Steel bar with 900MPa-grade tensile strength for infrastructure threaded rod and preparation method of steel bar

Abstract

The invention discloses a steel bar with 900MPa-grade tensile strength for an infrastructure threaded rod and a preparation method of the steel bar. The steel bar comprises the following chemical components in percentage by weight: 0.35 to 0.50 percent of C, 0.17 to 0.45 percent of Si, 0.60 to 1.0 percent of Mn, 0.90 to 1.20 percent of Cr, 0.04 to 0.06 percent of Al, 0.015 to 0.04 percent of Nb, 0.06 to 0.10 percent of V, 0.01 to 0.03 percent of N and the balance of Fe and inevitable impurities. The steel has excellent strength, toughness, plasticity and anti-fatigue performance, the yield strength is larger than or equal to 550 MPa, the tensile strength is larger than or equal to 900 MPa, the section elongation is larger than or equal to 15%, the section shrinkage rate is larger than or equal to 30%, the V-shaped notch impact KV2 at the temperature of-20 DEG C is larger than or equal to 50 J / cm < 2 >, and the steel is suitable for manufacturing the high-strength capital construction threaded rod.

Description

Technical Field

[0001] The invention belongs to the technical field of steel, and specifically relates to a steel bar with a tensile strength of 900 MPa for infrastructure threaded rods and a preparation method thereof. Background Art

[0002] In the field of infrastructure construction, threaded rods are widely used to support, fix and carry various loads. When these threaded rods are subjected to high-intensity loads, they need to have excellent mechanical properties such as high strength, high toughness, high plasticity and good welding performance.

[0003] However, existing threaded rod materials and production processes have certain limitations and are difficult to meet the growing performance requirements. Therefore, it is an urgent need to develop a new type of high-strength infrastructure threaded rod steel bar and a preparation method thereof.

[0004] Traditional threaded rod materials mainly include carbon steel, alloy steel, stainless steel, etc. These materials have certain deficiencies in strength, toughness, plasticity and fatigue resistance, especially under high-intensity loads, which are prone to problems such as stress concentration, loosening, excessive wear, etc., seriously affecting the stability and safety of infrastructure. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a steel bar for infrastructure threaded rod with a tensile strength of 900 MPa and a preparation method thereof, which has excellent strength, toughness, plasticity and fatigue resistance, and is suitable for manufacturing high-strength infrastructure threaded rods.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A steel bar for infrastructure threaded rods with a tensile strength of 900 MPa. The chemical composition and weight percentage of the steel bar are: C: 0.35-0.50%, Si: 0.17-0.45%, Mn: 0.60-1.0%, Cr: 0.90-1.20, P: ≤0.01%, S: ≤0.005%, Al: 0.04-0.06%, Nb: 0.015-0.04%, V: 0.06-0.10%, N: 0.01-0.03%, B: ≤0.005%, and the balance is Fe and unavoidable impurities.

[0008] The metallographic structure of the steel bar is ferrite and pearlite, and the grain size reaches above level 8.

[0009] The steel bar has a yield strength of ≥550MPa, a tensile strength of ≥900Mpa, a cross-sectional elongation of ≥15%, a cross-sectional shrinkage of ≥30%, and a V-notch impact KV2 of ≥50J / cm at -20°C. 2 .

[0010] The present invention also provides a method for preparing the steel bar with a tensile strength of 900 MPa for infrastructure threaded rods, and the preparation method comprises the following steps: smelting - continuous casting - hot rolling - online normalizing.

[0011] Furthermore, the smelting step includes the following process steps: blast furnace molten iron smelting - converter steelmaking - LF refining - RH vacuum degassing.

[0012] In the converter tapping step, control C≥0.010%, P≤0.015%, and the tapping temperature≥1620°C.

[0013] In the LF refining step, the LF refining time is controlled to be ≥40 min, 2.5-4 kg / t of white lime is added, and the white slag refining time is ≥20 min; diffusion deoxidation is performed throughout the LF refining process to ensure that the sum of the contents of FeO and MnO in the final slag is <1.0%.

[0014] In the RH vacuum degassing step, the deep vacuum time is ≥10min, and the vacuum degree of the deep vacuum is ≤100Pa; the soft blowing time is ≥15min, and the soft blowing ensures that the liquid surface is not exposed.

