CN111663084A - Round steel for titanium-containing 16.9-grade bolt and production method thereof - Google Patents

Round steel for titanium-containing 16.9-grade bolt and production method thereof Download PDF

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CN111663084A
CN111663084A CN202010603491.4A CN202010603491A CN111663084A CN 111663084 A CN111663084 A CN 111663084A CN 202010603491 A CN202010603491 A CN 202010603491A CN 111663084 A CN111663084 A CN 111663084A
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round steel
temperature
heating
titanium
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汪开忠
尹德福
胡芳忠
龚梦强
于同仁
丁雷
张晓瑞
姜婷
牟祖茂
孙凯
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Maanshan Iron and Steel Co Ltd
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Abstract

The invention discloses round steel for a titanium-containing 16.9-grade bolt and a production method thereof, and belongs to the technical field of steel for fasteners. The round steel for the titanium-containing 16.9-grade bolt comprises the following chemical components in percentage by weight: 0.55 to 0.60 percent of C, 1.80 to 2.00 percent of Si, 0.25 to 0.35 percent of Mn, 1.05 to 1.35 percent of Cr1, 50 to 1.80 percent of Mo1, 0.12 to 0.2 percent of Ti0, 0.10 to 0.30 percent of Ni0, 0.20 to 0.35 percent of Cu0.20, 0.015 to 0.040 percent of Als0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.0010 percent of O, less than or equal to 0.005 percent of N, and the balance of Fe and other inevitable impurities. By adopting the technical scheme, the atmospheric corrosion resistance and delayed fracture resistance of the round steel for the bolt can be effectively improved, and further, the requirements of light weight and high safety of an automobile can be met.

Description

Round steel for titanium-containing 16.9-grade bolt and production method thereof
Technical Field
The invention belongs to the technical field of steel for fasteners, and particularly relates to round steel for a titanium-containing 16.9-grade bolt and a production method thereof.
Background
The fastener is a basic industry of equipment manufacturing industry in China and is widely applied to various fields of national economy. In recent years, with the rapid development of various industries such as automobiles, wind power, machinery, buildings and the like in China, the requirements of design stress and light weight are provided for materials used for manufacturing parts such as various fasteners (such as bolts, nuts and the like), and the most effective way is to achieveThe measure is to increase the strength of the fastener. The light weight of the automobile body is to improve the fuel efficiency of the automobile and reduce CO2One of the effective methods for emissions is that fasteners are used in a higher tensile load environment than ever due to the demand for smaller and lighter engine and chassis parts, and therefore, it is necessary to solve the technical problems of reduced fatigue strength due to surface defects or non-metallic inclusions in steel, and delayed fracture associated with increased atmospheric corrosion and hydrogen sensitivity.
The ultrahigh strength fastener is used as a fastener of a connecting part and other cold heading forming parts, the requirements of high design stress and light weight are provided, in this respect, the requirements of the automobile manufacturing industry are the strongest, and the original automobile fastener, especially an engine bolt, cannot meet the requirement of high stress of an automobile engine easily. However, since the environment for operating the automobile is complicated, the bolt may be corroded when used in various atmospheric environments, and in order to prolong the service life of the bolt, the high-strength bolt used for connecting the automobile is subjected to corrosion prevention in a coating manner, such as electroplating or hot galvanizing. However, the corrosion prevention time limit of the methods such as surface spraying is generally 5-10 years, the service life of the bolt can be reduced due to aging and differentiation of the coating, and the corrosion prevention effect is not ideal; meanwhile, the H element introduced in the processes of electroplating and hot galvanizing of the ultrahigh-strength bolt can also increase the problem of hydrogen-induced delayed fracture in the using process of the bolt, so that the ultrahigh-strength fastener for the automobile must have excellent corrosion resistance and also needs to have excellent delayed fracture resistance so as to meet the requirements of light weight and high safety of the automobile.
Through search, the patent of the steel for the bolt has related disclosures. For example, the chinese patent application No. 01129512.0 discloses a delayed fracture-resistant high-strength bolt steel having a strength of 1400 to 1600MPa, which comprises the following specific components: 0.35-0.5% of C, 0.01-0.09% of Si, less than or equal to 0.30% of Mn, less than or equal to 0.010% of P, less than or equal to 0.008% of S, 0.5-1.5% of Cr0.7-1.5% of Mo0.20-0.50% of V, 0.01-0.08% of Nb0.002-0.04% of RE, 0.005-0.05% of Al, 0.006-0.015% of N, 0.01-0.15% of any one or the sum of two of Ti and Zr, and the balance of Fe and inevitable impurities. The maximum tensile strength of the bolt is only 1580MPa, the performance requirement of a 16.9-grade high-strength bolt cannot be met, RE and the like are added into chemical components, and the production cost is obviously increased.
For another example, chinese patent application No. 200810049411.4 discloses a method for making a 16.9-grade bolt resistant to delayed fracture, the chemical composition range of the steel ingot should be controlled to be C0.15-0.19%, Mn not more than 0.10%, Si not more than 0.10%, S not more than 0.005%, P not more than 0.008%, S + P not more than 0.010%, cr 1.80-2.00%, ni 9.50-10.50%, co 13.50-14.50%, mo 0.90-0.10%, Ti not more than 0.015%, O not more than 0.0020%, N not more than 0.0015%. The steel for the bolt not only adopts the more complex production processes of vacuum induction melting, vacuum consumable melting, forging forming, composite heat treatment and the like, but also has higher content of noble elements such as Ni, Co and the like, so that the production cost is higher, and the steel is not suitable for industrial production.
