CN103703150B

CN103703150B - The method of hot working tool steel and manufacture hot working tool steel

Info

Publication number: CN103703150B
Application number: CN201280021117.7A
Authority: CN
Inventors: J.安德森; H.杰斯珀森; H-O.安德伦; L-E.斯文森
Original assignee: Uddeholms AB
Current assignee: Uddeholms AB
Priority date: 2011-03-04
Filing date: 2012-03-01
Publication date: 2015-12-23
Anticipated expiration: 2032-03-01
Also published as: KR20150047636A; SE536596C2; US20140056749A1; CA2828962A1; SE1150200A1; BR112013022606A2; TWI535863B; EP2681340B1; DK2681340T3; EP2681340A1; CA2828962C; SI2681340T1; PT2681340E; KR20140015445A; KR102012950B1; RU2013142584A; JP2014512456A; TW201303043A; ES2540905T3; WO2012119925A1

Abstract

A kind of low chromium hot working tool steel, it consists of (in % by weight): C0.08 ~ 0.40, N0.015 ~ 0.30, C+N0.30 ~ 0.50, Cr1 ~ 4, Mo1.5 ~ 3, V0.8 ~ 1.3, Mn0.5 ~ 2, Si0.1 ~ 0.5, optionally, Ni < 3, Co≤5, B < 0.01, the outer surplus of the removal of impurity is Fe; There is with a kind of manufacture the method for the low chromium hot work tools steel work of the tempering resistance of enhancing.

Description

The method of hot working tool steel and manufacture hot working tool steel

Technical field

The present invention relates to a kind of low chromium hot working tool steel and manufacture the method for low chromium hot work tools steel work.

Background technology

Term " hot work tools " is applied to many different types of instruments for intermetallic composite coating or shaping at relatively high temperature, such as the instrument of die casting, as pressing mold (dies), inset and core (insertsandcores), inlet part, nozzle, knockout element (ejectorelements), piston, pressurizing chamber etc.; For the instrument of extrusion processing, as pressing mold, die holder, lining (liners), pressure-bearing pad and bar (pressurepadsandstems), axle (spindles) etc.; For the instrument of hot pressing, as the instrument for aluminium, magnesium, copper, copper alloy and steel hot pressing; For the model of plastics, as the model for injection molding, compression molding method and extrinsion pressing; And the instrument of other kind various, as the anti-wear component used in high temperature process for the instrument of hot shearing, shrink-ring/axle collar (shrink-rings/collars) and being intended to.Low-alloy hot working tool steel in following application for the instrument of small-medium size, very high to the requirement of tempering resistance and thermal fatigue in this application.Tempering resistance refers to that hot working tool steel at high temperature keeps the ability of its hardness for a long time.Hot working tool steel is developed in the intensity be exposed to for a long time under high temperature and hardness, and usually uses the alloy that a large amount of carbide is formed.

The tool steel of another kind of type is rapid steel, its for up to or temperature more than 760 DEG C under still must keep in the cutting tool of intensity and hardness.In order to reduce required tungsten and the consumption of chromium, such as, being respectively 18 % by weight and 4 % by weight, developing the mutation of use 5 ~ 10 % by weight molybdenum.Rapid steel is had any different with hot-work steel on composition and price, and rapid steel can not be used as the surrogate of hot-work steel.

Summary of the invention

An object of the present invention is to provide the low chromium hot working tool steel with enhanced property overview (profile), the tempering resistance particularly improved.Steel in the present invention is particularly suitable for small tool, and it does not need the steel composition with high-hardenability (hardenability) to manufacture for it.

This object is realized by the low chromium hot working tool steel providing claim 1 to limit, and namely this steel is made up of (in % by weight) following component:

Optionally

Ni＜3

Co≤5

B＜0.01

The outer surplus of the removal of impurity is Fe.

