CN112011738A - A kind of low-cost composite rare earth structural steel and production method thereof - Google Patents

Abstract

The invention provides a low-cost composite rare-earth structural steel and a production method thereof, and relates to the technical field of metallurgy. By adding suitable rare-earth compounds to play the role of micro-alloying, the added amount of precious metal elements can be reduced, grain refinement and precipitation strengthening can be achieved. , to achieve the improvement of material strength, plasticity and low temperature toughness; the method includes: converter: carbon content at the end point > 0.04%, end point temperature 1640 ± 15 ° C; refining: calcium treatment; RH vacuum treatment: after adding rare earth vacuum cycle recompression and soft blowing Shanghai Steel; continuous casting: the liquidus temperature is 1521℃, the superheat degree of the molten steel in the first tundish is 25～35℃, the drawing speed: 1.0～1.2m/min; hot rolling: the slab heating temperature is 1180～1220℃; The time in the furnace is 180 to 300 minutes; first rough rolling, finishing rolling and then cooling. The technical solution provided by the present invention is suitable for the production process of structural steel.

Description

A kind of low-cost composite rare earth structural steel and production method thereof

【Technical field】

The invention relates to the technical field of metallurgy, in particular to a low-cost composite rare earth structural steel and a production method thereof.

【Background technique】

In the 21st century, the market has gradually put forward higher requirements for the development of high strength, high toughness and product reduction. It is required that structural steel should have the ability to withstand brittle failure and seismic strength in the service stage of large buildings and ships. It is used in construction machinery, hoisting machinery and equipment, ships, pipeline steel and other fields. Rare earth elements, as a series of cheap micro-alloying elements, play the mechanism of purifying molten steel and metamorphic inclusions in steel, thereby refining the target grain structure, effectively improving the strength, plasticity and toughness of materials, and developing a low-cost Rare earth structural steel products.

Patent 201310669853.X discloses a rare earth-treated high-strength steel sheet for construction machinery, which has good low-temperature impact properties and Z-direction properties. After rare-earth treatment, the morphology of inclusions is changed, the structure and grains are refined, and the yield strength is greater than 460MPa, -20 The low temperature impact toughness at ℃ is greater than 200J, but it does not involve reducing the amount of other alloying elements, and the cost of raw materials is high.

Patent 201811397212.2 discloses a rare-earth-treated Q450NQR1 steel for railway carriages and a preparation method thereof. It mainly describes the addition of rare-earth elements on the basis of the national standard, so that the steel plate has excellent corrosion resistance and improves the service life of the product. There is no research on rare-earth substitution. Or replace a small amount of the performance change of one of the precious metals, the research is too single, and it is not conducive to the development requirements of industrial low-cost.

Patent 201811335977.3 discloses a rare earth treated low temperature resistant X80M pipeline steel and its preparation method. In order to ensure the safe operation of pipelines at low temperature, after adding rare earth elements, the low temperature impact performance and drop weight shear area of the material can be improved, but the effect of rare earth elements is not described. Mechanism characteristics.

Therefore, it is necessary to study a low-cost composite rare earth structural steel and its production method to deal with the deficiencies of the prior art, so as to solve or alleviate one or more of the above problems.

[Content of the invention]

In view of this, the present invention provides a low-cost composite rare-earth structural steel and a production method thereof. By adding suitable rare-earth compounds to play the role of micro-alloying, the addition amount of precious metal elements can be reduced, grain refinement and precipitation strengthening can be achieved. Realize the improvement of material strength, plasticity and low temperature toughness.

In one aspect, the present invention provides a low-cost composite rare-earth structural steel, characterized in that the composite rare-earth structural steel, in terms of mass percentage, has the following chemical components: C 0.06-0.07%, Si≤0.050%, Mn 1.35-1.45 %, P≤0.015%, S≤0.005%, Nb 0.020～0.030%, Ti 0.020～0.030%, Als 0.030～0.040%, Ca0.0010～0.0030%, RE 0.0025～0.0050%, the balance is Fe and other raw materials residual elements.

