CN113198989A - Method for improving reduction of area of chromium-molybdenum steel high-strength bolt for automobile - Google Patents
Method for improving reduction of area of chromium-molybdenum steel high-strength bolt for automobile Download PDFInfo
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- CN113198989A CN113198989A CN202110348779.6A CN202110348779A CN113198989A CN 113198989 A CN113198989 A CN 113198989A CN 202110348779 A CN202110348779 A CN 202110348779A CN 113198989 A CN113198989 A CN 113198989A
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- 238000000034 method Methods 0.000 title claims abstract description 62
- 230000009467 reduction Effects 0.000 title claims abstract description 46
- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 29
- 239000010959 steel Substances 0.000 title claims abstract description 29
- VNTLIPZTSJSULJ-UHFFFAOYSA-N chromium molybdenum Chemical compound [Cr].[Mo] VNTLIPZTSJSULJ-UHFFFAOYSA-N 0.000 title claims abstract description 17
- 238000010438 heat treatment Methods 0.000 claims abstract description 63
- 238000005096 rolling process Methods 0.000 claims abstract description 50
- 230000008569 process Effects 0.000 claims abstract description 43
- 238000005496 tempering Methods 0.000 claims abstract description 42
- 238000010791 quenching Methods 0.000 claims abstract description 37
- 230000000171 quenching effect Effects 0.000 claims abstract description 37
- 238000009749 continuous casting Methods 0.000 claims abstract description 33
- 238000009628 steelmaking Methods 0.000 claims abstract description 13
- 238000001816 cooling Methods 0.000 claims abstract description 11
- 238000005516 engineering process Methods 0.000 claims abstract description 9
- 238000007711 solidification Methods 0.000 claims abstract description 9
- 230000008023 solidification Effects 0.000 claims abstract description 9
- 238000003756 stirring Methods 0.000 claims abstract description 9
- 238000005266 casting Methods 0.000 claims abstract description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 18
- 239000011651 chromium Substances 0.000 claims description 11
- 229910052750 molybdenum Inorganic materials 0.000 claims description 11
- 229910052804 chromium Inorganic materials 0.000 claims description 9
- 229910052742 iron Inorganic materials 0.000 claims description 9
- 238000009987 spinning Methods 0.000 claims description 9
- 239000012535 impurity Substances 0.000 claims description 8
- 239000000126 substance Substances 0.000 claims description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 3
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 abstract description 14
- 239000002253 acid Substances 0.000 description 14
- 238000000137 annealing Methods 0.000 description 14
- 238000005554 pickling Methods 0.000 description 14
- 238000003754 machining Methods 0.000 description 7
- 238000004321 preservation Methods 0.000 description 6
- 229910045601 alloy Inorganic materials 0.000 description 5
- 239000000956 alloy Substances 0.000 description 5
- 238000001514 detection method Methods 0.000 description 5
- 230000009286 beneficial effect Effects 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- 239000011733 molybdenum Substances 0.000 description 3
- 229910001562 pearlite Inorganic materials 0.000 description 3
- 238000005204 segregation Methods 0.000 description 3
- 229910000859 α-Fe Inorganic materials 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 2
- 229910001563 bainite Inorganic materials 0.000 description 2
- 229910000734 martensite Inorganic materials 0.000 description 2
- 239000011159 matrix material Substances 0.000 description 2
- 230000035882 stress Effects 0.000 description 2
- 229910000851 Alloy steel Inorganic materials 0.000 description 1
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- FBPFZTCFMRRESA-JGWLITMVSA-N D-glucitol Chemical group OC[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO FBPFZTCFMRRESA-JGWLITMVSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- 230000001427 coherent effect Effects 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000004880 explosion Methods 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 230000004807 localization Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000004513 sizing Methods 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 230000008646 thermal stress Effects 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/114—Treating the molten metal by using agitating or vibrating means
- B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
-
- 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
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/12—Accessories for subsequent treating or working cast stock in situ
- B22D11/1206—Accessories for subsequent treating or working cast stock in situ for plastic shaping of strands
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
- B23P15/00—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass
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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
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/0093—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for screws; for bolts
-
- 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
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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
- C22C38/04—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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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Abstract
The invention provides a method for improving the reduction of section of a chromium-molybdenum steel high-strength bolt for an automobile, which comprises the processes of continuous casting for steelmaking, cogging, wire heating, controlled rolling and controlled cooling of wires and quenching and tempering heat treatment after the bolt is machined and formed; the superheat degree of the steelmaking continuous casting process is controlled to be 15-40 ℃, the steel drawing speed is 0.65-0.75 m/min, the electromagnetic stirring I of a crystallizer is =360 +/-10A, the dynamic soft reduction technology of a solidification tail end is adopted, and the section size of a casting blank is 280 x (325-380) mm; the cogging process comprises the steps of heating the continuous casting slab to 1150-1220 ℃, preserving heat for 180-240 min, descaling and rolling the continuous casting slab into a square billet. The method for producing the bolt can obviously improve the reduction of area of the bolt, the reduction of area of the bolt is more than or equal to 50 percent, and the bolt has no drawing micro-cracks inside, thereby improving the quality reliability and the service life of the automobile bolt.
