CN108385037A - A kind of ocean platform Ti microalloying medium managese steel cut deals and preparation method thereof - Google Patents

Abstract

A kind of ocean platform Ti microalloying medium managese steel cut deals and preparation method thereof, which is characterized in that its chemical composition is by weight percentage：C：0.03~0.1%, Mn：4.0~8.0%, Ti：0.02~0.10%, Si：0.10~0.40%, S：＜ 0.005%, P：＜ 0.005%, Al：0.02~0.05%, Cr：0.10~0.40%, Ni：0.10~0.30%, Mo：0.10~0.40%, Cu：0.10~0.30%, remaining is Fe and other inevitable impurity；Preparation method：1) ocean platform is forged into blank with Ti microalloying medium managese steel cut deal alloy cast ingots, with being kept the temperature after stove heat, the blank after being heated；2) by the blank after heating, multistage hot deformation is carried out, is quenched after hot rolled plate is made；3) cut deal after quenching is put into stove and heats and keeps the temperature, be air-cooled to room temperature, obtain medium managese steel cut deal, be organized as tempered martensite and tiny adverse transformation austenite duplex structure.

Description

Ti microalloyed medium manganese steel plate for offshore platform and preparation method thereof

technical field

The invention belongs to the field of iron and steel production in the metallurgical industry, and in particular relates to a Ti microalloyed medium-manganese steel plate for offshore platforms and a preparation method thereof.

Background technique

Marine engineering equipment is the premise and foundation for the development of the national marine economy. It is in the core link of the marine industry value chain and has broad market application prospects. The average proven rates of my country's offshore oil and natural gas resources are 12.3% and 10.9%, respectively, which are far lower than the world's average proven rates of 73.0% and 60.5%. Compared with land, offshore oil and gas exploration and development have great potential. As an important part of offshore engineering equipment, the demand for medium and thick steel plates on the platform continues to expand, but my country still cannot meet the demand in the field of high-end offshore engineering equipment manufacturing, especially the special steel for core equipment. At present, China has about 70 % of marine engineering equipment and equipment need to be imported. Therefore, the development of marine engineering medium-thick steel plates with independent intellectual property rights, low energy consumption in the preparation process, and high strength and toughness is of strategic significance for improving my country's energy structure system and realizing a strong industrialized country.

As the development of oil and gas resources gradually develops from land and shallow seas to polar and deep sea regions, the demand for special performance steels with large specifications, ultra-high strength and toughness matching has increased sharply. The traditional 355MPa, 420MPa and 460MPa steel for offshore platforms can no longer meet the requirements of some high-grade steel for special occasions. It is difficult to ensure uniform distribution of composition, deformation and cooling rate in the thickness direction, resulting in large differences in strength and toughness in the thickness direction. At present, the high-strength and toughness medium-thick plates of traditional offshore platforms at home and abroad need to use niobium, vanadium, and titanium alloying components in terms of composition design. A large amount of expensive Ni-Mo is added to ensure the low-temperature impact toughness of the steel plate. In terms of manufacturing process , it is necessary to use multi-stage heat treatment to achieve uniform microstructure and properties in the thickness direction, resulting in high production costs and high energy consumption of steel plates.

Contents of the invention

Aiming at the current problems of uneven microstructure and properties in the thickness direction, complicated preparation process, and single strengthening mechanism of extra-thick plates, the invention provides a Ti micro-alloyed medium-manganese steel plate for offshore platforms and a preparation method thereof. The technical scheme of this method is:

A Ti microalloyed medium-manganese steel plate for offshore platforms, the chemical composition of which is: C: 0.03-0.1%, Mn: 4.0-8.0%, Ti: 0.02-0.10%, Si: 0.10-0.40 %, S: <0.005%, P: <0.005%, Al: 0.02～0.05%, Cr: 0.10～0.40%, Ni: 0.10～0.30%, Mo: 0.10～0.40%, Cu: 0.10～0.30%, the rest For Fe and other unavoidable impurities;

The medium-thick plate structure is a dual-phase structure of tempered martensite and fine reverse-transformed austenite.

