CN108531821A - One kind extrusion die steel containing aluminothermy and its production method - Google Patents

Abstract

The invention relates to an aluminum-containing hot extrusion die steel and a production method thereof. The hot extrusion die steel increases the C content on the basis of H13 steel, reduces the Si, Cr, and Mo contents, and the total alloy content is about 2.5-2.5% less than that of H13. 3.5%, the mass percentage of each main alloy element is: C 0.45～0.60%, Si≤0.30%, Mn≤0.30%, Cr 3.00～4.50%, Mo 0.30～0.80%, V 0.30～0.60%, Al 0.50～0.90 %, P<0.015%, S<0.015%, Fe balance. High tempering resistance can be obtained through the balance of Cr and Mo, and at the same time, AlN high wear-resistant strengthening phase can be formed after adding Al to the matrix and surface nitriding treatment. The preparation process of the steel of the present invention is as follows: batching, smelting, pouring, then electroslag remelting and annealing; then high-temperature homogenization heat treatment, multi-directional forging, annealing; then superfine heat treatment and isothermal annealing treatment; finally quenching Temper heat treatment. The steel of the invention has the advantages of low cost, high toughness, high wear resistance and excellent tempering resistance under conditions comparable to H13 steel.

Description

A kind of aluminum-containing hot extrusion die steel and its production method

technical field

The invention belongs to the technical field of alloy steel manufacturing technology, and in particular relates to an economical aluminum-containing hot extrusion die steel and its preparation, heat treatment and surface treatment methods.

Background technique

Hot extrusion dies are used under severe conditions such as high temperature, high pressure, wear and thermal fatigue. Hot extrusion is a process in which a plastic metal blank passes through an extrusion die cavity under pressure to form a profile or pipe of the required shape. my country's current hot extrusion die steel uses 3Cr2W8V and H13 (4Cr5MoSiV1) steel in the national standard GB/T 1299-2000.

The traditional hot extrusion die steel is 3Cr2W8V, which began to be used in industry in the 1920s. It is widely used in ferrous and non-ferrous metal hot extrusion dies. It is a hot work die steel with high thermal strength and has good forging properties. And machinability, the use temperature can reach 650 ℃. However, W-series die steel has poor thermal conductivity and thermal fatigue resistance, low plasticity and toughness, and is prone to early fracture. In the early 1980s, China introduced the chromium-based hot work die steel H13 (4Cr5MoSiV1), which is commonly used abroad. Compared with the high thermal strength hot work die steel 3Cr2W8V, H13 has high toughness and thermal fatigue resistance, so it can replace the The 3Cr2W8V steel that fails due to insufficient toughness or thermal fatigue is used to manufacture hot extrusion dies, but this substitution is generally limited to the condition that the operating temperature does not exceed 600°C. In addition to the limited operating temperature, H13 steel also has Large size effect (size effect means that many materials will lose their original usable properties when the size changes to a certain limit), after the cross-section exceeds 120mm×120mm, the transverse toughness of the core decreases significantly, while the impact toughness of the core Also only 30-40% of the longitudinal surface.

The hot work die steel for hot extrusion mainly focuses on wear resistance, temper softening resistance and cold and heat fatigue resistance during use. As a hot extrusion die steel, H13 steel contains relatively high molybdenum, chromium, vanadium and a certain amount of carbon in its chemical composition. Some liquefied carbides are present, resulting in insufficient toughness of the material. In addition, forming a high-hardness nitriding layer on the cavity channel of the hot extrusion die can significantly improve the life of the die and the surface quality of the extruded profile, so the hot extrusion die steel should have good nitriding ability, while the surface of the traditional H13 steel The hardness of nitriding treatment is 900-1000HV, and the wear resistance is not enough.

Contents of the invention

Aiming at the existing technical defects, the object of the present invention is to provide an aluminum-containing hot extrusion die steel and a production method thereof.

