In‐situ Investigation during Tempering of a High Speed Steel with X‐ray Diffraction

Abstract

The combined use of a X-ray diffractometer and a high temperature chamber allows in-situ determination of microstructure during heat treatment. X-ray diffractograms are recorded during tempering of high speed steels. The Rietveld method is used in connection with size-strain analysis. Lattice parameters of austenite and martensite are utilized for estimating the change of car-bon content that has massive influence on the secondary hardening. Nevertheless, it was shown that the heat treatment of deep-frozen high speed steel cannot be deduced a priori from the applied tempering process under conventional quenching conditions. The differently conditioned microstructures are based on different phase amounts and microstrain-situations.

Retained Austenite Transformation during Heat Treatment of a 5 Wt Pct Cr Cold Work Tool Steel

“…Similar observations can be found in the literature [22,[27][28][29] and are explained with carbon diffusion (partitioning) from martensite to austenite or relaxation of stresses in the microstructure. It is not clear what the dominating process is or if other unidentified mechanisms are also involved.…”

“…This is a reflection of a large driving force for precipitation of carbides and a more rapid diffusion of carbon in martensite than in RA. [22] As suggested by the changes in the RA lattice parameter (Table IV), it is likely that precipitation starts already at shorter aging times but on a scale too fine to be observed by SEM. Further, M s and M f temperatures increased with longer holding time at 798 K (525°C) (Figure 9), suggesting that the RA changed to a less stable condition.…”

Residual Stresses and Dimensional Changes Related to the Lattice Parameter Changes of Heat-Treated JIS SKD 11 Tool Steels

“…The austenite and martensite lattice parameters were used to estimate the changes in carbon content that are substantially influenced by tempering. 10) Iron carbides are precipitated when tempering is conducted at 473 to 573 K, and secondary carbides (alloy carbides) are precipitated at 673 to 873 K. 6) Das categorized the carbides into primary carbides (with size > 5 µm) and secondary carbides (with size¯5 µm). 9) Cryogenic treatment promotes the formation of refined secondary carbides and increases the carbide volume fraction, leading to a more uniform carbide distribution compared to that in conventionally heat-treated D2 steel.…”

“…Austenite and martensite lattice parameters were used to estimate the change in carbon content, which has a massive influence on secondary hardening. 10) In the tempering process study, the amount of retained austenite in the specimens was tremendously reduced by tempering at temperatures higher than 723 K in conventionally treated specimens. The ironcarbon transitional carbide is precipitated at 473 to 573 K, and the alloy carbide for secondary hardening is precipitated at 473 to 573 K. These precipitation reactions cause a macroscopic size change in JIS SKD 11 steel and microscopic change in the c axis length in martensite.…”

Advanced X-ray Diffraction Techniques for Quantitative Phase Content and Lattice Defect Characterization during Heat Treatment of High Speed Steels

“…The resulting loss of carbon and alloying elements destabilizes the retained austenite that partially transforms to martensite during cooling from tempering temperature to room temperature. Secondary hardening causes a hardness maximum at the temperature range between 540 °C and 570 °C depending on the alloy composition, tempering temperature, and time [1]. Originalarbeit rectly determined by measuring the length changes that accompany phase transformations.…”