Microstructure And Mechanical Properties Of High Nickel Cast Iron Rod By Horizontal Continuous Casting

In recent years,with the rapid development of marine economy,the demand of high nickel cast iron for marine equipment manufacturing industry is increasing,which brings forward the higher request to the performance and production efficiency for high nickel cast iron.Under the premise of ensuring the strength and hardness of high nickel cast iron,improving the production efficiency and subsequent processing is the key to produce high quality high nickel cast iron.High nickel cast iron for horizontal continuous casting has many advantages,such as compact structure,small graphite flake,few casting defects,excellent comprehensive machining performance,high material utilization efficiency and so on,therefore the production for horizontal continuous casting get more and more applications.In this paper,high nickel cast iron rod with diameter 54mm were prepared by horizontal continuous casting.The microstructure of as cast high nickel cast iron rod was investigated by means of metallurgical microscope and scanning electron microscope and the microstructure formation mechanism of high nickel cast iron bar for horizontal continuous casting was studied.Under the condition of as cast,high nickel cast iron rod have certain strength and hardness,but the plasticity and toughness are poor,and there are hard particles,which affect the machinability,Therefore,high-nickel cast iron rod are subjected to normalizing and annealing treatment respectively.The effect of heat treatment on the microstructure and mechanical properties of high nickel cast iron rod was studied.The mechanical properties of high nickel cast iron rod with horizontal continuous casting before and after heat treatment were tested,the influence of heat treatment process on the mechanical properties of high nickel cast iron rod was investigated.The following conclusions were drawn:(1)The molten iron is under the condition that adopting duplex melting technolog,and the casting temperature is about 1440?.Inoculation agent is 75 ferrosilicon about adding 1.2%,and also titanium ferritin was added before pouring about 0.2%.The tensile strength of the rod is 272.7MPa.The hardness(HB)is 131.1 and the elongation is 3.0%.The mechanical properties are in accordance with ASTM A43684(2015)standard.(2)The external microstructure of high nickel cast iron rod is a kind of advanced austenite+D type graphite+a small amount of carbides,and the center of the rod is coarse dendritic austenite+D type graphite+a small amount of E-type graphite and carbide.The external carbides of high nickel cast iron rod for the horizontal continuous casting are distributed in the austenite secondary crystal axis and the austenite grain boundaries,which are small lumps and long rods.The carbides in the core are mainly distributed in the austenite grain boundaries department,which was massive.(3)In the temperature range of 950??1050?,with the increase of temperature,the decomposition speed of carbide is accelerated and the diffusion rate of carbon and chromium atoms is accelerated.Carbide content in high nickel cast iron rod is decreases.The size of residual carbides decreases and the morphology tends to round.After heat insulation at 1050?,the bars have the least carbide content,the smallest size and the most rounded shape.(4)The best heat treatment process is normalizing about 1050?.The normalizing ensures the strength and hardness of the horizontal high nickel cast iron rod by horizontal continuous casting and at the same time it reducing and reducing carbide size and quantity.The tensile,strength hardness(HB)and elongth of the rod after heat treatment were 525.8MPa,215.6 and 3%.