X80 pipeline steel hot rolled steel as well as preparation method and application thereof

Abstract

The invention relates to X80 pipeline steel hot rolled steel and a preparation method and application thereof, and relates to the field of microalloy high-strength steel manufacturing, and the X80 pipeline steel hot rolled steel comprises the following components in percentage by mass: 0.055-0.065% of C, 0.16-0.2% of Si, 1.7-1.8% of Mn, less than or equal to 0.012% of P, less than or equal to 0.004% of S, 0.18-0.22% of Ni, 0.2-0.24% of Cr, 0.2-0.24% of Mo, 0.03-0.05% of Nb, 0.04-0.06% of V, 0.01-0.018% of Ti, and the balance of Fe and inevitable impurities. According to the X80 pipeline steel hot rolled steel provided by the invention, through reasonable matching of alloy components, uniform distribution of acicular ferrite structures and uniform dispersion and precipitation of carbonitrides such as Nb and V are realized, so that the uniformity and stability of the mechanical property of the hot rolled steel strip are ensured on the basis of meeting the obdurability.

Description

Technical Field

[0001] The present invention relates to the technical field of microalloy high-strength steel manufacturing, and specifically to an X80 pipeline steel hot-rolled steel, a preparation method and use thereof, and more particularly to an X80-grade hot-rolled steel strip product for spiral seam submerged arc welded pipes having uniform and stable mechanical properties such as strength and toughness, a preparation method and use thereof. Background Art

[0002] At present, X80-grade pipeline steel is the main material used in domestic long-distance natural gas pipeline projects. With the increase in the use of this grade of pipeline steel products and the increase in service years, quality problems that affect service safety have been exposed. One of the core problems is the insufficient uniformity and stability of the mechanical properties such as strength and toughness of X80-grade pipeline steel products.

[0003] X80 grade hot rolled steel strip for spiral submerged arc welded pipes is a typical microalloyed high strength steel produced by controlled rolling and controlled cooling process. Its yield strength is not less than 555MPa and the Charpy impact energy is generally between 200-300J.

[0004] For example, CN106319387A discloses an X80 large deformation resistant pipeline steel and a manufacturing method, in which the mass percentage of the chemical composition of the steel is C 0.04-0.09%, Si 0.15-0.55%, Mn 1.50-1.75%, Nb0.04-0.10%, V 0.02-0.08%, Ti 0.01-0.03%, Cu 0.15-0.55%, Ni 0.15-0.55%, Cr0-0.15%, Mo 0.15-0.45%, Al 0.025-0.045%, N 0.0002-0.011%, P≤0.015%, S≤0.005%, and the rest are Fe and other inevitable impurity elements. The following process route is adopted: material preparation → converter or electric furnace smelting → refining outside the furnace → casting → slab reheating → controlled rolling → controlled cooling, after two-phase zone quenching, tempering is used or not.

[0005] CN1318631C discloses a method for manufacturing pipeline steel and its hot-rolled coil, and particularly relates to a method for manufacturing high-strength and high-toughness X80 pipeline steel and its hot-rolled coil. The invention solves the defect of the existing X80 pipeline steel having insufficient impact toughness. The weight percentage of the components is as follows: carbon 0.025-0.08%, silicon 0.19-0.3%, manganese 1.7-1.9%, titanium 0.01-0.02%, aluminum 0.015-0.04%, vanadium 0.055-0.065%, nickel ≤0.3%, chromium ≤0.02%, boron ≤0.0002%, phosphorus ≤0.018%, sulfur ≤0.005%, calcium 0.002-0.003%, molybdenum 0.2-0.4%, copper ≤0.3%, niobium 0.02-0.08%, nitrogen ≤0.006%, oxygen ≤0.004%, hydrogen ≤0.00025, and the balance is iron and trace impurities.

[0006] However, the widely used X80 grade spiral submerged arc welded pipe products currently have the problem of large fluctuations in mechanical properties within the same batch. For example, the yield strength fluctuation range is above 100MPa, which can easily cause uneven deformation and stress concentration when the pipeline is subjected to external forces during its service stage. In particular, the location of the pipeline's girth weld can easily lead to a weak-strong mismatch where the weld strength is lower than the pipe strength, making the girth weld a weak point of deformation and endangering the safety of the pipeline service. Summary of the Invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide an X80 pipeline steel hot-rolled steel and its preparation method and use, so as to solve the defects of poor strength, toughness, performance uniformity and stability of hot-rolled steel strip for X80 grade spiral seam submerged arc welded pipe.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides an X80 pipeline steel hot-rolled steel, wherein the X80 pipeline steel hot-rolled steel comprises, by weight percentage:

[0010] C 0.055-0.065%, Si 0.16-0.2%, Mn 1.7-1.8%, P≤0.012%, S≤0.004%, Ni0.18-0.22%, Cr 0.2-0.24%, Mo 0.2-0.24%, Nb 0.03-0.05%, V 0.04-0.06%, Ti0.01-0.018%, and the balance is Fe and unavoidable impurities.

[0011] The X80 pipeline steel hot-rolled steel provided by the present invention realizes the uniform distribution of acicular ferrite structure and the uniform dispersion and precipitation of carbonitrides such as Nb and V through the reasonable matching of alloy components, thereby achieving the purpose of controlling the uniformity and stability of the mechanical properties of the hot-rolled steel strip in different directions on the basis of meeting the basic strength and toughness requirements of X80 pipeline steel.

[0012] As a preferred technical solution of the present invention, the Pcm value of the X80 pipeline steel hot-rolled steel is 0.17-0.19%, Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

[0013] In a second aspect, the present invention provides a method for preparing the X80 pipeline steel hot-rolled steel as described in the first aspect, the preparation method comprising:

[0014] Continuously casting the molten iron obtained by smelting to obtain ingots;

[0015] The ingot is sequentially heated, rough rolled, finish rolled, cooled, coiled and heat treated to obtain X80 pipeline steel hot rolled steel.

