CN110343963B - A kind of hot work die steel and preparation method thereof - Google Patents

Abstract

The invention discloses a hot work die steel and a preparation method thereof. The hot work die steel is composed of the following constituent elements: carbon 0.396-0.397wt%, silicon 0.975-1.03wt%, manganese 0.427-0.514wt%, molybdenum 1.55wt% ‑1.59wt%, chromium 4.94‑5.10wt%, vanadium 0.984‑1.04wt%, titanium 0.044‑0.127wt%, and the balance is iron and inevitable impurities. In the hot work die steel of the present invention, Ti element is added on the basis of the H13 steel composition, on the one hand, it can control the grain size, prevent the excessive growth of the grains, and increase the precipitation strengthening and fine grain strengthening, thereby improving the strength of the steel. and hardness; on the other hand, titanium carbide reacts with carbon to form titanium carbide, which has the advantages of high hardness and good thermal stability, plays a role in precipitation strengthening, and forms micro-Ti alloying. The room temperature Rockwell hardness, room temperature tensile strength, room temperature tensile section shrinkage rate, high temperature tensile section shrinkage rate and high temperature tensile strength of the hot work die steel of the present invention are significantly improved, and the comprehensive mechanical properties are significantly enhanced.

Description

A kind of hot work die steel and preparation method thereof

technical field

The present application relates to the technical field of new materials, in particular to a hot work die steel and a preparation method thereof.

Background technique

Hot work dies are tooling used to make heated metal or liquid metal into desired products, such as hot forging dies, hot upsetting dies, hot extrusion dies, die casting dies and high-speed forming dies, etc. All kinds of hot work dies are Work at higher temperature, especially in hot extrusion of steel and die casting of steel, the temperature of steel is in the range of 1200 ~ 1500 ℃, so the most important performance requirement for hot work die steel is the heat resistance of steel properties, followed by toughness and thermal fatigue resistance. The various mold steels used in hot work dies are collectively referred to as hot work die steels.

H13 steel is a commonly used steel for hot work die steel, mainly used for die casting dies, hot forging dies and hot extrusion dies, accounting for more than 50% of the total output of hot work die steel. It has good hardenability, red hardness, resistance to Grinding and excellent thermal crack resistance, grade 4Cr5MoSiV1. H13 steel is widely used in aluminum extrusion die due to its high cost performance and good process performance. However, H13 steel has the following shortcomings: the heat treatment deformation rate is low, the section shrinkage rate is low, and the tensile strength is low. When the service temperature is higher than 540 °C, the hardness decreases rapidly. Therefore, the hot work die prepared with H13 steel will appear plastic deformation, cracking, blunting, washboard pattern and thermal wear during use.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide a hot work die steel with good high temperature performance, specifically a hot work die steel with high section shrinkage and high high temperature tensile strength.

The second object of the present invention is to provide a preparation method of hot work die steel.

For achieving the above object, the technical scheme of the present invention is:

A hot work die steel is composed of the following constituent elements: carbon 0.396-0.397wt%, silicon 0.975-1.03wt%, manganese 0.427-0.514wt%, molybdenum 1.55-1.59wt%, chromium 4.94-5.10wt%, vanadium 0.984-1.04wt%, titanium 0.044-0.127wt%, the balance is iron and inevitable impurities.

The hot work die steel of the present invention adds titanium element on the basis of the H13 steel composition, on the one hand, it can control the grain size, prevent the grain from excessively growing, and increase the precipitation strengthening and fine grain strengthening, thereby improving the strength of the steel. and hardness; on the other hand, the added titanium element forms micro-titanium alloying, and titanium reacts with carbon to form titanium carbide, which plays a role in precipitation strengthening, thereby increasing the hardness and thermal stability of hot work die steel. Titanium, vanadium and carbon The reaction generates MC-type carbides, and MC-type carbides with good stability are beneficial to prevent the hardness decrease in the thermal cycle of the material, delay the growth of M ₂₃ C ₆ -type carbides, improve the high temperature stability of die steel, and improve its thermal stability. Fatigue resistance.

