CN111286665A - Preparation method of BG960 ultrahigh-strength steel - Google Patents

Abstract

The invention discloses a preparation method of BG960 ultra-high-strength steel. In the preparation method, the continuous casting, rolling and coiling of the steel plate is carried out by annealing the coiled plate, so that the internal stress can be released, and further It is ensured that the BG960 ultra-high strength steel has an excellent shape and a good uncoiling effect. The preparation method of the BG960 ultra-high strength steel has the advantages of excellent comprehensive performance, low production cost, excellent shape, and good uncoiling effect.

Description

A kind of preparation method of BG960 ultra-high strength steel

technical field

The invention discloses and relates to the technical field of iron and steel smelting, in particular to a preparation method of BG960 ultra-high-strength steel.

Background technique

With the progress of society and the development of science and technology, the standards and requirements for construction machinery are also higher, which not only requires higher working efficiency and longer service life of construction machinery, but also requires lower manufacturing and use costs of construction machinery. By realizing the development of construction machinery in the direction of high-parameterization, large-scale and light-weight, the work efficiency of construction machinery is improved, the energy consumption of construction machinery is reduced, and the self-weight is reduced. Therefore, a large number of high-strength steels must be used in the manufacture of construction machinery.

At present, my country's ultra-high-strength structural steel cannot be completely domestically produced and needs to be imported in large quantities, resulting in high manufacturing costs of construction machinery. The main difficulties include the matching of comprehensive performance, the control of plate shape, and the cost. The ultra-high-strength steel produced by domestic steel mills is mainly quenched and tempered steel, that is, by adding a large amount of alloying elements to the steel, and then through subsequent quenching and tempering treatment, the ultra-high-strength steel that meets the performance requirements is produced. When this preparation method is used, the composition ratio of the alloying elements added directly affects the comprehensive properties of the ultra-high strength steel, and subsequent quenching and tempering treatment is required, which increases the preparation cost. In addition, when preparing ultra-high-strength steels with a thickness of less than 6.0mm in China, due to the large internal stress, it is very difficult to control the shape and uncoil.

Therefore, how to develop a new preparation method to ensure the excellent shape of the plate and reduce the difficulty of unwinding has become an urgent problem to be solved.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a preparation method of BG960 ultra-high-strength steel, so as to solve the problems of difficulty in plate shape control and difficulty in uncoiling.

The technical solution provided by the present invention is, in particular, a preparation method of BG960 ultra-high strength steel, which is characterized in that comprising the following steps:

Pretreatment of molten iron: pretreatment of molten iron;

Converter: the pretreated molten iron is alloyed according to the designed element content, and the ladle is purged with argon before tapping;

Refining: refining the molten steel after the converter;

Continuous casting: the refined molten steel is continuously cast into slabs by a continuous casting machine;

Rolling and coiling: using hot rolling method, the slab is put into the heating furnace for heating, rolling and coiling;

Annealing: The coiled sheet is annealed.

Preferably, the annealing treatment specifically adopts bell annealing.

Further preferably, the temperature of the bell annealing is 450°C-600°C, and the temperature is kept for 4-8 hours, followed by natural cooling.

Further preferably, in the refining step, after adopting LF refining and RH refining dual-path refining, calcium-silicon wire is used for calcium treatment, and the LF refining and RH refining dual-path refining are as follows: the molten steel is sequentially subjected to LF refining and RH refining .

Further preferably, in the rolling and coiling steps, the heating temperature is 1200-1260° C., and the holding time is 30 minutes.

Further preferably, the rolling and coiling steps are controlled by the selection of 3+3 modes of blank rolling passes, the final rolling temperature is ≥820°C, the coiling temperature is ≤300°C, and the cooling method is continuous and uniform cooling in the front section.

The preparation method of the above-mentioned BG960 ultra-high strength steel provided by the present invention, the steel plate after continuous casting, rolling and coiling is annealed by annealing the coiled plate, so that its internal stress can be released, thereby ensuring that the BG960 ultra-high-strength steel can be released. The high-strength steel has excellent shape and good decoiling effect.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not intended to limit the disclosure of the present invention.

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description serve to explain the principles of the invention.

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. In other words, other drawings can also be obtained based on these drawings without creative labor.

1 is a hot-rolled metallographic structure diagram of the BG960 ultra-high-strength steel provided by the disclosed embodiment of the present invention;

FIG. 2 is an annealed metallographic structure diagram of the BG960 ultra-high strength steel provided by the disclosed embodiment of the present invention.

Detailed ways

Exemplary embodiments will be described in detail herein, examples of which are illustrated in the accompanying drawings. Where the following description refers to the drawings, the same numerals in different drawings refer to the same or similar elements unless otherwise indicated. The implementations described in the illustrative examples below are not intended to represent all implementations consistent with the present invention. Rather, they are merely examples of methods consistent with some aspects of the invention as recited in the appended claims.

