Intergranular corrosion(IGC) behavior of the stabilized ultra-pure 430 LX ferritic stainless steel(FSS) was investigated by using double loop electrochemical potentiokinetic reactivation(DL-EPR) and oxalic acid etch t...Intergranular corrosion(IGC) behavior of the stabilized ultra-pure 430 LX ferritic stainless steel(FSS) was investigated by using double loop electrochemical potentiokinetic reactivation(DL-EPR) and oxalic acid etch tests to measure the susceptibility of specimens given a two-step heat treatment. The results reveal that IGC occurs in the specimens aged at the temperature range of 600–750℃ for a short time. The aging time that is required to cause IGC decreases with the increase of aging temperature. A longer aging treatment can reduce the susceptibility to IGC. The microstructural observation shows that M(23)C6 precipitates form along the grain boundaries, leading to the formation of Cr-depleted zones. The presence of Cr-depleted zones results in the susceptibility to IGC. However, the atoms of stabilizing elements replace chromium atoms to form MC precipitates after long-time aging treatment, resulting in the chromium replenishment of Cr-depleted zones and the reduction of the susceptibility to IGC.展开更多
The microstructure evolution and intergranular corrosion(IGC) behavior of high nitrogen martensitic stainless steels(MSSs) by partial replacing C by N were investigated by using microscopy, X-ray diffraction, nitric a...The microstructure evolution and intergranular corrosion(IGC) behavior of high nitrogen martensitic stainless steels(MSSs) by partial replacing C by N were investigated by using microscopy, X-ray diffraction, nitric acid tests and double-loop electrochemical potentiokinetic reactivation(DL-EPR) tests. The results show that the partial replacement of C by N first reduces and then increases the size and content of precipitates in high nitrogen MSSs, and converts the dominant precipitates from M23C6 to M2N,furthermore first improves and then deteriorates the IGC resistance. The high nitrogen MSS containing medium C and N contents provides good combination of mechanical properties and IGC resistance.展开更多
Austenitic stainless steels,when exposed to welding conditions or aging for length of service,it's observed the formation of numerous deleterious phases,such as several kinds of carbides type MC,M6C,M7C3,M23C6,and...Austenitic stainless steels,when exposed to welding conditions or aging for length of service,it's observed the formation of numerous deleterious phases,such as several kinds of carbides type MC,M6C,M7C3,M23C6,and intermetallic secondary phases(sigma,chi,laves),which cause the process of intergranular corrosion.The aim of this work was verifying the formation of the types of carbides and/or intermetallic phases existing in the stainless AISI 304 at 800℃,varying the timing of heat treatment between 30,360 and 1,440 min.The optical microscopy analysis revealed the predominant formation of the carbide type M23C6.The results of DL-EPR(double loop electrochemical potentiokinetic reactivation)tests showed a gradual increase in the precipitation of this carbide with the increase of treatment time.The potentiodynamic polarization showed that the precipitation of this carbide reduce the formation of the Cr2O3 passive layer,suggesting that the precipitate carbide to be predominantly of the Cr23C6 type.展开更多
The aim of this work is evaluate the intergranular corrosion on UNS S31803 steel,with heat treatments at 800℃,varying treatment times of 30 mins,360 mins and 1,440 mins.The results confirm the formation of o phases a...The aim of this work is evaluate the intergranular corrosion on UNS S31803 steel,with heat treatments at 800℃,varying treatment times of 30 mins,360 mins and 1,440 mins.The results confirm the formation of o phases and secondary austenite(γ2).For the analysis of the influence of o andγ2 phases,metallographic analysis were conducted through optical microscopy,potentiokinetic reactivation electrochemical techniques and potentiodynamic polarization in NaCI 3.5%solution.Microstructural analysis has shown a formation ofγ2 and o phase in heat treatment,due to diffusion of chromium and molybdenum fromδphase to y phase,precipitating onδ/γandδ/δinterfaces.The DL-EPR(Double loop electrochemical potentiokinetic reactivation)results have shown an increase of the DOS(degree of sensitization)for long periods of time on heat treatment.The results of potentiodynamic polarization showed a reduction of the corrosion and pitting potentials,followed by an increase of the current density when the UNS S31830 steel is heat treated during long periods of time.展开更多
