NM600级超高强耐磨钢组织调控技术研究

发布时间：2018-06-17 06:02

本文选题：超高强耐磨钢 + 马氏体　；参考：《北京科技大学》2016年博士论文

【摘要】：使用更高强度的耐磨钢板可以提高工程机械设备磨损部件的使用寿命,降低设备自重,在节约能源和材料同时也有着积极的经济意义。目前国内可稳定生产的耐磨钢板硬度级别较低,高级别的耐磨钢板产品往往存在韧性不足的问题,长期依赖进口。本文以NM600级超高强耐磨钢板的实验室开发为出发点,充分发挥多种强韧化手段的作用,从成分和工艺两方面调控实验钢的微观组织,最终获得强韧性匹配良好、耐磨性优良的实验钢板。在此过程中的具体研究内容如下：设计碳含量0.4wt.%的中碳合金耐磨钢,对分别添加0、0.030和0.062(wt.%,下同)Nb的三种实验钢进行基础物性参数研究和实验室试制,证明Nb添加可在高温时抑制本文中碳合金钢的奥氏体晶粒长大,在奥氏体区热变形时可抑制再结晶软化。实验室两阶段轧制后进行900℃再加热淬火和200～400℃低温回火(QT),力学性能测试和SEM、TEM分析表明添加0.062%Nb起到细晶强化和析出强化的作用,所得综合性能优于无Nb钢,其中200℃回火处理后的实验钢硬度达到600 HBW以上,力学性能指标达到NM600级超高强耐磨钢板要求。针对含Nb量0.062%的实验钢设计出TMCP-DP短流程钢板试制新工艺,即两阶段控制轧制和随后的水冷-过冷奥氏体水冷-直接碳配分。所得实验钢性能优良,强度2200 MPa以上时还可获得12%的延伸率,硬度620 HBW,-20℃冲击功达到28 J以上。利用OM、SEM、TEM和XRD对处于不同处理状态的实验钢进行显微组织表征发现：与传统QT工艺相比,新工艺所得钢板组织中原始奥氏体细小,马氏体板条最为细密：TMCP过程充分发挥了Nb微合金化细晶强化和析出强化的作用,确保轧后晶粒细小,相变前的水冷过程可防止轧后细化的组织再次长大,水冷后在较低温度空冷时利于位错回复,避免轧后位错过多遗传到最终组织而增加脆性,随后的直接碳配分则充分利用实验钢过冷奥氏体稳定性高的特点,为未转变奥氏体增碳稳定创造条件,从而改善室温组织的韧性。销盘磨损试验结果表明,耐磨性与硬度密切相关,TMCP-DP钢耐磨性仅次于硬度更高的轧后水淬处理的钢。在扫描透射模式下采用EDX-Mapping面扫技术观察到TMCP-DP工艺获得的超高强耐磨钢实验钢中弥散分布的析出物内均匀分布Nb、Ti和Mo元素,三种元素并未出现局部偏聚。TEM下选区衍射花斑和三维原子探针层析术(3D-APT)确认钢中析出物为(Nb,Ti,Mo)C,证明钢中有少量的Mo均匀并入到Nb、Ti的碳化物析出中。3D-APT获得残余奥氏体相的三维形貌,对其成分分析发现其碳含量明显高于与其相邻的马氏体相区,碳富集浓度约是基体平均碳浓度的5-7倍,这是其能稳定存在于室温的保证。一步法QP与直接碳配分(DP)的对比研究证明了DP过程碳配分的有效性,1℃/s处理后获得最高残余奥氏体含量,体积分数为9.16%,且对应奥氏体中的碳含量高于其他冷速时。对获得的残余奥氏体含量不同的试样进行冲击磨损试验表明：冲击磨损时磨损机理以磨粒嵌入引发的表面材料直接脆性剥落或疲劳脱落为主；残余奥氏体含量较高的试样磨损失重越大,说明残余奥氏体对耐磨性不利；综合考虑其对实验钢塑韧性的有益贡献,钢中还应适当保持少量的残余奥氏体相。
[Abstract]:The use of higher strength wear-resistant steel plate can improve the service life of the worn parts of the engineering machinery, reduce the weight of the equipment, and also have the positive economic significance in saving energy and materials. At present, the hardness level of the durable steel plate in China is low, and the high grade wear resistant steel plate often has the problem of lack of toughness. Based on the laboratory development of the NM600 super high strength wear-resistant steel plate, this paper makes full use of the role of a variety of strong and toughening means, regulates the microstructure of the experimental steel from two aspects of composition and technology, and finally obtains the experimental steel plate with good strength and toughness matching and excellent wear resistance. The specific contents of this process are as follows: The medium carbon alloy wear-resistant steel with a carbon content of 0.4wt.% and three kinds of experimental steels adding 0,0.030 and 0.062 (wt.%, the same) Nb respectively are studied and tested in laboratory. It is proved that the addition of Nb can inhibit the austenite grain growth of the carbon alloy steel in this paper at high temperature, and the recrystallization softening can be suppressed in the thermal deformation of the Ordovician zone. After two stage rolling, reheating and quenching at 900 C and low temperature tempering (QT) at 200~400 degrees C, mechanical properties test and SEM, TEM analysis show that adding 0.062%Nb to fine grain strengthening and precipitation strengthening is better than non Nb steel, of which the hardness of the steel after tempering treatment at 200 c is above 600 HBW, and the mechanical performance index reaches NM6 00 stage super high strength wear resistant steel plate requirements. A new TMCP-DP short process steel plate is designed for the experimental steel with Nb 0.062%. The two stage controlled rolling and the subsequent Water Cooling Austenite