The room temperature Rockwell hardness, the room temperature tensile strength, the room temperature tensile section shrinkage, the high temperature tensile section shrinkage and the high temperature tensile strength of the hot work die steel of the present invention are significantly improved, and the comprehensive mechanical properties are significantly enhanced. The hardness at room temperature reaches 51.0HRC～51.9HRC, the tensile strength reaches 1755MPa～1803MPa, and the section shrinkage rate reaches 40.0%～46.4%; the tensile strength reaches 1512MPa～1531MPa at high temperature (450℃), and the section shrinks at high temperature (450℃) The rate reaches 49.0% to 50.0%.

In order to further improve the reduction in area and tensile strength of the hot work die steel, preferably, the inevitable impurities include element sulfur, element phosphorus, element nitrogen and element oxygen.

In order to further improve the reduction in area and tensile strength of the hot work die steel, preferably, the content of the sulfur element is ≤0.0037wt%, the content of the phosphorus element is ≤0.0064wt%, and the content of the nitrogen element is ≤0.0044wt% %, the content of the oxygen element is less than or equal to 20ppm.

In order to further improve the grain refinement strengthening effect and the precipitation strengthening effect, preferably, the sum of 3.4 times the nitrogen element content and 3 times the sulfur element content is less than the content of the titanium element.

A preparation method of hot work die steel, comprising the following steps:

(1) Select raw material iron, silicon-containing raw material, manganese-containing raw material, molybdenum, chromium, ferrovanadium, and titanium according to the weight percentage of each constituent element in the hot work die steel, and smelt at 1570-1650 ° C under a protective atmosphere to obtain molten steel. The silicon-containing raw material is silicon or ferrosilicon; the manganese-containing raw material is manganese or ferromanganese;

(2) The melt is kept at 1570-1650°C for 2.5-3 hours, and vacuum die-casting is performed to obtain a casting;

(3) Forging and annealing the casting to obtain annealed parts after forging;

(4) Quenching and tempering the annealed parts after forging.

In the preparation method of hot work die steel of the present invention, by selecting raw materials with a specific composition, selecting a specific smelting temperature of 1570-1650° C., and smelting in a protective atmosphere, the reduction of silicon-containing raw materials, manganese-containing raw materials, molybdenum, chromium, and vanadium is reduced. Oxidation of iron and titanium; not only the preparation method of hot work die steel is simplified, but also the obtained hot work die steel has a suitable crystal phase, which improves the room temperature Rockwell hardness, room temperature tensile strength, and room temperature tensile section shrinkage of the hot work die steel. rate, tensile shrinkage at high temperature and tensile strength at high temperature.

In order to further remove impurities in the hot work die steel, preferably, in step (1), the raw material iron is vacuum smelted at 1570-1650° C. before smelting in a protective atmosphere.

In order to further optimize the composition structure of the crystal phase in the hot work die, preferably, the forging ratio of the forging in step (3) is 7-8.

In order to further reduce the stress in the hot work die, preferably, in step (3), the annealing is carried out at 900-950° C. for 6-7 hours, and the temperature is lowered from 900-950° C. to 500-550° C. and then air-cooled.

In order to further improve the hardness of the hot work die, preferably, the holding temperature for quenching in step (4) is 1040-1050° C., and the holding time is 25-30 min.

In order to further reduce the stress in the hot work mold, preferably, the tempering in step (4) is secondary tempering, the holding temperature of the first tempering is 580-600°C, and the holding time of the first tempering is 2h , the holding temperature of the second tempering is 580 ~ 600 ℃, and the holding time of the second tempering is 2h.

Preferably, the protective atmosphere is one or more of argon, nitrogen and helium.

Preferably, the pressure of the protective atmosphere is 20000Pa.

Detailed ways

The embodiments of the present invention will be further described below with reference to specific examples. In the following examples, industrial pure iron bars, electrolytic manganese, ferromanganese, industrial silicon bars, ferrosilicon, industrial molybdenum bars, metallic chromium, ferrovanadium alloys, sponge titanium, smelting, stirring, vacuum die casting, mold, forging, annealing, quenching , tempering and other equipment and raw materials can be obtained through commercially available conventional channels.

