Guo Dong Wang’s research while affiliated with Harbin Institute of Technology at Weihai and other places

The generating, floating and collapsing of arc bubble is a special phenomenon in underwater flux-cored wet welding. The configuration changing process of bubble will change the stress on droplet and influence the droplet transfer process. In this study, the shape changing of bubble is captured in graphic and the real-time electric signal data is obtained. The impact of bubble floating and collapsing results in the globular repelled transfer mode, which also reduces the arc stability. A self-designed gas-shield cover is used as a bubble constraint device to improve the welding process stability and weld appearances by limiting the free floating and expansion of arc bubble. The relationships between the cover diameter and the characteristics of weld appearance are studied.

In this work, a novel type of δ-TRIP steel was designed, and the content and stability of retained austenite in δ-TRIP specimens under different annealing processes were detected and studied, respectively. The volume fraction of austenite was determined by X-ray diffraction (XRD). The microstructure and mechanical properties were analyzed systematically. The results show that a complex microstructure composed of three phases (ferrite, bainite and retained austenite) was obtained in the δ-TRIP steel. With the increasing of annealing temperature, both retained austenite and bainite content in the specimen increased, while the carbon content in retained austenite decreased, leading to a poor stability for retained austenite. Both tensile and yield strength improved with the increasing of annealing temperature, while the elongation reduced. The feature of retained austenite led to an excellent combination of ductility and strength, which was better than traditional TRIP steel.

In this study, an energy‐efficient processing route involving hot rolling, direct quenching, and air cooling partitioning (DQ&P) is proposed for the large‐scale industrial production. The carbon partitioning is completed through waste heat of the steel coils. The effect of quenching temperature (QT) and the kinetics of non‐isothermal carbon partitioning were investigated in a low carbon steel 0.19C‐1.5Si‐1.6Mn (wt%). A stable volume fraction of retained austenite (RA) ≈11.1–13.5% is obtained in the QT range of ≈240–360 °C, which provides a wide quenching window for industrial production. In addition, when the QT was 320 °C, the carbon partitioning was adequate at cooing rate of less than 1 °C s⁻¹ and the volume fraction of RA was more than 11%. When the cooling rate is increased to 5 and 10 °C s⁻¹, ≈10% RA with high carbon content of ≈1.3 wt% is interestingly obtained. A large scale industrial coils of hot Q&P (Quenched and Partitioned) steel is successfully produced using a commercial steel 0.13C‐1.2Si‐1.5Mn‐0.25Cr (wt%). The mechanical properties are uniform for the entire steel coil with tensile strength of ≈1258–1319 MPa and total elongation of ≈13.7–16%. The present work confirms the viability to introduce Q&P process in the hot rolling production line.

Grain-oriented silicon steel was produced by strip casting route. The effect of different annealing temperature on primary annealing and secondary annealing was investigated. The result showed that the average grain diameter increased and the grain uniformity was gradually destroyed with the increasing annealing temperature. Regardless of annealing temperature, the primary texture consisted of strong γ-fiber and weak λ-fiber. With the increase of annealing temperature, the γ-fiber intensity increased. In addition, the Goss component was not shown at 780-880 °C but appeared at 980 °C. After secondary annealing, complete abnormal grain growth occurred in all samples and the average grain diameter increased with the primary annealing temperature. The Goss sharpness of secondary grains firstly increased and then decreased with a peak value obtained at 830 °C. This result was explained in terms of the combination of the inhibiting force, primary grain diameter and primary texture.

Direct quenching and dynamic partitioning (DQ&P) process is a promising approach and there continues to be lack of understanding concerning cooling condition in the hot strip rolling line. Here, the authors have simulated DQ&P process in low carbon Si–Mn steel using a thermal simulator. The effect of quenching temperature, relaxation process, and cooling rate on microstructure and hardness is studied. The results suggest that retained austenite is less sensitive to quenching temperature and the volume fraction of retained austenite including film-like and blocky shape is ≈7–11%. The relaxation process leads to ferrite transformation and recovery of defects, resulting in increase in retained austenite, and reduced hardness. It is interesting that the quenching temperature and hardness do not show an inverse relation. It is important that the isothermal transformation at high quenching temperature below Ms promotes retained austenite. Moreover, the low coiling cooling rate less than 0.1 °C s−1 from quenching temperature to room temperature is adequate for carbon partitioning. In the view of thermodynamics and kinetics, an appropriate processing window of coiling temperature between 200 and 320 °C plus low cooling rate less than 0.1 °C s−1 is proposed for hot rolled DQ&P steels.

