208 Prakt. Met. Sonderband 52 (2018) 
cycles a constant change of plastic strain ensues. However, the mechanism is quite 
different to what is normally understood under ratchetting considering the full temperature 
cycle and phase transformation involved. It was found that this ratchet strain is much 
larger in the first cycle than in the following cycles and that martensite start temperature 
decreases slightly with each cycle. For each austenite to martensite transformation the 
transformation induced plasticity (TRIP) effect produces a high density of dislocations, 
which only partially recrystallize and recover upon heating back into an austenitic state, 
due to the short dwell time at high temperature. However, the higher the dislocation 
density, the higher the driving force for recrystallization and recovery. Therefore, if the 
rates of temperature change and holding times are unaltered for each cycle, a steady state 
is reached after some cycles. 
Similar studies, investigating different aspects of the effect of thermal transformation 
cycling have been carried out in [4]-[6]. It should be noted that martensite variant selection MS 
due to prior plastic deformation (cf. strain-induced martensite) generally reduces the 
number of packets that form within grains [7] due to the combined effect of grain ip at 
refinement and nucleation defect preselection. Particularly, a correlation of packet 300 
selection with the largest resolved shear stress on {111}, has been reported [8], [9]. Such Ci 
texture effects are quite resilient and are reported to reproduce even after thermal finds 
transformation cycling [10]. After some cycles the size of the prior austenite grain (PAG) is Fi 
so small that grains mainly transform to one martensite packet. The accommodation effect fe 
of the hierarchical arrangement of martensite now extends over several PAGs. In any case I 
the strong influence of thermal cycling on the material and transformation behavior can be anes. 
attributed to the combined effect of PAG refinement [11] as well as a higher initial 
dislocation density on selected slip systems increasing the probability to form certain 
active nucleation sites for the martensite. 
This study focuses on microstructural differences (final overall texture, boundary 
character) upon transforming the Marval X12 martensitically under a certain load after 
thermal cycling. Very fine sub-block features are emphasized 
2. Experimental setting 
In this study tension-torsion specimens are considered, see [2], [3]. Specimens are, after 
machining, heated up to 1100° C in air, held there for 30 min., and air-cooled to room 
temperature. The material has been initially rolled and the ensuing texture cannot fully be 
removed even upon heating to 1200° C. Prior to all tests, the specimens were heated to at 
least 840° C at a heating rate of 0.5 K/s and held there for 30 min. to ensure full 
austenitization. The specimens are then cooled down to room temperature at a cooling 
rate of 2 K/s until about 50° above M; (which lies at 150 + 10° C) and at a lower cooling 
rate of 0.2 K/s from there in order to set an accurate timing of load changing before the 
start of the transformation. 
In this work three specimens have been investigated. All of them have been thermally Thera 
cycled 6 times. It was found that the resulting block size (grain) size remains foro: 
approximately constant after 4 cycles. Two specimens are annealed at 840°C and one at fers 
1100° C for 30 minutes respectively. One of the specimens annealed at the lower Fen 
temperature (designated as TR25) is loaded with a tensile load of 120 MPa and the other m= 
one (designated as TR32) is loaded in torsion such that a shear stress equivalent to oe 
120 MPa Mises stress is obtained. The specimen annealed at the higher temperature be on 
(designated as TA03), is not loaded during transformation. Bon 
has na