Embodiment 1 of the hot work die steel of the present invention

The hot work die steel of this embodiment is composed of the following elements: carbon 0.397wt%, silicon 1.03wt%, manganese 0.514wt%, molybdenum 1.59wt%, chromium 4.94wt%, vanadium 1.04wt%, titanium 0.044wt% , the balance is iron and inevitable impurities.

Embodiment 2 of the hot work die steel of the present invention

The hot work die steel of this embodiment is composed of the following elements: carbon 0.396wt%, silicon 0.975wt%, manganese 0.427wt%, molybdenum 1.55wt%, chromium 5.10wt%, vanadium 0.984wt%, titanium 0.127wt% , the balance is iron and inevitable impurities.

Embodiment 1 of the preparation method of hot work die steel of the present invention

The preparation method of the hot work die steel of the present embodiment comprises the following steps:

(1) The hot work die steel is composed of the following elements: carbon 0.397wt%, silicon 1.03wt%, manganese 0.514wt%, molybdenum 1.59wt%, chromium 4.94wt%, vanadium 1.04wt%, titanium 0.044wt% , the balance is iron and inevitable impurities; according to the weight percentage of each constituent element in the hot work die steel, raw materials are selected from industrial pure iron bars, industrial silicon bars, electrolytic manganese, industrial molybdenum bars, metallic chromium, ferrovanadium, and sponge titanium; Add the industrial pure iron rods into the aluminum-magnesium crucible, send electricity to heat up and start smelting, the smelting temperature is 1570℃, and keep the vacuum degree below 10pa during the whole smelting process. The pressure is 20000Pa, add industrial silicon strips, electrolytic manganese, industrial molybdenum strips, metal chromium, ferrovanadium, sponge titanium, stir to obtain a rough smelting melt; add a refining agent to the evenly mixed rough smelting melt, and let stand for 20min After removing the slag, a melt is obtained;

(2) heating the melt in step (1) to 1570°C, vacuum die-casting into a mold after heat preservation for 2.5h, the mold contains a mold, and the pressure is maintained for 2s, and the mold is removed to obtain a casting; the material of the mold is cast iron;

(3) The casting is forged and annealed to obtain the annealed part after forging; the forging ratio of forging is 7; the annealing is kept at 900 ℃ for 6 hours, and then cooled from 900 ℃ to 500 ℃, and then air-cooled;

(4) Quenching and tempering: quenching and tempering the annealed parts after forging, that is, the hot working die steel; the quenching holding temperature is 1040℃, and the holding time is 25min; the tempering is the second tempering, the first tempering The holding temperature is 580°C, the holding time for the first tempering is 2h, the holding temperature for the second tempering is 600°C, and the holding time for the second tempering is 2h.

Embodiment 2 of the preparation method of hot work die steel of the present invention

The preparation method of the hot work die steel of the present embodiment comprises the following steps:

(1) The hot work die steel is composed of the following elements: carbon 0.396wt%, silicon 0.975wt%, manganese 0.427wt%, molybdenum 1.55wt%, chromium 5.10wt%, vanadium 0.984wt%, titanium 0.127wt% , the balance is iron and unavoidable impurities; according to the weight percentage of each constituent element in the hot work die steel, the raw materials industrial pure iron rod, ferrosilicon, ferromanganese, industrial molybdenum strip, metal chromium, ferrovanadium and sponge titanium are selected; The industrial pure iron rods are put into the aluminum-magnesium crucible, and the temperature is 1650℃. The vacuum degree of the whole melting process is kept below 10pa. The pressure is 20000Pa, add ferrosilicon, ferromanganese, industrial molybdenum bars, metal chromium, ferrovanadium, sponge titanium, stir to obtain a rough smelting melt; add a refining agent to the evenly mixed rough smelting melt, and remove it after standing for 20 minutes Slag, get melt;

