A high-performance rare earth marine engineering steel plate and its production method

Abstract

A high-performance rare-earth marine engineering steel plate and its production method belong to the field of steel material processing technology. Its chemical composition and mass content are: C: 0.05-0.08%, Si: 0.30-0.40%, Mn: 1.40-1.50%, P≤0.009%, S≤0.0020%, Cr: 0.10-0.20%, Al: 0.020-0.040%, Ce: 0.008-0.012%, with the balance being Fe and unavoidable impurities. The production method includes stepped heating, rolling, and rapid cooling after rolling; it does not include a tempering process. This invention, by adding a high Ce content, eliminates the need for adding precious metal elements such as Ni, V, and Nb. Combined with stepped heating and rapid cooling after rolling, it fully refines the grains, improves comprehensive mechanical properties, and eliminates the need for tempering and offline quenching + tempering. The production process is simple, low-cost, and yields steel plates with excellent comprehensive mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of steel material processing technology, and relates to a high-performance rare earth marine engineering steel plate and its production method. Background Technology

[0002] Rare earth elements play a role in purifying steel, removing impurities, and microalloying. In steel, rare earth elements preferentially form rare earth oxides and rare earth sulfides or rare earth oxysulfides, reducing the oxygen and sulfur content. The addition of rare earth elements to steel can alter the properties, morphology, and distribution of inclusions. Rare earth elements dissolved in steel often concentrate at grain boundaries, reducing the segregation of impurity elements at grain boundaries and strengthening them. Furthermore, rare earth compound particles can act as heterogeneous nucleation sites for solidification, crystallization, and solid-state phase transformation, promoting grain refinement and thus improving the overall performance of the steel.

[0003] Offshore steel is widely used in critical components of offshore platforms and offshore wind power plants, operating in harsh environments that place extremely stringent demands on the steel plates' comprehensive performance, especially their plasticity and low-temperature toughness. Currently, plates thicker than 95mm are typically produced using TMCP + tempering or offline quenching + tempering processes. These processes are lengthy and often involve the addition of precious metals such as Ni, V, and Nb to enhance performance, resulting in high production costs, complex processes, high energy consumption, and significant performance fluctuations.

[0004] Patent application CN2025114013626 discloses a rare-earth marine engineering steel plate containing Ni and Nb, the production method of which includes heating, rolling, rapid cooling and tempering processes. Although this scheme can achieve certain performance, the composition design contains Ni and Nb, which are precious metal elements, and the process includes a tempering process, so it still suffers from high alloy cost and complex process.

[0005] Therefore, developing a thick-gauge rare earth marine engineering steel plate that can maintain excellent comprehensive performance without the addition of precious metals and its low-cost, short-process production method has significant industrial value. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a high-performance rare earth marine engineering steel plate and its production method. The steel plate does not contain precious metal elements such as Ni, V, and Nb. By adding a high content of rare earth element Ce, combined with stepped heating and rapid cooling after rolling, grain refinement is achieved, resulting in excellent comprehensive mechanical properties. Moreover, no tempering is required, the production process is simple and the cost is low.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A high-performance rare earth marine engineering steel plate has the following chemical composition and mass percentage: C: 0.05-0.08%, Si: 0.30-0.40%, Mn: 1.40-1.50%, P≤0.009%, S≤0.0020%, Cr: 0.10-0.20%, Al: 0.020-0.040%, Ce: 0.008-0.012%, with the balance being Fe and unavoidable impurities.

[0008] The thickness of the steel plate is 95-120 mm.

[0009] The microstructure of the steel plate is bainite and ferrite.

[0010] The steel plate has a yield strength of 400-485 MPa, a tensile strength of 580-630 MPa, an elongation of ≥25.0%, a transverse impact energy of ≥280 J at -40℃, and a thickness Z-direction performance of ≥65%.

[0011] The production method of the above-mentioned high-performance rare earth marine steel plates includes stepped heating, rolling, and rapid cooling after rolling; but does not include tempering.

[0012] The rolling process adopts a two-stage controlled rolling process, with the reduction amount in the first two passes of the first stage rolling being ≥40mm; The post-rolling rapid cooling process involves quenching the steel plate online to ≤550℃ at a cooling rate of ≥12℃ / s after rolling.

[0013] The stepped heating process includes: the first step is a preheating section with a temperature of 500-600℃ and a holding time of 1-2 hours; the second step is a heating section with a temperature of 1180-1200℃ and a holding time of 1-2 hours; the third step is a homogenizing section with a temperature of 1150-1180℃ and a holding time of 1-2 hours; the heating rate of the entire heating process is 280-400℃ / h.

[0014] The rolling process has a first-stage rolling temperature of ≥1000℃, a second-stage initial rolling temperature of 880~900℃, and a final rolling temperature of 800~830℃.

[0015] In the post-rolling rapid cooling process, the steel plate is water-quenched online to ≤550℃ and then air-cooled to room temperature.

[0016] The beneficial effects of adopting the above technical solution are as follows: 1. This invention employs a novel composition design, eliminating the need for precious metal elements such as Ni, V, and Nb, thus reducing alloy costs. By adding a high content of Ce rare earth elements, the invention fully leverages the role of rare earth elements in purifying steel, removing impurities, and microalloying, thereby improving the mechanical properties of the steel and reducing alloy costs.

[0017] 2. The present invention adopts a stepped heating process, which makes the steel billet heat evenly, reduces internal stress, provides a good microstructure for subsequent rolling, and helps to improve the performance of steel plates.

[0018] 3. The present invention controls the reduction of the first two passes of rolling to ≥40mm, which is beneficial for the rolling to penetrate into the core and improve the internal quality of the steel plate.

