Yes, a dishwasher can potentially ruin the temper of a knife. The high heat, strong detergents, and harsh agitation in a dishwasher can have adverse effects on the tempering of a knife blade. The temper is the heat treatment process that gives a knife its hardness, durability, and ability to hold an edge.
Exposure to high temperatures in the dishwasher can cause the metal of the knife blade to expand and contract rapidly, potentially leading to warping or bending. Additionally, the strong detergents and chemicals used in dishwashers can be corrosive and may damage the knife blade over time. The agitation and movement within the dishwasher can also cause the blades to collide with other objects, leading to nicks or dings.
To preserve the quality and longevity of your knives, it is generally recommended to hand wash them with mild soap and warm water, immediately drying them afterward. Avoid soaking the knives for extended periods and do not leave them wet or damp as this can lead to corrosion. Regularly sharpening and honing your knives using appropriate tools will help maintain their sharpness and performance.