Bainite steel rail welded joint production method free of joint heat treatment

Abstract

The invention discloses a bainite steel rail welding joint production method free of joint heat treatment, and belongs to the technical field of steel rail welding, and the bainite steel rail welding production process comprises the steps of rust removal, welding, rough milling, aging treatment, straightening, accurate grinding, finished product inspection and flaw detection. Based on the components, the structure and the cooling characteristics of the bainite steel rail, on the premise that the strength, the hardness and the toughness of a connector are guaranteed, the structure transformation characteristics of the bainite steel rail are combined, and compared with a traditional steel rail welding production process, the normalizing heat treatment process step is omitted, the production process is shortened, and the energy consumption and the production cost are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of rail welding, and in particular relates to a method for producing a bainite rail welding joint free of joint heat treatment. Background Art

[0002] Rail fixed flash welding is an important method for railway rail welding, which has many advantages and difficulties. Rail fixed flash welding has high quality, can form a good metallurgical bond between rails, the weld strength is high, close to the parent material, can effectively ensure the safety of train operation; welding efficiency is high, the degree of automation is relatively high, the welding process is relatively stable, and the welding operation can be completed in a short time, reducing construction time; stable performance, the toughness and wear resistance of the welded joint are stable, can adapt to various complex track environments and climatic conditions, and reduce later maintenance costs. However, fixed flash welding has high requirements for equipment and high equipment costs, and the maintenance and commissioning of the equipment requires professional technicians, requiring large technical and financial investment; parameter control is difficult, and welding parameters such as current, voltage, and flash speed need to be precisely controlled, otherwise it will affect the welding quality. These parameters are affected by environmental factors (such as temperature and humidity), and it is difficult to always keep them in the best state. The personnel quality requirements are high, and operators need to undergo rigorous professional training to master welding technology.

[0003] Bainitic rails belong to a low-carbon medium alloy composition system. The alloy content is significantly higher than that of pearlite rails. The weldability is poor, and cold cracks are prone to occur in the heat-affected zone during welding. The performance matching relationship between the welded joint and the parent material is poor. Too much heat input will make the structure of the heat-affected zone coarse and reduce the performance; too little heat input may lead to incomplete welding. Since welding is a non-equilibrium process of local heating, rapid heating and cooling, the welding residual stress inside the weld joint is high and unevenly distributed, especially large tensile stress will be generated on the weld surface. The weld is prone to surface cracks or even fracture during service. Therefore, the welding process parameters of bainitic rails also need to be precisely controlled to ensure the welding quality.

[0004] The patent with publication number CN112695189A provides a heat treatment process for bainitic rail welded joints, which heats the bainitic rail welded joints that have not been subjected to any heat treatment at 550℃-650℃ and cools the joints naturally. This process does not completely austenitize the weld microstructure, resulting in a joint tensile strength of only 1210MPa and an impact strength of only 13J, which does not achieve the purpose of refining the structure and improving the strength and toughness of the joint.

[0005] The patent with publication number CN110331275A provides a post-weld heat treatment method for bainitic rails, wherein the bainitic rail welded joint is first cooled to 260-350°C, then heated to 780-870°C, second cooled to 360-420°C, and then third cooled to room temperature. The average hardness of the weld obtained by this process is 80-85% of the rail parent material, which does not meet the standard requirement of greater than or equal to 90%. The joint collapses during service, affecting driving stability.

[0006] The patent with publication number CN107385188B provides a post-weld heat treatment method for bainitic rail welded joints, which cools the joint naturally to 150-250°C, heats the first cooled joint to 880-960°C, and then cools it to 180-250°C, and then cools it to room temperature. The average hardness of the weld obtained by this process is 87% of the rail base material, which does not meet the standard requirement of greater than or equal to 90%, and the joint fatigue is about 3 million times. Summary of the invention

[0007] The purpose of the present invention is to provide a method for producing bainitic rail welding joints without joint heat treatment. By optimizing the welding process and simplifying the production process, while ensuring the strength, hardness and toughness of the joint, compared with the traditional rail welding production process, the normalizing heat treatment and tempering heat treatment process steps are omitted, thereby simplifying the production process, reducing the production cost and improving the production efficiency.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for producing a bainite rail welded joint without joint heat treatment, comprising: rust removal → welding → rough milling → normalizing heat treatment → aging treatment → tempering heat treatment → straightening → fine grinding → finished product inspection → flaw detection; wherein:

[0010] Grind and remove rust from the end faces of two bainite rails of the same cross section. The rust removal depth should be ≤0.2mm. The rail surface in the rust removal area should have a metallic luster.

