粉末高速钢丝锥剖析

Dissection and analysis of powder metallurgy high speed steel tap

通过化学成分分析、金相显微镜和扫描电镜等观察,对M12粉末高速钢丝锥进行了剖析。分析结果表明,丝锥中的碳和合金含量很高,其中Co和V含量分别高于10%(质量分数,下同)和4%,合金总含量超过了40%,钢质纯净,夹杂物很少。丝锥硬度高达70 HRC左右,表面经过Ti(C、N)涂层,厚度约2μm,与基体结合紧密,能够切削硬度高于50 HRC的超高强度钢。丝锥中的碳化物类型为M6C和MC,单颗碳化物直径≤3μm,分布比较均匀;但碳化物粘连现象较严重,并有部分沿奥氏体晶界延伸生长等过热缺陷,使丝锥脆性增大。这是由于钢中合金含量很高,碳化物数量多且细小,使其容易合并、长大、粘连。因此在粉末高速钢的生产过程中,应根据这些特点合理制定生产工艺并严格执行,避免产生过热,使粉末高速钢的高性能特点得到充分发挥。

A M12 powder metallurgy high speed steel（PMHSS）tap was dissected and analyzed by means of chemical composition analysis and metallographic and SEM observation.Results show that this tap has rich carbon and alloys with Co more than 10% and V more than 4%,and the total alloy content in this tap is more than 40%.The PMHSS matrix of the tap is very clean with few inclusions.The hardness is about 70 HRC.The surface is coated by Ti（C,N）layer with thickness about 2 μm and compact binding with the substrate.All this makes the tap be capable of cutting ultra high strength steel with hardness more than 50 HRC.Carbides in the tap are main of M6C and MC,and they are homogeneously distributed,the single carbide size is ≤3 μm,but there exist relatively serious carbide conglutination and growth along austenite grain boundary which result in brittleness of the tap.It is because of high alloy content and large amount of fine carbides in PMHSS,this makes the carbides prone to merge and conglutination.Therefore,in the production of PMHSS,it should be based on these characteristics and reasonably establish the process and strictly implement to avoid overheating and make the high-performance of PMHSS in application fully realized.