[0016] As a preferred technical solution of the present invention, the smelting includes: converter smelting, LF refining and RH refining performed in sequence.

[0017] Preferably, the P element in the molten steel obtained by smelting has a mass percentage content of ≤0.012%.

[0018] Preferably, the S element in the molten steel obtained by smelting has a content of ≤0.003% by mass.

[0019] As a preferred technical solution of the present invention, a superheat of 15-20°C above the liquidus is adopted during the continuous casting.

[0020] Preferably, the casting speed during the continuous casting is 1-1.2 m / min.

[0021] Preferably, the total downward pressure during continuous casting is 4-6 mm.

[0022] As a preferred technical solution of the present invention, the heating insulation temperature is 1160-1220°C.

[0023] Preferably, the heating holding time is 180-300 minutes.

[0024] As a preferred technical solution of the present invention, the rough rolling is performed n times, where n≥7.

[0025] Preferably, the pressing amount of the (n-1)th rolling in the rough rolling is ≥25%.

[0026] Preferably, the pressing amount of the nth rolling in the rough rolling is ≥20%.

[0027] Preferably, the temperature of the nth rolling in the rough rolling is 920-960°C.

[0028] As a preferred technical solution of the present invention, the finish rolling is performed at least 7 times.

[0029] Preferably, the start rolling temperature of the finish rolling is ≤950°C.

[0030] Preferably, the cooling rate of the cooling is 20-30°C / s.

[0031] Preferably, the coiling temperature is 330-380°C.

[0032] As a preferred technical solution of the present invention, the heat treatment includes: performing heat preservation treatment on the whole coil of steel strip obtained by coiling, and then cooling it with the furnace.

[0033] Preferably, the insulation temperature of the insulation treatment is 460-500°C.

[0034] Preferably, the insulation time of the insulation treatment is 4-8 hours.

[0035] Preferably, the terminal temperature of the furnace cooling is 10-40°C.

[0036] In a third aspect, the present invention provides a use of the X80 pipeline steel hot-rolled steel as described in the first aspect, the use comprising: using the X80 pipeline steel hot-rolled steel to produce a spiral submerged arc welded pipe.

[0037] Compared with the existing technical solutions, the present invention has the following beneficial effects:

[0038] (1) The X80 pipeline steel hot-rolled steel provided by the present invention ensures the basic strength and toughness requirements of the X80 pipeline steel hot-rolled steel strip through reasonable alloy element design, the synergistic effect of micro-alloying elements such as Mn, Ni, Cr, Mo, Nb, V and Ti, and the combination of strengthening mechanisms such as solid solution strengthening and precipitation strengthening.

[0039] (2) The X80 pipeline steel hot-rolled steel provided by the present invention is manufactured through continuous casting, rough rolling, finishing rolling, controlled cooling, coiling and other processes, and the process temperature is precisely controlled to obtain a structure dominated by acicular ferrite; at the same time, through the reasonable combination of deformation and temperature in the rolling stage, grain refinement is achieved, the proportion of large-angle grain boundaries is increased, and the strength and toughness of the hot-rolled steel strip are improved.

[0040] (3) The X80 pipeline steel hot-rolled steel provided by the present invention adopts a whole-roll heat treatment process to weaken the degree of anisotropy of the hot-rolled steel strip structure, promote the re-precipitation of second-phase particles such as VC, thereby reducing the anisotropy of the hot-rolled steel strip performance and achieving the homogenization and stabilization performance characteristics of the X80 pipeline steel hot-rolled steel strip. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a transverse SEM photograph of the X80 pipeline steel hot-rolled steel obtained in Example 1 of the present invention;

[0042] Figure 2 This is a SEM photograph of the rolling direction of the X80 pipeline steel hot-rolled steel obtained in Example 1 of the present invention;

[0043] Figure 3 This is a 45° SEM photograph of the X80 pipeline steel hot-rolled steel obtained in Example 1 of the present invention;

[0044] Figure 4 This is a picture of nano-scale second phase particles dispersed and precipitated in the X80 hot-rolled pipeline steel after heat treatment in Example 1 of the present invention, 1 μm;

[0045] Figure 5 This is a diagram of nano-scale second phase particles dispersed and precipitated in the X80 hot-rolled pipeline steel after heat treatment in Example 1 of the present invention, 50 nm;

[0046] Figure 6 1 is a graph showing the yield strength results of hot-rolled X80 pipeline steel in Examples 1-4 of the present invention;

[0047] Figure 7 This is a graph showing the tensile strength results of the hot-rolled X80 pipeline steel in Examples 1-4 of the present invention.

[0048] The present invention is further described in detail below. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION

[0049] To better illustrate the present invention and facilitate understanding of the technical solutions of the present invention, typical but non-limiting embodiments of the present invention are as follows:

[0050] The currently used X80 pipeline steel hot-rolled steel can no longer meet the toughness requirements due to the increasingly severe operating conditions. At the same time, the widely used X80 grade spiral seam submerged arc welded pipe products have the problem of large fluctuations in mechanical properties within the same batch. For example, the yield strength fluctuation range is above 100 MPa, which easily causes uneven deformation and stress concentration when the pipeline is subjected to external forces during the service stage; especially the position of the pipeline's girth weld, which easily causes the weak-strong matching phenomenon where the weld strength is lower than the pipe strength, making the girth weld a weak point of deformation, endangering the safety of pipeline service. Based on this, the present invention improves the toughness of the obtained steel by rationally designing the composition of the X80 pipeline steel hot-rolled steel, and further enhances the toughness and reduces the anisotropy of the hot-rolled steel strip performance by optimizing the preparation process, as follows:

[0051] 1. This embodiment provides an X80 pipeline steel hot-rolled steel, wherein the X80 pipeline steel hot-rolled steel comprises, by weight percentage:

[0052] C 0.055-0.065%, Si 0.16-0.2%, Mn 1.7-1.8%, P≤0.012%, S≤0.004%, Ni0.18-0.22%, Cr 0.2-0.24%, Mo 0.2-0.24%, Nb 0.03-0.05%, V 0.04-0.06%, Ti0.01-0.018%, and the balance is Fe and unavoidable impurities.