Disclosure of Invention
1. Problems to be solved
The invention aims to overcome the defects that the corrosion prevention effect is not ideal when the existing high-strength bolt is subjected to corrosion prevention by adopting a coating mode, and the problem of delayed fracture caused by hydrogen in the using process of the bolt is increased, and provides round steel for a titanium-containing 16.9-grade bolt and a production method thereof. By adopting the technical scheme of the invention, the problems can be effectively solved, the atmospheric corrosion resistance and the delayed fracture resistance of the automobile are effectively improved, and the requirements of light weight and high safety of the automobile can be met.
2. Technical scheme
In order to solve the problems, the technical scheme adopted by the invention is as follows:
the round steel for the titanium-containing 16.9-grade bolt comprises the following chemical components in percentage by weight: 0.55 to 0.60 percent of C, 1.80 to 2.00 percent of Si, 0.25 to 0.35 percent of Mn, 1.05 to 1.35 percent of Cr1, 50 to 1.80 percent of Mo1, 0.12 to 0.2 percent of Ti0, 0.10 to 0.30 percent of Ni0, 0.20 to 0.35 percent of Cu0.20, 0.015 to 0.040 percent of Als0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.0010 percent of O, less than or equal to 0.005 percent of N, and the balance of Fe and other inevitable impurities.
Furthermore, the weight percentage of each chemical component in the round steel for the titanium-containing 16.9-grade bolt meets the requirement that 0.86 is less than or equal to 0.28 [% Mo ] +2.25 [% Ti ] +0.05 [% Si ] < 0.98.
Further, the weight percentage of C and Si satisfies 3.0 ≦ ([ Si ]/[ C ]) 3.35.
Furthermore, the weight percentages of the elements in the round steel for the titanium-containing 16.9-grade bolt also meet the following requirements:
26.01(％Cu)+3.88(％Ni)+1.20(％Cr)+1.49(％Si)+17.28(％P)-7.29(％Cu)(％Ni)-9.10(％Ni)(％P)-33.39(％Cu)2)≥9.0。
the invention relates to a production method of round steel for a titanium-containing 16.9-grade bolt, which comprises the following chemical components: electric furnace smelting → LF + RH vacuum refining → 250mm square billet continuous casting → flaw detection, coping → excellent rod heating furnace heating → KOCKS controlled rolling and controlled cooling → round steel finished product → packaging and warehousing.
Furthermore, the heating temperature of the excellent rod heating furnace is 980-1070 ℃ when the excellent rod heating furnace is heated, and the furnace time of the square billet is not more than 170 min.
Furthermore, the process parameters of rolling control and cooling control are as follows: the initial rolling temperature is 880-945 ℃, and the final rolling temperature is 780-840 ℃.
Furthermore, the round steel needs to be subjected to performance inspection, and the heat treatment process during inspection comprises quenching heating treatment and high-temperature tempering treatment, wherein the heating temperature during quenching heating is 900-960 ℃, and the tempering temperature during high-temperature tempering is 590-610 ℃.
Furthermore, the round steel is subjected to double-cycle heat treatment subsequently, and the specific process comprises the following steps: the steel is subjected to oil quenching and heating treatment at the heating temperature of 910-930 ℃, then is subjected to tempering treatment at the tempering temperature of 490-510 ℃, and then is subjected to air cooling; then carrying out oil quenching and heating treatment at the heating temperature of 860-880 ℃, carrying out tempering treatment at the tempering temperature of 140-160 ℃, and then carrying out air cooling.
3. Advantageous effects
Compared with the prior art, the invention has the beneficial effects that:
(1) according to the round steel for the titanium-containing 16.9-grade bolt, disclosed by the invention, aiming at the performance requirements which the round steel needs to meet, the chemical components and the content of the round steel are optimally designed, and microalloying elements such as Ti, Mo and the like are added, and the comprehensive coordination action of the elements is utilized, so that the atmospheric corrosion resistance of the obtained round steel can be effectively improved, the delayed fracture resistance of the round steel can be better improved, the problems caused by the adoption of a coating for corrosion prevention of the existing bolt are avoided, the strength grade of the round steel is ensured, and the use requirements of a high-strength fastener can be met.
(2) According to the round steel for the titanium-containing 16.9-grade bolt, the contents of Si, Mo and the like are further limited, and the compounding coordination effect of each element is utilized, so that the hydrogen embrittlement resistance is improved, and the delayed fracture resistance of the round steel is further improved; the added Mo also obviously improves the tempering softening resistance, and realizes the ultrahigh strength at high temperature; the added Mo can also improve the atmospheric corrosion resistance of the round steel.
(3) According to the round steel for the titanium-containing 16.9-grade bolt, the content of C, Si element is further limited on the basis of limiting elements such as Si, Mo and the like, the content of C is increased, the content of Si is greatly increased, and the relative content of C, Si is controlled, so that the deterioration of delayed fracture resistance of the round steel can be avoided, and the delayed fracture resistance and the atmospheric corrosion resistance of the round steel are further ensured. In addition, the corrosion resistance of the round steel is further ensured by adding elements such as Ni and Cu and further limiting the content of each element according to the corrosion resistance index.
