KR20200060414A - High-strength marine steel with excellent low-temperature toughness and its one-stage multi-stage heat treatment process - Google Patents

Abstract

It provides high-strength marine steel with excellent low-temperature toughness and a single-stage multi-stage heat treatment process, and the chemical composition (mass percentage) of the steel is C 0.12-0.15%, Si 0.20-0.30%, Mn 1.40-1.70%, Ni 0.12-0.15% , Cr 0.16-0.25%, Mo 0.08-0.12%, Nb 0.020-0.030%, Ti 0.012-0.018%, V≤0.02%, P≤0.015%, S≤0.002%, B 0.0020-0.0030%, and residual Fe and It is an inevitable impurity. By combining various quenching and tempering processes, it is possible to produce high-strength, maximum-thickness 50mm marine steel sheets that have excellent low-temperature toughness and meet E460 ~ E550 strength grades, which have low alloy cost and wide process adaptability.

Description

High-strength marine steel with excellent low-temperature toughness and its one-stage multi-stage heat treatment process

The present invention belongs to the field of metallurgy technology and relates to a ship steel and heat treatment process thereof, and more particularly, to a high-strength ship steel excellent in low temperature toughness and a one-steel multi-grade heat treatment process.

As the scientific and technological and economic globalization progresses into the 21st century, the marine resource development and marine transportation industries are getting more and more attention. In the shipbuilding industry, the global market share of Chinese shipbuilding completed in 2010 was 41.9%, the world market share of new orders was 48.5%, and the world market share of previously secured orders was 40.8%, ranking first in the world. China is already the center of the global shipbuilding industry. The rapid growth of the offshore engineering equipment manufacturing industry will provide opportunities for the upstream steel industry while driving the growth of offshore steel demand.

Control rolling and control cooling processes are currently adopted for most of heavy plate production, but the stability of tissue and mechanical performance does not reach the quenching and tempering production process (high temperature quenching + high temperature tempering) instead of low production cost. Therefore, the tempering process is still used as an important means of producing heavy plates. Recently, there have been some achievements in terms of producing high-strength marine steel with excellent low-temperature toughness, and some patents have been published publicly. Chinese Patent No. CN103361551A discloses "VN microalloy based high toughness marine steel sheet and its manufacturing method" and added various alloy elements such as V, Ti, Nb to strengthen the strength of steel sheet by using the action of strengthening fine particles and strengthening precipitation Although the vortex and impact toughness were improved, the yield strength was only 395 MPa and only the impact toughness at -20 ° C was provided. China Patent No. CN104357742A discloses "Thick 420MPa grade hot rolled steel sheet for marine engineering and its manufacturing method", while reducing the amount of precious metals while reducing the amount of precious metals by strengthening the employment of low-cost metals C and Mn and optimizing the mixing ratio of other alloy elements in the steel sheet. Although the strength was ensured, the shock absorption energy at -40 ° C was only 88J.

In summary, reducing the cost of precious metal alloy elements and implementing a one-steel multi-grade flexible manufacturing method to lower production costs but improve production efficiency is an urgent problem to be solved in the production of high-performance marine steel. .

The technical problem to be solved by the present invention is to solve the problems of the prior art, which requires a different alloy component method to the ship steel according to the current strength class, thickness, alloy cost is high, and the production process is complex, high strength with excellent low-temperature toughness The present invention is to provide a high-strength marine steel having excellent low-temperature toughness and a single-steel multi-stage heat treatment process that can be used in a ship steel component scheme and a one-steel multi-grade (E460-E550) flexible manufacturing process method.

The technical solution of the present invention for solving the above technical problem is as follows.

In high-strength marine steel with excellent low-temperature toughness, the chemical composition according to the mass percentage of the marine steel is C: 0.12-0.15%, Si: 0.20-0.30%, Mn: 1.40-1.70%, Ni: 0.12-0.15%, Cr : 0.16-0.25%, Mo: 0.08-0.12%, Nb: 0.020-0.030%, Ti: 0.012-0.018%, V≤0.02%, P≤0.015%, S≤0.002%, B: 0.0020-0.0030%, and The remaining amount of Fe and unavoidable impurities. In the high-strength marine steel component having excellent low-temperature toughness of the present invention, the total content of Nb + V + Mo is 0.17% or less.

