Effect of Alloy Composition on Carburizing Performance of Steel
- PDF / 377,981 Bytes
- 7 Pages / 593.972 x 792 pts Page_size
- 73 Downloads / 222 Views
Basic and Applied Research: Section I
Effect of Alloy Composition on Carburizing Performance of Steel Olga K. Rowan and Richard D. Sisson Jr.
(Submitted July 27, 2008; in revised form February 4, 2009) This paper investigates the effect of alloy composition on the gas carburizing performance of AISI 1018, 4820, 5120, and 8620 steels. The mass-transfer coefficients and carbon diffusivities were calculated from experimental measurements using direct flux integration. Although steels with high concentration of austenite-stabilizing elements (Si, Ni) increased carbon diffusivity in austenite, they significantly reduced the kinetics of carbon transfer from the atmosphere to the steel surface and resulted in lower weight gain. Despite lowering the carbon diffusivities, steels alloyed with carbide-forming elements (Cr, Mo) significantly increased the mass-transfer coefficient in the atmosphere and enhanced the rate of carbon profile evolution. The experimentally determined carbon diffusivities were in good agreement with the carbon diffusivities obtained from the thermodynamic and kinetic databases in DICTRA. Overall, using the concentration dependent mass-transfer coefficient and carbon diffusivity in various alloy steels helped explain the experimentally observed variations in the carbon concentration profiles and the effective case depths. Recommendations are made to help achieve better case depth uniformity within a carburizing workload.
Keywords
carbon activity, carbon diffusivity, gas carburizing, kinetics, mass-transfer coefficient, modeling
1. Introduction Gas carburizing is an important heat treatment process used for surface hardening of automotive and aerospace steel components. Despite its worldwide application, the process faces certain challenges in the process control and case depth variability. Carburizing performance of steel is influenced by the furnace design, the process parameters (i.e., gas atmosphere composition, carburizing temperature, and time), and by the steel composition. Considerable research has been done to investigate the effect of these process parameters on the carburizing performance. In practice, however, even with a well-controlled process, some variation in the effective case depth and surface carbon concentration are observed that remain unresolved. Therefore, the goal of this work is to develop a better understanding of the effect of steel composition on the kinetics of carbon transfer during the process and on the overall carburizing performance of steel. Specifically, the objective is to qualitatively and quantitatively investigate the contribution of the major alloying elements on the mass-transfer
Olga K. Rowan, Caterpillar, Inc., Technical Center, Mossville, IL, USA; Richard D. Sisson, Jr., Center for Heat Treating Excellence, Materials Science and Engineering, Worcester Polytechnic Institute, 100 Institute Road, Worcester, MA 01609, USA. Contact e-mails: [email protected] and [email protected].
coefficient in the gas atmosphere and on the carbon diffusivity in austenite. T
Data Loading...
