Investigation of the mechanical properties of steel 40KhFA by the mathematical statistics method

Conclusions

• 1. Calibrated rolled steel 40KhFA, used for manufacturing high-pressure spindles, has substantial differences in the values of$\delta _5$ in a given range of$\sigma _{\text{b}}$ after heat treatment.

• 2. The number of samples with mechanical properties not satisfying GOST 10493-63 specifications is 19.3% of the total number tested in the range of$\sigma _{\text{b}} = 80 - 90{\text{ kg/mm}}^{\text{2}}$. The theoretical probability of$\delta _5 \leqslant 17\%$ in this range is 12.3%.

• 3. The specific elongation specified by GOST 10493-63$\delta _5 \leqslant 18\%$ can be obtained with a probability of 95% only in the range of$\sigma _{\text{b}} = 70 - 86{\text{ kg/mm}}^{\text{2}}$. In the range of$\sigma _{\text{b}} = 80 - 96{\text{ kg/mm}}^{\text{2}}$ the probability of at least 95% can be obtained only with$\delta _5 \geqslant 16\%$.