CN100494461C - Alloy tool steel in multi-type super-fine carbonates - Google Patents

Abstract

This invention relates to alloying and heat treatment craft of tool die steel, it belongs to one kind of DM8B-2 multi-types superfine carbide high carbon alloy tool steel. Using alloy design method which voluntarily developing, do the phase equilibrium thermo dynamics, electronic/atom level binding energy computation,quenching and the tempered hardness computation as well as to synthesis appraisal its toughness and sintensity. Its ingredient characteristic is appropriate C quantity and Cr/ (W+Mo) ratio, reasonable Si, Mn as well as few Ni; Its microstructure characteristic has the superfine carbide, annealing carbide size is between 0.05-0.8mum, when quenching, the undissolved carbide size should not to be smaller than 0.5mum. after quenching to add 200degree C-300degree C, tempering may enable the tempering hardness to achieve 61-64HRC by using carbide precipitation hardening. It has high yield strength and the impact toughness.In the thin edge cutting tool, cutting die and weightily attacking die areas, it has widespread application prospect.

Description

Series superfine carbide interalloy tool steel

Technical field

The present invention relates to mould steel, relate in particular to the design and the thermal treatment process thereof of DM8B-2 type steel alloy.

Technical background

Carbide refinement improves important influence to the performance of mould steel.But when people attempted to improve wear resistance and increase alloy content and make it become the high-carbon Medium Alloy Steel, the refinement of carbide but became a difficult problem.At this moment, because the quenching remained austenite content is more much higher than high-carbon low-alloy steel, certainly will require higher tempering temperature to cause hardness to descend on the contrary.Therefore, mould steel always lacks high-carbon Medium Alloy Steel kind both at home and abroad.Development along with processing industry, when requirement such as thin edged knife tool, shearing die and heavy Impact mould had than longer work-ing life of high-carbon low-alloy steel tool and mould and better processing quality, the new steel grade of the interalloy tool steel of the superfine carbide of a kind of DM8B-2 by name had just arisen at the historic moment.Studies show that multicomponent alloy high carbon steel composition designs when suitable, having the polymorphic type carbide in the steel is M ₃C, M ₂₃C ₆, M ₇C ₃, M ₆C and MC, because of its crystalline structure difference, under differing temps all kinds of carbide forming cores, growth and in austenite the dissolved thermodynamics and kinetics widely different, under processing of the forging rolling of routine and thermal treatment process condition, just can obtain the carbide of very refinement.The annealing carbide size of this class steel is between 0.05～0.8 μ m, and quenching undissolved carbide size is less than 0.5 μ m, with carbide in the common high-carbon alloy steel relatively, can be rated as superfine carbide.This class steel is when lower quenching temperature, because of M ₃C and M ₂₃C ₆A large amount of dissolvings, the carbon when having guaranteed to hang down quenching temperature in the austenite and the solid solubility of alloy are so can obtain higher quenching hardness; All kinds of carbide precipitation accumulative temperature range differences in the drawing process, temper resistance is improved, and increase with the alloy of solid solution in the original austenite and carbon amount and to raise, appropriate C r/ (W+Mo) than the time, when 200 ℃ of-300 ℃ of tempering, can make tempered-hardness reach 61-64HRC because of carbide precipitation sclerosis.

Series superfine carbide interalloy tool steel DM8B-2 is to use our alloy design method of research and development to design.This method synthesis has used calculating, thermal treatment process and the quenching of bound energy on balance each other calculation of thermodynamics and carbide phase transformation law, electronics, the atom level and tempered-hardness to calculate and its intensity and toughness are predicted, the starting point of its design obtains a kind of superfine carbide high-carbon Medium Alloy Steel exactly, 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

The purpose of this invention is to provide a kind of series superfine carbide alloy DM8B-2 steel.The principle of design of new steel grade is:

(1) reasonably C, Cr, W, Mo, V content guarantee carbide refinement, guarantee high rigidity carbide quantity; Suitable Si, Mn and minor N i guarantee high-yield strength and toughness, and reduce the surface decarburization tendency, and the bonding force that improves matrix and carbide; (2) rational Cr/ (W+Mo) ratio obtains the high rigidity under relatively low quenching temperature and the relative higher tempering temperature; (3) high yield strength and impact toughness index.

