CN100469938C - Multi-type ultra-fine carbide high-alloy tool steel - Google Patents

Abstract

The invention discloses a high-alloy tool and die steel and its heat treatment process. The steel belongs to a multi-type superfine carbide high-alloy steel. Using the self-developed alloy design method, the phase equilibrium thermodynamic calculation, electronic/atomic level binding energy calculation, quenching and tempering hardness calculation were carried out, and the strength and toughness were comprehensively evaluated according to the carbide phase transformation law. Its composition characteristics are suitable C content and Cr/(W+Mo) ratio, reasonable Si, Mn and a small amount of Ni; its microstructure is characterized by ultrafine carbides, and the average size of annealed carbides is 0.8-1.0 μm, the size of undissolved carbides during quenching is less than 0.5 μm. After quenching and high temperature tempering, the hardness is 61-64HRC, with high yield strength and impact toughness. It has broad application prospects in industries such as thin-edged tools, shearing dies and heavy impact dies.

Description

Series superfine carbide high alloy tool steel

Technical field

The present invention relates to the alloy designs and the thermal treatment process thereof of mould steel, relate in particular to the research and development of DM6S-2 steel.

Background technology

Carbide refinement has important effect to the performance raising of mould steel.But, because carbide quantity is many, distribution density is big, very easily assembles and grow up in most of high-carbon high-alloy steels, though also be difficult to reach the purpose of refinement by forging rolling processing and thermal treatment.Moreover complicated forging rolling processing or thermal treatment can increase technologic difficulty again, and consume the more energy.So again then developed matrix steel, however because matrix steel does not have the residue of quenching carbide causes wearing no resistance, crystal grain is easily grown up when quenching heating, as the wedge angle tool and mould quasi-cleavage crack can take place, and has reduced use properties.Development along with processing industry, requirements such as thin edged knife tool, shearing die and heavy Impact mould have than high-carbon low-alloy steel tool and mould and have longer work-ing life and better processing quality, in order to realize this target, we are devoted to the research and development of the high alloy tool steel of superfine carbide for many years always.We studies show that, multicomponent alloy high carbon steel composition designs when suitable, has the polymorphic type carbide in the steel, such as M ₃C, M ₂₃C ₆, M ₇C ₃, M ₆C and MC.In the annealing temperature interval, different and their forming core, growth and dissolved thermodynamics and kinetics difference in austenite under differing temps because of dissimilar carbide crystalline structures, its carbide mean sizes is between 0.8～1.0 μ m, the undissolved carbide size is less than 0.5 μ m during quenching, with carbide in the common high quality steel relatively, can be described as superfine carbide.This class steel appropriate C r/ (W+Mo) than the time, secondary hardening will make tempered-hardness be increased to 61-64HRC when 500 ℃ of-560 ℃ of tempering.

The high alloy tool steel DM6S-2 of superfine carbide is to use our alloy design method of research and development to design.This method synthesis used bound energy on balance each other calculation of thermodynamics and carbide phase transformation law, the electronics/atom level calculating, thermal treatment process and quenching and tempered-hardness Calculation Method, the intensity and the toughness of new steel grade have been made prediction.The starting point of its design is to obtain the superfine carbide high-carbon high-alloy steel, makes the tool and mould of its manufacturing that high rigidity, high-wearing feature and high cutting edge sharpness can be arranged by adopting rational heat treatment technology.

Summary of the invention

Proposition of the present invention aims to provide a kind of series superfine carbide high-carbon high-alloy DM6S-2 steel.Its principle of design is (1) reasonably C, Cr, W, Mo, V content assurance carbide refinement, guarantees high rigidity carbide quantity, and minor N i guarantees that the bonding force of yield strength and toughness, raising matrix and carbide also reduces the surface decarburization tendency; (2) rational Cr/ (W+Mo) ratio utilizes the secondary hardening of high tempering to make it to obtain high tempered-hardness; (3) high yield strength and impact toughness index.

