Effect Of Nickel And Molybdenum Content On Microstructure And Properties Of High Chromium Cast Iron Grate Bars On Sinter Machine

Grate bars are important component and wearing part of sintering machine trolley.Its service life determines the production cost of sinter and the production efficiency of sintering machine equipment.Currently,it is mainly made of high chromium cast iron.In order to further improve the performance of the grate bars to meet the needs of different working conditions,alloying is often carried out by adding elements such as nickel and molybdenum.This article took five kinds of high-chromium cast iron grate bars with different nickel and molybdenum elements produced by the lost foam casting process as the research object.In order to obtain high-performance grate bars with longer life and lower cost,the influence of the content of nickel and molybdenum elements on the structure and performance of the high-chromium cast iron grate bars of the sintering machine were systematic researched by microstructure observation,heat resistance test,corrosion resistance test and wear resistance test.Observation of as-cast structure showed that the as-cast structure of grate bars with different contents of nickel and molybdenum was mainly composed of pre-eutectic dendrite and eutectic structure between dendrites,mainly austenite,carbide and martensite.The addition of nickel element was beneficial to stabilize austenite,and the austenite content had increased,and the molybdenum element was beneficial to the refinement of dendrite structure and improved the morphology and distribution of carbides.Under different contents of nickel and molybdenum,the hardness of the cast grate bars varied within the range of 37.9-42.1 HRC.When the nickel content was about 1.2%,increasing the molybdenum content was beneficial to increase the hardness.The heat resistance test showed that the microstructure of the grate bars after heat insulation and air cooling at different temperatures were still mainly composed of austenite,carbide and martensite,but the austenite matrix had obviously transformed into martensite.The hardness of the grate bars tend to decrease after air-cooling at lower temperatures,while at higher temperatures the hardness increased significantly and was gradually higher than the ascast hardness.As the oxidation temperature increased,the weight gain of oxidation increased significantly,and the anti-oxidation performance of the grate bars decreased.When the thermal fatigue temperature increased,the anti-fatigue performance of the grate bars decreased significantly.With the compound addition of nickel and molybdenum elements,the oxidation resistance and high temperature thermal fatigue resistance of the grate bars were improved.When the molybdenum content was about 1.0%,increasing the nickel content was beneficial to increase the heat resistance.The abrasion resistance test showed that as the load increased,the weight loss of the grate bars increased and the abrasion increased in the abrasive wear test.The wear mechanisms were mainly microscopic cutting mechanism and fatigue spalling mechanism.In the static corrosion test,compared with the corrosion resistance under alkaline and neutral conditions,the corrosion current density of the grate bars under acidic conditions was larger and the self-corrosion potential was negative,and the corrosion resistance was poor.In the erosive abrasive wear test,compared with the weight loss of neutral and alkaline corrosive medium,the grate bars had a larger weight loss under acidic corrosive medium,and the wear resistance was poor.The wear mechanisms under different corrosive mediums were mainly corrosion wear mechanism and abrasive wear mechanism.Under different wear conditions,the compound addition of nickel and molybdenum elements is beneficial to improve the wear resistance of the grate bars,and when the contents of nickel and molybdenum were about 1.2% and 1.0%,the wear resistance was best.Comprehensive analysis believed that by properly controlling the content of nickel and molybdenum elements,it had a significant effect on improving the microstructure and performance of high-chromium cast iron grate bars.When the contents of nickel and molybdenum were about 1.2% and 1.0%,the overall performance of the grate bars was better,and the service life was expected to be extended from 18 months to 24 months,which provided a certain reference basis for the production of high-performance high-chromium cast iron grate bars on sintering machine with long service life and low economic cost.