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CN-122013041-A - Stainless steel for high-efficiency brazing without stress annealing and preparation method thereof

CN122013041ACN 122013041 ACN122013041 ACN 122013041ACN-122013041-A

Abstract

The invention belongs to the technical field of stainless steel, and in particular relates to stainless steel for processing by avoiding stress annealing and high-efficiency brazing and a preparation method thereof, wherein the stainless steel comprises the following components in percentage by mass: 0.010-0.035% of C, 0.01-0.5% of Si, 0.1-1.2% of Mn, 0.04% of P, 0.03% of S, 17.2-20.0% of Cr, 7.5-10.0% of Ni, 1.0-3.5% of Cu, 0.010-0.045% of N, 0.035% < C+N less than or equal to 0.065%, 0.01-0.4% of Mo, and 17.8% < Cr+3.3Mo less than or equal to 20%, one or more of B, V, ti, nb, zr and rare earth elements RE are contained, and the balance of Fe and unavoidable impurities. The stainless steel provided by the invention can avoid stress annealing and improve the brazing processing efficiency.

Inventors

  • Zheng Shijuan

Assignees

  • 郑仕娟

Dates

Publication Date
20260512
Application Date
20260213

Claims (10)

  1. 1. The stainless steel for the high-efficiency brazing processing without stress annealing is characterized by comprising the following components ：C 0.010%-0.035%,Si 0.01%-0.5%,Mn 0.1%-1.2%,P<0.04%,S<0.03%,Cr 17.2%-20.0%,Ni 7.5%-10.0%,Cu 1.0%-3.5%,N 0.010%-0.045%,0.035%＜C+N≤0.065%,Mo 0.01%-0.4%, in percentage by mass, which satisfy the conditions of Cr+3.3Mo being less than or equal to 17.8% and less than or equal to 20%, and further comprising one or more of microalloying elements B, V, ti, nb, zr and rare earth elements RE, and the balance being Fe and unavoidable impurities.
  2. 2. The stainless steel for a stress free annealing and efficient brazing process according to claim 1, wherein MD =551－462*(W C +W N )－8.2*W Si －8.5*W Mn －30*(W Ni +W Cu )－14.0*W Cr －18.0*W Mo ≤－60, of the stainless steel wherein W C 、W N 、W Si 、W Mn 、W Ni 、W Cu 、W Cr and W Mo represent mass contents of the respective elements in%.
  3. 3. The stainless steel for a high-efficiency brazing process free of stress annealing according to claim 1, wherein the ratio of mass percent of manganese Mn to mass percent of sulfur S is controlled to be 40-500, and the ratio of mass percent of copper Cu to mass percent of manganese Mn is controlled to be 2-10.
  4. 4. The stainless steel for high-efficiency brazing process without stress annealing according to claim 1, wherein the micro-alloying elements B, V, ti, nb, zr, RE are added in amounts of 0.001% -0.05% of B, 0.001% -0.20% of Ti, 0.001% -0.20% of Nb, 0.001% -0.20% of V, 0.001% -0.20% of Zr, and 0.001% -0.20% of RE, respectively.
  5. 5. The stainless steel for high-efficiency brazing process without stress annealing according to claim 4, wherein said trace elements B, zr and RE are added singly in an amount not exceeding the above-mentioned requirements, and said trace elements V, nb and Ti are added in a total amount not exceeding 0.30%, and said trace elements RE and Zr are added in a total amount of 0.0015 to 0.30% in combination with V, nb and Ti.
  6. 6. The preparation method of the stainless steel for the high-efficiency brazing processing without stress annealing is characterized by comprising the following steps of: (1) Smelting and forging, namely preparing materials and smelting according to the components required by the method of claim 1, casting the materials into ingots, cooling the ingots at a cooling speed of more than or equal to 30 ℃ per second, heating the ingots along with a furnace after cooling, wherein the heating temperature is 1000-1250 ℃, the heat preservation time is 50-250min, discharging and forging, the initial forging temperature is not higher than 1180 ℃, the final forging temperature is higher than 900 ℃, and cooling the ingots by air after forging; (2) Hot rolling, namely hot rolling the forged billet by milling off surface oxide skin, heating at 1000-1250 ℃ and preserving heat for 60-150min, then starting rolling, wherein the initial rolling temperature is not more than 1200 ℃, and the final rolling temperature is controlled to be more than 850 ℃, and then performing air cooling or water cooling after rolling; (3) Homogenizing annealing, namely annealing the hot rolled steel plate at 930-1100 ℃ for 1-5min, and pickling to obtain a white skin surface, wherein the surface is clean and has no oxide skin residue; (4) Cold rolling, namely cold rolling the hot rolled steel plate subjected to acid washing and surface polishing, and annealing and acid washing after the cold rolling is finished to obtain the stainless steel cold rolled steel strip.
  7. 7. The method for preparing the stainless steel for the high-efficiency brazing process without stress annealing according to claim 6, wherein in the step (1), molten steel with qualified components is obtained by electric furnace smelting, AOD furnace refining and LF furnace refining in sequence, and a continuous casting slab is obtained by continuous casting, wherein the thickness of the continuous casting slab is 160-220mm.
  8. 8. The method for producing a stainless steel for a high-efficiency brazing process free from stress annealing according to claim 6, wherein in the step (2), the continuous casting slab is heated in a heating furnace at 1000 to 1250 ℃ and is kept for 150 to 230 minutes and then is rolled.
  9. 9. The method for producing a stainless steel for a high-efficiency brazing process free from stress annealing according to claim 6, wherein in the step (4), single-pass cold rolling is adopted for round trip rolling or continuous rolling, and the total rolling reduction of the cold rolling is not less than 50% to 90%.
  10. 10. The method for producing a stainless steel for a high-efficiency brazing process without stress annealing according to claim 6, wherein in the step (4), a reducing atmosphere bright annealing furnace is used for annealing, the temperature of bright annealing is 930-1100 ℃, the annealing time is 1-5min, the annealing TV value is controlled to 30-100 m/min, the grain size of the stainless steel sheet is controlled to 5-8 grades, and the surface roughness Ra is ensured to 0.003-0.3mm.