The thickness of the medium plate is 20-100mm, the yield strength is 710-780MPa, the tensile strength is 855-920MPa, the elongation is 23.6-28.9%, and the impact energy at -60°C is greater than 100J.

A preparation method for Ti microalloyed medium-manganese steel plate for offshore platform, comprising the following process steps:

Step 1, billet heating:

Forge the ingot of Ti microalloyed medium-manganese steel medium-thick plate alloy for the offshore platform into a billet, heat it with the furnace to 1100-1250 ° C, keep it for 1-3 hours, and obtain the heated billet;

Step 2: Hot Rolling Treatment:

(1) The heated billet is subjected to multi-pass hot rolling, the total reduction rate is 28.6% to 85.7%, the starting rolling temperature is 960 to 1050°C, and the final rolling temperature is 880 to 970°C to obtain 20 to 100mm thick hot-rolled plate;

(2) Quenching: Rapidly water-cool the hot-rolled plate to room temperature at a cooling rate of 5-20° C./s to obtain a hot-rolled and quenched medium-thick plate.

Step 3: Tempering treatment:

After heating the furnace to 620-680°C, put the quenched medium-thick plate into the furnace to heat and keep it warm for 30-90 minutes, then air-cool to room temperature, and finally obtain Ti micro-alloyed medium-manganese steel medium-thick plate for offshore platforms.

The preparation method of the Ti microalloyed medium-manganese steel plate for the above-mentioned offshore platform, wherein:

In the step 1, the offshore platform forges a 140 mm thick billet with Ti microalloyed medium manganese steel plate alloy ingot.

In the step 2, 5-13 passes of hot rolling are carried out, and the reduction ratio of a single pass is 7-25%.

In the step 2, the microstructure of the plate after hot rolling and quenching is lath martensite and a small amount of retained austenite.

In the step 3, the microstructure of the tempered medium-thick plate is tempered martensite and fine reverse-transformed austenite bidirectional structure.

The advantage of the present invention is that: aiming at the technical problems existing in the existing ultra-high-strength steel for offshore platforms, the present invention carries out the research and development of Ti micro-alloyed medium-manganese steel plate, adopts low-carbon medium-manganese micro-alloyed design, and uses cheap The Mn element replaces the expensive Ni-Mo alloy system. Mn can significantly enhance the hardenability of the steel plate, and is a strong austenite stabilizing element, thereby enhancing the uniformity of the microstructure and properties in the thickness direction, and through ferrite-austenite The tempering process in the two-phase zone controls the content and stability of reverse transformed austenite, greatly improves the toughness and plasticity of the steel plate, and reduces the yield ratio. The innovative Ti microalloying technology is used to pin the original austenite grain boundary with TiN precipitates during the reheating process by adding Ti element, thereby inhibiting the abnormal growth of austenite and refining the quenched martensite plate Article, improve the fine-grain strengthening effect. During the tempering process in the ferrite-austenite two-phase region, the remaining Ti atoms combine with C atoms to form nanoscale TiC precipitates, which play a significant role in precipitation strengthening. In turn, a fine lath martensite and reverse transformed austenite dual phase structure is obtained, which effectively improves the strength and plastic toughness of the center of the steel plate. The medium manganese steel adopts micro-Ti treatment, which can greatly improve the welding performance, refine the structure of the welding heat-affected zone, and improve the low-temperature impact toughness. The yield strength of the prepared Ti microalloyed medium manganese steel plate is 710-780MPa, the tensile strength is 855-920MPa, the elongation is 23.6-28.9%, and the impact power at -60°C is greater than 100J. The test steel production process includes simple quenching and tempering treatment, the control operation is simple, no need to change the existing production equipment, and it is easy to realize industrialization.

