Study On High Carbon Cast Steel Grit Used For Blast Cleaning

High carbon cast steel grit is the most commonly used metal abrasive for sand-blast cleaning of steel substrates before application of paints and related products. It has been widely used in some industries having high requirements on surface treatment, such as ship, bridge, container, steel structure, natural gas and oil pipelines and so on. Improving the properties of high carbon cast steel grit, choosing the reasonable type, making surface cleaning quality meet the requirements of anti-corrosion performance of coating layer protective system and reducing the cost of sand-blast cleaning are the noteworthy issues.In this paper, high carbon cast steel grits are quenched and tempered by different heat treatment processes. The microstructures of high carbon cast steel grits are observed by the metallographic microscope, the hardness is measured by the microhardness tester. The influence of particle size and heat treatment on Ervin life is measured by Ervin life testing machine, the cleanliness of steel surface is compared by using standard images in GB/T 8923.1-2011, the coverage rates are compared by using standard coverage rate comparison specimens and the roughness is measured by the Roughness Measuring Instrument of Stylus. We compare the cleaning effect and cost of different high carbon cast steel grits, giving guidance for the selection of them. We observe the fracture and wear topography by means of SEM, analyzing and discussing the failure mode of high carbon cast steel grit.The results show:the metallographic structures of high carbon cast steel grits are coarse plate martensite and retained austenite after the first quenching. The second quenching can eliminate coarse plate martensite and reduce the serious composition segregation. The metallographic structures are transformed into fine plate martensite and retained austenite. During the process of tempering after the second quenching, the metallographic structures are transformed into tempered martensite, tempered troostite and tempered sorbite in order with the elevating of the tempering temperature. The hardness declines at the same time. We can select the appropriate tempering temperature according to the required hardness in production.With the increase of the particle size, the Ervin life of high carbon cast steel grits treated by the same heat treatment increases, the roughness of the steel plate increases, the coverage rate declines, the cleaning time extends reaching the equivalent cleanliness and the cleaning efficiency reduces. Through analyzing the cost, we draw the conclusion that the cost of high carbon cast steel grits reduces with the decline of the particle size in the process of sand blasting, but the roughness must be satisfied, and this conclusion has been confirmed in the work field. Tempering HQ GH16 high carbon cast steel grit, the Ervin life increases with the increase of the temper temperature and the decrease of the hardness of high carbon cast steel grits. The first stage is before 300℃, the Ervin life increases slowly; The second stage is 300～450℃, the Ervin life increases rapidly; The third stage is 450～650℃, the increase rate of the Ervin life reduces gradually. But the coverage rate declines, the cleaning time extends reaching the equivalent cleanliness and the cleaning efficiency reduces with the increase of the tempering temperature and the decrease of the hardness. The impact of tempering time on the Ervin life and cleaning efficiency is less than tempering temperature. Tempering temperature is the main dominant factor. Through analyzing the cost, we draw the conclusion that the cost of the high carbon cast steel grit declines with the increase of tempering temperature below 400℃, on the contrary, the cost increases above 400℃.The failure modes of high carbon cast steel grits are fracture and wear. The fracture is divided into chunk brittle fracture and falling off. The chunk brittle fracture mainly occurs at the beginning of the cycle. The numerous cracks remained from the breaking process grow rapidly during the impact process, thus the fracture occurs. Falling off is divided into center falling off, bulk falling off and sheet falling off. Wear occurs by the means of surface peeling off.