The technical solution adopted by the present invention is: a kind of aluminum-containing hot extrusion die steel and its production method, the mass percentage of the elements contained in the steel is: C 0.45～0.60%, Si≤0.30%, Mn≤0.30% , Cr 3.00-4.50%, Mo 0.30-0.80%, V 0.30-0.60%, Al 0.50-0.90%, P<0.015%, S<0.015%, the balance is Fe; the above Si, Mn, V, P, S is all greater than zero, and the production steps of the above-mentioned steel include the following:

Step 1, smelting: batching according to the above mass percentage, then using induction melting or electric arc furnace melting, pouring into steel ingots after melting, to be used in the next step;

Step 2, electroslag remelting: the steel ingot poured in step 1 is placed in the electroslag remelting device as a consumable electrode for electroslag remelting, the slag melting voltage is 55-65V, and the current is 3500-5500A; It is: voltage 55-60V, current 11500-12500A, capped voltage 58-62V; further remove inclusions by slag washing and floating in the molten pool; thereby eliminating or alleviating various macro and micro defects, improving the composition and structure of the steel ingot Uniformity;

Step 3, after electroslag remelting, heat it at 750°C-850°C for 8-10 hours and then cool with the furnace;

Step 4, high-temperature homogenization: the homogenization temperature is 1200-1260°C, and the homogenization time is 8-12 hours;

Step 5, forging: cooling the steel ingot after high-temperature homogenization heat treatment to a temperature range of 1080-1180°C for multi-directional forging processing, the forging ratio is ≥6, and the final forging temperature is ≥900°C;

Step 6, annealing after forging: keep warm at 840°C-890°C for 8-10 hours, and cool with the furnace;

Step 7, ultra-fine: the ultra-fine temperature is 1090-1130°C, and the ultra-fine time is 7-12h; then oil-cooled or water-cooled to below 250°C; and then heated back to the heat treatment furnace for the next step;

Step 8, isothermal annealing: the first-stage isothermal annealing temperature is 820-840°C, and the annealing time is 6-8h; the second-stage isothermal annealing temperature is 710-740°C, and the annealing time is 8-12h;

Step 9, heat treatment: Quenching at 1030-1100°C, using oil cooling or gas cooling; then tempering at 560-630°C, tempering three times, each tempering heat preservation 2-4 hours;

Step 10, surface treatment: nitriding at 530-570°C for 8-12 hours, the nitriding atmosphere is ammonia gas, the flow rate is 580-620mL/min, and the pressure in the furnace is 630-670Pa.

Compared with the prior art, the present invention has the advantages of: through optimized alloy design and recommended heat treatment process, it overcomes the shortcomings of insufficient tempering resistance and wear resistance of H13 steel widely used in hot extrusion dies under the same toughness conditions. Compared with the commonly used H13 steel, it increases C, reduces the content of Si, Cr, and Mo, and the total alloy content is 2.5-3.5% less than that of H13, which reduces the alloy cost of hot extrusion die steel; through the balance of Cr and Mo, it makes The steel type of the present invention obtains high tempering resistance; at the same time, adding Al element to the matrix can form AlN strengthening phase after surface nitriding, and the hardness is as high as 1100HV, which is 100-150HV higher than the surface hardness formed after nitriding of H13 steel. The thickness of the nitriding layer of the steel after nitriding is about 80-120 μm higher than that of the H13 steel after nitriding, which greatly improves the surface wear resistance of the hot extrusion die.

Description of drawings

Figure 1 is a comparison of the impact toughness of Example 1 of the present invention and H13 steel in the quenched and tempered state.

Fig. 2 is a comparison of thermal stability between Example 1 of the present invention and H13 steel.

Fig. 3 is a comparison of microhardness gradients between Example 1 of the present invention and the nitriding layer of H13 steel.

Fig. 4 is a comparison diagram between Example 1 of the present invention and the nitriding layer of H13 steel.

Fig. 5 is a comparison of the impact toughness of Example 2 of the present invention and H13 steel in the quenched and tempered state.

Fig. 6 is a comparison of thermal stability between Example 2 of the present invention and H13 steel.

Fig. 7 is a comparison of microhardness gradients between Example 2 of the present invention and the nitriding layer of H13 steel.

Fig. 8 is a comparison diagram between Example 2 of the present invention and the nitriding layer of H13 steel.

