CN111842485A - Heating method for reducing decarburization layer depth of aluminum alloy-containing structural steel wire rod - Google Patents
Heating method for reducing decarburization layer depth of aluminum alloy-containing structural steel wire rod Download PDFInfo
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- CN111842485A CN111842485A CN202010570726.4A CN202010570726A CN111842485A CN 111842485 A CN111842485 A CN 111842485A CN 202010570726 A CN202010570726 A CN 202010570726A CN 111842485 A CN111842485 A CN 111842485A
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 123
- 229910000746 Structural steel Inorganic materials 0.000 title claims abstract description 30
- 238000000034 method Methods 0.000 title claims abstract description 22
- 229910000838 Al alloy Inorganic materials 0.000 title claims abstract description 20
- 238000005261 decarburization Methods 0.000 title abstract description 37
- 238000005096 rolling process Methods 0.000 claims abstract description 78
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 43
- 239000010959 steel Substances 0.000 claims abstract description 43
- 238000001816 cooling Methods 0.000 claims abstract description 41
- 238000009987 spinning Methods 0.000 claims abstract description 12
- 238000002791 soaking Methods 0.000 claims description 24
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 18
- 229910052782 aluminium Inorganic materials 0.000 claims description 10
- 238000004321 preservation Methods 0.000 claims description 10
- 239000000446 fuel Substances 0.000 claims description 9
- 229910052742 iron Inorganic materials 0.000 claims description 9
- 229910052804 chromium Inorganic materials 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 5
- 229910052748 manganese Inorganic materials 0.000 claims description 5
- 229910052750 molybdenum Inorganic materials 0.000 claims description 5
- 229910052759 nickel Inorganic materials 0.000 claims description 5
- 229910052710 silicon Inorganic materials 0.000 claims description 5
- 229910052717 sulfur Inorganic materials 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims 1
- 230000003647 oxidation Effects 0.000 abstract description 8
- 238000007254 oxidation reaction Methods 0.000 abstract description 8
- 230000008569 process Effects 0.000 abstract description 6
- 230000008646 thermal stress Effects 0.000 abstract description 5
- 229910000734 martensite Inorganic materials 0.000 abstract description 3
- 230000015572 biosynthetic process Effects 0.000 abstract 1
- 238000001556 precipitation Methods 0.000 abstract 1
- 239000010410 layer Substances 0.000 description 19
- 229910045601 alloy Inorganic materials 0.000 description 11
- 239000000956 alloy Substances 0.000 description 11
- 125000004432 carbon atom Chemical group C* 0.000 description 11
- 238000004519 manufacturing process Methods 0.000 description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 8
- 229910052760 oxygen Inorganic materials 0.000 description 8
- 239000001301 oxygen Substances 0.000 description 8
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 6
- 229910001566 austenite Inorganic materials 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 5
- 239000002184 metal Substances 0.000 description 5
- 229910000859 α-Fe Inorganic materials 0.000 description 5
- 238000009749 continuous casting Methods 0.000 description 4
- 238000005336 cracking Methods 0.000 description 4
- 238000010791 quenching Methods 0.000 description 4
- 230000000171 quenching effect Effects 0.000 description 4
- 238000005496 tempering Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 238000009792 diffusion process Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 230000000977 initiatory effect Effects 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 238000010923 batch production Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- CSJDCSCTVDEHRN-UHFFFAOYSA-N methane;molecular oxygen Chemical compound C.O=O CSJDCSCTVDEHRN-UHFFFAOYSA-N 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 238000010583 slow cooling Methods 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- 230000009466 transformation Effects 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- 229910001149 41xx steel Inorganic materials 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- FBPFZTCFMRRESA-JGWLITMVSA-N D-glucitol Chemical compound OC[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO FBPFZTCFMRRESA-JGWLITMVSA-N 0.000 description 1
- 229910001563 bainite Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 238000005262 decarbonization Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 238000004886 process control Methods 0.000 description 1
- 230000001172 regenerating effect Effects 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
- B21B3/02—Rolling special iron alloys, e.g. stainless steel
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
- B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/004—Heating the product
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
- B21B45/0203—Cooling
- B21B45/0209—Cooling devices, e.g. using gaseous coolants
-
- 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
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
-
- 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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- 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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- 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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- 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
