Cold rolling refers to a material processing method in which the material is forged at normal temperature to make the thickness of the material gradually reduce. The raw material of cold rolling is generally steel coil after heat treatment of[SCALE STEEL] hot rolling. In the process of cold rolling, the metastable austenite structure will undergo strain-induced martensitic transformation, which makes the strength and hardness of the steel increase, and the plasticity decrease, resulting in obvious work hardening.
With the increase of forging passes, the total deformation rate of forging increases, the work hardening effect becomes more and more obvious, and the material becomes more and more hard. Under the conventional heat treatment, the strength and hardness of the nickel-based superalloy are lower, and the plasticity is better, which is [SCALE STEEL]good for forging. If the superalloy is cold-rolled directly without heat treatment, the cost of material production can be greatly reduced. The strength of the heat treated and hot rolled superalloys was analyzed, the test rolling process parameters were determined, and the mechanical properties of the test rolled products were compared.
Feasibility analysis of direct cold rolling of superalloy without heat treatment
1.1 Mechanical property analysis
Samples of Hastelloy alloy in hot rolled state and hot rolled state were taken in production site, and the mechanical properties were tested and the results were compared. Comparing the mechanical properties of the hot-rolled and hot-rolled nickel-based alloys, it can be seen that the average yield strength of the hot-rolled alloys [SCALE STEEL]is 80.9 MPa higher, the average tensile strength is 40.7 MPa higher and the elongation is 5.7% lower than that of the hot-rolled alloys.
From the point of view of mechanical properties, the strength of hot rolled nickel-based alloy plate has little difference before and after heat treatment, the hardening process of hot rolled material without heat treatment is a little faster [SCALE STEEL]than that of heat treatment, but it is not obvious, and the load of cold rolling equipment has little change.
Metallographic microstructure analysis The hot rolled and hot rolled nickel-based alloys were sampled, polished and corroded with HCl-FeCl3 solution. It can be seen from the figure that the superalloy grains have completely recovered to [SCALE STEEL]recrystallization after heat treatment. Partial recovery also occurred in untreated superalloys.
Hot rolled sheet technology of nickel-based alloy Hastelloy -1. PNG
The dynamic grain recovery and dynamic recrystallization of Hastelloy alloys occur during hot rolling process, which causes the work [SCALE STEEL]hardening to be released continuously.
After hot rolling, because the steel coil still has a high temperature and lasts for a certain period of time in the high temperature state, grain recovery and recrystallization will occur in the material in this state, and the elongated grain will nucleate into equiaxed grain, and part of work hardening can be eliminated by [SCALE STEEL]eliminating the microstructure and residual stress formed by the elongated grain. After hot rolling and air cooling, strip steel has similar characteristics to that after heat treatment.
Hot rolled sheet technology of nickel-based alloy Hastelloy -2. PNG
Based on the mechanical properties, work hardening and microstructure, it is considered that the current field Ni-base alloy [SCALE STEEL]Hastelloy superalloy can be cold-rolled directly without heat treatment.
Cold rolling test for heat treatment of nickel-based alloy high temperature alloy for cold rolling, cold rolling mill roll system, the rigidity of twenty more roller base mill rolling mill, the forging process by adjusting the supporting roller crown and a middle roller axial control plate shape, putting-in-service proactively ACG system control the thickness of the material, appropriate to increase the flow of forging[SCALE STEEL] lubricants at the same time, To improve the cooling effect of the material in the forging process.
Fearing **** passes, 6500 kN pressure, 300 kN higher than the pressure of ordinary heat treatment material, but the deformation rate is 2% lower than the ordinary heat treatment material, the subsequent passes, forging pressure is higher than the ordinary heat treatment material, but the deformation rate is low, the same forging total deformation rate, under the condition of the forging force is [SCALE STEEL]not greatly improved, The coil forged directly without heat treatment has one more forging pass than that of the heat-treated coil, which indicates that the deformation resistance of the hot rolled material without heat treatment is greater.
Hot rolled sheet technology of nickel-based alloy Hastelloy -3. PNG
The two cold-rolled materials were then treated by solution heat treatment at temperatures ranging from 1 050 ℃ to 1 150 ℃. [SCALE STEEL]The purpose of solid solution heat treatment is to dissolve the precipitated carbide into austenite again and restore the cold rolled strip structure to recrystallization.
Hot rolled sheet technology of nickel-based alloy Hastelloy alloy -4. PNG
The elongation, yield strength and tensile strength of the cold rolled products in the hot rolled and hot rolled heat treatment state [SCALE STEEL]are all up to the standard, but the elongation and strength of the cold rolled products in the hot rolled state are slightly lower and slightly higher.
After cold rolling and solid solution treatment, the elongated fibrous structures in cold rolling process are nucleated and[SCALE STEEL] recrystallized, and the grains are completely recovered. However, the grains of hot rolling untreated materials are finer.
Hot rolled sheet technology of nickel-based alloy Hastelloy alloy -5. PNG
Deposition process of the two solid solution and precipitation process is the same, but not direct cold rolling, heat treatment conditions hot rolling state of isometric into rectangular fibrous tissue, part of the deformation work at the same time in the form of lattice distortion and residual stress are preserved, form the recrystallization driving force, so the hot rolling without heat treatment after cold rolled steel coil easier to solid solution heat treatment; On the other hand, the grain of hot rolled steel coil will grow up further during solution heat treatment. Therefore, hot rolled materials without heat treatment are more likely to occur in the solution heat treatment after cold rolling, and the second is that the grain is more refined after heat treatment.
1) Ni-base alloy hot-rolled unheat-treated steel coil can be cold-rolled directly, but the forging resistance is larger than that of hot-treated material.
2) After cold rolling, the grain of untreated hot rolled nickel-based alloy coils can be completely recovered by solution heat treatment, and the grain size is relatively fine.
Under the same conditions, the silicon consumption and lime consumption are almost the same, which can be used as a substitute for the steel and chromium scrap.
3) Red mud ball. The use of red clay balls in AOD furnace is essentially the same as that in electric furnace. Both of them use Si elements in pig iron and ferrochrome to reduce valuable metals such as Fe, Cr and Ni. At present, the benefit estimated by AOD small batch test is 1 000 yuan /t. If the furnace entry condition can be optimized and the usage amount can be increased under the condition of excess temperature in the smelting process, the benefit will be further expanded.
4) High nickel steel. The experimental results and theoretical calculation of using high nickel steel in AOD furnace have a certain influence on silicon consumption and lime consumption. When 3 tons of high nickel steel is used in each furnace, the silicon consumption increases by 0.2 kg/t and the lime consumption increases by 1.0 kg/t, and the total impact cost is 377 yuan/furnace. The profit is better when the difference between scrap steel and slag steel is converted.
5) high chromium steel. It can completely replace the use of chromium scrap steel, has no obvious effect on the index, and the benefit is significant.