[0053] In the present invention, the C element in the X80 pipeline steel hot-rolled steel is calculated as a percentage by mass of 0.055-0.065%, for example, it can be 0.055%, 0.056%, 0.057%, 0.058%, 0.059%, 0.06%, 0.061%, 0.062%, 0.063%, 0.064% or 0.065%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0054] In the present invention, the Si element in the X80 pipeline steel hot-rolled steel is 0.16-0.2% by mass, for example, it can be 0.16%, 0.162%, 0.164%, 0.166%, 0.168%, 0.17%, 0.172%, 0.174%, 0.176%, 0.178%, 0.18%, 0.182%, 0.184%, 0.186%, 0.188%, 0.19%, 0.192%, 0.194%, 0.196%, 0.198% or 0.2%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0055] In the present invention, the Mn element in the X80 pipeline steel hot-rolled steel is 1.7-1.8% by mass, for example, 1.7%, 1.71%, 1.72%, 1.73%, 1.74%, 1.75%, 1.76%, 1.77%, 1.78%, 1.79% or 1.8%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0056] In the present invention, the P element in the X80 pipeline steel hot-rolled steel is ≤0.012% by mass, and can be, for example, 0.012%, 0.011%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002%, 0.001% or 0.0001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0057] In the present invention, the S element in the X80 pipeline steel hot-rolled steel is ≤0.004% by mass, for example, it can be 0.004%, 0.0035%, 0.003%, 0.0025%, 0.002%, 0.0015%, 0.001%, 0.0008%, 0.0006%, 0.0004%, 0.0002% or 0.0001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0058] In the present invention, the Ni element in the X80 pipeline steel hot-rolled steel is 0.18-0.22% by mass, for example, it can be 0.18%, 0.182%, 0.184%, 0.186%, 0.188%, 0.19%, 0.192%, 0.194%, 0.196%, 0.198%, 0.2%, 0.202%, 0.204%, 0.206%, 0.208%, 0.21%, 0.212%, 0.214%, 0.216%, 0.218% or 0.22%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0059] In the present invention, the Cr element in the X80 pipeline steel hot-rolled steel is calculated as 0.2-0.24% by mass, for example, it can be 0.2%, 0.202%, 0.204%, 0.206%, 0.208%, 0.21%, 0.212%, 0.214%, 0.216%, 0.218%, 0.22%, 0.222%, 0.224%, 0.226%, 0.228%, 0.23%, 0.232%, 0.234%, 0.236%, 0.238% or 0.24%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0060] In the present invention, the Mo element in the X80 pipeline steel hot-rolled steel is calculated as a percentage by mass of 0.2-0.24%, for example, it can be 0.2%, 0.202%, 0.204%, 0.206%, 0.208%, 0.21%, 0.212%, 0.214%, 0.216%, 0.218%, 0.22%, 0.222%, 0.224%, 0.226%, 0.228%, 0.23%, 0.232%, 0.234%, 0.236%, 0.238% or 0.24%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0061] In the present invention, the Nb element in the X80 pipeline steel hot-rolled steel is 0.03-0.05% by mass, for example, it can be 0.03%, 0.031%, 0.032%, 0.033%, 0.034%, 0.035%, 0.036%, 0.037%, 0.038%, 0.039%, 0.04%, 0.041%, 0.042%, 0.043%, 0.044%, 0.045%, 0.046%, 0.047%, 0.048%, 0.049% or 0.05%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0062] In the present invention, the V element in the X80 pipeline steel hot-rolled steel is 0.04-0.06% by mass, for example, it can be 0.04%, 0.041%, 0.042%, 0.043%, 0.044%, 0.045%, 0.046%, 0.047%, 0.048%, 0.049%, 0.05%, 0.051%, 0.052%, 0.053%, 0.054%, 0.055%, 0.056%, 0.057%, 0.058%, 0.059% or 0.06%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0063] In the present invention, the Ti element in the X80 pipeline steel hot-rolled steel is 0.01-0.018% by mass, for example, it can be 0.01%, 0.0105%, 0.011%, 0.0115%, 0.012%, 0.0125%, 0.013%, 0.0135%, 0.014%, 0.0145%, 0.015%, 0.0155%, 0.016%, 0.0165%, 0.017%, 0.0175% or 0.018%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0064] The Pcm value of the X80 pipeline hot-rolled steel is 0.17-0.19%, where Pcm = C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B. For example, the Pcm value may be 0.17%, 0.172%, 0.174%, 0.176%, 0.178%, 0.18%, 0.182%, 0.184%, 0.186%, 0.188% or 0.19%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0065] In the present invention, the Pcm value refers to the welding crack sensitivity index.

[0066] 2. This embodiment provides a method for preparing X80 hot-rolled pipeline steel, the method comprising:

[0067] Continuously casting the molten iron obtained by smelting to obtain ingots;

[0068] The ingot is sequentially heated, rough rolled, finish rolled, cooled, coiled and heat treated to obtain X80 pipeline steel hot rolled steel.

[0069] The smelting includes: converter smelting, LF refining and RH refining performed in sequence.

[0070] The X80 pipeline steel hot-rolled steel comprises, by mass percentage, the following elements: C 0.055-0.065%, Si 0.16-0.2%, Mn 1.7-1.8%, P≤0.012%, S≤0.004%, Ni 0.18-0.22%, Cr 0.2-0.24%, Mo 0.2-0.24%, Nb 0.03-0.05%, V 0.04-0.06%, Ti 0.01-0.018%, and the balance being Fe and unavoidable impurities.

