铌微合金化高强度灰铁气缸盖的开发

Development of Nb Micro-Alloyed High Strength Gray Iron Cylinder Heads

研究了微量铌元素对灰铁组织和力学性能的影响，成功开发出一种铌微合金化高强度灰铁气缸盖。结果表明，微量铌元素的加入使石墨、共晶团、碳化物及磷共晶细化，珠光体片间距减小，基体得到强化，灰铁试样的抗拉强度、韧性、疲劳性能和热疲劳性能都得到提高。当加入的W（Nb）=0．20％时，材料的综合力学性能较好。铌在灰铁中以两种形式存在：绝大多数在共晶团边界处形成独立的富铌相，少数固溶于珠光体基体中。采用W（Nb）为0．20％的微合金化灰铁浇注的气缸盖，本体强度均在300MPa以上，达到HT300牌号的要求。气缸盖通过了1000h冷热冲击耐久性和2000h“11工况”耐久性台架试验考核，满足使用要求。

The effects of Nb on the microstructure and mechanical properties of gray iron were explored, and Nb micro-alloyed high strength gray iron cylinder heads were developed successfully. The results show that by increasing Nb, the graphite, eutectic cell, carbide and steadite are refined, the lamellar spacing of pearlite is reduced, and the matrix is strengthened. Thus the mechanical properties are improved altogether, including tensile strength, toughness, fatigue property and thermal fatigue property. When the mass fraction of Nb is 0.20%, the mechanical properties of gray iron are better. There are two forms of Nb in gray iron： only a small amount of niobium dissolves in the matrix, most of the niobium forms niobium-rich phase that embeds in the boundary of eutectic cell. The body strength of cylinder head which is made of 0.20 % Nb micro-alloyed gray iron is above 300 MPa and reaches HT300 grade. This kind of cylinder heads have been suffered 1000 hours hot-cold shock durability bench test and 2000 hours durability bench test under 11 working conditions, which can meet the application requirements.