Other object can be realized by low chromium hot working tool steel of the present invention, and it meets one or more (in % by weight) in following condition:

The preferred implementation of low chromium hot working tool steel can meet one or more (in % by weight) in following condition:

The preferred embodiment of low chromium hot working tool steel can meet one or more (in % by weight) in following condition:

N0.042 ~ 0.15 preferably 0.045 ~ 0.12

C+N0.39～0.41

Cr1.3 ~ 2.3 preferably 1.4 ~ 2.1

The even preferred embodiment of low chromium hot working tool steel can meet one or more (in % by weight) in following condition:

According to design of the present invention, low chromium hot working tool steel can have the composition (in % by weight) according to following examples:

Optionally

The outer surplus of the removal of impurity is Fe, or

Optionally

The outer surplus of the removal of impurity is Fe, or

Optionally

B0.001～0.01

Mo/V1.8～2.3

Cr/V＜2

The outer surplus of the removal of impurity is Fe, or

Optionally

B0.001～0.01

Mo/V1.8～2.3

Cr/V＜2

The outer surplus of the removal of impurity is Fe, or

Optionally

B0.001～0.005

Mo/V1.8～2.3

Cr/V＜2

The outer surplus of the removal of impurity is Fe.

Another object of the present invention is to provide a kind of goods with the low chromium hot working tool steel of enhanced property overview, the tempering resistance particularly improved.

According to the present invention, above-mentioned purpose is passed through method as claimed in claim 11 and is realized, i.e. a kind of method comprised the following steps:

A) provide as any one of claim the low chromium hot working tool steel that limits;

B) steel work is formed by described steel compositions;

C) being up at the temperature of 1200 DEG C, by step b) the described steel work that obtains carries out austenitizing process and is about half an hour, quench subsequently; And

D) at the temperature of 500 ~ 700 DEG C, by the steel work tempering at least twice through quenching, about 2 hours at every turn.

The method is listed preferred embodiment in dependent claims 12 ~ 15.

Have high chromium content that is 9 ~ 12 % by weight creep resistant steel in, at relatively low temperature that is 1020 ~ 1050 DEG C, vanadium carbide nitride (vanadiumcarbide-nitride) may dissolve.But if the content of chromium low (being less than about 4 ~ 5 % by weight), nascent (primary) vanadium carbide nitride will generate in melts, and in fact they can not dissolve later.

In steel of the present invention, the total amount of carbon and nitrogen should be adjusted to 0.30≤(C+N)≤0.50, preferably 0.36≤(C+N)≤0.44.The content of nominal should about 0.40 % by weight.Meanwhile, advantageously regulate the N of nitrogen content to 0.015 ~ 0.30, the preferably N of 0.015 ~ 0.15, and even more preferably 0.015 ~ 0.10, and can preferably regulate carbon to be at least 0.20 % by weight.Preferred scope is listed in claim to a product.

When by nitrogen content balance to about 0.05 ~ 0.10 % by weight time, can Formed vanadium nitride, it can be partly dissolved and then separate out with nano-sized particles form in tempering step process in austenitizing step process.The thermostability of vanadium carbide nitride is better than vanadium carbide, and therefore, the tempering resistance of low chromium hot work tools steel work can significantly be improved.In addition, by least double tempering process, tempering curve (display hardness is as the function of tempering temperature) can have two higher minor peaks.

In most preferred embodiment of the present invention, nitrogen content is preferably about 0.05 % by weight.The numerical value that above-mentioned numeric ratio is larger produces better properties.At quenching, the nitrogen content of about 0.05 % by weight has higher secondary hardening potential than higher nitrogen content, therefore makes steel have higher hardness.But about 0.10 % by weight nitrogen content has demonstrated its secondary hardening peak value and has been transferred to favourable tempering temperature higher a little.Preferred scope is listed in claim to a product.In addition, the test carried out and model calculate and show, improve requirement of nitrogen and improve austenitizing temperature.

Chromium promotes hardening capacity and the solidity to corrosion of steel.Too low content can have a negative impact to solidity to corrosion.Therefore, the minimum value of chromium content in steel is set as 1 % by weight.Maximum level is set as 4 % by weight is such as, in order to avoid undesirably generating rich chromium carbide/carbonitride, M ₂₃c ₆.Chromium content preferably more than 3 % by weight, and even more preferably no more than 2.6 % by weight.In an embodiment of the invention, chromium content is 1.5 ~ 1.7 % by weight.Preferred scope is listed in claim to a product.Low chromium content postpones the precipitation of chromium carbide in microstructure, and is conducive to more heat-staple rich chromium carbonitride.Therefore, the recovery of material is slowed down, and tempering resistance is improved.

