退火温度对H13钢等离子堆焊Ni60/WC覆层组织和硬度的影响

Effect of annealing temperature on microstructure and hardness of Ni60/WC coating on H13 steel by plasma transfer arc welding

采用等离子堆焊技术在H13钢基体表面上制备了Ni60/WC复合覆层。研究了退火温度对基体、热影响区和Ni60/WC复合覆层组织、硬度的影响。结果表明:经退火处理后消除了覆层裂纹敏感性,WC分布得到改善。800℃退火后花瓣状枝晶得到细化,组织更为均匀。焊态下覆层热影响区组织主要由粗大片状马氏体和板条马氏体以及残留奥氏体组成,600℃退火后热影响区组织主要由板条状铁素体、针状铁素体和颗粒状渗碳体组成,800℃退火后热影响区组织主要由等轴状铁素体和粒状渗碳体组成,退火处理后热影响区组织得到明显改善。经过600℃退火后覆层硬度略微下降,淬硬区得到缓和; 800℃退火后覆层硬度分布均匀,淬硬区消失,基体到覆层过渡处的硬度呈梯度上升,进而改善了基体与覆层之间的结合,提高了覆层的力学性能。

Ni60/WC composite coatings were prepared on the surface of H13 steel substrate by plasma transfer arc welding technology. The effects of annealing temperature on the microstructure and hardness of the substrate,heat affected zone and Ni60/WC composite coatings were studied. The results show that the crack sensitivity of the coatings is eliminated after annealing,and the WC distribution is improved. After annealing at 800 ℃,the dendritic petal dendrites are refined and the microstructures are more uniform. The heat affected zone of unannealed coatings mainly consists of coarse lamellar martensite,lath martensite and retained austenite. After annealing at 600 ℃,the microstructure in the heat affected zone is mainly composed of lath ferrite,acicular ferrite and granular cementite. After annealing at 800 ℃,the heataffected zone is mainly composed of equiaxed ferrite and cementite,and the microstructure of the heat affected zone is improved. After annealing at 600 ℃,the hardness of the coatings decreases slightly and the hardened area is relaxed. After annealing at 800 ℃,the hardness of the coatings is uniform and the hardened zone disappears,the hardness from the substrate to the coatings increases gradually,thus improving the bonding between the substrate and the coatings and the mechanical properties of the coatings.