[0071] In the present invention, the C element in the X80 pipeline steel hot-rolled steel is calculated as a percentage by mass of 0.055-0.065%, for example, it can be 0.055%, 0.056%, 0.057%, 0.058%, 0.059%, 0.06%, 0.061%, 0.062%, 0.063%, 0.064% or 0.065%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0072] In the present invention, the Si element in the X80 pipeline steel hot-rolled steel is 0.16-0.2% by mass, for example, it can be 0.16%, 0.162%, 0.164%, 0.166%, 0.168%, 0.17%, 0.172%, 0.174%, 0.176%, 0.178%, 0.18%, 0.182%, 0.184%, 0.186%, 0.188%, 0.19%, 0.192%, 0.194%, 0.196%, 0.198% or 0.2%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0073] In the present invention, the Mn element in the X80 pipeline steel hot-rolled steel is 1.7-1.8% by mass, for example, 1.7%, 1.71%, 1.72%, 1.73%, 1.74%, 1.75%, 1.76%, 1.77%, 1.78%, 1.79% or 1.8%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0074] In the present invention, the P element in the X80 pipeline steel hot-rolled steel is ≤0.012% by mass, and can be, for example, 0.012%, 0.011%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002%, 0.001% or 0.0001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0075] In the present invention, the S element in the X80 pipeline steel hot-rolled steel is ≤0.004% by mass, for example, it can be 0.004%, 0.0035%, 0.003%, 0.0025%, 0.002%, 0.0015%, 0.001%, 0.0008%, 0.0006%, 0.0004%, 0.0002% or 0.0001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0076] In the present invention, the Ni element in the X80 pipeline steel hot-rolled steel is 0.18-0.22% by mass, for example, it can be 0.18%, 0.182%, 0.184%, 0.186%, 0.188%, 0.19%, 0.192%, 0.194%, 0.196%, 0.198%, 0.2%, 0.202%, 0.204%, 0.206%, 0.208%, 0.21%, 0.212%, 0.214%, 0.216%, 0.218% or 0.22%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0077] In the present invention, the Cr element in the X80 pipeline steel hot-rolled steel is calculated as 0.2-0.24% by mass, for example, it can be 0.2%, 0.202%, 0.204%, 0.206%, 0.208%, 0.21%, 0.212%, 0.214%, 0.216%, 0.218%, 0.22%, 0.222%, 0.224%, 0.226%, 0.228%, 0.23%, 0.232%, 0.234%, 0.236%, 0.238% or 0.24%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0078] In the present invention, the Mo element in the X80 pipeline steel hot-rolled steel is calculated as a percentage by mass of 0.2-0.24%, for example, it can be 0.2%, 0.202%, 0.204%, 0.206%, 0.208%, 0.21%, 0.212%, 0.214%, 0.216%, 0.218%, 0.22%, 0.222%, 0.224%, 0.226%, 0.228%, 0.23%, 0.232%, 0.234%, 0.236%, 0.238% or 0.24%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0079] In the present invention, the Nb element in the X80 pipeline steel hot-rolled steel is 0.03-0.05% by mass, for example, it can be 0.03%, 0.031%, 0.032%, 0.033%, 0.034%, 0.035%, 0.036%, 0.037%, 0.038%, 0.039%, 0.04%, 0.041%, 0.042%, 0.043%, 0.044%, 0.045%, 0.046%, 0.047%, 0.048%, 0.049% or 0.05%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0080] In the present invention, the V element in the X80 pipeline steel hot-rolled steel is 0.04-0.06% by mass, for example, it can be 0.04%, 0.041%, 0.042%, 0.043%, 0.044%, 0.045%, 0.046%, 0.047%, 0.048%, 0.049%, 0.05%, 0.051%, 0.052%, 0.053%, 0.054%, 0.055%, 0.056%, 0.057%, 0.058%, 0.059% or 0.06%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0081] In the present invention, the Ti element in the X80 pipeline steel hot-rolled steel is 0.01-0.018% by mass, for example, it can be 0.01%, 0.0105%, 0.011%, 0.0115%, 0.012%, 0.0125%, 0.013%, 0.0135%, 0.014%, 0.0145%, 0.015%, 0.0155%, 0.016%, 0.0165%, 0.017%, 0.0175% or 0.018%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0082] The Pcm value of the X80 pipeline hot-rolled steel is 0.17-0.19%, where Pcm = C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B. For example, the Pcm value may be 0.17%, 0.172%, 0.174%, 0.176%, 0.178%, 0.18%, 0.182%, 0.184%, 0.186%, 0.188% or 0.19%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0083] In the present invention, the Pcm value refers to the welding crack sensitivity index.

[0084] The P element in the molten steel obtained by the smelting is ≤0.012% by mass, for example, it can be 0.012%, 0.011%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002%, 0.001%, 0.0005% or 0.0001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0085] The S element in the molten steel obtained by the smelting is ≤0.003% by mass, for example, it can be 0.003%, 0.0028%, 0.0026%, 0.0024%, 0.0022%, 0.002%, 0.0018%, 0.0016%, 0.0014%, 0.0012%, 0.001%, 0.0005% or 0.0001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0086] In which, the superheat degree adopted in the continuous casting is 15-20°C higher than the liquidus line, for example, it can be 15°C, 15.5°C, 16°C, 16.5°C, 17°C, 17.5°C, 18°C, 18.5°C, 19°C, 19.5°C or 20°C, etc., but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0087] Wherein, the drawing speed in the continuous casting is 1-1.2 m / min, for example, it can be 1 m / min, 1.02 m / min, 1.04 m / min, 1.06 m / min, 1.08 m / min, 1.1 m / min, 1.12 m / min, 1.14 m / min, 1.16 m / min, 1.18 m / min or 1.2 m / min, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0088] Among them, the total downward pressure of the continuous casting is 4-6mm, for example, it can be 4mm, 4.2mm, 4.4mm, 4.6mm, 4.8mm, 5mm, 5.2mm, 5.4mm, 5.6mm, 5.8mm or 6mm, but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0089] Among them, the heating insulation temperature is 1160-1220℃, for example, it can be 1160℃, 1165℃, 1170℃, 1175℃, 1180℃, 1185℃, 1190℃, 1195℃, 1200℃, 1205℃, 1210℃, 1215℃ or 1220℃, etc., but is not limited to the listed values. Other unlisted values ​​within this range also meet the requirements.

