CN105671458B - The excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability and its manufacture method - Google Patents
The excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability and its manufacture method Download PDFInfo
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- CN105671458B CN105671458B CN201510628966.4A CN201510628966A CN105671458B CN 105671458 B CN105671458 B CN 105671458B CN 201510628966 A CN201510628966 A CN 201510628966A CN 105671458 B CN105671458 B CN 105671458B
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
Abstract
The present invention relates to a kind of excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability and its manufacture method.The medium carbon steel Micro Alloying wire rod, in terms of weight %, including：Carbon (C)：0.35~0.5%, silicon (Si)：0.001~0.6%, manganese (Mn)：0.8~1.8%, chromium (Cr)：0.05~0.2%, aluminium (Al)：0.01~0.05%, nickel (Ni)：0.05~0.2%, phosphorus (P)：0.01~0.03%, sulphur (S)：Less than 0.06%, nitrogen (N)：Less than 0.01%, vanadium (V)：0.02~0.15% and titanium (Ti)：One or more of 0.005~0.03% element, remaining is to be made of Fe and inevitable impurity；Microscopic structure is made of the ferrite that area fraction is 20~35% with remaining pearlite complex tissue.
Description
Technical field
The present invention relates to a kind of Micro Alloying wire rod, more specifically, be related to a kind of Surface hardened layer heat-treatability it is excellent in
Carbon steel Micro Alloying wire rod and its manufacture method.
Background technology
Under normal circumstances, medium carbon steel wire rod is chiefly used in cold working, at this time, in order to improve the processing characteristics of medium carbon steel wire rod,
Implement the heat treatment such as process annealing heat treatment or nodularization heat treatment, after the processing such as forging, implementing to be used to assign physics
Quenching and tempering (quenching and tempering) heat treatment of property.
However, in the case that the accessory or requirement high to digital required precision reduces heat treatment expense, it is main to use province
The non-hardened and tempered steel of slightly above-mentioned heat treatment.
The non-hardened and tempered steel, is heat-treated after wire rod is manufactured without process annealing heat treatment and nodularization, but can be straight
Overstretching and direct cold forging are connected to manufacture product.As described above, in order to manufacture product in the case of without Overheating Treatment, institute
High tenacity need to be possessed by stating Micro Alloying wire rod, be currently known, and the microscopic structure especially ferrite fraction of wire rod produces toughness
It is raw to influence.
In addition, the method for the toughness for the raising Micro Alloying wire rod being currently known has, Ti, Nb, V etc. can be fixed by addition
The carbide and nitride forming element of ferrite grain boundaries, and the miniaturization of austenite grain and thick is prevented by controlled rolling
Bigization, forms ferrite in austenite grain boundary, toughness is improved by ferrite miniaturization.
However, the above method need to control the precipitate formed by Ti, Nb, V etc., and due to the use of block iron (bloom)
Deng furnace temp need to being increased to more than 1200 DEG C, therefore there are the restricted shortcoming of use of enterprise.
Also, the manufacture method as the high tenacity non-hardened and tempered steel of good economy performance has, in the range of 0.2 weight % medium carbon steel
The method of ferrite+pearlite lamellar tissue is formed using Bao Xingge effects (Bauschinger effect).
Above-mentioned lamellar tissue has the advantages that impact flexibility maximization and the utilization ordinary carbon steel that can make steel, still,
Because of lamellar tissue, material has directionality in itself, therefore has the shortcomings that using restricted.
The content of the invention
(1) technical problems to be solved
One aspect of the present invention, effectively ensures Surface hardened layer heat-treatability to improve non-tune its purpose is to provide one kind
The medium carbon steel Micro Alloying wire rod and its manufacture method of the wearability of matter wire rod.(2) technical solution
One aspect of the present invention, there is provided a kind of excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability, it is described
Wire rod, in terms of weight %, including：Carbon (C)：0.35~0.5%, silicon (Si)：0.001~0.6%, manganese (Mn)：0.8~1.8%,
Chromium (Cr)：0.05~0.2%, aluminium (Al)：0.01~0.05%, nickel (Ni)：0.05~0.2%, phosphorus (P)：0.01~0.03%,
Sulphur (S)：Less than 0.06%, nitrogen (N)：Less than 0.01%, vanadium (V)：0.02~0.15% and titanium (Ti)：In 0.005~0.03%
More than one elements, remaining is is made of Fe and inevitable impurity；Microscopic structure is 20~35% by area fraction
Ferrite and remaining pearlite complex tissue form.
