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Why are the excavator's "steel teeth" so indestructible? A metallographic analysis reveals the secret to their toughness!
2025-11-07
How do excavators manage to chew through rocks? The key lies in their foremost "steel teeth"—the bucket teeth. Today, we'll use a LABTTor metallographic microscope to uncover the microscopic secrets behind their hardness!
I. Sampling and Sample Preparation
The material grade of this bucket tooth is kept secret; all that's known is that it's a low-alloy ultra-high-strength steel. Samples were cut from the cross-section of the bucket tooth and then mounted.
We first used a LABTTor fully automatic polishing machine with 180# sandpaper to remove cutting marks from the sample surface. We then switched to 400# and 800# wet sandpaper, rotating the sample 90 degrees after each sandpaper change to ensure complete removal of the previous scratch.
Next, we polished the sample with 3μm diamond polishing compound and silk polishing cloth until a mirror-like surface was free of scratches.
Finally, we used a 4% nitric acid alcohol solution as an etching agent for etching. After the sample surface darkened, it was immediately rinsed with water, sprayed with alcohol, and quickly dried.
II. The Microscopic World
The etched sample was observed under a Neibo metallographic microscope at 100x magnification. Microstructural details were difficult to discern, but a review of the entire metallographic surface revealed a highly uniform microstructure.
At 500x magnification, the microstructure of the bucket tooth was found to be dense medium-carbon martensite. This acicular martensite structure forms the strong, impact-resistant core of the bucket tooth. Based on the discoloration of the etched sample and the microstructural characteristics observed under the microscope, it was determined that the bucket tooth underwent a quenching and low-temperature tempering process.
This low-temperature tempered medium-carbon martensite structure allows the material to maintain relatively good toughness while retaining ultra-high strength. This is crucial for bucket teeth subjected to impact loads. This tempered medium-carbon martensite significantly reduces the risk of brittle fracture when excavating hard rock or encountering foreign objects.
The bucket teeth have a relatively large cross-sectional dimension, especially the thicker part at the root. Metallographic observation of different parts of the bucket teeth reveals a relatively uniform tempered martensite structure, indicating excellent hardenability and ensuring the uniformity of the overall performance (strength, hardness, and toughness) of the bucket teeth.
Slight decarburization and oxide pits are observed on the surface of the bucket teeth, with a decarburized layer depth of 0.09 mm. Surface decarburization significantly weakens the fighting ability of the bucket teeth, causing them to wear out prematurely.
Through this in-depth metallographic journey into the microscopic world, we have witnessed the true strength of excavator bucket teeth—the "steel teeth" of engineering machinery. Behind them lies the combined effect of a dense tempered martensite structure, precise heat treatment processes, and excellent hardenability. Every trace of digging is a testament to the wisdom of materials science.
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