[0090] The heating holding time is 180-300 min, for example, it can be 180 min, 190 min, 200 min, 210 min, 220 min, 230 min, 240 min, 250 min, 260 min, 270 min, 280 min, 290 min or 300 min, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0091] The rough rolling is performed for n times, where n≥7, for example, 7 times, 8 times, 9 times or 10 times, etc., but is not limited to the listed values, and other values ​​not listed within the range also meet the requirements.

[0092] Among them, the pressing amount of the n-1th rolling in the rough rolling is ≥25%, for example, it can be 25%, 26%, 28%, 30%, 32%, 34%, 36%, 38% or 40%, etc., but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0093] Among them, the pressing amount of the nth rolling in the rough rolling is ≥20%, for example, it can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38% or 40%, etc., but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0094] Among them, the temperature of the nth rolling in the rough rolling is 920-960℃, for example, it can be 920℃, 925℃, 930℃, 935℃, 940℃, 945℃, 950℃, 955℃ or 960℃, etc., but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0095] The finishing rolling is performed at least 7 times, for example, 7 times, 8 times, 9 times or 10 times, etc., but is not limited to the listed values, and other values ​​not listed within the range also meet the requirements.

[0096] Among them, the starting rolling temperature of the finishing rolling is ≤950℃, for example, it can be 950℃, 940℃, 930℃, 920℃, 910℃, 900℃, 890℃, 880℃, 870℃, 860℃, 850℃, 840℃, 830℃, 820℃ or 810℃, etc., but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0097] The cooling rate is 20-30°C / s, for example, it can be 20°C / s, 21°C / s, 22°C / s, 23°C / s, 24°C / s, 25°C / s, 26°C / s, 27°C / s, 28°C / s, 29°C / s or 30°C / s, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0098] The coiling temperature is 330-380°C, for example, 330°C, 335°C, 340°C, 345°C, 350°C, 355°C, 360°C, 365°C, 370°C, 375°C or 380°C, but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0099] The heat treatment comprises: performing heat preservation treatment on the whole coil of steel strip obtained by coiling, and then performing furnace cooling.

[0100] Among them, the insulation temperature of the insulation treatment is 460-500℃, for example, it can be 460℃, 465℃, 470℃, 475℃, 480℃, 485℃, 490℃, 495℃ or 500℃, but is not limited to the listed values. Other unlisted values ​​within this range also meet the requirements.

[0101] Among them, the insulation time of the insulation treatment is 4-8h, for example, it can be 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h, but is not limited to the listed values. Other unlisted values ​​within this range also meet the requirements.

[0102] Among them, the terminal temperature of the furnace cooling is 10-40°C, for example, it can be 10°C, 15°C, 20°C, 25°C, 30°C, 35°C or 40°C, but is not limited to the listed values. Other values ​​not listed in this range also meet the requirements.

[0103] 3. This embodiment provides uses of X80 pipeline steel hot-rolled steel, which includes: using X80 pipeline steel hot-rolled steel to produce spiral seam submerged arc welded pipes.

[0104] The X80 pipeline steel hot-rolled steel comprises, by mass percentage, the following elements: C 0.055-0.065%, Si 0.16-0.2%, Mn 1.7-1.8%, P≤0.012%, S≤0.004%, Ni 0.18-0.22%, Cr 0.2-0.24%, Mo 0.2-0.24%, Nb 0.03-0.05%, V 0.04-0.06%, Ti 0.01-0.018%, and the balance being Fe and unavoidable impurities.

