Study Of The Inner-stainless Steel/mild Steel Bimetallic Tube By Diffusion Under Inner Pressure

Stainless steel inner-clad mild steel bimetallic tube is a new type of material that has been invented in the 20th century. It has a lot of advantages. For example, saving of rare element, higher rate of capability and price etc. For recent years, it has been more and more developed and used. But, in our country, the study of stainless steel inner-clad mild steel bimetallic tube is more behindhand out and away than development country. Nowadays, although there are many producing methods of stainless steel inner-clad mild steel bimetallic tube, a simple effective method is to be invented. Stainless steel /mild steel bimetallic rod is made by putting stainless steel rod into mild steel tube, which is diffused after transmogrification at high temperature. This method can simulate stainless steel/mild steel bimetallic tube. We researched the production method of stainless steel/mild steel bimetallic tube, this method produce stainless steel/mild steel bimetallic tube by diffussion under inner pressure at high temperature after putting stainless steel tube into mild steel tube.Interface diffusion behaviors of stainless steel/steel bimetallic rod and stainless steel inner-clad carbon steel bimetallic tube have been investigated by means of optical microscope, scanning electron microscope (SEM) and alternating bending test. The influences of process parameters, such as surface preparation method, pressure, diffusion temperature and time, on interface bonding strength of stainless steel-steel bimetal have been analyzed.Diffusion bonding results of stainless steel /steel bimetallic rod indicate that the interface situations are different merely by a cold drawing and then a diffusing process in different temperature. The result in high temperature is better than in low temperature and the inter diffusion phenomenon near the interface of stainless steel /steel was observed. The result of stainless steel /steel bimetallic rod dilacerated approved that interface of bimetallic rod is bonded.Bimetallic tube under inner pressure 10Mpa has been diffused for two hours within 1000~1150, the result show that the higher the temperature, the more the interfaceshear strength ,the highest shear strength can reach 300Mpa after 1150 treated, and the repeat bending times can reach 5. The tube has been stayed at 1050 for 1~7 hours when the pressure keep invariable, the result show that the highest shear strength can reach 250 MPa for 4 hours diffusion treatment, the repeat bending times can reach 3. At various temperatures, the repeat bending times of the tube without pressure are 66%~70% fewer than that under inner pressure 10MPa At various temperature, the white secondary phase is separate out in the side of the stainless steel, which is Cr23C6 carbide confirmed by XRD analysis.