Pre-forging heat treatment method for steel ingot for 300t-grade martensitic stainless steel forging

Abstract

A pre-forging heat treatment method for a steel ingot for a 300t-grade martensitic stainless steel forging. The method comprises: subjecting a steel ingot to a soaking treatment, so as to obtain a first pre-treated steel ingot, wherein the soaking treatment is performed at a temperature of 600-650°C for 8-22 h; heating the first pre-treated steel ingot to 1180-1200°C at a first heating rate, and holding the temperature for 80 h or more, so as to obtain a second pre-treated steel ingot; cooling the second pre-treated steel ingot to 1090-1110°C, and holding the temperature for 18-22 h, so as to obtain a third pre-treated steel ingot; and heating the third pre-treated steel ingot to 1160-1180°C at a second heating rate, and holding the temperature for 24 h or more, so as to obtain a billet. The method can reduce or eliminate the segregation of alloying elements in the as-cast structure of a billet during forging, so as to prevent the billet from cracking during forging.

Description

Forging pre-heat treatment method for 300t grade martensitic stainless steel ingot for forging piece TECHNICAL FIELD

[0001] The present application relates to the technical field of forging piece manufacturing, in particular to a forging pre-heat treatment method for 300t grade martensitic stainless steel ingot for forging piece. BACKGROUND

[0002] The large-scale integral forging runner forging piece is generally a 300t grade martensitic stainless steel forging piece with a material of 04Cr13Ni5Mo, which is a core component of a super-large capacity impulse water turbine unit and has the characteristics of super-large size and super-large weight; since the alloy element content in the material of the large-scale integral forging runner forging piece is relatively high and the size of the forging piece is large, the alloy element segregation in the as-cast structure of the blank is serious in the forging process, which can easily cause the blank to crack in the forging process.

[0003] SUMMARY

[0004] The present application solves the problem of how to reduce the alloy element segregation in the as-cast structure of the blank in the forging process to prevent the blank from cracking in the forging process for the forging of the 300t grade martensitic stainless steel forging piece with a material of 04Cr13Ni5Mo.

[0005] To solve the above problems, the present application provides a forging pre-heat treatment method for 300t grade martensitic stainless steel ingot for forging piece, comprising:

[0006] Step S1, the steel ingot is subjected to heat preservation treatment to obtain a first pretreated steel ingot; wherein the material of the steel ingot is 04Cr13Ni5Mo, the temperature of the steel ingot is 450-600℃, the temperature of the heat preservation treatment is 600-650℃, and the time is 8-22h;

[0007] Step S2, the first pretreated steel ingot is heated to 1180-1200℃ at a first heating rate, and is heat preserved for more than 80h to obtain a second pretreated steel ingot;

[0008] Step S3, the second pretreated steel ingot is cooled to 1090-1110℃, and is heat preserved for 18-22h to obtain a third pretreated steel ingot;

[0009] Step S4, the third pretreated steel ingot is heated to 1160-1180℃ at a second heating rate, and is heat preserved for more than 24h to obtain a blank.

[0010] Preferably, in the step S1, when the temperature of the steel ingot is 450-499℃, the time of the heat preservation treatment is 18-22h.

[0011] Preferably, in the step S1, when the temperature of the ingot is 500-549℃, the holding time is 13-17h.

[0012] Preferably, in the step S1, when the temperature of the ingot is 550-600℃, the holding time is 8-12h.

[0013] Preferably, in the step S2, the first heating rate is not higher than 50℃ / h.

[0014] Preferably, in the step S3, the cooling rate during the process of cooling the second pre-processed ingot to 1090-1110℃ is 10-60℃ / h.

[0015] Preferably, in the step S4, the second heating rate is not higher than 50℃ / h.

[0016] Preferably, in the step S1, the diameter of the ingot is 2900-3200mm.

[0017] Preferably, in the step S1, the mass of the ingot is 250-300t.