Technical solution of the present invention is achieved in that

A kind of series superfine carbide interalloy tool steel is characterized in that containing weight %C 0.76～0.85, Si 0.45～0.6, Mn 0.25～0.45, Cr 1.7～2.1, W 1.7～1.95, Mo 0.9～1.05, V 0.3～0.4, Ni 0.25～0.6, S≤0.015, P≤0.02, Fe surplus.

The method that described series superfine carbide interalloy tool steel is heat-treated comprises that employing induction furnace+esr carries out melting and at 870 ℃～1150 ℃ forging rollings, it is characterized in that also comprising following processing step:

(1) annealing, 820 ℃～840 ℃ heating 2～4h, stove is cold subsequently;

(2) quench, 850 ℃～890 ℃ rate of heating 2min/mm, water-cooled or oil are cool afterwards;

(3) deepfreeze, the back deep cooling that quenches are to-80 ℃～-120 ℃, and cold insulation 0.5～1h also slowly rises to room temperature;

(4) tempering, 200 ℃～300 ℃, constant temperature 2～4h.

Compared with prior art, the invention has the advantages that by rational Alloying Design, make the polymorphic type carbide realize super-refinement in its solid solution and precipitation hardening process, promptly make the even refinement of carbide by annealing, mean sizes is less than 0.8 μ m; Make the even refinement of undissolved carbide by quenching, mean sizes is less than 0.6 μ m, martensitic needles can be less than 6 μ m, after by deepfreeze and tempering, make the even refinement of tempered martensite, residual austenite is less than 12%, thereby makes mould and the cutlery made by this steel grade have high rigidity, high-wearing feature and high sharpness.

Description of drawings

Drawings attached 7 width of cloth of the present invention, wherein:

Fig. 1 is the carbide phase equilibrium diagram of prescribing a time limit on alloy content of the present invention is.

Fig. 2 is the carbide phase equilibrium diagram of prescribing a time limit during alloy content of the present invention is.

Fig. 3 is the carbide phase equilibrium diagram of alloy content of the present invention for prescribing a time limit down.

Fig. 4 is Si, the graph of a relation that Ni content can influence interatomic bond.

Fig. 5 is the graph of a relation of tempering temperature to the hardness influence.

Metallographic structure figure when Fig. 6 is 830 ℃ of annealing.

Fig. 7 is metallographic structure figure after 890 ℃ of quenchings.

Embodiment

As Fig. 1～a kind of series superfine carbide interalloy tool steel shown in Figure 3.Its composition and content such as table 1, thermal treatment process such as table 2, mechanical property is as shown in table 3.The manufacturing process route of mould and cutlery is: forging rolling → annealing → alignment → corase grind → quenching → alignment → (deepfreeze) → tempering → alignment → mill processing → finished product.

Table 1 composition weight %

C	Si	Mn	Cr	W	Mo	V	Ni	S	P	Fe
											0.76- 0.85	0.45- 0.6	0.25- 0.45	1.7-2. 1	1.7-1. 95	0.9-1. 05	0.3-0. 4	0.25-0. 6	≤0.015	≤0.02	Surplus

