A low carbon equivalent high strength and high toughness steel plate and preparation method thereof

Abstract

The invention discloses a low carbon equivalent high strength and high toughness steel plate and a preparation method thereof. The steel plate composition is designed as (by mass percentage): C: 0.15-0.19%, Cr: 0.30-0.60%, Ni: ≤1.4%, Mo: 0.25-0.45%, Mn: 0.60-0.90%, Si: ≤0.30%, V: 0.01-0.03%, Nb: 0.008-0.015%, Ti: 0.003-0.005%, Cu: ≤0.03%, P: ≤0.02%, S: ≤0.008%, and the rest is Fe and inevitable impurities. The rolled steel plate is austenitized, subjected to electric pulse treatment, and cooled to obtain the steel plate. The invention produces a low-carbon equivalent high-strength and high-toughness steel plate with a tensile strength of ≥1400MPa, an elongation of ≥12.5%, and an impact toughness of ≥50J at -60°C. The equipment is simple, the processing is efficient, and the energy consumption is low.

Description

Technical Field

[0001] The invention relates to a low-carbon equivalent high-strength and high-toughness steel plate and a preparation method thereof, belonging to the technical field of metal heat treatment processes. Background Art

[0002] With the rise of large-scale and super-large projects in various fields of the country, construction machinery and equipment are gradually developing in the direction of "high-end, high-tech content, high added value and large tonnage", which puts forward higher requirements for high-strength steel materials for construction machinery. In recent years, my country has successively developed 690MPa, 890MPa, 960MPa, and 1100MPa grade hot-rolled steel plates for construction machinery to meet the needs of medium and large construction machinery equipment of domestic engineering machinery benchmarking enterprises. However, the high-strength and high-toughness steel plates above 1300MPa for heavy machinery still have a gap with the world's advanced production level, and still rely on imported brands, such as the StrenX1300 series quenched and tempered ultra-high strength steel developed by SSAB of Sweden. In order to solve the "neck-stuck" problem of localization of high-toughness ultra-high strength steel plates above 1300MPa, meet the domestic market's needs for such ultra-high strength steel plates, and fill the application gap of 1300MPa grade ultra-high strength steel, the research and development of related technologies is imperative.

[0003] Second-phase particle precipitation strengthening is an important strengthening method for strengthening and toughening low-carbon equivalent high-strength steel plates. The second-phase particles hinder the deformation process such as dislocation movement and twinning and refine the grains, which can take into account both the strength and toughness of the steel. By adding a certain amount of C, Mn, Ni, Nb, V, Ti, Cr, Mo and other elements, dispersed carbide particles are precipitated in the matrix to achieve the purpose of fine grain strengthening and precipitation strengthening. However, in order to ensure the welding performance of the steel plate, the design requirements of low carbon equivalent are required, and it is difficult to generate a sufficient number and density of second-phase particles to achieve a good strengthening effect. For this reason, how to promote the dispersion and precipitation of carbide particles and improve the strength of the steel plate under the premise of low carbon equivalent design has become a key difficulty in the development of such products. CN111996441A discloses a method for producing a high-toughness TiC reinforced martensitic steel plate, with a carbon equivalent CEV≤0.65%. The quenching + tempering heat treatment process is adopted, and the tensile strength of the 20mm thick steel plate can reach 1305MPa, and the elongation reaches 11.0%, but the impact energy at -40°C is only 28J, which is a certain gap from the requirements of high strength and high toughness, and the quenching and tempering heat treatment efficiency is low and the energy consumption is large. CN113388774A discloses a method for manufacturing a hot-rolled air-cooled bainitic high-toughness and high-strength steel plate with a tensile strength ≥1300MPa, which eliminates the energy consumption caused by the quenching and tempering treatment, and improves the defects of poor plate shape and inappropriate shaping after the quenching and tempering treatment, but the medium carbon component design adopted makes the carbon equivalent CEV higher than 0.70%, which is a certain gap from the lower carbon equivalent (CEV≤0.67%) of the world's advanced level. Therefore, a method and technology that can fully tap the performance potential of steel and improve its strength and toughness is needed. Summary of the invention

[0004] Purpose of the invention: The first purpose of the present invention is to provide a low-carbon equivalent high-strength and high-toughness steel plate. The second purpose of the present invention is to provide a method for preparing a low-carbon equivalent high-strength and high-toughness steel plate.

