Wear behaviour of forging steels with different microstructure during dry sliding
Introduction
Microalloyed (MA) medium carbon forging steels with a pearlite–ferrite microstructure have gained acceptance as a replacement for the traditional quenched and tempered (Q–T) grades in automotive and some other applications. The driving force for the use of MA steels is cost reduction due to elimination of postforging heat treatment, straightening and stress relieving, and improved machinability [1].
The increased use of MA forging steels in production applications should be supplemented with an increased understanding of not only the strengthening mechanisms that occur in these steels; but also the effects of the composition and forging parameters on these mechanisms. The size and percentage distribution of ferrite and pearlite within the microstructure play an important role in the final mechanical properties. Each of the microstructure variables is highly influenced by the composition of the MA steels, the forging parameters utilized and the post forging cooling rate [2], [3], [4]. The strength and toughness of MA steels can be enhanced by thermomechanical processing through grain refinement, dislocation hardening, strain induced precipitation of fine micro-alloying carbide and carbonitride particles. Variation in the cumulative amount of deformation, working temperatures and post cooling rates can engender a variety of microstructure [5]. Investigations relating to MA steels processed through forging route have not been explored much, although several studies have been made on structure and properties [6], [7].
It is well known that the mechanical properties such as strength and hardness of structural steel are usually enhanced by the martensite phase transformation method. In many industrial applications, hardness has always been used as an index to reflect the wear resistance performance. As a result, steel is quenched to a large extent in order to increase the hardness and wear-resistance performance. In general, from the wear mechanism, no exact relationship between the hardness and wear resistance of materials can be formulated. Also there are few conclusive studies on the effects of running procedures on wear resistance performance [8]. Therefore in this study, the effect of microstructure on the hardness and dry sliding wear behaviour of medium carbon MA steel were determined in the forged and cooled conditions.
Section snippets
Experimental procedure
The chemical compositions of the steels used in this study are shown in Table 1. The steels are medium carbon MA steels with different amount of vanadium and aluminium contents. The steels were supplied in the form of 36 mm diameter and 500 mm length billets. Initially, steel-1 and steel-2 were cut into 50 mm length and 9 steel samples were obtained for heat treatment. Afterwards, specimens were heated at 1100 °C for 30 min and forging operation was carried out. Deformation of 36% was applied by
Microstructure
The variation in wear behaviour of medium carbon MA forging steel can be explained in terms of microstructure obtained during different cooling rates. Fig. 2 shows the evaluation of the microstructure for both of the MA steels under as-received and various cooling conditions. Table 2 also shows volume fraction of ferrite and pearlite and mean linear intercept grain sizes of pearlite in as-received, sand and air cooled samples. As can be seen, for both steels, proeutectoid ferrite appears as a
Conclusion
This paper had the aim of investigating the effect of microstructure resulted in the forging and different cooling rates on the hardness and dry sliding wear behaviour of MA medium carbon steels. The main conclusions from this study are as follows:
- 1.
Higher hardness and wear resistance can be achieved in steel-1 and steel-2 by forging followed by water cooling. This hardness and wear resistance obtained is due to martensite phase in water cooled samples contained higher amount of carbon in solid
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