A heat treatment free 15CrMo heat resistant alloy steel hot continuous rolling coil and a csp process production method thereof

Abstract

This invention provides a heat-treatment-free hot-rolled 15CrMo heat-resistant alloy steel coil and its CSP process production method, belonging to the field of heat-resistant alloy steel manufacturing technology. It solves the problem that 15CrMo coils lack heat-treatment-free production and their performance cannot meet application requirements. The invention includes the following steps: pre-treatment of molten iron followed by converter smelting; refining in an LF furnace; casting via a continuous casting machine; cooling in a secondary cooling section before entering a soaking furnace; descaling after exiting the furnace; rolling on a 6-stand continuous rolling mill; cooling the rolled strip to the coiling temperature after inspection; forming a coil using a set coiling tension; and air-cooling to room temperature to obtain a ferrite + pearlite microstructure. This invention fully utilizes existing CSP technology and equipment, controlling the C content within a narrow range, employing a medium-carbon, low-manganese scheme, and comprehensively utilizing controlled rolling and cooling technologies. It can produce thin-gauge low-alloy steel strips resistant to low-temperature impact without the need for traditional heat treatment processes, meeting user requirements.

Description

Technical Field

[0001] This invention belongs to the field of heat-resistant alloy steel manufacturing technology, specifically relating to a heat-resistant alloy steel hot-rolled coil of 15CrMo without heat treatment and its CSP process production method. Background Technology

[0002] 15CrMo exhibits high thermal strength and oxidation resistance at high temperatures due to the addition of Cr and Mo elements. In recent years, there has been a certain demand for 15CrMo coils, mainly used in boiler heat-resistant structural components. Currently, the published production methods are mainly for 15CrMo medium-thick plates, while production methods for 15CrMo coils, especially CSP production methods, are rarely discussed.

[0003] 15CrMo is generally used in high-temperature environments of 500℃. Currently, 15CrMo medium and heavy plates are produced using controlled rolling and tempering heat treatment processes. Coil production lines are generally not equipped with heat treatment processes. The performance indicators of coils produced by existing coil production lines according to the medium and heavy plate process are poor and cannot meet the user requirements. Therefore, there is an urgent need to develop 15CrMo coil products that do not require heat treatment and whose performance meets the user requirements. Summary of the Invention

[0004] The purpose of this invention is to provide a heat-resistant 15CrMo heat-resistant alloy steel hot-rolled coil without heat treatment and its CSP process production method, so as to solve the problem that 15CrMo coil lacks heat treatment and its performance cannot meet the requirements for use.

[0005] The technical solution of this invention is: a heat-resistant 15CrMo heat-resistant alloy steel hot-rolled coil that does not require heat treatment. The raw material of the coil is composed of the following chemical composition by weight percentage: C: 0.16-0.18, with the C content controlled by a narrow composition, Si: 0.20-0.35, Mn: 0.45-0.65, P: ≤0.023, S: ≤0.010, Als: 0.020-0.045, Cr: 0.85-0.95, Mo: 0.45-0.55, with the remainder being Fe, Ca, and other unavoidable trace elements.

[0006] A CSP process for producing heat-resistant 15CrMo heat-resistant alloy steel hot-rolled coils without heat treatment includes the following steps: Step 1: After pretreatment of molten iron, it is smelted in a converter, then refined in an LF furnace with argon blowing throughout the process. After refining, the molten steel is fed into the tundish and then cast through a continuous casting machine. The protective slag for the continuous casting crystallizer is a special protective slag for medium carbon steel with high basicity. Step 2: After the continuously cast billet from Step 1 is cooled in the second cooling section, it enters the soaking furnace. Step 3: After the continuously cast billet heated in Step 2 is taken out of the furnace, it is descaled. After one high-pressure water descaling, it enters the 6-stand continuous rolling mill for rolling. The secondary descaling water is turned off after the F1 and F2 stands, and the cooling water between the F1 and F3 stands is turned off. Step 4: After the strip rolled in Step 3 exits the F6 last stand, it is inspected and then cooled to the coiling temperature. After cooling, a coil is made using the set coiling tension. The coil is then air-cooled to room temperature to obtain a ferrite + pearlite microstructure.

