Hot-rolled round steel of Cr-Mo-Nb-V alloy system and manufacturing process of hot-rolled round steel

Abstract

The invention discloses hot-rolled round steel of a Cr-Mo-Nb-V alloy system and a manufacturing process of the hot-rolled round steel, and aims to solve the problem that in the prior art, the production cost is increased due to the fact that the Mo element is high in content, the hot-rolled round steel of the Cr-Mo-Nb-V alloy system mainly comprises, by mass, 0.30%-0.4% of C, 0.15%-0.35% of Si, 1.05%-1.35% of Mn, 1.20%-1.50% of Cr, 0.15%-0.30% of Mo, 0.01%-0.06% of Nb, 0.01%-0.08% of V, smaller than or equal to 0.008% of P, smaller than or equal to 0.003% of S, smaller than or equal to 0.10% of Ni and the balance Fe. The hot-rolled round steel comprises the following components in percentage by weight: 0.12%-0.12% of Cu, 0.015%-0.060% of Al and the balance of Fe, 0.01%-0.06% of Nb and 0.01%-0.08% of V are added into the hot-rolled round steel, so that the content of Mo can be reduced, the hot-rolled round steel is suitable for multiple fields of materials, metallurgy and the like, the corresponding structural strength can be kept, and the production cost of the hot-rolled round steel can be reduced.

Description

Technical Field

[0001] This application relates to the technical field of materials and metallurgy, and in particular to hot-rolled round steel bars of the Cr-Mo-Nb-V alloy system and their manufacturing process. Background Technology

[0002] Drilling tools are often used in extreme environments, such as drilling and metallurgy, which requires them to be able to withstand high temperatures and complex alternating stresses.

[0003] With increasingly fierce competition in the drill steel market, how to ensure quality while reducing costs and increasing efficiency, and highlighting market competitiveness, has become a key issue in the industry.

[0004] In existing technologies, during the development of drill steel products, a relatively high amount of molybdenum (Mo) is often added to ensure the product's strength, impact toughness, and other mechanical properties. While adding a higher Mo content improves the mechanical properties of drill steel products, it also significantly increases development costs.

[0005] Its drawback is that the higher content of Mo leads to increased production costs.

[0006] The information disclosed in this background section is intended only to enhance the understanding of the overall background of this application and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this application is to provide a hot-rolled round bar of Cr-Mo-Nb-V alloy system and its manufacturing process to solve the problem of increased production costs caused by the high content of Mo in existing materials.

[0008] To achieve the above objectives / to solve the above technical problems, this application adopts the following technical solution: On the one hand, this application provides a hot-rolled round steel of Cr-Mo-Nb-V alloy system, which mainly includes the following chemical composition by mass percentage: carbon C: 0.30%~0.4%, silicon Si: 0.15%~0.35%, manganese Mn: 1.05%~1.35%, chromium Cr: 1.20%~1.50%, molybdenum Mo: 0.15%~0.30%, niobium Nb: 0.01%~0.06%, vanadium V: 0.01%~0.08%, phosphorus P: ≤0.008%, sulfur S: ≤0.003%, nickel Ni: ≤0.10%, copper Cu: ≤0.12%, aluminum Al: 0.015%~0.060%, and the balance is iron Fe.

[0009] In some embodiments, the yield strength of the round steel is 930MPa~1050MPa.

[0010] In some embodiments, the tensile strength of the round steel is 1050MPa~1150MPa.

[0011] In some embodiments, the elongation after fracture of the round steel is 17% to 22%.

[0012] In some embodiments, the cross-sectional shrinkage rate of the round steel is 55% to 65%.

[0013] In some embodiments, the impact energy of the round steel at -20°C is 100J~130J.

[0014] On another front, this application provides a manufacturing process for hot-rolled round steel in a Cr-Mo-Nb-V alloy system, comprising the following steps: S1. Electric furnace melting: melting raw materials into molten steel; S2, LF furnace refining: the molten steel is blown, and the molten steel is subjected to precipitation deoxidation and alloying; S3. Vacuum degassing: Vacuum degassing is carried out using the VD method. After breaking the vacuum, the large bag covering agent is added and Ar gas is gently blown and stirred. S4. Continuous casting billet: Electromagnetic stirring of the crystallizer is used during the continuous casting process; S5. Heating and rolling of continuously cast billets: The heating section of the heating furnace is controlled at 1220℃, the soaking section is controlled at 1230℃, the temperature difference of the billet cross section is 25℃, and the billet is subjected to multiple rough rolling passes followed by intermediate and fine rolling. S6. Quenching treatment: Quenching temperature is 870℃, furnace time is 180 minutes, tempering temperature is 580℃, furnace time is 210 minutes, and then water-cooled to room temperature after removal from the furnace.