[0105] In the present invention, the C element in the X80 pipeline steel hot-rolled steel is calculated as a percentage by mass of 0.055-0.065%, for example, it can be 0.055%, 0.056%, 0.057%, 0.058%, 0.059%, 0.06%, 0.061%, 0.062%, 0.063%, 0.064% or 0.065%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0106] In the present invention, the Si element in the X80 pipeline steel hot-rolled steel is 0.16-0.2% by mass, for example, it can be 0.16%, 0.162%, 0.164%, 0.166%, 0.168%, 0.17%, 0.172%, 0.174%, 0.176%, 0.178%, 0.18%, 0.182%, 0.184%, 0.186%, 0.188%, 0.19%, 0.192%, 0.194%, 0.196%, 0.198% or 0.2%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0107] In the present invention, the Mn element in the X80 pipeline steel hot-rolled steel is 1.7-1.8% by mass, for example, 1.7%, 1.71%, 1.72%, 1.73%, 1.74%, 1.75%, 1.76%, 1.77%, 1.78%, 1.79% or 1.8%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0108] In the present invention, the P element in the X80 pipeline steel hot-rolled steel is ≤0.012% by mass, and can be, for example, 0.012%, 0.011%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002%, 0.001% or 0.0001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0109] In the present invention, the S element in the X80 pipeline steel hot-rolled steel is ≤0.004% by mass, for example, it can be 0.004%, 0.0035%, 0.003%, 0.0025%, 0.002%, 0.0015%, 0.001%, 0.0008%, 0.0006%, 0.0004%, 0.0002% or 0.0001%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0110] In the present invention, the Ni element in the X80 pipeline steel hot-rolled steel is 0.18-0.22% by mass, for example, it can be 0.18%, 0.182%, 0.184%, 0.186%, 0.188%, 0.19%, 0.192%, 0.194%, 0.196%, 0.198%, 0.2%, 0.202%, 0.204%, 0.206%, 0.208%, 0.21%, 0.212%, 0.214%, 0.216%, 0.218% or 0.22%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0111] In the present invention, the Cr element in the X80 pipeline steel hot-rolled steel is calculated as 0.2-0.24% by mass, for example, it can be 0.2%, 0.202%, 0.204%, 0.206%, 0.208%, 0.21%, 0.212%, 0.214%, 0.216%, 0.218%, 0.22%, 0.222%, 0.224%, 0.226%, 0.228%, 0.23%, 0.232%, 0.234%, 0.236%, 0.238% or 0.24%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0112] In the present invention, the Mo element in the X80 pipeline steel hot-rolled steel is calculated as a percentage by mass of 0.2-0.24%, for example, it can be 0.2%, 0.202%, 0.204%, 0.206%, 0.208%, 0.21%, 0.212%, 0.214%, 0.216%, 0.218%, 0.22%, 0.222%, 0.224%, 0.226%, 0.228%, 0.23%, 0.232%, 0.234%, 0.236%, 0.238% or 0.24%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0113] In the present invention, the Nb element in the X80 pipeline steel hot-rolled steel is 0.03-0.05% by mass, for example, it can be 0.03%, 0.031%, 0.032%, 0.033%, 0.034%, 0.035%, 0.036%, 0.037%, 0.038%, 0.039%, 0.04%, 0.041%, 0.042%, 0.043%, 0.044%, 0.045%, 0.046%, 0.047%, 0.048%, 0.049% or 0.05%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0114] In the present invention, the V element in the X80 pipeline steel hot-rolled steel is 0.04-0.06% by mass, for example, it can be 0.04%, 0.041%, 0.042%, 0.043%, 0.044%, 0.045%, 0.046%, 0.047%, 0.048%, 0.049%, 0.05%, 0.051%, 0.052%, 0.053%, 0.054%, 0.055%, 0.056%, 0.057%, 0.058%, 0.059% or 0.06%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0115] In the present invention, the Ti element in the X80 pipeline steel hot-rolled steel is 0.01-0.018% by mass, for example, it can be 0.01%, 0.0105%, 0.011%, 0.0115%, 0.012%, 0.0125%, 0.013%, 0.0135%, 0.014%, 0.0145%, 0.015%, 0.0155%, 0.016%, 0.0165%, 0.017%, 0.0175% or 0.018%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0116] The Pcm value of the X80 pipeline hot-rolled steel is 0.17-0.19%, where Pcm = C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B. For example, the Pcm value may be 0.17%, 0.172%, 0.174%, 0.176%, 0.178%, 0.18%, 0.182%, 0.184%, 0.186%, 0.188% or 0.19%, etc., but is not limited to the listed values. Other values ​​not listed within this range also meet the requirements.

[0117] In the present invention, the Pcm value refers to the welding crack sensitivity index.

[0118] Furthermore, in order to illustrate the excellent mechanical properties that can be achieved by the X80 hot-rolled pipeline steel provided by the present invention, the following actual examples are used for illustration, as follows:

[0119] Example 1

[0120] This embodiment provides an X80 pipeline steel hot-rolled steel, wherein the X80 pipeline steel hot-rolled steel comprises, by weight percentage:

[0121] C 0.058%, Si 0.17%, Mn 1.74%, P 0.008%, S 0.0012%, Ni 0.2%, Cr 0.21%, Mo 0.21%, Nb 0.04%, V 0.04%, Ti 0.012%, the balance is Fe and unavoidable impurities;

[0122] The Pcm value is 0.183%, Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B;

[0123] The preparation process is as follows:

[0124] Continuously casting the molten iron obtained by smelting to obtain ingots;

[0125] The ingot is sequentially heated, rough rolled, finish rolled, cooled, coiled and heat treated to obtain X80 pipeline steel hot rolled steel;

[0126] The smelting comprises: converter smelting, LF refining and RH refining performed in sequence; the P element content in the molten steel obtained by the smelting is 0.008% by mass, and the S element content is 0.0012% by mass;

[0127] During continuous casting, the superheat degree was 17℃ above the liquidus, the casting speed was 1.15m / min, and the total pressure was 5.5mm.

[0128] The heating holding temperature is 1160℃ and the holding time is 220min;

[0129] The rough rolling is performed for n times, where n=7. The pressing force of the n-1th time, i.e., the sixth time, in the rough rolling is 25%; the pressing force of the nth time, i.e., the seventh time, in the rough rolling is 20%; and the temperature of the nth time, i.e., the seventh time, in the rough rolling is 920° C.

[0130] Finish rolling was performed for 7 times, with the starting rolling temperature at 905°C;

[0131] The cooling rate of cooling is 24°C / s;

[0132] The coiling temperature is 350°C;

[0133] The heat treatment includes: heat preservation treatment of the whole coiled steel strip obtained by coiling, and then cooling it with the furnace; the heat preservation temperature of the heat preservation treatment is 480°C, the heat preservation time is 6 hours; the terminal temperature of the furnace cooling is 20°C.

[0134] The obtained steel has uniform and stable performance. The microstructure of X80 pipeline steel hot-rolled strip is shown in the figure. Figure 1 、 Figure 2 and Figure 3 As shown in the TEM image of the nano-scale second phase particles dispersed and precipitated after heat treatment, Figure 4 and Figure 5 shown.

