S420-grade marine steel and production method therefor

Abstract

The present invention relates to the technical field of ferrous metallurgy, and in particular to an S420-grade marine steel and a production method therefor. The S420-grade marine steel comprises the following chemical components in mass percent: C: 0.05%-0.09%, Si: 0.10%-0.30%, Mn: 1.30%-1.60%, P: ≤0.015%, S: ≤0.003%, Nb: 0.020-0.040%, V: 0.020-0.050%, Ti: 0.008-0.030%, Cr: 0.10-0.30%, Ni: 0.10%-0.30%, Mo: 0.10-0.20%, Cu: ≤0.0:50%, Al: 0.020%-0.050%, B: ≤0.00050%, Ca: 0.0006%-0.0030%, N≤0.0050%, H≤0.0002%, and the balance Fe and inevitable impurities. The present invention uses the design of low-carbon combined fine grained strengthened alloy and the technology of clean steel smelting combined with heavy reduction casting to improve the core structure of casting billets, and uses a controlled rolling and controlled cooling process to achieve a structural form dominated by bainite, satisfying product requirements for welding, impact at -40 degree and CTOD performance.

Description

S420 grade marine engineering steel and production method thereof Technical Field

[0001] The present invention relates to the technical field of steel metallurgy, and in particular to an S420 grade marine engineering steel and a production method thereof. Background Art

[0002] With the advancement of oil and gas extraction technology, the design and manufacturing of supporting marine engineering equipment have received unprecedented attention and development. For example, the successful launching of the world's first 100,000-ton deep-water semi-submersible production and storage platform "Deep Sea No. 1" marks the gradual development of domestic marine engineering equipment from nearshore to offshore and deep sea, and at the same time puts forward higher requirements on the service performance of steel materials in deep-sea environment.

[0003] Deep-sea marine engineering structures are welded together from a large number of structural modules. The welding process will deteriorate the microstructure and properties of the joints and produce defects such as residual stress. The joints are the weakest part of the entire platform and are prone to crack initiation, expansion, and even unstable fracture when serving in the low-temperature ocean environment. Therefore, the material is required to have low levels of harmful elements such as P and S, excellent welding performance, and low-temperature fracture toughness to resist grain coarsening during the welding process, which may lead to severe damage to the low-temperature impact toughness.

[0004] The marine environment is complex and changeable. Offshore platforms are constantly subjected to harsh climate and environmental tests such as low temperatures, waves, and typhoons. The structural stability and fatigue life of offshore platforms are closely related to the safety of offshore operations. According to international practice, post-weld heat treatment is required to eliminate the stress generated during the welding process and improve low-temperature fracture toughness. However, offshore platforms are typical large-scale welded engineering components. Post-weld heat treatment is difficult, time-consuming, and costly. In order to shorten the manufacturing cycle and reduce manufacturing costs of offshore platform structures, the development of materials that do not require post-weld stress treatment has extremely obvious practical significance. To this end, it is necessary to study the post-weld CTOD performance of the material to evaluate the low-temperature fracture toughness of the material under the condition of no post-weld stress treatment. Generally, according to international practice, when the CTOD characteristic value reaches 0.15mm at the service temperature, post-weld stress treatment can be waived.

[0005] Based on the above-mentioned special service environment and project requirements of marine engineering, there is an urgent need to develop S420-grade marine engineering steel that meets the requirements of deep-sea service and operation, develop a maximum thickness of 10 to 50 mm, and apply for classification society certification.

[0006] Summary of the Invention

[0007] In response to the above-mentioned technical problems, the present invention overcomes the shortcomings of the existing technology and provides an S420-grade marine engineering steel and a production method thereof. The steel adopts a low-carbon combined with fine-grained strengthening alloy design, adopts clean steel smelting combined with large-reduction casting technology to improve the core structure of the casting, and realizes a bainite-based microstructure through a controlled rolling and controlled cooling process, thereby meeting the product's welding, -40-degree impact and CTOD performance requirements.

[0008] In a first aspect, the present invention provides an S420 grade marine engineering steel, whose chemical composition and mass percentage are as follows: C: 0.05% to 0.09%, Si: 0.10% to 0.30%, Mn: 1.30% to 1.60%, P: ≤0.015%, S: ≤0.003%, Nb: 0.020 to 0.040%, V: 0.020 to 0.050%, Ti: 0.008 to 0.030%, Cr: 0.10 to 0.30%, Ni: 0.10% to 0.30%, Mo: 0.10 to 0.20%, Cu: ≤0.050%, Al: 0.020% to 0.050%, B: ≤0.00050% , Ca: 0.0006% ~ 0.0030%, N ≤ 0.0050%, H ≤ 0.0002%, the balance is Fe and inevitable impurities, a lower carbon content is conducive to ensuring the strength stability of the product, and a lower carbon content can improve the low-power stability of the ingot. The use of high-temperature casting technology and dynamic light pressing technology can promote the formation of acicular ferrite in the ingot, increase the ferrite content of the rolled steel plate, ensure the stability of the steel plate bainite, and improve the impact and welding performance of the product. The use of Nb, V, and Ti refines the grain size of the organization. The Cr and Mo elements improve the strength of the product and also ensure the hardenability in the thickness direction under hot rolling conditions, ensuring the stability of the welding process.

