A NO8810 series alloy forging method

Abstract

The invention discloses a NO8810 series alloy forging method. The technical scheme comprises the following steps: step S1, preparing a steel ingot: firstly, preparing a metal raw material according to a design formula to prepare a formed steel ingot; step S2: sending the steel ingot into a trolley furnace for heating, comprising: a preheating stage: heating the steel ingot to 600 DEG C and keeping the temperature; a heating stage: heating the steel ingot to 910-940 DEG C and keeping the temperature, and then heating the steel ingot to 1180±15 DEG C; step S3: forging the steel ingot, wherein the opening forging temperature of the steel ingot is greater than 1000 DEG C, the final forging temperature is not less than 850 DEG C, the edges are chamfered, the edges are pulled out, the bottom is chopped and the riser is chopped, and then the steel ingot is returned to the furnace for keeping the temperature; step S4: secondary forging of the steel ingot into a material. The invention has the advantages that, by designing alloy elements and matching a suitable process, the precipitation of titanium nitride, carbide and carbonitride is reduced, thereby reducing the generation of γ' phase, refining the alloy structure and strengthening the mechanical properties of the alloy.

Description

Technical Field

[0001] The invention relates to the technical field of nickel-based alloy steel manufacturing, and in particular to a NO8810 series alloy forging method. Background Art

[0002] Iron-nickel-based corrosion-resistant alloy is based on nickel, with nickel content greater than 30%, and nickel content and iron content greater than 50%. It has certain high-temperature strength and other comprehensive properties and can resist oxidation or water-prone medium corrosion. Because this alloy has good resistance to reduction, oxidation and medium corrosion, and has good performance, which ordinary stainless steel 304 cannot do, so this alloy is widely used in marine development, aerospace, energy and petrochemical industries. With the rapid development of the economy and the continuous improvement of the level of the industrial field, more and more projects require higher-grade stainless steel.

[0003] The traditional iron-nickel based corrosion resistant alloy contains a small amount of precipitated titanium nitride, carbide and carbonitride. When the alloy works in an environment with a temperature above 700°C, titanium nitride, carbide and carbonitride will precipitate γ' phase. On the one hand, the excessively precipitated γ' phase is enriched at the grain boundary, resulting in coarse intergranular structure and affecting the uniformity of the structure, thus affecting the performance of the alloy. On the other hand, the toughness of the γ' phase itself is relatively low, and internal stress is also accumulated during the precipitation of the γ' phase. Combined with the above factors, the fracture sensitivity of the alloy is increased. Summary of the invention

[0004] In view of the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a NO8810 series alloy forging method, which has the advantage of reducing the precipitation of titanium nitrides, carbides, and carbonitrides by designing alloy elements and matching suitable processes, thereby reducing the generation of γ' phase, refining the alloy structure, and strengthening the mechanical properties of the alloy.

[0005] The above technical objectives of the present invention are achieved through the following technical solutions:

[0006] A NO8810 series alloy forging method comprises the following steps:

[0007] Step S1, preparing steel ingots: firstly, preparing metal raw materials according to the designed formula, and using the metal raw materials to prepare steel ingots in an electric furnace;

[0008] Step S2: sending the steel ingot into the trolley furnace for heating, including:

[0009] Preheating stage: the steel ingot is heated to 600℃ and kept warm;

[0010] Heating stage: the ingot is heated to 910-940℃ and kept warm, then the ingot is heated to 1180±15℃;

[0011] Step S3: forging the steel ingot, the starting forging temperature of the steel ingot is greater than 1000°C, the final forging temperature is not less than 850°C, chamfering, drawing, cutting the bottom and cutting the riser, and then returning to the furnace for heat preservation;

[0012] Step S4: The steel ingot is forged into a material for secondary forging.

[0013] Further, in step S1, the steel ingot includes the following components counted in mass percentage: C: 0.05-0.10%; Mn: 1.50%; Si: 1.00%; P: 0.030%; S: 0.015%; Cr: 19.0-23.0%; Ni: 30.0-35.0%; Cu: 0.75%; Ti: 0.15-0.60%; Al: 0.15-0.60%; Fe: 38.0-47.0%.

[0014] Furthermore, the specifications of the steel ingots range from 700 to 800 mm in thickness, 1500 to 1650 mm in width, 2000 to 3000 mm in length, and 500 mm in riser height.

[0015] Furthermore, in step S2, during the preheating stage at 600°C, the holding time is 3 hours.

[0016] Furthermore, in step S2, during the temperature rise stage from 910 to 940°C, the temperature rise rate is 38 to 42.5°C / h, and the temperature holding time is 5h.

[0017] Furthermore, in step S2, during the temperature rise stage at 1180±15°C, the temperature rise rate is 80-90°C / h, and the temperature holding time is more than 8h.