Technical solution of the present invention is achieved in that

A kind of high alloy tool steel of series superfine carbide is characterized in that containing (weight %) C 0.67～0.75, Si 0.4～0.55, Mn 0.25～0.5, Cr 6.5～7.5, W 3.0～3.8, Mo 1.3～1.6, V 1.0～1.4, Ni 0.15～0.6, S≤0.015, P≤0.02, Fe surplus; The preparation method of this alloy tool steel comprise adopt induction furnace or induction furnace+electroslag furnace remelting and 870 ℃～1150 ℃ forging rollings after, anneal again, quenching, deepfreeze and temper step, its processing condition are:

(1) annealing is heated 840 ℃～860 ℃, and is cold with stove after 2～4 hours;

(2) quench, heat 1060 ℃～1100 ℃, water-cooled or oil cooling after the insulation 1.5min/mm;

(3) deepfreeze, the back deep cooling of quenching is to-80 ℃～-120 ℃, and cold insulation 0.5～1 hour slowly is warming up to room temperature;

(4) tempering, 520 ℃～560 ℃ constant temperature 2～4 hours.

Compared with prior art, the invention has the advantages that by rational Alloying Design, make the polymorphic type carbide in its solid solution and precipitation hardening process, realize super-refinement, promptly can make the even refinement of carbide by annealing, mean sizes is less than 0.8 μ m, and one time massive carbide is less than 5%; Make the even refinement of undissolved carbide by quenching, mean sizes is less than 0.5 μ m, and martensitic needles length is less than 6 μ m, residual austenite 15～25%; Promote residual austenite to decompose the refinement carbide by deepfreeze; By the even refinement of carbide that tempering is separated out tempered martensite, remaining Austriaization body drops to below 15%.

Description of drawings

The present invention has accompanying drawing 7 width of cloth, wherein:

Fig. 1 is that composition is the carbide phase equilibrium diagram of lower limit;

Fig. 2 is the carbide phase equilibrium diagram of prescribing a time limit during composition is;

Fig. 3 is the carbide phase equilibrium diagram of prescribing a time limit on composition is;

Fig. 4 is the quenching hardness graphic representation;

Fig. 5 is the tempered-hardness graphic representation;

Fig. 6 is an annealing micro-organization chart;

Fig. 7 is a quenching micro-organization chart.

Embodiment

High alloy tool steel as a kind of series superfine carbide of Fig. 1～shown in Figure 7.

Its component content such as table 1:

The composition of table 1 steel (wt%)

C	Si	Mn	Cr	w	Mo	v	Ni	S	P	Fe
											0.67-0.75	0.4-0.55	0.25-0.5	6.5-7.5	3.0-3.8	1.3-1.6	1.0-1.4	0.15-0.6	≤0.015	≤0.02	Surplus

Thermal treatment process such as table 2:

Table 2 thermal treatment process

Operation	Technological process and explanation	Hardness	Tissue and note
				Annealing	840 ℃-860 ℃ heating are cold with stove after 2-4 hour, and higher annealing temperature is corresponding with interalloy, can obtain good spherodized structure.	HB227-235	The even refinement of carbide, mean sizes are less than 0.8um, and one time massive carbide is less than 5%.
Quench	Water-cooled or oil cooling after 1060 ℃-1100 ℃ heating 1.5min/mm, medium quenching temperature can obtain good quenching structure with reasonably Cr/ (W+Mo) ratio is corresponding.	HRC62-64	The even refinement of undissolved carbide, mean sizes be less than 0.5um, and martensitic needles length is less than 6um, residual austenite 15-25%
				Deepfreeze	Quench the back deep cooling to-80 ℃--120 ℃, cold insulation 0.5-1 hour, slowly be warming up to room temperature.Promote that residual austenite is decomposed, the refinement carbide.	HRC63-65	This technology requires to adopt or do not adopt according to working conditions.
Tempering	520 ℃-560 ℃ constant temperature 2-4 hour, adopt higher relatively tempering temperature, fully tempering reduces residual austenite, improves toughness, utilizes secondary hardening to obtain high rigidity.	HRC61-63; HRC62-64 (adding deepfreeze)	Tempered martensite, the even refinement of carbide, residual austenite is less than 15%

