CN105132811A - Die steel with strong heat stability, and preparation method thereof - Google Patents

Abstract

The invention discloses a die steel with strong heat stability, and a preparation method thereof. The die steel comprises, by mass, 0.36-0.39% of C, 0.11-0.19% of Si, 0.31-0.39% of Mn, 4.86-5.17% of Cr, 2.22-2.28% of Mo, 0.45-0.69% of V, below 0.02% of P, below 0.005% of S, and the balance of Fe and inevitable impurities. The preparation method of the die steel comprises the following steps: casting to form steel ingots, forging, carrying out austenite-martensite transformation twice, and carrying out heat treatment. The die steel has the following advantages: the Rockwell hardness HRC of the die steel after continuous heat insulation at 650DEG C for 3.0h is 46; the Rockwell hardness HRC of the die steel after continuous heat insulation at 650DEG C for 6.0h is 44; and the heat strength of the die steel disclosed in the invention is above 50% higher than that of traditional 4Cr5MoSiV1 hot work die steel.

Description

Die steel that a kind of thermostability is strong and preparation method thereof

Technical field

The present invention relates to a kind of heat-flash stability hot-work die steel had under high-temperature service working order and preparation method thereof, refer more particularly to a kind of working temperature and reach 650 DEG C and the hot-work die steel material with hot strength and hot hardness and excellent tiny microstructure, for the die casting of copper alloy, the hot extrusion shaping mold of the high heat-intensity materials such as refractory alloy, superalloy, cupronickel, the manufacture of titanium alloy creep forming mould.

Background technology

Heat-flash stability die steel is the material category belonging to hot-work die steel, and hot-work die steel is for the manufacture of the shaping die steel of the metal or liquid metal that are heated to more than recrystallization temperature.Such mould mainly for the manufacture of hammer forging die, pressing machine forging die, hot extruding die and transfer mold, at work not only by the effect of greater impact load but also the effect by rapid heat cycle or high temperature, thus make the working conditions of mould complicated, badly change.Mould operationally contacts with thermometal, and cavity surface can be heated and be warming up to 500 ~ 730 DEG C (hot extruding dies).Therefore hot-work die steel should have enough thermostabilitys, has hot strength and hardness.

At present, on domestic and international moulding stock market, most widely used hot-work die steel material is modified hardenable martensitic steel, (composition quality percentage ratio is 4Cr5MoSiV1: C0.32 ~ 0.45%, Si0.80 ~ 1.20%, Mn0.20 ~ 0.50%, Cr4.75 ~ 5.50%, V0.80 ~ 1.20%, P 0.030%, S 0.030%), their thermal treatment process is tempering type of quenching, its tempered structure of quenching is the carbide reinforced phase of a certain size the M23C7 that tempered martensite+matrix distributes, when temperature reaches 650 DEG C, they all inevitably occur to reply softens, tempered martensite matrix will decompose, carbide agglomeration, matrix softens, the decline of material at high temperature intensity and hardness is caused to cause the inefficacy of material.

Traditional hot-work die steel 4Cr5MoSiV1 steel adopts Electric furnace steel making, forging is become a useful person, the technique of Tempering and Quenching (quenching+tempering), thermal treatment process adopts the processing parameter of 1050 ~ 1070 DEG C of quenchings+550 ~ 570 DEG C of tempering, and the heat resistance index of its key is: 650 DEG C of Rockwell hardness HRC31 continued after insulation 3.0h; 650 DEG C of Rockwell hardness HRC28 continued after insulation 6.0h.Lasting military service at high temperature can cause the agglomeration of the decomposition of tempered martensite and tiny carbide to cause the absent-mindedness of grain boundaries bonding force to cause the final inefficacy of material, and the hot-work die of such martensite die steel material manufacture will be very restricted the work-ing life in 650 DEG C of processes used.

For addressing these problems, Chinese patent CN101392353 discloses the modified high heat-intensity hot-work die steel of a kind of tungstenalloy element strengthening, the mechanism of its strengthening is mainly by the process of martenaging martempering, the carbide of separating out tungsten forms the strengthening effect of alloy carbide to reach high-strength effect, the strengthening of this carbide utilizing tungstenalloy element to be formed and sclerization reach the effect of high temperature strongization, but its defect is the toughness that have lost material, what the loss of the toughness of material caused the work-ing life of material under some environment for use drops to cost.Chinese patent CN101440456 discloses the hot-work die steel material of a kind of microalloying strengthening, main reduces carbon content and the microstructure adding that micro alloying element Nb and N element improve material, improves intensity and the hardness of steel.But the deficiency of the obvious existence of this material is reduction of the wear resisting property of material, thus material is obviously declined work-ing life in wearing and tearing rig floor lower end.