(2) heating the melt in step (1) to 1650°C, vacuum die-casting into a mold after heat preservation for 3h, the mold contains a mold, and the pressure is maintained for 2s, and the mold is removed to obtain a casting; the material of the mold is cast iron;

(3) The casting is forged and annealed to obtain a post-forging annealed piece; the forging ratio of forging is 8; the annealing is kept at 950 ° C for 7 hours, and then cooled from 950 ° C to 550 ° C and then air-cooled;

(4) Quenching and tempering: quenching and tempering the annealed parts after forging, that is, the hot working die steel; the heat preservation temperature of quenching is 1050℃, and the heat preservation time is 30min; the tempering is the second tempering, the first tempering The holding temperature is 600℃, the holding time of the first tempering is 2h, the holding temperature of the second tempering is 580℃, and the holding time of the second tempering is 2h.

Comparative example 1 of the preparation method of hot work die steel of the present invention

The preparation method of the hot work die steel of this comparative example comprises the following steps:

(1) The hot work die steel is composed of the following elements: carbon 0.381wt%, silicon 0.895wt%, manganese 0.334wt%, molybdenum 1.62wt%, chromium 5.11wt%, vanadium 0.983wt%, and the balance is iron and unavoidable impurities; according to the weight percentage of each constituent element in the hot work die steel, the raw materials industrial pure iron bars, industrial silicon bars, electrolytic manganese, industrial molybdenum bars, metallic chromium, and ferrovanadium are selected; the industrial pure iron bars are added into aluminum magnesium In the crucible, the melting temperature is 1570℃, and the vacuum degree of the whole melting process is kept below 10pa. After all the iron rods are melted, argon gas is introduced, and the pressure of argon gas is 20000Pa. Electrolytic manganese, industrial molybdenum bars, metallic chromium, and ferrovanadium are stirred to obtain a rough smelting melt; add a refining agent to the evenly mixed rough smelting melt, and after standing for 20 minutes, remove the slag to obtain a melt;

(2) heating the melt in step (1) to 1570°C, vacuum die-casting into a mold after heat preservation for 2.5h, the mold contains a mold, and the pressure is maintained for 2s, and the mold is removed to obtain a casting; the material of the mold is cast iron;

(3) The casting is forged and annealed to obtain the annealed part after forging; the forging ratio of forging is 7; the annealing is kept at 900 ℃ for 6 hours, and then cooled from 900 ℃ to 500 ℃, and then air-cooled;

(4) Quenching and tempering: quenching and tempering the annealed parts after forging, that is, the hot working die steel; the quenching holding temperature is 1040℃, and the holding time is 25min; the tempering is the second tempering, the first tempering The holding temperature is 580°C, the holding time for the first tempering is 2h, the holding temperature for the second tempering is 600°C, and the holding time for the second tempering is 2h.

Test example:

Mechanical property test:

According to the national standard of the People's Republic of China GB/T228-2010 "Metallic Materials Tensile Test Part 1: Test Method at Room Temperature", the hot work die steel prepared in Examples 1-2 and Comparative Example 1 of the preparation method of hot work die steel was prepared. The samples were processed into standard tensile specimens, and were subjected to room temperature tensile tests and high temperature (450°C) tensile tests on a SHIMADZU AG-I 250KN universal tensile testing machine, with a tensile rate of 1 mm/min. The hardness of the samples was measured with a 200HRS-150 digital Rockwell hardness tester. The mechanical properties of the hot work die steel prepared in Comparative Example 1 and Examples 1-2 are shown in Table 1.