[0005] Technical solution: A low carbon equivalent, high strength and high toughness steel plate of the present invention comprises the following elements (in terms of mass percentage): C: 0.15-0.19%, Cr: 0.30-0.60%, Ni: ≤1.4%, Mo: 0.25-0.45%, Mn: 0.60-0.90%, Si: ≤0.30%, V: 0.01-0.03%, Nb: 0.008-0.015%, Ti: 0.003-0.005%, Al: 0.04-0.08%, Cu: ≤0.03%, B: 0.0010-0.0040%, P: ≤0.02%, S: ≤0.008%, and the rest are Fe and unavoidable impurity elements.

[0006] The method for preparing the low carbon equivalent high strength and high toughness steel plate of the present invention comprises the following steps:

[0007] (1) austenitizing the rolled low-carbon steel sheet and water quenching to obtain a steel sheet with a high-strength martensitic structure;

[0008] (2) subjecting the steel plate obtained in step (1) to electric pulse heat treatment;

[0009] (3) The steel plate subjected to the electric pulse heat treatment in step (2) is placed in air for cooling to obtain a low carbon equivalent high strength and high toughness steel plate.

[0010] Furthermore, in step (1), the carbon equivalent CEV of the low carbon steel plate is ≤0.65%.

[0011] Furthermore, in step (1), the temperature of the austenitizing treatment is 840-900° C., and the austenitizing holding time is 1-1.5 h.

[0012] Furthermore, in step (1), the tensile strength of the high-strength martensitic steel plate is 1400-1450 MPa.

[0013] Furthermore, in step (2), the current density of the electric pulse heat treatment is 19 to 23 A / mm 2 The current action time of the electric pulse heat treatment is 10 to 30 seconds, and the peak temperature of the electric pulse heat treatment is 130 to 230°C.

[0014] Furthermore, in step (2), the pulse input mode of the electric pulse heat treatment is a unidirectional pulse.

[0015] Furthermore, in step (2), the duty cycle of the pulse power supply of the electric pulse heat treatment is 50%, and the pulse frequency of the electric pulse heat treatment is 0 to 10 Hz.

[0016] Furthermore, in step (2), the equipment used for the electric pulse heat treatment includes a programmable DC power supply, a transformer, a clamping device, a temperature detection device, a control system and a connecting device.

[0017] Principle of the invention: The electric pulse treatment adopted in the present invention has thermal effect and non-thermal effect, wherein the thermal effect refers to the Joule heating effect, where the electric energy is converted into Joule heat, which directly causes the temperature to rise, while the non-thermal effect includes electron wind force and electromigration effect. On the one hand, the electron wind force can promote the movement of internal dislocations, change the dislocation configuration, and restore the mobility of the originally entangled and pinned dislocations, thereby increasing the number of movable dislocations and further improving the plasticity of the steel plate. On the other hand, under the action of electric pulses, the energy carried by the pulse current can be directly transferred to electrons or atoms, causing atomic movement in a short time, increasing the atomic migration rate, promoting the precipitation and dispersed distribution of fine carbides, and enhancing the interaction between dislocations in the steel plate and nano-scale precipitation phases, so that the dislocation movement is hindered, thereby maintaining a certain strength, so that the treated steel plate has high strength while maintaining good plasticity.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0019] (1) The present invention adopts traditional quenching + electric pulse tempering treatment, which has the advantages of simple production equipment and energy-saving process. In addition, the electric pulse treatment time is short and can be completed within 10 to 30 seconds. The treatment is efficient and has low energy loss.

[0020] (2) The present invention uses electric pulse treatment to promote the precipitation of fine carbides. The carbides are nanometer-sized and dispersed among the martensite and form a bead-like distribution at the grain boundaries, which is beneficial for the interaction between dislocations and precipitated phases, thereby maintaining the strength without significant reduction during tempering.

[0021] (3) The present invention uses a series of effects produced by electric pulse treatment, which is beneficial to promoting internal dislocation movement and changing dislocation configuration, thereby improving the plasticity of the steel plate.

[0022] (4) The present invention adopts traditional quenching treatment combined with electric pulse tempering treatment to produce ultra-high strength low carbon equivalent steel plate with production tensile strength ≥1400MPa, elongation ≥12.5%, strength-ductility product of up to 17.5GPa% and impact toughness ≥50J at -60℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a SEM image of the low carbon equivalent high strength and high toughness steel plate prepared in Example 1;

[0024] Figure 2 TEM and HRTEM images of the low carbon equivalent high strength and high toughness steel plate prepared in Example 1;

[0025] Figure 3 is a SEM image of the test steel plate prepared in Comparative Example 1. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0027] The production method of the low carbon equivalent high strength and high toughness steel plate of the present invention comprises the following steps:

[0028] (1) The low carbon steel plate after rolling treatment is austenitized in a furnace at a temperature of 840-900°C for 1-1.5 hours. The treated steel plate is then placed in a water tank and rapidly cooled to room temperature to complete quenching, thereby obtaining a steel plate with an ultra-high strength martensitic structure. The chemical composition of the steel plate is shown in Table 1.

