Steel for high-strength annealing-free load-bearing chain and production method thereof

Abstract

The invention relates to steel for a high-strength annealing-free bearing chain. The steel comprises the following components in percentage by mass: 0.18-0.21% of C, 0.04-0.08% of Si, 0.90-1.10% of Mn, less than or equal to 0.012% of P, less than or equal to 0.008% of S, 0.19-0.25% of Cr, 0.0020-0.0030% of B, less than or equal to 15% of Ti: [% Ti] / [% B], 0.030-0.045% of Al, less than or equal to 0.0040% of O, less than or equal to 0.0050% of N, less than or equal to 0.0080% of total content of five harmful elements (Pb, As, Sn, Sb and Bi), and the balance of iron. The invention further provides a production method of the steel for the high-strength annealing-free load-bearing chain. In the production process, low-temperature heating is carried out; through staged low-temperature large-area-reduction-rate controlled rolling and controlled cooling, deformation is fully permeated, austenite is recrystallized, and crystal grains are continuously refined; the spinning temperature is controlled to be matched with the Stelmor roller way speed and the opening and closing number of the heat preservation covers, and the phase change and sufficiency in the wire rod covers are effectively controlled. And finally, the high-strength annealing-free bearing chain steel which is fine and uniform in grain, high in ferrite content and appropriate in hardness is obtained, a wire rod is good in machinability in a non-annealing state, the welding and heat treatment process adaptability is high, the comprehensive cost of the wire rod and the chain is low, and the high-strength annealing-free bearing chain steel can be applied to the high-strength bearing chain manufacturing industry more easily.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a high-strength annealing-free steel for load-bearing chains and a production method thereof. Background Art

[0002] At present, the parent materials used in the domestic mainstream round link chain market are all 20Mn2A or 25MnV hot-rolled wire rods / round steel, and the usage of 20Mn2A parent materials accounts for more than 80%, mainly used in the production of f 18 mm and below specifications 80 kg grade high-strength round link chain (quenched and tempered), products include agricultural chain, mining chain, marine chain, load-bearing chain and slings, etc., among which specifications f 5.0mm~ f 10.3 / 10 mm load-bearing chain (corresponding parent material specifications f 5.5 mm~ f 11 mm) accounts for more than 75% of the commonly used specifications of load-bearing chains. In recent years, with the continuous development of the load-bearing chain industry, higher process and technical requirements have been put forward for the stability and safety of load-bearing chains. A large number of practices in the industry have shown that the parent material for high-strength load-bearing chains requires excellent welding performance and quenching performance, relatively low hardness, and the cold-drawn hardness of the parent material after drawing is moderate, usually controlled at no more than 130~155 HB.

[0003] From the perspective of "composition / performance control characteristics", 20Mn2A belongs to low C, medium Si, high Mn alloy steel (most manufacturers control the Mn content above 1.50%, or even higher. If the composition control is slightly improper, its carbon equivalent is prone to fluctuations, affecting welding performance), with moderate strength, but the hardness of the steel wire after drawing is often high. Directly braiding the cold drawn wire is easy to cause the chain link R to break, and the springback of the chain link bending is large. Therefore, for the production of 20Mn2A material load-bearing chain, the parent material / steel wire must be annealed before braiding; at the same time, the 20Mn2A material itself is prone to overheating, decarburization sensitivity and temper brittleness during heat treatment, especially the second type of temper brittleness. Generally speaking, if the heat treatment of the Mn-containing steel of 20Mn2A material is slightly improper, tempering between 450~650℃ and slow cooling, the chain link is prone to the second type of temper brittleness, and the fracture microstructure is mostly "intergranular brittle fracture" characteristics. There are two main reasons for this type of temper brittleness: one is that the tempering temperature is too high, and the other is that the cooling rate is slow. This promotes the segregation of impurity elements in the steel at the grain boundaries - the alloy elements in the steel will affect the segregation of impurities, and elements such as Si, Mn, P, and As often segregate with impurity elements and promote the segregation of impurity elements. It is undeniable that this type of high-temperature temper brittleness is "reversible" - even if the brittleness is very serious, as long as the chain link is heated to above 650 ℃, it can be suppressed by rapid cooling by water or oil cooling after proper insulation. However, the occurrence of such a situation will directly affect the production cycle, increase unnecessary material and energy consumption, and also bring many uncertainties to the stability of product quality and the safety of subsequent products during service. Therefore, the study of high-strength annealing-free load-bearing chain steel is of great practical significance to improve the quality stability and safety of load-bearing chains during service. Summary of the invention

