CN107747061A - A 630MPa grade high-strength and toughness hot-rolled ribbed steel bar and its production method - Google Patents

Abstract

The invention discloses a 630 MPa-grade high-strength and high-toughness hot-rolled ribbed steel bar and a production method thereof, wherein the ribbed steel bar comprises the following chemical components in percentage by mass: c: 0.20 to 0.25%, Mn: 1.50-1.60%, Si: 0.60-0.75%, V: 0.08-0.15%, Cr: 0.30-0.35%, N: 0.012-0.025%, P: 0.005-0.025%, S: 0.005-0.025%, and the balance of Fe and inevitable impurities; the production method of the ribbed steel bar comprises the working procedures of smelting, refining, continuous casting, heating and rolling. The invention uses cheap alloy elements to replace expensive alloy elements such as nickel, niobium, molybdenum and the like, reduces the cost of hot rolling the ribbed steel bar and improves the practicability and safety of the building to a certain extent; the simple smelting process and rolling process are adopted, and the low-cost large-scale production is favorably realized.

Description

A 630MPa grade high-strength and toughness hot-rolled ribbed steel bar and its production method

technical field

The invention belongs to the technical field of metallurgy, and in particular relates to a 630MPa grade high-strength and toughness hot-rolled ribbed steel bar and a production method thereof.

Background technique

Hot-rolled ribbed steel bar is the most widely used steel material at present. It has certain ductility, high strength, good seismic performance and welding performance. Developed countries such as Europe have widely used 500MPa grade hot-rolled ribbed steel bars, and 600MPa grade has also been used to a certain extent. In my country's revised national standard GB1499.2-2013, a new 600MPa-level ribbed steel bar has been added. This type of steel has the advantages of high strength and low consumption. It is especially suitable for high-rise and large-span buildings, and can also solve the "fat beam" problem. Fat column" and other issues. Further research and development of 630MPa hot-rolled ribbed steel bars is of great strategic significance for adjusting the backward production capacity of my country's steel industry and implementing sustainable development.

The Chinese patent application No. 201110350194.4 discloses "a 600MPa grade alum-containing high-strength hot-rolled steel bar and its production method". %, V: 0.08-0.12%, N: 0.005-0.040%, S≤0.040%, P≤0.040%, and the rest are iron and unavoidable impurities. The manufacturing method is "in the smelting process, vanadium, nitrogen and nitrogen fixation processes are adopted, and the rolling process is adopted to reduce the rolling temperature and finish rolling temperature to ensure low temperature and high pressure, to achieve fine grain, solid solution and precipitation strengthening to improve strength. ". There are the following deficiencies: ① lowering the rolling temperature and finish rolling temperature to ensure low temperature and high pressure, so as to improve the strength, has high requirements on the rolling mill, and is not suitable for wide application. ②The nitrogen content is too high between 0.005-0.040%. Excessive nitrogen content affects the elongation of the steel bar, making the steel bar tend to become brittle; blowing nitrogen throughout the process to increase nitrogen may easily cause too many bubbles and affect the quality of the product.

Chinese patent No. 201310444163.4 discloses "a 630MPa grade high-strength hot-rolled steel bar and its production process", the specific components are: C: 0.38-0.43%, Cr: 0.8-1.1%, Mn: 0.75-1.0%, Mo : 0.15～0.25%, Si: 0.15～0.3%, P≤0.035%, S≤0.035%S, N≤0.035%, and the rest is Fe. The specific process is: put the steel bar into the heating furnace and heat it to 1000-1200 ° C, then cool the steel bar to 610-630 ° C through the first online cooling process, and then use water or quenching liquid in the quenching device for 12-14 seconds Quenched, then heated to 550-560°C in a tempering furnace for tempering, and then cooled to normal temperature through the second cooling process. The disadvantages of this process are: ① Increase the strength of the steel bar by increasing the carbon content and lose the elongation, and it is not conducive to the welding performance. ②The heat treatment process of the steel bar is complicated, which increases the cost of the product. ③ Excessive chromium content is not good for elongation. ④The carbon equivalent is too high, the welding performance is poor, and the construction is difficult.

