RU2798438C1 - Hot-rolled i-steel for rolling and forming blanks of special shape from it and method for its manufacturing - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention is related to hot-rolled I-beam steel used in construction of offshore oil platforms. Hot-rolled I-beam steel contains the following chemical components, wt.%: С: 0.04-0.08, Si: ≤0,25, Mn: 1.25-1.45, V: 0,04-0,10, Ni: 0,2-1,0, Р: ≤0.02, S: ≤0.01, Nb: 0.02-0.06, Al: 0.02-0.06, N: ≤0.015, О: ≤0.005, the rest is Fe and unavoidable impurities. I-beam steel has a flange thickness of 18-24 mm, the yield strength of the upper and lower shelves is greater than or equal to 420 MPa, the energy of transverse impact at a temperature of -40°C is greater than or equal to 34 J and the energy of longitudinal impact at a temperature of -60°C is greater than or equal to 120 J.

EFFECT: low-temperature resistant hot-rolled I-steel for marine equipment is obtained, which has the required mechanical properties, easy to produce in industrial conditions and reduces the requirements for rolling equipment.

7 cl, 1 dwg, 3 tbl, 3 ex

Description

Cross-reference to related applications

This application claims the priority of PRC Patent Application No. 2019112501386, filed December 9, 2019, which is incorporated herein by reference in its entirety.

FIELD OF TECHNOLOGY

The present invention relates to the field of metallurgical technology. In particular, the present invention relates to a hot-rolled H-beam for rolling and forming and a method for making the same. The production method and the molding method are described.

BACKGROUND OF THE INVENTION

As the demand for oil and gas resources increases, offshore oil platforms are gradually expanding in difficult climatic regions, and the quality and requirements for platform construction are becoming more demanding. As a result, hot-rolled H-steels to be used for platform construction are not only in high demand, but also place higher demands on their toughness in low-temperature environments. As for the hot-rolled H-steels currently used at home and abroad, the requirements for toughness are mainly imposed on the longitudinal impact, which is found along the rolling direction. As a rule, there are no special requirements for transverse impact due to the complex shape of the I-beam, complex structural changes and large structural differences of the flanges along the transverse part. However, with the development of technology, platform designs are becoming more complex. In combination with changing conditions in the regions of application, higher requirements are gradually being put forward on the indicators of transverse impact strength. And profiles with good transverse toughness are encouraged to be used within standards and projects.

For medium and large size H-steels, rolling and forming are mainly used, and it is more difficult to provide microstructures for microalloying applications in the H-steel industry. With a combination of many factors, this ultimately affects the transverse toughness. Especially for industrial production, stability is a problem. In order to provide lateral impact, different patents give different technical ideas.

Patent CN103556055 B discloses hot-rolled I-beam steel used in the construction of offshore gas production platforms and a method for its manufacture. One aspect of the present invention is a hot-rolled I-beam steel used in the construction of offshore gas production platforms, which contains (wt.%): C: 0.10-0.17, Si: 0.10-0.40, Mn: 1.00 -1.60, P: ≤0.025, S: ≤0.015, Nb: 0.02-0.05, Ti: ≤0.025, the rest: Fe with unavoidable impurities. Mechanical properties, transverse and longitudinal impact energy at -20°C, surface quality of hot-rolled H-steel used in the construction of offshore gas production platforms discussed in the present invention can fully meet the technical requirements for H-steel used in the construction of offshore gas production platforms. The invention mainly uses medium carbon steels and Nb and Ti microalloyed steels. Due to the influence of the compositional mechanism of Nb and Ti microalloying, the rolling force in the actual rolling process is higher, which places higher demands on rolling equipment.