In the high-strength marine steel single-stage heat treatment process having excellent low-temperature toughness of the present invention, for different strength grades of E460-E550, the heat treatment process adopts normal quenching or intercritical quenching. The normal quenching temperature is 880-930 ° C, the normal quenching temperature holding time is 20-60 minutes, then water-cooled to room temperature, tempering is performed on the billet cooled to room temperature through quenching, and the tempering temperature is 600-670 ℃, and the tempering temperature holding time is 30-90 minutes. Abnormal zone quenching temperature is 790-850 ℃, abnormal zone temperature holding time is 20-60 minutes, then water cooled to room temperature, tempering is performed on the billet cooled to room temperature through quenching, and tempering temperature is 440- 635 ° C, and the quenching temperature holding time is 30-90 minutes.

The present invention manufactures high-strength marine steel with excellent low-temperature toughness based on the following technical idea. ① Mo, Nb, V and other precious metal alloy elements can play a role of strengthening fine particles and strengthening precipitation. However, excessive alloying elements not only increase the cost of the alloy, but can also adversely affect the performance of the steel (for example, Mo can lower the low-temperature toughness of the steel). Therefore, when designing a component, the total content of Nb + V + Mo is reduced to 0.17% or less (the total content of Nb + V + Mo in E500 and E550 marine steels is usually higher than 0.25%) and low-cost metal content such as Mn and B Increases the strength of the steel and improves the low-temperature toughness and hardenability of the steel, effectively reducing the cost of the alloy. ② All of the normal quenching heat treatment processes of the present invention are complete austenitizing. That is, the quenching heating temperature is higher than the A _c3 point (generally 880-960 ° C), after which tempering is performed at a higher temperature (generally 600-670 ° C), the energy consumption is serious and the performance of the obtained product is specific Only steel grade requirements can be met and process adaptability is low. However, the quenching process in the abnormal region has a low quenching temperature (typically 720-850 ° C) and a low tempering temperature (400-640 ° C), a wide process window and low energy consumption. ③ Since the quenching process in the abnormal region of the present invention performs quenching in the α + γ abnormal region, high plasticity and toughness of ferrite, as well as high toughness using hard tempering structure due to martensite transformation Optimal formulation is achieved. In addition, since the anomaly content constantly changes as the quenching temperature changes, the resulting change in strength meets the various strength class requirements of E460 ~ E550, and the flexible production of a single stage is realized in a situation where the composition of steel does not change. Depending on the strength class and thickness, different alloy composition methods must be applied to marine steel, and the alloy cost is high and the production process solves the problems of the conventional technology.

The beneficial effects of the present invention are as follows.

1. By optimizing the components, the contents of precious metals such as Mo, Nb, and V were reduced, and the strength and hardenability were reduced by adding low-cost elements such as Mn and B. The above-described composition method solved the problem of high production cost and complicated tissue production by simultaneously meeting the requirements of marine steel according to the grade and thickness of E460-E550.

2. Providing two quenching processes, normal quenching and abnormal zone quenching, combined with other tempering processes to produce high-strength marine steels with excellent low-temperature toughness according to different strength grades of E460 ~ E550, which have wide process adaptability and high strength. Of flexible production.

3. The ideal zone quenching + low temperature tempering process has realized the optimum formulation of toughness, and it replaces the quenching tempering treatment, and at the same time guarantees the excellent low-temperature toughness and elongation of the high-strength steel, reduces energy consumption and shortens the production cycle.

The present invention implements flexible manufacturing of a single stage by solving the problem that it is difficult to produce tissue due to the need for different components depending on the steel grade and the thickness of the steel sheet, and shortens the production cycle by adopting an abnormal region quenching and a relatively low temperature tempering process. Reduced energy consumption and lowered production costs.

