Prediction of Decarburized Ferrite Depth of Hypoeutectoid Steel with Simultaneous Oxidation

Abstract

The objective of this paper is to describe a method of calculating the decarburized ferrite depth and scale thickness during heating and cooling for hypoeutectoid steel in ambient atmosphere. The decarburization behavior in hypoeutectoid steel is divided into three regions. In temperature region above A3 ferrite is not formed during decarburization from austenite with a carbon concentration C = 0.0 wt%. In temperature region below A3 (C = 0.0 wt.%) and above A3 (C = C0) the decarburized ferrite forms from austenite during decarburization, but its carbon concentration ranges from 0.0 to the nominal carbon concentration C0. Finally, in the temperature region below A3 (C = C0) austenite transforms to ferrite + austenite or ferrite + cementite and the decarburized ferrite forms from ferrite + austenite or ferrite + cementite by surface decarburization with the appropriate equilibrium concentration. Separate decarburization models were developed for the three temperature regions due to the difference in decarburization behavior. The proposed model also handles simultaneous oxidation. The quantitative information obtained on the oxidation and decarburization characteristics is in good agreement with the experiments.

Effects of Temperature and Oxygen Concentration on the Characteristics of Decarburization of 55SiCr Spring Steel

“…Nomura et al 8) reported a model predicting the ferrite decarburizing depth of spring steel assuming that no oxidation occurred. Choi et al 9) proposed a model to explain the coupled growth of oxide layers and ferrite decarburization in steels based on phase transformation and diffusion calculation during heating and cooling. Badu et al 10) investigated the influence of relative humidity on oxidation and decarburization.…”

Surface Decarburization of the Hypo-Eutectoid Carbon Steel C45 during Annealing in Steady Air at Temperatures T > AC1

“…All are based on Fick's 2nd law. The uncorrected and corrected Van-Ostrand-Dewey equation [5,6,8,22,23] is used for annealing temperatures T a > T G , as well as a Fourier analysis [23]. The Van-Ostrand-Dewey equation is also used and corrected for creating a diffusion model of decarburization that is based on microhardness measurements [21].…”

“…The Van-Ostrand-Dewey equation is also used and corrected for creating a diffusion model of decarburization that is based on microhardness measurements [21]. For annealing temperatures T a < T G the equations for the calculation of the completely decarburized surface ferrite layers are known [5,9,22,24]. Some equations also take into account the oxidation of the surface [6,9,16,22,24,25].…”

An Approach to Predict the Depth of the Decarburized Ferrite Layer of Spring Steel Based on Measured Temperature History of Material during Cooling

“…The profiles of carbon concentration changes as a function of time and distance (from steel surface to its center direction) during decarburization. 15) In region (c), which is below A 3 (C = C 0 ), austenite in the matrix is transformed into ferrite + austenite or ferrite + cementite, and the decarburized ferrite phase is formed during the decarburization.…”

“…(9) and (10) was calculated by stepwise method suggested by Choi and Zwaag. 15) The stepwise method calculates the depths of scale and decarburized ferrite layer during cooling or heating, based on the model of isothermal heat treatment. The cooling history is divided into discrete isothermal steps, and each decarburized depth and scale thickness are computed at the discrete temperature.…”