Springs are the mechanical parts which have many application in industries. Static and dynamic forces cause relaxation in these parts so that they lose some of their free length and reaction force. Springs constant are very important in airplane and vailway industry since constant and variable forces are applied to them in period time, therefore it is necessary to avoid decreasing in spring constant in this condition. In this research, at first manufactured springs were stress relieved under different temperatures. In the next step constant displacements were applied to stress relieved springs by means of designed fixture. Springs constant changes and rate of these changes during different stages of the test were obtained. Results shownd that the stress relieving at 300 ° C has the best effect on prevention of decreasing in springs constant and free length under static long-term load.