[0019] 4. This invention adopts a post-rolling rapid cooling process, which fully refines the grains and eliminates the need for tempering and offline quenching + tempering processes, simplifying the production process and reducing energy consumption and costs.

[0020] 5. The steel plates produced by this invention can reach a thickness of 95-120mm, have excellent comprehensive mechanical properties, yield strength of 400-485MPa, tensile strength of 580-630MPa, elongation ≥25.0%, transverse impact energy at -40℃ ≥280J, and Z-direction performance ≥65%, which fully meets the performance requirements of thick-gauge marine engineering steel plates.

[0021] This invention achieves high performance by increasing the rare earth Ce content and employing a stepped heating process. The core lies in utilizing the multiple mechanisms of rare earth elements—purifying steel, mitigating inclusions, and microalloying—to replace the strengthening function of precious elements such as Ni and Nb. Simultaneously, precise control of microstructure and stress is achieved through temperature gradient control, thus eliminating the need for tempering heat treatment and achieving the dual goals of "low cost + high performance." Attached Figure Description

[0022] Figure 1 This is a metallographic diagram of the rare earth marine engineering steel plate from Example 1. Detailed Implementation

[0023] Examples 1-6 and Comparative Examples 1-2 A method for producing high-performance rare-earth marine engineering steel plates includes stepped heating, rolling, and post-rolling rapid cooling processes, eliminating the need for tempering or offline quenching and tempering. The specific process steps are as follows: (1) Step heating process: The first step is the preheating section, with a temperature of 500-600℃ and a holding time of 1-2h; the second step is the heating section, with a temperature of 1180-1200℃ and a holding time of 1-2h; the third step is the heat equalization section, with a temperature of 1150-1180℃ and a holding time of 1-2h; the heating rate is 280-400℃ / h.

[0024] (2) Rolling process: A two-stage controlled rolling process is adopted. The reduction of the first two passes in the first stage of rolling is ≥40mm. The final rolling temperature of the first stage is ≥1000℃. The starting rolling temperature of the second stage is 880~900℃ and the final rolling temperature is 800~830℃.

[0025] (3) Rapid cooling process after rolling: After the steel plate is rolled, it is water quenched online to ≤550℃ at a cooling rate of ≥12℃ / s and then air cooled to room temperature.

[0026] All embodiments and comparative examples were produced using 330mm cast billets. The parameters of each production process are shown in Tables 1 and 2. The chemical composition and mass percentage of the steel plates are shown in Table 3. The specifications and properties of the steel plates are shown in Table 4.

[0027] Table 1. Step heating process parameters for each embodiment and comparative example

[0028] Table 2. Parameters for rolling and post-rolling rapid cooling processes in each embodiment and comparative example.

[0029] Table 3 Chemical composition and mass percentage (%) of steel plates in each embodiment and comparative example

[0030] The remaining components in Table 3 are Fe and unavoidable impurities.

[0031] Table 4. Specifications and mechanical properties of steel plates from various embodiments and comparative examples.

[0032] As shown in Table 3, the steel plates of Examples 1-6 of this invention possess excellent comprehensive mechanical properties, especially their low-temperature impact toughness and Z-axis properties, which are significantly superior to those of Comparative Examples 1 and 2. Comparative Examples 1 and 2, due to the absence of the rare earth element Ce, exhibit poorer performance. The rare earth steel of this invention boasts excellent performance and offers the dual advantages of low alloy cost and low processing cost.

Claims

1. A high-performance rare earth marine engineering steel plate, characterized in that, The chemical composition and mass percentage of the steel plate are as follows: C: 0.05-0.08%, Si: 0.30-0.40%, Mn: 1.40-1.50%, P≤0.009%, S≤0.0020%, Cr: 0.10-0.20%, Al: 0.020-0.040%, Ce: 0.008-0.012%, with the balance being Fe and unavoidable impurities.

2. The high-performance rare earth marine engineering steel plate according to claim 1, characterized in that, The thickness of the steel plate is 95-120 mm.

3. The high-performance rare earth marine engineering steel plate according to claim 2, characterized in that, The microstructure of the steel plate is bainite and ferrite.

4. The high-performance rare earth marine engineering steel plate according to claim 3, characterized in that, The steel plate has a yield strength of 400-485 MPa, a tensile strength of 580-630 MPa, an elongation of ≥25.0%, a transverse impact energy of ≥280 J at -40℃, and a thickness Z-direction performance of ≥65%.

5. A method for producing high-performance rare earth marine engineering steel plates according to any one of claims 1-4, characterized in that, Includes stepped heating, rolling, and rapid cooling after rolling; excludes tempering. The rolling process adopts a two-stage controlled rolling process, with the reduction amount in the first two passes of the first stage rolling being ≥40mm; The post-rolling rapid cooling process involves quenching the steel plate online to ≤550℃ at a cooling rate of ≥12℃ / s after rolling.

6. The method for producing high-performance rare earth marine engineering steel plates according to claim 5, characterized in that, The stepped heating process includes: The first stage is the preheating section, with a temperature of 500-600℃, and the temperature is maintained for 1-2 hours. The second step is the heating section, with a temperature of 1180-1200℃, and the temperature is maintained for 1-2 hours. The third step is the heat equalization zone, with a temperature of 1150-1180℃, and the temperature is maintained for 1-2 hours. The heating rate for the entire heating process is 280–400 °C / h.

7. The method for producing high-performance rare earth marine engineering steel plates according to claim 5, characterized in that, The rolling process has a first-stage rolling temperature of ≥1000℃, a second-stage initial rolling temperature of 880~900℃, and a final rolling temperature of 800~830℃.

8. The method for producing high-performance rare earth marine engineering steel plates according to claim 5, characterized in that, In the post-rolling rapid cooling process, the steel plate is water-quenched online to ≤550℃ and then air-cooled to room temperature.

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