[0029] (2) clamping the two ends of the steel plate obtained in step (1) on electrodes connected to an electric pulse device so that a high-energy pulse current flows through the steel plate, thereby generating thermal and non-thermal effects;

[0030] (3) The parameters of the electric pulse device in step (2) are set as follows: the pulse input mode is a unidirectional high-energy pulse, the duty cycle of the pulse power supply is 50%, and the current density is controlled at 19-23 A / mm 2 Within the range, the current size is calculated according to the thickness of the steel plate, the pulse frequency is controlled at 0-10Hz, and the electric pulse treatment time is 10-30s;

[0031] (4) Cooling the steel plate after the electric pulse treatment in step (3) in air to obtain a low carbon equivalent high strength and high toughness steel plate.

[0032] Among them, the carbon equivalent of low carbon equivalent high strength and high toughness steel plate CEV≤0.65%, tensile strength>1400MPa, elongation>12.5%, strength-plasticity product can reach more than 17.5GPa%, and impact toughness at -60℃≥50J.

[0033] The electric pulse processing uses a pulse processing device composed of a high-power programmable DC power supply, a transformer, a clamping device, a temperature measuring instrument, a control system and a connecting device.

[0034] Table 1 Chemical composition of high strength steel plate (wt%)

[0035] C Ni Mn Cr Mo Si V Nb Al Cu 0.179 1.30 0.786 0.474 0.371 0.207 0.0159 0.0109 0.0669 0.0217 Zn Pb Sn Co Te Ti B P S Fe 0.0105 0.0086 0.0076 0.0072 0.0049 0.0038 0.0021 0.0172 0.0074 96.5

[0036] As can be seen from Table 1, the designed composition of the steel plate is low carbon and low alloy, and its carbon equivalent CEV is calculated using the formula CEV=[C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15]×100%, which is 0.57%, which is a low carbon equivalent hot-rolled steel plate.

[0037] Embodiment 1:

[0038] According to the above method, a low carbon equivalent high strength and high toughness steel plate is prepared, specifically: the rolled steel plate (the chemical composition of the steel plate is shown in Table 1) is austenitized in a furnace, the austenitization temperature is 850°C, the holding time is 1h, and then the treated steel plate is placed in a water tank, and quickly cooled to room temperature to complete quenching. The quenched high strength steel plate is subjected to electric pulse tempering treatment, the process parameters of the electric pulse treatment are shown in Table 2, and the peak temperature of the electric pulse treatment reaches 200°C.

[0039] The low carbon equivalent high strength and high toughness steel plate obtained in this embodiment was subjected to scanning electron microscope (SEM) analysis, and the results are as follows: Figure 1 shown. Figure 1 is a SEM image of the low carbon equivalent high strength and high toughness steel plate prepared in Example 1. Figure 1 It can be seen that the original austenite grains after austenitizing treatment at this temperature are relatively small, only at the level of several microns. The structure after electric pulse treatment is composed of lath martensite and dispersed carbides distributed between the laths, achieving the goal of large-area carbide precipitation under low carbon equivalent conditions, and the precipitation strengthening effect is obvious.

[0040] The low carbon equivalent high strength and high toughness steel plate obtained in this embodiment was analyzed by transmission electron microscopy (TEM) and high magnification transmission electron microscopy (HRTEM). The results are as follows: Figure 2 shown. Figure 2 TEM and HRTEM images of the low carbon equivalent high strength and high toughness steel plate prepared in Example 1, wherein a is a TEM image and b is a HRTEM image. Figure 2 It can be seen that the martensite after electric pulse treatment maintains a slender, narrow-spaced lath morphology, which can provide higher matrix strength, and there are carbides precipitated in a bead-like arrangement at the interface of the lath martensite, which can reduce stress concentration, thereby improving plasticity and achieving the mechanical properties requirements of high strength and high toughness.

[0041] The performance test of the low carbon equivalent high strength and high toughness steel plate obtained in this embodiment shows that the tensile strength of the low carbon equivalent high strength and high toughness steel plate is 1452 MPa, the elongation is 14.0%, and the low temperature (-60°C) impact toughness is 58 J. The comprehensive mechanical properties comparison can be seen in Table 3.

