SSRG International Journal of Material Science and Engineering ( SSRG – IJMSE ) Volume 2 Issue 3 Sep to Dec 2016 ISSN: 2394 - 8884 www.internationaljournalssrg.org Page 6 Use of Hollomon Equation in Combination with Conventional Equation, for Finding Change in strain Hardening Exponent Value, among Differently Aged and Tensile tested Maraging Steel Samples Bineeth Benny #1 # Junior Research Fellow- CARS-DRDL Project , School of Mechanical Engineering VIT University Vellore Bineeth Benny, School of mechanical Engineering, VIT university Vellore,632014 Abstract strain hardening exponent can be found using all the available tensile data such as Tensile strength, 0.2% yield strength and Strain at fracture. And compare the heat treated sample for change in strain hardening exponent. Keywords — Hollomon equation, Strain hardening exponent, Compare aged samples .Calculating the change in length. Fracture toughness from tensile data, Hahn and Rosen field equation. I. INTRODUCTION Maraging steels are high strength and low ductile materials. Usually maraging steels are cold rolled for improving the strength of the product, however maraging steel is poor in responding to cold work and it is evident from literature available [1] thus maraging steels are aged after cold working to improve the strength. Strain hardening exponent (n) declares the amount of cold work done. If Value nears zero it shows that the material is perfectly plastic and a value one shows that the material is perfectly elastic. II. JUSTIFICATION FOR COMBININGHOLLOMON EQUATION AND CONVENTIONAL EQUATION WHICH CORRELATES STRAIN HARDENINGEXPONENT AND THE STRENGTH COEFFICIENT WITH THE YIELD STRESS-STRAIN Cold-rolled maraging steel will have certain amount of strain hardening and aging will definitely introduce retained austenite which may give Transformation induced plasticity. By combining Hollomon equation with conventional equation for finding, strain hardening exponent (n) we stand a chance of finding accurate value with high accuracy in terms of material property difference. Hollomon Equation The true strain to necking, ε n , in a uniaxial tensile test provides a valuable measure of the stretch formability of a material (1) – the stretch formability increasing with increasing ε n and it is expressed as. [2] (σ) = K . n - (1) n - Strain hardening exponent K-Strength coefficient (MPa) -True strain at fracture (σ)-True stress at fracture (MPa)  = ln (L/Lo) L - Gauge length after tensile testing. Lo - Original gauge length before tensile testing. (σ) = σN .(1+ N) (MPa) σN = Normal stress at fracture (MPa) N = Normal strain at fracture III. CONVENTIONAL RELATIONSHIP CORRELATING THE STRAIN HARDENING EXPONENT WITH THE 0.2% YIELD STRESS [3] (σ0.2) = K. (0.002) n - (2) n - Strain hardening exponent K-Strength coefficient (σ 0.2 ) - 0.2% Yield strength COMBINING EQUATION (1) AND (2) (σ) = K . n (1) (σ0.2) = K. (0.002) n (2) Equation (1) can be written as (taking natural log) ln(σ) = ln K +n. ln() ( 3) Same way Equation (2) can be written ln(σ0.2) = lnK+ n.ln(0.002) ( 4)