CN105215574A - A kind of iron-based solder for stainless steel braze welding - Google Patents

Abstract

The invention is an iron-based solder used for stainless steel brazing. In view of the relatively high production cost of traditional nickel-based solder, the copper in pure copper solder is easy to contact with acidic substances and active sulfides in high-temperature gear oil, and a corrosion reaction occurs to cause corrosion failure of the oil cooler. The invention solves the problems that the existing iron-based solder used for brazing the stainless steel EGR oil cooler has high melting temperature and poor corrosion resistance. According to the mass percentage, the solder is: Ni powder 15.0-25.0, Cr powder 6.0-17.0, Si powder 2.0-6.0, Cu powder 1.5-5.0, P powder 5.0-10.0, B powder 0-1.5, Mo powder 1.0-4.5, Graphite powder 0～1.0, the total mass fraction of B and graphite powder is not less than 0.25, and the balance is iron powder. The brazing material of the invention obtains a brazing joint with strong corrosion resistance at a brazing temperature of 1050° C., and the shearing strength of the brazing joint reaches 71.2 MPa.

Description

A kind of iron-based solder for stainless steel brazing

technical field

The invention is a novel iron-based solder used for stainless steel brazing.

Background technique

Exhaust gas recirculation cooler (EGR for short) can effectively reduce nitrogen oxides (NO _x ) and particulates (PM ) content, has become one of the indispensable important parts of the car. EGR oil cooler needs to have high strength, high corrosion resistance and oxidation resistance under special working environment.

When brazing the EGR stainless steel oil cooler with pure copper brazing material, the requirement for vacuum degree is relatively low and the production cost can be reduced at the same time. Strict requirements. At the same time, copper is easy to contact with acidic substances and active sulfides in high-temperature gear oil to cause corrosion reactions, which will eventually lead to engine corrosion failure. The traditionally used nickel-based solder can make brazing joints have high strength and high corrosion resistance, but due to the high content of Ni (at least 60%), the cost of nickel-based solder is about 600 yuan/kg, expensive nickel Increase the cost of heat exchanger and EGR oil cooler. The corrosion resistance of the iron-based solders currently used is not good, and most of the iron-based solders have relatively high melting temperatures, and excessively high temperatures will lead to excessive dissolution of the base metal stainless steel and growth of base metal grains, eventually lead to deterioration of joint performance.

Contents of the invention

The purpose of the present invention is to design and provide a low-melting-point iron-based brazing filler metal for the characteristics of high cost of traditional nickel-based brazing filler metal, corrosion failure of pure copper brazing filler metal and high brazing temperature of iron-based brazing filler metal. Its purpose is mainly to solve the problems of high melting temperature and poor corrosion resistance of the existing iron-based solder used for brazing stainless steel EGR oil coolers

The purpose of the present invention is achieved through the following technical solutions:

The present invention proposes a novel iron-based solder for stainless steel brazing, characterized in that: the iron-based solder for stainless steel brazing consists of Ni powder 15.0-25.0, Cr powder 6.0-17.0, Si powder 2.0-6.0 , Cu powder 1.5~5.0, P powder 5.0~10.0, B powder 0~1.5, Mo powder 1.0~4.5, graphite powder 0~1.0, the total mass fraction of B and graphite powder is not less than 0.25, and the balance is iron powder.

The technical solution of the present invention is to add B, C, Mo elements. According to the phase diagram of Fe-B and Fe-C, adding a small amount of B and C can significantly reduce the melting point of the solder alloy. Mo can interact with elements such as Ni in the base metal, causing changes in the structure, chemical composition and energy of the grain boundaries, refining the grains, and improving the wettability, joint strength and mechanical properties of the brazing seam.

The chemical composition and weight percentage of the solder are: Ni powder 15.0-25.0, Cr powder 6.0-17.0, Si powder 2.0-6.0, Cu powder 1.5-5.0, P powder 5.0-10.0, B powder 0-1.5, Mo powder 1.0 ～4.5, graphite powder 0～1.0, the total mass fraction of B and graphite powder is not less than 0.25, and the balance is iron.

