The packet size of
bainitic steel can be refined by a special relaxation -precipitation-control phase transformation (RPC)
technology. When processed by
RPC process, the low carbon
bainitic steel composes of two kinds of main intermediate transforma-
tion phases. One is ultra-fine lath-like bainitic ferrite and the lath is less than 1μm in width and about 6μm in length, the alignment
of laths forms a refined packet, and the size of packets is about 5-7μm in length and about 3-4μm in width. The other is acicular
structure. The morphology and distribution of these acicular structures are influenced by relaxation process, the thin and short acicu-
lar structures cut the prior austenite grain and refine the bainitic packet size. For the optimum relaxation time, the packet size can be
refined to the finest. The mechanical properties are influenced by relaxation time and the 800 MPa grade low carbon bainitic steel
with excellent toughness can be obtained by RPC process.