Band 34, Heft 7 -

In order to investigate the loss of the ductility of Ti-bearing ship plate steel under 1000 °C, where the ductility begins to reduce rapidly, so the hot ductility of Ti-bearing ship plate steel has been obtained using the Gleeble 1500 thermal-mechanical simulator and also the studies about the effect of grain boundary ferrite films and precipitates containing Ti on the ductility has been carried out. The result showed that the TiN particles precipitating at 950 °C with a larger size and smaller volume fraction cannot effectively suppress the occurrence of recrystallization and the ductility still retains at a high level, although R.A. value presents a certain degree of decline compared with 1000 °C. A large number of smaller Ti(C,N) particles precipitate at 900 °C and can induce the formation of a very small amount of fine grain boundary ferrite, which deteriorates the adhesion strength of the grain boundary, so the R.A. value rapidly reduces to less than 50%. When the temperature falls to close Ae3 (827 °C), the amount of the grain boundary ferrite films increase due to the ferrite phase transformation, but the ferrite film thickness becomes more uneven at the same time, which results in the increase of strain concentration and plays a leading role in causing the decrease of ductility, so the R.A. value has been kept less than 40% as the temperature cooling to 800 °C from 850 °C. When the temperature further decreases, the ductility starts to recover due to the increase of average ferrite film thickness to a greater degree which greatly reduces the strain concentration of the grain boundary.

Dispersive Al 3 Ti particles introduced into alloy 2618-Ti are enclosed gradually by ternary Al 18 Mg 3 Ti 2 phase during homogenization, which can be described as a “peritectic reaction”. This reaction is sensitive to homogenization temperature and time within 24 h but not so sensitive to homogenization time after 24 h because of its special growth pattern. The evolution of the intermetallic compounds during homogenization process of alloy 2618-Ti is further confirmed by means of diffusion couple of (Al-25Mg)/(Al-10Ti). After homogenization, much Al 3 Ti particles coexist with Al 18 Mg 3 Ti 2 which depends on the composition of Al-Mg-Ti system and only a few single Al 18 Mg 3 Ti 2 appear. The occurrence of single Al 18 Mg 3 Ti 2 phase, within which Al 3 Ti disappears, can be attributed to the local fluctuation of alloy compositions.

To improve the additional value of phosphorusenrichment phase in slag, it is necessary to make phosphorus to be enriched in the slag. This paper elaborates the effects of different P 2 O 5 content and basicity on phosphorus enrichment in the CaO-SiO 2 -Fe t O-P 2 O 5 slag system through the experiment. Slag morphology can be observed by SEM+EDS and the composition of the phase can be ascertained by XRD. Then Lp and Cp in both phosphorus-enrichment phase and matrix phase were calculated respectively. It has been found that P 2 O 5 content in the slag and the basicity of the slag have effects on the existing form of the phosphorus in the slag, and also influence the distribution ratio of P 2 O 5 in the slag.

In this present study, wear behaviours of high chromium white iron valve seat inserts and tappets used in the automotive sector were investigated. Wear behaviours of three different rates of high chromium white cast irons (containing 10, 12 and 14% chromium) were examined under heavy service conditions. For that purpose, the produced valve seat inserts were characterized through Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD) and hardness measurements. They were tested at a sliding speed of 1 ms−1, under 120 N load and for six different sliding distances (500, 1000, 1500, 2000, 2500, 3000 m) by using a standard wear apparatus (pin-on-disk type). The result showed that as the amount of Cr increased in the alloys, their hardness decreased. The decrease in the hardness were considered to be as the result of transformation of M 7 C 3 carbides into M 23 C 6 carbides in the structure. This decrease in hardness with increasing chromium content also increased the weight loss. Thus, it was determined that the white iron with 14% Cr (which had a greater amount of M 23 C 6 carbides) was subjected to the highest wear.

The deep understanding of flow behaviors of as-extruded 7050 aluminum alloy significantly contributes to the accuracy simulation for its various plastic forming processes. In order to obtain the improved Arrhenius-type equation with variable parameters for this alloy, a series of compression tests were performed at temperatures of 573 K, 623 K, 673 K, 723 K and strain rates of 0.01 s −1 , 0.1 s −1 , 1 s −1 , 10 s −1 with a height reduction of 60% on Gleeble-1500 thermo-mechanical simulator. It is obvious that strain rate, strain and temperature all have a significant effect on the hot flow behaviors, and the true stress–true strain curves indicate three types after the peak value: decreasing gradually to a steady state with sustaining DRX softening till a balance with work hardening, decreasing continuously with sustaining increasing DRX softening beyond work hardening and maintaining higher stress level after the peak value with a balance between work hardening and DRV softening. Based on the experimental data, the improved Arrhenius-type constitutive model was established to predict the high temperature flow stress of as-extruded 7050 aluminum alloy. The accuracy and reliability of the improved Arrhenius-type model were further evaluated in terms of the correlation coefficient ( R ), here 0.98428, the average absolute relative error ( AARE ), here 3.5%. The results indicate that the improved Arrhenius-type constitutive model presents a good predictable ability.

