CN105671458A - Non-quenched and tempered medium carbon steel wire having excellent surface hardening thermal treatment performance and manufacturing method thereof - Google Patents
Non-quenched and tempered medium carbon steel wire having excellent surface hardening thermal treatment performance and manufacturing method thereof Download PDFInfo
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- CN105671458A CN105671458A CN201510628966.4A CN201510628966A CN105671458A CN 105671458 A CN105671458 A CN 105671458A CN 201510628966 A CN201510628966 A CN 201510628966A CN 105671458 A CN105671458 A CN 105671458A
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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
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Abstract
The invention relates to a non-quenched and tempered medium carbon steel wire having excellent surface hardening thermal treatment performance and manufacturing method thereof. The non-quenched and tempered medium carbon steel wire comprises one or more components, by weight %: Carbon (C): 0.35-0.5%, silicon (Si): 0.001-0.6%, manganese (Mn): 0.8-1.8%, chromium (Cr): 0.05 to 0.2%, aluminum (Al): 0.01-0.05%, a nickel (Ni): 0.05-0.2%, phosphorus (P): 0.01-0.03%, sulfur ( S): 0.06% or less, nitrogen (N): 0.01% or less, vanadium (V): 0.02-0.15%, and titanium (Ti): 0.005-0.03%. The rest is Fe and unavoidable impurities; a fine structure is constituted by area fraction of 20 to 35% of ferrite and pearlite composite structure.
Description
Technical field
The present invention relates to a kind of Micro Alloying wire rod, more specifically, it relates to the medium carbon steel Micro Alloying wire rod of a kind of surface hardening heat-treatability excellence and manufacture method thereof.
Background technology
Generally, medium carbon steel wire rod is used for cold working, now, in order to improve the processing characteristics of medium carbon steel wire rod, implement the thermal treatment such as low-temperature annealing thermal treatment or ball heat-transmission process, after waiting processing through forging, implement Quench and temper (quenchingandtempering) thermal treatment for giving physical properties.
But, when the accessory high to numeral accuracy requirement or requirement reduce thermal treatment expense, main use omits above-mentioned heat treated non-hardened and tempered steel.
Described non-hardened and tempered steel, processes without low-temperature annealing thermal treatment and ball heat-transmission after manufacturing wire rod, but directly can manufacture product by stretching with direct cold forging. As mentioned above, it is necessary, in order to manufacture product in without heat treated situation, described Micro Alloying wire rod need to possess high tenacity, at present it is known that the microscopic structure of wire rod especially ferrite fraction toughness is had an impact.
In addition, the method of the toughness of raising Micro Alloying wire rod known at present has, the carbide that can fix the ferrite grain boundaries such as Ti, Nb, V by adding and nitride form element, and miniaturization and the coarsening of austenite crystal is stoped by controlled rolling, form ferrite at austenite grain boundary, improve toughness by ferrite miniaturization.
But, aforesaid method need to control the precipitate formed by Ti, Nb, V etc. well, and owing to using block iron (bloom) etc., furnace temp need to be increased to more than 1200 DEG C, and what therefore there is enterprise uses restricted shortcoming.
Further, the manufacture method as the high tenacity non-hardened and tempered steel of good economy performance has, and utilizes Bao Xingge effect (Bauschingereffect) to form the method for ferrite+perlite lamellar structure within the scope of 0.2 weight % medium carbon steel.
Above-mentioned lamellar structure has impelling strength maximumization that can make steel and the advantage utilizing plain carbon stool, but, because of lamellar structure, material itself has directivity, therefore has and uses restricted shortcoming.
Summary of the invention
(1) technical problem solved
An aspect of the present invention, its object is to provide a kind of and effectively guarantees that surface hardening heat-treatability is to improve medium carbon steel Micro Alloying wire rod and the manufacture method thereof of the wear resistance of Micro Alloying wire rod.