A kind of another aspect of the present invention, there is provided the system of the excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability
Method is made, it comprises the following steps：Prepare the steel for meeting the constituent；The steel is added at a temperature of less than 1050 DEG C
Heat treatment less than 150 minutes；The heated steel is implemented into hot finishing within the temperature range of 780~800 DEG C；And
After the hot finishing, cooled down with the cooling velocity of 0.5~3 DEG C/s.
(3) beneficial effect
According to the present invention, in the case of the expensive element of no addition, using the teaching of the invention it is possible to provide a kind of not only tenacity excellent, but also
The medium carbon steel Micro Alloying wire rod of hardness and excellent in abrasion resistance can be improved after Surface hardened layer heat treatment.
Embodiment
[the most preferably mode to carry out an invention]
Under normal circumstances, the complex tissue group by ferrite and pearlite is formed in order to improve the toughness of Micro Alloying wire rod
Into microscopic structure while realize the ferritic granular.This complex tissue is because it is with lamellar tissue and with punching
The physical property of tenacity excellent is hit, but, the place of abrasion-proof physical property is being needed to have, portion is likely to result in because of soft
The problem of part service life shortens.To overcome this problem, as process method, using a kind of by being carried out to common steel
Carburizing or nitrogen treatment improve case hardness to improve hardness, or by local sensing heating, so as to improve wearability
Method.
In the present invention, for solving the problems, such as that the scheme on material as described above is to have complex group to above-mentioned
While the Micro Alloying wire rod progress Surface hardened layer heat treatment knitted during the heat treatment is carried out, pass through and improve heat treatment
Property improves hardness, so that it is guaranteed that excellent wearability.
For this reason, the present inventor confirms when optimizing the microscopic structure of Micro Alloying wire rod, it is particularly brilliant in optimization ferrite
During particle size, Surface hardened layer heat-treatability can be greatly improved, obtains the excellent physical property to be reached, and be finally completed
The present invention.
In the following, the present invention is described in detail.
The excellent medium carbon steel Micro Alloying wire rod of the Surface hardened layer heat-treatability of one aspect of the present invention, in terms of weight %,
Preferably include：Carbon (C)：0.35~0.5%, silicon (Si)：0.001~0.6%, manganese (Mn)：0.8~1.8%, chromium (Cr)：0.05
~0.2%, aluminium (Al)：0.01~0.05%, nickel (Ni)：0.05~0.2%, phosphorus (P)：0.01~0.03%, sulphur (S)：
Less than 0.06%, nitrogen (N)：Less than 0.01%, vanadium (V)：0.02~0.15% and titanium (Ti)：One kind in 0.005~0.03%
Above element.
In the following, the reasons why to limiting constituent as described above in the medium carbon steel Micro Alloying wire rod of the present invention, carries out in detail
Describe in detail bright.Here, unless otherwise indicated, the content of component element is represented with weight %.
C：0.35~0.5%
In the present invention, when the content of carbon (C) is less than 0.35%, ferritic transformation can be excessive, due in Surface hardened layer
Ae3 points are high during heat treatment and ferrite can not all dissolve, and the possibility that ferritic phase is partly remained after heat treatment becomes higher.As above
Described, if part residual ferritic phase after heat treatment, can reduce the hardness of steel, the wearability of final steel is low, therefore not
It is preferred that.Therefore, the content of C is preferably more than 0.35%.
Simply, when the content of C is more than 0.5%, ferritic transformation is insufficient, and is predominantly converted to pearlite, therefore difficult
To ensure the impact flexibility to be reached.It is therefore preferred that the content of C is controlled 0.35~0.5% in the present invention.
Si：0.001~0.6%
Silicon (Si) is typical displaced type element, and the processing hardening capacity to steel produces a very large impact.Especially, without soft
Change heat treatment step, but directly carry out after the stretch in the non-hardened and tempered steel of cold-heading, the content increase of the Si can cause to process
Hardening increase, triggers the deterioration of die life.It is therefore preferred that by the control of the content of the Si in low content, if the Si
Content more than 0.6%, then hardening of steel amount increase and cause flexibility to decline, ultimately result in impact toughness decreased.
