Experimental and numerical investigation on temperature field and tailored mechanical properties distribution of 22MnB5 steel in spray quenching process

Functional gradient high-strength steel structures on the basis of a novel tailored spray quenching process can achieve an excellent crashworthiness and weight reduction, which own a promising future in advanced automotive and mechanical engineering. This paper focuses on the temperature distributions and mechanical properties characteristics of high strength 22MnB5 steel under complex spray jetting conditions. A spray density based physical modeling method is simplified to describe the spray flow field and the water film evolution on the hot 22MnB5 surface during the spray quenching process. Fluid characteristics of spray jetting with single/twin nozzles and corresponding heat transfer intensity are systematically investigated by self-developed experimental scenarios. The results reveal that the fluid-solid heat transfer coefficient (IHTC) is dependent on the spray quenching temperature distribution, which owns an intense correlation between post-quenched mechanical property and the jetting parameters involving the spray jetting pressure (SJP), the spray jetting height (SJH), the nozzle distance (ND), and initial quenching temperature (IQT). The average cooling rate under the single/twin nozzles jetting conditions can reached as 28.5-170.5 degrees C/s and 36.84-137.42 degrees C/s, corresponding to the peak IHTCs are 10.11-49.47 kW/(m(2) K) and 9.69-44.76 kW/(m(2) K), respectively. The hardness firstly increases and then decreases from the central point/zone to the edge along the radial direction after the spray quenching process. The largest radial hardness after the single/double nozzles spray quenching can be up to 50.21 % and 31.58 % larger than the lowest value, respectively. Moreover, the in-plane temperature field and corresponding post-quenched mechanical properties are further numerically predicted by introducing into the time-dependent IHTC and coupling with the CFD and Johnson-Mehl-Avrami (JMA) modeling. Finally, a validation work of U type specimen was conducted to show the spray quenching technology owns a prospective future for gaining more complex-shaped parts with tailored mechanical properties.