Effect of Velocity of Impact on Mechanical Properties and Microstructure of Medium Carbon Steel during Quenching Operations

Joseph Babalola Agboola,Edeki Mudiare,Michael Bolaji Adeyemi,Oladiran Abubakre Kamardeen

doi:10.4236/eng.2015.77039

Abstract

Theoretical analysis of the effects of velocity of impact using suitable heat transfer equations expressed in forms of finite difference method was developed and used to determine their effects on the characteristic cooling parameters during quenching process. Various velocities of impact obtained by varying the heights of specimen drops were also used to experimentally determine their effects on characteristic cooling parameters and mechanical properties of medium carbon steel using water as the quenching medium. At height of drop of 0.5 m, 1.0 m, 1.5 m, and 2.0 m, the tensile strength of the material is 410.4, 496.12, 530.56, and 560.40 N/mm2 respectively. The corresponding hardness values are 42.4, 45.2, 46.2, 50.5 HRC respectively. It is found that as the velocity of impact increases, maximum cooling rate increases. Hardness and ultimate tensile strength also increase. There are good agreements between theoretical and experimentally determined values of critical cooling parameters of water during quenching operations.

Highlights

Quenching of steel involves heating a part above upper critical temperature to austenitizing temperature and holding at this temperature for a specified soaking time followed by intense cooling in a suitable quenching medium to transform it into the hard structure—martensite
The nucleate boiling stage begins during which the vapour film collapses and cool quenchant comes into contact with the hot metal surface resulting in violent boiling and high extraction rates
The experimental investigation was conducted using a standard probe made of a cylindrical medium carbon steel specimen of 12.5 mm diameter × 60 mm long

Summary

Introduction

Quenching of steel involves heating a part above upper critical temperature to austenitizing temperature and holding at this temperature for a specified soaking time followed by intense cooling in a suitable quenching medium to transform it into the hard structure—martensite. This is generally achieved by cooling at a sufficiently. The first stage of cooling is characterized by the formation of a vapour film around the component This is a period of relatively slow cooling during which heat transfer occurs by radiation and conduction through the vapor blanket. The duration of the vapour phase and the temperature at which the maximum cooling rate occurs have a critical influence on the ability of the steel to harden fully [2]

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Discussion

Conclusion