CN110480138A - The technique of control electrode upper limit Mn content R350HT rail flash welding joint microstructure - Google Patents

Abstract

The invention discloses a kind of techniques of control electrode upper limit Mn content R350HT rail flash welding joint microstructure, belong to rail flash welding technique field.The present invention easily leads to R350HT WELDING JOINT for solution in the prior art and the technical issues of martensitic structure occurs, provides a kind of technique of control electrode upper limit Mn content R350HT rail flash welding joint microstructure, including welding procedure and after welding treatment；In welding procedure, control thermal weld stress is that the pulsation of 8.5~9.5MJ or preheating flash butt welding connect, and welding upset amount is 15.5~16.0mm；In after welding treatment, connector is naturally cooled to 575~585 DEG C, then heat preservation is cooled to≤250 DEG C, last cooled to room temperature.Pass through the comprehensively control cooling to rail chemical component, hot rolling technology, welding procedure, postwelding, it is ensured that it is martensite-free in WELDING JOINT to wait abnormal structures, and guarantee joint mechanical property simultaneously.

Description

The technique of control electrode upper limit Mn content R350HT rail flash welding joint microstructure

Technical field

The invention belongs to rail flash welding technique fields, and in particular to a kind of control electrode upper limit Mn content R350HT rail The technique of flash welded tool joint tissue.

Background technique

As gapless track technology is in the railway constructions such as passenger traffic, shipping and high speed, heavy duty worldwide quick Development, the quality of rail joint increasingly cause the attention of relevant departments.Direct carrier of the railway track as train operation, The reliability of quality is the key that safe train operation.WELDING JOINT belongs to the weak link of entire route, quality Quality can directly affect the safety of railway.And in the matrix of WELDING JOINT, martensitic structure belongs to hard crisp phase, It is that more serious abnormity is influenced on base material and connector in rail welding production process with very high hardness and extremely low toughness Tissue easily causes rail be broken on the line, chip off-falling or even generation phenomena such as take off lid, the safety for seriously affecting train are transported Row.

Currently, both at home and abroad in the rail flash welding standard and enterprise technology condition of mainstream, the shape of martensite in butt joint State and content have done different degrees of regulation.Europe superscript BS EN 14587-2:2009 " Rail way applications- Track-Flash butt welding of rails.Part 2:New R220 R260 R260Mn and R350HT Grade rails by mobile welding machines at sites other than a fixed plant " standard Middle regulation, using optical microscopy 100 × amplification factor under observed, there can be no the nocuousness such as martensite or bainite Tissue, sample position are rail vertical central plane, should take 1 in rail head and the low sampling of rail, rail head position, sample size 20 × 20mm, two rail bottom feet respectively take 1,10 × 20mm of sample size；Europe superscript R350HT rail is EN 13674-1-2011 《Railway applications-Track-Rail Part 1:Vignole railway rails 46kg/m and Above " heat-treated rail specified in standard, C content is that 0.70~0.82%, Mn content is that 0.65~1.25%, Si contains Amount be 0.13~0.60%, Cr content≤0.15%, mechanical property be Rm >=1175MPa, A >=9%, tyre tread hardness >= 350HB is widely used in foreign country, state iron and subway line.Also, countries in the world are to the shape of martensite in WELDING JOINT State and content requirement are high.How to inhibit and eliminate WELDING JOINT by welding procedure and after welding treatment technique The generation of middle martensite is WELDING JOINT quality key factor whether up to standard.

However, the R350HT rail composition range of EN standard is wider, the alloying element design steel grade chemistry of high Mn is commonly used Ingredient, the mechanical property after only considering rail hot rolling meet EN standard qualification, do not consider the welding of user in use Acceptance criteria variation, causes the metallographic microstructure inspection of the median plane under flash welding connector tyre tread to be constantly present martensite group It knits, can not be examined by solder type.

