Cyclic Softening
Cyclic softening is the reduction of flow stress under repeated loading. It is caused by the rearrangement and reduction of dislocation structures.
Physicochemical mechanism of action
Under cyclic loading, dislocation structures are rearranged within the material. These structures can degrade over time, leading to a reduction in flow stress.
Metallurgical relevance & risks in welding
Excessive cyclic softening can lead to a loss of strength and toughness of the material. This increases the risk of cracking and failure under load. In martensitic or work-hardened microstructures, the flow stress is particularly sensitive to cyclic loading.
Workshop practice & action guidelines
To minimize cyclic softening during welding, the following should be observed:
• Choose an optimal cooling curve (e.g., t8/5 between 10 and 20 seconds)
• Apply a uniform cooling process
• For highly stressed components, perform postweld heat treatment (PWHT)
These measures help stabilize the dislocation structures and increase the flow stress.