Description of drawings

Fig. 1 is the technological schematic diagram of the preparation method of Ti microalloyed medium-manganese steel medium and thick plate in Embodiment 1 to 3 of the present invention for offshore platforms;

The metallographic structure of Ti microalloyed medium-manganese steel medium and thick plate prepared by Fig. 2 embodiment 2 of the present invention for offshore platform;

Fig. 3 is the EBSD structure morphology of Ti microalloyed medium-manganese steel plate for offshore platform prepared in Example 2 of the present invention.

Fig. 4 is the TEM structure morphology of Ti microalloyed medium-manganese steel plate for offshore platform prepared in Example 2 of the present invention.

Fig. 5 The TEM microstructure of the second phase of Ti microalloyed medium-manganese steel medium-thick plate prepared by Example 2 of the present invention

Specific implementation method

The hot-rolling mill that the present invention implements adopts is the Φ 450mm hot-rolling mill that Northeastern University Rolling Technology and State Key Laboratory of Continuous Rolling Automation design and manufacture;

The heating furnace used in the heat treatment of the present invention is a high-temperature box-type resistance furnace, and the model is RX4-85-13B;

The equipment for observing metallographic structure in the embodiment of the present invention is Leica DMIRM-2500M metallographic microscope;

The equipment for observing the SEM structure in the embodiment of the present invention is a Zeiss Ultra55 scanning electron microscope;

The equipment for observing the TEM structure in the embodiment of the present invention is a Tecnai G ² F20 field emission transmission electron microscope from FEI Company.

The process schematic diagram of the preparation method of Ti microalloyed medium-manganese steel plate for offshore platform in the following embodiment is shown in FIG. 1 .

Example 1

A Ti microalloyed medium-manganese steel plate for offshore platforms, the chemical composition of which is: C: 0.10%, Mn: 4.0%, Ti: 0.02%, Si: 0.12%, S: 0.001%, P : 0.004%, Al: 0.02%, Cr: 0.40%, Ni: 0.11%, Mo: 0.10%, Cu: 0.12%, and the rest are Fe and other unavoidable impurities.

A preparation method for Ti microalloyed medium-manganese steel plate for offshore platform, comprising the following process steps:

Step 1, billet heating:

The ocean platform is forged with a Ti microalloyed medium-manganese steel medium-thick plate alloy ingot to form a 140mm thick billet, heated to 1250°C with the furnace, and kept for 1 hour to obtain the heated billet. The chemical composition of the heated billet is: C: 0.10 %, Mn: 4.0%, Ti: 0.02%, Si: 0.12%, S: 0.001%, P: 0.004%, Al: 0.02%, Cr: 0.40%, Ni: 0.11%, Mo: 0.10%, Cu: 0.12 %, the rest is Fe and other unavoidable impurities.

Step 2: Hot Rolling Treatment:

(1) Hot-rolling the heated billet for 13 times, the reduction rate in a single pass is 23%, the total reduction rate is 85.7%, the starting rolling temperature is 960°C, and the final rolling temperature is 880°C to obtain 20mm thick hot-rolled plate;

(2) Quenching: The hot-rolled plate is quickly water-cooled to room temperature at a cooling rate of 20°C/s to obtain a hot-rolled and quenched medium-thick plate, whose microstructure is lath-shaped martensite and a small amount of retained austenite .

Step 3: Tempering treatment:

After the heating furnace was heated up to 620°C, the quenched medium-thick plate was put into the furnace to be heated and kept for 30 minutes, and then air-cooled to room temperature. Finally, Ti micro-alloyed medium-manganese steel medium-thick plate for offshore platforms was obtained, and its microstructure was as follows: Two-way structure of fire martensite and fine reverse transformed austenite.

The mechanical properties of the medium-thick plate with a thickness of 20mm prepared in this embodiment: the yield strength is 780MPa, the tensile strength is 855MPa, the elongation after fracture is 23.6%, and the impact energy at -60°C is 120J.