[0015] In the continuous casting step, protective casting is adopted, and the secondary cooling water volume is 0.20-0.30 L / kg.

[0016] In the hot rolling step, the temperature of the preheating section is ≤800°C; the temperature of the first heating section is 600-900°C; the temperature of the second heating section is 1050-1150°C; the temperature of the first soaking section is 1190-1230°C; the temperature of the second soaking section is 1190-1210°C, and the total heating time is 240-250 minutes. The heated alloy material is subjected to high-pressure plastic deformation to obtain the desired shape and size.

[0017] In the online normalizing step, air cooling is performed on a cooling bed with a heat preservation cover at a rate of less than 40° C. / min, and packaging and collection are performed when the temperature is lower than 300° C.

[0018] In the steel bar for infrastructure threaded rod with a tensile strength of 900 MPa provided by the present invention, the control and function of each component are as follows:

[0019] Carbon (C): Carbon is one of the most important alloying elements in steel, which directly affects the strength and hardness of steel. As the carbon content increases, the strength and hardness of the steel increase, but the plasticity and toughness decrease. The present invention controls the C content to be 0.35-0.50%, and the carbon content within this range is intended to balance the strength, hardness and toughness of the steel. Too low a carbon content will result in insufficient strength of the steel, while too high a carbon content will significantly reduce the weldability and toughness of the steel, increase brittleness, and deteriorate welding performance.

[0020] Silicon (Si): Silicon is mainly used as a deoxidizer, which can significantly improve the oxidation resistance and corrosion resistance of steel. At the same time, silicon can also improve the strength and hardness of steel. The present invention controls the Si content to 0.17-0.45%. An appropriate amount of silicon can effectively deoxidize and improve the performance of steel. If the silicon content is too low, the deoxidation effect is insufficient, but too much silicon will cause the plasticity and toughness of steel to decrease.

[0021] Manganese (Mn): Manganese is a good deoxidizer and desulfurizer, which can significantly improve the strength and hardness of steel and improve the hardenability of steel. The present invention controls the Mn content to be 0.60-1.0%. An appropriate amount of manganese can significantly improve the performance of steel. If the manganese content is too low, the deoxidation and desulfurization effects are insufficient, but too much manganese will cause the toughness of steel to decrease and increase the tendency of hot cracking.

[0022] Chromium (Cr): Chromium is one of the main elements that improves the corrosion resistance and heat resistance of steel. At the same time, chromium can also improve the hardness and wear resistance of steel. The present invention controls the Cr content to be 0.90-1.20%. If the chromium content is too low, the corrosion resistance and heat resistance are insufficient; and if the chromium content is too high, the brittleness of the steel increases.

[0023] Phosphorus (P) and sulfur (S): Phosphorus and sulfur are harmful elements in steel. They will significantly reduce the plasticity and toughness of steel and increase the brittleness of steel. In order to maintain good performance of steel, the content of phosphorus and sulfur must be strictly controlled at an extremely low level. The present invention controls P≤0.01% and S≤0.005%.

[0024] Aluminum (Al): Aluminum is a strong deoxidizer and can significantly improve the purity and oxidation resistance of steel. A proper amount of aluminum can effectively deoxidize and improve the performance of steel, but too much aluminum will cause the toughness of steel to decrease. The present invention controls Al0.04-0.06%.

[0025] Niobium (Nb) and vanadium (V): Niobium and vanadium are strong carbide-forming elements, which can significantly improve the strength and toughness of steel, and improve the hardenability and hot working properties of steel. Appropriate amounts of niobium and vanadium can significantly improve the properties of steel, but excessive addition will lead to a decrease in the toughness of steel and poor processing properties. The present invention controls Nb to 0.015-0.04% and V to 0.06-0.10%.

[0026] Nitrogen (N): Nitrogen exists in steel mainly in the form of interstitial atoms, which can improve the strength and hardness of steel, but excessive nitrogen will lead to a decrease in the toughness of steel and poor welding performance. The present invention controls N to 0.01-0.03%.

[0027] Boron (B): Boron is one of the microalloying elements, which can significantly improve the hardenability and hot working properties of steel. A trace amount of boron can significantly improve the properties of steel, but too much boron will lead to a decrease in the toughness of steel. The present invention controls B≤0.005%.

