On February 22, 2023, Yangjiang News, at the “New Track, Great Future–Qingshan S32001 Duplex Steel Channel Market Launch Conference” hosted by Qingyi Steel Industry, more than 70 material suppliers from all over the country gathered around “Qingshan The mission of S32001 duplex steel tube sheet under the new historical background and its application and layout in the terminal market” were fully exchanged.
In the exchange session, users asked the vice president of Guangqing Research Institute Lin Hongliang questions about the issues they were most concerned about. Today, the highlights of the exchange session were summarized and extracted. The details are as follows:
Q: In the field of agriculture, what are the advantages of S32001 compared with 304?
Answer: I think the first thing to do with 304 is to have high strength, and the lightweight design may require professional evaluation. Compared with 32001 and 304, it is no problem to reduce the thickness by 30%. This is an advantage. The second is corrosion resistance. Considering the agricultural environment, you must use 304. At the same time, you must also consider the corrosiveness of the environment. Corrosion is corrosion in the atmosphere, including marine environments and chlorine-containing environments. Corrosion and S32001 duplex steel has been proved by a large number of experiments that its corrosion resistance is not worse than 304. So from these two perspectives, I think it has great advantages.
Question: Now we are using an 8K surface. We have obtained a comparison in the experiment, that is, using S32001 to throw it. The brightness of the mirror surface is the same as that of the mirror surface thrown by 304 and 201. It is almost the same, but the shading If you look closely, the texture it throws out will be more obvious, but the gloss of 32001 will be brighter than 304.
A: You said just now that after polishing the S32001 duplex steel, the texture may look more obvious from the side. This possible reason:
The cold-rolled structure of S32001 duplex steel is strip-shaped, with austenite and ferrite structures interspersed. If you are 304, it is equiaxed, which is difficult to avoid.
Let’s also consider whether we can make some optimizations in this area:
For the distribution of cold rolling, can it be tested by doing a small reduction in the previous pass, we also found that if this is done in 8K, in the case of cold rolling at this time, if you lower the pressure in the first pass, Put it a little smaller, this is for this roll diameter to use a small roll diameter to press, this is better for the overall polishability.
Do some tests like this next time to see if there is any improvement in this area.
Question: Another one is about color plating, that is, vacuum plating and water plating. We use S32001, which is different from the 201 and 304 we are currently using in the market. Does the color difference, or the process, need to be adjusted?
Answer: Regarding the color plating, there is not much information collected so far, but I have also asked Hongwang to professionally evaluate the finished products they brought back, and they think the quality is very good.
Question: 304 is used for food grade now, the kind with a lot of nickel, like our S32001 Duplex Steel, will there be some pollution if food fluid or food grade fluid such as milk is used?
Answer: Your question is very good. In fact, we have done S32001-related food-grade tests. We have no preparations on site today, and we can provide them to you after the meeting.
In fact, the key to relevant food-grade tests is to do some dissolution tests in related environments to see if they can meet the standards. What the 304 can do, the S32001 can do the same.
In addition, let me add one more point, that is, duplex steel S32001. Having said so many advantages, does it have any disadvantages? Of course, there are:
First, duplex steel has a temperature of 475 degrees, and its brittleness is similar to that of ferrite. It is brittle at 475 degrees, so duplex steel is generally not used in very high-temperature application environments, so if it is a structural part, there is a high-temperature application environment, is not recommended. Therefore, in terms of high temperature, duplex stainless steel is not recommended.
The second is duplex stainless steel, such as 2205 and 2507, which have relatively more precipitation, and the precipitation has a greater impact on its performance. S32001 duplex steel is of course economical, and it will perform better without molybdenum. The recommended temperature for all duplex steels is not too high. The temperature used is basically below 300 degrees, and it will not be particularly low. When the temperature is particularly low, the brittleness is relatively large. It is not as tough as 304, so it is said He has a scope of application, and it is not recommended to use below minus 80.
But the normal temperature is very good. The rebound ratio of S32001 duplex steel is in the range of 80 to 90, and the ratio of 304 is about 50-60. In the process of using, customers should leave enough margin when folding. Not too much of an issue.
