The technique for controlling lower 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 lower 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/T 1632, and post weld heat treatment includes normalizing and restores rail head hardness and the postwelding that uses owes speed and quenches
Fire;The welding point of fixed flash welding should be heated using medium frequency electric induction mode, and the welding point of mobile flash welding is preferably adopted
With medium frequency electric induction mode, fired heater swing mode can also be used and heat;When being heated using medium frequency electric induction mode, rail head
The initial temperature on surface should be lower than 500 DEG C, and heating temperature preferably uses 900 ± 20 DEG C;Mode is swung using fired heater to heat
When, the initial temperature of rail 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 slack quenching should be cooling using injection compressed air.And method used by other domestic scholars is post weld heat treatment, i.e.,
Reach different purposes by the control rate of heat addition, the peak temperature of heating, cooling rate and the finishing temperature of pressure cooling.
Foreign countries strengthen heat-treated rail flash welding connector just for rail head, empty using compression during connector postwelding natural cooling
Gas is forced to cool down to welded seam area, achievees the purpose that improve connector hardness, and such method to the inhibition of martensite and is eliminated simultaneously
Without help, if control is improper, martensite content in connector will increase instead;And it is directed at part heat-treated rail and all heat
Rail kind is managed, 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 lower 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, including welding procedure and after welding treatment;Wherein, R350HT rail base material Mn content is
0.85~0.95wt%;In welding procedure, control thermal weld stress is that the pulsation of 5.0~7.0MJ or preheating flash butt welding connect, and is welded
Upset amount is 12.0~14.5mm.
Wherein, in the technique of control lower limit Mn content R350HT rail flash welding joint microstructure described above, weldering
In post-processing, after Flash Butt Welding, connector is placed in cooled to room temperature in air.
Wherein, in the technique of control lower limit Mn content R350HT rail flash welding joint microstructure described above, institute
It states R350HT rail base material C content and is in lower limit, Si content≤0.30wt%, Cr content is 0.10~0.11wt%.
Wherein, in the technique of control lower limit Mn content R350HT rail flash welding joint microstructure described above, 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 lower limit Mn content R350HT rail chemical component, hot rolling technology, welding procedure, postwelding
Comprehensively control so that R350HT rail ingredient Mn content is in the case where 0.85~0.95wt%, it is ensured that flash welding in rail
Martensite-free equal abnormal structures in connector, and guarantee that connector hardness, quiet curved and fatigue behaviour meet EN 14587-2 simultaneously:
The technical requirements of 2009 standards;The present invention carries out keeping the temperature cooling control using easy attemperator, preferably controls postwelding
Cooling velocity;The present invention controls simple process, can the mating great welding skill solved on R350HT rail promotion and application road
Art problem 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 lower 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 0.85~0.95wt%;In welding procedure,
Control thermal weld stress is that the pulsation of 5.0~7.0MJ or preheating flash butt welding connect, and welding upset amount is 12.0~14.5mm.
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 lower limit (0.85~0.95wt%), and thermal weld stress is 5.0~7.0MJ and welding upset amount
Best match can be reached for 12.0~14.5mm, 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
In the M of T0sOr less could occur;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
MsPoint 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 being lower than MfOr less.
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, the rail base material of Mn ingredient certainly will cause Mn microcell to be segregated, the chemical component of line of segragation high-content
It moves to right CCT curve seriously, is particularly easy to cause dotted martensitic structure occur in postwelding connector process air cooler.In general,
The average mass fraction of Mn element is higher in steel, and the probability that the segregation of Mn occurs is bigger;But Mn element is reduced to certain level
Afterwards, under the conditions of same cooling velocity, then it is not likely to produce the tissue such as harmful martensite.In the present invention, Mn content is in rail
0.85~0.95%, therefore the present invention can be made it below Critical cooling speed, martensitic phase is not being occurred using whole natural cooling
While change, guarantee that joint performance is excellent.
The present invention is suitable to the R350HT rail of C0.70~0.82wt%, Si0.13~0.60wt%, Cr≤0.15wt%
With;And inventor in practice, it has been found that when R350HT rail base material C content be in lower limit (C content is generally 0.72~
It 0.78wt%), being capable of better control joint metallographic using the method for the present invention when Si≤0.30wt%, Cr0.10~0.11%
Tissue.
