Jing Tao Han

Structure change of 430 stainless steel in the heating process

The microstructure analysis was employed for the ferritic stainless steel (SUS430) with the carbon content from 0.029wt% to 0.100wt% under the simulated heating process condition. The higher carbon sample (430H) contains the duplex phase micro-structure at the temperature of 1150℃; on the other hand, the lower carbon content sample (430L) does not touch two phase area even at the temperature of 1450℃ and has the single phase ferritic microstructure. The carbon content need be well controlled for the 430 ferritic stainless steel since it can significantly affect the heating process curve, and the heating process may not be done in the two phase area due to the uncontrolled carbon content. With the low carbon content and the proper soaking time, the grain size is not sensitive to the heating process temperature and the soaking time. In the present heat treatment experiments, the soaking time is about 10 min, and the processing parameters can be chosen according to the requirement of the gross energy, the efficiency and the continual forming.

Modeling Uniaxial Tensile Deformation of Polycrystalline Al Using CPFEM

The crystal plasticity finite element modeling (CPFEM) is realized in commercial finite element code ABAQUS with UMAT subroutine on the basis of the crystal plasticity theory of rate dependent polycrystal constitutive relations in the mesoscopic scale. The initial orientations obtained by electron backscatter diffraction (EBSD) are directly input into the CPFEM to simulate the mechanical response of polycrystalline 1050 pure Al in uniaxial tensile deformation. Two polycrystal models and two tensile strain rates were used in the simulations. The stress-strain curves of tensile deformation were analyzed. The predictions and the corresponding experiment result show reasonable agreement and slight deviation with experiments. The flow true stress of strain rate 0.01 s^(-1) higher than that of strain rate 0.001 s^(-1) At the strain less than 0.05, the stress saturated rate of the experiment is higher than the simulated results. However, the stress saturated rate of the experiment becomes gentler than the corresponding simulated predictions at the strain over 0.05. Also, necking was simulated by the two models, but the necking strain is not well predicted. Tensile textures at strain 0.25 were predicted at the low strain rate of 0.001 s^(-1). The predictions are in good accord with the experimental results.

Modeling texture development during cold rolling of IF steel by crystal plasticity finite element method

Abstract With the consideration of slip deformation mechanism and various slip systems of body centered cubic (BCC) metals, Taylor-type and finite element polycrystal models were embedded into the commercial finite element code ABAQUS to realize crystal plasticity finite element modeling, based on the rate dependent crystal constitutive equations. Initial orientations measured by electron backscatter diffraction (EBSD) were directly input into the crystal plasticity finite element model to simulate the development of rolling texture of interstitial-free steel (IF steel) at various reductions. The modeled results show a good agreement with the experimental results. With increasing reduction, the predicted and experimental rolling textures tend to sharper, and the results simulated by the Taylor-type model are stronger than those simulated by finite element model. Conclusions are obtained that rolling textures calculated with 48 {110}〈111〉+{112}〈111〉+{123}〈111〉 slip systems are more approximate to EBSD results.

Effect of plastic deformation on diffusion-rolling bonding of steel sandwich plates

Abstract Diffusion bonding is one of the most important techniques for composite materials, while bonding temperature, holding time, and rolling reduction are the key parameters that affect the bonding strength of sandwich plates. To study the effect of plastic deformation on the bonding strength, laboratory experiments were carried on a Gleeble Thermal Simulator to imitate the diffusion-rolling bonding under different reductions for steel sandwich plates. The bonding strength and interlayer film thickness were measured, and the element diffusion was analyzed using line scanning. The relationship between the bonding strength and “diffused interlayer” thickness was investigated. It has been found that the bonding strength increases with reduction, whereas the interlayer film thickness decreases gradually as the reduction increases. The diffusion under plastic deformation is obviously enhanced in comparison with that of nil reduction. The mechanism of plastic deformation effect on the diffusion bonding and related models have been discussed.

An Analysis on the Inhomogeneous Microstructure in Crack Healing Area

Three hypo-eutectoid steels were chosen to study the inhomogenoues microstructure in crack healing area. Internal cracks were made in 20, 20MnMo and 45 steel samples. The precracks in 20 and 20MnMo steel can mostly be healed under the conditions of hot plastic deformation in which the reduction of hot pressing were 35.6% and 44.9% respectively, and the healing area is a ferrite band. The process of crack healing in crack tips in 45 steel could be finished in a very short time during upsetting, but there exists inhomogeneity in healing area which include more ferrite, fine grain size and many micro-voids. The reason why ferrite aggregated in healing area is that large deformation and high strain energy at high temperature and low strain rate around crack produce pro-eutectoid ferrite grain precipitating in hypo-eutectoid steels. Due to numerous voids restraining the migration of grain boundaries, the grain growth in a healing area becomes a slow process in the crack tips in 45 steel. This results in the grain size in crack tips healing area much finer than that in the steel matrix in 45 steel even after a long time of heat treatment at high temperature.

