AGMA 94FTM4-1994 pdf free

08-14-2021 comment

AGMA 94FTM4-1994 pdf free.Load Carrying Capacity of Nitrided Gears.
MATERIAL AND GEAR CONFIGURATIONS – The test gears were made from Mod. 39CrM0V13.9 steel forged bars. The chemical composition of the steel is shown in Table 1. The bars were cut and upset forged into blanks. The blanks were then normalized and hardened to two strength levels. The hardness and core tensile strengths (based on hardness) of the test gears after forging and heat treatment are shown in Table 2. Gear configuration and design parameters for the bending and pitting gears are listed in Table 3. The machined gears were nitrided by the ammonia gas nitriding process. Bending and pitting type test gears were nitrided separately at different times and to different case depths. The bending gears were nitrided to a minimum case depth of 0.94 mm (0.037 inches) to HRC 40. while the pitting gears were nitrided to a depth of (0.027 inches). A nitriding time of 240 hours or more at a nitriding temperature of 540°C (1004°F) was required to achieve the case depth of 0.94 mm. About 150 hours were needed to produce a case depth of 0.69 mm. The hardness gradient of the nitrided case in two bending gears of different core hardness is shown in Figure 1. A typical microstructure of the nitnded case is shown in Figure 2, and details of the white layer are depicted In Figure 3. Precipitation reactions in the nitrided case after long nitriding times caused preferential carbide formation along prior austenite grain boundaries. X-ray crystallography showed the compound layer to be y (Fe4N) with no £-phase (Fe2.N) present. Microprobe analysis showed the porous white layer to be rich in oxygen (oxides). The layer was quite soft (DPH 296- 318) in comparison to the adjacent diffusion zone (DPH
772-802). Using x-ray diffraction techniques, the residual stress distnbution in the nitnded case with increasing depth was determined in a gear tooth test coupon. The residual stress distribution had the form as shown in Figure 4. The surface exhibited moderate residual compressive stresses near the pitch diameter location and a relatively high residual stress at the root fillet. Low residual compressive stresses at the surface of funded Cr-Mo-V steels are apparently common after long nitriding times because of precipitation reactions occurring In the diffusion zone as was shown by Mittemeijer[1]. High compressive residual stresses were found below the surface with maximum values being at a depth of about 0.4 mm (0.015 in.). The flanks of the test gears were ground after nitriding. The tooth root area was left as heat treated.
BENDING FATIGUE TESTS – The bending fatigue tests were carried Out Ofl a mechanical resonance pulsator of 200 kN capacity. The frequency was 50 Hz. The gear teeth were clamped and loaded in such a way that the load direction was tangent to the base cirde. The bending fatigue gear test set up is shown in Figure 6. A preload of 5 to 7 kN was used. The fatigue equipment is set up to make twelve separate tests on each gear. The endurance strength in bending was calculated by the DIN 3990(2] method.
The bending fatigue S-N curves for 50% failure probability of the Mod. 39CMoV13.9 gears with two different core strengths are given in Figures 6 and 7. The curves are practically identical, with the lower core strength material showing a slightly higher endurance limit value at 5 x 106 load cycles (c,0 of 1020 MPa or 148 ksi versus 1008 MPa or 146 ksi, respectively). The fatigue endurance limit for this material is rather high when compared to other nitriding steels tested at FZG. The carbido banding in the diffusion zone and the presence of the white layer in the root area apparently did not have an adverse affect on the bending strength curve in the low cyclic regime and the presence of a noticeable “knee” in the S-N curve after a relatively short cyclic life (105 cycles) suggest a material which is prone to overload damage. Tests have shown that through- hardened, carburized, and induction hardened gears are relatively immune to overload effects. Their damage lines according to French[3] are generally close to and parallel to the S-N curves. Nitrided gears, on the other hand, have damage lines which typically deviate substantially from their S-N curves.
Therefore, the material’s performance under occasional overloads was investigated.AGMA 94FTM4 pdf download.

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