| RST330 steel is one of the enamel steel that used to make water heater liner,it need to have a good forming performance,enameling properties and good resistance to water erosion.There are two annular weld joints and one straight weld seam at the water heater liner,Weld joints are the weakest point of the water heater liner,they are determine the overall life of the water tanks.But every year a lot of water tanks are scrapped because of water leakage problem in weld joint.Therefore,in view of the above problems,this paper mainly studied on the mechanical properties,enameling properties and corrosion resistance of RST330 enamel steel.To found the reasons of water leaking problem at the weld joint,the mechanical properties,enameling properties,hydrogen permeation performance and the number and distribution of the precipitated phases of the weld joint were studied,and compared with RST330 steel substrate and Ti-bearing weld joint.In addition,in order to meet the diverse requirements of the usage of enamel steel,in this paper we also tried to enamel on stainless steel,and rolled enamel composite panels,they microstructure,mechanical properties,enameling properties were evaluated.The microstructure of RST330 steel were ferrite and some small pearlite colony at room temperature,with excellent mechanical properties,can meet the requirement of the production of water heater liner.Enameled RST330 steel at 800 ?,825 ?,850 ?,875 ?,900 ?,by comparing the surface quality of the enamel coating and the interface morphology of the steel/steel coating,the results shown that 850 ?~875 ? is the best enamel temperature range.The combination of steel and enamel coating at 800 ? and825 ? is weak,and at 900 ? enamel coating surface was uneven due to the excessive flow of enamel coating at 900 ?;at the temperature of 850 ?,875 ?,many island shaped anchor points appeared at the interface,The enamel coating and substrates were closely bonded under the combination effect of physical and chemical.Also Marangoni convection effect enabled the formation of interlocking topography at the interface.The more the anchor points,the bigger the contact area at the interface.The corrosion weight losses of the RST330 steel plate after enameling at 850? in 5% and 10% HCl solution is much smaller than uncoated RST330 steel and 316 L stainless steel plate.The steel plate after enameling has excellent corrosion resistance.The mechanical properties of ER50-6 weld joint and Ti-bearing weld joint could meet the welding technology standards.The microstructure of ER50-6 weld joint and Ti-bearing weld joint were normal at room temperature,more coarse than RST330 steel substrate.Coated RST330 steel,ER50-6 weld joint and Ti-bearing weld joint at 850?,the surface quality of enamel coating were good.The enamel coating of RST330 steel was evenly,the bubbles in the enamel coating of RST330 steel were evenly distributed and independent of each other,without cracks.However,there is a small amount of cracks in the ER50-6 weld and the Ti-containing weld,which is mainly due to uneven distribution of stress at the weld and the unevenness of the organization.The presence of cracks in the enamel layer of the weld makes it easy to fall off,which is one of the reasons of fish-scaling problem of the weld joints.Hydrogen permeation test results shown that the hydrogen diffusion coefficient of RST330 steel plate is 1.38×10-6cm2/s,and the hydrogen storage property of RST330 steel was the best.The diffusion coefficient of ER50-6 weld is 3.58×10-6cm2/s,the hydrogen storage property was the worst.The diffusion coefficient of the Ti-bearing weld joint was2.33×10-6cm2/s,which is higher than that of the RST330 steel,but lower than the hydrogen diffusion coefficient of the ER50-6 weld.The hydrogen storage ability of Ti-bearing weld joint was better than ER50-6 weld joint.The number of hydrogen traps per unit volume of RST330 steel was highest,followed by Ti-bearing weld joint,ER50-6 weld joint was least.These results shown that the use of Ti-bearing weld wire can improve the hydrogen storage property to a certain extent,then fishing scaling resistance was improved of the weld joint.In RST330 steel,a large of second phase particles were appeared,the second phase particles were mainly Ti N,they acted as hydrogen trap,which could greatly improve fish-scaling resistance,the number of second phase particles of RST330 steel was increased after enameling,Which is beneficial to the hydrogen storage property of the steel.In the ER50-6 weld joint,Ti N particles were also present,but the number was much less than that of the RST330 steel,and the number of Ti N particles in the ER50-6 weld after enameling was not change significantly.In the Ti-bearing weld joint,the number of second-phase particles was higher than that of the ER50-6 weld due to the addition of Ti element in the wire,and its hydrogen storage property was better than that of the ER50-6weld.But duo to coarse microstructure and uniform stress distribution at the weld joint,thehydrogen storage property of Ti-bearing weld joint was still worse than the substrate.The water leakage problem of the weld joint was the result of combination of multiple causes.The stainless steel was enameled at different temperatures,the enamel property was good when enameled above 850 ?.However,since the thermal expansion coefficient of the enamel coating was not match with the 321 stainless steel,the edge of the enamel product would shrink and collapse.The stainless steel-enameled steel composite plate obtained by hot rolling method presented good metallurgical combination.At the interface area of the composite plate,the hardness was increased duo to serious plastic deformation during rolling process.Enameled the enamel steel side on the composite plate,the enamel property was good with good adhesion.Which can meet the diverse requirements of usage of enamel products. |
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