Description
Technical Field
The invention relates to a method for improving the reduction of area of a high-strength chromium-molybdenum steel bolt for an automobile, in particular to a method for improving the reduction of area of a high-strength 10.9-12.9-grade bolt for an automobile.
Background
The 10.9-12.9-grade high-strength automobile bolt is generally applied to a connecting piece of an automobile engine cylinder cover and an engine base body, is complex in stress condition, and needs to bear the indirect action of pretightening force generated by fastening, thermal stress generated by engine operation and air pressure generated by combustion and explosion in the cylinder. The mechanical property of the 10.9-12.9-grade high-strength bolt not only requires high strength, but also requires that the bolt has enough plasticity, and the reduction of area of a plastic index is more than or equal to 48 percent.
The research of automobile fastener manufacturers shows that the problem that the reduction of area in the mechanical property of a 10.9-12.9-grade chromium-molybdenum steel high-strength bolt often fails to reach the standard, so that a standard part is directly degraded and scrapped, and great economic loss is brought to automobile standard part production enterprises, so that how to improve the reduction of area of the chromium-molybdenum steel high-strength bolt is a problem which is urgently needed to be solved by the industry.
Regarding the problem of the reduction of area of a high-strength bolt, authors such as Dian Zhai Yi and the like published a paper "analysis and improvement on unqualified reduction of area of a high-strength bolt level 10.9" in the 6 th stage of "steelmaking" in 2018, and the authors analyze the reason and improvement measure for the lower reduction of area of the bolt, although the reduction of area is improved to a certain extent by adjusting the tempering temperature and the tempering time of the bolt, the requirement of a user on the numerical value is met, but microcracks inside the bolt cannot be solved all the time, the quality and potential safety hazard are caused for the subsequent service burying of the high-strength bolt for an automobile, and the quality requirement of the automobile localization on the high-grade special fastener is difficult to meet; in addition, although the bolt section shrinkage can be improved to a certain extent by increasing the tempering temperature and the tempering time, the production cost of users is increased, and the production efficiency is reduced.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for improving the reduction of area of the high-strength chrome-molybdenum steel bolt for the automobile, and the method can be used for producing the high-strength chrome-molybdenum steel bolt for the automobile with higher reduction of area without changing the hardening and tempering process of a user, and the interior of the bolt has no microcrack, so that the service safety and the service life of the bolt for the automobile are improved, the economic loss caused by unqualified reduction of area to the user is avoided, and the production cost of the user is not increased.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
the method for improving the reduction of area of the chromium-molybdenum steel high-strength bolt for the automobile comprises the steps of steel-making continuous casting, cogging, wire heating, wire controlled rolling and controlled cooling, and quenching and tempering heat treatment after the bolt is machined and formed.
