Selection of Carburizing Gear Steel for Carburizing Furnace
1. Requirements for Hardenability of Carburized Gear Steel for Carburizing Furnace
The hardenability of steel is mainly to ensure the hardness of different gears to meet the requirements of contact fatigue strength and bending fatigue strength. At the same time, the hardenability bandwidth fluctuation should be as small as possible to facilitate the control of heat treatment deformation of gears. For low-speed and heavy-duty gears, enough core hardness should be guaranteed, that is to say, the core strength should be guaranteed. ME class gears require that the core hardness be above 35 HRC. Therefore, for large size workpieces with high hardenability requirements, only the way to choose steel is found, that is, high and medium alloy carburized steel with good hardenability is selected to manufacture. For example, the surface hardness of 20CrMnTi rod with diameter of 60mm is over 30HRC after quenching and tempering, and the hardness of the central part is about 25HRC. After quenching and tempering, the hardness of the center of the rod reaches 37HRC, so 20CrMnTi material is suitable for manufacturing gears with modulus less than 12.
The diameter of 20CrNi2Mo rod is 60mm. After quenching and tempering, the surface hardness of 20CrNi2Mo rod is more than 35HRC, 1/2R is more than 30HRC, and the central part is about 27HRC. After quenching and tempering, the surface hardness of the rod with diameter of 25 mm is over 39 HRC, at 1/2R it is over 37 HRC, and the hardness of the central part is about 36 HRC.
Therefore, gears requiring high speed (low speed) heavy load and safe and reliable operation should be made of 20CrNi2Mo. For gears with low speed, heavy load and large cross-section, materials with better hardenability can be chosen, such as 17CrNiMo6 (domestic 17Cr2Ni2Mo), 18Cr2Ni4WA, 18CrMnNiMoA, 20Cr2Ni4A, etc.
2. Steel for Carburizing Gear in Carburizing Furnace
The result of carburizing is to change the chemical composition and properties of the metal surface, so that the surface of the workpiece of this kind of steel has the characteristics of high hardness and wear resistance after quenching of common high carbon steel, while the core still retains the good plasticity and toughness after quenching of low carbon steel. Therefore, low carbon steel and low carbon alloy steel are mostly used for carburizing gear.