铬对铸铁组织和性能的影响

Effect of Chromium on Microstructure and Properties of Cast Iron

介绍了铬元素的理化性能和Fe-Cr、Fe-Cr-C平衡相图的区域分布及特征,综述了铬对铸铁组织和性能的影响情况。随着含铬量的增加,稳定系和亚稳定系铸铁共晶温度之间的差距变小,易使铸铁形成白口组织;铬强烈形成碳化物,不仅在铸铁共晶转变时反石墨化促使形成白口组织,而且在共析转变时也反石墨化促使形成珠光体组织。在普通灰铸铁中,抗拉强度和硬度都随含铬量的增加提高,一般每增加0.1%的铬量,可使抗拉强度提高3%~4%、硬度大约提高10 HBW,但含铬量不应超过0.5%;对于高铬白口抗磨铸铁,含铬量超过12%,形成Cr_(7)C_(3)型碳化物,它的硬度比渗碳体(Fe_(3)C)要高,因而有更高的抗磨性能;对于球墨铸铁,加铬可使珠光体中的渗碳体稳定,退火后可得到粒状珠光体组织,在抗拉强度不变的情况下,除硬度有所下降外,伸长率和冲击韧性均有增高。此外,少量的铬可阻碍铸铁内、外表面的氧化。

The physical and chemical properties of chromium and the regional distribution and characteristics of Fe-Cr and Fe-Cr-C equilibrium phase diagrams are introduced.The influence of chromium on microstructure and properties of cast iron is reviewed.With the increase of chromium content,the difference between the eutectic temperature of stable cast iron and metastable cast iron becomes smaller,which makes the cast iron forming white microstructure easily.Chromium strongly forms carbides,and not only in the eutectic transition of cast iron,but also in the eutectic transition,the antigraphitization of chromium leads to the formation of the white grain structure,and the formation of the pearlite structure.In ordinary gray cast iron,the tensile strength and hardness are increased with the increase of chromium content.Generally,every 0.1%increase of chromium content can increase the tensile strength by 3%~4%and hardness by about 10 HBW,but the chromium content should not exceed 0.5%.For high chromium white grinding cast iron,the chromium content is more than 12%,forming Cr_(7)C_(3) type carbide,its hardness is higher than the cementite(Fe3C),so it has higher wear resistance.For nodular cast iron,adding chromium can make the cementite in pearlite stable,after annealing can get granular pearlite structure,in the case of constant tensile strength,in addition to hardness decreased,elongation and impact toughness are increased.In addition,a small amount of chromium can inhibit the oxidation of the inner and outer surface of cast iron.