(4) According to the production method of the round steel for the titanium-containing 16.9-grade bolt, disclosed by the invention, the chemical components, the content and specific process parameters in the production process are optimally designed, the comprehensive action of each element is utilized, the double-circulation heat treatment process is added subsequently, and the specific process parameters of the double-circulation heat treatment process are optimally designed, so that the mechanical property of the round steel for the titanium-containing 16.9-grade bolt is further ensured, the corrosion resistance and the delayed fracture resistance of the round steel are effectively improved, the requirements of light weight and high safety of an automobile are met, and the production method of the round steel for the ultrahigh-strength bolt can also save energy and reduce the cost.
Drawings
FIG. 1 is a graph of the chemical composition and austenite grain size (wt%) of examples 1 to 7 of the present invention and comparative examples 1 to 2.
FIG. 2 is a graph showing mechanical properties, delayed fracture resistance and corrosion resistance of examples 1 to 7 of the present invention and comparative examples 1 to 2.
FIG. 3 is a diagram of notched tensile delayed fracture specimens in accordance with the present invention.
Detailed Description
The invention provides round steel for a titanium-containing 16.9-grade bolt, which comprises the following chemical components in percentage by weight: 0.55 to 0.60 percent of C, 1.80 to 2.00 percent of Si, 0.25 to 0.35 percent of Mn, 1.05 to 1.35 percent of Cr1, 50 to 1.80 percent of Mo1, 0.12 to 0.2 percent of Ti0, 0.10 to 0.30 percent of Ni0, 0.20 to 0.35 percent of Cu0.20, 0.015 to 0.040 percent of Als0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.0010 percent of O, less than or equal to 0.005 percent of N, and the balance of Fe and other inevitable impurities. And the weight percentage satisfies:
①、0.86≤0.28[％Mo]+2.25[％Ti]+0.05[％Si]≤0.98；
②、3.0≤([Si]/[C])≤3.35；
③、26.01(％Cu)+3.88(％Ni)+1.20(％Cr)+1.49(％Si)+17.28(％P)-7.29(％Cu)(％Ni)-9.10(％Ni)(％P)-33.39(％Cu)2)≥9.0。
the round steel for the titanium-containing 16.9-grade bolt can effectively solve the problems that the corrosion prevention effect is not ideal and the hydrogen-induced delayed fracture problem is increased in the using process of the bolt when the high-strength bolt for the automobile is subjected to corrosion prevention by adopting an electroplating or hot galvanizing coating mode. The round steel for the titanium-containing 16.9-grade bolt is different from a wire rod for a high-strength bolt in chemical composition, performance and production process, and because the cold heading process is not required when the round steel is used for producing the bolt, the influence of the high content of Si on cold heading and cold extrusion is not required to be considered. In order to meet the requirement of high strength performance, the invention optimally designs each chemical component and content of the round steel for the titanium-containing 16.9-grade bolt, adds micro-alloying elements such as Ti, Mo and the like, and utilizes the comprehensive coordination effect of each element, thereby effectively improving the atmospheric corrosion resistance of the obtained round steel, also better improving the delayed fracture resistance of the round steel, avoiding the problem caused by the corrosion resistance of the coating adopted by the existing bolt, ensuring the mechanical property of the round steel, and enabling the round steel to meet the use requirement of a high-strength fastener.
The invention further limits the content ranges of Mo, Ti and Si by adopting a formula, and utilizes the compounding coordination effect of each element to disperse and separate Mo series, Ti series and composite carbon-nitrogen alloy compounds with the size of less than 45nm during high-temperature tempering, thereby being beneficial to improving the hydrogen embrittlement resistance of the round steel and further improving the delayed fracture resistance of the round steel; on the other hand, the carbides precipitated in a dispersion mode, particularly Mo, can obviously improve tempering softening resistance, so that the carbides are fine, uniform and spheroidized, the ultrahigh strength at high temperature is realized through precipitation hardening and strengthening of a prior austenite crystal boundary, the creep deformation performance is realized, the added Mo element can also reduce the amount of hydrogen invading into the steel surface, the generation of corrosion pits is inhibited, and the atmospheric corrosion resistance of the round steel is improved.
The invention further limits the content of C, Si element by formula II on the basis of further limiting Si, Ti and Mo element by formula I, slightly increases C content on the basis of SCM435, greatly increases Si content, controls relative content of C, Si, reduces corrosion resistance deterioration caused by C content increase, and increases the amount of hydrogen invading on the surface of steel, avoids delayed fracture resistance deterioration, and further ensures delayed fracture resistance of round steel; by limiting the weight percentage of C, Si elements, Si which has no influence on the corrosion resistance of steel is used for ensuring that the strength (namely [ Si ]/[ C ] in a formula) is between 3.0 and 3.35), and high strength is ensured, and meanwhile, excellent corrosion resistance and delayed fracture resistance are obtained.
In addition, the added elements such as Ni and Cu not only improve the corrosion resistance, but also inhibit the generation and absorption of hydrogen in a corrosion environment, and simultaneously obtain higher notch toughness. In order to ensure the corrosion resistance, the content of each element is further limited according to a formula III, and the chemical composition of the steel needs to meet the requirement that the atmospheric corrosion resistance index is more than or equal to 9.0, so that the corrosion resistance of the round steel is further ensured. In addition, by adding Ti and controlling the addition amount, compared with the addition of V, Nb and other elements, the invention effectively improves the cross-sectional shrinkage and the austenite grain size, and effectively improves partial mechanical properties.
