CN111206190A - Non-quenched and tempered cold heading steel for weather-resistant fastener, weather-resistant fastener and production methods of non-quenched and tempered cold heading steel and weather-resistant fastener - Google Patents
Non-quenched and tempered cold heading steel for weather-resistant fastener, weather-resistant fastener and production methods of non-quenched and tempered cold heading steel and weather-resistant fastener Download PDFInfo
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Abstract
The invention discloses non-quenched and tempered cold heading steel for a weather-resistant fastener, a weather-resistant fastener and production methods of the non-quenched and tempered cold heading steel and the weather-resistant fastener, wherein the non-quenched and tempered cold heading steel comprises the following chemical components in percentage by weight: 0.10 to 0.20 percent of C, 0.30 to 0.50 percent of Si, 1.30 to 1.50 percent of Mn, 0.60 to 0.80 percent of Cr, 0.20 to 0.30 percent of Ni, 0.20 to 0.30 percent of Cu, 0.05 to 0.10 percent of V, 0.040 to 0.060 percent of Alt, 0.010 to 0.020 percent of Ti, 0.010 to 0.015 percent of N, less than or equal to 0.0015 percent of O, less than or equal to 0.030 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and other inevitable impurities, wherein the weather resistance index I is ensured to be more than 6.5 on the chemical component; and Ni/Cu is more than or equal to 0.8, and (Ti + V)/N is more than or equal to 5.5; the non-quenched and tempered cold heading steel for the weather-resistant fastener has good weather resistance, and can be directly drawn into a fastener with the strength grade of more than 9.8 without annealing.
Description
Technical Field
The invention belongs to the technical field of cold heading steel, and particularly relates to non-quenched and tempered cold heading steel for a weather-resistant fastener, a weather-resistant fastener and production methods of the non-quenched and tempered cold heading steel and the weather-resistant fastener.
Background
China is wide in territory and complex in natural climate environment, and along with the development of construction, higher requirements are put forward on cold forging steel for fasteners, and the development of cold forging steel materials for fasteners with excellent weather resistance is urgently needed. The fastener is mainly formed by cold heading, a workpiece is usually subjected to 70-80% of total deformation in the manufacturing process, and low hardness and good plasticity before cold machining are required to obtain low deformation resistance and high deformation capacity. Therefore, the cold heading steel wire is usually subjected to pickling, drawing, annealing, secondary drawing and the like before cold heading, and then subjected to thermal refining after cold heading. Annealing and tempering are the largest energy-consuming and time-consuming processes in the fastener industry, not only increase production cost, but also increase emission and pollute environment, and if the process is improperly controlled, the quality of the fastener is unstable. The non-quenched and tempered cold forging steel is an important development direction of the cold forging steel.
At present, the weather-resistant building steel such as plates and section steel in China is researched more, and the product is relatively mature. Although the weathering resistant cold heading steel has certain research accumulation, most strength grades are lower or the cost is higher, the application is not very wide, and the research on the non-quenched and tempered cold heading steel with weathering resistance is almost blank. Along with the requirements of the complex application environment and the green development of energy conservation and cost reduction of the fastener for rail transit, the non-quenched and tempered cold forging steel material with weather resistance and processing cost saving needs to be developed.
Disclosure of Invention
In order to solve the technical problems, the invention provides non-quenched and tempered cold heading steel for a weather-resistant fastener, the weather-resistant fastener and production methods of the non-quenched and tempered cold heading steel and the weather-resistant fastener, wherein the non-quenched and tempered cold heading steel for the weather-resistant fastener has good weather resistance, can be directly drawn into a fastener with the strength grade of more than 9.8 without annealing, and is energy-saving and time-saving.
The technical scheme adopted by the invention is as follows:
the non-quenched and tempered cold heading steel for the weather-resistant fastener comprises the following chemical components in percentage by weight: 0.10 to 0.20 percent of C, 0.30 to 0.50 percent of Si, 1.30 to 1.50 percent of Mn, 0.60 to 0.80 percent of Cr, 0.20 to 0.30 percent of Ni, 0.20 to 0.30 percent of Cu, 0.05 to 0.10 percent of V, 0.040 to 0.060 percent of Alt, 0.010 to 0.020 percent of Ti, 0.010 to 0.015 percent of N, less than or equal to 0.0015 percent of O, less than or equal to 0.030 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and other inevitable impurities, wherein the weather resistance index I is ensured to be more than 6.5 on the chemical component; and Ni/Cu is more than or equal to 0.8, and (Ti + V)/N is more than or equal to 5.5.