The superheat degree of the steelmaking continuous casting process is controlled to be 15-40 ℃, the steel drawing speed is 0.65-0.75 m/min, the electromagnetic stirring I =360 +/-10A of a crystallizer, the dynamic soft reduction technology of a solidification tail end is adopted, and the section size of a casting blank is 280 x (325-380) mm;
the cogging process comprises the steps of heating the continuous casting slab to 1150-1220 ℃, preserving heat for 180-240 min, descaling and rolling the continuous casting slab into a square billet.
The wire heating process comprises the following steps: heating the square billet to 1100-1150 ℃, preserving heat for 120-160 min, and then descaling and rolling.
After the wire is heated, the wire is subjected to rough rolling, intermediate rolling, finish rolling and reducing sizing in sequence, after the rolling is finished, the required size is achieved, the final rolling temperature of the rolling and cooling process is controlled to be 780-820 ℃, the spinning temperature is 780-830 ℃, the roller speed is 9-14 m/min, and the heat-insulating cover and the fan are all closed.
The produced wire rod is produced into a high-strength bolt by a two-drawing and one-retreating process, and the specific main processing process flow is as follows: wire rod → acid pickling phosphorization → rough drawing → pot spheroidizing annealing → acid pickling phosphorization → fine drawing → cold heading → thread rolling → tempering.
The quenching and tempering heat treatment process after the bolt is machined and molded comprises the steps of quenching and heating at 860-880 ℃ for 60-80 minutes, quenching medium oil at 500-540 ℃ for 80-90 minutes.
The carbon content of the high-strength bolt is 0.33-0.43%.
The high-strength bolt comprises the following chemical components in percentage by mass: c: 0.33 to 0.43%, Si: 0.15 to 0.35%, Mn: 0.60-0.90%, P is less than or equal to 0.020%, S is less than or equal to 0.015%, Cr: 0.90-1.20%, Mo: 0.15-0.30%, and the balance of iron and inevitable impurity elements.
The theoretical analysis of the component proportion and the process adjustment is as follows:
1. the chromium-molybdenum steel high-strength bolt contains high-content chromium (Cr) and molybdenum (Mo) elements, the Cr and the Mo are elements which are difficult to diffuse in steel, the enrichment mainly comes from a continuous casting process, if effective measures cannot be taken to control the homogenization of alloy elements, a martensite and bainite hard phase structure is easy to appear in a segregation zone after rolling, drawing cold cracks are easy to appear in a drawing process of a user, the two-drawing one-retreating process of the user is difficult to adapt, the cracks are finally transmitted to a bolt part, and the existence of component zonal segregation enables a tempering structure to be uneven, so that the reduction of the section shrinkage ratio plasticity index of the bolt is finally reduced. Therefore, reasonable production process flow and process parameters must be designed to improve the enrichment of the alloy elements. By adopting the technical flows of bloom continuous casting, cogging and wire rolling and reasonably designing the bloom continuous casting parameters and the cogging heating temperature, the segregation of the chromium-molybdenum steel alloy elements can be better improved, and important preconditions and guarantee are provided for finally improving the reduction of the bolt section.
2. Because the wire raw materials used by the chromium-molybdenum steel high-strength bolt have more alloy content, bainite and martensite hard phase structures are easy to appear in the production process, internal cracks are easy to appear in the drawing and cold machining process of a user, and further the hidden danger of the subsequent quenching and tempering treatment of the product is buried, so that the improvement of the reduction of area is influenced. In order to adapt to the 'two-drawing one-annealing' process of users, the wire rod must be ensured to be a ferrite and pearlite easily deformable soft phase structure. The process combining low-temperature rolling and slow cooling is adopted, the finish rolling temperature is controlled to be 780-820 ℃, the spinning temperature is 780-830 ℃, the roller speed is 9-14 m/min, and the heat-insulating cover is completely closed. The process enables the steel to deform in a phase transition region, accelerates the transformation rate of super-cooled austenite to ferrite and pearlite, is beneficial to obtaining easily deformable ferrite and pearlite structures, and is beneficial to drawing and cold processing of users.
