柳睿,于佳成,杨琪帆,吴志杰,席明哲,高士友.激光功率对DH36船用钢力学性能及强化机制的影响[J].表面技术,2023,52(3):408-417.
LIU Rui,YU Jia-cheng,YANG Qi-fan,WU Zhi-jie,XI Ming-zhe,GAO Shi-you.Effect of Laser Power on Mechanical Property and Strengthening Mechanism of DH36 Marine Steel[J].Surface Technology,2023,52(3):408-417
激光功率对DH36船用钢力学性能及强化机制的影响
Effect of Laser Power on Mechanical Property and Strengthening Mechanism of DH36 Marine Steel
  
DOI:10.16490/j.cnki.issn.1001-3660.2023.03.039
中文关键词:  激光功率  Rosenthal模型  力学性能  析出相  强化机制
英文关键词:laser power  Rosenthal solution  mechanical properties  precipitation  strengthening mechanism
基金项目:国家自然科学基金(51875502、U21A20138)
作者单位
柳睿 燕山大学 机械工程学院,河北 秦皇岛 066004 
于佳成 燕山大学 机械工程学院,河北 秦皇岛 066004 
杨琪帆 燕山大学 机械工程学院,河北 秦皇岛 066004 
吴志杰 燕山大学 机械工程学院,河北 秦皇岛 066004 
席明哲 燕山大学 机械工程学院,河北 秦皇岛 066004 
高士友 燕山大学 机械工程学院,河北 秦皇岛 066004 
AuthorInstitution
LIU Rui School of Mechanical Engineering, Yanshan University, Hebei Qinhuangdao 066004, China 
YU Jia-cheng School of Mechanical Engineering, Yanshan University, Hebei Qinhuangdao 066004, China 
YANG Qi-fan School of Mechanical Engineering, Yanshan University, Hebei Qinhuangdao 066004, China 
WU Zhi-jie School of Mechanical Engineering, Yanshan University, Hebei Qinhuangdao 066004, China 
XI Ming-zhe School of Mechanical Engineering, Yanshan University, Hebei Qinhuangdao 066004, China 
GAO Shi-you School of Mechanical Engineering, Yanshan University, Hebei Qinhuangdao 066004, China 
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中文摘要:
      目的 提高DH36船用钢表面力学性能及研究其强化机制。方法 采用不同激光功率对DH36船用钢表面进行激光重熔。随后使用OM、SEM、TEM、万能力学试验机和维氏硬度计研究了激光功率对DH36船用钢组织转变、析出相和力学性能的影响。利用Rosenthal模型计算出了熔池内的温度梯度、冷却速率和凝固速度。分析讨论了不同激光功率下重熔层内显微组织的转变过程。比较了不同激光功率作用后DH36船用钢的拉伸性能和显微硬度。结果 激光功率为1 500 W时,最大的屈服强度和抗拉强度分别为495.7 MPa和615.5 MPa。重熔层内显微硬度沿z方向呈逐渐下降趋势,激光功率为1 000 W时,具有最大的硬度值448HV。随着激光重熔功率(P)的增加,熔池内的温度梯度的最大值(Gmax)单调增加,而凝固速度的最大值(Rmax)则与P无关。当v =10 mm/s时,激光重熔DH36钢的熔池内有Rmax = 0.098 3 m/s。在P = 2 500 W时,熔池内有Gmax = 107 700 K/m。功率为1 000 W时,晶粒内弥散着纳米渗碳体,强化机制为第二相强化;功率为2 500 W时,晶粒内和晶界处出现尺寸较大的析出相,强化机制为固溶强化。不考虑P =1 000 W,激光功率越大,重熔层硬度的提升效果越明显。结论 激光重熔工艺可有效地提高DH36船用钢表面力学性能。不同激光功率下,船用钢重熔层内的强化机制不同。
英文摘要:
      The laser remelting experiment was carried out in the in-house system, which consists of a 3 300 W fiber laser and a CNC four-axis working substrate. The DH36 marine steel plate is 200 mm long, 120 mm wide and 12 mm thick. An argon purged chamber with oxygen content less than 8×10‒6 was used to prevent the molten pool from oxidation. The laser remelting processing parameters were as follows:laser power 1 000, 1 500, 2 000 and 2 500 W, spot size 3 mm, laser scanning velocity 10 mm/s, overlapping ratio 50%. After grinding and polishing, the cubics cut by wire-electrode were etched with 4% nitric acid alcohol. The microstructure of yz section of DH36 marine steel was observed under ZEISS AX10 metallographic microscope (OM). The effect of different laser remelting power on the mechanical properties of DH36 Marine steel was studied by Zwick Z010 universal mechanical testing machine which the tensile speed was 1 mm/min. QPIX automatic vickers hardness tester was used to test the microhardness with the load of 200 g and the retention time of 20 s. JEM-2010 transmission electron microscope was used to observe the microstructure and size of precipitates in the xy plane after laser remelting process, and the element distribution was analyzed by mapping. The temperature gradient、cooling rate and solidification speed of molten pool during laser remelting process was simulated by Rosenthal solution. When P=1 000 W, the microstructure of the molten pool is mainly of AF and the overlapping zone consists of QF. It crosses the AF forming region on the CCT curve when the laser power is 1 000 W. The core of AF is Mn and a small amount of Si and Ti in the alloy, which grows fast in the shape of plate. Nanoscale cementites appear intragranular which the average length is 120-140 nm and the width is 20 nm. From the point of view of phase transformation, the carbon content of austenite is much higher than that of ferrite. Because of the lack of carbon content of DH36 steel, the pre-eutectoid reaction inevitably occurs when the molten pool goes through the cooling process. At a certain temperature gradient, however, the diffusion of C is inhibited, which makes it free from the ferrite boundary. At the same time, owing to the large cooling rate, the cementites don’t have enough time to connect and grow into lamellae and disperse in the grain as particles. Meanwhile, a certain amount of Ti and Nb precipitates in the crystal to form (Nb,Ti)C which reduces the nucleation barrier and promotes AF nucleation. From the energy point of view, the high temperature gradient in the molten pool provides sufficient driving force to satisfy the interface energy difference resulting from the formation of nanoscale cementites. When P increases to 2 500 W, spherical precipitates are produced in the grain and at the grain boundary. The average grain size in remelted layer is about 2 μm. The intracrystular precipitates pins for the dislocations, while the dislocations are wound into cells distributed around the grain boundary precipitates. The maximum size of precipitate is about 0.8 μm. There is a high content of Fe in the intragranular precipitates, while the grain boundary precipitates seldom contains of Fe and are mainly composed of Mn, Ti and Al elements. The diffusion driving force of Fe is much higher than that of Mn, Ti and Al. Therefore, it forms compounds intragranular as solid solution rather than moves to the grain boundary. When P=1 500 W, it has the maximum yield strength and extension strength, which is 495.7 MPa and 615.5 MPa, increased 7.5% and 3.2% compared with the DH36 steel. When P=1 000 W, AF appears at the bottom of remelting layer, and the microhardness is significantly increased to 448HV, which is 70.49% higher than that of DH36 steel. The microhardness of the remelting layer decreases gradually along the z direction which is the remelting zone > heat affected zone > DH36 steel.
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