MICROSTRUCTURE AND MECHANICAL PROPERTIES OF SOME EXTRA LOW-CARBON - MANGANESE - SILICON STEELS.

The investigation described was primarily designed to assess the feasibility of using manganese and silicon in amounts much larger than now customary in developing new steels with a lath martensite structure and good mechanical properties. The following two laboratory steels seem promising. Both contain 0. 03% carbon. One, with 2. 6% Mn and 1. 0% Si, which has a lath structure only on quenching, has a proof strength in excess of 77 kg/mm**2 with good impact properties down to minus 70 degree C in the 1000 degree C water quenched condition. The other, which has a composition of 5Mn-1. 5Si and forms lath structures over a wide range of cooling rates, when identically heat treated, has a proof strength in excess of 95 kg/mm**2 with good impact properties down to minus 18 degree C. It is suggested that the 2. 6Mn-1Si composition may be rendered air hardening by altering its manganese content and thus become more useful.