It is therefore preferred that the content of Si is controlled below 0.6% in the present invention, simply in view of the manufacture work of steel
Sequence, it may include more than 0.001% Si.
Mn：0.8~1.8%
Manganese (Mn) is that substitutional solid solution is formed in matrix, and reduces Al temperature come between making between pearlite layer
The element of gap miniaturization.
The effect above in order to obtain, preferably includes more than 0.8% Mn, however, when the content of Mn is more than 1.8%, deposits
Occur based on manganese segregation nonuniform organization possibility increase the problem of.As described above, when tissue becomes uneven, into
The possibility for the bainite structure for forming part according to the deviation of cooling velocity during row cooling is very high, therefore, is carrying out steel afterwards
Internal cracking is likely to occur during processing.That is, manganese segregation is because relatively low compared to other elements diffusion coefficient, therefore encourages segregation
Area, and the hardening capacity improved therefrom can become the main original for forming centre martensitic structure (core martensite)
Cause.
In addition, when the content of the Mn is less than 0.8%, although influence of the manganese segregation for line of segragation is relatively small,
May have a negative impact since the gap between pearlite layer becomes thick to the impact flexibility of Micro Alloying wire rod.
It is therefore preferred that Mn contents are controlled 0.8~1.8% in the present invention.
Cr：0.05~0.2%
Chromium (Cr) is the important element for the hardenability for improving steel, especially, in the present invention, carries out Surface hardened layer heat treatment
When, it is not only useful in hardenability to ensuring, but also also act as ferritic smoothly to dissolve by carrying out granular to carbide
Effect.
In order to obtain the effect above, the content of Cr is preferably more than 0.05%, simply, when the content of Cr is more than 0.2%,
Since the hardenability of steel excessively increases, it is possible to form cryo tissue, therefore it is not preferred.
It is therefore preferred that Cr contents are controlled 0.05~0.2% in the present invention.
Al：0.01~0.05%
Aluminium (Al) not only acts as the effect of deoxidier, and with the oxygen in steel with reference to and form Al2O3Oxide, forms institute
State after oxide remaining Al and N with reference to and form AlN nitride.
The AlN nitride has the effect for the growth for suppressing austenite grain, and the effect preferably includes in order to obtain
More than 0.01% Al.Simply, when the content of Al is more than 0.05%, thick AlN nitride can be formed, steel can be hindered on the contrary
Physical property, it is therefore not preferred.
It is therefore preferred that the content of Al is controlled 0.01~0.05% in the present invention.
Ni：0.05~0.2%
Under normal circumstances, nickel (Ni) is added to improve corrosion resistance, but in the present invention, nickel (Ni) is to improve
The toughness of steel and add.When the content of Ni is less than 0.05%, the effect above can not be substantially ensured that, on the contrary, when the content of Ni
During more than 0.2%, because of high-priced alloying element, product price is caused to rise, there are the problem of price competitiveness decline.
P：0.01~0.03%
The main reason for phosphorus (P) is segregated in crystal boundary, is to hinder toughness, reduction resistance for delayed fracture, it is therefore preferred that
Its content is as far as possible low.Preferably, in the present invention the content of the P is controlled below 0.03%, but is based on to improve
The oxidative resistance of the P, its content are preferably more than 0.01%.
It is therefore preferred that the content of P is controlled 0.01~0.03% in the present invention.
S：Less than 0.06% (except 0)
Sulphur (S) is low melting point element, is segregated in crystal boundary and reduces toughness, and forms sulfide, to resistance for delayed fracture
And stress relaxation characteristics have a negative impact, it is therefore preferred that its content is as far as possible low.Simply, the S and Mn with reference to and formed
MnS, will effectively improve machinability, it is contemplated that the factor, it is preferable that by the content control of the S, (0 removes below 0.06%
Outside).
N：Less than 0.01% (except 0)
Nitrogen (N) and precipitate generation element with reference to and generate various nitride etc..The nitride plays limitation austenite
The effect of crystallite dimension, when the content of N is more than 0.01%, most nitride becomes thick and can make the physical of steel on the contrary
Matter is low.Accordingly, it is considered to arrive this factor, it is preferable that in the present invention control the content of N below 0.01% (except 0).
In addition to mentioned component, it is preferable that medium carbon steel Micro Alloying wire rod of the invention further includes V：0.02~0.15%
And Ti：One or more of 0.005~0.03% element.The V and Ti are the important elements to form carbide and nitride.
