WO2021000729A1 - Non-brittle steel for prestressed concrete steel bar, and production method therefor - Google Patents

Abstract

Disclosed are a non-brittle steel for a prestressed concrete steel bar, and a production method therefor. The steel comprises the following chemical components in percentages by mass: 0.25% - 0.35% of C, 1.10% - 1.40% of Si, 0.55% - 0.75% of Mn, P ≤ 0.025%, S ≤ 0.010%, with the balance being Fe and inevitable impurities. By means of the method, it can be ensured that material gases, inclusions, mechanical properties, etc. meet material requirements, the requirements for machining a steel bar by means of wires are met, a heat treatment tempering temperature is increased without reducing the strength of the steel bar, the fracture ratio of a prestressed concrete steel bar is greatly reduced, the yield and the production efficiency are improved, energy is saved, and production costs are saved for a user.

Description

Steel for prestressed concrete steel rod not easy to brittle fracture and production method thereof Technical field

The invention belongs to the field of alloy smelting, and relates to a steel for prestressed concrete steel rods, in particular to a steel for prestressed concrete steel rods that are not easily brittle fracture and a production method thereof.

Background technique

The steel grades of prestressed concrete steel rods are generally high-silicon steel (Si>1.40%) and low-silicon steel (Si: 0.70-1.10%); it has high strength and toughness, low relaxation, and strong bondability with concrete. Good weldability, upsetting, saving materials (such as

Steel rod can be substituted

Hot-rolled steel bars) have been widely used in high-strength pre-stressed concrete centrifugal pipe piles, electric poles, viaduct piers, railway sleepers and other pre-stressed components abroad. It has a very broad market in the world, especially in Asia.

Traditional prestressed concrete steel rods are designed with low silicon (Si content is generally 0.70～0.90%) composition, which has a high fracture ratio and poor relaxation during use, which brings certain risks and hidden dangers to its stability in use.

Summary of the invention

In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide a steel for prestressed concrete steel rods that is not easy to be brittle fracture.

In order to solve the above technical problems, the present invention adopts the following technical solutions: a steel for prestressed concrete steel rods that is not easily brittle fracture, which includes the following mass percentages of chemical composition, C: 0.25 to 0.35%, Si: 1.10 to 1.40%, Mn: 0.55 to 0.75%, P: ≤0.025% and S: ≤0.010%, the balance is Fe and unavoidable impurities.

Optimally, it is composed of the following mass percentages of chemical components, C: 0.29～0.34%, Si: 1.20～1.30%, Mn: 0.64～0.72%, P: ≤0.018% and S: ≤0.010%, the balance is Fe And unavoidable impurities; specifically preferably, it is composed of the following mass percentage of chemical components, C: 0.32%, Si: 1.25%, Mn: 0.68%, P: ≤ 0.015% and S: ≤ 0.008%, the balance is Fe And inevitable impurities.

Another object of the present invention is to provide a method for preparing steel for prestressed concrete steel bars with a number of rows that are not easily brittle fracture, which includes the following steps:

(a) Using molten iron and scrap steel as raw materials for converter steelmaking to obtain molten steel; the tapping temperature of the molten steel is 1600-1650°C. When the molten steel is tapped, 3 to 5 kg of lime and 1 to ferrosilicon alloy are added to each ton of molten steel. 1.5kg and 8-10kg of silico-manganese alloy, and control the mass percentage content of C in the molten steel to 0.05-0.15%, the mass percentage content of P to 0.001-0.020%, and the mass percentage content of S to 0.005-0.030%;

(b) Performing LF refining on the molten steel; the LF refining includes using auxiliary materials to make white slag to deoxidize the molten steel, and the addition amount of the auxiliary materials is 4 to 5 kg of lime, 2 to 4 kg of fluorite and calcium carbide particles per ton of molten steel. 0.5～1.5kg; the temperature at which the molten steel enters the LF furnace is 1530～1580℃, and the temperature at which the molten steel exits the LF furnace is 1540～1580℃;

(c) Continuously casting the molten steel obtained in step (b) to obtain a slab, and the superheat of the continuous casting is 15-40°C;

(d) The casting slab may be rolled and formed.

Optimally, in step (b), the LF refining time is 20-40 min, and the white residue retention time is 10-20 min.

Optimally, in step (b), after the LF refining is completed, a silicon-calcium wire is fed into the molten steel, and then argon is softly blown into the molten steel; the addition amount of the silicon-calcium wire is 0.1-0.3kg per ton of molten steel, The soft argon blowing time is 10-20 minutes, and the soft argon blowing flow intensity is 0.5-1.0 NL/min/t.

