Production method of 420MPa-grade low-temperature-resistant H-shaped steel for ocean engineering

Abstract

The invention discloses a production method of 420MPa-grade low-temperature-resistant H-shaped steel for ocean engineering. The production method comprises the following steps: blast-furnace molten iron is prepared; pretreating molten iron; converter smelting, LF refining, VD vacuum treatment, beam blank continuous casting and casting blank stacking and slow cooling are conducted; feeding is conducted; a stepping heating furnace; dephosphorizing with high-pressure water; bD cogging is conducted; performing CCS universal rolling; hot sawing; cooling by a stepping cooling bed; the H-shaped steel comprises the following chemical components in percentage by mass: 0.09%-0.15% of C, 0.30%-0.45% of S i, 1.25%-1.35% of Mn, less than or equal to 0.02% of P, less than or equal to 0.010% of S, 0.05%-0.09% of V, 0.02%-0.04% of Nb, 0.15%-0.20% of N i, 0.01%-0.03% of T i and the balance of Fe and impurities. The prepared H-shaped steel has high strength, stable impact toughness and good corrosion resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel rolling, and particularly relates to a production method of 420MPa grade low-temperature resistant H-shaped steel for offshore engineering. Background Art

[0002] An offshore platform is a tool for humans to develop marine resources and belongs to an ultra-large welded steel structure. It is applied in severe marine working environments such as waves, tides, storms, and cold ice floes. These characteristics determine that the steel used for offshore platforms must have high strength, high toughness, fatigue resistance, resistance to lamellar tearing, and good weldability and cold working properties. Since the 1960s, some countries in Europe, America, and Japan have begun to research and develop steel for offshore oil platforms. Currently, S355 steel is still commonly used in the main structures of domestic offshore oil and gas development projects. As the domestic offshore oil and gas development gradually moves towards deep water, the plate thickness of offshore engineering structures increases, the quality continuously increases, and the number of welding layers also increases significantly. As a result, the welding residual stress and the level of diffusible hydrogen accumulated in the weld seam continuously increase, and at the same time, the probability of welding defects also increases, leading to the occurrence of welding cold cracks and welding deformation problems, and the construction difficulty continuously increases. If higher-strength steel is used for offshore platforms, the plate thickness of the steel used can be correspondingly reduced, the above problems can be alleviated to a certain extent, and at the same time, the weight can be reduced by about 20%, the construction difficulty can be reduced, and the development cost can be saved.

[0003] With the development needs of diversification, multi-functionality, large-scale, and lightweight of offshore engineering and shipbuilding equipment at home and abroad, the problem of traditional product upgrading needs to be solved urgently. The successful development of 420MPa grade high-strength and tough low-temperature H-shaped steel can not only greatly improve the safe service ability, but also increase the load-bearing capacity of equipment, reduce the steel consumption, and provide advanced steel material support for the realization of lightweight and green development of equipment manufacturing in the offshore engineering and shipbuilding fields.

[0004] As a typical high-strength and low-temperature steel, S420MLO steel has good strength and toughness, and the stability of its microstructure and mechanical properties. It is the preferred structural material for these major engineering constructions. Therefore, it is necessary to put forward new composition design ideas, develop a short-process production process route based on microstructure control, and realize the reduction of high-quality steel product manufacturing and the reduction of production costs. Summary of the Invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a production method of 420MPa grade low-temperature resistant H-shaped steel for offshore engineering.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A production method of 420MPa grade low-temperature resistant H-beam for ocean engineering, comprising: blast furnace molten iron; hot metal pretreatment; converter smelting, LF refining, VD vacuum treatment, special-shaped billet continuous casting, billet stacking and slow cooling; feeding; walking beam reheating furnace; high-pressure water descaling; BD blooming; CCS universal rolling; hot sawing; walking beam cooling bed cooling; straightening; sawing; characterized in that:

[0008] During the converter smelting process, the end point C > 0.03%, the end point temperature is greater than 1620 °C, and aluminum iron is used for deoxidation during the converter tapping process;

[0009] During the LF refining process, desulfurization, composition fine-tuning and temperature rise are carried out according to the composition and temperature of the converter molten steel. Ferro-niobium and ferrophosphorus are added in the later stage of refining to ensure that the composition of the molten steel meets the internal control requirements;

[0010] During the VD vacuum treatment process, the deep vacuum time ≥ 15 min, the target deep vacuum degree < 0.1 KPa, the weak stirring time ≥ 15 min after breaking the vacuum, calcium-silicon wire is fed, and the soft blowing time ≥ 15 min;

