CN1123845A

CN1123845A - Corrosionproof steel against sulfuric acid at dew point

Info

Publication number: CN1123845A
Application number: CN 94111544
Authority: CN
Inventors: 郑文龙; 俞亚鹏
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-12-26
Filing date: 1994-12-26
Publication date: 1996-06-05

Abstract

The steel being able to resist sulfuric acid corrosion contains Sb, Ti and B besides Cu and Cr and features high anticorrosion nature to sulfuric acid, so that it may be made into pipes or sections used in low-temp. fume containing sulfuric acid.

Description

Sulfuric acid dew point corrosion resistant steel

The invention belongs to the field of alloy steel, and relates to sulfuric acid dew point corrosion resistant steel which is mainly suitable for energy-saving, dust removal and various desulfurization devices, such as an air preheater, an economizer, a flue gas dust remover, a pipeline, a flue, a desulfurization device and the like.

When fuel is combusted to form SO₂And further oxidized to SO₃When the temperature of the flue gas is reduced to below 300 ℃, the flue gas begins to condense, sulfuric acid droplets constitute a severe corrosion of metals. The sulfuric acid dew point refers to the temperature at which the rate of evaporation of sulfuric acid from the surface is in equilibrium with the rate of condensation on the surface, and when the temperature is below the sulfuric acid dew point, the sulfuric acid causes corrosion of the material surface, commonly referred to as sulfuric acid dew point corrosion.

At present, petroleum, chemical industry, electric power and metallurgy need more and more energy fuels such as heavy oil, petroleum gas, coal and the like, and in order to improve the heat efficiency, reduce pollution and meet the requirement of environmental protection, energy-saving, dust-removing and various desulfurization equipment configured on energy power equipment, such as an air preheater, an economizer, a flue dust remover, a pipeline, a flue and a desulfurization device, are also successively disclosed. The use of these devices can reduce the exhaust gas temperature above 350 ℃ to 130-180 ℃. The utilization rate of heat energy is improved, but the corrosion of equipment is also getting worse. The loss of these devices due to corrosion at home and abroad is very disastrous. Therefore, the development and production of high sulfuric acid resistance low temperature dew point corrosion materials is urgent.

Japanese patent laid-open Nos. Showa 41-7923, Showa 46-8092, Showa 46-29254, Showa 47-1876 and Showa 47-46644 are five types of sulfuric acid dew point corrosion resistant steels developed in Japan. The chemical composition of five different compositions of sulfuric acid dew point corrosion resistant steel is listed in the table.

Production plant	Name (R)	C	Si	Mn	P	S	Cu	Cr	Ni	Others
Production plant	Name (R)	C	Si	Mn	P	S	Cu	Cr	Ni	Others	New day iron	S—TEN1	≤ 0.14	≤ 0.55	≤ 0.70	≤ 0.025	≤ 0.025	0.25～ 0.50			Sb ≤0.15
Japanese Steel pipe	NAC—1	≤ 0.15	≤ 0.40	≤ 0.50	≤ 0.030	≤ 0.030	0.20～ 0.60	0.30～ 0.90	0.30～ 0.80	Sn 0.04～0.35 Sb0.20～0.35	New day iron	S—TEN1	≤ 0.14	≤ 0.55	≤ 0.70	≤ 0.025	≤ 0.025	0.25～ 0.50			Sb ≤0.15
Japanese Steel pipe	NAC—1	≤ 0.15	≤ 0.40	≤ 0.50	≤ 0.030	≤ 0.030	0.20～ 0.60	0.30～ 0.90	0.30～ 0.80	Sn 0.04～0.35 Sb0.20～0.35	Kawasaki (Kawasaki)	RIVER— TEN—41S	≤ 0.15	≤ 0.40	0.20～ 0.50	0.020～ 0.060	≤ 0.040	0.20～ 0.50	0.20～ 0.60	≤ 0.50	Nb ≤0.04
Sumitomo Metal	CRIA	≤ 0.13	0.20～ 0.80	≤ 1.40	≤ 0.025	0.013 ～ 0.030	0.25～ 0.35	1.00～ 1.50			Kawasaki (Kawasaki)	RIVER— TEN—41S	≤ 0.15	≤ 0.40	0.20～ 0.50	0.020～ 0.060	≤ 0.040	0.20～ 0.50	0.20～ 0.60	≤ 0.50	Nb ≤0.04
Sumitomo Metal	CRIA	≤ 0.13	0.20～ 0.80	≤ 1.40	≤ 0.025	0.013 ～ 0.030	0.25～ 0.35	1.00～ 1.50			Shenhu (the god of the family) Steel making	TAICOR —S	≤ 0.15	≤ 0.50	≤ 1.00	≤ 0.040	0.015 ～ 0.040	0.15～ 0.50	0.90～ 1.50		Al 0.03～0.15

Chemical composition of sulfuric acid dew point corrosion resistant steel in the united states: less than or equal to 0.05 percent of C, less than 0.35 percent of Mn, less than 0.020 percent of P, less than 0.045 percent of S, more than 0.40 percent of Cu and 0.05-0.15 percent of Mo0.