[0135] Example 2

[0136] This embodiment provides an X80 pipeline steel hot-rolled steel, wherein the X80 pipeline steel hot-rolled steel comprises, by weight percentage:

[0137] C 0.065%, Si 0.16%, Mn 1.%, P 0.01%, S 0.001%, Ni 0.18%, Cr 0.22%, Mo 0.22%, Nb 0.05%, V 0.045%, Ti 0.018%, the balance is Fe and unavoidable impurities;

[0138] The Pcm value is 0.189%, Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B;

[0139] The preparation process is as follows:

[0140] Continuously casting the molten iron obtained by smelting to obtain ingots;

[0141] The ingot is sequentially heated, rough rolled, finish rolled, cooled, coiled and heat treated to obtain X80 pipeline steel hot rolled steel;

[0142] The smelting comprises: converter smelting, LF refining and RH refining performed in sequence; the P element content in the molten steel obtained by the smelting is 0.01% by mass, and the S element content is 0.001% by mass;

[0143] During continuous casting, the superheat degree was 18℃ above the liquidus, the casting speed was 1.1m / min, and the total pressure was 5mm.

[0144] The heating holding temperature is 1220℃ and the holding time is 300min;

[0145] The rough rolling is performed for n times, where n=7. The pressing force of the n-1th time, i.e., the sixth time, in the rough rolling is 30%. The pressing force of the nth time, i.e., the seventh time, in the rough rolling is 30%. The temperature of the nth time, i.e., the seventh time, in the rough rolling is 960° C.

[0146] Finish rolling was performed for 7 times, with the starting rolling temperature at 940°C;

[0147] The cooling rate of cooling is 28°C / s;

[0148] The coiling temperature is 380°C;

[0149] The heat treatment includes: heat preservation treatment of the whole coiled steel strip obtained by coiling, and then cooling it with the furnace; the heat preservation temperature of the heat preservation treatment is 50°C, the heat preservation time is 4 hours; the terminal temperature of the furnace cooling is 25°C.

[0150] Example 3

[0151] This embodiment provides an X80 pipeline steel hot-rolled steel, wherein the X80 pipeline steel hot-rolled steel comprises, by weight percentage:

[0152] C 0.055%, Si 0.2%, Mn 1.8%, P 0.012%, S 0.0012%, Ni 0.22%, Cr 0.24%, Mo 0.24%, Nb 0.045%, V 0.05%, Ti 0.01%, the balance is Fe and unavoidable impurities;

[0153] The Pcm value is 0.188%, Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B;

[0154] The preparation process is as follows:

[0155] Continuously casting the molten iron obtained by smelting to obtain ingots;

[0156] The ingot is sequentially heated, rough rolled, finish rolled, cooled, coiled and heat treated to obtain X80 pipeline steel hot rolled steel;

[0157] The smelting comprises: converter smelting, LF refining and RH refining performed in sequence; the P element content in the molten steel obtained by the smelting is 0.012% by mass, and the S element content is 0.0012% by mass;

[0158] During continuous casting, the superheat degree was 15℃ above the liquidus, the casting speed was 1m / min, and the total pressure was 4mm.

[0159] The heating holding temperature is 1210℃ and the holding time is 260min;

[0160] The rough rolling is performed for n times, where n=7. The pressing force of the n-1th time, i.e., the sixth time, in the rough rolling is 35%; the pressing force of the nth time, i.e., the seventh time, in the rough rolling is 20%; and the temperature of the nth time, i.e., the seventh time, in the rough rolling is 940° C.

[0161] Finish rolling was performed for 9 times, with the starting rolling temperature at 925°C;

[0162] The cooling rate of cooling is 30°C / s;

[0163] The coiling temperature is 330°C;

[0164] The heat treatment includes: heat preservation treatment of the whole coiled steel strip obtained by coiling, and then cooling it with the furnace; the heat preservation temperature of the heat preservation treatment is 480°C, the heat preservation time is 5 hours; the terminal temperature of the furnace cooling is 10°C.

[0165] Example 4

[0166] This embodiment provides an X80 pipeline steel hot-rolled steel, wherein the X80 pipeline steel hot-rolled steel comprises, by weight percentage:

[0167] C 0.06%, Si 0.18%, Mn 1.76%, P 0.009%, S 0.0008%, Ni 0.2%, Cr 0.2%, Mo 0.2%, Nb 0.03%, V 0.06%, Ti 0.015%, the balance is Fe and unavoidable impurities;

[0168] The Pcm value is 0.187%, Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B;

[0169] The preparation process is as follows:

[0170] Continuously casting the molten iron obtained by smelting to obtain ingots;

[0171] The ingot is sequentially heated, rough rolled, finish rolled, cooled, coiled and heat treated to obtain X80 pipeline steel hot rolled steel;

[0172] The smelting comprises: converter smelting, LF refining and RH refining performed in sequence; the P element content in the molten steel obtained by the smelting is 0.009% by mass, and the S element content is 0.0008% by mass;

[0173] During continuous casting, the superheat was 20°C above the liquidus, the casting speed was 1.2m / min, and the total pressure was 6mm.

[0174] The heating holding temperature is 1180℃ and the holding time is 180min;

[0175] The rough rolling is performed for n times, where n=7, and the pressing force of the n-1th, i.e., the 7th, rolling in the rough rolling is 35%; the pressing force of the nth, i.e., the 7th, rolling in the rough rolling is 35%; and the temperature of the nth, i.e., the 7th, rolling in the rough rolling is 920° C.;

[0176] Finish rolling was performed for 8 times, with the starting rolling temperature at 900°C;

[0177] The cooling rate of cooling is 20°C / s;

[0178] The coiling temperature is 360°C;

[0179] The heat treatment includes: heat preservation treatment of the whole coiled steel strip obtained by coiling, and then cooling it with the furnace; the heat preservation temperature of the heat preservation treatment is 460°C, the heat preservation time is 8 hours; the terminal temperature of the furnace cooling is 40°C.

[0180] Comparative Example 1

[0181] The only difference from Example 1 is that the composition of the steel material includes, by mass percentage:

[0182] C 0.04%, Si 0.2%, Mn 1.85%, P 0.009%, S 0.0021%, Ni 0.24%, Cr 0.25%, Cu 0.15%, Mo 0.26%, Nb 0.075%, Ti 0.018%, Pcm=0.181%;

[0183] During the preparation process, the heating and holding temperature is 1240°C, the heating and holding time is 180 minutes, the final rolling temperature of rough rolling is 920°C, the start rolling temperature of finishing rolling is 895°C, the cooling rate is 30°C / s, and the coiling temperature is 400°C.

