Hot-rolled round steel for high-toughness drill rod and preparation method of hot-rolled round steel

Abstract

The invention discloses hot-rolled round steel for a high-strength and high-toughness drill rod and a preparation method of the hot-rolled round steel. The hot-rolled round steel for the high-strength and high-toughness drill rod comprises the following chemical components in percentage by weight: 0.26-0.33% of C; 0.90 to 1.30% of Si; 1.30% to 1.80% of Cr; 0.90% to 1.30% of Mn; 0.15% to 0.35% of Mo; 0.040% to 0.10% of Ti; 0.018 to 0.022 percent of Al; less than or equal to 0.020% of P; less than or equal to 0.015% of S; n < = 100 ppm; the balance is iron and inevitable impurities; a small amount of Mo element is used, precious metal elements such as Nb, V and Ni do not need to be added, the alloy consumption is reduced, the production cost is low, the high strength and toughness are achieved, the yield strength is larger than or equal to 1600 MPa, the tensile strength is larger than or equal to 1600 MPa, the elongation is larger than or equal to 9%, the percentage reduction of area is larger than or equal to 40%, AKV2 is larger than or equal to 25 J, and the hardness is larger than or equal to 50 HRC.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled round steel technology, specifically relating to a high-strength and high-toughness hot-rolled round steel for drill rods and its preparation method. Background Technology

[0002] The drill rod is a consumable part of the rock drilling tool. It is subjected to various alternating loads such as impact, wear, and bending, so the drill rod is required to have high strength.

[0003] Currently, the main materials for drill rods are CrMo series, CrNiMo series, and SiMnMo series steels, which contain high levels of elements such as Ni, Mo, and V, resulting in higher production costs.

[0004] Chinese patent CN 113136529 A discloses a low-carbon medium-manganese steel and a medium-manganese drill rod, as well as a method for their preparation. The chemical composition of the steel, by mass fraction, is: C: 0.05%-0.25%, Si: 0.20%-2.0%, Mn: 5.0%-9.0%, P: ≤0.010%, S: ≤0.001%, with the remainder being Fe and unavoidable impurities. This patent uses Mn as the main alloying element, resulting in a high Mn content, high production costs, and the low-carbon medium-manganese steel and medium-manganese drill rod disclosed in this patent have poor strength and toughness. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a hot-rolled round steel bar for high-strength and tough drill rods and its preparation method.

[0006] The technical solution adopted in this invention is as follows:

[0007] This invention provides a hot-rolled round steel bar for high-strength and high-toughness drill rods. The chemical composition and weight percentage of the hot-rolled round steel bar for high-strength and high-toughness drill rods are as follows: C: 0.26%~0.33%; Si: 0.90~1.30%; Cr: 1.30%~1.80%; Mn: 0.90%~1.30%; Mo: 0.15%~0.35%; Ti: 0.040%~0.10%; Al: 0.018~0.022%; P≤0.020%; S≤0.015%; N≤100ppm; the balance being iron and unavoidable impurities.

[0008] The metallographic structure of the hot-rolled round steel used for the high-strength and tough drill rod is pearlite and ferrite.

[0009] The high-strength and toughness drill rod hot-rolled round steel has a yield strength ≥1600MPa, tensile strength ≥1600MPa, elongation ≥9%, reduction of area ≥40%, AKV2 ≥25J, and hardness ≥50HRC.

[0010] The present invention also provides a method for preparing the hot-rolled round steel for high-strength and tough drill rods, the method comprising the following steps: smelting—continuous casting—hot rolling.

[0011] The smelting steps include blast furnace smelting, converter smelting, LF refining, and RH vacuum degassing.

[0012] In the blast furnace smelting process, the proportion of scrap steel in the raw materials of blast furnace molten iron shall not exceed 30%; in the converter smelting process, the C content of the converter tapped steel shall be ≥0.010%, the P content shall be ≤0.015%, and the tapping temperature shall be ≥1630℃.

