本文選題：9Ni鋼焊材 + 焊材強韌化��； 參考：《江蘇科技大學》2017年碩士論文

【摘要】：我國是能源大國,過度依賴煤炭,隨著能源結(jié)構(gòu)調(diào)整和環(huán)保壓力增加,清潔能源的供給迫在眉睫。液化天然氣(Liquefied Natural Gas,簡稱LNG)因體積小,燃燒放熱大且無污染等優(yōu)點,其需求逐年增漲。LNG存儲設備要求鋼材在超低溫服役環(huán)境具備足夠的強度及韌性儲備,目前我國LNG儲罐用9Ni鋼,已完全實現(xiàn)國產(chǎn)化,但配套鎳基焊接材料仍然依賴進口,且焊接技術不成熟,因此開展焊材國產(chǎn)化研制,對天然氣產(chǎn)業(yè)裝備建設自主化、保障國家能源安全意義重大。本文在闡述了全球LNG儲罐用9Ni鋼及其焊接問題研究基礎上,獨立研制了9Ni鋼焊條,總結(jié)了Nb對熔敷金屬的顯微組織影響規(guī)律,采用拉伸試驗、彎曲、硬度和沖擊試驗檢測力學性能,結(jié)合掃描電鏡以及熱力學計算等方法,研究了熔敷金屬的強韌化機理,結(jié)果表明:采用鎳基焊條,焊縫形成奧氏體組織,Nb具有減小枝晶寬度、細化晶粒的作用,在晶間處以碳化物的形式析出強化晶界,阻礙裂紋的萌生和擴展,隨著Nb含量升高,析出相尺寸變大數(shù)量增多,塑韌性有所損傷。經(jīng)檢測,自主研制的2號焊條(Nb含量1.30%),熔敷金屬性能優(yōu)良,抗拉強度為705MPa,屈服強度為478MPa,低溫沖擊功Akv116J,符合LNG儲罐設備的要求。為研究9Ni鋼焊材的工藝適應性,分別使用焊條電弧焊和埋弧焊進行焊接試驗。利用金相顯微鏡和掃描電鏡對焊條電弧焊接頭顯微組織進行分析,力學性能檢測使用拉伸、彎曲、硬度和沖擊試驗進行,同時對接頭熔合區(qū)奧氏體-馬氏體結(jié)晶界面凝固理論進行研究。結(jié)果表明:自行研制的焊條與國產(chǎn)9Ni鋼焊接工藝適應性良好,焊縫組織為奧氏體,熱影響區(qū)為馬氏體,熔合區(qū)為狹窄的平面晶組織。焊縫強度高于母材,側(cè)彎完好無裂紋,焊縫與母材界面處結(jié)合良好,熱影響區(qū)出現(xiàn)硬度最高值為360HV5,焊縫至熱影響區(qū)沖擊韌性逐漸升高,焊縫平均沖擊韌性達到115J,符合低溫韌性要求。埋弧焊焊縫組織為奧氏體,存在析出相提高了焊縫強度,彎曲性能良好,熱影響區(qū)硬度值最高為339HV5,焊縫平均沖擊韌性達到94J,斷口分析顯示接頭各位置均屬韌性斷裂。
[Abstract]:China is a large country of energy, relying too much on coal. With the adjustment of energy structure and the increasing pressure of environmental protection, the supply of clean energy is imminent. Because of the advantages of small volume, large combustion heat release and no pollution, the demand of LNG storage equipment for liquefied natural gas (LNG) is increasing year by year. It requires steel to have sufficient strength and toughness reserve in ultra-low temperature service environment. At present, 9Ni steel is used for LNG storage tank in our country. Although the welding materials based on nickel are still dependent on import and the welding technology is immature, it is of great significance to develop the domestic welding materials for the equipment construction of natural gas industry and to ensure the national energy security. In this paper, based on the study of 9Ni steel and its welding for global LNG storage tank, the welding rod of 9Ni steel has been developed independently, and the effect of NB on microstructure of deposited metal has been summarized. The tensile test and bending have been used to study the effect of NB on the microstructure of deposited metal. The mechanical properties were tested by hardness and impact test. The strengthening and toughening mechanism of deposited metal was studied by means of scanning electron microscope and thermodynamic calculation. The results showed that the austenitic microstructure and NB of weld formed by nickel base electrode could reduce the width of dendrite. The effect of grain refinement is to precipitate and strengthen grain boundaries in the form of carbides between crystals, which hinders the initiation and propagation of cracks. With the increase of NB content, the size of precipitated phases increases and the ductility is damaged. The test results show that the NB content of No.2 electrode developed by ourselves is 1.30%, the deposited metal has excellent properties, the tensile strength is 705MPa, the yield strength is 478MPa, and the low temperature impact energy Akv116J is satisfied with the requirements of LNG storage tank equipment. In order to study the process adaptability of 9Ni steel welding, welding experiments were carried out by welding electrode arc welding and submerged arc welding respectively. The microstructure of electrode arc welding joint was analyzed by metallographic microscope and scanning electron microscope. The mechanical properties were tested by tensile, bending, hardness and impact tests. At the same time, the solidification theory of austenitic-martensite interface was studied. The results show that the welding rod developed by ourselves has good adaptability to domestic 9Ni steel. The weld microstructure is austenite, the heat affected zone is martensite, and the fusion zone is plane crystal structure. The strength of the weld is higher than that of the base metal, the lateral bending is intact without cracks, the interface between the weld and the base metal is well bound, the maximum hardness of the HAZ is 360HV5, and the impact toughness of the weld to the heat-affected zone increases gradually. The average impact toughness of weld seam is 115J, which meets the requirement of low temperature toughness. The microstructure of submerged arc welding weld is austenite, and the strength of weld is improved with precipitated phase, and the bending property is good. The hardness of HAZ is 339HV5, the average impact toughness of weld is 94J, and the fracture analysis shows that the joints are ductile fracture in every position.
【學位授予單位】：江蘇科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TE972

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本文編號：1923073