610MPa-grade high-strength steel plate with low welding crack sensitivity and manufacturing method of 610MPa-grade high-strength steel plate

Abstract

The invention discloses a 610 MPa-grade high-strength steel plate with low welding crack sensitivity and a manufacturing method thereof. The steel plate comprises the following chemical components: 0.04%-0.05% of C, 0.20%-0.35% of Si, 1.30%-1.40% of Mn, less than or equal to 0.008% of P, less than or equal to 0.003% of S, 0.30%-0.40% of Ni, 0.15%-0.25% of Cr, 0.15%-0.25% of Mo, 0.020%-0.030% of V, less than or equal to 0.0003% of B, less than or equal to 0.04% of Cu and the balance of Fe and inevitable impurity elements. The welding crack sensitivity index Pcm ranges from 0.15% to 0.16%; the manufacturing method comprises the steps of EAF smelting, LF refining, VD vacuum treatment, controlled rolling and controlled cooling and tempering heat treatment. The steel plate provided by the invention is high in strength and good in low-temperature toughness, and the transverse impact energy at-50 DEG C is 200-300J.

Description

Technical Field

[0001] The present invention belongs to the field of metal materials, and in particular relates to a 610MPa-grade high-strength steel plate with low welding crack sensitivity and a manufacturing method thereof. Background Art

[0002] With the rapid development of the national economy, the engineering structures of energy, petroleum, chemical, hydropower and other industries are developing in the direction of large-scale and lightweight, which puts forward higher and higher requirements on the performance of steel plates. For example, pressure steel pipes for large power stations, steel for volutes, crude oil storage tanks, spherical tanks, long-span bridges, etc., these large engineering structures are all welded, which puts forward higher and newer requirements on the welding performance of steel plates. Pcm is the welding crack sensitivity index, which represents the tendency and risk of cracking in the heat affected zone (HAZ) during the welding process and after welding of steel plates. The smaller the Pcm value, the smaller the tendency of cracking after welding of steel plates. Improving the intrinsic quality of steel, reducing the content of harmful elements P and S, reducing gas, inclusions and center segregation in steel, can reduce the crack sensitivity of large steel structures after welding, improve the low-temperature toughness after welding, and improve the safety factor of equipment. The disadvantage of traditional steel is that while the strength is improved, its impact toughness and welding performance are significantly reduced, and the welding crack sensitivity increases, which brings difficulties to the manufacture of large steel structures, especially posing a threat to the safety of equipment. Therefore, while pursuing high strength, reducing the crack sensitivity of steel plates has received increasing attention. Summary of the invention

[0003] The present invention aims to provide a 610MPa grade high-strength steel plate with low welding crack sensitivity and a manufacturing method thereof, so as to obtain a high-strength steel plate above 610MPa grade under the condition of Pcm=0.15%-0.16%, and the steel plate has good low-temperature toughness.

[0004] To achieve the above object, the technical solution adopted by the present invention is: A 610MPa grade high-strength steel plate with low welding crack sensitivity, whose chemical composition and mass percentage are as follows: C: 0.04%-0.05%, Si: 0.20%-0.35%, Mn: 1.30%-1.40%, P≤0.008%, S≤0.003%, Ni: 0.30%-0.40%, Cr: 0.15%-0.25%, Mo: 0.15%-0.25%, V: 0.020%-0.030%, B≤0.0003%, Cu≤0.04%, and the rest are Fe and unavoidable impurity elements; the steel plate welding crack sensitivity index Pcm is 0.15%-0.16%.

[0005] The calculation formula of welding crack sensitivity index Pcm is: Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B; it can be seen that the most important factors affecting welding crack sensitivity index Pcm are B and C, among which the residual level of B in steel is below 0.0003%, and the influence on Pcm value is almost negligible; the contribution coefficient of C is 1, which is the largest except B; therefore, the main task of controlling Pcm value is to control lower C content, but C is one of the main strengthening elements of steel. In order to ensure a higher strength level, C cannot be controlled too low. The present invention controls C content to 0.04% to 0.05%.

[0006] Si will deteriorate the impact toughness of the welding heat affected zone and increase the welding crack sensitivity index, so it should not be too high. Therefore, the present invention sets it to 0.20% to 0.35%.

