Q960E steel plate and heat treatment method and production method thereof

Abstract

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

Description

Technical Field

[0001] The invention belongs to the technical field of metal materials, and in particular relates to a Q960E steel plate and a heat treatment method and a production method thereof. Background Art

[0002] With the rapid development of equipment manufacturing industry towards high performance, large-scale and reduced volume, the market demand for engineering machinery steel with yield strength above 960MPa has increased. Q960E complies with the national standard GB / T16270, and its typical performance characteristics are high strength and poor toughness. The standard requires yield strength ≥960MPa, tensile strength 980-1150MPa, elongation ≥10%, and -40℃ longitudinal impact value ≥27J.

[0003] As competition in the construction machinery industry intensifies, how to improve the cost-effectiveness of products has become a problem that steel companies and workers need to break through. Steel plates not only need to meet customers' mechanical performance requirements, but also need to be low-priced, have a short production cycle, be easy to weld, and have excellent flatness.

[0004] At present, for the production of 960MPa grade high-strength steel, the heat treatment method of quenching and tempering (offline quenching + high temperature tempering) is generally adopted, combined with high content of Mn, Cr, Mo, Ni, Nb, V and other alloy elements in the steel to achieve the goal of high strength. This method has high production costs and is bound to cause consumption of mineral resources and energy.

[0005] Chinese patent CN 114134419 A discloses a high-strength steel plate with a yield strength of 960 MPa and a method for manufacturing the same. However, the disadvantages of the steel plate are that 0.1% to 0.4% of Cr, 0.3% to 0.6% of Ni, Nb and other alloy elements are added at the same time, resulting in a relatively high alloy cost. In addition, a heat treatment method of online quenching + 150 to 300°C tempering is adopted, which increases the heat treatment cost and energy consumption. The thickness of the steel plate is 10 to 30 mm.

[0006] Chinese patent CN 114752851 A discloses a low crack sensitivity steel plate with a yield strength of 960 MPa and a manufacturing method thereof. The disadvantages thereof are that 1.15% to 1.35% of Cr alloy elements are added at the same time, and the alloy cost is relatively high; and a heat treatment method of online quenching + 450 to 600°C tempering is adopted, which increases the heat treatment cost and energy consumption. The thickness of the steel plate is less than 20 mm, and the CEV is less than 0.54%. Summary of the invention

[0007] The invention provides a Q960E steel plate and a heat treatment method and a production method thereof. The invention adopts an appropriate amount of carbon, silicon and manganese, appropriately adds chromium and boron hardenability elements, adds a small amount of niobium, a grain refining element, and exerts the grain refining and hardenability improving effects of the aluminum element. The Q960E steel plate with a thickness of 6 to 25 mm is produced through controlled rolling + sub-temperature quenching. The Q960E steel plate meets the requirements of a transverse impact value of greater than 30 J at -40°C, a yield strength of 1000 to 1050 MPa, a tensile strength of 1050 to 1150 MPa, an elongation of greater than 14%, a CEV of less than or equal to 0.50%, and excellent welding performance.

[0008] The functions and controls of the components in the Q960E steel plate provided by the present invention are as follows:

[0009] Carbon: The most effective element to improve the strength of steel, forming chromium carbide to ensure the strength of the steel plate. However, the higher the carbon content, the lower the welding performance, impact toughness and elongation, so this steel grade is selected at 0.15-0.19%.

[0010] Manganese: It improves hardenability, promotes martensitic transformation, and improves strength in the steel. However, Mn is a major segregation element. Too high a content will cause the center of the continuous casting billet to segregate to form MnS, which will have an adverse effect on the fracture toughness, lamellar tearing resistance, and welding performance of the steel plate. Therefore, the content of this steel is selected to be 1.30-1.50%.

[0011] Silicon: It plays a role of solid solution strengthening in the steel. However, too high Si content will deteriorate the toughness of martensitic high-strength steel, increase welding crack sensitivity, and cause the surface quality of the steel plate to deteriorate. Therefore, this steel grade is selected to be 0.30-0.40%.

