本文關(guān)鍵詞：易切削非調(diào)質(zhì)鋼中硫化物生成行為與均勻化控制研究　出處：《北京科技大學(xué)》2015年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 易切削鋼 非調(diào)質(zhì)鋼 硫化物 形成機(jī)理 熱力學(xué)計(jì)算

【摘要】：易切削非調(diào)質(zhì)鋼是硫系易切削鋼的一種,由于具有優(yōu)良的切削性能與力學(xué)性能,已在國(guó)外汽車零部件上得到廣泛應(yīng)用,并且隨國(guó)產(chǎn)汽車行業(yè)的快速發(fā)展具有良好的國(guó)內(nèi)應(yīng)用前景。硫在非調(diào)質(zhì)鋼中主要以硫化物的形式存在,對(duì)比分析表明,國(guó)外鋼中硫化物往往尺寸控制合理、分布均勻,而國(guó)產(chǎn)非調(diào)質(zhì)鋼中硫化物往往為大尺寸細(xì)長(zhǎng)條形且群聚分布,導(dǎo)致力學(xué)性能與切削性能均較差,不能達(dá)到國(guó)內(nèi)用戶對(duì)高品質(zhì)汽車用非調(diào)質(zhì)鋼的要求,因此尚需大量進(jìn)口國(guó)外非調(diào)質(zhì)鋼。為提高我國(guó)非調(diào)質(zhì)鋼中硫化物控制水平,本課題系統(tǒng)地研究了成分設(shè)計(jì)、凝固過程、熱加工變形及均質(zhì)化處理對(duì)硫化物生成行為與形貌變化的影響。 利用熱力學(xué)計(jì)算得到凝固過程中隨Mn、S在液相中的富集,大部分MnS于平衡凝固末端析出,析出量占總量的83%。初始析出溫度隨C、Si、Al含量增加而降低,隨Mn、S含量增加而升高。Fe-Mn-S三元系相圖計(jì)算表明,MnS的析出類型主要包括共晶反應(yīng)與偏晶反應(yīng)。 通過控制非調(diào)質(zhì)鋼凝固冷卻速率與鋼中A1含量,研究了不同種類MnS的形成機(jī)理。非調(diào)質(zhì)鋼中第1類MnS為偏晶反應(yīng)生成,較快冷速下與基體分離生長(zhǎng)；第1I類MnS為共晶反應(yīng)析出,與基體合作生長(zhǎng)且聚集分布；塊狀第1II類MnS則表現(xiàn)為離異共晶形貌,分布較為均勻。冷速為0.24℃/s、酸溶鋁含量為0.044%時(shí)可以促進(jìn)大量均勻分布的第1II類MnS生成,有利于改善鋼中硫化物的分布。200℃/s的較高冷速會(huì)促進(jìn)第1I類MnS生成,不利于改善鑄態(tài)非調(diào)質(zhì)鋼中MnS的分布。 熱力學(xué)計(jì)算結(jié)果表明S是影響MnS析出行為的重要元素,針對(duì)國(guó)產(chǎn)非調(diào)質(zhì)鋼中S含量控制波動(dòng)較大的現(xiàn)狀,研究了S含量變化對(duì)硫化物析出的影響。在試驗(yàn)研究范圍內(nèi)(0.025%-0.065%),隨S含量增加,第1II類MnS的比例下降,MnS析出溫度提高、數(shù)量增多、尺寸增大且沿晶聚集分布的現(xiàn)象加劇。單獨(dú)MnS以及MnS-V(C, N)復(fù)合硫化物均可作為晶內(nèi)鐵素體的有效形核核心,細(xì)化非調(diào)質(zhì)鋼鑄態(tài)組織。 鑄坯中各類MnS在熱加工過程中容易發(fā)生伸長(zhǎng),拉伸原位觀察表明這會(huì)導(dǎo)致鋼材產(chǎn)生各向異性。與縱向拉伸相比,橫向拉伸時(shí)鋼中長(zhǎng)條狀MnS的受力情況決定了其與基體更易發(fā)生分離,分離處將成為裂紋的起始源,并促使裂紋沿MnS擴(kuò)展,從而危害非調(diào)質(zhì)鋼橫向性能。因此,需要采取合理的后續(xù)加工工藝以減小硫化物的尺寸并使其分布均勻化。 通過鑄態(tài)試樣高溫壓縮試驗(yàn)研究了變形參數(shù)對(duì)硫化物相對(duì)塑性與分布的影響。整體上,低應(yīng)變速率(0.01s-1)、大變形量(80%)下基體容易發(fā)生動(dòng)態(tài)再結(jié)晶。此變形條件下MnS的相對(duì)塑性較小,尤其在變形溫度1050℃和1250℃下進(jìn)行熱加工可以使MnS發(fā)生充分碎化而減小尺寸,同時(shí)碎化后MnS的分布得到一定的改善,有利于提高非調(diào)質(zhì)鋼力學(xué)性能。 通過對(duì)熱加工后非調(diào)質(zhì)鋼進(jìn)行等溫均質(zhì)化處理,可以進(jìn)一步改善鋼中硫化物的尺寸與分布。隨加熱與保溫時(shí)間的增加,非調(diào)質(zhì)鋼中長(zhǎng)條狀MnS的尖端首先發(fā)生圓化,整體形貌逐漸向圓柱形發(fā)展,隨后部分位置發(fā)生徑向的收縮,導(dǎo)致MnS最終斷裂碎化,生成的較小尺寸MnS會(huì)進(jìn)一步發(fā)生球化。計(jì)算表明MnS長(zhǎng)大與碎化的控制因素為S元素在基體中的擴(kuò)散。在1250℃和1050℃下分別保溫3h和5h進(jìn)行均質(zhì)化處理可使非調(diào)質(zhì)鋼中大量的MnS發(fā)生碎化,降低了硫化物的尺寸并改善了硫化物的分布。
[Abstract]:Easy cutting non quenched and tempered steel is a kind of sulfur free cutting steel, due to its cutting performance and excellent mechanical properties, has been widely used in auto parts, and with the rapid development of the domestic automobile industry has a good application prospect in domestic. The sulfur non quenched and tempered steel is mainly in the form of sulfide, contrast the analysis shows that foreign steel sulfide often size reasonable control, uniform distribution, while the domestic non quenched and tempered steel sulfide is often large size and slender bar cluster distribution, which leads to the mechanical properties and cutting performance are poor, can not reach the domestic users of non quenched and tempered steel demand for high-quality cars, so still need to import large quantities of foreign non quenched and tempered steel. In order to improve the control level of nonsulfide steel, this paper studies the composition design, solidification process, thermal deformation and homogenization of sulfur compounds generated The effect of change in behavior and morphology.
The calculated solidification process with Mn using thermodynamics, accumulation of S in liquid phase, most of the MnS in the balance at the end of solidification precipitation, precipitation accounted for 83%. of the total initial precipitation temperature with C, Si, Al content increased, with Mn, S content increased three yuan,.Fe-Mn-S phase diagram calculation indicates that precipitation type MnS mainly includes the reaction of eutectic reaction and partial crystal.