[0018] Furthermore, in step S2, the temperature uniformity of the trolley furnace is within ±15°C, and the H2 concentration in the furnace is controlled at 1.5ppm.

[0019] Furthermore, in step S3, the heat preservation time after forging is ≥3h.

[0020] Furthermore, in step S3, the forging machine pressure specification is above 6000T, and the dimensions of the steel ingot after riser cutting are 490mm in thickness and 1650mm in width.

[0021] Furthermore, in step S4, the forging machine pressure specification is above 6000T, and the forging size is 320mm in thickness and 1610mm in width.

[0022] In summary, the present invention has the following beneficial effects:

[0023] 1. By redesigning the alloy components to change the ratio of carbon and other metal elements, and coordinating the appropriate forging and heat treatment processes, it is beneficial to the precipitation of chromium carbides, thereby reducing the precipitation of titanium nitrides, carbides, and carbonitrides, inhibiting the generation of γ' phase, and then reducing the coarse structure between grains, which is beneficial to a more uniform grain structure, giving full play to the solid solution strengthening effect, and reducing the γ' phase with poor toughness, so as to improve the mechanical properties of the alloy.

[0024] 2. During the forging hot working process, it is first preheated to 600℃ and kept warm, mainly to minimize the temperature difference between the inside and outside of the ingot so that the ingot can be heated evenly. In the preheating process, internal stress can also be eliminated to reduce the cracking sensitivity of the alloy. In the first heating stage, a slower heating rate is used, and the grain structure gradually transforms into single crystal austenite. Then in the second heating stage, which is the solid solution strengthening stage, a larger heating rate is used to promote the transformation of single crystal austenite. In addition, during this heat treatment process, titanium nitrides, carbides, and carbonitrides in the structure decompose, and more Cr, Ti, and Ni elements are released, further accelerating the content of single crystal austenite. At the same time, sufficient holding time is required to release the internal stress generated by the precipitation of single crystal austenite.

[0025] 3. During the forging hot working process, the H2 concentration in the trolley furnace is controlled at 1.5ppm. Since H2 is a strong reducing gas, it can inhibit excessive oxidation and decarburization of the alloy during the heat treatment process.

[0026] 4. Strictly limit the start forging temperature and forging temperature to ensure that the alloy structure has sufficient deformation properties to meet the requirements of forging deformation, strictly control the pressure of the forging hammer, ensure that the coarse-grained structure is fully crushed during the forging process, and give full play to the good mechanical properties of single crystal austenite. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the steps of the NO8810 series alloy forging method.

[0028] Figure 2 This is a metallographic examination diagram of the product obtained in Example 1.

[0029] Figure 3 This is a metallographic examination diagram of the product obtained in Example 2.

[0030] Figure 4 This is a metallographic examination diagram of the product obtained in Example 3. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present invention more clear, the solution proposed by the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are in a very simplified form and are not in precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the implementation methods of the present invention.

[0032] Embodiment 1:

[0033] A NO8810 alloy forging method, such as Figure 1 As shown, the following steps are included:

[0034] Step S1, preparing steel ingot: firstly, prepare metal raw materials according to the designed formula, and use the metal raw materials to prepare the steel ingot by electric furnace. The steel ingot includes the following components counted by mass percentage: C: 0.05-0.10%; Mn: 1.50%; Si: 1.00%; P: 0.030%; S: 0.015%; Cr: 19.0-23.0%; Ni: 30.0-35.0%; Cu: 0.75%; Ti: 0.15-0.60%; Al: 0.15-0.60%; Fe: 38.0-47.0%.

[0035] The specifications of the prepared steel ingots range from 700 to 800 mm in thickness, 1500 to 1650 mm in width, 2000 to 3000 mm in length, and 500 mm in riser height. The specifications of the steel ingots are 20 tons.

[0036] Step S2: sending the steel ingot into the trolley furnace for heating, including:

[0037] Preheating stage: The steel ingot is heated to 600℃ and kept warm for 3h. The H2 concentration in the furnace is controlled at 1.5ppm.

[0038] Heating stage: First, the steel ingot is heated to 915℃ and kept warm at a rate of 38-42.5℃ / h for 5h. Then, the steel ingot is heated to 1165℃ at a rate of 80-90℃ / h for 9h. The H2 concentration in the furnace is controlled at 1.5ppm.

[0039] Step S3: ingot forging, the starting forging temperature of the ingot is greater than 1000°C, the final forging temperature is not less than 850°C, the ingot is chamfered, the ingot is drawn, the bottom and the riser are chopped, and the size of the ingot after the riser is chopped is 490mm thick and 1650mm wide, and then it is returned to the furnace for insulation, and the insulation time after forging is ≥3h.

[0040] Step S4: The steel ingot is forged for the second time. The forging machine pressure specification is 6000T or more. The forging size is 320mm thick and 1610mm wide.