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
-
- 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
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
- B21B2003/001—Aluminium or its alloys
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
- B21B45/0203—Cooling
- B21B45/0209—Cooling devices, e.g. using gaseous coolants
- B21B2045/0212—Cooling devices, e.g. using gaseous coolants using gaseous coolants
Abstract
The invention belongs to the technical field of heating, and discloses a heating method for reducing the depth of a decarburized layer of an aluminum alloy-containing structural steel wire rod. Heating the steel billet in a three-section heating furnace at the temperature of not higher than 1230 ℃ for 2.5-3 hours, wherein the two sections before heating are low in heating temperature to inhibit decarburization and make the temperature of the steel billet uniform, so that the steel billet is prevented from generating thermal stress cracks when being heated rapidly; heating the third section to raise the temperature to make the oxidation speed of the steel greater than the decarburization speed, inhibit the formation of decarburization and make the as-cast structure fully austenitized to have the condition of initial rolling; the finishing mill group and the mini machine group adopt low-temperature rolling at the temperature of not higher than 920 ℃, and the spinning temperature adopts low temperature at the temperature of not higher than 820 ℃; in the early stage of controlled cooling, a fan is adopted to rapidly and forcibly cool to a temperature not higher than 600 ℃, oxidation and decarburization are inhibited after rolling, and then a heat-preserving cover is closed to slowly cool so as to reduce the precipitation of martensite. The process effectively reduces the depth of the decarburization layer of the aluminum alloy containing structural steel wire rod.
Description
Technical Field
The invention belongs to the technical field of heating, relates to a heating process of steel, and particularly relates to a heating method for reducing the depth of a decarburized layer of an aluminum-alloy-containing structural steel wire rod.
Background
The alloy structural steel refers to steel used as mechanical parts and various engineering components and containing one or more certain amounts of alloy elements, and common alloy elements include Cr, Mo, Mn, V, B, Si, Ti, Ni, Cu, and the like. The alloy structural steel has proper hardenability, and after proper metal heat treatment, the microstructure is uniform sorbite, bainite or superfine pearlite, so that the alloy structural steel has higher tensile strength and yield ratio, higher toughness and fatigue strength and lower toughness-brittleness transition temperature, and can be used for manufacturing machine parts with larger section size.
The aluminum-containing alloy structural steel is a component of quenched and tempered structural steel, and a high Al element is added on the basis of general CrMo steel to improve cold forming plasticity of the steel, and meanwhile, the aluminum-containing alloy structural steel can obtain high enough strength and hardness through quenching and tempering heat treatment, so that the aluminum-containing alloy structural steel is often used for processing metal structural parts with large deformation and high mechanical property requirements. In the heating process of the steel billet, the decarburization tendency is obviously intensified due to the higher Al element contained in the steel, and the aluminum alloy containing structural steel hot rolled wire rod produced by adopting the conventional production process has a deeper decarburized layer and even a complete decarburized layer. The mechanical property and fatigue property of the processed metal structural part with a deeper decarburized layer or complete decarburized layer are obviously reduced, and the problems of deformation, fracture, reduction of fatigue life, failure initiation and the like caused by insufficient hardness of the surface layer of the part exist.
At present, in most domestic steel mills, two main solutions of a two-fire forming process route and adding an anti-decarburization coating to a steel billet are adopted for reducing decarburization of an aluminum-containing alloy structural steel wire rod, but at present, a scheme for effectively reducing decarburization of the aluminum-containing alloy structural steel wire rod and realizing batch production by accurately controlling heating temperature and adopting temperature control and combined control and cooling control processes is not provided.
Disclosure of Invention
The invention aims to provide a heating method for reducing the decarburization depth of an aluminum-alloy-containing structural steel wire rod, which can effectively reduce the decarburization depth of the aluminum-alloy-containing structural steel wire rod and solve the problems of deformation, fracture, fatigue life reduction, failure initiation and the like caused by insufficient surface hardness of a metal structural member after quenching and tempering heat treatment due to obvious decarburization of the aluminum-alloy-containing structural steel hot rolled wire rod. Finally, the total decarburization depth of the wire rod is less than or equal to 0.02mm, and no ferrite decarburization phenomenon exists.