The chemical composition and weight percentage of the solder are: Ni powder 15.0-25.0, Cr powder 6.0-17.0, Si powder 2.0-6.0, Cu powder 1.5-5.0, P powder 5.0-10.0, B powder 0-1.0, Mo powder 1.0 ～4.5, graphite powder 0～1.0, the total mass fraction of B and graphite powder is not less than 0.25, and the balance is iron.

The chemical composition and weight percentage of the solder are: Ni powder 15.0-25.0, Cr powder 6.0-17.0, Si powder 2.0-6.0, Cu powder 1.5-5.0, P powder 5.0-10.0, B powder 0-1.0, Mo powder 1.0 ～3.5, graphite powder 0～1.0, the total mass fraction of B and graphite powder is not less than 0.25, and the balance is iron.

The chemical composition and weight percentage of the solder are: Ni powder 15.0-25.0, Cr powder 6.0-17.0, Si powder 2.0-6.0, Cu powder 1.5-5.0, P powder 5.0-10.0, B powder 0-1.0, Mo powder 1.0 ～3.5, graphite powder 0.25～1.0, the total mass fraction of B and graphite powder is not less than 0.25, and the balance is iron.

The iron-based solder is used in the form of paste, atomized alloy powder, and extremely cold foil strip.

The advantage of the technical proposal of the invention is that compared with the traditional nickel-based solder, the production cost can be significantly reduced (iron-based: 150-300 yuan/kg; nickel-based: 600 yuan/kg). The problem of copper corrosion failure caused by the use of pure copper solder is overcome. Due to the addition of B and C elements, the solder melting temperature of the present invention is 1050°C, which is higher than that of Sweden's The iron-based solder BrazeLetF300 (melting temperature 1080°C) invented by the company has a low melting temperature. The brazing seam structure can be observed under a metallographic microscope, and the ductile FeCrNi-rich phase surrounds the hard and brittle FeCrNiP-rich phase. Due to the effect of Mo element, the crystallization of the brazing joint is uniform, and most of them are fishbone-like bright and dark areas intertwined. The shear strength of the lap joint structure brazed with this solder reaches 71.2MPa. When F300 solder is used, the shear strength of the structure is 57.2MPa. _The weight loss percentage of the paste solder is 16.65% after soaking in dilute sulfuric _acid solution for 96 hours, and the weight loss ratio of the ribbon solder is 0.209% under the same conditions, indicating that the solder has good Corrosion resistance.

detailed description

Below in conjunction with embodiment technical solution of the present invention will be described in further detail:

Table 1 shows 8 embodiments of the present invention and the chemical composition and mass percentage composition in each embodiment.

The high-temperature solder described in the foregoing embodiments is prepared according to the following process route:

(1) Select high-purity Fe, Ni, Cr, Si, Cu, B, P, C, Mo with a purity of not less than 99.9% (mass percentage), wherein B, P can be Fe-B, Fe-P alloy Add in the form of and weigh according to the weight ratio:

(2) The alloy is smelted into an alloy ingot by arc melting under the protection of argon.

(3) Prepare solder by one of the following methods:

A, using argon atomization powder making equipment to prepare alloy powder solder;

B. Under the condition of argon protection, the extremely cold foil material preparation equipment is used to prepare the quenched foil strip solder. For the rapid solidification process of the single roll method, the single roll needs to rotate at a high speed of 1000-10000r/min, and the cooling rate of the solder ingot is between 103-106K/s after melting and forming a liquid state.

C. Add additives and roll from powdered solder to make flexible thin strip solder.

D. Alloy strips are directly made from alloy ingots through multiple high-temperature rolling and heat treatment processes.

E. It is used after cutting the alloy ingot by wire electric discharge cutting method and then mechanically polishing the front and back sides.

F. Add alloy powder, hydroxymethyl element and ethanol in a mass ratio of 20:4:1 to make paste solder and use it directly.

In the example, No. 1 brazing filler metal is prepared by the F method, and the metal powder with a particle size of 300 meshes is selected, and the powder is mixed evenly by the method of mechanical powder mixing, and the alloy powder is added with hydroxymethyl element and ethanol in a mass ratio of 20:4:1. Add it to make solder paste, put the paste solder on the side of the surface to be connected, and complete the stainless steel lap joint experimental assembly. After assembly, put it directly into the VDW-30 multifunctional vacuum diffusion welding furnace and keep it warm at 1000 ° C for 35 minutes. Keep warm at ℃ for 30 minutes, then cool to room temperature with the furnace. After the brazing experiment, the shear strength of the brazed joint was 60.6 MPa, and the weight loss after soaking in 10% sulfuric acid solution for one week was 17.56%.