Nanoscale cementite can be obtained in 0.17% carbon steel during isothermal treatment at 500oC after ultra fast cooling (UFC) and thermo-mechanical treatment. The precipitation strengthening contribution to yield strength was more than 250 MPa, when the heat treatment time was less than 20 min. The carbon diffusion is impacted by Mn and Si, which are redistributed during the precipitation process. All the effects induced by substitutional elements can be manifested through the restricted carbon diffusion, which is equal to the carbon diffusion multiplied by adjustable parameters. Based on this, a kinetic model has been adapted to simulate the precipitation behaviors of cementite involving the evolution of the number density per unit volume, radius of cementite over time, and the evolution of carbon concentration in matrix. An excellent agreement in mean radius of particles between the predictions of the model and experimental observations was obtained. It was found that the nucleation period of cementite was very short and did not exceed 0.2 s, and there was an overlap between the nucleation period and the growth period, and the coarsening period began at about 1s. In the growth stage, the carbon concentration in the matrix dropped rapidly and the mean radius of particles increased quickly. In the coarsening stage, the carbon concentration remained unchanged and the number of particles per unit volume fell sharply.

High silicon steel was fabricated by twin-roll strip casting. The cracks on the surfaces of the processed strips were obtained and analyzed by digital camera after series of surface treatment. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to observe and characterize the microstructure nearby crack and fracture surface along the normal direction, respectively, and the crack formation mechanism was further analyzed in conjunction with processing parameters utilized during twin-roll strip casting process. The results indicated that morelongitudinal cracks along the rolling direction were observed in comparison with transverse cracks along the transverse direction on the strip surfaces. Trans granular and intergranular fracture modes both worked during the formations of longitudinal and transverse cracks on the processed strips. The dominant factor causing the formation of crack on the surface of the processed strips was the inhomogeneous transfer of heat during casting and rolling. The inhomogeneous transfer of heat induced by gas gap during casting resulted in variations of dendrite length and secondary dendrite spacing (SDAS). Meanwhile, the casting velocity influenced the formation of gas gap, which further influenced the thermal contraction. So the control of velocity of casting above a certain level proved beneficial to enhancing the performance of strip casting and to improving the quality of strip products.

We describe here the relationship between electron microscopy and mechanical property studies in industrially processed titanium bearing microalloyed steel plates that involved processing using the recently developed ultrafast cooling (UFC) approach. Given that the segregation of manganese is generally responsible for microstructural banding in low-alloy steels, which can deteriorate the tensile property in the direction of thickness, the manganese-content was reduced by ~0.6-0.8% with the objective to obtain uniform microstructure across the thickness of the steel plate. Besides, non-uniform distribution of accelerated cooling along the thickness direction also leads to inhomogeneous microstructure across the plate thickness. In order to obtain near-uniform microstructure and similar mechanical properties from the surface to the center of plate, fast and effective cooling process is necessary. In this regard, refined and uniform microstructure that was free of microstructural banding was obtained via UFC process across the plate thickness, with strict control and faster cooling rate on the run-out table. Furthermore, grain refinement and random precipitation in the ferrite matrix contributed ~100 MPa toward yield strength. The study underscores the potential of processing medium and heavy plates of titanium bearing microalloyed steels plates with uniform and refined microstructure across the thickness via thermo-mechanical controlled processing (TMCP) involving UFC.

According to the characteristics of firebricks palletization and the structure of the manipulator, this paper puts forward the concept of using group policy to palletize firebricks by robot. On this basis, the concept of “Horizontal bar “and” Horizontal slice " is introduced with features of stacking firebricks. Then mathematical model is constructed to palletize Firebricks in shortest time. The firebrick robot palletising optimization model has been applied in the enterprise.

By using sol-gel method, Nb/SnO2 gel was prepared,and spin coating method was used to coat on glass substrates, which dried and calcined to obtain a homogeneous Nb / SnO2 composite films.Under the same experimental conditions, the different doping amount of nickel, calcination temperature on the structure and morphology of Nb/SnO2 film were discussed. By using XRD, IR, SEM and other testing methods, the structure and morphology of Nb / SnO2 composite film were characterized.At 500 °C, the film particle had high crystallization and small size,and the surface of the film was well-distributed.Its optical and electrical properties were tested by the ultraviolet-visible spectrophotometer and four-probe resistivity meter.UV-Vis spectra showed that Nb / SnO2 film absorbance in the near ultraviolet region had increased significantly, but the absorbance showed a downward trend with the increasing amount of Nb⁵⁺ doped;Conductivity analysis showed: Nb⁵⁺ doping amount of 8% (the amount of material), the conductivity of Nb/SnO2 composite films was best.