Three ways to remedy unqualified heat treatment
Introduce several methods of using heat treatment to remedy unqualified parts, so that heat treatment can meet the requirements of performance and avoid unnecessary losses.
1. Improve graphitization annealing process to remedy ductile iron castings
For fork rods with a grade of 0o-7, considering the processing performance and use performance, the technical requirements for its graphitization annealing are: annealing hardness 147-210I-IB; matrix structure 50%-80% pearlite (P) +Add% to 50% ferrite (F). The graphitization annealing process is 900-920oC×1.5h, the furnace is cooled to 720oC, and the furnace is air cooled.
There are a batch of fork rods after annealing, the test hardness is 180I-IB; the metallographic structure is 4%-5% pearlite + 95%-96% ferrite. The matrix organization is unqualified. The chemical composition of this batch of fork rods is unqualified, and the carbon content is low, which is the reason for the too little pearlite in the matrix structure after annealing. The air-cooling temperature of nodular cast iron during graphitization annealing process determines the content of pearlite and ferrite in the matrix structure after annealing. This is due to the higher the eutectoid transformation temperature. The higher the actual carbon content in austenite, the more pearlite content after eutectoid transformation and the less ferrite content. Through process tests, we can find out the reasonable temperature of the fork rod to reach the annealing technology requirements to make up for its lack of chemical composition. The process test method is: install 40 pieces of furnace, 900-920oC×1.5h. Respectively furnace-cooled to 850oC, 800oC, 780oC, 750oC, air-cooled 10 pieces each.
It is known from the above test results that when the air cooling temperature is 780°C, it meets the requirements of the hardness and matrix structure of the workpiece after graphitization and annealing. The improved graphitization annealing process was used to remedy the deficiencies of this batch of ductile iron castings due to the low carbon content.
2. Normalizing to refine the grains and remedy the coarse-grained carburized parts
The clutch for XYD1 drilling rig is made of cr, the carburizing layer depth is 1. plus l+50mm, and the tooth quenching hardness is 56-62HRC. During the gas carburizing process of a furnace clutch, the temperature of the carburizing furnace was caused by a temperature control instrument problem. The metallographic structure of the furnace workpiece was detected. The carburized layer was about 1.70tma; the grain size was 4-6, and a small amount was 5. The carburized part of this furnace has an out-of-poor penetration and coarse grains, which are unqualified parts. From the shape and use of the clutch, the clutch tooth thickness is 7.5mm, and the carburized layer is 1.70tran, which will not affect the use of the workpiece. We can adjust the induction hardening parameters to control the hardened layer of the tooth within 1.50mm. Coarse grains can be refined by normalizing. In order to prevent the surface oxidation and decarburization of the workpiece during the normalizing heating process, kerosene can be dropped during the heating process to control the atmosphere in the furnace. The process is 880-900℃×lh, kerosene 6o drops/min, and the furnace is cold.
After normalizing, the metallographic inspection result of the clutch is that the carburized layer is 1.73nm; the grain size is 6-7. After high-frequency quenching and tempering, the tooth hardness reaches the technical requirement of 56-Co2HRC.
3. Increase the carburizing process to remedy the parts with insufficient carbon content
Fork rod N58/4-57 for automobile drilling rig, material 35 steel, technical requirement: z and 16tara×20ram notch quenching hardness 40-45mtc. After a batch of workpieces are high-frequency quenched, the hardness is tested to 2OHRC, and the carbon content is 0+15% after testing.
From the perspective of its use, the fork lever only requires wear resistance at the notches and grooves, but the overall strength is not required. Therefore, the carburizing process is used to remedy the low carbon content of the workpiece. The carburized layer is 0.801.20ram. After carburizing, high-frequency quenching and tempering are performed on the f section and the 16ram × plus Ⅱ Ⅱ rI. The hardness of the two parts has reached the technical level. Claim.
For the specific requirements of unqualified parts, heat treatment can be used to meet the performance requirements and reduce unnecessary losses. Of course, for parts with strict requirements that cannot meet the performance requirements by heat treatment, they must be scrapped.