Furthermore, the metallographic structure of the non-quenched and tempered cold heading steel for the weather-resistant fastener is ferrite and martensite, wherein the proportion of the martensite is 18-23%; the grain size is more than or equal to 11 grades.
The invention also provides a production method of the non-quenched and tempered cold heading steel for the weather-resistant fastener, which comprises the following steps: electric arc furnace or converter smelting → LF furnace refining → RH or VD vacuum degassing → square billet continuous casting → square billet heating → high speed wire low temperature controlled rolling controlled cold rolling → wire rod finished product.
Furthermore, in the billet continuous casting step, the size of the billet obtained by continuous casting is 150mm multiplied by 150 mm-250 mm multiplied by 250mm, and the problem of central alloy segregation caused by continuous casting of round billets can be effectively avoided by adopting the continuous casting billet.
In the step of heating the square billets, the soaking temperature of a heating furnace is 1050-1150 ℃, surface decarburization can be generated in the heating furnace when the soaking temperature is higher than 1150 ℃, and the tapping temperature is insufficient when the soaking temperature is lower than 1200 ℃, so that the rolling difficulty is caused.
In the high-speed wire low-temperature controlled rolling and controlled cooling rolling step, the finish rolling temperature is 780-doping 830 ℃, the spinning temperature is 770-820 ℃, subsequent phase change structures are coarse when the temperature is higher than the temperature range, and carbonitrides are not favorably formed to precipitate and form ferrite nucleation points when the temperature is lower than the temperature range.
The fan is fully opened, the air volume is adjusted to 100%, the heat-insulating cover is fully opened, and the cooling speed is controlled to be 15-17 ℃/s, so that the martensite phase transformation is fully promoted, and an ideal ferrite and martensite structure is obtained.
The diameter of the wire rod is phi 5.5-10 mm, and if the diameter is higher than the specification, the control of martensite structure formation during rolling is not facilitated.
The invention also provides a fastener processed by the weather-resistant fastener by using the non-quenched and tempered cold heading steel, and the strength of the fastener can reach over 9.8 grades.
The invention also provides a processing method of the fastener, which is characterized in that 15-25% of drawing amount is applied to non-quenched and tempered cold heading steel for drawing the weather-resistant fastener, hexagonal bolts, flange bolts and the like are processed according to conventional cold heading or other cold processing steps after drawing, and the fastener with the strength reaching over 9.8 grades can be directly drawn without annealing and quenching and tempering heat treatment, so that the energy and the time are saved.
The non-quenched and tempered cold forging steel for the weather-resistant fastener comprises the following components in action and control:
c: c is a main element for controlling the performance of the low-carbon martensite, the strength of the low-carbon martensite is in a linear direct proportion relation with the carbon content, the plasticity and the toughness of the steel are obviously reduced along with the increase of the carbon content, and the carbon content is reduced as much as possible under the condition of ensuring the strength in order to obtain lath-shaped martensite as much as possible. The content of C is controlled between 0.10 percent and 0.20 percent.
Si: si can accelerate the first precipitation of the eutectoid ferrite, promote the carbon enrichment of austenite, improve the stability of austenite and finally convert into martensite with higher carbon content. Silicon is mainly enriched on the surface of steel, and the stability of a rust layer and the corrosion resistance are improved. However, the increase of the Si element increases the diffusion of carbon in the steel, and thus the decarburization of the steel is promoted. The Si content is controlled between 0.30 percent and 0.50 percent.
Mn: mn stabilizes austenite and improves hardenability elements, and has strong inhibiting effect on pearlite and bainite transformation. However, excessive Mn lowers the plasticity of the steel. The addition of Mn is simultaneously beneficial to forming a rust layer on the surface of steel, the corrosion resistance of steel is improved, excessive Mn can cause the growth of corrosion product particles, and the corrosion rate is reduced. The Mn content is controlled to be 1.30-1.50%.
Cr: cr element remarkably improves the toughness and the strength in steel, is precipitated in a carbide form, increases hydrogen capture points and improves delayed fracture resistance. Cr dissolves in austenite to improve austenite stability and promote the formation of lath martensite, but excessive Cr increases the brittleness tendency of steel. Cr can form a compact oxide film on the surface of steel, thereby improving the passivation capability of the steel and the weather resistance of the steel. The Cr content is controlled to be 0.60-0.80 percent.
