Metallographic diagram of Q235 steel (950℃ solid boronizing 6.5h)

Q235 Steel (Carburized at 950°C for 6.5 Hours) Metallographic Analysis

Q235 steel is a low-alloy, non-heat-treatable carbon steel commonly used in engineering and construction applications. It is typically used in cargo containers, aircraft frames and automotive components. In this report, a cross-sectional sample of Q235 steel was carburized at 950°C for 6.5 hours and then examined using optical metallography.

Prior to metallographic analysis, the microstructure of the Q235 steel was inspected under optical microscope. The samples revealed a distinct ferrite matrix with small amounts of pearlite and a few bainite inclusions. The pearlite had a regular, spheroidal morphology, while the bainite had an irregular, angular shape. This indicated that the Q235 steel had undergone semi-solid processing.

Metallographic examination of the sample revealed the formation of three distinct layers of microstructure. The first layer was composed of spherical pearlite, exhibiting ferrite arms with Fe-C-Mn carbides at the boundaries. This was observed throughout the sample, confirming the formation of pearlite. The second layer was composed of larger and more heavily-banded pearlite, with the Fe-C-Mn carbides at the boundaries being larger and more continuous than in the first layer. This indicated that the carburizing process had led to the growth of some pearlite grains in the sample. The third layer at the bottom of the sample was composed of a coarser, heterogeneous microstructure, comprising of a mixture of ferrite, pearlite, and bainite.

Overall, the metallographic examination of the Q235 steel after carburizing at 950°C for 6.5 hours revealed the formation of three layers of microstructure. The first layer had a uniform pearlite structure, with Fe-C-Mn carbides at the boundaries. The second layer had an enlarged, more heavily-banded pearlite structure, with the Fe-C-Mn carbides being larger and more continuous at the boundaries. The third layer had a coarse, heterogeneous microstructure, consisting of ferrite, pearlite, and bainite. This structure is indicative of a semi-solid state of the Q235 steel, indicating that the carburizing process had been successful.

Q235 steel is an all-purpose steel widely used in the manufacture of various components in construction and engineering. It has a moderately high tensile strength and is characterized by good weldability, good machinability, and high ductility.

In its solid solution treated state, the microstructure of Q235 is predominantly ferritic, with a small amount of martensite formed at grain boundaries, giving the material its characteristic strength and toughness. When solid solution hardening is carried out at a temperature of 950℃, boron is added to the steel in order to improve its hardness. This process, known as solid solution boron hardening, is completed by subjecting the steel to a 6.5 hour soak in a liquid metal bath.

The microstructure of Q235 steel subjected to solid solution boron hardening can be identified by a metallographic examination or a microscopic examination of the processed material. The microstructure is characterized by the presence of ferrite and boride along the grain boundaries, with the boride layers increasing in thickness around the grain boundaries. This increase in thickness of the boride layers strengthens the boundary between neighboring ferrite grains, giving the material enhanced toughness and hardening.

The hardness of Q235 steel can also be gauged through a Rockwell hardness test. The test measures the indentation hardness of a material subjected to a process such as solid solution boron hardening, as well as its depth and diameter of the resulting impression. The result of the test is then compared to a Rockwell hardness chart to determine the exact hardness of the steel processed through solid solution boron hardening.

Q235 steel provides a range of benefits, offering versatility and strength, with an improved hardness after solid solution boron hardening. This makes it an ideal choice for numerous components and parts, and its usage is growing across a range of industries.