###### Abstract  
The degradation of a quenching cooling medium is a particularly important technical aspect in the technology of primary and final thermal treatments. This paper studied the effect of the thermal cycles of heating and cooling on a tempering medium type of 2.5% carboxymethyl cellulose solution in water. The main characteristic of a cooling medium is the absorption of heat from the part, which is influenced by the physico-chemical characteristics of the cooling liquid according to the degree of thermal fatigue. For this, the main properties of the environment are analyzed, such the chemical composition, corrosion capacity, wetting capacity and cooling characteristics. To analyze the change in properties during the operation, we studied the effect of thermal cycles on the physico-chemical characteristics of the quenching medium to determine the optimal period when the quenching medium could function in good parameters without the necessary corrections. For this purpose, cyclic and linear corrosion tests, FTIR compositional analyses and contact angle measurements were conducted.  
carboxymethyl; quenching; thermal cycles; treatments; contact angle; EDX; SEM 20231  
The quenching media for quenching must meet certain specific characteristics such as being cheap and having high cooling rates in the range of the minimum stability of supercooled austenite at 800-500 \({}^{\circ}\)C and having low cooling rates in the range of the beginning of the transformation of austenite into martensite in order not to introduce dangerous structured stresses for cracking and deformation [3; 4]. Water corresponds with both from an economic perspective and the cooling speed in high-temperature ranges, but it has too high speeds in the temperature ranges of structural transformations. Thermal treatment oil perfectly corresponds technically, but it is expensive and flammable. In this context, the palette of cooling media has been diversified, creating polymeric cooling media and organic cooling media resulting from secondary products from the production process. Carboxymethyl cellulose belongs to the last category, being a secondary product obtained from paper processing [5].  
Carboxymethyl cellulose is an organic polymeric substance obtained as a by-product from the manufacture of paper, having the chemical formula C8H16O8 [6]. Dissolved in water with or without additions in a percentage of less than 5%, it is used industrially as a quenching medium with a medium cooling rate, which is favorable for quenching parts made of steels sensitive to cracking or parts with shapes that generate tension concentrators [7; 8]. Due to the use in high-capacity industrial tempering basins, it is necessary to study the maintenance of the quality and physical-chemical characteristics of the substance dissolved in water after a certain number of reuses [9]. The exact number of cycles that can be used without damaging the tempering process is not well determined.  
In this paper, the effect of thermal wear on the quenching characteristics of carboxymethyl cellulose media was studied; namely, the cooling curves, the corrosion capacity, the contact angle between the non-thermally used and used quenching fluids [10; 11] and the surfaces of improved steel parts [12]. This result established the suitable number of cycles of the CMC quenching medium used in industrial processes [13].  
If the tempering medium does not correspond in terms of properties after a certain period of use, it is recommended to regenerate the tempering bath by adding additives for correction [14; 15]. These additives can be preservative substances because carboxymethyl cellulose is organic and, therefore, decomposes over time, or they can be soluble or insoluble substances that can increase the number of vapor formation centers slowing down cooling or they can reduce the surface tension of the liquid [16].