CN111304549B - High-strength high-toughness Cu-containing low-alloy high-strength steel and heat treatment method thereof - Google Patents
High-strength high-toughness Cu-containing low-alloy high-strength steel and heat treatment method thereof Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 23
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Abstract
The invention relates to the field of low-alloy high-strength steel, in particular to high-strength high-toughness Cu-containing low-alloy high-strength steel and a heat treatment method thereof. The Cu-containing low-alloy high-strength steel comprises the following chemical components in percentage by mass: c0.035-0.070%; 3.5 to 4.5 percent of Ni; 0.8-1.2% of Cr; 0.35-0.65% of Mo; 0.25-0.65% of Mn; si < 0.05%; s is less than or equal to 0.010 percent; p is less than or equal to 0.010 percent; 0.025 to 0.055 percent of Nb; 1.0-2.0% of Cu, and the balance of Fe. The heat treatment method comprises quenching and tempering treatment, namely, quenching at 840-920 ℃ to obtain a martensite structure, and then tempering at 400-600 ℃ to obtain a tempered martensite structure. After heat treatment, the requirements of the Cu-containing low-alloy high-strength steel on the comprehensive properties such as strength, elongation, low-temperature impact toughness and the like can be met, the problem that the traditional Cu-containing low-alloy high-strength steel is poor in obdurability matching is solved, and the Cu-containing low-alloy high-strength steel has a good application prospect.
Description
Technical Field
The invention relates to the field of low-alloy high-strength steel, in particular to high-strength high-toughness Cu-containing low-alloy high-strength steel and a heat treatment method thereof.
Background
The low-alloy high-strength steel with low C and Cu content is used as one of the steels for high-end marine equipment, has higher strength, better toughness and excellent weldability, and is widely used for building ships, offshore oil platforms and the like.
Compared with the traditional Fe-Cr-Ni-Mo high-strength steel, the Cu-containing low-alloy high-strength steel (such as HSLA-100 alloy steel) has lower C content, and after tempering treatment, Cu is separated out in the form of nano Cu-rich clusters which are fine in size and are distributed in a dispersing way, so that the precipitation strengthening effect is achieved, and the strength loss caused by low C is made up. And if the Cu-rich clusters are tempered at 450-500 ℃, the number density of the Cu-rich clusters is the maximum, so that the peak strength is obtained, and compared with the quenched state, the yield strength is improved by about 150 MPa. It is worth noting that the impact toughness of the alloy steel is very low, the impact energy at the temperature of minus 20 ℃ is less than 20J, and the matching of the toughness and the toughness is poor. In order to obtain good impact performance, the Cu-containing low-alloy high-strength steel is usually tempered at a higher temperature. After the tempering treatment at 550 ℃, the low-temperature impact toughness is improved, the impact energy at-20 ℃ is about 150J, but the strength is obviously reduced, the yield strength is only about 50MPa higher than the quenched yield strength, the strengthening effect of Cu is obviously weakened, and the toughness matching is not ideal. Therefore, the problem that the existing Cu-containing low-alloy high-strength steel has poor obdurability matching is solved, and the expansion application of the alloy steel is limited. Upon retrieval, there are the following related patent documents relating to low alloy high strength steels, which will be specifically analyzed.
The Chinese invention patent (publication No. CN105177445A) discloses high-toughness 3.5Ni steel, wherein the content of C is 0.04-0.07%, and the steel does not contain Cu. And (3) carrying out on-line quenching treatment after rolling, cooling to below 300 ℃, and carrying out tempering treatment at 570-620 ℃. The impact energy of the alloy steel at-120 ℃ is as high as 227-278J, but the yield strength is low and is only 425-492 MPa, and the toughness matching of the alloy steel is poor. In addition, the alloy steel needs to adopt the rolling processes of rough rolling and finish rolling (both hot rolling), has high requirements on rolling control, larger actual production difficulty and higher production cost.
