CN-122007240-A - Ultralow-temperature forming method for stainless steel integral box bottom

Abstract

The invention relates to the technical field of metal plate forming, and discloses an ultralow-temperature forming method for a stainless steel integral box bottom. The method comprises the steps of providing a stainless steel plate blank, reversely solving the target deformation degree and the required cooling temperature of each region according to the ultralow temperature phase change strengthening rule and the deformation distribution of the bottom of the box, putting the plate blank into a die and cooling to the target temperature, pressing a flange with high-pressure side force to enable a central region to deform and paste a die in a double-tensile stress state, gradually reducing the pressure side force to enable the flange region to deform and paste the die to the target depth in a tensile-pressure state, and finally opening the die and taking out a piece. The method solves the problem of cooperative control of wrinkling and cracking during integral forming of the ultra-thin ultra-high strength stainless steel complex curved surface by cooperative control of ultra-low temperature phase change strengthening and staged stress paths, and realizes the manufacture of the rocket bottom with large size and consistent reinforcement of welding seams and parent metals.

Inventors

• FAN XIAOBO
• YUAN SHIJIAN

Assignees

• 大连理工大学

Dates

Publication Date

20260512

Application Date

20260410

Claims (8)

1. 1. The ultra-low temperature forming method for the stainless steel integral box bottom is characterized in that a stainless steel sheet subjected to plate state splice welding is formed into the integral box bottom with a weld joint reinforced in accordance with a base metal through ultra-low temperature phase change reinforcement and staged stress path control, and the method comprises the following steps of: S1, providing a stainless steel slab; s2, reversely solving the deformation degree required to be achieved in each target area of the plate blank after forming and the required ultralow-temperature cooling temperature according to the stainless steel ultralow-temperature phase change strengthening relation and the deformation distribution rule of the box bottom, and obtaining the required forming depth according to the required deformation degree; S3, placing the stainless steel slab into a forming die, and cooling the stainless steel slab to the ultralow-temperature cooling temperature determined in the step S2 by utilizing a low-temperature medium; S4, pressing a flange area of the plate blank by using a first blank pressing force, simultaneously controlling a male die to descend, enabling a central area of the plate blank to deform and be abutted against the male die in a bidirectional tensile stress state until the deformation of the central area reaches the required forming depth reversely calculated in the step S2; S5, gradually reducing the edge pressing force from the first edge pressing force to the second edge pressing force, and simultaneously controlling the male die to continue to move downwards to enable the plate blank in the flange area to deform and be abutted against the die under the tension-compression composite stress state until the deformation of the flange area reaches the required forming depth reversely calculated in the step S2; And S6, opening the mould and taking out the formed stainless steel integral box bottom.
2. 2. The ultralow temperature forming method of a stainless steel integral tank bottom according to claim 1, wherein in the step S1, the stainless steel slab is an integral slab or an integral slab formed by welding a plurality of stainless steel slabs in a flat plate state.
3. 3. The method for ultralow temperature forming of a stainless steel integral tank bottom according to claim 2, wherein the splice welding is one of laser welding, argon arc welding, resistance welding or submerged arc welding.
4. 4. The ultralow temperature forming method of the integral stainless steel tank bottom of claim 1, wherein in the step S1, the stainless steel slab is a stainless steel solid solution state plate or a stainless steel hard state plate.
5. 5. The method for ultralow temperature forming a stainless steel integral tank bottom according to claim 1, wherein in step S3, the low-temperature medium is one or more of liquid argon, liquid nitrogen and liquid helium.
6. 6. The method for ultralow temperature forming a stainless steel integral tank bottom according to claim 1, wherein in step S3, the low temperature cooling temperature is normal temperature to-196 ℃.
7. 7. The method for ultralow temperature forming of a stainless steel integral tank bottom according to claim 1, wherein step S3 comprises the steps of forming a sealed cavity between a slab and a die after die assembly, introducing a low-temperature medium into the sealed cavity for cooling, pressurizing the low-temperature medium after the slab is cooled to a set temperature, and preforming the slab to a set height by using the low-temperature medium to enable the slab in a central area to be fully deformed.
8. 8. The method of ultralow temperature forming a stainless steel integral tank bottom according to claim 7, wherein in step S3, the cooling temperature and the forming pressure of the slab are controlled by controlling the gas-liquid mixing ratio of the low temperature medium and/or by utilizing the vaporization and pressurization of the low temperature medium.