[0011] A preheating fixed flash welder is used for rail welding, wherein the welding process of 60kg / m rail is as follows: primary voltage 390-410V, joint amount 7-9mm, arching amount 0.35-0.55mm, preheating times 8 times, secondary preheating current 58-63KA, upsetting amount 10-13mm, upsetting force ≥560KN, total welding time 110-115s, final melting speed 2.35-2.40mm / s;

[0012] 5) The welding process of 75kg / m rail is as follows: primary voltage 420-425V, steel joint amount 10-12mm, arching amount 0.35-0.55mm, preheating times 9 times, secondary preheating current 63-68KA, upsetting amount between 12-14mm, upsetting force ≥650KN, total welding time 115-120s, final melting speed 1.80-1.85mm / s;

[0013] 6) After the flash welding is completed, the embossing process should be completed automatically, and the time from top forging to embossing completion should be ≤ 20s;

[0014] 7) After the joint is pushed out, the joint can be air-cooled or slowly cooled, and the cooling rate of the joint should not be greater than 1.5℃ / s;

[0015] 8) Grind the weld bar to make it smooth. The height of the weld bar after grinding should not exceed 0.5mm. Aging treatment should be ≥24h, followed by straightening, fine grinding, finished product inspection and flaw detection.

[0016] Furthermore, the chemical composition of the rail is C: 0.16-0.25%, Si: 0.70-1.20%, Mn: 1.60-2.45%, Cr: 0.60-1.20%, Ni: 0.20-0.70%, Mo: 0.15-0.60%, P≤0.015%, S≤0.010%, Al: ≤0.010%, and the rest is Fe and impurities.

[0017] Furthermore, the rail is produced through smelting, continuous casting, slow cooling of steel billets, rolling and heat treatment. The rolling compression ratio of the rail should not be less than 9:1, and the final rolling temperature should not be higher than 950°C, so as to ensure the grain size of the original austenite of the rail.

[0018] Furthermore, the obtained joint tensile strength is ≥1190MPa, the yield strength is ≥1010MPa, the joint elongation is ≥8.9%, the joint surface shrinkage is ≥37%, and the joint impact is ≥34J.

[0019] Furthermore, the ratio of the average hardness of the joint to the average hardness of the base material is Hj / Hp≥0.98.

[0020] Furthermore, the ratio of the average hardness of the joint soft spot to the average hardness of the base material is Hj1 / Hp≥0.85.

[0021] Furthermore, the width W of the joint softening zone is ≤10 mm.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are:

[0023] Based on the above invention content, the obtained joint tensile strength is ≥1190MPa, yield strength is ≥1010MPa, joint extension is ≥8.9%, joint surface shrinkage is ≥37%, joint impact is ≥34J, the ratio of the joint hardness average value to the parent material hardness average value Hj / Hp is ≥0.98, the ratio of the joint soft point hardness average value to the parent material hardness average value Hj1 / Hp is ≥0.85, the joint softening zone width W is ≤10mm, and all mechanical properties of the joint meet the standard requirements. The present invention combines the characteristics of air-cooled bainite rail microstructure transformation, so that the joint has the characteristics of higher strength, hardness, plasticity and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below in conjunction with the accompanying drawings.

[0025] Figure 1 This is the test curve of the softening zone width at 0.9Hp. DETAILED DESCRIPTION

[0026] A method for producing a bainite rail welded joint without joint heat treatment, comprising:

[0027] 1) The bainite rail welded by the present invention has C, Mn, Si, Cr, Ni and Mo as main alloying elements, and the weight percentage of the chemical composition of the rail is C: 0.16-0.25%, Si: 0.70-1.20%, Mn: 1.60-2.45%, Cr: 0.60-1.20%, Ni: 0.20-0.70%, Mo: 0.15-0.60%, P≤0.015%, S≤0.010%, Al: ≤0.010%, and the rest is Fe. The rails with the above components are produced by smelting, continuous casting, slow cooling of steel billets, rolling, heat treatment, etc.

[0028] 2) Rail production with the above components through smelting, continuous casting, slow cooling of steel billets, rolling, heat treatment, etc. The rolling compression ratio of the rail should not be less than 9:1, and the final rolling temperature should not be higher than 950℃, so as to ensure the grain size of the original austenite of the rail; the rolling sections of the rail include 60kg / m (60, 60N) and 75kg / m (75, 75N).

[0029] 3) The production process flow of bainite rail welding of the present invention is: rust removal → welding → rough milling → aging treatment → straightening → fine grinding → finished product inspection → flaw detection.

[0030] 4) Grind and remove rust from the end faces of two bainitic rails of the same cross-section. The rust removal depth should be ≤0.2mm. The surface of the rail in the rust removal area should have a metallic luster.

[0031] 5) A preheating fixed flash welder is used for rail welding, and the welding process of 60kg / m (60, 60N) rail is as follows: primary voltage 390-410V, joint amount 7-9mm, arching amount 0.35-0.55mm, preheating times 8 times, secondary preheating current 58-63KA, upsetting amount 10-13mm, upsetting force ≥560KN, total welding time 110-115s, final melting speed 2.35-2.40mm / s.

[0032] 6) The welding process of 75kg / m (75, 75N) rail is: primary voltage 420-425V, steel joint amount 10-12mm, arching amount 0.35-0.55mm, preheating times 9 times, secondary preheating current 63-68KA, upsetting amount between 12-14mm, upsetting force ≥650KN, total welding time 115-120s, final melting speed 1.80-1.85mm / s.

[0033] 7) After the flash welding is completed, the embossing process should be completed automatically, and the time from top forging to embossing completion should be ≤20s.