Ni: ni is an austenite-forming element and strongly retards the transformation between pearlite and bainite, and the combination of Ni and Cr makes it possible to obtain a martensitic steel excellent in toughness. The corrosion resistance of Ni is similar to that of Cr, and the addition of Cu and Ni can also accelerate the cathodic reduction of a rust layer and inhibit the anodic dissolution. The Ni element is a noble metal element, and excessive addition thereof results in excessive cost. The Ni content is controlled to be 0.20-0.30%.
Cu: the prominent role of Cu in steel is to improve the corrosion resistance of steel. The cathode contact between the steel and the Cu secondarily precipitated on the surface can promote the anodization of the steel and form a rust layer with better protection. Copper also changes the moisture absorption of the rust layer, thereby increasing the critical humidity. But Cu produces high crack sensitivity in steel. The Cu content is controlled to be 0.20-0.30%.
In addition, the contents of Ni and Cu are required to satisfy the above ranges, and it is also required to ensure that Ni/Cu is 0.8 or more, and sufficient Ni is added to compensate for the reduction in hot ductility of the steel during rolling accompanying the increase in Cu. The Ni/Cu ratio is preferably 1.0 or more.
V, Ti, N: after V, Ti and N are added into the steel, the second phase particles precipitated at high temperature play a pinning role on the original austenite grain boundary, the austenite is refined, the particles precipitated at low temperature region become nucleation points transformed from proeutectoid ferrite, the ferrite nucleation rate is improved, and the ferrite is refined. Finally, the produced steel has ultrafine grains, presents excellent strength and plastic matching, and can be directly drawn and cold headed without annealing. The content of V is controlled to be 0.05-0.10 percent of V, the content of Ti is controlled to be 0.010-0.020 percent of Ti, and the content of N is controlled to be 0.010-0.015 percent of N. In order to fully utilize the fine grain function of titanium nitride and vanadium nitride, the ratio of (Ti + V)/N is controlled to be more than or equal to 5.5.
Al: al is a strong deoxidizing element, and simultaneously improves the oxidation resistance of the steel, and carbide particles formed by Al and C, N can refine grains. However, as the Al content increases, the amount of coarse carbonitride-based inclusions increases. The content of Alt is controlled to be 0.040-0.060%.
P, S: p, S are all impurity elements segregated, harmful to the homogeneity of cold heading steel structure and properties, and are required to be low in order to improve drawing properties and cold heading properties. The content of P is controlled to be less than or equal to 0.030 percent, and the content of S is controlled to be less than or equal to 0.020 percent.
O: the T.O forms oxide inclusions in steel, so that the fasteners are cracked in the machining or service process, and the T.O is controlled to be less than or equal to 0.0015 percent.
The invention ensures that the weather-proof index I is more than or equal to 6.5 by controlling the chemical composition of steel, obtains the non-quenched and tempered cold heading steel for the weather-proof fastener, which has good weather-proof performance and is suitable for manufacturing the weather-proof fastener, simultaneously ensures that the wire rod structure is a ferrite and martensite dual-phase structure, has the grain size of more than 11 grades, presents excellent strength and plasticity matching, can be directly drawn without annealing, saves energy and time; the drawing deformation amount is controlled properly when the fastener is manufactured, and the processing strengthening can be realized, so that the strength of the final fastener can reach over 9.8 grades.
Drawings
FIG. 1 is a metallographic structure diagram of a non-quenched and tempered cold heading steel for a weather-resistant fastener according to example 1.
Detailed Description
The present invention will be described in detail below with reference to examples and comparative examples.
The invention adopts steel grades with specific components, and the production process of the non-quenched and tempered cold heading steel for the weather-resistant fastener in each embodiment is controlled as follows:
(1) electric furnace smelting: oxygen is determined before tapping, and steel retaining operation is adopted in the tapping process, so that slag is prevented from being discharged;
(2) and (4) LF furnace: adjusting each alloy element to a target value;
(3) vacuum degassing: the pure degassing time is more than or equal to 15 minutes, the content of [ H ] after vacuum treatment is ensured to be less than or equal to 1.5ppm, and the risk of bolt hydrogen induced fracture is reduced;
(4) continuous casting: the target temperature of the tundish molten steel is controlled to be 10-40 ℃ above the liquidus temperature, and a square billet with the thickness of 150mm multiplied by 150 mm-250 mm multiplied by 250mm is continuously cast.
