An Investigation of Structures and Properties of a Mn-Mo-Co Maraging Steel by Rapid Solidification

A new maraging steel,Mn-Mo-co steel,has been made with the aim ofsaving the alloy elements,Co and Ni.Although the strength of the steel can reaoh to or even overtake the strength level of commercial 18Ni maraging steel,the toughness of this steel is quite low.It is probably that the second phases vere precipitated along the grain boundaries before the ageing pro-cess to be carried out. In order to improve the properties of the steel,a rapid solidification technique has been used and the relationships between structures and mechanical properties have been studied as well.
The experimental results shown that the rapid cooling thin metal belt has a very fine grain size and high solid solubility of alloy elements.In thls microstructure,the vacancies and dislocation are so high that an homogeneous cell structure are formed.The transverse section of the rapid cooling belt consists of two layers,upper and lower layers.The microstructure of lower layer which is direct contact with the roller surface consists of equiaxed fine crystals with a diameter less than lμm,and the upper layer make up of fine columnar crystals.It has been also found that the rapid cooling layer always has a tough fracture,but columnar crystal layer,i.e.upper layer, usually has a cleavage fracture. In the ageing condition, the hardness of the rapid cooling belt is always higher than that of quenched steel having the same chemical composition. However,other mechanical properties of the mi-crocrystal steel formed by rapid solidification are still remained for further investigation.