(2) technical scheme
An aspect of the present invention, the medium carbon steel Micro Alloying wire rod of a kind of surface hardening heat-treatability excellence is provided, described wire rod, in weight %, comprise: 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): more than one elements in 0.005～0.03%, all the other are for be made up of Fe and inevitable impurity, microscopic structure by area fraction be 20～35% ferrite and remaining perlite complex tissue form.
Another aspect of the present invention, it is provided that the manufacture method of the medium carbon steel Micro Alloying wire rod of a kind of surface hardening heat-treatability excellence, it comprises the following steps: the steel preparing to meet described moiety; By described steel heat treated less than 150 minutes at lower than the temperature of 1050 DEG C; The described steel heated is implemented hot finishing in the temperature range of 780～800 DEG C; And, after described hot finishing, cool with the speed of cooling of 0.5～3 DEG C/s.
(3) useful effect
According to the present invention, when not adding expensive element, it may be possible to provide one is tenacity excellent not only, and can improve the medium carbon steel Micro Alloying wire rod of hardness and excellent in abrasion resistance after surface hardening thermal treatment.
Embodiment
[implementing the most preferably mode of invention]
Generally, while improving the toughness of Micro Alloying wire rod and forming the microscopic structure being made up of the complex tissue of ferrite and pearlite, described ferritic granular is realized. This kind of complex tissue has the physical properties of impelling strength excellence because it has lamellar structure, but, is needing the place possessing abrasion-proof physical character, likely causes the problem of parts shortening in work-ing life because of soft. For overcoming this kind of problem, as operation method, adopt a kind of by common steel being carried out carburizing or nitriding treatment improves hardness, or improve surface hardness by the induction heating of local, thus improve the method for wear resistance.
In the present invention, scheme for the problem solved on material as above is, carry out the above-mentioned Micro Alloying wire rod with complex tissue carrying out in described heat treated process while that surface hardening being heat treated, hardness is improved by improving heat-treatability, so that it is guaranteed that the wear resistance of excellence.
For this reason, the present inventor confirms when optimizing the microscopic structure of Micro Alloying wire rod, particularly when optimizing ferrite grain size, it is possible to significantly improves surface hardening heat-treatability, obtains the physical properties of the excellence to be reached, and finally complete the present invention.
Below, the present invention is described in detail.
The medium carbon steel Micro Alloying wire rod of the surface hardening heat-treatability excellence of an aspect of the present invention, in 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): more than one elements in 0.005～0.03%.
Below, reason moiety limited as described above in the medium carbon steel Micro Alloying wire rod of the present invention is described in detail. At this, unless otherwise explanation, the content of composition element all represents with weight %.
C:0.35～0.5%
In the present invention, when the content of carbon (C) is lower than 0.35%, ferritic transformation can excessively, and owing to when surface hardening thermal treatment, Ae3 point is high and ferrite cannot all dissolve, the possibility of thermal treatment rear section residual ferritic phase becomes height. If as mentioned above, it is necessary, part remains ferritic phase after heat treatment, then can reduce the hardness of steel, the wear resistance of final steel is low, therefore not preferred. Therefore, the content of C is preferably more than 0.35%.
Just, when the content of C is more than 0.5%, ferritic transformation is insufficient, and is predominantly converted to perlite, therefore, it is difficult to guarantee the impelling strength to be reached. It is preferred, therefore, that in the present invention the content of C is controlled 0.35～0.5%.
Si:0.001～0.6%
Silicon (Si) is typical displaced type element, the work hardening amount of steel is produced a very large impact. Especially, without softening heat treatment step, but directly carrying out in the non-hardened and tempered steel of cold-heading after the stretch, the content increase of described Si can cause work hardening to increase, and causes the deterioration of die life. It is preferred, therefore, that control the content of described Si at low levels, if the content of described Si is more than 0.6%, then Hardening Of Steel amount increases and causes flexibility to decline, and finally causes impelling strength to decline.
It is preferred, therefore, that control below 0.6% by the content of Si in the present invention, just consider the manufacturing process of steel, the Si of more than 0.001% can be comprised.
