多向锻造和单向轧制304不锈钢高温退火后的晶界面分布

GRAIN BOUNDARY PLANE DISTRIBUTIONS IN 304 STEEL ANNEALED AT HIGH TEMPERATURE AFTER A PARALLEL PROCESSING OF MULTIPLE FORGING AND DIRECT ROLLING

固溶处理后的2组304不锈钢样品分别经应变量ε=2的多向锻造（MF）和单向轧制（DR）后，再经900℃高温退火2—120min．采用电子背散射衍射（EBSD）技术和五参数晶界面分析方法（FPA），研究了样品的晶界特征分布（GBCD）和晶界面分布（GBPD）．结果表明，2组样品中∑3n（n=1，2，3）特殊晶界的比例均不超过45％，并且在退火过程中，非共格∑3晶界逐渐共格化，∑9和∑27晶界比例也随之下降．分别经MF和DR处理后再经120min退火的样品中，一般大角度晶界（过滤掉∑3n）一般均以（111）扭转晶界和（110）倾侧晶界为主，表明样品中均存在明显的晶界织构（GBT）；在某些特定取向差条件下，一般大角度晶界的GBPD在样品中存在显著差异，表明退火之前的加工过程对304不锈钢的GBPD有显著影响．

It is well-recognized that low ∑-CSL boundaries are highly populated in the grain boundary character distribution （GBCD） for austenitic stainless steel （SS） processed by low strain and subsequent annealing. However, large-strain plus annealing typically tends to introducing numerous random high angle grain boundaries （RHABs） instead of producing high fraction of ∑3, ∑9 and ∑27 boundaries. In this case, the distribution of grain boundary planes of RHABs must be very relevant to the properties of material. The current study is to explore the evolution of GBCD and grain boundary plane distribution （GBPD） in 304 austenitic SS after large strain and subsequent annealing using electron backscatter diffraction （EBSD） and five-parameter analysis （FPA）. After solid solutiontreatment, 304 steel samples were separately processed by multiple forging （MF） and direct rolling （DR） with true strain ε=2 followed by same annealing at 900 °C for 2-120 min. Then the GBCDs and GBPDs of the two groups of samples were examined. The results show that the total ∑3n （n=l, 2, 3） special boundaries in any sample as processed take a length fraction of lower than 45% out of the entire boundaries, and with annealing proceeding the incoherent ∑3 boundaries tend to be tuned into coherent ones and consequently the summation fractions of ∑9 and ∑27 boundaries decrease accordingly. In the two samples which were separately processed by MF and DR but followed by the same annealing at 900 °C for 120 min, their random boundaries or general high angle boundaries ∑3n special boundaries filtered） mostly appeare to be the （111） twist and （110）tilt boundaries, indicating there exist grain boundary textures （GBT） in both samples. However, in the condition of some mis-orientations, the GBPDs of random boundaries are quite different in the two samples. For grain boundaries of （111）/30-40° misorientation, more grain boundaries of twist type nearly on the exact {111} plane are found in the specimen processed by DR and annealing for 120 rain （DR120） compared to that processed by MF and annealing for 120 min （MF120）. For the grain boundaries of （110）/50°misorientation, it was found that most of such boundaries in MF120 are tilt type and positioned on {112}, {113} and {115} planes, whereas those in DR120 are tilt or mixed type positioned on {001}, {111} and {012}. It was suggested that there are distinct effects of pre-processing on the GBPDs of annealed 304 steel.