It is to be noted that C is an element required for ensuring hardenability and strength, and as the content thereof increases, ductility and corrosion resistance thereof decrease. A relatively high C content is advantageous for the strength and the like of the steel, but is extremely disadvantageous for the cold heading property, plasticity and toughness of the steel, and also causes a reduction in yield ratio, an increase in decarburization sensitivity, and deterioration in fatigue resistance and workability of the steel. Si is a main deoxidizing element in steel, has a strong solid solution strengthening effect, can also improve the stability of a rust layer, and effectively improves the corrosion resistance. Mn is an element that improves hardenability and is useful for achieving high strength performance, but Mn and P tend to be strongly intergranular co-segregated during high-temperature tempering of quenched steel, thereby promoting temper brittleness, and excessively high Mn content deteriorates the weather resistance of steel, promotes segregation to grain boundaries, lowers grain boundary strength, and thus tends to cause delayed fracture. The Cr element is the most commonly used alloy element in high-strength bolt steel, Cr can effectively improve the hardenability and the tempering resistance of the steel so as to obtain the required high strength, meanwhile, the composite addition of Cr and Cu can obviously improve the weather resistance of the steel, the effect is difficult to be achieved when the Cr content is small, but the toughness and the cold workability of the steel are deteriorated when the Cr content is large.
Mo element is also a more commonly adopted alloy element in high-strength bolt steel, so that the tempering resistance of the steel can be obviously improved, and carbide Mo formed by the Mo element2C has a trapping effect on hydrogen and can also improve the delayed fracture resistance of the steel; the segregation of Mo element in the prior austenite grain boundary can also improve the grain boundary bonding strength of steel; in addition, Mo also can reduce the amount of hydrogen entering the steel surface, inhibit the generation of corrosion pits and further improve the corrosion resistance of the round steel. S, P, the delayed fracture resistance is greatly reduced, the P element can form micro segregation when the molten steel is solidified, and then at the austenitizing temperatureThe alloy is deviated and gathered at a grain boundary during heating, so that the brittleness of the steel is obviously increased, and the delayed fracture sensitivity of the steel is increased; the S element forms MnS inclusion to be segregated in the grain boundary, thereby increasing the delayed fracture sensitivity of the steel, and the grain boundary strengthening can be realized by reducing Mn which promotes the grain boundary segregation while reducing the impurity P, S as much as possible.
Besides the functions of grain refinement, precipitation strengthening and fixation N, S, the dispersed and precipitated TiC is one of hydrogen traps with the highest trap energy in steel, and can trap hydrogen to be uniformly dispersed in the grains, so that the diffusion of the hydrogen is inhibited, and the delayed fracture resistance of the steel is improved. The above effect cannot be obtained when the Ti content is low, but the ductility and toughness of the steel are deteriorated by coarse nitrides formed when the Ti content is high. The addition of the Ni element can improve the structure of a rust layer, improve the compactness and the cohesiveness to the surface of steel, improve the corrosion resistance of the steel, inhibit the adsorption of hydrogen and further be beneficial to improving the delayed fracture resistance. The addition of Cu is an element effective for improving corrosion resistance and inhibiting hydrogen from entering, further improving delayed fracture resistance, and forming a rust layer with good protection, and the Cu element can also change the hygroscopicity of the rust layer, so that the critical humidity is improved, but the high Cu content can reduce the high-temperature plasticity of steel, easily generates cracks in the hot working process, and becomes a cause of cost increase. O forms various oxide inclusions in steel, and under the action of stress, stress concentration is easily generated at the oxide inclusions to cause the initiation of microcracks, so that the mechanical properties, particularly the toughness and the fatigue resistance of the steel are deteriorated, therefore, proper measures are required to be taken to reduce the content of the oxide inclusions as much as possible in metallurgical production; n precipitation of Fe in steel4N, the diffusion rate is slow, resulting in the steel being time-efficient, and N also reduces the cold workability of the steel.
The invention relates to a production method of round steel for a titanium-containing 16.9-grade bolt, which comprises the following chemical components: electric furnace smelting → LF + RH vacuum refining → 250mm square billet continuous casting → flaw detection, coping → excellent rod heating furnace heating → KOCKS controlled rolling and controlled cooling → round steel finished product → packaging and warehousing.
When smelting in an electric furnace, performing deoxidation alloying on the steel, and strictly controlling slag discharge in the steel tapping process; during refining in an LF furnace, adjusting elements such as C, Si, Cr, Mn, Mo, Ti, Ni, Cu and the like to target values; when the RH furnace is used for vacuum degassing, the pure degassing time is not less than 20 minutes, and H is not more than 0.00015 percent after vacuum treatment; when a large round billet is continuously cast, the target temperature of molten steel in a tundish is stably controlled to be 10-30 ℃ above the liquidus temperature, and a square billet with the thickness of 250mm is continuously cast.
Round steel rolling route: 250mm square billet → flaw detection, coping → excellent rod heating furnace heating → KOCKS controlled rolling and controlled cooling → cooling bed → 18-30 mm phi hot rolled round steel finished product, preferably 20-26 mm hot rolled round steel finished product. Wherein the heating temperature of the excellent rod heating furnace is 980-1070 ℃ when the excellent rod heating furnace is used for heating, the optimal rod heating furnace is 1020-1050 ℃, and the furnace time of the square billet is not more than 170min, and the optimal rod heating furnace is 140-160 min; it is worth to say that the higher the temperature of the soaking section is, the longer the furnace time is, the more easily the steel billet is decarburized, and finally the decarburization performance index of the round steel is not good and easily exceeds the standard. When the round steel is rolled in a controlled rolling and controlled cooling mode, the initial rolling temperature is 880-945 ℃, preferably 900-920 ℃, the final rolling temperature is 780-840 ℃, and preferably 800-820 ℃; it is worth to say that the low initial rolling temperature is because the soaking section temperature of the heating furnace is low, the final rolling temperature is low, the grain size of the material can be refined, and the tensile strength is improved. The round steel is required to be subjected to performance inspection, the heat treatment process during inspection comprises quenching heating treatment and high-temperature tempering treatment, and the heating temperature is 900-960 ℃ during quenching heating, preferably 910-930 ℃; the tempering temperature is 590-610 ℃ during high-temperature tempering.
