Production and preparation method of low-cost high-strength fire-resistant hot-rolled H-shaped steel

Abstract

The invention discloses a production and preparation method of low-cost high-strength fire-resistant hot-rolled H-shaped steel, and belongs to the technical field of material metallurgy. The preparation method comprises the following steps: controlling the technical parameters in a rolling process as follows: the heating temperature is 1150-1200 DEG C, and the heat preservation time is greater than or equal to 2 hours and less than or equal to 2.5 hours; the initial rolling temperature is less than or equal to 1050 DEG C; the finish rolling temperature is less than or equal to 850 DEG C; the close-packed cooling space of the cooling bed is less than 10mm; the steel comprises the following chemical components in percentage by mass (wt%): 0.12-0.14% of C, 1.45-1.55% of Mn, 0.30-0.35% of Si, 0.40-0.50% of Cr, 0.12-0.16% of Mo, less than or equal to 0.010% of P and less than or equal to 0.005% of S. According to the invention, the yield strength is greater than or equal to 420 MPa, the tensile strength is greater than or equal to 650 MPa, the yield ratio is less than or equal to 0.70, the percentage elongation after fracture is greater than or equal to 16%, and the normal temperature impact toughness KV2 is greater than or equal to 34 J.

Description

Technical Field

[0001] The present invention belongs to the technical field of material metallurgy, and in particular relates to a production method for high-strength, low-cost, fire-resistant hot-rolled H-shaped steel. Background Art

[0002] A search revealed document CN108220798A, which discloses a 460 MPa-grade earthquake-resistant and fire-resistant construction steel and its preparation method. Its chemical composition is: C: 0.03-0.08%, Mn: 1.0-1.8%, Si: 0.1-0.5%, Cr: 0.2-0.7%, Mo: 0.1-0.3%, Ti: 0.05-0.12%, V: 0.04-0.12%, Nb: 0.01-0.06%, Al: 0.01-0.05%, P: ≤0.008%, S: ≤0.002%, with the remainder being iron and unavoidable trace elements. This steel is produced through a controlled rolling and cooling process, followed by isothermal treatment in the two-phase zone, to produce 460 MPa-grade, low-yield ratio earthquake-resistant steel plate. However, its production process is complex and is suitable only for construction steel plates. H-beams are rolled from profiled billets. The above composition system contains Al, and C is within the peritectic range. During the continuous casting process, nozzle nodules, unstable casting speeds, and liquid level fluctuations can occur, leading to cracks in the billet. Furthermore, for H-beams with complex shapes, the complex shape can easily lead to uneven temperatures during controlled rolling, making it difficult to control the rolling process. Furthermore, it is difficult to ensure uniform cooling rates at different locations during the controlled cooling process. Therefore, this type of steel is not very adaptable to H-beams.

[0003] A search revealed document CN103866188A, which discloses a 460 MPa yield strength fire-resistant, corrosion-resistant, and earthquake-resistant construction steel and its production method. The steel's chemical composition by weight is as follows: C: 0.095-0.180%, Si: 0.28-0.55%, Mn: 1.40-1.60%, P: ≤0.008%, S: ≤0.002%, Nb: 0.014-0.045%, Ti: 0.004-0.030%, V: 0.034-0.044%, Mo: 0.09-0.29%, W: 0.06-0.12%, Mg: 0.0080-0.0100%, Sn: 0.08-0.13%, O: ≤0.0016%. The process involves hot metal desulfurization, converter smelting, vacuum treatment, slab heating, staged rolling, cooling, and standby. To improve strength, this steel has a relatively high carbon content, which impacts its weldability. Furthermore, due to its high carbon content, the Ti, V, and Nb content should not be too high. Excessive Ti, V, and Nb content, combined with high carbon content, can easily lead to the precipitation of large carbides and carbonitrides during solidification and high-temperature rolling. This not only affects the precipitation strengthening effects of Ti, V, and Nb, but also negatively impacts toughness due to the large precipitates. Therefore, the alloy design of this patent is not conducive to widespread use.

[0004] A search revealed document CN201110080774.6, which discloses a low-cost, high-strength, high-toughness, earthquake-resistant, and fire-resistant steel and its preparation process. The steel contains the following components, by weight: C: 0.05-0.09%, Si: 0.10-0.30%, Mn: 0.60-1.00%, Mo: 0.20-0.40%, C: r < 0.10%, Cu: < 0.10%, Ni: < 0.10%, Nb: 0.02-0.04%, V: 0.01-0.04%, Ti: 0.01-0.04%, Al: 0.02-0.04%, N: ≤ 0.006%, P: ≤ 0.010%, S: ≤ 0.006%, as well as Fe and impurities. The preparation process includes sequential heat preservation, two-stage rolling, and cooling. The invented steel adopts Mo+Nb alloy system, which has simple composition, low content of precious alloy elements and low alloy cost. However, it adopts controlled rolling and controlled cooling technology, and the process cost is higher than traditional hot rolling followed by air cooling, and it does not have weather resistance.