[0007] Mn, as the main element for phase transformation strengthening and solid solution strengthening in steel, can improve the strength of the steel plate, expand the austenite phase region and reduce the Ar3 point temperature; but Mn will segregate during the casting process and reduce the impact toughness of the steel plate. Therefore, the Mn content is set to 1.30%~1.40%.

[0008] Ni can expand the austenite region, improve hardenability, and reduce the carbon content of eutectoid pearlite, thereby improving the low-temperature toughness of the steel plate; but Ni is a precious alloy, so Ni is set to 0.30% to 0.40%.

[0009] Cr can increase the hardenability of steel, ensure that the steel plate obtains bainite structure in the subsequent ultra-fast cooling process, and make up for the lack of strength caused by low carbon through solid solution strengthening. Therefore, the Cr content is set to 0.15%~0.25%.

[0010] Mo can improve the hardenability and temper softening resistance of the steel plate, but will damage the welding performance of the steel plate and also increase the production cost of the steel plate. Therefore, the Mo content is set to 0.15% to 0.25%.

[0011] V can precipitate in bainite laths through V (C, N), thereby improving the strength and temper softening resistance of the steel plate, but it will impair the welding performance of the steel plate. Therefore, the V content is set to 0.020% to 0.030%.

[0012] B is a grain boundary segregation element, which tends to promote austenite coarsening and significantly increase the welding crack sensitivity of steel. Therefore, B is limited to ≤ 0.0003%.

[0013] P and S are harmful elements in steel, which will cause cold brittleness and hot brittleness of steel respectively. The lower the control, the better. Considering that too low P and S will increase production costs, they are set at P≤0.008% and S≤0.003%.

[0014] Furthermore, the low welding crack sensitivity 610MPa grade high strength steel plate of the present invention has a thickness of 38-50mm and is formed by continuous casting of 300mm thick billets.

[0015] Furthermore, the tensile strength of the 610MPa grade high-strength steel plate with low welding crack sensitivity of the present invention is 630-690MPa, and the transverse impact energy at -50°C is 200-300J.

[0016] Furthermore, the method for manufacturing the 610MPa grade high-strength steel plate with low welding crack sensitivity of the present invention comprises: EAF smelting, LF refining, VD vacuum treatment, controlled rolling and controlled cooling, and tempering heat treatment.

[0017] Furthermore, the EAF smelting of the present invention adopts oxygen blowing at a relatively low temperature of 1540-1550°C for dephosphorization and decarburization until P≤0.005% and C≤0.03% when steel is tapped.

[0018] Furthermore, the LF refining of the present invention includes: adding lime and low-boron refining slag in batches to make slag, feeding 600-700m aluminum wire, using large amount of argon gas for stirring, deoxidation and desulfurization, and lifting the electrode to prevent carbon increase, using low-carbon and low-boron alloy for alloying to reduce carbon increase and boron increase.

[0019] Furthermore, the VD vacuum treatment of the present invention has a vacuum degree of 20 to 40 Pa and a holding time of 15 to 20 minutes.

[0020] Furthermore, the controlled rolling and controlled cooling of the present invention: the starting rolling temperature of stage II is ≤850°C, the maximum pass reduction rate is ≥20%, and the steel is put into water for rapid cooling after rolling. The final cooling temperature is controlled at 150-200°C, and the yield strength and toughness of the steel are improved through dislocation strengthening and grain refinement.

[0021] The Pcm value of high-strength steel plates above 610MPa is usually 0.17% to 0.20%, while the Pcm of the present invention is as low as 0.15% to 0.16%. Therefore, a larger pass reduction rate and strong controlled cooling measures are required. Through dislocation strengthening and grain refinement strengthening, a high strength level above 610MPa can still be obtained under the condition of extremely low Pcm value, and good low-temperature impact toughness of -50°C can be obtained.

[0022] Furthermore, the tempering heat treatment of the present invention has a tempering temperature of 500-550° C., a holding time of 2.5-3.0 min / mm, and air cooling to room temperature after being taken out of the furnace.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) A composition design with a smaller welding crack sensitivity index of Pcm of 0.15% to 0.16% was adopted to produce steel plates with a thickness of 38 to 50 mm.

[0024] (2) By adopting strong controlled rolling and controlled cooling measures, a high strength level of more than 610MPa is obtained under extremely low Pcm value conditions, while having good low temperature toughness at -50℃.

