CN102304667A - X100 pipeline steel plate with good low temperature toughness and preparation method thereof - Google Patents

Abstract

An X100 pipeline steel plate with excellent low-temperature toughness and a preparation method thereof belong to the technical field of high-strength pipeline steel production. The mass percentage of chemical composition of steel is: C: 0.03～0.07%, Si: 0.10～0.45%, Mn: 1.50～1.79%, P: ≤0.012%, S: ≤0.003%, Alt: 0.02～0.06%, Nb: 0.05～0.10%, V: 0.02～0.08%, Ti: 0.005～0.040%, Ni: 0.20～0.50%, Mo: 0.20～0.50%, N: ≤0.008%, H: ≤0.0002%, the balance is Fe and Unavoidable impurity elements. The preparation method includes molten iron desulfurization, converter smelting, out-of-furnace refining, continuous casting, heating, rolling, cooling and straightening. The advantage is that X100 steel plate has excellent low temperature toughness, Charpy impact toughness: -20 ℃, full-size 10×10×55mm V-notch specimen, Charpy impact energy (CNV) ≥ 330J, Charpy impact shear area ≥ 90 %; drop weight performance: -20 ℃, full wall thickness sample drop weight shear area (DWTT SA) ≥ 85%.

Description

A kind of X100 pipeline steel plate with excellent low temperature toughness and its preparation method

technical field

The invention belongs to the technical field of high-strength pipeline steel production, and in particular relates to an X100 pipeline steel plate with excellent low-temperature toughness and a preparation method thereof.

Background technique

As an efficient and clean energy, natural gas is attracting more and more attention. Since natural gas fields are generally located in remote desert areas far from the market, how to safely and economically transport natural gas to the consumer market has always been one of the key issues in the development of the natural gas industry. The most effective way to reduce the cost of long-distance natural gas transmission is through technological innovation and the use of higher pressure and higher strength pipelines. Increasing the transmission pressure is the most obvious trend in the development of long-distance natural gas pipelines. The transmission pressure of natural gas pipelines has increased from the initial 0.2MPa to 14MPa in 50 years. Increased delivery pressures require higher strength pipeline steels. Today, the construction of long-distance natural gas pipelines around the world has developed from the X52, X60 and X65 pipeline steel used in the past to the pipeline steel dominated by X70 and X80, and X100-X120 ultra-high-strength pipeline steel is being developed.

The development of X100 and X80 started almost at the same time, but the results of their actual application are quite different. X80 has been widely used in the world, especially since the beginning of this century, three X80 long-distance natural gas pipelines have been built successively in North America and Asia (the Cheyenne Plain Pipeline in the United States, the Rocky Pipeline and the Second West-East Gas Pipeline in my country. Pipeline) has made the X80 long-distance natural gas pipeline grow by leaps and bounds, but the X100 pipeline is still in the construction stage of the test section. During the period before and after the 2006 International Pipeline Conference, the research and development of X100 and X120 became a hot topic for a time. Pipeline steel researchers all over the world focused on the research and development of X100. The process technology and product performance of X100 pipeline steel have made great achievements made some progress.

But so far, according to the literature or patents about X100 pipeline steel in the world, the low-temperature toughness index of X100 is relatively low, and the Charpy impact energy at -20°C is mostly distributed between 150 and 290J. Therefore, experts in the pipeline steel industry once It is believed that X100 pipeline steel cannot rely on the toughness of the steel pipe itself for crack arrest, and crack arresters must be added, and the project cost will be greatly increased. If the Charpy impact toughness of the base metal of X100 pipeline steel cannot reach more than 300J, the prospect of large-scale engineering application of X100 products will be greatly reduced and unrealistic. Therefore, X100 pipeline steel with excellent low-temperature toughness and its technology are urgently needed to be developed.

Contents of the invention

The purpose of the present invention is to provide an X100 pipeline steel plate with excellent low-temperature toughness and its preparation method, which solves the above-mentioned shortcomings of low low-temperature toughness index of X100 in the prior art, and the product has self-cracking ability.

