Abstract
From last epoch till to date, AISI 4340 and AISI 4140 have been widely used in different engineering applications. These applications include bolt, screws, gears, drive shafts, crane shaft and piston rods for engines due to its upright mechanical properties, cost-effective and easily available in market. In present work, deep cryogenic treatment effect on the mechanical properties of AISI 4340 and AISI 4140 have been studied. Present work was carried out at laboratory scale and can be extended for mass production. Our work is simple, straight forward safe and economical. In our work, samples were heat treated in simple muffle furnace and followed by cryogenic treatment in liquid nitrogen. Before cryogenic treatment, all samples were normalized at 860°C to obtain homogenized micro structure. Samples were also compared conventionally heat treatment with quenched in oil quenchant. Experimental results showed that after cryogenic treatment with tempering treatment, one could easily increase the tensile strength, impact toughness and hardness. Advanced optical microscopy (IMM 901) and SEM (Scanning Electron Microscopy), FIT Quanta 200 methods have also been deployed to reveal and interpret the internal structure of samples. It was found from micro structure that cryogenic treated sample increases the impact strength, hardness and tensile strength as compared conventional heat treated quenching approaches.
Highlights
From last epoch till to date, AISI 4340 and AISI 4140 have been widely used in different engineering applications
The hardness testing was done with the help of Rockwell hardness testing machine using scale C (HRC)
A magnified view of the center of the specimen as shown in Fig. 8(h) dimple rupture and tearing shows ductile failure mode in medium carbon low alloy steel. This experimental work was conducted to analyze the effect of cryogenic treatment on mechanical properties of AISI 4140 and AISI 4340
Summary
Rom 1930-1940s, to improve the performance of Fcutting tool steels, cryoprocessing was used as the method of conventional heat transfer [1]. The fine precipitation of carbides in martensitic matrix leads to an increase in hardness, impact toughness and tensile strength of medium carbon low alloy steel (i.e. AISI 4340 and AISI 4140) [16]. It was believed that transient carbide called -carbide precipitated from the decomposition of martensite during tempering after deep cryogenic treatment These fine carbide particles enhance the strength and toughness of the martensite matrix and improve wear resistance []. Another claim is based on the strengthening of the material brought about by precipitation of fine carbides because of the cryogenic treatment [14] In this experimental work, the mechanical properties i.e. hardness, tensile strength and impact toughness of medium carbon alloy steel after deep cryogenic treatment are studied [15]. At low temperature processing an increase in carbide formation increases the hardness of medium carbon low alloy steel
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