A heating method for reducing the depth of a decarburized layer of an aluminum alloy-containing structural steel wire rod comprises the following steps: heating by a heating furnace, rolling by a finishing mill group, rolling by a mini unit, spinning, cooling by a water mist fan and a heat preservation cover, and the steps are as follows:
(1) heating the steel billet by a heating furnace for 2.5-3 hours at the temperature of not higher than 1230 ℃;
Further, the preferred heating temperature: the first heating section is 700-750 ℃, the second heating section is 890-920 ℃, and the soaking section is 1180-1230 ℃. In the aspect of heating time, the actual heating time of the soaking section is not more than half an hour, and the actual total heating time of the first heating section and the second heating section is not less than 1 hour. In terms of air-fuel ratio, the first heating section, the second heating section and the soaking section are respectively controlled to be 0.50-0.60, 0.50-0.55 and 0.65-0.75.
(2) Rolling the rolled piece in a finishing mill group, wherein the rolling temperature of the finishing mill group is not higher than 920 ℃;
further, the preferable rolling temperature is 890-920 ℃;
(3) rolling the rolled piece rolled by the finishing mill group into a mini unit to be rolled into a finished wire rod specification, wherein the rolling temperature of the mini unit is not higher than 920 ℃, and the final rolling temperature is not higher than 950 ℃;
further, the preferable rolling temperature is 890-920 ℃, and the final rolling temperature is 920-950 ℃;
(4) after finishing rolling, the wire rod is looped by a wire laying machine, and the wire laying temperature is not higher than 820 ℃;
further, the preferable spinning temperature is 800-820 ℃;
(5) and starting a fan to cool to be not higher than 600 ℃ in the early stage of cooling control, and then covering a heat preservation cover to slowly cool to be not higher than 450 ℃.
Further, the preferred cooling method is: and starting a fan at the early stage of controlled cooling to cool to 550-600 ℃ at a cooling rate of 10-15 ℃/s, and then covering a heat preservation cover to cool to 400-450 ℃ at a cooling rate of 0.3-0.5 ℃/s.
The range of the wire rod components is C: 0.35-0.42%, Si: 0.20 to 0.45%, Mn: 0.30-0.60%, P is less than or equal to 0.020%, S is less than or equal to 0.020%, Cr: 1.35-1.65%, Ni is less than or equal to 0.25%, Cu is less than or equal to 0.25%, Mo: 0.15-0.25%, Al: 0.70-1.10% and the balance of iron.
The main process control process of the present invention will be described in detail below with respect to the effect of reducing the decarburized layer depth of the structural steel wire rod containing aluminum alloy.
Heating a steel billet: the continuous casting square billet with the section of 160mm x 160mm is heated by a regenerative heating furnace.
In the aspect of heating temperature, the first heating section is 700-750 ℃, the second heating section is 890-920 ℃, and the soaking section is 1180-1230 ℃. The heating is carried out for one section at 700-750 ℃, the cast structure of the billet steel can not be transformed when the billet steel is heated for one section, and the kinetic condition of the chemical reaction between carbon and oxygen is insufficient under the temperature condition, so that the decarburization hardly occurs. But the steel billet can be well preheated under the temperature condition so as to ensure that the temperature rise of the subsequent heating second section and the soaking section is normally carried out and avoid the thermal stress cracking of the steel billet caused by the over-quick temperature rise. If the conventional low-temperature heating scheme at 700-800 ℃ is adopted at the first heating stage, the decarburization of the billet steel is still obviously increased. If the heating temperature is controlled below 700 ℃, the billet is not preheated enough, and the billet can generate thermal stress cracking due to too fast temperature rise in the subsequent heating process.
And the second heating section is 890-920 ℃, the decarburization tendency of the steel is very low under the temperature condition, and no obvious decarburization occurs. If the temperature is controlled to be above 920 ℃, the decarburization of the steel is increased due to the increase of the temperature, and the high-temperature oxidation scheme which is the same as that of the subsequent soaking section cannot be adopted due to the lower temperature of the steel entering the heating section, because the steel billet can generate thermal stress cracking due to the overhigh heating rate if no transition temperature exists. If the heating temperature is lower than 890 ℃, the decarburization of the billet is also obviously increased. If the heating second section is continuously heated according to the low temperature of the heating first section, the billet is not preheated enough, and the billet can generate thermal stress cracking due to too fast temperature rise in the subsequent heating process.
And in the soaking section 1180-1230 ℃, the decarburization tendency of the steel is remarkably increased under the temperature condition, the decarburization behavior is intensified, but the oxidation speed of the steel is greatly increased due to the increase of the temperature, the oxidizing atmosphere is kept in the furnace because of the air-fuel ratio, the oxidation speed of the steel is higher than the decarburization speed, and the decarburized layer of the steel is basically and completely oxidized, so that the depth of the decarburized layer of the structural steel containing the aluminum alloy is effectively reduced.