[0028] The steel rod for infrastructure threaded rod with a tensile strength of 900 MPa provided by the present invention reasonably utilizes the precipitation of lamellar cementite by the C element after hot rolling, thereby improving the strength of the steel; the solid solution strengthening effect of the Mn and Cr elements in the iron matrix improves the strength, improves the welding performance, and has good welding adaptability. Nb, V and N, C form a large number of compounds that precipitate at the grain boundaries, which play a role of dispersed precipitation strengthening. At the same time, the precipitates can prevent the growth of grains and significantly refine the grains. Due to the precipitation strengthening and fine grain strengthening effects, the strength and toughness of the steel are improved. The fine grains and precipitated particles can inhibit the generation and propagation of microcracks, thereby improving the fatigue life of the material.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The steel rod for infrastructure threaded rod with a tensile strength of 900 MPa provided by the present invention has high strength, high toughness, fatigue resistance and good welding performance, can effectively solve the problems of stress concentration, looseness, wear and tear that occur in the use of existing threaded rods, and improves the stability and safety of infrastructure.

[0031] The method for preparing the steel rod provided by the invention has high efficiency and controllable production process, and is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the metallographic structure diagram of the steel bar for infrastructure threaded rod in Example 1, the metallographic structure is ferrite and pearlite, and the grain size is level 9;

[0033] Figure 2 This is the metallographic structure diagram of the steel bar for infrastructure threaded rod in Example 2, the metallographic structure is ferrite and pearlite, and the grain size is level 9;

[0034] Figure 3 This is the metallographic structure diagram of the steel bar for infrastructure threaded rod in Comparative Example 1, the metallographic structure is ferrite and pearlite, and the grain size is level 5;

[0035] Figure 4 This is the metallographic structure diagram of the steel bar for infrastructure threaded rod in Comparative Example 2. The metallographic structure is ferrite and pearlite, and the grain size is level 5. DETAILED DESCRIPTION

[0036] The invention provides a steel rod for infrastructure threaded rod with a tensile strength of 900 MPa. The chemical composition and weight percentage of the steel rod are: C: 0.35-0.50%, Si: 0.17-0.45%, Mn: 0.60-1.0%, Cr: 0.90-1.20, P: ≤0.01%, S: ≤0.005%, Al: 0.04-0.06%, Nb: 0.015-0.04%, V: 0.06-0.10%, N: 0.01-0.03%, B: ≤0.005%, and the balance is Fe and unavoidable impurities.

[0037] The method for preparing the steel bar with a tensile strength of 900 MPa for infrastructure threaded rods comprises the following steps: blast furnace molten iron smelting - converter steel tapping - LF refining - RH vacuum degassing - continuous casting - hot rolling - online normalizing.

[0038] In the blast furnace iron smelting step, use iron + scrap steel, pay attention to the type of scrap steel, and reduce the introduction of residual alloy elements;

[0039] In the converter tapping step, control C ≥ 0.010%, P ≤ 0.015%, and tapping temperature ≥ 1620°C;

[0040] In the converter tapping step, slag and alloy are added during the tapping process.

[0041] In the LF refining step, the LF refining time is controlled to be ≥40min, and 2.5-4kg / t of white ash and slag-reducing agent are added to ensure the foamability and fluidity of the refined slag. The white slag refining time is ≥20min;

[0042] Diffusion deoxidation is carried out throughout the LF refining process to ensure that the final slag FeO+MnO is less than 1.0%, and [O] is required to be ≤25ppm. Titanium-iron alloy is added after the deoxidation effect is ensured;

[0043] In the RH vacuum degassing step, the deep vacuum time is ≥10min, and the vacuum degree of the deep vacuum is ≤100Pa; the soft blowing time is ≥15min, and the soft blowing ensures that the liquid surface is not exposed;

[0044] In the continuous casting step, protective casting is adopted, and the secondary cooling water ratio is 0.25L / Kg; the diameter of the continuous casting billet is Φ300mm;

[0045] In the hot rolling step, the temperature control range of the preheating section is: ≤800°C; the temperature control range of the first heating section is: 600-900°C; the temperature control range of the second heating section is: 1050-1150°C; the temperature control range of the first soaking section is: 1190-1230°C; the temperature control range of the second soaking section is: 1190-1210°C.

