On the Carbide Precipitation by Heating in Solution-Treated High-Manganese Steel

Study on austenitic high manganese steels-I

Abstract

Carbide precipitations in isothermal and continuous heated Hadfield steel after solution-treatment were studied. Results obtained were as follows:
1) Solution-treateds steel precipitated primary carbide isothermally in accordance with an C-curve which has the nose at about 650-700°C, and also precipitated secondary pearlitic constituent isothermally with an C-curve which has the nose at about 600°C
2) At the primary stage, carbide films were formed at austenitic grain boundary. In the low temperature range, carbide film formations were delayed markedly, and then, platelet carbide were formed along the cleavage plane of grains. In the high temperature range, carbide films changed to granular particles and gradually takes coherent shapes.
3) The nucleations of pearlitic constituents were most rapid at about 600°C, but growth velocities of pearlite has max. value at about 500°C.
4) Secondary precipitates, pearlitic constituents, were very fine lamellar pearlite, and lower temperature precipitates has finer lamellar than precipitates at higher temperature.
5) In continuous heating, steels precipitated boundary carbides, platelet carbides and pearlitic constituents at about 500-600°C. It suggested that no pearlites were precipitated when heated at a velocity of above about 15°C/mn and also no carbides were precipitated when heated at a velocity of above about 45°C/mn.
6) Mechanical properties were injured by heating at above about 350°C, since platelet carbide precipitations began at that temperature. Tensile strength lowered to minimum value at 750°C, since carbide films markedly grew at that temperature, and impact value, elongation and reduction fo area lowered to minimum value at pearlite precipitation range. Increased hardness were mainly affected by platelet carbide precipitations.