本文選題：V-N-Ti鋼 + 大線能量焊接��； 參考：《燕山大學(xué)》2016年博士論文

【摘要】：V元素作為重要的合金元素之一,通過與N元素的配合使用能夠顯著提高材料的強度和韌性,然而V和N元素對焊接粗晶熱影響區(qū)(Coarse grain heat affected zone(CGHAZ))的組織和韌性的影響一直存在爭議。本文借助Gleeble-3800熱模擬試驗機、掃描電鏡(SEM)和透射電鏡(TEM)等分析技術(shù),結(jié)合力學(xué)性能測試,系統(tǒng)研究了N對低碳V-Ti鋼CGHAZ的IGF組織和強韌性的調(diào)控作用。研究了N含量對低碳V-Ti鋼CGHAZ連續(xù)冷卻轉(zhuǎn)變行為的影響。結(jié)果表明,首先,增N后試驗鋼CGHAZ相變開始溫度升高。其次,增N降低了臨界t8/5時間tc1和tc2,,減小了貝氏體區(qū)域的大小;第三,增N改變了不同t8/5時間下CGHAZ的組織類型,促進了多邊形鐵素體和針狀鐵素體的形成。最后,與N鋼相比,增N顯著降低了CGHAZ的硬度。研究了N含量對低碳V-Ti鋼CGHAZ組織和韌性的影響。結(jié)果表明,試驗鋼CGHAZ的50%FATT是有效晶粒尺寸、固溶N和析出強化綜合作用的結(jié)果。當試驗鋼的N含量從44 ppm增加到94 ppm,有效晶粒尺寸(晶粒取向差角≥15o)細化,CGHAZ的50%FATT降低;N含量繼續(xù)增加,試驗鋼CGHAZ中固溶N、析出強化對韌性的降低作用增加使CGHAZ的50%FATT降低。當N含量為94 ppm時,試驗鋼CGHAZ獲得了最佳的強韌性匹配。研究了焊接熱輸入對低碳V-Ti鋼CGHAZ的組織和韌性的影響。結(jié)果表明,試驗鋼的模擬CGHAZ的屈服強度隨著焊接熱輸入的增加而降低。由于增N促進了TiN粒子的析出,有效細化了原始奧氏體晶粒尺寸和有效晶粒尺寸,導(dǎo)致91N鋼模擬CGHAZ的50%FATT隨著有效晶粒尺寸的減小而降低,且顯著高于32鋼。原始奧氏體晶粒和有效晶粒尺寸的細化可以降低固溶N對韌性的損害作用。與32鋼相比,91N鋼的CGHAZ能夠獲得良好的強韌性匹配。研究了N對低碳V-Ti鋼焊接熱循環(huán)過程中析出粒子的影響。結(jié)果表明,對于低N鋼的目次析出粒子的類型為富Ti的(Ti,V)(C,N)粒子,經(jīng)過焊接熱循環(huán)后發(fā)生粗化,從而導(dǎo)致奧氏體晶粒的粗化。對于增N鋼,母材的析出粒子類型為富Ti的(Ti,V)(C,N)、富V的(V,Ti)(C,N)粒子和V(C,N)。在焊接熱循環(huán)過程中,富V的(V,Ti)(C,N)粒子和V(C,N)發(fā)生完全的溶解,而富Ti的(Ti,V)(C,N)部分溶解。焊接峰值溫度和焊接冷卻過程中尺寸小于50 nm的富Ti的(Ti,V)(C,N)粒子能夠有效的釘扎奧氏體晶界,從而細化奧氏體晶粒。N含量從44 ppm增加到190 ppm降低了基體中固溶Ti元素的含量,使富Ti的(Ti,V)(C,N)粒子的粗化速率降低,最終細化了富Ti的(Ti,V)(CN)粒子尺寸。研究了(Ti,V)(C,N)析出粒子促進CGHAZ晶內(nèi)鐵素體(IGF)形成機理。焊接冷卻過程中,未溶解的富Ti粒子可以作為富V粒子的形核質(zhì)點,并且使富Ti的(Ti,V)(C,N)粒子達到臨界形核尺寸。富V粒子的形成提高了富Ti的(Ti,V)(C,N)復(fù)合析出粒子促進鐵素體形核的能力,其作為形核質(zhì)點促進了晶內(nèi)鐵素體的形成,且復(fù)合析出相和晶內(nèi)鐵素體之間的取向關(guān)系為B-N關(guān)系,導(dǎo)致鐵素體相變開始溫度升高。
[Abstract]:As one of the most important alloy elements, the V element can significantly improve the strength and toughness of the material through the use of N element. However, the effect of V and N elements on the microstructure and toughness of coarse grain heat affected zonezonium (CGHAZ) in the coarse heat affected zone (HAZ) has always been controversial. By means of Gleeble-3800 thermal simulation test machine, scanning electron microscope (SEM) and transmission electron microscope (TEM), combined with mechanical properties test, the effect of N on the structure and strength of CGHAZ of low carbon V-Ti steel was studied systematically. The effect of N content on the continuous cooling transition behavior of low carbon V-Ti steel CGHAZ was studied. The results show that, firstly, the initial temperature of CGHAZ phase transition increases after N addition. Secondly, the increase of N decreases the critical t8 / 5 tc1 and Tc2N, and decreases the size of the bainite region. Thirdly, the increase of N changes the structure types of CGHAZ at different t8 / 5 times, and promotes the formation of polygonal ferrite and acicular ferrite. Finally, compared with N steel, the hardness of CGHAZ was significantly decreased by increasing N. The effect of N content on the microstructure and toughness of low carbon V-Ti steel CGHAZ was studied. The results show that the 50TT of CGHAZ is the result of effective grain size, solid solution N and precipitation strengthening. When the N content of the test steel increased from 44 ppm to 94 ppm, the effective grain size (grain orientation difference angle 鈮，

本文編號：2035143