Example 2

A Ti microalloyed medium-manganese steel plate for offshore platforms, the chemical composition of which is: C: 0.06%, Mn: 6.0%, Ti: 0.05%, Si: 0.25%, S: 0.001%, P : 0.003%, Al: 0.024%, Cr: 0.10%, Ni: 0.20%, Mo: 0.25%, Cu: 0.20%, and the rest are Fe and other unavoidable impurities.

A preparation method for Ti microalloyed medium-manganese steel plate for offshore platform, comprising the following process steps:

Step 1, billet heating:

The offshore platform is forged with a Ti microalloyed medium-manganese steel medium-thick plate alloy ingot to form a 140mm thick billet, heated to 1200°C with the furnace, and kept for 2 hours to obtain the heated billet. The chemical composition of the heated billet is: C: 0.06 %, Mn: 6.0%, Ti: 0.05%, Si: 0.25%, S: 0.001%, P: 0.003%, Al: 0.024%, Cr: 0.10%, Ni: 0.20%, Mo: 0.25%, Cu: 0.20 %, the rest is Fe and other unavoidable impurities.

Step 2: Hot Rolling Treatment:

(1) The heated billet is hot-rolled 9 times, the reduction rate in a single pass is 18%, the total reduction rate is 57.1%, the starting rolling temperature is 1000°C, and the final rolling temperature is 950°C, and the obtained 60mm thick hot-rolled plate;

(2) Quenching: The hot-rolled plate is quickly water-cooled to room temperature at a cooling rate of 10°C/s to obtain a hot-rolled and quenched medium-thick plate, whose microstructure is lath-shaped martensite and a small amount of retained austenite .

Step 3: Tempering treatment:

After the heating furnace was heated to 650°C, the quenched plate was placed in the furnace to heat and hold for 60 minutes, then air-cooled to room temperature, and finally Ti microalloyed medium-manganese steel plate for offshore platforms was obtained, the microstructure of which was as follows: Two-way structure of fire martensite and fine reverse transformed austenite.

The metallographic structure of the medium-thick plate with a thickness of 60mm obtained in this embodiment is shown in Figure 2, the EBSD structure is shown in Figure 3, the TEM structure is shown in Figure 4, and the second phase TEM structure The appearance is shown in Figure 5, and its mechanical properties: yield strength is 745MPa, tensile strength is 870MPa, elongation after fracture is 26.5%, and impact energy at -60°C is 135J.

Example 3

A Ti microalloyed medium-manganese steel plate for offshore platforms, the chemical composition of which is: C: 0.03%, Mn: 8.0%, Ti: 0.10%, Si: 0.39%, S: 0.002%, P : 0.003%, Al: 0.05%, Cr: 0.40%, Ni: 0.30%, Mo: 0.35%, Cu: 0.30%, and the rest are Fe and other unavoidable impurities.

A preparation method for Ti microalloyed medium-manganese steel plate for offshore platform, comprising the following process steps:

Step 1, billet heating:

The ocean platform is forged with a Ti microalloyed medium-manganese steel medium-thick plate alloy ingot to form a 140mm thick billet, heated to 1100°C with the furnace, and kept for 3 hours to obtain the heated billet. The chemical composition of the heated billet is: C: 0.03 %, Mn: 8.0%, Ti: 0.10%, Si: 0.39%, S: 0.002%, P: 0.003%, Al: 0.05%, Cr: 0.40%, Ni: 0.30%, Mo: 0.35%, Cu: 0.30 %, the rest is Fe and other unavoidable impurities.

Step 2: Hot Rolling Treatment:

(1) Hot rolling the heated billet for 3 times, the single pass reduction ratio is 7%, the total reduction ratio is 28.6%, the starting rolling temperature is 1050°C, and the final rolling temperature is 970°C, and the obtained 100mm thick hot-rolled plate;

(2) Quenching: The hot-rolled plate is quickly water-cooled to room temperature at a cooling rate of 5°C/s to obtain a hot-rolled medium-thick plate after quenching, and its microstructure is lath-shaped martensite and a small amount of retained austenite .

