Effect of residual magnesium content on thermal fatigue cracking behavior of high-silicon spheroidal graphite cast iron
- PDF / 1,523,523 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 70 Downloads / 294 Views
I. INTRODUCTION THERMAL fatigue cracking originates from cyclic thermal stress in a component subjected to repeated heating and cooling. Restated, plastic deformation or crack initiation occurs if the thermal stress attributed to deep temperature gradients exceeds the yield stress of the material. Repetitive thermal cycles enable the cracks to propagate until the component fails. Typical structural components produced by cast irons that incur thermal shock and a heating/cooling cyclic condition are wear plates of slab continuous casting machines, ingot molds, and exhaust manifolds.[1,2,3] These components are periodically operated at a high-temperature range from approximately 500 8C to 970 8C.[3] Spheroidal graphite (SG) cast iron used to be the most promising candidate alloy for these components, owing to its low cost, fair mechanical properties, and good castability. Some reports recognize that the thermal fatigue cracking behavior of SG cast irons may be influenced by factors such as the chemical composition, microstructure of the matrix, and the material properties, including the thermal conductivity, thermal expansion coefficient, Young’s modulus, and tensile strength.[3–7] High-silicon SG cast iron, which has a ferritic matrix in the as-cast condition, is more appropriate for elevated-temperature applications, owing to its better oxidation ¨ resistance and structural stability.[8,9] However, Roehrig[3] indicated that the lower ductility and thermal conductivity of high-silicon SG cast iron may reduce its thermal fatigue resistance. According to Rukadikar and Reddy,[10] cast irons with a higher silicon content have lower thermal conductivity, inducing a larger thermal stress during thermal cyclic C.P. CHENG, Graduate Student, and T.S. LUI and L.H. CHEN, Professors, are with the Department of Materials Science and Engineering, National Cheng Kung University, Tainan, Taiwan 70101, Republic of China. Manuscript submitted August 4, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
conditions. Therefore, the utilization of high-silicon SG cast iron at an elevated temperature might be restricted. Furthermore, our previous investigation indicated that the susceptibility for thermal fatigue cracking of ferritic SG cast iron increases with its silicon content.[11] However, the major factors for the thermal fatigue cracking of high-silicon SG cast iron have not yet been elucidated. According to our previous study,[12] for the high-silicon SG cast iron, MgO inclusions generally cluster in the eutectic cell-wall region that solidified last during the solidification process. Weronski[13] observed that the thermal fatigue cracks of a material might be initiated from the grain-boundary sulfide or oxide inclusions, which have different thermal properties from the matrix phase. Therefore, the relation between the extent of MgO inclusions agglomerating in the eutectic cell-wall region and the thermal fatigue cracking behavior of high-silicon SG cast iron must be elucidated. This study explores how MgO inclusions influence the
Data Loading...