[0025] (3) The method of the present invention eliminates the offline quenching process, the production process is simple, and the production cost is low; a high-strength steel plate is obtained under low Pcm conditions, and the steel plate has good low-temperature toughness, which meets the domestic demand for steel for hydropower and petrochemical industries. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below in conjunction with the embodiments. Example 1

[0027] The thickness of the 610MPa grade high-strength steel plate with low welding crack sensitivity in this embodiment is 38mm, and the chemical composition and welding crack sensitivity index Pcm are shown in Table 1; its manufacturing method includes EAF smelting + LF refining + controlled rolling and controlled cooling + tempering heat treatment; the specific process control is as follows: (1) EAF smelting: oxygen blowing at a relatively low temperature of 1550℃ is used to dephosphorize and decarburize until the steel is discharged with a P of 0.003% and a C of 0.02%.

[0028] (2) LF refining: Lime and low-boron refining slag are added in batches to make slag, and 600m aluminum wire is fed. Large amounts of argon are used for stirring to carry out deoxidation and desulfurization. At the same time, the electrode is lifted to prevent carbon increase. Low-carbon and low-boron alloys are used for alloying to reduce carbon increase and boron increase.

[0029] (3) VD vacuum treatment: vacuum degree 40Pa, holding time 20min.

[0030] (4) Controlled rolling and controlled cooling: The starting rolling temperature in stage II is 850°C, the maximum pass reduction rate is 20%, and the steel is put into water for rapid cooling after rolling. The final cooling temperature is controlled at 200°C.

[0031] (5) Tempering heat treatment, tempering temperature 550℃, holding time 2.5min / mm, air cooling to room temperature after taking out of the furnace.

[0032] The tensile properties and -50°C transverse impact properties of the steel plate of this embodiment are shown in Table 2. Example 2

[0033] The thickness of the 610MPa grade high-strength steel plate with low welding crack sensitivity in this embodiment is 45mm, and the chemical composition and welding crack sensitivity index Pcm are shown in Table 1; its manufacturing method includes EAF smelting + LF refining + controlled rolling and controlled cooling + tempering heat treatment; the specific process control is as follows: (1) EAF smelting: oxygen blowing is used at a relatively low temperature of 1540℃ to dephosphorize and decarburize until the steel is discharged with a P of 0.004% and a C of 0.03%.

[0034] (2) LF refining: Lime and low-boron refining slag are added in batches to make slag, and 700m aluminum wire is fed. Large amounts of argon are used for stirring to carry out deoxidation and desulfurization. At the same time, the electrode is lifted to prevent carbon increase. Low-carbon and low-boron alloys are used for alloying to reduce carbon increase and boron increase.

[0035] (3) VD vacuum treatment: vacuum degree 20Pa, holding time 15min.

[0036] (4) Controlled rolling and controlled cooling: The starting rolling temperature in stage II is 835°C, the maximum pass reduction rate is 22%, and the steel is put into water for rapid cooling after rolling. The final cooling temperature is controlled at 150°C.

[0037] (5) Tempering heat treatment, tempering temperature 500℃, holding time 3.0min / mm, air cooling to room temperature after taking out of the furnace.

[0038] The tensile properties and -50°C transverse impact properties of the steel plate of this embodiment are shown in Table 2. Example 3

[0039] The thickness of the 610MPa grade high-strength steel plate with low welding crack sensitivity in this embodiment is 50mm, and the chemical composition and welding crack sensitivity index Pcm are shown in Table 1; its manufacturing method includes EAF smelting + LF refining + controlled rolling and controlled cooling + tempering heat treatment; the specific process control is as follows: (1) EAF smelting: oxygen blowing is used at a relatively low temperature of 1545℃ to dephosphorize and decarburize until the steel is discharged with a P of 0.005% and a C of 0.03%.

[0040] (2) LF refining: Lime and low-boron refining slag are added in batches to make slag, and 650m aluminum wire is fed. Large amounts of argon are used for stirring to carry out deoxidation and desulfurization. At the same time, the electrode is lifted to prevent carbon increase. Low-carbon and low-boron alloys are used for alloying to reduce carbon increase and boron increase.