Table 2 thermal treatment process

Operation	Technological process and explanation	Hardness	Tissue and note
				Annealing	820 ℃-840 ℃ heating are cold with stove after 2-4 hour, and higher annealing temperature is corresponding with interalloy, can obtain good spherodized structure.	HB207-235	The even refinement of carbide, mean sizes is less than 0.8 μ m.
Quench	Water-cooled or oil cooling after 850 ℃-890 ℃ heating 2min/mm, medium quenching temperature can obtain good quenching structure with reasonably Cr/ (W+Mo) ratio is corresponding.	HRC63-66	The even refinement of undissolved carbide, mean sizes are less than 0.6 μ m, and martensitic needles length is less than 6 μ m, residual austenite 12-20%
				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.	HRC64-67	This technology adopts or does not adopt according to using.
Tempering	200 ℃-300 ℃ constant temperature 2-4 hour, adopt higher relatively tempering temperature, fully tempering reduces residual austenite, improves toughness, utilizes the low temperature secondary hardening to obtain high rigidity.	HRC60-63; HRC63-65 (adding deepfreeze)	Tempered martensite, the even refinement of carbide, residual austenite is less than 12%

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 κ/J/cm 2
								Q-tempering	200	61-63	3950	3400	0.86	4.7	88
Quenching deepfreeze tempering	240	62-64	4100	3510	0.86	5.1	91

The composition design of this steel grade is carried out according to the phase equilibrium diagram of Fig. 1, Fig. 2 and Fig. 3.The calculated value of its matrix composition and hardness is shown in the table 4,5,6.

During table 4 C is, the matrix composition and the hardness calculation value of different quenching in limited time on the alloy

Quench/℃	C	Cr	W	Mo	V	Si	Ni	Mn	Quenching hardness	Tempered-hardness
											840	0.63	1.68	0.52	0.39	0.02	0.50	0.37	0.39	64.4	200℃/61.5
860	0.66	1.78	0.60	0.44	0.03	0.50	0.37	0.39	65.1	240℃/62.5
											880	0.67	1.79	0.70	0.50	0.04	0.50	0.37	0.39	65.3	240℃/62.7

Table 5 C and alloy are down the matrix composition and the hardness calculation value of different quenching in limited time

Quench/℃	C	Cr	W	Mo	V	Si	Ni	Mn	Quenching hardness	Tempered-hardness
											840	0.65	1.60	0.55	0.39	0.02	0.40	0.31	0.36	64.7	200℃/61.4
860	0.66	1.64	0.63	0.44	0.03	0.40	0.31	0.36	65.1	200℃/62
											880	0.67	1.64	0.73	0.50	0.04	0.40	0.31	0.36	65.2	220℃/62.2

Table 6 C and V are the upper limit, other be in limited time the matrix composition and the hardness calculation value of different quenching

Quench/℃	C	Cr	W	Mo	V	Si	Ni	Mn	Quenching hardness	Tempered-hardness
											840	0.65	1.59	0.54	0.38	0.02	0.46	0.34	0.39	64.9	200℃/62
860	0.70	1.73	0.62	0.43	0.03	0.45	0.34	0.39	65.8	220℃/62.5
											880	0.71	1.74	0.72	0.49	0.04	0.45	0.34	0.39	66	220℃/63

Alloying element Ni to interatomic bond can influence and tempering temperature to the influence of changes in hardness, then be shown in the Figure 4 and 5 respectively.In conjunction with these charts, can do a simple and clear analysis with influence to the effect of alloying element.Carbon content is higher than the upper limit, and microstructure coarsening is lower than lower limit, and hardness and wear resistance are low; Silicon content is higher than the upper limit, and surface decarburization increases the weight of and fragility is increased, and is lower than the lower limit yield strength and descends; Manganese content is higher than the upper limit, and fragility increases, and is lower than the lower limit yield strength and descends; Chrome content is higher than the upper limit, and the carbide degree of irregularity increases the weight of and remained austenite content is increased, and is lower than lower limit low-temperature sludge hardening effect and weakens; Tungstenic and molybdenum amount are higher than the upper limit, and the carbide degree of irregularity increases the weight of and big block primary carbide occurs, and the carbide quantity that is lower than lower limit tungsten and molybdenum is few, and refinement and reduce wear resistance is unfavorable for annealing; Vanadiumcontent is higher than the upper limit, is easy to produce block primary carbide, is lower than lower limit, and the carbide quantity of vanadium is few, is unfavorable for refinement and reduces wear resistance; Nickel content is higher than the upper limit, and the ability of raising yield strength weakens and makes annealing nodularization difficulty, is lower than the lower limit yield strength and reduces.