[0012] Chromium: Improves the hardenability of steel, inhibits the formation of polygonal ferrite and pearlite, promotes the transformation of low-temperature microstructures such as bainite or martensite, and improves the strength and corrosion resistance of steel. However, too high a Cr content will affect the toughness of the steel and reduce the welding performance of the steel plate. Therefore, this steel grade is selected at 0.30-0.40%.

[0013] Aluminum: A strong deoxidizing element, and it also has a strong affinity with N, which can eliminate the aging sensitivity caused by N. The precipitation of N compounds refines the austenite grains and protects the hardenability of B. If the content is too high, inclusions such as Al2O3 are likely to be produced, which reduces the plastic toughness of the steel plate. Therefore, this steel grade is selected at 0.060-0.070%.

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

[0015] Boron: It improves the hardenability of steel plates, thereby reducing the amount of other precious metals added and reducing costs. However, if the boron exceeds 0.0050%, it is easy to segregate and form borides, which seriously deteriorates the toughness of the steel plate and reduces the hardenability. Therefore, this steel grade is selected at 0.0015-0.0025%.

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

[0017] The technical solution adopted by the present invention is as follows:

[0018] A Q960E steel plate comprises the following chemical components in 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%, and the balance is 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 6-25 mm; its -40°C transverse impact value is greater than 30 J, its yield strength is 1000-1050 MPa, its tensile strength is 1050-1150 MPa, its elongation is greater than 14%, and its CEV is ≤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°C, and the water cooling rate is ≥10°C / s; if the quenching temperature is too high, it is not conducive to impact, and if the quenching temperature is too low, the strength will be unqualified;

[0023] In the tempering step, the holding temperature is 465±15° C., and a sub-temperature quenching step is performed to obtain a steel plate that meets the target strength and toughness requirements.

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

[0025] Table 1

[0026]

[0027] In Table 1, the unit of water volume is m3 / h; water pressure 0.83±0.2MPa; water temperature 18~26℃.

[0028] In the sub-temperature quenching step, for steel plates with a thickness of less than 14 mm, the furnace time is 4.0H minutes, and for steel plates with a thickness of 14-25 mm, the furnace time is 2.5H minutes, where H is the thickness of the steel plate in mm. Different holding times are set according to different plate thicknesses, which is conducive to uniform temperature of the steel plate and 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, and if the holding time is too long, the steel plate will have low strength.

[0030] The present invention also provides a production method of the Q960E steel plate, which comprises the following steps: steelmaking, billet heating, rolling and heat treatment; the heat treatment adopts the heat treatment method of the present invention.

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

[0032] In the converter smelting process, the slide plate and slag plug are used to block the slag, and the P content is required to be ≤0.012% when the steel is tapped. When 1 / 4 of the steel is tapped, the aluminum block is added in the order of "aluminum block-medium silicon manganese". Ferrosilicon, medium carbon ferrochromium, ferroniobium and ferroboron are added during the refining process.

[0033] In the LF refining process, the heating and slag making time is 40 to 50 minutes, and [S] is controlled to be ≤ 0.005%. After the composition is uniform, 100 to 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 in the range of 10-30℃, a 226mm thick section casting machine is used, a casting speed of 1.0m / min, a secondary cooling water volume of 0.8L / kg, and a crystallizer liquid level fluctuation in the range of ±3mm to obtain ingots with high surface and internal quality.

[0035] In the billet heating step, the temperature of the slab entering the heating furnace is 350-550°C; the temperature of the slab preheating section is 700-900°C, the temperature of the first heating section is 1100-1200°C, the temperature of the second heating section is 1200-1250°C, the soaking temperature is 1200-1240°C, and the time in the furnace is (0.85-1.10)×h minutes, where h is the thickness of the slab in mm. The present invention adopts low-temperature heating to extend the time of the slab in the furnace, so that the composition and grain size of the slab are uniform.

[0036] In the rolling step, one-stage rolling is adopted; the rough rolling starting temperature is greater than 1000° C., the roller speed is ≤2.5 m / s, and the pass reduction rate is 10-12%; the final rolling temperature is 850-880° C., and air cooling or weak cooling is performed after rolling.

