When the surface of the hydraulic piston rod is quenched, it is mainly tempered by its own residual heat, and because the tempering temperature is gradually reduced, there is no complete tempering and heat preservation process, the tempering time is short, and the stress is eliminated. Incomplete, there is a large residual stress in some products. Therefore, further processing is needed.

This is because in the later processing of the hydraulic piston rod, if there is still a large residual stress, the internal stress generated during grinding will be superimposed on it. When the stress exceeds the tensile strength of the material, the surface of the piston rod will Stress cracks are generated. If the stress does not exceed the tensile strength of the material and is present in the product as residual stress, the plating may be cracked due to redistribution of stress during subsequent chrome plating or during use, causing cracks in the chrome plating layer.

In order to prevent such problems, the hydraulic piston rod must be annealed before chrome plating to eliminate the internal stress generated by grinding and surface treatment. The stress-free annealing heating temperature is 200-230 ° C, and after 190 min of heat preservation, the furnace is cooled to 160 ° C to be air-cooled.

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