Optimally, in step (d), the slab is heated by a regenerative blast furnace gas heating furnace so that the temperature difference between its head, tail, and middle does not exceed 30°C, and the slab is produced at 930-990°C Steel rolling.

The beneficial effects of the present invention are that the steel for prestressed concrete steel bars that is not easy to be brittle fracture of the present invention adopts a chemical composition of a specific mass percentage, so that the steel bars have uniform steel quality, high cleanliness, good surface quality, and low inclusion content. The synergistic effect of high purity, small segregation and fluctuation of the components of the cleaning rod, stable mechanical properties, fine grain size, etc.; and the preparation method of the non-brittle prestressed concrete steel rod can ensure the material gas, inclusions, mechanical properties, etc. Meet the requirements of wire processing steel rods, reduce the fracture ratio of steel rods, ensure the steel quality of prestressed concrete steel rods that are not easily brittle fracture, and increase the heat treatment and tempering temperature without reducing the strength of the steel rods to increase the yield and yield It also saves energy, reduces carbon dioxide emissions, protects the environment, and saves user production costs.

Detailed ways

The steel for prestressed concrete steel rods that is not easily brittle fracture of the present invention includes the following chemical components in mass percentages: C: 0.25-0.35%, Si: 1.10-1.40%, Mn: 0.55-0.75%, P: ≤0.025% and S: ≤0.010%, the balance being Fe and unavoidable impurities. By increasing the silicon content, reducing the manganese content, and adjusting the content of other elements to obtain a specific mass percentage of the chemical composition, the steel bar has a uniform steel quality, high cleanliness, good surface quality, low inclusion content, high purity, and cleaning rod composition Synergistic effects such as small segregation and fluctuation, stable mechanical properties, and fine grains.

It preferably includes the following chemical components in mass percentages, C: 0.29～0.34%, Si: 1.20～1.30%, Mn: 0.64～0.72%, P: ≤0.018% and S: ≤0.010%, the balance is Fe and unavoidable Most preferably, C: 0.32%, Si: 1.25%, Mn: 0.68%, P: ≤ 0.015% and S: ≤ 0.008%, the balance being Fe and unavoidable impurities.

The method for preparing the steel for prestressed concrete steel bars that is not easy to break easily includes the following steps: (a) molten iron and scrap steel are used as raw materials for converter steelmaking to obtain molten steel; the tapping temperature of the molten steel is 1600-1650°C, When the molten steel is tapped, 3 to 5 kg of lime, 10 to 15 kg of ferrosilicon and 8 to 10 kg of silicomanganese are added to each ton of molten steel, and the mass percentage of C in the molten steel is controlled to be 0.05 to 0.15% and the mass percentage of P The content is 0.001 to 0.020% and the mass percentage content of S is 0.005 to 0.030%; (b) performing LF refining on the molten steel, the LF refining includes using auxiliary materials to make white slag to deoxidize the molten steel, and the auxiliary material addition amount Add 4-5kg of lime, 2-4kg of fluorite and 0.5-1.5kg of calcium carbide particles per ton of molten steel; the temperature of the molten steel entering the LF furnace is 1530-1580°C, and the temperature of the outlet LF furnace is 1550-1580°C; (c ) Continuously casting the molten steel obtained in step (b) to obtain a slab, the superheat of the continuous casting is 15-40° C.; (d) rolling the casting slab to form a wire rod. This can ensure that material gases, inclusions, mechanical properties, etc. meet the requirements of wire processing steel rods, reduce the fracture ratio of the steel rods, and ensure the steel quality of the prestressed concrete steel rods that are not easily brittle, and the strength of the steel rods is not reduced. Under the circumstances, the heat treatment tempering temperature is increased, the yield rate and production efficiency are improved, and energy is saved, carbon dioxide emissions are reduced, the environment is protected, and the user's production cost is saved.

In step (b), when the temperature at which the molten steel enters the LF furnace is 1530-1580°C and the temperature at which the LF furnace is led out is 1540-1580°C, the LF refining time is 20-40 min, and the white slag retention time is 10~ 20min. In step (b), after the LF refining is completed, the silicon-calcium wire is fed into the molten steel, and then argon is softly blown onto the molten steel; the addition amount of the silicon-calcium wire is 0.1-0.3kg per ton of molten steel, and the soft The argon blowing time is 10-20min, and the soft argon blowing flow intensity is 0.5-1.0NL/min/t, which can effectively remove the inclusions in the steel.