Summary of the invention

This technology is that one high stable heat-flash hot in nature under high-temperature condition makes die steel and preparation method thereof.Its objective is the proportioning by a kind of newly-designed Chemical Composition, form the carbide reinforced effect of M2C and MC type of material, and by structure refinement thermal treatment manufacturing technology, invent a kind of hot-work die steel at 650 DEG C of temperature with stable high heat-intensity, improve the product competitiveness of die steel manufacturing concern.

Main purpose of the present invention is to provide a kind of high heat-intensity hot-work die steel stable under ultra high temp condition, promotes the steady heat epistasis of hot forming dies materials under 650 DEG C of high temperature operating conditions.

To achieve these goals, technical scheme of the present invention is as follows:

The die steel that a kind of thermostability is strong, it forms by with following elements, in mass percentage: C0.36 ~ 0.39%, Si0.11 ~ 0.19%, Mn0.31 ~ 0.39%, Cr4.86 ~ 5.17%, Mo2.22 ~ 2.28%, V0.45 ~ 0.69%, P<0.02%, S<0.005%, surplus is Fe and inevitable impurity.

Wherein, carbon is strengthening body tissue and the element expanding austenite region, when carbon content increases, suitably can reduce the content of manganese, thus alleviate the cold working hardening phenomenon of steel.Meanwhile, the raising of carbon content, can improve the intensity of matrix, and can form different M2C and MC type carbide with other alloying elements, reaches the effect of strengthening matrix; But when carbon content is too high, cause negative impact by the toughness of steel, and reduce the thermal fatigue resistance energy of steel.

Silicon is one of element common in steel, and the avidity of silicon and oxygen is only second to aluminium and titanium, and is better than manganese, chromium, vanadium.So in the process of steel-making, as reductive agent and reductor.Silicon does not form carbide in steel, but is present in austenite with the form of sosoloid, and it is extremely strong that its improves the intensity of sosoloid and the effect of cold deformation cementation index in steel, is only second to phosphorus.Silicon is conducive to carbide and separates out in high-temperature aging process, can also increase the dispersity of carbide precipitate, improves high-temperature oxidation resistance and matrix drag.

Manganese forms austenitic fundamental element in this invention steel, can reach stable austenite phase, and can increase the cylinder block strength of material, material can be made to keep austenite structure, obtain the phase of stable austenite structure during material at high temperature when high temperature.Because high mangaenese steel exists cold working hardening phenomenon, when its too high levels, be unfavorable for machining, therefore the content of manganese will be selected in a rational scope.

Chromium adds machinability and the antioxidant property that significantly can improve steel in steel, increases the resistance to corrosion of steel.Chromium also can dissolve in austenite, plays solution strengthening effect.Chromium element can increase the hardening capacity of material simultaneously, and in the process of cooling of material, separates out corresponding alloy carbide play strengthening effect.In addition, chromium can form stable austenite with coordinating of manganese, therefore can reduce the add-on of manganese.

Molybdenum belongs to the element reducing austenite phase field, and molybdenum is present in solid solution phase and carbide in steel.In Carbide Phases, when molybdenum content is lower, form the cementite of compound with iron and carbon, when the content is higher, then form its alloy carbide.The velocity of diffusion of molybdenum is much smaller than Carbon diffusion speed.The effect of molybdenum in steel can be summarized as raising hardening capacity, improves heat resistance, prevents temper brittleness, improve remanent magnetism and coercive force, improves the corrosion stability in some medium and prevents spot corrosion tendency etc.Molybdenum dissolves in austenite, solution strengthening matrix, also can form carbide, enhances the hot strength of steel, hardness and wear resistance.When the content of molybdenum is more than 2.5%, easily cause the decarburization of steel, its content will obtain conservative control.

Vanadium is one of reinforced ferrite and austenite phase field forming element, and it and carbon, nitrogen, oxygen have extremely strong avidity, forms with it corresponding very stable compound.Mainly exist with the form of MC carbide in steel.Its Main Function in steel is: the tissue of refinement steel and crystal grain, improves grain coarsening temperature, thus reduces the superheated susceptivity of steel, and improves intensity and the toughness of steel; Increase steel belt roof bolt stability.Vanadium is carbide, in ag(e)ing process, by the combination of vanadium and carbon, and the VC that disperse educt is a large amount of, strengthening matrix.The microhardness (HV) of vanadium carbide reaches 2500-2800, after its content exceedes certain value, will harden because coherence separates out alloy carbide.Vanadium is in Austenitic Hot Work Die Steel, and all right fining austenite grains, increases intensity and the toughness of steel, improve the wear resistance of steel.