In another aspect, the present invention provides a method for producing a low-cost composite rare earth structural steel, characterized in that the production method is used to produce the composite rare earth structural steel according to claim 1;

The production method replaces all or part of precious metal elements by adding rare earth elements, and plays the role of purifying molten steel, refining crystal grains, and precipitation strengthening in steel grades.

Aspects as described above and any possible implementation manner, further provide an implementation manner, and the steps of the production method include:

S1. Converter: the carbon content at the end point is greater than 0.04%, and the end point temperature is 1640±15℃;

S2, refining: feeding calcium wire for calcium treatment;

S3, RH vacuum treatment: after adding rare earth, vacuum cycle for a predetermined time and then re-press, soft blow for a certain period of time and then steel;

S4. Continuous casting: the liquidus temperature of the steel is 1521°C, and the superheat of the molten steel in the first tundish is 25-35°C; the casting machine adopts a constant pulling speed, and the pulling speed range is 1.0-1.2m/min;

S5, hot rolling, the process includes:

S5.1. Heating: the heating temperature is controlled at 1180～1220℃; the time in the furnace is controlled at 180～300min;

S5.2, rolling: first rough rolling and then finish rolling; rough rolling adopts 3+3 mode or 1+5 mode, rough rolling finish rolling temperature is less than or equal to 1100 ℃; finishing rolling opening temperature is controlled at 950 ~ 1050 ℃; finishing rolling The temperature is controlled at 800～830℃;

S5.3. Cooling: The cooling speed of the steel strip is controlled at 15-25°C for uniform cooling, and the coiling temperature is at 520-560°C.

According to the above aspect and any possible implementation manner, an implementation manner is further provided. The content of S1 further includes: using ferromanganese and/or ferrosilicon alloy for alloying, and using aluminum iron for final deoxidation.

The above-mentioned aspect and any possible implementation mode further provide an implementation mode, the content of S2 also includes: the process control of slagging, deoxidation, desulfurization and removal of inclusions is carried out in the LF furnace, and the molten steel composition is added according to the molten steel composition. The ferromanganese, ferrosilicon and/or ferroniobium alloy fine-tune the composition of molten steel to a target range; the target range is a range corresponding to the composition of the low-cost composite rare earth structural steel.

The above aspects and any possible implementations further provide an implementation. The specific content of S3 includes: adding La-Ce composite rare-earth iron alloy, re-pressing in vacuum cycle for 3 minutes, and ensuring soft blowing for 7-8 minutes and then on Steel; the slag surface of the ladle remains calm during the soft blowing period, and the molten steel surface shall not be exposed to the air.

The above aspect and any possible implementation manner further provide an implementation manner, the 1+5 mode in the S5.2 is specifically: 1# roughing mill rolling for 1 pass, 2# rough rolling mill rolling for 5 times Passes; 3+3 mode is specifically: 1# rough rolling mill rolling 3 passes, 2# rough rolling mill rolling 3 passes.

According to the above aspect and any possible implementation manner, an implementation manner is further provided. The finishing rolling process in S5.2 uses a 2250 mm finishing rolling mill for rolling.

According to the above-mentioned aspect and any possible implementation manner, an implementation manner is further provided, in which the encryption laminar cooling process is adopted in the S5.3.

According to the above aspect and any possible implementation manner, an implementation manner is further provided. In the S5.2, both before rough rolling and before finishing rolling, high-pressure water phosphorus removal operation is performed.

Compared with the prior art, the present invention can obtain the following technical effects: by adding suitable rare earth compounds to play a role of microalloying, the addition amount of precious metal elements can be reduced, and the formed rare earth fine particles can replace niobium, titanium and carbon. The fine compounds formed by nitrogen and nitrogen prevent the growth of grains, play the mechanism of grain refinement and precipitation strengthening, and realize the improvement of material strength, plasticity and low temperature toughness; the performance of composite rare earth structural steel is relatively large. The material added with rare earth elements will also have a better effect on subsequent welding processes and corrosion resistance.

