Effect of N addition on tensile and corrosion behaviors of CD4MCU cast duplex stainless steels

Abstract

The effect of N addition on the microstructure, tensile, and corrosion behaviors of CD4MCU (Fe-25Cr-5Ni-2.8Cu-2Mo) cast duplex stainless steel was examined in the present study. The slow strain rate tests were also conducted at a nominal strain rate of 1 ϫ 10 Ϫ6 /s in air and 3.5 pct NaCl ϩ 5 pct H 2 SO 4 solution for studying the stress corrosion cracking (SCC) behavior. It was observed that the volume fraction of austenitic phase in CD4MCU alloy varied from 38 to 59 pct with increasing nitrogen content from 0 to 0.27 wt. pct. The tensile behavior of CD4MCU cast duplex stainless steels, which tended to vary significantly with different N contents, appeared to be strongly related to the volume changes in ferritic and austenitic phases, rather than the intrinsic N effect. The improvement in the resistance to general corrosion in 3.5 pct NaCl ϩ 5 pct H 2 SO 4 aqueous solution was notable with 0.13 pct N addition. The further improvement was not significant with further N addition. The resistance to SCC of CD4MCU cast duplex stainless steels in 3.5 pct NaCl ϩ 5 pct H 2 SO 4 aqueous solution, however, increased continuously with increasing N content. The enhancement in the SCC resistance was believed to be related to the volume fraction of globular austenitic colonies, which tended to act as barriers for the development of initial pitting cracks in the ferritic phase into the sharp ones.

Effect of different Cr contents on tensile and corrosion behaviors of 0.13 pct N-containing CD4MCU cast duplex stainless steels

“…4. The resistance to SCC in 3.5 pct NaCl ϩ 5 pct H 2 SO 4 for CD4MCU alloys with different Cr contents showed a similar trend as observed in the polarization and the potentiostatic test results. Unlike the general corrosion test results, however, the SCC resistance of CD4MCU23 alloy was substantially greater than that of CD4MCU28 alloy due to the break down of stable passive film during tensile deformation.…”

“…Our previous studies on the effect of N on the microstructural evolution of CD4MCU cast duplex stainless steel suggest that the globulization of austenitic phase is strongly related to the N content in the ferrite matrix. [4,7] The presence of Cr in the ferrite matrix is reported to increase the N solubility in the ferrite matrix, and the increased N content in the ferrite would encourage the globulization of austenitic phase. However, further studies are required to confirm this notion.…”

“…[1,2,3] Since the development of first-generation duplex stainless steels in the 1930s, continuing research efforts have been exerted to improve both mechanical and corrosion properties, particularly by controlling alloying elements. [4][5][6][7][8] The Cu is, for example, often added to improve the resistance to pitting corrosion in chloride-containing environments. [9,10] The N is highly beneficial for improving the crevice corrosion resistance of the austenitic phase [11] and reduces the partitioning of Cr, enabling a higher Cr content to be maintained in the austenite.…”

<i>In-situ</i> Observation of <i>δ</i>↔<i>γ</i> Phase Transformations in Duplex Stainless Steel Containing Different Nitrogen Contents

“…Therefore, DSS is replacing conventional austenitic or ferritic stainless steels in many industrial applications because of its combined advantages of better mechanical and corrosion properties. [1][2][3][4][5] DSS contains austenite stabilizing elements like Ni, Mn, C, N and Cu as well as ferrite stabilizing elements like Cr, Mo and Si. The recent skyrocketing raw material cost stimulates development of the DSSs with less alloying.…”

Effect of Alloying Elements on Corrosion, Microstructure and Mechanical Properties for Casted Free-Nickel Duplex Stainless Steels

“…Since the development of first-generation duplex stainless steels in the 1930s, considerable research efforts have been conducted to improve both mechanical and corrosion properties, particularly by controlling alloying elements, such as N, Cr, and Mo [3,[6][7][8][9][10][11][12][13][14][15][16]. Charles [4], for example, reported that the addition of Cr and/or Mo improved the resistance to pitting corrosion and stress corrosion cracking of duplex stainless steels.…”