[0046] The heated alloy material is subjected to high pressure plastic deformation to obtain the desired shape and size;

[0047] In the online normalizing step, the deformed round bars are air-cooled on a cooling bed with a heat preservation cover at an air cooling rate of less than 40°C / min, and are packaged and collected when the temperature is lower than 300°C.

[0048] The present invention is described in detail below with reference to the embodiments.

[0049] The chemical composition and weight percentage of the steel bars for infrastructure threaded rods in various embodiments and comparative examples are shown in Table 1, and the remainder is iron and unavoidable impurities.

[0050] Table 1

[0051] C Si Mn Cr P S Al Nb V N B Example 1 0.40 0.27 0.85 1.05 0.008 0.005 0.045 0.030 0.061 0.01 0.003 Example 2 0.43 0.33 0.65 0.95 0.006 0.003 0.050 0.025 0.071 0.02 0.004 Comparative Example 1 0.40 0.27 0.85 0.85 0.009 0.004 0.043 0.005 0.008 0.02 0.005 Comparative Example 2 0.40 0.27 0.85 1.05 0.006 0.004 0.046 0.040 0.021 0.03 0.002 Comparative Example 3 0.35 0.27 0.75 0.95 0.007 0.002 0.052 0.030 0.051 0.01 0.001

[0052] The hot rolling process parameters of the steel bars for infrastructure threaded rods in the embodiments and comparative examples are shown in Table 2.

[0053] Table 2

[0054]

[0055] The properties of the steel bars for infrastructure threaded rods in the embodiments and comparative examples are shown in Table 3.

[0056] Table 3

[0057]

[0058] The detailed description of a steel bar with a tensile strength of 900 MPa for infrastructure threaded rod and its preparation method with reference to the above-mentioned embodiment is illustrative rather than restrictive, and several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A steel bar for infrastructure threaded rod with a tensile strength of 900 MPa, characterized in that: The chemical composition and weight percentage of the steel bar are: C: 0.35-0.50%, Si: 0.17-0.45%, Mn: 0.60-1.0%, Cr: 0.90-1.20, P: ≤0.01%, S: ≤0.005%, Al: 0.04-0.06%, Nb: 0.015-0.04%, V: 0.06-0.10%, N: 0.01-0.03%, B: ≤0.005%, and the balance is Fe and unavoidable impurities.

2. The steel bar for infrastructure threaded rod with a tensile strength of 900 MPa according to claim 1, characterized in that: The metallographic structure of the steel bar is ferrite and pearlite, and the grain size reaches above level 8.

3. The steel bar for infrastructure threaded rod with a tensile strength of 900 MPa according to claim 1, characterized in that: The steel bar has a yield strength of ≥550MPa, a tensile strength of ≥900Mpa, a cross-sectional elongation of ≥15%, a cross-sectional shrinkage of ≥30%, and a V-notch impact KV2 of ≥50J / cm at -20°C. 2 .

4. The method for preparing a steel bar for infrastructure threaded rod with a tensile strength of 900 MPa as claimed in any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: smelting - continuous casting - hot rolling - online normalizing.

5. The preparation method according to claim 4, characterized in that: The smelting step includes the following process steps: blast furnace molten iron smelting - converter tapping - LF refining - RH vacuum degassing.

6. The preparation method according to claim 5, characterized in that: In the converter tapping step, control C≥0.010%, P≤0.015%, and the tapping temperature≥1620°C.

7. The preparation method according to claim 5, characterized in that: In the LF refining step, the LF refining time is controlled to be ≥40 min, 2.5-4 kg / t of white lime is added, and the white slag refining time is ≥20 min; diffusion deoxidation is performed throughout the LF refining process to ensure that the sum of the contents of FeO and MnO in the final slag is <1.0%.

8. The preparation method according to claim 4, characterized in that: In the continuous casting step, protective casting is adopted, and the secondary cooling water volume is 0.20-0.30 L / kg.

9. The preparation method according to claim 4, characterized in that: In the hot rolling step, the preheating temperature is ≤800°C; the heating temperature is 600-900°C; the heating temperature is 1050-1150°C; the soaking temperature is 1190-1230°C; the soaking temperature is 1190-1210°C, and the total heating time is 240-250 minutes.

10. The preparation method according to claim 4, characterized in that: In the online normalizing step, air cooling is performed on a cooling bed with a heat preservation cover at a rate of less than 40° C. / min, and packaging and collection are performed when the temperature is lower than 300° C.

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