Effect of chromium addition on transformation characteristics of nickel and manganese alloy steel

Transformation characteristics of five 0.35 to 0.4% carbon alloy steels containing nickel, manganese and chromium were studied. It was observed that an acicular type of ferrite was precipitated in the intermediate transformation range of all the alloy steels investigated, but the amount of this type of all the alloy steels investigated, but the amount of this type of ferrite was maximum in chromium bearing steels. The hardness characteristics of isothermally transformed products were also determined and the curves plotted did not follow the usual trend and on the contrary, in the intermediate transformation ranges, hardness not only failed to increase with the decrease of isothermal transformation temperatures but it decreased considerably with decrease of isothermal transformation temperature. The extent of this irregularity was maximum in chromium steel. The irregularities in the hardness curve of intermediate transformation range were attributed to precipitation of acicular type ferrite, which resulted in the carbon enrichment of untransformed austenite leading to stabilization of austenite bainite reaction. (Dr. R.K. Dubey and Mr. P.K. Gupte, Scientists, National Metallurgical Laboratory, Jamshedpur)