In the aspect of heating time, the actual heating time of the soaking section does not exceed half an hour because the burning loss of steel is large; the actual total heating time of the first heating section and the second heating section is not less than 1 hour, so as to ensure the temperature uniformity of the steel billet.
In the aspect of air-fuel ratio, the first heating section, the second heating section and the soaking section are respectively controlled to be 0.50-0.60, 0.50-0.55 and 0.65-0.75, and the first heating section and the second heating section adopt lower air-fuel ratio to keep reducing atmosphere in the furnace and prevent excess air from deepening decarburization; the soaking section adopts relatively high air-fuel ratio to keep oxidizing atmosphere in the furnace, so as to be beneficial to improving the oxidation speed of the steel at high temperature and leading the actual oxidation speed to be greater than the decarburization speed, thereby reducing the depth of the decarburized layer of the billet.
Rough and medium rolling and pre-finishing rolling mill set rolling: and the heated steel billet enters a rough and medium rolling mill set for continuous rolling so as to ensure that the rolled piece is in a sufficient austenitizing state in the rolling process of the rough and medium rolling mill set and ensure that the rolling process is smoothly carried out. The ideal rolling temperature range of the rough and medium rolling mill set is also 890-920 ℃, but because the rough and medium rolling mill set and the pre-finishing rolling mill set of the high-speed wire production line are used as basic deformation stages, the rolling and cooling control means are less, the deformation rate is relatively fixed, and the influence on the temperature rise and temperature drop of a rolled piece is relatively stable, the control on the rough and medium rolling mill set and the pre-finishing rolling mill set is realized by setting a heating process.
Rolling by a finishing mill group: and cooling the rolled piece rolled by the rough and medium mill set through water, then, rolling the rolled piece in the finish mill set, and controlling the temperature of the rolled piece entering the finish mill set to be 890-920 ℃.
Under the condition of 890-920 ℃, the rolled piece is still in a complete austenite state, and on one hand, the rolled piece has good plasticity and can ensure the smooth rolling process; on the other hand, because the carbon atoms are fully dissolved in the iron body in an austenite state, and because the temperature is relatively low, the reaction between the carbon atoms in the steel and the oxygen in the air is slow. If the rolling temperature is lower than 890 ℃, the steel gradually enters ferrite and austenite, and carbon atoms are not fully dissolved in the iron body any more but begin to diffuse, and the diffusion process is accelerated by being reflected by oxygen in the air, so that obvious decarburization is increased. If the rolling temperature is higher than 920 ℃, although the rolled piece is in a complete austenitizing state, the rolling can be smoothly carried out, carbon atoms can be fully and fixedly dissolved in an iron organism, but the carbon-oxygen activity can be obviously increased due to the rise of the temperature, the chemical reaction of the carbon atoms and the oxygen is also intensified, and the decarburization can also be obviously increased.
And (3) rolling by a mini unit: the rolled piece after finish rolling enters a mini unit to be rolled into a finished wire rod specification, the rolling temperature of the mini unit is controlled to be 890-920 ℃, the rolled piece is still in a complete austenite state, and on one hand, the rolled piece has good plasticity and can ensure that the rolling process is smoothly carried out; on the other hand, because the carbon atoms are fully dissolved in the iron body in an austenite state, and because the temperature is relatively low, the reaction between the carbon atoms in the steel and the oxygen in the air is slow. If the rolling temperature is lower than 890 ℃, the steel gradually enters ferrite and austenite, and carbon atoms are not fully dissolved in the iron body any more but begin to diffuse, and the diffusion process is accelerated by being reflected by oxygen in the air, so that obvious decarburization is increased. If the rolling temperature is higher than 920 ℃, although the rolled piece is in a complete austenitizing state, the rolling can be smoothly carried out, carbon atoms can be fully and fixedly dissolved in an iron machine body, but the carbon-oxygen activity can be obviously increased due to the rise of the temperature, the chemical reaction of the carbon atoms and the oxygen is also intensified, the decarburization can also be obviously increased, and the control mechanism of the decarburization is the same as that of a finishing mill group.