The isothermal compressions of as-forged Ti-10V-2Fe-3Al alloy at the deformation temperature range of 948–1,123 K and the strain rates in the range of 0.001–10 s −1 with a height reduction of 60% were conducted on a Gleeble-3500 thermo-mechanical simulator. The flow behaviors show nonlinear sensitivity to strain, strain rate and temperature. Based on the experimental data, an artificial neural network (ANN) with back-propagation algorithm was developed to deal with the complex deformation behavior characteristics. In the present ANN model, strain, strain rate and temperature were taken as inputs, and flow stress as output. A comparative study on the constitutive relationships based on regression and ANN methods was conducted. According to the predicted and experimental results, the predictabilities of the two models have been evaluated in terms of correlation coefficient ( R ) and average absolute relative error ( AARE ). The R -value and the AARE-value at strain of 0.5 from the ANN model is 0.9998 and 0.572%, respectively, better than 0.9902 and 6.583% from the regression model. The predicted strain–stress curves outside of experimental conditions indicate similar characteristics with experimental curves. The results have sufficiently articulated that the well-trained ANN model with back-propagation algorithm has excellent capability to deal with the complex flow behaviors of as-forged Ti-10V-2Fe-3Al alloy.

The present study reports the effect of microwave power and microwave heating time on activated carbon adsorption ability. The waste bamboo was used to preparing high surface area activated carbon via microwave heating. The bamboo was carbonized for 2 h at 600°C to be used as the raw material. According to the results, microwave power and microwave heating time had a significant impact on the activating effect. The optimal KOH/C ratio of 4 was identified when microwave power and microwave heating time were 700 W and 15 min, respectively. Under the optimal conditions, surface area was estimated to be 3441 m 2 /g with pore volume of 2.093 ml/g and the significant proportion of activated carbon was microporous (62.3%). The results of Fourier transform infrared spectroscopy (FTIR) were illustrated that activated carbon surface had abundant functional groups. Additionally the pore structure is characterized using Scanning Electron Microscope (SEM).

Non-metallic inclusions in high-strength low-alloyed steel refined by slag with basicity ( B ) 2–5 and Al 2 O 3 content 20%–30% (in mass percent) were investigated by slag–metal equilibrium experiments in laboratory and thermodynamic calculations. Most inclusions in equilibrium were quasi-spherical CaO-MgO-Al 2 O 3 -SiO 2 system and the sizes were less than 5 µm. The average content ratio, CaO/Al 2 O 3 and CaO/SiO 2 of the inclusions, increased with slag basicity increasing when Al 2 O 3 content in slag was around 25%, MgO/Al 2 O 3 and CaO/Al 2 O 3 increased with Al 2 O 3 content in slag decreasing when slag basicity was around 3.3. The MgO/Al 2 O 3 of the inclusions was influenced mainly by Al 2 O 3 content in slag and CaO/Al 2 O 3 was influenced mainly by slag basicity. To make the inclusions out of relative lower melting region (<1,773 K), the values of CaO/Al 2 O 3 , MgO/Al 2 O 3 and (CaO+MgO)/Al 2 O 3 of the inclusions should be enhanced by increasing basicity and decreasing Al 2 O 3 content in slag properly.

This paper presents the results of investigations carried out on processing and characterization of CrB 2 -based novel composites. Niobium metal powder was used as additive to form new composites. Hardness and fracture toughness of chromium boride increased by addition of niobium. CrB 2 composites were prepared by addition of 2.5, 10 and 20 wt.% Nb. Density of higher than 95% ρ th was achieved in all the samples. Hot pressed samples were analyzed to contain reaction products of NbB 2 , Cr 2 B 3 and Cr 3 B 4 phases along with CrB 2 . Hardness of CrB 2 composite was increased from 18.46 GPa to 21.89 GPa by increasing the Nb content from 2.5 to 10 wt.%. Fracture toughness of composites prepared by addition of 2.5 and 10% was measured as 3.11 and 3.38 MPa.m 1/2 respectively. Addition of 20% Nb resulted in increased fracture toughness of 4.32 MPa.m 1/2 .

