Effect of Aluminum Content on the Microstructure and Mechanical Properties of Hypereutectoid Steels

Abstract

Hypereutectoid steels with 0, 0.69, 1.29, and 1.95 wt pct aluminum were prepared. The samples were hot rolled at 1100°C followed by cooling in air. The microstructure of the as-rolled samples was characterized using field emission-scanning electron microscopy (FE-SEM). The electron backscattered diffraction (EBSD) technique was used to identify the grain boundary phases. The steels have a pearlitic microstructure with different amounts of grain boundary cementite. A continuous grain boundary cementite network is present in the 0 wt pct Al steel. Grain boundary cementite formation is completely suppressed in the 1.29 wt pct Al steel. Phase diagram calculations show that aluminum increases the eutectoid temperature. However, the interlamellar spacing and pearlite colony size decrease with increase in aluminum content. Dilatometry measurements show that aluminum addition increases the undercooling below the eutectoid temperature. The yield strength increases with the decrease in interlamellar spacing and colony size. Very high ultimate tensile strengths (1200 to 1400 MPa) and improved elongations to failure (7 to 9 pct) are achieved in the as-rolled condition.

Effects of alloying elements and cooling rates on the high-strength pearlite steels

“…In order to compare the effects of alloying elements and the cooling rates on the interlamellar spacing of pearlite and the mechanical properties between previous studies and this study, Figure 12 shows the relationship between the tensile strength and the values of interlamellar spacing in previous studies [4–6,11,14]. The experimental steels in literatures mainly contain Mn and Si, while the amount of Cr is small or few in pearlite steels.…”

“…While, in this study, the tensile strengths of high-Cr–low-Mn steel are higher than 1500 MPa and the values of interlamellar spacing are thinner than 145 nm, which show an excellent combination between the mechanical properties and microstructures.

Figure 12 The variation of tensile strength of steels versus the interlamellar spacing of pearlite under different compositions and technologies [4–6,11,14].

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“…The higher eutectoid transformation temperature increases the degree of undercooling and then increases the nucleation density of the pearlite colonies, which results in a thinner interlamellar spacing of pearlite. However, the amount of Cr is less in previous studied pearlite steels [4][5][6][7][8]10,11]. In this paper, two pearlite steels containing different contents of Cr and Mn were designed, with the aims of studying the effects of alloying elements of Cr, Mn on the microstructures and mechanical properties of pearlite steel, and developing a highstrength steel with full pearlite microstructure.…”

The Non-Steady State Growth of Pearlite outside the Hultgren Extrapolation

“…This observed partitioning trend is in good agreement with the results reported by other authors [ 10 , 16 ]. On the other hand, in the case of Al-steel, the Al content in cementite is negligible as it could be expected due to its low solubility [ 25 , 26 ]. The concentration of Al in ferrite remains approximately constant and close to the LE values.…”

Microstructure of Hot Rolled 1.0C-1.5Cr Bearing Steel and Subsequent Spheroidization Annealing

“…Daeubler et al [8] reported that finer pearlite interlamellar and finer prior austenite grain size were beneficial to resisting the surface fatigue crack propagation. The work of Taleff et al [9] and Jang et al [10] indicated the decrease of both pearlite interlamellar spacing and pearlite colony size would increase the tensile strength. It should be noted that the bearing steels need to be subjected to heat treatments after hot rolling.…”