The temperature of the mini group is selected to be consistent with that of the finishing mill group, and because a cooling water tank is arranged between the finishing mill group and the mini group, a rolled piece rolled by the finishing mill group can be cooled down although the temperature of the rolled piece is raised, so that the temperature of the rolled piece entering the mini group is consistent with that of the finishing mill group. The controlled rolling of the mini unit effectively ensures that the finishing rolling temperature is 920-950 ℃.
Spinning: after finish rolling, the wire rod is looped by a wire laying machine, the wire laying temperature is controlled to be 800-820 ℃ through water cooling of a water tank, and favorable conditions are provided for subsequent cooling control. If the spinning temperature is too high, the time required for cooling by the fan below the desired temperature will increase, and the corresponding decarburization will also increase; if the spinning temperature is too low, the resistance of the wire rod to be spun and looped can be obviously increased, so that the spinning is difficult, and the actual batch production can not be met.
And (3) cooling control: and the controlled cooling of the rolled wire rod is realized on a stelmor controlled cooling line, 2-3 fans are started to cool to 550-600 ℃ at a cooling rate of 10-15 ℃/s in the early stage of controlled cooling, and then a heat preservation cover is covered to cool to 400-450 ℃ at a cooling rate of 0.3-0.5 ℃/s so as to reduce the martensite structure transformation. If the early cooling rate is lower than 10 ℃/s, the rapid cooling of the wire rod cannot be ensured, carbon atoms are not fully dissolved in the iron body any more, but begin to diffuse, the diffusion process is accelerated to be reflected by oxygen in the air, and further the decarburization is obviously increased. The increase of the decarburized layer depth of the finished wire rod can cause the insufficient hardness of the surface layer of the metal structural member after quenching and tempering heat treatment, thereby causing the problems of deformation, fracture, fatigue life reduction, failure initiation and the like. However, if the early cooling rate is higher than 15 ℃/s, the transformation of the wire rod into martensite is increased, and the hot rolled wire rod is brittle.
The invention has the advantages that: the one-fire material small square billet is adopted for rolling, and a two-fire material process is not needed, so that the production cost of similar wire rods is greatly reduced; the blank is not required to be treated by adding the anti-decarbonization coating, so that the production cost is further reduced, the production efficiency is improved, and meanwhile, the energy consumption and the environmental pollution caused by the production and the use of the coating are reduced; the invention reasonably distributes the temperature settings of the first heating section, the second heating section and the soaking section; the soaking section adopts high-temperature heating to realize that the oxidation speed of the steel is higher than the decarburization speed, and finally the purpose of reducing the depth of the decarburized layer is achieved. In the rolling process, the finishing mill group and the mini unit adopt reasonable rolling temperature control. After rolling, a fan is adopted for cooling to improve the cooling rate, then the combined scheme of slow cooling is carried out immediately, the total decarburized layer depth of the wire rod is less than or equal to 0.02mm through scientific combination of controlled rolling and controlled cooling, and the phenomenon of ferrite decarburization is avoided.
Detailed Description
The production of an aluminum-containing alloy structural steel 38CrMoAlA wire rod (phi 10.0mm) is taken as an example:
the specific components of 38CrMoAlA are as follows:
Wt，％
| number plate | C | Si | Mn | P | S | Cr | Mo | Al | Ni | Cu |
| 38CrMoAlA | 0.35-0.42 | 0.20-0.45 | 0.30-0.60 | ≤0.020 | ≤0.020 | 1.35-1.65 | 0.15-0.25 | 0.70-1.10 | ≤0.25 | ≤0.25 |
The production process flow comprises the following steps: the method comprises the steps of a heat accumulating type heating furnace, a rough and medium rolling and pre-finishing rolling unit, a mini unit, a laying head, a fan cooling, closing a heat preservation cover for slow cooling and bundling. The conditions which are not limited are conventional conditions and have no influence on the decarburization of the wire rod.
Example 1
1. Heating of steel billets
The steel billet comprises the following components: 0.38%, Si: 0.30%, Mn: 0.49%, P: 0.011%, S: 0.008%, Cr: 1.51%, Ni: 0.11%, Cu: 0.10%, Mo: 0.21%, Al: 0.91 percent.
Heating a continuous casting square billet with the section of 160mm x 160mm at the temperature of 700-1230 ℃ for 2.7 hours, wherein the set temperature of a first heating section is 700-750 ℃, the actual temperature is 705-740 ℃, the set temperature of a second heating section is 890-920 ℃, the actual temperature is 893-910 ℃, the set temperature of a soaking section is 1180-1230 ℃, and the actual temperature is 1182-1220 ℃. The air-fuel ratio of the first heating section, the second heating section and the soaking section is respectively controlled to be 0.50-0.60, 0.50-0.55 and 0.65-0.75; the actual heating time of the soaking section is 0.5 hour, and the actual total heating time of the first heating section and the second heating section is 1.2 hours and 1 hour respectively.