Vanadium (V) forms VC, VN, V (C, N) etc., when these carbide and nitride are with appropriate rolling, makes iron plain
Body miniaturization, has the effect for the toughness for improving Micro Alloying wire rod.When the content of the V is less than 0.02%, V base precipitates
Distribution is reduced, it is impossible to ferrite grain boundaries is fully fixed, so that the effect for improving toughness dies down, on the contrary, when the content of the V surpasses
When 0.15%, thick precipitate can be formed, therefore there can be the problem of reducing toughness on the contrary.
Titanium (Ti) generates thick precipitate when being heated at high temperature steel, and ferrite is used as when austenite is changed into ferrite
Karyogenesis point (site) so that with improve ferrite fraction effect.When the content of the Ti is less than 0.005%, Ti
The distribution of base precipitate is reduced, and can not fully obtain the effect above, on the contrary, when the content of the Ti is more than 0.03%, can shape
Into thick precipitate, there is the problem of main faults generation point as field trash fracture becomes higher.
In addition to above-mentioned constituent, remaining component of medium carbon steel Micro Alloying wire rod of the invention by Fe and can not be kept away
The impurity composition exempted from.
Preferably, the medium carbon steel Micro Alloying wire rod of the invention of above-mentioned constituent is met, its microscopic structure is by ferrite
Formed with pearlite complex tissue, at this time, the ferritic area fraction is more preferably 20~35%.
When the ferritic area fraction is less than 20%, steel processing is likely to result in because the intensity of steel excessively improves
Impatient acute decline, on the contrary, when the ferritic area fraction is more than 35%, may nothing although steel processability improves
Method ensures the intensity for the steel to be reached.
Especially, it is preferable that medium carbon steel Micro Alloying wire rod of the invention is in the thin of the i.e. L sections of parallel cut of rolling direction
Aspect ratio (major axis/minor axis, aspect ratio) of the micro-assembly robot from steel surface to the ferrite crystal grain in 0.2D depth for 3 with
Under, the average minor axis length of the ferrite crystal grain is less than 10 μm (except 0).
The ferrite grain size not only influences the raising of the toughness of steel, but also in follow-up heat treatment, that is, Surface hardened layer
To realizing that easily dissolving has an impact ferrite during heat treatment.
If from wire surface to the aspect ratio of the ferrite crystal grain in 0.2D depth more than 3, ferrite crystal grain at this time
Average minor axis length more than 10 μm, then do not simply fail to fully ensure the toughness of steel, and the meeting after Surface hardened layer heat treatment
Undissolved ferrite is remained, therefore the problem of presence can not ensure sufficient hardness, wherein, the D represents diameter
(diameter)。
Also, maximum deviation (the maximum-most of the pearlite beam size on right-angle cross-section, that is, C sections of rolling direction
Small value) average value be preferably less than 30 μm.When the maximum deviation of the pearlite beam is more than 30 μm, it may occur that the physics of steel
Property section becomes non-uniform problem.
And, it is preferable that medium carbon steel Micro Alloying wire rod of the invention includes V bases precipitate in steel and/or Ti bases separate out
Thing, at this time, precipitate are preferably one or more of VC, VN, V (C, N), TiC and TiN.
Especially, it is preferable that the content for the precipitate that average-size is below 50nm is 30% (face in the whole precipitate
Fraction) more than, if the area fraction for the precipitate that average-size is below 50nm is less than 30%, because of heat exchange after rolling
And the growth of austenite grain can not be suppressed.
The grain growth inhibition of precipitate as described above results from that there are corresponding area during precipitate in crystal boundary
Surface energy is reduced, in order to realize the effect, it is necessary to keep precipitate and the matching of matrix phase.The mistake of different precipitates
Go the size with the matching of matrix phase to have differences, matching can be lost when generally full-size is more than 50nm.
Therefore, it may be preferable that in the present invention, the average-size of the V bases precipitate in steel and/or Ti base precipitates is controlled
In below 50nm, when meeting that the area fraction of precipitate of the condition is at least more than 30%, austenite grain ruler can be obtained
Very little control effect.
