Effect Of Cerium On Microstructure And Mechanical Properties Of HSLA100 Steel

HSLA100 steel is mainly used in the field of warships.In order to further improve the military strength at sea,higher requirements are put forward for the mechanical properties of HSLA100steel.This paper takes HSLA100 steel as the research object.The effects of aging time,aging temperature and Cerium on the mechanical properties and microstructure of HSLA100 steel were studied.The mechanical properties of HSLA100 steel after different aging processes and adding cerium were tested.The microstructure of HSLA100 steel was observed by OM,SEM and TEM,and the reasons for the changes of strength and plasticity were analyzed,so as to provide reference for the improvement of comprehensive mechanical properties of HSLA100 steel.The main results are as follows:(1)HSLA100 steel was aged at 500℃,550℃,600℃and 650℃for 2 hours respectively.The results show that with the increase of aging temperature,the strength of HSLA100 steel decreases gradually,while the plasticity decreases first and then increases.When the aging temperature is550℃,the plasticity is the lowest.The mechanical properties of HSLA100 steel are determined by precipitation strengthening and matrix softening.When the aging temperature rises from 500℃to 550℃,the amount of Cu rich phase increases,resulting in the gradual improvement of precipitation strengthening effect,but the matrix softening effect is dominant,so the strength of HSLA100 steel decreases.When the aging temperature is 550℃,the amount of Cu rich phase is the largest,and a large amount of Cu rich phase coherent with the matrix precipitates,resulting in the lowest plasticity of HSLA100 steel.When the aging temperature exceeds 550℃,the size and quantity of precipitates gradually grow and decrease,resulting in the weakening of precipitation strengthening effect,so the strength of HSLA100 steel further decreases.When the aging temperature is above 600℃,the precipitated Cu rich phase loses the coherence with the matrix,and the matrix structure recovers and recrystallizes,so the plasticity of HSLA100 steel is improved.(2)HSLA100 steel was aged at 600℃for 0.5 h,1 h,2 h,3 h and 4 h respectively.The effects of aging time on the microstructure and mechanical properties of HSLA100 steel were studied.The results show that with the extension of aging time,the strength of HSLA100 steel first increases and then decreases,while the plasticity first decreases and then increases.When the aging time is 1 h,the strength reaches the highest value and the plasticity reaches the lowest value.When the aging time is 1 h,the number of precipitated phases is large and the spacing is small,which leads to the peak of precipitation strengthening effect,so the strength reaches the highest,At this time,the precipitation is in the metastable structure transformed to fcc structure,resulting in the lowest plasticity of HSLA100 steel.When the aging time is more than 1 h,the smaller precipitate dissolves and the larger precipitate coarsens,resulting in the weakening of precipitation strengthening effect,so the strength decreases gradually.The precipitates are gradually transformed into fcc structure,so the plasticity is gradually improved.(3)HSLA100 steel with different Ce content was aged at 600℃for 2 h.The effect of Ce content on the microstructure and mechanical properties of HSLA100 steel was studied.The results show that when the Ce content increases from 0 to 0.038%,the strength of HSLA100 steel increases gradually,The plasticity increases first and then decreases.When the Ce content is0.016%,the plasticity is the highest.Ce can promote the precipitation of Cu rich phase.When the content of Ce is 0.038%,the number density of Cu rich phase reaches 312/μm~2,Cu precipitation has a good strengthening effect.When the Ce content increases from 0.016%to 0.038%,the size of Ce inclusion grows up,resulting in the decrease of plasticity.