27CrMoV石油套管钢夹杂物控制研究

发布时间：2018-04-30 18:25

本文选题：石油套管钢 + 夹杂物控制　；参考：《北京科技大学》2016年博士论文

【摘要】：油套管钢是高技术含量、高附加值、高风险的冶金产品,对钢材的强度、韧性、焊接性能、抗氢致裂纹(HIC)、抗硫化物应力腐蚀断裂(SSCC)等性能有较高要求。这就对钢中的硫、氧、磷、氮、氢等杂质元素和夹非金属杂物的控制提出了严格的要求。目前攀钢集团攀枝花钢钒有限公司(以下简称攀钢)生产油套管钢过程中存在钙处理效果不稳定、钢水浇铸性能差和成品抗硫化物应力腐蚀性能不达标的问题。上述问题均与石油套管钢中的非金属夹杂物密切相关,因此,本文以BOF→LF→RH→CC流程生产的27CrMoV石油套管钢为对象,对不同钙处理工艺路线钢、精炼渣和夹杂物变化进行对比,并对钢中夹杂物的生成和控制机理、钙处理中间产物及夹杂物演变机理进行研究,在此基础上,提出改进措施,并在工业验证试验和批量生产中取得了理想效果。本文的主要创新点和工作如下：对三种钙处理工艺路线的钢、精炼渣和夹杂物进行分析,其中夹杂物的研究借助FactSage平衡模块和CaO-Al2O3-MgO-CaS四元相图,结果表明：三种路线钢中总氧、氮、钙、硫等成分含量控制较为理想,但保护浇铸仍存在问题,易发生二次氧化现象。精炼渣各成分变化相似,精炼渣碱度为8-27,曼内斯曼指数为0.38～0.96,熔化温度为1300～1375℃,主要物相为12CaO·7Al2O3。路线A中间包钢样中多为高CaS含量的Al2O3-CaO-CaS系、Al2O3-CaS系和CaO-CaS系固态夹杂物,易引起水口堵塞；路线B中包钢样中多为Al2O3-CaO-CaS和Al2O3-CaO-MgO-CaS系夹杂物,多数位于50%-100%液相区域之内；路线C中包钢样中除Al2O3-CaO-MgO-CaS系和Al2O3-CaO-CaS系夹杂物,还存在大量二次氧化生成的A1203和Al2O3-MgO系夹杂物。针对现存评价方法的局限性,提出一种以夹杂物改性指数评估钙处理改性夹杂物效果的方法,并据此确定最优钙处理工艺路线。针对攀钢生产27CrMoV石油套管钢的工艺特点和钢水成分,同时考虑活度二次相互作用系数和平衡元素的浓度变化对钢中氧化物夹杂的生成和控制机理进行热力学研究,并利用格缪尔吸附方程对氧硫复合夹杂物的生成机理进行研究,结果表明：[A1]s=0.05%,若要将夹杂物成分控制在12CaO·7Al2O3附近,则[Ca]=27×10-6, [Ca]/[Al]s=0.054。当MgOAl2O3活度为1,钢液中[A1]s=0.05%-0.07%时,溶解镁只要达到0.34×10-6和0.38×10-6,钢中便可生成MgOAl2O3尖晶石。当[A1]s=0.05%,[Mg]=4×10"6-8×10-6时,钢中[Ca]含量只要分别达到2.2×10-6和8.0×10-6,钢液中的MgOAl2O3便开始向CaOAl2O3转变。夹杂物观测结果同上述热力学计算结果较吻合。钙处理后钢液中的溶解钙对后续工序中二次氧化产物具有一定的改性作用,为了将二次氧化产物改性为液态,应降低二次氧化过程中的增氧量,并提高钢液中的溶解钙含量。硫含量为0.003%时,硫在12CaO·7Al2O3夹杂物表面的覆盖度达到90%以上,易生成CaS外壳,钢样中观测到的氧硫复合夹杂物多基于此机理生成。建立钙处理中间产物生成动力学模型,对钙处理中间产物CaS、CaO的生成机理进行研究,并详细阐述了钙处理中间产物对氧化物的改性机理。对精炼前期MgO-Al2O3系或高熔点的CaO-Al2O3系夹杂物的生成次序,尚未见文献报道的CaO-Al2O3-MgO(环状)系夹杂物的生成机理进行了研究。结果表明：在钙处理后的短时间内,根据不同的氧、硫含量会生成不同的中间产物,当钢中溶解氧为4×10-6时,临界硫含量为11×10-6。钙处理中间产物CaO、 CaS均可将氧化铝夹杂改性为液态钙铝酸盐夹杂物,不同的钙处理中间产物对氧化铝夹杂有着不同的改性机理。钙处理中间产物CaO对氧化物的改性速率快于CaS,且CaS、CaO对MgO·Al2O3夹杂物进行改性的难度低于对A1203的进行改性。精炼渣CaO/Al2O3=1.4为A1203生成MgO-Al2O3系或高熔点CaO-Al2O3系夹杂物的临界值。当钢液中的[Mg]含量较高时,[Mg]将夹杂物外围的CaO或A1203成分还原出来,形成CaO-Al2O3-MgO(环状)系夹杂物。精炼过程钢液中夹杂物的演变路径为：Al2O3→Al2O3-MgO系和高熔点Al2O3-CaO系夹杂物→Al2O2-CaO-MgO系或Al2O3-CaO系液态夹杂物→点块状或环状MgO、CaS为外壳,低熔点钙铝酸盐或钙镁铝酸盐为核心的复合夹杂物。改进和优化脱氧制度、造渣制度、钙处理工艺和连铸保护浇铸制度后,进行工业验证试验和批量生产,结果表明：试验炉次精炼过程脱硫脱氧效果较好,中间包中主要为Al2O3-MgO-CaO系、Al2O3-CaO-CaS系复合夹杂物,大多数位于50%-100%液相区域内,夹杂物改性指数大幅提高至0.77。工业生产中因水口堵塞造成的流次断浇率降至2.0%以下,单中间包连浇炉数由小于5炉提高到7-10炉。氧含量、氮含量、硫含量、非金属夹杂评级和耐硫化物应力腐蚀破裂等性能完全满足产品标准的要求。
[Abstract]:Oil and casing steel is a high technical, high value-added, high risk metallurgical product. It has high requirements for steel strength, toughness, welding performance, hydrogen induced crack (HIC), resistance to sulfide stress corrosion cracking (SSCC) and so on. This is a strict requirement for the control of sulfur, oxygen, phosphorus, nitrogen, hydrogen and other impurity elements in steel and the control of non metallic inclusion in steel. At present, the production of oil and casing steel in Panzhihua steel vanadium Co., Ltd. of Panzhihua Iron and Steel Group (hereinafter referred to as "Panzhihua Steel") has a problem of unstable calcium treatment, poor casting properties of steel and the resistance to sulphide stress corrosion resistance of finished products. All these problems are closely related to non gold inclusions in the oil casing steel. Therefore, this paper is BOF to LF. The 27CrMoV oil casing steel produced