Chinese patent No. 20161086739.9 discloses "a 630MPa high-strength hot-rolled steel for steel and its preparation method", the specific components are: C: 0.22-0.28%, Si: 0.40-0.80%, Mn: 1.40-1.60%, Nb: 0.02-0.04%, V: 0.05-0.07%, Cr: 0.02-0.40%, N: 0.008-0.012%, P≤0.035%, S≤0.035%, and the rest are Fe and unavoidable impurity elements. The specific process is: smelting in converter, electric arc furnace or other smelting furnace; argon blowing and refining in ladle outside the furnace; continuous casting of 140 or 150 billets; rolling of bars by thermomechanical rolling process; cooling. Although this process is simple, the alloy composition uses the more expensive metal element niobium, which increases the manufacturing cost of steel bars; at the same time, the precipitation of niobium is greatly affected by the cooling rate and hot rolling deformation rate, and the performance of large-scale steel bars fluctuates greatly. The overall performance stability is poor.

Contents of the invention

The technical problem to be solved by the present invention is to provide a 630MPa-grade high-strength and toughness hot-rolled ribbed steel bar; meanwhile, the present invention also provides a production method of a 630MPa-grade high-strength and toughness hot-rolled ribbed steel bar. The invention obtains a 630MPa grade high-strength toughness steel bar suitable for wide production and application by optimizing the alloy composition and a simple rolling process.

In order to solve the above technical problems, the technical solution adopted by the present invention is: a 630MPa grade high-strength toughness hot-rolled ribbed steel bar, the chemical composition and mass percentage of the ribbed steel bar are: C: 0.20-0.25%, Mn : 1.50～1.60%, Si: 0.60～0.75%, V: 0.08～0.15%, Cr: 0.30～0.35%, N: 0.012～0.025%, P: 0.005-0.025%, S: 0.005-0.025%, and the rest Fe and unavoidable impurities.

The ratio of vanadium to nitrogen in the chemical composition of the ribbed steel bar in the invention is controlled at 4-7; the diameter of the ribbed steel bar is 10-32mm.

The microstructure of the ribbed steel bar in the present invention is pearlite+ferrite, and the grain size is 11-12 grades.

The mechanical properties of the ribbed steel bar in the present invention are: yield strength ≥ 630MPa, tensile strength ≥ 760MPa, elongation after fracture ≥ 15%, and strength-to-yield ratio ≥ 1.25.

The invention also provides a production method of 630MPa grade high-strength and toughness hot-rolled ribbed steel bars, the production method comprising smelting, refining, continuous casting, heating and rolling processes.

In the smelting process of the present invention, the components are roughly adjusted by smelting in a converter, an electric arc furnace or other smelting furnaces.

In the refining process described in the present invention, argon gas is introduced outside the ladle, the composition is fine-tuned for refining, and ferrovanadium and manganese nitride are added at the argon blowing station. Considering the yield of the alloy, the ratio of the effective components of vanadium to nitrogen added by mass ratio is 3:1-6:1.

In the continuous casting process of the present invention, the tundish baking temperature is 1050-1100° C., the crystallizer is arc-aligned, and the whole process of protective pouring is adopted; the billets with a section of 150 mm×150 mm are continuously cast.

In the heating process of the present invention, the billet is heated at a temperature of 1100-1200° C. and kept for 1-2 hours.

The rolling process of the present invention adopts a rod and wire rod hot rolling mill for rolling, the starting rolling temperature is controlled at 1050-1150°C, the reduction of each pass is controlled at 7-30%; the finish rolling temperature is controlled at 850-1050°C, The reduction in each pass is controlled at 10-35%; the final rolling temperature is 800-1000°C; after rolling, it is naturally cooled to room temperature on a cooling bed.

The effect of trace alloy elements of the present invention in steel is as follows:

Vanadium is considered to be one of the most suitable elements to increase the strength of low carbon steel. First of all, vanadium is a strong carbon compound element, which has a significant effect of preventing the growth of austenite grains and plays a role of fine-grain strengthening. Secondly, the main forms of vanadium in low carbon steel are solid solution, VC, VN and V (C, N), and the nitrogen content directly determines the distribution of vanadium in steel. When the nitrogen content is very low, vanadium is mainly dissolved in the steel and plays a role of solid solution strengthening. Adding an appropriate amount of nitrogen to the steel can separate the solid solution vanadium and form carbides or carbonitrides dispersed in the steel to play a role in precipitation strengthening. The precipitation strengthening improves the strength more than the solid solution strengthening. Nitrogen is an element with strong solid solution strengthening effect, but if it is too high, it will seriously damage the ductility of steel, so it is appropriate to control it below 190ppm. The present invention mainly fixes the ratio of vanadium to nitrogen in a range, so that the precipitation amount of VC, VN and V(C, N) is relatively increased, and the precipitated second phase is small, round and evenly distributed in the steel.

