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Abstract

This paper gives the results of an investigation into the effect of low-temperature heat-treatment upon the static properties of a hardened and tempered spring steel which had been previously subjected to torsional overstrain.

The results show that the textural stresses may be relieved by low-temperature heat-treatment without reducing the beneficial body stresses produced by the torsional overstrain. At large overstrains the textural stresses are so great that plastic deformation in the reverse direction takes place on unloading. Such deformations reduce the residual body stresses, and therefore the elastic limit strength, after low-temperature heat-treatment. To prevent the plastic deformation on unloading the specimens should be given the low-temperature heat-treatment before removal of the load.

Tests on six springs showed that the results obtained from torsion specimens are directly applicable to springs.

The improvement in the elastic-limit strength after low-temperature heat-treatment is considerable, about 33 per cent, while the increase in 0.1 per cent proof stress, although marked, is somewhat less and of the order of 8.5 per cent.

After the low-temperature heat-treatment the elastic-limit strength range (that is, the sum of the elastic-limit strengths in the positive and reverse directions) and the 0.1 per cent proof stress range are unaffected by the degree of overstrain. That is, for the steel tested and within the range of strain examined, torsional overstrain does not work-harden the material, any increase in strength in one direction being offset by an equal reduction in strength in the reverse direction.

The change of strengths in the two directions is approximately equal to the corresponding body stresses induced by the overstrain.

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The Effect of Torsional Overstrain upon the Static Strength of Spring Steel

Abstract

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References