by RH to CC is the object. The changes of the steel, refining slag and inclusions in different calcium treatment process are compared. The formation and control mechanism of inclusions in the steel and the mechanism of the intermediate product and inclusion evolution mechanism of the calcium treatment are studied. On the basis of this, the improvement measures are put forward, and the test and batch of industrial verification and batch are also put forward. The main innovation and work of this paper are as follows: the analysis of steel, refining slag and inclusions in three kinds of calcium treatment process, including the use of FactSage balance module and CaO-Al2O3-MgO-CaS four element phase diagram, shows that the content of total oxygen, nitrogen, calcium and sulfur in the three kinds of route steel is controlled. The system is ideal, but there are still problems in the protection casting. Two oxidation phenomena are easy to occur. The composition of the refining slag is similar, the alkalinity of the refining slag is 8-27, the MannesMann index is 0.38 ~ 0.96, the melting temperature is 1300~1375, and the main phase is the Al2O3-CaO-CaS system with high CaS content in the 12CaO. 7Al2O3. route of A. The Al2O3-CaS system and the Al2O3-CaS system are the main components. CaO-CaS is a solid inclusion, which is easy to cause the blockage of the nozzle; in the route B, most of the steel samples are Al2O3-CaO-CaS and Al2O3-CaO-MgO-CaS inclusions, most of which are located in the 50%-100% liquid phase. In the route C, there are a large number of A1203 and Al2O3-MgO clips formed by two oxidation in addition to the Al2O3-CaO-MgO-CaS and Al2O3-CaO-CaS system inclusions in the Baotou steel samples. In view of the limitations of the existing evaluation methods, a method is proposed to evaluate the effect of calcium treatment modified inclusions by inclusion modification index, and the optimal calcium treatment process is determined accordingly. In view of the technological characteristics and steel composition of the 27CrMoV oil cased steel produced in Panzhihua steel, the two times interaction coefficient and balance element of the activity are considered. The formation and control mechanism of oxide inclusions in steel are studied thermodynamically, and the formation mechanism of oxygen and sulfur compound inclusions is studied by using the method of the [A1]s=0.05%. The results show that if the inclusion composition is controlled near 12CaO 7Al2O3, [Ca]=27 x 10-6 and [Ca]/[Al]s=0.054. are the activity of MgOAl2O3. For 1, when the molten steel is [A1]s=0.05%-0.07%, as long as the dissolved magnesium reaches 0.34 * 10-6 and 0.38 x 10-6, the MgOAl2O3 spinel can be generated in the steel. When [A1]s=0.05%, [Mg]=4 x 10 "6-8 * 10-6, the [Ca] content of the steel is 2.2 * 10-6 and 8 x 10-6, and the MgOAl2O3 in the molten steel begins to change to the CaOAl2O3. The inclusion observation results with the above thermodynamics. The calculation results are more consistent. The calcium dissolved in the molten steel after calcium treatment has a certain modification effect on the two oxidation products in the subsequent process. In order to change the two oxidation