Currently, the common method for inhibiting and eliminating WELDING JOINT martensitic structure is at postwelding heat both at home and abroad Postwelding, i.e., is cooled to the connector of lower temperature, using electromagnetic induction coil or flame heating device, by joint welding region by reason After being reheated to a certain temperature, the welded seam area after heating is cooled down with certain cooling rate.For pearlitic steel Rail provides in iron mark TB/T1632, and post weld heat treatment includes normalizing and restores rail head hardness and the postwelding slack quenching that uses； The welding point of fixed flash welding should be heated using medium frequency electric induction mode, during the welding point of mobile flash welding preferably uses Frequency electric induction mode can also be used fired heater swing mode and heat；When being heated using medium frequency electric induction mode, rail head surface Initial temperature should be lower than 500 DEG C, heating temperature preferably uses 900 ± 20 DEG C；When being heated using fired heater swing mode, rail The initial temperature of head surface should be lower than 500 DEG C, and 50 ± 10mm of width of heating, heating temperature preferably uses 850~950 DEG C；Rail head is owed Speed quenching should be cooling using injection compressed air.And method used by other domestic scholars is post weld heat treatment, that is, is passed through It controls the rate of heat addition, the peak temperature of heating, cooling rate and forces cooling finishing temperature to reach different purposes.It is external Strengthen heat-treated rail flash welding connector just for rail head, during connector postwelding natural cooling, using compressed air pair Welded seam area forces cooling, achievees the purpose that improve connector hardness, and such method has no side to the inhibition and elimination of martensite It helps, if control is improper, will increase martensite content in connector instead；And for part heat-treated rail and whole heat- treated steels Rail kind does not use any after welding treatment measure, i.e. postwelding natural cooling.

Summary of the invention

Present invention solves the technical problem that being the welding and heat treatment technique of the prior art, R350HT rail flash is easily led to There is martensitic structure in welding point.

There is provided a kind of control electrode upper limit Mn content R350HT steel for the technical solution of present invention solution above-mentioned technical problem The technique of rail flash welded tool joint tissue, it is characterised in that: including welding procedure and after welding treatment；Wherein, R350HT rail is female Material Mn content is 1.15~1.25wt%；In welding procedure, pulsation or pre- heat-lightening that control thermal weld stress is 8.5~9.5MJ Photocoagulation, welding upset amount are 15.5~16.0mm.

Wherein, in the technique of control electrode upper limit Mn content R350HT rail flash described above welding joint microstructure, weldering In post-processing, after Flash Butt Welding, by welding point naturally cool to driving face Weld pipe mill position temperature be 575~ 585 DEG C, then heat preservation is cooled to temperature≤250 DEG C of driving face Weld pipe mill position, last cooled to room temperature.

Wherein, in the technique of control electrode upper limit Mn content R350HT rail flash described above welding joint microstructure, institute State the region that Weld pipe mill is each 150~200mm in connector melt run two sides.

Wherein, in the technique of control electrode upper limit Mn content R350HT rail flash described above welding joint microstructure, institute Stating heat preservation cooling uses thickness >=30mm aluminosilicate cellucotton for heat-barrier material.

Wherein, in the technique of control electrode upper limit Mn content R350HT rail flash described above welding joint microstructure, institute It states R350HT rail base material C content and is in lower limit, Si≤0.30wt%.

Wherein, in the technique of control electrode upper limit Mn content R350HT rail flash described above welding joint microstructure, institute R350HT rail base material to be stated to produce using universal rolling line and burning optimization on line line, mechanical property meets Rm >=1175MPa, A >=9%, tyre tread hardness >=350HB.

Beneficial effects of the present invention:

The present invention passes through cooling to pole upper limit Mn content R350HT rail chemical component, hot rolling technology, welding procedure, postwelding Comprehensively control so that R350HT rail ingredient Mn content is not needed connector again in the case where 1.15~1.25wt% Heating, it is ensured that martensite-free equal abnormal structures in WELDING JOINT, and guarantee connector hardness, quiet curved and tired simultaneously Performance meets the technical requirements of EN 14587-2:2009 standard；The present invention keep the temperature using easy attemperator cold But it controls, preferably controls postwelding cooling velocity；The present invention controls simple process, to fixed flash welding and mobile flash of light Weldering is applicable, mating can solve the problems, such as the great welding technique on R350HT rail promotion and application road, has good Popularization and application foreground.

Detailed description of the invention

Fig. 1 is that R350HT rail flash of the present invention welds connector metallographic structure figure.

