Production method of 500mpa high-strength and high-toughness crescent rib anchor rod steel

Abstract

This invention relates to the field of rolling composite technology, specifically to a production method for 500MPa high-strength, high-toughness crescent-rib anchor steel. During the heating and rolling process in the furnace, the steel billet successively enters the roughing, intermediate rolling, pre-finishing, and finishing rolling zones, followed by controlled cooling. The initial rolling temperature, controlled rolling temperature, and controlled cooling temperature are all controlled within the temperature range of 950-1000℃. After rolling, the steel billet is placed on a cooling bed, with the cooling bed temperature consistent with the initial rolling temperature. A heat insulation cover is installed at the entrance side of the cooling bed, and the cooling bed is kept warm by the heat insulation cover for a time controlled within 2 minutes. The temperature difference between the steel billet entering and exiting the heat insulation cover is controlled within 50℃. This invention, through a combination of low S / P and low O steel billet composition, constant temperature rolling throughout the entire process, controlled rolling and cooling, and heat insulation on the cooling bed, produces 500MPa high-strength, high-toughness crescent-rib anchor steel resistant to impact pressure in deep coal mines (kilometer-deep shafts), exhibiting excellent dimensional stability and mechanical properties throughout its length.

Description

Technical Field

[0001] This invention relates to the field of rolling composite technology, specifically to a method for producing 500MPa high-strength and high-toughness crescent-ribbed anchor steel. Background Technology

[0002] With the rapid development of the coal industry and the continuous strengthening of safety management, anchor steel support, as a relatively safe and economical form of coal mine support, has gradually been accepted and promoted by various coal mines, becoming the primary material for coal mine support. As coal seams are continuously excavated and mine roadways become deeper, deep-well coal mines (thousands of meters deep) place high demands on anchor steel for high strength, high toughness, and high resistance to impact pressure. According to standard YB / T 4364-2014 "Hot-rolled Ribbed Steel Bars for Anchor Bolts," the mechanical properties of MG500 grade anchor steel are: yield strength not less than 500 MPa, tensile strength not less than 630 MPa, elongation after fracture not less than 20%, and impact absorption energy (KV2) not less than 40 J (test temperature 20℃). However, in practical applications, with the increase in mine depth, the requirements for MG500 grade anchor steel become even more stringent; merely meeting the standard mechanical properties is insufficient to satisfy the requirements for high strength, high toughness, and high resistance to impact pressure.

[0003] MG500 grade anchor bolts produced using conventional hot rolling processes are prone to developing harmful structures such as Widmanstätten structure, network cementite, and bainite due to factors such as billet composition, initial rolling temperature, and controlled rolling and cooling temperatures. Furthermore, secondary diameter reduction and thread rolling during the production of MG500 grade anchor bolt steel can easily lead to cracking defects, significantly reducing impact performance, toughness, and strength. It is difficult for all mechanical properties to simultaneously meet standards, posing a certain safety hazard to underground roadway support. Summary of the Invention

[0004] To address the technical problem that existing 500MPa grade anchor steel is difficult to simultaneously meet the requirements of high strength, high toughness, and high resistance to ground pressure, this invention provides a production method for 500MPa high-strength and high-toughness crescent-ribbed anchor steel. Its room temperature impact energy, elongation after fracture, tensile strength, and yield strength are significantly better than those of standard YB / T 4364-2014 "Hot-rolled ribbed steel bars for anchor bolts", and it can be used in deep coal mines at depths of over 1,000 meters.

[0005] The technical solution of this invention is as follows:

[0006] A production method for 500MPa high-strength and high-toughness crescent-rib anchor steel involves the following steps: during the heating and rolling process in a heating furnace, the steel billet successively enters the roughing, intermediate rolling, pre-finishing, and finishing rolling zones, followed by controlled cooling. The initial rolling temperature, controlled rolling temperature, and controlled cooling temperature are all controlled within the temperature range of 950-1000℃. After rolling, the steel billet is placed on a cooling bed, with the cooling bed temperature consistent with the initial rolling temperature. A heat insulation cover is installed at the entrance side of the cooling bed, and the cooling bed is kept warm by the heat insulation cover for a time controlled within 2 minutes. The temperature difference between the steel billet entering and exiting the heat insulation cover is controlled within 50℃.

[0007] The steel billet is composed of the following elements by weight percentage: C 0.19%-0.25%, Si 0.40%-0.60%, Mn 1.30%-1.50%, S ≤0.03%, P ≤0.03%, V 0.060%-0.080%, O ≤0.005%, with the remainder being Fe and unavoidable impurities.

[0008] Furthermore, during the heating and rolling of the steel billet in the heating furnace, the use of full-line micro-tension technology, looper precision control technology, and K1-K3 full-rolling guide technology provides equipment and technical support for the stability of the entire length.