In step (d), the slab is heated by a regenerative blast furnace gas heating furnace so that the temperature difference between its head, tail and middle part does not exceed 30°C, and the casting slab is tapped and rolled at 930-990°C ; This is because the regenerative blast furnace gas heating furnace has a water beam structure, which can ensure the elimination of black marks on the surface of the billet; and its heating capacity of up to 1250°C can ensure that the billet is tapped at 960±30°C for rolling, and 20m long The three-stage heating method can ensure that the temperature of the core surface of the slab is kept consistent to ensure the quality of the cast slab. During the rolling process, the rolling mill adopts the conventional horizontal and vertical alternate arrangement to avoid the twisting of the rolling piece during rolling and improve the surface quality of the rolling piece; in the pre-finishing rolling mill and the finishing mill, high hardness and high wear resistance are adopted. The material roll ring rolls the rolled piece to ensure that the surface of the rolled piece is smooth and the quality meets the user's requirements. The product size can meet the requirements of class C accuracy in GB/T14981. During the rolling process, the rolled piece is cooled (slowly cooled) to control the rolling temperature of the product, so as to further control the dynamic recrystallization and dynamic recovery of the product structure to achieve the purpose of controlling the uniformity of the product structure. In the cooling process after the product is rolled, the product can be spun into loops at a temperature range of 10-20℃ higher than the phase transition temperature by controlling the cooling equipment, and can control the incubation period and phase transition of the product before the phase transition The cooling rate during the process is not more than 1℃/s, which makes the product's structure transformation close to the equilibrium structure, so that the product can obtain a coarse and uniform ferrite structure, so that the product can obtain more excellent plastic processing performance. It is beneficial for the product to undergo greater deformation during subsequent processing without surface cracking.

The following detailed description of the present invention will be given below in conjunction with the shown embodiments:

Examples 1-3 and Comparative Example 1-2 respectively provide a steel for prestressed concrete steel bars and a preparation method thereof. The chemical composition of the steel in each embodiment is shown in Table 1:

Table.1 Example 1-3, Comparative Example 1-2 The chemical element content table of steel for prestressed concrete steel bar

Content (wt%)	C	Si	Mn	P	S
Example 1	0.25	1.40	0.55	0.025	0.010
Example 2	0.35	1.10	0.75	0.020	0.005
Example 3	0.29	1.30	0.72	0.018	0.008
Example 4	0.34	1.20	0.64	0.015	0.005
Example 5	0.32	1.25	0.68	0.015	0.005
Comparative example 1	0.25	0.86	0.70	0.015	0.005
Comparative example 2	0.25	1.25	0.95	0.015	0.005

The method for preparing the steel for prestressed concrete steel rods that is not easy to break easily includes the following steps:

(a) Using molten iron and scrap steel (the mass of scrap steel is about 20% of the total raw material mass) as raw materials, the molten steel is produced by converter steelmaking; when preparing for tapping, the temperature of molten steel is adjusted to be about 1600-1650°C. Add 3～5kg of lime, 10～15kg of ferrosilicon and 8～10kg of silicomanganese per ton of molten steel (the specific addition amount in each embodiment is selected according to the chemical composition content to be controlled), and control the mass percentage content of C in molten steel as 0.05～0.15%, the mass percentage content of P is 0.001～0.020%, and the mass percentage content of S is 0.005～0.030%;

(b) LF refining of molten steel: LF refining includes the use of auxiliary materials to make white slag to deoxidize molten steel. The amount of auxiliary materials added is 4 to 5 kg of lime, 2 to 4 kg of fluorite and 0.5 to 1.5 kg of calcium carbide per ton of molten steel (each The specific addition amount in the embodiment is selected according to the content of chemical components to be controlled); the temperature of molten steel entering the LF furnace is 1530-1580°C, and the temperature of the outlet LF furnace is 1540-1580°C, and the LF refining time is 20-40min. The white slag retention time is 10-20min; after the LF refining is completed, the silicon-calcium wire is fed into the molten steel, and then the molten steel is softly blown with argon; the addition amount of the silicon-calcium wire is 0.1-0.3kg per ton of molten steel, and soft argon is added The time is 10-20min, and the flow intensity of soft argon blowing is 0.5-1.0NL/min/t;

(c) Continuously casting the molten steel obtained in step (b) to obtain a slab, and the superheat of the continuous casting is 15-40°C;

(d) Use a regenerative blast furnace gas heating furnace to heat the cast slab so that the temperature difference between the head, tail and middle does not exceed 30°C, so that the cast slab is tapped and rolled at 930-990°C to obtain wire rod; In the cooling process after rolling, by controlling the cooling equipment, the rolled product is directly spun into loops at a temperature range of 10-20℃ higher than the phase transition temperature (870～890℃) (specification is Φ6.5-20) ).

