Tianliang Fu

The quenching deformation of ultra-high-strength steel sheets is a technical challenge in the steel industry. Although air-jet quenching can effectively improve shape quality, it requires substantial energy consumption. How to improve the heat transfer intensity of air jets by improving key components has become the keypoint of using this technology in industry. In this study, a CFD model was established to investigate the impacts of nozzle shapes and jet arrangements on the flow structure, wall heat transfer intensity and wall heat transfer uniformity under the same total flow rate. The results show that the impingement heat transfer could only be realized by adopting a symmetrical nozzle design (including the symmetric nozzle shape and jet arrangement). And the intensity and uniformity of wall heat transfer were hardly affected by the specific symmetrical nozzle shape. Moreover, under the S/B (ratio of slot spacing to slot width) condition adopted in this study, multiple jets did not significantly enhance heat transfer uniformity but instead tended to reduce the overall heat transfer intensity. In this paper, the configuration of the horizontal nozzle with the central single jet was optimal due to its high heat transfer intensity, good heat transfer uniformity and lower energy consumption.

As an important cornerstone of the development of human civilization, metal materials are the most widely used materials in modern society

The high flatness quenching of ultra-high-strength steel sheets is a technical problem in the steel industry. In this study, the traditional water and spray quenching methods were abandoned, and the roller-constrained slot air-jet quenching method was proposed for steel sheets below 3 mm thickness, which provided a theoretical reference for producing thinner, wider, and higher-flatness steel sheets. A 2D roller-constrained slot air-jet numerical model was established to study the flow field and heat transfer characteristics under the conditions of Reynolds number 24,644–41,076, a dimensionless jet height of 16–24, and a jet angle of 45°–135°. The results showed that the average Nusselt number on the heat transfer surface was proportional to Re^m. At the same time, high-intensity heat transfer was achieved when the dimensionless height and jet angle were properly combined. At the same Reynolds number, the heat transfer intensity could be increased by 289%. In addition, the position of the peak Nusselt number was affected by reducing the jet angle, which served as an effective strategy for adjusting the martensite ratio and obtaining ideal mechanical properties.

The complexity of roller quenching equipment restricts research on the heat transfer mechanism of ultrathick plates, and the cooling law requires further clarification. In this study, the distributions of temperature gradient, average cooling speed, and heat loss during quenching are analyzed using a 220 mm thick steel plate, and inverse heat conduction is used to determine the surface heat transfer conditions. An ultrathick steel plate is subjected to high‐pressure and low‐pressure water in turn for strong and lasting cooling. Due to the different flow regions on the upper and lower surfaces, the flow from the lower nozzle is slightly higher than that from the upper nozzle, thereby resulting in a good cooling symmetry between the upper and lower surfaces. The results provide an important basis for the optimization of roller quenching technology for ultrathick steel plates.

During the quenching of high‐temperature steel plate, Leidenfrost phenomenon takes place, which prevents the coolant from extracting heat from high‐temperature wall. Adding surfactant to the basic fluid can reduce the surface tension, increase the solid–liquid contact area, and ultimately increase the cooling speed. Herein, aqueous solutions of 240 ppm cetyl trimethyl ammonium bromide (CTAB), 600 ppm sodium dodecyl sulfate (SDS), and 56 ppm polyoxyethy‐lene (20) sorbaitan monolaurate (Tween‐20) are used as coolants. Using a 50 mm thick high‐temperature AISI304 stainless steel plate, free surface jet experiments are designed and completed to study the influence of different coolants on the surface heat transfer and internal thermal conductivity. The experimental results show that surfactants can reduce the surface tension, which enhance the wettability of the fluid on the surface, whereas the time it takes for the fluid to completely wet the experimental region is shortened by up to 13.87%. The foaming can increase the width of wetting front and hinder the expansion speed of the wetted region. When aqueous Tween‐20 with low surface tension and low foaming is used as the coolant, the maximum heat flux increases by 12.11%, 7.03%, 9.33%, 7.70%, and 4.41% compared with that of pure water.

In this paper, a 300 mm thickness ultra-heavy steel plate was selected as the research object. In addition, special roller quenching equipment and a new testing method were used to measure the quenching temperature curve at different positions of the steel plate. The relationships and corresponding interaction mechanisms between cooling rate, microstructure, and mechanical properties of an ultra-heavy steel plate during roller quenching were investigated. The results indicated that the cooling rate, strength, hardness, and impact energy decreased gradually along the thickness direction of the plate, while the cooling rate, average grain size, and mechanical properties were relatively uniform with little change along the length direction of the plate. The experimental results provide an effective way to further control the microstructure and properties of ultra-heavy steel plates during roller quenching.

The industrial application of nanofluids had been explored by many researchers since nanofluids were proposed. However, there were different opinions on the effect in jet cooling. In this paper, 0.4 vol%, 0.8 vol%, 1.2 vol%, 1.8 vol%, 2.4 vol% Al₂O₃-water, TiO₂-water, SiO₂-water nanofluids and pure water were used as quenching coolants to complete single jet cooling experiments on the free surface of 50 mm high-temperature steel plate. The results showed that using low concentration (0.4–1.2 vol%) nanofluids could significantly improve the maximum heat fluxes, cooling speed peaks, and moving velocities of peaks along the thickness direction compared with pure water. However, the cooling uniformity in the horizontal direction was reduced, especially with high concentration nanofluids (≥1.8 vol%). Through comprehensive comparison, when 1.2 vol% Al₂O₃ + water was used as coolant, the optimal cooling efficiency could be achieved, and cooling speed peaks along the thickness were 8.14%–19.70%, 2.16%–3.48% and 0.74%–1.44% higher than that of pure water respectively.

The temperature drop curves of an ultra‐heavy plate with a thickness of 137 mm after quenching are measured at different positions using a jet quenching equipment and a multi‐channel steel plate temperature recorder. The effect of the jet impact (Z1), intersection interference (Z2), and transverse flow (Z3) heat transfer zones on the temperature gradient of an ultra‐heavy steel plate during jet quenching was investigated. The corresponding relationships and interaction mechanisms between cooling rate, microstructure, and mechanical properties during jet quenching are studied. The results indicate that Z2 and Z3 had a greater influence on temperature gradient and microstructure evolution, and Z1 and Z2 had a greater influence on the cooling rate and mechanical properties. The experimental results have guiding significance for the development of new quenching equipment for ultra‐heavy steel plates and their industrial application.