Mn:0.8～1.8%
Manganese (Mn) forms displaced type sosoloid in matrix, and reduces Al temperature to make the element of the gap miniaturization between pearlite layer.
In order to obtain above-mentioned effect, it is preferable that comprise the Mn of more than 0.8%, but, when the content of Mn is more than 1.8%, there is the problem occurring the possibility of the uneven microstructure based on manganese segregation to increase. As mentioned above, it is necessary, when tissue becomes uneven, when cooling, the possibility of the bainite structure of deviation forming section according to speed of cooling is very high, therefore, adds and man-hour internal cracking likely occurs carrying out steel afterwards. That is, manganese segregation is relatively low because comparing other Elements Diffusion coefficients, therefore encourages segregation district, and improve therefrom rigid meeting can become the major cause at position, formation center martensitic stucture (coremartensite).
In addition, when the content of described Mn is lower than 0.8%, although manganese segregation is relatively little for the impact in segregation district, but, the impelling strength of Micro Alloying wire rod may be had a negative impact greatly owing to the gap between pearlite layer is thicker.
It is preferred, therefore, that in the present invention Mn content is controlled 0.8～1.8%.
Cr:0.05～0.2%
Chromium (Cr) is the important element of the quenching improving steel, especially, in the present invention, when carrying out surface hardening thermal treatment, not only useful to guaranteeing in quenching property, but also plays and dissolve ferritic effect smoothly by carbide is carried out granular.
In order to obtain above-mentioned effect, the content of Cr is preferably more than 0.05%, just, when the content of Cr is more than 0.2%, owing to the quenching of steel excessively increases, it is possible to form low temperature tissue, therefore not preferred.
It is preferred, therefore, that in the present invention Cr content is controlled 0.05～0.2%.
Al:0.01～0.05%
Aluminium (Al) not only plays the effect of reductor, and the oxygen in steel is combined and forms Al2O3Oxide compound, after forming described oxide compound, remaining Al and N combines and forms AlN nitride.
Described AlN nitride has the effect of the growth suppressing austenite crystal, in order to obtain the Al that described effect preferably includes more than 0.01%. Just, when the content of Al is more than 0.05%, thick AlN nitride can be formed, the physical properties of steel can be hindered on the contrary, therefore not preferred.
It is preferred, therefore, that in the present invention the content of Al is controlled 0.01～0.05%.
Ni:0.05～0.2%
Generally, nickel (Ni) adds to improve solidity to corrosion, but in the present invention, nickel (Ni) is the toughness in order to improve steel and adds. When the content of Ni is lower than 0.05%, cannot fully guarantee above-mentioned effect, on the contrary, when the content of Ni is more than 0.2%, because of high price alloying element, cause product price to rise to there is the problem of price competitiveness decline.
P:0.01～0.03%
Phosphorus (P) is segregated in crystal boundary, is hinder toughness, reduces the major cause of resistance for delayed fracture, it is preferred, therefore, that its content is as far as possible low. Preferably, content by described P controls below 0.03% in the present invention, but in order to improve the scale resistance based on described P, its content is preferably more than 0.01%.
It is preferred, therefore, that in the present invention the content of P is controlled 0.01～0.03%.
Below S:0.06% (except 0)
Sulphur (S) is low melting point element, is segregated in crystal boundary and reduces toughness, and forms sulfide, resistance for delayed fracture and stress relaxation characteristics is had a negative impact, it is preferred, therefore, that its content is as far as possible low. Just, described S and Mn combination and form MnS, will effectively improve machinability, it is contemplated that to this factor, it may be preferred that controlled by the content of described S below 0.06% (except 0).
Below N:0.01% (except 0)
Nitrogen (N) is combined and generate various nitride etc. with precipitate generting element. Described nitride plays the effect of restriction austenite grain size, and when the content of N is more than 0.01%, the nitride of major part is thicker can make greatly and on the contrary the physical properties of steel low. Thus it is contemplated that to this kind of factor, it may be preferred that in the present invention the content of N is controlled below 0.01% (except 0).