The chemical composition of the steel plate of the present invention is: C: 0.03-0.07%, Si: 0.10-0.45%, Mn: 1.50-1.79%, P: ≤0.012%, S: ≤0.003%, Alt: 0.02-0.06%, Nb: 0.05～0.10%, V: 0.02～0.08%, Ti: 0.005～0.040%, Ni: 0.20～0.50%, Mo: 0.20～0.50%, N: ≤0.008%, H: ≤0.0002%, and the balance is Fe and unavoidable impurity elements; both percentages by weight.

Using the above-mentioned chemical composition design, through RH vacuum treatment + enhanced controlled rolling and controlled cooling, the present invention has prepared a yield strength of more than 690MPa, a tensile strength of more than 760MPa, and a yield strength ratio of less than 0.92;

Charpy impact toughness: -20°C, full-size 10×10×55mm V-notch specimen, Charpy impact energy (CNV) ≥ 330J, Charpy impact shear area ≥ 90%.

The preparation method of the present invention includes molten iron desulfurization, converter smelting, refining outside the furnace, continuous casting, heating, rolling, cooling, and straightening procedures; the following technical parameters are controlled in the process:

(1) RH refining: argon flow rate 800-1200NL/min, vacuum treatment time 15-35min.

(2) Heating system: heat the billet to 1150-1250°C, and soak for 40-60 minutes.

(3) Rolling process: The steel billet is rolled in two stages, and the middle is waited for temperature. The final rolling temperature of the first stage is 980-1060°C, and the thickness of the intermediate billet is controlled at 3-5 times the thickness of the finished product. The rolling temperature is controlled at 840-890°C, and the final rolling temperature is controlled at 760-820°C.

(4) Cooling process: water cooling is carried out quickly after hot rolling, the water inlet temperature is controlled at 750-810°C, the final cooling temperature is controlled at 90-190°C, and the cooling rate is controlled at 15-25°C/s.

The key points of the content of the present invention are based on the following understanding: Mn improves the strength through solid solution strengthening, and can also reduce the γ-α transformation temperature, thereby refining the ferrite grains. However, as we all know, Mn is an element that is easy to segregate, which will cause serious segregation in the center of the slab, resulting in serious banded structure in the center of the steel plate, causing anisotropy, resulting in delamination or brittle fracture at the impact fracture, and greatly reducing the low temperature toughness and toughness of the steel plate. Anti-HIC performance. The present invention has carried out a large number of experiments, by adding different Mn content, finds: when the content of Mn is greater than 1.90%, the tensile strength of steel plate is very high, but impact toughness is relatively poor; When the content of Mn is lower than 1.80%, through With reasonable process control, the strength and toughness of the steel plate can achieve a better match, as shown in Figure 2. Therefore, the content of Mn in the present invention is controlled in the range of 1.50-1.79%, and the good strength and toughness of the X100 pipeline steel is obtained.

Nb is one of the most important elements in modern microalloyed pipeline steels, and it has a significant role in solid solution strengthening and grain refinement. The strain-induced precipitation of Nb(NC) in the hot rolling process hinders the recovery and recrystallization of deformed austenite, and through controlled rolling and controlled cooling, the deformed austenite rolled in the non-recrystallized zone in the finishing rolling stage is transformed into Fine phase transformation products, thereby improving the strength and toughness of steel. In addition, the nano-scale Nb(NC) precipitated after the phase transformation also plays a precipitation strengthening effect, further improving the toughness of the thick wall pipeline steel. An appropriate amount of vanadium is added in the composition design, mainly used in combination with Nb, and the growth of austenite grains is inhibited by the fine precipitation of NbV(CN) in the austenite during the heating process. At the same time, an appropriate amount of vanadium The addition of alloy can improve the strength and stability of X100.

