【摘要】：汽車(chē)工業(yè)的持續(xù)迅猛發(fā)展給能源和生態(tài)環(huán)境帶來(lái)了巨大的負(fù)擔(dān),高強(qiáng)鋼的研究與應(yīng)用顯得尤為重要。淬火配分鋼(QP鋼)作為第三代汽車(chē)先進(jìn)高強(qiáng)度用鋼,由于具備良好的強(qiáng)度和塑性,在汽車(chē)制造行業(yè)有著廣闊的發(fā)展前景。本文主要研究循環(huán)加載方式對(duì)QP980超高強(qiáng)鋼力學(xué)性能的影響,并從微觀角度對(duì)其進(jìn)行機(jī)理分析。主要內(nèi)容包括:首先,對(duì)QP980超高強(qiáng)鋼進(jìn)行單向拉伸試驗(yàn),獲取材料的力學(xué)性能參數(shù),并對(duì)材料的各向異性進(jìn)行研究;其次,進(jìn)行拉伸-卸載-拉伸循環(huán)加載試驗(yàn),通過(guò)與單向拉伸試驗(yàn)對(duì)比分析QP980超高強(qiáng)鋼的力學(xué)特性,包括材料彈性模量、屈服強(qiáng)度、抗拉強(qiáng)度、延伸率等方面,來(lái)獲悉循環(huán)加載方式對(duì)材料力學(xué)性能的影響;最后,對(duì)不同應(yīng)變量下的試樣進(jìn)行OM、SEM、TEM、XRD等微觀檢測(cè)試驗(yàn),解釋超高強(qiáng)鋼在循環(huán)加載條件下的變形機(jī)理。通過(guò)單向拉伸試驗(yàn)可以得知QP980超高強(qiáng)鋼擁有很高的強(qiáng)度和良好的塑性,具備優(yōu)良的綜合力學(xué)性能;循環(huán)加載方式會(huì)對(duì)材料產(chǎn)生增強(qiáng)增塑的效果;除此以外,循環(huán)加載中的彈性模量不是固定不變的值,而是隨著應(yīng)變量的變化,呈現(xiàn)先增大后逐漸減小的趨勢(shì);并且卸載與重新加載路徑體現(xiàn)了非線性特性,即隨著應(yīng)力的增加,彈性模量發(fā)生變化,卸載與重新加載曲線的起點(diǎn)和終止點(diǎn)重合,形成一個(gè)封閉區(qū)域。微觀檢測(cè)試驗(yàn)得出:QP980超高強(qiáng)鋼在應(yīng)力作用下發(fā)生馬氏體相變;馬氏體含量的不斷增加導(dǎo)致了材料強(qiáng)度的升高;并且由于馬氏體含量增加使晶粒得到細(xì)化,增強(qiáng)了材料的塑性;材料內(nèi)部殘余應(yīng)力、馬氏體相變以及位錯(cuò)運(yùn)動(dòng)產(chǎn)生的微小塑性應(yīng)變導(dǎo)致彈性模量的變化及卸載-重新加載曲線的非線性;循環(huán)加載過(guò)程,由于在卸載時(shí)位錯(cuò)發(fā)生反向滑移,為馬氏體的繼續(xù)增長(zhǎng)提供了條件,導(dǎo)致相同的應(yīng)變條件下,循環(huán)加載比單向拉伸試樣的馬氏體含量高,說(shuō)明循環(huán)加載方式對(duì)馬氏體相變起到一定的促進(jìn)作用。
[Abstract]:The continuous rapid development of automobile industry has brought a huge burden to energy and ecological environment, and the research and application of high strength steel is particularly important. As the third generation advanced high strength steel for automobile, quenched steel (QP) has a broad prospect in automobile manufacturing industry because of its good strength and plasticity. In this paper, the effect of cyclic loading on the mechanical properties of QP980 ultra-high strength steel is studied, and the mechanism is analyzed from the microscopic point of view. The main contents are as follows: firstly, the uniaxial tensile test of QP980 ultra-high strength steel is carried out to obtain the mechanical properties of the material, and the anisotropy of the material is studied. Secondly, the mechanical properties of QP980 ultra-high strength steel, including elastic modulus, yield strength, tensile strength, elongation and so on, are compared with uniaxial tensile test. To learn the effect of cyclic loading on the mechanical properties of materials; Finally, the microcosmic tests such as OM,SEM,TEM,XRD were carried out to explain the deformation mechanism of ultra-high strength steel under cyclic loading. The uniaxial tensile test shows that QP980 ultra high strength steel has high strength, good plasticity and excellent comprehensive mechanical properties. In addition, the modulus of elasticity in cyclic loading is not a fixed value, but with the change of strain, it increases first and then decreases gradually. The unloading and reloading paths reflect the nonlinear characteristics, that is, the elastic modulus changes with the increase of the stress, and the starting point and the ending point of the unloading and reloading curves coincide to form a closed region. The microcosmic test results show that martensite transformation occurs in QP980 ultra-high strength steel under stress, the increasing of martensite content leads to the increase of the strength of the material, and the grain size is refined because of the increase of martensite content, and the plasticity of the material is enhanced. The internal residual stress, martensitic transformation and tiny plastic strain caused by dislocation movement lead to the change of elastic modulus and the nonlinearity of unloading-reloading curve. During cyclic loading, the reverse slip of dislocation occurs during unloading, which provides the condition for the further growth of martensite, resulting in higher martensite content in cyclic loading than in uniaxial tensile specimen under the same strain condition. The results show that cyclic loading plays an important role in promoting martensite transformation.
【學(xué)位授予單位】：北方工業(yè)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TG142.1

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