【作者】 戴建东；

【导师】 李大勇；

【作者基本信息】 哈尔滨理工大学 ， 材料科学与工程， 2013， 博士

【摘要】 油田射孔弹是一种为提高油田采油效率而使用的井下射孔工具。弹体是射孔弹的关键部件,主要作用是增强射孔弹侧向爆轰波冲量,提高金属射流的动能,延缓并降低稀疏波对金属射流的干扰,保证射孔深度。实践表明,弹体强度越高射孔弹穿深值越大,因此提高弹体强度是提高射孔弹穿深有效途径之一。由于弹体结构比较复杂,机械加工成本极高,采用冷挤压技术虽然提高了生产效率,使生产成本相对降低,但弹体材料选择受到很大限制,目前只能用20钢通过冷挤压制造弹体,而20钢弹体爆炸后碎片尺寸较大,极易发生卡井事故,增加打捞作业成本。近年出现的斜井和水平井开采技术以及无枪身射孔器和全通径射孔技术都对弹体提出了新的更高的技术要求,开发新的弹体材料和制造工艺是当前急需研究的课题。本文通过对材料组织和性能及成形工艺的研究,探索采用粉末冶金材料及工艺方法制备新型射孔弹弹体的可行性,为实现产业化提供理论基础和技术支撑,以满足快速发展的石油工业对新型射孔弹的需求。依据热力学原理和粉末冶金烧结合金化机理,优化设计了Fe-Cu-C系、Fe-Ni-C系和Fe-Ni-Cu-C系三种合金材料,研究了不同含量的Ni、Cu、C合金元素对弹体用不同合金系组织和性能的影响规律,分析了合金元素强化机理。研究表明：Cu对合金材料的组织和性能强化效果十分明显,Cu促进珠光体组织形成,细化珠光体层片间距,随着Cu含量的增加,合金抗拉强度和硬度增大,基体组织孔隙率增加,延伸率降低；Cu熔化后形成的孔隙均匀分布在基体组织中,在Cu含量大于2%缓慢冷却时,组织中出现游离Cu和富Cu相。Ni也促进珠光体组织形成,Ni含量增加使合金组织中铁素体含量减少而珠光体含量明显增多,合金的抗拉强度和硬度呈增大趋势变化；在C含量不变的情况下,合金延伸率随着Ni含量的增加,出现先增加后降低的变化趋势,在Ni含量为3%时,延伸率达到极值后逐渐减小；当Ni含量为2%时,在颗粒晶界出现富Ni奥氏体层,并且随着Ni含量的增加奥氏体层有逐渐增厚的趋势。材料性能试验结果表明：对于铁基粉末冶金材料,Cu和Ni共同使用对性能的强化效果远大于单个元素的强化效果,起到优势互补作用。比较而言,Fe-Ni-Cu-C系合金综合力学性能优于Fe-Ni-C系和Fe-Cu-C系合金。对压制成形方式、初压压力、复压压力和保压时间等成形工艺参数对压坏组织结构及密度分布的影响规律进行了深入研究。通过对不同的压制成形方式理论分析和工艺试验,确定了弹体压制成形方式；对弹体结构、弹体初压和复压成形模具进行了优化设计。研究结果表明：初压压力和复压压力对初压密度和复压密度影响很大,当初压坯密度接近7.1g/cm3以及复压压坯密度达到7.4g/cm3时,继续提高压力压坯密度也不会增加,即复压密度不超过理论密度的95%。弹体初压密度过高或过低都对复压产生不利影响,初压压力在600MPa,复压压力在800MPa时,压坯组织及密度较为适宜。常规的初压和复压方式很难使弹体获得较高的密度及均匀的密度分布,本文采用补偿挤压强化致密的工艺方法获得了具有一定密度梯度分布的高密度粉末冶金弹体,弹体平均密度达到7.3g/cm3。该项技术对获得高密度粉末冶金制品具有重要的作用与意义。弹体材料性能试验表明：密度对力学性能有很大影响。当压坯烧结密度超过6.9g/cm3时,抗拉强度和延伸率增加的幅度变大,而硬度随材料密度的变化幅度则相对平稳。当弹体密度为7.3g/cm3时,Fe-Ni-Cu-C系合金抗拉强度和延伸率分别达到647MPa和3.78%。对弹体烧结过程进行了系统研究,分析探讨了烧结强化机理和烧结动力学。烧结动力学分析表明：粉末的烧结速度t要取决于烧结温度。烧结温度对弹体的组织、密度和性能均有较大影响。随着烧结温度的提高,弹体材料的密度呈现先降低后增加的趋势变化,当温度达到1200℃时密度增加变缓趋于稳定；组织中的孔隙数量随着烧结温度的提高逐渐减少,形状由不规则逐渐变成椭圆形或球形,且独立分布；随着烧结温度的提高,烧结体的抗拉强度、硬度、延伸率都随之提高。实验表明：Cu和Ni对烧结过程均有强化烧结作用。Cu在烧结温度大于1083℃时会产生液相烧结,对合金元素的扩散起到强化作用,但Cu熔化形成的孔隙,会使弹体烧结体积膨胀、密度降低,产生反致密化；Ni与Fe晶粒形成的富Ni奥氏体层为Fe原子和合金元素提供了快速扩散通道,使弹体烧结体积产生收缩,产生致密化烧结作用,可有效弥补Cu反致密化产生的不利影响。Cu一方面起到强化烧结的作用,另一方面Cu熔化后形成一定数量的孔隙,通过对烧结工艺参数的调整控制基体组织的孔隙形态,使弹体爆炸后更易形成小的碎片,从而使弹体具有优异的低碎屑。试验结果表明：初烧温度在850℃,保温1小时,复烧温度在1100℃-1150℃,保温1.5小时的烧结工艺烧结效果最佳。本文还利用有限元模拟深入分析了不同工艺参数对弹体粉末坏料冷挤压成形时塑性变形规律、流动行为、应力状态等的影响。研究结果表明：在圆柱形坯料成形中,轴向拉应力的峰值显著高于其它方案,而采用端部带凹坑的锥台形坯料成形时,除整体的变形流动均匀性显著提高外,成形所需挤压力和模具的有效应力值最小,可实现一次挤压成形,为制定合理的工艺方案提供设计依据。对开辟弹体新的制备工艺途径具有重要指导意义。不同弹体的爆靶试验对比结果表明,粉末冶金弹体在钢靶及混凝土靶的爆靶穿深值和孔径都超过爆靶标准值,爆靶穿深值均比20钢弹体高且具有优异的碎屑性,完全可以取代20钢弹体。更多还原

【Abstract】 To improve the oil extraction in the oilfield, the perforating bullet is widely used to perforate downhole. Bullet body, a key component of perforating bullet, can enhance the lateral perforating bomb wave impulse, improve the kinetic energy of the metal jet, delay and reduce the interference of rarefaction wave on metal jet, and ensure the perforation depth. The results showed that the higher the strength of bullet body is, the greater the value of the perforating depth is. So, increasing the strength of bullet body is one of effective ways to improve the perforating depth. Because of the complex structure and high machining cost, the bullet body is made by the cold extrusion technology which can improve the production efficiency and decrease the production costs while the choice of body materials is limited into20#steel. However, the explosion fragments of20#steel are very large and prone to form the lock down-hole accident, which will append the salvage. In recent years, new technical requirements are proposed with the development of the exploitation technologies of tilted and horizontal wells, and full-bore perforating technique. So, developing