Influence of Tempering in Different Melting Routes on Toughness Behavior of AISI 4340 Steel
- PDF / 6,050,511 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 0 Downloads / 246 Views
JMEPEG https://doi.org/10.1007/s11665-020-05164-3
Influence of Tempering in Different Melting Routes on Toughness Behavior of AISI 4340 Steel M. Manokaran, Abhishek S. Kashinath, Jyoti S. Jha
, Suraj P. Toppo, and Rajkumar P. Singh
(Submitted August 7, 2020; in revised form September 11, 2020; Accepted: 22 September 2020) Martensitic microstructure of AISI 4340 steel can be heat treated to achieve the desired mechanical properties. However, mechanical properties degrade owing to the impurities and cleanliness during the steel production. In this work, AISI 4340 steel was produced through three different routes, such as vacuum degassing (VD), electro slag remelting (ESR), and vacuum arc remelting (VAR), followed by austenizing, hardening, and tempering. Further, mechanical characterization such as tensile, hardness, and toughness were carried out in a wide range of tempering temperatures (171-649 °C). A variation in mechanical properties was observed due to the evolution of precipitated carbide with the tempering temperature in all three routes. A thicker carbide layer along the martensitic lath boundary led to higher embrittlement in VD and VAR for tempering regime 171-427 °C. The absence or lesser embrittlement in ESR attributes to the homogeneously distributed fragmented carbides. Martensitic lath coarsening, ferritic phase formation along with the precipitated carbide distribution, significantly enhances the fracture toughness over the impact toughness at higher tempering temperature (> 316 °C). The difference in the mechanical properties in all the three routes is found to be sensitive toward the chemical composition causing a marked difference in the carbide precipitation and its distribution along the martensitic lath boundaries. Keywords
AISI 4340 steel, embrittlement, melting routes, tempering, toughness
1. Introduction Nickel-chromium-molybdenum alloy steel AISI 4340 is extensively used in aerospace, defense and automotive application due to its high strength and toughness (Ref 1-3). The thermomechanical processing of this steel is well established for various applications, which comprises normalizing, hardening, and tempering (Ref 4, 5). Generally, forging is carried out in the austenitic region, followed by normalizing. In the hardening stage, different rates of cooling determine the microstructure morphology (Ref 6, 7). A very fast rate of cooling yields the martensitic microstructure with a small fraction of retained austenite. However, desirable mechanical properties in AISI 4340 steel can be achieved by optimizing the tempering temperature (Ref 8). Tempering at temperature (< 200 °C) does not cause much martensitic morphology change obtained in the normalizing stage, only the residual stress developed in the previous stage is relieved (Ref 9). On the other hand, at a higher tempering temperature, martensitic laths coarsen, and martensitic to ferritic transformation occur as well. The ferritic phase fraction significantly increases at a tempering temperature above 650 °C (Ref 5). Moreover, during th
Data Loading...