3. The bolt is subjected to quenching and tempering heat treatment to obtain a tempered sorbite structure, the atom mobility is enhanced by optimizing a heat treatment system, atoms of iron, carbon and other alloy elements are diffused rapidly, alloy compounds precipitated in the tempering process are continuously aggregated and grown up, precipitates and a matrix are separated from a coherent relationship, the internal stress of the matrix is reduced, and the plasticity of the bolt is improved.
The invention has the beneficial effects that:
by the method, the chromium-molybdenum steel high-strength bolt for the automobile with higher reduction of area can be produced on the basis of not changing the quenching and tempering process of a user, the reduction of area of the bolt is not less than 50%, no microcrack exists in the bolt, the safety of the automobile bolt in service is improved, the service life of the automobile bolt is prolonged, and the requirements of the high-end use field of the automobile on the reduction of area of the bolt and the safety of the bolt are met. Not only the economic loss caused by unqualified reduction of area to the user is avoided, but also the production cost of the user is not increased.
Drawings
FIG. 1 is a metallographic picture (1500X) of a bolt prepared in example 1.
FIG. 2 is a metallographic picture (3000X) of the bolt prepared in example 1.
Detailed Description
The present invention will be described in further detail with reference to specific examples.
Example 1
The high-strength bolt of the embodiment comprises the following chemical components in percentage by mass: c: 0.33%, Si: 0.20%, Mn: 0.60%, P: 0.012%, S: 0.006%, Cr: 1.0%, Mo: 0.25% of iron and the balance of inevitable impurity elements.
The production process of the high-strength bolt of the embodiment is as follows:
(1) steel making and continuous casting: the superheat degree is 15 ℃, the steel drawing speed is 0.70m/min, the electromagnetic stirring I =365A of a crystallizer is realized, the dynamic soft reduction technology of the solidification tail end is adopted, the continuous casting billet is a rectangular billet, and the section size is 380 x 280 mm;
(2) cogging: after the continuous casting process is finished, heating a rectangular billet with the cross section size of 380 x 280mm to 1180 ℃, preserving heat for 200min, and then carrying out descaling and rolling to obtain a square billet with the size of 150 x 150 mm;
(3) heating, rolling and cooling the wire: heating the square billet to 1140 ℃, preserving heat for 120min, rolling and controlling the cold of the square billet, wherein the finish rolling temperature is 800 ℃, the spinning temperature is 780 ℃, the speed of a controlled-cold middle roller way is 12m/min, and a heat preservation cover and a fan are all closed.
(4) Bolt heat treatment: the wire is produced into the high-strength bolt by a two-drawing one-annealing process, and the specific main processing process flow is as follows: wire rod → acid pickling phosphorization → rough drawing → pot spheroidizing annealing → acid pickling phosphorization → fine drawing → cold heading → thread rolling → tempering. And (3) carrying out quenching and tempering heat treatment on the bolt in a machining and forming mode, wherein the quenching and heating temperature is 860 ℃, the quenching and heating time is 67 minutes, the quenching medium is oil, the tempering temperature is 500 ℃, and the tempering time is 80 minutes.
Detecting the mechanical property of the quenched and tempered bolt, wherein the reduction of area is 55%; metallographic examination of the bolt revealed no microcracks inside the bolt, as shown in figure 1.
Example 2
The high-strength bolt of the embodiment comprises the following chemical components in percentage by mass: c: 0.34%, Si: 0.20%, Mn: 0.90%, P: 0.016%, S: 0.011%, Cr: 0.95%, Mo: 0.25% of iron and the balance of inevitable impurity elements.