In order to provide enough precipitation potential and obtain enough tempering resistances and the high temperature strength properties of expectation thus, the vanadium that content is at least 0.8 % by weight in steel, should be comprised.Separate out in order to avoid forming too much M (C, N), it leaves the risk of carbon and nitrogen in the risk of the insoluble precipitate of bulk and lossy matrix in the base after increasing thermal treatment, the upper limit of vanadium is 1.3 % by weight.Content of vanadium is preferably between 1.0 ~ 1.3 % by weight.Preferred scope is listed in claim to a product.

In order to obtain required MC phase, the ratio of Cr/V preferably should be less than 2, is more preferably less than 1.8.Reason is that can be considered to MC phase be harmful to chromium.

In steel, the content of silicon should in 0.1 ~ 0.5 % by weight, and preferably 0.2 ~ 0.4 % by weight.By keeping low silicone content, metastable M may be obtained ₃the initial precipitation of C carbide.These carbide using as the reservoir of carbon for the precipitation of M (C, N) particle needed for follow-up.Further, the rich chromium M not conforming to hope on crystal grain boundary and crystal lattice interface is avoided ₂₃c ₆the precipitation of particle.Preferred scope is listed in claim to a product.

The existence of manganese is to give steel enough hardening capacity, when the chromium of the relative low levels particularly in steel and molybdenum.Fe content in steel between 0.5 ~ 2 % by weight, preferably 1.0 ~ 2.0 % by weight.Preferred scope is listed in claim to a product.

In order to provide the secondary hardening in drawing process and increase hardening capacity, the molybdenum content existed in steel should between 1.5 ~ 3 % by weight, and preferably 2.2 ~ 2.8 % by weight.Preferred scope is listed in claim to a product.

Part molybdenum can replace tungsten in a kind of originally known mode, but preferably, described steel should not comprise the tungsten of any addition intentionally, and the content namely comprising tungsten should not exceed impurity level, this is because some shortcoming that the existence of W elements relates to.

In order to obtain precipitation order that proeutectoid carbide wishes and separate out potential, the ratio of Mo/V should preferably 1.8 ~ 2.3 scope, more preferably 1.9 ~ 2.1.It is known that Mo stablizes M ₂c phase, and by regulating the content of Mo and V to fall in the scope of 1.8 ~ 2.3, the M of rich molybdenum ₂c also can be formed, and compared with the MC phase of rich vanadium, this has higher coarsening rate mutually.

Nickel and cobalt are the elements that can be included in steel, and its content reaches 3 % by weight and 5 % by weight respectively.Cobalt can increase the hardness under high temperature, and it is conducive to some application of steel.If interpolation cobalt, significant quantity is about 4 % by weight.Nickel can increase the solidity to corrosion of steel, hardening capacity and toughness.Preferred scope is listed in claim to a product.

In principle, austenitizing can the temperature between softening annealing temperature 820 DEG C and maximum austenitizing temperature 1200 DEG C carry out, but the austenitizing of steel work preferably carries out at the temperature of about 1050 ~ 1150 DEG C, preferably at 1080 ~ 1150 DEG C, typically be 1100 DEG C.Close beta shows that higher austenitizing temperature makes tempered-hardness be offset to higher temperature, and namely secondary hardening peak value can be offset to higher temperature, and this represents the hardness that can reach hope under higher initial tempering temperature.Therefore, material can improved tempering resistance and can improve the processing temperature of instrument.

Through quenching steel work preferably at least carry out double tempering process, retention time is 2 hours, temperature between 500 ~ 700 DEG C, preferably 550 DEG C ~ 680 DEG C.In the most preferred embodiment of steel compositions, carry out at the temperature of tempering in 600 ~ 650 DEG C, preferably 625 ~ 650 DEG C.

By adding nitrogen with Regular casting methods to form melt, cast this melt to form ingot, and can obtain through the mode of this ingot of thermal treatment homogenizing the nitrogen content that scope is 0.05 ~ 0.10 % by weight.The interpolation of nitrogen can produce large nascent rich vanadium M (C, N) and separate out, and it can cause the hardness of material uneven on the contrary.But if nitrogen content reduces and had homogenizing thermal treatment before forging subsequently, so this nascent carbonitride greatly would not produce.

