~25 mm, the furnace time is 2.5 H minutes, where H is the thickness of the steel plate in mm.

5. The production method according to claim 3, characterized in that, In the tempering step, the furnace time is 1.5 × H + 30 minutes, where H is the thickness of the steel plate in mm.

6. The production method according to claim 3, characterized in that, The steelmaking process includes the following steps: Converter smelting, LF refining, RH vacuum refining, continuous casting, billet cleaning.

7. The production method according to claim 3, characterized in that, In the billet heating step, the billet temperature entering the heating furnace is 350~550℃; the preheating section temperature is 700-900℃, the first heating section temperature is 1100-1200℃, the second heating section temperature is 1200-1250℃, the soaking temperature is 1200-1240℃, and the furnace time is (0.85-1.10)×h minutes, where h is the billet thickness in mm.

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