[0007] Furthermore, in step one, the converter smelting time is 40-44 minutes, and the converter tapping temperature is 1580-1620℃.

[0008] Furthermore, in step one, the refining temperature in the LF furnace is >1500℃, the refining time is 45-60min, and the furnace exit temperature is 1570-1590℃.

[0009] Furthermore, in step one, the temperature of the molten steel in the tundish is 1535-1555℃, the casting speed of the continuous casting machine is 3.6m / s, the cooling water flow rate of the continuous casting crystallizer is controlled at 5600-6400L / min, the crystallizer water temperature is 40-41℃, the basicity of the protective slag is 1.32-1.34, and the slab thickness is controlled at 60-70mm.

[0010] Furthermore, in step two, the temperature of the continuously cast billet entering the heating furnace is 920-980℃, the heating temperature is 1120-1180℃, and the residence time of the continuously cast billet in the heating furnace is 15-20 minutes.

[0011] Furthermore, in step three, the descaling inlet pressure is ≥19 MPa, the outlet pressure is ≥29 MPa, the continuous rolling start temperature is 1020-1080℃, and the final rolling temperature is 880-940℃.

[0012] Furthermore, in step four, the rolled strip is cooled through eight laminar flow cooling sections at a coiling temperature of 810-850℃, and then coiled through a two-stage PSC model after cooling.

[0013] The beneficial effects of this invention are as follows: The carbon content is controlled within a narrow range of 0.16-0.18%. The mold flux for the continuous casting crystallizer uses a special mold flux for medium carbon steel with high basicity, which effectively avoids the peritectic region of the CSP production line steel, preventing steel leakage and achieving stable casting on the CSP production line. Argon blowing throughout the process allows large inclusions to float fully, resulting in fine and uniformly distributed inclusions with good low-temperature impact performance. Using existing CSP technology and equipment, air cooling after rolling and air cooling of coiled steel coils to room temperature between other off-line coils can achieve the same mechanical properties as tempering in a tempering furnace after rolling, reducing heat treatment steps and greatly saving production costs.

[0014] In this invention, controlling the heating temperature in the soaking furnace effectively reduces the deformation resistance and rolling load of each stand in the CSP continuous rolling mill, improving rolling stability. Continuous rolling is performed using a 6-stand finishing mill, with the secondary descaling water shut off after stands F1 / F2 and the cooling water shut off between stands F1 / F2 / F3. This method effectively reduces process temperature drop, further minimizing material deformation. Controlling the final rolling temperature in continuous rolling reduces the exit speed, ensuring stability during the threading process. Eight-stage laminar flow cooling uses air cooling, and controlling the coiling temperature further reduces the material cooling rate, preventing excessively rapid cooling that could lead to bainitic phase transformation. By controlling the placement of the coiled steel coil between other downstream coils for air cooling to room temperature, a ferrite + pearlite microstructure is obtained, significantly increasing the strength, hardness, plasticity, and toughness of the coil. This ensures good product shape while maintaining product strength and plasticity indicators.

[0015] The CSP continuous casting and rolling process produces hot-rolled steel sheets that are air-cooled and then high-temperature coiled. The coils are then air-cooled again, and the coils themselves are used for tempering, reducing the number of heat treatment steps. This process achieves the same or even better microstructure and properties as the controlled rolling and tempering heat treatment process, resulting in the production of lower-cost 15CrMo heat-resistant alloy steel hot-rolled coils with a yield strength of 298-390MPa, a tensile strength of 493-530MPa, and an elongation after fracture of 27.5-34.5%.

