超(超)临界核阀用耐热钢激光熔覆钴基合金修复研究

A Research on Laser Cladding Co-Based Alloy to Repair Heat Resistant Steel of the Valves Used in Ultra-Super Critical Nuclear Power Plants

整体式阀门阀座是超(超)临界核电机组中的关键重要部件。实现阀门密封面的现场修复是核电装备制造领域的研究热点之一。本文针对核阀常用F91耐热钢开展了激光熔覆Stellite 6钴基合金修复试验研究,通过改变工艺参数制备了一系列熔覆厚尺寸修复试样,并开展了金相、硬度、三点弯曲、室温冲击等分析测试。结果表明:激光熔覆Stellite 6钴基合金组织具有典型的外延生长凝固特征,主要由面心立方γ-Co固溶体组成;修复试样的硬度可达450~500 HV,抗弯强度可达1246~1582 MPa,室温冲击功可达40~60 J,修复层与基材的结合强度高。熔覆层内易出现气孔、熔合不良等缺陷,熔覆工艺参数的选择应遵循能量密度低、可靠性高的原则。

An integral valve seat is an essential component in ultrasuper critical(USC)nuclear power plants.Onsite remanufacturing of the valveseat sealing face is a major focus of nuclear power plant manufacturing.In this paper,a laser cladding Stellite 6 Cobased alloy repair study was carried out for the commonly used F91 heat resistant steel for nuclear valves.A series of cladding thicksize repair samples were prepared by changing the process parameters,and the metallographic observation,hardness testing,threepoint bending testing,and impact testing at room temperature were performed.The cladding layers consisted of a facecenteredcubicγ-Co solid solution with epitaxial growth solidification characteristics.The hardness,bending strength,and impact energy of the repaired samples were 450‒500 HV,1246‒1582 MPa,and 40‒60 J,respectively.Bonding strength between the cladding layer and substrate was very high.The gas pore and bad bonding often exist in a cladding layer.The selection of cladding process parameters should follow the principles of low power density and high reliability.