product into liquid, the amount of oxygen increasing in the two oxidation process should be reduced and the content of calcium dissolved in the molten steel is increased. When the sulfur content is 0.003%, the sulfur is on the surface of the 12CaO. 7Al2O3 inclusion. The coverage of CaS is more than 90%, and the formation of oxygen and sulfur composite inclusions in steel samples is mostly generated based on this mechanism. A kinetic model for the formation of intermediate products of calcium treatment is established. The formation mechanism of CaS and CaO, the intermediate product of calcium treatment, is studied, and the modification mechanism of the intermediate products of calcium treatment to the oxide is described in detail. The formation of the inclusions in the CaO-Al2O3 system of the early MgO-Al2O3 or high melting point has not yet been studied. The results show that in the short time after calcium treatment, the sulfur content will produce different intermediate products according to the different oxygen, when the dissolved oxygen in the steel is 4 * 10-6. The boundary sulfur content is 11 x 10-6. calcium treatment intermediate product CaO, CaS can change alumina inclusion into liquid calcium aluminate inclusions. Different intermediate products of calcium treatment have different modification mechanism to alumina inclusion. The modification rate of calcium treatment intermediate product CaO to oxide is faster than CaS, and CaS and CaO modify the MgO. Al2O3 inclusion. The difficulty is lower than the modification of A1203. The refining slag CaO/Al2O3=1.4 is a critical value for the formation of MgO-Al2O3 or high melting point CaO-Al2O3 inclusions in A1203. When the [Mg] content in the molten steel is high, [Mg] reduces the CaO or A1203 components outside the inclusions to form a CaO-Al2O3-MgO (ring) inclusion. The evolution of inclusions in the molten steel in the refining process. The path is: Al2O3, Al2O3-MgO and high melting point Al2O3-CaO inclusions, Al2O2-CaO-MgO or Al2O3-CaO liquid inclusions, dot or ring MgO, CaS as a shell, low melting point calcium aluminate or calcium magnesium aluminate as the core composite inclusions. Improvement and optimization of deoxidization system, slag making system, calcium treatment process and casting protection casting system After the industrial test and batch production, the results show that the desulfurization deoxidization effect of the secondary refining process is better, the main package in the middle bag is Al2O3-MgO-CaO, Al2O3-CaO-CaS is a compound inclusion, most of them are located in the 50%-100% liquid phase region, the inclusion modification index is greatly improved to the 0.77. industrial production due to the plugging of the nozzle. The rate of flow breaking was reduced to less than 2%, and the number of single tundish continuous pouring furnace increased from less than 5 to 7-10. The oxygen content, nitrogen content, sulfur content, non-metallic inclusion rating and sulfide stress corrosion cracking were fully satisfied with the requirements of the product standard.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TF76;TG142

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