Description

Ultralow-temperature forming method for stainless steel integral box bottom Technical Field The invention relates to the technical field of metal plate forming, in particular to an ultralow-temperature forming method for a stainless steel integral box bottom. Background With the development of reusable and low-cost carrier rockets, stainless steel is gradually the first choice material for new generation rocket body structures due to the excellent comprehensive properties of the stainless steel. The bottom of the rocket fuel storage tank is used as a key ellipsoidal curved surface bearing member, and the manufacturing technology directly influences the reliability and cost of the rocket. The density of the stainless steel is about 3 times of that of the aluminum alloy, so that the structural coefficient of the stainless steel is similar to that of the aluminum alloy of the main body structural material of the active rocket, the thickness of the stainless steel structure needs to be reduced to less than 1/3 of that of the aluminum alloy, and the strength needs to be about 3 times of that of the aluminum alloy. Therefore, the stainless steel tank bottom is an ultra-thin and ultra-high strength ellipsoidal curved surface structure, for example, the wall thickness of the tank bottom of a rocket with the diameter of 4m is less than 2mm, and the normal-temperature tensile strength requirement exceeds 1200 megapascals, which is far beyond the limit of the traditional integral forming. The existing process route is forced to adopt a hard stainless steel plate to form a plurality of melon petals and a top cover, the number of melon petals forming the bottom of a storage tank of a rocket with the diameter of 4 meters is generally more than ten, and then the bottom is spliced and welded. The method has the problems that the assembly welding period is long (one bottom in twenty days), the welding performance loss is caused by the fact that the hard stainless steel is formed and welded, the welding defects can not be repaired, the reliability and the light weight level are low, and the like, and is difficult to meet the development requirements of a repeatable rocket with low cost and high efficiency. If the integral stainless steel slab is adopted for integral forming, the wrinkling and cracking problems in the forming process can not be solved by the traditional cold forming or hot forming technology due to the ultra-thin and ultra-high strength requirements of the slab. Therefore, development of a new method capable of realizing integral forming of the stainless steel box bottom is urgently needed, the method is applicable to splice welding of plate blanks and integral plate blanks, and solves the problem of coordinated control of wrinkling and cracking in forming of ultrathin ultrahigh-strength stainless steel curved surface pieces through ultralow-temperature phase change strengthening and staged stress path control. Disclosure of Invention The invention aims to provide an ultralow temperature forming method for a stainless steel integral tank bottom, which solves the problems existing in the prior art and realizes integral forming of a large-size ultrathin ultrahigh-strength stainless steel tank bottom curved surface piece. In order to achieve the above object, the present invention provides the following solutions: The invention provides an ultralow temperature forming method of a stainless steel integral box bottom, which utilizes the ultralow temperature phase transformation strengthening effect of stainless steel and welding seams thereof to form a stainless steel sheet in a flat plate state into the integral box bottom with the welding seams reinforced in accordance with base materials through ultralow temperature cooling and staged stress path control, and comprises the following steps: S1, providing a stainless steel slab; S2, reversely solving the deformation degree required to be achieved in each target area of the plate blank after forming and the required ultralow-temperature cooling temperature according to the ultralow-temperature transformation strengthening relation of the stainless steel and the deformation distribution rule of the box bottom; S3, placing the stainless steel slab into a forming die, and cooling the stainless steel slab to the ultralow-temperature cooling temperature determined in the step S2 by utilizing a low-temperature medium; S4, pressing a flange area of the plate blank by using a first blank pressing force, simultaneously controlling a male die to descend, enabling a central area of the plate blank to deform and be abutted against the male die in a bidirectional tensile stress state until the deformation of the central area reaches the required forming depth reversely calculated in the step S2; S5, gradually reducing the edge pressing force from the first edge pressing force to the second edge pressing force, and simultaneously controlling the male die to continue to move dow