In this work, the influences of a magnetic field of 2.4 T on the macro residual stress and the status of structural defects, including grain boundaries, dislocations and the Fe-rich clusters of Ti-6Al-4V were investigated by X-ray Diffraction (XRD), Electron Backscatter Diffraction (EBSD) and magnetic measurement. The XRD test results show that the applied magnetic field can cause the relaxation and homogenization of macro residual stress. The maps of Kernel Average Misorientation (KAM) values obtained by EBSD tests present a significant dislocation multiplication caused by a magnetic field, and the rise of dislocation density was estimated to be about 32% by XRD tests. The EBSD test results also show an increase in the fraction of Coincidence Site Lattice (CSL) grain boundaries and a decrease in the fraction of low-angle grain boundaries. The results of magnetic measurement show that Ti-6Al-4V has mixed magnetism consisting of paramagnetism and weak ferromagnetism, and that the ferromagnetic saturation magnetization decreased after exposing the alloy to the magnetic field, which suggests the dissolution of the Fe-rich clusters in the alloy. These magnetically-induced changes are related to magnetoplastic effects, a kind of phenomena on which there have been some research, and the possible mechanism of them is discussed in this paper.

High-temperature plastic flow is the underlying process that governs the product quality in many advanced metal manufacturing technologies, such as extrusion, rolling, and welding. Data and models on the high-temperature flow behavior are generally desired in the design of these manufacturing processes. In this paper, quantitative constitutive analysis is carried out on 3Cr-1Si-1Ni ultra-high strength steel, which sheds light on the mathematic relation between the flow stress and the thermal-mechanical state variables, such as temperature, plastic strain, and strain rate. Particularly, the hyperbolic-sine equation in combination with the Zener-Hollomon parameter is shown to be successful in representing the effect of temperature and strain rate on the flow stress of the 3Cr-1Si-1Ni steel. It is found that the flow stress of the 3Cr-1Si-1Ni steel is significantly influenced by strain. The strain-dependence on flow stress is not identical at different temperatures and strain rates. In the constitutive model, the influence of strain in the constitutive analysis is successfully implemented by introducing strain-dependent constants for the constitutive equations. Fifth-order polynomial equations are employed to fit the strain-dependence of the constitutive constant. The proposed constitutive equations which considers the compensation of strain is found to accurately predict flow stress of the 3Cr-1Si-1Ni steel at the temperatures ranging from 800 °C to 1250 °C, strain rate ranging from 0.01/s to 10/s, and strain ranging from 0.05 to 0.6.

During the welding process of B containing 9% Cr martensitic heat resistant steel (9Cr-B steel), austenite memory effect (referred to that the prior austenite grains in the heat affected zone (HAZ) after welding inherit the shape and size of prior austenite grains before welding) occurs in its normalized sub-zone of HAZ and the grain refinement is suppressed, which can effectively prevent type IV crack, and improve the service life of the welded joint at high temperatures. In the present article, α/γ reverse transformation behavior in the normalized sub-zone of 9Cr-B steel HAZ is reviewed. Austenite memory effect of 9Cr-B steel is derived from B addition. The main mechanisms of austenite memory effect during α/γ reverse transformation are discussed. Various models of boron causing austenite memory effect are discussed in detail. Matrix microstructure also plays an important role in austenite memory effect. Effects of heating rate, peak temperature, and holding time at peak temperature on austenite memory effect are also discussed.

It is of great significance to reduce welding hot cracks and improve the corrosion resistance of nuclear power components by controlling the dilution ratio of the cladding weld bead formed by gas tungsten arc welding (GTAW). This paper presents a method to predict the dilution ratio by using the ratio of the thermal power of forming a unit length weld to the cross-section of the fuse, that is, the linear energy of forming a unit volume of deposited metal, which is characterized by the “Heat Equivalent for Melting Welding Wire” (HEMW). It is found that there is a linear positive correlation between the HEMW and the dilution ratio. With the increase in HEMW, the proportion of deposition heat energy in the whole effective heat input energy decreases, the proportion of base metal melting heat energy increases, and the proportion of non-melting heat energy diffused to the base metal remains basically unchanged. The HEMW is used to predict and control the dilution rate under the condition of pulse welding. By increasing the wire feeding speed under the condition of pulse peak current and reducing the welding speed, a high deposition efficiency, low dilution rate and low heat input is realized, which plays an important guiding role in improving the deposition quality.

During the welding of 690 nickel-based alloy, solidification cracking (SFC) and ductility-dip cracking (DDC) easily forms, which has a negative effect on the quality of welded joints and service life. The present study examined the effects of welding heat input and cladding layers on the SFC and DDC, as well as their formation mechanism. The microstructure observation, elemental distribution, and Varestraint test were carried out. The results show that SFC and DDC were formed for the Inconel filler metal 52M, and SFC is more prone to form than DDC. The alloy elements such as Fe, Si, C, and P from base metal can expand the solidification temperature range, such that the SFC sensitivity increases. With the increase of welding heat input, the grain size of cladding metal is increased with a great SFC sensitivity. The increasing welding heat input also makes DDC possible due to the formation of a large angle grain boundary.

Low pressure turbine rotors are manufactured by welding thick sections of 25Cr2Ni2MoV rotor steel using tungsten inert gas (TIG) backing weld, and submerged arc welding (SAW) filling weld. In this study, the microstructure of columnar grain zones and reheated zones in weld metal was characterized meticulously by Optical Microscope (OM), Scanning Electron Microscope (SEM) and Electron Back-Scatter Diffraction (EBSD). The results showed that, compared with SAW weld metal microstructure, TIG weld metal microstructure was relatively fine and homogeneous, due to its lower heat input and faster cooling rate than SAW. The maximum effective grain size in TIG and SAW weld were 7.7 μm and 13.2 μm, respectively. TIG weld metal was composed of lath bainite (LB) and blocky ferrite (BF), while SAW weld metal was composed of acicular ferrite (AF), lath bainite (LB)and ferrite side plate (FSP). Tempered martensite (TM) was detected along columnar grain boundaries in both TIG and SAW weld metals, which was related to the segregation of solute elements during weld solidification. Electron Probe Micro-Analysis (EPMA) results showed that the contents of Ni and Mn at the dendritic boundaries were 50% higher than those at the dendritic core in TIG weld. Similarly, 30% of Ni and Mn segregation at dendritic boundaries was also found in SAW weld. In addition, the microhardness of the two welded joints was tested.