Papers by Keyword: Carburising

Abstract: This study was undertaken to evaluate the likely effect on the wear rate of changing the pinion material in a rack and pinion steering box from carburised SAE-AISI grade 8617 H steel to induction hardened SAE-AISI grade 4140 steel of the same hardness. Accordingly, pin on disc wear tests were conducted using carburised 8617 H pins and through hardened 4140 pins. The surface hardness of the pins was approximately 60 HRC for both materials. The discs were made of SAE-AISI grade 1040 steel through hardened to a hardness of 45 HRC. The results showed that both the pins and the discs wore more rapidly when the tests were carried out with 4140 pins. The study indicates that the wear rate would be increased on both the rack and the pinion if the pinion material were changed from case hardened 8617 H to induction hardened 4140.

Abstract: The contact fatigue performance of two pairs of case carburised gears with either an as-ground or superfinished surface finish was studied. This comparison test was carried out using a back-to-back gear test rig. Test results showed that superfinished gears provided an enhanced contact fatigue resistance with only the development of minor scratches and light micropitting after running, while as-ground gears failed through a sequence of initial micropitting, progressive micropitting, macropitting and scuffing.

Abstract: The carbon diffusion in steel, where the carbon diffusivity varies with the carbon content, was solved with the integral methods under the third boundary condition. The variation of carbon diffusivity in steel with the carbon content was described with two different functions, linear dependence and exponential dependence. The integral approximation for both cases was improved with the numerical computation to more accurately predict the carbon profiles. The integral solution is more accurate than the formulation based on the assumption of a constant diffusivity or those based on the assumption of a constant diffusivity and/or constant carbon content at part surface. It is also more easily used in practice than the numerical method to describe the carburising process and predict the carbon content at steel surface and carbon profiles in treated layer.

Abstract: The novel low temperature plasma alloying technique that simultaneously introduces both nitrogen and carbon into the surface of austenitic stainless steel has been used in the past to create a hybrid N-C S-Phase. This S-Phase layer boasts of high hardness and wear resistance without any detriment to corrosion resistance. In this study, the afore mentioned hybrid N-C S-Phase was successfully implemented in the surface of two medical grade austenitic stainless steels: ASTM F138 and F1586. At an optimum process temperature of 430°C a very hard, 20μm precipitate-free S-Phase layer was created. Anodic Polarization tests in Ringer’s solution showed that the corrosion resistance of this layer was similar to that of the untreated alloys. Both dry-wear and corrosion-wear (Ringer’s) behaviour of the surface treated alloys showed an improvement of more than 350% and 40% respectively when compared to the untreated material.

Abstract: This paper gives a brief review on the three low temperature plasma surface alloying processes that have been developed in recent years to engineer the surfaces of austenitic stainless steels to achieve much enhanced surface hardness and wear resistance, without compromising their corrosion resistance. These include low temperature plasma nitriding, low temperature plasma carburizing and the newly developed hybrid process involving the simultaneous incorporation of nitrogen and carbon to form a dual layer structure. The processing, structural and property characteristics of each process are discussed briefly in this paper.

Abstract: It is important to suppress grain coarsening during the carburizing treatment of automobile components such as gears and shafts so that high strength is maintained and heat treatment distortion is minimized. Two manufacturing methods are often used for the cost reduction. One is the increasing carburizing temperature. The other is the adoption of cold forging instead of hot forging. These methods are likely to result in grain coarsening in the case of conventional steels. It is well known that the key factors to control the grain growth are the initial austenite grain size and the volume and mean size of precipitates. In this study, the grain growth property of Ti-modified steel was investigated to confirm the influence of precipitates, and compared with those of Nb-modified and conventional steels. The influence of forging temperature on the grain growth property in a Ti-modified steel was also investigated.