[0018] Preferably, in the step S1, the components of the ingot, by weight percentage, include: C: 0.01-0.04%, Si: 0-0.6%, Mn: 0.50-1.00%, P: 0-0.020%, S: 0-0.008%; Cr: 12.0-13.5%, Ni: 4.50-6.00%, Mo: 0-0.025%, Cu: 0-0.50%, W: 0-0.10%, V: 0-0.07%, the balance being Fe and inevitable impurities.

[0019] Compared with the prior art, firstly, the steel ingot with the material of 04Cr13Ni5Mo is treated at 600-650 DEG C for heat preservation, so that the temperature inside and outside the steel ingot is consistent and slightly higher than the austenite transformation temperature of the steel ingot, thus the inside and outside of the steel ingot can start austenitizing simultaneously, which is beneficial to the uniform distribution of alloy elements in the steel ingot; on this basis, the steel ingot is treated at high temperature of 1180-1200 DEG C for long-term heat preservation, since the heat preservation temperature is higher than the initial forging temperature of the steel ingot and the heat preservation is carried out at the temperature, high-temperature ferrite is not produced, thus the alloy elements in the steel ingot can be effectively dissolved, so that the alloy elements in the steel ingot are homogenized, which is beneficial to reducing or eliminating the segregation of alloy elements in the cast structure of the blank during the forging process, thereby preventing the blank from cracking during the forging process; after the high-temperature heat preservation of the steel ingot, the steel ingot is cooled, so that the temperature of the core is rapidly reduced to not higher than the initial forging temperature of the steel ingot, the time for the steel ingot to reach the initial forging temperature is shortened, and the purpose of energy saving and consumption reduction can be achieved; finally, the steel ingot is heated to 1160-1180 DEG C for heat preservation treatment, and the blank for subsequent casting is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0020] Fig. 1 is a flowchart of the forging heat treatment method of the steel ingot for 300t level martensitic stainless steel forgings in the embodiment of the present application;

[0021] Fig. 2 is a metallographic structure picture of the forgings prepared in Example 1;

[0022] Fig. 3 is a real object picture of the blank during the forging process in Example 1;

[0023] Fig. 4 is a real object picture of the blank during the forging process in the comparative example. DETAILED DESCRIPTION

[0024] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings. Although some embodiments of the present application are shown in the drawings, it should be understood that the present application can be realized in various forms, and should not be interpreted as being limited to the embodiments described herein, on the contrary, these embodiments are provided for a more thorough and complete understanding of the present application. It should be understood that the drawings and embodiments of the present application are only for exemplary purposes, and are not intended to limit the scope of protection of the present application.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the specification of the present application is only for the purpose of describing specific embodiments and is not intended to limit the present application;

[0026] As used herein, the term "includes" and its variants are open-ended, meaning that "includes but is not limited to"; the term "based on" means "based, at least in part, on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments." Related terms shall be construed accordingly. It should be noted that the concepts mentioned in the present application are used to distinguish different objects, and are not used to describe a specific order or primary and secondary relationship. In addition, the terms "first", "second" are only for description purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more features. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0027] It should be noted that the 300t grade martensitic stainless steel forging in the present application, wherein "300t grade" refers to the mass of the steel ingot used for forging the forging is 250-350t.

[0028] As shown in FIG. 1, the present application provides a 300t grade martensitic stainless steel ingot for forging before forging heat treatment method, comprising:

[0029] Step S1, the steel ingot is treated by heat preservation to obtain a first pretreated steel ingot; wherein the material of the steel ingot is 04Cr13Ni5Mo, the temperature of the steel ingot is 450-600℃, the temperature of the heat preservation treatment is 600-650℃, and the time is 8-22h;

[0030] Step S2, the first pretreated steel ingot is heated to 1180-1200℃ at a first heating rate, and is heat preserved for more than 80h to obtain a second pretreated steel ingot;

[0031] Step S3, the second pretreated steel ingot is cooled to 1090-1110℃, and is heat preserved for 18-22h to obtain a third pretreated steel ingot;

[0032] Step S4, the third pretreated steel ingot is heated to 1160-1180℃ at a second heating rate, and is heat preserved for more than 24h to obtain a blank.