Mechanical property such as table 3:

Table 3 mechanical property

	Tempering temperature/℃	Hardness/HRC	Bending strength σ bb/MPa	Yield strength σ bs/MPa	σ bs/σ bb	Amount of deflection/mm	Impact toughness a K/J/cm 2
								Q-tempering	540	61-63	4100	3420	0.83	4.1	86
Quenching deepfreeze tempering	540	62-64	4180	3510	0.84	4.7	89

The manufacturing process route of mould and cutlery is:

Forging rolling → annealing → alignment → corase grind → quenching → alignment → (deepfreeze) → tempering → alignment → mill processing → finished product.

The design of the composition of this steel grade is carried out according to Fig. 1,2,3 carbide phase equilibrium diagram respectively, and matrix composition and Hardness Design the results are shown in the table 4,5,6.In conjunction with these charts, can do a simple and clear analysis to the effect of alloying element and influence, carbon content is higher than in limited time, microstructure coarsening, it is low to be lower than prescribe a time limit down hardness and wear resistance; Silicon content is higher than in limited time, and surface decarburization increases the weight of and fragility is increased, and being lower than down in limited time, yield strength descends; Manganese content is higher than in limited time, and fragility increases, and being lower than down in limited time, yield strength descends; Chrome content is higher than in limited time, and the carbide degree of irregularity increases the weight of and remained austenite content is increased, and being lower than down in limited time, quenching hardness reduces; Tungstenic and molybdenum amount are higher than in limited time, and the carbide degree of irregularity increases the weight of and big block primary carbide quantity increases, and are lower than down that the carbide quantity of tungsten and molybdenum is few in limited time, and refinement and reduce wear resistance is unfavorable for annealing; Vanadiumcontent is higher than in limited time, is easy to produce a large amount of block primary carbides, and the carbide quantity that is lower than the vanadium of prescribing a time limit down is few, is unfavorable for refinement and reduces wear resistance; Nickel content is higher than in limited time, and the ability of raising yield strength weakens and makes annealing nodularization difficulty, and being lower than down in limited time, yield strength reduces.

Be that it is the temperature range of M23C6 → M6C that annealing temperature is chosen in the carbide transformation, is higher or lower than this temperature range and can not obtains thinning microstructure to heat treated evaluation; Quenching temperature is higher than the upper limit, and remained austenite content is too much and tempered-hardness is reduced; Be lower than lower limit and quench, the secondary hardening effect descends when 500 ℃ of-540 ℃ of tempering, and tempered-hardness is reduced; Tempering temperature is higher than upper limit hardness and descends, and it is too much to be lower than the lower limit remained austenite content; Carrying out deepfreeze as required is to obtain more high performance favourable measure.

Table 4 composition lower limit differing temps lower substrate interalloy content (wt%) and hardness calculation value (HRC)

Temperature/℃	C	Cr	w	Mn	Mo	v	Si	Ni	Quenching hardness	Tempered-hardness
											1060	0.52	6.52	2.25	0.26	1.06	0.47	0.40	0.15	63.0	63.2
1080	0.54	6.51	2.49	0.25	1.14	0.53	0.40	0.15	63.7	63.7
											1100	0.56	6.45	2.75	0.25	1.21	0.60	0.40	0.15	64.4	64.2

Limit differing temps lower substrate interalloy content (wt%) and hardness calculation value (HRC) in table 5 composition

Temperature/℃	C	Cr	w	Mn	Mo	v	Si	Ni	Quenching hardness	Tempered-hardness
											1060	0.49	7.04	2.19	0.39	1.07	0.47	0.48	0.36	62.6	62.2
1080	0.51	7.03	2.42	0.39	1.15	0.54	0.48	0.36	63.2	62.6
											1100	0.54	7.02	2.66	0.38	1.22	0.61	0.48	0.36	64.1	63.3

