Titanium effect on the microstructure and properties of laminated high boron steel plates

High-boron steel is an important material used for thermal neutron shielding. The appropriate amount of added boron must be de- termined because excessive boron may deteriorate the steel＇s workability. A uniform microstructure can be formed by adding titanium to boron steel. In this study, casting and hot rolling were used to fabricate laminated high-boron steel plates whose cores contained 2.25wt% boron and 0wt%-7.9wt% titanium. The effects of titanium content and hot-rolling and heat-treatment processes on the microstructure and properties of the laminated plates were studied. The results indicated that the optimum titanium content was 5.7wt% when the boron content was 2.25wt%, and that the best overall properties were obtained after heat treatment at 1100℃ for 4 h. The tensile strength, yield strength, and elongation at the specified temperature and holding time were as high as 526.88 MPa, 219.36 MPa, and 29%, respectively.

Effect of hot/warm roll-forming process on microstructural evolution and mechanical properties of local thickened U-rib for orthotropic steel deck

To improve the strength-toughness of traditional U-rib（ TUR） and solve the problem of insufficient penetration between TUR and deckplate,a new local thickened U-rib（ LTUR） has been proposed to improve the fatigue resistance of the weld joint under the premise of not increasing thickness and strength of the TUR material. And a hot /warm roll-forming process（ RFP） adopting partially induction heating to 700- 1 000℃ was carried out to fabricate LTUR. The deformation behaviors in the forming process and microstructure of LTUR have been investigated.Mechanical properties and fracture mechanism of the LTUR after hot / warm RFP have been systematically discussed. Moreover,the results are compared with those obtained in cold RFP. Mechanical properties of the LTUR deformed above the critical transformation temperature（ A_（c3）） show high performance characteristics with marked fatigue resistance and superior toughness. Upon increasing the heating temperature from 700 to 900 ℃,the initial coarse ferrite-pearlite structure transform into equiaxed ultrafine ferrite（ 1- 3 μm） and precipitates such as（ Nb,Ti）（ C,N） are uniformly distributed in the matrix. The average dislocation density of the specimens after hot rollforming at heating temperature of 900 ℃ decreases dramatically compared with those of the specimens subjected to the cold RFP. Furthermore,a typical characteristic of ductile fracture mechanism and the high impact energy are more convinced that the specimens deformed above 900 ℃ have obtained an optimal combination of strength and toughness.

Homogenization heat treatment of Mg-7.0 wt%Y-1.0 wt%Nd-0.5 wt%Zr alloy

The microstructures and mechanical properties of Mg-7.0 wt%Y-1.0 wt%Nd-0.5 wt%Zr magnesium alloy were investigated both in as-cast condition and after homogenization heat treatment by differential scanning calorimetry(DSC),optical microscopy(OM),X-ray diffraction(XRD),scanning electron microscopy(SEM)and hardness measurement.The results indicate that the ascast alloy consists ofα-Mg matrix,Mg24 Y5 and Mg41 Nd5 phases,which are eutectic phases(cubic Y-rich phase).With the increase in homogenization temperature and time,the Mg24 Y5 and Mg41 Nd5 phases are completely dissolved into matrix,and only yttrium of intermetallic compounds leaves around boundary.After homogenization heat treatment,the elements distributed uniformly and the grains grow up not obviously,only yttrium element of intermetallic compounds left around boundary.The optimum homogenization condition is at 537℃for 16 h.The mechanical properties are improved after homogenization,with tensile strength ofσb=181 MPa,yielding strength ofσ(0.2)=144 MPa and elongation ofδ=5.5%,which are better than those of as-cast alloy.

Microstructure and texture evolution of Mg–7Y–1Nd–0.5Zr alloy sheets with different rolling temperatures

The extruded Mg-7Y-1Nd-0.5Zr(wt%)alloy were performed to the same strain hot rolling with different temperatures.The microstructure and texture evolution of the sheets were investigated by optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and electron back-scattered diffraction(EBSD).The results indicate that the microstructure becomes homogeneous after hot rolling process and precipitated phase distributes at grain boundaries along rolling direction.With the increase in rolling temperature,the grains of sheet grow up.The sheet rolling at 400℃is composed of recrystallization grains,the necklace of the precipitated phase in the grain boundaries and excessive dislocations.The structure of necklace of the precipitated phase is fcc structure with lattice constant of a=0.75 nm.With rolling temperatures increasing from 400 to 450℃,the content of recrystallized grains in volume fraction with relatively random orientations increases significantly.Compared with the rolling process at 400℃,the amount of precipitated phases is reduced at the grain boundary,and the precipitated phase begins to appear in the grain interior when rolling at 450℃.The structure of the precipitated phase is fcc with lattice constant of a=2.22 nm.The recrystallization grains begin to grow in the rolling process at 500℃.The basal texture is obviously produced during the rolling process at 400 and 450℃;however,the basal texture is weak in the rolling process at 500℃.