[0015] In some embodiments, in step "S3, vacuum degassing", the vacuum level is set to 0.7 mbar, the vacuum holding time is 25 min, and the time for soft blowing Ar gas is 17 min.

[0016] In some embodiments, in the step "S4, continuous casting of billet", the superheat of the continuous casting machine is 25°C, the casting speed is 0.54 m / min and constant casting speed is performed; the frequency of the electromagnetic stirring of the crystallizer is 2 Hz and the current of the crystallizer is 300 A; end electromagnetic stirring is performed, the frequency of the end electromagnetic stirring is 6 Hz and the current of the crystallizer is 700 A.

[0017] In some embodiments, during the "continuous casting billet heating and rolling" process, the billet is subjected to six passes of rough rolling followed by intermediate and finish rolling; the temperature exiting the continuous rolling mill is 920°C, the temperature of the upper cooling bed is 720°C, and the temperature of the lower cooling bed is 470°C.

[0018] Compared with the prior art, the beneficial effects achieved by this application are as follows: In this invention, 0.01% to 0.06% of niobium (Nb) and 0.01% to 0.08% of vanadium (V) are added to hot-rolled round steel, thereby reducing the content of molybdenum (Mo) while maintaining the corresponding structural strength, thus reducing the production cost of hot-rolled round steel. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of some embodiments of the hot-rolled round steel production process of the Cr-Mo-Nb-V alloy system provided in this application. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application or use. Example 1

[0022] This embodiment introduces a hot-rolled round steel with a Cr-Mo-Nb-V alloy system, which mainly includes the following chemical composition by mass percentage: carbon: C: 0.30%~0.4%, silicon Si: 0.15%~0.35%, manganese Mn: 1.05%~1.35%, chromium Cr: 1.20%~1.50%, molybdenum Mo: 0.15%~0.30%, niobium Nb: 0.01%~0.06%, vanadium V: 0.01%~0.08%, phosphorus P: ≤0.008%, sulfur S: ≤0.003%, nickel Ni: ≤0.10%, copper Cu: ≤0.12%, aluminum Al: 0.015%~0.060%, and the balance is iron Fe.

[0023] The above chemical composition includes increased niobium and vanadium content, which reduces the molybdenum content in hot-rolled round steel.

[0024] By using the above-mentioned components, the amount of molybdenum used can be reduced while maintaining the strength of hot-rolled round steel, thereby significantly reducing the cost of using hot-rolled round steel.

[0025] Preferably, the yield strength of the round steel is 930 MPa to 1050 MPa. More preferably, the tensile strength of the round steel is 1050 MPa to 1150 MPa.

[0026] The aforementioned yield strength and tensile strength allow the hot-rolled round steel in this embodiment to continue to be used in drilling tools.

[0027] In some embodiments, the elongation after fracture of the round steel is 17% to 22%. Preferably, the reduction of area after fracture of the round steel is 55% to 65%. Further, the impact energy of the round steel at -20°C is 100J to 130J.

[0028] The aforementioned elongation and shrinkage after fracture allow hot-rolled round steel to continue to be used stably in drilling tools, and its impact energy at -20℃ is 100J~130J, thus enabling drilling tools using this hot-rolled round steel to cope with extreme conditions.

[0029] This embodiment will compare with the original S135 steel grade high Mo joint through the following three implementation methods: In the first embodiment, the hot-rolled round steel with the Cr-Mo-Nb-V alloy system is mainly composed of the following chemical components by mass percentage: carbon: C: 0.335%, silicon: Si: 0.25%, manganese: Mn: 1.10%, chromium: Cr: 1.25%, molybdenum: Mo: 0.22%, niobium: Nb: 0.03%, vanadium: V: 0.06%, phosphorus: P: 0.007%, sulfur: S: 0.0015%, nickel: Ni: 0.03%, copper: Cu: 0.045%, aluminum: Al: 0.03%, with the balance being iron (Fe) and unavoidable impurities.

