Metallographic diagram of QT500-5 steel (350℃ for 1h)

QT500-5 steel is commonly used for automobile and engineering components due to its good mechanical properties and wear resistance. Some parts are made of QT500-5 steel, as they require additional protection against heat or fire. Before using QT500-5 steel, it is important to understand the metallurgical structure of the material.

Metallographic studies are often conducted on QT500-5 steel to view the internal microstructure of a material. This process requires the surface of the material to be polished using a polishing medium, such as diamond or alumina. Metallographic studies are usually conducted at 350℃with 1 hour of insulation. By studying at this temperature, it will be possible to obtain a proper analysis of the material, as the microstructures at this temperature absence of detrimental changes due to cooling.

When analyzing the microstructure of the QT500-5 steel, it is important to note the austenite grain size, the ferrite grain size, and the pearlite grain size. Additionally, it is also important to determine the morphology of iron carbide, its size, and its distribution throughout the material.

The austenite grain size of the QT500-5 steel is determined under the microscope by counting the amount of grains in a unit area. It is typically measured in a unit called ASTM Grain Size Number (GSN). It is important to understand that the smaller the ASTM Grain Size Number that is obtained, the finer the austenite grain size.

The ferrite grain size of the QT500-5 steel can be measured by the same method used to measure the austenite grain size. However, instead of measuring the number of grains in a unit area, the width of the ferrite grains must be measured. The width of ferrite grains is usually measured in micrometers. It is important to note that the finer the ferrite grain size, the better the mechanical properties of the material will be.

The pearlite grain size is also determined under the microscope. It is typically measured in micrometers. The pearlite grain size is generally larger than the austenite grain size, and it typically has a higher strength.

Finally, in order to analyze the morphology of iron carbide, it is important to use the method of image analysis. This method consists of taking several photographs of the samples and carefully analyzing them to identify the shape and size of the iron carbide particles. It is also important to note the distribution of the particles throughout the sample.

Ultimately, metallographic studies of the QT500-5 steel provide essential information on the microstructure and properties of the material. This information can be used to better understand the composition of the material and its useful applications.

QT500-5 is a special steel manufactured in China, belonging to Chinese grade 5 grey stone. Its chemical composition is C 0.50-0.60, Si 0.30-1.00, Mn 0.40-0.70, P≤0.040, S≤0.040. Its performance parameters such as yield strength Rm/MPa, tensile strength Rp/MPa and elongation A/%: Rm>490-590, Rp>615-735, A>14-21.

QT500-5 steel has good plasticity, machinability and welding performance, so it is widely used in various structural parts, bearing seat, frame and welded parts. In order to ensure the suitable process performance of this kind of steel material, the heat treatment process is often taken by preheating the parts to 350°C and holding for an hour, and then continuing with the normal processing or cutting process.

The microstructure of the QT500-5 steel 250×400 mm sample after preheating at 350°C for 1 hour heat treatment is shown in the figure. It includes pearlite, ferrite and some new entrained phases like spheroidite and residual austenite. Its seen from the picture that there is no temper embrittlement phenomenon in the sample, which indicates that the properties of this steel material can meet the requirements after the heat treatment process.

In summary, QT500-5 steel is a kind of special steel material. The heat treatment process of preheating the parts to 350°C for an hour can improve its process performance and ensure its properties meet the standard requirements. The microstructure of the QT500-5 steel after the heat treatment is composed of pearlite, ferrite and spheroid.