The Carburizing Behavior of High‐Temperature Short‐Time Carburizing Gear Steel: Effect of Nb Microalloying

Abstract

Herein, the carburizing behavior of 20MnCr5 gear steel with different Nb contents after carburizing with the temperature from 900 to 950 °C and the corresponding holding time from 8 to 5 h are investigated. The theoretical results of carbon content and the depth of carburized layer for the two experimental carburizing processes should be the same according to the classical diffusion model. However, the experimental results show that the carbon content of the entire hardened layer increases, and the depth of carburized layer increases by 35% after high‐temperature carburizing. The carbon content of 0.061%Nb steel on the outer surface increases, but the depth of carburized layer remains unchanged. It is found that the theoretical D values at 900 °C and 950 °C are 2.0 × 10−7 and 3.3 × 10−7 cm2 s−1, respectively. However, the experimental D value is much larger than 5.0 × 10−7 cm2 s−1. The carbon diffusion is greatly promoted by high‐temperature carburizing because the number of excess carbides on the outer surface decreases. The diffusion coefficient decreases after the addition of Nb due to forming a large number of small particles of Cr7C3 and NbC, but the effect is only obvious on the outer surface.

Effect of Case Depth and Hardness Distribution on the Rolling Contact Fatigue Performance of G20CrNi2MoA Carburized Steel

“…The volume fraction of RA is typically higher when the surface carbon content is higher. [12] Previous studies [13,14] state that grain size and grain boundary misorientation are also factors that affect fatigue performance. Therefore, the grain size and grain boundary misorientation of the surfaces of the specimens were tested after heat treatment using EBSD.…”

A novel CrCx/C-Cr multilayer PVD coating for cotton picking spindle: committed to replacing traditional electroplated chromium coating

“…However, as a low carbon steel, the hardness and wear resistance of 20CrMnTi is poor [4]. When used as wearresistant materials, surface strengthening treatments such as carburizing and chromium plating are necessary [1,5].…”

Effect of Precipitated Particles on Austenite Grain Growth of Al- and Nb-Microalloyed 20MnCr Gear Steel

“…High-temperature carburization for gears is becoming more and more attractive in the past years because it can remarkably shorten the processing time, improve the production efficiency of the gear steel carburizing process, and reduce production costs [9][10][11][12]. However, the heating temperature has a significant impact on the grain growth of austenite; thus, prior austenite grains growing abnormally will reduce the properties of the materials [13][14][15][16].…”