Effect of Alloy Composition on Carburizing Performance of Steel (original) (raw)
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A model for carbon transfer in gas-phase carburization of steel
Journal of Heat Treating, 1980
Studies using 1010 steel shimstock in a controlled atmosphere tubular furnace have allowed rate constants to be determined for a number of important carburizing and decarburizing reactions. Carburizing data obtained in a small commercial furnace confirm that the combination of CO and H2 to form C and H2O is the major carbon transfer reaction to the parts in a typical furnace system. The hydrocarbon injected in the furnace for enrichment deposits carbon on the heating surfaces initially as a result of catalytic cracking reactions. Due to the temperature differential between heating surfaces and parts, the CO-H2 reaction acts as a “carbon pump” in transferring this carbon to the reactive surface of the parts to be carburized. Carbon control by monitoring the concentration of CO and CO2 or CO, H2, and H2O is most efficient in the later stages of a typical furnace cycle as the carbon concentration at the surface of the parts approaches the carbon potential in the gas phase.
Gas carburization of low alloy steels
1988
Metallurgical Engineering, BUET for his valuable suggestions, inspiring guidance and constant encouragement in all stages of the projects as well as in preparing this thesis. .The author is very much grateful and expresses his profound gratitude to Dr. Md. Serajul Islam, Prof. and Head, Dept. of Metallurgical Engineering for his kind help at various stages of this research work particularly in the design and construction of the gas fired gas carburizing furnace with automatic control system and for the many helpful discussions he had with him. The author is very much indepted to Prof. M. Ibrahim for his inspiration and for the many helpful discussions he had with him.
Surface Engineering of Steels: Understanding Carburizing
2017
CARBURIZING IS THE ADDITION OF CARBON TO THE SURFACE of low carbon steels. It is generally accomplished at temperatures between 850 1000°C. Once quenched, the high-carbon surface layer yields a high hardness martensitic case with excellent wear and fatigue resistance [1]. This carburized case surrounds the tough, low carbon steel core. The case hardness is primarily a function of the carbon content. There is little advantage increasing the carbon content beyond 0.65% to increase hardness. Higher carbon content can increase microstructural properties such as wear, sliding contact fatigue, and rolling contact fatigue [2]. Too high carbon content can result in excessive carbide networks or massive carbides. The case depth is a function of time temperature and chemistry, of the process, and the available carbon (carbon potential) at the surface of the steel. This follows Fick’s Second Law of Diffusion for the concentration of a diffusing species as a function of time, t, and position C(...
Non-steady state carburisation of martensitic 9–12%Cr steels in CO2 rich gases at 550°C
Corrosion Science, 2014
Two martensitic steels were reacted with Ar-50%CO 2 at 550°C for exposure times up to 150 h. Microstructural analyses and glow discharge optical emission spectroscopy revealed that internal carburisation of both steels beneath external oxide scales occurred, in spite of the very low equilibrium carbon activity of the atmosphere. The carbon concentration at the metal-scale interface increased throughout the reaction and the carbon uptake varied approximately linear with time. A model is proposed to describe the non steady-state carburisation kinetics whereby the usual diffusion equation describing carbon movement into the alloy is modified to account for loss of carbon as precipitated carbides.
Mathematical modeling of a carburizing process of a SAE 8620H steel
Surface and Coatings Technology, 1999
Pack carburizing experiments have been conducted employing samples of an SAE 8620H steel. Three different carburizing mixtures have been used, each with a different content of carbonate, added to a metallurgical coke as catalyst. The change in carbon concentration along the case depth has been determined quantitatively by means of chemical analysis conducted at every 0.1 mm from the outer surface of the workpiece. It has been shown that the carbon concentration profile can be satisfactorily modeled employing the classical solution derived from Fick's second law. For this purpose, a two-step optimization procedure has been developed in order to compute, as a first step, the optimum values of the activation parameters (activation energy for diffusion and the diffusivity coefficient) of carbon in austenite, as well as the carbon potential that is established at the surface of the carburizing specimen under different processing conditions. The second step of the algorithm involves the re-computation of the carbon potential at the surface, once the activation parameters are assumed to be constant. In general, it has been observed that the addition of carbonates (BaCO 3 and NaCO 3 ) to the metallurgical coke gives rise to an increase in the carburization rate and case depth which allows the achievement of the required carbon concentration profiles more efficiently. High carburization temperatures are observed to give rise to undesired acicular structures in the workpiece at low temperatures, due to the austenite grain growth during the carburizing processing.
