Abstract
This paper examines how the initial austenite grain size in quench and partitioning (Q-P) processes influences the final mechanical properties of Q-P steels. Differences in austenite grain size distribution may result, for example, from uneven heating rates of semi-finished products prior to a forging process. In order to quantify this influence, a carefully defined heat treatment of a cylindrical specimen made of the Q-P-capable 42SiCr steel was performed in a dilatometer. Different austenite grain sizes were adjusted by a pre-treatment before the actual Q-P process. The resulting mechanical properties were determined using the upsetting test and the corresponding microstructures were analyzed by scanning electron microscopy (SEM). These investigations show that a larger austenite grain size prior to Q-P processing leads to a slightly lower strength as well as to a coarser martensitic microstructure in the Q-P-treated material.
Highlights
The development of new steel grades, characterized by very high strengths and reasonably good ductility, is a key requirement to realize innovative light-weight concepts
The material used for the experimental investigations was an AHS steel 42SiCr with the chemical composition summarized in Table
The present work analyzed the influence of austenite grain size at the beginning of identical quench and partitioning (Q-P)
Summary
The development of new steel grades, characterized by very high strengths and reasonably good ductility (i.e., advanced high strength steels; AHSS), is a key requirement to realize innovative light-weight concepts. This steel grade provides a good opportunity to produce advanced high strength products using bulk forming processes and a subsequent Q-P process. Q-P process (shown schematically in Figure 1), the austenitic material is quenched rapidly to promote the martensitic transformation, but the cooling is stopped at a quench-temperature QT prior to reaching the martensite finish temperature. This results in a microstructure composed of martensite and some retained austenite. Diffusion of carbon from the supersaturated martensite into the adjacent austenite
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