Method for reducing straightening fracture of steel for drilling tool
Through the comprehensive process, including heating, high-pressure water descaling, billet rolling, continuous rolling, annealing and straightening processes, the problem of brittle fracture of steel for brazing tools is solved, and hardness control and production cost reduction are achieved.
Patent Information
- Application Number
- CN202510167429.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-16
- Publication Date
- 2025-06-13
AI Technical Summary
Steel 23SiMnNi2Mo for brazing tools is prone to brittle fracture during straightening, which cannot meet the user's hardness requirements, resulting in high production costs and low efficiency.
The comprehensive process of heating, high-pressure water descaling, billet rolling, continuous rolling, annealing and straightening processes is adopted, including preheating and homogenizing of stepping beam heating furnaces, three-stage insulation annealing of annealing equipment, and straightening treatment of seven-roll continuous straightening machines.
It effectively reduces the brittleness of steel used in brazing tools, controls the strength and toughness of the material, prevents breakage during straightening, reduces production costs, and improves production efficiency.
Smart Images
Figure CN120138290A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of iron and steel smelting, and particularly relates to a method for reducing straightening fracture of steel for drill tools. Background Art
[0002] Drill steel refers to the drill steel drill tools used for impact drilling. The main use of drill steel drill tools is to be matched with rock drilling machinery and is a tool for drilling blast holes in rock or rock and soil drill and blast method construction. When working, the drill tool needs to transmit the impact power output by the rock drilling machinery, withstand the high-frequency impact and torsional moment of the rock drill at 2600 - 3000 times / min, and transmit the impact energy of more than 85 - 750 J in the form of impact stress waves; at the same time, during the process of drilling blast holes, the water holes inside the drill tool need to convey the ore water with a pressure of 0.4 MPa to ensure dust removal and discharge of rock powder; the outer surface of the drill tool also needs to generate strong abrasion with the rock surface.
[0003] Steel for drill tools usually uses rolled steel bars as raw materials and manufactures drill tools through forging and machining. Steel for drill tools requires high strength and wear resistance. By adding alloys to the steel, strengthening is generated to achieve the purpose of improving strength, hardness, and wear resistance. The steel type involved in the present invention is 23SiMnNi2Mo, and the alloying elements contained in this steel type are Mn, Ni, Mo, Cr, V. The addition of the alloy greatly improves the strength and wear resistance, but at the same time reduces the plasticity and toughness. Due to the high hardness, the hot-rolled bars cannot be sawed, and usually, users require annealing treatment when purchasing raw materials, and the hardness is generally required to be ≤280 HBW. It is found in the actual heat treatment process that the hardness of this material is still relatively high at 280 - 310 HBW after one stress relief annealing, which cannot meet the user's requirements. After heat treatment, the bars need to be straightened to ensure that the straightness of the bars is ≤3 mm / m. Due to the high hardness and brittleness of the material, the annealed rolled materials often show brittle fracture during the straightening process, and the cost loss per ton of steel is about 4000 yuan. The conventional annealing process cannot meet the user's requirements. Therefore, it is necessary to develop a production process that can not only meet the user's hardness requirements but also solve the problem of material fracture during straightening, reduce production costs, and improve production efficiency. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to provide a method for reducing straightening fracture of steel for drill tools. This method mainly reduces the brittleness of steel 23SiMnNi2Mo for drill tools, controls the strength and toughness of the material (room temperature Ku≥15 J), prevents fracture during straightening, and reduces production costs.
[0005] To solve the above technical problems, the technical solution adopted by the present invention is as follows: a method for reducing the straightening fracture of steel for drill tools, the method comprising the steps of heating, high-pressure water descaling, blooming rolling, continuous rolling, annealing, and straightening; in the blooming rolling step, the rough rolling starting temperature is 1020 - 1080 °C, and after 7 - 11 passes of reciprocating rolling to increase the deformation speed, the rolling speed of the blooming mill is controlled at 1.5 - 2.0 m / s, and at the same time, the roll cooling water and the ground roll cooling water are turned on for cooling to obtain an intermediate billet; in the continuous rolling step, the inlet continuous rolling temperature is 920 - 950 °C, and the continuous rolling speed is controlled at 0.7 - 1.5 m / s. Controlling the rolling temperature and the deformation speed is mainly to increase the stored deformation energy and improve the driving force for recrystallization enhancement.
[0006] The heating equipment for the heating step of the present invention is a walking beam type heating furnace. Cold billets enter the heating furnace, the temperature in the preheating zone is 600 - 700 °C, and the Φ600 mm round continuous casting billets are loaded into the heating furnace for preheating and then heated up to 1175 - 1255 °C for soaking. The soaking time is 250 - 300 min to reduce the microsegregation of the billets.