As described above, all meet that the constituent of steel and the medium carbon steel Micro Alloying wire rod of the invention of microscopic structure have
Following feature：Room temperature impact toughness (U-notch) is very excellent for more than 58J, and because Surface hardened layer heat-treatability is excellent,
It is able to ensure that the hardness after heat treatment is more than 45HRc.
Refer to here, Surface hardened layer heat-treatability is excellent, when the medium carbon steel Micro Alloying wire rod progress surface to the present invention is hard
When changing heat treatment, since the ferrite in steel is all dissolved, it is ensured that sufficient hardness, so that it is guaranteed that steel is excellent wear-resisting
Property.
In the following, the manufacture method of the medium carbon steel Micro Alloying wire rod excellent to the Surface hardened layer heat-treatability of the present invention carries out in detail
Describe in detail bright.
Following manufacture method it is merely meant that the preferred embodiment of the manufacture method of the medium carbon steel Micro Alloying wire rod of the present invention,
It's not limited to that for its manufacture method.
First, prepare after meeting the steel of above-mentioned constituent, it is preferable that heat at a temperature of less than 1050 DEG C
Less than 150 minutes.
The heating is being heated to less than being carried out in 1050 DEG C of heating furnace, if the temperature of the heating furnace
Reach more than 1050 DEG C, then the precipitate formed in steel can melt, and cause the fixed effect of austenite grain to die down, and be formed thick
Austenite, finally had an impact to forming ferrite core, can there is the problem of overall ferrite fraction declines.Also, work as
When heating time is long more than 150 minutes, it is possible to which precipitate grows and becomes thick, therefore not preferred.That is, the temperature of heating furnace
Degree higher and heating time is longer, and precipitate becomes thicker, therefore, for the matching by keeping precipitate and matrix phase
To obtain austenite grain size inhibition, it is preferable that carry out low-temperature heat within the time of restriction.
It is therefore preferred that the present invention heating be heat at a temperature of less than 1050 DEG C 150 minutes with
Under, it is highly preferred that heating 60~150 minutes more than 950 DEG C and within the temperature range of being less than 1050 DEG C.
Preferably, the steel being heat treatment as described above is subjected to hot finishing.
When carrying out the hot finishing, temperature produces large effect, therefore, institute in order to obtain to austenite grain size
The microscopic structure to be reached, it is preferable that implement hot finishing within the temperature range of 780~800 DEG C.
When hot finishing temperature is less than 780 DEG C, because temperature is in two-phase section temperature range, intensity can be not only improved to institute
Need more than intensity, but also may have a negative impact to the raising of toughness, thus it is not preferred.On the contrary, when hot finishing temperature surpasses
When crossing 800 DEG C, the ferrite fraction final because of thick austenite grain is reduced, and causes toughness to decline.
After carrying out hot finishing as described above, it is preferable that implement refrigerating work procedure with the cooling velocity of 0.5~3 DEG C/s.
When cooling velocity when cooled is less than 0.5 DEG C/s, austenite grain and ferrite crystal grain life in cooling procedure
It is long, excessively tufftride and there is the problem of being unable to reach target strength, on the contrary, when cooling velocity is more than 3 DEG C/s, formation low temperature
Tissue, is possible to produce internal cracking in processing, therefore not preferred.
As described above, the medium carbon steel of the invention that can be manufactured to process [the smart bundle-cooling of heating-heat] process is non-
Quenched wire rod carries out Surface hardened layer heat treatment.
Surface hardened layer heat treatment is to carry out sensing heating by being able to carry out the copper coil of internal water cooling, refer to by
Wire rod inside copper coil continually by sensing electric current is produced, so that the method quickly heated.At this time, it is preferable that 900~
In the range of 1200 DEG C, within heating 10 seconds, water cooling or oil hardening (oil quenching) are then carried out.
The medium carbon steel Micro Alloying wire rod of the present invention has when the Surface hardened layer is heat-treated, whole ferritic phases in steel
All it is dissolved in a short time, the advantages of so as to ensure the hardness to be reached.
In the following, the present invention is explained in more detail by embodiment.Simply, following embodiments is to say in further detail
Bright of the invention and exemplary, it does not limit the interest field of the present invention.The interest field of the present invention is recorded by claims
Content and the content that thus rationally derives determine.