[0016] This process is simple and has low production costs. It makes full use of existing CSP technology and equipment, controls the carbon content in a narrow composition, adopts a medium carbon and low manganese scheme, and comprehensively utilizes controlled rolling and controlled cooling technology. It can produce thin-gauge low-alloy steel strips that are resistant to low-temperature impact without the need for traditional heat treatment processes, thus meeting the user's requirements. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to the embodiments.

[0018] Example 1 The raw material for the coil consists of the following chemical composition by weight percentage: C: 0.16, with C content controlled within a narrow range of 0.16; Si: 0.20, Mn: 0.45, P: 0.023, S: 0.010, Als: 0.020, Cr: 0.85, Mo: 0.45, with the remainder being unavoidable trace elements such as Fe and Ca. Step 1: After pretreatment, the molten iron is smelted in a converter for 40 minutes at a tapping temperature of 1580℃. After smelting, it is transferred to an LF furnace for refining at 1550℃ for 45 minutes at a tapping temperature of 1570℃. Argon is blown throughout the process. After refining, the molten steel enters the tundish through the sliding nozzle at the bottom of the ladle. The tundish temperature is 1535℃. Then, it is cast using a continuous casting machine at a speed of 3.6 m / s. The cooling water flow rate of the continuous casting crystallizer is controlled at 5600 L / min, and the crystallizer water temperature is 40℃. The protective slag used in the continuous casting crystallizer is a special high-basicity protective slag for medium carbon steel with a basicity of 1.32. The slab thickness is controlled at 60 mm. Step 2: After the continuous casting billet cast in Step 1 is cooled in the second cooling section, it enters the soaking furnace. The temperature of the continuous casting billet entering the furnace is 920℃, the heating temperature is 1120℃, and the residence time of the continuous casting billet in the furnace is 15 minutes.

[0019] Step 3: After the continuously cast billet heated in Step 2 is taken out of the furnace, it is descaled. The descaling inlet pressure is 19 MPa and the outlet pressure is 29 MPa. After one high-pressure water descaling, it enters the 6-stand continuous rolling mill for rolling. The continuous rolling start temperature is 10200℃ and the finish rolling temperature is 880℃. The secondary descaling water after the F1 / F2 stands is turned off, and the cooling water between the F1-F3 stands is turned off. Step 4: After the strip rolled in Step 3 exits the F6 last stand, it is tested by a multi-function instrument and then cooled to the coiling temperature of 810℃ through an 8-section laminar flow cooling section. After cooling, the coil is made using the coiling tension set by the secondary PSC model. The coil is then placed between other coils from the production line and air-cooled to room temperature to obtain a ferrite + pearlite microstructure.

[0020] Example 2 The raw material for the coil consists of the following chemical composition by weight percentage: C: 0.17%, with the C content controlled at a narrow percentage of 0.17%; Si: 0.30%, Mn: 0.50%, P: 0.022%, S: 0.009%, Als: 0.035%, Cr: 0.90%, Mo: 0.50%, with the remainder being unavoidable trace elements such as Fe and Ca. Step 1: After pretreatment, the molten iron is smelted in a converter for 42 minutes at a tapping temperature of 1600℃. After smelting, it is transferred to an LF furnace for refining at 1600℃ for 50 minutes at a tapping temperature of 1580℃. Argon is blown throughout the process. After refining, the molten steel enters the tundish through the sliding nozzle at the bottom of the ladle. The molten steel temperature in the tundish is 1545℃. Then, it is cast using a continuous casting machine at a speed of 3.6 m / s. The cooling water flow rate of the continuous casting crystallizer is controlled at 6000 L / min, and the crystallizer water temperature is 40℃. The protective slag used in the continuous casting crystallizer is a special high-basicity protective slag for medium carbon steel with a basicity of 1.33. The slab thickness is controlled at 65 mm. Step 2: After the continuous casting billet cast in Step 1 is cooled in the second cooling section, it enters the soaking furnace. The temperature of the continuous casting billet entering the furnace is 950℃, the heating temperature is 1150℃, and the residence time of the continuous casting billet in the furnace is 17 minutes.

