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

Abstract

Martensitic steels are tempered to increase the toughness of the metastable martensite, which is brittle in the as-quenched state, and to achieve a more stable microstructure. During the tempering of steels, several particular overlapping effects can arise. Classical dilatometric investigations can only detect effects by monitoring the integral length change of the sample. Additional in-situ diffractometry allowed a differentiation of the individual effects such as transformation of retained austenite and formation of cementite during tempering. Additionally, the lattice parameters of martensite and therefrom the tetragonality was analyzed. Two low-alloy steels with carbon contents of 0.4 and 1.0 wt.% and a high-alloy 5Cr-1Mo-steel with 0.4 wt.% carbon were investigated by dilatometry and in-situ diffractometry. In this paper, microstructural effects during tempering of the investigated steels are discussed by a comparative study of dilatometric and diffractometric experiments. The influence of the chemical composition on the tempering behavior is illustrated by comparing the determined effects of the three steels. The kinetics of tempering is similar for the low-alloy steels and shifted to much higher temperatures for the high-alloy steel. During tempering, the tetragonality of martensite in the steel with 1.0 wt% carbon shifts towards a low carbon behavior, as in the steels with 0.4 wt.% carbon.

Mechanical and thermal stability of retained austenite in plastically deformed bainite-based TRIP-aided medium-Mn steels

“…However, the precipitation started after 1300 s. An opposite trend was observed at 200 °C in 5Mn steel. In this case, the RCL increased from 0.138% to 0.153% after 450 s. This observation confirmed that some amount of carbides were formed in RA or thermal decomposition of RA into ferrite and carbides took place [33]. Such effect was not noted for the alloy containing 3% of manganese.…”

Microstructure Evolution and Mechanical Properties of X6CrNiMoVNb11-2 Stainless Steel after Heat Treatment

“…From Figure 6 b,d, the microstructure, after quenching and tempering, is formed of tempered martensite and carbide. Thus, austenitizing at 1040 °C for 30 min and then quenching in oil can ensure that the austenite is mainly transformed into lath martensite, but this is not sufficient to completely dissolve the carbides [ 28 , 37 , 38 ]. Moreover, the distribution of Nb(C,N) in Figure 6 a is not uniform, in comparison with the microstructure seen after the quenching and tempering processes in Figure 6 b.…”

Mechanical and Microstructural Behavior of Tempered CPM® 3V High-Density Sintered Tool Steel

“…As the as-quenched martensite transitions to tempered martensite, there is precipitation of secondary carbides. Precipitation of carbides lowers the amount of alloy elements dissolved into the matrix, which ultimately reduces stored energy (strain) in the lattice of the Fe-matrix [22,24].…”