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

[0038] The Q960E steel plate provided by the present invention does not add precious alloys of nickel and molybdenum, and the alloy cost is only about 200 yuan / ton. The recrystallization temperature of the steel is 850°C. By controlling the final rolling temperature to 850-880°C, not only the austenite grains are refined, but also strain-induced precipitation is favorable. After rolling, the steel plate obtains a certain amount of ferrite, and a small amount of ferrite in the steel improves the low-temperature toughness of the steel, and the process flow is short. Through sub-temperature quenching and medium-temperature tempering, the strength and toughness matching of Q960E is achieved, and its yield strength is greater than 1000MPa, the tensile strength is 1050-1150MPa, the elongation is greater than 12%, the -40°C longitudinal impact value is greater than 40J, and the steel plate unevenness is less than 3mm / m. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0041] Figure 3 This is the phase transformation law of the Q960E steel plate during quenching and cooling in Example 3. DETAILED DESCRIPTION

[0042] The present invention is described in detail below with reference to the embodiments.

[0043] The invention provides a Q960E steel plate, comprising the following chemical components in 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%, and the balance is Fe and inevitable impurities.

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

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

[0046] In the converter smelting process, the slide plate and slag plug are used to block the slag, and the P content is required to be ≤0.012% when the steel is tapped. When 1 / 4 of the steel is tapped, the aluminum block is added in the order of "aluminum block-medium silicon manganese". Ferrosilicon, medium carbon ferrochromium, ferroniobium and ferroboron are added during the refining process.

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

[0048] During the pouring process, the superheat was controlled in the range of 10-30°C, a 226mm thick section casting machine was used, the casting speed was 1.0m / min, the secondary cooling water volume was 0.8L / kg, and the crystallizer liquid level fluctuation was within the range of ±3mm.

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

[0050] In the rolling step, one-stage rolling is adopted; the rough rolling starting temperature is greater than 1000° C., the roller speed is ≤2.5 m / s, and the pass reduction rate is 10-12%; the final rolling temperature is 850-880° C., and air cooling or weak cooling is performed after rolling.

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

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

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

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

[0055] The present invention is described in detail below with reference to the embodiments.

[0056] Example 1

[0057] A Q960E steel plate, whose chemical composition and weight percentage are as shown in Example 1 in Table 1, and the rest are Fe and unavoidable impurities.

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

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

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

[0061] 3) Rolling process: one-stage rolling, rough rolling start temperature 1058℃, high temperature, low speed and large reduction rolling, roll speed ≤2.5m / s, pass reduction rate 10%, final rolling temperature 856℃, rolling to 6mm; air cooling after rolling;

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

[0063] Example 2

[0064] A Q960E steel plate, whose chemical composition and weight percentage are shown in Example 2 in Table 1, and the rest are Fe and unavoidable impurities.

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

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

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

[0068] 3) Rolling process: one-stage rolling, rough rolling start temperature 1058℃, high temperature, low speed and large reduction rolling, roll speed ≤2.5m / s, pass reduction rate 11%, final rolling temperature 856℃, rolling to 10mm; air cooling after rolling;

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

[0070] Example 3

[0071] A Q960E steel plate, whose chemical composition and weight percentage are shown in Example 3 in Table 1, and the rest are Fe and unavoidable impurities.

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

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

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

[0075] 3) Rolling process: one-stage rolling, rough rolling start temperature 1058℃, high temperature, low speed and large reduction rolling, roll speed ≤2.5m / s, pass reduction rate 12%, final rolling temperature 856℃, rolling 16mm; air cooling after rolling;

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

[0077] Example 4

[0078] A Q960E steel plate, whose chemical composition and weight percentage are shown in Example 4 in Table 1, and the rest are Fe and unavoidable impurities.

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

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

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

[0082] 3) Rolling process: one-stage rolling, rough rolling start temperature 1058℃, high temperature, low speed and large reduction rolling, roll speed ≤2.5m / s, pass reduction rate 11%, final rolling temperature 856℃, rolling 20mm; air cooling after rolling;

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

[0084] Example 5

[0085] A Q960E steel plate, whose chemical composition and weight percentage are shown in Example 5 in Table 1, and the rest are Fe and unavoidable impurities.