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 5.6MJ, upset amount is the Flash Butt Welding technique of 12.8mm, and the mass fraction to Mn is
Europe superscript R350HT heat-treated rail that 0.85%, the mass fraction of Cr is 0.10% (C content is in lower limit, and Si≤
0.30wt%, Cr 0.10~0.11wt%, Rm >=1175MPa, A >=9%, tyre tread hardness >=350HB) carry out Flash Butt Welding.In
Connector is directly placed in cooled to room temperature in air after Flash Butt Welding.
It tests according to 14587.2 standard of EN to the connector obtained using the above welding procedure and after welding treatment method
Analysis, connector center face rail head and rail bottom foot specified position microscopic structure are pearlite, have no the adverse tissues such as martensite;It removes
Connector hardness outside softened zone is in base material average hardness -30HV~+60HV range;The quiet curved test 2000kN of three-point bending is not
It is disconnected, maximum defluxion 26.3mm;Do not break for supported at three point full scall fatigue test 5,000,000 times, indices are all satisfied EN 14587.2
Standard requirements.
Embodiment 2
Use heat input for 5.0MJ, upset amount is the Flash Butt Welding technique of 12.0mm, and the mass fraction to Mn is
Europe superscript R350HT heat-treated rail that 0.95%, the mass fraction of Cr is 0.10% (C content is in lower limit, and Si≤
0.30wt%, Cr 0.10~0.11wt%, Rm >=1175MPa, A >=9%, tyre tread hardness >=350HB) carry out Flash Butt Welding.In
Connector is directly placed in cooled to room temperature in air after Flash Butt Welding.
It tests according to 14587.2 standard of EN to the connector obtained using the above welding procedure and after welding treatment method
Analysis, connector center face rail head and rail bottom foot specified position microscopic structure are pearlite, have no the adverse tissues such as martensite;It removes
Connector hardness outside softened zone is in base material average hardness -30HV~+60HV range;The quiet curved test 2000kN of three-point bending is not
It is disconnected, maximum defluxion 25.9mm;Do not break for supported at three point full scall fatigue test 5,000,000 times, indices are all satisfied EN 14587.2
Standard requirements.
Embodiment 3
Use heat input for 7.0MJ, upset amount is the Flash Butt Welding technique of 14.5mm, and the mass fraction to Mn is
Europe superscript R350HT heat-treated rail that 0.91%, the mass fraction of Cr is 0.11% (C content is in lower limit, and Si≤
0.30wt%, Cr 0.10~0.11wt%, Rm >=1175MPa, A >=9%, tyre tread hardness >=350HB) carry out Flash Butt Welding.In
Connector is directly placed in cooled to room temperature in air after Flash Butt Welding.
It tests according to 14587.2 standard of EN to the connector obtained using the above welding procedure and after welding treatment method
Analysis, connector center face rail head and rail bottom foot specified position microscopic structure are pearlite, have no the adverse tissues such as martensite;It removes
Connector hardness outside softened zone is in base material average hardness -30HV~+60HV range;The quiet curved test 2000kN of three-point bending is not
It is disconnected, maximum defluxion 26.5mm;Do not break for supported at three point full scall fatigue test 5,000,000 times, indices are all satisfied EN 14587.2
Standard requirements.
Embodiment 4
Use heat input for 6.8MJ, upset amount is the Flash Butt Welding technique of 13.1mm, and the mass fraction to Mn is
Europe superscript R350HT heat-treated rail that 0.89%, the mass fraction of Cr is 0.11% (C content is in lower limit, and Si≤
0.30wt%, Cr 0.10~0.11wt%, Rm >=1175MPa, A >=9%, tyre tread hardness >=350HB) carry out Flash Butt Welding.In
Connector is directly placed in cooled to room temperature in air after Flash Butt Welding.
It tests according to 14587.2 standard of EN to the connector obtained using the above welding procedure and after welding treatment method
Analysis, connector center face rail head and rail bottom foot specified position microscopic structure are pearlite, have no the adverse tissues such as martensite;It removes
Connector hardness outside softened zone is in base material average hardness -30HV~+60HV range;The quiet curved test 2000kN of three-point bending is not
It is disconnected, maximum defluxion 26.1mm;Do not break for supported at three point full scall fatigue test 5,000,000 times, indices are all satisfied EN 14587.2
Standard requirements.