[0030] In this embodiment, the sampling location is set at 1 / 2 R, where R is the cross-sectional radius, the yield strength is 961 MPa, the tensile strength is 1070 MPa, the elongation after fracture is 19%, the shrinkage after fracture is 56%, and the impact energy at -20℃ is 117 J, 114 J, and 113 J, respectively.

[0031] In the second embodiment, the hot-rolled round steel with the Cr-Mo-Nb-V alloy system is mainly composed of the following chemical components by mass percentage: carbon: C: 0.37%, silicon: Si: 0.24%, manganese: Mn: 1.09%, chromium: Cr: 1.24%, molybdenum: Mo: 0.21%, niobium: Nb: 0.029%, vanadium: V: 0.061%, phosphorus: P: 0.008%, sulfur: S: 0.002%, nickel: Ni: 0.02%, copper: Cu: 0.054%, aluminum: Al: 0.029%, with the balance being iron (Fe) and unavoidable impurities.

[0032] In this embodiment, the sampling location is set at 1 / 2 R, where R is the cross-sectional radius, the yield strength is 969 MPa, the tensile strength is 1075 MPa, the elongation after fracture is 18%, the shrinkage after fracture is 57%, and the impact energy at -20℃ is 113 J, 115 J, and 112 J, respectively.

[0033] In the third embodiment, the hot-rolled round steel with the Cr-Mo-Nb-V alloy system is mainly composed of the following chemical components by mass percentage: carbon: C: 0.36%, silicon: Si: 0.27%, manganese: Mn: 1.11%, chromium: Cr: 1.246%, molybdenum: Mo: 0.22%, niobium: Nb: 0.031%, vanadium: V: 0.059%, phosphorus: P: 0.008%, sulfur: S: 0.002%, nickel: Ni: 0.03%, copper: Cu: 0.049%, aluminum: Al: 0.033%, with the balance being iron (Fe) and unavoidable impurities.

[0034] In this embodiment, the sampling location is set at 1 / 2 R, where R is the cross-sectional radius, the yield strength is 958 MPa, the tensile strength is 1049 MPa, the elongation after fracture is 20%, the shrinkage after fracture is 59%, and the impact energy at -20℃ is 117 J, 116 J, and 119 J, respectively.

[0035] The table below compares the chemical composition of the three embodiments described above with that of existing S135 grade high-Mo joints: C Si Mn P S Cr Mo Cu Ni Al V Nb S135 steel grade high Mo joint 0.36 0.25 0.95 0.015 0.008 1.15 0.30 0.060 0.04 0.030 0.003 0.002 Implementation Method 1 0.355 0.25 1.10 0.007 0.0015 1.25 0.22 0.045 0.03 0.030 0.060 0.030 Implementation Method 2 0.37 0.24 1.09 0.008 0.002 1.24 0.21 0.054 0.02 0.029 0.061 0.029 Implementation Method 3 0.36 0.27 1.11 0.008 0.002 1.26 0.22 0.049 0.03 0.033 0.059 0.031 Table 1: Comparison of Chemical Composition of Three Implementation Methods and S135 Grade High Mo Joints The table below compares the mechanical properties of the three implementation methods described above with those of existing S135 steel grade high Mo joints: Sampling location Yield strength, MPa Tensile strength, MPa Elongation after fracture, % Reduction rate after rupture, % Impact energy at -20℃, J High Mo S135 steel grade connector 1 / 2 R 950 1050 18 57 118 / 115 / 120 Implementation Method 1 1 / 2 R 961 1070 19 56 117 / 114 / 113 Implementation Method 2 1 / 2 R 969 1075 18 57 113 / 115 / 112 Implementation Method 3 1 / 2 R 958 1049 20 59 117 / 116 / 119 Table 2: Comparison of Mechanical Properties of Three Implementation Methods and S135 Steel Grade High Mo Joints According to Tables 1 and 2 above, it can be seen that the hot-rolled round steel of the Cr-Mo-Nb-V alloy system used in this embodiment has similar mechanical properties to the original high Mo S135 steel grade joint, which allows the hot-rolled round steel of the Cr-Mo-Nb-V alloy system to reduce production costs while meeting the strength requirements. Example 2

