Research And Control Of Near Singular Grain Boundary Of 00Cr12 Ferritic Stainless Steel

00Cr12 ferritic stainless steel is a kind of typical low Ni and low Cr ferritic stainless steel,which will be affected by intergranular corrosion during use,resulting in failure of parts.Different from the low stacking fault energy(SFE)face-centered cubic(FCC)austenitic stainless steels,high SFE body-centered cubic(BCC)ferritic stainless steels are hardly to produce structure-stable and corrosion-resistant singular boundaries or namely the coherent twin boundaries during recrystallization after deformation.Some studies have shown that {0 1 1}/{0 1 1} near singular grain boundary is a grain boundary with good corrosion resistance in ferritic stainless steel.Hereby,how to increase the proportion of {0 1 1}/{0 1 1} near singular grain boundary is the key problem to improve the intergranular corrosion resistance of 00Cr12 ferritic stainless steel.Therefore,the {0 1 1}/{0 1 1} near singular grain boundaries were characterized by five-parameter analysis and grain boundary interface matching.The effects of different rolling temperatures,rolling deformations and annealing time on the {0 1 1}/{0 1 1} near singular grain boundaries of00Cr12 ferritic stainless steel were studied.The main results of this paper are as following :After solution treatment at 1170℃ for 40 min,00Cr12 ferritic stainless steel with a total deformation of about 80% was rolled by multi-pass unidirectional rolling.The samples obtained by recrystallization annealing at 750℃ for 2 h were used as the initial samples of this experiment.The proportion of {0 1 1}/{0 1 1} near singular grain boundaries in the initial sample is 4.03%.Different rolling temperatures have a significant effect on the {0 1 1}/{0 1 1} near singular grain boundaries in the samples.The initial samples were subjected to unidirectional rolling at350℃,500℃,580℃,650℃ and 690℃ with a total thickness reduction of 70%,and then annealed at 750℃ for 2h to recrystallization.The ratio of {0 1 1}/{0 1 1} near-singular grain boundaries increased first and then decreased with the increase of rolling temperature,and the ratio of {0 11}/{0 1 1} near-singular grain boundaries reaches a maximum of 6.82% for the sample rolled at650℃.This is because {1 1 0}<1-1 0> and its diffuse texture are formed in the recrystallized samples rolled at 650℃.Different rolling deformation has a significant effect on the {0 1 1}/{0 1 1} near singular grain boundaries in the samples.The initial samples were subjected to unidirectional rolling at650℃ with thickness reduction of 30 %,50 % and 70 %,respectively,and then annealed at 750℃ for 2h.The proportion of {0 1 1}/{0 1 1} near-singular grain boundaries decreased with the decrease of rolling deformation.The proportion of {0 1 1}/{0 1 1} near-singular grain boundaries in recrystallized samples with 30% rolling deformation is only 3.42%.This is due to the different strength of {1 1 0}<1-1 0> and its diffuse texture in the three groups of samples,resulting in different proportions of {0 1 1}/{0 1 1} near-singular grain boundaries in the three groups of samples.Different annealing time has significant effects on {0 1 1}/{0 1 1} near-singular grain boundary.The initial sample was rolled by 70% unidirectional rolling at 650℃ and then annealed for 1h,2h and 3h,respectively.The proportion of {0 1 1}/{0 1 1} near singular grain boundaries in the sample decreased with the increase of annealing time.The proportion of {0 1 1}/{0 1 1}near singular grain boundaries in the recrystallized sample annealed for 3h was only 3.81%.This is because with the increase of annealing time,the grain boundary migrates towards lower energy field,so the proportion of {0 1 1}/{0 1 1} near-singular grain boundary increased first.After annealing for 3h,the phase deformation nucleus recrystallization occurred,and a large number of random grain boundaries appear,resulting in an increase in the total number of grain boundaries and a decrease in the proportion of near singular grain boundaries.The off-line in-situ surface etching test shows that the corrosion resistance of {0 1 1}/{0 1 1}near singular grain boundaries in 00Cr12 ferritic stainless steel is significantly better than that of general high angle grain boundaries.O lattice calculation shows that the atomic periodic order of{0 1 1}/{0 1 1} near singular grain boundaries is better than that of general grain boundaries,which is the reason for the strong corrosion resistance of {0 1 1}/{0 1 1} near singular grain boundary.