Of course, any product implementing the present invention does not necessarily need to achieve all the above-mentioned technical effects at the same time.

【Description of drawings】

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

FIG. 1 is a metallographic morphology diagram of a hot-rolled steel with different composite rare earth elements and no rare earth element added according to an embodiment of the present invention.

【Detailed ways】

In order to better understand the technical solutions of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

It should be understood that the described embodiments are only some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. As used in the embodiments of the present invention and the appended claims, the singular forms "a," "the," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise.

The present invention explains that the composition of RE is a low-cost process and method for preparing structural steel, and RE is the abbreviation of rare earth element. Based on the concept of replacing common precious metal elements with rare earth elements, combined with the controlled rolling, controlled rolling and controlled cooling process, an appropriate amount of rare earth compounds is determined to form dispersed and fine rare earth precipitated particles to replace niobium and titanium carbon-nitrogen compounds to compensate and reduce the loss of precious metal elements It shows that the second item of particulate matter formed by an appropriate amount of composite rare earth compound further drags the grain boundary, refines the grain size, increases the dislocation density of the structure, further improves the low temperature impact toughness of the material, and reduces the ductile-brittle transition temperature of the material. , so as to achieve suitable rare earth compounds to replace other precious metal elements, and develop a low-cost composite rare earth structural steel product.

A low-cost composite rare earth structural steel, in terms of mass percentage, its chemical composition is: C 0.06～0.07%, Si≤0.050%, Mn 1.35～1.45%, P≤0.015%, S≤0.005%, Nb 0.020～0.030 %, Ti 0.020-0.030%, Als 0.030-0.040%, Ca 0.0010-0.0030%, RE 0.0025-0.0050%, the balance is Fe and other residual elements in the raw materials.

As a series of cheap microalloying elements, the added rare earth elements preferentially react with [S] and [O] in the molten steel in the steel, and play the role of purifying the molten steel and the mechanism of metamorphic inclusions, thereby refining the target grains structure, effectively improve the strength, plasticity and toughness of the material, and develop a low-cost rare earth structural steel product.

Rare earth elements react with [S] and [O] in molten steel. The specific reactions are as follows:

RE+3[O]+[Al]=CeAlO ₃

RE+[O]+[S]=REO ₂ S

Among them, large particles of rare earth composite inclusions are formed, so that the inclusions float up into the slag, which plays a role in deeply purifying molten steel; while an appropriate amount of composite rare earth elements has a mutual coupling mechanism, which further metamorphos the chain and angular shapes in molten steel. The inclusions form ellipsoid or nearly spherical rare earth composite particles, pinning the grain boundaries and hindering the growth of grains.

A production method of low-cost composite rare earth structural steel, comprising:

Step 1: Converter process: the carbon content at the end point is controlled to be greater than 0.04%, and the end point temperature is 1640±15°C to improve the cleanliness of molten steel;

Step 2: Refining process: feeding calcium wire for calcium treatment;

Step 3: RH vacuum treatment process: after adding rare earth, vacuum cycle for 3 minutes to repress, to ensure that the steel is loaded after 7-8 minutes of soft blowing; the rare earth elements are rare earth La and Ce;

Soft blowing generally takes the actual steel liquid level as a reference, and observes the change of liquid level. After calcium treatment, the soft blowing (Blowing Ar) time is calculated, and 7-8min is obtained from empirical analysis data, which has certain theoretical guidance;

Step 4: Continuous casting process: the liquidus temperature of the steel is 1521°C, the superheat degree of the molten steel in the first tundish is 25-35°C, the casting machine adopts a constant pulling speed, and the control range is 1.0-1.2m/min;

Step 5: Hot rolling process: the heating temperature of the slab is controlled at 1180～1220℃, and the time in the furnace is controlled at 180～300min; 3+3 mode or 1+5 mode is used for rough rolling; the starting temperature of finishing rolling is controlled at 950～1050 ℃; the finishing rolling temperature is controlled at 800-830℃; the coiling temperature is 520-560℃.