[0007] The heating equipment for the heating step of the present invention is a walking beam type heating furnace, which is divided into a preheating zone, a heating zone (zones 1 - 5), and a soaking zone (zones 6 - 8). The total length of the preheating zone is 13 m; the total length of the heating zone is 19 m, where the length of zone 1 is 4.3 m, the length of zone 2 is 3.7 m, the length of zone 3 is 3.7 m, the length of zone 4 is 3.7 m, and the length of zone 5 is 3.6 m; the total length of the soaking zone is 16 m; where the length of zone 6 is 5.6 m, the length of zone 7 is 4.8 m, and the length of zone 8 is 5.6 m. Cold billets enter the heating furnace, the billet specification is Φ600 mm, the heating temperature in the preheating zone is 600 - 700 °C, the total heating time of the billets ≥ 1.5 mm / min, the heating temperature in zone 1 of the heating zone is 700 - 800 °C, the heating temperature in zone 2 of the heating zone is 850 - 950 °C, the heating temperature in zone 3 of the heating zone is 850 - 1050 °C, the heating temperature in zone 4 of the heating zone is 1050 - 1150 °C, the heating temperature in zone 5 of the heating zone is 1150 - 1200 °C, the heating temperature in zone 6 of the soaking zone is 1200 - 1250 °C, the heating temperature in zone 7 of the soaking zone is 1220 - 1270 °C, and the heating temperature in zone 8 of the soaking zone is 1240 - 1275 °C.
[0008] In the high-pressure water descaling step of the present invention, the water pressure is 27 - 31 Mpa, and descaling is carried out circumferentially around the round continuous casting billets for 6 - 10 s to reduce the rolling-in of scale.
[0009] For the annealing process of the present invention, the annealing equipment used is a trolley-type annealing furnace, and the annealing process adopts three-stage heat preservation annealing. The annealing temperatures are 710 - 730 °C, 670 - 690 °C, and 630 - 650 °C respectively. There are two purposes: First, to fully recrystallize the deformed grains and improve the toughness of the steel; second, to keep it warm below the AC1 line to allow the carbides to precipitate and grow sufficiently, thereby reducing the matrix hardness. Considering that the cooling rate of the laboratory furnace is too fast, isothermal treatment is carried out in temperature segments to reduce the cooling rate of the furnace.
[0010] For the annealing process of the present invention, the loading amount does not exceed 60% of the total quota. It is heated to 710 - 730 °C at a rate of ≤40 °C / h, kept warm for 10 - 15 h, then cooled to 670 - 690 °C at a cooling rate of ≤15 °C / h, kept warm for 5 - 10 h, and then cooled to 630 - 650 °C at a cooling rate of ≤15 °C / h, kept warm for 4 - 6 h. The furnace is cooled at a rate of ≤15 °C / h to below 400 °C and then taken out of the furnace.
[0011] For the straightening process of the present invention, the straightening machine is a seven-roll continuous straightening machine. The camber of the incoming bar stock shall not exceed 10 mm / m, and the reverse bending amount is 13 - 15 mm to avoid fracture caused by excessive reverse bending amount.
[0012] The hardness of the steel for rock drills obtained by the method of the present invention after annealing is ≤250 HBW (the hardness of the stress relief annealing of conventional products is 280 - 310 HBW). The structure is tempered sorbite, and the precipitated carbide particles are finer and distributed in a dot shape.
[0013] The chemical composition and weight percentage of the steel for rock drills produced by the method of the present invention are as follows: C: 0.23 - 0.25%, Si: 1.42 - 1.47%, Mn: 1.40 - 1.45%, P ≤ 0.015%, S ≤ 0.005%, Alt: 0.018 - 0.030%, Cr: 0.40 - 0.50%, V: 0.15 - 0.20%, Ni: 1.75 - 2.00%, Mo: 0.5 - 0.65%, and the rest are Fe and inevitable residual elements.
[0014] The diameter of the rolled steel for rock drills produced by the method of the present invention is 80 - 150 mm.
[0015] The tensile strength of the steel for rock drills produced by the method of the present invention is ≥1600 MPa, the yield strength is ≥1200 MPa, the elongation after fracture is ≥10%, the reduction of area is ≥40%, and the impact energy at room temperature (U-notch) is ≥15 J.
[0016] The beneficial effects of adopting the above technical solution are as follows: Through process optimization, the present invention not only ensures that the hardness of the steel for drill tools is ≤250 HBW, but also reduces the straightening fracture ratio from the original 30 - 45% to less than 1%, and the loss per ton of steel is reduced by 3,800 yuan. Brief Description of the Drawings
[0017] Appendix Figure 1 This is the annealing process flow chart of the present invention. Detailed Description of the Invention
[0018] The present invention will be further described in detail below with reference to specific embodiments.
