【正文】 固陽離子主要是通過熱提取的側(cè)壁，但在區(qū)域 1 的凝固主要是由以前的焊點(diǎn)的熱提取。圖 2（ b）。圖 2（ a）主要是通過熱傳遞到前一個(gè)焊點(diǎn)（然后對基體金屬）冷卻 ，但冷卻區(qū) 2，通過將熱量從側(cè)壁的基體金屬。熔池的溫度分布領(lǐng)域的影響由這兩個(gè)散熱器。 Fig. 1 Pseudo binary sec tion of FeCrNi system at 70% iron Table 1 Chemical position (in wt.%) 區(qū)域 I 和 II 之間，存在一個(gè)很窄的頻帶的材料，它是由下一個(gè)脈沖焊接，即，在區(qū) II 區(qū) I 的 HAZ 的熱的影響。圖 2（ a），從固相線 fication 柄的角度來看，兩個(gè)區(qū)域可以被識別： 區(qū)域 I 是部分焊縫金屬重熔在下一個(gè)脈沖，方可徹底冷卻。當(dāng)兩個(gè)脈沖之間的增加的時(shí)間（或距離），高的冷卻速率可能會(huì)導(dǎo)致早期斑點(diǎn)完全凝固之前的 下一個(gè)脈沖（參考文獻(xiàn) 11）相重合。 100)1( ???? vTD fvOf (Eq 1) 其中 T 是脈沖持續(xù)時(shí)間中， v 是焊接速度， f 是激光頻率， D 是指在工件上測量為 177。該蝕刻劑是 Beraha（ K2S2O5 鹽酸在 20 毫升 100 毫升溶液）。激光焊接機(jī)是 IQL10，用脈沖 Nd： YAG 激光的連接到一個(gè)計(jì)算機(jī)控制的工作表，具有最大平均激光功率為 400 W 的激光參數(shù)的可用范圍為 11000 赫茲脈沖頻率， 0 40 J 的脈 沖能量，脈沖持續(xù)時(shí)間為 ? 20 毫秒。然而，可以有一個(gè)DSS 合金的微觀結(jié)構(gòu)，關(guān)于如何由快速脈動(dòng)特性的熱源的影響，由于焊點(diǎn)的連續(xù)熔化和凝固，會(huì)發(fā)生的問題（參考文獻(xiàn) 1113）。這也可以影響 DSS 焊縫的機(jī)械性能和耐腐蝕性（參考 27）。在室溫下的鍛造合金顯微組織是由奧氏體和鐵素體相互參雜的（參考文獻(xiàn) 1， 2）。在高重疊的因素，在焊 縫中心線的陣列形成連續(xù)的軸向顆粒。 a168。 10 HV, in parison with zone 2 a hardness of 328 177。 mm. and Discussion 3 Figure 2 shows the top view of welds at a low and high overlapping. As observed from the ?gure, the weld spots are clearly distinguishable from each other specially at lower overlapping. When the time (or distance) between two pulses increases, high cooling rates can cause the earlier spots to solidify pletely before coincident of the next pulse (Ref 11). On the other hand, when the time (or distance) between two pulses decreases, the former spot temperature can still be high enough to the extent that semisolid condition is dominant and the next pulse can raise the temperature to a degree which can almost disappear the fusion line. The solidi?cation pattern of the weld metal was found to vary with the travel speed and/ or frequency because of variations of the overlap factor. With a low overlapping factor, as shown in Fig. 2(a), from a solidi ?cation pattern point of view, two zones can be identi?ed Zone I is the part of the weld metal which is remelted by the next pulse before being cooled thoroughly. In this zone, the grains nucleate on the previous spot epitaxially and grow toward the center. Zone II refers to a single pulse microstructure which is not affected by the next pulse heat and is solidi?ed mainly from the base metal. In this part, the grain boundaries were relatively ?ner and more jagged. Fig. 1 Pseudo binary sec tion of FeCrNi system at 70% iron 4 Table 1 Chemical position (in wt.%) Element C Si Mn P S Cr Ni Mo Fe w t.% Bal. Between zones I and II, there exists a very narrow band of material which is affected by the heat of the next pulse welding, ., the HAZ of zone I in zone II. In Fig. 2(a), this region is marked as 3, and from a solidi?cation pattern point of view, it is a part of zone II. The development of the observed solidi?ca tion patterns is because in pulse laser welding, when the weld spots are not too close to each other, the previous weld spot is relatively cool when the next pulse strikes, and therefore, effectively two different peting routes exist for the extraction of heat from any point in the molten weld pool. The ?rst route is directly through the side walls (fusion line with the base metal), and the second route is through the previous weld spot (fusion line between consecutive weld spots). The temperature distribution ?eld of the weld pool is affected by both of these two heat sinks. Proximity of any point in the weld pool to each of these two routes of heat extraction is one of the factors determining the dominant cooling route and solidi?cation orientation. The preferential solidi?cation orien tation is also affected by the orientation of the grains on which the weld metal grows epitaxially. Zone 1 shown in Fig. 2(a) is mainly cooled through heat transfer to the previous weld spot (and then to the base metal), but zone 2 is cooled through transferring heat from side walls to the base metal. Also, when weld spots overlap each other extensively, zone 2 almost disappears and bees only limited to a narrow band just next to the two side walls. In such condition (high overlapping), zone 1 solidi?cation pattern dominates most of the weld metal central part, and they can effectively grow on each other epitaxially without being disturbed by zone 1 grains ing in between. Here, the grains in the consecutive zone 1 s form a clear preferred orientation, and the axial solidi?cation pattern is formed as shown in Fig. 2(b). The authors have experienced pulsed laser welding of various alloys including carbon steel, aluminum alloys, and titanium. However, it was in the case of DSS that such progress in understanding of the process of weld microstructures development became possible. It would be interesting to study the weld microstructures in other alloys in the light of the knowledge gained. As stated earlier, solidi? cation in zone 2 is dominated by heat extraction to the side walls, but solidi?cation in zone 1 is dominated by heat extraction to the previous weld spot. The larger grain sizes in zone 1 are due to a higher effective preheat temperature of the material the heat of which escapes to ., the metal which itself has been molten just a little earlier. However, the sidewalls are expected to have a lower temperature, as a steeper temperature gradient occurs for solidi?cation of zone 2. Thus, the cooling rate in zone 1 is expected to be paratively lower resulting in a coarser microstructure. Now, our attention turns to the post 5 Fig. 2 Mic rostruc tures of the w elds w ith various overlap factors as view ed from top direc tion at (a) 55% (sample B2) and (b) 73% (sample B4) SEM mic rostruc ture various parts of the w eld metal and the base metal. (a) Zone I in Fig. 2(a). (b) Zone II in Fig. 2(a). (c) The bulk of the w eld metal (aw ay from axial grains) in Fig.