The hot rolling process specifically includes:

Step 5.1: Heating system: the heating temperature of the slab is controlled at 1200±20℃, and the time in the furnace is controlled at ≥180min to ensure the solid solution and full austenitization of the alloy components in the slab; the soaking temperature is 1190-1230℃, and the The heating time is 35～60min;

Step 5.2: Rolling process: use high-pressure water to remove phosphorus, fix the width of the press, roll in E1R1 roughing mill and E2R2 roughing mill; choose 1# roughing mill for 1 pass, and 2# rough rolling mill for rolling 5 passes; or 1# roughing mill rolling 3 passes, 2# roughing mill rolling 3 passes; rough rolling mill finishing temperature≤1100℃; flying shear; high-pressure water phosphorus removal; 2250mm finishing mill rolling, finishing rolling The starting rolling temperature is controlled at 950-1050°C; the finishing rolling temperature is controlled at 800-830°C; the deformation of the pass and proper temperature control are further ensured, and the microstructure type of the finished product is determined.

Step 5.3: Cooling system: adopt densified laminar cooling, and the cooling rate of the steel strip is controlled at 15-25°C for uniform cooling to ensure the dispersion and uniform precipitation of rare earth particles and the uniformity of the structure; the coiling temperature is 520-560°C.

The advantages of the present invention include:

1) For the production of structural steel, a small amount of compound rare earth elements is added, combined with the 2250mm on-line controlled rolling and cooling process to reduce the amount of precious metal elements added. It can prevent the growth of grains, play the mechanism of grain refinement and precipitation strengthening, and realize the improvement of material strength, plasticity and low temperature toughness, and has wide application prospects.

2) In the present invention, the low-cost composite rare earth structural steel prepared by adding an appropriate amount of rare earth composite compounds to replace other microalloying elements has a large margin in various properties, and the material added with rare earth elements will also affect the subsequent welding process and corrosion resistance. to a better effect.

Example 1:

1. Smelting of materials

1.1 Converter: The carbon content at the end point is controlled to be greater than 0.04%, and the end point temperature is 1640±15°C to improve the cleanliness of molten steel; the steel is alloyed with ferromanganese, ferrosilicon and other alloys, and the final deoxidation is made of aluminum and iron.

1.2 Refining: LF furnace controls the process of slag making, deoxidation, desulfurization and removal of inclusions. According to the composition of molten steel, alloys such as ferromanganese, ferrosilicon and ferroniobium are added to fine-tune the composition of molten steel to the target range, and calcium wire is fed for calcium treatment.

1.3 RH treatment process: add La-Ce composite rare earth iron alloy and re-press in vacuum for 3 minutes to ensure that the steel is loaded after soft blowing for 7-8 minutes; after the vacuum treatment, soft blowing is performed. During the soft blowing, the slag surface of the ladle remains calm, and no molten steel is allowed. face exposed to the air.

1.4 Continuous casting: the liquidus temperature of this steel is 1521℃, the superheat degree of molten steel in the first tundish is 25～35℃, the casting machine adopts constant pulling speed, and the control range is 1.0～1.2m/min.

2. Controlled rolling and controlled cooling process

Step-by-step heating furnace is used to heat the slab, and the specific process is shown in Table 1. The rough rolling adopts 3+3 mode or 1+5 mode, and the finishing rolling adopts F1~F7.

Rolling stage: the finishing rolling temperature is controlled at 950～1050℃; the finishing rolling temperature is controlled at 800～830℃; the coiling temperature is controlled at 520～560℃.

Table 1 Billet heating process parameters

Slab thickness mm Heating temperature °C in furnace time min Soaking temperature °C Soaking time min Baking temperature °C 230 1180～1220 180～300 1190～1230 35～60 1200±20

The performance of the composite rare earth structural steel produced by the production method of the present application is analyzed below:

According to the production process of the present application, the chemical composition of the specification product after smelting is shown in Table 2. The content of RE can show the change of the amount of rare earth added. The content of rare earth is from 0 ppm (comparative example) to 56 ppm (Example 3), and the amount of rare earth is increasing.

