Zhenbo Zhao

A new empirical formula for the bainite upper temperature limit of steel

AbstractThe definition of the practical upper temperature limit of the bainite reaction in steels is discussed. Because the theoretical upper temperature limit of bainite reaction, B0, can neither be obtained directly from experimental measurements, nor from calculations, then, different models related to the practical upper temperature limit of bainite reaction, BS, are reviewed and analyzed first in order to define the B0 temperature. A new physical significance of the BS and B0 temperatures in steels is proposed and analyzed. It is found that the B0 temperature of the bainite reaction in steels can be defined by the point of intersection between the thermodynamic equilibrium curve for the austenite→ferrite transformation by coherent growth (curve Z

A new method for improving the resistance of high strength steel wires to room temperature creep and low cycle fatigue

\gamma \to \overrightarrow \alpha

A re-examination of the B0 and BS temperatures of steel

) and the extrapolated thermodynamic equilibrium curve for the austenite→cementite transformation (curve ES in the Fe-C phase diagram). The BS temperature for the bainite reaction is about 50–55 °C lower than the B0 temperature in steels. Using this method, the B0 and BS temperatures for plain carbon steels were found to be 680 °C and 630 °C, respectively. The bainite reaction can only be observed below 500 °C because it is obscured by the pearlite reaction which occurs prior to the bainite reaction in plain carbon steels. A new formula, BS(°C) =, 630-45Mn-40V-35Si-30Cr-25Mo-20Ni-15W, is proposed to predict the BS temperature of steel. The effect of steel composition on the BS temperature is discussed. It is shown that BS is mainly affected by alloying elements other than carbon, which had been found in previous investigations. The new formula gives a better agreement with experimental results than for 3 other empirical formulae when data from 82 low alloy steels from were examined. For more than 70% of these low alloy steels, the BS temperatures can be predicted by this new formula within ±25°C. It is believed that the new equation will have more extensive applicability than existing equations since it is based on data for a wide range of steel compositions (7 alloying elements).

A new empirical formula for the calculation of MS temperatures in pure iron and super-low carbon alloy steels

Abstract The time dependent deformation at room temperature of a high strength steel was investigated. The room temperature creep tests showed that creep can occur below 1/3 σ0.2 (yield strength at 0.2% offset). The resulting creep behavior consists of only two stages, including primary creep and steady-state creep, each of which has its own distinctive strain–time features. The effects of creep stress, creep time, steel hardness and heat treatment schedule on the room temperature creep were investigated. It is believed that the increased creep strains can be attributed to higher applied stresses, longer creep times, lower hardnesses and the existence of an inhomogeneous microstructure. However, increasing the number of cycles in cyclic creep tests at room temperature resulted in a decrease in creep strain. Possible room temperature creep mechanisms have been proposed and discussed.

Design of air-cooled bainitic microalloyed steel for a heavy truck front axle beam

Abstract The effects of warm deformation treatments on the room temperature creep and the low cycle fatigue resistance of high carbon patented steel wires and high strength low carbon low alloy (HSLCLA) steel wires were studied. The low temperature creep strains of high carbon patented steel wires and high strength low carbon low alloy steel were decreased 85 and 65%, respectively, by the warm working treatments for the optimum warm deformation parameters (3% axial tensile plastic deformation at 300°C for 5 min). The low cycle fatigue lives of both steels were increased by 30–35% after warm deformation at the optimum deformation parameters. It is shown that the warm deformation treatment only affected the micro states such as lattice distortion, internal stress, dislocation density, sub-grain size and the amount of solute atoms in solid solution but did not change the overall microstructure or strength of the steel wires. Internal friction studies at different temperatures showed that the amount of solute atoms re-dissolved is different for different warm deformation temperatures and reaches a maximum at 300°C. It is considered that the improvement in the resistance of high strength steel wires to room temperature creep and low cycle fatigue can be attributed to the reduction of the amount of mobile dislocations through the rearrangement of dislocations and strengthening of matrix by the re-dissolution of solute atoms and dislocation pinning.

Carbonitriding of Tetragonal Zirconia

The bending strengths of 2Y-TZP ceramics treated by different methods were compared after annealing in water at 200°C. Surface GeO2- and CeO2-doped materials did not show the decrease in bending strength shown when GeO2 and CeO2 are doped through the bulk 2Y-TZP ceramic. This behavior is attributed to surface doping leading to an improvement in the resistance of Y-TZP to low temperature hydrothermal corrosion. The thermal stability of 2Y-TZP can be improved by surface doping without loss of fracture strength when the doped layer is less than the critical flaw length.

Surface Modification of Yttria‐Stabilized Tetragonal Zirconia Polycrystal/Alumina Composites by Incorporation of Mullite as a Second Phase

Abstract A new explanation of the physical significance of the B 0 (the theoretical upper temperature limit) and the B S (the practical upper temperature limit) temperatures in steel is proposed. It is found that the B 0 temperature of the bainite reaction in steel should be defined by the point of intersection between the thermodynamic equilibrium curve of austenite→ferrite transformation by coherent growth (curve Z γ→ α → ) and the thermodynamic equilibrium curve of austenite→cementite transformation (curve ES in the Fe–C phase diagram). The B S temperature for the bainite reaction is approximately 50∼55°C lower than the B 0 temperature. Using this method, the B S and B 0 temperatures for plain carbon steel were found to be 630°C and 680°C, respectively. The effects of steel composition on the B S temperature are discussed. The formula B S (°C)=630−45 Mn−40 V−35 Si−30 Cr−25 Mo−20 Ni−15 W can be used to predict the B S temperature of a wide range of commercial steels.