The production process of the high-strength bolt of the embodiment is as follows:
(1) steel making and continuous casting: the superheat degree is 38 ℃, the steel drawing speed is 0.75m/min, the electromagnetic stirring I =360A of a crystallizer is realized, the solidification tail end dynamic soft reduction technology is adopted, the continuous casting billet is a rectangular billet, and the section size is 380 x 280 mm;
(2) cogging: after the continuous casting process is finished, heating a rectangular billet with the size of 380 x 280mm in cross section to 1150 ℃, preserving heat for 220min, and then descaling and rolling the rectangular billet into a rectangular billet with the size of 150 x 150 mm;
(3) heating, rolling and cooling the wire: heating the square billet to 1140 ℃, preserving heat for 130min, rolling and controlling the cold of the square billet, wherein the finish rolling temperature is 780 ℃, the spinning temperature is 800 ℃, the speed of a controlled-cold middle roller way is 10m/min, and a heat preservation cover and a fan are all closed.
(4) Bolt heat treatment: the wire is produced into the high-strength bolt by a two-drawing one-annealing process, and the specific main processing process flow is as follows: wire rod → acid pickling phosphorization → rough drawing → pot spheroidizing annealing → acid pickling phosphorization → fine drawing → cold heading → thread rolling → tempering. And (3) carrying out quenching and tempering heat treatment on the bolt in a machining and forming mode, wherein the quenching and heating temperature is 880 ℃, the quenching and heating time is 70 minutes, the quenching medium is oil, the tempering temperature is 530 ℃, and the tempering time is 85 minutes.
Detecting the mechanical property of the quenched and tempered bolt, wherein the reduction of area is 56%; and carrying out metallographic detection on the bolt, wherein the result shows that no microcrack exists in the bolt.
Example 3
The high-strength bolt of the embodiment comprises the following chemical components in percentage by mass: c: 0.35%, Si: 0.35%, Mn: 0.65%, P: 0.018%, S: 0.008%, Cr: 1.2%, Mo: 0.18% and the balance of iron and inevitable impurity elements.
The production process of the high-strength bolt of the embodiment is as follows:
(1) steel making and continuous casting: the superheat degree is 40 ℃, the steel drawing speed is 0.69m/min, the electromagnetic stirring I =370A of the crystallizer is realized, the solidification tail end dynamic soft reduction technology is adopted, the continuous casting billet is a rectangular billet, and the section size is 325 x 280 mm;
(2) cogging: after the continuous casting process is finished, heating a rectangular billet with the cross section size of 325 x 280mm to 1190 ℃, preserving heat for 200min, and then carrying out descaling and rolling to obtain a square billet with the size of 150 x 150 mm;
(3) heating, rolling and cooling the wire: heating the square billet to 1130 ℃, preserving heat for 160min, rolling and controlling the cold of the square billet, wherein the finish rolling temperature is 810 ℃, the spinning temperature is 780 ℃, the speed of a controlled-cold middle roller way is 12m/min, and a heat preservation cover and a fan are all closed.
(4) Bolt heat treatment: the wire is produced into the high-strength bolt by a two-drawing one-annealing process, and the specific main processing process flow is as follows: wire rod → acid pickling phosphorization → rough drawing → pot spheroidizing annealing → acid pickling phosphorization → fine drawing → cold heading → thread rolling → tempering. And (3) carrying out quenching and tempering heat treatment on the bolt in a machining and forming mode, wherein the quenching and heating temperature is 870 ℃, the quenching and heating time is 75 minutes, the quenching medium is oil, the tempering temperature is 510 ℃, and the tempering time is 80 minutes.
Detecting the mechanical property of the quenched and tempered bolt, wherein the reduction of area is 54%; and carrying out metallographic detection on the bolt, wherein the result shows that no microcrack exists in the bolt.
Example 4
The high-strength bolt of the embodiment comprises the following chemical components in percentage by mass: c: 0.34%, Si: 0.17%, Mn: 0.68%, P: 0.014%, S: 0.006%, Cr: 0.95%, Mo: 0.30 percent, and the balance of iron and inevitable impurity elements.
