Influence of production process chain on grain size stability of a microalloyed 20CrMo5 case hardening steel

Abstract

Within the scope of a research project in cooperation with steelmakers and steel users, the whole production process chain of gear parts was investigated concerning the influence on the grain size stability. Three different case hardening steels were investigated in a basic and a microalloyed state. This paper discusses the results gained with a case hardening steel with a new alloying concept, called 20CrMo5. The grain size stabilities of four different industrially produced states of the microalloyed material are compared to the standard material produced in a standard production chain. As a result, it emerged that additional annealing treatments above the eutectoid temperature within the production process chain reduce the grain stability of microalloyed steels.     

Plasma carburising: exotic with potential

Abstract

Low pressure carburising in combination with high pressure gas quenching has gained an increasing importance in the case hardening of highly stressed components. With the introduction of acetylene as carburising gas and the further development of the systems engineering, this technology has found broad acceptance in the heat treatment industry. Plasma carburising with methane as process gas was first introduced more than 20 years ago but has only been utilised in a few special cases on an industrial scale. The advantage of this type of low pressure carburising is the opportunity to achieve a partial case hardening by simply mechanical masking of the parts to be treated. The ALD Own & Operate GmbH Companies have a 10 year of practical experience with the partial plasma carburising process in the serial production of automotive and aerospace parts. By means of two examples the plasma processes and furnace equipment as well as the masking and the results of the treatment will be presented. Other possible applications of this heat treatment method will also be given.     

GTA welding of AISI 316L metal injection moulded components

Abstract

The thin sections and residual porosity typical of metal injection moulded (MIM) components pose challenges when using welding as a joining technology, but if welding can be successfully applied the potential commercial benefits are considerable. Process development of gas tungsten arc (GTA) welding for MIM parts to tubing and wrought components are described and the suitability of MIM 316L products in welded applications, particularly fluid system components, is discussed.     

Development of steel grades for heat treated power train components: a review

Abstract

The development of new carburising steel grades by Daido Steel for heat treated transmission parts is reviewed. These developments are driven by the need for cost reduction, weight saving, fuel economy and higher mechanical performance in new car models under development in response to environmental and economic demands. The next generation of gears will be peened, then vacuum carburised to improve fatigue and impact strength in lighter components designed with smaller tooth cross-sections, and new steels giving improved performance have been developed. Case studies of new steels for pulleys (allowing shorter carburising times) and constant velocity joints are also described.     

Vacuum carburising and high pressure gas quenching technology in automotive industry

Abstract

As the conventional gas carburising furnaces and oil quenching baths used for powertrain parts in the automotive industry have become outmoded, introduction of new equipment and technology is of increasing urgency. Recent demands to improve the mechanical properties of parts and productivity while minimising environmental impact have made vacuum carburising/high pressure gas quenching technology an attractive alternative. However, problems with over carburising and soot in vacuum carburising, and the low cooling ability and high running cost of high pressure gas quenching constitute barriers to adoption of this technology. Attempts to solve these problems by experiments and numerical simulation are reported.     

Corrosion and corrosion wear behaviour of plasma carburised Stellite 21 Co–Cr alloy

Abstract

Low temperature plasma surface alloying with carbon (i.e. plasma carburising) of Stellite 21 Co–Cr alloy was conducted at temperatures from 400 to 500°C for 15 h in a gas mixture of 98 vol.-%H₂ and 2 vol.-%CH₄. The surface treated layers were characterised by XRD, SEM and microhardness tests. The corrosion and corrosive wear behaviour of the plasma carburised Stellite 21 Co–Cr alloy were studied respectively using electrochemical tests and well designed reciprocating wear tests in 3·5% NaCl solution. The results show that low temperature (≤460°C) plasma carburising can improve the corrosion resistance of Stellite 21 alloy; the corrosive wear resistance of Stellite 21 can be enhanced by up to three times; and the best corrosive wear resistance is achieved at the highest treating temperature (500°C). The detailed studies on the wear tracks indicate that the corrosive wear process was dependent on the individual wear and corrosion, as well as the synergetic effect.     

Effect of boron on vacuum carburising depth of iron powder metallurgy compacts

Abstract

The work was aimed at determining the effect of boron on vacuum carburising of iron compacts with density over 7·2 g cm^–3. An attempt was made to determine the effectiveness of boron on carbon diffusion rate into the material of compacts with no additional effect of interconnected porosity. Vacuum carburising of compacts made of iron powder with an addition of boron was carried out at 1050°C in a laboratory vacuum furnace.

The effect of boron content within 0·005 to 0·02% on the vacuum carburising depth was analysed. It was found that the boron addition up to 0·01% increased the carburising depth by ～0% in comparison with the compacts of pure iron.     

Acicular ferrite formation during hot plate rolling for pipeline steels

Abstract

The transformation of supercooled austenite in a commercial pipeline steel was investigated by means of continuous cooling transformation (CCT) and hot simulation experiments. Based on the obtained results, an improved thermomechanical control process (TMCP) was proposed, which could produce a mixed microstructure dominated by acicular ferrite. Results indicated that an increase in the cooling rate could improve the percentage of acicular ferrite in the final microstructure under the present experimental conditions. Furthermore, the acicular ferrite dominated microstructure could be obtained by a two stage controlled rolling in the austenite recrystallisation region plus the non-recrystallisation region and controlled cooling at a cooling rate of 30 K s^-1.     

Influence of process parameters on short fatigue crack growth on carburised case of DIN 20MnCr5 steel

Abstract

Carburising, quenching, tempering and shot peening treatments are widely used on mass production of automotive industry, such as pinion gears and master gears. Variations on these processes may influence the flexural fatigue life of described components. The aim of this work was to study the influence of variations in shot peening time and variations in tempering temperature, of short fatigue cracks growth of carburised case of DIN 20MnCr5 steel. Samples blasted about 30 min and 1 h and tempered at 160°C, showed the best results relative to crack growth and to fatigue life.