Table 2 Chemical composition of materials

C Si Mn P S Nb Al_S Ti Ca RE Comparative ratio 0.07 0.03 1.44 0.012 0.003 0.030 0.028 0.025 0.0008 0 Example 1 0.06 0.02 1.52 0.015 0.001 0.025 0.033 0.027 0.0001 0.0036 Example 2 0.06 0.03 1.48 0.010 0.001 0.024 0.040 0.029 0.0001 0.0047 Example 3 0.08 0.02 1.52 0.013 0.002 0.023 0.037 0.026 0.0004 0.0056

According to the above-mentioned composition design and the hot rolling process of the present application, the material properties are shown in Table 3.

Table 3 Tensile properties and impact properties

The metallographic structure of the product is mainly ferrite. The specific structure is shown in Figure 1. When the compound rare earth element is 36ppm, it is smaller than the ferrite without rare earth element (0ppm RE); it is better than the compound rare earth element, which is 47ppm. And 56ppm, that is, when the rare earth content exceeds 36ppm, as the amount of rare earth elements increases, the ferrite structure of the product is coarse, and even mixed crystal or band defects appear. Adding an appropriate amount of rare earth elements (36ppm) can replace the precipitation of niobium and titanium carbonitrides, which can drag the grain boundaries, significantly refine the grains, and improve the overall performance of the material; on the contrary, adding excessive rare earth elements fails. When the grain is refined, mixed crystal defects appear, which deteriorates the overall performance of the material. 36ppm is the best addition amount for this type of product. Usually, when the addition amount reaches 47ppm or more, the product performance has deteriorated significantly. For Table 3, there is no obvious change in tensile properties compared with those without rare earth addition, and there is no downward trend in tensile properties with the increase of rare earth content. increasing trend. But for the low temperature toughness of the material, when the rare earth content is 36ppm, the low temperature toughness at -40℃ is the best.

The method for producing a low-cost composite rare earth structural steel provided by the embodiments of the present application has been described in detail above. The description of the above embodiment is only used to help understand the method of the present application and its core idea; meanwhile, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific embodiment and the scope of application, In conclusion, the content of this specification should not be construed as a limitation on the present application.

As certain terms are used in the specification and claims to refer to particular components. It should be understood by those skilled in the art that hardware manufacturers may refer to the same component by different nouns. The present specification and claims do not use the difference in name as a way to distinguish components, but use the difference in function of the components as a criterion for distinguishing. As mentioned in the entire specification and claims, "comprising" and "including" are open-ended terms, so they should be interpreted as "including/including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range, and basically achieve the technical effect. Subsequent descriptions in the specification are preferred embodiments for implementing the present application, however, the descriptions are for the purpose of illustrating the general principles of the present application and are not intended to limit the scope of the present application. The scope of protection of this application should be determined by the appended claims.

It should also be noted that the terms "comprising", "comprising" or any other variation thereof are intended to encompass non-exclusive inclusion, such that a commodity or system comprising a list of elements includes not only those elements, but also includes not explicitly listed other elements, or elements inherent to the commodity or system. Without further limitation, an element defined by the phrase "comprising a..." does not preclude the presence of additional identical elements in the article or system that includes the element.

It should be understood that the term "and/or" used in this document is only an association relationship to describe the associated objects, indicating that there may be three kinds of relationships, for example, A and/or B, which may indicate that A exists alone, and A and B exist at the same time. B, there are three cases of B alone. In addition, the character "/" in this document generally indicates that the related objects are an "or" relationship.

The above description shows and describes several preferred embodiments of the present application, but as mentioned above, it should be understood that the present application is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various various other combinations, modifications and environments, and can be modified within the scope of the concept of the application described herein, using the above teachings or skill or knowledge in the relevant field. However, modifications and changes made by those skilled in the art do not depart from the spirit and scope of the present application, and should all fall within the protection scope of the appended claims of the present application.