The Chinese invention patent (publication No. CN104046917A) discloses a Cu-rich cluster-reinforced ultrahigh-strength ferritic steel, the C content is 0.05-0.10%, a tempered martensite structure is obtained after quenching and tempering treatment at 550 ℃ for 2h, high-density and fine-size nano Cu-rich clusters are dispersedly distributed, the yield strength is 1000-1150 MPa, and the elongation is lower than 15%. Meanwhile, the content of alloy elements is high, the content of Cu is up to 2.5%, the content of Mn is up to 1.5%, and in addition, 1.5% of W and 0.25% of V are also contained, so that the production cost is increased. It is worth noting that the patent does not mention the impact performance, however, as can be seen from the alloying element content of the alloy steel, the total alloying element content is higher, wherein the W atom size is large, and the impact energy is not good although the strength can be improved by solid solution in the matrix; v is a strong carbide forming element, and if the content is high, alloy carbides with large quantity and large size are precipitated, so that the strength is improved, but the impact energy is damaged. From this, it is presumed that the alloy steel is inferior in impact toughness and does not have a good toughness matching.
The Chinese invention patent (publication No. CN105177425A) discloses a Cu-containing nano-phase reinforced low alloy steel, which improves the hot rolling capability and hardenability of the steel by adding a certain B element to replace Mo element. After quenching and tempering, the yield strength of the alloy steel reaches 1500MPa, but the elongation and the impact property are not mentioned.
The Chinese invention patent (publication No. CN106636961A) discloses a Cu-containing nano-phase strengthened easy-to-weld steel, which adopts the rolling process of rough rolling and finish rolling (both hot rolling), and then after quenching and tempering treatment at 550 ℃, the yield strength is 1000-1050 MPa, the elongation is more than 17%, and the impact energy at minus 80 ℃ is more than 100J. The alloy steel has better obdurability matching, but the Ni content in the alloy steel is up to 6 percent, and the alloy cost is higher. Meanwhile, the requirement on rolling control is strict, and the actual production difficulty is higher.
The Chinese invention patent (publication No. CN106756612A) discloses a bainite/martensite/austenite high-toughness easily welded ship plate steel, which is directly subjected to online quenching after rolling, and then subjected to two-phase zone quenching and tempering treatment, wherein the tempering treatment temperature is up to 654 ℃. The impact energy of the alloy steel at the temperature of minus 84 ℃ is more than or equal to 150J, the elongation is more than 23 percent, but the yield strength is less than 660MPa, and the obdurability matching is poor. Meanwhile, the higher tempering temperature increases the production cost.
The low-alloy high-strength steel disclosed in the above patent has a problem of poor toughness matching on the one hand; on the other hand, the alloy steel has the problems of high preparation process requirement and high production cost, and has certain limitations. However, the continuous development of '21 st century offshore silk road' puts forward higher requirements on steel materials, and not only high strength is required, but also good low-temperature impact performance is required, namely, the toughness and the toughness are well matched, so that the key for ensuring the safe service of the alloy steel structural material is realized. Analysis of the above patents has revealed that in order to obtain good low temperature impact toughness, Cu-containing low alloy high strength steels are generally tempered at high temperatures, such as: HSLA-100 steels are typically tempered at 550 ℃. Notably, high temperature tempering results in significant strength degradation of the alloy steel. In fact, the reason for the high temperature tempering treatment is: when the alloy steel is tempered at a lower temperature (such as 450 ℃), the impact energy of the alloy steel is low, and the use requirement cannot be met. Aiming at the problem of poor impact power during low-temperature tempering of Cu-containing low-alloy high-strength steel, the method for regulating and controlling the Mn element is adopted to achieve the purpose of changing Cu precipitation behavior, good toughness matching can be obtained after proper heat treatment, and the low-temperature high-strength steel has high strength, high low-temperature impact toughness and good shaping and breaks through the bottleneck problem of low impact power during low-temperature tempering.
Disclosure of Invention
The invention aims to provide high-strength high-toughness Cu-containing low-alloy high-strength steel and a heat treatment method thereof, alloy steel with good obdurability matching is obtained by regulating and controlling the Mn content and optimizing the heat treatment system, the problem that the existing Cu-containing low-alloy high-strength steel is poor in obdurability matching is solved, and the safe use requirement of the high-strength steel in a special environment can be met.
The technical scheme of the invention is as follows:
the Cu-containing low-alloy high-strength steel with high strength and high toughness comprises the following chemical components in percentage by mass: c0.035-0.070%; 3.5 to 4.5 percent of Ni; 0.8-1.2% of Cr; 0.35-0.65% of Mo; 0.25-0.65% of Mn; si < 0.05%; s is less than or equal to 0.010 percent; p is less than or equal to 0.010 percent; 0.025 to 0.055 percent of Nb; 1.0-2.0% of Cu, and the balance of Fe.