Phosphorus is the element be harmful to very much in high mangaenese steel, and its solubleness in molten steel is extremely low, and often appears on crystal boundary with phosphide film, makes foundry goods be easy to crack, and particularly during carbon content height, more exacerbates this hazardness of phosphorus.

Sulphur, it is generally acknowledged that it is one of harmful element remained in steel, so specify that in high-quality steel its content must not be greater than 0.04%, even if in general carbon steel, also must not limit and is greater than 0.005%.Under certain conditions, harm can change into benefit, as in sulphur free-cutting steel, improves the content of its sulphur and manganese exactly, the manganese sulfide particulate making formation more, to improve the machinability of steel.

In steel, p and s forms phosphide and sulfide precipitates at austenite grain boundary in process of setting.Thus produce intercrystalline brittleness, the plasticity of steel is reduced, also can make to crack in line of segragation during steel ingot forging rolling, reduce the mechanical property of steel.

A preparation method for die steel of the present invention, it comprises the steps:

A) steel ingot is poured into after each raw material being carried out melting at 1540 ~ 1600 DEG C;

B) by step a) in the steel ingot that obtains forge, controlling to open forging temperature is 1150 ~ 1200 DEG C, and stopping forging temperature is more than 850 DEG C, obtains steel forgings, and this material can be made like this to be conducive to the high temperature deformation of material and not cause being out of shape the generation of crackle;

C) by step b) in the steel forgings that obtains carry out twice austeno-martensite transformation;

D) by step c) in product heats to the 850 ~ 870 DEG C temperature that obtains after 3 ~ 4 hours, be cooled to room temperature with the speed being less than 30 DEG C/h, obtain product.

Preferably, described step c) comprise following operation: by step b) in the steel forgings that obtains be cooled to below its martensite transformation temperature, carry out first time austeno-martensite and change; And then be heated to 1080 ~ 1120 DEG C of insulations 2 ~ 3 hours, then by being cooled to martensite transformation temperature region, carrying out second time austeno-martensite and changing.

Preferably, the described type of cooling is air cooling.

After forging first time air cooling to martensite transformation temperature (310 DEG C) below, form martensitic transformation, the austenite crystal that the original high temperature for a long time of destruction causes is thick, and prevent the carbide of chain from causing degradation along crystal boundary precipitation, for the tissue improvement of lower step creates conditions.Adopt and be heated to 1080 ~ 1120 DEG C of insulations 2 ~ 3 hours, after dissolved carbon compound, second time fast wind is chilled to Martensite temperature region, material is made to become martensitic stucture from austenitic transformation again, the autstenitic grain size of material is made to become martensite behavior by diauxic shift again and obtain refinement, and reduce the precipitation of proeutectoid carbide phase again, thus for the fine microstructures after follow-up sofening treatment with stablely to lay the foundation; After material is changed by twice austeno-martensite, reduce the precipitation risk of chain-like carbide, obtain comparatively tiny acicular martensitic structure, tiny austenite structure is formed again by the insulation of 3 ~ 4 hours of 850 ~ 870 DEG C of temperature, and by being less than 30 DEG C per hour slowly cool to room temperature and can obtain tiny sorbite microstructure, meet high-end die steel market to the strict demand of material microstructure.

No matter dominant mechanism of the present invention is that such steel is under normal temperature or high temperature operating conditions, the carbide reinforced state of matrix disperse all the time can not form growing up of carbide at this temperature, thus causes the reply of martensite die steel to soften problem.

The invention has the advantages that: for the problem of heat resistant type hot-work die steel high-temperature behavior deficiency at 650 DEG C of temperature, the proportioning of rational alloying element chosen by steel of the present invention, selected alloying element is with chromium, molybdenum, vanadium alloy element forms alloying element as main matrix solution strengthening element mutually with the dispersion-strengthened of separating out MC carbide, and by after air cooling process after forging and air-cooled process this " air cooling+air-cooled " the twice cooling process technique again after austenitizing, obtain tiny acicular martensitic structure and prepare a kind of hot-work die steel can at 650 DEG C of temperature with the heat-flash stability of good thermal stability energy, the heat resistance index of the key of this steel under 650 DEG C of heat-retaining conditions is: 650 DEG C of Rockwell hardness HRC46 continued after insulation 3.0h, 650 DEG C of Rockwell hardness HRC44 continued after insulation 6.0h, its thermostrength is compared traditional 4Cr5MoSiV1 hot-work die steel and is promoted more than 50%.