The round steel can be subjected to double-cycle heat treatment subsequently, and the specific process comprises the following steps: the steel is subjected to oil quenching and heating treatment at the heating temperature of 910-930 ℃, then is subjected to tempering treatment at the tempering temperature of 490-510 ℃, and then is subjected to air cooling; then carrying out oil quenching and heating treatment at the heating temperature of 860-880 ℃, carrying out tempering treatment at the tempering temperature of 140-160 ℃, and then air cooling; the grain size of the austenite is more than or equal to 10.0 grade after the double-circulation heat treatment. The invention adopts a double-circulation heat treatment process, effectively improves the grain size of austenite, and improves the mechanical properties such as strength and the like.
In the heat treatment process of performance test, in order to fully dissolve alloy elements such as Ti, Mo and the like into austenite, the quenching heating temperature cannot be too low; but at the same time, the overhigh temperature easily causes the excessive growth of austenite grains and the easy decarburization, which causes the poor toughness and the poor delayed fracture resistance of the fastener, therefore, the heating temperature is set to 900-960 ℃, preferably 910-930 ℃ during quenching heating. The precipitation strengthening property of carbide formed by Ti, Mo and other alloy elements can be shown at the temperature of more than 500 ℃, but the carbide grows excessively at the high temperature, which is not beneficial to precipitation strengthening; meanwhile, the high-temperature tempering heat treatment can finely disperse carbides in prior austenite grains and improve the delayed fracture characteristic of the fastener, so the tempering temperature is preferably 590-610 ℃ during high-temperature tempering.
According to the invention, through carrying out optimization design on chemical components, contents and specific process parameters in the production process, utilizing the comprehensive action of each element, controlling the specific parameters in the process steps, and subsequently adding a double-circulation heat treatment process, and through carrying out optimization design on the specific process parameters of the double-circulation heat treatment process, the mechanical property of the round steel for the titanium-containing 16.9-grade bolt is further ensured, the corrosion resistance and delayed fracture resistance of the round steel are ensured, and the requirements of light weight and high safety of an automobile are met. The round steel for the titanium-containing 16.9-grade bolt produced by the invention has the tensile strength R after heat treatmentmMore than or equal to 1600MPa and the yield ratio RP0.2/RmMore than or equal to 0.9 percent, the elongation A after fracture is more than or equal to 10 percent, the reduction of area Z is more than or equal to 50 percent, the structure is tempered sorbite and fine carbide which is evenly dispersed, the content of the tempered sorbite is more than or equal to 90 percent, and the normal temperature impact absorption power KV2More than or equal to 50J, austenite grain size more than or equal to 10.0 grade after double-cycle heat treatment, fatigue life more than or equal to 1000 ten thousand times under 750MPa cyclic stress condition, slow strain rate tensile test (SSRT) evaluation at room temperature, and delayed fracture strength ratio R ═ Rch/Rch0Greater than 0.55 (notched tensile strength R of the hydrogen-charged specimen)chThe notched tensile strength of the non-hydrogenated sample is Rch0) The notch sensitivity was evaluated by using a notch intensity ratio, NSR ═ σc/RmGreater than 1 (tensile strength of smooth specimen R)mNotched tensile Strength of σc) Atmospheric corrosion resistance index of round steelI≥9.0。
The round steel for the bolt produced by adopting the components and the process flow is subjected to performance test, and the specific test process and test results are as follows:
tensile, impact and notched tensile delayed fracture performance test: quenching the steel at 910-930 ℃, and then carrying out oil cooling after heat preservation for 30 min; and then tempering at 590-610 ℃, preserving heat for 120min, and processing into a standard tensile sample with phi 10mm and a notch tensile delayed fracture sample with phi 5mm after an air cooling heat treatment process, as shown in figure 3. The mechanical properties after quenching and tempering heat treatment are shown in fig. 2.
And (3) fatigue test: the rotating bending fatigue test was carried out according to the standard GB/T4337-2015 rotating bending method for fatigue test of metal materials. The rough processed and heat treated steel is processed into a rotary bending fatigue sample, 20 fundamental tests are carried out on a PQ1-6 fatigue testing machine, axial strain control is adopted, the strain cyclic ratio R is-1, the frequency is 83Hz, the room temperature is 20 ℃, the loading waveform of the fatigue test is positive sine wave, and the test finishing criterion is 107Secondary or sample failure.
Atmospheric corrosion resistance test: in order to verify the atmospheric corrosion performance of the steel, 288h weekly immersion corrosion test and 72h salt spray corrosion test are carried out according to the methods of GB/T19746-2018 'Metal and alloy corrosive salt solution weekly immersion test' and GB/T10125-2012 'Artificial atmosphere corrosion test salt spray test'. The test results are shown in FIG. 2.
The invention is further described with reference to specific examples.
