AUSTENITIC ACID CORROSION-RESISTANT STAINLESS STEEL OF Al-Mn-Si-N SERIES

Abstract: The invention relates to an Al-Mn-Si-N stainless acid-resisting steel substantially free of both Cr and Ni elements, which comprises the following elements: 0.06-0.12 C, 4-5 Al, 16-18 Mn, 1.2-1.5 Si, 0.15-0.30 N, 0.1-0.2 Re and the balance Fe. The corrosion resistance and mechanical properties of the steel can be further improved by adding a small amount of element(s) selected from the group consisting of Cr, Ni, Co, Ti, Nb, Cu, Mo, Zr, Hf, W and the like. The stainless steel has good corrosion resistance, pressure processing charateristics and welding performance, which can be made into a variety of stainless steel product and can be used in a broad field.

Description: The invention relates to an Al-Mn-Si-N austenitic acid-resisting steel, which can be used to substitute for conventional 18-8 type austenitic stainless steel. 18-8 type austenitic stainless steel, such as 1Cr18Ni9, 1Cr18Ni9Ti and 0Cr18Ni9 is conventional austenitic stainless steel. It has found an extensive and long-term application in the industry because of its superior corrosion resistance, combined mechanical properties and processing properties. However, because it contains a large amount of expensive Cr and Ni, the price of the steel is very high, thereby limiting its application in a broader field. Furthermore, because both Cr and Ni are scarce in the earth, it is a long-term goal of the metallurgical field to develop an austenitic stainless steel containing little or no Cr, Ni so as to substitute for 18-8 type Cr-Ni austenitic stainless steel. Up to now, however, it has not been reported that a stainless steel without Cr and Ni can provide corrosion resistance, combined mechanical properties and processing properties equivalent to that by conventional 18-8 type Cr-Ni austenitic stainless steel. JP-A-63 035 758 discloses an oxide dispersion-strengthened-type high-manganese austenitic steel, having excellent strength and toughness, obtained by providing a composition consisting of, by weight, 0.01-1% C, 12-50% Mn, 2-20% Cr, 0.1-5% Si, 0.01-4% Al, ≤ 0.25% N, 0.15% Y 2 O 3 and the balance Fe with inevitable impurities. TheY 2 O 3 is dispersed in the form of grains with ≤ 1 µm grain size. The composition further comprises 0.1-5% Mo and/or 0.01-5% W and/or 0.01-1% Ti, 0.1-1% Nb, 0.01-1% Ta and 0.005-0.2% Zr to improve strength. The composition further comprises ≤10% Ni, ≤5% Co and ≤ 10% Cu to improve oxidation resistance. It is a main object of the invention to provide an Al-Mn-Si-N austenitic acid-resisting steel. It is another object of the invention to provide an Al-Mn-Si-N austenitic acid-resisting steel which can improve corrosion resistance, especially in sulfuric acid or a reductive medium. Further objects of the invention are: to provide an Al-Mn-Si-N austenitic acid-resisting steel which is particularly resistant to intergranular-corrosion. to provide an Al-Mn-Si-N austenitic . acid-resisting steel which has an improved toughness at a low temperature, especially at a temperature of -120°C. to provide an Al-Mn-Si-N austenitic acid-resisting steel which has an improved corrosion resistance in hydrochoric acid, diluted sulfuric acid, basic solution and seawater. to provide an Al-Mn-Si-N austenitic acid-resisting steel which has an improved resistance to oxidation, heat fatigue and hot corrosion. to provide an Al-Mn-Si-N austenitic acid-resisting steel which has an improved resistance to wear and high temperature. The technical solution of the invention is achieved as follows (all contents hereafter are percentages by weight of the steel, unless otherwise specified). The invention relations to an Al-Mn-Si-N austenitic acid-resisting steel comprising: 0.06-0.12 wt% C, 4-5 wt% Al, 16-18 wt% Mn, 1.2-1.5 wt% Si, 0.15-0.30 wt% N, 0.1-0.2 wt% rare earth metal(s), and optionally 1-3 wt% Ti, optionally 1-3 wt% Nb, optionally 2-4 wt% Ni, optionally 3-5 wt% Cr, optionally 0.5-1wt% Zr, optionally 0.5-1 wt% Hf, optionally 0.5-1 wt% V, optionally 0.3-1 wt% Co, optionally 0.2-0.8 wt% W, optionally 2-3 wt% Cu, optionally 1-3 wt% Mo, the balance being Fe and unavoidable impurities. Preferred Al-Mn-Si-N austenitic stainless acid-resisting steels according to the invention are as follows: Al-Mn-Si-N austenitic stainless acid-resisting steel comprising the following elements: 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel resistant to intergranular-corrosion containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 1-3 Ti, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel resistant to intergranular-corrosion containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 1-3 Nb, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel resistant to intergranular-corrosion containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 1-3 Ti, 1-3 Nb, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel, which has an improved toughness at a low temperature, especially at -120°C, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 2-4 Ni, the balance Fe and unavoidable impurities Al-Mn-Si-N austenitic acid-resisting steel, which has an improved toughness at a low temperature, especially at -120°C, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 3-5 Cr, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resistingsteel, which has an improved toughness at a low temperature, especially at -120°C, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 3-5 Cr, 2-4 Ni, the balance Fe and unavoidable impurities Al-Mn-Si-N austenitic acid-resisting steel, which has an improved corrosion resistance in hydrochoric acid, diluted sulfuric acid, basic solution and seawater, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 0.5-1 V, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel, which has an improved corrosion resistance in sulfuric acid or reductive medium, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 2-3 Cu, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel, which can particularly improve corrosion resistance in sulfuric acid or reductive medium, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 1-3 Mo, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel, which can particularly improve corrosion resistance in sulfuric acid or reductive medium, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 2-3 Cu, 1-3 Mo, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel, which can further improve corrosion resistance, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 0.5-1 Zr, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel, which can further improve corrosion resistance, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 0.5-1 Hf, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel, which can further improve corrosion resistance, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 0.5-1 Zr, 0.5-1 Hf, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel, which can improve resistance to oxidation, heat fatigue and hot corrosion, containing 0.06-0.12 C, 4-5 A1, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 0.3-1 Co, the balance Fe and unavoidable impurities. Al-Mn-Si-N austenitic acid-resisting steel, which can improve corrosion resistance to wear and high-temperature, containing 0.06-0,12 C, 4-5 Al, 16-18 Mn, 1.2-1.5 Si, 0.15-0.3 N, 0.1-0.2 rare earth metal(s), 0.2-0.8 W, the balance Fe and unavoidable impurities. The choice of these elements in the Al-Mn-Si-N austenitic acid-resisting steels and content ranges thereof are based on the reasons given below: A certain quantity of Al can provide steel with corrosion resistance and improve its toughness at a low temperature and oxidation resistance. However, on one hand, when the content of Al is below 4 (wt.)%, the corrosion resistance of the steel is not significent; on the other hand, when the content of Al increases, the corrosion resistance will improve while the steel is ready to fracture during forge and roll, thereby resulting in a poor heat processing property. Therefore, it is preferred to use a content of A1 of 4-5%. The element Mn has the ability to enlarge the austenitic area and to stabilize austenite. However, this ability is about a half of that of Ni. Therefore, the content of Mn is limited to 16-18%. Si can react to produce a compact SiO 2 film on the surface of steel, which can prevent acids from further erosion to the interior of steel and is especially effective to improve corrosion resistance of steel in a high concentration of nitric acid. However, when the content of Si is too high, it will make steel deformation difficult. Therefore, the content of Si is limited to 1.2-1.5 (wt.)