The study of heterostructured materials (HSMs) answered one of the most pressing questions in the metallurgical field: “is it possible to greatly increase both the strength and the strain hardening, to avoid the “inevitable” loss of ductility?”. From the synergy between the deformation modes of zones with greatly different flow stress, low stacking fault energy (SFE) alloys can reduce their typical trade-off between strength and ductility. Stainless steel (SS) is a low-SFE material, which is widely applied for structural, biomedical, biosafety, food-processing, and daily applications. The possibility to combine its corrosion resistance and biocompatibility with the outstanding mechanical behaviour of HSMs can convert SS into a promising option for low-cost and high-effective advanced material. This paper reviews all the microstructural aspects of HS SS obtained by different processing methods and their correlation with crystallographic texture and properties such as mechanical, corrosion, biological, and magnetic characteristics. The critical comparison between experimental and modelling findings is also presented in terms of the deformation mechanisms, microstructural and texture features. Thus, the processing-microstructure-properties relationship in HS SS is the focus of this publication. The multi-disciplinary perspectives of HS SS are also discussed. This review paper will serve as a reference for understanding and designing new multi-functional HS SSs. 

Heterostructured stainless steel: Properties, current trends, and future perspectives

The heat affected zone of X20Cr13 martensitic stainless steel after multiple repair welding: Microstructure and mechanical properties assessment

The invention relates to a nonlinear ultrasonic phased array imaging method for micro-crack detection. According to the method, an ultrasonic phased array detection system is utilized to collect the detection signals in the sequence focusing mode and the parallel focusing mode, the appropriate receiving delay tr and the width T of the time-domain intercepting window are determined, the intercepted detection signals are subjected to Fourier transform, the sound kinetic energies Es and Ep of the sequence focusing method and the parallel focusing method and the relative energy difference gamma of the two focusing methods are respectively calculated, and the nonlinear source position is determined according to the gamma, ie., the micro-defect position.

Nonlinear ultrasonic phased array imaging method for micro-crack detection

The invention discloses a small-diameter pipe nondestructive detecting method based on an electromagnetic ultrasonic phased array focusing principle. The small-diameter pipe nondestructive detecting method is implemented by a solenoid bias magnetic field generating unit which is arranged outside a small-diameter pipe and is coaxial with the small-diameter pipe, and an electromagnetic ultrasonic probe which is formed by electromagnetic ultrasonic exciting coil units coaxially arranged in the small-diameter pipe and array detection coil units arranged uniformly along the circumferential direction of the pipe. The small-diameter pipe nondestructive detecting method comprises the following steps: firstly, generating a high bias magnetic field along the axial direction of the small-diameter pipe by an electrified solenoid; setting the exciting time of each exciting coil in the electromagnetic ultrasonic exciting coil units according to a focusing law, and exciting the coils sequentially by the electromagnetic ultrasonic device so as to generate ultrasonic waves; meanwhile, detecting voltage signals caused by the ultrasonic waves by the array detection coil units circumferentially arranged on the pipe cross section on which focusing points are located; and detecting the small-diameter pipe comprehensively and rapidly with the assistance of axial machinery scanning. The method provided by the invention has the advantages of high detection rate, high detection speed, high efficiency and the like, and can be widely applied to nondestructive detection on the interiors of small-diameter pipes with complex outer shapes and on debonding defects of a multi-layer pipe HIP (Hot isostatic press) welding interface.

Small-diameter pipe nondestructive detecting method based on electromagnetic ultrasonic phased array focusing principle

The invention discloses an oblique incident ultrasonic synthetic aperture focusing-based thick wall structure defect detection method, and belongs to the technical field of nondestructive detection. The method comprises the following steps: a thick wall structure test block is detected through using a phased array electron scanning function by using an ultrasonic detection system comprising a phased array ultrasonic flaw detector, a phased array ultrasonic probe and an oblique organic glass wedge in order to obtain the A scanning signal set of all phased array elements; the Fermat's theorem is used to solve the emission point positions of all the phased array elements and image reconstruction points in the wedge/test block interface, and all A scanning signals undergo time delaying and amplitude superposing processing; and the processed A scanning signals undergo Hilbert transformation, and a difference function is used to obtain a reconstructed ultrasonic detection B scanning image. The method has the advantages of high defect detection resolution, large detection range, detection efficiency increase, and provision of an effective solving technology for the nondestructive detection problem of the defect of a thick wall structure. The method also can be embedded to the flaw detector to realize automatic real-time imaging, and has high engineering application values.

