Impact Tests of Strained Wrought Iron and Cast Steel

Abstract

In the proof tests of chain cables and crane chains in several leading countries, it isrequired that the chain should. stand a load which is nearly 72% of the breaking strength.
Wrought iron may, however, become brittle after it was strained by a stress beyond a certain limit and if this embrittling occur by the proof test, the chain will be used in a brittle condition after the test, which must, therefore, be revised.
Izod tests were made on test-pieces taken from three samples of wrought iron, which were strained to various degrees by a tensile testing machine to know the limit and the extent of embrittling by the strain.
The same tests were made on test pieces of a low carbon cast steel, as cast steel is often employed for chain cables recently.
The results of tests were as follows:-
(1) The Izod value of wrought iron is reduced after it was strained by a tensile stress over 60% of the breaking strength.
(2) The degree of embrittling is variable according to the material, some samples become only slightly brittle and the others lose. nearly 2/3 of thpir impact value after they were loaded about 72% of the breaking stress.
(3) In some cases the impact value of strained samples is greatly reduced at low temperatures while non-strained material remains the same.
(4) Low carbon cast steel becomes brittle by strain when stressed in the annealed state, but it does not when it was hardened and tempered.
It may thus be concluded that either the proof test for chains specifying excess load should be reasonably altered or the chains must be properly heat-treated so that the impact value will not be reduced by the strain of the proof test