A Study Of Fatigue-thermal Deformation Of 35CrMo Steel At High Temperature

This paper studies low cycle fatigue and ratcheting deformation of 35CrMo steel under uniaxial stress-controlled loading.The microscopic analysis of fracture deformation and the effects of stress rates,ratcheting deformation and fatigue life for0.125MPa/s,0.5MPa/s,2.5MPa/s,10MPa/s,25MPa/s and 40MPa/s,and peak stresses?^max for 200MPa,300MPa,400MPa and 500MPa are discussed in detail.The results present that:?1?The ratcheting evolution curves with increasing number of cycles under these cases are similar to traditional static creep curves.The fatigue strain range decreases in the primary stage?Stage I?until it reaches the secondary stage?Stage II?with an steady fatigue strain range,then the fatigue strain range accelerates rapidly to final rupture in the tertiary stage?Stage III?.And the viscous stress component?^v increases obviously with the decrease of stress rate.This indicates that the viscous stress is the key factor for the ratcheting effect of 35CrMo steel under high temperature.?2?Shakedown behavior occurs when?is greater than or equal to 2.5MPa/s for?^max=200MPa,but ratcheting happens for the other loads.The creep damage is the main failure mode when the stress rate is less than 2.5MPa/s,while the fatigue damage is the primary fracture factor for those loads with greater frequency at?^max=500MPa.The maximum fracture strains for various stress rates remain approximately 11.6%,which can be used as the strain limit to monitor the fatigue life.?3?The analysis of microscopic fracture morphology is that the material's fatigue-creep interaction let to the material has a lot of creep pores inside,and mostly are inside of the material.The smaller the stress rate,the greater the creep hole.Moreover,the inclusions and cementite in the core with the creep hole growing,mutual formation would form inter-granular cracks on creep-fatigue inter actions and finally led to the fracture.