Fig. 9 is a comparison of the impact toughness of Example 3 of the present invention and H13 steel in the quenched and tempered state.

Figure 10 is a comparison of the thermal stability of Example 3 of the present invention and H13 steel.

Fig. 11 is a comparison of microhardness gradients between Example 3 of the present invention and the nitriding layer of H13 steel.

Fig. 12 is a comparison diagram between Example 3 of the present invention and the nitrided layer of H13 steel.

Detailed ways

Specific examples of the present invention will now be described as follows.

Example 1

C: 0.56%, Si: 0.20%, Mn: 0.24%, Cr: 3.00%, Mo: 0.42%, V: 0.36%, Al: 0.70%, P: 0.010%, S: 0.012%, Fe balance.

In this example, the process steps of preparation, heat treatment and surface treatment of economical aluminum-containing hot extrusion die steel are as follows:

1. Electric furnace smelting: smelting in an electric arc furnace according to the above-mentioned ratio of alloying elements, the melting temperature is greater than 1500°C, casting into Ф400mm electrode rods and air cooling;

2. Electroslag remelting: Place the poured steel ingot as a consumable electrode in the electroslag remelting device for electroslag remelting. The slag melting voltage is 55-65V, the current is 3500-5500A, and the electric system is: voltage 55~60V, current 11500~12500A, capping voltage 58~62V, current time 40min, electroslag remelting into 500Kg electroslag ingot;

3. After electroslag remelting, hold at 800°C for 10 hours and then cool with the furnace;

4. High-temperature homogenization: heat the steel ingot after electroslag remelting to 1250°C for high-temperature homogenization treatment, keep it warm for 12 hours, uniform structure, and reduce component segregation;

5. Forging: Cool the steel ingot after high temperature homogenization heat treatment to 1150°C for multi-directional forging processing, the forging ratio is ≥6, and the final forging temperature is 900°C;

6. Annealing after forging: heat preservation at 860°C for 10 hours, then cool with the furnace;

7. Superfine: The superfine temperature is 1120℃, and the superfine time is 12h; then it is quickly cooled to below 250℃; and then heated back to the heat treatment furnace;

8. Isothermal annealing: the first stage isothermal annealing temperature is 840°C, annealing time is 8h; the second stage isothermal annealing temperature is 720°C, annealing time is 12h;

9. Heat treatment: Quenching at 1030°C, using oil cooling; followed by tempering at 600°C, tempering three times, and holding for 2 hours each time;

10. Surface nitriding treatment: Nitriding at 550°C for 10 hours, the nitriding atmosphere is ammonia gas, the flow rate is 600mL/min, and the pressure in the furnace is 650Pa.

After the above-mentioned smelting, thermal processing and heat treatment of the hot work die steel of the present invention, the final finished product specification is Ф260mm round steel, which is sampled for performance testing and compared with H13 steel under the same conditions:

1. Hardness in quenched and tempered state

Quenching hardness: 55HRC; Tempering hardness: 45HRC.

2. Impact toughness in quenched and tempered state

Take a transverse impact sample on the billet, the size of the sample is 10mm×10mm×55mm, and open a V2-shaped notch (according to the NADCA#207 standard of the North American Die Casting Association). Room temperature impact energy value: the steel grade of the present invention is 18J, which is greater than 14J of the H13 steel, and the test results are shown in Figure 1, meeting the NADCA#207 standard super steel impact energy requirements.

3. Thermal stability

The steel of the present invention was subjected to a stability comparison test with the steel H13 at 620°C. After quenching and tempering, the steel H13 had the same hardness value as the steel of the present invention, both of which were 45HRC. The test results are shown in Figure 2. With the prolongation of the holding time, the hardness difference between the steel of the present invention and the H13 steel is getting larger and larger, and the hardness of the H13 steel decreases faster than that of the steel of the present invention. Judging from the change of the thermal stability curve at 620°C for 20 hours, the steel of the present invention The resistance to temper softening is better than that of H13 steel.