Table 6 composition upper limit differing temps lower substrate interalloy content (wt%) and hardness calculation value (HRC)

Temperature/℃	C	Cr	w	Mn	Mo	v	Si	Ni	Quenching hardness	Tempered-hardness
											1060	0.47	7.57	2.13	0.53	1.08	0.48	0.56	0.63	62.3	61.1
1080	0.50	7.56	2.35	0.52	1.16	0.54	0.56	0.62	63.0	61.7
											1100	0.52	7.55	2.59	0.52	1.23	0.61	0.56	0.62	63.8	62.3

Influence for quenching hardness and tempered-hardness is:

(1) 1060 ℃-1100 ℃ reach maximum hardness 63HRC; Temperature further raises, and remained austenite content increases, and quenching hardness descends.

(2) separate out M2C and the MC type carbide that small and dispersed distributes during 520-560 ℃ of tempering and produce the secondary hardening effect, maximum hardness is near 64HRC.

(3) microstructure is shown in Fig. 6 and Fig. 7.Fig. 6 shows at 840 ℃ of annealing carbide more tiny, and particle mean size is 0.5 μ m, and indivedual bulk carbide are 1.0-1.5 μ m.Fig. 7 shows that 1100 ℃ of quenching carbide particle mean sizess be 0.23 μ m, and the big block MC carbide of minute quantity is 0.6-0.8 μ m.The invention will be further described below in conjunction with embodiment.

Make timber slicing cutter with steel grade of the present invention, its chemical ingredients and thermal treatment process are shown in table 7 and the table 8 respectively.

Table 7 composition

	C	Si	Mn	Cr	W	Mo	V	Ni	S	P
											Embodiment
1	0.70	0.50	0.45	6.68	3.34	1.30	1.19	0.29	0.013	0.016
											Embodiment 2	0.72	0.45	0.35	6.65	3.24	1.45	1.30	0.24	0.015	0.018
Embodiment 3	0.75	0.47	0.50	7.26	3.12	1.52	1.29	0.22	0.012	0.014

Table 8 thermal treatment process and application

	Annealing	Quench	Deepfreeze	Tempering	Timber slicing cutter is used
						Embodiment 1	840 ℃ of 4 hours stoves are cold	1060 ℃ of shrends		520 ℃ 4 hours, HRC62	2.1 ten thousand/sharpening 1 time
Embodiment 2	840 ℃ of 4 hours stoves are cold	1080 ℃ of shrends	-80 ℃ 4 hours	540 ℃ 4 hours, HRC63	2.4 ten thousand/sharpening 1 time
						Embodiment 3	850 ℃ of 4 hours stoves are cold	1100 ℃ of shrends	-119 ℃ 4 hours	540 ℃ 4 hours, HRC64	2.8 ten thousand/sharpening 1 time

Claims (1)

1, a kind of high alloy tool steel of series superfine carbide is characterized in that containing (weight %) C0.67～0.75, Si 0.4～0.55, Mn 0.25～0.5, Cr 6.5～7.5, W 3.0～3.8, Mo 1.3～1.6, V 1.0～1.4, Ni 0.15～0.6, S≤0.015, P≤0.02, Fe surplus; This alloy tool steel preparation method comprise adopt induction furnace or induction furnace+electroslag furnace remelting and 870 ℃～1150 ℃ forging rollings after, anneal again, quenching, deepfreeze and temper step, its processing condition are:

(1) annealing is heated 840 ℃～860 ℃, and is cold with stove after 2～4 hours;

(2) quench, heat 1060 ℃～1100 ℃, water-cooled or oil cooling after the insulation 1.5min/mm;

(3) deepfreeze, the back deep cooling of quenching is to-80 ℃～-120 ℃, and cold insulation 0.5～1 hour slowly is warming up to room temperature;

(4) tempering, 520 ℃～560 ℃, constant temperature 2～4 hours.

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