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

Abstract

Effects of temperature and oxygen concentration on decarburization of 55SiCr spring steel were investigated at the temperature range of 500°C-1 200°C by using a Muffle furnace (an atmosphere of ambient air) and a Simultaneous Thermal Analyzer (low oxygen concentration with 2% O2 and 98% N2). In ambient air, the decarburization behavior can be divided roughly into five temperature ranges: T≥1 200°C, no decarburization; TG (A3 for 55SiCr when its carbon concentration equals to zero)<T<1 200°C, partial decarburization; A3<T<TG, complete and partial decarburization; T<A3, complete decarburization; T<A1, no decarburization. However, it is observed that complete decarburization did not occur in all the testing temperature ranges under low oxygen concentration. For 55SiCr spring steel, decarburization behavior under low oxygen concentration can be divided into two regions: T<700°C, no decarburization; T>700°C, only partial decarburization. Lower oxygen concentration results in decrease in a growth rate of the oxide scale and leads to different characteristics of decarburization.KEY WORDS: 55SiCr spring steel; complete decarburization; partial decarburization; oxygen concentration; growth rate of oxide scale.

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

“…Their thickness was larger than 1.0 mm, which is comparable to the calculated results (Figure 3). A comparison of the calculated results with the experimental-analytical results of the oxidation of steel 55SiCr with 1.51 wt % Si and 0.70 wt % Cr [8] shows that the 55SiCr steel oxidizes more slowly than the C45 steel [(a) T a = 750 • C, t a = 1 h, steel 55SiCr: measured d ox = 30 µm, result calculated with Equation (1) , which is certainly a consequence of the higher content of silicon and the added chromium. Our calculated results are comparable with the measured thicknesses of the oxide layer on carbon steel with the carbon content C = 0.76 wt % (defined as base composition in [4].…”

“…Visible decarburization depends on the oxidation potential of the annealing atmosphere, which also determines the degree of oxidation of the surface. This is the reason for the great differences in the visible decarburization that occurs when annealing in air or, e.g., in a mixture of N2 + 2% O2 [8]. Visible decarburization is always larger when annealing in atmospheres with a low oxygen content [8,10].…”

“…Both strong oxidation and decarburization of the steel's surface occur when annealing at these temperatures in an oxidizing atmosphere [3][4][5][6][7][8][9]. The decarburization occurs as the steel shifts towards the thermodynamic equilibrium between itself and the atmosphere, but in an oxidizing atmosphere this equilibrium cannot be achieved.…”

“…In practice, it is not necessary that all the mentioned microstructures will be visible after cooling. The reason is the velocity of the simultaneous reactions of oxidation and decarburization of the surface at the annealing temperature [5][6][7][8][9][10][11]. If the oxidation lags behind the complete decarburization then there is a reduced, completely decarburized layer as well as a whole, partially decarburized layer visible after cooling.…”

Effect of Top Slag with Low Basicity on Transformation Control of Inclusions in Spring Steel Deoxidized by Si and Mn

“…It has been proven that nonmetallic inclusions as crack initiation have a great effect on the in-service life of spring wire. [1][2][3] As a result, inclusions with small size, little quantity, and good plasticity are preferred. Some researches indicate that the major factor influencing the plastic deformation of inclusions is the melting point, which has a close relationship with the chemical composition.…”