[0033] The embodiment of the present application first carries out the heat preservation treatment on the steel ingot with the material 04Cr13Ni5Mo at 600-650 DEG C, so that the temperature of the inside and outside of the steel ingot is consistent, and is slightly higher than the austenite transformation temperature of the steel ingot, so that the inside and outside of the steel ingot can start the austenitization simultaneously, which is beneficial to the homogenization distribution of the alloy elements in the steel ingot; on this basis, the steel ingot is subjected to long-term heat preservation at a high temperature of 1180-1200 DEG C, since the heat preservation temperature is higher than the initial forging temperature of the steel ingot, and the heat preservation is carried out at the temperature, no high-temperature ferrite is produced, so that the alloy elements in the steel ingot can be effectively dissolved, thereby homogenizing the alloy elements in the steel ingot, which is beneficial to reducing or eliminating the segregation of the alloy elements in the cast structure of the blank during the forging process, thereby preventing the blank from cracking during the forging process; after the heat preservation of the steel ingot, the steel ingot is cooled, so that the temperature of the core is rapidly reduced to not higher than the initial forging temperature of the steel ingot, the time for the steel ingot to reach the initial forging temperature is shortened, and the purpose of energy saving and consumption reduction can be achieved; finally, the steel ingot is heated to 1160-1180 DEG C for heat preservation treatment, and the blank for subsequent casting is obtained.

[0034] In some embodiments of the present application, in the step S1, when the temperature of the steel ingot is 450-499 DEG C, the heat preservation time is 18-22h; when the temperature of the steel ingot is 500-549 DEG C, the heat preservation time is 13-17h; in the step S1, when the temperature of the steel ingot is 550-600 DEG C, the heat preservation time is 8-12h. Thus, the temperature of the inside and outside of the steel ingot is consistent, and is slightly higher than the austenite transformation temperature of the steel ingot,

[0035] In some embodiments of the present application, in the step S2, the first heating rate is not higher than 50 DEG C / h.

[0036] In some embodiments of the present application, in the step S3, the cooling rate in the process of cooling the second preprocessed steel ingot to 1090-1110 DEG C is 10-60 DEG C / h.

[0037] In some embodiments of the present application, in the step S4, the second heating rate is not higher than 50 DEG C / h.

[0038] In some embodiments of the present application, in the step S1, the diameter of the steel ingot is 2900-3200mm, and the mass of the steel ingot is 250-300t.

[0039] In some embodiments of the present application, the components of the ingot in step S1 include, in percentage by weight: C: 0.01-0.04%, Si: 0-0.6%, Mn: 0.50-1.00%, P: 0-0.020%, S: 0-0.008%; Cr: 12.0-13.5%, Ni: 4.50-6.00%, Mo: 0-0.025%, Cu: 0-0.50%, W: 0-0.10%, V: 0-0.07%, and the balance of Fe and inevitable impurities.

[0040] The present application is further described below in conjunction with specific embodiments.

[0041] Embodiment 1

[0042] A1, the ingot is subjected to a heat preservation treatment to obtain a first pretreated ingot; wherein the components of the ingot include, in percentage by weight: C: 0.03%, Si: 0.3%, Mn: 0.80%, P: 0.010%, S: 0.004%; Cr: 12.5%, Ni: 5.00%, Mo: 0.015%, Cu: 0-0.25%, W: 0.05%, V: 0-0.03%, and the balance of Fe and inevitable impurities; the mass of the ingot is 270t, the diameter is 3100mm, and the temperature is 570℃; the temperature of the heat preservation treatment is 650℃, and the time is 10h.

