Tissue control method for spring steel hot-rolled wire rod
By controlling the rolling and cooling process, the pre-spherized structure of the hot-rolled coil strip surface of spring steel is solved, and the problems of high energy consumption and process complexity in the prior art are achieved, and efficient production and cost reduction are achieved.
Patent Information
- Application Number
- CN202510315392.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-18
- Publication Date
- 2025-07-25
AI Technical Summary
The prior art has problems of high energy consumption, process complexity and material performance damage in spring steel strip processing, especially in the process of high surface reduction and extraction, which requires multiple normalized heat treatments, resulting in high energy consumption, increased cost and grain coarsening.
By controlling the rolling and cooling process, the pre-spherization structure of the hot-rolled coil strips on the spring steel is formed, and the large deformation amount and dynamic recrystallization are controlled during the rolling process. Combined with the slow cooling process, the hardness and hardening coefficient of the coil strips are reduced, and the number of normalized heat treatments is reduced.
The surface reduction rate of single-pass pulling is improved, the number of pulling trails or normalized heat treatments is reduced, energy consumption and production costs are reduced, and production efficiency is improved.
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Figure CN120362246A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of special steel smelting, and particularly relates to a method for controlling the microstructure of hot-rolled spring steel wire rods. Background Art
[0002] As a core mechanical functional component, the spring plays a key role in the following fields by virtue of its unique elastic deformation characteristics: (1) Industrial equipment field: applied to the pressure vessel sealing system, rail transit shock absorption base, and industrial robot joint buffer module; (2) Precision instrument field: as the core component of the precision balance calibration mechanism and the dynamic balance adjustment part of medical devices (such as the rotating bracket of a CT scanner); (3) Special environment field: maintaining good stiffness stability under extreme temperatures (-50°C to 300°C) or corrosive working conditions.
[0003] Its technical functions include: dynamic load buffering, mechanical energy storage and release, system resonance frequency adjustment, stress relaxation resistance under long-term service, etc.
[0004] In order to obtain higher wire strength and finer grain size, the spring steel wire rods need to be drawn one or more times during the processing and use process. The traditional process pursues a uniform lamellar pearlite structure inside and outside. Some studies have shown that when the difference in pearlite colony size ≤ 0.5 μm, the dislocation migration channels are blocked. During the drawing process with a cumulative reduction ratio > 80%, the dislocation density increases by an order of magnitude of 1014 m-2 per pass. When the Vickers hardness exceeds 480 Hv, the plastic reserve drops to < 5%. Especially during profiled drawing, due to a relatively larger stress concentration factor, the critical size for surface crack initiation will also decrease.
[0005] To solve this problem, after one or more passes of drawing, the wire needs to be normalized to eliminate the internal stress of the wire and then continue drawing. For wires with a high final reduction ratio, it may even be necessary to normalize and draw again after one normalization and drawing.
[0006] The improvement scheme of the traditional process has caused new technical and economic problems: 1) Energy consumption cost: Each pass of normalizing heat treatment needs to heat up to [Ac3 + 30°C] (typical value 850 - 920°C), and the energy consumption reaches 150 - 200 kWh / ton. Industry research data shows that the energy consumption of the normalizing process accounts for 15% - 20% of the total production cost (Issue 6, 2021, Metal Products).
[0007] 2) Process complexity: Wires with a high reduction ratio (> 80%) need to perform 2 - 3 normalization - drawing cycles. Each additional normalization treatment increases the comprehensive cost by 8% - 12%.
[0008] 3) Material property damage: Repeated normalizing leads to grain coarsening and an increase in the depth of the surface decarburized layer. Summary of the Invention
[0009] The technical problem to be solved by the present invention is to provide a method for controlling the microstructure of hot-rolled spring steel wire rods in view of the above-mentioned prior art. This method can form a pre-spheroidized microstructure on the surface layer of the spring steel wire rods. Compared with the lamellar microstructure, this microstructure has lower hardness and work hardening coefficient, can increase the reduction ratio of single-pass drawing in the subsequent process, reduce the number of drawing passes, or at least reduce one normalizing heat treatment, improve production efficiency, and reduce energy consumption and costs.
[0010] The technical solution adopted by the present invention to solve the above problems is as follows: A method for controlling the microstructure of hot-rolled spring steel wire rods, which controls the rolling and cooling to regulate the surface layer microstructure of the wire rods. Specifically: Step 1: Blank finishing, finish the surface of the blank. A better choice is to grind after peeling to remove surface decarburization, scale and defects. There are no burrs on the surface of the blank, and the corners are smoothly transitioned.
[0011] Step 2: Heating the blank in the furnace, the soaking temperature is 900 - 1240 °C, and the soaking time is ≥ 45 min, so that the inside of the blank is fully heated and softened, and the alloying elements are fully dissolved and homogenized.