[0009] Furthermore, the full-line micro-tension technology uses six vertical loopers to ensure that the tension value of the entire line is controlled at ≤1%.

[0010] Furthermore, the precise control technology for loopers ensures that the looper height is controlled between 150-250mm, the looper take-off time is ≤200ms when the head bites in, and the looper drop-off time is ≤300ms after the tail leaves the rolling mill.

[0011] Furthermore, K1 and K2 use tungsten carbide rolls, which have good wear resistance, providing technical assurance for the qualitative determination of the surface quality and dimensions of the finished product.

[0012] Furthermore, the steel billet is smelted in a heating furnace before being heated and rolled.

[0013] Furthermore, the smelting of steel billets includes LF refining, strong deoxidation, calcium feeding wire, soft argon blowing, full-process protective casting, and electromagnetic stirring.

[0014] Calcium feeding wire can control the gas content and composition of molten steel, improve the purity and uniformity of molten steel, and enhance the impact toughness of steel.

[0015] Furthermore, the amount of calcium wire added is 1.5-2 m / t steel.

[0016] Furthermore, the electromagnetic stirrer has a current of 200A and a frequency of 4Hz.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention provides a production method for 500MPa high-strength and high-toughness crescent-rib anchor steel. By combining low S / P and low O billet composition, constant temperature rolling throughout the process, controlled rolling and cooling, and cold bed insulation control, a 500MPa high-strength and high-toughness crescent-rib anchor steel with impact resistance for deep coal mines (kilometer-deep shafts) is produced. It has excellent dimensional stability and mechanical properties, with room temperature impact energy exceeding 130J, elongation after fracture exceeding 28%, tensile strength exceeding 710MPa, and yield strength exceeding 530MPa. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions in the embodiments of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0020] Example 1: Rolling Φ18 specification 500MPa high-strength and high-toughness crescent-ribbed anchor bolt steel

[0021] A method for producing 500MPa high-strength and high-toughness crescent-ribbed anchor bolt steel includes the following steps:

[0022] (1) Smelting steel billets: LF refining, strong deoxidation, calcium wire feeding, calcium wire addition amount is 1.5m / t steel, soft blowing argon, full protection casting, electromagnetic stirring is turned on, electromagnetic stirring current is 200A and frequency is 4Hz, and steel billets are smelted.

[0023] The steel billet is composed of the following elements by weight percentage: C 0.19%, Si 0.40%, Mn 1.30%, S 0.010%, P 0.030%, V 0.060%, O 0.0030%, with the remainder being Fe and unavoidable impurities.

[0024] (2) Heating and rolling: The billet enters the steel rolling furnace for heating and then enters the roughing, intermediate rolling, pre-finishing and finishing rolling areas. During heating, full-line micro-tension technology, looper precision control technology and K1-K3 full rolling guide technology are adopted. K1 and K2 use tungsten carbide rolls with good wear resistance. After rolling, controlled cooling is performed.

[0025] The full-line micro-tension technology uses six vertical loopers to ensure that the tension value of the entire line is controlled at ≤1%; the looper precision control technology controls the looper height at 150-250mm, the looper take-off time when the head bites in is ≤200ms, and the looper drop-off time after the tail leaves the mill is ≤300ms.

[0026] This process employs a full-process constant temperature rolling + controlled rolling and controlled cooling process, meaning that the initial rolling temperature, controlled rolling temperature, and controlled cooling temperature are all controlled at the same temperature, which is 950℃.

[0027] (3) Cooling bed insulation: The temperature of the steel billet on the cooling bed is 950℃. An insulation cover is set on the inlet side of the cooling bed (the insulation cover is the same length as the cooling bed, which is 108m and the width of the insulation cover is 2m). The cooling bed is insulated with the insulation cover. The insulation time is controlled within 2 minutes. The temperature difference between the steel billet entering and leaving the insulation cover is controlled within 50℃. Finally, Φ18 specification 500MPa high strength and high toughness crescent rib anchor steel is rolled out.

[0028] According to the test, the metallographic structure of the Φ18 specification 500MPa high-strength and high-toughness crescent rib anchor steel is ferrite + pearlite, the yield strength is 530MPa, the tensile strength is 750MPa, the yield strength ratio is 0.71, the elongation after fracture is 32%, and the impact energy (20℃) is 130J.

[0029] Example 2: Rolling Φ20 specification 500MPa high-strength and high-toughness crescent-ribbed anchor bolt steel

[0030] The difference from Example 1 is that (1) when smelting the steel billet, the amount of calcium wire added is 2m / t of steel, and the steel billet is composed of the following elements by weight percentage: C 0.20%, Si 0.60%, Mn 1.45%, S 0.025%, P 0.025%, V 0.072%, O 0.001%, and the remainder is Fe and unavoidable impurities. (2) during hot rolling, the initial rolling temperature, controlled rolling temperature and controlled cooling temperature are all controlled at the same temperature, which is controlled at 1000℃. (3) when the cooling bed is kept warm, the temperature of the steel billet on the cooling bed is 1000℃, and finally Φ20 specification 500MPa high strength and high toughness crescent rib anchor steel is rolled out.