Claims (10)

1. A low-cost composite rare earth structural steel, characterized in that the chemical composition of the composite rare earth structural steel and the mass percentage of each component are: C 0.06～0.07%, Si≤0.050%, Mn 1.35～1.45%, P ≤0.015%, S≤0.005%, Nb 0.020～0.030%, Ti 0.020～0.030%, Als 0.030～0.040%, Ca 0.0010～0.0030%, RE0.0025～0.0050%, the balance is Fe and other raw material residual elements. 2. A production method of low-cost composite rare earth structural steel, wherein the production method is used to produce the composite rare earth structural steel as claimed in claim 1; The production method replaces all or part of precious metal elements by adding rare earth elements, and plays the role of purifying molten steel, refining crystal grains, and precipitation strengthening in steel. 3. The production method of low-cost composite rare earth structural steel according to claim 2, wherein the steps of the production method comprise: S1. Converter: the carbon content at the end point is greater than 0.04%, and the end point temperature is 1640±15℃; S2, refining: feeding calcium wire for calcium treatment; S3, RH vacuum treatment: after adding rare earth, vacuum cycle for a predetermined time and then re-press, soft blow for a certain period of time and then steel; S4. Continuous casting: the liquidus temperature of the steel is 1521°C, and the superheat of the molten steel in the first tundish is 25-35°C; the casting machine adopts a constant pulling speed, and the pulling speed range is 1.0-1.2m/min; S5, hot rolling, the process includes: S5.1. Heating: the heating temperature is controlled at 1180～1220℃; the time in the furnace is controlled at 180～300min; S5.2, rolling: first rough rolling and then finish rolling; rough rolling adopts 3+3 mode or 1+5 mode, rough rolling finish rolling temperature is less than or equal to 1100 ℃; finishing rolling opening temperature is controlled at 950 ~ 1050 ℃; finishing rolling The temperature is controlled at 800～830℃; S5.3. Cooling: The cooling speed of the steel strip is controlled to be uniformly cooled at 15-25°C. 4 . The method for producing low-cost composite rare earth structural steel according to claim 3 , wherein the content of S1 further comprises: using ferromanganese and/or ferrosilicon alloy for alloying, and finally deoxidizing by using aluminum ferrous alloy. 5 . 5 . The method for producing low-cost composite rare earth structural steel according to claim 3 , wherein the content of S2 further comprises: the process control of slagging, deoxidation, desulfurization and removal of inclusions in the LF furnace, according to 5 . Molten steel composition Add ferromanganese, ferrosilicon and/or ferroniobium alloy to fine-tune the molten steel composition to the target range. 6. The method for producing low-cost composite rare-earth structural steel according to claim 3, wherein the specific content of S3 comprises: adding La-Ce composite rare-earth iron alloy, recompressing in a vacuum cycle for 3 minutes, and ensuring soft blowing for 7~7 Ladle slag surface shall be kept calm during soft blowing, and no molten steel surface shall be exposed in the air. 7 . The method for producing low-cost composite rare earth structural steel according to claim 3 , wherein the 1+5 mode in S5.2 is specifically: 1# roughing mill rolling 1 pass, 2# roughing mill rolling 5 passes of rolling; 3+3 mode is specifically: 1# rough rolling mill rolling 3 passes, 2# rough rolling mill rolling 3 passes. 8 . The method for producing low-cost composite rare earth structural steel according to claim 3 , wherein the finishing rolling process in S5.2 is rolled by a 2250 mm finishing mill. 9 . 9 . The method for producing low-cost composite rare earth structural steel according to claim 3 , characterized in that, in S5.3 , a densified laminar cooling process is adopted. 10 . 10 . The method for producing low-cost composite rare-earth structural steel according to claim 3 , wherein, in the S5.2, both before rough rolling and before finishing rolling, high-pressure water dephosphorization operation is performed. 11 .

Images