[0019] Examples 1 - 5
[0020] A method for reducing the straightening fracture of steel for drill tools (grade 23SiMnNi2Mo) includes the processes of heating, high-pressure water descaling, blooming rolling, continuous rolling, annealing, and straightening;
[0021] 1) Heating process: The heating equipment is a walking beam type heating furnace. The cold billets are fed into the heating furnace. The temperature in the preheating zone is 600 - 700 °C. The 600 mm round continuous casting billets are loaded into the heating furnace for preheating and then heated to 1150 - 1270 °C for soaking. The soaking time is ≥300 min to reduce the microsegregation of the billets. The control parameters of each example are shown in Table 1.
[0022] Table 1 Control Parameters of the Heating Process in Each Example
[0023]
[0024] Table 1 Control Parameters of the Heating Process in Each Example (Continued)
[0025]
[0026] 2) High-pressure water descaling process: The water pressure is 27 - 31 MPa. Descaling is carried out all around the circumference of the round continuous casting billets for 6 - 10 s. The purpose is to reduce the scale rolling in. The control parameters of each example are shown in Table 2.
[0027] 3) Blooming rolling process: The rough rolling starting temperature is 1020 - 1080 °C. After 7 - 11 passes of reciprocating rolling to increase the deformation speed, the rolling speed of the blooming mill is controlled at 1.5 - 2.0 m / s. At the same time, the roll cooling water and the ground roll cooling water are turned on for cooling to obtain the intermediate billets. The control parameters of each example are shown in Table 2.
[0028] 4) Continuous rolling process: The continuous rolling inlet temperature is 920 - 950 °C. The continuous rolling speed is controlled at 0.7 - 1.5 m / s. The control parameters of each example are shown in Table 2.
[0029] Table 2 Control Parameters of High-Pressure Water Descaling, Bloom Rolling and Continuous Rolling Processes in Each Example
[0030]
[0031] 5) Annealing process: The annealing equipment used is a trolley-type annealing furnace. The annealing process adopts three-stage heat preservation annealing. The loading amount does not exceed 60% of the total quota. It is heated to 710 - 730°C at a rate of ≤40°C / h, held for 10 - 15 h, then cooled at a rate of ≤15°C / h to 670 - 690°C, held for 5 - 10 h, and then cooled at a rate of ≤15°C / h to 630 - 650°C, held for 4 - 6 h. The furnace cooling is carried out at a rate of ≤15°C / h to below 400°C and then taken out of the furnace. The control parameters of each example are shown in Table 3.
[0032] 6) Straightening process: The straightening machine is a seven-roll continuous straightening machine. The camber of the bar stock incoming material shall not exceed 10 mm / m, and the reverse bending amount is 13 - 15 mm to avoid fracture caused by excessive reverse bending amount. The control parameters of each example are shown in Table 3.
[0033] The steel for rock drill bits obtained by the methods of each example has a structure of tempered sorbite. The chemical composition is shown in Table 4 and the properties are shown in Table 5.
[0034] Table 3 Control Parameters of Annealing and Straightening Processes in Each Example
[0035]
[0036]
[0037] Table 4 Chemical Composition and Mass Percentage Content (%) of Steel for Rock Drill Bits in Each Example
[0038] Embodiment C Si Mn P S Alt Cr V Ni Mo 1 0.244 1.470 1.400 0.0096 0.0050 0.0259 0.450 0.167 1.854 0.650 2 0.242 1.420 1.415 0.0128 0.0047 0.0235 0.400 0.169 2.000 0.641 3 0.230 1.436 1.423 0.0103 0.0036 0.0270 0.446 0.165 1.750 0.545 4 0.241 1.430 1.423 0.0119 0.0034 0.0260 0.485 0.150 1.831 0.547 5 0.238 1.450 1.450 0.0094 0.0034 0.0248 0.455 0.172 1.924 0.500 6 0.235 1.446 1.430 0.0088 0.0040 0.0198 0.458 0.170 1.848 0.560 7 0.239 1.432 1.421 0.0089 0.0030 0.0180 0.500 0.175 1.832 0.558 8 0.250 1.454 1.407 0.0113 0.0030 0.0204 0.436 0.174 1.750 0.560 9 0.249 1.467 1.427 0.0128 0.0039 0.0300 0.460 0.161 1.846 0.564 10 0.246 1.464 1.440 0.0150 0.0043 0.0220 0.470 0.200 1.839 0.585
[0039] Table 5 Specifications and Properties of Steel for Rock Drill Bits in Each Example
[0040]
[0041]
[0042] According to the implementation of the present invention, the hardness of the steel for rock drill bits after annealing is ≤250 HBW, and the fracture ratio during the straightening process is controlled below 0.5%. The annealing hardness of the products produced by the conventional process is 280 - 310 HBW, and the fracture ratio is 35 - 45%. At the same time, the steel for rock drill bits obtained in the examples of the present invention has a structure of tempered sorbite, more carbide precipitates, larger particles, and has been distributed in a dot shape. It can be seen that the present invention can obtain steel for rock drill bits with better performance.
