Development and performance test of 904L super austenitic stainless steel

In this paper, 904L super austenitic stainless steel was successfully smelted in a multi-functional medium frequency induction melting furnace in the laboratory and hot rolling experiments were carried out. The structure and inclusions of the cast slab were analyzed, and the solution treatment and performance test of the hot rolled plate were carried out at different temperatures. The results show that the structure of 904L slab after smelting is uniform, with coarse and long columnar crystal as the main component, less inclusions and small quantity; there are some differences in properties after solution treatment at different temperatures, and the microstructure is fine and uniform after solution treatment at 1120 ℃.

904L (015cr21ni26mo5cu2) is a kind of ultra-low carbon high chromium nickel molybdenum stainless steel, and also a typical representative of super austenitic stainless steel. Its corrosion resistance is far better than the traditional 304 and 316L austenitic stainless steel, and its service life is many times of the conventional stainless steel. 904L has good resistance to intergranular corrosion, pitting corrosion, crevice corrosion and high stress corrosion. It is commonly used in strong corrosion environment, mainly used to make key equipment in petroleum, chemical industry, environmental protection, papermaking and other industries operating in harsh environment for a long time.

However, 904L is a kind of high alloy material with ultra-low carbon and multi-element composite action. In the smelting process, C and N are not easy to control, so high alloy is difficult to be melted and easy to produce segregation. At the same time, a large number of solid solution atoms will produce solution strengthening effect and increase deformation resistance. The precipitation of secondary phase greatly reduces the hot workability of steel, In the process of hot working, the steel, especially the thick plate, is easy to crack in layers or on the surface, which makes the hot deformation difficult.
904L stainless steel was successfully smelted in a medium frequency induction melting furnace of 200kg in a pilot plant. The simulated rolling was carried out on a 450 pilot mill. The macrostructure and inclusions of the slab were detected. The solid solution test and performance test were carried out on the hot rolled plate.

Test process

Smelting test

In the smelting test, 309S austenitic stainless steel is used as the base material, and other alloy materials are added for smelting. See Table.1 for specific ingredients. The pilot smelting furnace is a 200kg multi-functional medium frequency induction smelting furnace for steelmaking. The furnace simulates the AOD Process through the top and bottom combined blowing function, the LF process through the DC LF power supply and the electrode lifting mechanism, and the ingot casting is realized through the furnace body tilting mechanism and the three-axis mobile ingot trolley. The smelting process is simulated by the actual production process on site.

Table.1 904L smelting test ingredients (kg)
309 return Ultra low carbon ferrosilicon Micro carbon ferrochrome Silicomanganese Ferromolybdenum Electrolytic nickel Electrolytic copper Total
65 0 15 0 7.7 18.5 1.8 108

The materials in Table 1 are added into the crucible of induction furnace for melting. When the molten steel is completely melted and the temperature reaches 1650 ℃, it enters the AOD refining stage. In order to ensure that the bottom air vent is not blocked, a certain amount of argon is blown into the air vent during the melting process of furnace materials, and then oxygen blowing and decarburization operation is carried out. Before oxygen blowing, lime and fluorite are added, and the power of induction furnace is reduced to a lower level, so as to maintain the steel At the same time, the temperature of molten steel should be well controlled during the refining process. The temperature in the period of oxygen blowing and decarbonization is 1650-1700 ℃, and the temperature in the period of reduction is 1600-1650 ℃. In the actual production process, the temperature of decarburization by blowing oxygen is 1654-1677 ℃, the reduction temperature is 1619-1675 ℃, and the opening pouring temperature is 1574 ℃.
Table 2 shows the final composition of the slab after smelting. From the composition after smelting, it can be calculated that CR equivalent Creq =% Cr +% Mo + 1.5% Si + 0.5% Nb = 25.6, Ni equivalent Nieq =% Ni + 30% (c + n) + 0.5% Mn = 27.0, Creq / Nieq = 0.95, smelting meets the requirements of the target composition. According to the solidification mode of austenitic stainless steel, combined with the phase diagram of Fe Cr Ni alloy with Creq = 25.8% (Fig. 1), under this composition, the solidification mode should belong to the typical a solidification mode: L-L + γ – γ, and the quality of slab is better. No shrinkage cavity, inclusion, micro crack and other defects were found in the slab after casting, which is consistent with the theoretical results.

Table.2 chemical composition after 904L smelting (mass fraction,%)

N

C

Mn

Si

P

S

Cr

Mo

Ni

Cu

0.048

0.009

0.412

1.414 0.023 0.0024 20.496 4.486 24.600 1.806

20200607002235 96529 - Development and performance test of 904L super austenitic stainless steel