[0021] Step 3: After the continuously cast billet heated in Step 2 is taken out of the furnace, it is descaled. The descaling inlet pressure is 20 MPa and the outlet pressure is 30 MPa. After one high-pressure water descaling, it enters the 6-stand continuous rolling mill for rolling. The continuous rolling start temperature is 1050℃ and the finish rolling temperature is 910℃. The secondary descaling water after the F1 / F2 stands is turned off, and the cooling water between the F1-F3 stands is turned off. Step 4: After the strip rolled in Step 3 exits the F6 last stand, it is tested by a multi-function instrument and then cooled to the coiling temperature of 830℃ through an 8-section laminar flow cooling section. After cooling, the coil is made using the coiling tension set by the secondary PSC model. The coil is then placed between other coils from the production line and air-cooled to room temperature to obtain a ferrite + pearlite microstructure.

[0022] Example 3 The raw material for the coil consists of the following chemical composition by weight percentage: C: 0.18%, with the C content controlled at a narrow percentage of 0.18%; Si: 0.35%, Mn: 0.65%, P: 0.021%, S: 0.008%, Als: 0.045%, Cr: 0.95%, Mo: 0.55%, with the remainder being unavoidable trace elements such as Fe and Ca. Step 1: After pretreatment, the molten iron is smelted in a converter for 44 minutes at a tapping temperature of 1620℃. After smelting, it is then transferred to an LF furnace for refining at 1650℃ for 60 minutes, with a tapping temperature of 1590℃. Argon is blown throughout the process. After refining, the molten steel enters the tundish through the sliding nozzle at the bottom of the ladle. The tundish temperature is 1555℃. The steel is then cast using a continuous casting machine at a speed of 3.6 m / s. The cooling water flow rate of the continuous casting crystallizer is controlled at 6400 L / min, and the crystallizer water temperature is 41℃. A special high-basicity protective slag for medium carbon steel is used in the continuous casting crystallizer, with a basicity of 1.34. The slab thickness is controlled at 70 mm. Step 2: After the continuous casting billet cast in Step 1 is cooled in the second cooling section, it enters the soaking furnace. The temperature of the continuous casting billet entering the furnace is 980℃, the heating temperature is 1180℃, and the residence time of the continuous casting billet in the furnace is 20 minutes.

[0023] Step 3: After the continuously cast billet heated in Step 2 is taken out of the furnace, it is descaled. The descaling inlet pressure is 21 MPa and the outlet pressure is 31 MPa. After one high-pressure water descaling, it enters the 6-stand continuous rolling mill for rolling. The continuous rolling start temperature is 1080℃ and the finish rolling temperature is 940℃. The secondary descaling water after the F1 / F2 stands is turned off, and the cooling water between the F1-F3 stands is turned off. Step 4: After the strip rolled in Step 3 exits the F6 last stand, it is tested by a multi-function instrument and then cooled to the coiling temperature of 850℃ through an 8-section laminar flow cooling section. After cooling, the coil is made using the coiling tension set by the secondary PSC model. The coil is then placed between other coils from the production line and air-cooled to room temperature to obtain a ferrite + pearlite microstructure.

[0024] As shown in Table 1, the finished product produced by this process meets and exceeds the industry standard GB / T 3077-2015 in terms of yield strength, tensile strength, and elongation after fracture. Furthermore, the performance values ​​of the finished product are significantly higher than those in the industry standard. This process is simple, has low production costs, and produces stable mechanical properties. It fully utilizes existing CSP technology and equipment, employs a narrow composition control of carbon content, adopts a medium-carbon, low-manganese scheme, and comprehensively utilizes controlled rolling and cooling technologies. It can produce thin-gauge low-alloy steel coils resistant to low-temperature impact without the need for traditional heat treatment processes, fully meeting user requirements. The thickness of the produced coils can be set according to usage needs. This manufacturing process can be implemented in most CSP continuous casting and rolling production lines, exhibiting strong versatility, high operability for large-scale industrial production, and ease of production.