The high-strength high-toughness Cu-containing low-alloy high-strength steel comprises the following chemical components in percentage by mass: c0.035-0.070%; 3.5 to 4.5 percent of Ni; 0.8-1.2% of Cr; 0.35-0.65% of Mo; 0.35-0.60% of Mn; si < 0.03%; s is less than or equal to 0.010 percent; p is less than or equal to 0.010 percent; 0.025 to 0.055 percent of Nb; 1.0-2.0% of Cu, and the balance of Fe.
The heat treatment method of the high-strength high-toughness Cu-containing low-alloy high-strength steel comprises quenching and tempering treatment, and comprises the following specific steps:
(1) quenching the steel, wherein the quenching temperature is 840-920 ℃, and water quenching is carried out to room temperature after heat preservation for 30-120 min;
(2) tempering the steel at 400-600 ℃, keeping the temperature for 0.5-100 h, and cooling to room temperature.
The heat treatment method of the high-strength high-toughness Cu-containing low-alloy high-strength steel is preferably used, in the step (2), the tempering temperature is 425-475 ℃, and the heat preservation time is 30-100 hours.
The heat treatment method of the high-strength high-toughness Cu-containing low-alloy high-strength steel is preferably characterized in that in the step (2), the tempering temperature is 525-575 ℃, and the heat preservation time is 0.5-10 h.
According to the heat treatment method of the high-strength high-toughness Cu-containing low-alloy high-strength steel, after the Cu-containing low-alloy high-strength steel is quenched and tempered, the yield strength of alloy steel is not less than 950MPa, the elongation is not less than 16%, and the impact energy at-50 ℃ is not less than 150J.
The design idea of the invention is as follows:
the starting point of the method is to improve the toughness matching of the alloy steel by regulating and controlling the precipitation behavior of the nano Cu-rich clusters. The concrete measures are as follows: the precipitation capability of the Cu-rich clusters is reduced by reducing the content of Mn element. The Mn element can reduce the interface energy of the Cu-rich cluster and the matrix, reduce the critical nucleation work of the Cu-rich cluster, and further promote the nucleation and precipitation of the Cu-rich cluster, so that the reduction of the content of the Mn element can weaken the precipitation capability of the Cu-rich cluster, reduce the local stress concentration and be beneficial to the impact performance. In addition, a tempered martensite structure is obtained by matching with proper quenching and tempering treatment at a lower temperature, and nano Cu-rich clusters with small sizes are dispersed and distributed so as to ensure the strength of the alloy steel. The high impact toughness of the alloy steel is ensured while the high strength is obtained.
The precipitation behavior of the Cu-rich clusters in the low alloy steel is closely related to the content of elements such as Mn and the like and the tempering treatment process and the like. The Mn element can promote the precipitation of Cu-rich clusters, increase the stability of austenite, delay martensite phase transformation, facilitate the refinement of original austenite grains and improve the toughness of alloy steel. The Mn content is low, so that the precipitation of Cu-rich clusters is not facilitated, and the strength of the alloy steel is further influenced; the Mn content is too high, Cu-rich clusters are separated out violently, and meanwhile, residual austenite is easy to generate, which is not beneficial to impact performance. Therefore, the Mn content is preferably 0.45 to 0.55 wt% in the present invention. In addition, the precipitation behavior of the Cu-rich clusters is also related to a tempering system, the tempering temperature is low, the tempering time is short, the full precipitation of the Cu-rich clusters is not facilitated, and the strengthening effect cannot be achieved; the tempering temperature is higher, the tempering time is longer, the precipitated Cu-rich clusters grow up and coarsen, and the strengthening capability is reduced. In order to realize good obdurability matching, the preferred tempering system in the invention is to keep the temperature at 425-475 ℃ for 30-100 h, and then to keep the temperature at 525-575 ℃ for 0.5-10 h, so that good obdurability matching can be obtained.
The invention has the advantages and beneficial effects that:
1. the Cu-containing low-alloy high-strength steel has the advantages that the component design is easy to implement, the precipitation behavior of Cu-rich clusters is adjusted only by optimizing the content of Mn elements, and the good toughness matching of alloy steel is realized.
2. The invention belongs to low alloy steel, which has similar components with HSLA-100 steel, and the heat treatment process is still the traditional quenching and tempering treatment and is easy to implement. Compared with HSLA-100 steel, although the tempering heat preservation time is longer, the tempering temperature is lower, so the cost is not increased.