[0043] A2, the first pretreated ingot is heated to 1200℃ at a first heating rate, and is preserved for 85h to obtain a second pretreated ingot; wherein the first heating rate is 25℃ / h.

[0044] A3, the second pretreated ingot is cooled to 1100℃, and is preserved for 18h to obtain a third pretreated ingot; wherein the cooling rate is 30℃ / h.

[0045] A4, the third pretreated ingot is heated to 1180℃ at a second heating rate, and is preserved for 24h to obtain a blank.

[0046] A5, the blank is subjected to subsequent forging to obtain a forged piece; the forged piece is a large-scale integral forging runner forged piece.

[0047] Embodiment 2

[0048] A1, the steel ingot is subjected to a heat preservation treatment to obtain a first pretreated steel ingot; wherein the components of the steel ingot include, in percentage by weight: C: 0.03%, Si: 0.3%, Mn: 0.80%, P: 0.010%, S: 0.004%; Cr: 12.5%, Ni: 5.00%, Mo: 0.015%, Cu: 0-0.25%, W: 0.05%, V: 0-0.03%, and the balance being Fe and inevitable impurities; the mass of the steel ingot is 270 t, the diameter is 3100 mm, the temperature is 530 ℃, and the temperature of the heat preservation treatment is 650 ℃, and the time is 15 h.

[0049] A2, the first pretreated steel ingot is heated to 1200 ℃ at a first heating rate, and is kept at 1200 ℃ for 90 h to obtain a second pretreated steel ingot; wherein the first heating rate is 25 ℃ / h.

[0050] A3, the second pretreated steel ingot is cooled to 1100 ℃, and is kept at 1100 ℃ for 22 h to obtain a third pretreated steel ingot; wherein the cooling rate is 30 ℃ / h.

[0051] A4, the third pretreated steel ingot is heated to 1160 ℃ at a second heating rate, and is kept at 1160 ℃ for 30 h to obtain a blank.

[0052] A5, the blank is subjected to subsequent forging to obtain a forged piece; the forged piece is a large-scale integral forging runner forged piece.

[0053] Example 3

[0054] A1, the steel ingot is subjected to a heat preservation treatment to obtain a first pretreated steel ingot; wherein the components of the steel ingot include, in percentage by weight: C: 0.03%, Si: 0.3%, Mn: 0.80%, P: 0.010%, S: 0.004%; Cr: 12.5%, Ni: 5.00%, Mo: 0.015%, Cu: 0-0.25%, W: 0.05%, V: 0-0.03%, and the balance being Fe and inevitable impurities; the mass of the steel ingot is 270 t, the diameter is 3100 mm, the temperature is 480 ℃, and the temperature of the heat preservation treatment is 650 ℃, and the time is 20 h.

[0055] A2, the first pretreated steel ingot is heated to 1200 ℃ at a first heating rate, and is kept at 1200 ℃ for 90 h to obtain a second pretreated steel ingot; wherein the first heating rate is 30 ℃ / h.

[0056] A3, the second pretreated steel ingot is cooled to 1100 ℃, and is kept at 1100 ℃ for 20 h to obtain a third pretreated steel ingot; wherein the cooling rate is 20 ℃ / h.

[0057] A4, the third pretreated steel ingot is heated to 1170 ℃ at a second heating rate, and is kept at 1170 ℃ for 30 h to obtain a blank.

[0058] A5, carrying out subsequent forging on the blank to obtain a forged piece; the forged piece is a large-scale integrally forged runner forged piece.

[0059] Comparative Example

[0060] The difference from Example 1 is that step A2 is: heating the first pretreated ingot to 1150℃ at a first heating rate, and keeping the temperature for 85h to obtain a second pretreated ingot; wherein the first heating rate is 25℃ / h.