By controlling the content of A1 in steel and steel solidification cooling rate of non quenched and tempered, forming mechanism of different types of MnS. First kinds of MnS non quenched and tempered steel for monotectic reaction, fast cooling speed and separation of matrix growth; class 1I MnS eutectic reaction precipitation and matrix cooperation growth and aggregation distribution; block the 1II MnS showed the divorced eutectic morphology, distribution is more uniform. The cooling rate is 0.24 DEG /s, the aluminum content of 0.044% soluble acid can promote the 1II MnS generated a large number of uniform distribution, is conducive to the improvement of the distribution of sulphide in steel.200 C /s high cooling rate will promote the formation of MnS 1I that is not conducive to improve the casting distribution of non quenched and tempered steel MnS.
The thermodynamic calculation results show that S is an important element affecting the MnS precipitation, the volatile content of the domestic situation of S control in non quenched and tempered steel, the effect of S content on sulfide precipitation. In the range of experimental study (0.025%-0.065%), with the increase of S content, the 1II MnS decreased the proportion of MnS precipitation temperature increase the number, size, and distribution of intergranular aggregation phenomenon intensified. MnS and MnS-V (C, N) composite sulfide can be used as the nucleation of intragranular ferrite, cast microstructure refinement of non quenched and tempered steel.
The slab of various MnS easily in the heating process occurred in situ observation showed that tensile elongation, which causes the steel material anisotropy. Compared with longitudinal tensile, transverse tensile stress of strip steel MnS decision matrix and more prone to separation, separation will become the source of crack initiation, and promote crack along the MnS extension, thereby endangering the transverse properties of non quenched and tempered steel. Therefore, need to follow a reasonable process to reduce the size of sulfide and the distribution uniformity.
The effect of as cast samples of high temperature plastic deformation parameters and relative distribution of sulfide. The overall compression test, low strain rate (0.01s-1), large deformation (80%) matrix to the dynamic recrystallization occurs. The smaller the relative plastic deformation under the conditions of MnS, especially the thermal processing can make MnS the fragmentation and reduce the size of the deformation temperature of 1050 DEG C and 1250 DEG C, and broken after the distribution of MnS was improved to a certain extent, is conducive to improve the mechanical properties of non quenched and tempered steel.
Based on the non isothermal thermal processing after homogenization treatment of quenched and tempered steel can be further improved, the size and distribution of sulphide in steel. With the increase of heating and heat preservation time, long strip MnS in non quenched and tempered steel tip of the first round, the overall shape gradually to the cylindrical development, radial shrinkage after part of the location, cause MnS final fracture fragmentation, the small size of MnS generated will further spheroidizing. The calculation shows that MnS growth and fragmentation factors for controlling the diffusion of S element in the matrix. In 1250 degrees and 1050 degrees respectively. 3H and 5h are homogenized at MnS can be a large number of non quenched and tempered steel in pieces and reduce the size and improve the sulfide sulfide distribution.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG142.1

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