Assessment of Retained Austenite in Fine Grained Inductive Heat Treated Spring Steel

Abstract

Advanced thermomechanical hot rolling is becoming a widely used technology for the production of fine-grained spring steel. Different rapid phase transformations during the inductive heat treatment of such steel causes the inhomogeneous mixture of martensitic, bainitic, and austenitic phases that affects the service properties of the steel. An important task is to assess the amount of retained austenite and its distribution over the cross-section of the inductive quenched and tempered wire in order to evaluate the mechanical properties of the material. Three different analytical methods were used for the comparative quantitative assessment of the amount of retained austenite in both the core and rim areas of the sample cross-section: neutron diffraction—for the bulk of the material, Mössbauer spectroscopy—for measurement in a surface layer, and the metallographic investigations carried by the EBSD. The methods confirmed the excessive amount of retained austenite in the core area that could negatively affect the plasticity of the material.

Successive Grinding and Polishing Effect on the Retained Austenite in the Surface of 42CrMo4 Steel

“…Due to the small amount of retained austenite in the microstructure and its ultra-fine grain size, an EBSD technique is not suitable for its detection. This statement was previously confirmed in [26]. On the other hand, CXMS proved to deliver the correct percentage of retained austenite in all samples.…”

“…The CXMS measurements on the samples were performed by Mössbauer spectrometer [12] in the mode of austenitemeter with a toroidal proportional gas flow counter [25] using 90%Ar + 10%CH 4 gas mixture and 57 Co(Rh) source with activity ~25 mCi at room temperature. This apparatus [12] was previously applied for the determination of retained austenite in spring steel [26], i.e. Isomer shifts of spectral components were given relative to the α-iron calibration sample.…”

Performance of Maraging Steel Sleeves Produced by SLM with Subsequent Age Hardening

“…Table 4. Contributions and hyperfine parameters of fitted Mössbauer spectra components for initial powder sample and the sleeve (the recognition of martensite-like and austenite-like components according to [29][30][31][32][33][34][35] The mean values <B hf > differs very slightly (32.41 T − 32.24 T = 0.17 T) i.e., about 0.5%. Such small difference is a strong proof that the local atomic ordering is very similar in both samples despite significant difference in morphology and metallographic microstructure.…”

Special Issue: Mechanical Properties in Progressive Mechanically Processed Metallic Materials

“…Contrary to conventional production technologies, the main advantage of such treatment is the possibility to precisely control structural phenomena, including grain size, substructure development, texture, and volumes and types of grains boundaries, all of which affect the final mechanical and utility properties. The strengthening mechanisms in modern high-temperature resistant alloyed steels after heat treatment were studied by L. Zhao et al [ 9 ], while A. Olina et al [ 10 ] investigated the occurrence of retained austenite in a fine-grained spring steel processed via thermomechanical rolling. J. Fumfera et al [ 11 ] then numerically and experimentally evaluated the cyclic hardening behavior in dependence with the strain range for a 08Ch18N10T austenitic stainless steel.…”