[0061] Experimental Example

[0062] Metallographic structure observation is carried out on the forged piece prepared in Example 1, and the result is shown in Figure 2. It can be seen from Figure 2 that the structure of the forged piece is uniform, and no obvious segregation occurs. Figures 3 and 4 are real object diagrams of the blank during the forging process in Example 1 and the comparative example, respectively. It can be seen from Figures 3 and 4 that the blank in Example 1 has no cracks on the surface during the forging process, and the blank in the comparative example is obviously cracked during the forging process.

[0063] Although the present application is disclosed as above, the protection scope of the present application is not limited to this. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application, and these changes and modifications shall fall within the protection scope of the present application.

Claims

1. A method for pre-forging heat treatment of a 300 t-class martensitic stainless steel ingot for a forged product, characterized by, The application relates to a method for preparing a steel ingot. Step S1: a steel ingot is subjected to heat preservation treatment to obtain a first pretreated steel ingot; wherein the material of the steel ingot is 04Cr13Ni5Mo, the temperature of the steel ingot is 450-600 DEG C, the temperature of the heat preservation treatment is 600-650 DEG C, and the time is 8-22 h; Step S2: the first pretreated steel ingot is heated to 1180-1200 DEG C at a first heating rate, and is preserved for more than 80 h to obtain a second pretreated steel ingot; Step S3: the second pretreated steel ingot is cooled to 1090-1110 DEG C, and is preserved for 18-22 h to obtain a third pretreated steel ingot; Step S4: the third pretreated steel ingot is heated to 1160-1180 DEG C at a second heating rate, and is preserved for more than 24 h to obtain a blank.

2. The method of the pre-forging heat treatment of the ingot of the 300 t-class martensitic stainless steel forging steel according to claim 1, characterized in that, In the step S1, when the temperature of the steel ingot is 450-499 DEG C, the time of the heat preservation treatment is 18-22 h.

3. The method of the pre-forging heat treatment of the ingot of the 300 t-class martensitic stainless steel for forged pieces according to claim 1, characterized in that, In the step S1, when the temperature of the steel ingot is 500-549 DEG C, the time of the heat preservation treatment is 13-17 h.

4. The method of claim 1, wherein the ingot is a 300 t-class martensitic stainless steel ingot for a forged product, and the ingot is heated at a temperature of 1,100 to 1,200 °C for 1 to 5 hours. In the step S1, when the temperature of the steel ingot is 550-600 DEG C, the time of the heat preservation treatment is 8-12 h.

5. The method of the pre-forging heat treatment of the 300 t-class martensitic stainless steel ingot for a forged product according to claim 1, characterized by, In the step S2, the first heating rate is not higher than 50 DEG C / h.

6. The method of the pre-forging heat treatment of the 300 t-class martensitic stainless steel ingot for a forged product according to claim 1, characterized by, In the step S3, the cooling rate in the process of cooling the second pretreated steel ingot to 1090-1110 DEG C is 10-60 DEG C / h.

7. The method of the pre-forging heat treatment of the ingot of the 300 t-class martensitic stainless steel for forged pieces according to claim 1, characterized in that, In the step S4, the second heating rate is not higher than 50 DEG C / h.

8. The method of the pre-forging heat treatment of the 300 t-class martensitic stainless steel ingot for a forged product according to claim 1, characterized by, In the step S1, the diameter of the steel ingot is 2900-3200 mm.

9. The method of the pre-forging heat treatment of the 300 t-class martensitic stainless steel ingot for a forged product according to claim 1, characterized in that, In the step S1, the mass of the steel ingot is 250-300 t.

10. The method of the pre-forging heat treatment of the 300 t-class martensitic stainless steel ingot for a forged product according to claim 1, characterized in that, In the step S1, the components of the steel ingot, in percentage by weight, include C: 0.01-0.04%, Si: 0-0.6%, Mn: 0.50-1.00%, P: 0-0.020%, S: 0-0.008%; Cr: 12.0-13.5%, Ni: 4.50-6.00%, Mo: 0-0.025%, Cu: 0-0.50%, W: 0-0.10%, V: 0-0.07%, and the balance is Fe and inevitable impurities.

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