Preparation and microstructure properties analysis of high nitrogen steel bolts for marine engineering
The bolts used in marine engineering are immersed in seawater for a long time,which requires high strength,low yield ratio and good corrosion resistance.A low-cost nickel-saving high nitrogen steel bolt was de-signed and prepared.The microstructure observation,XRD detection,mechanical properties test,immersion corro-sion test and potentiodynamic polarization curve test were carried out and compared with 316 stainless steel bolts commonly used in marine engineering.The results show that microstructure of the bolts in this test is austenite,and the microstructure contains a large number of twins and a small amount of second phase nitride precipitation.The tensile strength of test bolts is 877 MPa,the yield strength is 690 MPa,the elongation after fracture is 7.3 mm,and the yield ratio is 0.79.Under the condition that the tensile strength of test bolts is not lower than 316 stainless steel bolts,the yield ratio and the elongation after fracture of test bolts is 84％and 2.16 times of that of 316 stain-less steel bolts,respectively.The mechanical properties are obviously better than those of 316 stainless steel bolts,which meet the requirements of 80 grade austenitic stainless steel bolts.The corrosion test of bolts immersed in 6％FeCl3 solution for 15 d shows that the corrosion weight loss ratio of the test bolts is 0.051％,which is 38.6％of the corrosion weight loss ratio(0.132％)of 316 stainless steel bolts.The results of potentiodynamic polarization curves show that the self-corrosion potential of the test bolts is more positive than that of 316 stainless steel bolts,the cor-rosion current density is smaller,and the local corrosion resistance is better.In summary,the high nitrogen steel bolts in the test has lower cost and better mechanical properties,pitting corrosion resistance and local corrosion re-sistance than 316 stainless steel bolts.This study provides a theoretical basis and data support for new materials of high strength bolts for marine engineering.
high nitrogen steel boltmechanical propertycorrosion resistanceweight loss ratepolarization curve
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NSTL
万方数据
