Agnieszka Betzwar-Kotas

Gigacycle fatigue response of tool steels produced by powder metallurgy compared to ingot metallurgy tool steels

Abstract In this work, the gigacycle fatigue response of several tool steel grades, produced by ingot metallurgy and powder metallurgy, has been studied using an ultrasonic frequency resonance testing device. In all cases the S–N curves exhibited a consistent drop up to 10 billion cycles, i. e. there is no fatigue “limit” with these materials. Surprisingly, there was virtually no effect of the composition and hardness of the materials, both for powder metallurgy and ingot metallurgy grades cold work tool steels and high speed steels exhibiting virtually the same S–N curves, however the powder metallurgy steels revealed significantly higher endurance strength levels than ingot metallurgy grades. In the ingot metallurgy tool steel grades, crack initiation started at large primary carbides or carbide clusters, while in the powder metallurgy grades, markedly smaller non-metallic inclusions turned out being the critical defects. Furthermore, it has been shown that it is very important to avoid introducing residual stresses into the specimen surfaces during preparation, since these stresses significantly affect the endurance strength levels and the location of crack initiating sites.

PM tool steels push the edge in fatigue tests

Austrian researchers fatigue tested PM cold work steel and high speed steels and found that they had remarkable fatigue resistance compared with similar conventional ingot steels. The results they obtained resembled those for high strength bearing and spring steels and they concluded that fatigue limits for these PM tool steels did not exist…

Gigacycle Fatigue Response of PM versus Ingot Metallurgy Tool Steels

In this work, the gigacycle fatigue response of several tool steel grades has been studied using an ultrasonic resonance testing device. It showed that both with ingot metallurgy (IM) and powder metallurgy (PM) tool steels, a true fatigue limit does not exist up to 10E10 cycles. PM steels resulted in significantly higher endurance strength levels than IM grades. However, there was virtually no effect of the composition and hardness of the materials, both for PM and IM grades cold work tool steels and high speed steels exhibiting virtually the same S-N curves. In the IM tool steel grades, crack initiation started at large primary carbides or carbide clusters, while in the PM grades, nonmetallic inclusions were the critical sites. In any case it is very important to avoid introducing residual stresses into the specimen surfaces during preparation, which would markedly shift the endurance strength levels.

Size Effects in Lead Free Solder-Joints

Due to the environmental and health concerns the usage of lead based solders in electrical and electronic equipment is restricted. Recent regulations require the replacement of these solders by non toxic lead free solders, thus numerous scientific and technical investigations has been performed on the properties of the solder joints produced using these new materials [1].