4. Nitriding layer microhardness gradient

The Vickers hardness test was carried out from the surface layer to the matrix after grinding and polishing the section of the sample after nitriding, and the results are shown in Figure 3. The surface hardness of the nitrided layer of the steel of the present invention is about 1200HV, while that of the H13 steel is 1000-1050HV, and the surface hardness of the nitrided layer of the steel of the present invention is higher than that of H13, which is about 150HV.

5. Nitriding layer structure

The section of the sample after nitriding was prepared according to the metallographic method, and observed after grinding, polishing and corrosion, as shown in Figure 4. Moreover, the thickness of the nitrided layer of the steel of the present invention is increased by 100 μm compared with that of H13.

Example 2

In this example, the chemical composition of economical aluminum-containing hot extrusion die steel is as follows:

C: 0.45%, Si: 0.21%, Mn: 0.23%, Cr: 3.00%, Mo: 0.30%, V: 0.30%, Al: 0.50%, P: 0.015%, S: 0.010%, Fe balance.

In this example, the process steps of preparation, heat treatment and surface treatment of economical aluminum-containing hot extrusion die steel are as follows:

1. Electric furnace smelting: smelting in an electric arc furnace according to the above-mentioned ratio of alloying elements, the melting temperature is greater than 1500°C, casting into Ф400mm electrode rods and air cooling;

2. Electroslag remelting: Place the poured steel ingot as a consumable electrode in the electroslag remelting device for electroslag remelting. The slag melting voltage is 55-65V, the current is 3500-5500A, and the electric system is: voltage 55~60V, current 11500~12500A, capping voltage 58~62V, current time 36min, electroslag remelting into 500Kg electroslag ingot;

3. After electroslag remelting, hold at 800°C for 8 hours and then cool with the furnace;

4. High-temperature homogenization: heat the steel ingot after electroslag remelting to 1250°C for high-temperature homogenization treatment, keep it for 10 hours, uniform structure, and reduce component segregation;

5. Forging: Cool the steel ingot after high-temperature homogenization heat treatment to 1100°C for multi-directional forging processing, the forging ratio is ≥6, and the final forging temperature is 900°C;

6. Annealing after forging: heat preservation at 850°C for 10 hours, then cool with the furnace;

7. Superfine: The superfine temperature is 1080°C, and the ultrafine time is 8h; then it is quickly cooled to below 250°C; and then heated back to the heat treatment furnace;

8. Isothermal annealing: the first stage isothermal annealing temperature is 840°C, annealing time is 8h; the second stage isothermal annealing temperature is 720°C, annealing time is 10h;

9. Heat treatment: Quenching at 1030°C, using oil cooling; followed by tempering at 600°C, tempering three times, and holding for 2 hours each time;

10. Surface nitriding treatment: Nitriding at 550°C for 10 hours, the nitriding atmosphere is ammonia gas, the flow rate is 600mL/min, and the pressure in the furnace is 650Pa.

After the above-mentioned smelting, thermal processing and heat treatment of the hot work die steel of the present invention, the final finished product specification is Ф260mm round steel, which is sampled for performance testing and compared with H13 steel under the same conditions:

1. Hardness in quenched and tempered state

Quenching hardness: 53HRC; Tempering hardness: 42HRC.

2. Impact toughness in quenched and tempered state

Take a transverse impact sample on the billet, the size of the sample is 10mm×10mm×55mm, and open a V2-shaped notch (according to the NADCA#207 standard of the North American Die Casting Association). Room temperature impact energy value: the steel grade of the present invention is 22J, which is greater than the 16J of H13 steel, and the test results are shown in Figure 5, meeting the NADCA#207 standard super steel impact energy requirements.

3. Thermal stability

The steel of the present invention was subjected to a stability comparison test with the steel H13 at 620°C. After quenching and tempering, the steel H13 had the same hardness value as the steel of the present invention, both of which were 42HRC. The test results are shown in Figure 6. With the prolongation of the holding time, the hardness of the steel of the present invention decreases slower than that of the H13 steel. From the change of the thermal stability curve at 620° C. for 20 hours, the steel of the present invention has better resistance to temper softening than that of the H13 steel.

