Metallographic diagram of 20CrMnTi and Q235 (resistance welding after 20CrMnTi carburizing and quenching)

Carbon Steels Q235 and 20CrMnTi

Carbon Steel is a group of steel alloys which contain varying amounts of carbon. The properties of carbon steels depend upon the carbon content and the alloying elements, such as manganese, sulfur, silicon or phosphorous which are added during the manufacturing process.

Q235 and 20CrMnTi are two of the most widely used carbon steels. Q235 is a general structural carbon steel of Chinese origin with a small content of carbon, silicon, manganese, and a small amount of phosphorus and sulfur for strength. 20CrMnTi is an alloy steel whose components include chromium, manganese, and titanium. The addition of titanium increases the strength and hardness of the alloy, making it a popular choice for applications with high wear and tear.

The metallography or microstructure of a material is an important feature which must be assessed prior to making any use of it. Metallography can indicate the homogeneity, grain size, distributes and other microstructural features of a material. 20CrMnTi and Q235 carbon steels are usually subjected to electrical discharge machining for welding and tempering which can bring about changes to the microstructure of the material, affecting its mechanical properties.

The following chart includes the microstructures of both steels after undergoing electrical discharge machining and tempering:

20CrMnTi

Ferrite: The amount of ferrite present increases with the reduction in temperature and the increasing amount of time spent in tempering. The microstructure appears as rounded and elongated crystallites, typically with a size of 37 µm.

Pearlite: The pearlite structure consisting of lamellar layers of ferrite and cementite is usually acquired as a result of the formation and recrystallization of austenite grains. Due to the presence of chromium and manganese, the pearlite structure appears finer than that of plain carbon steels.

Q235

Ferrite: The microstructure of the ferrite typically exists as strips, which may be represented by islands or regions with a maximum grain size of about 35 µm. There is a certain degree of shape recovery and edge rounding due to the tempering process.

Pearlite: The pearlite structure appears as lamellar layers of ferrite and cementite, separated by thin boundaries that form a banded matrix structure.

Based on the observations made, it can be concluded that both steels exhibit a ferrite-pearlite microstructure, however, the grain size and distribution of ferrite and pearlite differ. Furthermore, Q235 steel displays a greater amount of shape recovery, indicating a more uniform grain size and microstructure. The ferrite present in 20CrMnTi is more elongated compared to that of Q235 due to the addition of chromium and manganese. Finally, the pearlite structure of 20CrMnTi is finer than that of its counterpart.

20CrMnTi is a grade of steel which is commonly used for development projects. It has the advantage of being highly resistant to wear and tear and has a longer lifespan than other grades of steel. This grade of steel is ideal for the production of car frames, bridges, and other components.

The microstructure of 20CrMnTi steel can be seen clearly when examined under an electron microscope. When looking at the 20CrMnTi sample, it is evident that it is composed of ferrite and austenite. The ferrite is harder and more wear and tear resistant than the austenite. The ferrite and austenite are co-existing in 20CrMnTi steel.

The microstructure of Q235 steel can also be observed under an electron microscope. The Q235 sample appears to be composed of a slightly more refined ferrite and a much finer austenite as compared to the 20CrMnTi. The ferrite appears to be more wear and tear resistant than the austenite, however the austenite still retains some of its properties.

The difference in the microstructure between the two steel grades can be seen with a metallurgical microscope. The 20CrMnTi steel sample appears to have relatively large grains, whereas the Q235 steel sample has much smaller grains. The 20CrMnTi has a much higher hardness than the Q235 because of its larger grain size.

The difference in the microstructure of the two steels also affects the strength and ductility of the materials. The 20CrMnTi can be hardened by a to a greater degree than the Q235 steel. This, in turn,allows the 20CrMnTi to show higher levels of ductility.

After the 20CrMnTi steel has been carburized and quenched then Resistance Welded it can be seen that the microstructure of the steel is roughly the same as it was before the process. The grain size however, looks to have decreased and is much more uniform throughout the sample. This indicates that the resistance welding process has allowed for more uniform heating and cooling in the steel.

Overall, both 20CrMnTi and Q235 steel grades of steel have their own advantages and disadvantages. 20CrMnTi has a higher strength and wear resistance as compared to Q235, whereas the Q235 steel has a better formability. Both grades of steel find application in various sectors. Some common uses include producing car frames, bridges, and other components.