Accompanying drawing explanation

Fig. 1 is 500 times of metallographs of the tiny acicular martensitic structure in the present invention after twice cooling process;

Fig. 2 is good sorbite microstructure 500 times of metallographs that die steel of the present invention obtains after complete improvement microstructure thermal treatment process.

Embodiment

Embodiment 1

A) with iron and inevitable impurity for surplus, pour into steel ingot after carrying out melting by the proportioning raw materials in table 1 at 1555 DEG C;

B) by step a) in the steel ingot that obtains forge, controlling to open forging temperature is 1160 DEG C, and stopping forging temperature is 870 DEG C, obtains steel forgings;

C) by step b) in the steel forgings air cooling to 230 DEG C that obtains, carry out first time austeno-martensite and change; And then be heated to 1090 DEG C of insulations 2.5 hours, then by being cooled to 200 DEG C, carrying out second time austeno-martensite and changing.

D) by step c) in product heats to the 860 DEG C temperature that obtains after 3.5 hours, be cooled to room temperature with the speed of 25 DEG C/h, obtain product.

Rockwell hardness HRC after adopting the heat-flash stability die steel of the present embodiment to continue insulation 3.0h at 650 DEG C is 46; 650 DEG C of Rockwell hardness HRC continued after insulation 6.0h are 44.Its result shows it and has excellent thermal stability.

Embodiment 2

A) with iron and inevitable impurity for surplus, pour into steel ingot after carrying out melting by the proportioning raw materials in table 1 at 1543 DEG C;

B) by step a) in the steel ingot that obtains forge, controlling to open forging temperature is 1150 DEG C, and stopping forging temperature is 860 DEG C, obtains steel forgings;

C) by step b) in the steel forgings air cooling to 300 DEG C that obtains, carry out first time austeno-martensite and change; And then be heated to 1080 DEG C of insulations 2 hours, then by being cooled to 230 DEG C, carrying out second time austeno-martensite and changing.

D) by step c) in product heats to the 860 DEG C temperature that obtains after 3 hours, be cooled to room temperature with the speed of 25 DEG C/h, obtain product.

Rockwell hardness HRC after adopting the heat-flash stability die steel of the present embodiment to continue insulation 3.0h at 650 DEG C is in table 2; 650 DEG C continue the Rockwell hardness HRC after insulation 6.0h in table 2.

Embodiment 3

A) with iron and inevitable impurity for surplus, pour into steel ingot after carrying out melting by the proportioning raw materials in table 1 at 1560 DEG C;

B) by step a) in the steel ingot that obtains forge, controlling to open forging temperature is 1200 DEG C, and stopping forging temperature is 880 DEG C, obtains steel forgings;

C) by step b) in the steel forgings air cooling to 290 DEG C that obtains, carry out first time austeno-martensite and change; And then be heated to 1090 DEG C of insulations 3 hours, then by being cooled to 210 DEG C, carrying out second time austeno-martensite and changing.

D) by step c) in product heats to the 850 DEG C temperature that obtains after 3 hours, be cooled to room temperature with the speed of 26 DEG C/h, obtain product.

Rockwell hardness HRC after adopting the heat-flash stability die steel of the present embodiment to continue insulation 3.0h at 650 DEG C is in table 2; 650 DEG C continue the Rockwell hardness HRC after insulation 6.0h in table 2.

Embodiment 4

A) with iron and inevitable impurity for surplus, pour into steel ingot after carrying out melting by the proportioning raw materials in table 1 at 1565 DEG C;

B) by step a) in the steel ingot that obtains forge, controlling to open forging temperature is 1180 DEG C, and stopping forging temperature is 850 DEG C, obtains steel forgings;

C) by step b) in the steel forgings air cooling to 250 DEG C that obtains, carry out first time austeno-martensite and change; And then be heated to 1120 DEG C of insulations 2.5 hours, then by being cooled to 220 DEG C, carrying out second time austeno-martensite and changing.

D) by step c) in product heats to the 860 DEG C temperature that obtains after 3.5 hours, be cooled to room temperature with the speed of 30 DEG C/h, obtain product.

Rockwell hardness HRC after adopting the heat-flash stability die steel of the present embodiment to continue insulation 3.0h at 650 DEG C is in table 2; 650 DEG C continue the Rockwell hardness HRC after insulation 6.0h in table 2.

Embodiment 5

A) with iron and inevitable impurity for surplus, pour into steel ingot after carrying out melting by the proportioning raw materials in table 1 at 1550 DEG C;

B) by step a) in the steel ingot that obtains forge, controlling to open forging temperature is 1160 DEG C, and stopping forging temperature is 870 DEG C, obtains steel forgings;

C) by step b) in the steel forgings air cooling to 230 DEG C that obtains, carry out first time austeno-martensite and change; And then be heated to 1100 DEG C of insulations 3 hours, then by being cooled to 220 DEG C, carrying out second time austeno-martensite and changing.

