1. Material and technical requirements of bow spring
The material of the bow spring is 60Si2MnA steel; the hardness of the technical requirements is hrc49 ~ 51, and the repeated loading test under the working state should meet the technical requirements. The process flow is as follows: blanking → acceptance → first quenching and tempering → initial forming → intermediate annealing → final forming → second quenching and tempering → pre deformation treatment → final tempering → inspection → warehousing.
2. Key points of heat treatment process for bow spring
1) The purpose of the first tempering and tempering is to adjust the structure of the steel plate. The blank of bow spring is 145.5 mm × 14.5 mm × 3 mm plate, with 3% samples in each batch (the size of test piece is 35 mm × 15 mm × 3 mm). The blank and sample are loaded into the spreader, heated in the salt bath furnace and cooled by oil.
Tempered parts shall be cleaned, degreased and sandblasted, and protective coatings shall be applied on the surface of parts and samples. The tempering temperature is 720 ℃± 10 ℃, holding for 60min, and air cooling. Check the hardness hrc26 (check the hardness after grinding the surface of the sample > 0.2mm).
2) Intermediate annealing is carried out after the initial forming of bow spring. Protective coating shall be applied before intermediate annealing, and residual iron wire coating shall be removed by light sand blasting after annealing, and then final molding shall be carried out.
3) The purpose of the second quenching and tempering is to shape the final performance of the parts. After the parts are finally formed, the iron wire (or special spreader) is bound, and then heated in a fully deoxidized salt bath, and then quenched with oil and cooled thoroughly. After oil quenching, the oil is cleaned and degreased with water at 60 ~ 80 ℃, and then tempered at 425 ℃± 10 ℃. After tempering, grind the surface of the sample to be ≥ 0.2mm, and the hardness should be hrc49 ~ 51.
4) Finally, after the hardness is qualified, the parts are subject to sandblasting treatment, and then the pre transformation treatment is carried out. The actual measurement position is pressurized to 55mm ± 1mm and maintained for 30 ~ 40H, and then the final tempering is carried out.