3. Compared with HSLA-100 steel, the Cu-containing low-alloy high-strength steel has higher strength and higher impact toughness. After the Cu-containing low-alloy high-strength steel is tempered at a lower tempering temperature of 450 ℃ for 50 hours, the yield strength reaches over 1000MPa, the elongation is 20 percent, and the impact energy at the temperature of minus 50 ℃ is 162J. Therefore, the bottleneck of poor impact power during low-temperature tempering of the Cu-containing low-alloy high-strength steel is broken through, the impact performance of the alloy steel is greatly improved on the premise of ensuring the strength, and meanwhile, the alloy steel is enabled to have better toughness matching.
Drawings
Fig. 1 is a graph comparing the distribution of Cu cluster-rich three-position atom probe (3DAP) analysis (5 at.% iso-concentration surface) of an alloy steel (component one) and a Cu-containing low alloy high strength steel (component two) of the present invention after tempering at 450 ℃ for 2 hours.
Detailed Description
In the specific implementation process, the invention achieves the purpose of controlling the precipitation behavior of the nano Cu-rich clusters by adjusting the content of the Mn element. Through a proper heat treatment process, a tempered martensite structure is obtained, and a large amount of Cu-rich clusters with small sizes are dispersed and distributed, so that the alloy steel has good toughness matching. The heat treatment method comprises the following steps: first, quenching treatment is performed. And (3) carrying out water quenching on the Cu-containing low-alloy high-strength steel to room temperature after heat preservation for 30-120 min at 840-920 ℃ to obtain a lath martensite structure. At this time, the Cu element is dissolved in the matrix. ② tempering treatment. And (3) placing the quenched alloy steel at 400-600 ℃, preserving heat for 0.5-100 h, and then cooling to room temperature by water to obtain a tempered martensite structure. During the tempering process, Cu element dissolved in the matrix is precipitated in the form of Cu-rich clusters, so that the strengthening effect is achieved.
The following examples are given to further illustrate the present invention, but not to limit the present invention, and modifications made to the present invention under the premise of the inventive concept are within the scope of the present invention.
The Cu-containing low-alloy high-strength steel ingot smelted in the embodiment of the invention is forged at about 1200 ℃ to ensure that the finish forging temperature is not lower than 800 ℃, forged blank with the thickness of 35mm and the width of 150mm is forged, and the forged blank is cooled to room temperature by air. Then hot rolling is carried out, the hot rolling temperature is 1150 ℃, the thickness is about 12mm from 35mm, and the air cooling is carried out to the room temperature. Finally, quenching and tempering heat treatment is carried out, the quenching temperature is 880 ℃, and water quenching is carried out to room temperature after heat preservation for 40 min; the tempering temperature is 400-600 ℃, the temperature is kept for 2-100 h, and the water is cooled to the room temperature.
As shown in table 1, the examples contain the components of Cu low alloy high strength steel.
TABLE 1 chemical composition (in mass%) of Cu-containing low-alloy high-strength steel in examples of the present invention
| C | Ni | Mn | Mo | Cr | Si | S | P | Nb | Cu | Fe | |
| Component A | 0.041 | 4.01 | 1.00 | 0.56 | 0.95 | 0.22 | 0.005 | 0.007 | 0.050 | 1.40 | Bal. |
| Component two | 0.060 | 4.10 | 0.47 | 0.53 | 1.02 | 0.01 | 0.002 | 0.002 | 0.043 | 1.44 | Bal. |
| Ingredient III | 0.05 | 4.08 | 0.03 | 0.53 | 1.02 | 0.01 | 0.002 | 0.002 | 0.046 | 1.43 | Bal. |
A total of 27 experiments were conducted on the steels of the examples, and the tempering system and mechanical properties of each example are shown in Table 2. Performing a tensile test by using a standard rod-shaped tensile sample of M10, and performing the tensile test at room temperature according to GB/T228.1-2010 part 1 room temperature test method of metal material tensile test; the impact performance is measured by adopting a V-shaped notched Charpy impact sample, the experimental temperature is-50 ℃, and the method is carried out according to GB/T229-2007 method for testing the impact of the Charpy pendulum in the summer of the metal material. As shown in Table 2, the composition-alloy steel contains 1% of Mn, and after tempering at different temperatures (<600 ℃) for different times, although the yield strength is 990-1050 MPa, the elongation can reach about 20%, and the impact energy at-50 ℃ is not more than 20J. Although the impact energy can be obviously