Step 3: Tempering treatment:

After the heating furnace was heated up to 680 °C, the quenched plate was put into the furnace to heat and hold for 90 minutes, then air-cooled to room temperature, and finally Ti microalloyed medium manganese steel plate for offshore platforms was obtained, the microstructure of which was as follows: Two-way structure of fire martensite and fine reverse transformed austenite.

The mechanical properties of the medium-thick plate with a thickness of 100mm obtained in this embodiment: the yield strength is 710MPa, the tensile strength is 920MPa, the elongation after fracture is 28.9%, and the impact energy at -60°C is 110J.

Claims (8)

1. a kind of ocean platform Ti microalloying medium managese steel cut deals, which is characterized in that its chemical composition by weight percentage For：C：0.03~0.1%, Mn：4.0~8.0%, Ti：0.02~0.10%, Si：0.10~0.40%, S：＜ 0.005%, P： ＜ 0.005%, Al：0.02~0.05%, Cr：0.10~0.40%, Ni：0.10~0.30%, Mo：0.10~0.40%, Cu： 0.10~0.30%, remaining is Fe and other inevitable impurity.

2. ocean platform described in claim 1 Ti microalloying medium managese steel cut deals, which is characterized in that the cut deal group It is woven to tempered martensite and tiny adverse transformation austenite duplex structure.

3. ocean platform described in claim 1 Ti microalloying medium managese steel cut deals, which is characterized in that the cut deal is thick Degree be 20~100mm, yield strength be 710~780MPa, tensile strength be 855~920MPa, elongation percentage be 23.6~ 28.9%, -60 DEG C of ballistic work ＞ 100J.

4. the ocean platform described in claim 1 preparation method of Ti microalloying medium managese steel cut deals, including following technique Step：

Step 1, blank heating：

Ocean platform is forged into blank with Ti microalloying medium managese steel cut deal alloy cast ingots, with stove heat to 1100~1250 DEG C, keep the temperature 1~3h, the blank after being heated；

Step 2：Hot rolling treatment：

(1) by the blank after heating, multistage hot deformation is carried out, total reduction is 28.6%~85.7%, start rolling temperature is 960~ 1050 DEG C, finishing temperature is 880~970 DEG C, and the hot rolled plate of 20~100mm thickness is made；

(2) it quenches：By hot rolled plate, with the quick water cooling of the cooling velocity of 5~20 DEG C/s to room temperature, the middle thickness after rolling and quenching is obtained Plate.

Step 3：Temper：

After heating furnace is warming up to 620~680 DEG C, cut deal after quenching is put into stove and heats and keep the temperature 30~90min, it is then empty It is cooled to room temperature, finally obtains ocean platform Ti microalloying medium managese steel cut deals.

5. the ocean platform according to claim 4 preparation method of Ti microalloying medium managese steel cut deals, feature exist In in the step 1, ocean platform is forged into the blank of 140mm thickness with Ti microalloying medium managese steel cut deal alloy cast ingots.

6. the ocean platform according to claim 4 preparation method of Ti microalloying medium managese steel cut deals, feature exist In in the step 2,5~13 passage hot rollings of progress, single pass reduction ratio is 7~25%.

7. the ocean platform according to claim 4 preparation method of Ti microalloying medium managese steel cut deals, feature exist In in the step 2, the cut deal microscopic structure after rolling and quenching is lath martensite and a small amount of retained austenite.

8. the ocean platform according to claim 4 preparation method of Ti microalloying medium managese steel cut deals, feature exist In in the step 3, the cut deal microscopic structure after tempering is tempered martensite and two-way group of tiny adverse transformation austenite It knits.