In order to solve the problems of high cost, difficult plate shape control, and difficulty in uncoiling existing BG960 ultra-high-strength steel preparation methods, the present embodiment provides a preparation method for BG960 ultra-high-strength steel, which specifically includes the following steps:

1) Pretreatment of molten iron: pretreatment of molten iron;

2) Converter: the pretreated molten iron is alloyed according to the designed element content, and the ladle is purged with argon before tapping;

3) Refining: refining the molten steel after the converter;

4) Continuous casting: the refined molten steel is continuously cast into slabs by a continuous casting machine;

5) Rolling and coiling: the hot rolling method is adopted, and the slab is put into the heating furnace for heating, rolling and coiling;

6) Annealing: the coiled sheet is annealed.

Among them, the annealing step can adopt bell annealing, and the temperature of bell annealing is 450 ℃-600 ℃, after 4-8 hours of heat preservation, natural cooling, this annealing step adopts appropriate annealing temperature and heat preservation time, so that after coiling The internal stress in the steel can be released, which avoids the poor control of the plate shape and the difficulty in uncoiling caused by excessive internal stress when using the existing ultra-high-strength steel preparation method when preparing the ultra-high-strength steel. , which can effectively improve the quality of the plate shape and obtain a better uncoiling effect.

In the refining step, after using LF refining and RH refining dual-path refining, calcium-silicon wire is used for calcium treatment, wherein the LF refining and RH refining dual-path refining is: the molten steel is sequentially subjected to LF refining and RH refining. The above-mentioned RH refining (vacuum cycle deoxidation method) is to blow in an inert gas, so that a small part of the molten steel enters the vacuum environment. After vacuum treatment, the contact area between the steel and the gas is increased, the degassing effect is improved, and the decarburization effect is good. LF refining (ie submerged arc heating furnace method) uses submerged arc to heat molten steel and blows inert gas into molten steel to achieve refining in a non-oxidizing atmosphere, thereby achieving the effects of desulfurization, deoxidation and removal of inclusions. The molten steel is subjected to LF refining and RH refining in sequence, so that the molten steel is more pure, which in turn makes the prepared ultra-high-strength steel have better mechanical properties and meets the comprehensive performance requirements of ultra-high-strength steel.

By adopting an ultra-low coiling temperature of less than or equal to 300°C, the martensite structure can be directly obtained, eliminating the quenching and tempering process in the existing ultra-high-strength steel preparation method, so that the ultra-high-strength steel prepared by the preparation method of the BG960 ultra-high-strength steel can be obtained. The high-strength steel further reduces the preparation cost while ensuring the comprehensive performance meets the standard.

In the above refining step, it is further preferred that during LF refining, positive pressure is maintained, the amount of increased N is controlled to be less than or equal to 10 ppm, and active lime and fluorite are used in LF refining to make reducing slag with good fluidity. By adding active lime and fluorite to make reducing slag with good fluidity, the fluidity of slag can be improved, and the efficiency of desulfurization and dephosphorization can be improved.

In the above rolling and coiling steps, the heating temperature is 1200-1260° C., and the holding time is 30 minutes. By controlling the heating temperature and holding time, the formation of iron oxide scale in the slab can be effectively reduced, the heating temperature of the slab can be uniform, and the generation of internal stress can be reduced, thereby providing a basis for ensuring the shape of the slab.

In the above-mentioned continuous casting steps, a constant pulling speed is maintained, and the continuous casting superheat degree is less than or equal to 25°C. By controlling the constant drawing speed and the continuous casting superheat, the internal and external quality of the slab can be ensured, thereby ensuring the comprehensive properties of the prepared ultra-high strength steel, and avoiding the ejector blank caused by excessive speed or excessive continuous casting superheat. Thin shells, easy steel breakouts, and increased non-metallic inclusions occur.

The composition design of the above-mentioned BG960 ultra-high-strength steel, specifically, by weight percentage, the ultra-high-strength steel contains C0.11-0.13%, Si 0.15-0.25%, Mn 1.15-1.25%, Al 0.020-0.045%, Cr+Mo 0.20 -0.80%, Nb+V+Ti 0.15-0.25%, B 0.0015-0.0025%, Ca 0.002-0.004%, P≤0.010%, S≤0.002%, N≤0.045%, O≤0.0020%, the balance is Fe and inevitable inclusions.

The present invention will be further explained below in conjunction with specific embodiments, but it is not intended to limit the protection scope of the present invention.