[0012] Step 3: Rolling: After the steel is discharged, descale with high-pressure water. The starting rolling temperature is 840 - 1150 °C. The blank is rough-rolled, medium-rolled, and pre-finish-rolled, and the total reduction ratio is ≥ 99%; control the temperature to enter the finish rolling mill at 750 - 800 °C, and the finish rolling reduction ratio is 33% - 83%; after leaving the finish rolling mill, cool through the water tank, control the temperature entering the sizing mill at 750 - 780 °C, and the sizing reduction ratio is 25% - 44%; after sizing, spin the wire, and control the spinning temperature at 750 - 780 °C; Control of the starting rolling temperature (840 - 1150 °C), calculated based on the Arrhenius-type constitutive equation. When the temperature < 840 °C: the critical strain ε of dynamic recrystallization c > 0.8 (resulting in the proportion of the non-recrystallized zone > 40%). Experimental data shows that when rolling at a temperature above 840 °C, the completion degree of dynamic recrystallization reaches 92% ± 3%. After the material is rough-rolled, medium-rolled, and pre-finish-rolled, large deformation and multi-pass rolling are carried out at a high temperature state, and the deformation heat is superimposed. The original austenite grains undergo dynamic and static recrystallization during or after deformation, and the grains are refined.
[0013] The finish rolling temperature window (750 - 800 °C) is in the dynamic recrystallization temperature range (T drx = 0.55T melt ± 50 °C), ensuring that the strain-induced precipitation phase (size < 50 nm) effectively pins dislocations, and the dislocation density is controlled at 10 13 -10 14 m-2 Optimized range.
[0014] Before the rolled material enters the finishing mill and the sizing mill, through water jet rapid cooling, the austenite on the surface of the wire rod cools first. Under low-temperature conditions, the austenite is elongated and deformed, and a large number of dislocations, deformation bands and defects are generated inside the grains, storing a large amount of deformation energy. Combined with a large degree of supercooling under low-temperature conditions, it becomes the driving force for the surface layer structure to transform first. During the subsequent cooling process, the austenite on the surface of the wire rod transforms before the inside of the wire rod, and nucleation occurs on the deformation bands before the grain boundaries, and the grains are fine.
[0015] Step 4: Cooling: The wire rod enters the heat preservation cover for cooling. The heat preservation cover is fully closed, the fan is fully closed, and the roller table speed is constant at 0.30 m / s. The temperature of the wire rod leaving the heat preservation cover is ≤500 °C.
[0016] The fully closed heat preservation cover + the closed fan form a quasi-adiabatic environment (heat dissipation coefficient <5 W / (m²·K)), establishing a radial temperature gradient (surface cooling rate 0.8 - 1.2 °C / s vs core 2.5 - 3 °C / s). The latent heat of phase change released by the transformation of the internal structure of the wire rod (when austenite → pearlite transformation releases latent heat of about 82 J / g) diffuses to the surface, giving the thermodynamic conditions for the spheroidization of the surface lamellar structure. The cementite lamellae break and form spheres, and the hardness decreases.
[0017] Compared with the prior art, the advantages of the present invention are as follows: Compared with the conventional production process with a unified and uniform structure control idea for the inside and outside of the wire rod, the present invention proposes a new method for controlling the structure of the wire rod. The surface layer structure is in a pre-spheroidized state, with low hardness and hardening coefficient, and is more suitable for the drawing production of large reduction ratio or special-shaped steel wires, which can increase the reduction ratio of single-pass drawing, thereby reducing the number of drawing passes, or at least reducing one normalizing heat treatment. Brief description of the drawings
[0018] Figure 1 It is the micrograph of the surface layer of the wire rod of the present invention magnified 100 times. Figure 2 It is the micrograph of the surface layer of the wire rod of the conventional process magnified 100 times. Figure 3 It is the micrograph of the surface layer of the wire rod of the present invention magnified 5000 times under the electron microscope. Specific embodiments
[0019] The technical solution of the present invention will be described in more detail in combination with the preferred embodiments of the present invention. However, these embodiments are only descriptions of the preferred embodiments of the present invention and cannot limit the scope of the present invention in any way. Embodiment 1
[0020] The diameter of the spring steel wire rod in this embodiment is Φ5.5 mm.
[0021] The cross-sectional size of the blank is 150 mm × 150 mm. The surface of the blank is treated by grinding wheel peeling to remove the surface scale, decarburization and surface defects. The surface has no burrs, and the corners are smoothly transitioned to reduce corner decarburization.
[0022] The blank is heated in the furnace, and the soaking temperature is 980 - 1030 °C, and the soaking time is 47 min.
[0023] After the billet is taken out of the furnace, it is descaled by high-pressure water. The rolling start temperature is 900 °C. After rough rolling, medium rolling, and pre-finishing rolling, the total reduction is 99.1%; then, the material is cooled by water through the water box, and the temperature is controlled to enter the finishing mill at 785 °C for rolling, and the finishing reduction is 83%; after finishing rolling, the material is cooled by water through the water box, and the temperature is controlled to enter the sizing mill at 767 °C, and the sizing reduction is 37.4%; after rolling, the material is cooled by water through the water box, and the laying head temperature is controlled at 770 °C.
