International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 04 Issue: 03 | Mar -2017
p-ISSN: 2395-0072
www.irjet.net
EFFECT OF TEMPERING PROCESS ON HYDROGEN DELAYED FRACTURE SUSCEPTIBILITY OF 4140 STEEL FASTENER Kalpana K1, Usha S2 1PG
Scholar, Department of Mechanical Engineering, Government college of Technology, Tamilnadu, India Professor, Department of Mechanical Engineering, Government College of Technology, Tamilnadu, India
2Assistant
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Abstract - Delayed fracture is a phenomenon that
residual stress. Hydrogen embrittlement susceptibility of martensitic steel decreases with the increase of the tempering temperature. hydrogen delayed fracture can be identified by intergranular fracture. An Intergranular fracture is a fracture that follows the grains of the material, where cracks that take place along the grain boundary.[3,4]. Susceptibility of steel to hydrogen embrittlement varies with composition, microstructure, and strength level. A354 BD rods are generally made from AISI 4140, a medium-carbon, low alloy steel that is heat treated by austenitizing, quenching and tempering to produce a tempered martensite microstructure. The tempering temperature controls the strength of this material. Strength level can be described in terms of yield strength, ultimate tensile strength, or hardness. Generally, as hardness increases, the resistance of AISI 4140 to hydrogen embrittlement decreases.[5]. The present work was done to investigate the effect of tempering process on the hydrogen –delayed fracture susceptibility of AISI 4140 steel fastener by using HCL solution.
happens due to the nascent hydrogen attacks at the grain boundaries of the metal slowly and makes the metal weaker thereby prone for fracture initiation. This can also be referred as hydrogen embrittlement. The susceptibility of Hydrogen delayed fracture of 4140 steel fastener has been studied with the influence of tempering temperature by means of hydrogen delayed tests. In order to solve the delayed fracture phenomenon of the steel fastener, the chamber electric furnace was used to carry out the tempering test. The specimen is machined as per ASTM standard for conducting the tensile test and it is immersed in a Hydrochloric acid for steel for the diffusion of hydrogen. The influence of various tempering temperatures on the hardness and tensile strength of steel fastener is analyzed. Fracture modes were investigated with the use of a scanning electron microscope (SEM). The results show that the performance of steel is most excellent when the tempering temperature is around 450°C to 480°C.
Table -1 Chemical composition of AISI 4140 steel fastener
Key Words: delayed fracture; tempering; hydrogen embrittlement, constant load test microstructure. 1.INTRODUCTION
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Impact Factor value: 5.181
C
Mn
Cr
P
S
Wt %
0.35-0.45
0.5-0.8
0.9-1.5
0.04
0.03
Table- 2 Heat treatment of experimental material
Delayed fracture generally comes under brittle fracture. High strength steels are usually mixed with hydrogen during smelting, processing and using. Generally, hydrogen which enters steel is extremely harmful. For many materials, even a trace of hydrogen can induce delay fracture through diffusion and enrichment. Hence the diffusion and enrichment of hydrogen in metals is the premise and bridge for delay fracture. Delayed fracture of high strength steel is mainly because the intrusion of the hydrogen in the steel, which is characterized by brittle, intergranular fracture, so the starting point of improving the delayed fracture performance is to improve the effectiveness of hydrogen trapping in the steel, reduce the concentration of diffusible hydrogen in the matrix and increase the grain boundary binding strength.[1,2]. Hydrogen embrittlement is a permanent loss of ductility in a metal caused by hydrogen in combination with stress, either externally applied or internal
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AISI 4140
No .of samples 1
350°C* 30min air cooling
2
400°C* 30min air cooling
3 4
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Heat treatment system
850°C * 30 min, water cooling
450°C* 30min air cooling 520°C* 30min air cooling
ISO 9001:2008 Certified Journal
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