Example 1

The preparation of high-strength steel is carried out as follows:

1) Pretreatment of molten iron: Pretreatment of molten iron is carried out, and the material is selected from refined scrap steel. 2) Converter: the pretreated molten iron is alloyed according to the designed element content, and the ladle is purged with argon before tapping. 3) Refining: After the molten steel after the converter is subjected to LF refining and RH refining, the positive pressure is maintained during LF refining, and the amount of N added is required to be less than or equal to 10ppm, and active lime and fluorite are used in LF refining to make reducing slag with good fluidity. Control the intensity of argon blowing, and use calcium-silicon wire for calcium treatment. 4) Continuous casting: The refined molten steel is continuously cast into slabs by a continuous casting machine, and the tundish is purged with argon gas before pouring. No molten steel is exposed during the pouring process. Speed, continuous casting superheat ≤ 25 ℃. 5) Rolling and coiling: In the hot rolling method, the slab is put into a heating furnace for heating, the heating temperature is 1200-1260°C, and the holding time is 30 minutes. 3+3 mode control is selected for the rough rolling pass, the final rolling temperature is ≥820℃, and the coiling temperature is ≤300℃. 6) Annealing: The coiled sheet is annealed by bell annealing. The bell annealing temperature is controlled at 450°C-600°C, and after being kept in the furnace for 4-8 hours, it is cooled with the furnace to obtain the finished product.

The above-mentioned finished products were subjected to component testing, as shown in Table 1.

Table 1:

C(%) Si(%) Mn(%) Al(%) Cr+Mo(%) Nb+V+Ti(%) 0.11-0.13 0.15-0.25 1.15-1.25 0.020-0.045 0.20-0.80 0.15-0.25 B% Ca% P% S% N% O% 0.0015-0.0025 0.002-0.004 ≤0.010 ≤0.002 ≤0.045 O≤0.0020

Comparative Example 1

The high-strength steel is prepared and obtained by adopting the quenching and tempering process in the prior art. Specifically: heat the steel strip to 720°C within 0-15 seconds, use resistance heating at the rear, heat it to 900°C within 2 minutes, hold for 5 minutes, use aerosol and air cooling for quenching, and then return to 600°C. Fire for 15 minutes.

The ingredients are detailed in Table 2.

Table 2:

Element C Si Mn P S Als Cr Mo Nb V Ti standard ≤0.2 ≤0.8 ≤2.0 ≤0.02 ≤0.01 ≥0.01 ≤1.5 ≤0.7 ≤0.06 ≤0.12 ≤0.05 actual value 0.14 0.18 1.33 0.006 0.001 0.34 0.46 0.39 0.031 0.09 0.023

Example 2

The high-strength steel in Example 1 and the high-strength steel in Comparative Example 1 were tested for performance, as shown in Table 3.

table 3:

The hot-rolled metallographic structure diagram of the BG960 ultra-high strength steel prepared in Example 1 is shown in FIG. 1 , and the annealing microstructure diagram of the BG960 ultra-high strength steel prepared in Example 1 is shown in FIG. 2 .

Other embodiments of the invention will readily suggest themselves to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the invention which follow the general principles of the invention and which include common knowledge or conventional techniques in the art not disclosed by the invention . The specification and examples are to be regarded as exemplary only, with the true scope and spirit of the invention being indicated by the claims.

It should be understood that the present invention is not limited to what has been described above, and various modifications and changes may be made without departing from its scope. The scope of the present invention is limited only by the appended claims.

Claims (6)

1. A preparation method of BG960 ultrahigh-strength steel is characterized by comprising the following steps:

pretreating molten iron: pretreating molten iron;

converter: alloying the pretreated molten iron according to the designed element content, and purging a steel ladle by adopting argon before tapping;

refining: refining the molten steel after the converter;

continuous casting: continuously casting the refined molten steel into a plate blank by adopting a continuous casting machine;

rolling and coiling: the slab is put into a heating furnace to be heated, rolled and curled by adopting a hot rolling mode;

annealing: and annealing the coiled plate.

2. The BG960 ultra-high strength steel preparation method of claim 1, wherein the annealing treatment is specifically a hood annealing.

3. The preparation method of BG960 ultra-high strength steel of claim 1, wherein the temperature of the hood annealing is 450 ℃ -600 ℃, and after heat preservation for 4-8 hours, the steel is naturally cooled.

4. The BG960 ultrahigh-strength steel preparation method of claim 1, wherein the refining step is performed by calcium treatment using a calcium silicon wire after LF refining and RH refining dual-path refining, wherein the LF refining and RH refining dual-path refining are as follows: and sequentially performing LF refining and RH refining on the molten steel.

5. The BG960 ultra-high strength steel preparation method as in claim 1, wherein in the rolling and coiling steps, the heating temperature is 1200-1260 ℃, and the holding time is 30 minutes.

6. The BG960 ultrahigh-strength steel preparation method of claim 1, wherein the rolling and coiling steps are controlled by selecting a 3+3 mode from a roughing pass, the finish rolling temperature is more than or equal to 820 ℃, the coiling temperature is less than or equal to 300 ℃, and the cooling mode is continuous and uniform cooling at the front section.

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