[0004] The purpose of the present invention is to provide a high-strength annealing-free steel for load-bearing chains. The load-bearing chains produced by the wire rod of the present invention have a strength of 80 kg after modulation, which effectively solves the problems of annealing, subsequent welding and modulation or high comprehensive cost in the process of making high-strength load-bearing chains using the material described in the background technology.

[0005] Another object of the present invention is to provide a production method for the above-mentioned high-strength annealing-free load-bearing chain steel, wherein the production process is carried out by low-temperature heating; staged low-temperature large-area reduction controlled rolling and controlled cooling to allow deformation to fully penetrate, austenite to recrystallize, and grains to be continuously refined; by controlling the matching of the spinning temperature with the Stelmor roller speed and the number of opening and closing of the insulation cover, the phase change in the wire rod cover and its sufficiency are effectively controlled. Finally, high-strength annealing-free load-bearing chain steel with fine and uniform grains, high ferrite content, and appropriate hardness is obtained. The wire rod has good machinability in the unannealed state, strong adaptability to welding and heat treatment processes, and low comprehensive cost of wire rod and chain, which is more conducive to application in the high-strength load-bearing chain manufacturing industry.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A high-strength annealing-free load-bearing chain steel comprises the following components by mass percentage: C: 0.18-0.21%, Si: 0.04-0.08%, Mn: 0.90-1.10%, P≤0.012%, S≤0.008%, Cr: 0.19-0.25%, B: 0.0020-0.0030%, Ti: [%Ti] / [%B]≤15, Al: 0.030-0.045%, O≤0.0040%, N≤0.0050%, the total content of five harmful elements (Pb, As, Sn, Sb, Bi) is ≤0.0080%, and the rest is iron.

[0007] The tensile strength of the above-mentioned high-strength annealing-free load-bearing chain steel is not less than 480 MPa, and the ferrite grain size is not less than grade 10; the entire production process of the high-strength load-bearing chain does not require annealing.

[0008] The production method of the above-mentioned high-strength annealing-free load-bearing chain steel includes the following steps: top and bottom combined blowing converter, LF refining, billet continuous casting, and high-speed wire rolling mill rolling. The high-speed wire rod rolling mill comprises the following steps: 1) Billet reheating temperature: 1010~1060 ℃, rolling temperature: 950~980 ℃; 2) The total reduction ratio of rough rolled products is >80%, and the total reduction ratio of medium and fine rolled products is >95%; 3) Sizing temperature: 860~900 ℃, total reduction rate of sizing rolled piece>35%, cooling rate: 60~200 ℃ / s; spinning temperature: 820~860 ℃; 4) Stelmor controlled cooling: match the inlet roller speed to 10~12 m / min, and then increase the roller speed of each section by a gradient of 6.5~8%; at the same time, open the 1st to 6th section insulation covers, and close the other insulation covers; turn off the fans of the entire line.

[0009] The tensile strength of the load-bearing chain steel produced by the above method is 500-600 MPa, and the ferrite grain size is 10-11.5 grade; the entire process of high-strength load-bearing chain production does not require annealing treatment.