new bullet body materials and machining technology are currently an urgent research project. In this work, the microstructure, properties and forming process are studied, and the feasibility of preparing the new bullet body by powder metalluary materials and craft method is explored. This can provide a theoretical basis and technical support for industrialization, and meet the oil industry demand for new perforating bullet.Based on thermodynamic principles and alloying powder metallurgy sintering mechanism, the Fe-Cu-C series, Fe-Ni-C series and Fe-Ni-Cu-C series alloys were optimized and designed. The effect of Ni, Cu and C alloying elements on microstructure and properties of bullet body were investigated. The strengthening mechanism of alloying elements was analyzed. The results showed that the strengthening effect of Cu on microstructure and properties is very obvious. Cu could promote the formation of the pearlite structure and reduce the pearlite lamellar spacing. The tensile strength, hardness and pore rate in the matrix increase while the elongation decreases with the increase of Cu content. Cu was melted and uniformly distributed in the pores matrix. With Cu is more than2%and cools slowly, the dissociative Cu and Cu-rich phase appeared. Ni Ni also promoted the formation of the pearlite. The ferrite content decreased and pearlite content significantly increased with increasing the Ni content. The tensile strength and hardness of the alloy tended to increase. At first the elongation of the alloy increased and then decreased with the increase of Ni content when the same C content was kept. The elongation of the alloy reached the highest value and then decreased at3%Ni content. The Ni-rich austenite layer in the grain boundaries appeared at2%Ni content. The Ni-rich austenite layer tended to thicken with the increase of Ni content. Mechanical test results showed that, for iron-based powder metallurgy materials, the comprehensive strengthening effect of Cu and Ni is much larger than the single element and they play a complementary role. As a comparison, the mechanical properties of Fe-Ni-Cu-C alloy are superior to Fe-Ni-C and Fe-Cu-C alloy.The effect of compaction-forming method, initial pressure, repeated pressure and holding time on microstructure and density distribution were systematically studied. The press forming method of bullet body was optimized by the theoretical analysis and process experimetns. The structure of bullet body, initial and repeated pressure forming mold was optimized. The results showed that the initial pressure and repeated pressure played an important role on the initial pressure density and repeated pressure density. When the initial pressure density was close to7.1g/cm3and repeated pressure density reached to7.4g/cm, the density did not increase when continuing to increase the pressure. Namely, the repeated pressure density did not exceed95%of the theoretical density. It had the adverse effects if the initial pressure density was too high or low. The microstructure and density distribution was better at the initial pressure of600MPa and repeated pressure of800MPa. The conventional multi-pressure method of bullet body is difficult to obtain a higher density and uniform density distribution. We used the compensatio extrusion and enhanced compaction method to obtain the high density powder metallurgy sintering bullet body with certain density gradient. The average density of the bullet body was7.3g/cm3. The technology