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

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

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

[0089] 3) Rolling process: one-stage rolling, rough rolling start temperature 1058℃, high temperature, low speed and large reduction rolling, roll speed ≤2.5m / s, pass reduction rate 10%, final rolling temperature 856℃, rolling 25mm; air cooling after rolling;

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

[0091] Comparative Example 1

[0092] A Q960E steel plate, whose chemical composition and weight percentage are shown in Comparative Example 1 in Table 1, and the rest are Fe and unavoidable impurities.

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

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

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

[0096] 3) Rolling process: one-stage rolling, rough rolling start temperature 1055℃, high temperature, low speed and large reduction rolling, roll speed ≤2.5m / s, pass reduction rate 11%, final rolling temperature 855℃, rolling 25mm; air cooling after rolling;

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

[0098] Comparative Example 2

[0099] A Q960E steel plate, whose chemical composition and weight percentage are shown in Comparative Example 2 in Table 1, and the rest are Fe and unavoidable impurities.

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

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

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

[0103] 3) Rolling process: one-stage rolling, rough rolling start temperature 1058℃, high temperature, low speed and large reduction rolling, roll speed ≤2.5m / s, pass reduction rate 10%, final rolling temperature 855℃, rolling 20mm; air cooling after rolling;

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

[0105] Table 1 Mass percentage of Q960E steel plate of Examples 1-5 and Comparative Example (wt%)

[0106]

[0107]

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

[0109] Table 2 Performance of Example 1-Example 5 and Comparative Example Q960E Steel Plate

[0110]

[0111] The steel plate of the present invention meets the following properties: tensile strength Rm: 1087-1142MPa, yield strength Rp0.2: 1012-1036MPa, elongation A (L0=200mm): 15.5-16.5%, -40℃ longitudinal V-type impact average value ≥40J, and meets the standard technical requirements of Q960E steel plate: yield strength greater than 960MPa, tensile strength 1000-1150MPa, elongation greater than 10%, -40℃ longitudinal impact absorption energy greater than 27J. The steel plate has moderate strength and good low-temperature impact performance, which fully meets the key stress-bearing parts of engineering machinery such as engineering crane booms, crawler crane pull plates, and concrete pump trucks, and has high requirements for steel plate strength, fracture toughness, surface quality, flatness, welding performance, etc.

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

Claims

1. A Q960E steel plate, characterized in that: The invention comprises the following chemical compositions in 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%, and the balance is Fe and unavoidable impurities.

2. The Q960E steel plate according to claim 1, characterized in that: The metallographic structure of the Q960E steel plate is martensite and bainite.

3. The Q960E steel plate according to claim 1, characterized in that: The thickness of the Q960E steel plate is 6-25 mm; its -40°C transverse impact value is greater than 30 J, its yield strength is 1000-1050 MPa, its tensile strength is 1050-1150 MPa, its elongation is greater than 14%, and its CEV is ≤0.50%.

4. The heat treatment method of Q960E steel plate according to any one of claims 1 to 3, characterized in that: The heat treatment method includes sub-temperature quenching and tempering; In the sub-temperature quenching step, the holding temperature is 870±10°C and the water cooling rate is ≥10°C / s; In the tempering step, the insulation temperature is 465±15°C.

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

6. The heat treatment method according to claim 4, characterized in that: In the tempering step, the time in the furnace is 1.5×H+30 minutes, where H is the thickness of the steel plate in mm.

7. The method for producing a Q960E steel plate according to any one of claims 1 to 3, characterized in that: The production method comprises the following steps: steelmaking, billet heating, rolling and heat treatment; the heat treatment adopts the heat treatment method according to any one of claims 4 to 6.

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

9. The production method according to claim 6, characterized in that: In the billet heating step, the temperature of the billet entering the heating furnace is 350-550°C; the temperature of the billet preheating section is 700-900°C, the temperature of the first heating section is 1100-1200°C, the temperature of the second heating section is 1200-1250°C, the soaking temperature is 1200-1240°C, and the time in the furnace is (0.85-1.10)×h minutes, where h is the billet thickness in mm.

10. The production method according to claim 6, characterized in that: In the rolling step, one-stage rolling is adopted; the rough rolling starting temperature is greater than 1000° C., the roller speed is ≤2.5 m / s, and the pass reduction rate is 10-12%; the final rolling temperature is 850-880° C., and air cooling or weak cooling is performed after rolling.

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