Mo: a strong bainite transformation control element. In high-strength microalloy steel, adding an appropriate amount of Mo element can obtain obvious bainite structure, and at the same time, due to the transformation to low temperature, the phase transformation structure can be further refined, and the strength and toughness of the steel can be greatly improved. It can also effectively reduce the yield-to-strength ratio. In the ultra-high-strength X100 pipeline steel, by adding a certain amount of Mo alloy, the phase transformation strengthening effect can be realized, and the strength stability and low temperature impact toughness of the X100 pipeline steel can be improved. Therefore, in the present invention, the Mo content is controlled in the range of 0.20-0.50%, and a fine and uniform lath bainite structure and excellent strength and toughness are obtained.

Ni: Nickel alloy can improve the strength of steel through solid solution strengthening, make up for the strength decrease caused by the increase of thickness in thick gauge steel, and improve the low temperature toughness of thick gauge pipeline steel. In ultra-high strength X100 pipeline steel, Ni alloy is used to improve the strength stability and low temperature toughness of X100. The present invention proves through a large number of experiments that when the Ni content is controlled below 0.20%, the Charpy impact energy of the steel plate basically changes little; Low temperature toughness of steel plate.

The basis for adopting this production process is: under the conditions of deep vacuum and strong stirring in the RH refining furnace, the nitrogen atoms and hydrogen atoms in the steel are easy to diffuse to the Ar bubbles in the molten steel, so that as the Ar bubbles float up in the steel, the steel The nitrogen content and hydrogen content in the steel are continuously reduced. By increasing the argon flow rate and prolonging the vacuum treatment time, the gas content in the molten steel is low, the inclusions are small, and the cleanliness of the molten steel is high, which lays the foundation for improving the low temperature toughness of the product. By controlling the heating temperature of the slab and the soaking time of the slab, the full dissolution of the second phase is ensured, and the growth of the original austenite grain is effectively inhibited; at the same time, the final rolling temperature of the first stage and the thickness of the intermediate slab to be heated are controlled to make the austenite The bulk grains are fully refined and homogenized; the second stage adopts low-temperature controlled rolling process, the key is to complete the second-stage deformation at a lower rolling temperature, and the starting rolling temperature is controlled in the range of 840-890°C, and Ensure that the termination rolling temperature is in the range of 760-820°C, make full use of the effect of low-temperature controlled rolling, accumulate dislocations inside the hardened austenite, provide more nucleation points for subsequent phase transformation, and finally enter water quickly after rolling, Accelerated cooling begins before the phase transformation to obtain a refined, uniform and flat bainite transformation structure, which improves the strength and low-temperature toughness of the X100 steel plate. The present invention has carried out a large number of tests, and by adopting different final cooling temperatures, it is found that: when the final cooling temperature is greater than 300°C, the tensile strength of the steel plate basically meets the X100 standard requirements, but the Charpy impact toughness is poor; when the final cooling temperature is less than At 200°C, the strength and toughness of the steel plate can reach a good match, the tensile strength is high, and the Charpy impact toughness is excellent, as shown in Figure 3. Therefore, in the present invention, the final cooling temperature is controlled in the range of 90-190° C., and the good low-temperature toughness of the X100 pipeline steel is obtained.

The invention has the advantages that: the X100 pipeline steel plate with excellent low-temperature toughness prepared by the invention adopts a unique composition design and production process system, and the product has Charpy impact toughness capable of self-cracking. Through a large number of tests in the composition design, the segregation-prone elements Mn, P, S, etc. that have an impact on low-temperature toughness are limited, and the alloying elements Nb, Mo, Ni, etc. that are suitable for grain refinement and phase transformation strengthening are increased, and the The strength and low temperature toughness of the product are improved. Its production process adopts RH refining technology and optimized controlled cooling technology, which reduces the gas elements N, H, etc. that are harmful to low-temperature toughness in molten steel, refines austenite grains and bainite structure, and the product has a high Matching toughness. The performance of the X100 pipeline steel plate produced according to the technical solution described in this patent reaches the following levels:

(1) Tensile properties: Yield strength ≥ 690MPa, tensile strength ≥ 760MPa, yield ratio ≤ 0.92.