基金financial support from the National Key Research and Development Program of China (No. 2018YFB0704400)the National Natural Science Foundation of China (Nos. 51501041, 51871061 and 51671059)
文摘Intergranular corrosion(IGC) behavior of the stabilized ultra-pure 430 LX ferritic stainless steel(FSS) was investigated by using double loop electrochemical potentiokinetic reactivation(DL-EPR) and oxalic acid etch tests to measure the susceptibility of specimens given a two-step heat treatment. The results reveal that IGC occurs in the specimens aged at the temperature range of 600–750℃ for a short time. The aging time that is required to cause IGC decreases with the increase of aging temperature. A longer aging treatment can reduce the susceptibility to IGC. The microstructural observation shows that M(23)C6 precipitates form along the grain boundaries, leading to the formation of Cr-depleted zones. The presence of Cr-depleted zones results in the susceptibility to IGC. However, the atoms of stabilizing elements replace chromium atoms to form MC precipitates after long-time aging treatment, resulting in the chromium replenishment of Cr-depleted zones and the reduction of the susceptibility to IGC.
基金supported by the National Natural Science Foundation of China [grant numbers 51434004, U1435205, 51774074]Fundamental Research Funds for the Central Universities [N172512033, N172507002]Transformation Project of Major Scientific and Technological Achievements in Shenyang [grant number Z17-5-003]
文摘The microstructure evolution and intergranular corrosion(IGC) behavior of high nitrogen martensitic stainless steels(MSSs) by partial replacing C by N were investigated by using microscopy, X-ray diffraction, nitric acid tests and double-loop electrochemical potentiokinetic reactivation(DL-EPR) tests. The results show that the partial replacement of C by N first reduces and then increases the size and content of precipitates in high nitrogen MSSs, and converts the dominant precipitates from M23C6 to M2N,furthermore first improves and then deteriorates the IGC resistance. The high nitrogen MSS containing medium C and N contents provides good combination of mechanical properties and IGC resistance.
文摘Austenitic stainless steels,when exposed to welding conditions or aging for length of service,it's observed the formation of numerous deleterious phases,such as several kinds of carbides type MC,M6C,M7C3,M23C6,and intermetallic secondary phases(sigma,chi,laves),which cause the process of intergranular corrosion.The aim of this work was verifying the formation of the types of carbides and/or intermetallic phases existing in the stainless AISI 304 at 800℃,varying the timing of heat treatment between 30,360 and 1,440 min.The optical microscopy analysis revealed the predominant formation of the carbide type M23C6.The results of DL-EPR(double loop electrochemical potentiokinetic reactivation)tests showed a gradual increase in the precipitation of this carbide with the increase of treatment time.The potentiodynamic polarization showed that the precipitation of this carbide reduce the formation of the Cr2O3 passive layer,suggesting that the precipitate carbide to be predominantly of the Cr23C6 type.
文摘The aim of this work is evaluate the intergranular corrosion on UNS S31803 steel,with heat treatments at 800℃,varying treatment times of 30 mins,360 mins and 1,440 mins.The results confirm the formation of o phases and secondary austenite(γ2).For the analysis of the influence of o andγ2 phases,metallographic analysis were conducted through optical microscopy,potentiokinetic reactivation electrochemical techniques and potentiodynamic polarization in NaCI 3.5%solution.Microstructural analysis has shown a formation ofγ2 and o phase in heat treatment,due to diffusion of chromium and molybdenum fromδphase to y phase,precipitating onδ/γandδ/δinterfaces.The DL-EPR(Double loop electrochemical potentiokinetic reactivation)results have shown an increase of the DOS(degree of sensitization)for long periods of time on heat treatment.The results of potentiodynamic polarization showed a reduction of the corrosion and pitting potentials,followed by an increase of the current density when the UNS S31830 steel is heat treated during long periods of time.