[0009] In a second aspect, the present invention further provides a method for producing S420 grade marine engineering steel, which is applicable to the S420 grade marine engineering steel described in the first aspect, comprising the following steps:

[0010] S1, adopt converter smelting, LF / RH vacuum refining, and calcium treatment to modify inclusions;

[0011] S2. The refined molten steel is sent to the continuous casting for casting. The casting temperature is 15-35 degrees, the dynamic soft pressure is 8-12mm, and the electromagnetic stirring process is not used. After the cast billet is piled and cooled, the surface inspection and billet processing are carried out;

[0012] S3. The billets that have passed the surface inspection are austenitized and heated, with the tapping temperature at 1110-1150 degrees, and two-stage rolling is adopted;

[0013] S4. The rolled steel plate is rapidly cooled with a water temperature of 770-790 degrees, a cooling rate of 20-30 degrees Celsius / min, and a red-hot temperature of 500-700 degrees Celsius;

[0014] S5. The cooled steel plates are stacked, sheared, marked and stored.

[0015] Furthermore, the calcium treatment in S1 is followed by static stirring for 8 to 13 minutes.

[0016] Furthermore, during the second-stage rolling in S3, the reduction rate of the final rough rolling pass is not less than 22%, and the reduction amount is not less than 26 mm.

[0017] Furthermore, the thickness of the steel plate is 10 to 50 mm.

[0018] The beneficial effects of the present invention are:

[0019] (1) The present invention adopts a lower carbon content, which is beneficial to ensuring the strength stability of the product. At the same time, the lower carbon content can improve the low-multiple stability of the ingot. The use of high-temperature casting technology and dynamic light pressing technology can promote the formation of acicular ferrite in the ingot, increase the ferrite content of the rolled steel plate, ensure the stability of the steel plate bainite, and improve the impact and welding performance of the product. The use of Nb, V, and Ti refines the grain size of the structure. The Cr and Mo elements improve the strength of the product and also ensure the hardenability in the thickness direction under hot rolling conditions, ensuring the stability of the welding process.

[0020] (2) The present invention uses a calcium treatment process to modify the inclusions in the molten steel. The static stirring and high-temperature casting process promotes the floating of the inclusions, thereby improving the purity of the product. Under high-temperature conditions, a large reduction technology is used without electromagnetic stirring. The columnar crystal structure of the ingot occupies 70% of the ingot area. The grains are more difficult to roll during the low-temperature austenite process. While refining the grain structure, the acicular ferrite becomes more dense and stable, effectively improving the low-temperature impact toughness and CTOD performance of the product.

[0021] (3) The present invention takes advantage of the equipment of the rolling mill, with large reduction and controlled rapid cooling technology to improve the adverse effects of the banded structure of the steel plate, improve the uniformity of the structure in the thickness direction of the steel plate, make the welding performance of the product more stable, and make the low-temperature impact toughness of the steel plate more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG1 is a metallographic structure diagram of S420 grade marine engineering steel in Example 1 of the present invention. DETAILED DESCRIPTION

[0023] Example 1

[0024] This embodiment provides an S420-grade marine engineering steel and a production method thereof. The chemical composition and mass percentage of the marine engineering steel are as follows: C: 0.07%, Si: 0.18%, Mn: 1.36%, P: 0.011%, S: 0.001%, Nb: 0.033%, V: 0.031%, Ti: 0.021%, Cr: 0.23%, Ni: 0.21%, Mo: 0.15%, Cu: 0.020%, Al: 0.033%, B: 0.00030%, Ca0.0019%, N: 0.00:31%, H: 0.000:1%, and the balance is Fe and unavoidable impurities.

[0025] The production method specifically includes:

[0026] S1, using converter smelting, LF / RH vacuum refining, and calcium treatment to modify inclusions, and static stirring for 11 minutes after calcium treatment;

[0027] S2. The refined molten steel is sent to the continuous casting for casting. The casting temperature is 23 degrees, the dynamic soft pressure is 11m, and the electromagnetic stirring process is not used. The cast billet is pile-cooled for 48 hours for surface inspection and billet processing;

[0028] S3. The billets that have passed the surface inspection are austenitized and heated, with a tapping temperature of 1133 degrees. Two-stage rolling is adopted, with a final roughing reduction of 26% and a reduction of 29 mm.

