Method for improving fatigue resistance of round-link chain

Abstract

The application discloses a method for improving fatigue resistance of round-link chain and belongs to the technical field of high-strength mining round-link chain processing and manufacturing. The round-link chain quality fraction chemical composition is disclosed; molten steel is subjected to calcium treatment modification sulfide inclusions; the rolling final rolling temperature is 920-960 DEG C, and after rolling, air cooling is performed to 620+ / -5 DEG C and then cold piling is performed; the quenching and tempering heat treatment is as follows: 910-940 DEG C is kept for 30-40 min, water quenching is performed, 510-540 DEG C is kept for 55-65 min, and air cooling is performed; the low-temperature stress relief is as follows: after tempering, 210-240 DEG C is kept for 110-130 min, and slow cooling is performed in the furnace to room temperature. The application aims to provide a set of whole-process collaborative control method, through the collaborative cooperation of components and process parameters, synchronous realization of inclusion refinement, grain ultra-refinement, precipitation strengthening and uniform release of residual stress, and significant improvement of the fatigue fracture resistance of the round-link chain under alternating load.

Description

Technical Field

[0001] This invention belongs to the field of high-strength mining circular link chain processing and manufacturing technology, and particularly relates to a method for improving the fatigue resistance of circular link chains. Background Technology

[0002] Existing mining circular link chains are mostly made of conventional Mn-V alloy steel, and the conventional smelting, rolling, and heat treatment processes have multiple defects. First, the inclusions in the steel are large in size and unevenly distributed, making them prone to fatigue crack initiation under alternating loads in the circular transition region of the chain links. Second, the lack of rare earth composite microalloying design results in coarse grains and insufficient number of nano-precipitated strengthening phases, limiting the improvement of fatigue strength. Third, the heat treatment only uses a single quenching and tempering process, causing coarse carbides to precipitate along the grain boundaries in the tempered structure, reducing the grain boundary bonding strength. Fourth, the lack of stress homogenization treatment after forming leads to residual stress concentration in the chain links, resulting in rapid crack propagation under long-term alternating loads.

[0003] Existing improvement solutions mostly focus on optimizing heat treatment or raw material composition, failing to achieve coordinated matching of composition, rolling, heat treatment, and stress relief throughout the entire process. This results in limited improvement in the fatigue cycle count of the finished circular chain, making it prone to early fatigue fracture under high-power fully mechanized mining equipment conditions, leading to frequent replacements and impacting continuous production operations. Summary of the Invention

[0004] To overcome the technical defects of existing circular link chain manufacturing processes, such as disconnect between composition, thermal processing, and heat treatment, poor control of inclusions, coarse grains, coarse grain boundary carbides, and concentrated residual stress, which lead to low fatigue life of circular link chains, a whole-process collaborative control method is provided. Through the coordinated coordination of composition and process parameters, inclusion refinement, grain ultrafineness, precipitation strengthening, and uniform release of residual stress are achieved simultaneously, significantly improving the fatigue fracture resistance of circular link chains under alternating loads.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] This invention discloses a method for improving the fatigue resistance of circular link chains. The circular link chain has the following chemical composition by mass fraction: C 0.19%-0.23%, Si 0.25%-0.45%, Mn 1.40%-1.70%, V 0.08%-0.13%, Nb 0.04%-0.07%, Ce-La mixed rare earth RE 0.015%-0.030%, S≤0.008%, P≤0.012%, with the balance being Fe and impurities. The molten steel is modified by calcium treatment to remove sulfide inclusions. The final rolling temperature is 920-960℃, followed by air cooling to 620±5℃ and then heat treatment. The heat treatment involves holding at 910-940℃ for 30-40 minutes. Water quenching, tempering at 510-540℃ for 55-65 minutes, and air cooling; low-temperature stress relief: after tempering, hold at 210-240℃ for 110-130 minutes, and then slowly cool to room temperature in the furnace.

[0007] Furthermore, during the smelting stage, the billet is heated to 1180-1230℃ and held for 90 minutes.

[0008] Furthermore, the mechanical properties of the finished circular link chain meet the following requirements: tensile strength ≥1180MPa, yield strength ≥980MPa, room temperature impact energy ≥72J, and fatigue cycle count ≥120,000 times.

[0009] Furthermore, the chemical composition of the circular ring chain by mass fraction is: C 0.21%, Si 0.33%, Mn 1.55%, V 0.10%, Nb 0.055%, RE 0.022%, S 0.006%, P 0.010%, with the balance being Fe and impurities.

[0010] Further, rolling: the billet is placed in the furnace at 1200℃ and held for 90 minutes, then continuously rolled, with a final rolling temperature of 940℃.

[0011] Furthermore, after rolling, it is air-cooled to 620°C for stack cooling.

[0012] Further tempering: water quenching at 925℃ for 35 minutes; tempering at 525℃ for 60 minutes, followed by natural cooling in air.