(2) Toughness performance: The Charpy V-notch impact energy of a 10×10×55mm sample at -20°C is above 330J, and the average shear area of the falling weight performance (DWTT) at -20°C is ≥85%.

Description of drawings

Fig. 1 is a metallographic structure diagram of the present invention.

Fig. 2 is the effect of different Mn contents on the strength and toughness of the steel plate in the present invention.

Fig. 3 is the effect of different final cooling temperatures on the strength and toughness of the steel plate in the present invention.

Detailed ways

According to the invention, an X100 pipeline steel plate with excellent low-temperature toughness and its preparation method are smelted on a 100-ton converter, refined on a 100-ton RH refining furnace, and produced by controlled rolling and controlled cooling on a 4300mm production line. The present invention will be further described below by way of examples. The chemical composition of the steel plate in the embodiment is shown in Table 1, the process system of the embodiment is described below, and the mechanical properties of the embodiment are shown in Table 2:

Example chemical composition

Table 1. The chemical composition (wt%) of the X100 pipeline steel plate embodiment of the present invention with excellent low temperature toughness

Embodiment process system

Example 1

The product specification is a steel plate with a thickness of 22.0mm and a width of 3725mm. The argon flow rate of the RH refining furnace is 1200NL/min, and the vacuum treatment time is 20min. Slab heating temperature: 1160°C, soaking time 60min; first stage final rolling temperature 1000°C, waiting temperature 3t, second stage rolling start temperature 840°C, steel plate finish rolling temperature 780°C; In the water cooling area, the inlet water temperature is 770°C, the final cooling temperature is 90°C, and the cooling rate is 15°C/s. The comprehensive mechanical properties of the steel plate are shown in Table 2 below.

Example 2

The product specification is a steel plate with a thickness of 22.0mm and a width of 3725mm. The argon flow rate of the RH refining furnace is 1100NL/min, and the vacuum treatment time is 21min. Slab heating temperature: 1180°C, soaking time 50min; first stage finish rolling temperature 1010°C, waiting temperature 3.5t, second stage start rolling temperature 850°C, steel plate finish rolling temperature 790°C; Entering the water cooling area, the entering water temperature is 780°C, the final cooling temperature is 190°C, and the cooling rate is 20°C/s. The comprehensive mechanical properties of the steel plate are shown in Table 2 below.

Example 3

The product specification is a steel plate with a thickness of 18.4mm and a width of 3725mm. The argon gas flow rate of the RH refining furnace is 1000NL/min, and the vacuum treatment time is 25min. Slab heating temperature: 1200°C, soaking time 50min; first stage final rolling temperature 1020°C, waiting temperature 3.5t, second stage start rolling temperature 870°C, steel plate end rolling temperature 800°C; Entering the water cooling area, the entering water temperature is 790°C, the final cooling temperature is 150°C, and the cooling rate is 22°C/s. The comprehensive mechanical properties of the steel plate are shown in Table 2 below.

Example 4

The product specification is a steel plate with a thickness of 15.0mm and a width of 3118mm. The argon flow rate of the RH refining furnace is 900NL/min, and the vacuum treatment time is 30min. Slab heating temperature: 1220°C, soaking time 40min; first stage final rolling temperature 1040°C, waiting temperature 4t, second stage rolling start temperature 890°C, steel plate end rolling temperature 810°C; In the water cooling area, the inlet water temperature is 800°C, the final cooling temperature is 120°C, and the cooling rate is 23°C/s. The comprehensive mechanical properties of the steel plate are shown in Table 2 below.