improved by increasing the tempering temperature to 600 ℃, the strength of the alloy steel is obviously reduced, and the toughness matching of the alloy steel is not ideal. When the Mn element is reduced to 0.47 wt% (i.e. the second component), the alloy steel is tempered at 450 ℃ for 10-120 h, the yield strength is greater than 1010MPa, the elongation can reach 20%, the impact energy at-50 ℃ is greater than 150J, and the alloy steel has good toughness matching. When the component two alloy steel adopts shorter tempering time, Cu-rich clusters are insufficiently separated out; and when the tempering time is longer, the Cu-rich clusters are coarsened seriously, which is not favorable for the obdurability matching of the alloy steel. When the tempering temperature is increased to 550 ℃, the obdurability of the component two-alloy steel is also better matched. When the Mn content is continuously reduced to 0.03% (namely the component III), the alloy steel is tempered at 450 ℃ for 10-120 h, the yield strength is 970-1020 MPa, the elongation is about 20%, but the impact energy at-50 ℃ is not more than 80J, and the toughness matching of the alloy steel is poor. It can be seen that the Mn content is only in a proper range, and the alloy steel can obtain good toughness matching after tempering treatment. As shown in fig. 1, three-position atom probe (3DAP) analysis of Cu-rich clusters in the Cu-containing low-alloy high-strength steel of the first component and the second component after tempering treatment at 450 ℃ for 2 hours revealed that the number density of Cu-rich clusters precipitated in the Cu-containing low-alloy high-strength steel of the second component decreased and the size decreased. Therefore, the content of Mn element is reduced, the effect of slowing the precipitation of Cu-rich clusters is achieved, and good toughness matching is finally obtained by combining a proper heat treatment process.
TABLE 2 mechanical properties of Cu-containing low-alloy high-strength steel according to the examples of the present invention
In conclusion, on one hand, from the perspective of optimizing the component proportion of the alloy, the content of the Mn element is properly reduced, the precipitation of Cu-rich clusters is slowed down, and the good impact performance is ensured. On the other hand, from the perspective of optimizing the tempering process, the alloy steel is tempered for a long time at low temperature or a short time at high temperature, a proper amount of Cu-rich clusters are precipitated, and the strength of the alloy steel is ensured. According to the specific embodiment, the component two-alloy steel is subjected to heat preservation for 30-100 h at 425-475 ℃ or tempering heat preservation for 0.5-10 h at 525-575 ℃, so that good obdurability matching is realized. After heat treatment, the requirements of the Cu-containing low-alloy high-strength steel on the comprehensive properties such as strength, elongation, low-temperature impact toughness and the like can be met, the problem that the traditional Cu-containing low-alloy high-strength steel is poor in obdurability matching is solved, and the Cu-containing low-alloy high-strength steel has a good application prospect.
Claims (4)
1. The Cu-containing low-alloy high-strength steel with high strength and toughness is characterized by comprising the following chemical components in percentage by mass: 0.060% of C; 4.10 percent of Ni; 1.02 percent of Cr; mo 0.53%; 0.47 percent of Mn; 0.01 percent of Si; 0.002% of S; 0.002% of P; nb 0.043%; 1.44 percent of Cu and the balance of Fe;
the heat treatment method of the Cu-containing low-alloy high-strength steel comprises quenching and tempering treatment, and comprises the following specific steps:
(1) quenching the steel, wherein the quenching temperature is 840-920 ℃, and water quenching is carried out to room temperature after heat preservation for 30-120 min;
(2) tempering the steel at 400-600 ℃, keeping the temperature for 0.5-100 h, and cooling to room temperature.
2. The high-strength high-toughness Cu-containing low-alloy high-strength steel as claimed in claim 1, wherein in the step (2), the tempering temperature is 425-475 ℃, and the holding time is 30-100 h.
3. The high-strength high-toughness Cu-containing low-alloy high-strength steel as claimed in claim 1, wherein in the step (2), the tempering temperature is 525-575 ℃ and the holding time is 0.5-10 h.
4. The high-strength high-toughness Cu-containing low-alloy high-strength steel as claimed in claim 1, wherein after quenching and tempering, the yield strength of the alloy steel is not less than 950MPa, the elongation is not less than 16%, and the impact energy at-50 ℃ is not less than 150J.
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