Specific embodiment

Specifically, the technique of control electrode upper limit Mn content R350HT rail flash welding joint microstructure, comprising the following steps: Including welding procedure and after welding treatment；Wherein, R350HT rail base material Mn content is 1.15~1.25wt%；In welding procedure, Control thermal weld stress is that the pulsation of 8.5~9.5MJ or preheating flash butt welding connect, and welding upset amount is 15.5~16.0mm.

Rail is during Flash Butt Welding, first by dodging the lintel explosion in flat stage, so that rail section to be welded is smooth Cleaning provides relatively uniform smooth advantage for subsequent flash of light and heating；Then pass through warm-up phase high current, low electricity The flash of light process of pressure accumulates heat, and certain temperature gradient is longitudinally formed in rail, the end face of rail is heated to enough temperature It spends and is that the Homogenization Process of flash of light is accelerated to establish condition；It finally carries out latter stage acceleration flash of light to burn, in entire welding region shape At the protective atmosphere for preventing end face from aoxidizing, suitable thermo parameters method is ultimately formed, provides condition for upset.It is defeated to control sweating heat Entering mainly is exactly the heat for controlling warm-up phase high current, the accumulation of the flash of light process of low-voltage, which directly affects rail end The temperature gradient in face.

After obtaining suitable temperature gradient, by applying the power along rail longitudinal direction on rail, draw close two rail. At this point, the rail with plastic deformation ability is deformed.Before and after upset, the amount of metal of rail leading portion consumption is exactly upset Amount.It is, in general, that forging force is bigger in the case where heat input is certain, upset amount is also bigger.It is found through experiment that when R350HT rail Mn content is in the pole upper limit (1.15~1.25wt%), and thermal weld stress is 8.5~9.5MJ and welding upset amount Best match can be reached for 15.5~16.0mm, the bond strength highest of rail joint, joint quality are most stable at this time.

For rail in smelting process, it is good deoxidier and desulfurizing agent, energy that Mn element, which easily forms manganese sulfide with S element, Harm of the sulphur in steel is reduced to a great extent.Mn, which dissolves in, simultaneously causes solution strengthening in ferrite, after improving steel hot rolling Hardness and strength.But when Mn content is higher, there is obvious temper brittleness phenomenon, while Mn plays the role of that crystal grain is promoted to grow up, So that steel can reduce the welding performance of steel to excessively thermo-responsive, and when the mass fraction of Mn is more than 1%.And in rail flash During plumb joint is cooling, the martensite being distributed in dotted or ribbon is easily formed in the region of Mn element microsegregation, Seriously affect joint performance.In general, the average mass fraction of Mn element is higher in steel, and the probability that the segregation of Mn occurs is got over Greatly, i.e. Mn content is higher, is more easy to produce martensitic structure.

It is carbon oversaturated interstitial solid solution in α-Fe for martensite essence.The tissue morphology of martensite mainly has two Kind: one is lath martensite, another kind is that (martensite referred in the present invention is mainly sheet geneva to lamellar martensite Body).Lamellar martensite is generally present in high-carbon steel of the C content greater than 0.6%, due to the phase of sample position, sometimes in light Learning under microscope is in needle-shaped or leaf of bamboo shape, therefore lamellar martensite is also known as acicular martensite or leaf of bamboo shape martensite.Lamellar martensite Another important feature be exactly there are a large amount of micro-flaws, the presence of micro-flaw increases the brittleness of high-carbon steel part, inside Micro-flaw will gradually be extended to macroscopic cracking under the action of stress, and joint cracking or joint fatigue service life can be caused bright Aobvious decline.As other solid-state phase changes, martensite transfor mation, which needs sufficiently large degree of supercooling just, can make phase driving force be greater than phase Variable resistance power, transformation of austenite to martensite occurs, but the difference is that the degree of supercooling needed for it is larger, it is necessary to be subcooled to remote low It could occur below the Ms point of T0；Martensite is carried out in the case where no diffusion, its phase transformation at a relatively low temperature Speed is exceedingly fast, and when showing as that austenite is changed into martensite in steel, is only reorganized as body-centered cubic lattice, nothing by face-centered cubic lattice Composition transfer；Meanwhile martensite transfor mation is carried out in certain temperature range.The horse in R350HT rail steel in the present invention The transformation of family name's body is carried out in continuous (i.e. alternating temperature) cooling procedure, and austenite is cooling all with the speed for being greater than critical quenching rate Ms point hereinafter, form a certain number of martensites immediately, with the decline of temperature, and forms a certain number of martensites, and first The martensite of formation is no longer grown up, and martensite transfor mation amount is gradually increased with the reduction of temperature, until lower than below Mf point.