%. N can impart steel corrosion resistance while facilitating the formation of austenite greatly so that it can partly substitute for Ni. Mo and Cu can further improve the corrosion resistance of steel in sulfuric acid or a reductive medium. When steel contains a certain quantity of Mo and Cu, the corrosion resistance will be more significant. Nb and Ti can react with C in the steel to produce a stable carbide. When it is required to restrain intergranular corrosion strictly, a certain quantity of Nb and/or Ti can be added to the steel. Zr and Hf can be resistant to intergranular corrosion. If it is required to confine intergranular corrosion more strictly, a certain quantity of Zr and/or Hf can be added to steel. V in the steel can be resistant to corrosion in hydrochoric aicd, diluted sulfuric acid, basic solutions and seawater. If a certain quantity of Co is included in steel, it can improve its resistance to oxidation, heat fatigue and hot corrosion. In order to improve resistance to wear and high temperature, a certain quantity of W can be added to the steel. Rare earth metal(s) (RE) can improve the corrosion resistance and oxidation resistance of steel, refine its crystal grain and upgrade the steel, thereby improving its processing properties. It is apparent from the following examples that the Al-Mn-Si-N austenitic acid-resisting steel according to the invention is better than traditional 18-8 type Cr-Ni stainless steel in terms of corrosion resistance, heat processing properties, welding performance and combined mechanical properties. Because the expensive and scarce Cr and Ni are substituted with elements which are inexpensive and ready to obtain such as Al, Mn, Si, N , the price of the steel of the invention is far below that of 18-8 type Cr-Ni stainless steel. The Al-Mn-Si-N austenitic acid-resisting steel of the invention can be smelted with a conventional electric-arc furnace and induction furnace so as to be cast into steel ingots and made into a variety of steel products in required shapes by conventional processing techniques such. as hot rolling, forging, cold rolling draw(draft). This invention will be further illustrated by the following examples. Example: Smelting is carried out in a half-ton three-phase electric-arc furnace. 10 kg Al ingot, 36 kg Mn, 3 kg crystalline Si, 1 kg Cr 2 O 3 are introduced sequentially into the bottom of the furnace with a good liner, then a clean rust-free liquid steel, which contains less than 0.12% carbon and has a size of about 100 mm, is added so as to cover the materials above. Power is then applied to melt the materials into a liquid. After the liquid becomes clear, a sample is taken for analysis. The slag is adjusted to keep the liquid in a good flowable condition. When the temperature of the liquid is higher than 1500°C, a reductive slag is selected to carry out a reductive reaction for 20 min. When the temperature of the liquid steel is 1540-1560°C, 0.5 kg mixed rare earth metals is added therein. After full agitation, the steel is discharged. The composition of the steel is shown in table 1. Element C Si Mn N Al RE Content(wt. %) 0.07 1.25 16.30 0.17 4.38 0.17 The mechanical properties of the steel are shown in table 2. The invention σ 0.2(MPa) 250 σ b(MPa) 550 σ s(%) 54 1Cr18Ni9 GB3280-92 ≥ 205 ≥ 520 ≥ 40 Corrosion resistance: its weight is reduced by 9.817g after the steel is subjected to a corrosion test in 5% sulfuric acid (boiling) for half an hour, which is far below the value stipulated by the China National Standard.

Claims: An Al-Mn-Si-N austenitic acid-resisting steel comprising: 0.06-0.12 wt% C 4-5 wt% Al 16-18 wt% Mn 1.2-1.5 wt% Si 0.15-0.30 wt% N 0.1-0.2 wt% rare earth metal(s) and optionally 1-3 wt% Ti optionally 1-3 wt% Nb optionally 2-4 wt% Ni optionally 3-5 wt% Cr optionally 0.5-1 wt% Zr optionally 0.5-1 wt% Hf optionally 0.5-1 wt% V optionally 0.3-1 wt% Co optionally 0.2-0.8 wt% W optionally 2-3 wt% Cu optionally 1-3 wt% Mo the balance being Fe and unavoidable impurities. An Al-Mn-Si-N austenitic acid-resisting steel according to claim 1 comprising: 0.07 wt% C, 4.38 wt% Al, 16.30 wt% Mn, 1.25 wt% Si, 0.17 wt% N, 0.17 wt% rare earth metals, the balance being Fe and unavoidable impurities. A process for producing an Al-Mn-Si-N austenitic acid-resisting steel according to claim 1 comprising smelting the components in a conventional electric-arc furnace or induction furnace and then casting into steel ingots. A process for producing an Al-Mn-Si-N austenitic acid-resisting steel according to claim 3 wherein the casting is carried out by hot rolling, forging or cold rolling draw.

Inventors: ZHAO XUESHENG, ZHAO, XUESHENG
Applicants: ZHAO XUESHENG, ZHAO, XUESHENG
Application year: 1996
Main classification: C22C38
IPC codes: C22C38