# The Efficient Way to Design Cooling Sections for Heat Treatment of Long Steel Products

^{*}

## Abstract

**:**

## 1. Introduction

^{−2}s

^{−1}]), which is commonly referred to as the impingement density [4]. Increasing the water mass flux increases the heat transfer coefficient for all surface temperatures [4,8,9]. There are different types of nozzles with different spray footprints (Figure 2). The water mass flux is influenced by the size of the nozzle (which determines the water flow rate) and the spray area (which is influenced by the distance between the nozzle and the cooled surface and by the shape of the jet). The use of nozzles allows a wide range of cooling rates to be achieved by changing the process water pressure. Increasing the water pressure increases the amount of water sprayed, which in turn increases the cooling rate. The Leidenfrost temperature and the temperature at which the critical heat flux occurs increase as the water mass flow increases [10,11].

## 2. Finding the Optimal Cooling Regime

## 3. Cooling Section Design: Nozzles Selection and Positioning

## 4. Description of Laboratory Measurement of Heat Transfer Coefficient

^{−1}. The recorded data are then transferred to a computer for analysis.

_{p}—specific heat of the steel, L—thickness of the steel specimen, T

_{0}(x)—initial (t = 0) temperature field in the steel specimen, x

_{l}—distance between measuring point and cooled surface (x = 0), ${T}_{i}^{*}$—temperatures measured by thermocouple in time steps t

_{i}, All in SI units). The scheme of the model is shown in Figure 12.

_{i}:

## 5. Simulation of the Real Cooling Process

## 6. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Dependences of the heat transfer coefficient (dashed line) and heat flux (solid line) on the surface temperature [3].

**Figure 2.**Different jet shapes and their footprints [12].

**Figure 3.**Laboratory heat treatment tests—(

**A**): stationary spray quenching test bench [30], (

**B**): photos of tests, (

**C**): Schematic of test specimen with holes for thermocouples.

**Figure 4.**Example of measurement results for two different cooling regimes and a sample thickness of 30 mm, steel grade S355: cooling curves at different positions from the cooled surface.

**Figure 5.**Example of measurement results for two different cooling regimes and a sample thickness of 30 mm, steel grade S355: measured hardness—Vickers HV30 (

**top**) and microstructure composition (

**down**).

**Figure 6.**Example of measurement results for cooling Regime 2 and a sample thickness of 30 mm, steel grade S355: microstructure analysis.

**Figure 7.**Example of preliminary design for steel flat strip:

**top**—nozzles positions (top and side view),

**bottom**—water distribution.

**Figure 8.**Example of preliminary design for steel tubes:

**left**—nozzles positions,

**right**—water distribution.

**Figure 9.**Schematic of the laboratory test bench for measuring the heat transfer coefficient: 1—headers with nozzles, 2—pressure gauge, 3—test plate, 4—motor moving trolley, 5—girder carrying trolley, 6—movable trolley, 7—data logger, 8—heater, 9—water tank, 10—pump, 11—control valve [31].

**Figure 13.**Measured temperature, computed surface temperature, and computed heat transfer coefficient (

**left**: all experiment,

**right**: detail of the first pass through the cooling section).

**Figure 15.**(

**Left**): HTC as a function of surface temperature, (

**right**): HTC as a function of position (50–900 °C).

**Figure 19.**Example of measured temperatures (test bench with rotating sample) for one-sided cooling of a 20 mm thick plate of S355 steel (simulation of two-sided cooling of a 40 mm thick plate). Cooling regime: Intensive cooling—8 bar, length 16 m (4 s) and then soft cooling—4 bar, length 42 m (10.5 s), product speed 4 m s

^{−1}. Total length of cooling section—58 m (14.5 s).

**Figure 20.**Measured Vickers hardness for material S355: original material and heat-treated (regime shown in Figure 19).

**Figure 21.**Results of Charpy pendulum tests for material S355: original material and heat-treated (regime shown in Figure 19).

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**MDPI and ACS Style**

Kotrbacek, P.; Chabicovsky, M.; Resl, O.; Kominek, J.; Luks, T.
The Efficient Way to Design Cooling Sections for Heat Treatment of Long Steel Products. *Materials* **2023**, *16*, 3983.
https://doi.org/10.3390/ma16113983

**AMA Style**

Kotrbacek P, Chabicovsky M, Resl O, Kominek J, Luks T.
The Efficient Way to Design Cooling Sections for Heat Treatment of Long Steel Products. *Materials*. 2023; 16(11):3983.
https://doi.org/10.3390/ma16113983

**Chicago/Turabian Style**

Kotrbacek, Petr, Martin Chabicovsky, Ondrej Resl, Jan Kominek, and Tomas Luks.
2023. "The Efficient Way to Design Cooling Sections for Heat Treatment of Long Steel Products" *Materials* 16, no. 11: 3983.
https://doi.org/10.3390/ma16113983