Except mentioned component, it may be preferred that the medium carbon steel Micro Alloying wire rod of the present invention also comprises more than one elements in V:0.02～0.15% and Ti:0.005～0.03%. Described V and Ti is the important element forming carbide and nitride.
Vanadium (V) forms VC, VN, V (C, N) etc., when these carbide and nitride are with suitable rolling, make ferrite miniaturization, has the effect of the toughness improving Micro Alloying wire rod. When the content of described V is lower than 0.02%, the distribution of V base precipitate reduces, and can not fully fix ferrite grain boundaries, thus the effect improving toughness becomes weak, on the contrary, when the content of described V is more than 0.15%, thick precipitate can be formed, therefore can there is the problem reducing toughness on the contrary.
Titanium (Ti) generates thick precipitate when heat steel, is used as ferritic karyogenesis point (site) when austenitic transformation is ferrite, thus has the effect improving ferrite fraction. When the content of described Ti is lower than 0.005%, the distribution of Ti base precipitate reduces, and cannot fully obtain above-mentioned effect, on the contrary, when the content of described Ti is more than 0.03%, forming thick precipitate, the possibility of the main faults generation point that existence is ruptured as inclusion becomes high problem.
Except above-mentioned moiety, all the other compositions of the medium carbon steel Micro Alloying wire rod of the present invention are made up of Fe and inevitable impurity.
Preferably, meeting the medium carbon steel Micro Alloying wire rod of the present invention of above-mentioned moiety, its microscopic structure is made up of ferrite and pearlite complex tissue, and now, described ferritic area fraction is more preferably 20～35%.
When described ferritic area fraction is lower than 20%, because the intensity of steel excessively improves and likely cause steel processibility sharply to decline, on the contrary, when described ferritic area fraction is more than 35%, although steel processibility improves, but possibly cannot guarantee the intensity of the steel to be reached.
Especially, preferably, the medium carbon steel Micro Alloying wire rod of the present invention is from steel surface to the aspect ratio (major axis/minor axis of the ferrite crystal grain in the 0.2D degree of depth at the parallel cross section of rolling direction and the microscopic structure in L cross section, aspectratio) being less than 3, the average minor axis length of described ferrite crystal grain is less than 10 μm (except 0).
Described ferrite grain size not only affects the raising of the toughness of steel, and easily dissolves when follow-up thermal treatment and surface hardening thermal treatment have an impact to realizing ferrite.
If, from wire surface to the aspect ratio of the ferrite crystal grain in the 0.2D degree of depth more than 3, the average minor axis length of ferrite crystal grain now is more than 10 μm, then not only cannot fully guarantee the toughness of steel, and undissolved ferrite can be remained after surface hardening thermal treatment, therefore there is the problem that cannot guarantee sufficient hardness, wherein, described D represents diameter (diameter).
Further, the mean value of the maximum deviation (maximum value-minimum value) of the perlite bundle size in the right-angle cross-section and C cross section of rolling direction is preferably less than 30 μm. When the maximum deviation of described perlite bundle is more than 30 μm, the problem that the physical properties part of steel becomes uneven can be there is.
And, it may be preferred that the medium carbon steel Micro Alloying wire rod of the present invention comprises V base precipitate and/or Ti base precipitate at steel, now, precipitate be preferably in VC, VN, V (C, N), TiC and TiN more than one.
Especially, preferably, in described whole precipitate, mean sizes is the content of the precipitate of below 50nm is more than 30% (area fraction), if the area fraction that mean sizes is the precipitate of below 50nm is lower than 30%, then after rolling, the growth of austenite crystal cannot be suppressed because of heat exchange.
The grain growing inhibition of precipitate as above is that the surface energy because of area corresponding to crystal boundary exists precipitate reduces, in order to realize described effect, it is necessary to keep the matching of precipitate with matrix phase. There is difference in the size losing the matching with matrix phase of different precipitates, overall dimension is more than losing matching during 50nm substantially.
