本文選題：硼　切入點(diǎn)：BN　出處：《北京科技大學(xué)》2015年博士論文　論文類型：學(xué)位論文

【摘要】：目前,硼對低碳鋼高溫力學(xué)性能及低碳鋼晶粒尺寸影響的觀點(diǎn)尚不統(tǒng)一。本文計(jì)算了低碳鋼中微量硼在凝固前沿硼的偏析、BN析出的熱力學(xué)和動力學(xué)及冷速對BN長大的影響、分析了硼在不同合金元素匹配下對高溫力學(xué)性能的影響機(jī)理、冷速對含硼鋼高溫力學(xué)性能的影響及硼對低碳鋼相變規(guī)律和強(qiáng)化機(jī)制的影響,探討了低碳鋼中硼的存在形式及其對鋼性能的影響機(jī)理,為含硼鋼的開發(fā)提供了理論基礎(chǔ)。本研究為擴(kuò)大合金元素硼在鋼鐵行業(yè)中的應(yīng)用,穩(wěn)定并提高含硼鋼性能提供了堅(jiān)實(shí)的理論基礎(chǔ)。 首先,通過熱力學(xué)計(jì)算分析了凝固前沿B的偏析、BN的生成及冷速對凝固前沿BN長大的影響,并通過實(shí)驗(yàn)對理論計(jì)算結(jié)果進(jìn)行了驗(yàn)證。研究表明,在不考慮溶質(zhì)偏析的情況下,凝固前沿BN無法生成。在考慮凝固偏析的情況下,凝固前沿硼的偏析十分明顯,BN生成的限制性環(huán)節(jié)為N的擴(kuò)散。冷速對凝固前沿B、N的偏析沒有影響。BN尺寸隨著冷速降低粗化的原因?yàn)槟虝r(shí)間相對延長。 采用高溫?zé)崂鞂?shí)驗(yàn)測定了不同硼含量低碳鋼和低碳Nb、Ti鋼的高溫力學(xué)性能。通過對鋼中析出物、斷口形貌及組織的分析,討論了硼對低碳鋼和低碳Nb、Ti鋼高溫力學(xué)性能的影響機(jī)理。結(jié)果表明,鋼中固溶硼能夠促進(jìn)動態(tài)再結(jié)晶、抑制沿晶鐵素體的析出,對改善鑄坯高溫塑性有利。低碳鋼中硼固N(yùn)的作用,減少了細(xì)小氮化物的生成量,促進(jìn)了動態(tài)再結(jié)晶,提高了鑄坯的高溫塑性；低碳Nb、Ti微合金鋼中硼固N(yùn)的作用沒有降低鋼中細(xì)小(Ti,Nb)(C,N)的析出,對改善高溫塑性不起作用。通過對冷速和復(fù)合加入Nb、Ti對低碳含硼鋼高溫塑性影響的研究發(fā)現(xiàn),提高冷速和復(fù)合加入Nb、Ti會導(dǎo)致低碳含硼鋼的高溫塑性下降。 采用熱模擬實(shí)驗(yàn)測定了不同硼含量低碳鋼的連續(xù)冷卻轉(zhuǎn)變曲線以及不同軋鋼工藝參數(shù)對低碳含硼鋼組織的影響,分析了硼對低碳鋼相變規(guī)律的影響和軋鋼工藝對組織的影響。通過模擬軋制實(shí)驗(yàn)研究了硼對鐵素體、珠光體型低碳鋼板強(qiáng)韌化機(jī)制的影響。結(jié)果表明,鐵素體和珠光體型低碳含硼鋼中,硼固定鋼中N,降低了細(xì)小氮化物生成所需的N含量,鋼材的強(qiáng)度和韌性同時(shí)下降；當(dāng)硼含量大于與鋼中N平衡的硼含量時(shí),繼續(xù)提高硼含量,固溶硼促進(jìn)了動態(tài)再結(jié)晶,晶粒細(xì)化提高了鋼材的強(qiáng)度和韌性。提高冷速和終軋變形量、降低終軋溫度和終冷溫度均有利于組織細(xì)化。提高冷速和降低終冷溫度,鋼中組織由鐵素體和珠光體向貝氏體和馬氏體轉(zhuǎn)變。
[Abstract]:At present, the effect of boron on the mechanical properties of low carbon steel at high temperature and grain size of low carbon steel is not uniform. In this paper, the thermodynamics and kinetics of boron segregation in low carbon steel at the solidification front and the effect of cooling rate on BN growth are calculated. The influence mechanism of boron on high temperature mechanical properties under different alloying element matching, the effect of cooling rate on high temperature mechanical properties of boron steel and the effect of boron on phase transformation and strengthening mechanism of low carbon steel were analyzed. The existence form of boron in low carbon steel and its influence mechanism on the properties of steel are discussed, which provides a theoretical basis for the development of boron steel. This study is intended to expand the application of alloying element boron in iron and steel industry. Stabilizing and improving the properties of boron steel provides a solid theoretical basis. Firstly, the formation of segregation BN of solidification front B and the effect of cooling rate on the growth of solidification frontier BN are analyzed by thermodynamic calculation. The theoretical calculation results are verified by experiments. The results show that the segregation of solute is not considered. Solidification frontier BN cannot be generated. When solidification segregation is considered, Boron segregation at solidification front is obviously restricted by N diffusion. The reason why the size of BN is coarsened with the decrease of cooling rate is the relative prolongation of solidification time. The high temperature mechanical properties of low carbon steel with different boron content and low carbon NB Ti steel were measured by high temperature hot tensile test. The precipitates, fractography and microstructure of the steel were analyzed. The effect of boron on the high temperature mechanical properties of low carbon steel and low carbon NB Ti steel is discussed. The results show that the solid solution boron in the steel can promote dynamic recrystallization and inhibit the precipitation of intercrystalline ferrite. The effect of boron fixation in low carbon steel reduces the amount of fine nitride, promotes dynamic recrystallization and improves the high temperature plasticity of billet. The effect of boron fixation on nitrogen fixation in low carbon NbsTi microalloyed steel does not reduce the precipitation of the fine TiNbNbCN in the steel, but does not contribute to the improvement of the high temperature plasticity. It is found that the effect of cooling rate and composite addition of NB + Ti on the high temperature ductility of low carbon boron steel is studied. The high temperature plasticity of low carbon boron steel can be decreased by increasing cooling rate and adding NB Ti. The continuous cooling transformation curve of low carbon steel with different boron content and the effect of different rolling process parameters on the microstructure of low carbon boron steel were measured by thermal simulation experiment. The effect of boron on the transformation law of low carbon steel and the effect of rolling process on microstructure were analyzed. The effect of boron on the strengthening and toughening mechanism of ferrite and pearlite low carbon steel plate was studied by simulated rolling experiment. In ferrite and pearlite type low carbon boron steel, the N content of boron fixed steel decreases the N content required for the formation of fine nitrides, and the strength and toughness of steel decrease simultaneously, and when the boron content is larger than the boron content in equilibrium with N in the steel, the boron content continues to increase. Solid solution boron promotes dynamic recrystallization, grain refinement improves the strength and toughness of steel, increasing cold rate and final rolling deformation, decreasing finish rolling temperature and final cooling temperature are beneficial to microstructure refinement, increasing cooling rate and decreasing final cooling temperature, The microstructure of steel is transformed from ferrite and pearlite to bainite and martensite.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TG142.1

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