Example 1
The round steel for the titanium-containing 16.9-grade bolt of the embodiment adopts the production process of the invention, and the process parameters are as follows: the pure degassing time in the RH furnace vacuum degassing is 20 minutes. The target temperature of the tundish molten steel is stably controlled to be 10 ℃ above the liquidus temperature during the continuous casting of the large round billet. The heating temperature of the excellent rod heating furnace is 980 ℃ and the time of the square billet in the furnace is 140 min. The initial rolling temperature of the round steel is 880 ℃ during rolling, and the final rolling temperature of the round steel is 780 ℃. The heating temperature is 900 ℃ when quenching and heating in the final heat treatment process, and the tempering temperature is 590 ℃ when high-temperature tempering is carried out. When the subsequent double-circulation heat treatment is carried out, the steel is firstly subjected to oil quenching and heating treatment, the heating temperature is 910 ℃, then the steel is subjected to tempering treatment, the tempering temperature is 490 ℃, and then air cooling is carried out; then the steel is treated by oil quenching and heating, the heating temperature is 860 ℃, and then is treated by tempering, the tempering temperature is 140 ℃, and then is air-cooled.
The chemical components and contents adopted in the embodiment are shown in figure 1, the contents of the chemical components meet the formulas of (i), (ii) and (iii), and the test results of tensile, impact and notch tensile delayed fracture performance tests and atmospheric corrosion resistance tests are shown in figure 2.
Example 2
The round steel for the titanium-containing 16.9-grade bolt of the embodiment adopts the production process of the invention, and the process parameters are as follows: the pure degassing time in the RH furnace vacuum degassing is 20 minutes. The target temperature of the tundish molten steel is stably controlled to be 10 ℃ above the liquidus temperature during the continuous casting of the large round billet. The heating temperature of the optimized rod heating furnace is 1070 ℃ when the optimized rod heating furnace is used for heating, and the furnace time of the square billet is 170 min. The start rolling temperature of the round steel during controlled rolling and controlled cooling is 945 ℃, and the finish rolling temperature is 840 ℃. The heating temperature is 960 ℃ during quenching and heating in the final heat treatment process, and the tempering temperature is 610 ℃ during high-temperature tempering. When the subsequent double-circulation heat treatment is carried out, the steel is firstly subjected to oil quenching and heating treatment, the heating temperature is 930 ℃, then is subjected to tempering treatment, the tempering temperature is 510 ℃, and then is cooled in air; then the steel is subjected to oil quenching heating treatment at the heating temperature of 880 ℃, and then is subjected to tempering treatment at the tempering temperature of 160 ℃, and then is cooled in air.
The chemical components and contents adopted in the embodiment are shown in figure 1, the contents of the chemical components meet the formulas of (i), (ii) and (iii), and the test results of tensile, impact and notch tensile delayed fracture performance tests and atmospheric corrosion resistance tests are shown in figure 2.
Example 3
The round steel for the titanium-containing 16.9-grade bolt of the embodiment adopts the production process of the invention, and the process parameters are as follows: the pure degassing time in the RH furnace vacuum degassing is 20 minutes. The target temperature of the tundish molten steel is stably controlled to be 10 ℃ above the liquidus temperature during the continuous casting of the large round billet. The heating temperature of the excellent rod heating furnace is 1020 ℃, and the time of the square billet in the furnace is 160 min. The initial rolling temperature of the round steel is 900 ℃ during rolling, and the final rolling temperature is 800 ℃. The heating temperature is 910 ℃ during quenching and heating in the final heat treatment process, and the tempering temperature is 600 ℃ during high-temperature tempering. When the subsequent double-circulation heat treatment is carried out, the steel is firstly subjected to oil quenching heating treatment, the heating temperature is 920 ℃, then the steel is subjected to tempering treatment, the tempering temperature is 500 ℃, and then air cooling is carried out; then the steel is subjected to oil quenching heating treatment at the heating temperature of 870 ℃, and then is subjected to tempering treatment at the tempering temperature of 150 ℃, and then is cooled in air.
The chemical components and contents adopted in the embodiment are shown in figure 1, the contents of the chemical components meet the formulas of (i), (ii) and (iii), and the test results of tensile, impact and notch tensile delayed fracture performance tests and atmospheric corrosion resistance tests are shown in figure 2.
Example 4
The round steel for the titanium-containing 16.9-grade bolt of the embodiment adopts the production process of the invention, and the process parameters are as follows: the pure degassing time in the RH furnace vacuum degassing is 20 minutes. The target temperature of the tundish molten steel is stably controlled to be 10 ℃ above the liquidus temperature during the continuous casting of the large round billet. The heating temperature of the excellent rod heating furnace is 1050 ℃ when the excellent rod heating furnace is used for heating, and the furnace time of the square billet is 150 min. The initial rolling temperature of the round steel is 920 ℃, and the final rolling temperature is 820 ℃. The heating temperature is 930 ℃ during quenching and heating in the final heat treatment process, and the tempering temperature is 600 ℃ during high-temperature tempering. When the subsequent double-circulation heat treatment is carried out, the steel is firstly subjected to oil quenching heating treatment, the heating temperature is 920 ℃, then the steel is subjected to tempering treatment, the tempering temperature is 500 ℃, and then air cooling is carried out; then the steel is subjected to oil quenching heating treatment at the heating temperature of 870 ℃, and then is subjected to tempering treatment at the tempering temperature of 150 ℃, and then is cooled in air.
The chemical components and contents adopted in the embodiment are shown in figure 1, the contents of the chemical components meet the formulas of (i), (ii) and (iii), and the test results of tensile, impact and notch tensile delayed fracture performance tests and atmospheric corrosion resistance tests are shown in figure 2.