4. Nitriding layer microhardness gradient

The Vickers hardness test was carried out from the surface layer to the matrix after grinding and polishing the section of the sample after nitriding, and the results are shown in Figure 7. The surface hardness of the nitrided layer of the steel of the present invention is greater than 1100HV, while that of the H13 steel is 1000-1050HV, and the surface hardness of the nitrided layer of the steel of the present invention is higher than about 100HV of H13.

5. Nitriding layer structure

The section of the sample after nitriding was prepared according to the metallographic method, and observed after grinding, polishing and corrosion, as shown in Figure 8. The thickness of the nitrided layer of the steel of the present invention is about 80 μm higher than that of H13.

Example 3

In this example, the chemical composition of economical aluminum-containing hot extrusion die steel is as follows:

C: 0.60%, Si: 0.18%, Mn: 0.20%, Cr: 4.50%, Mo: 0.80%, V: 0.60%, Al: 0.90%, P: 0.015%, S: 0.010%, Fe balance.

In this example, the process steps of preparation, heat treatment and surface treatment of economical aluminum-containing hot extrusion die steel are as follows:

1. Electric furnace smelting: smelting in an electric arc furnace according to the above-mentioned ratio of alloying elements, the melting temperature is greater than 1500°C, casting into Ф400mm electrode rods and air cooling;

2. Electroslag remelting: Place the poured steel ingot as a consumable electrode in the electroslag remelting device for electroslag remelting. The slag melting voltage is 55-65V, the current is 3500-5500A, and the electric system is: voltage 55~60V, current 11500~12500A, capping voltage 58~62V, current time 48min, electroslag remelting into 500Kg electroslag ingot;

3. After electroslag remelting, hold at 850°C for 10 hours and then cool with the furnace;

4. High-temperature homogenization: heat the steel ingot after electroslag remelting to 1250°C for high-temperature homogenization treatment, keep it warm for 12 hours, uniform structure, and reduce component segregation;

5. Forging: Cool the steel ingot after high temperature homogenization heat treatment to a temperature range of 1180°C for multi-directional forging processing, forging ratio ≥ 6, and final forging temperature 920°C;

6. Annealing after forging: heat preservation at 880°C for 10 hours, then cool with the furnace;

7. Superfine: The superfine temperature is 1130°C, and the ultrafine time is 12h; then it is quickly cooled to below 250°C; and then heated back to the heat treatment furnace;

8. Isothermal annealing: the first stage isothermal annealing temperature is 840°C, annealing time is 8h; the second stage isothermal annealing temperature is 740°C, annealing time is 12h;

9. Heat treatment: Quenching at 1030°C, using oil cooling; followed by tempering at 600°C, tempering three times, and holding for 2 hours each time;

10. Surface nitriding treatment: Nitriding at 550°C for 10 hours, the nitriding atmosphere is ammonia gas, the flow rate is 600mL/min, and the pressure in the furnace is 650Pa.

After the above-mentioned smelting, thermal processing and heat treatment of the hot work die steel of the present invention, the final finished product specification is Ф260mm round steel, which is sampled for performance testing and compared with H13 steel under the same conditions:

1. Hardness in quenched and tempered state

Quenching hardness: 57HRC; Tempering hardness: 46HRC.

2. Impact toughness in quenched and tempered state

Take a transverse impact sample on the billet, the size of the sample is 10mm×10mm×55mm, and open a V2-shaped notch (according to the NADCA#207 standard of the North American Die Casting Association). Impact energy value at room temperature: 17J of the steel grade of the present invention is greater than 13J of H13 steel, and the test results are shown in Figure 9, meeting the impact energy requirement of super steel in NADCA#207 standard.

3. Thermal stability

The steel of the present invention was subjected to a stability comparison test with the steel H13 at 620°C. After quenching and tempering, the steel H13 had the same hardness value as the steel of the present invention, both of which were 46HRC. The test results are shown in Figure 10. With the prolongation of the holding time, the hardness of H13 steel decreases faster than that of the steel of the present invention. From the change of the thermal stability curve at 620° C. for 20 hours, the steel of the present invention has better resistance to temper softening than that of the steel of H13.