Martensitic structure involved in the present invention mainly appears on along rail vertical central plane, melt run two sides 5mm, Because C, Mn is segregation element, after Mn content is improved to 1.15~1.25wt% in rail, the rail base material gesture of high Mn ingredient Mn microcell must be caused to be segregated, the chemical component of line of segragation high-content moves to right CCT curve seriously, is particularly easy to lead to postwelding connector Occurs dotted martensitic structure in process air cooler.Therefore the present invention naturally cools to welding point after Flash Butt Welding The temperature of driving face Weld pipe mill position is 575~585 DEG C, then heat preservation be cooled to the temperature of driving face Weld pipe mill position≤ 250 DEG C, last cooled to room temperature is in suitable range by the cooling velocity in control rail joint cooling procedure, Critical cooling speed is made it below, while martensitic traoformation does not occur, guarantees that joint performance is excellent.

Specific heat treatment step are as follows: after Flash Butt Welding, first using infrared thermometer to natural cooling Rail joint driving face Weld pipe mill position carries out thermometric, when temperature drops to 575~585 DEG C, uses heat-proof device immediately Welded seam area is kept the temperature；Continue in the process monitor connector temperature, when driving face Weld pipe mill position temperature be down to≤ At 250 DEG C, device is removed, connector is finally placed in cooled to room temperature in air；Wherein, Weld pipe mill is connector melt run The region of each 150~200mm in two sides；Heat preservation cooling uses thickness >=30mm aluminosilicate cellucotton for heat-barrier material.

High temperature section natural cooling speed is fast, and cooling speed is about 3~5 DEG C/s, and low-temperature zone natural cooling speed is slow, cooling 0.2 DEG C/s of rate about <；By the way that controls such as heat preservation initial temperature, attemperators, rate when heat preservation is cooling is 1~2 DEG C/s.

The present invention is applicable in the R350HT rail of C0.70~0.82wt%, Si0.13~0.60wt%；And inventor In practice, it has been found that when R350HT rail base material C content is in lower limit (C content is generally 0.72~0.78wt%), Si≤ It, being capable of preferably control joint metallographic structure using the method for the present invention when 0.30wt%.

The R350HT rail that the present invention uses is produced using universal rolling line and burning optimization on line line, and mechanical property is full Sufficient Rm >=1175MPa, A >=9%, tyre tread hardness >=350HB.

In the present invention, the content is mass percentage.

Below by embodiment, invention is further described in detail, but does not therefore limit the scope of the present invention Among the embodiment described range.

In embodiment, steel rail static bending test is to use widest rail joint overall performance evaluation side both at home and abroad at present Method has regulation in all rail joint test stones, mainly includes two indexs, i.e. load and amount of deflection.

Quiet curved test is that the method using 3 points or four-point supporting is applied to rail joint and carried with certain loading speed Lotus then determines the quiet curved performance of connector when to reach standard specified value continuous for load, and maximum defluxion is greater than standard specified value Qualification, different rail types correspond to different load and deflection value.In the standard of various countries, Russian STO RZD 1.08.002: The quality requirement highest of 2009 standards, it is desirable that the minimum load of connector and amount of deflection are not less than 2100kN and 30mm (65kg/m steel respectively Rail, rail head are pressurized), being converted to lowest load when 60kg/m rail head of rail is pressurized is 1907kN and 30mm.European standard BS EN14587-2:2009 requires the minimum load of connector and amount of deflection be not less than respectively 1600KN and 20mm (60kg/m rail, rail head by Pressure).It is 900MPa that Australia, which marks AS1085.20-2012 and requires connector rail bottom minimum stress, minimum load and amount of deflection point after converting It Bu little Yu not 1670KN and 20mm (60kg/m rail, rail head are pressurized).China is that Breaking load is not small for quiet curved standard requirements In 1450kN (60kg/m, rail head are pressurized), amount of deflection is not required.

