Rolls produced by forging of steel ingots. Forging can forge the metallurgical defects such as porosity and shrinkage inside the ingot, and break the coarse cast structure to obtain high-quality rolls with dense structure and uniform composition. Forged steel rolls have better strength, toughness, surface hardness uniformity and fatigue resistance than similar cast rolls. In order to meet the specific requirements of different rolling mills and rolling conditions, different alloying elements can be added to the steel for the rolls to improve the performance of the rolls. A certain content of carbon and alloying elements have the following different effects on the structure and properties of forged steel rolls: carbon can increase the hardness and strength of the roll, reduce plasticity, and improve wear resistance; manganese can increase hardenability and strength; Improve strength; chromium can increase hardenability and strength, improve wear resistance; molybdenum can increase hardenability, strength and hot hardness; vanadium can control the grain size of steel and increase strength.
The production process of forged steel rolls includes main processes such as smelting, ingot casting, forging, post-forging heat treatment, rough machining, final heat treatment, and finishing. The selection and control of equipment and process parameters for the production of forged rolls must ensure that they meet the requirements of the finished rolls for chemical composition, mechanical properties, microstructure, metallurgical quality, dimensional tolerances, internal stress distribution, and surface conditions.
Forged steel ingots are cooled to above 600 ℃ in the die, stripped and directly loaded into a high temperature furnace for heating, which is called hot charging. The heating rate of heating to the forging temperature during shrink-fitting can be unlimited. The heating system of cold steel ingots shall be carried out according to special specifications. Depending on the size and material of the ingot, the forging process can be carried out on a hydraulic press, a hydraulic press or a free forging hammer. Ingots are forged into finished blanks with roughing allowances. The entire forging process must be kept within the temperature range to obtain the recrystallization process and grain refinement of the rolled steel, and to ensure sufficient plasticity and prevent forging cracks. There are strict regulations on the initial and final forging temperatures of various types of rolls.
Forging consists of basic procedures such as press clamp, chamfering, upsetting, billet drawing and compaction, and precision forging. When forging the roll sleeve, there are still processes such as punching and reaming. The forging ratio is one of the important indicators reflecting the quality of the forgings. The forging ratio of the hot roll is generally not less than 2.5; the cold roll is not less than 3; the backup roll is not less than 2. With the improvement of smelting and forging technology, the forging ratio can be appropriately reduced. The riser of the ingot should have enough cutout to remove the shrinkage cavity and segregation of the ingot. Usually, the utilization rate of forging ingots for hot rolls is 55% to 62%; for cold rolls and backup rolls, it is 55% to 60%. After the roll ingot is upsetting, different forging methods are selected according to the type, weight and size of the roll to carry out the billet-drawing and compacting process. Wide anvil and large reduction forging method (KD method) is suitable for high, medium and low plasticity, large and medium-sized cold and hot rolling work rolls and backup rolls; wide flat anvil strong reduction forging method (wHF method) The stress forging method (FM method) is suitable for large and extra-large backup rolls with high and medium plasticity; the center compaction method can be used in conjunction with the WHF method or the FM method.