To heat treated evaluation be, should make annealing temperature be chosen in carbide M23C6 and M6C transition temperature interval, be higher or lower than this temperature range, can not obtain thinning microstructure; Quenching temperature is higher than the upper limit, and remained austenite content is too much and make microstructure coarsening, is lower than lower limit, and quenching precipitation hardening effect when 200 ℃ of-300 ℃ of tempering acutely descends, and 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.

Si and Ni show that to martensite bound energy influence curve the content of Si or Ni was at 0.2%～0.6% o'clock, and Ni content is higher than Si to interatomic bound energy influence.The content of Si or Ni is elevated at 0.8% o'clock by 0.6%, is converted to Si content interatomic bound energy influence is higher than Ni.

The tempered-hardness curve then shows, can obtain higher tempered-hardness HRC61-64 200 ℃ of-240 ℃ of tempering owing to precipitation hardening when quenching temperature is higher than 850 ℃.Microstructure picture is shown in Fig. 6 and Fig. 7, and Fig. 6 is that 830 ℃ of annealing carbide are of a size of 0.4-0.6 μ m; Metallographic structure figure when Fig. 7 is 890 ℃ of quenchings, long≤5 μ m of martensitic needles; Carbide mean sizes≤0.5 μ m.

The invention will be further described below in conjunction with embodiment.

Make the timber rotary cutter with DM8-2 steel grade of the present invention, the composition of steel is shown in table 7, and thermal treatment process and application are shown in table 8.

Table 7 composition weight %

	C	Si	Mn	Cr	W	Mo	V	Ni	S	P
											Embodiment
1	0.79	0.53	0.40	1.76	1.83	0.98	0.35	0.34	0.013	0.018
											Embodiment 2	0.80	0.53	0.31	1.96	1.88	0.96	0.38	0.33	0.011	0.015
Embodiment 3	0.84	0.52	0.28	2.02	1.81	1.01	0.32	0.42	0.009	0.011

Table 8 thermal treatment process and application

	Annealing	Quench	Deepfreeze	Tempering	Timber rotary-cut cutter is used
						Embodiment 1	820 ℃ of 4 hours stoves are cold	850 ℃ of shrends		200 ℃ 4 hours, HRC61	12 hours/sharpening 1 time
Embodiment 2	830 ℃ of 4 hours stoves are cold	870 ℃ of shrends	-80 ℃ 4 hours	200 ℃ 4 hours, HRC63	14 hours/sharpening 1 time
						Embodiment 3	840 ℃ of 4 hours stoves are cold	880 ℃ of shrends	-119 ℃ 4 hours	240 ℃ 4 hours, HRC64	16 hours/sharpening 1 time

Claims (2)

1, a kind of series superfine carbide interalloy tool steel is characterized in that containing weight %C0.76～0.85, Si 0.45～0.6, Mn 0.25～0.45, Cr 1.7～2.1, W 1.7～1.95, Mo 0.9～1.05, V 0.3～0.4, Ni 0.25～0.6, S≤0.015, P≤0.02, Fe surplus.

2, a kind of method that the described series superfine carbide interalloy of claim 1 tool steel is heat-treated comprises that employing induction furnace+esr carries out melting and at 870 ℃～1150 ℃ forging rollings, it is characterized in that also comprising following processing step:

(1) annealing, 820 ℃～840 ℃ heating 2～4h, stove is cold subsequently;

(2) quench, 850 ℃～890 ℃ rate of heating 2min/mm, water-cooled or oil are cool afterwards;

(3) deepfreeze, the back deep cooling that quenches are to-80 ℃～-120 ℃, and cold insulation 0.5～1h also slowly rises to room temperature;

(4) tempering, 200 ℃～300 ℃, constant temperature 2～4h.

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