[0011] During the special-shaped billet continuous casting process, protective casting is adopted throughout the process, and the billet stacking and slow cooling is for more than 48 h;

[0012] The temperature of the preheating section is controlled at ≤ 1000 °C, the temperature of the first heating section is controlled at ≤ 1200 °C, the temperature of the second heating section is controlled at 1100 - 1330 °C, the temperature of the soaking section is controlled at 1100 - 1330 °C, and the total heating duration of the billet is controlled at 3 - 5 h;

[0013] Before the billet enters BD1, high-pressure water descaling must be carried out to prevent the generation of surface defects of the finished H-beam caused by the pressing-in of oxidized iron billets;

[0014] The blooming mill is designed to roll 8 passes, no controlled rolling is carried out in the blooming area, and the rolling start temperature is controlled at 1170 - 1180 °C;

[0015] The CCS universal rolling mill is designed to roll 5 passes and carry out controlled rolling to generate sufficiently uniform deformation bands in the austenite grains, and ferrite nucleates in the grains and on the deformation bands to refine the grains. The final rolling temperature is controlled at 880 - 920 °C; control the temperature of the finished H-beam entering the cooling bed, the temperature of entering the cooling bed ≥ 830 °C, and carry out close-packed cooling;

[0016] The mass percentage content of the chemical composition of the H-beam includes: C 0.09% - 0.15%, Si 0.30% - 0.45%, Mn 1.25% - 1.35%, P ≤ 0.02%, S ≤ 0.010%, V 0.05% - 0.09%, Nb 0.02% - 0.04%, Ni 0.15% - 0.20%, Ti 0.01% - 0.03%, and the rest are Fe and impurities, and the total mass fraction is 100%.

[0017] Furthermore, the size of the 420MPa low-temperature resistant H-beam steel for ocean engineering is 618*306*18*35mm.

[0018] Furthermore, the mass percentage content of the chemical components of the H-beam steel includes: C 0.095%, Si 0.318%, Mn 1.25%, P 0.0173%, S 0.015%, V 0.056%, Nb 0.032%, Ni 0.167%, Ti 0.015%, and the rest are Fe and impurities, and the total mass fraction is 100%.

[0019] Furthermore, the mass percentage content of the chemical components of the H-beam steel includes: C 0.115%, Si 0.376%, Mn 1.27%, P 0.0107%, S 0.009%, V 0.059%, Nb 0.027%, Ni 0.171%, Ti 0.019%, and the rest are Fe and impurities, and the total mass fraction is 100%.

[0020] Furthermore, the mass percentage content of the chemical components of the H-beam steel includes: C 0.133%, Si 0.354%, Mn 1.26%, P 0.0111%, S 0.012%, V 0.057%, Nb 0.033%, Ni 0.192%, Ti 0.028%, and the rest are Fe and impurities, and the total mass fraction is 100%.

[0021] Furthermore, the mass percentage content of the chemical components of the H-beam steel includes: C 0.141%, Si 0.369%, Mn 1.33%, P 0.0090%, S 0.011%, V 0.063%, Nb 0.025%, Ni 0.152%, Ti 0.021%, and the rest are Fe and impurities, and the total mass fraction is 100%.

[0022] Furthermore, the -40°C impact energy of the produced 420MPa low-temperature resistant H-beam steel for ocean engineering meets the requirement of ≥80 Akv / J.

[0023] Furthermore, the elongation of the produced 420MPa low-temperature resistant H-beam steel for ocean engineering meets the requirement of ≥24J.

[0024] The reasons for limiting the main chemical components of the present invention are as follows:

[0025] C: Element C is the most effective element in enhancing the strength of steel. The increase in the C content can raise the tensile strength and yield strength of the steel, but the elongation and impact toughness will decline to some extent. To ensure that the 420 MPa grade low-temperature resistant H-shaped steel for ocean engineering obtains good comprehensive properties, the C element content of the steel in this invention is designed to be 0.09 - 0.15%.

[0026] Mn: Mn is an important element for strengthening and toughening, and it has a low cost. With the increase in the manganese content, the strength of the steel is significantly improved, and the processing performance of the steel is improved, while the ductile-brittle transition temperature hardly changes. However, if the manganese content is too high, it will inhibit the transformation of ferrite, affect the yield strength of the steel, and is not conducive to the control of the yield ratio. The Mn element content of the steel in this invention is designed to be 1.25 - 1.35%.

[0027] Si: Si can increase the strength of the steel. By increasing the Si element, the strength of the steel can be improved to a certain extent. However, with the further increase in the mass percentage of Si, it is easy to form martensite structure in the steel. Therefore, the mass percentage of Si is controlled at 0.30 - 0.45%.