Oblique incident ultrasonic synthetic aperture focusing-based thick wall structure defect detection method

Method for ultrasonically detecting weld quality of main loop pipeline of nuclear power plant by phased array

Heat-affected zone (HAZ) of welding joints critical to the equipment safety service are commonly repeatedly welded in industries. Thus, the effects of repeated welding up to six times on the microstructure and mechanical properties of HAZ for AISI 304N austenitic stainless steel specimens were investigated by a Gleeble simulator. The temperature field of HAZ was measured by in situ thermocouples. The as-welded and one to five times repeated welding were assigned as-welded (AW) and repeated welding 1–5 times (RW1–RW5), respectively. The austenitic matrices with the δ-ferrite were observed in all specimens by the metallography. The δ-ferrite content was also determined using magnetic and metallography methods. The δ-ferrite had a lathy structure with a content of 0.69–3.13 vol.%. The austenitic grains were equiaxial with an average size of 41.4–47.3 μm. The ultimate tensile strength (UTS) and yield strength (YS) mainly depended on the δ-ferrite content; otherwise, the impact energy mainly depended on both the austenitic grain size and the δ-ferrite content. The UTS of the RW1–RW3 specimens was above 550 MPa following the American Society of Mechanical Engineers (ASME) standard. The impact energy of all specimens was higher than that in ASME standard at about 56 J. The repeated welding up to three times could still meet the requirements for strength and toughness of welding specifications.

Microstructure and Mechanical Properties of Heat-Affected Zone of Repeated Welding AISI 304N Austenitic Stainless Steel by Gleeble Simulator

The invention discloses a method for establishing an FDTD (Finite Difference Time Domain) ultrasonic detection simulation model of a coarse crystal material based on an EBSD (Electron Back-Scattered Diffraction) spectrum and belongs to the technical field of ultrasonic nondestructive detection. The method comprises the following steps: obtaining a crystal orientation spectrum of the coarse crystal material by directly using the EBSD technology, selecting a threshold value for defining crystal grains in the spectrum according to an actual crystal grain structure in a macroscopic metallograph, packing the crystal grains with color corresponding to a principal orientation, and carrying out grey processing to obtain an image consisting of square pixel points, wherein the orientations of the crystal grains are represented by eulerian angles phi1, phi and phi2 corresponding to gray values and can be used for quantitatively calculating elastic anisotropic stiffness matrixes of the crystal grains. Compared with a previous model, the model has the advantages of being capable of accurately describing the structures and the orientations of the crystal grains, realizing high operation efficiency and the like; a model basis is provided for realizing purposes of defect quantification and location and quality determination in ultrasonic detection of the coarse crystal material. The method also can be used for establishing the ultrasonic simulation models of other elastic anisotropic polycrystalline materials such as austenitic welding lines and two-phase titanium alloys; the method has bright popularization and application prospects.

Method for establishing FDTD (Finite Difference Time Domain) ultrasonic detection simulation model of coarse crystal material based on EBSD (Electron Back-Scattered Diffraction) spectrum

An automatic phased array ultrasonic detection method of welding seams on main pipelines in a nuclear power plant belongs to the field of nondestructive testing and includes the steps of: 1) selecting an area array probe and a wedge according to the material of the welding seam on the main pipeline, and ensuring that the surface status satisfies detection demand; 2) forming a clear marker that is required in the detection on the surface of the welding seam on the main pipeline; 3) assembling the probe and the wedge with a solid flexible coupling medium to form a coupled fixture; 4) fixing the coupled fixture onto a scanning detection apparatus by a probe support; 5) respectively setting related parameters of a phased array ultrasonic detector and an automatic scanning detection controller, and detecting the welding seam on the main pipeline; and 6) quantifying defects according to a B scanning detection image of a detection result. The method avoids the influence on the defect detection due to artificial factor and inconsistent coupling in a manual ultrasonic detection process in the prior art, improves defect detection rate and defect quantification precision, can perform continuous automatic scanning detection to the welding seam on a main pipeline of which the perimeter exceeds 2 m, is improved in detection efficiency significantly and has important engineering application value.

Automatic phased array ultrasonic detection method of welding seams on main pipelines in nuclear power plant

The invention provides an ultrasonic relative time propagation technology suitable for inclined crack quantifying and imaging, and belongs to the technical field of ultrasonic nondestructive testing. According to the propagation technology, the length, the width, the inclined angle and the position of cracks are set in a two-dimensional section model, a probe with N array elementsis arranged in the model by means of signal parameters of a phased array linear array probe, N2 TXT files representing A scanning signals are formed according to phased array all-capture signal collection, the TXT files are read through software, a TFM image of the cracks is obtained, an upper tip end coordinate point (xR, zR) and a lower tip end coordinate point (xD, zD) on the cracks are found in the image through MATLAB software, and the length delta and the inclined angle gamma of the cracks are calculated. The propagation technology solves the problems that a traditional relative time propagation technology is poor in inclined crack quantifying precision and cannot be used for measuring the inclined angle of the cracks. Besides, by means of the propagation technology, the cracks can be visually imaged and accurately positioned. A solution is provided for further improving quantifying precision of the cracks in workpieces, and good application and popularization prospects are achieved.

Zhang Donghui

Papers

Method for ultrasonically detecting weld quality of main loop pipeline of nuclear power plant by phased array

Microstructure and Mechanical Properties of Heat-Affected Zone of Repeated Welding AISI 304N Austenitic Stainless Steel by Gleeble Simulator

Method for establishing FDTD (Finite Difference Time Domain) ultrasonic detection simulation model of coarse crystal material based on EBSD (Electron Back-Scattered Diffraction) spectrum

Automatic phased array ultrasonic detection method of welding seams on main pipelines in nuclear power plant

Ultrasonic relative time propagation technology suitable for inclined crack quantifying and imaging