[0041] (3) VD vacuum treatment: vacuum degree 30Pa, holding time 18min.

[0042] (4) Controlled rolling and controlled cooling: The starting rolling temperature in stage II is 843°C, the maximum pass reduction rate is 21%, and the steel is put into water for rapid cooling after rolling. The final cooling temperature is controlled at 186°C.

[0043] (5) Tempering heat treatment, tempering temperature 530℃, holding time 2.8min / mm, air cooling to room temperature after taking out of the furnace.

[0044] The tensile properties and -50°C transverse impact properties of the steel plate of this embodiment are shown in Table 2. Example 4

[0045] The thickness of the 610MPa grade high-strength steel plate with low welding crack sensitivity in this embodiment is 47mm, and the chemical composition and welding crack sensitivity index Pcm are shown in Table 1; its manufacturing method includes EAF smelting + LF refining + controlled rolling and controlled cooling + tempering heat treatment; the specific process control is as follows: (1) EAF smelting: oxygen blowing is used at a relatively low temperature of 1543℃ to dephosphorize and decarburize until the steel is discharged with a P of 0.003% and a C of 0.02%.

[0046] (2) LF refining: Lime and low-boron refining slag are added in batches to make slag, and 660m aluminum wire is fed. Large amounts of argon are used for stirring to carry out deoxidation and desulfurization. At the same time, the electrode is lifted to prevent carbon increase. Low-carbon and low-boron alloys are used for alloying to reduce carbon increase and boron increase.

[0047] (3) VD vacuum treatment: vacuum degree 25Pa, holding time 18min.

[0048] (4) Controlled rolling and controlled cooling: The starting rolling temperature in stage II is 838°C, the maximum pass reduction rate is 22%, and the steel is put into water for rapid cooling after rolling. The final cooling temperature is controlled at 165°C.

[0049] (5) Tempering heat treatment, tempering temperature 542℃, holding time 2.6min / mm, air cooling to room temperature after taking out of the furnace.

[0050] The tensile properties and -50°C transverse impact properties of the steel plate of this embodiment are shown in Table 2. Example 5

[0051] The thickness of the 610MPa grade high-strength steel plate with low welding crack sensitivity in this embodiment is 40mm, and the chemical composition and welding crack sensitivity index Pcm are shown in Table 1; its manufacturing method includes EAF smelting + LF refining + controlled rolling and controlled cooling + tempering heat treatment; the specific process control is as follows: (1) EAF smelting: oxygen blowing is used at a relatively low temperature of 1546℃ to dephosphorize and decarburize until the steel is discharged with a P of 0.004% and a C of 0.02%.

[0052] (2) LF refining: Lime and low-boron refining slag are added in batches to make slag, and 630m aluminum wire is fed. Large amounts of argon are used for stirring to carry out deoxidation and desulfurization. At the same time, the electrode is lifted to prevent carbon increase. Low-carbon and low-boron alloys are used for alloying to reduce carbon increase and boron increase.

[0053] (3) VD vacuum treatment: vacuum degree 32Pa, holding time 17min.

[0054] (4) Controlled rolling and controlled cooling: The starting rolling temperature in stage II is 840°C, the maximum pass reduction rate is 26%, and the steel is put into water for rapid cooling after rolling. The final cooling temperature is controlled at 178°C.

[0055] (5) Tempering heat treatment, tempering temperature 518℃, holding time 2.8min / mm, air cooling to room temperature after taking out of the furnace.

[0056] The tensile properties and -50°C transverse impact properties of the steel plate of this embodiment are shown in Table 2. Example 6

[0057] The thickness of the 610MPa grade high-strength steel plate with low welding crack sensitivity in this embodiment is 42mm, and the chemical composition and welding crack sensitivity index Pcm are shown in Table 1; its manufacturing method includes EAF smelting + LF refining + controlled rolling and controlled cooling + tempering heat treatment; the specific process control is as follows: (1) EAF smelting: oxygen blowing is used at a relatively low temperature of 1548℃ to dephosphorize and decarburize until the steel is discharged with a P of 0.002% and a C of 0.03%.

[0058] (2) LF refining: Lime and low-boron refining slag are added in batches to make slag, and 680m aluminum wire is fed. Large amounts of argon are used for stirring to carry out deoxidation and desulfurization. At the same time, the electrode is lifted to prevent carbon increase. Low-carbon and low-boron alloys are used for alloying to reduce carbon increase and boron increase.