water cooling direct carbon partition. The experimental steel has excellent performance, and the strength of the steel can be 12% elongation at the hardness of 620 HBW and -20 centigrade when the strength is above 2200 MPa. The work reached more than 28 J. Using OM, SEM, TEM and XRD, the microstructure of the experimental steel in different treatment states was characterized. Compared with the traditional QT process, the original austenite in the steel plate was finer and the martensitic plate was the most fine. The TMCP process fully exerts the effect of fine grain strengthening and precipitation strengthening of Nb microalloying. The grain is fine after rolling, and the water cooling process before the phase change can prevent the refined tissue to grow up again. After water cooling, it is beneficial to the dislocation recovery at a lower temperature and air cooling, avoiding the post rolling position missing and increasing brittleness in the final tissue. The subsequent direct carbon distribution makes full use of the high stability of the austenite in the experimental steel, which is not changed. The austenite Carbon Stabilization creates conditions to improve the toughness of the tissue at room temperature. The wear test results show that the wear resistance is closely related to the hardness, and the wear resistance of TMCP-DP steel is second only to the higher hardness of the steel after the rolling. In the scanning transmission mode, the high strength and wear resistance obtained by the EDX-Mapping surface scanning technique is observed by the TMCP-DP process. Nb, Ti and Mo elements are evenly distributed in the dispersed and distributed precipitates in steel experimental steel. The three elements do not appear in the local segregation.TEM zone diffraction spots and three dimensional atomic probe chromatography (3D-APT) to confirm that the precipitates in the steel are (Nb, Ti, Mo) C. It is proved that a small amount of Mo in the steel is uniformly incorporated into Nb, and the residual austenite is obtained from the carbide precipitation of the Ti. It is found that the carbon content of the body phase is obviously higher than that of its adjacent martensite. The concentration of carbon enrichment is about 5-7 times of the average carbon concentration of the matrix, which is the guarantee for its stable existence at room temperature. The comparison of one step method QP and direct carbon partition (DP) proves the effectiveness of carbon distribution in the DP process, after 1 C /s treatment. The highest retained austenite content was obtained, the volume fraction was 9.16%, and the carbon content in austenite was higher than that of other cold speed. The impact wear test of the samples with different retained austenite content showed that the wear mechanism of the retained austenite was mainly caused by the direct brittle peeling or fatigue shedding of the surface material caused by the abrasive particles. The greater the wear loss of the specimens with high residual austenite content, the results indicate that the retained austenite is unfavorable to the wear resistance. Considering the beneficial contribution of the retained austenite to the ductility of the experimental steel, a small amount of retained austenite should be maintained in the steel.
【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】：TG142.1

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