本文選題：TWIP鋼 + 疲勞行為�。� 參考：《北京科技大學》2015年博士論文

【摘要】：TWIP(Twinning induced plasticity)鋼是國內外目前正在積極研發(fā)中的一種新一代高強度交通用鋼,具有高強度、高塑性、高應變硬化能力等顯著優(yōu)點,并且具有良好的加工性能。在TWIP鋼從實驗室推向實際生產的過程中,存在以下問題：一是與力學性能相比,TWIP鋼的材料應用性能方面的研究還較少,其應用特性還不明確,例如其耐腐蝕性能、疲勞性能、低溫韌性等；二是在生產和應用中,遇到了難涂鍍、難焊接、延遲斷裂等技術問題,限制了這一新型鋼種的進一步推廣與應用。 本文在實驗室條件下,綜合應用掃描電鏡、透射電鏡、電化學充氫、有限元模擬等手段,設計并制備了不同稀土含量的TWIP鋼以研究稀土元素對TWIP鋼力學性能、疲勞性能和延遲開裂的影響,研究了TWIP鋼的低周疲勞行為特征、疲勞破壞機制和延遲斷裂機制,探索并提出了TWIP鋼延遲斷裂的控制手段。 稀土元素對TWIP鋼的主要影響包括：細化晶粒,改善夾雜物形態(tài),增加夾雜物總量,與鋼中的氫結合從而影響可擴散氫含量等。從力學性能來看,TWIP鋼添加稀土元素后的力學性能和疲勞性能都有所降低,微量的稀土元素會使其延遲斷裂性能惡化,但合適的添加量則可以對延遲斷裂起到抑制作用。 TWIP鋼具有優(yōu)異的疲勞性能與強塑性的綜合性能,其低周疲勞壽命遠高于一般800MPa級別高強鋼,又比具有相近疲勞性能的316L不銹鋼具有更高的強塑積和更好的加工性能。TWIP鋼在疲勞載荷下的變形機制是孿晶、滑移和駐留滑移帶的共同作用。破壞機制則是孿晶和滑移帶對晶界、夾雜物附近的相界面的碰撞,形成微孔洞,并連接成微裂紋,隨疲勞載荷擴展。稀土元素引入的夾雜物由于形態(tài)圓滑,不會直接成為疲勞裂紋的萌生源,但增加的相界面增加了微裂紋的萌生的可能性。 TWIP鋼的延遲斷裂行為是在充分的沖壓變形量、殘余應力及應力梯度、較高的基體氫含量、強烈的缺口敏感性的共同作用下產生的。在充分的沖壓變形量下,由于TWIP鋼具有強加工硬化性能,會導致其接近抗拉強度的峰值殘余應力。而充分的應力梯度誘導的氫擴散會在殘余應力最大處產生氫富集,氫含量增大導致的氫致軟化使TWIP鋼容易萌生微裂紋。缺口敏感性和進一步的應力誘導氫擴散使得微裂紋迅速擴展,從而發(fā)生延遲斷裂。 通過合理添加稀土元素,以及控制試樣成型過程的條件,包括嚴格控制切邊質量和深沖變形量,均能對TWIP鋼的延遲斷裂起到控制作用。適量的稀土元素的添加能有效降低奧氏體中的可擴散氫含量,從而抑制延遲斷裂傾向。嚴格控制切邊質量及限制沖壓件的深沖變形量,均可以有效的控制峰值殘余應力與峰值氫濃度在安全范圍內,從而減小發(fā)生延遲斷裂的風險。
[Abstract]:TWIP(Twinning induced plasticity steel is a new generation of high strength transportation steel which is being developed at home and abroad. It has many remarkable advantages such as high strength, high plasticity, high strain hardening ability, and has good processability.In the process of TWIP steel from laboratory to actual production, there are the following problems: first, compared with mechanical properties, there is less research on the applied properties of TWIP steel, and its application characteristics are not clear, such as corrosion resistance, fatigue property, etc.Second, in production and application, some technical problems such as hard coating, difficult welding and delayed fracture are encountered, which limit the further popularization and application of this new steel.In this paper, using scanning electron microscope, transmission electron microscope, electrochemical hydrogen charging and finite element simulation, TWIP steels with different rare earth contents were designed and prepared to study the mechanical properties of rare earth elements on TWIP steel.The effects of fatigue properties and delayed cracking on the low cycle fatigue behavior, fatigue failure mechanism and delayed fracture mechanism of TWIP steel were studied. The control methods of delayed fracture of TWIP steel were explored and put forward.The effects of rare earth elements on TWIP steel include refining grain, improving the shape of inclusions, increasing the total amount of inclusions, and binding with hydrogen in steel to influence the content of diffusible hydrogen, etc.According to the mechanical properties of TWIP steel the mechanical properties and fatigue properties of TWIP steel are decreased after adding rare earth elements. The delayed fracture properties of TWIP steel can be deteriorated by trace rare earth elements but the delayed fracture can be inhibited by adding appropriate amount of rare earth elements.The low cycle fatigue life of TWIP steel is much higher than that of 800MPa grade high strength steel.Compared with 316L stainless steel with similar fatigue properties, the deformation mechanism of TWIP steel under fatigue load is the joint action of twin, slip and resident slip band, and the deformation mechanism of TWIP steel under fatigue load is higher than that of 316L stainless steel with similar fatigue properties.The failure mechanism is the collision of twin and slip band to the grain boundary and the phase interface near the inclusions to form micropores and to form microcracks which propagate with fatigue loading.Because of its smooth shape, the inclusion introduced by rare earth elements will not be a direct source of fatigue crack initiation, but the increase of phase interface increases the possibility of micro-crack initiation.The delayed fracture behavior of TWIP steel is caused by the combined action of sufficient stamping deformation, residual stress and stress gradient, high hydrogen content in matrix and strong notch sensitivity.Under sufficient stamping deformation, due to the strong working-hardening property of TWIP steel, it will be close to the peak residual stress of tensile strength.The hydrogen diffusion induced by sufficient stress gradient will lead to hydrogen enrichment at the maximum residual stress, and the hydrogen softening caused by the increase of hydrogen content will lead to the initiation of microcracks in TWIP steel.Notch sensitivity and further stress-induced hydrogen diffusion lead to rapid growth of microcracks, resulting in delayed fracture.The delay fracture of TWIP steel can be controlled by adding rare earth elements reasonably and controlling the conditions of specimen forming process, including strictly controlling the cutting quality and deep drawing deformation.The addition of rare earth elements can effectively reduce the diffusible hydrogen content in austenite and thus restrain the tendency of delayed fracture.Strictly controlling the cutting mass and limiting the deep drawing deformation of stamping parts can effectively control the peak residual stress and peak hydrogen concentration in a safe range, thus reducing the risk of delayed fracture.
【學位授予單位】：北京科技大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TG142.1