Example 5
The round steel for the titanium-containing 16.9-grade bolt of the embodiment adopts the production process of the invention, and the process parameters are as follows: the pure degassing time in the RH furnace vacuum degassing is 20 minutes. The target temperature of the tundish molten steel is stably controlled to be 10 ℃ above the liquidus temperature during the continuous casting of the large round billet. The heating temperature of the excellent rod heating furnace is 1050 ℃ when the excellent rod heating furnace is used for heating, and the furnace time of the square billet is 150 min. The initial rolling temperature of the round steel is 910 ℃, and the final rolling temperature of the round steel is 810 ℃. The heating temperature is 920 ℃ during quenching and heating in the final heat treatment process, and the tempering temperature is 600 ℃ during high-temperature tempering. When the subsequent double-circulation heat treatment is carried out, the steel is firstly subjected to oil quenching heating treatment, the heating temperature is 920 ℃, then the steel is subjected to tempering treatment, the tempering temperature is 500 ℃, and then air cooling is carried out; then the steel is subjected to oil quenching heating treatment at the heating temperature of 870 ℃, and then is subjected to tempering treatment at the tempering temperature of 150 ℃, and then is cooled in air.
The chemical components and contents adopted in the embodiment are shown in figure 1, the contents of the chemical components meet the formulas of (i), (ii) and (iii), and the test results of tensile, impact and notch tensile delayed fracture performance tests and atmospheric corrosion resistance tests are shown in figure 2.
Example 6
The round steel for the titanium-containing 16.9-grade bolt of the embodiment adopts the production process of the invention, and the process parameters are as follows: the pure degassing time in the RH furnace vacuum degassing is 20 minutes. The target temperature of the tundish molten steel is stably controlled to be 10 ℃ above the liquidus temperature during the continuous casting of the large round billet. The heating temperature of the excellent rod heating furnace is 1050 ℃ when the excellent rod heating furnace is used for heating, and the furnace time of the square billet is 150 min. The initial rolling temperature of the round steel during controlled rolling and controlled cooling is 910 ℃, and the final rolling temperature is 810 ℃. The heating temperature is 920 ℃ during quenching and heating in the final heat treatment process, and the tempering temperature is 600 ℃ during high-temperature tempering. When the subsequent double-circulation heat treatment is carried out, the steel is firstly subjected to oil quenching heating treatment, the heating temperature is 920 ℃, then the steel is subjected to tempering treatment, the tempering temperature is 500 ℃, and then air cooling is carried out; then the steel is treated by oil quenching and heating, the heating temperature is 860 ℃, and then is treated by tempering, the tempering temperature is 150 ℃, and then is cooled in air.
The chemical components and contents adopted in the embodiment are shown in figure 1, the contents of the chemical components meet the formulas of (i), (ii) and (iii), and the test results of tensile, impact and notch tensile delayed fracture performance tests and atmospheric corrosion resistance tests are shown in figure 2.
Example 7
The round steel for the titanium-containing 16.9-grade bolt of the embodiment adopts the production process of the invention, and the process parameters are as follows: the pure degassing time in the RH furnace vacuum degassing is 20 minutes. The target temperature of the tundish molten steel is stably controlled to be 10 ℃ above the liquidus temperature during the continuous casting of the large round billet. The heating temperature of the excellent rod heating furnace is 1050 ℃ when the excellent rod heating furnace is used for heating, and the furnace time of the square billet is 150 min. The initial rolling temperature of the round steel during controlled rolling and controlled cooling is 910 ℃, and the final rolling temperature is 810 ℃. The heating temperature is 920 ℃ during quenching and heating in the final heat treatment process, and the tempering temperature is 600 ℃ during high-temperature tempering. When the subsequent double-circulation heat treatment is carried out, the steel is firstly subjected to oil quenching heating treatment, the heating temperature is 920 ℃, then the steel is subjected to tempering treatment, the tempering temperature is 500 ℃, and then air cooling is carried out; then the steel is subjected to oil quenching heating treatment at the heating temperature of 870 ℃, and then is subjected to tempering treatment at the tempering temperature of 150 ℃, and then is cooled in air.
The chemical components and contents adopted in the embodiment are shown in figure 1, the contents of the chemical components meet the formulas of (i), (ii) and (iii), and the test results of tensile, impact and notch tensile delayed fracture performance tests and atmospheric corrosion resistance tests are shown in figure 2.
The invention also provides a comparative example 1 and a comparative example 2, the production process of the invention is adopted, the chemical components and the contents are different from those of the examples 1-7, the contents do not satisfy the formulas ①, ② and ③, concretely, the figure 1 is shown, the test results of tensile, impact and notch tensile delayed fracture performance test, fatigue test and atmospheric corrosion resistance test are shown in the figure 2, as can be seen from the figure 2, the strength of the examples 1-7 reaches 1600MPa, the elongation reaches more than 10 percent, the face shrinkage reaches more than 50 percent, the excellent delayed fracture performance and plastic toughness are shown, the examples 1-7 have the excellent fatigue property of the fatigue strength more than 750MPa, and compared with the comparative examples 1 and 2, the corrosion rate of the week immersion test of the examples 1-7 is less than 0.7 g/(m) and compared with the comparative examples 1 and 22H) corrosion rate of less than 0.6 g/(m) in salt spray test2H), the corrosion resistance is better.