Q: It also has good corrosion resistance. For example, when we visited our workshop today, we saw the frosted brushed surface. For example, the 304 surfaces have been damaged, and it is usually polished. The last handrail, as a brushed surface, is damaged. There is this gap in it, and the corrosion resistance is better than 304, is that what you mean?
Answer: As far as the wire drawing is concerned, it is not particularly obvious. There may be some differences in roughness. Real crevice corrosion is the existence of crevices caused by the assembly process or design problems. This part is most prone to corrosion, which is actually localized corrosion. , duplex stainless steel is generally better than ordinary austenitic stainless steel, that is, it is born with this characteristic.
Question: Is it equivalent to S32001 polishing, the iron is rubbed for a while, and then the iron will sticks to the surface slightly?
Answer: The contact between the stainless steel and the plain carbon steel pipe you mentioned is actually not crevice corrosion. Many crevice corrosions have that kind of joint parts, typically such as bolts and nuts. In the electrolyte environment, This is very prone to problems.
In fact, when looking at crevice corrosion, you can basically refer to pitting corrosion. Basically, if the resistance to pitting corrosion is good, the resistance to crevice corrosion will definitely be better. This is the law.
Q: Does S32001 duplex steel also contain copper?
Answer: There is basically no copper, and it is very low. Because we will add a little scrap steel during the processing. Scrap steel will have a little copper, so the copper content is extremely low, basically negligible.
Q: What is the bending effect of S32001 duplex steel?
For bent pipes, we can also add a little bit of copper here, which is not a lot. Adding 0.1 copper now has no effect on the performance of S32001 duplex steel. It has not been seen yet, because we have done it since last year and have done a lot. So far we have not seen a difference in performance.
The structure of S32001 duplex steel is a combination of ferrite and austenite. The basic phase ratio is half and half, most are 4:6, which is basically within this range, but the best is 5:5, and the general control will not be so precise.
Generally, we will involve its ratio in all aspects of production. After hot rolling, it will be annealed and pickled, and the black skin will be washed into white skin. The annealing process will also determine its ratio. The temperature is very critical. We are currently relatively mature in the control of the phase ratio, and we are sure that it will not deviate too much. Basically, it is in the range of 40 to 50.
Also, speaking of magnetism, this one is indeed magnetic because it is half ferrite after all. 304 stainless steel is also magnetic, especially after processing, without annealing, the magnetism is also very strong. In this regard, we need to do some popular science for customers.
Question: Nowadays, many biddings are very standardized. If there is no standard, the designer may not be able to pass the test, so this product must go in the direction of the standard. In the civil field, the problem of magnetism can be explained. But if it is applied in the industrial field and engineering projects, it is better to come up with the standard no matter how much it is said.
Answer: Now duplex steel is actually used in many chemical fields, such as oil and gas pipelines, chemical tankers, seawater desalination, heat exchangers, etc., and 2507 is used in desulfurization towers in high corrosion-resistant environments. There are also many uses because I also investigated at the end of last year, the production of duplex steel in various steel mills in China, TISCO, Dongte, and Posco, are all doing it.
If S32001 duplex steel is pushed out, the amount of duplex steel will definitely increase sharply, because the output of duplex steel according to the statistics of the third-party platform last year was more than 300,000 tons, of which 2205 duplex steel accounted for the main weight.
After the S32001 duplex steel was produced by Tsingshan, it attracted the attention of the entire industry, and other steel mills are now discussing the possibility of doing this.
In fact, many steel mills have been discussing this matter, but the technical aspect of this steel type is still relatively high. I think it is still difficult to do well now, and it is even more difficult to make it cheap and good.
S32001 duplex steel has the characteristics of high strength, high elongation, and high corrosion resistance, and has extremely high-cost performance. The product has the composition characteristics of low C, high Cr, and Ni saving; the performance characteristics of high strength, high elongation, high corrosion resistance, and easy welding. It is very advantageous in load-bearing structures and industrial fields; it has the structural characteristics of both austenite and ferrite two-phase advantages.