The production process of the high-strength bolt of the embodiment is as follows:
(1) steel making and continuous casting: the superheat degree is 34 ℃, the steel drawing speed is 0.72m/min, the electromagnetic stirring I =370A of the crystallizer is realized, the solidification tail end dynamic soft reduction technology is adopted, the continuous casting billet is a rectangular billet, and the section size is 350 x 280 mm;
(2) cogging: after the continuous casting process is finished, heating a rectangular billet with the cross section size of 350 x 280mm to 1210 ℃, preserving heat for 220min, and then descaling and rolling the rectangular billet into a square billet with the size of 150 x 150 mm;
(3) heating, rolling and cooling the wire: heating the square billet to 1100 ℃, preserving heat for 150min, rolling and controlling cold of the square billet, wherein the finish rolling temperature is 800 ℃, the spinning temperature is 780 ℃, the speed of a controlled-cold middle roller way is 10m/min, and a heat preservation cover and a fan are all closed.
(4) Bolt heat treatment: the wire is produced into the high-strength bolt by a two-drawing one-annealing process, and the specific main processing process flow is as follows: wire rod → acid pickling phosphorization → rough drawing → pot spheroidizing annealing → acid pickling phosphorization → fine drawing → cold heading → thread rolling → tempering. And (3) carrying out quenching and tempering heat treatment on the bolt in a machining and forming mode, wherein the quenching and heating temperature is 870 ℃, the quenching and heating time is 60 minutes, the quenching medium is oil, the tempering temperature is 530 ℃, and the tempering time is 85 minutes.
Detecting the mechanical property of the quenched and tempered bolt, wherein the reduction of area is 57%; and carrying out metallographic detection on the bolt, wherein the result shows that no microcrack exists in the bolt.
Example 5
The high-strength bolt of the embodiment comprises the following chemical components in percentage by mass: c: 0.38%, Si: 0.15%, Mn: 0.75%, P: 0.011%, S: 0.008%, Cr: 0.98%, Mo: 0.15% and the balance of iron and inevitable impurity elements.
The production process of the high-strength bolt of the embodiment is as follows:
(1) steel making and continuous casting: the superheat degree is 30 ℃, the steel drawing speed is 0.65m/min, the electromagnetic stirring I =350A of a crystallizer is realized, the dynamic soft reduction technology of the solidification tail end is adopted, the continuous casting billet is a rectangular billet, and the section size is 380 x 280 mm;
(2) cogging: after the continuous casting process is finished, heating a rectangular billet with the size of 380 x 280mm in cross section to 1200 ℃, preserving heat for 180min, and then descaling and rolling the rectangular billet into a square billet with the size of 150 x 150 mm;
(3) heating, rolling and cooling the wire: heating the square billet to 1150 ℃, preserving heat for 140min, rolling and controlling cold of the square billet, wherein the finish rolling temperature is 820 ℃, the spinning temperature is 830 ℃, the speed of a roller way in controlling cold is 9m/min, and a heat preservation cover and a fan are all closed.
(4) Bolt heat treatment: the wire is produced into the high-strength bolt by a two-drawing one-annealing process, and the specific main processing process flow is as follows: wire rod → acid pickling phosphorization → rough drawing → pot spheroidizing annealing → acid pickling phosphorization → fine drawing → cold heading → thread rolling → tempering. And (3) carrying out quenching and tempering heat treatment on the bolt in a machining and forming mode, wherein the quenching and heating temperature is 880 ℃, the quenching and heating time is 80 minutes, the quenching medium is oil, the tempering temperature is 520 ℃, and the tempering time is 90 minutes.
Detecting the mechanical property of the quenched and tempered bolt, wherein the reduction of area is 53%; and carrying out metallographic detection on the bolt, wherein the result shows that no microcrack exists in the bolt.
Example 6
The high-strength bolt of the embodiment comprises the following chemical components in percentage by mass: c: 0.43%, Si: 0.15%, Mn: 0.70%, P: 0.015%, S: 0.010%, Cr: 0.90%, Mo: 0.20 percent, and the balance of iron and inevitable impurity elements.