[0010] Compared with the prior art, the present invention has the following beneficial effects: The high-strength annealing-free load-bearing chain steel provided by the present invention has the comparative advantages of suitable wire rod hardness, good machinability in a non-annealing state, strong adaptability to welding and heat treatment processes, and low comprehensive cost of wire rod and chain. DETAILED DESCRIPTION

[0011] The technical solutions and effects of the present invention are further described below in conjunction with several embodiments, but the protection scope of the present invention is not limited thereto.

[0012] Example 1 The mass percentages of the elements in the high-strength annealing-free load-bearing chain steel in this embodiment are: C: 0.19%, Si: 0.06%, Mn: 1.05%, P: 0.010%, S: 0.005%, Cr: 0.20%, B: 0.0023%, Ti: [%Ti] / [%B]=14, Al: 0.035%, O: 0.0028%, N: 0.0037%, the total content of the five harmful elements (Pb, As, Sn, Sb, Bi) is 0.0075%, and the rest is iron.

[0013] The production method of high-strength annealing-free load-bearing chain steel in this embodiment includes top and bottom combined blowing converter, LF refining, billet continuous casting, and high-speed wire mill rolling. Among them, the specific process of high-speed wire mill rolling is: the reheating temperature of the 150 mm×150 mm cross-section billet is 1040 ℃, the furnace time is 120 min, high-pressure water dephosphorization, high-speed wire rolling temperature is 960 ℃; rough rolling is 6 times, the total reduction rate of the rolled piece is 81.40%; medium and fine rolling is 20 times, the total reduction rate of the rolled piece is 99.10%; the rolling temperature of the rolled piece is 860 ℃, the sizing reduction rolling is 4 times, the total reduction rate of the rolled piece is 40.00%, the cooling rate is 200 ℃ / s, and the wire laying temperature is 820 ℃.

[0014] Furthermore, the Stelmor controlled cooling process: the wire rod after spinning enters the Stelmor roller, the entrance roller speed is matched to be 12 m / min, and then the roller speed of each section is increased by a gradient of 8%.

[0015] Furthermore, in the Stelmor controlled cooling process: the Stelmor roller conveyor opens the first section of the insulation cover, and the remaining insulation covers are closed; and the fans of the entire line are closed.

[0016] The performance indicators of the high-strength annealing-free load-bearing chain steel wire rod produced in this embodiment and the corresponding high-strength load-bearing chain performance indicators are shown in Table 1 and Table 2.

[0017] Table 1 Performance indexes of high-strength annealing-free load-bearing chain steel wire rod produced in this embodiment It can be seen from the data in Tables 1 and 2 that the 5.5 mm wire rod produced in this embodiment has moderate strength and excellent toughness and plasticity. Compared with the corresponding 5.0 mm 80 kg high-strength load-bearing chain produced by the 20Mn2A base material, the high-strength annealing-free load-bearing chain wire rod base material produced in this example has a suitable cold drawing hardness and can be directly braided without annealing to reduce the hardness, and the subsequent pickling process required for annealing is omitted, saving production costs. The 80 kg high-strength load-bearing chain finally obtained after tempering treatment has better strength.

[0018] Example 2 The mass percentages of the elements in the high-strength annealing-free load-bearing chain steel in this embodiment are: C: 0.20%, Si: 0.08%, Mn: 0.98%, P: 0.008%, S: 0.007%, Cr: 0.24%, B: 0.0028%, Ti: [%Ti] / [%B]=10, Al: 0.042%, O: 0.0035%, N: 0.0043%, the total content of the five harmful elements (Pb, As, Sn, Sb, Bi) is 0.0071%, and the rest is iron.

[0019] The production method of high-strength annealing-free load-bearing chain steel in this embodiment includes top and bottom combined blowing converter, LF refining, billet continuous casting, and high-speed wire mill rolling. Among them, the specific process of high-speed wire mill rolling is: the reheating temperature of the 150 mm×150 mm cross-section billet is 1060°C, the furnace time is 140 min, high-pressure water dephosphorization, high-speed wire rolling temperature is 980°C; rough rolling is 6 times, the total reduction rate of the rolled piece is 81.40%; medium and fine rolling is 14 times, the total reduction rate of the rolled piece is 96.50%; the rolling temperature of the rolled piece is 880°C, the sizing rolling is 4 times, the total reduction rate of the rolled piece is 35.42%, the cooling rate is 60°C / s, and the wire laying temperature is 845°C.