4. Nitriding layer microhardness gradient

The Vickers hardness test was carried out from the surface layer to the matrix after grinding and polishing the section of the sample after nitriding, and the results are shown in Figure 11. The hardness of the surface nitrided layer of the steel of the present invention is 1230HV, while that of the H13 steel is 1000-1050HV, and the hardness of the nitrided surface of the steel of the present invention is higher than about 180HV of H13.

5. Nitriding layer structure

The section of the sample after nitriding was prepared according to the metallographic method, and observed after grinding, polishing and corrosion, as shown in Figure 12. Moreover, the thickness of the nitrided layer of the steel of the present invention is 120 μm higher than that of H13.

The invention increases the C content on the basis of H13 steel, reduces the content of Si, Cr and Mo, the total alloy content is about 2.5-3.5% less than that of H13, and obtains high tempering resistance through the balance of Cr and Mo, and at the same time adds Al to the matrix After surface nitriding treatment, AlN high wear-resistant strengthening phase can be formed, which solves the defects of insufficient temper softening resistance and wear resistance after surface nitriding treatment of H13 steel. At the same time, the reduction of the alloy content also greatly reduces the production cost, making it have a high cost performance. Therefore, the present invention satisfies the current situation of lack of special steel varieties for hot extrusion dies in my country, and enables my country to have the ability to independently develop high-performance, long-life hot extrusion die steels. This patent adopts an economical alloying method, makes full use of the effect of alloying element ratio on high temperature tempering stability and wear resistance, adds Al element to improve nitriding ability, and develops economical alloying alloy with high tempering resistance and nitriding ability. Aluminum hot extrusion die steel, its tempering resistance is three times that of H13 steel.

Claims (1)

1. An aluminum-containing hot extrusion die steel and a production method thereof, characterized in that the steel contains elements by weight in a mass percentage of: C 0.45-0.60%, Si≤0.30%, Mn≤0.30%, Cr 3.00 ～4.50%, Mo 0.30～0.80%, V 0.30～0.60%, Al 0.50～0.90%, P<0.015%, S<0.015%, the balance is Fe; the production steps of the above steel include the following: Step 1, smelting: batching according to the above mass percentage, then using induction melting or electric arc furnace melting, pouring into steel ingots after melting, to be used in the next step; Step 2, electroslag remelting: the steel ingot poured in step 1 is placed in the electroslag remelting device as a consumable electrode for electroslag remelting, the slag melting voltage is 55-65V, and the current is 3500-5500A; It is: voltage 55-60V, current 11500-12500A, capping voltage 58-62V; further remove inclusions by slag washing and floating in the molten pool; Step 3, after electroslag remelting, heat it at 750°C-850°C for 8-10 hours and then cool with the furnace; Step 4, high-temperature homogenization: the homogenization temperature is 1200-1260°C, and the homogenization time is 8-12 hours; Step 5, forging: cooling the steel ingot after high-temperature homogenization heat treatment to a temperature range of 1080-1180°C for multi-directional forging processing, the forging ratio is ≥6, and the final forging temperature is ≥900°C; Step 6, annealing after forging: keep warm at 840°C-890°C for 8-10 hours, and cool with the furnace; Step 7, ultra-fine: the ultra-fine temperature is 1090-1130°C, and the ultra-fine time is 7-12h; then oil-cooled or water-cooled to below 250°C; and then heated back to the heat treatment furnace for the next step; Step 8, isothermal annealing: the first-stage isothermal annealing temperature is 820-840°C, and the annealing time is 6-8h; the second-stage isothermal annealing temperature is 710-740°C, and the annealing time is 8-12h; Step 9, heat treatment: Quenching at 1030-1100°C, using oil cooling or gas cooling; then tempering at 560-630°C, tempering three times, each tempering heat preservation 2-4 hours; Step 10, surface treatment: nitriding at 530-570°C for 8-12 hours, the nitriding atmosphere is ammonia gas, the flow rate is 580-620mL/min, and the pressure in the furnace is 630-670Pa.