Preferentially, in the present invention, therefore, the mean sizes of the V base precipitate in steel and/or Ti base precipitate is controlled at below 50nm, when the area fraction of the precipitate meeting this condition is at least more than 30%, the control effects of austenite grain size can be obtained.
As mentioned above, the medium carbon steel Micro Alloying wire rod all meeting the moiety of steel and the present invention of microscopic structure has following feature: room temperature impact toughness (U-notch) is very excellent for more than 58J, and because of surface hardening heat-treatability excellence, it is possible to guarantee that the hardness after thermal treatment is more than 45HRc.
At this, surface hardening heat-treatability excellence refers to, when the medium carbon steel Micro Alloying wire rod of the present invention is carried out surface hardening thermal treatment, owing to the ferrite in steel is all dissolved, it is ensured that hardness fully, so that it is guaranteed that the wear resistance of the excellence of steel.
Below, the manufacture method of the medium carbon steel Micro Alloying wire rod of the surface hardening heat-treatability excellence of the present invention is described in detail.
Following manufacture method just represents the preferred embodiment of the manufacture method of the medium carbon steel Micro Alloying wire rod of the present invention, and its manufacture method is not limited thereto.
First, after the steel preparing to meet above-mentioned moiety, it may be preferred that heat treated less than 150 minutes at lower than the temperature of 1050 DEG C.
Described heat treated carries out being heated in the process furnace lower than 1050 DEG C, if the temperature of described process furnace reaches more than 1050 DEG C, the precipitate then formed in steel can melt, the fixed effect of austenite crystal is caused to become weak, form thick austenite, finally formation ferrite core is had an impact, can there is the problem of overall ferrite fraction decline. Further, when heated between more than 150 minutes cross long time, it is possible to precipitate growth and greatly thicker, therefore not preferred. That is, the temperature of process furnace is more high and heat-up time is more long, and precipitate becomes more thick, therefore, in order to by keeping the matching of precipitate and matrix phase to obtain austenite grain size inhibition, it may be preferred that carry out low-temperature heat within the time limited.
It is preferred, therefore, that the heat treated of the present invention is heat treated less than 150 minutes at lower than the temperature of 1050 DEG C, it is more preferable to ground, be greater than 950 DEG C and lower than the temperature range of 1050 DEG C in heat treated 60～150 minutes.
Preferably, the steel being heat treatment as described above is carried out hot finishing.
When carrying out described hot finishing, austenite grain size is produced bigger impact by temperature, therefore, in order to obtain the microscopic structure to be reached, it may be preferred that implement hot finishing in the temperature range of 780～800 DEG C.
When hot finishing temperature is lower than 780 DEG C, because temperature is in two-phase region temperature range, not only intensity can be increased to more than desirable strength, but also the raising of toughness may be had a negative impact, therefore not preferred. On the contrary, when hot finishing temperature is more than 800 DEG C, because of thick austenite crystal, final ferrite fraction reduces, and causes toughness to decline.
After carrying out hot finishing as described above, it may be preferred that implement cooling operation with the speed of cooling of 0.5～3 DEG C/s.
When speed of cooling when cooled is less than 0.5 DEG C/s, austenite crystal and ferrite crystal grain growth in process of cooling, too tufftride and there is the problem that cannot reach target strength, on the contrary, when speed of cooling is more than 3 DEG C/s, formation low temperature tissue, likely produces internal cracking adding man-hour, therefore not preferred.
As mentioned above, it is necessary, the medium carbon steel Micro Alloying wire rod of the present invention manufactured through [heat treated-Re essence pricks-cooling] operation can be carried out surface hardening thermal treatment.
Described surface hardening thermal treatment is that the copper coil by performing internal water cooling carries out induction heating, refers to wire rod continually by copper coil inside to produce induced current, thus the method for rapid heating. Now, it may be preferred that within the scope of 900～1200 DEG C, heat within 10 seconds, then carry out water-cooled or oil quenching (oilquenching).
