High temperature steam pipe forging process for supercritical unit

Abstract

The invention discloses a forging forming technology for a high-temperature steam pipeline of a supercritical unit. The forging forming technology comprises the steps that firstly, a heat-resisting steel ingot is selected and used; secondly, the steel ingot is heated up to 580 DEG C to 620 DEG C, and heat preservation is carried out for 3 hours; the steel ingot is heated up to 830 DEG C to 870 DEG C at a rate ranging from 55 DEG C / h to 60 DEG C / h; heat preservation is carried out for 4 hours; the steel ingot is heated up to 1130 DEG C to 1170 DEG C at a rate ranging from 78 DEG C / h to 82 DEG C / h; heat preservation is carried out for 4 hours; the steel ingot is heated up to 1210 DEG C to 1250 DEG C at a rate ranging from 78 DEG C / h to 82 DEG C / h; heat preservation is carried out for 2 hours; thirdly, the heated steel ingot is taken from a furnace, the head and the tail of the steel ingot are chopped off; fourthly, upsetting is carried out on a forging stock, and an upset piece is drawn out to form a square flat forging stock; fifthly, a tilted three-way forge piece is formed by the forging stock; sixthly, a branch pipe hole is punched; seventhly, main pipe holes are punched at the two ends of a main pipe body of the tilted three-way forge piece respectively; eighthly, heat treatment is carried out after forging. According to the forming technology, the production efficiency is high, internal organizations of the forge piece is even and dense, the forming technology is applicable to forging forming of tilted three-way forge pieces of supercritical units and ultra supercritical units with various specifications.

Description

technical field [0001] The invention belongs to the technical field of forging, and in particular the invention relates to a free forging process for oblique triangles of main steam pipes of nuclear power or thermal power supercritical generating sets. Background technique [0002] Supercritical and ultra-supercritical generator sets are advanced and efficient power generation technologies that improve power generation efficiency by increasing steam parameters, and have significant energy-saving and environmental-improving effects. The pressure of the working medium at the outlet of the unit boiler exceeds or far exceeds the critical pressure of the working medium. The common main steam parameters of the supercritical units put into operation are 23.5-26.5MPa, 538-566°C, and the main steam parameters of the ultra-supercritical units even reach 35 MPa, 700°C or higher, so supercritical and ultra-supercritical units have unparalleled economics, and the efficiency of a single u...

AI Technical Summary

Problems solved by technology

First of all, the main and branch pipes, especially the main pipe holes, are deep and long holes. The punches are used to punch the holes, and the punches cannot be withdrawn from the blank, so it is difficult to punch the holes. Upsetting and elongating or forming; although domestic and foreign countries have begun to use forging and then machining to make oblique tees, that is, first forging a forged billet with its outline, and then conducting deep holes and deep holes on the forged billet. Drilling of branch pipe holes, and cutting and removal of outer profile materials, and finally form the finished oblique tee

Although this production process improves the mechanical properties of the oblique tee through forging and improves the internal structure defects of the material, it has many shortcomings: firstly, the utilization of materials is low, and most of the materials are machined and become waste materials that are difficult to reuse. Far more than the actual amount of material used, resulting in a great waste of high-quality alloy materials, the material utilization rate is often lower than 15%, and the larger the size of the inclined tee, the lower the utilization rate

Second, the technological process is complicated and the production efficiency is low. After the steel ingot is forged into a square blank, the main and branch pipe holes and the outer contour are processed. Since the main pipe and branch pipes are deep and long holes, they need to be drilled and then boring Hole to a predetermined size, so the workpiece needs to be transferred in multiple processes, the production cycle is long and the efficiency is low

Third, since the weight of the blank is several times the weight of the finished product, it is difficult to ensure the purity of molten steel during the smelting process of such a large steel ingot, and it is difficult to heat through and compact such a thick cake solid forging during the forging process , there are differences in the thermodynamic and dynamic conditions of the inner layer, outer layer, core and upper part of the steel ingot, resulting in defects such as segregation, porosity and shrinkage cavities inside the steel ingot, which often lead to cracks, coarse grains and other quality of forgings in the subsequent forging process Problems that lead to the scrapping of forgings in severe cases

Fourth, the material of the oblique tee ingot is martensitic heat-resistant steel, which has poor thermal processing performance, and it is difficult for the core material of this large forging to obtain sufficient forging pressure due to the "bridge arch" effect of the outer material. A small deformation area is formed in the part, which cannot effectively forge the porosity defects such as shrinkage porosity and shrinkage cavity inside the billet, and cannot crush the as-cast dendrites inside it, resulting in anisotropy of the forging, especially the main pipe of the inclined tee and the The connection area of ​​the branch pipe is just located in the center of the box-shaped forging, and this connection area is the place where the thermal shock and thermal stress are most concentrated, and is the weakest area of ​​the oblique tee; therefore, the existing forging and re-machining The actual pass rate of the oblique tee is very low

Fifth, the forging process of the square blank mainly adopts the cross forging method, and the flow of metal in all directions destroys the fiber structure of the forging, which cannot guarantee the consistency of the axial mechanical properties of the main pipe and branch pipes

Images