Chemical components of the China martial steel for resisting sulfuric acid dew point corrosion (9Cu W Sn): less than 0.12 percent of C, 0.17-0.37 percent of Si, 0.35-0.65 percent of Mn, less than or equal to 0.04 percent of P, less than or equal to 0.04 percent of S, 0.20-0.50 percent of Cu0.10-0.30 percentof W and 0.20-0.40 percent of Sn0.20.

From the background technology, a small amount of Cu and Cr elements are generally added into low-carbon steel, and Cu is enriched on the surface of the steel to form a passive film, so that the steel has corrosion resistance.

The disadvantages of the prior art are that: the electrode potential on the surface of the low alloy steel is low; the passive film is not dense enough, resulting in poor corrosion resistance.

The invention aims to provide the sulfuric acid dew point corrosion resistant steel which has good sulfuric acid dew point corrosion resistance, is easy to roll, has higher strength and is simple in production process.

The chemical components (weight percent) of the sulfuric acid dew point corrosion resistant steel are as follows: less than or equal to 0.12 percent of C, 0.17-0.37 percent of Si, 0.35-0.65 percent of Mn, 0.25-0.50 percent of Cu, 0.70-1.10 percent of Cr, 0.04-0.12 percent of Sb0.04, less than or equal to 0.10 percent of Ti, less than or equal to 0.10 percent of B, less than or equal to 0.15 percent of Ni, less than or equal to 0.15 percent of Mo, less than or equal to 0.035 percent of S, and less than or equal to 0.

The invention is realized by adopting the following measures: because the influence of the alloy elements on the sulfuric acid dew point corrosion resistant steel of the low alloy steel is combined, the influence of the alloy elements on the sulfuric acid dew point corrosion resistance of the low alloy steel is difficult to clearly evaluate, and in order to find out the effect of the alloy elements, the influence of the change of a single element on the corrosion performance of the low alloy steel is usually analyzed while the content of other elements is fixed.

The alloying elements are added in order to transform the surface of the steel from an activated state to a passivated state, and the corrosion rate of the steel will be significantly reduced. Since passivation controls the corrosion rate of steel, the rate of corrosion can be significantly reduced if a dense passivation film can be formed or if ions of corrosion are deposited to a slightly higher potential.

The simplest and intuitive design approach when considering the alloy composition is to select the element with the lowest corrosion rate in a particular medium as the alloying element. 99.99% Mo, 99.99% Cu, 99.5% Ni, 99.41% Cr corrosion rate (mg/dm) for metal²，day) 53 63 260 5500

The research proves that the carbon steel is 30 percent H at 50 DEG C₂SO₄The medium polarization curve is not passivated, and the polarization curve added with Cu is passivated. Cu element forms Cu on the surface of steel₂The S film can inhibit anode reaction, so that the corrosion potential of the steel surface is increased, and the low-dimensional inert current is achieved. From an electrochemical point of view, the corrosion rate is mainly determined by the vergent current. The Vicat current controls the corrosion process of the steel, and can enable the steel to have high corrosion resistance under the condition of sulfuric acid dew point corrosion.

At 110 ℃ 85% H₂SO₄In solution, it is advantageous to add Cr to the alloy steel.

The addition of Sb can further increase the surface enrichment degree of Cu, reduce the Victorian current of a Victorian passivation region and resist the first-stage corrosion of sulfuric acid dew point corrosion.

Ti and B stabilize the enrichment of Cu and Sb on the surface in low alloy steel, and can form a compact passive film,and the difference from other sulfuric acid dew point corrosion resistant steels is that after the steel is corroded by sulfuric acid, a bright protective layer is formed on the surface, and the steel has high sulfuric acid dew point corrosion resistance.

The microstructure of the steel is ferrite plus pearlite, the pearlite content is about 15%, the inclusions are mainly sulfides (0.5 level) and a small amount of oxides (0.5 level), and the grain size is 8-9 levels.