[0184] Comparative Example 2

[0185] The only difference from Example 1 is that the composition of the steel material includes, by mass percentage:

[0186] C 0.068%, Si 0.2%, Mn 1.65%, P 0.0079%, S 0.0024%, Ni 0.2%, Cr 0.3%, Cu 0.2%, Mo 0.18%, Nb 0.08%, Ti 0.016%, Pcm=0.198%;

[0187] During the preparation process, the heating and holding temperature is 1280°C, the heating and holding time is 240 minutes, the final rolling temperature of rough rolling is 900°C, the start rolling temperature of finishing rolling is 880°C, the cooling rate is 26°C / s, and the coiling temperature is 420°C.

[0188] The steel products obtained in the above examples and comparative examples were subjected to mechanical and impact property tests according to the national standards GB / T 228 Tensile test of metal materials, GB / T 229 Charpy pendulum impact test method for metal materials, and GB / T 8363 Drop weight tear test method for steel. The test results are detailed in Table 1.

[0189] Table 1

[0190]

[0191]

[0192] As shown in Table 1, the toughness values ​​(i.e., -20°C Charpy impact energy and -15°C DWTT) of Examples 1-4 in various sampling directions are significantly higher than those of the comparative example. In addition, the strength of the comparative example shows obvious differences in different orientations, with the maximum difference in yield strength reaching 42MPa and 73MPa, while the yield strength of the examples shows higher uniformity and stability, as shown in Table 1. Figure 6 and Figure 7 shown.

[0193] By comparing the data of the embodiments and the comparative examples, it can be seen that through the reasonable design of the alloy element ratio in the present invention and the innovative optimization of the process parameters in the manufacturing method, the X80 grade pipeline steel hot-rolled steel is achieved with uniform and stable strength in different directions on the basis of excellent strength and toughness. The yield strength of the obtained X80 grade pipeline steel hot-rolled steel is: ≥590 MPa in the transverse direction, ≥579 MPa in the 45° direction, and ≥583 MPa in the rolling direction; tensile strength: ≥706 MPa in the transverse direction, ≥699 MPa in the 45° direction, and ≥698 MPa in the rolling direction; elongation: ≥27% in the transverse direction, ≥29.5% in the 45° direction, and ≥28% in the rolling direction; Charpy impact energy CVN at -20°C: ≥306 J in the transverse direction, ≥310 J in the 45° direction, and ≥304 J in the rolling direction; DWTT at -15°C: ≥96 J in the transverse direction, ≥95 J in the 45° direction, and ≥95 J in the rolling direction.

[0194] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0195] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0196] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. An X80 pipeline steel hot-rolled steel, characterized in that: The X80 pipeline steel hot-rolled steel comprises, by weight percentage: C 0.055-0.065%, Si 0.16-0.2%, Mn 1.7-1.8%, P≤0.012%, S≤0.004%, Ni0.18-0.22%, Cr 0.2-0.24%, Mo 0.2-0.24%, Nb 0.03-0.05%, V 0.04-0.06%, Ti0.01-0.018%, and the balance is Fe and unavoidable impurities.

2. The X80 hot-rolled pipeline steel according to claim 1, characterized in that: The Pcm value of the X80 pipeline hot-rolled steel is 0.17-0.19%, where Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

3. A method for preparing X80 hot-rolled pipeline steel according to claim 1 or 2, characterized in that: The preparation method comprises: Continuously casting the molten iron obtained by smelting to obtain ingots; The ingot is sequentially heated, rough rolled, finish rolled, cooled, coiled and heat treated to obtain X80 pipeline steel hot rolled steel.

4. The preparation method according to claim 3, wherein The smelting includes: converter smelting, LF refining and RH refining carried out in sequence; Preferably, the P element in the molten steel obtained by smelting is ≤0.012% by mass; Preferably, the S element in the molten steel obtained by smelting has a mass percentage content of ≤0.003%.

5. The preparation method according to claim 3 or 4, characterized in that The continuous casting adopts a superheat of 15-20°C above the liquidus; Preferably, the casting speed during the continuous casting is 1-1.2 m / min; Preferably, the total downward pressure during continuous casting is 4-6 mm.

6. The preparation method according to any one of claims 3 to 5, characterized in that The heating holding temperature is 1160-1220°C; Preferably, the heating holding time is 180-300 minutes.

7. The preparation method according to any one of claims 3 to 6, wherein The rough rolling is performed n times, where n≥7; Preferably, the pressing amount of the n-1th rolling in the rough rolling is ≥25%; Preferably, the pressing amount of the nth rolling in the rough rolling is ≥20%; Preferably, the temperature of the nth rolling in the rough rolling is 920-960°C.

8. The preparation method according to any one of claims 3 to 7, wherein The finishing rolling is performed at least 7 times; Preferably, the start rolling temperature of the finishing rolling is ≤950°C; Preferably, the cooling rate of the cooling is 20-30°C / s; Preferably, the coiling temperature is 330-380°C.

9. The preparation method according to any one of claims 3 to 8, wherein The heat treatment comprises: performing heat preservation treatment on the whole coiled steel strip obtained by coiling, and then performing furnace cooling; Preferably, the heat preservation temperature of the heat preservation treatment is 460-500°C; Preferably, the heat preservation time of the heat preservation treatment is 4-8 hours; Preferably, the terminal temperature of the furnace cooling is 10-40°C.

10. Use of the X80 hot-rolled pipeline steel according to claim 1 or 2, characterized in that: The application includes: using the X80 pipeline steel hot-rolled steel to produce spiral seam submerged arc welded pipes.

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