[mode to carry out an invention]
(embodiment)
First, the steel with constituent as shown in the following Table 1 is prepared.Using the steel prepared as sample, it is cast as
The steel ingot (ingot) of 50kg, then at a temperature of 1200 DEG C by the steel ingot carry out 20 it is small when homogeneity be heat-treated, then
It is air-cooled to room temperature.Afterwards, each material is welded on to the rear end of the square steel billets (billet) of 160mm, and it is cold in actual wire rod
But hot rolling is implemented on line.At this time, heating furnace Extracting temperature is 1040 DEG C, in table 2 below it is shown it is various under the conditions of it is real respectively
Apply the heating within 150 minutes.Also, the hot rolling is the material of 26mm, its temperature conditions represents in table 2 below.Institute
After stating hot rolling, each wire rod is cooled down with the cooling velocity of 0.5~0.8 DEG C/s.
Ferritic fraction in the microscopic structure of each wire rod manufactured as described above is measured, also, it is ferritic vertical
It is horizontal than being measured by observing the microscopic structure in the parallel face (L sections) of rolling direction.Moreover, ferrite crystal grain
Average minor axis length is to draw average value by measuring the ferrite thickness in tissue.
Moreover, to measure the impact flexibility of the wire rod produced, after being fabricated to the test piece of 10 × 10mm specifications, U-shaped is utilized
Notch (U-notch) measures.
The measurement result is represented in following table 2.
In addition, Surface hardened layer heat treatment is carried out to each wire rod manufactured.At this time, heat treatment is as sensing heating heat
Processing, is implemented using the condition within being heated 10 seconds in the range of 900~1200 DEG C to all test pieces.
After the sensing heating heat treatment has been carried out, heat is judged by observing case hardness and surface element microscopic structure
The appropriateness of processing.For the appropriateness of the heat treatment, it is heat-treated when by applying identical frequency and equal-wattage
When, soft nitrogen ferritic phase is all solid-solubilized in Effects of Heat Treatment portion, so as to form uniform tempered martensite (tempered
It is most excellent to be determined as heat treatment appropriateness when martensite), and to sensing heatings such as frequency at this time, the quantity of power applied
Heat treatment parameter is not adjusted.
[table 1]
[table 2]
In the table 2, " ferrite fraction " represents area fraction (%), and " aspect ratio " represents deep from steel surface to 0.2D
The major axis/minor axis ratio of ferrite crystal grain in degree, " crystal grain minor axis length " represent the average minor axis length (μm) of ferrite crystal grain.
" hardness is not inconsistent " is the constituent for considering steel, when less than theoretical hardness value 80% when, be judged as hardness not
Symbol, here, theoretical hardness value is drawn by the hardometer formula of the carbon content (%C) in ASTM A255-02.It is theoretical
Formula is to have followed H=35.395+6.990 (%C)2- 821.744 (%C)3+ 1015.479 (%C)4- 538.346 (%C)5, its
In, H represents HRC values.
As shown in the table 2, it can confirm, with the increase of the ferrite fraction in wire rod microscopic structure, On Impact Toughness
Value has an impact, also, case hardness is also had an impact when sensing heating is heat-treated.
Moreover, can confirm, notched bar impact strength shows the increase with ferrite fraction, and notched bar impact strength continuation is increased to incline
To, on the contrary, after heat treatment, ferritic fraction is more reduced, case hardness will more increase, and as defined in reaching during the value above
It will show defined value.This is because it is driven whether meeting in carrying out sensing heating heat treatment is by ferritic solid solution.That is,
, can shape in the sensing heating heat treatment with short heat treatment time when ferritic fraction is high or ferrite is thick
Do not change phase into what ferritic phase will not be transformed into austenite phase, eventually influence superficial hardness number.
In addition, can confirm, as with the relevant process factor of ferrite fraction, hot finishing temperature and cooling velocity produce it
Raw influence is maximum, and when hot finishing temperature is excessive, On Impact Toughness has a negative impact.
Claims (7)
1. a kind of excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability, the wire rod, in terms of weight %, by carbon (C)：
0.35~0.5%, silicon (Si)：0.001~0.6%, manganese (Mn)：0.8~1.8%, chromium (Cr)：0.05~0.2%, aluminium (Al)：
0.01~0.05%, nickel (Ni)：0.05~0.2%, phosphorus (P)：0.01~0.03%, sulphur (S)：Less than 0.06%, nitrogen (N)：
Less than 0.01%, selected from vanadium (V)：0.02~0.15% and titanium (Ti)：One or more of 0.005~0.03% element, surplus
Fe and inevitable impurity composition；Microscopic structure is answered by the ferrite that area fraction is 20~35% with remaining pearlite
It is combined and knits composition；And the wire rod includes V bases precipitate and/or Ti base precipitates, V bases precipitate and/or Ti the bases analysis
The area fraction for going out the precipitate that average-size is below 50nm in thing whole precipitate is more than 30%.
