High carbon chromium bearing steel raw material defects

2021 - high carbon chromium bearing steel raw material defects 01 - 20 Sun Qinhe ( Hangzhou horse bearing co. , LTD. Quality assurance department) High carbon chromium bearing steel in the process of raw materials into the factory inspection and production use, will find some defects affect the product quality of the bearing. This article will focus on the defects of high carbon chromium bearing steel, summarized the sorts and presented in a typical picture form. 1 material surface crack bearing steel bar stock inspection, found along the direction of steel rolling bearing steel bar with a clear surface crack, the length and the length of the steel bar is the same, the deepest is around 1 mm ( See figure 1) 。 Figure 1 with surface crack of bearing steel bar stock for sample and after hot acid pickling, crack on the surface of the bearing steel bar stock more clear, and the crack depth of 1 ~ 2 mm ( See figure 2) 。 Under normal circumstances, the bearing steel bar diameter or hot samples can be seen after acid pickling. Figure 3, figure 2 has a surface crack of bearing steel bar by the medium frequency induction heating, blanking, upsetting, cake outer diameter surface rendering obvious crack, the depth of 2 ~ 3 mm. Figure 4 forgings after punching diameter surface has very obvious crack, depth of 2 ~ 3 mm. Figure 3 ( b） Figure 4 shows, if there is obvious scratch or crack of bearing steel bar used for forging production of bearing ring, bar surface defects after forging processing will further open, form of waste. If the bearing steel bar surface crack depth is not deep, be processed into bearing forging after grinding machining diameter also see obvious crack, crack ring with above defects after picking out must be scrapped. Figure 5 bearing steel ring car parts turning processing is completed, outer diameter surface have obvious crack; Figure 6 bearing steel ring pieces by the car grinding processing is completed, outer diameter and obvious crack surface. Figure 5 figure 62 bearing steel material capillary crack bearing steel bar ends have crack, bearing steel bar with medium frequency induction heating after blanking has obvious crack found on both ends of the bar stock center, ends with a transverse crack of bearing steel bar stock generally is 100 ~ 200 mm in length, or even longer, See figure 7) 。 Found that the crack of forging must be scrapped. Figure 73 crack of bearing steel bar the core taking sample bearing steel bar, the hot acid ( Sample put in 50% hydrochloric acid solution, heated to 80 ℃, time of 30 min or so, after cold water to wash the dry) And discovered that there are about 20 mm long face the heart of the penetrating crack, as shown in figure 8. Figure 8 if there is a crack, the center of bearing steel bar by the medium frequency induction heating, blanking, upsetting and nesting after forging, machining, bar the core crack will further open, lead to waste ( See figure 9) 。 As a result, found in incoming inspection or the production process such as cracking of bearing steel bar stock is the core, to deal with this batch of bearing steel bar isolation scrap or return. （ b） Figure 94 hole of bearing steel bar material the core bearing steel bar medium frequency induction heating were found in the heart of end face significantly after shearing blanking hole, as shown in figure 10. If there is a hollow bearing steel bar used in forging bearing ring, the center hole after forging will further open, form, as shown in figure 11. Figure 10 ( b） Figure 11 found during production of bearing steel bar stock of empty heart, to deal with this batch of bearing steel bar isolation scrap or return. 5 bearing a large block of non-metallic inclusion within the steel bar diameter is 75 mm bearing steel bar stock cutting of medium frequency induction heating, after blanking, found that the center of a single bearing steel bar stock with white non-metallic inclusions ( As shown in figure 12 and figure 13) 。 Figure 12 figure 13 bearing steel in the process of production may be due to steel furnace wall, cut by molten steel in ladle refractory peeling into liquid steel, casting ingot solidification, the large lump of inclusions along the rolling direction, lead to bearing steel bar produced large block of non-metallic inclusions. Bearing steel middle massive inclusions can cause stress concentration and speed up the rolling surface fatigue spalling, bearing damage in advance. Therefore, for machining process, the big massive inclusions parts visible to the naked eye, must pick out the scrap, cannot flow into the next process. Is shown in figure 14, high carbon chromium bearing steel by forging, turning, heat treatment and grinding process in the raceway of the non-metallic inclusions on the surface of a large block physical shape. Figure 14 figure 15 shows the bearing steel bearing ring grinding roll on one big block non-metallic inclusions in metallographic microscope down 100 times larger shape. （ 一) 100× （ b） 100× Figure 156. Excessive amounts of ribbon or reticulate carbide bearing steel bar according to standard GB/T182542016 requires taking sample, sampling for quenching specimen, after deep etching nitric acid alcohol solution under the metallurgical microscope magnified 100 times observed banded carbide ( See figure 16) And the carbide network ( See figure 17) ； According to GB/T182542016 standard for high carbon chromium bearing steel, the rating figure 6, 8 evaluation for 3. Level 5 and level 3, according to GB/T182542016 standard clause 6 high carbon chromium bearing steel. 11 carbide to determine the provisions of the inhomogeneity is unqualified, isolation and return to the batch bearing steel bar. Figure 16 figure 17 above is bearing manufacturing enterprise, the author was responsible for the heat treatment of material and quality technical work more than 30 years to accumulate some of the defect images, the classified will exist in inappropriate places, looking forward to get the guidance of the relevant experts. Source: the metal processing ( Hot working) 09, 2019