Abstract
To draw benefits from fast quenching to strengthen and toughen as well as to increase the fatigue strength by taking advantage of residual stress, the stresses given rise to in steels during and after quenching were computed.
The quenching stress, which is due to thermal strain and transformation strain, was presented as a function of changes of temperature distribution, while the method of quenching and the sizes of steel articles were conceived as the factors that determined the temperature distribution.For the steel articles state during quenching, elastic parts and plastic parts were discriminated on the basis of the maximum shear stress theory, and the transient stress distributions were obtained by integrating the stress from the quenching temperature down to an instantanius temperature.
The computations revealed:
1) The superficial tensile stress becomes maximum during quenching just before the transformation at the center is completed, whereas, in cases of imperfect quench, the central tensile stress becomes maximum when the steel as a whole is cooled to the room temperature.
2) For the case of perfect quench, the superficial tensile stress is the greater the severer the quenching, though it decreases beyond a certain limit of quenching speed even becoming comperession.
3) For imperfect quench, the stress distribution, though much depends on the quenched structure and the severity of quenching, is generally such that the superficial stress is compressive and often a sharp peak of tensile stress exists at just below the surface.
A few practical applications have been presented and discussed.
