Abstract
The hot deformation behaviour of air-hardening martensitic forging steels (of type 1.5132) is presented. The newly developed steels are characterized through dilatometric tests as well as through microstructure analyses with LOM and SEM and hardness measurements. Additionally, the influence of alloying elements on the flow curves at high temperatures is discussed. It is demonstrated that the higher alloying content does not increase the equivalent stresses in comparison to the reference alloys and contrariwise reduces the offset for dynamic recrystallization at temperatures below 1100 . Furthermore, the effect of different alloying elements on the strain hardening behaviour during hot compression of 4 medium manganese steels is presented. It is shown that boron reduces the offset for dynamic recrystallization if present in solid solution, while the combined addition of titanium and niobium annihilates the solid drag effect on the prior austenite grain boundaries.
Highlights
Martensitic steels are broadly used in the forging industry especially if the applications require a decent balance of strength and toughness
These materials belong to the group of medium manganese steels (MMnS), as the martensitic microstructure is achieved by an addition of manganese of 4 wt.–%
Investigations with light optical microscopy (LOM) show that all samples had a martensitic matrix with regions of increased carbide density
Summary
Martensitic steels are broadly used in the forging industry especially if the applications require a decent balance of strength and toughness. Bainitic forging steels, especially transformation induced plasticity (TRIP) assisted alloys [3], achieve properties very close to those of Q + T steels, but their cooling from the forging heat is not easy and specific cooling routes have to be applied This complicates the process control immense, for forging parts with large diameters. Air-hardening ductile forging steels (AHDs) were added to the list, which achieve their martensitic microstructure through air-cooling from the forging heat, but show similar static mechanical properties as Q + T steels [4]. These materials belong to the group of medium manganese steels (MMnS), as the martensitic microstructure is achieved by an addition of manganese of 4 wt.–%. These alloys show a cyclic material behaviour [5]
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