Patent Application CN1421286A discloses a rolling process for Nb-containing H-steel. Using the principle of physical metallurgy of metals, this method regulates and optimizes the normal process conditions, and also controls the amount of deformation in one pass, using controlled rolling in the recrystallization zone and controlled rolling in the non-recrystallized region, in order to allow ferrite to be nucleated in the deformation zone to obtain fine particles, ferrite grains, thereby uniformly refining the metallographic structure, and obtaining an H-beam with high strength, high toughness and good weldability. The resulting H-steel has a tensile strength of 490-610 MPa and a transverse impact energy at -20°C of 34-98 J, which meets the requirements of the American Petroleum Institute for class II steel in the technical characteristics of the platform structure. In this invention, the conditions for controlling the deformation temperature and the amount of deformation are very severe, which also increases the load on the rolling mill. It is extremely difficult to adjust the decline in real time, which has a great impact on the performance of the product. Therefore, there are fluctuations in the performance of the product, and the qualification rate of the product is significantly reduced.

Thus, it is necessary to specifically develop methods for smelting and rolling H-steel, so that it not only meets the requirements of melting and reduces the rolling load, but at the same time, the state of the structure after rolling can satisfy the requirement of high transverse toughness under low temperature conditions.

SUMMARY OF THE INVENTION

In order to meet the needs of offshore oil platform construction in various regions and harsh and difficult environments, the present invention provides a hot-rolled H-beam for rolling and forming and a method for manufacturing the same. The technical scheme of the present invention is as follows:

A method is proposed for manufacturing hot-rolled I-beam steel for rolling and forming, containing chemical components (wt.%): C: 0.04-0.08; Si: ≤0.25; Mn: 1.25-1.45; V: 0.04-0.10; Ni: 0.2-1.0; Р ≤0.02; S≤0.01; Nb: 0.02-0.06, Al: 0.02-0.06; N ≤0.015; About ≤0.005; the rest: Fe with inevitable impurities.

Preferably, the chemical components of the molten steel are preferably (wt %): C: 0.05-0.07; Si: ≤0.25; Mn: 1.25-1.45; V: 0.04-0.06; Ni: 0.2-0.7; P ≤ 0.02; S≤0.01; Nb: 0.02-0.04, Al: 0.02-0.05; N≤0.015; About ≤0.005.

The production method mainly includes the steps of converter smelting, ladle furnace refining, continuous casting, hot rolling and forming, which include:

1) melting and continuous casting process:

smelting using a converter, refining in a ladle furnace, and casting into a continuous casting billet with residual Fe and unavoidable impurities; liquid casting height during continuous casting is from 900mm to 950mm using full protection pouring process; casting speed is controlled at the level of 0.7-1.3 m/min;

2) rolling process:

heating: heating the continuous casting billet in a digitally controlled heating furnace, and descaling with high pressure water after being discharged from the furnace;

rolling: water-cooled rough rolling for controlled cooling, finish rolling by warm rolling and water-cooled rolling, the degree of deformation in the non-recrystallized region exceeds 30%, preferably 30%-45%; start-up equipment for pre- and post-cooling for forced cooling of H-steel, allowing control of the final rolling temperature in the range of 750°C-820°C;

Cooling: According to different specifications, the beam steel being cooled by air or water, then enters the cooling bath for centralized cooling, thus including the complete precipitation of carbonitride, while at the same time achieving a grain size of 8.5; and after forming, the temperature of the steel falls below 100°C, and finally, cutting the beam steel into pieces of a given length, stacking and tying.

Preferably, the heating temperature in step 2) is controlled in the range of 1220°C-1260°C for a heating period of 90-180 minutes.

Preferably, the initial rolling temperature in rough rolling in step 2) is controlled at 1030° C.-1130° C., and the number of rolling passes is 5-7.

Preferably, the starting rolling temperature of the finish rolling in step 2) is controlled in the range of 900° C.-1000° C.; and the number of finishing passes is 3-5.

Preferably, in step 2) for forced cooling of the lower legs of the I-steel flanges, a water nozzle is used to control the temperature difference between the upper and lower flanges in the range less than or equal to 10°C and to control the final rolling temperature in the range of 780°C-810°C. The present invention uses low-carbon and micro-alloy composition: V, Nb and Al in combination with controlled rolling of the beam steel hole pattern to obtain cold-resistant H-steel products with good transverse toughness based on rolling and forming and achieve industrial production of H-steel products. with shelf thickness specification 18 mm - 24 mm. According to embodiments of the present invention, a method for manufacturing low-temperature H-steel with good transverse toughness used for shipbuilding includes converter smelting, ladle furnace refining, full shield continuous casting, a rough rolling and finish rolling process, and a water-cooling control process. in real time.