[0028] V: V can play the roles of precipitation strengthening, grain refinement strengthening, and grain boundary strengthening in the steel, and can reduce the ductile-brittle transition temperature. The carbonitrides of V can effectively refine the ferrite grains. In low-temperature steel, a small amount of V makes the grains refined and the toughness increased. The V element content of the steel in this invention is designed to be 0.05% - 0.09%.

[0029] P: P has strong solid solution strengthening and cold work hardening effects in the steel. P acts on ferrite. Although it can improve the strength and hardness of the steel, the biggest harm is that it has serious segregation, increases temper brittleness, significantly reduces the plasticity and toughness of the steel, resulting in the phenomenon that the steel is prone to brittle fracture during cold processing, that is, the so-called "cold brittleness" phenomenon. Therefore, the P element content of the steel in this invention is designed to be ≤0.020%.

[0030] S: S is an element of hot brittleness and easy machinability. It is known that the cutting performance improves with the increase in the mass percentage of sulfur, but the hot workability deteriorates with the increase in the sulfur content. Therefore, the mass percentage of S in the 420 MPa grade low-temperature resistant H-shaped steel for ocean engineering described in this invention is limited to S ≤ 0.015%.

[0031] Nb: Adding trace alloying element Nb to the steel has a strong effect of preventing the growth of austenite grains and is easy to obtain a fine-grained structure. Niobium will produce significant grain refinement and moderate precipitation strengthening during controlled rolling. The Nb element content of the steel in this invention is designed to be 0.02% - 0.04%.

[0032] Ni: Ni is an austenite-forming element that expands the austenite phase region. Ni reduces the resistance to dislocation movement in steel, improves the toughness of the matrix, and enhances the low-temperature toughness of the steel. Adding Ni element to the steel can also achieve solid solution strengthening and improve hardenability. At the same time, adding a certain amount of Ni element to the steel can not only enrich in the rust layer to hinder the penetration of Cl- into the matrix, but also shift the self-corrosion potential of the steel in the positive direction, thereby improving the corrosion resistance of the steel. The Ni element content of the steel in this invention is designed to be 0.15% - 0.20%.

[0033] Ti: Ti has the functions of refining grains, preventing intergranular corrosion, and improving welding performance in steel. The Ti element content of the steel in this invention is designed to be 0.01% - 0.02%.

[0034] Compared with the prior art, the beneficial technical effects of this invention are as follows:

[0035] The H-beam prepared by reasonably controlling the contents of Nb, V, Ni, and Ti elements in this invention has high strength and stable impact toughness. At the same time, the process of controlling the finish rolling temperature is adopted to make the product performance meet the requirements of this steel type, reducing the production cost. Specific embodiments

[0036] Table 1 is the chemical composition and content table of the steel types in each embodiment, Table 2 is the control table of the starting rolling temperature and finish rolling temperature in each embodiment, and Table 3 is the detection result of the mechanical properties in each embodiment.

[0037] Table 1 Chemical compositions (mass percentage / %) of each embodiment

[0038]

[0039] Table 2 Control of the starting rolling temperature and finish rolling temperature in each embodiment

[0040] Example Initial rolling temperature (°C) Final rolling temperature (°C) Example 1 1169 920 Example 2 1174 910 Example 3 1177 890 Example 4 1183 915

[0041] Table 3 Mechanical properties of each embodiment

[0042]

[0043] It can be seen from the above embodiments that the H-beam has high strength and stable low-temperature impact toughness. The chemical composition of the high-strength and low-temperature-resistant hot-rolled H-beam for ocean engineering in this invention is simple, and it has the advantages of simple control, low manufacturing cost, and strong operability for steel production.

[0044] The embodiments described above are only used to describe the preferred mode of this invention, and do not limit the scope of this invention. Without departing from the design spirit of this invention, various deformations and improvements made by those of ordinary skill in the art to the technical solution of this invention shall fall within the protection scope determined by the claims of this invention.