The simulation of carburization profiles for online computer aided control of carburizing processes and offline case hardening engineering represent the most important technical application of carbon diffusion coefficients in austenite. The question of whether substitutional alloying elements such as Cr, Mn, Mo, Ni or Si, at low concentrations around 1 wt.% typical of the used steels influence the diffusivity considerably, is increasingly raised recently. In the present paper, the materials science tool SimCarb Diffusivity is introduced as one module of the stand-alone SimCarb program package for the numerical simulation of case hardening. The Windows expert software suite comprises the process steps of carburizing, quenching and tempering. The new program SimCarb Diffusivity calculates alloy dependent diffusion coefficients of carbon in the austenite of, e.g., case hardening steels for SimCarb simulations. The implemented physically based model is described in detail. A numerical process study indicates a crucial alloy related effect of the diffusivity on the resulting carburization and hardness profiles, even within the specification of individual steel grades. Carburizing experiments on 18NiCrMo14-6 and 15NiCr13 are evaluated. The carbon distributions are measured by secondary ion mass spectroscopy. Strong evidence is found that the diffusion coefficient of carbon in austenite depends significantly on the steel composition, which should be taken into account in the process control of carburizing.
Metallurgical concepts for optimized processing and properties of carburizing steel
Advances in Manufacturing, 2016
Carburized steel grades are widely used in applications where high surface near hardness is required in combination with good core toughness as well as high strength and fatigue resistance. The process of carburizing lower to medium carbon containing steel can generally provide this combination of properties and has been practiced for several decades. Such steel is essential in the vehicle power-train, machines and power generation equipment. However, the increasing performance demands by such applications as well as economical considerations forced steel producers to develop better alloys and fabricators to design more efficient manufacturing processes. The present paper describes recent concepts for alloy design optimization of carburizing steel and demonstrates the forthcoming beneficial consequences with regard to manufacturing processes and final properties. Keywords High temperature carburizing Á Grain size control Á Distortion control Á Integrated manufacturing Á Plasma nitriding Á Micro pitting Á Tooth root fatigue strength Á Molybdenum steel Á Niobium microalloying
Study on Upgradation in Carburizing Technologies for steel strength
Journal of Applied and Emerging Sciences, 2019
Carburizing technologies are used to provide strength on low quality metals. This technology is being developing with novel improvements significantly. The carburizing process consists of, first releasing Carbon mono-oxide from charcoal material and then transfers carbon to raw metal. There are favorable upgradation in these technologies from researchers which have a paramount industrial importance. In Vacuum gas carburizing, the steel metal is carburized with (Acetylene and Propane) gases. These gases are at low pressure and high temperature. The results show that the metal is 1.5 times harder than its raw form. There are also used mathematical models to validate the results. It used gas and solid phases for validation. In pulse carburizing, carbon diffusion on steel is investigated with heat treatment. This process includes several carburizing stages. This process is based on Darken bi velocity and drift velocity. It accounts to demonstrate the kinetics of carbon transfer on steel...
Industrial Engineering Journal, 2018
Gas carburization has been used in order to improve mechanical properties of steel surface hardening in engineering industries. In this investigation optimization of gas carburization process parameters for wear resistance on AISI 1020 low carbon steel has been done by using Taguchi approach. 4 Design of experiments is done on the basis of an orthogonal array L9 (3). Nine experiments are performed on the basis of L9 Taguchi approach by using various process parameters like carburizing temperature, soaking time, tempering temperature and temperature time. Signal to noise (S/N) ratios, MEAN ratio Taguchi analysis is performed in order to obtain response variable like wear rate. It is observed during investigation that heat treatment is followed by quenching and tempering tremendously improves wear resistance of AISI 1020. In order to predict optimal parameter, confirmation test is conducted for implementation of L9 Taguchi approach. This study concludes that wear resistance has been improved after the gas carburization process.
The Effects of Rust on the Gas Carburization of AISI 8620 Steel
The effects of rust on the carburization behavior of AISI 8620 steel have been experimentally investigated. AISI 8620 steel samples were subjected to a humid environment for time of 1 day to 30 days. After the exposure, a part of the samples was cleaned by acid cleaning. Both cleaned and non-cleaned samples have been carburized, followed by quenching in mineral oil, and then tempered. To determine the effect of rust on gas carburizing, weight gained by the parts and the surface hardness were measured. Surface carbon concentration was also measured using mass spectrometry. Carbon flux and mass transfer coefficient have been calculated. The results show that acid cleaning removes the rust layer effectively. Acid cleaned samples displayed the same response to carburization as clean parts. Rusted parts had a lower carbon uptake as well as lower surface carbon concentration. The surface hardness (Rc) did not show a significant difference between the heavily rusted sample and clean sample. It has been observed that the carbon flux and mass transfer coefficient are smaller due to rust layer for the heavily rusted samples. These results are discussed in terms of the effects of carbon mass transfer on the steel surface and the resulting mass transfer coefficient.