Atomic force microscopy (AFM) was used to analyze grain boundary sliding. This method was applied to measure the out-of-plane component of grain boundary sliding on two 304H grades and one X-750 grade. The main objective was to examine the initial stage of grain boundary sliding, after short-time constant load tests. The results showed that grain boundary sliding is activated at initial loading, producing a few tens nm high steps. The influences of grain boundary trace orientation, the applied load and the crystallographic misorientation were analyzed. The latter is the most distinctive parameter on grain boundary sliding propensity. An 'initial stage' of grain boundary sliding was identified. The proposed method allows early detection of intergranular damage sensitivity of industrial grades after short-time tests, and can be used to refine further long-time tests on heavier experimental devices, such as creep tests or stress corrosion cracking tests.