Quiet curved load the major embodiment bond strength of connector, joint appearance and internal flaw index, the main body of amount of deflection Connector obdurability index is showed.If Joint Welding is bad, it is most likely that because the defects of greyness, incomplete fusion or burning leads It is broken before causing connector load value as defined in not up to standard, or because connector heat input and the flux matched improper, postwelding of upset Processing method is improper to cause connector partially hard or partially soft, makes connector amount of deflection that standard requirements be not achieved.

Rail object fatigue performance is similar with quiet curved test, the method for mostly using or four-point supporting at 3 points, with certain frequency Rate and amplitude apply alternating load to rail joint, until to reach standard specified value continuous for cycle-index, then determine that connector is quiet curved Performance is qualified, and different rail types corresponds to different rail bottom maximum stresses.

Embodiment 1

Use heat input for 8.9MJ, upset amount is the Flash Butt Welding technique of 15.3mm, and the mass fraction to Mn is 1.15% Europe superscript R350HT heat-treated rail (C content is in lower limit, Si≤0.30wt%, Rm >=1175MPa, A >=9%, and tyre tread is hard Degree >=350HB) carry out Flash Butt Welding.After Flash Butt Welding, first using infrared thermometer to the rail of natural cooling Connector driving face Weld pipe mill position carries out thermometric, when temperature drops to 585 DEG C, uses thickness >=30mm aluminosilicate immediately The region of cellucotton heat-proof device, each 200mm in butt joint melt run two sides is kept the temperature；Continue to monitor connector temperature in the process Degree removes device after driving face Weld pipe mill position temperature is lower than 250 DEG C, finally connector is placed in air and is naturally cooled to Room temperature.

It is tested analysis using the connector that the above welding procedures and after welding treatment method obtain according to 14587.2 Duis of EN, Connector center face rail head and rail bottom placement of foot microscopic structure are pearlite, have no the adverse tissues such as martensite；In addition to softened zone Connector hardness in base material average hardness -30HV~+60HV range；The quiet curved test 2000kN of three-point bending is continuous, maximum Amount of deflection is 27.4mm；Do not break for supported at three point full scall fatigue test 5,000,000 times, indices are all satisfied EN standard requirements.

Embodiment 2

Use heat input for 9.5MJ, upset amount is the Flash Butt Welding technique of 16.0mm, and the mass fraction to Mn is 1.21% Europe superscript R350HT heat-treated rail (C content is in lower limit, Si≤0.30wt%, Rm >=1175MPa, A >=9%, and tyre tread is hard Degree >=350HB) carry out Flash Butt Welding.After Flash Butt Welding, first using infrared thermometer to the rail of natural cooling Connector driving face Weld pipe mill position carries out thermometric, when temperature drops to 575 DEG C, uses thickness >=30mm aluminosilicate immediately The region of cellucotton heat-proof device, each 200mm in butt joint melt run two sides is kept the temperature；Continue to monitor connector temperature in the process Degree removes device after driving face Weld pipe mill position temperature is lower than 250 DEG C, finally connector is placed in air and is naturally cooled to Room temperature.

It is tested analysis using the connector that the above welding procedures and after welding treatment method obtain according to 14587.2 Duis of EN, Connector center face rail head and rail bottom placement of foot microscopic structure are pearlite, have no the adverse tissues such as martensite；In addition to softened zone Connector hardness in base material average hardness -30HV~+60HV range；The quiet curved test 2000kN of three-point bending is continuous, maximum Amount of deflection is 27.8mm；Do not break for supported at three point full scall fatigue test 5,000,000 times, indices are all satisfied EN standard requirements.

