Investigation And Properties Of Pack Boriding On Fe-Ni Alloy By Electroplating On Steel

The boronized layer on steel has a broad application prospect for its high temperature hardness,high temperature oxidation resistance and good wear resistance.However,the brittleness and poor impact resistance of boronized layer has limited its application.In this paper,we used a combined method which boriding after electroplating Fe-Ni alloy on40Cr Ni Mo steel to promote the formation of(Fe,Ni)₂B phase,which have better toughness.And the?-(Fe,Ni)on the comb teeth at the boronized layer/matrix interface can buffer the stress from the quenching heat treatment after boriding.The microstructure and mechanical properties of the boronized layers were studied.The results were listed as follows:A series of electroplated layers with different relative contents of Fe and Ni can be obtained by regulating the additions of FeSO₄ and NiSO₄.Samples with Fe contents of 9 wt.%,23 wt.%,32 wt.%,48 wt.%,58 wt.%,78 wt.%,85 wt.%and 91wt.%in the electroplated layer were prepared on 40Cr Ni Mo steel.When the Fe content is?91 wt.%,the Fe-Ni layer is mainly composed of?-(Fe,Ni).Pack boriding was used for the above specimens,and it was found that when the Fe content in the electroplated layers were high(?78 wt.%),boronized layers consisted of(Fe,Ni)₂B and Fe₂B,but with more pores.Using samples with high Fe content(?78 wt.%),decreasing the boriding temperature to840°C and increasing the B₄C in boriding medium to 8%,low porosity(Fe,Ni)₂B layers with thickness more than 20?m could be obtained,but the surface hardness of boronized layers was low,only 398.2 HV_0.025,581.3 HV_0.025 and 1062 HV_0.025 for 78 wt.%Fe,85 wt.%Fe and 91wt.%Fe,respectively.Changing both the boriding temperature and the electric field voltage could change the electric field current.When the electric field voltage was 75V,at 750°C,the current in the tank was very small;at 800 and 840?,the current increased significantly in the beginning,then,it decreased rapidly after reaching the maximum until it is smooth.At 750?+75V,?-(Fe,Ni)existed between the comb teeth at the interface of the boronized layer and the substrate.The samples with Fe content at 78-91 wt.%were borided at 800?+75V,the thickness of the boronized layer was 63-63.8?m,respectively,and the surface pores of the boronized layer were reduced,the maximum hardness of the boronized layer was 2050HV_0.05.The samples with Fe content of 78-91 wt.%were borided at 800°C+100V,the thicknesses of boronized layers ranged from 82?m to 91.1?m and maximum hardness of boronized layers were 2100-2150 HV_0.05.