The medium carbon steel Micro Alloying wire rod of the present invention has when described surface hardening thermal treatment, and the whole ferritic phases in steel are all dissolved within the short period of time such that it is able to guarantee the advantage of the hardness to be reached.
Below, by embodiment, the present invention is described in further detail. Just, following embodiment is in order to illustrate the present invention more in detail and example, and it does not limit the interest field of the present invention. The content that the interest field of the present invention is carried by claim secretary and the content thus rationally derived determine.
[implementing the mode of invention]
(embodiment)
First, prepare to have the steel of moiety as shown in the following Table 1.Using the steel for preparing as sample, it is cast as the steel ingot (ingot) of 50kg, then at the temperature of 1200 DEG C, described steel ingot is carried out the homogeneity thermal treatment of 20 hours, then air-cooled to room temperature. Afterwards, each material is welded on the rear end of the square steel billets (billet) of 160mm, and implements hot rolling on the wire rod cooling line of reality. Now, process furnace Extracting temperature is 1040 DEG C, the heating within implementing respectively 150 minutes under the various conditions shown in table 2 below. Further, described hot rolling is the material of 26mm, and its temperature condition represents in table 2 below. After described hot rolling, each wire rod is all cooled with the speed of cooling of 0.5～0.8 DEG C/s.
Measure ferritic mark in the microscopic structure of each wire rod manufactured as described above, and, the microscopic structure that ferritic aspect ratio is the parallel face (L cross section) by observing rolling direction is measured. And, the average minor axis length of ferrite crystal grain is that the ferrite thickness by measuring in tissue draws mean value.
And, for measuring the impelling strength of the wire rod produced, after being made into the test piece of 10 × 10mm specification, utilize U v notch v (U-notch) to measure.
Described measuring result is represented in following table 2.
In addition, the described each wire rod manufactured is carried out surface hardening thermal treatment. Now, thermal treatment, as induction heating thermal treatment, is adopt the condition within all test pieces being heated 10 seconds within the scope of 900～1200 DEG C to implement.
After having carried out described induction heating thermal treatment, judge heat treated appropriateness by observing surface hardness and surface element microscopic structure. For described heat treated appropriateness, when being heat-treated by applying same frequency and equal-wattage, soft nitrogen ferritic phase is all solid-solubilized in thermal treatment affects portion, thus it is the most excellent to be defined as thermal treatment appropriateness when forming uniform tempered martensite (temperedmartensite), and the induction heating thermal treatment parameters such as the quantity of power of frequency now, applying are adjusted.
[table 1]
[table 2]
In described table 2, " ferrite fraction " represents area fraction (%), " aspect ratio " represents the major axis/minor axis ratio from steel surface to the ferrite crystal grain in the 0.2D degree of depth, and " crystal grain minor axis length " represents average minor axis length (μm) of ferrite crystal grain.
" hardness is not inconsistent " is, it is contemplated that the moiety of steel, when being less than the 80% of theoretical hardness value, is judged as that hardness is not inconsistent, and at this, theoretical hardness value is drawn by the sclerometer formula of the carbon content (%C) in ASTMA255-02. Theoretical formula have followed H=35.395+6.990 (%C)2-821.744 (%C)3+ 1015.479 (%C)4-538.346 (%C)5, wherein, H represents HRC value.
As shown in described table 2, can confirm, along with the increase of the ferrite fraction in wire rod microscopic structure, notched bar impact strength be had an impact, and, when induction heating thermal treatment, surface hardness is also had an impact.
And, can confirm, notched bar impact strength display is along with the increase of ferrite fraction, notched bar impact strength continues the tendency increased, on the contrary, after heat treatment, ferritic mark more reduces, and surface hardness will more increase, and will show the value of regulation when reaching more than the value of regulation. This is because carrying out induction heating thermal treatment is understood by whether ferritic solid solution is driven. That is, when ferritic mark height or ferrite are thick, when the induction heating thermal treatment with short heat treatment time, what can form that ferritic phase can not be transformed into austenite phase does not change phase, finally can affect surface hardness value.