[0013] Furthermore, low-temperature stress relief: hold at 225℃ for 120 minutes, then cool to room temperature in the furnace at a rate of 30℃ / h.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0015] (1) The synergistic effect of Ce-La rare earth composite V and Nb microalloys refines and spheroidizes sulfide inclusions, eliminates long strip-shaped harmful inclusions, and reduces fatigue crack initiation sites;

[0016] (2) Temperature control during rolling combined with microalloy precipitation refines austenite grains to 8-12μm, and fine grain strengthening enhances the fatigue resistance of the matrix;

[0017] (3) Precise control of the tempering range suppresses the precipitation of coarse carbides at grain boundaries, and the tempered bainite + fine lath martensite complex structure enhances the resistance of grain boundaries to crack propagation.

[0018] (4) The low-temperature long-term stress relief process releases residual stress from molding and welding, eliminates stress concentration at the arc of the chain link, and delays the propagation of fatigue cracks.

[0019] (5) The entire process is matched, no new large equipment is needed, the existing production line can be directly adapted, the fatigue life of the finished product is increased by more than 60% compared with the conventional process, the strength and toughness are matched simultaneously, and there is no obvious performance degradation. Detailed Implementation

[0020] Example 1

[0021] Smelting process: Prepare the steel composition (mass fraction): C 0.21%, Si 0.33%, Mn 1.55%, V 0.10%, Nb 0.055%, RE 0.022%, S 0.006%, P 0.010%, balance iron; after refining the steel, feed calcium wire to modify inclusions, and continuously cast to obtain qualified billets.

[0022] Rolling: The billet is placed in the furnace at 1200℃ and held for 90 minutes. It is then continuously rolled to a final rolling temperature of 940℃. After rolling, it is air-cooled to 620℃ and then transferred to a slow-cooling stack for further cooling.

[0023] Forming: Rolling into formed round bars, medium-frequency bending, flash butt welding, grinding to remove weld protrusions, and correcting chain link dimensions.

[0024] Tempering: Hold at 925℃ for 35 minutes, then water quench; temper at 525℃ for 60 minutes, then air cool naturally.

[0025] Low-temperature stress relief: Hold at 225℃ for 120 minutes, then cool to room temperature in the furnace at a rate of 30℃ / h.

[0026] Finished product testing: tensile strength 1225MPa, yield strength 1016MPa, room temperature impact energy 78J, fatigue cycle count 132,000 times.

[0027] Comparative example (conventional process)

[0028] The raw material is 20MnV, which is free of Nb and rare earth elements, with a composition of 0.22% C, 1.52% Mn, and 0.10% V, and is free of Nb and RE. The rolling and forming processes are the same as in the previous example. The heat treatment is only water quenching at 920℃ and tempering at 525℃, omitting the low-temperature stress relief process.

[0029] Finished product testing: tensile strength 1140MPa, room temperature impact energy 53J, fatigue cycle count 79000 times.

[0030] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for improving the fatigue resistance of circular link chains, characterized in that, The chemical composition of the circular ring chain by mass fraction is as follows: C 0.19%-0.23%, Si 0.25%-0.45%, Mn 1.40%-1.70%, V 0.08%-0.13%, Nb 0.04%-0.07%, Ce-La mixed rare earth RE 0.015%-0.030%, S≤0.008%, P≤0.012%, with the balance being Fe and impurities; the molten steel is modified by calcium treatment to remove sulfide inclusions; the final rolling temperature is 920-960℃, followed by air cooling to 620±5℃ and then heat treatment; the quenching and tempering heat treatment is performed by holding at 910-940℃ for 30-40 minutes followed by water quenching, tempering at 510-540℃ for 55-65 minutes followed by air cooling; the low-temperature stress relief treatment is performed by holding at 210-240℃ for 110-130 minutes after tempering, followed by slow cooling in the furnace to room temperature.

2. The method for improving the fatigue resistance of circular link chains according to claim 1, characterized in that, During the smelting stage, the billet is heated to 1180-1230℃ and held for 90 minutes.

3. The method for improving the fatigue resistance of circular link chains according to claim 1, characterized in that, The mechanical properties of the finished circular link chain meet the following requirements: tensile strength ≥1180MPa, yield strength ≥980MPa, room temperature impact energy ≥72J, and fatigue cycle count ≥120,000 times.

4. The method for improving the fatigue resistance of circular link chains according to claim 1, characterized in that, The chemical composition of the circular ring chain by mass fraction is: C 0.21%, Si 0.33%, Mn 1.55%, V 0.10%, Nb 0.055%, RE 0.022%, S 0.006%, P 0.010%, with the balance being Fe and impurities.

5. The method for improving the fatigue resistance of circular link chains according to claim 4, characterized in that, Rolling: The billet is placed in the furnace at 1200℃ and held for 90 minutes, then continuously rolled to a final rolling temperature of 940℃.

6. The method for improving the fatigue resistance of circular link chains according to claim 1, characterized in that, After rolling, air-cool to 620℃ for stack cooling.

7. The method for improving the fatigue resistance of circular link chains according to claim 1, characterized in that, Tempering: Water quenching at 925℃ for 35 minutes; tempering at 525℃ for 60 minutes, followed by natural cooling in air.

8. The method for improving the fatigue resistance of circular link chains according to claim 1, characterized in that, Low-temperature stress relief: Hold at 225℃ for 120 minutes, then cool to room temperature in the furnace at a rate of 30℃ / h.