The production process of the high-strength bolt of the embodiment is as follows:
(1) steel making and continuous casting: the superheat degree is 35 ℃, the steel drawing speed is 0.65m/min, the electromagnetic stirring I =360A of the crystallizer is realized, the solidification tail end dynamic soft reduction technology is adopted, the continuous casting billet is a rectangular billet, and the section size is 380 x 280 mm;
(2) cogging: after the continuous casting process is finished, heating a rectangular billet with the cross section size of 380 x 280mm to 1220 ℃, preserving heat for 240min, and then descaling and rolling the rectangular billet into a square billet with the size of 150 x 150 mm;
(3) heating, rolling and cooling the wire: heating the square billet to 1130 ℃, preserving heat for 150min, rolling and controlling cold of the square billet, wherein the finish rolling temperature is 810 ℃, the spinning temperature is 830 ℃, the speed of a controlled-cold middle roller way is 14m/min, and a heat preservation cover and a fan are all closed.
(4) Bolt heat treatment: the wire is produced into the high-strength bolt by a two-drawing one-annealing process, and the specific main processing process flow is as follows: wire rod → acid pickling phosphorization → rough drawing → pot spheroidizing annealing → acid pickling phosphorization → fine drawing → cold heading → thread rolling → tempering. And (3) carrying out quenching and tempering heat treatment on the bolt in a machining and forming mode, wherein the quenching and heating temperature is 880 ℃, the quenching and heating time is 80 minutes, the quenching medium is oil, the tempering temperature is 540 ℃, and the tempering time is 90 minutes.
Detecting the mechanical property of the quenched and tempered bolt, wherein the reduction of area is 52%; and carrying out metallographic detection on the bolt, wherein the result shows that no microcrack exists in the bolt.
Claims (6)
1. A method for improving the reduction of area of a chromium-molybdenum steel high-strength bolt for an automobile is characterized by comprising the following steps: the method comprises the quenching and tempering heat treatment processes of continuous casting for steel making, cogging, wire heating, controlled rolling and controlled cooling of the wire and bolt processing and forming; wherein:
the superheat degree of the steelmaking continuous casting process is controlled to be 15-40 ℃, the steel drawing speed is 0.65-0.75 m/min, the electromagnetic stirring I of a crystallizer is =360 +/-10A, the dynamic soft reduction technology of a solidification tail end is adopted, and the section size of a casting blank is 280 x (325-380) mm;
the cogging process comprises the steps of heating the continuous casting slab to 1150-1220 ℃, preserving heat for 180-240 min, descaling and rolling the continuous casting slab into a square billet.
2. The method for improving the reduction of area of the chromium molybdenum steel high-strength bolt for the automobile as claimed in claim 1, wherein the method comprises the following steps: the wire heating process comprises the following steps: heating the square billet to 1100-1150 ℃, preserving heat for 120-160 min, and then descaling and rolling.
3. The method for improving the reduction of area of the chromium molybdenum steel high-strength bolt for the automobile as claimed in claim 1, wherein the method comprises the following steps: the finishing temperature of the wire controlled rolling and cooling process is 780-820 ℃, the spinning temperature is 780-830 ℃, the roller speed is 9-14 m/min, and the heat-insulating cover and the fan are all closed.
4. The method for improving the reduction of area of the chromium molybdenum steel high-strength bolt for the automobile as claimed in claims 1 to 5, characterized in that: the quenching and tempering heat treatment process after the bolt is machined and formed is that the quenching and heating temperature is 860-880 ℃, the quenching and heating time is 60-80 minutes, the quenching medium is oil, the tempering temperature is 500-540 ℃, and the tempering time is 80-90 minutes.
5. The method for improving the reduction of area of the chromium molybdenum steel high-strength bolt for the automobile as claimed in claim 1, wherein the method comprises the following steps: the carbon content of the high-strength bolt is 0.33-0.43%.
6. The method for improving the reduction of area of the chromium molybdenum steel high-strength bolt for the automobile as claimed in claim 5, wherein: the high-strength bolt comprises the following chemical components in percentage by mass: c: 0.33 to 0.43%, Si: 0.15 to 0.35%, Mn: 0.60-0.90%, P is less than or equal to 0.020%, S is less than or equal to 0.015%, Cr: 0.90-1.20%, Mo: 0.15-0.30%, and the balance of iron and inevitable impurity elements.
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