1 is a metal structure diagram after heat treatment according to Example 2 of the present invention.
2 is a metal structure diagram after heat treatment according to Example 4 of the present invention.
3 is a metal structure diagram after heat treatment according to Example 10 of the present invention.

Example 1:

The thickness of the steel sheet in this example is 42 mm, and the chemical composition according to the mass percentage is C 0.13%, Si 0.20%, Mn 1.45%, Ni 0.12%, Cr 0.16%, Mo 0.08%, Nb 0.023%, Ti 0.014%, V ≤0.02%, P≤0.015%, S≤0.0022%, B 0.002% and residual Fe.

A billet is prepared according to the above components, and the billet is heated to 1050-1150 ° C to control rolling to a prescribed thickness, cooled to room temperature after rolling, and then subjected to heat treatment. After taking samples from the finished steel sheet for ships, tensile and low-temperature impact tests are performed.

The test steel heat treatment process is as follows.

(1) Abnormal zone quenching: The test steel is heated to 820 ° C., the temperature is maintained for 50 minutes, and then water cooled to room temperature.

(2) Tempering: After quenching, the sample cooled to room temperature is heated to 635 ° C., the temperature is maintained for 60 minutes, and then removed from air cooling.

After the treatment, the yield strength of the test steel was 505 MPa, the tensile strength was 605 MPa, the elongation was 22.20%, and the shock absorption energy at -40 ° C was 216/240 / 250J, respectively, which could satisfy the E460 strength rating requirements.

Example 2:

The thickness of the steel sheet in this example is 27 mm, and its chemical composition is the same as in Example 1.

The test steel heat treatment process is as follows.

(1) Quenching of abnormal areas: The test steel is heated to 790 ° C, and the temperature is maintained for 35 minutes, followed by water cooling to room temperature.

(2) Tempering: After quenching, the sample cooled to room temperature is heated to 600 ° C., the temperature is maintained for 45 minutes, and then taken out from air cooling.

After the treatment, the tempering tissue is ferrite + tempered sorbite as shown in Figure 1, and the ferrite volume fraction is 32%. The yield strength of the test steel is 521MPa, the tensile strength is 615MPa, the elongation is 22.60%, and the shock absorption energy of -40 ° C is 218/216 / 215J, respectively, which can satisfy the requirements of the E460 strength class.

Example 3:

The thickness of the steel sheet in this example is 50 mm, and the chemical composition according to the mass percentage is C 0.12%, Si 0.24%, Mn 1.56%, Ni 0.14%, Cr 0.23%, Mo 0.09%, Nb 0.025%, Ti 0.012%, V ≤0.02%, P≤0.015%, S≤0.002%, B 0.0027% and residual amount Fe.

A billet is prepared according to the above components, and the billet is heated to 1050-1150 ° C to control rolling to a prescribed thickness, cooled to room temperature after rolling, and then subjected to heat treatment. After taking samples from the finished steel sheet for ships, tensile and low-temperature impact tests are performed.

The test steel heat treatment process is as follows.

(1) Quenching of abnormal areas: The test steel is heated to 790 ° C, and the temperature is maintained for 60 minutes, followed by water cooling to room temperature.

(2) Tempering: After quenching, the sample cooled to room temperature is heated to 560 ° C., the temperature is maintained for 90 minutes, and then taken out from air cooling.

After the treatment, the yield strength of the test steel was 580 MPa, the tensile strength was 662 MPa, the elongation was 21.28%, and the shock absorption energy at -40 ° C was 202/204 / 211J, respectively, which could meet the E500 strength rating requirements.

Example 4:

The thickness of the steel sheet in this example is 30 mm, and the chemical composition according to the mass percentage is C 0.12%, Si 0.26%, Mn 1.57%, Ni 0.12%, Cr 0.20%, Mo 0.12%, Nb 0.027%, Ti 0.008%, V ≤0.02%, P≤0.015%, S≤0.002%, B 0.0024% and residual amount Fe.