[0042] Example 2

[0043] The rolled steel plate (chemical composition of the steel plate is shown in Table 1) is austenitized in a furnace at 850°C for 1 hour. The treated steel plate is then placed in a water tank and quickly cooled to room temperature to complete quenching. The quenched high-strength steel plate is subjected to electric pulse tempering treatment. The process parameters of the electric pulse treatment are shown in Table 2. The peak temperature of the electric pulse treatment reaches 211°C. The mechanical properties test shows that its tensile strength is 1446MPa, the elongation is 13.5%, the strength-plasticity product is 19.529GPa%, and the -60°C impact toughness is 55J. The comprehensive mechanical properties comparison can be seen in Table 3.

[0044] Example 3

[0045] The rolled steel plate (chemical composition of the steel plate is shown in Table 1) is austenitized in a furnace at 850°C for 1 hour. The treated steel plate is then placed in a water tank and quickly cooled to room temperature to complete quenching. The quenched high-strength steel plate is subjected to electric pulse tempering treatment. The process parameters of the electric pulse treatment are shown in Table 2. The peak temperature of the electric pulse treatment reaches 209°C. The mechanical properties test shows that its tensile strength is 1410MPa, the elongation is 12.5%, the strength-plasticity product is 17.625GPa%, and the -60°C impact toughness is 52J. The comprehensive mechanical properties comparison can be seen in Table 3.

[0046] Example 4

[0047] The rolled steel plate (chemical composition of the steel plate is shown in Table 1) is austenitized in a furnace at 850°C for 1 hour. The treated steel plate is then placed in a water tank and quickly cooled to room temperature to complete quenching. The quenched high-strength steel plate is subjected to electric pulse tempering treatment. The process parameters of the electric pulse treatment are shown in Table 2. The peak temperature of the electric pulse treatment reaches 340°C. The mechanical properties test shows that the tensile strength is 1160MPa, the elongation is 12.4%, and the strength-ductility product is 14.386GPa%. The comprehensive mechanical properties comparison can be seen in Table 3.

[0048] Example 5

[0049] The rolled steel plate (chemical composition of the steel plate is shown in Table 1) is austenitized in a furnace at 850°C for 1 hour. The treated steel plate is then placed in a water tank and quickly cooled to room temperature to complete quenching. The quenched high-strength steel plate is subjected to electric pulse tempering treatment. The process parameters of the electric pulse treatment are shown in Table 2. The peak temperature of the electric pulse treatment reaches 120°C. The mechanical properties test shows that the tensile strength is 1440MPa, the elongation is 5.4%, and the strength-ductility product is 7.776GPa%. The comprehensive mechanical properties comparison can be seen in Table 3.

[0050] Table 2 Example electric pulse treatment process parameters

[0051]

[0052] Comparative Example 1

[0053] In order to reflect the difference from the traditional heat treatment process, a high-strength steel plate with the same rolling process and chemical composition as Example 1 is used, and the same austenitizing and quenching treatment is carried out, and tempering treatment is carried out in the furnace, and the tempering temperature is controlled to be consistent with the peak temperature of the electric pulse in Example 1. The specific process flow is: the steel plate after rolling treatment is austenitized in the furnace, the austenitizing temperature is 850°C, and the holding time is 1h. The treated steel plate is then placed in a water tank and quickly cooled to room temperature to complete the quenching. The high-strength steel plate obtained after quenching is tempered in the furnace. The tempering process adopts a low-temperature treatment of 200°C and a holding time of 1h. The treated steel plate is then placed in the air to cool to room temperature.

[0054] The steel plate obtained in this comparative example was subjected to scanning electron microscopy analysis, and the results are as follows: Figure 3 shown. Figure 3 is a SEM image of the test steel plate prepared in Comparative Example 1. Figure 3 It can be seen that the precipitation phase in the steel plate after traditional tempering treatment is not as obvious as that after electric pulse treatment, and there is a certain difference in the thickness of the lath, so the strength is slightly reduced compared with the quenched state. In addition, due to the low content of the tough second phase, its impact toughness is low.

[0055] The steel plate obtained in this comparative example was subjected to performance testing. The tensile strength of the steel plate was 1417 MPa, the elongation was 11.7%, the low temperature (-60°C) impact toughness was 40 J, and the comprehensive mechanical properties comparison can be seen in Table 3.