In the present invention, for industrial production of I-beam steel products with flange thickness specifications in the range of 18-24 mm, low carbon and micro-alloyed composition is used: V and Nb in the rolling process; the matrix structure is refined by controlling Nb recrystallization rolling combined with temperature control during rolling. In the finishing rolling process, to obtain a fine and uniform ferrite structure; meanwhile, nanoscale vanadium carbonitride is deposited in the cooling stage to enhance the strength of the steel, ultimately ensuring that the hot-rolled H-steel of this specification has good transverse toughness.

Other manufacturing methods not mentioned in the present invention may also use the proposed technology.

Compared with today's low-temperature H-steel with requirements for transverse toughness and its manufacturing method, the present invention has the following advantages:

1. Through the use of mechanisms of fine-grain hardening and settling hardening, the composite microalloy composition is more suitable for the manufacture of fine-grained structures, thereby obtaining hot-rolled I-beam steels with a tensile strength of more than 510 MPa, used in shipbuilding.

2. By using the whole process of on-line controlled cooling process, combined with rolling of recrystallized and non-recrystallized areas, and micro-alloy composition with: Nb, V, Al, Ni, which is suitable for the production of low-temperature hot-rolled H-beam steel while ensuring good transverse toughness.

3. Compared with the chemical component designs in other patents, the average rolling force is reduced by 10%-30%, so it is easy to industrialize, and the requirements for rolling equipment are reduced.

4. The low-temperature H-steel product for marine applications of the present invention has good mechanical properties, its tensile strength exceeds 510 MPa, especially its transverse impact energy at -40°C exceeds 34 J, and the energy longitudinal impact at a temperature of -60°C exceeds 120 J, so it is suitable for use in rooms with extreme temperature conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a diagram showing the microstructure of a 24 mm thick shelf according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following specific examples are given to illustrate the present invention. It should be noted that the examples are provided only to further illustrate the present invention and not to limit the scope of protection of the present invention. Any minor modifications and adjustments made by any other persons to the invention are still within the scope of protection of the present invention.

All continuous casting blanks in the following examples were produced in accordance with the following method: in accordance with the established range (Table 1), chemical components: C, Si, Mn, S, P and Fe as raw materials were subjected to converter melting, refining, continuous casting , direct casting, heating or uniform heating of cast billets. Method steps 1-4c include:

1. Melting:

The content of As and Sn in the molten iron in the furnace was less than 80 ^ppm ; all slag material must be added 3 minutes before the end. The final alkalinity of the slag was controlled in the range of 2.9-3.9. The amount of slag in the converter was controlled at 55 mm using a double slag retention process for steelmaking. Bottom-argon purge for mixing was carried out during the entire refining process in such a way as to ensure complete flotation of the inclusions. The time of soft argon purge during refining was at least 20 minutes. To ensure uninterrupted production, 100 m of calcium wire were fed until the end of refining.

2. Continuous casting: A full protection pouring process was used, and the casting speed was controlled at 0.7-1.3m/min.

3. Rolling during the hot rolling process and controlled cooling: Rolling during the hot rolling process and controlled cooling after rolling has used temperature control as the main means. The outer surface of the shelves was determined at the final rolling temperature, and the rolled materials after rolling were subjected to centralized slow cooling in a cooling rack to ensure complete precipitation of vanadium carbonitride. In FIG. 1 is a diagram showing the microstructure of a 24 mm thick shelf according to the present invention. The chemical components and specific processes of examples 1-4 were listed in the table below.