Example 5

The product specification is a steel plate with a thickness of 15.0mm and a width of 3118mm. The argon gas flow rate of the RH refining furnace is 900NL/min, and the vacuum treatment time is 35min. Slab heating temperature: 1220°C, soaking time 60min; first stage final rolling temperature 1050°C, waiting temperature 5t, second stage rolling start temperature 890°C, steel plate end rolling temperature 810°C; In the water cooling area, the inlet water temperature is 800°C, the final cooling temperature is 100°C, and the cooling rate is 25°C/s. The comprehensive mechanical properties of the steel plate are shown in Table 2 below.

Example mechanical properties

The metallographic structure of the medium-thick plate of X100 pipeline steel with excellent low-temperature toughness produced by the present invention is uniform and fine lath bainite structure, refer to the accompanying drawing 1 . The mechanical properties of the steel plates of the examples are shown in Table 2 below.

Table 2. Embodiment X100 steel plate mechanical properties

The invention adopts a special alloy formula and utilizes an accelerated cooling rate device (ACC) to realize ultra-low temperature phase transformation, fully refine the phase transformation structure, and improve the strength and toughness of the X100 pipeline steel. At the same time, through the RH refining furnace, the argon flow rate is appropriately increased and the vacuum treatment time is prolonged, so that the gas content in the molten steel is low, the inclusions are small, and the cleanliness of the molten steel is high, laying a foundation for improving the low-temperature toughness of the product. The X100 pipeline steel plate produced by the present invention has a Charpy impact toughness of more than 330J at -20°C, which makes the X100 pipeline steel itself have a self-cracking ability, and does not need to be equipped with a crack arrester, and the project cost will be greatly reduced, making the X100 The prospect of large-scale engineering application of the product becomes possible, and it can be widely used in the construction of oil and gas pipeline projects in the near future.

Claims (3)

1. the X100 pipeline steel plate of an excellent in low temperature toughness; It is characterized in that: said steel plate chemical ingredients is: C:0.03～0.07%; Si:0.10～0.45%; Mn:1.50～1.79%; P :≤0.012%; S :≤0.003%; Alt:0.02～0.06%, Nb:0.05～0.10%, V:0.02～0.08%; Ti:0.005～0.040%; Ni:0.20～0.50%, Mo:0.20～0.50%, N :≤0.008%; H :≤0.0002%, surplus is Fe and inevitable impurity element; Be weight percentage.

2. the X100 pipeline steel plate of excellent in low temperature toughness as claimed in claim 1, it is characterized in that: the performance of steel plate is:

Yield strength reaches more than the 690MPa, and tensile strength is more than 760MPa, and yield tensile ratio is below 0.92;

Summer is than impacting toughness :-20 ℃, and full-scale 10 * 10 * 55mm v-notch sample, Charpy-V impact power (CNV) >=330J, the summer is than impacting shear area >=90%;

Block hammer performance :-20 ℃, the total wall thickness sample shear area (DWTT SA) >=85% of dropping hammer.

3. the preparation method of the X100 pipeline steel plate of the described excellent in low temperature toughness of claim 1; Comprise desulfurizing iron, converter smelting, external refining, continuous casting, heating, rolling, cooling, aligning operation, it is characterized in that: the following technical parameter of control in the technology:

(1) RH refining: argon flow amount 800～1200NL/min, vacuum processing time 15～35min;

(2) heating cycle: steel billet is heated to 1150-1250 ℃, soaking zone time 40～60min;

(3) rolling technology: steel billet is rolled in two stages; Temperature is treated in the centre, and fs finishing temperature 980-1060 ℃, intermediate blank treats that temperature thickness is controlled at 3-5 times of finished product thickness; The subordinate phase start rolling temperature is controlled at 840-890 ℃, and finishing temperature is controlled at 760-820 ℃ of scope;

(4) process for cooling: carry out water-cooled after the hot rolling fast, go into water temp and be controlled at 750-810 ℃, final cooling temperature is controlled at 90-190 ℃, and speed of cooling is controlled at 15-25 ℃/s.

Images