[0031] Testing revealed that the metallographic structure of the Φ20 specification 500MPa high-strength and high-toughness crescent rib anchor steel is ferrite + pearlite, with a yield strength of 540MPa, a tensile strength of 710MPa, a yield-to-tensile ratio of 0.76, an elongation after fracture of 28%, and an impact energy (20℃) of 140J.

[0032] Example 3: Rolling Φ22 specification 500MPa high-strength and high-toughness crescent-ribbed anchor bolt steel

[0033] The difference from Example 1 is that (1) the billet is composed of the following elements by weight percentage: C 0.25%, Si 0.50%, Mn 1.5%, S 0.03%, P 0.015%, V 0.075%, O 0.003%, with the remainder being Fe and unavoidable impurities. (2) During hot rolling, the initial rolling temperature, controlled rolling temperature, and controlled cooling temperature are all controlled at the same temperature, which is 980℃. (3) During the cooling bed heat preservation, the temperature of the billet on the cooling bed is 980℃, and finally, Φ22 specification 500MPa high-strength and high-toughness crescent rib anchor steel is rolled out.

[0034] According to the test, the metallographic structure of the Φ22 specification 500MPa high-strength and high-toughness crescent rib anchor steel is ferrite + pearlite, the yield strength is 575MPa, the tensile strength is 741MPa, the yield strength ratio is 0.78, the elongation after fracture is 31%, and the impact energy (20℃) is 135J.

[0035] Comparative Example 1

[0036] The difference from Example 1 is that (1) the steel billet is composed of the following elements by weight percentage: C 0.19%, Si 0.40%, Mn 1.30%, S 0.060%, P 0.035%, V 0.075%, O 0.005%, with the remainder being Fe and unavoidable impurities. (2) During hot rolling, the initial rolling temperature is 950℃, the controlled rolling temperature is 1050℃, and the controlled cooling temperature is 920℃. (3) During the cooling bed heat preservation, the temperature of the steel billet on the cooling bed is 920℃.

[0037] According to the test, the metallographic structure of the Φ18 specification 500MPa high strength and high toughness crescent rib anchor steel is ferrite + pearlite + bainite, the yield strength is 510MPa, the tensile strength is 635MPa, the elongation after fracture is 21%, and the impact energy (20℃) is 50J.

[0038] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for producing 500MPa high-strength, high-toughness crescent-ribbed anchor bolt steel, characterized in that, During the heating and rolling process in the furnace, the steel billet successively enters the roughing, intermediate rolling, pre-finishing, and finishing rolling zones, followed by controlled cooling. The initial rolling temperature, controlled rolling temperature, and controlled cooling temperature are all controlled within the temperature range of 980-1000℃. After rolling, the steel billet is placed on a cooling bed, with the cooling bed temperature consistent with the initial rolling temperature. A heat insulation hood is installed on the entrance side of the cooling bed, and the cooling bed is kept warm by the heat insulation hood. The heat insulation hood is the same length as the cooling bed, 108m in length, and 2m in width. The heat insulation time is controlled within 2 minutes, and the temperature difference between the steel billet entering and exiting the heat insulation hood is controlled within 50℃. The steel billet is composed of the following elements by weight percentage: C 0.19%-0.25%, Si 0.40%-0.60%, Mn 1.30%-1.50%, S≤0.03%, P≤0.03%, V 0.060%-0.080%, O≤0.005%, with the remainder being Fe and unavoidable impurities; The steel billet is smelted before being heated and rolled in a heating furnace; The steel billet smelting process includes LF refining, strong deoxidation, calcium feeding wire, soft argon blowing, full-process protective casting, and electromagnetic stirring. The amount of calcium wire added is 1.5-2 m / t of steel; The electromagnetic stirrer has a current of 200A and a frequency of 4Hz. The steel billet is heated and rolled in the heating furnace using full-line micro-tension technology, looper precision control technology and K1-K3 full-rolling guide technology; The full-line micro-tension technology uses six vertical loopers to ensure that the tension value of the entire line is controlled at ≤1%; the looper precision control technology controls the looper height at 150-250mm, the looper take-off time when the head bites in is ≤200ms, and the looper drop-off time after the tail leaves the mill is ≤300ms. K1 and K2 use tungsten carbide rolls; The amount of calcium wire added is 1.5-2 m / t of steel; The electromagnetic stirrer has a current of 200A and a frequency of 4Hz.