[0013] In the LF refining step, the LF refining time is ≥40min, and the white residue refining time is ≥20min.

[0014] In the RH vacuum degassing step, the RH deep vacuum time is ≥15min and the soft blowing time is ≥15min.

[0015] In the hot rolling step, the billet is in the furnace for ≥600 min, the initial rolling temperature is 1100±20℃, and the final rolling temperature is ≥860℃.

[0016] C: It is the main element to ensure the strength of steel. A content of 0.26% to 0.33% can ensure that the drill rod reaches the ideal strength after heat treatment, and can also reduce the tendency of heat treatment deformation and cracking.

[0017] Cr: can improve the hardenability of steel, and together with carbides, it can refine the grain and improve the strength of the drill rod. In this invention, the Cr content is controlled to be 1.30%~1.80%.

[0018] Mn can significantly improve the hardenability of steel and has a good effect on improving strength and wear resistance. It can also play a role in deoxidation and desulfurization during the smelting process, improving the cleanliness of steel. At the same time, Mn alloys are relatively inexpensive and have low production costs. In this invention, the Mn content is controlled at 0.90%~1.30%.

[0019] Mo can refine the grains of steel, maintain sufficient strength and creep resistance at high temperatures, improve austenite stability, and improve the overall mechanical properties of the drill rod. In this invention, the content of Mo is controlled to be 0.15%~0.35%.

[0020] Ti: It can form strong TiC refined grains, thereby improving the strength and toughness of steel. In this invention, the Ti content is controlled to be 0.040%~0.10%.

[0021] Through the combination of the above components, the hot-rolled round steel provided by the present invention has high strength and toughness, with a yield strength ≥1200MPa, tensile strength ≥1600MPa, elongation ≥9%, reduction of area ≥40%, AKV2 ≥30J, and hardness ≥50HRC.

[0022] In the preparation method of high-strength and toughness hot-rolled round steel for drill rods provided by the present invention, high-purity molten steel is smelted by controlling the parameters of each process step, and hot-rolled steel with pearlite and ferrite microstructure is obtained after protective casting and hot rolling, thus ensuring the strength and toughness of the hot-rolled round steel.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The hot-rolled round steel for high-strength and tough drill rods provided by this invention uses a small amount of Mo, eliminating the need to add precious metal elements such as Nb, V, and Ni, thus reducing the amount of alloy used and lowering production costs.

[0025] Compared to typical drill rods with a yield strength of 850 MPa and a tensile strength of 1250 MPa, the hot-rolled round steel provided by this invention exhibits significantly improved strength and toughness. Attached Figure Description

[0026] Figure 1 The image shows the metallographic structure of the hot-rolled round steel used for the high-strength and tough drill rod in Example 1. Detailed Implementation

[0027] The present invention provides a hot-rolled round steel for high-strength and tough drill rods, the chemical composition and weight percentage of which are as follows: C: 0.26%~0.33%; Si: 0.90~1.30%; Cr: 1.30%~1.80%; Mn: 0.90%~1.30%; Mo: 0.15%~0.35%; Ti: 0.040%~0.10%; Al: 0.018~0.022%; P≤0.020%; S≤0.015%; N≤100ppm; the balance being iron and unavoidable impurities.

[0028] The method for preparing hot-rolled round steel for high-strength and tough drill rods includes the following steps: blast furnace smelting—converter smelting—LF refining—RH vacuum degassing—continuous casting—hot rolling—heat treatment.

[0029] In the blast furnace smelting process, the proportion of scrap steel in the raw materials of blast furnace molten iron shall not exceed 30%.

[0030] In the converter smelting process, the steel tapped from the converter has a carbon content of ≥0.010%, a phosphorus content of ≤0.015%, and a tapping temperature of ≥1630℃.

[0031] In the LF refining step, the LF refining time is ≥40min, and the white residue refining time is ≥20min.