A billet is prepared according to the above components, and the billet is heated to 1050-1150 ° C to control rolling to a prescribed thickness, cooled to room temperature after rolling, and then subjected to heat treatment. After taking samples from the finished steel sheet for ships, tensile and low-temperature impact tests are performed.

The test steel heat treatment process is as follows.

(1) Quenching of abnormal areas: The test steel is heated to 850 ° C., the temperature is maintained for 40 minutes, and then water cooled to room temperature.

(2) Tempering: After quenching, the sample cooled to room temperature is heated to 635 ° C., the temperature is maintained for 54 minutes, and then removed from air cooling.

After the treatment, the tempering tissue is ferrite + tempered sorbite as shown in Figure 2, and the ferrite volume fraction is 11.5%. The yield strength of the test steel was 587 MPa, the tensile strength was 659 MPa, the elongation was 19.84%, and the shock absorption energy at -40 ° C was 224/239 / 228J, respectively, which could satisfy the requirements of the E500 strength class.

Example 5:

The thickness of the steel sheet in this example is 46 mm, and the chemical composition according to the mass percentage is C 0.13%, Si 0.30%, Mn 1.60%, Ni 0.15%, Cr 0.22%, Mo 0.10%, Nb 0.020%, Ti 0.018%, V ≤0.02%, P≤0.015%, S≤0.002%, B 0.0026% and residual amount Fe.

A billet is prepared according to the above components, and the billet is heated to 1050-1150 ° C to control rolling to a prescribed thickness, cooled to room temperature after rolling, and then subjected to heat treatment. After taking samples from the finished steel sheet for ships, tensile and low-temperature impact tests are performed.

The test steel heat treatment process is as follows.

(1) Quenching of abnormal areas: The test steel is heated to 790 ° C, and the temperature is maintained for 60 minutes, followed by water cooling to room temperature.

(2) Tempering: After quenching, the sample cooled to room temperature is heated to 440 ° C., the temperature is maintained for 90 minutes, and then removed from air cooling.

After the treatment, the yield strength of the test steel was 606 MPa, the tensile strength was 750 MPa, the elongation was 17.88%, and the shock absorption energy at -40 ° C was 166/162 / 171J, respectively, which could meet the E550 strength rating requirements.

Example 6:

The thickness of the steel sheet in this example is 18 mm, and its chemical composition is the same as in Example 5.

The test steel heat treatment process is as follows.

(1) Abnormal zone quenching: The test steel is heated to 820 ° C, and the temperature is maintained for 27 minutes, followed by water cooling to room temperature.

(2) Tempering: After quenching, the sample cooled to room temperature is heated to 520 ° C, maintained at a temperature for 40 minutes, and then taken out from air cooling.

After the treatment, the yield strength of the test steel was 635 MPa, the tensile strength was 739 MPa, the elongation was 19.84%, and the shock absorption energy at -40 ° C was 195/114 / 183J, respectively, which could meet the E550 strength rating requirements.

Example 7:

The thickness of the steel sheet in this example is 16 mm, and the chemical composition according to the mass percentage is C 0.15%, Si 0.25%, Mn 1.70%, Ni 0.13%, Cr 0.18%, Mo 0.10%, Nb 0.026%, Ti 0.017%, V ≤0.02%, P≤0.015%, S≤0.002%, B 0.0025% and residual amount Fe.

A billet is prepared according to the above components, and the billet is heated to 1050-1150 ° C to control rolling to a prescribed thickness, cooled to room temperature after rolling, and then subjected to heat treatment. After taking samples from the finished steel sheet for ships, tensile and low-temperature impact tests are performed.

The test steel heat treatment process is as follows.

(1) Abnormal zone quenching: The test steel is heated to 850 ° C, and the temperature is maintained for 25 minutes, followed by water cooling to room temperature.

(2) Tempering: After quenching, the sample cooled to room temperature is heated to 540 ° C., the temperature is maintained for 35 minutes, and then removed from air cooling.

