Effect of Heat Treatment on Microstructure and Mechanical Properties of NF6357A Cast Alloy for Wear Resistance Application
Affiliation(s)
Department of Metallurgical and Materials Engineering, University of Lagos Akoka, Yaba,Lagos, Nigeria. Department of Metallurgical and Materials Engineering, Ahmadu Bello University, Zaria,Nigeria.
Department of Metallurgical and Materials Engineering, University of Lagos Akoka, Yaba,Lagos, Nigeria. Department of Metallurgical and Materials Engineering, Ahmadu Bello University, Zaria,Nigeria.
ABSTRACT
The solidification structure of the as-cast consists of the matrix structure that is predominantly austenite and precipitated chromium carbide along the grain boundary. Under these circumstances and where the level of impact is relatively modest, such alloys in as-cast condition will perform. However, at higher levels of impact energy, a point is reached where excessive stress are built up within the component and eventually the materials strength is exceeded and the outcome is complete failure in a characteristic stress fracture mode. If this is to be prevented, it is therefore imperative that the casting be subjected to appropriate heat treatment, to obtain a structure which consist of Cr7C3 carbide and martensite at a hardness range of 650-750HB. The microstructure of NF6357A cast chromium steel containing 2.59% C- 0.7%Si-0.91%Mn-18.54%Cr-0.019%P-0.01%S- balance–Fe after appropriate heat treatment such as quenching and tempering process have been characterised by means of optical microscope, micro hardness tester, optical emission spectrometer and charpy testing machine. The results show that oil quenched samples were found to retained microstructural consistency for casting thicker than 120mm section. For economic argument, air quenched castings of less than 120mm thickness is not only cheaper alternative, but it is also environment friendly. The fracture toughness was found to be fairly consistent between 2.4-2.6%C range. However, at higher carbon level, the fracture process is dominated by the presence of segregated carbide network which act as a weak link in the microstructure. This weak link encourages dislocation pile-up and impaired material toughness.
The solidification structure of the as-cast consists of the matrix structure that is predominantly austenite and precipitated chromium carbide along the grain boundary. Under these circumstances and where the level of impact is relatively modest, such alloys in as-cast condition will perform. However, at higher levels of impact energy, a point is reached where excessive stress are built up within the component and eventually the materials strength is exceeded and the outcome is complete failure in a characteristic stress fracture mode. If this is to be prevented, it is therefore imperative that the casting be subjected to appropriate heat treatment, to obtain a structure which consist of Cr7C3 carbide and martensite at a hardness range of 650-750HB. The microstructure of NF6357A cast chromium steel containing 2.59% C- 0.7%Si-0.91%Mn-18.54%Cr-0.019%P-0.01%S- balance–Fe after appropriate heat treatment such as quenching and tempering process have been characterised by means of optical microscope, micro hardness tester, optical emission spectrometer and charpy testing machine. The results show that oil quenched samples were found to retained microstructural consistency for casting thicker than 120mm section. For economic argument, air quenched castings of less than 120mm thickness is not only cheaper alternative, but it is also environment friendly. The fracture toughness was found to be fairly consistent between 2.4-2.6%C range. However, at higher carbon level, the fracture process is dominated by the presence of segregated carbide network which act as a weak link in the microstructure. This weak link encourages dislocation pile-up and impaired material toughness.
Cite this paper
J. Agunsoye, V. Aigbodion and O. Sanni, "Effect of Heat Treatment on Microstructure and Mechanical Properties of NF6357A Cast Alloy for Wear Resistance Application," Journal of Minerals and Materials Characterization and Engineering, Vol. 10 No. 11, 2011, pp. 1077-1086. doi: 10.4236/jmmce.2011.1011082.
J. Agunsoye, V. Aigbodion and O. Sanni, "Effect of Heat Treatment on Microstructure and Mechanical Properties of NF6357A Cast Alloy for Wear Resistance Application," Journal of Minerals and Materials Characterization and Engineering, Vol. 10 No. 11, 2011, pp. 1077-1086. doi: 10.4236/jmmce.2011.1011082.
References
[1] Zhang MX, Kelly PM, Gates JD, Journal of materials science, Vol 36 ,No16, 3865-3875. 2001 [2] John Udodua, Quality Control Report Nigerian Foundry Limited. Vol 2, No 6, 20-21, July 1996. [3] Mhasshimoto Int. Conf. on ‘’Abrasion Wear Resistance alloyed White Cast Iron for rolling and pulverising Mills’’ Fukuoka Japan, August 16-20, 2002 yesu hiro matsubara 195-206. [4] A. Sinatra: Int Conf on ‘’Abrasion Wear Resistance alloyed White Cast Iron for rolling and pulverising Mills’’ Fukuoka Japan, August 16-20, 2002 yesuhiro matsubara 23-31. [5] G. Laird: AFS Trans, 1991, 99. 339-357 [6] Kogi Y. Matsubara and K .Matsuda: AFS Trans 1981, 89, 197-294
[1] Zhang MX, Kelly PM, Gates JD, Journal of materials science, Vol 36 ,No16, 3865-3875. 2001 [2] John Udodua, Quality Control Report Nigerian Foundry Limited. Vol 2, No 6, 20-21, July 1996. [3] Mhasshimoto Int. Conf. on ‘’Abrasion Wear Resistance alloyed White Cast Iron for rolling and pulverising Mills’’ Fukuoka Japan, August 16-20, 2002 yesu hiro matsubara 195-206. [4] A. Sinatra: Int Conf on ‘’Abrasion Wear Resistance alloyed White Cast Iron for rolling and pulverising Mills’’ Fukuoka Japan, August 16-20, 2002 yesuhiro matsubara 23-31. [5] G. Laird: AFS Trans, 1991, 99. 339-357 [6] Kogi Y. Matsubara and K .Matsuda: AFS Trans 1981, 89, 197-294