Sintering Of Powder Metallurgy Low Alloy Steel, Hardened

Sinter-hardening is the method which can improve the hardness and strength of P/M parts and lower the producing cost by quick-quenching in the sintering temperature.As a new sinter technology sinter-hardening has been quickly used in abroad.In this paper,the research background based on the fast development of sinter-hardening process.We do a lot of essential experimental researches concerning the sinter-hardening manufacture and the sinter-hardening process.Some kinds of sinter-hardening low-alloy steels with different content of alloying elements and different alloying methods were studied.The powder involve the admixed powders which chemical composition are Fe-0.5Mo-2Cu-4Ni-0.1Mn-0.8C,Fe-1Mo-2Cu-4Ni-0.8C and prealloyed powdersATOMET4701,ATOMET4601 which are produced by Hoganas corp.The effect of mixer style and time,sintering temperature,compact pressure,cooling rate on material properties was investigated. The experimental results show that,high density(7.07g/cm~3),high apparent hardness(31HRC)and high tensile strength(636MPa)with champion properties can be achieved at those conditions,which are the admixed powder contains 0.8%graphite,2%copper,4%Ni,Mo0.5%～1%Mo and ferros,admixed powders is milled by 12 hours and compacted in 700Mpa,samples are sintered at the temperature 1200C and cool at fast speed in vacuum or hydrogen furnace.In a wide range, increasing the compact pressure and the sinter temperature could enhance the densification of the material and raise the mechanical properties.At the same time,increasing the cooling rate could be good for increasing the condensate depression of the materials and promoting the martensite transformation process.Except the addition of copper and graphite are affective for improving the mechanical properties,in the sinter-hardening experiment,add Mo,Ni and some elements else can affect the hardenability effectual.By using prealloyed powders which produced by Hoganas corp.we can get more uniform microstructure and gain more martensite thus produce the material with better mechanical properties.All the prealloyed samples are better than the admixed ones.Taking Hoganas prealloyed powder- ATOMET4701,ATOMET4601,we get the sinter-hardening low-alloy P/M steels with a excellent properties with hardness 37HRC,35HRC respective,tensile strength 662MPa,694Mpa.Besides it,the prealloyed powders could also resolve the oxidize problem of Mn,Cr,on the other hand,due to using pre-alloy powder,the elements could diffusion more easily and more uniform than before.Therefore,the required sintering temperature decreases and save the cost of production.Sinter-hardening technology and microwave sintering both can reduce the sintering time greatly.Comparing the final performance of the samples which sintered in the two different sintering methods,the tensile strength of the two sintering methods are similar,but the hardness and tensile strength of sinter-hardening samples are much higher than the one that sintered by microwave sintering.