After the treatment, the yield strength of the test steel was 734 MPa, the tensile strength was 789 MPa, the elongation was 17.04%, and the shock absorption energy at -40 ° C was 191/203 / 193J, respectively, which could meet the E550 strength rating requirements.

Example 8:

The thickness of the steel sheet in this example is 38 mm, and the chemical composition according to the mass percentage is C 0.12%, Si 0.27%, Mn 1.40%, Ni 0.14%, Cr 0.20%, Mo 0.11%, Nb 0.030%, Ti 0.018%, V ≤0.02%, P≤0.015%, S≤0.002%, B 0.0028% and residual amount Fe.

A billet is prepared according to the above components, and the billet is heated to 1050-1150 ° C to control rolling to a prescribed thickness, cooled to room temperature after rolling, and then subjected to heat treatment. After taking samples from the finished steel sheet for ships, tensile and low-temperature impact tests are performed.

The test steel heat treatment process is as follows.

(1) Normal quenching: The test steel is heated to 880 ° C., the temperature is maintained for 40 minutes, and then water cooled to room temperature.

(2) Tempering: After quenching, the sample cooled to room temperature is heated to 670 ° C., the temperature is maintained for 60 minutes, and then removed from air cooling.

After the treatment, the yield strength of the test steel was 655 MPa, the tensile strength was 696 MPa, the elongation was 20.48%, and the shock absorption energy at -40 ° C was 226/248 / 230J, respectively, which could satisfy the E550 strength rating requirements.

Example 9:

The thickness of the steel sheet in this example is 22 mm, and the chemical composition according to the mass percentage is C 0.14%, Si 0.25%, Mn 1.50%, Ni 0.10%, Cr 0.25%, Mo 0.09%, Nb 0.024%, Ti 0.014%, V ≤0.02%, P≤0.015%, S≤0.002%, B 0.0030% and residual amount Fe.

A billet is prepared according to the above components, and the billet is heated to 1050-1150 ° C to control rolling to a prescribed thickness, cooled to room temperature after rolling, and then subjected to heat treatment. After taking samples from the finished steel sheet for ships, tensile and low-temperature impact tests are performed.

The test steel heat treatment process is as follows.

(1) Normal quenching: The test steel is heated to 900 ° C., the temperature is maintained for 30 minutes, and then water cooled to room temperature.

(2) Tempering: After quenching, the sample cooled to room temperature is heated to 635 ° C., the temperature is maintained for 40 minutes, and then taken out from air cooling.

After the treatment, the yield strength of the test steel was 740 MPa, the tensile strength was 778 MPa, the elongation was 18.76%, and the shock absorption energy at -40 ° C was 215/215 / 210J, respectively, which could meet the E550 strength rating requirements.

Example 10:

The thickness of the steel sheet in this example is 10 mm, and the chemical composition according to the mass percentage is C 0.15%, Si 0.28%, Mn 1.65%, Ni 0.15%, Cr 0.18%, Mo 0.10%, Nb 0.030%, Ti 0.012%, V ≤0.02%, P≤0.015%, S≤0.002%, B 0.0028% and residual amount Fe.

A billet is prepared according to the above components, and the billet is heated to 1050-1150 ° C to control rolling to a prescribed thickness, cooled to room temperature after rolling, and then subjected to heat treatment. After taking samples from the finished steel sheet for ships, tensile and low-temperature impact tests are performed.

The test steel heat treatment process is as follows.

(1) Normal quenching: The test steel is heated to 930 ° C, and the temperature is maintained for 20 minutes, followed by water cooling to room temperature.

(2) Tempering: After quenching, the sample cooled to room temperature is heated to 600 ° C., the temperature is maintained for 30 minutes, and then taken out from air cooling.

After the above treatment, the tempering structure is a sorbite tempered as shown in Fig. 3, and there is no proeutectoid ferrite. The yield strength of the test steel is 772MPa, the tensile strength is 816MPa, the elongation is 17.32%, and the shock absorption energy at -40 ° C is 188/220 / 192J, respectively, which can meet the E550 strength rating requirements.