If the Ti is replaced by V, Nb, the weight percentages of the elements are as follows: 0.55 to 0.60 percent of C, 1.80 to 2.00 percent of Si, 0.10 to 0.20 percent of V, 0.05 to 0.15 percent of Nb0.05 to 0.15 percent of Mn, 0.25 to 0.35 percent of Cr, 1.05 to 1.35 percent of Cr, 1.50 to 1.80 percent of Mo1, 0.10 to 0.30 percent of Ni0.20 to 0.35 percent of Cu0.20, 0.015 to 0.040 percent of Als0.015 to 0.040 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.00015 percent of H, less than or equal to 0.0010 percent of O, less than or equal to 0.005 percent of; and the weight percentage of the alloy meets the conditions that [ Si ]/[ C ]) is more than or equal to 3.0, and 0.55 is less than or equal to 0.25 [% Mo ] +0.20 [% V ] +0.10 [% Nb ] +0.08 [% Si is less than or equal to 0.65.
Meanwhile, the production process omits double-circulation heat treatment, and the other process parameters are as follows: the heating comprises quenching heating treatment and high-temperature tempering treatment, wherein the heating temperature is 900-960 ℃ during quenching heating, and the tempering temperature is 580-600 ℃ during high-temperature tempering; the heating temperature of the excellent rod heating furnace is 950-1000 ℃ during heating, and the furnace time of the square billet is not more than 170 min; the technological parameters of controlled rolling and controlled cooling are as follows: the initial rolling temperature is 860-920 ℃, and the final rolling temperature is 780-840 ℃; and finally quenching the round steel, wherein the temperature of the round steel is 840-880 ℃, and then water cooling is carried out, and the temperature of a quenching medium is 20-40 ℃. The produced round steel has relatively low reduction of area and austenite grain size, the reduction of area Z is more than or equal to 45 percent, the austenite grain size is more than or equal to 8 grade, and partial performances of the round steel are to be further improved.

Claims (9)

1. The round steel for the titanium-containing 16.9-grade bolt is characterized by comprising the following chemical components in percentage by weight: 0.55 to 0.60 percent of C, 1.80 to 2.00 percent of Si, 0.25 to 0.35 percent of Mn, 1.05 to 1.35 percent of Cr1, 50 to 1.80 percent of Mo1, 0.12 to 0.2 percent of Ti0, 0.10 to 0.30 percent of Ni0, 0.20 to 0.35 percent of Cu0.20, 0.015 to 0.040 percent of Als0.010 percent of P, less than or equal to 0.010 percent of S, less than or equal to 0.0010 percent of O, less than or equal to 0.005 percent of N, and the balance of Fe and other inevitable impurities.
2. The round steel for the grade 16.9 bolt containing titanium according to claim 1, which is characterized in that: the weight percentage of each chemical component in the round steel for the titanium-containing 16.9-grade bolt meets the requirement that 0.86 is less than or equal to 0.28 [% Mo ] +2.25 [% Ti ] +0.05 [% Si ] < 0.98.
3. The round steel for the grade 16.9 bolt containing titanium according to claim 2, which is characterized in that: the weight percentage of C and Si also satisfies that ([ Si ]/[ C ]) is less than or equal to 3.0 and less than or equal to 3.35.
4. The round steel for the grade 16.9 titanium-containing bolt according to claim 4, wherein the weight percentages of the chemical components in the round steel for the grade 16.9 titanium-containing bolt further satisfy that:
26.01(％Cu)+3.88(％Ni)+1.20(％Cr)+1.49(％Si)+17.28(％P)-7.29(％Cu)(％Ni)-9.10(％Ni)(％P)-33.39(％Cu)2)≥9.0。
5. a method for producing round steel for 16.9-grade bolts containing titanium, which is characterized by comprising the chemical composition as defined in any one of claims 1 to 4, and the method specifically comprises the following steps: electric furnace smelting → LF + RH vacuum refining → square billet continuous casting → flaw detection, coping → excellent rod heating furnace heating → KOCKS controlled rolling and controlled cooling rolling → round steel finished product → packaging and warehousing.
6. The method for producing round steel for a titanium-containing 16.9-grade bolt according to claim 5, wherein: the heating temperature of the excellent rod heating furnace is 980-1070 ℃ during heating, and the time of the square billet in the furnace is not more than 170 min.
7. The production method of the round steel for the titanium-containing 16.9-grade bolt, which is disclosed by the claim 6, is characterized in that the process parameters of rolling control and cooling control are as follows: the initial rolling temperature is 880-945 ℃, and the final rolling temperature is 780-840 ℃.
8. A method for producing round steel for a titanium-containing 16.9-grade bolt according to any one of claims 5 to 7, characterized in that: the round steel needs to be subjected to performance inspection, the heat treatment process during inspection comprises quenching heating treatment and high-temperature tempering treatment, the heating temperature during quenching heating is 900-960 ℃, and the tempering temperature during high-temperature tempering is 590-610 ℃.
9. The method for producing the round steel for the grade 16.9 containing titanium bolt according to any one of the claims 5 to 7, characterized in that the round steel is subsequently subjected to a double-cycle heat treatment, and the specific process is as follows: the steel is subjected to oil quenching and heating treatment at the heating temperature of 910-930 ℃, then is subjected to tempering treatment at the tempering temperature of 490-510 ℃, and then is subjected to air cooling; then carrying out oil quenching and heating treatment at the heating temperature of 860-880 ℃, carrying out tempering treatment at the tempering temperature of 140-160 ℃, and then carrying out air cooling.
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Application publication date: 20200915