Shield Performance of High Boron Alloyed Stainless Steel Composite Plate

The shield thermal neutron performance of two high boron alloyed stainless steel composite plates(HBASSCP) was studied by the method of neutron beam transmission of neutron source reactor. The testing results indicate that the shield performance of the composite material is heavily affected by the size and distribution of the boride. Although the radiationresistance of high boron alloyed stainless steel increases with boron content, but blocky and sparse hypereutectic boride will appear in matrix when boron content is high (more than 3%), and these borides are difficult to be broken during hot deformation, so the thermal neutron is easy to penetrate directly through the space and can not be absorbed effectively. The difference between the shield performance obtained from experiments and the theoretical calculation is small for HBASSCP containing hypoeutectic boride in core material, but it is great for HBASSCP containing hypereutectic boride in core material.

Investigation of High Strength Steel for Automotive Roll-Forming Parts

In recent years, the number of automobiles has been steadily increasing, which has significantly impacted on the society and human life, and led to many social problems such as fuel crisis, environment pollution. Therefore, lightweight designing becomes a focused issue. Lightweight materials application, optimized structure design and advanced manufacturing process are the main ways to achieve the lightweight. However, low plasticity and ductility of high strength steel constrain the application of high strength steel. In this paper, the basic principle of roll forming for automotive parts is investigated, and it is innovatively applied in the hot roll forming process of the ultra high strength steel.

Fabrication and compressive performance of plain carbon steel honeycomb sandwich panels

Plain carbon steel Q215 honeycomb sandwich panels were manufactured by brazing in a vacuum furnace. Their characteristic parameters, including equivalent density, equivalent elastic modulus, and equivalent compressive strength along out-of-plane (z-direction) and in-plane (x- and y-directions), were derived theoretically and then determined experimentally by an 810 material test system. On the basis of the experimental data, the compressive stress-strain curves were given. The results indicate that the measurements of equivalent Youngs modulus and initial compressive strength are in good agreement with calculations, and that the maximum compressive strain near to solid can be up to 0.5-0.6 along out-of-plane, 0.6-0.7 along in-plane. The strength-to-density ratio of plain carbon steel honeycomb panels is near to those of Al alloy hexagonal-honeycomb and 304L stainless steel square-honeycomb, but the compressive peak strength is greater than that of Al alloy hexagonal-honeycomb.

Study on rolling process optimization of high carbon steel wire

Abstract The existing problems in the manufacture of SWRH82B high carbon steel wire were discussed by sampling and testing the microstructure and properties of the steel from the workshop. To solve the problems, the experimental parameters for thermal simulation were optimized, and the thermal simulating experiments were carried out on a Gleeble1500 thermal simulator. The process parameters for the manufacture were optimized after analysis of the data, and the productive experiments were performed after the water box in front of the no-twist blocks was reconstructed, to control the temperature of the loop layer. The results from the productive experiments showed that the cooling rate of 10–15 °C/s was reasonable before phase transformation, about 5 °C/s during phase transformation, and 600–620 °C was the suitable starting temperature for phase transformation. The ultimate strength of the ϕ11.0 mm wire was increased to 1150-1170 MPa with an increase of 20-30 MPa, the percentage reduction of section was to 34%-36% with an increase of 1%–3% by testing the finished products after reconstruction.

In Situ Observation of the Micro-Hole Healing Process

The Research on the mechanism of the internal crack healing in metals is an important basic work for improving metal quality and prolonging its lifetime, and it is very significant for developing the theory of materials. In the paper, in situ observation of the internal crack healing process on the section of pure copper sample under high temperature microscope, the fine structure of healed micro-holes are observed under scanning electron microscope. Observation results showed that the micro-voids of tens micron begin to be healed at the temperature of 750 , and obviously healed at the temperature of 900 . The fine structure of the healed micro-holes consists of some agglomerate particles at the scale of micrometer and much smaller particles on these agglomerate particles. According to the above observation, phenomenological model of micro-hole healing are presented, the healing process is passivating of hole edge on the observation section, shape regularization of micro hole;inner interface motion of micro hole in the matrix. 1.Introduction Metal materials play a dominant part in the field of engineering materials due to the following advantages such as low price, abundant sources, steady properties and being recycled easily. However, in the process of preparation and processing and forming and use of metal materials, inner or surface defects will appear inevitably. And the existence and expansion of micro-defect are mainly responsible for the decrease of strength and toughness and stiffness and remaining life. Under the influence of certain exterior factors (load, temperature changes and corrosion media), macro-cracks will come into being because of continuous expansion and merge, which lead to fracture failure finally. Micro-crack is the key factor to cause fracture failure of material. It is always an important subject in the research of engineering material that how to avoid fracture. The usually emphasizing point is customarily limited to some methods, such as adjustment of chemical composition and improvement of process technology. By these methods, we can ameliorate its microstructure construction to expect the delay and retardation of crack extension. Then, obtain higher anti-failure ability. The researchers seldom pay more attention on the reverse course of material failure. Supported by National Nature Science Foundation of P.R.China(59889101) Key Engineering Materials Online: 2004-10-15 ISSN: 1662-9795, Vols. 274-276, pp 817-822 doi:10.4028/www.scientific.net/KEM.274-276.817