Description

Stainless steel for high-efficiency brazing without stress annealing and preparation method thereof Technical Field The invention belongs to the technical field of stainless steel, and particularly relates to stainless steel for processing by avoiding stress annealing and high-efficiency brazing and a preparation method thereof. Background Along with the high-price operation of copper, the production cost of refrigeration industries such as air conditioners, refrigerators and the like is increased. Meanwhile, copper pipes are easy to corrode in many service environments, and leakage of the copper pipes can be caused. The austenitic stainless steel has good corrosion resistance and is relatively low in price, and if the stainless steel is used for replacing copper to manufacture a refrigerant transmission pipeline of the heat exchanger, the production cost of the refrigeration industry can be greatly reduced. The austenitic stainless steel SUS304 or SUS304L is widely applied to civil and industrial production due to the advantages of good molding processability, corrosion resistance and low life cycle cost, can be connected by adopting a conventional welding process, and is also suitable for various conventional processing such as stamping, bending, spinning and the like. However, in some application fields, such as the air conditioner heat exchange industry, the processing requirements on heat exchange materials are higher, and the welding of dissimilar metals, such as the welding of stainless steel and copper, is often performed by adopting a brazing process, so that the stainless steel needs to have brazing filler metal spreadability equivalent to copper so as to adapt to the rapid brazing processing between the stainless steel and copper or between the stainless steel and the stainless steel. Stainless steel SUS304 or SUS304L is difficult to meet the requirement of high spreadability of brazing, and is used as a connecting pipe in a heat exchange system, stainless steel and a copper pipe are used for tunnel furnace brazing, and brazing solder is prepared by using a copper-phosphorus component with higher silver content, and then brazing of stainless steel and a copper sleeve is completed. And in the subsequent assembly stage of the air conditioner parts, copper brazing is carried out on copper pipes at two ends of the two stainless steel pipes, and finally, the connection of the steel replaced copper pipes is realized. Tunnel furnace brazing is also performed simultaneously as a step of stress relief annealing in SUS304 or SUS304L stainless steel forming. The process partially realizes the replacement of copper by stainless steel, but the brazing process is long, the connection of stainless steel and copper sleeve is completed by tunnel furnace brazing, the production efficiency is greatly reduced, and the cost reduction effect of the replacement of copper by stainless steel is also reduced. The stress relief annealing of the stainless steel pipe fitting can be synchronously realized by utilizing the brazing heating of the tunnel furnace, the stress corrosion cracking in the using process of the air conditioner is reduced, and the precision of the pipe fitting installation is improved. However, if the tunnel furnace brazing adopts an ammonia decomposition hydrogen reduction annealing protection mode, heating at a high temperature (1000-1080 ℃) can not avoid nitriding the surface of the stainless steel, particularly Cr 2 N and other precipitated phases formed by nitriding the grain boundary, and the partial chromium deficiency of the stainless steel can also be caused, so that the corrosion resistance of the stainless steel is affected. If the tunnel furnace welding adopts full hydrogen protection, the cost of long-time brazing is also obviously increased. SUS304 or SUS304L stainless steel brazing spreadability is poor, only special brazing filler metals such as tin bronze or a higher silver-containing brazing filler metal tunnel furnace can be used for brazing, and the welding process needs to last 80-100 minutes to ensure the sealing property of a brazing welding line, so that the requirement of a pressurizing leakage test is met. Tunnel furnace brazing results in low welding efficiency, high carbon emissions and a risk of subsequent intergranular sensitized corrosion failure. Therefore, it is necessary to find a novel stainless steel material, which can achieve the brazing wettability effect equivalent to that of copper materials, and simultaneously, can reduce the deformation stress generated in the processing of bent pipes of stainless steel pipes, and the like, and does not need to adopt stress relief annealing to eliminate the deformation stress, thereby realizing the rapid brazing processing integrating high efficiency, low cost and environmental friendliness. At present, manufacturers develop soft stainless steel designs such as SUS304ES developed in Japan, bao-Steel De Sheng and other low-streng