Einsatz hochfester umweltfreundlicher Sinterstähle für hochbelastete Bauteile

FKM 2000
Issue No. 252
Project No. 197

Abstract:
In the powder metallurgy of ferrous materials, nickel and copper have so far been among the most important alloying elements due to their strength-enhancing properties. Due to the rejection of scrapped copper-containing sintered parts for melting metallurgical steel production on the one hand and the health hazard posed by free nickel on the other, investigations are required with Cu-free alloys or with bound Ni on suitable heat treatment processes for the production of highly stressed components in single sintering technology from the point of view of fatigue and rolling strength. Furthermore, a transferability model of samples to gears is to be developed with regard to the rolling strength behavior. Two ready-alloyed sintered steels, Fe-4.0%Ni-0.5%Mo (MSP4) and Fe-1.5%Mo (Astaloy Mo), were selected and, depending on the heat treatment process, 0.5% (high-temperature sintering) or 0.7% (heat-treated from the sintering heat) carbon was added. For the alloy Fe-1 .5%Mo, a variant with the addition of 5% carbonyl iron powder (CEP) was also produced. In order to determine application-relevant material characteristics with the optimum material conditions, tests were carried out on the fatigue strength of unnotched and notched samples at stress ratios of around 0 and on the rolling strength without and with superimposed friction (slip of -24%) in the area of fatigue and endurance strength. In the fatigue strength behavior, the rapidly cooled variant for both stress ratios and notch shapes shows a significantly lower load capacity compared to the quenched and tempered variants, where the alloy (Fe-1.5%Mo) is slightly superior to the alloy (Fe-4%Ni-0.5%Mo) in the fatigue strength range. For the alloy with fine powder addition of 5% carbonyl iron, the highest load-bearing capacity was determined with unnotched samples under pure alternating stress. However, a very large scattering of the test results is noticeable for this alloy. In the notched condition or under threshold load (R = 0), however, the fatigue strength is lower than that of the other quenched and tempered variants. The medium stress sensitivity is also significantly higher compared to the other alloys. Compared to the quenched and tempered samples, the fatigue strength of bainitized samples is significantly lower. No differences were found in the rolling strength behavior between the alloy (Fe-1.5%Mo)+0.5%C without and with the addition of carbonyl iron powder within the scatter. The development of an easy-to-use model for the transferability of characteristic values of fatigue and rolling strength determined on samples to real components is based on the concept of the highest stressed material volume to take into account the influence of size. The calculations were checked with experimentally determined results on sintered gears in the alloys. When calculating the flank load capacity of the sintered gears on the basis of the rolling strength values determined on samples, there was good agreement between the calculated flank load capacity and the experimentally determined flank load capacity. The prerequisite for this was the derivation of characteristic values from the known relationships of the fatigue strength. Scope of report:
60 pages, 118 images, 5 tables, 79 references Start of work:
01.07.1995: End of work:
30.06.1998 Funding body:
AVIF (Funding no. A 93) Research institute: Fraunhofer Institute for Structural Durability LBF Bartningstr. 47, 64289 Darmstadt Head:
Prof. Gerd Müller Processors and authors:
Dr. Klaus Lipp Prof. Dr.-Ing.lng. Cetin Morris Sonsino Chairman of the working group:
Dr. rer. nato Hans-Peter Koch, Robert Bosch GmbH Chairman of the advisory board:
Dipl.-lng. J. Rabe, Sachsenring AG