ANALYSIS AND THERMODYNAMIC STABILITY OF NUCLEI IN SPHEROIDAL GRAPHITE IN Fe–C–Si ALLOYS

The paper describes the graphite nuclei constitution for spheroidal graphite cast iron melted in a cupola furnace, which is treated by the addition of magnesium and inoculated with a barium-based inoculant. Two samples of spheroidal cast iron were analysed, differing only in tin content. Field-emission scanning electron microscopy (FE -SEM) with energy-dispersive X-ray spectroscopy (EDS) was used to analyse the nuclei. The thermodynamic calculation of the phase equilibria and the associated free formation energies of the alloys were calculated and compared with metallographic observations. It was found that the nuclei in the spheroidal graphite are different in shape and composition. Spherical and rectangular ones were found, and in many cases the porosity was present at the nuclei. The nuclei consisted of different compounds such as (Mg,Ca)S, MgO, (Mg,Al,Si)N. The amount of Sn only affected the pearlite content, and there were no Ba and rare earths present in the nuclei.

Preparation of heavy-section ductile iron with improved mechanical properties through quenching and tempering

In order to prepare heavy-section ductile iron with high strength and excellent elongation, a series of quenching- tempering experiments was conducted. A relationship between quenching-tempering time and temperature and the contents of martensite and pearlite was established by adjusting different quenching mediums and process parameters, and different microstructures in the iron matrix led to different mechanical properties. The content of martensite in the iron matrix reached over 94% after quenching at 880°C or a higher temperature. Further, the pearlite content could reach over 91% after tempering at 570°C or a higher temperature, thus resulting in improved mechanical properties. The investigated ductile iron yielded mechanical properties of a tensile strength of 970 MPa and an elongation of 6% after quenching in water at 880°C and tempering at 570°C. This will provide more possibilities for the application of heavy-section ductile iron parts.

Mechanical Properties of Thin Wall Ductile Iron: Experimental Correlation Using ANOVA and DOE

The present study was undertaken to investigate the effect of different metallurgical parameters such as casting techniques, wall thickness, inoculant technique, carbon equivalent, nodule count, ferrite and pearlite percent on the mechanical properties of thin wall ductile iron castings (TWDI). Understanding of the effect of chemistry, casting techniques, melting and molten treatment on the mechanical properties and microstructural features of TWDI castings would help in selecting conditions required to achieve optimum mechanical properties and alloy high strength to weight ratio. The use of the design of experiment (DOE) and the analysis of variance (ANOVA) can be a useful methodology to reach this objective. The analysis of the effects of each variable and their interaction on the mechanical properties of TWDI castings using green sand, green sand with insulation and investment casting techniques plays a key role in improved materials performance.The results indicate that nodule count, pearlite content and the interaction between carbon equivalent, nodule count and pearlite content have a significant effect on the tensile strength of TWDI castings. The impact toughness values decrease with smaller section thickness and increased nodule count. Using investment casting technique, decreasing the pearlite percent and nodule count, and increasing the wall thickness and ferrite percent reduce the values of ultimate tensile strength and yield strength. The results of percent elongation and impact toughness show a reverse trend compared with those of ultimate tensile strength and yield strength in terms with different metallurgical parameters.

Influence of Cooling Rate and Chemical Composition on Phase Transformation and Hardness of C70S6 Steel

The influence of cooling rate and chemical composition on phase transformation and hardness of C70S6 steel were studied by Gleeble-3800 thermal simulation testing machine and box type electric furnace. The results showed that when the cooling rate was between 0.3 and 5 °C/s, the transformation products of two experimental steels were mainly composed of ferrites, pearlite and sorbite. The pearlite content gradually decreased with the cooling rate increasing, while the sorbite content increased and the ferrite content changed little. Both the ferrite and pearlite transformation starting temperature and ending temperature decreased with the cooling rate increasing. Besides, the hardness increased with the cooling rate. At the same cooling rate, the phase transformation temperature increased slightly with the carbon equivalent decreasing, and the pearlite content increased, while the hardness decreased. The hardness of C70S6 steel was reduced by cooling rate decreasing. However, it was difficult to realize the method of decreasing the hardness by adjusting the cooling rate in the case of higher carbon equivalent. Therefore, in order to obtain an appropriate hardness, the Ceq must be controlled. And a Ceq=0.83% was recommended.

Effect of Hot Deformation Temperature on Texture Formation Regularity of CGO Silicon Steel under High Deformation Rate

The influence of hot deformation temperature on microstructure and texture of CGO silicon steel under the condition of a high deformation rate (100 s-1) was studied by SEM and EBSD techniques. The results indicate that the typical microstructures at room temperature consist of ferrite and pearlite under different hot deformation temperatures. The higher deformation temperature is beneficial to obtain a more uniform recrystallization microstructure and lower pearlite content. Cubic texture{100}001and rotated cubic texture{100}011are dominant texture components in the tested steels, and{111}112texture inγfiber is also strong, the intensity of which is higher than that of{111}110texture. Goss texture{110}001is weak. With the rising of the hot deformation temperature,{100}011texture decreases firstly and then increases at 1100°C. When the hot deformation temperature raises from 800°C to 900°C,{111}112texture shows an increasing trend, while{111}110texture content is stable. When the temperature further increases to 1100°C and 1150°C,{111}112and{111}110textures are slightly weakened.

Alloy Design and Microstructure Control for the Production of Heavy Ductile Irons Used in Large-Scale Windmills

The primary purpose of this research is to establish the optimal alloy design and microstructure for achieving the desired mechanical properties (tensile strength, yield strength, elongation and low temperature impact value) of key components used in large-scale windmills. In order to meet the impact requirement (I-40°C≥10J) of spec. EN-GJS-350-22U-LT, the Si content should be kept below 1.97%, and also the maximum pearlite content shouldn’t exceed 7.8%. On the other hand, the optimal alloy designs that can comply with specification EN-GJS-700-2U include 0.25%Mn+0.8%Cu+0.01%Sn , 0.25%Mn+0.6%Cu+0.05%Sn and 0.45%Mn+0.6%Cu+0.01%Sn. Furthermore, based upon the experimental results, multiple regression analyses have been performed to correlate the mechanical properties with chemical compositions and microstructures. The derived regression equations can be used to attain the optimal alloy design for castings with targeted specifications. Furthermore, by employing these regression equations, the mechanical properties can be predicted based upon the chemical compositions and microstructures of cast irons.

Effect of Vanadium-Nitrogen Concentration and Cooling Rate on Grain Refinement in V-N Steel

Effect of vanadium and nitrogen concentration in V-N steel and cooling rate after deformation on grain refinement has studied in this paper. The results show that with the increase of vanadium and nitrogen concentration, ferrite grain size is smaller compared with carbon steel; with the increase of cooling rate after deformation, ferrite grain size is finer and pearlite content of microstructure significantly is reduced too. Compared with the Nb-bearing steel, as long as selecting reasonable the process parameters and adding the appropriate vanadium, nitrogen to the steel, V-N steel can also get a good strength and toughness, and the cost is lower than Nb-bearing steel. This method of producing the steel with good Strength and toughness is very suitable to China who possesses the abundant vanadium resource, but is lack of niobium.