The C, N, Si, and Mn elements added to steel are common solid solution strengthening elements in steel. C and N have the greatest effect of solid solution strengthening, but the increase of carbon content will reduce the weldability and ductility, so it needs to be controlled between 0.20 and 0.25%. Nitrogen in combination with vanadium has been mentioned above. When Si>1.1% or Mn>1.8%, the plasticity and toughness of the steel will be greatly reduced, so silicon and manganese are required to increase the solid solution strengthening as much as possible without damaging its plasticity, so it is limited to Si: 0.40～ 0.95% and Mn: 1.30-1.75%, preferably, in the present invention, Si: 0.60-0.75% and Mn: 1.50-1.60%.

There are three main functions of Cr element: solid solution, which plays a role of solid solution strengthening in steel; improves hardenability; shifts the S point to the left in the iron-carbon phase diagram, and obtains more interlayer pearlite structures. This increases the strength of the steel. Both the core and the edge of the obtained steel bar are ferrite and pearlite.

Refer to GB/T1499.2-2007 and GB/T 228.1-2010 for the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar product and performance testing method of the present invention.

The beneficial effects produced by adopting the above technical scheme are: 1. The present invention adjusts the vanadium-nitrogen ratio by optimizing the alloy content, so that vanadium is precipitated in the form of carbides, nitrides, and carbonitrides, "small, round, and uniform" Dispersed in the steel, the effect of precipitation strengthening is increased as much as possible, and the content of C, Mn, Si, Cr and other elements is adjusted at the same time, so that the formation of this steel is mainly based on precipitation strengthening, supplemented by fine grain strengthening and solid solution strengthening. The strengthening mechanism can increase the yield strength without affecting the plasticity and weldability. 2. The present invention uses cheap alloy elements to replace expensive alloy elements such as nickel, niobium, and molybdenum, and reduces the cost of hot-rolled ribbed steel bars. 3. The present invention raises the yield strength of steel bars to more than 630 MPa, greatly reduces the amount of steel bars used, and at the same time improves the practicality and safety of buildings to a certain extent. 4. The present invention adopts simple smelting process and rolling process, which makes production easier and more feasible, and is conducive to realizing low-cost mass production.

Description of drawings

Fig. 1 is the room temperature microstructure diagram of the ribbed steel bar gained in embodiment 1;

Fig. 2 is the room temperature microstructure diagram of the ribbed steel bar gained in embodiment 2;

Fig. 3 is the room temperature microstructure diagram of the ribbed steel bar gained in embodiment 3;

Fig. 4 is the microstructure diagram of the ribbed steel bar obtained in Example 4 at room temperature.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1

In this embodiment, the diameter of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar is 16mm, and the chemical composition and mass percentage of the steel bar are: C: 0.20%, Mn: 1.51%, Si: 0.70%, V: 0.125%, Cr: 0.30%, N: 0.025%, P: 0.010%, S: 0.006%, the rest is Fe and unavoidable impurities; the ratio of vanadium to nitrogen is 5.

The production method of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar of this embodiment includes smelting, refining, continuous casting, heating and rolling processes, and the specific process steps are as follows:

(1) Smelting process: smelting in a converter for rough adjustment of ingredients;

(2) Refining process: argon gas is introduced outside the ladle, fine-tuning is carried out for refining, and ferrovanadium and manganese nitride are added at the argon blowing station according to the effective vanadium-nitrogen mass ratio of 4:1;

(3) Continuous casting process: the baking temperature of the tundish is 1060°C, the crystallizer is arc-aligned, and the whole process of protective pouring is adopted; continuous casting is made into a billet with a cross-section of 150mm×150mm;

(4) Heating process: billet heating temperature 1150°C, heat preservation 1h;

(5) Rolling process: the ribbed steel bar with a diameter of 16mm is rolled by a hot bar rolling mill, the starting rolling temperature is controlled at 1060°C, and the reduction of each pass is controlled at 20%; the finishing rolling temperature is controlled at 950°C, The reduction in each pass is controlled at 15%; the final rolling temperature is 800°C; after rolling, it is naturally cooled to room temperature on a cooling bed.

The tensile strength of the 630MPa-grade high-strength and toughness hot-rolled ribbed steel bar in this embodiment is 821MPa, the yield strength is 652MPa, the maximum elongation is 21.12%, the elongation of the steel bar to the maximum force is 12.82%, and the strength-to-yield ratio is 1.26.

The structure of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar in this example is pearlite + ferrite, and the microstructure at room temperature is shown in Fig. 1; the measured average grain intercept is 5.858 μm, and the grain size is 11.5 grade.

