The theory of grinding burn refers to the metallographic changes that occur on the surface of a workpiece due to local high temperatures during grinding, especially when the surface of the workpiece is subjected to instantaneous high temperatures, resulting in uneven annealing, softening, blackening, or yellowing of the surface of the workpiece. Grinding machining is a process of squeezing and cutting the surface of high-speed running parts through the negative rake angle of grinding wheels. The metal cutting chip layer is small and thin, and less than 10% of the cutting heat is carried away. 70% to 80% of the heat is transferred from the grinding surface to the part. Therefore, the temperature in the surface area of the part during grinding machining will sharply increase, especially the instantaneous temperature can reach 800-1000 ℃ or even higher. When the temperature exceeds the critical point of material metallographic change, a structural change will occur on the surface layer of the material matrix, resulting in an extreme decrease in the hardness and strength of the surface layer of the part. Afterwards, the surface of the part begins to cool until it finally cools down, causing thermal expansion and contraction of the surface layer of the part, resulting in different residual stresses from the surface to the internal layers. These different residual stresses can cause microcracks.
After grinding burn occurs, the metallographic structure of the substrate surface undergoes significant changes. As for quenched steel, its grinding burn characteristics are shown in Figure 2. According to the instantaneous temperature generated during grinding, the surface of grinding burns can generally be divided into tempering burns (tempering layer), quenching burns (between over tempering layer and secondary quenching layer), and annealing burns (between secondary quenching layer and grinding surface).