Claims

1. A CSP process for producing heat-resistant 15CrMo heat-resistant alloy steel hot-rolled coils without heat treatment, characterized in that: The raw material of the coil is composed of the following chemical composition by weight percentage: C: 0.16-0.18, Si: 0.20-0.35, Mn: 0.45-0.65, P: ≤0.023, S: ≤0.010, Als: 0.020-0.045, Cr: 0.85-0.95, Mo: 0.45-0.55, with the remainder being Fe, Ca, and other unavoidable trace elements; The production method includes the following steps: Step 1: After pretreatment of molten iron, it is smelted in a converter, then refined in an LF furnace with argon blowing throughout the process. After refining, the molten steel is fed into the tundish and then cast through a continuous casting machine. The protective slag for the continuous casting crystallizer is a special protective slag for medium carbon steel with high basicity and a basicity of 1.32-1.

34. Step 2: After the continuous casting billet cast in Step 1 is cooled in the second cooling section, it enters the soaking furnace. The temperature of the continuous casting billet entering the furnace is 920-980℃, and the heating temperature is 1120-1180℃. Step 3: After the continuously cast billet heated in Step 2 is taken out of the furnace, it is descaled. After one high-pressure water descaling, it enters the 6-stand continuous rolling mill for rolling. The final rolling temperature is 880-940℃. The secondary descaling water after F1 and F2 stands is turned off, and the cooling water between F1 and F3 stands is turned off. Step 4: After the strip rolled in Step 3 exits the F6 last stand, it is inspected and then cooled to the coiling temperature. After cooling, a coil is made using the set coiling tension. The coil is then air-cooled to room temperature to obtain a ferrite + pearlite structure. The rolled strip is cooled through 8 laminar flow cooling sections, and the coiling temperature is 810-850℃.

2. The CSP process production method for a heat-treatable 15CrMo heat-resistant alloy steel hot-rolled coil without heat treatment according to claim 1, characterized in that: In step one, the converter smelting time is 40-44 minutes, and the converter tapping temperature is 1580-1620℃.

3. The CSP process production method for a heat-treatable 15CrMo heat-resistant alloy steel hot-rolled coil without heat treatment according to claim 1, characterized in that: In step one, the refining temperature in the LF furnace is >1500℃, the refining time is 45-60min, and the furnace exit temperature is 1570-1590℃.

4. The CSP process production method for heat-resistant 15CrMo heat-resistant alloy steel hot-rolled coils according to claim 1, characterized in that: In step one, the molten steel temperature in the tundish is 1535-1555℃, the continuous casting machine speed is 3.6m / s, the cooling water flow rate of the continuous casting crystallizer is controlled at 5600-6400L / min, the crystallizer water temperature is 40-41℃, and the slab thickness is controlled at 60-70mm.

5. The CSP process production method for a heat-treatable 15CrMo heat-resistant alloy steel hot-rolled coil without heat treatment according to claim 1, characterized in that: In step two, the continuous casting billet stays in the heating furnace for 15-20 minutes.

6. The CSP process production method for a heat-treatable 15CrMo heat-resistant alloy steel hot-rolled coil without heat treatment according to claim 1, characterized in that: In step three, the descaling inlet pressure is ≥19 MPa, the outlet pressure is ≥29 MPa, and the continuous rolling start temperature is 1020-1080℃.

7. The CSP process production method for a heat-treatable 15CrMo heat-resistant alloy steel hot-rolled coil without heat treatment according to claim 1, characterized in that: In step four, after cooling, the winding is performed using a two-stage PSC model.

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