[0036] This embodiment provides a manufacturing process for hot-rolled round steel in a Cr-Mo-Nb-V alloy system, including the following steps: S1. Electric furnace melting: melting raw materials into molten steel; S2 and LF furnace refining: the steel is blown, and the steel is precipitated, deoxidized and alloyed; S3. Vacuum degassing: Vacuum degassing is carried out using the VD method. After breaking the vacuum, the large bag covering agent is added and Ar gas is gently blown and stirred. S4. Continuous casting billet: Electromagnetic stirring of the crystallizer is used during the continuous casting process; S5. Heating and rolling of continuously cast billets: The heating section of the heating furnace is controlled at 1220℃, the soaking section is controlled at 1230℃, the temperature difference of the billet cross section is 25℃, and the billet is subjected to multiple rough rolling passes followed by intermediate and fine rolling. S6. Quenching treatment: Quenching temperature is 870℃, furnace time is 180 minutes, tempering temperature is 580℃, furnace time is 210 minutes, and then water-cooled to room temperature after removal from the furnace.

[0037] Specifically, in this embodiment, the molten steel can be blown. Specifically, alloys and composite aluminum are added after the furnace. Then, the molten steel undergoes precipitation deoxidation and alloying. Preferably, aluminum shot, high-purity graphite carbon material, and high-purity silicon carbide are added to the molten steel. Specifically, these can be added in small batches, and the refining time in the LF furnace can be set to 55 minutes.

[0038] By setting the above parameters, the molten steel can reach the required composition standards during the LF furnace refining process, thereby improving the quality of the molten steel and facilitating subsequent processing.

[0039] In some embodiments, in step "S3, vacuum degassing", the vacuum level is set to 0.7 mbar, the vacuum holding time is 25 min, and the time for soft blowing Ar gas is 17 min.

[0040] Understandably, vacuum degassing can be performed after the LF furnace refining components reach the required temperature. A VD vacuum degassing furnace can be used, with the vacuum level maintained at 0.7 mbar for 25 minutes. After breaking the vacuum, a large ladle covering agent can be added, followed by a soft-blowing Ar gas process for 17 minutes. During the soft-blowing Ar gas process, static stirring can be performed until the slag surface shows only slight movement and no visible light.

[0041] After the vacuum degassing step is completed, the vacuum-treated molten steel can be hoisted into a large billet continuous casting machine for casting. Preferably, four castings can be performed.

[0042] In some embodiments, in the step "S4, continuous casting of billet", the superheat of the continuous casting machine is 25°C, the casting speed is 0.54 m / min and constant casting speed is performed; the frequency of the electromagnetic stirring of the crystallizer is 2 Hz and the current of the crystallizer is 300 A; end electromagnetic stirring is performed, the frequency of the end electromagnetic stirring is 6 Hz and the current of the crystallizer is 700 A.

[0043] In other words, electromagnetic stirring can be performed in a crystallizer during the continuous casting of square billets, and stirring can be carried out simultaneously with casting. It is worth noting that end-stage electromagnetic stirring is possible.

[0044] By using the above conditions to continuously cast molten steel, the central segregation, central shrinkage cavity, and central porosity of the billet can all be lower than grade 1.0, thereby effectively improving the surface strength of the billet.

[0045] In the continuous casting billet heating and rolling process, the large billet is loaded into a walking beam furnace and heated in a reducing atmosphere, with the residual oxygen content of the flue gas controlled at 2.5%. The heating section of the furnace is controlled at 1220℃, the soaking section at 1230℃, the temperature difference across the billet cross section is 25℃, and the billet undergoes multiple roughing and finishing rolling passes.

[0046] In some embodiments, during the "continuous casting billet heating and rolling" process, the billet undergoes six passes of rough rolling followed by intermediate and finish rolling; the exit temperature of the continuous rolling mill is 920°C, the upper cooling bed temperature is 720°C, and the lower cooling bed temperature is 470°C. The rolled round bars can be collected in a pit for slow cooling.

[0047] The above-mentioned steps of heating and rolling the continuously cast billet enable the rolled round steel to have better mechanical properties to meet the needs of existing drilling tools.

