發(fā)布時(shí)間：2018-05-20 18:55

  本文選題：熱輸入 + 粒狀貝氏體��； 參考：《蘭州理工大學(xué)》2017年碩士論文

【摘要】：隨著科學(xué)技術(shù)的進(jìn)步,工程結(jié)構(gòu)向大型化和輕量化發(fā)展。綜合力學(xué)性能優(yōu)異的高強(qiáng)鋼可大大降低工程結(jié)構(gòu)重量,從而減少在生產(chǎn)運(yùn)輸過程中的經(jīng)濟(jì)成本及碳化物的排放,進(jìn)一步降低對(duì)能源的消耗,這使得高強(qiáng)鋼在工程結(jié)構(gòu)中愈發(fā)得到重視。但是在諸多高強(qiáng)鋼結(jié)構(gòu)中存在焊縫金屬低溫韌性低于母材的問題,限制了高強(qiáng)鋼進(jìn)一步推廣應(yīng)用。而焊接接頭的機(jī)械性能是由接頭的組織來決定,當(dāng)焊材和母材被確定后,接頭的組織和性能則是由焊接工藝來決定。而熱輸入則是焊接工藝中較為重要的因素之一,因此研究熱輸入對(duì)焊縫金屬組織性能的影響十分必要。本文采用金屬粉芯焊絲,以焊縫金屬作為研究對(duì)象,研究了熱輸入對(duì)低碳貝氏體焊縫組織性能的影響規(guī)律;在最佳熱輸入下,研究了Ni元素對(duì)焊縫金屬組織性能的影響;并分析了Ni含量為6%的焊縫金屬產(chǎn)生熱裂紋的原因及解決方法。研究結(jié)果表明:(1)Ni0、Ni2的原始焊縫(蓋面焊縫)、焊縫內(nèi)再熱區(qū)組織是由粒狀貝氏體和準(zhǔn)多邊形鐵素體組成,而Ni4的原始焊縫(蓋面焊縫)、焊縫內(nèi)再熱區(qū)組織是由板條貝氏體(LB)和準(zhǔn)多邊形鐵素體構(gòu)成。并且,隨著熱輸入的逐漸增大,三種Ni含量的焊縫金屬的原始焊縫、焊縫內(nèi)再熱區(qū)的粒狀貝氏體或板條貝氏體含量呈現(xiàn)出先升高后降低的變化趨勢(shì)。在熱輸入為17.9kJ/cm時(shí),粒狀貝氏體或板條貝氏體的含量達(dá)到最大值。焊縫金屬的屈服強(qiáng)度、抗拉強(qiáng)度則隨著熱輸入的增加先增大后減小,在熱輸入為17.9kJ/cm時(shí),屈服強(qiáng)度、抗拉強(qiáng)度均達(dá)到峰值;沖擊韌性則是隨著熱輸入的增大而逐漸降低。(2)在15.8kJ/cm的最佳熱輸入下,當(dāng)焊縫金屬中Ni含量由0逐漸增加到4%時(shí),原始焊縫、焊縫內(nèi)再熱區(qū)的顯微組織由粒狀貝氏體(GB)+準(zhǔn)多邊形鐵素體逐漸轉(zhuǎn)變?yōu)榘鍡l貝氏體(LB)+準(zhǔn)多邊形鐵素體;隨著焊縫金屬中Ni含量的逐漸增大,焊縫金屬的抗拉強(qiáng)度、屈服強(qiáng)度、沖擊韌性、維氏硬度均呈現(xiàn)出逐漸增大的趨勢(shì)。(3)在Ni含量為6%的第一層焊縫金屬中,由于Fe、Ni、Si、Mn、S等合金元素的存在,特別是Ni元素的偏析,易于形成較多的低熔點(diǎn)共晶,在焊縫金屬冷卻凝固過程中形成的拉伸應(yīng)力作用下產(chǎn)生熱裂紋,并逐漸向其它焊道擴(kuò)展;無論是增大熱輸入還是降低熱輸入到8.2kJ/cm,焊縫金屬中均出現(xiàn)了大量的熱裂紋,故在當(dāng)前的焊接工藝和選用的焊材下熱裂紋的萌生擴(kuò)展是無法避免的。
[Abstract]:With the progress of science and technology, engineering structure develops to large-scale and light-weight. High strength steel with excellent comprehensive mechanical properties can greatly reduce the weight of engineering structure, thus reducing the economic cost and the emission of carbides in the process of production and transportation, and further reducing the consumption of energy. This makes high-strength steel more and more important in engineering structure. However, in many high strength steel structures, the low temperature toughness of weld metal is lower than that of base metal, which limits the further application of high strength steel. The mechanical properties of welded joints are determined by the structure of the joints, and the microstructure and properties of the joints are determined by the welding process when the welding materials and base materials are determined. Heat input is one of the most important factors in welding process, so it is necessary to study the effect of heat input on microstructure and properties of weld metal. In this paper, the effect of heat input on microstructure and properties of low carbon bainite weld metal was studied by using metal powder cored wire, and the effect of Ni element on microstructure and properties of weld metal was studied under optimum heat input. The causes and solutions of hot cracks in weld metal with Ni content of 6% were analyzed. The results show that the original weld (cover weld), the reheat zone microstructure in the weld is composed of granular bainite and quasi polygonal ferrite, and the microstructure of the weld is composed of granular bainite and quasi polygonal ferrite. The original weld of Ni4 is composed of lath bainite and quasi polygonal ferrite. Moreover, with the increase of heat input, the content of granular bainite or lath bainite in the reheat zone of three kinds of weld metal with Ni content increased first and then decreased. When the heat input is 17.9kJ/cm, the content of granular bainite or lath bainite reaches the maximum. The yield strength and tensile strength of weld metal first increase and then decrease with the increase of heat input. When the heat input is 17.9kJ/cm, the yield strength and tensile strength reach the peak value. The impact toughness decreases gradually with the increase of heat input.) under the optimum heat input of 15.8kJ/cm, when Ni content in weld metal increases gradually from 0 to 4, the original weld seam, The microstructure of the reheating zone in the weld gradually changed from granular bainite (GB) quasi-polygonal ferrite to lath bainite / LB) quasi-polygonal ferrite, and the tensile strength and yield strength of the weld metal increased with the increase of Ni content in the weld metal. The impact toughness and Vickers hardness of the first layer of weld metal with Ni content of 6% are gradually increasing. Due to the presence of Fe Ni Si Si mn S and other alloy elements, especially the segregation of Ni elements, it is easy to form more low melting point eutectic. Under the action of tensile stress formed during the cooling and solidification of the weld metal, hot cracks are produced and gradually extended to other welds, whether the heat input is increased or decreased to 8.2 kJ / cm, a large number of hot cracks occur in the weld metal. Therefore, the hot crack initiation and propagation under the current welding process and the selected welding material is unavoidable.
【學(xué)位授予單位】：蘭州理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG441.7

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