The domestic manufactured CT80, Φ33×3.18 coiled tubing is supplied as heat-treated low-alloy steel. The relationship between thermo cycle, microstructure, tensile properties and hardness were researched for butt welded joint. The results show that CT80 is very sensitive to welding heat input, and the thermo accumulation was obvious for small dimension coiled tubing, varying degrees of softening always exist in HAZ. The reasons include growing of block ferrite, decreasing and isolating of continuous directional bainite. In order to get good properties, the strength of consumable welding wire should be properly matched with base metal, keep uniform strength distribution along welded joint, and avoid the plastic strain concentrate in local area.

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In order to improve the wear resistance of the sprag clutch under the work condition, the chemical vapor deposition technology is used on the surface of sprag. The hardness of surface is HV0.11700~2300, the thickness is 5~8μm, and the adhesion force isn’t less than 65N. In the end, the wear resistant life of the sprag surface used the chemical vapor deposition process is improved 5 times than that of the sprag surface used the physical vapor deposition process by the low cycle fatigue test. The life of the sprag clutch is effectively improved.