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Fatigue Failure Of Drill Rod
After heat treatment of 55SiMnMo drill rod, the rod body is austenitized at 900 °C for 30 minutes and then air-cooled. The air-cooling speed is very sensitive to the metallographic structure of 55SiMnMo steel. Due to the north-south region and seasonal changes, the 55SiMnMo drill rod is heat treated, and the rod body is austenitized at 900 °C for 30 minutes, and the air cooling speed is very sensitive to the metallographic structure of 55SiMnMo steel. The metallurgical plant producing the drill rods is subject to strict control due to changes in the north and south regions and seasons. Therefore, the air cooling rate should be strictly controlled. • The factors affecting the fatigue failure of the drill rod are briefly described as follows
• (1) The effect of metallographic structure on fatigue failure
• As shown, the source of fatigue fracture originates from the inner or outer surface. In actual use, the fatigue source originates from the inner surface and accounts for 80% of the fatigue fracture. A drill rod with a rock drilling life of more than 100 meters is dissected, and the macroscopic fatigue crack on the inner surface is abnormal. See Figure 68. A cross-section ground metallographic specimen was taken anywhere in the section and it was found that the crack propagated toward the center as shown.
• (2) the effect of inclusions on fatigue failure
• The drill rod, the fatigue source originates from the outer surface, which is a drill rod fracture with a rock drilling life of only 50 m/root.
• Generally speaking, the fatigue source originates from the inner surface, and the life of the drill rod is relatively high; if the fatigue source originates from the outer surface, the life is relatively low. Because the crack on the inner surface expands slowly due to the relationship between the force state and the action of the mineral water medium, the crack on the outer surface expands faster due to the relationship of the stress state.