[0059] (3) VD vacuum treatment: vacuum degree 38Pa, holding time 16min.

[0060] (4) Controlled rolling and controlled cooling: The starting rolling temperature in stage II is 836°C, the maximum pass reduction rate is 23%, and the steel is put into water for rapid cooling after rolling. The final cooling temperature is controlled at 192°C.

[0061] (5) Tempering heat treatment, tempering temperature 540℃, holding time 2.7min / mm, air cooling to room temperature after taking out of the furnace.

[0062] The tensile properties and -50°C transverse impact properties of the steel plate of this embodiment are shown in Table 2.

[0063] Table 1 Melting composition wt / % of low welding crack sensitivity steel plates in various examples

[0064] The remaining components in Table 1 are Fe and inevitable impurity elements.

[0065] Table 2 Mechanical properties of low welding crack sensitivity steel plates in various examples

[0066] It can be seen from Table 1 and Table 2 that the smelting method of the present invention can achieve the low Pcm smelting composition shown in Table 1. The steel plate obtained by the rolling and heat treatment method of the present invention eliminates the offline quenching process, has a low production cost, and obtains a high-strength steel plate under low Pcm conditions. The steel plate has good low-temperature toughness and meets the domestic demand for steel for hydropower and petrochemicals.

Claims

1. A 610MPa grade high strength steel plate with low welding crack sensitivity, characterized in that: The chemical composition and mass percentage of the steel plate are: C: 0.04%-0.05%, Si: 0.20%-0.35%, Mn: 1.30%-1.40%, P≤0.008%, S≤0.003%, Ni: 0.30%-0.40%, Cr: 0.15%-0.25%, Mo: 0.15%-0.25%, V: 0.020%-0.030%, B≤0.0003%, Cu≤0.04%, and the rest are Fe and unavoidable impurity elements; the welding crack sensitivity index Pcm of the steel plate is 0.15%-0.16%.

2. The low welding crack sensitivity 610MPa grade high strength steel plate according to claim 1, characterized in that: The thickness of the steel plate is 38-50 mm.

3. The low welding crack sensitivity 610MPa grade high strength steel plate according to claim 1, characterized in that: The tensile strength of the steel plate is 630-690 MPa, and the transverse impact energy at -50°C is 200-300 J.

4. The method for manufacturing the 610MPa grade high strength steel plate with low welding crack sensitivity according to claim 1, characterized in that: Including EAF smelting, LF refining, VD vacuum treatment, controlled rolling and controlled cooling, and tempering heat treatment.

5. The method for manufacturing a 610 MPa grade high strength steel plate with low welding crack sensitivity according to claim 4, characterized in that: The EAF smelting adopts oxygen blowing at a relatively low temperature of 1540-1550°C for dephosphorization and decarburization until P≤0.005% and C≤0.03% when steel is tapped.

6. The method for manufacturing a 610MPa grade high strength steel plate with low welding crack sensitivity according to claim 4, characterized in that: The LF refining comprises adding lime and low-boron refined slag in batches to make slag, feeding 600-700 m of aluminum wire, using large amounts of argon gas for stirring, deoxidizing and desulfurizing, lifting electrodes to prevent carbon addition, and using low-carbon and low-boron alloys for alloying.

7. The method for manufacturing a 610 MPa grade high strength steel plate with low welding crack sensitivity according to claim 4, characterized in that: The VD vacuum treatment: vacuum degree 20-40 Pa, holding time 15-20 min.

8. The method for manufacturing a 610 MPa grade high strength steel plate with low welding crack sensitivity according to claim 4, characterized in that: The controlled rolling and controlled cooling: the starting rolling temperature of stage II is ≤850°C, the maximum pass reduction rate is ≥20%, and the steel is put into water for rapid cooling after rolling, and the final cooling temperature is controlled at 150-200°C.

9. The method for manufacturing a 610 MPa grade high strength steel plate with low welding crack sensitivity according to claim 4, characterized in that: The tempering heat treatment comprises: a tempering temperature of 500 to 550° C., a heat preservation time of 2.5 to 3.0 min / mm, and air cooling to room temperature after being taken out of the furnace.

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