[0029] S4, the steel plate after rolling is rapidly cooled, the water temperature is 786 degrees, the cooling rate is 26 degrees / min, and the red-return temperature is 610 degrees;

[0030] S5. The cooled steel plates are stacked, sheared, marked and stored.

[0031] Example 2

[0032] This embodiment provides an S420-grade marine engineering steel and a production method thereof. The chemical composition and mass percentage of the marine engineering steel are as follows: C: 0.08%, Si: 0.23%, Mn: 1.55%, P: 0.012%, S: 0.002%, Nb: 0.033%, V: 0.042%, Ti: 0.023%, Cr: 0.22%, Ni: 0.26%, Mo: 0.11%, Cu 0.030%, Al: 0.036%, B: 0.00020%, Ca: 0.0021%, N: 0.0041%, H: 0.0001%, and the balance is Fe and unavoidable impurities.

[0033] The production method specifically includes:

[0034] S1, adopt converter smelting, LF / RH vacuum refining, and calcium treatment to modify inclusions, and static stirring for 10 minutes after calcium treatment;

[0035] S2. The refined molten steel is sent to the continuous casting for casting. The casting temperature is 31 degrees, the dynamic soft pressure is 10mm, and the electromagnetic stirring process is not used. The cast billet is pile-cooled for 48 hours for surface inspection and billet processing;

[0036] S3. The billets that have passed the surface inspection are austenitized and heated, with a tapping temperature of 1123 degrees. Two-stage rolling is adopted, with a final rough rolling reduction of 24% and a reduction of 30 mm.

[0037] S4, the steel plate after rolling is rapidly cooled, with a water temperature of 786 degrees, a cooling rate of 22 degrees Celsius / min, and a red-return temperature of 630 degrees Celsius;

[0038] S5. The cooled steel plates are stacked, sheared, marked and stored.

[0039] Table 1 shows the -40 degree impact mechanical properties of Examples 1 and 2

[0040] Table 2 shows the CTOD test parameters of the products of Examples 1 and 2.

[0041] As shown in Tables 1 and 2, the method provided by the present invention adopts low-carbon combined with fine-grained strengthening alloy design and clean steel smelting combined with large-pressure casting technology to improve the core structure of the casting, and realizes a bainite-based microstructure through a controlled rolling and controlled cooling process, meeting the product's welding, -40-degree impact and CTOD performance requirements, and the product meets the classification society certification requirements.

[0042] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection required by the present invention.

Claims

1. An S420 grade marine engineering steel, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.05%~0.09%, Si: 0.10%~0.30%, Mn: 1.30%~1.60%, P:≤0.015%, S:≤0.003%, Nb: 0.020~0.040%, V: 0.020~0.050%, Ti: 0.008~0.030%, Cr: 0.10~0.30%, Ni: 0.10%~0.30%, Mo: 0.10~0.20%, Cu:≤0.0:50%, Al: 0.020%~0.050%, B:≤0.00050%, Ca: 0.0006%~0.0030%, N≤0.0050%, H≤0.0002%, and the balance is Fe and unavoidable impurities.

2. A method for producing S420 grade marine engineering steel according to claim 1, characterized in that: The following steps are involved: S1, adopt converter smelting, LF / RH vacuum refining, and calcium treatment to modify inclusions; S2. The refined molten steel is sent to the continuous casting for casting. The casting temperature is 15-35 degrees, the dynamic soft pressure is 8-12mm, and the electromagnetic stirring process is not used. After the cast billet is piled and cooled, the surface inspection and billet processing are carried out; S3. The billets that have passed the surface inspection are austenitized and heated, with the tapping temperature at 1110-1150 degrees, and two-stage rolling is adopted; S4. The rolled steel plate is rapidly cooled with a water temperature of 770-790 degrees, a cooling rate of 20-30 degrees Celsius / min, and a red-hot temperature of 500-700 degrees Celsius; S5. The cooled steel plates are stacked, sheared, marked and stored.

3. The method for producing S420 grade marine engineering steel according to claim 2, characterized in that: After the calcium treatment in S1, the mixture was stirred for 8 to 13 minutes.

4. The method for producing S420 grade marine engineering steel according to claim 2, characterized in that: During the two-stage rolling in S3, the reduction rate of the final rough rolling pass is not less than 22%, and the reduction amount is not less than 26 mm.

5. The method for producing S420 grade marine engineering steel according to claim 2, characterized in that: The thickness of the steel plate is 10 to 50 mm.

Images