[0043] The above embodiments are only used to illustrate rather than 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: modifications or equivalent replacements can still be made to the present invention, and any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.
Claims
1. A method for reducing straightening fracture of steel for drilling tools, characterized in that: The method comprises heating, high-pressure water descaling, slab rolling, continuous rolling, annealing and straightening processes; in the slab rolling process, the rough rolling temperature is 1020-1080°C, and after 7-11 reciprocating rolling passes, the deformation speed is increased, the slab mill rolling speed is controlled at 1.5-2.0 m / s, and the roller cooling water and the ground roller cooling water are turned on for cooling to obtain the intermediate slab; in the continuous rolling process, the continuous rolling temperature is 920-950°C, and the continuous rolling speed is controlled at 0.7-1.5 m / s.
2. A method for reducing straightening fracture of steel for drilling tools according to claim 1, characterized in that: The heating equipment of the heating process is a walking beam heating furnace, which is divided into a preheating zone, a heating zone (zones 1-5), and a soaking zone (zones 6-8). The cold billet enters the heating furnace, the heating temperature of the preheating zone is 600-700°C, the total heating time of the billet is ≥1.5mm / min, the heating temperature of heating zone 1 is 700-800°C, the heating temperature of heating zone 2 is 850-950°C, the heating temperature of heating zone 3 is 850-1050°C, the heating temperature of heating zone 4 is 1050-1150°C, the heating temperature of heating zone 5 is 1150-1200°C, the heating temperature of soaking zone 6 is 1200-1250°C, the heating temperature of soaking zone 7 is 1220-1270°C, and the heating temperature of soaking zone 8 is 1240-1275°C.
3. A method for reducing straightening fracture of steel for drilling tools according to claim 1, characterized in that: The high-pressure water descaling process has a water pressure of 27-31 MPa, and descaling is performed in all directions in the circumferential direction of the round continuous casting billet for 6-10 seconds.
4. A method for reducing straightening fracture of steel for drilling tools according to claim 1, characterized in that: The annealing process adopts a trolley-type annealing furnace as the annealing equipment, and the annealing process adopts a three-stage heat preservation annealing, and the annealing temperatures are 710-730°C, 670-690°C, and 630-650°C respectively.
5. A method for reducing straightening fracture of steel for drilling tools according to claim 1, characterized in that: The annealing process is to heat up to 710-730°C at a rate of ≤40°C / h, keep it at that temperature for 10-15h, then cool it down to 670-690°C at a rate of ≤15°C / h, keep it at that temperature for 5-10h, then cool it down to 630-650°C at a rate of ≤15°C / h, keep it at that temperature for 4-6h, and then cool it down to below 400°C at a rate of ≤15°C / h before taking it out of the furnace.
6. A method for reducing straightening fracture of steel for drilling tools according to any one of claims 1 to 5, characterized in that: In the straightening process, the straightening machine is a seven-roller continuous straightening machine, the curvature of the incoming bar material shall not exceed 10mm / m, and the reverse bending amount is 13-15mm.
7. A method for reducing straightening fracture of steel for drilling tools according to any one of claims 1 to 5, characterized in that: The steel for drill tools obtained by the method has a hardness of ≤250 HBW after annealing.
8. A method for reducing straightening fracture of steel for drilling tools according to any one of claims 1 to 5, characterized in that: The chemical composition and weight percentage of the steel for brazing tools produced by the method are as follows: C: 0.23-0.25%, Si: 1.42-1.47%, Mn: 1.40-1.45%, P≤0.015%, S≤0.005%, Alt: 0.018-0.030%, Cr: 0.40-0.50%, V: 0.15-0.20%, Ni: 1.75-2.00%, Mo: 0.5-0.65%, and the rest are Fe and inevitable residual elements.
9. A method for reducing straightening fracture of steel for drilling tools according to any one of claims 1 to 5, characterized in that: The diameter of the steel for the drill tool produced by the method is 80-150 mm.
10. A method for reducing straightening fracture of steel for drilling tools according to any one of claims 1 to 5, characterized in that: The steel for drilling tools produced by the method has a tensile strength of ≥1600MPa, a yield strength of ≥1200MPa, an elongation after fracture of ≥10%, a cross-sectional shrinkage of ≥40%, and an impact energy (U-shaped mouth) at room temperature of ≥15J.