[0041] Embodiment 2:

[0042] The steps different from Example 1 are:

[0043] Step S2: sending the steel ingot into the trolley furnace for heating, including:

[0044] Preheating stage: The steel ingot is heated to 600℃ and kept warm for 3h. The H2 concentration in the furnace is controlled at 1.5ppm.

[0045] Heating stage: First, the steel ingot is heated to 930℃ and kept warm at a rate of 38-42.5℃ / h for 5h. Then, the steel ingot is heated to 1180℃ at a rate of 80-90℃ / h for 12h. The H2 concentration in the furnace is controlled at 1.5ppm.

[0046] Embodiment 3:

[0047] The steps different from Example 1 are:

[0048] Step S2: sending the steel ingot into the trolley furnace for heating, including:

[0049] Preheating stage: The steel ingot is heated to 600℃ and kept warm for 3h. The H2 concentration in the furnace is controlled at 1.5ppm.

[0050] Heating stage: First, the steel ingot is heated to 9940℃ and kept warm at a rate of 38-42.5℃ / h for 5h. Then, the steel ingot is heated to 1192℃ at a rate of 80-90℃ / h for 15h. The H2 concentration in the furnace is controlled at 1.5ppm.

[0051] Alloy microscopic inspection:

[0052] Experimental preparation: The sampling in Example 1 is recorded as Sample 1; the sampling in Example 2 is recorded as Sample 2; the sampling in Example 3 is recorded as Sample 3.

[0053] Test method: ASTM E112-2013

[0054] Metallographic testing of samples:

[0055] Experimental preparation: The sampling in Example 1 is recorded as Sample 1; the sampling in Example 2 is recorded as Sample 2; the sampling in Example 3 is recorded as Sample 3.

[0056] Sample 1: Figure 2 As shown, the magnification specification is 100μm, the grain size is 3.0, there is no intergranular mixed crystal structure, and there is no grain unevenness.

[0057] Sample 2: Figure 3As shown, the magnification specification is 100μm, the grain size is 1.0, there is no intergranular mixed crystal structure, and there is no grain unevenness.

[0058] Sample 3: Figure 4 As shown, the magnification specification is 100μm, the grain size is 2.0, there is no intergranular mixed crystal structure, and there is no grain unevenness.

[0059] Mechanical test: The results are shown in Table 1.

[0060] Testing conditions: room temperature stretching

[0061]

[0062] Table 1

[0063] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A NO8810 alloy forging method, characterized in that: The following steps are involved: Step S1, preparing steel ingots: firstly, preparing metal raw materials according to the designed formula, and using the metal raw materials to prepare steel ingots in an electric furnace; The steel ingot includes the following components counted by mass percentage: C: 0.05-0.10%; Mn: 1.50%; Si: 1.00%; P: 0.030%; S: 0.015%; Cr: 19.0~23.0%; Ni: 30.0~35.0%; Cu: 0.75%; Ti: 0.15~0.60%; Al: 0.15~0.60%; Fe: 38.0~47.0%; Step S2: sending the steel ingot into the trolley furnace for heating, including: Preheating stage: the steel ingot is heated to 600℃ and kept warm; In step S2, during the preheating stage at 600°C, the holding time is 3h; Heating stage: the ingot is heated to 910-940℃ and kept warm, then the ingot is heated to 1180±15℃; In step S2, during the heating stage from 910 to 940°C, the heating rate is 38 to 42.5°C / h, and the holding time is 5h; In step S2, during the heating stage at 1180±15°C, the heating rate is 80-90°C / h, and the holding time is more than 8h; Step S3: forging the steel ingot, the starting forging temperature of the steel ingot is greater than 1000°C, the final forging temperature is not less than 850°C, the steel ingot is chamfered, the steel ingot is drawn, the bottom is cut and the riser is cut, and then the steel ingot is returned to the furnace for heat preservation; Step S4: The steel ingot is forged into a material for secondary forging.

2. A NO8810 alloy forging method according to claim 1, characterized in that: In step S1, the specifications of the steel ingot range from 700 to 800 mm in thickness, 1500 to 1650 mm in width, 2000 to 3000 mm in length, and a riser height of 500 mm.

3. A NO8810 series alloy forging method according to claim 1, characterized in that: In step S2, the temperature uniformity of the trolley furnace is ±15°C, and the H2 concentration in the furnace is controlled at 1.5ppm.

4. A NO8810 alloy forging method according to claim 3, characterized in that: In step S3, the heat preservation time after forging is ≥3h.

5. A NO8810 series alloy forging method according to claim 4, characterized in that: In step S3, the forging machine pressure specification is 6000T or more, and the size of the steel ingot after riser cutting is 490mm in thickness and 1650mm in width.

6. A NO8810 series alloy forging method according to claim 5, characterized in that: In step S4, the forging machine pressure specification is 6000T or more, and the forging size is 320mm in thickness and 1610mm in width.

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