Comparative Examples 1-2 respectively provide a method for preparing steel for prestressed concrete steel bars, which is basically the same as that in Example 5. The difference is that the content of silicon and manganese of the steel is different (Comparative Example 1, Comparing Proportion 2 needs to be controlled as low silicon and high manganese).

The steel (wire rod) for the prestressed concrete steel bars prepared in the above examples was tested for performance, and the results are listed in Table 2.

Table 2 Performance Test Table of Wire Rods Prepared in Example 1-Example 3, Comparative Example 1-Comparative Example 2

The above-mentioned embodiments are only to illustrate the technical concept and characteristics of the present invention, and their purpose is to enable those familiar with the technology to understand the content of the present invention and implement them accordingly, and cannot limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims (7)

1. A steel for prestressed concrete steel rods that is not easy to brittle fracture, characterized in that it includes the following mass percentages of chemical composition, C: 0.25 to 0.35%, Si: 1.10 to 1.40%, Mn: 0.55 to 0.75%, P: ≤0.025% and S: ≤0.010%, the balance is Fe and unavoidable impurities.
2. The non-brittle fracture-resistant prestressed concrete steel bar according to claim 1, characterized in that it is composed of the following mass percentages of chemical components, C: 0.29 to 0.34%, Si: 1.20 to 1.30%, Mn: 0.64 ~0.72%, P: ≤0.018% and S: ≤0.010%, the balance being Fe and unavoidable impurities.
3. The non-brittle fracture-resistant prestressed concrete steel rod steel according to claim 1, characterized in that it is composed of the following mass percentages of chemical components, C: 0.32%, Si: 1.25%, Mn: 0.68%, P: ≤0.015% and S: ≤0.008%, the balance is Fe and unavoidable impurities.
4. The method for preparing steel for prestressed concrete steel rods that is not easily brittle fracture according to any one of claims 1 to 3, characterized in that it comprises the following steps:

   (a) Using molten iron and scrap steel as raw materials for converter steelmaking to obtain molten steel; the tapping temperature of the molten steel is 1600-1650°C. When the molten steel is tapped, 3 to 5 kg of lime and 1 to ferrosilicon alloy are added to each ton of molten steel. 1.5kg and 8-10kg of silico-manganese alloy, and control the mass percentage content of C in the molten steel to 0.05-0.15%, the mass percentage content of P to 0.001-0.020%, and the mass percentage content of S to 0.005-0.030%;

   (b) Performing LF refining on the molten steel; the LF refining includes using auxiliary materials to make white slag to deoxidize the molten steel, and the addition amount of the auxiliary materials is 4 to 5 kg of lime, 2 to 4 kg of fluorite and calcium carbide particles per ton of molten steel. 0.5～1.5kg; the temperature at which the molten steel enters the LF furnace is 1530～1580℃, and the temperature at which the molten steel exits the LF furnace is 1540～1580℃;

   (c) Continuously casting the molten steel obtained in step (b) to obtain a slab, and the superheat of the continuous casting is 15-40°C;

   (d) The casting slab may be rolled and formed.
5. The method for preparing steel for prestressed concrete steel bars that is not easy to brittle fracture according to claim 4, characterized in that: in step (b), the LF refining time is 20-40 min, and the white slag retention time is 10-20 min.
6. The method for preparing steel for prestressed concrete steel rods that is not easy to brittle fracture according to claim 4, characterized in that: in step (b), after the LF refining is completed, a silicon-calcium wire is fed into the molten steel, and then the molten steel is softened. Argon blowing; the addition amount of the silicon calcium wire is 0.1-0.3kg per ton of molten steel, the soft argon blowing time is 10-20 min, and the soft argon blowing flow intensity is 0.5-1.0 NL/min/t.
7. The method for preparing steel for prestressed concrete steel rods that is not easy to brittle fracture according to claim 4, characterized in that: in step (d), the casting billet is heated by a regenerative blast furnace gas heating furnace so that its head, The temperature difference between the tail part and the middle part does not exceed 30°C, and the cast slab is tapped and rolled at 930-990°C.