In the mutation of steel, the nitrogen content higher than preferred implementation is also conceivable.In this mutation, nitrogen can altogether up to 0.30 % by weight.In order to obtain higher nitrogen content, conventional castmethod is inadequate.Alternatively, nitrogen can be added by mode below, first the powdered steel being essentially required composition (except nitrogen) is manufactured, then by comprising the fluid such as nitrogen of nitrogen, the powder of this solid state of nitrogenize, then at inferior this powder of quiet hot pressing of pressure of the temperature of about 1150 DEG C and about 76Mpa to form ingot.By by powder metallurgic method fabrication tool steel, avoid the problem of the primary carbide generating bulk.

Preferably, ingot forges at about 1270 DEG C of temperature, and then softening annealing at the temperature of about 820 DEG C, subsequently with 10 DEG C of speed hourly be cooled to 650 DEG C temperature and then in atmosphere naturally cooling get ready to be austenitizing.

The tempering resistance that steel tool of the present invention is significantly improved, this makes it in hot-work application, have longer product life.As what pointed out above, nitrogen content has been preferably about 0.05 % by weight, and chromium content is preferably less than 3 % by weight, and namely 1.2 ~ 2.6 or 1.3 ~ 2.3.

Steel work of the present invention should also preferably meet following some that require:

-good tempering resistance,

-good hot strength,

-good thermal conductivity,

-not there is unacceptable large thermal expansivity.

Accompanying drawing explanation

Below with reference to preferred embodiment present invention is described in more detail with accompanying drawing.

Fig. 1 is that the hardness of exemplary nonnitrogenous low chromium hot working tool steel in display prior art is to tempering temperature schematic diagram.

Fig. 2 is under being presented at different tempering temperature, (content is in % by weight) Cr15, Mo1, C0.6 and Cr15 in prior art, the hardness schematic diagram of the steel of Mo1, C0.29, N0.35.

Fig. 3 illustrates the schematic diagram of low chromium content to M (C, N) stability influence in austenite.

Fig. 4 is display M ₆the molar fraction of C, M (C, N) and bcc matrix is as the schematic diagram of the function of temperature.(equilibrium phase: austenitic matrix)

Fig. 5 is display M (C, N) phase and metastable state M ₂the amount of C is as the schematic diagram of temperature function.(equilibrium phase: ferrite)

Fig. 6 be display tested alloys N0.05, N0.10 and N0.30 hardness to the schematic diagram of tempering temperature curve.

Fig. 7 is the back scattering SEM picture of undissolved little M (C, N) precipitate and spherical mixed oxide-sulfide grain in display N0.05.

Fig. 8 is the back scattering SEM picture of undissolved nascent M (C, N) on previous austenite crystal interface in display alloy N0.10.

Fig. 9 is the back scattering SEM picture of display primary particle in the N0.10 of softening annealing.

Figure 10 is undissolved M (C, N) equally distributed back scattering SEM picture in display N0.30.

Figure 11 is the back scattering SEM picture that some discovery in display N0.30 do not dissolve M (C, N) bunch.

Embodiment

Interalloy (mediumalloyed) hot working tool steel of molybdenum and vanadium has the resistance of good thermal fatigue, softening and high temperature creep.The nominal chemical composition that such prior art steel is exemplary is listed in table 1.

Table 1

C	Cr	Mo	V	Mn	Si	Fe
							0.38	2.6	2.3	0.9	0.75	0.3	92.8

The hot properties of someone steel in proposition table 1 is owing to the precipitation of nano-scale vanadium carbide in drawing process.These hard MC type carbide (2900HV) make this material secondary harden.Fig. 1 shows the tempering curve (hardness is to tempering temperature) of exemplary prior art tool steel.These samples are austenitizing at 1030 DEG C, and then from temper twice under the differing temps of 200 DEG C to 700 DEG C, tempering time is 2+2 hour.Can find out, in the interval of 500 ~ 650 DEG C, have a significant secondary hardening peak value at 550 DEG C.Research afterwards also shows there is metastable rich molybdenum M in prior art tool steel exemplary in drawing process at 625 DEG C ₂c significantly separates out, and it promotes secondary hardening effect.

Hot working tool steel at high temperature keeps ability and the tempering resistance thereof of its hardness for a long time, usually relevant with initial tempering temperature; If under material is held in the temperature significantly lower than initial tempering temperature, so it would not soften.Close to or higher than the maintenance temperature of initial tempering temperature under softening will be more significant.

