Abstract: The high-temperature relaxation resistance of spring steel is improved by providing a specified composition of the steel, and subjecting that steel composition to a controlled heat treatment. The high-temperature relaxation resistance, which can not be estimated from the mechanical properties (e.g. strength and hardness) of steel materials at an ordinary temperature, is improved by these conditions which the inventors have found out from many experiments. Especially, the temper-softening resistance is enhanced by an increase of the Si content. The density of dislocation is lowered by providing fine carbides (MO.sub.2 C) serving as inhibitors for the migration of dislocation. These are precipitated by a controlled heat treatment without reducing hardness in the tempered state. Consequently, the obtained spring steel can be used operated in a high-temperature environment for a long time without a deterioration in its properties.

Abstract: The present invention relates to a vibration-damping metal sheet.Conventional vibration-damping metal sheets such as single metal sheets of Mn-Cu base alloys, etc., and sandwich steel sheets having an intermediate plastic material had individually some disadvantages in connection with critical temperatures for use, heat resistance, weldability, conductivity and other properties.In the present invention, metal plates (1) and (2) are joined together through minute inclusions (3) permitted to be substantially uniformly present therebetween and bit thereinto and, optionally, through the diffusion of a portion of the metal plates into which the minute inclusions are bit. At another portion, the metal plates (1) and (2) only come into contact with each other. Metal or ceramic powders, or wiry or network materials may be used as the minute inclusions (3).