Possible mechanisms of metal micropowders grinding during high-voltage electric discharge processing in hydrocarbon liquid are considered in the present paper. Conditions for melting of Fe and Ti powder particles in plasma discharge channel and in microplasma channels between particles are found out. Regularities of nanopores movement and electromagnetic particle compression are evaluated. It is shown that the current density in the discharge channel is an important parameter, allowing the assessment of the efficiency of the electrodischarge dispersion of metal particles.

The dynamic recrystallization (DRX) behavior of as-extruded 3Cr20Ni10W2 heat-resistant alloy was investigated by hot compressions with a fixed height reduction of 60% over a temperature range from 1,203 to 1,403 K and a strain rate range from 0.01 to 10 s −1 . Results show that DRX occurs more easily at lower temperatures and higher strain rates, the stress level increases significantly with the increase of deformation temperature or the decrease of strain rate. Under such wide range of deformation conditions the flow stress evolution generally indicates two characteristics: work hardening (WH) followed by DRX, or by dynamic recovery (DRV). The variation of the average size of grains refined by DRX behavior in the alloy is characterized by linking the deformation conditions during hot compression process. At a fixed temperature, the average grain size linearly decreases with increasing strain rate in log scale. At a lower strain rate, the average grain size rapidly increases with increasing temperature, while it remains almost constant at strain rate of 10 s −1 . At a higher strain rate, grain size data sets tend to be closer to the average size value, which indicates that as strain rate increases, the microstructures become more and more uniform. The effects of the temperatures and strain rates on the average grain size can be represented by Zener–Hollomon parameter, Z , and the relationships between the average grain size and Z parameter can be described as a nonlinear equation, which indicates that the average grain size decreases with increasing Z parameter. On the plot of average grain size DA$${D_A}$$–lnZ$${\rm{ln}}\,Z$$, the regions corresponding to DRV (ln Z≤77.9$${\rm{ln}}\ Z\,\le \,77.9$$) and DRX (ln Z>77.9$${\rm{ln}}\ Z\,\gt \,77.9$$) were clarified clearly.

The hot workability of Ti–6Al–4V alloy was investigated according to the measured stress–strain data and their derived forms from a series of hot compressions at the temperatures of 1,023–1,323 K and strain rates of 0.01–10 s −1 with a height reduction of 60%. As the true strain was 0.3, 0.5, 0.7 and 0.9, respectively, the response maps of strain rate sensitivity ( m -value), power dissipation efficiency (η$\eta $-value) and instability parameter (ξ$\xi $-value) to temperature and strain rate were developed on the basis of dynamic material model (DMM). Then the processing map was obtained by superimposition of the power dissipation and the instability maps. According to the processing map, the stable regions (η>0$\eta \gt 0$ and ξ>0$\xi \gt 0$) and unstable regions (η<0$\eta \lt 0$ or ξ<0$\xi \lt 0$) were clarified clearly. Further, the stable regions (temperatures of 1,198–1,248 K and strain rates of 0.01–0.1 s −1 ) with higher η$\eta $ value (>$ \gt $0.3) corresponding to the ideal deformation mechanisms involving globularization and superplasticity were identified and recommended. The microstructures of the deformed samples were then observed by microscopy. And homogeneous microstructures with refined grains were found in the recommended parameter domains. The optimal working parameter domains identified by processing map and validated by microstructure observations contribute to the design in reasonable hot forming process of Ti–6Al–4V alloy without resorting to expensive and time-consuming trial-and-error methods.

This paper deals with evaluation of creep damage of ~11 years service exposed primary hydrogen reformer tube made of HP-40 grade of steel in a petrochemical industry, which has been carried out in terms of Kachanav’s continuum damage mechanics (CDM) model (K-model) and Bogdanoff model (B-model) based on Markov process. Residual life of the tubes was estimated based on hot tensile, conventional creep deformation under identical test conditions, optical microscopy and fractography. Accumulation of damage due to creep has been quantified through microstructural studies. The as received tubes did not reveal any degradation in the material like creep cavitation or voids, but there was indeed loss of tensile strength from room temperature to 870°C for the bottom portion of the tube due to ageing and overheating. Scatter in creep deformation behaviour of the material is probably due to variation in mode of fracture and scatter in voids. From statistical point of view, Weibull distribution pattern for analysing probability of rupture due to void area shifts with increase in true strain towards the higher population of void. The estimation of mean time to reach a specific damage state from K- model and B-model is in close agreement with that of experimental data and can describe the sudden changes of the creep damage in the tertiary region as well. A remnant life of >10 years is estimated at the operating stress–temperature conditions of the top as well as bottom portion of the tube.