2. the excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability according to claim 1, the wire rod from
Surface to the ferrite crystal grain in 0.2D depth aspect ratio (major axis/minor axis) be less than 3, the ferrite crystal grain it is average short
Shaft length is less than 10 μm, except 0, wherein, the D represents diameter.
3. the excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability according to claim 1, the pearl of the wire rod
The maximum deviation of body of light beam size is less than 30 μm.
4. the excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability according to claim 1, the room of the wire rod
Warm impact flexibility is more than 58J.
5. a kind of manufacture method of the excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability, it comprises the following steps：
Prepare steel, the steel, in terms of weight %, by carbon (C)：0.35~0.5%, silicon (Si)：0.001~0.6%, manganese (Mn)：
0.8~1.8%, chromium (Cr)：0.05~0.2%, aluminium (Al)：0.01~0.05%, nickel (Ni)：0.05~0.2%, phosphorus (P)：
0.01~0.03%, sulphur (S)：Less than 0.06%, nitrogen (N)：Less than 0.01%, selected from vanadium (V)：0.02~0.15% and titanium
(Ti)：One or more of 0.005~0.03% element, the Fe of surplus and inevitable impurity composition；
The steel is heated less than 150 minutes at a temperature of less than 1050 DEG C；
The heated steel is implemented into hot finishing within the temperature range of 780~800 DEG C；And
After the hot finishing, cooled down with the cooling velocity of 0.5~3 DEG C/s.
6. the manufacture method of the excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability according to claim 5, institute
After stating cooling, the aspect ratio (major axis/minor axis) from steel surface to the ferrite crystal grain in 0.2D depth is less than 3, the iron element
The average minor axis length of body crystal grain is less than 10 μm, except 0.
7. the manufacture method of the excellent medium carbon steel Micro Alloying wire rod of Surface hardened layer heat-treatability according to claim 5,
After the cooling, Surface hardened layer heat treatment step is further included.
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| KR101819343B1 (en) * | 2016-07-01 | 2018-01-17 | 주식회사 포스코 | Wire rod having excellent drawability and method for manufacturing the same |
| KR101867677B1 (en) * | 2016-07-22 | 2018-06-15 | 주식회사 포스코 | Steel wire rod having enhanced delayed fracture resistance and method for manufacturing the same |
| KR101977467B1 (en) * | 2017-05-29 | 2019-05-13 | 주식회사 포스코 | Wire rod having excellent strength and cold forging characteristics and method for manufacturing same |
| WO2021172604A1 (en) * | 2020-02-24 | 2021-09-02 | 주식회사 포스코 | Non-heat treated wire rod with excellent wire drawability and impact toughness and manufacturing method therefor |
| CN114262851A (en) * | 2020-09-16 | 2022-04-01 | 宝山钢铁股份有限公司 | High-strength and high-toughness non-quenched and tempered steel and round steel for hot forging and manufacturing method thereof |
| KR102429603B1 (en) * | 2020-11-27 | 2022-08-05 | 주식회사 포스코 | Wire rod for cold working with improved stress corrosion resistance and method for manufacturing the same |
| KR102464609B1 (en) * | 2021-07-21 | 2022-11-07 | 현대제철 주식회사 | Non-tempered steel for steering rack bar and manufacturing method thereof |
| KR20230096258A (en) | 2021-12-23 | 2023-06-30 | 주식회사 포스코 | Medium carbon structural steel having excellent surface hardenability and machinability, and its manufacturing process |
| WO2023229428A1 (en) * | 2022-05-27 | 2023-11-30 | 주식회사 포스코 | Non-quenched and tempered steel rod wire for hot forging with improved machinability and toughness and method for manufacturing same |
| CN115537663B (en) * | 2022-10-13 | 2023-06-02 | 宝武杰富意特殊钢有限公司 | High-silicon high-nitrogen non-quenched and tempered steel and preparation method thereof |
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