(5) Wire rod rolling route: heating a square billet → low-temperature controlled rolling and controlled cooling of a high-speed wire rod → a finished wire rod of phi 5.5-10 mm. Wherein the soaking temperature of the heating furnace is controlled to be 1050-1150 ℃, the finish rolling temperature is 780-830 ℃, the spinning temperature is 770-820 ℃, the fan is fully opened, the air volume is adjusted to be 100%, the heat preservation cover is fully opened, the cooling speed is controlled to be 15-17 ℃/s, the ferrite and martensite structures are ensured to be obtained, and the martensite content is 18-23%.
The ingredients and specific process parameters of the examples and comparative examples are shown in tables 1 and 2:
TABLE 1 chemical composition (wt%) of steel in examples and comparative examples
TABLE 2 Process parameters for the examples and comparative examples
The steel performance detection method comprises the following steps:
hot rolled wire rod structure and grain size: taking a test sample with the length of 15mm from a wire rod, polishing the cross section, corroding by using 4% nitric acid alcohol, and evaluating the structure and the grain size according to GB/T13298 metal microstructure inspection method and GB/T6394 metal average grain size determination method; whether the wire rod has excellent use performance such as drawing or not in the process of processing the fastener can be judged through the structure. The results are shown in Table 2.
Weight loss rate in 100h week immersion test (see table 3): sampling is carried out on the square billet, the sample is processed according to TB/T2375-1993 periodic infiltration corrosion test method of weather-resistant steel for railways, 100-hour immersion test is completed, corrosion weight loss rate is calculated, 10 groups are numbered, and average value is calculated. The weather resistance of the steel can be judged through the weekly immersion test, and the weight loss rate of the 100h weekly immersion test is less than or equal to 0.5m2High weather resistance at h, 0.5m2H < weight loss rate not more than 1.2m2H is judged as general weather resistance, and the weight loss rate is more than 1.2m2H is judged to have no weather resistance. Wherein the corrosion weight loss ratio (W) is calculated according to the following formula:
in the formula: w-weight loss ratio, g/(m)2H); g0 — sample original weight, G; g1-weight after test specimen, G; a-specimen length, mm; b-test specimenWidth, mm; c-specimen thickness, mm; t-test time, h. The results are shown in Table 3.
The cold heading steels prepared in the examples and the comparative examples are drawn according to the drawing deformation in the table 3, and then are processed into hexagonal bolts, flange bolts and the like according to the conventional cold heading or other cold processing steps, and fasteners with strength reaching over 9.8 grade can be directly drawn without annealing and quenching and tempering heat treatment, so that the energy and the time are saved.
And (3) bolt tensile test: according to the GB/T3098.1 middle tensile test method for mechanical performance bolts, screws and studs of fasteners, R of the fasteners is measured in a normal-temperature test environmentm、Rp0.2Elongation, face shrinkage. The results are shown in Table 3.
TABLE 3 mechanical properties and weather resistance of bolts of examples of the present invention and comparative examples
The steel of the embodiments 1-5 is properly controlled in chemical composition and production process, the chemical composition of the steel ensures that the weather-resistant index I is more than or equal to 6.5, the steel has good weather-resistant performance, and is suitable for manufacturing weather-resistant fasteners, and meanwhile, the steel wire rod structure is a ferrite and martensite dual-phase structure through the matching of the components and the production method, the grain size is more than 11 grade, the steel wire rod structure presents excellent strength and plasticity matching, can be directly drawn without annealing, and is energy-saving and time-saving; the drawing deformation amount is controlled properly when the fastener is manufactured, and the processing strengthening is realized, so that the strength of the final fastener can reach more than 9.8 grades.
Comparative examples 1 to 2 are cases where the steel production process was not properly controlled, and although the chemical composition was properly controlled, bainite was still produced in the structure, and the structure was no longer a ferrite + martensite dual phase structure, and the direct drawing fracture was frequently observed and required annealing for use.
Comparative example 3 is the case where the weather resistance index I is lower than 6.5, and the weather resistance is relatively general and is not suitable for manufacturing a weather-resistant bolt resistant to an industrial atmospheric environment.
Comparative example 4 is a case where the Ni/Cu ratio does not reach 0.8, and brittle fracture of the steel occurs during rolling because sufficient Ni is not added to compensate for the decrease in the hot ductility of the steel during rolling accompanying the Cu increase.
Comparative example 5 is a case where (Ti + V)/N does not reach 5.5, and although the composition range and the production process meet the requirements, the finished wire rod product has coarse grains, and the steel has insufficient plasticity and cold workability, and is not suitable for direct drawing to manufacture non-quenched and tempered bolts.
