Vacuum Carburizing in a Pit Furnace: A 21st Century Solution to Large Component Case Hardening

Low pressure carburizing (LPC) is a proven, robust case hardening process whose potential is only limited by the style and size of vacuum furnace. Today, LPC is typically used in horizontal vacuum furnaces where the opportunity to carburize large parts is limited. In this paper we present a new adaptation of the technology in large pit type vacuum furnaces, capable of opening to air at elevated temperature. This underscores the potential of LPC to carburize larger, more massive parts in a clean, effective and efficient process. The result is quality casehardened parts without the undesirable side effects of atmosphere gas carburizing such as the use of a flammable atmosphere, reduced CO and NOx emissions, no intergranular oxidation, and limited retort life. Another significant advantage is decreased process time. The case study presented here shows that eliminating furnace conditioning and increasing process temperature can significantly reduce cycle durations by nearly three times and cut utility costs in half. Under these conditions, a return on investment (ROI) is in the neighborhood of 1 – 2 years is possible, making LPC in a pit style furnace a cost-effective solution than traditional atmosphere gas carburizing technologies.

Factors Affecting the Hardness Characteristics of Microstructures in Gas Carburized Chromium Alloy Steels

We analyzed the factors affecting the gas carburizing microstructure of parts for constant velocity joints. Gas carburizing 0.15-0.20C1.13-1.14Cr chromium alloy steel used in automobile drive units is characterized by changing the properties of the carburizing layer in the depth direction. The experimental conditions were set to enable field application. The components of the specimen to be used for gas carburization were analyzed by X-ray fluorescence. Changes in the mechanical properties of the carburized layer were analyzed by micro-hardness, microstructure, and carburizing content. The gas carburization cycle was selected based on the simulation results. The characteristics change before and after carburization of two samples with different carbon and chromium content were analyzed. The carburization temperature that can be used for manufacturing automobile parts was 930°C, the carbon potential required for carburization was 0.90wt%, and the carbon potential required for diffusion was 0.75wt%. The inner and outer hardness values of the carburized layer satisfying the effective hardening depth of 550Hv were 400Hv-740Hv. In the case of 0.20C alloy steel, the effective hardening depth with a carburizing amount of 0.36wt% and a hardness of 550Hv was 1.467 mm. also in the case of 0.15C steel, its effective hardening depth was 0.746 mm. The simulation results for selecting the carburizing heat treatment conditions and the carbon change in the carburizing layer showed a similar trend. The carburizing structure related to hardness change was martensite. As a result of EPMA, SEM, and XRD analysis, the amount of carburized and the amount of martensite structure correlated, and the martensite increased as the amount of carburized increasing. As a result of EPMA analysis, the smaller the carburizing content the greater the depth of carburization. We intend to proceed with optimization conditions for mass production in connection with wear resistance and fatigue. It is expected that these results will contribute to the improvement of durability of automobile driving parts.

Study on Upgradation in Carburizing Technologies for steel strength

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 surface. This design is very useful by regarding carburizing time for this process design. In Plasma carburizing, the mixtures of gases are used to harden the steel. The carburizing temperature was varied in cementite and martensitic. The favorable results show that these specimens have (Lower surface roughness, higher surface hardness and Low wear rate). It is a most novel diffusion controlled novel process till the present time. The carburized metal is used in industry by including (Turbine gears and Air craft engine). Henceforth, It is of great importance to study the carburizing technologies for providing better strength on metal.

The Effect of Surface Self-Nanocrystallization on Low-Temperature Gas Carburization for AISI 316L Steel

In this work, the effect of surface self-nanocrystallization on low-temperature gas carburizing for AISI316L austenitic stainless steel has been studied. The surface ultrasonic rolling processing (SURP) was used to prepare nanostructured surface layers, and then the un-SURP and SURP samples were treated by LTGC at 470 °C for 10 h, 20 h and 30 h. In order to analyze the effect of surface self-nanocrystallization on low-temperature gas carburizing, optical microscopy (OM), atomic force microscope (AFM), scanning electron probe micro-analyzer (EPMA) and nano-indentation analyzer were used. The results show depth of SURP-induced plastic deformation layer was about 330 μm. Meanwhile, the surface hardness and elastic modulus were increased but the surface roughness decreased obviously after SURP. After low-temperature gas carburizing, according to the results of the thickness, carbon concentration, nano-hardness and elastic modulus of the carburized layer, the conclusion is that surface self-nanocrystallization carried by SURP has a negative effect on the low-temperature gas carburizing for AISI316L austenitic stainless steel and with the increase of carburizing time, the greater the adverse effect on carburizing.

Low-temperature gas carburizing of austenitic X5CrNi18-10 steel activated with a thin iron coating

The study investigated the effectiveness of X5CrNi18-10 stainless steel activation by means of a thin iron coating for low temperature carburizing and the usefulness of the generator endothermic atmosphere for this process. In order to activate the steel surface an iron coating with a thickness of 1–2 µm was applied on it electrolytically electroless. Carburizing was carried out at the temperatures of 450–500oC in the atmospheres based on the generator endothermic atmosphere with the addition of nitrogen or hydrogen. Coating modification by adding a few per cent of sulphur to iron resulted in a reduction of the dispersion of hardness on the surface, and the appearing soot showed a loose connection with the coating. Alternative activation by means of the short-term oxy-nitriding and the following diffusion annealing promoted an increase of hardness on the surface and a reduction of its dispersion after carburizing. After carburizing in endogas of X5CrNi18-10 steel at 470oC during 30 h, a carburized layer with a thickness of approx. 35 μm and the surface hardness of approx. 1150 HV0,05 were obtained. Lowering the carburizing temperature by 20oC resulted in a decrease of the layer thickness by 20% after 24 hours of carburizing. The changes in the thickness of the layer carburized in endogas and the hardness on the surface since the carburization were determined.

Influence of Carburizing Time of Iron Powder Samples on the Carbon Content after Gas-Carburizing - Sintering Process

The paper presents experimental results of the influence of carburizing time of iron powder samples on the carbon content in the sample’s depth by layers, subjected to a GCS (Gas-Carburizing Sintering) method. Sintered steel elaboration by GCS method consist of enriching the Fe powder with carbon in gas medium in a single thermal cycle including the carburising operation followed by sintering, thereby achieving the sintered carbon steel. Numerical simulations were made using Abaqus/CAE software for mass diffusion analysis in order to find the appropriate diffusion coefficient value.