Table 1: Preparation method of hot work die steel The hot work die steel prepared in Examples 1-2 and Comparative Example 1

Mechanical properties

The results show that the hot work die steel prepared by the present invention has higher Rockwell hardness at room temperature, tensile strength at room temperature, tensile area shrinkage at room temperature, and higher tensile strength and area shrinkage at high temperature (450°C). The mechanical properties are significantly enhanced. Among them, compared with the hot work die steel in Comparative Example 1, the hardness and tensile strength of the hot work die steel prepared in Example 2 increased by 4.7HRC and 258MPa respectively at room temperature, reaching 51.9HRC and 1803MPa respectively. It increased from 35.0% to 46.4%; the tensile strength at high temperature (450°C) reached 1531MPa, an increase of 192MPa, and the area shrinkage rate increased from 38.8% to 50.0%. It shows that the hot work die steel of the present invention is particularly suitable for the field of hot extrusion die which has the requirements of high strength, high hardness and high area shrinkage at room temperature and high temperature.

Claims (7)

1. A hot work die steel, characterized in that, it is composed of the following constituent elements: carbon 0.396-0.397wt%, silicon 0.975-1.03wt%, manganese 0.427-0.514wt%, molybdenum 1.55-1.59wt%, chromium 4.94 -5.10wt%, vanadium 0.984-1.04wt%, titanium 0.044-0.127wt%, the balance is iron and inevitable impurities; The preparation method of the hot work die steel comprises the following steps: (1) Select raw material iron, silicon-containing raw material, manganese-containing raw material, molybdenum, chromium, ferrovanadium, and titanium according to the weight percentage of each constituent element in the hot work die steel, and smelt at 1570~1650 ° C under a protective atmosphere to obtain a molten The silicon-containing raw material is silicon or ferrosilicon; the manganese-containing raw material is manganese or ferromanganese; (2) The melt is kept at 1570~1650℃ for 2.5~3h, and vacuum die-casting is performed to obtain castings; (3) Forging and annealing the castings to obtain annealed parts after forging; the forging ratio of the forging is 7~8; the annealing is to keep the temperature at 900~950℃ for 6~7h, and cool down from 900~950℃ to 500~ Air-cooled after 550℃; (4) Quenching and tempering the annealed piece after forging, and that is obtained; the quenching holding temperature is 1040~1050°C, and the holding time is 25~30min. 2. The hot work die steel according to claim 1, wherein the inevitable impurities include elemental sulfur, elemental phosphorus, elemental nitrogen and elemental oxygen. 3. The hot work die steel according to claim 2, wherein the content of the sulfur element is ≤0.0037wt%, the content of the phosphorus element is≤0.0064wt%, and the content of the nitrogen element is≤0.0044wt%, The content of the oxygen element is less than or equal to 20ppm. 4 . The hot work die steel according to claim 2 , wherein the sum of 3.4 times the nitrogen element content and 3 times the sulfur element content is less than the content of the titanium element. 5 . 5. a preparation method of hot work die steel as claimed in claim 1, is characterized in that, comprises the following steps: (1) Select raw material iron, silicon-containing raw material, manganese-containing raw material, molybdenum, chromium, ferrovanadium, and titanium according to the weight percentage of each constituent element in the hot work die steel, and smelt at 1570~1650 ° C under a protective atmosphere to obtain a molten The silicon-containing raw material is silicon or ferrosilicon; the manganese-containing raw material is manganese or ferromanganese; (2) The melt is kept at 1570~1650℃ for 2.5~3h, and vacuum die-casting is performed to obtain castings; (3) Forging and annealing the castings to obtain annealed parts after forging; the forging ratio of the forging is 7~8; the annealing is to keep the temperature at 900~950℃ for 6~7h, and cool down from 900~950℃ to 500~ Air-cooled after 550℃; (4) Quenching and tempering the annealed piece after forging, and that is obtained; the quenching holding temperature is 1040~1050°C, and the holding time is 25~30min. 6 . The method for preparing hot work die steel according to claim 5 , wherein in step (1), the raw material iron is vacuum smelted at 1570-1650° C. and before smelting in a protective atmosphere. 7 . 7. The preparation method of hot work die steel according to claim 5, wherein the tempering in step (4) is secondary tempering, the holding temperature of the first tempering is 580-600°C, and the first tempering is 580-600°C. The holding time of fire is 2h, the holding temperature of the second tempering is 580~600℃, and the holding time of the second tempering is 2h.