[0048] During the quenching process, the quenching temperature is 870℃, and the furnace is heated for 180 minutes. The furnace is then cooled with quenching fluid. The tempering temperature is 580℃, and the furnace is heated for 210 minutes. The parts are then water-cooled to room temperature to obtain the tempered joint. The round steel is then die-forged into drill pipe joints.

[0049] The joint steel obtained by the above process has high strength and toughness, and its elongation and reduction of area after fracture are greatly improved, thus maintaining its strength in use while reducing production costs.

[0050] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0051] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A hot-rolled round steel of a Cr-Mo-Nb-V alloy system, characterized by, In mass percentage, the steel mainly comprises the following chemical components: carbon C: 0.30%~0.4%, silicon Si: 0.15%~0.35%, manganese Mn: 1.05%~1.35%, chromium Cr: 1.20%~1.50%, molybdenum Mo: 0.15%~0.30%, niobium Nb: 0.01%~0.06%, vanadium V: 0.01%~0.08%, phosphorus P: ≤0.008%, sulfur S: ≤0.003%, nickel Ni: ≤0.10%, copper Cu: ≤0.12%, aluminum Al: 0.015%~0.060%, and the balance of iron Fe.

2. The hot rolled round steel of the Cr-Mo-Nb-V alloy system according to claim 1, characterized in that, The yield strength of the round steel is 930MPa~1050MPa.

3. The hot rolled round steel of the Cr-Mo-Nb-V alloy system according to claim 1, characterized in that, The tensile strength of the round steel is 1050MPa~1150MPa.

4. The hot rolled round bar of the Cr-Mo-Nb-V alloy system according to claim 1, characterized in that, The elongation after fracture of the round steel is 17%~22%.

5. The hot rolled round bar of the Cr-Mo-Nb-V alloy system as claimed in claim 1, wherein, The reduction of area after fracture of the round steel is 55%~65%.

6. The hot rolled round bar of the Cr-Mo-Nb-V alloy system according to claim 1, characterized in that, The impact energy of the round steel at -20℃ is 100J~130J.

7. The process for manufacturing a hot rolled round steel of Cr-Mo-Nb-V alloy system according to claim 1, characterized in that, The method comprises the following steps: S1, electric furnace melting: melting raw materials into molten steel; S2, LF furnace refining: blowing the molten steel, and performing sedimentation deoxidization and alloying on the molten steel; S3, vacuum degassing: performing vacuum degassing by VD method, and after breaking the vacuum, increasing the coating agent and soft blowing Ar gas for stirring; S4, continuous casting billet: adopting mold electromagnetic stirring during continuous casting; S5, continuous casting billet heating and rolling: controlling the heating section of the heating furnace at 1220℃, controlling the soaking section at 1230℃, controlling the cross-section temperature difference of the billet at 25℃, and performing multi-pass rough rolling and then intermediate and finish rolling on the billet; S6, quenching treatment: quenching heating temperature 870℃, in the furnace for 180 minutes, tempering heating temperature 580℃, in the furnace for 210 minutes, and water cooling to room temperature after discharging.

8. The process for producing a hot-rolled round steel of a Cr-Mo-Nb-V alloy system according to claim 7, characterized by, In the step of "S3, vacuum degassing", the vacuum degree is set to 0.7mbar, the vacuum keeping time is 25min, and the soft blowing Ar gas time is 17min.

9. The process for producing a hot-rolled round steel of a Cr-Mo-Nb-V alloy system according to claim 7, characterized by, In the step of "S4, continuous casting billet", the superheat degree of the continuous casting machine is 25℃, the casting speed is 0.54m / min, and constant casting speed casting is performed; the mold electromagnetic stirring frequency is 2Hz, and the current of the mold is 300A; end electromagnetic stirring is performed, the frequency of the end electromagnetic stirring is 6Hz, and the current of the mold is 700A.

10. The process for producing a hot rolled round steel of Cr-Mo-Nb-V alloy system according to claim 7, characterized in that, In the process of "continuous casting billet heating and rolling", the billet is subjected to 6-pass rough rolling and then intermediate and finish rolling; the temperature after continuous rolling is 920℃, the temperature on the cooling bed is 720℃, and the temperature on the lower cooling bed is 470℃.

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