Example 2

In this embodiment, the diameter of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar is 20mm, and the chemical composition and mass percentage of the steel bar are: C: 0.24%, Mn: 1.58%, Si: 0.75%, V: 0.097%, Cr: 0.34%, N: 0.0185%, P: 0.015%, S: 0.016%, the rest is Fe and unavoidable impurities; the ratio of vanadium to nitrogen is 5.24.

The production method of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar of this embodiment includes smelting, refining, continuous casting, heating and rolling processes, and the specific process steps are as follows:

(1) Smelting process: smelting in a converter for rough adjustment of ingredients;

(2) Refining process: argon gas is introduced outside the ladle, fine-tuning is carried out for refining, and ferrovanadium and manganese nitride are added at the argon blowing station according to the effective vanadium-nitrogen mass ratio of 4.5:1;

(3) Continuous casting process: the baking temperature of the tundish is 1080°C, the crystallizer is arc-aligned, and the whole process of protective pouring is adopted; continuous casting is made into a billet with a cross-section of 150mm×150mm;

(4) Heating process: billet heating temperature 1200 ℃, heat preservation 1h;

(5) Rolling process: the ribbed steel bar with a diameter of 20mm is rolled by a hot bar rolling mill, the starting rolling temperature is controlled at 1100°C, and the reduction of each pass is controlled at 25%; the finishing rolling temperature is controlled at 950°C, The reduction in each pass is controlled at 25%; the final rolling temperature is 950°C; after rolling, it is naturally cooled to room temperature on a cooling bed.

In this embodiment, the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar has a tensile strength of 850MPa, a yield strength of 659MPa, a maximum elongation of 22.72%, an elongation of the steel bar to the maximum force of 13.26%, and a strength-to-yield ratio of 1.29.

The structure of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar in this example is pearlite + ferrite, and the microstructure at room temperature is shown in Fig. 2;

Example 3

The diameter of the 630MPa high-strength and toughness hot-rolled ribbed steel bar in this embodiment is 32mm, and the chemical composition and mass percentage of the steel bar are: C: 0.25%, Mn: 1.50%, Si: 0.60%, V: 0.15%, Cr: 0.35%, N: 0.021%, P: 0.005%, S: 0.025%, the rest is Fe and unavoidable impurities; the ratio of vanadium to nitrogen is 6.81.

The production method of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar of this embodiment includes smelting, refining, continuous casting, heating and rolling processes, and the specific process steps are as follows:

(1) Smelting process: smelting in a converter for rough adjustment of ingredients;

(2) Refining process: argon gas is introduced outside the ladle, fine-tuning is carried out for refining, and ferrovanadium and manganese nitride are added at the argon blowing station according to the effective vanadium-nitrogen mass ratio of 6:1;

(3) Continuous casting process: the baking temperature of the tundish is 1050°C, the crystallizer is arc-aligned, and the whole process of protective pouring is adopted; continuous casting is made into a billet with a section of 150mm×150mm;

(4) Heating process: billet heating temperature 1100 ℃, heat preservation 1.5h;

(5) Rolling process: the ribbed steel bar with a diameter of 30mm is rolled by a hot bar rolling mill, the starting rolling temperature is controlled at 1050°C, and the reduction of each pass is controlled at 7%; the finishing rolling temperature is controlled at 850°C, The reduction in each pass is controlled at 10%; the final rolling temperature is 870°C; after rolling, it is naturally cooled to room temperature on a cooling bed.

The tensile strength of the 630MPa-grade high-strength and toughness hot-rolled ribbed steel bar in this embodiment is 842MPa, the yield strength is 648MPa, the maximum elongation is 20.08%, the elongation of the steel bar to the maximum force is 14.04%, and the strength-to-yield ratio is 1.25.

The structure of the 630MPa high-strength and toughness hot-rolled ribbed steel bar in this example is pearlite + ferrite, and the microstructure at room temperature is shown in Fig. 3;

Example 4

In this embodiment, the diameter of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar is 10 mm, and the chemical composition and mass percentage of the steel bar are: C: 0.25%, Mn: 1.60%, Si: 0.65%, V: 0.08%, Cr: 0.32%, N: 0.012%, P: 0.025%, S: 0.005%, the rest is Fe and unavoidable impurities; the ratio of vanadium to nitrogen is 6.67.