[0032] In the RH vacuum degassing step, the RH deep vacuum time is ≥15min and the soft blowing time is ≥15min.

[0033] In the hot rolling step, the billet is in the furnace for ≥600 min and the initial rolling temperature is 1100±20℃.

[0034] The present invention will now be described in detail with reference to the embodiments.

[0035] The chemical composition and weight percentage of the hot-rolled round steel in each embodiment and comparative example are shown in Table 1, with the balance being iron and unavoidable impurities.

[0036] Table 1

[0037]

[0038] The production process parameters of the hot-rolled round steel in each embodiment and comparative example are shown in Table 2.

[0039] Table 2

[0040]

[0041] The properties of the hot-rolled round steel in each embodiment and comparative example after treatment are shown in Table 3.

[0042] Table 3

[0043]

[0044] As can be seen from the above, the technical solution provided by this invention can be used to prepare hot-rolled round steel for high-strength and high-toughness drill rods with a yield strength ≥1600MPa, tensile strength ≥1600MPa, elongation ≥9%, reduction of area ≥40%, AKV2 ≥25J, and hardness ≥50HRC.

[0045] In Comparative Examples 1-3, the impact toughness was lower than that of the Examples because the chemical composition content was not controlled within the range required by the present invention.

[0046] The above detailed description of a hot-rolled round steel bar for high-strength and tough drill rods and its preparation method is illustrative rather than limiting. Several embodiments can be listed according to the defined scope. Therefore, variations and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A hot-rolled round steel bar for high-strength and high-toughness drill rods, characterized in that, The chemical composition and weight percentage of the hot-rolled round steel for the high-strength and high-toughness drill rod are as follows: C: 0.26%~0.33%; Si: 0.90~1.30%; Cr: 1.30%~1.80%; Mn: 0.90%~1.30%; Mo: 0.15%~0.35%. Ti: 0.040%~0.10%; Al: 0.018~0.022%; P≤0.020%; S≤0.015%; N≤100ppm; balance is iron and unavoidable impurities.

2. The hot-rolled round steel for high-strength and high-toughness drill rods according to claim 1, characterized in that, The metallographic structure of the hot-rolled round steel used for the high-strength and tough drill rod is pearlite and ferrite.

3. The hot-rolled round steel for high-strength and high-toughness drill rods according to claim 1, characterized in that, The high-strength and toughness drill rod hot-rolled round steel has a yield strength ≥1600MPa, tensile strength ≥1600MPa, elongation ≥9%, reduction of area ≥40%, AKV2 ≥25J, and hardness ≥50HRC.

4. The method for preparing hot-rolled round steel for high-strength and high-toughness drill rods as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: smelting, continuous casting, hot rolling, and heat treatment.

5. The preparation method according to claim 4, characterized in that, The smelting steps include blast furnace smelting, converter smelting, LF refining, and RH vacuum degassing.

6. The preparation method according to claim 5, characterized in that, In the blast furnace smelting process, the proportion of scrap steel in the raw materials of blast furnace molten iron shall not exceed 30%; in the converter smelting process, the C content of the converter tapped steel shall be ≥0.010%, the P content shall be ≤0.015%, and the tapping temperature shall be ≥1630℃.

7. The preparation method according to claim 5, characterized in that, In the LF refining step, the LF refining time is ≥40min, and the white residue refining time is ≥20min.

8. The preparation method according to claim 5, characterized in that, In the RH vacuum degassing step, the RH deep vacuum time is ≥15min and the soft blowing time is ≥15min.

9. The preparation method according to claim 4, characterized in that, In the hot rolling step, the billet is in the furnace for ≥600 min, the initial rolling temperature is 1100±20℃, and the final rolling temperature is ≥860℃.

10. The preparation method according to claim 4, characterized in that, In the heat treatment step, the material is first quenched at 880±15℃ and then tempered at 230±20℃.

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