[0034] 8) After the joint is pushed out, the joint can be air-cooled or slowly cooled, and the cooling rate of the joint should not be greater than 1.5℃ / s.

[0035] 9) Grind the weld bar to make it smooth. The height of the weld bar after grinding should not exceed 0.5mm. Aging treatment should be ≥24h, followed by straightening, fine grinding, finished product inspection and flaw detection.

[0036] During the implementation process, the mechanical properties of the joint of the present invention were tested, and the test results of the rail head (test line 1) on the longitudinal section of the joint are shown in Table 1.

[0037] Table 1 Test results of rail head (test line 1) on longitudinal section

[0038]

[0039]

[0040] The Rockwell hardness test data of each measuring point on the rail head (test line 1) on the longitudinal section of the welded joint is used to draw a hardness curve on the coordinate graph. The width of the hardness value below 0.9Hp on both sides of the weld is taken as the softening zone width, recorded as W. The standard requires W≤20mm. The test results are shown in the softening zone width test curve Figure 1 .

[0041] From Table 1, Figure 1It can be seen that the ratio of the average hardness of the joint of the present invention to the average hardness of the base material is Hj / Hp≥0.98, the ratio of the average soft spot hardness of the joint to the average hardness of the base material is Hj1 / Hp≥0.85, and the width of the joint softening zone is W≤10mm. At the same time, the tensile and impact properties of the joint are tested, and the tensile strength of the joint is ≥1190MPa, the yield strength is ≥1010MPa, the elongation of the joint is ≥8.9%, the surface shrinkage of the joint is ≥37%, and the impact of the joint is ≥34J. All mechanical properties of the joint meet the standard requirements. The present invention combines the characteristics of the microstructure transformation of air-cooled bainitic rails, so that the joint has the characteristics of higher strength, hardness, plasticity and toughness.

[0042] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing a bainite rail welded joint without joint heat treatment, characterized in that: include: Rust removal → welding → rough milling → normalizing heat treatment → aging treatment → tempering heat treatment → straightening → fine grinding → finished product inspection → flaw detection; among them: Grind and remove rust from the end faces of two bainite rails of the same cross section. The rust removal depth should be ≤0.2mm. The rail surface in the rust removal area should have a metallic luster. A preheating fixed flash welder is used for rail welding, wherein the welding process of 60kg / m rail is as follows: primary voltage 390-410V, joint amount 7-9mm, arching amount 0.35-0.55mm, preheating times 8 times, secondary preheating current 58-63KA, upsetting amount 10-13mm, upsetting force ≥560KN, total welding time 110-115s, final melting speed 2.35-2.40mm / s; 5) The welding process of 75kg / m rail is as follows: primary voltage 420-425V, steel joint amount 10-12mm, arching amount 0.35-0.55mm, preheating times 9 times, secondary preheating current 63-68KA, upsetting amount between 12-14mm, upsetting force ≥650KN, total welding time 115-120s, final melting speed 1.80-1.85mm / s; 6) After the flash welding is completed, the embossing process should be completed automatically, and the time from top forging to embossing completion should be ≤ 20s; 7) After the joint is pushed out, the joint can be air-cooled or slowly cooled, and the cooling rate of the joint should not be greater than 1.5℃ / s; 8) Grind the weld bar to make it smooth. The height of the weld bar after grinding should not exceed 0.5mm. Aging treatment should be ≥24h, followed by straightening, fine grinding, finished product inspection and flaw detection.

2. The method for producing a bainite rail welded joint without joint heat treatment according to claim 1, characterized in that: The chemical composition of the rail is C: 0.16-0.25%, Si: 0.70-1.20%, Mn: 1.60-2.45%, Cr: 0.60-1.20%, Ni: 0.20-0.70%, Mo: 0.15-0.60%, P≤0.015%, S≤0.010%, Al: ≤0.010%, and the rest is Fe and impurities.

3. The method for producing a bainite rail welded joint without joint heat treatment according to claim 2, characterized in that: The rail is produced by smelting, continuous casting, slow cooling of steel billets, rolling and heat treatment. The rolling compression ratio of the rail should not be less than 9:1, and the final rolling temperature should not be higher than 950°C, so as to ensure the grain size of the original austenite of the rail.

4. The method for producing a bainite rail welded joint without joint heat treatment according to claim 2, characterized in that: The obtained joint tensile strength is ≥1190MPa, the yield strength is ≥1010MPa, the joint extension is ≥8.9%, the joint surface shrinkage is ≥37%, and the joint impact is ≥34J.

5. The method for producing a bainite rail welded joint without joint heat treatment according to claim 2, characterized in that: The ratio of the average joint hardness to the average parent material hardness is Hj / Hp≥0.

98.

6. The method for producing a bainite rail welded joint without joint heat treatment according to claim 2, characterized in that: The ratio of the average hardness of the joint soft point to the average hardness of the base material is Hj1 / Hp≥0.

85.

7. The method for producing a bainite rail welded joint without joint heat treatment according to claim 2, characterized in that: The width of the joint softening zone W≤10mm.

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