HOT LINE: +86-510-80628100This article mainly introduces diesel engine valve body forgings made of 4Cr10Si2Mo steel. 4Cr10Si2Mo belongs to chromium silicon molybdenum martensitic valve steel, which has high thermal strength, high alloy element content, poor thermal conductivity, and a narrower forging temperature range than general materials. It is often used to make intake valves for internal combustion engines and exhaust valves for light-duty engines. This article analyzes and studies the small linear defects on the surface of forgings.
The material specification for this study is φ 60mm × 66mm, the forging temperature is 900-1100 ℃, and the cooling method after forging is ash cooling. The defect is located in the stem of the valve body forging, which is a linear defect and consistent with the fiber streamline of the raw material. The chemical composition of the selected defect site meets the requirements of GB/T1221, but when cut horizontally along the strip defect, oxidation was found inside the defect, and the end was blunt. Further observation revealed decarburization on both sides and decarburization on both sides of the entire defect.
After analysis, it is believed that the forging temperature of 900-1100 ℃ and the post forging cooling method of ash cooling are reasonable processes. The final forging temperature and initial forging temperature both meet the process requirements, and there is no problem of surface cracks caused by the forging process temperature being lower than the final forging temperature. The ash cooling method after forging is reasonable and will not produce surface cracks.
Through high magnification inspection of the dissected forging, it was found that the metal grains in the defective area were small and uniform, with no signs of overheating or overburning. Through high and low magnification observation of the defect area, it was found that the end of the defect was round and blunt, with signs of convergence, and oxidation was visible inside the defect. There were obvious decarburization layers on both sides of the edge, indicating that the defect was folded. Usually, folding is caused by the unreasonable flow of metal during the forging process, or by the convergence of two or more streams of metal convection; Or it can be formed by a rapid and massive flow of metal carrying the surface metal of adjacent areas, and the two merging to form; Or formed due to the bending or reflow of deformed metal; Or part of the metal undergoes local deformation and is pressed into another part of the metal to form.
Through analysis of the forging, it was found that the metal distribution of the billet was unreasonable. During the forging process, there was a local shortage of material, while excess material flowed back from other parts, resulting in folding. The forging is formed using a 60mm diameter bar material. When hammered into the final forging cavity, due to the large cross-sectional area of the billet, it cannot fit well with the mold during initial forging. During the rapid striking process, the metal flow is unreasonable, resulting in two or more metal streams converging and forming folds.
After recalculating and analyzing the mold design process, it was found that the secondary bending angle of the mold blank groove was relatively small. Through recalculation, the secondary bending angle was increased, and the material specifications were re selected. Finally, a bar with a size of 50mm was chosen. After trial production, there are no surface defects and all have passed magnetic particle inspection.
