Research On Microstructure And Properties Of Austempered Gray Iron

With the rapid development of social economy, the auto industry is more and moreimportant in the national economy. As the internal combustion engine is the powercomponents of the car, the cylinder is one of the main wearing parts of internal combustionengine, so the usage of cylinder jacket has a big influence to the auto industry.This articleusing the gray cast iron cylinder, austeniting processing first, and then in the salt bathfurnace isothermal quenching, air cooling after a certain period of time as to obtainaustenite and ferrite as main matrix organization. Because the austenitizing temperature hasnot much influence on organizational changing, we mainly discuss the effect of differentisothermal quenching process on the microstructure and mechanical properties ofaustempered gray iron(AGI).The gray cast iron in the test after austenitizing1h, thenaustempered under different temperature(240℃,260℃,280℃,290℃,300℃,310℃), andafter1h austenitizing, then290℃austempered for different time(0.5h,1h,1.5h,2h).Study thedifferent organizations and performance they obtain. Main conclusions are as follows:1. After900℃austenitizing for1h, organization complete austenitizing, austenite content isdifferent after different isothermal quenching process, the austenite content of290℃austempered AGI is the highest, as was25.1%.And carbon content of retained austenite isbetween240℃to280℃has slightly increased with temperature rise, rise gently between280℃to310℃, about2.2%.2. After heat treatment, as the austempered temperature increase from240℃to310℃,Brinell hardness reduced from447HB to302HB, as the as-cast hardnees is251HB,it has anobvious improvement.As the austempered time increase，the hardnees gradually reducedtoo..3. Through the study of AGI mechanical properties,it has been found that the tensileproperties and wear properties of the AGI after290℃isothermal quenching process issuperior to AGI after other austempered temperature.Tensile strength of290℃up to400MPa, break elongation ratio reached2%.In the case of oil lubrication piston ring material asfriction pair, force400N test conditions, at290℃has the lowest friction coefficient is0.0847, less than0.0976before heat treatment. Illustrates that the heat treatment processobviously improve the performance of gray cast iron, achieved the purpose of heattreatment.4. Using Ansys finite element analysis software, based on the dynamic simulation betweenpiston ring and cylinder, contrast the stress state of the cylinder jacket’s inner wall beforeand after heat treatment. Due to the elastic modulus is higher, the coefficient of frictionwere lower, before and after heat treatment the simulated stress value from18.1803MPa to13.6584MPa, the strain values from0.115×10-3reduce to0.091×10-3, reduce deformationfrom4.097μm to3.333μm.