FB2馬氏體耐熱鋼在焊接熱作用下奧氏體相變過程研究FB2馬氏體耐熱鋼在焊接熱作用下奧氏體相變過程研究RESEARCH ON AUSTENITE TRANSFORMATION OF FB2 HEAT-RESISTANT STEEL DURING WELDING HEATING PROCESS FB2馬氏體耐熱鋼是一種含B量約為100 ppm的新型9% Cr馬氏體耐熱鋼，主要用于制造服役于620 ℃的火電厚壁構(gòu)件。本研究發(fā)現(xiàn)FB2鋼的焊接熱影響區(qū)呈現(xiàn)出“無粗晶區(qū)”的特點，并通過開展焊接熱模擬實驗驗證了這一現(xiàn)象。借助光鏡、掃描電鏡分析對比了熱模擬前后的組織狀態(tài)，認(rèn)為FB2鋼在快速加熱條件（≥100 ℃/s）下的奧氏體相變是切變型的，表現(xiàn)出奧氏體記憶效應(yīng)；而在慢速加熱條件（≤5 ℃/s）下其奧氏體相變是擴(kuò)散型的，該過程是受原子短程擴(kuò)散控制的，并且無奧氏體記憶效應(yīng)發(fā)生。FB2鋼在焊接過程中特殊的相變過程是其焊接熱影響區(qū)呈現(xiàn)出“無粗晶區(qū)”的主要原因。結(jié)合已有的文獻(xiàn)報道，初步提出了B元素改變FB2鋼在加熱過程中奧氏體相變類型的機理模型，進(jìn)一步發(fā)展了現(xiàn)有的研究結(jié)果。 The improvement of steam parameters in fossil power plants requires the development of new kinds of 9% Cr martensitic heat-resistant steels, among which FB2 steel is a 100 ppm boron containing steel mainly used for manufacturing components with thick walls. In our study, it was found that the welding heat affected zone (HAZ) of FB2 steel was characterized by “no coarsened grain”, which differed much from that of conventional 9% Cr heat-resistant steels. Welding thermal simulation work was conducted to verify the phenomenon. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to compare the microstructures before and after thermal simulation, and it was concluded that the austenization of FB2 steel at rapid heating rates (≥ 100 ℃/s) took place by shear mechanism, demonstrating austenite memory effect. While at slow heating rates (≤ 5 ℃/s) the austenization was by atom short range diffusion mechanism, without austenite memory effect. The special phase transformation of austenization is the main cause for the formation of special HAZ with no coarsened zone. Based on the previous research carried out by other researchers, a preliminary model was proposed to describe how boron atoms change austenite transformation type, which developed the previous ideas about the phenomenon.
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