The sulfuric acid dew point corrosion resistant steel of the invention emits a special glow in rolling, which is a symbol of Cu enrichment on the surface of the steel.

Compared with the foreign sulfuric acid dew point corrosion resistant steel, the invention adds Sb, Ti and B elements, improves the enrichment degree of Cu on the surface, enables the Cu to be uniformly distributed, and improves the density of a passive film, thereby greatly improving the sulfuric acid dew point corrosion resistant capability of the steel.

The invention is suitable for various electric furnaces and non-vacuum induction furnaces, and basically adopts the conventional process for operation, and can also adopt new technologies such as top-bottom composite blowing, external refining and the like.

Alloying Cu in a furnace, alloying Sb and B in a tank, generally pouring by a down-pouring method, and blowing argon in the tank.

And (4) cooling the steel ingot pit or the steel ingot mould for not less than 6 hours, demoulding, and finishing and sending to a blooming mill.

The sulfuric acid dew point corrosion resistant steel has good sulfuric acid dew point corrosion resistance and good comprehensive performance.

The invention will be furtherelucidated with reference to the preferred embodiments: according to the designed chemical composition range, the steel grade is smelted on a 10-ton electric furnace, and the specific chemical composition (weight percent) is as follows: c0.10, Si0.30, Mn0.44, Cu0.34, Cr0.92, Sb0.11, Ti0.09, B0.075, Ni0.12, Mo0.13, S0.032 and P0.028 steel ingot mold cooling for 6.5 hours, finishing and sending to a blooming mill after demolding, hot rolling a blank to phi 75mm, blanking and punching after acid cleaning and coping, drawing to phi 40 multiplied by 2.5 and phi 42 multiplied by 3 specifications, sampling and sending to a sea material for performance detection, wherein the results are as follows:

	at 50% H₂SO₄Corrosion rate (mg) at 70 ℃ cm²·h)	Mechanical Properties
		Mechanical Properties			σ0.2(MPa)	σ(MPa)	δ5(％)
		φ40×2.5	7.302	365	σ0.2(MPa)	σ(MPa)	δ5(％)	420	36
φ42×3	7.408	φ40×2.5	7.302	365	280	422	37	420	36

Steel grades and A of the invention₃Steel, Japan sulfuric acid dew point corrosion resistant Steel Corten, CRIA, 50% H at 70 ℃₂SO₄The medium corrosion rate results were as follows:

steel grade	The invention steel grade	A₃	Coren	CRIA
steel grade	The invention steel grade	A₃	Coren	CRIA	Corrosion rate mg/cm²h	7.30	103.5	63.0	13.4

Mixing the steel of the invention with A₃The sulfuric acid dew point corrosion resistant steels such as CRIA, Corten, S-ten, etc. are processed at 70 ℃ and 50% H₂SO₄After soaking in the solution for six hours, A₃The steel has been etched through the holes, the surface being covered with a layer of white corrosion products,the CRIA, Corten and S-ten steel has section with pores, and the steel of the present invention has bright section and surface, and after being corroded with sulfuric acid solution, the section has one layer of compact corrosion product on the surface.

Since sulfuric acid dew point corrosion is a process corrosion, except for 50% H at 70 ℃ in the laboratory₂SO₄The solution is soaked for 6 hours for a quick corrosion test, and a field pipe loading test is also carried out, the smelted sulfuric acid dew point corrosion resistant steel is directly rolled and formed into a waste heat boiler economizer and an air preheater, after the device of the steel grade is changed from 4 months in 1992, the waste heat boiler economizer and the air preheater are still in good operation, the service life of the waste heat boiler economizer is 20 times longer than 20g, the corrosion resistance of Corten in Japan is more than 5 times higher than that of CRIA in Japan.

From the above results, it can be seen that the sulfuric acid dew point corrosion resistant steel of the present invention has good overall properties. Can be made into various sectional materials and pipes for use in energy-saving, dust-removing and various desulfurization equipment.

Claims

The sulfuric acid dew point corrosion resistant steel is characterized by comprising the following chemical components (by weight percent) of less than or equal to 0.14 of C, 0.17-0.37 of Si, 0.35-0.65 of Mn, 0.25-0.50 of Cu, 0.70-1.10 of Cr0.04-0.12 of Sb0.04, less than or equal to 0.10 of Ti, less than or equal to 0.10 of B, less than or equal to 0.15 of Ni, less than or equal to 0.15 of Mo, less than or equal to 0.035 of S, and less than or equal to 0.035 of P.