A Criterion for the Change from Fast to Slow Regime of Cementite Dissolution in Fe-C-Mn Steels

The present study clarifies the role of Mn in cementite on the driving force of cementite dissolution and the growth of austenite. From an experimental study, the effects of manganese composition and temperature on the cementite dissolution were shown. From a theoretical analysis based on thermodynamic and kinetics considerations, a criterion for the change from fast to slow regime of cementite dissolution was proposed. This criterion is in good agreement with the experimental results. It can be easily calculated and can define the composition and temperature ranges where the cernentite dissolution is slow or fast.

Research on the dissolution behavior of cementite in the GCr15 steel surface layer induced by surface nanocrystallization

Dissolution of cementite was found in the surface layer of 1.0C-1.5Cr steel plates during the process of surface mechanical attrition treatment(SMAT),and its evolution was characterized by transmission electron microscope(TEM),three-dimensional atom probe(3DAP)and Mssbauer spectroscopy.The average grain size contained in the top surface of SMAT specimen was 10nm,and no diffraction ring corresponding to cementite grain was identified in the selected area election diffraction(SAED)pattern,which indicated the disappearance of cementite.3DAP analysis showed the average carbon concentration in ferrite(0.75 at%)after SMAT,which was almost 100 times higher than that in matrix(0.008 at%),which suggested cementite dissolve in the process of SMAT.The results of Mssbauer spectroscopy indicated that partial cementite dissolved in the process of SMAT,the saturation of cementite dissolution is about 47%.Evolution of cementite involved three sub-stages:①inoculation stage,in the first 5 min of treated duration,cementite fraction is reduced only by 0.4%;②dissolution stage,within the following 25 min cementite fraction significantly is reduced from 14.6% to 8.4%;③saturation stage,when treatment exceeds 30 min,the fraction of cementite nearly remains the same.

Effect of V and N on Microstructures and Properties of Grade-70 Tire Cord Steel during Cold Drawing

Commercial grade-70 tire cord steel was microalloyed with V and N to explore the possibility of substitu- ting V for C and the effect of V and N on cementite dissolution during cold drawing process. Tensile strength, elon- gation and torsion laps of cold-drawn wires were determined. Microstructures of secondary phases were studied by transmission electron microscopy （TEM） and energy dispersive spectroscopy （EDS）. Saturation magnetization was measured by using a vibrating sample magnetometer （VSM） to evaluate cementite dissolution during cold drawing process. Experimental results showed that with the increase of V content, tensile strength increased, elongation slightly decreased, and the torsion laps of the cold-drawn wires decreased. Results also showed that with the increase of N content, a peak （increasing first and then decreasing） appeared in the tensile strength graph, and an increase of elongation and a decrease of torsion laps of the cold-drawn wires occured. N is soluble in ferrite when its content is low. The increase in the content of N to 82 × 10^-6 will result in the precipitation of the V-containing secondary pha- ses. Also, cementite tended to be stable during cold drawing process with the increase of V and N contents. Grade-80 tire cord steel can be replaced by grade 70 tire cord steel microalloyed with 0. 086 mass% V.