Study On The Surface Aging-hardened High Speed Steel Of 25Cr2Mo2v

A new kind of high speed steel which has low carbon contention, was hardened by the diffusion of intermetallic compounds has been found. Its properties include high speed hardening, the maximum hardness of HRC68 and good resistence of being softened during a long time of tempering. The main idea of this dissertation is that a surface aging-hardened alloy layer is formed on the surface of a kind of low-alloy steel named 25Cr2Mo2V with double glow plasma alloying tech. The surface alloying layer has a certain depth and contention of W, Mo, Co. After quenching and aging, intermetallic compounds of W, Mo, Co and Fe were deposited in the basic phase. So the surface aging-haredened alloy layer was finally formed. By this way, the high hardness of the surface and good wearability of a cheap steel material could be reached. In the experiment, a powder pressedboard whose concentration of W, Mo, Co was 35%, 20% , 45% seperately was regarded as a source pole. Under the hollow cathode effection of incordinate voltage, the Ar atom was ionized to Ar+. Then the source pole and the specimen one were cleaned by a great amount of Ar+. Their temperature was increased to about 1100℃.The particles of W, Mo, Co were spluttered and deposited on the surface of the steel. And these elements were diffused into the inside phase. At last, an alloy layer of a certain depth was formed.Firstly, the alloying process was discussed. It had been founded that different proceeding parameters result in different depth and alloy concentration of the alloy layer. And the reason was discussed in detail. The anticipated alloy layer was fianally formed whose concentration of the W, Mo, Co was nearly thesame as that of the metallurgical aging high speed steel. On the other hand, some factors such as the crystalloid structure, the diameter of the crystalls and different appetencies ect was discussed. Then quenching and aging was needed. The experiments with different quenching temp and aging temp weredone. The results showed that quenching with the temperature of 1240癈 and lasting time of 5min followed with aging at the temperature of 540℃ and lasting 30min would result in the best hardening effection. Just like the normal aging high speed steel, the surface alloy layer also had the properties of high-speed aging and high maxmium hardness. The deposited compounds during the aging treatment was tested by XRD. At the same time, the capacity of resistance of being softened during a long time of tempering. It was found that its surface hardness could remain a high level of 680HV. At last, the wearing test was carried out under different loadness. The excellent wearability of the surface aging-hardened alloy was been proved.