The parameters and specifications of the hot rolling process for specimens 1-4 are shown in Table 2. BS EN ISO 377-1997 was used as a standard for the arrangement and preparation of specimens for mechanical testing. Methods for measuring yield strength, tensile strength and relative elongation referred to the standard IS06892-1-2009: Metallic materials - tensile test at ambient temperature. The impact energy measurement method was ISO 148-1-Metallic Materials - Charpy Pendulum Impact Test.

Parameters and technical characteristics are given in table 2.

As can be seen from the table above, the yield strength of the upper and lower shelves in examples 1-4 of the present invention is maintained above 420 MPa, which indicates good toughness, which in all cases meets the conditions for using components for offshore oil platforms in extremely low conditions environment.

Finally, it should be noted that the above examples are only intended to illustrate the technical scheme of the present invention and not to limit the scope of the invention. Although the present invention has been illustrated in detail with reference to the above examples, any person of ordinary skill in the art should understand that all modifications or equivalent substitutions made to the technical scheme of the present invention do not depart from the spirit and scope of the technical scheme of the present invention. , and all this should be included in the scope of the claims.

Claims (12)

1. Hot-rolled I-beam steel for rolling and forming, characterized in that it contains chemical components, wt.%: C: 0.04-0.08, Si: ≤0.25, Mn: 1.25-1.45, V: 0.04-0.10, Ni: 0.2-1.0, P: ≤0.02, S: ≤0.01, Nb: 0.02-0.06, Al: 0.02- 0.06, N: ≤0.015, O: ≤0.005, the rest is Fe and unavoidable impurities; wherein the specified I-beam steel has a thickness of the shelves 18-24 mm, the yield strength of the upper and lower shelves is greater than or equal to 420 MPa, the transverse impact energy at a temperature of -40°C is greater than or equal to 34 J and the longitudinal impact energy at a temperature of -60°C is greater or equal to 120 J. 2. Hot-rolled I-beam steel according to claim 1, characterized in that it contains chemical components, wt.%: C: 0.05-0.07, Si: ≤0.25, Mn: 1.25-1.45, V: 0.04-0.06, Ni: 0.20.7, P: ≤0.02, S ≤0.01, Nb: 0.02-0.04, Al: 0.02-0.05 , N: ≤0.015, O: ≤0.005, the rest is Fe and unavoidable impurities. 3. A method for manufacturing hot-rolled H-steel according to claim 1 or 2 for rolling and forming, including the following steps: the process of melting and continuous casting to obtain a billet of continuous casting, smelting is carried out using a converter, refining is carried out in a ladle furnace, and continuous casting is carried out using a pouring process with full protection while ensuring a liquid casting height of 900 mm to 950 mm, and casting is carried out at a speed of 0.7- 1.3 m/min; rolling process to produce I-beam steel, at the same time, the continuous casting billet is heated and the scale is removed after unloading from the furnace, the billets are rolled, including rough hot rolling with water cooling, finishing rolling by warm rolling and and subsequent cooling is carried out using equipment for forced cooling of the lower legs of the I-steel shelves, ensuring the control of the final rolling temperature in the range of 750°C-820°C, the resulting I-beam steel is cooled with air or water, and then fed to the cooling rack for centralized cooling, after which carry out editing on the right machine after the temperature drops below 100°C. 4. The manufacturing method according to claim 3, characterized in that the continuous casting blank is heated to a temperature in the range of 1220°C-1260°C during a heating period of 90-180 minutes at the rolling stage. 5. The manufacturing method according to claim 3, characterized in that at the rolling stage, the initial temperature of rough hot rolling is controlled in the range of 1030°C-1130°C, and the number of rolling passes is 5-7. 6. The manufacturing method according to claim 3, characterized in that at the rolling stage, the initial temperature of the finish rolling is controlled in the range of 900°C-1000°C, and the number of passes of the finish rolling is 3-5. 7. The manufacturing method according to claim 3, characterized in that at the rolling stage for forced cooling of the lower legs of the I-beam steel shelves, a water nozzle is used to control the temperature difference between the upper and lower legs of the shelves in the range less than or equal to 10 ° C.

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