Fig.1 phase diagram of Fe Ni Cr at 25.8% Cr

Rolling test

The rolling test is carried out on 450 pilot rolling test machine. The size of the test blank is 45mm × 110mm × 175mm. The temperature of the test blank is required to be 850 ℃, and then heated to 1260 ℃ for 1H. The opening rolling temperature is ≥ 1080 ℃, and the finishing rolling temperature is ≥ 850 ℃. 11 passes of rolling are adopted. The total reduction rate is 93%, and the maximum reduction rate is 34%. The rolling force and temperature in the actual rolling process are shown in Figure 2. It can be seen from the figure that the maximum rolling force of 4-6 passes in the rolling process is about 1300-1400kn, the opening rolling temperature is 1160 ℃, and the finishing rolling temperature is 710 ℃, which fails to meet the requirements of finishing rolling temperature not lower than 850 ℃; after rolling, except for slight cracks on the edge of the steel plate, the rest of the surface quality is good. In the second test rolling process, the In one step, the rolling process is optimized, the rolling passes are reduced, the rolling speed is increased, and the edge cracks of the rolled steel plate are reduced compared with the first time. Through the summary of the two rolling experiments, it can be seen that the rolling passes can be further reduced, the reduction rate of passes can be increased, the temperature drop in the rolling process can be reduced, and the final rolling temperature can be increased.
20200607002842 91522 - Development and performance test of 904L super austenitic stainless steel

Fig.2 relationship between 904L rolling force, rolling temperature and rolling pass (a rolling force B rolling temperature)

Test result 

The low power structure and inclusion analysis of the cast billet after pouring were carried out, and the solid solution test, metallographic structure and property test of the hot rolled steel plate at different temperatures were carried out.

Macrostructure and inclusions of slab

Cut, polish and polish 904L slab along the thickness direction, then use hydrochloric acid solution to erode the polishing surface, and observe the low power structure of slab, as shown in Figure 3. It can be seen from the figure that the columnar crystal area of the slab is developed and thick, showing a continuous columnar dendrite structure with the same directionality, accounting for more than 90%, while the fine crystal area on the surface and the equiaxed crystal area in the center are less, with a narrow range; the composition analysis of the slab sampling is basically the same as that shown in Table 2, which confirms that the composition distribution is uniform, and no segregation phenomenon is found. Figure 4 shows the number and distribution of inclusions in the slab. The inclusion size is small, basically 5-10 μ m, and the number is small.

20200607003235 11595 - Development and performance test of 904L super austenitic stainless steel 20200607003408 17502 - Development and performance test of 904L super austenitic stainless steel
Fig.3 as cast macrostructure of 904L Figure.4 inclusion distribution in 904L slab

Experimental results of steel plate solution treatment

After hot rolling, the steel plate is kept at 1060 ℃, 1090 ℃, 1120 ℃ and 1150 ℃ for 30min for solution treatment. The performance test results after solution treatment are shown in Figure 5. It can be seen from the figure that with the change of solution treatment temperature, 904L performance changes, yield strength and tensile strength decrease to some extent, but the change is not obvious, the elongation increases to some extent, and the hardness decreases first and then increases, all of which meet the relevant provisions of GB/t4237-2012 standard. According to the comprehensive test performance, it shows comprehensive after annealing at 1150 ℃ Mechanical properties.
20200607003755 80721 - Development and performance test of 904L super austenitic stainless steel

Figure.5 properties of 904L hot rolled plate at different temperatures (a, strength; B, elongation; C, HV)

Microstructure

Figure 6 shows the microstructure of 904L plate after solution treatment at 1120 ℃. It can be seen from the figure that the high-temperature precipitated phase at the grain boundary after solution treatment has basically dissolved in the austenite matrix, and the structure is basically a single austenite structure with equiaxed crystal, a small amount of twinning structure appears, but no obvious strip and second phase structure appears. The grains are uniform, the grain size is between 40-50 μ m, and the grain size is between 40-50 μ M The degree is 5-6.
20200607010922 43846 - Development and performance test of 904L super austenitic stainless steel

Fig.6 microstructure of 904L hot rolled solid solution treated (a, edge; B, center)

Conclusion

  • 1) Through the smelting and rolling of 904L pilot test, the relevant systems and processes of decarburization, blowing, temperature control, etc. have been formed in the smelting process. The preliminary understanding and mastery of the decarburization effect of pilot test furnace, the control of bottom blowing N amount and the hot processing technology have been obtained.
  • 2) The microstructure of 904L slab is uniform, mainly composed of coarse and long columnar crystals, with few inclusions and small quantity. There are some differences in the properties after solution treatment at different temperatures. The microstructure after solution treatment at 1120 ℃ is basically all of equiaxed austenite, with an average grain size of 40-50 μ M. the grains are fine and uniform, without banded structure.
  • 3) The content of Cr, Mo and N in 904L alloy is high, and the deformation resistance is large in the process of hot working. The cracking of steel plate after rolling can be prevented and reduced by reasonably controlling the temperature of opening and finishing rolling.

Source: China 904L Flanges Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

Summary
development and performance test of 904l super austenitic stainless steel - Development and performance test of 904L super austenitic stainless steel
Article Name
Development and performance test of 904L super austenitic stainless steel
Description
904L super austenitic stainless steel was successfully smelted in a multi-functional medium frequency induction melting furnace in the laboratory and hot rolling experiments were carried out.
Author
Publisher Name
www.steeljrv.com
Publisher Logo

Related News

العربيةБългарски简体中文繁體中文DanskNederlandsEnglishFrançaisDeutschBahasa IndonesiaItaliano日本語한국어LatinPortuguêsРусскийEspañolதமிழ்ไทยTürkçe