Table 1 Chemical composition range (wt%) according to an embodiment of the present invention

Table 2 Mechanical performance according to an embodiment of the present invention

It can be seen from Table 2 that the mechanical performance of each embodiment can meet the requirements of the grade of the corresponding marine steel and there is some margin.

In addition to the above embodiments, there may be other embodiments in the present invention. Any technical solutions formed by equivalent substitutions or equivalent conversions are all within the scope of the present invention.

Claims (5)

In high-strength marine steel with excellent low-temperature toughness,
Chemical composition according to the mass percentage of the ship steel is C: 0.12-0.15%, Si: 0.20-0.30%, Mn: 1.40-1.70%, Ni: 0.12-0.15%, Cr: 0.16-0.25%, Mo: 0.08- 0.12%, Nb: 0.020-0.030%, Ti: 0.012-0.018%, V≤0.02%, P≤0.015%, S≤0.002%, B: 0.0020-0.0030%, and the residual amount of Fe and inevitable impurities High-strength marine steel with excellent low-temperature toughness. According to claim 1,
High-strength marine steel with excellent low-temperature toughness, characterized in that a billet is prepared according to the above components, the billet is heated to 1050-1150 ° C, controlled rolling to a prescribed thickness, and then cooled to room temperature after rolling to perform heat treatment. For different strength classes of E460-E550, the heat treatment process adopts normal quenching or intercritical quenching;
The normal quenching temperature is 880-930 ° C, the normal quenching temperature holding time is 20-60 minutes, and then water-cooled to room temperature, tempering is performed on the billet cooled to room temperature through quenching, and the tempering temperature is 600- 670 ° C, and the tempering temperature holding time was 30-90 minutes;
The anomaly zone quenching temperature is 790-850 ° C, the abnormal zone temperature holding time is 20-60 minutes, and then water-cooled to room temperature, tempering is performed on the billet cooled to room temperature through quenching, and the tempering temperature is 440. -635 ℃, and the quenching temperature holding time is 30-90 minutes. According to claim 3,
Plate thickness is 42mm, heat treatment process is 820 ℃ quenching, 50 minutes temperature maintenance, 635 ℃ tempering, 60 minutes temperature maintenance;
Plate thickness is 27mm, heat treatment process is 790 ℃ quenching, 35 minutes temperature maintenance, 600 ℃ tempering, 45 minutes temperature maintenance;
Plate thickness is 50mm, heat treatment process is 790 ℃ quenching, 60 minutes temperature maintenance, 560 ℃ tempering, 90 minutes temperature maintenance;
Plate thickness is 30mm, heat treatment process is 850 ℃ quenching, 40 minutes temperature maintenance, 635 ℃ tempering, 54 minutes temperature maintenance;
Plate thickness is 46mm, heat treatment process is 790 ℃ quenching, 60 minutes temperature maintenance, 440 ℃ tempering, 90 minutes temperature maintenance;
Plate thickness is 18mm, heat treatment process is 820 ℃ quenching, temperature maintenance at 27 minutes, tempering at 520 ℃, temperature maintenance at 40 minutes;
Plate thickness is 16mm, heat treatment process is 850 ℃ quenching, 25 minutes temperature maintenance, 540 ℃ tempering, 35 minutes temperature maintenance;
One-stage multi-stage heat treatment process of high-strength marine steel excellent in low-temperature toughness, characterized in that. According to claim 3,
Plate thickness is 38mm, heat treatment process is 880 ℃ quenching, 40 minutes temperature maintenance, 670 ℃ tempering, 60 minutes temperature maintenance;
The plate thickness is 22 mm, the heat treatment process is quenched at 900 ° C, temperature maintained at 30 minutes, tempering at 635 ° C, temperature maintained at 40 minutes;
Plate thickness is 10mm, heat treatment process is 930 ℃ quenching, 20 minutes temperature maintenance, 600 ℃ tempering, 30 minutes temperature maintenance;
One-stage multi-stage heat treatment process of high-strength marine steel excellent in low-temperature toughness, characterized in that.

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