had an important role in obtaining high density powder metallurgy products. Mechanical experimental results showed that the density had a great influence on the mechanical properties. When the sintering density of the billet was above6.9g/cm3, the tensile strength and elongation increase significantly while the hardness slightly changed. When the density of bullet body was7.3g/cm3, the tensile strength and elongation of Fe-Ni-Cu-C alloy could reach647MPa and3.78%, respectively.Sintering process of bullet body was systematically studied. The strengthening mechanism of sintering and sintering kinetics was analyzed and discussed. Sintering kinetic analysis shows that the sintering rate depends primarily on the sintering temperature. Sintering temperature had a great influence on microstructure, density and properties of bullet body. At first the density of bullet body alloy decreased and then increased with increasing the sintering temperature. The density tended to a stabilized value when the temperature reaches1200℃. The pore volume decreased with increasing the sintering temperature. The shape of the pore became irregular oval or spherical and distributed independently. The tensile strength, hardness and elongation of bullet body increased with increasing sintering temperature. The results show that Cu and Ni had an enhanced sintering effect on the sintering process. Cu could produce liquid phase sintering and play a strengthening effect on the diffusion of the alloy elements when the sintering temperature is higher than1083℃. Cu was melted and easy to form pores. It caused the volume expansion, the decreasing of the density and anti-densification. Ni-rich austenite grain layer formed by Ni and Fe grains provided a fast diffusion path for Fe atoms and alloy elements. The sintering volume shrinkage of the bullet body appeared and resulted in sintering densification. This could compensate for the anti-densification of Cu. Cu had an enhanced sintering effect. On the other hand, a number of molten Cu pores formed. The explosion of bullet body was easy to form small pieces by adjusting the sintering parameters to control the porous shape. So the bullet body presented excellent low debris. The results show that the sintering technology is the best with the beginning of sintering temperature of850℃, holding time of1hour and the repeated sintering temperature of1100℃-1150℃, holding time of1.5hours.In this paper, the effect of process parameters on plastic deformation, flow behavior and stress was analyzed using finite element simulation of bullet body by adopting cold extrusion of powder billet. The results show that the peak of the axial tensile stress was significantly higher than other technology in a cylindrical shape. With a frustoconical black in the process of the molding, the whole deformation was easy to flow uniformly. The required extrusion pressure and the minimum value of the effective stress were the lowest. The formation could be realized after simple extrusion. The simulation provided the basis of reasonable process design and a new pathway preparation of fabricating the bullet body.As a comparision of different burst tests, the results show that the critical target penetration depth and pore size of the bullet body by powder metallurgy exceeded the standard value. Penetration depth of the bullet body was higher than that of20#steel bullet body. The bullet body presented excellent low debris and could completely replace20#steel bullet body.更多还原