Effects of Rapid Induction Heating on Transformations in 0.6% C Steels

Rapid induction hardening of martensitic steel can attain the very high strength levels needed for light-weighting components subjected to high operating stresses. Specimens of martensitic 0.6% C steels were heat treated using a dilatometer to investigate the effects of heating rates of 5 to 500 °C/s to temperatures of 850 to 1050 °C on the transformation to austenite and subsequent transformation to martensite during quenching. Selected specimens were quenched after partial transformation to austenite to assess the initial cementite precipitate size formed in ferrite during heating. Other specimens were isothermally held at the austenitizing temperature to assess cementite dissolution rates. Higher heating rates increased the Ac1 and Ac3 temperatures, and lowered the Ms temperature. Alloy content and prior microstructure also influenced the transformation temperatures.

Enhanced Corrosion Resistance of SA106B Low-Carbon Steel Fabricated by Rotationally Accelerated Shot Peening

The corrosion resistance of a SA106B carbon steel with a gradient nanostructure fabricated by rotationally accelerated shot peening (RASP) for 5, 10, 15 and 20 min was investigated. Electrochemical tests were carried out in the 0.05 M H2SO4 + 0.05 M Na2SO4 and 0.2 M NaCl + 0.05 M Na2SO4 solutions. The experimental results showed that the sample RASP-processed for 5 min exhibited the best corrosion resistance among them. TEM analysis confirmed that the cementite dissolution and formation of nanograins, which improved the corrosion resistance of the steel. Prominent micro-cracks and holes were produced in the samples when the RASP was processed for more than 5 min, resulting in the decrease of corrosion resistance.

Influence of the Electric Current Pulse with Different Pulse Width on the Eutectoid Microstructure of Hypoeutectic Fe-C Alloys

The influence of the eutectoid structure of hypoeutectic Fe-C alloys by applying electric current pulse (ECP) is carried out. The experiment results show that ECP treatment can produce Joule heating. Joule heating increases the diffusion capability of atoms and the driving force of austenite growth, which promotes austenite crystal growth and accelerate cementite dissolution. In view of the influence of the electron-wind-force made by ECP, it can increase the quantity of moving dislocation. The dislocation pile-up which made by the dislocation motion lead to cementite dissolution. Cementite dissolution can lead to concentration fluctuation in Austenite. ECP can also make the phase transformation barrier and the phase transition drive force of graphite formation decrease. As the result, these phenomena can make cryogenic ledeburite become less and graphite increase. Furthermore, it can also increase the nucleation rate and growth rate of ferrite, which can make the relative amount of ferrite increase and the relative amount of pearlite decrease. Based on our experiments, the effect becomes more obvious with the pulse width increase.