Study of Microstructural Development of Bainitic Steel using Eddy Current and Synchrotron XRD in-situ Measurement Techniques during Thermomechanical Treatment∗

Abstract

In the field of massive forged components the mechanical engineering industry searches for processes with increasing energy and resource efficiency. The new generation bainitic steels are promising for such application because of the high strength, toughness and fatigue properties. In order to achieve the desired mechanical properties, the development of the bainitic microstructure depending on the parameters of the thermomechanical process and on the cooling procedure must be well-known. In the present work diverse experimental techniques were applied for the investigation of the microstructural development during thermomechanical treatment and subsequent continuous cooling through the bainitic transformation range. The thermomechanical processes were simulated using dilatometers and at the same time, the specimens were analyzed using an eddy current sensor or using in-situ X-ray diffraction measurements at synchrotron (DESY). The results show that the eddy current sensor is suitable for the monitoring of the microstructural development during cooling and during deformation. From the investigations suitable process parameters were deduced for achieving a possibly fine bainitic microstructure. The main factors are a relatively low deformation temperature in austenitic range, a fast cooling (> 2 K/s) into the bainitic range, bainitic transformation and/or a short deformation in the lower bainite range, and finally a slower cooling until room temperature.

Comparative Study of the Tempering Behavior of Different Martensitic Steels by Means of In-Situ Diffractometry and Dilatometry

“…For the high-alloy steel SAE H13, the cementite precipitation is shifted to the holding step at 650 °C, similar to the transformation of the retained austenite. It is assumed that the higher Si content in the high-alloy steel SAE H13 prevents cementite precipitation and stabilizes the retained austenite [ 25 , 26 ]. Independent of the transformation temperature, for all steels, the cementite formation and the retained austenite transformation overlaps, as already reported [ 6 , 7 , 8 ].…”

Influence of Plasma Nitriding with a Nitrogen Rich Gas Composition on the Reciprocating Sliding Wear of a DIN 18MnCrSiMo6-4 Steel

“…Continuous cooling bainitic steel has an increasing use in industrial processes owing to its excellent outstanding combination of yield strength and toughness [1][2][3] , the possibility to reduce the process chain and reduced energy consumption [4][5][6][7] .…”

Microstructure and Wear Properties of a Low Carbon Bainitic Steel on Plasma Nitriding at Different N2-H2 Gas Mixtures

“…The new generation of continuous cooling bainitic steels allows the formation of different bainitic morphologies, such as granular bainite, degenerate upper bainite, and lower bainite, and may contain other phases such as retained austenite and ferrite [5][6][7][8][9] . Unlike quenched and tempered steels, which need further heat treating to obtain properties suitable for their applications 10,11 , continuous cooling bainitic steels already present high levels of strength and toughness after hot rolling or forging, presenting the potential to shorten processing routes 5,6,8,12 .…”