Hot Deformation Behavior of Low Carbon Steel during Compression at Elevated Temperature

Hot compression tests of low carbon steel were carried out on Gleeble-3500 system in the temperature range from 750 to 900 ℃ and in the strain rate range from 0.001 to 1.0 s^-1, and the associated microstructural evolution was studied by observations with a metallographic microscope. The results show that the stress-strain curves exhibit a peak stress at critical strain, after which the flow stresses decre.ase monotonically until reaching high strains, showing a dynamic flow softening. The peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by the Zener-Hollomon parameter Z in the hyperbolic sine equation. The flow stress increases with increasing strain rate and decreasing deforming temperature. The flow stress can be described by constitutive equation in hyperbolic sine function and can also be described by a Zener-Hollomon parameter Z. With increasing deformation temperature and deereasing strain rate, the grain size as well as the volume fraction of the reerystaUized grains increase. The safe region for hot working of the alloy has been determined according to the processing map and microstructure at the true strain of 0.5, which is the deformation temperature of 840-940 ℃ and the strain rate of 0.001-1.0 s^-1.

Analysis of χ Phase Precipitation in Aged 2205 Duplex Stainless Steel

Analysis ofZ phase precipitation in 2205 duplex stainless steel aged at 700 and 750 ~C has been investigated systematically. The experimental results showed that X phase forms prior to the precipitation of δ phase and disappears once tr phase starts to precipitate. This phenomenon indicates that a phase nucleated and consumed the Z phase. The δ phase nucleated mairdy at ferrite/austenite interface and grew inwards into the ferrite phase. The morphology of a phase reveals a coral-like structure at the temperature of 700 ℃ for 120 min followed by quenching in water. The decomposition of ferrite occurs via the following eutectoid reaction： F---＊o＇＋y2. The selected area diffraction pattern of zone axes is[3 1 3-][3 1 3], indicating a characteristic orientation relationship between X phase and δ-ferrite.

Analysis of Microstructure and Mechanical Properties of Ultrafine Grained Low Carbon Steel

A novel design scheme of hot stamping, quenching and partitioning process was conducted in a quenchable boron steel to obtain the nanometric duplex microstructure comprising ultrafine retained austenite and martensite. It is shown that the materials possess excellent mechanical properties and the ductility can be further improved without compromising the strength. The newly treated steel shows excellent mechanical properties and the total elongation of the steel increases from 6.6% to 14.8% compared with that of hot stamped and quenched steel. Therefore, this kind of steel has become another group of advanced high-strength steels. The microstructure which is mainly responsible for such excellent mechanical properties was investigated.