Ageing effect on cyclic plasticity of a tempered martensitic steel

Abstract

Specific isothermal cyclic deformation tests were carried out on a tempered martensitic steel 55NiCrMoV7 at four hardness levels in the temperature range 20-600 °C. The cyclic stress response generally shows an initial exponential softening for the first few cycles, followed by a gradual softening without saturation. The influences of initial hardness obtained after tempering, temperature, strain rate and ageing on cyclic plasticity are discussed by means of hardness measurements and equivalent ageing experiments. Compared to hardness measured after ageing without fatigue loading, hardness dramatically decreases when the specimen is simultaneously subjected to ageing and fatigue at elevated temperature. Cyclic softening intensity increases with testing temperature from 300 to 600 °C, but the maximal softening intensity occurs at room temperature. This is inconsistent with hardness measurements performed on the specimen after a fatigue test conducted at room temperature. The final discussion focuses on the mechanisms involved in the softening of martensitic steels to explain the last result.

Influence of silicon content on the precipitation of secondary carbides and fatigue properties of a 5%Cr tempered martensitic steel

“…Concerning the cyclic loading, martensitic or bainitic steels have typical fatigue behaviour: an overall significant softening till rupture [9][10][11][12][13][14][15][16][17][18][19][20] as shown in Fig. 2.…”

Evaluation of fatigue crack growth rate for iron-carbon metals based on degradation-entropy generation theorem

“…The second process includes a tempering at temperature of 400 °C, holding for 2 hours and cooling at room temperature to form tempered martensite. This tempering temperature was chosen because traditionally, low carbon steel is tempered after heat treatment between 200 °C and 600 °C [13][14][15]. …”

Influence of Tempering Temperature on Low Cycle Fatigue of High Strength Steel

“…For instance, the fatigue performances of 55NiCrMoV7 steel were reduced for elevated tempering temperature over 500°C because of the drop of hardness accompanied with cyclic softening. 8) Thus, to achieve the desired fatigue properties in high strength steels, it is crucial to understand the tempering and subsequent deformation mechanisms in order to find the conditions leading to optimal performances.…”