Embodiment 3

Use heat input for 8.5MJ, upset amount is the Flash Butt Welding technique of 15.5mm, and the mass fraction to Mn is 1.18% Europe superscript R350HT heat-treated rail (C content is in lower limit, Si≤0.30wt%, Rm >=1175MPa, A >=9%, and tyre tread is hard Degree >=350HB) carry out Flash Butt Welding.After Flash Butt Welding, first using infrared thermometer to the rail of natural cooling Connector driving face Weld pipe mill position carries out thermometric, when temperature drops to 580 DEG C, uses thickness >=30mm aluminosilicate immediately The region of cellucotton heat-proof device, each 200mm in butt joint melt run two sides is kept the temperature；Continue to monitor connector temperature in the process Degree removes device after driving face Weld pipe mill position temperature is lower than 250 DEG C, finally connector is placed in air and is naturally cooled to Room temperature.

It is tested analysis using the connector that the above welding procedures and after welding treatment method obtain according to 14587.2 Duis of EN, Connector center face rail head and rail bottom placement of foot microscopic structure are pearlite, have no the adverse tissues such as martensite；In addition to softened zone Connector hardness in base material average hardness -30HV~+60HV range；The quiet curved test 2000kN of three-point bending is continuous, maximum Amount of deflection is 27.3mm；Do not break for supported at three point full scall fatigue test 5,000,000 times, indices are all satisfied EN standard requirements.

Embodiment 4

Use heat input for 9.2MJ, upset amount is the Flash Butt Welding technique of 15.8mm, and the mass fraction to Mn is 1.25% Europe superscript R350HT heat-treated rail (C content is in lower limit, Si≤0.30wt%, Rm >=1175MPa, A >=9%, and tyre tread is hard Degree >=350HB) carry out Flash Butt Welding.After Flash Butt Welding, first using infrared thermometer to the rail of natural cooling Connector driving face Weld pipe mill position carries out thermometric, when temperature drops to 580 DEG C, uses thickness >=30mm aluminosilicate immediately The region of cellucotton heat-proof device, each 200mm in butt joint melt run two sides is kept the temperature；Continue to monitor connector temperature in the process Degree removes device after driving face Weld pipe mill position temperature is lower than 250 DEG C, finally connector is placed in air and is naturally cooled to Room temperature.

It is tested analysis using the connector that the above welding procedures and after welding treatment method obtain according to 14587.2 Duis of EN, Connector center face rail head and rail bottom placement of foot microscopic structure are pearlite, have no the adverse tissues such as martensite；In addition to softened zone Connector hardness in base material average hardness -30HV~+60HV range；The quiet curved test 2000kN of three-point bending is continuous, maximum Amount of deflection is 27.7mm；Do not break for supported at three point full scall fatigue test 5,000,000 times, indices are all satisfied EN standard requirements.

Claims (6)

1. the technique of control electrode upper limit Mn content R350HT rail flash welding joint microstructure, it is characterised in that: including Welder Skill and after welding treatment；Wherein, R350HT rail base material Mn content is 1.15~1.25wt%；In welding procedure, sweating heat is controlled Input is that the pulsation of 8.5~9.5MJ or preheating flash butt welding connect, and welding upset amount is 15.5~16.0mm.

2. the technique of control electrode upper limit Mn content R350HT rail flash welding joint microstructure according to claim 1, It is characterized in that: in after welding treatment, after Flash Butt Welding, welding point being naturally cooled into driving face Weld pipe mill position Temperature is 575~585 DEG C, and then heat preservation is cooled to temperature≤250 DEG C of driving face Weld pipe mill position, is finally naturally cooled to Room temperature.

3. welding the technique of joint microstructure according to claim 2 control electrode upper limit Mn content R350HT rail flash, feature exists In: the Weld pipe mill is the region of each 150~200mm in connector melt run two sides.

4. welding the technique of joint microstructure according to claim 2 control electrode upper limit Mn content R350HT rail flash, feature exists In: the heat preservation cooling uses thickness >=30mm aluminosilicate cellucotton for heat-barrier material.

5. the technique of control electrode upper limit Mn content R350HT rail flash welding joint microstructure, feature exist according to claim 1 In: the R350HT rail base material C content is in lower limit, Si≤0.30wt%.

6. the technique of any one control electrode upper limit Mn content R350HT rail flash welding joint microstructure according to claim 1~5, It is characterized by: the R350HT rail base material is produced using universal rolling line and burning optimization on line line, mechanical property is full Sufficient Rm >=1175MPa, A >=9%, tyre tread hardness >=350HB.