Effect of La on inclusions and fracture toughness of low-alloy ultrahigh-strength 40CrNi2Si2MoVA steel

The effect of La on inclusions and fracture toughness of 40CrNi2Si2MoVA steel was investigated via the optical microscope,scanning electron microscope,image software and electronic universal testing machine.The results reveal that the inclusions in steel without La are mainly MnS and Al_(2)O_(3)–MnS,while the inclusions in steels with La primarily contain La–O–S,La–S and other rare earth complex inclusions contain P and As.La–O–S and La–S are formed under the steelmaking temperature and act as the nucleation core of rare earth complex inclusions containing P and As.According to the segregation model,La–O–S–P–As and La–S–P–As are formed through chemical reactions during the solidification stage.As La content in steels increases from 0 to 0.032 mass%,the average spacing of inclusions is gradually increased from 5.28 to 15.91μm.The volume fraction of inclusions in steels containing less than 0.018 mass%La approaches 0.006%;however,it is significantly improved to 0.058%when La content is increased to 0.032 mass%.With the increase in La content,the fracture toughness is firstly improved from 63.1 to 80.0 MPa m^(1/2)due to the increase in average spacing of inclusions and then decreases to 69.6 MPa m^(1/2)owing to the excessive increase in volume fraction of inclusions.The optimal fracture toughness is found in 40CrNi2Si2MoVA steel with 0.018 mass%La.

Mechanism of Effect of Microwave Modification on Pulverized Coal Combustion Properties

The mechanism of microwave modification or： facilitating the combustion properties of pulverized coal （PC） was investigated. Experimental researches on granularity and functional group as well as combustion properties of PC before and after modification were carried out. Micromorphology observation indicated that the size of PC par- ticles was relatively small, which was in accordance with the results of granularity analysis of PC. FT-IR （Fourier- transform infrared） spectra of two PCs indicated that the proportion of the functional groups with high activity in- creased after microwave irradiation. Furthermore, no valid effect of microwave was found on carbon matrix except small variations in PC particle size, which only led to subtle improvement in combustion of residual coke. Activation energies of Yungang and Yangquan PCs in temperature zone between 450--650 ℃ were reduced by 12.00% and 10.13%, respectively, which meant that microwave modification might effectively facilitate the combustion proper- ties of PC. Nevertheless, decrease in activation energies of residual cokes was 3.560% and 3.67% respectively, which was subtle and can be regarded as the result of smaller particle size produced by microwave irradiation.

Hot deformation characteristics and hot working window of as-cast large-tonnage GH3535 superalloy ingot

Deformation characteristics and range of optimized hot working parameters of a 6.5 tons GH3535 superalloy ingot with an average columnar grain size of over 1 mm in diameter were investigated. Axial compression experiments were performed in temperature range of 900-1240 ℃ and strain rate range of 0.001-30 s;at a total strain of 0.8. The hot deformation activation energy of the experimental GH3535 alloy is calculated to be 483.22 kJ/mol. Furthermore, the deformation constitutive equation is established by the peak stresses obtained from the stress-strain curves under various conditions. The hot working window of the alloy ingot at a strain of 0.8 can be preliminarily discussed based on the deformed microstructures and processing maps. The optimized hot working window was thus determined at the strain of 0.95 for 6.5 tons GH3535 alloy ingot by the supplementary compression tests. A large-size GH3535 superalloy ring with a dimension of 03010 mm x 410 mm was ultimately manufactured.