[0024] The heat preservation cover is fully closed, and the fan is fully closed. After the wire rod is laid head, it enters the heat preservation cover for slow cooling. The roller table speed is 0.30 m / s, and the temperature out of the cover is 470 °C. Example 2
[0025] The diameter of the spring steel wire rod in this example is Φ8 mm.
[0026] The cross-sectional size of the blank is 200 mm × 200 mm. The surface of the blank is treated by grinding wheel peeling to remove the surface scale, decarburization and surface defects. The surface has no burrs, and the corners are smoothly transitioned to reduce corner decarburization.
[0027] The blank is heated in the furnace, and the soaking temperature is 1060 - 1100 °C, and the soaking time is 53 min.
[0028] After the billet is taken out of the furnace, it is descaled by high-pressure water. The rolling start temperature is 980 °C. After rough rolling, medium rolling, and pre-finishing rolling, the total reduction is 99.4%; then, the material is cooled by water through the water box, and the temperature is controlled to enter the finishing mill at 790 °C for rolling, and the finishing reduction is 57.9%; after finishing rolling, the material is cooled by water through the water box, and the temperature is controlled to enter the sizing mill at 763 °C, and the sizing reduction is 42.7%; after rolling, the material is cooled by water through the water box, and the laying head temperature is controlled at 778 °C.
[0029] The heat preservation cover is fully closed, and the fan is fully closed. After the wire rod is laid head, it enters the heat preservation cover for slow cooling. The roller table speed is 0.30 m / s, and the temperature out of the cover is 488 °C.
[0030] In the wire rod produced by the above process, pre-spheroidization appears in the surface microstructure, and the surface structure has a lower hardness compared with the matrix structure. See Table 1 for details.
[0031] Table 1 Comparison of the properties and drawing processes of the wire rods in Example 1, Example 2 and the conventional process
[0032] Embodiments 1 and 2 are the preferred embodiments of the present application.
[0033] Although the preferred embodiments of the present invention have been described in detail above, it should be clearly understood that various changes and modifications can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.
Claims
1. A method for controlling the microstructure of hot-rolled wire rods of spring steel, which controls the rolling and cooling to regulate the surface microstructure of the wire rods, and is characterized in that: The method specifically is as follows: Step 1: Finish machining of the blank; Step 2: Heat the blank in a furnace, with soaking temperature of 900 - 1240 °C and soaking time ≥ 45 min; Step 3: Rolling: After tapping, descale with high-pressure water. The rolling start temperature is 840 - 1150 °C. The blank undergoes rough rolling, medium rolling, and pre-finishing rolling, with a total reduction of ≥ 99%. Control the temperature to enter the finishing mill at 750 - 800 °C, and the finishing rolling reduction is 33% - 83%. After finishing rolling, cool through a water tank, control the temperature to enter the sizing mill at 750 - 780 °C, and the sizing reduction is 25% - 44%. After sizing, spin the wire, and control the spinning temperature at 750 - 780 °C; Step 4: Cooling: The wire rod enters the heat preservation cover for cooling. The heat preservation cover is fully closed, the fan is fully closed, and the roller table speed is constant at 0.30 m / s. The temperature of the wire rod when it exits the heat preservation cover is ≤ 500 °C.
2. The method for controlling the microstructure of a hot-rolled wire rod of spring steel according to claim 1, characterized in that: In the above Step 1, finish machine the surface of the blank, grind it after peeling to remove surface decarburization, scale, and defects. There are no burrs on the surface of the blank, and the corners have smooth transitions.
3. The method for controlling the microstructure of a hot-rolled wire rod of spring steel according to claim 1, characterized in that: In the third step, the finish rolling temperature window is 750 - 800 °C, which is within the dynamic recrystallization temperature range T drx = 0.55T melt ± 50 °C, ensuring that the strain-induced precipitation phase size < 50 nm effectively pins dislocations, and the dislocation density is controlled at 10 13 -10 14 m -2 Optimization range.
4. The microstructure control method of a hot-rolled wire rod of spring steel according to claim 1, characterized in that: In the above Step 3, before entering the finishing mill and sizing mill, the rolled material is rapidly cooled through water. The austenite on the surface layer of the wire rod cools first. During subsequent cooling, the austenite on the surface layer of the wire rod undergoes a phase transformation prior to the interior of the wire rod, and nucleation occurs on the deformation bands prior to the grain boundaries, resulting in fine grains.
5. The microstructure control method of a hot-rolled wire rod of spring steel according to claim 1, characterized in that: In the above Step 4, the fully closed heat preservation cover + closed fan form a quasi-adiabatic environment, with a heat dissipation coefficient < 5 W / m²·K, establishing a radial temperature gradient. The surface cooling rate is 0.8 - 1.2 °C / s while the core cooling rate is 2.5 - 3 °C / s. The latent heat of phase transformation released by the internal structure transformation of the wire rod is 82 J / g when the austenite → pearlite transformation occurs.