[0005] The above patent documents have the following common shortcomings: the preparation process is relatively complicated, and both require controlled rolling and controlled cooling, which makes it difficult to meet the production needs of H-shaped steel with complex shapes. Summary of the Invention

[0006] The purpose of the present invention is to provide a low-cost, high-strength, fire-resistant hot-rolled H-shaped steel production and preparation method. The steel is delivered in a hot-rolled state, does not require a complex heat treatment process, has a wide process window, and meets the following performance requirements: yield strength ≥420MPa, tensile strength ≥650MPa, yield strength ratio ≤0.70, elongation after fracture ≥16%, room temperature impact toughness KV2 ≥34J, and fire resistance: its yield strength is ≥300MPa after being kept at 600°C for 15 minutes.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for producing and preparing low-cost, high-strength, refractory hot-rolled H-shaped steel. The steelmaking process includes: converter - refining outside the furnace - continuous casting of beam blanks; and the rolling process includes: walking beam furnace - high-pressure water dephosphorization - BD initial rolling - CCS finishing rolling - cooling - straightening - sawing - inspection - packaging - warehousing - shipping. The method is characterized in that the technical parameters controlled in the rolling process are:

[0009] 1) Heating temperature 1150-1200℃, holding time ≤2 hours ≤2.5 hours;

[0010] 2) Rolling temperature ≤ 1050℃;

[0011] 3) Final rolling temperature ≤850℃;

[0012] 4) The cooling beds are densely packed and the spacing is less than 10mm;

[0013] The chemical composition of the H-shaped steel is as follows by mass percentage: C: 0.12-0.14%, Mn: 1.45-1.55%, Si: 0.30-0.35%, Cr: 0.40-0.50%, Mo: 0.12-0.16%, P: ≤0.010%, S: ≤0.005%, and the rest are iron and inevitable trace chemical elements.

[0014] Furthermore, the chemical composition of the H-beam is as follows by mass percentage: C: 0.12%, Mn: 1.48%, Si: 0.32%, Cr: 0.45%, Mo: 0.15%, P: 0.009%, S: 0.002%, and the rest are iron and inevitable trace chemical elements.

[0015] Furthermore, the chemical composition of the H-beam is as follows by mass percentage: C: 0.13%, Mn: 1.52%, Si: 0.34%, Cr: 0.44%, Mo: 0.15%, P: 0.010%, S: 0.003%, and the rest are iron and inevitable trace chemical elements.

[0016] Furthermore, the heating temperature is 1180° C. and the holding time is 2.25 hours.

[0017] Furthermore, the starting rolling temperature is 1050°C.

[0018] Furthermore, the final rolling temperature is 850°C.

[0019] Furthermore, the cooling beds are closely packed with a cooling spacing of 8 mm.

[0020] The main chemical components of the present invention are limited for the following reasons:

[0021] C: C is the most effective element for increasing steel strength. Increasing C content increases the tensile strength and yield strength of steel, but decreases elongation and impact toughness, as well as corrosion resistance. Furthermore, the heat-affected zone (HAZ) of the steel can be hardened, leading to cold cracks. To ensure optimal overall performance, the C content of the steel in this invention is designed to be 0.12-0.14%.

[0022] Mn: Mn is an important strengthening and toughening element, and it's inexpensive. Increasing the manganese content significantly increases the strength of the steel and improves its workability, while barely changing the ductile-brittle transition temperature. However, excessive manganese content inhibits the ferrite transformation, affecting the steel's yield strength and hindering yield ratio control. The Mn content of the steel of this invention is designed to be 1.45-1.55%.

[0023] Cr: Cr improves steel's strength, hardness, and atmospheric corrosion resistance, particularly when added to other alloying elements. Chromium slows the decomposition of austenite, significantly improving the steel's hardenability and providing secondary hardening, but it also increases the steel's tendency to temper brittleness. However, excessive chromium content can reduce the toughness of the base material and heat-affected zone. The Cr content of the steel of this invention is designed to be 0.40-0.50%.

[0024] Mo: Mo improves corrosion uniformity and inhibits localized corrosion. It is also the most effective element for improving the high-temperature strength of steel plates. Generally, a higher Mo content increases the high-temperature strength, but Mo is expensive, and excessive amounts can reduce weldability. The Mo content of the steel of this invention is designed to be 0.12-0.16%.

[0025] Si: Si improves the corrosion resistance of steel and is often added to stainless steel, low-alloy steel, and corrosion-resistant alloys to enhance these alloys' corrosion resistance, imparting resistance to chloride stress corrosion cracking, pitting, hot concentrated nitric acid, oxidation, and seawater corrosion. Studies have shown that Si significantly improves the atmospheric corrosion resistance of carbon steel and low-alloy steel in hot and humid atmospheric environments. Furthermore, Si can enhance the corrosion resistance of low-alloy steel in the seawater splash zone. The Si content of the steel of this invention is designed to be 0.30-0.35%.

