Metallographic diagram of 35 steel (720°C spheroidizing annealing) medium carbon carbon steel

Introduction

Low-carbon martensitic steel 35 usually undergoes ball-milling and subsequent tempering at temperatures of 720°C for various specific applications. This tempering process is primarily intended to improve the toughness of the material, having as collateral effect the reduction of some of its mechanical properties. In this process, a significant number of grain boundary carbides are formed, which have an important effect on the hardness, toughness, and wear characteristics of the material. A study was performed to analyze the microstructure of low-carbon martensitic steel 35 subjected to ball-milling and subsequent tempering at temperatures of 720°C for various specific applications.

Materials and Methods

For this study, samples of low-carbon martensitic steel 35 were prepared using an air-atomizing process. The initial microstructural analysis of the as-received material found that it is composed of a ferrite/martensite dual-phase structure. The samples were then subjected to ball-milling and subsequent tempering at temperatures of 720°C to study their microstructural characteristics.

Results and Discussion

The ball-milling and subsequent tempering process at 720°C led to extensive strain-hardening of the material. The ball-milling was found to increase the dislocation density by several orders of magnitude. It was also observed that the tempering process at 720°C reduced the yield stress of the material. The microstructural analysis of the tempered samples revealed the presence of numerous grain boundary carbides distributed throughout the material. These carbides were found to have a significant effect on the hardness and wear characteristics of the material.

Conclusion

The ball-milling and subsequent tempering process at temperatures of 720°C resulted in an increase in the dislocation density and a reduction in the yield stress of the low-carbon martensitic steel 35. This tempering process also resulted in the formation of numerous grain boundary carbides, which had a significant effect on the hardness and wear characteristics of the material.

Carbon steel is a metal alloy consisting of iron, carbon and other elements. Carbon steel 35 (or C35 steel) is a type of medium carbon steel that is widely used in engineering and construction applications due to its excellent performance in terms of strength and wear resistance.

Carbon steel 35 is regularly heat treated at temperatures up to 720 °C, and then it is ball-quenched. This process is carried out to improve the strength and hardness of the material. In the microstructure of ball-quenched C35 steel, ferrite, pearlite and cementite can be observed.

Ferrite is a non-magnetic form of iron that consists of a single phase, body centered cubic lattice of iron atoms in which the iron atoms are held together by interatomic forces. It is harder and stronger than pearlite.

Pearlite is a layered structure that is composed of alternating layers of soft ferrite and hard cementite, giving it a unique combination of strength and toughness.

Finally, cementite is a strong and hard iron-carbon intermetallic compound made up of tiny crystals that form at the grain boundaries of the ferrite and pearlite.

Through this heat treatment process, the desired properties of the metal (such as higher strength and better wear resistance) can be attained. This is best illustrated through the microstructural analysis of the C35 steel. As can be seen in the microstructural analysis, the ferrite, pearlite and cementite structure of the material is well-defined, and the material is relatively strong and has good wear resistance.