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Uncommon high temperature intragranular acicular ferrite (IAF) transformation was found and discussed during semi-solid M2 steel cooling processing. The nucleation and growth behavior of IAF was clarified by combining in situ microscopy and other microstructural characterization methods. The effect of IAF on mechanical properties was investigated. The results showed that the fraction, morphology of IAF matrix and carbides was affected by the semi-solid cooling conditions. The high alloying elements and semi-solid controlled cooling contributed to the precipitation of granular and nano vanadium carbide (VC). The precipitation of nano VC carbide during semi-solid cooling could play an effective nucleation substrate for IAF. The orientation relationship between the VC carbide and IAF followed (011)α//(200)VC, [111]α//[011]VC orientation relationship and the lattice misfit was about 4.57%. Semi-solid processing could provide a new method for obtaining IAF. The growth rate of IAF during semi-solid processing is a relatively slow range of 0.7–7 μm/s. The IAF transformation during semi-solid cooling happened at extremely high temperature but much lower growth rate. The growth behavior might follow the diffusional transformation mode. The strength and hardness for semi-solid specimen were higher as compared with conventional forming procedure specimen. The compressive strength and hardness for semi-solid M2 steel could reach 4474 MPa and 65.6 HRC, respectively. The formation of IAF and fine carbide precipitation during semi-solid cooling process was the key factor for the mechanical response. The co-existence of IAF and fine carbide could be a new microstructural construction strategy to tailor the mechanical properties of semi-solid alloy steel.

The purpose of this study is to obtain a constitutive equation of high-accuracy flow stress in superalloy 718, which allows fabrication of highly reliable disks for gas turbine engines. Hot compression tests using superalloy 718 at deformation temperatures from 850 to 1100 °C, a 67% height reduction, and strain rates of 1, 10, and 25 s−1 were performed to investigate the flow stress behavior, which excludes environmental effects during hot working by inverse analysis. The effects of dynamic recrystallization and strain-induced dynamic precipitation on the flow stress were also investigated. The dynamically precipitated δ phases deformed at 1050 °C and γ″ phases deformed at 950 °C might affect the increase in the plastic modulus F1 and the decrease in the critical strain εc, deteriorating the accuracy of regression in terms of, for example, the strain rate sensitivity m and the temperature sensitivity A. A constitutive equation for a generalized flow curve for superalloy 718 is proposed by considering these effects.

Hard materials were mixed with alloy powders and thermally sprayed at an ultra rapid cooling rate of more than 106°C/s. For example, 65Ni15Cr16P4B at% alloy powder containing tungsten carbide was thermally sprayed. SEM image showed tungsten carbide paticles were scattered in the amorphous alloy coatings. The resulting thermal coatings showed low friction and high wear resistance in a reciprocating-slide-type friction-testing machine because tungsten carbides exhibited cleavage fracture. The stress analysis of an amorphous alloy coating with low friction was also carried out by the finite element method.

In this study, multilayer carbon-fiber-reinforced plastic sheets with various pre-impregnated thicknesses were developed. Specimens were fabricated by the hand lay-up process from standard and thin-ply unidirectional carbon fiber/epoxy resin prepreg sheets, which were also cured in an autoclave. Tensile tests from room temperature to 120°C and interlaminar shear strength tests at room temperature were first conducted to investigate the mechanical behavior of the laminated carbon-fiber-reinforced plastic sheets. Furthermore, with a view to increase the formability, in this study, a state-of-the-art drawing process for laminated carbon-fiber-reinforced plastic sheets at an elevated temperature was investigated, and the drawing ratio was also determined for the case of elliptical cup drawing. To achieve this, the relation between the punch load and stroke, and the distribution of thickness were determined by measurement. To clarify the forming behavior in this case, evaluation of the effect of increasing the number of drawing steps was performed to investigate the deformation history. The microstructures showed reduced delamination with increasing radius of the punch. The experimental results obtained in this study are expected to help designers perform the press forming of multilayer carbon fiber/epoxy resin sheets.

A new method of near-liquidus squeeze casting (NLSC), which obtains globular crystal, has been developed. The research focuses on the formation and growth mechanism of globular crystals of ADC12 alloy by NLSC. Globular crystal transforms into rosette crystal, average grain size (AGS) increases, and average globular coefficient (ASC) decreases with the rise of pouring temperature. But AGS decreases to 17.8 μm directly and ASC increases directly to 0.46 when the pouring temperature is 650°C. NLSC globular crystal of different sizes (AGS is 22.5 μm; ASC is 0.73) distributes uniformly in matrix. Heterogeneous nucleation grows on the solid particles of metal walls and fusing grains. The formation and growth modes of globular crystal include normal grain growth, annexation of small globular crystal, and fracture and spherulization of rosette crystal. NLSC globular crystal critical radius is inversely proportional to degree of supercooling. The pressure has very little influence on critical radius by increase of melting point and thermal conductivity, but it affects critical radius greatly by changing the degree of supercooling. NLSC globular crystal has no enough time to exceed the critical radius.

Geometry and mechanical properties are the most important functions that are required in formed products. Numerical analysis of plastic deformation and microstructure evolution in hot forming is the key tool usable for simultaneous optimization of the geometry and mechanical properties of a formed product. It is helpful not only in reducing time and cost for optimization but also in renovating the design sequence of a metal product.Novel designs of metal products will be combined designs of forming conditions and alloy composition, operated fully on digital computers. Here, their components are (1) macro-process simulation, (2) micro-process simulation, (3) mechanical properties simulation as a function of microstructure, and (4) material genome. Behind material genome, (5) nano-scale simulations are located. Nano-scale simulations enable us to clarify, ‘how the microstructure is formed’ and ‘how the microstructure exhibits mechanical properties of metal products at a macro-scale’.Analytical methods for analysis of plastic deformation and microstructure evolution in industrial hot rolling are reviewed in this paper. Their present status and recent achievements are explained, and the advances expected in future are discussed. [ABSTRACT FROM AUTHOR]

Friction stir welding (FSW) was applied to a low carbon alloyed steel in order to stabilize the austenite phase which can effectively maintain a preferable toughness. A Cr-Mo steel sheet (0.20 wt.%C-1.07%Cr-0.16%Mo-0.24%Si-0.61%Mn-bal. Fe) with a ferrite pearlite structure was friction stir welded under the conditions in which the sample was reheated above the A3 temperature at the maximum. The microstructure observations in the stir zone clarified martensite with several area fractions of retained austenite and elongated ferrite. The retained austenite provides a high ductility with a high strength in the stir zone. In order to clarify the formation mechanism of the austenite, compression tests were conducted at various strain rates up to 10/s using an ultrahigh-speed compression testing machine. When the sample was compressed at the high strain rate, the elongated ferrite grains and retained austenite were formed. This microstructure was similar to the microstructure in the FSW stir zone, suggesting that the efficient accumulation of plastic strain in the austenite during the FSW plays an important role in obtaining the retained austenite. [ABSTRACT FROM AUTHOR]