[0026] P, S: P and S are impurity elements in steel. P has a certain effect on improving corrosion resistance, but it is an element that is prone to segregation, causing severe segregation in local areas of the steel, reducing plasticity and toughness, and is extremely detrimental to low-temperature toughness. The element S is easily segregated and enriched in steel, making it an element that is detrimental to corrosion resistance. The steel of the present invention strictly controls the sulfur and phosphorus content levels in terms of metallurgical quality, namely P: ≤0.010% and S: ≤0.005%, to meet the steel grade requirements for purity, impact toughness, weldability, and corrosion resistance.

[0027] Compared with the prior art, the present invention has the following beneficial technical effects:

[0028] 1) Fewer alloying elements are added. The Mo content of most domestic refractory steels is above 0.30%. The cost of 0.01% Mo is about 36 yuan, and reducing Mo by 0.14% can reduce the cost by about 504 yuan.

[0029] 2) In the chemical composition design process of this patent, Mn and Cr are used to increase the hardenability of steel, allowing the material to obtain a large amount of bainite structure under air cooling to increase the fire resistance, thereby reducing the content of the expensive alloying element Mo, with the characteristic of low cost.

[0030] Performance requirements: yield strength ≥420MPa, tensile strength ≥650MPa, yield strength ratio ≤0.70, elongation after fracture ≥16%, impact toughness at room temperature KV2 ≥34J, fire resistance: yield strength ≥300MPa after 15 minutes of heat preservation at 600℃. DETAILED DESCRIPTION

[0031] The present invention will be further described below by means of specific examples. The examples are for illustrative purposes only, and the protection scope of the present invention is not limited to these examples.

[0032] The present invention will be further described below:

[0033] Table 1 is a list of chemical compositions and weight percentages of various embodiments of the present invention.

[0034] Table 2 is a list of the test results of mechanical and fire resistance properties of various embodiments of the present invention.

[0035] Table 1 Chemical composition and weight percentage content (wt%) of the examples

[0036] Example C Si Mn P S Cr Mo 1 0.12 0.32 1.48 0.009 0.002 0.45 0.15 2 0.13 0.34 1.52 0.01 0.003 0.44 0.15

[0037] Each embodiment: heating temperature 1180°C, holding time 2.25 hours, starting rolling temperature 1050°C, finishing rolling temperature 850°C, cooling bed close-packed with 8mm spacing.

[0038] Table 2 shows the test results of mechanical and fire resistance properties of various examples.

[0039]

[0040] From the data in Table 2 we can see that:

[0041] The yield strength, yield strength ratio, elongation, impact toughness and fire resistance of the steel products of the embodiments of the present invention all reach the requirements of a low-cost, high-strength, fire-resistant hot-rolled H-shaped steel production and preparation method.

[0042] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for producing high-strength, refractory hot-rolled H-beam at low cost, comprising a steelmaking process consisting of a converter, refining outside the furnace, and continuous casting of beam blanks; and a rolling process consisting of a walking beam furnace, high-pressure water dephosphorization, BD initial rolling, CCS finishing rolling, cooling, straightening, sawing, inspection, packaging, storage, and dispatching. The method is characterized in that: The technical parameters controlled in the rolling process are: 1) Heating temperature 1150-1200℃, holding time ≤2 hours ≤2.5 hours; 2) Rolling temperature ≤ 1050℃; 3) Final rolling temperature ≤850℃; 4) The cooling beds are densely packed and the spacing is less than 10mm; The chemical composition of the H-shaped steel is as follows by mass percentage: C: 0.12-0.14%, Mn: 1.45-1.55%, Si: 0.30-0.35%, Cr: 0.40-0.50%, Mo: 0.12-0.16%, P: ≤0.010%, S: ≤0.005%, and the rest are iron and inevitable trace chemical elements.

2. The method for producing low-cost, high-strength, fire-resistant hot-rolled H-beam according to claim 1, characterized in that: The chemical composition of the H-shaped steel is as follows by mass percentage: C: 0.12%, Mn: 1.48%, Si: 0.32%, Cr: 0.45%, Mo: 0.15%, P: 0.009%, S: 0.002%, and the rest are iron and inevitable trace chemical elements.

3. The method for producing low-cost, high-strength, fire-resistant hot-rolled H-beam according to claim 1, characterized in that: The chemical composition of the H-shaped steel is as follows by mass percentage: C: 0.13%, Mn: 1.52%, Si: 0.34%, Cr: 0.44%, Mo: 0.15%, P: 0.010%, S: 0.003%, and the rest are iron and inevitable trace chemical elements.

4. The method for producing low-cost, high-strength, fire-resistant hot-rolled H-beam according to claim 1, characterized in that: The heating temperature is 1180° C. and the holding time is 2.25 hours.

5. The method for producing low-cost, high-strength, fire-resistant hot-rolled H-beam according to claim 1, characterized in that: The rolling temperature is 1050°C.

6. The method for producing low-cost, high-strength, fire-resistant hot-rolled H-beam according to claim 1, characterized in that: The final rolling temperature is 850°C.

7. The method for producing low-cost, high-strength, fire-resistant hot-rolled H-beam according to claim 1, characterized in that: The spacing between the close-packed cooling beds is 8 mm.

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