Claims

1. A method for producing 420MPa-grade low-temperature-resistant H-shaped steel for marine engineering, comprising: Blast furnace hot metal; Hot metal pretreatment; Converter smelting, LF refining, VD vacuum treatment, continuous casting of special-shaped billets, slow cooling of billet stacking; loading; walking beam heating furnace; high-pressure water dephosphorization; BD billet opening; CCS universal rolling; hot sawing; walking beam cooling bed cooling; straightening; sawing; its characteristics are: During converter smelting, the end point C>0.03%, the end point temperature is greater than 1620℃, and aluminum iron deoxidation is used during converter steel tapping; During the LF refining process, desulfurization, composition fine-tuning and temperature increase are carried out according to the composition and temperature of the molten steel in the converter. Ferroniobium and ferrophosphorus are added in the later stage of refining to ensure that the composition of the molten steel meets the internal control requirements; During the VD vacuum treatment process, the deep vacuum time is ≥15min, the deep vacuum degree target is <0.1KPa, the weak stirring time after breaking the air is ≥15min, the silicon calcium wire is fed, and the soft blowing time is ≥15min; During the continuous casting of beam billets, protective pouring is used throughout the process, and the billets are stacked and slowly cooled for more than 48 hours; The temperature of the preheating section is controlled at ≤1000℃, the temperature of the first heating section is controlled at ≤1200℃, the temperature of the second heating section is controlled at 1100-1330℃, the temperature of the soaking section is controlled at 1100-1330℃, and the total heating time of the ingot is controlled at 3-5h; Before the ingot is put into BD1, it must be dephosphorized with high-pressure water to prevent the surface defects of the finished H-beam caused by the pressing of the iron oxide ingot; The blanking mill is designed to roll 8 times, and the blanking area is not subjected to controlled rolling, and the rolling temperature is controlled at 1170-1180℃; The CCS universal rolling mill is designed to roll 5 times and perform controlled rolling to produce sufficiently uniform deformation bands in the austenite crystals, nucleate ferrite in the crystals and on the deformation bands, refine the grains, and control the final rolling temperature at 880-920℃; control the upper cooling bed temperature of the finished H-beam to ≥830℃, and perform close cooling; The mass percentage of the chemical composition of the H-beam includes: C 0.09%-0.15%, Si 0.30%-0.45%, Mn 1.25%-1.35%, P≤0.02%, S≤0.010%, V 0.05%-0.09%, Nb 0.02%-0.04%, Ni0.15%-0.20%, Ti 0.01%-0.03%, and the rest is Fe and impurities, with a total mass fraction of 100%.

2. The method for producing 420MPa-grade low-temperature-resistant H-shaped steel for marine engineering according to claim 1, characterized in that: The size of 420MPa grade low temperature resistant H-beam for marine engineering is 618*306*18*35mm.

3. The method for producing 420MPa-grade low-temperature-resistant H-shaped steel for marine engineering according to claim 1, characterized in that: The mass percentage of the chemical composition of the H-beam includes: C 0.095%, Si 0.318%, Mn 1.25%, P0.0173%, S 0.015%, V 0.056%, Nb 0.032%, Ni 0.167%, Ti 0.015%, and the rest is Fe and impurities, with a total mass fraction of 100%.

4. The method for producing 420MPa-grade low-temperature-resistant H-shaped steel for marine engineering according to claim 1, characterized in that: The mass percentage of the chemical composition of the H-beam includes: C 0.115%, Si 0.376%, Mn 1.27%, P0.0107%, S 0.009%, V 0.059%, Nb 0.027%, Ni 0.171%, Ti 0.019%, and the rest is Fe and impurities, with a total mass fraction of 100%.

5. The method for producing 420MPa-grade low-temperature-resistant H-shaped steel for marine engineering according to claim 1, characterized in that: The mass percentage of the chemical composition of the H-beam includes: C 0.133%, Si 0.354%, Mn 1.26%, P0.0111%, S 0.012%, V 0.057%, Nb 0.033%, Ni 0.192%, Ti 0.028%, and the rest is Fe and impurities, with a total mass fraction of 100%.

6. The method for producing 420MPa-grade low-temperature-resistant H-shaped steel for marine engineering according to claim 1, characterized in that: The mass percentage of the chemical composition of the H-beam includes: C 0.141%, Si 0.369%, Mn 1.33%, P0.0090%, S 0.011%, V 0.063%, Nb 0.025%, Ni 0.152%, Ti 0.021%, and the rest is Fe and impurities, with a total mass fraction of 100%.

7. The method for producing 420MPa-grade low-temperature-resistant H-shaped steel for marine engineering according to claim 1, characterized in that: The 420MPa grade low temperature resistant H-shaped steel produced for marine engineering meets the requirement of ≥80Akv / J at -40℃ impact energy.

8. The method for producing 420MPa-grade low-temperature-resistant H-shaped steel for marine engineering according to claim 1, characterized in that: The elongation of the 420MPa grade low-temperature resistant H-shaped steel produced for marine engineering meets the requirement of ≥24J.

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