Research On The Thermal Fatigue Behaviour Of Electro-slag Melting And Casting Steel-bonded Carbide DGJW50

Electro-slag melting and casting steel-bonded carbide DGJW50 is one newly of the WC particle reinforced steel matrix composite. Thermal fatigue behaviour of this material is experimentally and numerically studied by observing the form of crack initiation and propagation. Heat-treatment and surface boronizing have been applied in DGJW50 to strengthen structure of steel matrix and improve surface hardness of whole material respectively, and influence of these two kinds of process on thermal fatigue property is analyzed.It is found that there is an incubation period of about 5-10 thermal cycles before the initiation of thermal crack in the notch of sample under the condition of this experiment. The main area of initiation is pinetree carbide and eutectic carbide. Under the impulse of thermal stress, the crack preferentially propagates in the hard WC phase for its brittleness. The approach of crack propagating in hard phase includes fracture of eutectic carbide, raw WC particle, interface of them and pinetree carbide. Broken raw WC particle still keeps raw shape, and eutectic carbide is severely smashed during thermal cycling.Compared with raw DGJW50 without heat-treatment, the whole mechanical property of the heat-treatment one has great improvement. At the same time, quadratic carbides as resultant of eutectoid reaction are dispersedly distributed in steel substrate during heat-treatment, they can passivate the tip of crack and reduce velocity of propagation. So heat-treatment greatly improves thermal fatigue property of DGJW50.Boronized layer greatly hardens surface of DGJW50 and delays crack initiation and propagation in it, so thermal fatigue property of surface borozing DGJW50 is higher than raw material.Thermal cycling causes some damage of the hard phases in DGJW50. However, the binder phase of steel as well as interface between hard and binder phases suffers little, so thermal fatigue property of DGJW50 is good. It is affirmed that thermal fatigue property of DGJW50 will be improved greatly when some effective measures are taken to enhance thermal fatigue property of hard phase, and they will facilitate application of this material to hot working die for laying a theoretical foundation and pointing out direction of research in future.