D) by step c) in product heats to the 870 DEG C temperature that obtains after 3.7 hours, be cooled to room temperature with the speed of 30 DEG C/h, obtain product.

Rockwell hardness HRC after adopting the heat-flash stability die steel of the present embodiment to continue insulation 3.0h at 650 DEG C is in table 2; 650 DEG C continue the Rockwell hardness HRC after insulation 6.0h in table 2.

Embodiment 6

A) with iron and inevitable impurity for surplus, pour into steel ingot after carrying out melting by the proportioning raw materials in table 1 at 1553 DEG C;

B) by step a) in the steel ingot that obtains forge, controlling to open forging temperature is 1170 DEG C, and stopping forging temperature is 890 DEG C, obtains steel forgings;

C) by step b) in the steel forgings air cooling to 260 DEG C that obtains, carry out first time austeno-martensite and change; And then be heated to 1110 DEG C of insulations 2.8 hours, then by being cooled to 250 DEG C, carrying out second time austeno-martensite and changing.

D) by step c) in product heats to the 870 DEG C temperature that obtains after 4 hours, be cooled to room temperature with the speed of 29 DEG C/h, obtain product.

Rockwell hardness HRC after adopting the heat-flash stability die steel of the present embodiment to continue insulation 3.0h at 650 DEG C is in table 2; 650 DEG C continue the Rockwell hardness HRC after insulation 6.0h in table 2.

Table 1

Embodiment	C	Si	Mn	Cr	Mo	V	P	S
									1	0.38	0.16	0.36	5.02	2.23	0.53	0.015	0.004
2	0.36	0.13	0.31	4.86	2.25	0.60	0.010	0.002
									3	0.37	0.11	0.36	4.90	2.22	0.45	0.013	0.003
4	0.39	0.18	0.39	4.96	2.27	0.69	0.011	0.004
									5	0.38	0.19	0.38	5.17	2.26	0.55	0.019	0.002
6	0.39	0.16	0.33	5.09	2.28	0.58	0.009	0.003

Table 2

Steel of the present invention is after forging after air cooling process and air-cooled process this " air cooling+air-cooled " the twice cooling process technique again after austenitizing, tiny acicular martensitic structure can be obtained, as shown in Figure 1, for follow-up final acquisition is tiny and uniform microstructure creates condition; High strength and toughness hot-work die steel SWDVA forges material finished product and obtains tiny martensitic stucture through twice cooling, as shown in Figure 2, then by Slow cooling after 850 ~ 870 DEG C of insulations in subsequent heat treatment operation, obtains the sorbite microstructure of fine uniform.

In sum, be only preferred embodiment of the present invention, not be used for limiting scope of the invention process, all equalizations of doing according to shape, structure, feature and the spirit described in the claims in the present invention scope change and modify, and all should be included in right of the present invention.

Claims (4)

1. the die steel that a thermostability is strong, it is characterized in that, the composition of described steel forms by with following elements, in mass percentage: C0.36 ~ 0.39%, Si0.11 ~ 0.19%, Mn0.31 ~ 0.39%, Cr4.86 ~ 5.17%, Mo2.22 ~ 2.28%, V0.45 ~ 0.69%, P<0.02%, S<0.005%, surplus is Fe and inevitable impurity.

2. a preparation method for die steel as claimed in claim 1, is characterized in that, comprises the steps:

A) steel ingot is poured into after each raw material being carried out melting at 1540 ~ 1600 DEG C;

B) by step a) in the steel ingot that obtains forge, controlling to open forging temperature is 1150 ~ 1200 DEG C, and stopping forging temperature is more than 850 DEG C, obtains steel forgings;

C) by step b) in the steel forgings that obtains carry out twice austeno-martensite transformation;

D) by step c) in product heats to the 850 ~ 870 DEG C temperature that obtains after 3 ~ 4 hours, be cooled to room temperature with the speed being less than 30 DEG C/h, obtain product.

3. preparation method according to claim 2, is characterized in that: described step c) comprise following operation: by step b) in the steel forgings that obtains be cooled to below its martensite transformation temperature, carry out first time austeno-martensite and change; And then be heated to 1080 ~ 1120 DEG C of insulations 2 ~ 3 hours, then by being cooled to martensite transformation temperature region, carrying out second time austeno-martensite and changing.

4. preparation method according to claim 3, is characterized in that: the described type of cooling is air cooling.