Du Linxiu

INFLUENCE OF CONTINUOUS ANNEALING PROCESS ON MICROSTRUCTURE AND PROPERTIES OF BORON CONTAINING ENAMEL STEEL

Enamel product has been developed and more widely used with the development of metallurgical technology and equipments.Its quality is closely related to its metal substrate which needs both nice mechanical properties to meet deep-drawing request and excellent hydrogen trapping ability to meet sufficient fish-scale resistance.In order to obtain those properties,the influence of continuous annealing process on microstructural characteristics,mechanical properties and hydrogen permeation behavior of boron containing enamel steel was investigated.The material was produced and processed in lab and the continuous annealing process was performed using a continuous annealing simulator.It was found that in annealed sheet using high temperature and short time soaking,the sizes of both ferrite grains and cemetite particles within matrix are relatively larger,pearlite exist independently;while using relatively low temperature and long time soaking,the size of ferrite grains is smaller,cemetite particles within matrix are fine and dispersed,pearlite exist as chains.Within the scope of the annealing process adopted,strengths and work hardening exponent n-values of annealed sheets do not differ much,elongations and plastic anisotropy ratio r-values are both high.High temperature and short time soaking is more advantageous to steel sheet obtaining strong γ-fiber texture,which benefits the deep-drawing of sheet.There are certain scale of MnS inclusions,pearliteand cementite particles,whose interfaces between matrixes can be used as effective hydrogen traps,so the hydrogen diffusion coefficient in steel is quite low.Relatively fine ferrite grains+degenerated pearlite chains and fine dispersive cementite particles in steel sheet annealed using relatively low temperature and long time soaking is more beneficial to reducing hydrogen diffusion rate,improving the fish-scale resistance of enamel steel.