Phase Transformation of ER70-Ti for Gas Shielded Wire

ER70-Ti is a high strength gas shielded welding wire steel, which is suitable for ships, bridges and other structures, and can be used for thick plate welding with high current. In the welding wire industry, ER70-Ti is a high-tech deep-processing product with high added value. In this study, the thermal expansion experiment of ER70-Ti wire rod was carried out. The critical temperature of ER70-Ti phase transformation was measured and the continuous cooling transformation curve (CCT curve) of undercooled austenite was drawn. The microstructure and hardness of the samples under different cooling rates were observed. The results show that Ac1 temperature of ER70-Ti sample was 690 °C, Ac3 temperature was 877°C, and Bs temperature was 575°C. When the cooling rate was low (0.1°C/s~2.5°C/s), the phase transformation products of ER70-Ti were equiaxed polygonal ferrite and granular bainite. With the increase of cooling rate, the grain size of ER70-Ti sample was refined and the bainite content increased from 53% to 85%. When the cooling rate was higher than 5°C/s, all the phase transformation products were bainite. The Vickers microhardness also increased with the increase of cooling rate, from 185HV to 325HV.

Measurement of Continuous Cooling Transformation Curve and High Temperature Mechanical Properties for 12Mn Steel

The dilatometer curves of continuous cooling transformation of 12Mn steel were measured with Formastor-FⅡthermal mechanical simulator．The steel's undercooled austenite phase continuous cooling transformation curves ( CCT curves) were established by means of the dilatometer method and the metallographic-hardness measurement method． The effect of cooling rate on microstructure and hardness of the steel was studied． CCT curve of test steel was simulated by JMatPro. The results show that the Ac1 and Ac3 of the experimental steel are 692 ℃ and 855 ℃ ; the microstructure obtained is made of ferrite，pearlite and bainite．The ferrite transformation and pearlite transformation occur at a slower cooling rate，in which the ferrite is dominant. When the cooling rate is greater than 4.25 ℃ / s bainite transformation happens．As the cooling rate increases，microstructure or grains become finer．The hardness of the tested steel with increasing cooling rate shows a trend of first fast increase and soon decrease．The simulation results are consistent with the measured CCT law. The high temperature mechanical properties of 12mn steel round billet were tested by gleeble-1500d thermal / mechanical simulator. The tensile strength, reduction of area and stress-strain curves of the billet were obtained in the range of 600-1300 ℃.

Effects of Final Cooling Temperature on Microstructure Transformation and Properties of Q550 Low Carbon Bainite Steel

The mechanical properties of low carbon bainite steel are closely related to the microstructure and proportion after phase transformation. The microstructure of the deformed austenite of low carbon bainite steel after isothermal transformation and continuous cooling transformation was studied by thermal simulation test. The metallographic structure was observed by optical microscopy (OM) and scanning electron microscopy (SEM). The metallographic and microhardness were used to judge the microstructure type, and the CCT (continuous cooling transformation) curve and TTT (time-temperature-transformation) curve of the test steel were drawn. It was found that at 700-430 °C isothermal, undergo a variety of medium-temperature microstructure transformations appeared for the test steels, such as ferrite, pearlite, granular bainite and lath bainite. The cooling rate and final cooling temperature have great influence on the type and performance of the final microstructure. The final cooling temperature was controlled at about 515°C. The mixed microstructures of granular bainite (GB) and fine martensite-austenite (M-A) island, a small amount of acicular ferrite and lath bainite were obtained. The yield and tensile strengths of this type of microstructure reached 639 MPa and 750 MPa respectively, the shrinkage rate reached 17%, and the better low-temperature impact performance was realized.

Study on Transformation Mechanism and Kinetics of α’ Martensite in TC4 Alloy Isothermal Aging Process

The law of microstructure evolution and transformation mechanism of the α′ martensite decomposition during 400–600 °C were studied by the isothermal dilatometry. The transformation process of α′ martensite was quantitatively characterized based on Johnson–Mehl–Avrami (JMA) model, and the microstructure evolution under different aging processes was observed and compared on Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The results showed that α′ → α + β is the elemental diffusion transformation, the position and shape of the precipitate gradually change with the holding time and temperature. The decomposition rate of α′ martensite was positively correlated with the aging temperature. The whole transformation process was divided into two stages based on the value of the Avrami exponent n, and the corresponding average values of the transformation activation energies Q are 46.1 kJ/mol and 116.8 kJ/mol, respectively. The calculated model had good agreement with the experimental data, and the transformation curve of α′ martensite with time and temperature during the isothermal aging at 400–600 °C was drawn.

A Proposed Methodology to Analyze Plant Growth and Movement from Phenomics Data

Image analysis of developmental processes in plants reveals both growth and organ movement. This study proposes a methodology to study growth and movement. It includes the standard acquisition of internal and external reference points and coordinates, coordinates transformation, curve fitting and the corresponding statistical analysis. Several species with different growth habits were used including Antirrhinum majus, A. linkianum, Petunia x hybrida and Fragaria x ananassa. Complex growth patterns, including gated growth, could be identified using a generalized additive model. Movement, and in some cases, growth, could not be adjusted to curves due to drastic changes in position. The area under the curve was useful in order to identify the initial stage of growth of an organ, and its growth rate. Organs displayed either continuous movements during the day with gated day/night periods of maxima, or sharp changes in position coinciding with day/night shifts. The movement was dependent on light in petunia and independent in F. ananassa. Petunia showed organ movement in both growing and fully-grown organs, while A. majus and F. ananassa showed both leaf and flower movement patterns linked to growth. The results indicate that different mathematical fits may help quantify growth rate, growth duration and gating. While organ movement may complicate image and data analysis, it may be a surrogate method to determine organ growth potential.

Austenite to Ferrite Transformation Kinetics in Fe-9 %Cr Alloys - I. General Kinetic Analysis

The paper considers theoretical aspects of the kinetics of austenite → ferrite transformation in an Fe–9 %Cr alloy, a common model of diffusionless transformation. In previous studies it was shown that this transformation under isothermal conditions shows a behaviour typical for nucleation site saturation, including the change of the Avrami exponentn(determined as the slow of transformation curve on double logarithmic scale) from 4 to 1. Activation energies determined in two ways: by the ‘nose’ temperature of the normal C-curve and by the slope of the C-curve re-drawn on a reverse temperature scale are unexpectedly similar (272–315 kJ/mole) and not temperature-dependent. But the complete TTT diagrams calculated using these values determined directly from experimental data and the precise formula of Cahn’s solution of grain face nucleated transformation problem do not provide good agreement with experiment in the whole temperature range. This may mean that the theory of site saturation needs some correction.