Study of an Economical and Effective Heat Treatment Method to Improve the Performance of Gear Steels

Abstract

Economic and environmental concerns have recently greatly stimulated efforts to extend the service life of machine components, such as gears, shafts, and cams. These parts often suffer from cyclic loading and thus undergo a severe risk of fatigue failure. [1][2][3] Case hardening steels are widely used for producing power transmission components due to the combination of the high hardness of the case and the good toughness of the core. Different surface engineering techniques were developed, such as carburizing, nitriding, induction hardening, and shot peening. [4][5][6] Carburizing is an extensively and successively applied technology in which steel components are heated to about 930 °C and then exposed to a carbonaceous atmosphere for several hours (≥7 h), where they undergo chemical reactions. [7,8] However, high carburizing temperatures and long carburizing times may lead to grain coarsening, so the problem of austenite grain growth control is particularly prominent for carburized gear steels. [9][10][11] Nb microalloying has been recently extensively used to develop new gear steels suitable for carburizing due to the pinning effect of Nb precipitates, which suppresses the austenite growth. [8,[12][13][14] Moreover, Nb-microalloyed gear steels exhibit excellent performance, including fatigue resistance, even after high-temperature carburizing. [15,16] However, microalloying of gear steels increases smelting costs, and the extent of grain refinement is also limited. Thus, optimizing the heat treatment process is necessary to achieve the maximum grain refinement effect.Cyclic quenching treatment is beneficial for grain refinement and improving mechanical properties and has recently gained increasing attention. [17][18][19] Jiang et al. [20] applied recycling phase transformation treatment three to four times on maraging stainless steel 00Cr13Ni7Co5Mo4Ti, and the grain size was refined to 10 μm equiaxed grains from the original grain size of 180 μm and leading to the significantly improved mechanical properties. Kościelna et al. [21] investigated the influence of individual parameters of cyclic heat treatment, for example, upper cycle temperature, heating and cooling rates between room temperature and the upper cycle temperature, and the number of cycles, on the grain refinement of Ti-48Al-2Cr-2Nb alloy. The cyclic heat treatment was efficient in the grain refinement of the Ti-48Al-2Cr-2Nb alloy with an initially coarse-grained lamellar microstructure. Mishra et al. [22,23] reported a simultaneous improvement in the ductility and strength of annealed AISI 1080 steel achieved by typical cyclic heat treatment. The plasticity (elongation = 34%) and reasonable strength (UTS = 942 MPa) of the material were significantly improved after four cycles. Cyclic heat treatments are not only favorable for refining the grain size of austenite but also for carbides, improving their morphology and making the carbide distribution more uniform. The simultaneous refinement of carbides and grain size (double refinement) can signific...

Thermodynamic Modelling for Heat Analysis and Prediction in Precision Transmission Systems: A Focus on Gear Operation

“…Traditional studies on gear heat have predominantly centered around conventional thermodynamic theories and empirical formulas, which have demonstrated the capacity to yield reasonably accurate results under specific conditions [25,26]. Nonetheless, these methodologies often reveal their limitations when confronted with intricate working environments characterized by variable loads, speeds, and lubrication conditions [27][28][29][30]. This is particularly evident when the dynamic characteristics and nonlinear behavior of gears are taken into consideration, domains in which traditional approaches exhibit deficiencies in terms of predictive accuracy and responsiveness.…”