Yogesh Mahajan Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 6( Version 1), June 2014, pp.44-47 www.ijera.com 44 | Page Failure Analysis of 9%Cr-Mo Steel Component Yogesh Mahajan, D. R. Peshwe Department of Metallurgical and Materials Engineering, Visvesvaraya National Institute of Technology, Nagpur, Maharashtra, India. ABSTRACT This paper presents the fractographic characterization of 9%Cr-Mo Steel which was failed during service in fossil fuel fire stream power plant. The fractured surfaces as well as the surface of the failed component were examined by visual examination and in a scanning electron microscope at suitable magnification. The energy dispersive spectroscopy was performed to analyze the steel quality. EDS analysis has indicated the poor quality of steel used for manufacturing component. From the characteristics of the fractured surface it is concluded that it is a tension overload failure. Keywords – EDS analysis, Fracture, Inclusion, 9%Cr-Mo steel, Torsion I. INTRODUCTION The quality of steel is the key requirement in any thermal power plant. It becomes more critical in fossil fuel fired steam power plant because of the stringent operating conditions and emission norms. These issues are usually tackled by increasing thermal efficiencies of power generating plants. Fuel can be conserved and hence less fuel is required for a given power output. This subsequently lower fuel consumption and hence lower emissions of environmentally damaging gases. Increase in the thermal efficiency of a power plant can be most effectively achieved by increasing the temperature and to a lesser extent, the pressure of the steam entering the turbine. High steam temperature along with the high pressure makes the high quality steel grades for the boiler operations. Most modern steam power stations now in operation reach efficiencies of around 42% with steam temperatures of 600 0 C and pressures of 25–30 MPa. The next generation of steam power plants should be capable of operating with steam at 625–650C, to enable thermal efficiencies of around 45% to be achieved [1]. Hence, the increasing operating temperatures and pressures impose increasingly stringent requirements on the materials of construction. The increase in the thermal efficiency has provided the incentive for the development of the 9% chromium steels. Many reports are published on investigation of the properties of 9% Cr steel with respect to its application as a pipe work and boiler steel operating at elevated temperatures [2]. These steel provide improved creep rupture strength. The alloying additions such as chromium, molybdenum, tungsten, vanadium, niobium, etc enhance the properties required for high temperature applications. Chromium improves high temperature strength and increases oxidation resistance. Molybdenum increases the creep resistance. Presence of Nickel and Manganese in smaller quantities increases hardenability of the steel. Three such 9-12% Cr martensitic steels which are mostly used are ASTM Grades- P91 (9Cr-1Mo-V-Nb), E911 (9Cr-1Mo-1W- V-Nb) and P92 (9Cr-0.5Mo-1.8W-V-Nb) [3]. The chemical composition of these steel as per ASTM A335 is given in table-1. Table-1 Chemical Composition of mostly used Cr- Mo Steel grades (As per ASTM A335) Element Composition Grade P91 Grade P92 Grade E911 C 0.08-0.12 0.07-0.13 0.090-0.30 Si 0.20-0.50 Max 0.50 0.10-0.50 Mn 0.30-0.60 0.30-0.60 0.3-0.6 P Max 0.020 Max 0.020 Max 0.020 S Max 0.010 Max 0.010 Max 0.010 Cr 8.00-9.50 8.50-9.50 8.50-10.50 Ni Max 0.40 Max 0.40 Max 0.40 Mo 0.85-1.05 0.30-0.60 0.9-1.10 V 0.18-0.25 0.15-0.25 0.18-0.25 N 0.03-0.07 0.03-0.07 0.04-0.09 Nb 0.06-0.10 0.04-0.09 0.06-0.10 Al Max 0.02 Max 0.02 Max 0.04 Ti Max 0.01 Max 0.01 Max 0.01 W ---- 1.50-2.00 0.90-1.10 B ---- 0.001- 0.006 0.0003- 0.0060 Other% ---- Zr Max 0.01 ---- Component fails due to many reasons and failure that commonly occur in service depending upon their possible modes of failure are Overload, Distortion, Fatigue, Corrosion, Wear etc. Every structure has a load limit beyond which it is RESEARCH ARTICLE OPEN ACCESS