The production method of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar of this embodiment includes smelting, refining, continuous casting, heating and rolling processes, and the specific process steps are as follows:

(1) Smelting process: smelting in a converter for rough adjustment of ingredients;

(2) Refining process: argon gas is introduced outside the ladle, fine-tuning is carried out for refining, and ferrovanadium and manganese nitride are added at the argon blowing station according to the effective vanadium-nitrogen mass ratio of 3:1;

(3) Continuous casting process: the baking temperature of the tundish is 1100°C, the crystallizer is arc-aligned, and the whole process of protective pouring is adopted; continuous casting is made into a billet with a cross-section of 150mm×150mm;

(4) Heating process: billet heating temperature 1200 ℃, heat preservation 2h;

(5) Rolling process: the ribbed steel bar with a diameter of 10mm is rolled by a wire rod hot rolling mill. The pass reduction is controlled at 35%; the final rolling temperature is 1000°C; after rolling, it is naturally cooled to room temperature on a cooling bed.

The tensile strength of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar in this embodiment is 842MPa, the yield strength is 663MPa, the maximum elongation is 20.08%, the elongation of the steel bar to the maximum force is 12.1%, and the strength-to-yield ratio is 1.27.

The structure of the 630MPa grade high-strength and toughness hot-rolled ribbed steel bar in this example is pearlite + ferrite, and the microstructure at room temperature is shown in Fig. 4;

The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that the present invention can still be modified or equivalently replaced without departing from it. Any modifications or partial replacements within the spirit and scope of the present invention shall fall within the scope of the claims of the present invention.

Claims (10)

1. A kind of 1. 630MPa levels high-strength tenacity hot rolled ribbed bars, it is characterised in that Ribbed Bar chemical composition composition and Its weight/mass percentage composition is：C：0.20~0.25%, Mn：1.50~1.60%, Si：0.60~0.75%, V：0.08~0.15%, Cr：0.30~0.35%, N：0.012~0.025%, P：0.005-0.025%, S：0.005-0.025%, remaining is Fe and can not kept away The impurity exempted from.
2. 2. a kind of 630MPa levels high-strength tenacity hot rolled ribbed bars according to claim 1, it is characterised in that described with ribbing Vanadium nitrogen is than controlling 4~7 in reinforcing bar chemical composition；The a diameter of 10-32mm of Ribbed Bar.
3. 3. a kind of 630MPa levels high-strength tenacity hot rolled ribbed bars according to claim 1, it is characterised in that described with ribbing Reinforcing bar microscopic structure is pearlite+ferrite, and grain size is 11-12 levels.
4. 4. a kind of 630MPa levels high-strength tenacity hot rolled ribbed bars according to claim 1, it is characterised in that described with ribbing Steel bar mechanics performance is：Yield strength >=630MPa, tensile strength >=760MPa, elongation after fracture >=15%, strong flexor ratio >= 1.25。
5. 5. the producer based on a kind of 630MPa levels high-strength tenacity hot rolled ribbed bars described in claim 1-4 any one Method, it is characterised in that the production method includes smelting, refining, continuous casting, heating and rolling process.
6. 6. a kind of production method of 630MPa levels high-strength tenacity hot rolled ribbed bars according to claim 5, its feature exist In, the smelting procedure, the melting progress composition coarse adjustment in converter, electric arc furnaces or other smelting furnaces.
7. 7. a kind of production method of 630MPa levels high-strength tenacity hot rolled ribbed bars according to claim 5, its feature exist In, the refining procedure, argon gas is passed through outside ladle, refining carries out trimming, adds vanadium iron and nitrogenized manganese at Argon station, examines Consider yield of alloy, its active ingredient vanadium nitrogen added is than being 3 in mass ratio:1-6:1.
8. A kind of 8. producer of 630MPa levels high-strength tenacity hot rolled ribbed bars according to claim 5-7 any one Method, it is characterised in that the continuous casting working procedure, baking of tundish temperature are 1050-1100 DEG C, and crystallizer is protected to arc using whole process Shield cast；It is casting continuously to form section 150mm × 150mm small billet.
9. A kind of 9. producer of 630MPa levels high-strength tenacity hot rolled ribbed bars according to claim 5-7 any one Method, it is characterised in that the heating process, 1100-1200 DEG C of billet heating temperature, be incubated 1-2h.
10. A kind of 10. producer of 630MPa levels high-strength tenacity hot rolled ribbed bars according to claim 5-7 any one Method, it is characterised in that the rolling process, using Bar Wire Product hot mill rolling, start rolling temperature is controlled at 1050~1150 DEG C, often Reduction in pass is controlled 7~30%；At 850~1050 DEG C, draught per pass is controlled 10~35% for final rolling temperature control；Eventually Temperature is rolled for 800-1000 DEG C；Room temperature is naturally cooled to after rolling on cold bed.