Hot deformation characteristics of a nitride strengthened martensitic heat resistant steel

Abstract

Constitutive equations including an Arrhenius term have been applied to analyze the hot deformation behavior of a nitride-strengthened (NS) martensitic heat resistant steel in the temperature range of 900-1200 °C and in the strain rate range of 10

Constitutive Modeling, Microstructure Evolution, and Processing Map for a Nitride-Strengthened Heat-Resistant Steel

“…Finally, DSIT happens when two preconditions, the critical strain for DSIT and the temperature being above Ar 3 , are met simultaneously. According to previous work, the DSIT occurred before DRX in the case of NS steel [9] and effected the evolution of microstructure greatly. This paper aims to establish the constitutive equations for an NS martensitic steel and to establish optimum processing parameters according to the processing map of energy dissipation efficiency.…”

“…1 [9] . [9] . The sample was heated up to 1200 °C and cooled down to the deformation temperature of 900-1200 °C after being homogenized for 5 min., then deformed at different strain rates of 10 shows the drum shape after large degree of deformation.…”

“…A separate set of figures, of these same data, was given in a previous publication [9] , to show the effect of strain-rate for each temperature. The critical strain, ε c , and the peak strain, ε p , which were determined through calculation of the deformation data using the method provided by previous researchers [6,10] , were marked on most of the curves.…”

The soften mechanisms of martensitic heat resistant steels during hot deformation

“…However, the increase of ln(ε c ) value slowed down and then levelled off at Z value beyond 40. This resulting hump recorded by Stewart et al was explained by the segregation of substitutional impurities (P in particular) to the subboundaries of newly nucleated DRX grains [3] . But Nanba acclaimed that the critical strain was expected to slightly depend on the temperature and have no apparent dependence on either the strain rate or the initial grain size for plain carbon steels [5] .…”

“…To control the microstructure during deformation, the softening mechanisms should be well analysed. Generally, whether a softening procedure occurs or not during a specific hot deformation，it could be identified through both analysing the stress-strain curves up to the peak and the microstructure observation [3] . The heat resistant steels being used in the utra-supercritcal (USC) power plants not only bear extrusion at high temperature but also experience a creep deformation under a constant stress at high temperature due to the service situation.…”