G52# alloy is a high-temperature, wear-resistant, non-magnetic special bearing material that introduced the G50# alloy bearing rings forging, turning process, and its production test.
In this paper, the forging and turning process of G52 # alloy bearing rings are tested and analyzed.
1. Forging of G52# alloy bearing rings
1.1 G52 # alloy forging characteristics
G52 # alloy Gr23Ni28Mo5Ti3AlV, Fe-Cr-Ni-based austenite precipitation hardening, high temperature, wear-resistant, non-magnetic materials, is my development of special bearing materials. The metal material is difficult to smelt, expensive, and characterized by:
- (1) More alloying elements (see Table 1), poor thermal conductivity, plasticity, forging deformation resistance, and sensitivity to crack extension tendency.
- (2) Hardness by solid solution strengthening, aging treatment between the matrix precipitation of metal compounds Ni3AlTi particles to achieve.
- (3) The coefficient of linear expansion is large.
Table.1 G52 # alloy steel chemical composition wt%
According to the above characteristics of the metal material, we must choose the appropriate forging method to reduce deformation cracking; ring billet in the forging to minimize the auxiliary production time, try to keep each billet forging temperature consistent, the final forging temperature consistent, reduce the size of the forging after cooling dispersion.
1.2 Forging process of G52# alloy bearing rings
G52 # alloy forging process is: billet → car OD to remove surface cracks → wire cutting into material segments → 740 ℃ preheating → 1170 ℃ high-temperature heating and insulation upsetting, molding → two fire heat insulation punching, leveling high → three fire reheating and rewarming reaming (i.e., ultimately, in the D51-250 reaming machine on the molding).
Problems: Although after three-fire heating, forging in each station was especially upsetting, the reaming station billet is still cracked, scrap rate is high. Analyze the reasons.
- (1) The raw material surface has potential cracks.
- (2) The heating and holding time are short.
- (3) Forging process parameters, mold design, and preheating are unreasonable.
1.2.2 Measures taken
- (1) Strictly control the surface quality of the billet before forging, before car off the surface cracks in the bar, because even if the surface has 0.1 mm cracks, the upsetting process will cause the billet cracking.
- (2) In the billet-making process, each process in the billet temperature drop is required to return to the furnace heating; strict control of the inner and outer ring furnace loading; the high-temperature zone must have appropriate holding time, usually in the middle-temperature zone, high-temperature zone holding time is strictly according to the control of the 1.5 mm/min, not only heat through but also cannot be heated for too long, so as not to grow up the grains; in the upsetting, shaping, punching, expanding holes in the forging wherever in the mold in contact with the workpiece Parts need to be preheated to 300 ℃.
- (3) Mold and workpiece contact surface roughness requirements of high in forging the best graphite lubrication.
By taking the above measures, the original three-fire, four-fire forging process to two-fire forging, the test proved that not only saves energy but also greatly reduces the scrap rate; after forging the ring by turning, aging treatment can achieve the hardness requirements of the final parts.
2. Turning of G52# alloy bearing rings
Given the special characteristics of G52# alloy, forging left a large amount, and forging after the ring hardness of up to 30 – 40 HRC, these factors increase the difficulty of turning and due to the G52 # alloy non-magnetic, sticky knife, cutting and processing of poor, resulting in poor tool heat dissipation, tool wear increased, reducing the cutting ability and life of the tool, so the productivity declined. This selection of different cutting tools and turning process parameters for comparison test.
2.1 Selection of tool material
Select high-strength carbide tools such as YB435, YW2, rough turning forging blanks, surface coating tool YB415, and fine turning forging blanks (see Table 2).
Table.2 Tool parameters and practical situation
|Tool parameters||Practical situation|
|Material||Hardness/HRC||Bending strength/(N.mm2)||Machined noodles||Shift production/piece||Tool usage/piece|
|YW2||≥90.5||1350||Coarse turning outer diameter||40||5|
|YW1||≥91.5||1180||Precision turning outer diameter||50||4|
From Table 2 can be seen that the rough turning G52 # alloy selection YB435 tool fine turning G52 # alloy selection YB415 tool is more reasonable and more efficient.
2.2 Selection of turning process parameters
In the turning process, generally, the higher the hardness of the workpiece material, the smaller the cutting speed should be. Because G52 # alloy materials do not have mature turning process parameters to choose from, concerning 9Gr18 and M50 steel bearing ring turning process, proposed G52 # alloy bearing ring turning process parameters (see Table 3), the use of good results.
Table.3 G52# alloy bearing ring turning process parameters
|Machine model||Tool material||Processing process||Lathe speed/(r·min-1)||Feed amount/(mm·r-1)|
|CA6140||YW1||Vehicle outer diameter||80-100||0.32-0.50|
|CA6140||YB435||Vehicle outer diameter||120-130||0.60-0.80|
2.3 Improvement of processing technology
Turning the outer diameter of the traditional process generally supports the inner diameter of a piece of turning, low efficiency. Now, the process is changed to wear a few pieces of shaft turning together, greatly improving productivity. Still, the new process requires processing before the inner diameter of the ring size unity small dispersion.
For the production of G52 # alloy bearings, some technical difficulties, such as controlling the grain size of forgings, improving the hardness of forgings, eliminating cracks in forgings, and reasonably determining the number of forgings to stay, etc., still need to be fully resolved. Improving the manufacturing precision of G52 # alloy bearings, improving production efficiency, reducing production costs, etc., still requires a lot of work.
Authors: Li Hong, Hao Xueling, Fang Fang, Wang Feng