In addition, can confirming, the impact it produced as the operation factor relevant to ferrite fraction, hot finishing temperature and speed of cooling is maximum, when hot finishing temperature is too high, impelling strength is had a negative impact.
Claims (8)
1. the medium carbon steel Micro Alloying wire rod of a surface hardening heat-treatability excellence, described wire rod, in weight %, comprise: 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): more than one elements in 0.005～0.03%, all the other are for be made up of Fe and inevitable impurity, microscopic structure by area fraction be 20～35% ferrite and remaining perlite complex tissue form.
2. the medium carbon steel Micro Alloying wire rod of surface hardening heat-treatability excellence according to claim 1, the aspect ratio (major axis/minor axis) from surface to the ferrite crystal grain in the 0.2D degree of depth of described wire rod is less than 3, the average minor axis length of described ferrite crystal grain is less than 10 μm, except 0, wherein, described D represents diameter.
3. the medium carbon steel Micro Alloying wire rod of surface hardening heat-treatability excellence according to claim 1, the maximum deviation of the perlite bundle size of described wire rod is less than 30 μm.
4. the medium carbon steel Micro Alloying wire rod of surface hardening heat-treatability excellence according to claim 1, described wire rod comprises V base precipitate and/or Ti base precipitate, and in described whole precipitate, mean sizes is the area fraction of the precipitate of below 50nm is more than 30%.
5. the medium carbon steel Micro Alloying wire rod of surface hardening heat-treatability excellence according to claim 1, the room temperature impact toughness of described wire rod is more than 58J.
6. a manufacture method for the medium carbon steel Micro Alloying wire rod of surface hardening heat-treatability excellence, it comprises the following steps:
Prepare steel, described steel, in weight %, comprise: 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): more than one elements in 0.005～0.03%, all the other are for be made up of Fe and inevitable impurity,
By described steel heat treated less than 150 minutes at lower than the temperature of 1050 DEG C;
The described steel heated is implemented hot finishing in the temperature range of 780～800 DEG C; And
After described hot finishing, cool with the speed of cooling of 0.5～3 DEG C/s.
7. the manufacture method of the medium carbon steel Micro Alloying wire rod of surface hardening heat-treatability excellence according to claim 6, after described cooling, it is less than 3 from steel surface to the aspect ratio (major axis/minor axis) of the ferrite crystal grain in the 0.2D degree of depth, the average minor axis length of described ferrite crystal grain is less than 10 μm, except 0.
8. the manufacture method of the medium carbon steel Micro Alloying wire rod of surface hardening heat-treatability excellence according to claim 6, after described cooling, also comprises surface hardening heat treatment step.
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| KR1020140173343A KR101674750B1 (en) | 2014-12-04 | 2014-12-04 | Non-quenched and tempered steel wire rod having excellent surface case hardening and manufacturing method thereof |
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Cited By (5)
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|---|---|---|---|---|
| CN107557663A (en) * | 2016-07-01 | 2018-01-09 | Posco公司 | The excellent wire rod of stretch process and its manufacture method |
| CN107641771A (en) * | 2016-07-22 | 2018-01-30 | 株式会社Posco | The excellent wire rod of delayed fracture resistance characteristics and its manufacture method |
| CN108929985A (en) * | 2017-05-29 | 2018-12-04 | 株式会社Posco | Intensity and the excellent middle carbon line material and its manufacturing method of cold-workability |
| 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 |
| CN115537663A (en) * | 2022-10-13 | 2022-12-30 | 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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| US20220235443A1 (en) * | 2020-02-24 | 2022-07-28 | Posco | Non-heat treated wire rod with excellent wire drawability and impact toughness and manufacturing method therefor |
| 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 |
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| 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 |
| CN115537663A (en) * | 2022-10-13 | 2022-12-30 | 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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| KR101674750B1 (en) | 2016-11-10 |
| KR20160068120A (en) | 2016-06-15 |
| CN105671458B (en) | 2018-04-20 |
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