Short austenitization treatment with subsequent press hardening: Correlation between process parameters, microstructure and mechanical properties

Characterization of Phase Transformations During Graded Thermo-Mechanical Processing of Press-Hardening Sheet Steel 22MnB5

“…At a lower austenitization temperature, the bainitic area was larger, which could be the result of undissolved carbides because of the intercritical austenitizing below the Ac 3 temperature and the short time austenitization. [18] Figure 6 shows the temperature-time curve and the Du y /DT curve for specimen P4, in which a thermo-mechanical treatment with a 10 pct elongation with subsequent compressed air quenching was carried out after a soaking duration of 10 seconds.…”

“…[25] Grydin et al found that in contrast to a conventionally austenitized material, the microstructure of a short austenitized material consists of ferrite, bainite, martensite, retained austenite, and a small amount of carbides. [18] These are the reasons for the higher bainite content and the slightly higher B s -temperature after austenitizing at 800°C compared to the areas austenitized at 850°C or at 900°C. Figure 10 shows digital light microscope and SEM images for two areas of interest of P4 austenitized at 850°C and 800°C.…”

“…A microstructure consisting of ferrite, bainite, martensite and not completely dissolved carbides is formed during steel cooling. [18,26] Furthermore, alloying elements such as manganese or chromium reduce the critical cooling rate. In microscopically small areas where high amounts of these alloying elements are present, for example around dissolved carbides, martensite is formed.…”

“…They normally precipitate from the martensite during the first tempering stage. [18,21,27] The results for lower austenitization temperatures are distorted due to the presence of untransformed retained ferrite, as cooling was initiated below the Ac 3 temperature. Furthermore, the curves in Figures 4 and 6 showed that the size of the peaks provides information about the dominant phase and therefore the hardness can be estimated.…”

Investigation on the mechanical properties of press-hardened boron steel sheets using the conductive heating technique

“…19 Similarly, in Taylor et al, 3 after heating the samples to 900 C for 3 min, and with an average cooling rate of 60 C/s, a hardness value of 477 HV10 was obtained with 100% martensite microstructure. In a more recent work, the samples were cooled from 850 C after keeping in the furnace for 6 min, an average hardness value of 472 HV5 was obtained 28 (Table 3). Consequently, the presented experimental hardness results agree very well with the literature, and thus the resultant hardness after press-hardening is independent of the heating method.…”