Comparative example 6 is quenching and tempering type cold heading steel commonly used in the market at present, does not have weather resistance, needs annealing and quenching and tempering treatment when in use, damages materials due to overlarge drawing deformation under the condition of not carrying out early annealing and fastener quenching and tempering treatment, is easy to crack during cold heading, and simultaneously, the prepared fastener has lower strength and plasticity.
The above detailed description of a non-quenched and tempered cold heading steel for a weather resistant fastener, a weather resistant fastener and a method for producing the same with reference to examples is illustrative and not restrictive, and several examples can be cited within the scope of the present invention, so that variations and modifications thereof without departing from the general concept of the present invention should fall within the scope of the present invention.
Claims (9)
1. The non-quenched and tempered cold heading steel for the weather-resistant fastener is characterized by comprising the following chemical components in percentage by weight: 0.10 to 0.20 percent of C, 0.30 to 0.50 percent of Si, 1.30 to 1.50 percent of Mn, 0.60 to 0.80 percent of Cr, 0.20 to 0.30 percent of Ni0.20, 0.20 to 0.30 percent of Cu, 0.05 to 0.10 percent of V, 0.040 to 0.060 percent of Alt, 0.010 to 0.020 percent of Ti0.010 to 0.015 percent of N, less than or equal to 0.0015 percent of O, less than or equal to 0.030 percent of P, less than or equal to 0.020 percent of S, and the balance of Fe and other inevitable impurities, wherein the weather resistance index I is ensured to be more than 6.5 on the chemical component; and Ni/Cu is more than or equal to 0.8, and (Ti + V)/N is more than or equal to 5.5.
2. The non-quenched and tempered cold heading steel for the weather-resistant fastener as claimed in claim 1, wherein the metallographic structure of the non-quenched and tempered cold heading steel for the weather-resistant fastener is ferrite + martensite, wherein the proportion of the martensite is 18-23%; the grain size is more than or equal to 11 grades.
3. The method of producing a non-quenched and tempered cold heading steel for weather-resistant fasteners as claimed in claim 2, wherein the method of producing comprises the steps of: electric arc furnace or converter smelting → LF furnace refining → RH or VD vacuum degassing → square billet continuous casting → square billet heating → high speed wire low temperature controlled rolling controlled cold rolling → wire rod finished product.
4. The production method according to claim 3, wherein in the billet continuous casting step, the billet obtained by continuous casting has a size of 150mm x 150mm to 250mm x 250 mm.
5. The production method according to claim 3, wherein in the billet heating step, the soaking temperature of the heating furnace is 1050-1150 ℃.
6. The production method as claimed in claim 3, wherein in the step of low-temperature controlled rolling and controlled cooling rolling of the high-speed wire, the finish rolling temperature is 780-830 ℃, the spinning temperature is 770-820 ℃, the fan is fully opened, the air volume is adjusted to 100%, the heat-insulating cover is fully opened, and the cooling speed is controlled to be 15-17 ℃/s.
7. The production method according to claim 3, wherein the wire rod diameter is Φ 5.5 to 10 mm.
8. A fastener machined from the non-quenched, cold-headed steel for the weatherable fastener of claim 1.
9. The method of processing a fastener according to claim 8, wherein the weather-resistant fastener of claim 1 is drawn by applying a drawing amount of 15 to 25% to the non-quenched and tempered cold heading steel and processed.
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| CN202010148374.3A CN111206190B (en) | 2020-03-05 | 2020-03-05 | Non-quenched and tempered cold heading steel for weather-resistant fastener, weather-resistant fastener and production methods of non-quenched and tempered cold heading steel and weather-resistant fastener |
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| CN112813346A (en) * | 2020-12-29 | 2021-05-18 | 河钢股份有限公司 | Cold heading steel suitable for 6.8 and 8.8-grade weather-resistant fasteners and production method thereof |
| CN113186450A (en) * | 2021-03-26 | 2021-07-30 | 南京钢铁股份有限公司 | Non-quenched and tempered steel weather-resistant high-strength bolt and manufacturing method thereof |
| CN115305410A (en) * | 2022-08-12 | 2022-11-08 | 张家港扬子江冷轧板有限公司 | High-weather-resistance high-strength steel for thin 700 MPa-grade carriage and preparation method thereof |
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| CN112813346A (en) * | 2020-12-29 | 2021-05-18 | 河钢股份有限公司 | Cold heading steel suitable for 6.8 and 8.8-grade weather-resistant fasteners and production method thereof |
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| CN111206190B (en) | 2021-09-28 |
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