[0020] Furthermore, in the Stelmor controlled cooling process, the wire rod after spinning enters the Stelmor roller, and the entrance roller speed is matched to be 10 m / min, and then the roller speed of each section is increased by a gradient of 7.0%.

[0021] Furthermore, in the Stelmor controlled cooling process: the Stelmor roller conveyor opens the 1st to 3rd insulation covers, and the other insulation covers are closed; and the fans of the entire line are closed.

[0022] The performance indicators of the high-strength annealing-free load-bearing chain steel wire rod produced in this embodiment and the corresponding high-strength load-bearing chain performance indicators are shown in Tables 3 and 4.

[0023] Table 3 Performance indicators of high-strength annealing-free load-bearing chain steel wire rod produced in this embodiment It can be seen from the data in Tables 3 and 4 that the 11.0 mm wire rod produced in this embodiment has moderate strength and excellent toughness and plasticity. Compared with the corresponding 10.0 / 10.3 mm 80 kg high-strength load-bearing chain produced by the 20Mn2A base material, the high-strength annealing-free load-bearing chain wire rod base material produced in this example has a suitable cold drawing hardness and can be directly braided without annealing to reduce the hardness, and the subsequent pickling process required for annealing is omitted, saving production costs. The 80 kg high-strength load-bearing chain finally obtained after tempering treatment has better strength.

Claims

1. A high-strength annealing-free steel for load-bearing chains, characterized in that: The high-strength annealing-free load-bearing chain steel includes the following components in mass percentage: C: 0.18~0.21%, Si: 0.04~0.08%, Mn: 0.90~1.10%, P≤0.012%, S≤0.008%, Cr: 0.19~0.25%, B: 0.0020~0.0030%, Ti: [%Ti] / [%B]≤15, Al: 0.030~0.045%, O≤0.0040%, N≤0.0050%, the total content of five harmful elements (Pb, As, Sn, Sb, Bi) is ≤0.0080%, and the rest is iron.

2. The high-strength annealing-free load-bearing chain steel according to claim 1, characterized in that: The tensile strength of the high-strength annealing-free load-bearing chain steel is not less than 480 MPa, and the ferrite grain size is not less than grade 10; the entire production process of the high-strength load-bearing chain does not require annealing.

3. A method for producing high-strength annealing-free load-bearing chain steel, characterized in that: The production method comprises the following steps: Top and bottom combined blowing converter, LF refining, billet continuous casting, high-speed wire mill rolling, among which, The high-speed wire rod rolling mill comprises the following steps: 1) Billet reheating temperature: 1010~1060 ℃, rolling temperature: 950~980 ℃; 2) The total reduction ratio of rough rolled products is ≥80%, and the total reduction ratio of medium and fine rolled products is ≥95%; 3) Sizing temperature: 860~900 ℃, total surface reduction rate of sizing rolled piece ≥35%, cooling rate: 60~200 ℃ / s; spinning temperature: 820~860 ℃; 4) Stelmor controlled cooling: match the inlet roller speed to 10~12 m / min, and then increase the roller speed of each section by a gradient of 6.5~8%; at the same time, open the 1st to 3rd section insulation covers, and close the other insulation covers; turn off the fans of the entire line.

4. The method for producing high-strength annealing-free load-bearing chain steel according to claim 3, characterized in that: The tensile strength of the load-bearing chain steel produced by this production method is 500-600 MPa, and the ferrite grain size is 10-11.5; the entire process of high-strength load-bearing chain production does not require annealing treatment.

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