【參考文獻】

相關期刊論文 前10條

1 丁洪志，邢修三，，朱鶴孫，王新民;氫致脆化區(qū)開裂模型應用于計算門楹值應力強度因子[J];北京理工大學學報;1995年01期

2 郭鋒,梅敦;稀土元素Ce對H62黃銅組織特征變化的作用[J];包頭鋼鐵學院學報;2000年03期

3 惠衛(wèi)軍,董瀚,翁宇慶;耐延遲斷裂高強度螺栓鋼的研究開發(fā)[J];鋼鐵;2001年03期

4 惠衛(wèi)軍,董瀚,王毛球,陳思聯(lián),翁宇慶,趙秀明;1300MPa級高強度螺栓鋼[J];鋼鐵;2002年03期

5 董瀚;;鋼鐵材料基礎研究的評述[J];鋼鐵;2008年10期

6 易煒發(fā);朱定一;楊澤斌;林淑梅;;銅含量對高碳TWIP鋼組織和力學性能的影響[J];鋼鐵;2011年11期

7 田洪福,董風林,潘修德,吳長春,何鎮(zhèn)明;鑄鋼件中稀土元素與氫的相互作用對機械性能的影響[J];機械工程材料;1992年04期

8 張峰;李光強;朱誠意;;稀土處理無取向硅鋼中的夾雜物與電磁性能變化[J];功能材料;2013年07期

9 米振莉;靖海濤;江海濤;唐獲;吳彥欣;;Fe-Mn-Si-Al系和Fe-Mn-C系TWIP鋼加工硬化行為[J];北京科技大學學報;2013年04期

10 戴起勛,王安東,程曉農;低溫奧氏體鋼的層錯能[J];鋼鐵研究學報;2002年04期

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