2. Controlled rolling
The set temperature of rough rolling is 890-920 ℃, the actual temperature is 890-920 ℃, the rolled piece enters a finishing mill group for rolling, the set temperature of the finishing mill group for rolling is 890-920 ℃, the actual temperature is 890-915 ℃, the rolled piece after the finishing mill group for rolling enters a mini unit for rolling into a wire rod finished product with the specification of phi 10.0mm, the set temperature of the mini unit for rolling is 890-920 ℃, the actual temperature is 890-910 ℃, the set temperature of final rolling is 920-950 ℃, and the actual temperature is 923-940 ℃.
3. Spinning
And (3) coiling the coil rod after final rolling by a wire laying machine, wherein the wire laying set temperature is 800-820 ℃, and the actual temperature is 803-819 ℃.
4. Controlled cooling
Starting 2 fans, wherein the air volume of each fan is 85%, the actual temperature of the wire rod at the outlet position of each started fan is 560-575 ℃, and the actual cooling rate is 12-12.5 ℃/s; and (4) closing all the heat-preservation covers corresponding to the fans which are not started, preserving heat, slowly cooling to 410-430 ℃, and actually cooling at the speed of 0.35-0.45 ℃/s.
Example 2
1. Heating of steel billets
The steel billet comprises the following components: 0.40%, Si: 0.31%, Mn: 0.50%, P: 0.013%, S: 0.010%, Cr: 1.55%, Ni: 0.10%, Cu: 0.05%, Mo: 0.20%, Al: 0.88 percent
And heating the continuous casting square billet with the section of 160mm x 160mm at the temperature of 700-1230 ℃ for 2.8 hours, wherein the first heating section is 715-750 ℃, the second heating section is 899-920 ℃, and the soaking section is 1192-1228 ℃. The air-fuel ratio of the first heating section, the second heating section and the soaking section is respectively controlled to be 0.50-0.60, 0.50-0.55 and 0.65-0.75; the actual heating time of the soaking section is 0.5 hour, and the actual total heating time of the first heating section and the second heating section is 1.3 hours and 1 hour respectively.
2. Controlled rolling
The rough rolling starting temperature is 890-920 ℃, the rolled piece enters a finishing mill group for rolling, the finishing mill group rolling temperature is 899-919 ℃, the rolled piece rolled by the finishing mill group enters a mini unit for rolling into a wire rod finished product with the specification of phi 10.0mm, the mini unit rolling temperature is 895-916 ℃, and the finishing temperature is 927-945 ℃.
3. Spinning
And (3) after finishing rolling, coiling the wire rod by a wire laying machine at the wire laying temperature of 801-811 ℃.
4. Controlled cooling
Starting 2 fans, wherein the air volume of each fan is 80%, the actual temperature of the wire rod at the position of an outlet of each started fan is 568-581 ℃, and the actual cooling rate is 12-12.3 ℃/s; and (4) closing all the heat-preservation covers corresponding to the fans which are not started, preserving heat, slowly cooling to 416-439 ℃, and actually cooling at the speed of 0.35-0.44 ℃/s.
Comparative example 1
Comparative example 1 the heating conditions for the billet were different from those of example 1.
Wherein the heating conditions are as follows: heating a continuous casting square billet with the section of 160mm x 160mm at the temperature of 700-1050 ℃, wherein the first heating section is 700-800 ℃, the second heating section is 800-900 ℃, and the soaking section is 950-1050 ℃. The air-fuel ratio of the first heating section, the second heating section and the soaking section is 0.50-0.60; the heating time was 1.5 hours, and the other conditions were the same as in example 1.
Comparative example 2
The heating first section in the heating of the billet steel in the step 1 of the embodiment 1 is replaced by 760-800 ℃, the heating second section is replaced by 800-880 ℃, and other conditions are the same as those of the embodiment 1.
Comparative example 3
The soaking section in the heating of the billet steel in the step 1 of the embodiment 1 is replaced by 1100-1170 ℃, and the other conditions are the same as the embodiment 1.