[0056] Table 3 Comparison of treatment process and comprehensive mechanical properties of Example 3 and Comparative Example 1

[0057] Heat treatment process Tensile strength(MPa) Elongation(%) Strength and plasticity product (GPa%) Impact toughness(J) Comparative Example 1 1417 11.7 16.579 40 Example 1 1452 14.0 20.328 58 Example 2 1446 13.5 19.529 55 Example 3 1410 12.5 17.625 52 Example 4 1160 12.4 14.386 Untested Example 5 1440 5.4 7.776 Untested

[0058] As shown in Table 3, the tensile strength of the high-strength steel plate treated by electric pulse tempering in Example 1 of the present invention reaches 1452MPa, the elongation reaches 14.0%, and the low-temperature (-60℃) impact toughness is excellent. Compared with the high-strength steel plate treated by conventional tempering heat treatment, the tensile strength of Example 1 is enhanced by 35MPa (2.5%), and the elongation is increased by 2.3% (19.7%). This can be attributed to the high-energy pulse passing through the steel plate, promoting atomic migration in a short time, changing the distribution morphology of carbides in the steel plate, and the emergence of bead-like precipitation phases distributed between the laths, which can pin dislocations and reduce stress concentration, thereby maintaining strength without reducing and improving plasticity. Examples 4 and 5 of the present invention were tested using current densities exceeding and falling below the specified range, respectively. From the results, it can be seen that when the current density is too high, the strength of the steel plate will drop significantly, and when the current density is too small, the plasticity of the steel plate is not significantly improved, reflecting that the electric pulse treatment within the specified range can achieve the expected effect. The steel plate treated by high-energy pulses in the present invention achieves the effects of high strength and high toughness, and provides a feasible solution for 1300MPa-grade high-strength, high-toughness, low-carbon equivalent hot-rolled steel plates for engineering equipment.

Claims

1. A low carbon equivalent high strength and high toughness steel plate, characterized in that: The low carbon equivalent high strength and high toughness steel plate includes the following elements in percentage by mass: C: 0.15-0.19%, Cr: 0.30-0.60%, Ni: ≤1.4%, Mo: 0.25-0.45%, Mn: 0.60-0.90%, Si: ≤0.30%, V: 0.01-0.03%, Nb: 0.008-0.015%, Ti: 0.003-0.005%, Al: 0.04-0.08%, Cu: ≤0.03%, B: 0.0010-0.0040%, P: ≤0.02%, S: ≤0.008%, and the rest are Fe and unavoidable impurity elements; The method for preparing the low carbon equivalent high strength and high toughness steel plate comprises the following steps: (1) austenitizing the rolled low carbon steel plate and water quenching it to obtain a steel plate with a high strength martensitic structure; (2) The steel plate obtained in step (1) is subjected to electric pulse heat treatment, and the current density of the electric pulse heat treatment is 19~23 A / mm 2 , the current action time of the electric pulse heat treatment is 10 ~ 30 s, the peak temperature of the electric pulse heat treatment is 130 ~ 230 ℃, the duty cycle of the pulse power supply of the electric pulse heat treatment is 50%, the pulse frequency of the electric pulse heat treatment is 0 ~ 10 Hz, and the pulse input mode of the electric pulse heat treatment is a unidirectional pulse; (3) The steel plate subjected to the electric pulse heat treatment in step (2) is placed in air for cooling to obtain a low carbon equivalent high strength and high toughness steel plate.

2. The method for preparing the low carbon equivalent high strength and high toughness steel plate according to claim 1, characterized in that: The following steps are involved: (1) austenitizing the rolled low carbon steel plate and water quenching it to obtain a steel plate with a high strength martensitic structure; (2) The steel plate obtained in step (1) is subjected to electric pulse heat treatment, and the current density of the electric pulse heat treatment is 19~23 A / mm 2 , the current action time of the electric pulse heat treatment is 10 ~ 30 s, the peak temperature of the electric pulse heat treatment is 130 ~ 230 ℃, the duty cycle of the pulse power supply of the electric pulse heat treatment is 50%, the pulse frequency of the electric pulse heat treatment is 0 ~ 10 Hz, and the pulse input mode of the electric pulse heat treatment is a unidirectional pulse; (3) The steel plate subjected to the electric pulse heat treatment in step (2) is placed in air for cooling to obtain a low carbon equivalent high strength and high toughness steel plate.

3. The preparation method according to claim 2, characterized in that: In step (1), the carbon equivalent CEV of the low carbon steel plate is ≤0.65%.

4. The preparation method according to claim 2, characterized in that: In step (1), the temperature of the austenitizing treatment is 840 to 900°C, and the austenitizing holding time is 1 to 1.5 h.

5. The preparation method according to claim 2, characterized in that: In step (1), the tensile strength of the high-strength martensitic steel plate is 1400-1450 MPa.

6. The preparation method according to claim 2, characterized in that: In step (2), the equipment used for the electric pulse heat treatment includes a programmable DC power supply, a transformer, a clamping device, a temperature detection device, a control system and a connecting device.

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