Supplemental Materials
Detailed experimental procedure
The initial hot-rolled 304L billet was austenitized at 1150C for 2 hours. The rods for
ECAP processing had a dimension of 8  45 mm and were cut from the annealed billet.
The ECAP procedure was performed using a split die made from a tool steel with two
channels intersecting at an inner angle of 90° (Φ and an outer angle of 30° (Ψ). Both the
inlet and outlet channels had the same diameter of 8 mm. The rods were coated with MoS2
lubricant and were pressed for 6 passes at RT. In order to avoid the instability of punch,
the pressing speed was selected to be slow (~9 mm/min). Route Bc was adopted, that is,
the sample was rotated round its longitudinal axis by 90° clockwise before each pass. The
equivalent von Mises strain for a single pass is ~1. After ECAP deformation, the deformed
rods were subjected to annealing treatment at 625 oC for 1 hour.
The dog-bone shaped tensile samples were cut from the annealed rods, with gauge
dimension of 1 mm × 2 mm × 8 mm. Uniaxial tensile tests were carried out on an
electromechanical materials testing machine at an initial strain rate of 5×10-4 s-1 at RT.
The microstructures of 304L samples before and after tension were characterized by
means of optical microscopy (OM), electron backscattered diffraction (EBSD),
transmission electron microscopy (TEM) and X-ray diffraction (XRD). For OM, EBSD
and XRD experiments, the specimens were ground and electro-chemically polished in a
solution of 10 g oxalic acid and 100 ml water at a voltage of 10 V. EBSD examinations
were performed on a JSM-7001F type field emission scanning electron microscope
equipped with a fully automatic EBSD analysis system. An area of 10 μm × 10 μm was
scanned with a step size of 50 nm. More than 90% of the raw data can be indexed by the
TSL OIM Data Collection 5 Software. TEM observations were performed on
JEM-2000FX II microscope and FEI 20 high resolution microscope, both of which were
operated at 200 kV. The TEM samples were sliced from annealed rods and tensile strained
specimens, ground to ~70 m thick and then thinned by the twin-jet polishing method in a
solution of 10% perchloric acid and 90% ethanol at -15 oC and at 18~22 V. XRD
experiments were carried out to determine the phase constitution by using a Rigaku
D/max-2400 X-ray diffractometer (12 kW) with Cu K radiation. In XRD experiments,
only the gauge part of tensile sample was scanned.
Figure S1. Optical images showing the initial and deformed UFG 304L sample at
different tensile strains. The Lüders bands can be seen on the sample surface.
Figure S2. XRD profiles for the UFG sample at different tensile strains. It can be seen that
there is no martensite diffraction peaks, which indicates that no strain-induced martensite
transformation occurred during tensile deformation.