Comparative example 4
Replacing the spinning temperature in the step 3 of the embodiment 1 with 850-880 ℃, replacing the controlled cooling in the step 4 of the embodiment 1 with closing the heat preservation cover to slowly cool to 400-500 ℃, wherein the cooling rate is 0.20-0.30 ℃/s, and the other conditions are the same as those of the embodiment 1.
In the hot-rolled wire rod microstructures of the examples 1 and 2 and the comparative examples 1, 2, 3 and 4, the depth of decarburized layer (including the total decarburized layer depth and the ferrite decarburized layer depth) and the near-surface hardness after heat treatment are detected, wherein the decarburized layer depth is detected on a hot-rolled wire rod sample, and the detection standard is GB/T224; the hardness is tested on the mechanical structure parts after heat treatment (the heat treatment process is 850 ℃ quenching and 250 ℃ tempering), and the test standard is GB/T230.1. The decarburized layer depth and hardness were compared as in the following Table 1:
TABLE 1
Claims (8)
1. A heating method for reducing the decarburized layer depth of an aluminum alloy-containing structural steel wire rod is characterized by comprising the following steps of: heating by a heating furnace, rolling by a finishing mill group, rolling by a mini group, spinning and cooling by a stelmor controlled cooling line, and the method comprises the following steps:
(1) heating the steel billet by a heating furnace at the temperature of not higher than 1230 ℃ for 2.5-3 hours;
(2) rolling in a finishing mill group, wherein the rolling temperature of the finishing mill group is not higher than 920 ℃;
(3) rolling the rolled piece rolled by the finishing mill group into a mini unit to be rolled into a finished wire rod specification, wherein the rolling temperature of the mini unit is not higher than 920 ℃, and the final rolling temperature is not higher than 950 ℃;
(4) after finishing rolling, the wire rod is looped by a wire laying machine, and the wire laying temperature is not higher than 820 ℃;
(5) And starting a fan to cool to be not higher than 600 ℃ in the early stage of cooling control, and then covering a heat preservation cover to slowly cool to be not higher than 450 ℃.
2. The heating method for reducing the decarburized layer depth of an aluminum alloy-containing structural steel wire rod according to claim 1, wherein: the wire rod comprises the following chemical components in percentage by mass: 0.35-0.42%, Si: 0.20 to 0.45%, Mn: 0.30-0.60%, P is less than or equal to 0.020%, S is less than or equal to 0.020%, Cr: 1.35-1.65%, Ni is less than or equal to 0.25%, Cu is less than or equal to 0.25%, Mo: 0.15-0.25%, Al: 0.70-1.10% and the balance of iron.
3. The heating method for reducing the decarburized layer depth of an aluminum alloy-containing structural steel wire rod according to claim 1, wherein: the heating temperature in the step (1) is divided into three sections, and the temperatures are respectively as follows: the first heating section is 700-750 ℃, the second heating section is 890-920 ℃, and the soaking section is 1180-1230 ℃.
4. The heating method for reducing the decarburized layer depth of an aluminum alloy-containing structural steel wire rod according to claim 3, wherein: in the aspect of heating time, the actual heating time of the soaking section is not more than half an hour, and the actual total heating time of the first heating section and the second heating section is not less than 1 hour respectively; in terms of air-fuel ratio, the first heating section, the second heating section and the soaking section are respectively controlled to be 0.50-0.60, 0.50-0.55 and 0.65-0.75.
5. The heating method for reducing the decarburized layer depth of an aluminum alloy-containing structural steel wire rod according to claim 1, wherein: and (3) in the step (2), the rolling temperature of the finishing mill group is 890-920 ℃.
6. The heating method for reducing the decarburized layer depth of an aluminum alloy-containing structural steel wire rod according to claim 1, wherein: in the step (3), the rolling temperature of the mini unit is 890-920 ℃, and the finishing temperature is 920-950 ℃.
7. The heating method for reducing the decarburized layer depth of an aluminum alloy-containing structural steel wire rod according to claim 1, wherein: in the step (4), the spinning temperature is 800-820 ℃.
8. The heating method for reducing the decarburized layer depth of an aluminum alloy-containing structural steel wire rod according to claim 1, wherein: and (5) performing cold control, wherein in the early cold control stage, a fan is started to cool to 550-600 ℃ at a cooling rate of 10-15 ℃/s, and then a heat-preservation cover is covered to cool to 400-450 ℃ at a cooling rate of 0.3-0.5 ℃/s.
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