Effect of Alloy Elements on Microstructure and Mechanical Properties of High Carbon Bainitic Steels
With the great demand on resource-saving and energy-saving,it is of necessity to develop high performance low cost steels.High performance steels,especially extremely high strength and good toughness steels,have wide application in the manufacturing of aircraft engine shafts,automotive and truck parts,crane arms,protective armors,and other important structures.The main goal is to reduce the weight and to improve the safety of the structures.The advanced high strength steels (AHSSs) with high ductility have been extensively studied with the aim.It is well known that carbide free bainitic steel,which has been developed since last decades,is one of them.Carbide-free bainitic steels exhibit excellent mechanical properties and are widely applied in industry.New carbide-free bainitic steels called Super Bainitic Steel or NANOBAIN represent a new generation of materials with high strength and toughness.Since the discovery of nanostructured bainitic steels,many researchers have been striving to explore both transformation mechanism and improvement on mechanical properties.It is well-known that both cobalt and aluminum can accelerate transformation by increasing the driving force.But majority of the investigations have been conducted to evaluate the mechanical properties of nanostructured bainitic steels with the alloys both Co and Al,there is little research has been reported about the effects of these tow alloys,respectively.So in the current paper,two new nanostructured bainitic steels were designed by addition of different amounts of Co and Al,respectively.The chemical compositions are given in Table 1.These two steels were austenitized at 1000 °C for 30 min and austempered at 220 °C for 24 h,240 °C for 12 h and 260 °C for 4 h.From XRD patterns and microstructures,it can be seen that bainitic ferrite (α) and retained austenite (γ) exist in these samples.The ultimate tensile strength and the yield strength of Al-contained steel are reached up to ~2000 MPa and ~1100 MPa,respectively,and accompanied by the elongation of ~16%,the Charpy impact energy of ~25 J and the hardness of ~600 HV3.Then the ultimate tensile strength and the yield strength of Co-contained steel are reached up to ~1900 MPa and ~1085 MPa,respectively,and accompanied by the elongation of ~9.5%,the Charpy impact energy of ~23 J and the hardness of ~650 HV3.From the data above,one can see that excellent combination of mechanical properties were achieved in Al-contained steel.This is owed to the fact that strength is mainly provided by the extremely fine bainitic ferrite and ductility is mainly controlled by the retained austenite.The extremely fine bainitic ferrite showed in the high magnification TEM images of the Al-contained steel specimens is ~35 nm-thickness which was smaller than the thickness (~48 nm) of the Co-contained steel specimens (Fig.1).The volume fraction of retained austenite in the Al-contained steel samples is ~36%,which is more than that (~30%) in the Co-contained steel samples.The specific influence mechanism remains to be further studied.
nanostructured bainitic steel alloy elements Al and Co austempering microstructure mechanical properties
YANG Jing WANG Tiansheng PENG Jinhua
School of Materials Science and Engineering, Northeastern University, Shenyang 110819, Liaoning, Chi State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao School of Resources and Materials, Northeastern University at Qinhuangdao, Qinhuangdao 066004, Hebei
国际会议
成都
英文
771-772
2016-11-16（万方平台首次上网日期，不代表论文的发表时间）