The experimental method of No. 2, No. 3, and No. 4 embodiments is shown in No. 1 embodiment. After the brazing experiment, the shear strength of the test brazed joint has reached 63.5MPa, 57.6MPa, and 58.8MPa respectively. At 10% (mass percentage Concentration) weight loss after immersion in the sulfuric acid solution for one week is 18.31%, 16.65%, 17.77%.

In the example, No. 5 brazing filler metal is prepared by method B: select metal powder with a particle size of 300 mesh, mix it evenly by mechanical powder mixing method, and prepare quenched foil ribbon brazing filler metal by using extremely cold foil material preparation equipment under the protection of argon. . For the rapid solidification process of the single roll method, the single roll needs to rotate at a high speed of 5000r/min, and the cooling rate after the solder ingot is melted into a liquid state is between 105K/s. Cut the finished foil strip into a size of 30mm×10mm×3mm and put it into a 304 stainless steel plate to be welded. After assembly, put it directly into a VDW-30 multifunctional vacuum diffusion welding furnace and keep it warm at 1000°C for 35min, and at 1050°C for 30min , cooled to room temperature with the furnace. After the brazing experiment, the shear strength of the brazed joint was 64.9 MPa, and the weight loss after soaking in 10% sulfuric acid solution for one week was 0.599%.

The experimental method of No. 6, No. 7, and No. 8 embodiments is shown in No. 5 embodiment. After the brazing experiment, the shear strength of the test brazed joint has reached 71.2MPa, 69.1MPa, and 68.7MPa respectively. At 10% (mass percentage Concentration) weight loss after immersion in sulfuric acid solution for one week is 0.209%, 0.284%, 0.304%.

Using the solder in the example shown in Table 1, alloy powder, hydroxymethyl element and ethanol are added in a mass ratio of 20:4:1 to make a paste solder or an extremely cold foil for use. .

The brazing material of the invention obtains a brazing joint with strong corrosion resistance at a brazing temperature of 1050° C., and the shearing strength of the brazing joint reaches 71.2 MPa.

Claims (5)

1. An iron-based solder for stainless steel brazing is characterized in that: according to mass percentage, the iron-based solder composition containing graphite powder for stainless steel brazing is Ni powder 15.0～25.0, Cr powder 6.0～ 17.0, Si powder 2.0~6.0, Cu powder 1.5~5.0, P powder 5.0~10.0, B powder 0~1.5, Mo powder 1.0~4.5, graphite powder 0~1.0, the total mass fraction of B and graphite powder is not less than 0.25, The balance is iron. 2. The iron-based solder according to claim 1, characterized in that: the chemical composition and mass percentage of the solder are: Ni powder 15.0-25.0, Cr powder 6.0-17.0, Si powder 2.0-6.0, Cu powder 1.5 ～5.0, P powder 5.0～10.0, B powder 0～1.0, Mo powder 1.0～4.5, graphite powder 0～1.0, the total mass fraction of B and graphite powder is not less than 0.25, and the balance is iron. 3. The iron-based solder according to claim 1, characterized in that: the chemical composition and mass percentage of the solder are: Ni powder 15.0-25.0, Cr powder 6.0-17.0, Si powder 2.0-6.0, Cu powder 1.5 ～5.0, P powder 5.0～10.0, B powder 0～1.0, Mo powder 1.0～3.5, graphite powder 0～1.0, the total mass fraction of B and graphite powder is not less than 0.25, and the balance is iron. 4. The iron-based solder according to claim 1, characterized in that: the chemical composition and mass percentage of the solder are: Ni powder 15.0-25.0, Cr powder 6.0-17.0, Si powder 2.0-6.0, Cu powder 1.5 ～5.0, P powder 5.0～10.0, B powder 0～1.0, Mo powder 1.0～3.5, graphite powder 0.25～1.0, the total mass fraction of B and graphite powder is not less than 0.25, and the balance is iron. 5. The iron-based solder according to claim 1, characterized in that: the iron-based solder is used in the form of paste, atomized alloy powder or extremely cold foil.