Effect of temperatures and strain rates on the average size of grains refined by dynamic recrystallization for as-extruded 42CrMo steel

Abstract

In order to study the dynamic recrystallization (DRX) behavior of as-extruded 42CrMo highstrength steel, a series of isothermal upsetting experiments were carried out in a temperature range of 1123~1348 K and a strain rate range of 0.01~10 s -1 on Gleeble 1500. It was found that DRX softening is more recognizable at higher temperatures and lower strain rates, and stress level increases with increasing strain rate and decreasing deformation temperature. The types of flow stress evolution were distinguished by the following three characteristics: WH followed by DRX, WH followed by DRV, and WH followed by no dynamic softening. At a fixed temperature, the average grain size refined by DRX linearly decreases with increasing strain rate in log scale. At a fixed strain rate, the average grain size remains almost constant below 1273 K, while it rapidly increases above 1273 K. At a larger strain rate, data set of grain sizes has a smaller standard deviation to the average size value, and data have tightly grouped. This indicates that as strain rate increases, the microstructure becomes more and more uniform. The relationships between the average grain size and Zener-Hollomon parameter were nonlinearly fitted by the equation D A = 319.81202 -13.6114 lnZ + 0.15322 (lnZ) 2 . The results from this equation show that the average grain size decreases with increasing Zener-Hollomon parameter. On the plot of D A versus lnZ, the regions corresponding to DRV (lnZ 37.8) and DRX (lnZ 37.8) were clarified clearly.

Numerical modeling of flow stress and grain evolution of an Mg AZ31B alloy based on hot compression tests

“…For a fixed temperature, as strain rate increases, recrystallized grains have not enough growth time, and stored energy (i.e., high nucleation rate) increases, thus more refined grains will be achieved. Similar results were found by Guo-zheng et al [29] processing 42CrMo Steel and Fatemi-Varzaneh et al [30] processing AZ31 alloy. Grain size measurements were performed according to ASTM E112-12 [31].…”

EBSD Investigation to Study the Restoration Mechanism and Substructural Characteristics of 23Cr–6Ni–3Mo Duplex Stainless Steel During Post-deformation Annealing

“…In this stage, the dislocation density increases as the strain enhances, promoting the subgrain formation [16]. It has also been reported that DRX initiates before reaching the stress peak, but it cannot be said that it is initiated in austenite or ferrite [17][18][19].…”

“…and WH[16]. No indication of steady-state flow is observed as WHR value does not reach zero, which corresponds to the onset of steady-state flow (balance between…”

The High-Speed 6xxx Aluminum Alloys in Shape Extrusion Industry

“…The effects of temperature and strain rate can be expressed in terms of the second-order function of the Zener-Hollomon parameter, Z, in an exponent-type function of temperature and strain rate, as follows [29]:…”