If secondary hardening peak value can be offset to higher temperature, meaning can be reached required hardness (such as 44 ~ 46HRC) by this under higher initial tempering temperature.Therefore, the tempering resistance of material can improve, and the processing temperature of instrument can improve.

The research early stage to high chromium steel shows, when being added in steel by nitrogen, may realize higher hardness in drawing process.Sample Cr15, Mo1, C0.6 and Cr15, Mo1, C0.29, N0.35 solution treatment at 1050 DEG C, be cooled to liquid nitrogen through water quenching subsequently, and then by they tempering 2 hours at different temperatures.As found out in Fig. 2, when adding nitrogen, peak hardness becomes significantly higher.As nitrogenous steel, martensitic initial hardness is lower, but in drawing process, this steel reaches higher hardness than unazotized steel.

Explanation about this is that nitrogen makes chromium more uniformly distribute in the base, and this is because chromium is in austenite middle solvability increase mutually.After quenching, martensitic phase inherits from austenitic equally distributed chromium, and the chromium nitride creating very Fine distribution in drawing process is separated out, and therefore produces stronger hardening effect in material.

In addition, the carbon of employing nitrogen replacement part realizes the hardness that martensitic steel matrix reaches higher.Originally the interpolation of nitrogen causes more substantial retained austenite.But above-mentioned austenite can be converted into martensite by cold working subsequently, and the hardness up to 68HRC may be realized by this way.

Low chromium content seems to produce active effect to tempering resistance.The contrast with two kinds of different hot working tool steels of 1.5 % by weight and 5.0 % by weight chromium shows, lower chromium content is delayed the precipitation of chromium carbide in microstructure, is conducive to the better rich vanadium MC of thermostability.Therefore, the recovery of material is slowed down and tempering resistance improves.

But the research about the steel (comprising the N of 0.06 % by weight) of typical creep resistance 9 ~ 12 % by weight chromium shows that low chromium content significantly stabilizes MX (X is C+N) particle, sees Fig. 3.If austenitizing carries out at 1100 DEG C, so all M (C, N) particles can be dissolved in the steel comprising 10 % by weight chromium.If chromium content is down to 2.5 % by weight (the low chromium tool steels with reference to exemplary in Fig. 1), so a large amount of M (C, N) still can be present in austenite.Apparently, the result of low chromium content is in austenitizing treating processes, only have a small amount of separation material (interstitials) can dissolve in austenite.

According to the present invention, there is the low chromium hot working tool steel strengthening tempering resistance and pass through to implement procedure of processing manufacture below:

A) as defined in any one claim to a method, add nitrogen to low chromium hot working tool steel melt composition, and obtain steel compositions thus;

B) steel work is formed by described steel compositions;

C) at the temperature of the highest 1200 DEG C, by step b) the steel work austenitizing process that obtains is about half an hour, quenches subsequently; And

D) at the temperature between 500 ~ 700 DEG C, by the steel work tempering at least twice through quenching, about 2 hours at every turn.

Consider that routine is in the art understood, these results are surprising, and this is that the minimizing being chromium content due to general instruction can cause hardening capacity to reduce and be difficult to dissolve nascent M (C, N) particle.

In the creep resistant steel with high chromium content (namely 9 ~ 12 % by weight), at relatively low temperatures, namely 1020 ~ 1050 DEG C, may dissolved carbon vanadium nitride.But if chromium content is low, be less than about 4 ~ 5 % by weight, nascent vanadium carbide nitride can be formed in melts, and they can not dissolve in fact later.

Contriver has been found that vanadium carbide nitride can generate, and it can be partly dissolved and separate out with the particle of nano-scale in tempering step subsequently in austenitizing step when in low-chrome steel, nitrogen content balance is to about 0.015 ~ 0.30 % by weight.These particles are about 1 μm ~ about 10 μm.At some when, wherein nitrogen content is low, and usually 0.05 % by weight, the mean sizes of particle is less than 1 μm.The thermostability of vanadium carbide nitride is better than vanadium carbide, and therefore the tempering resistance of low chromium hot work tools steel work can significantly be improved.In addition, through at least double tempering, tempering curve (display hardness is as the function of tempering temperature) has two higher minor peaks.

In the preferred implementation of steel, nitrogen content is preferably about 0.05 % by weight.Above-mentioned value provides better properties than larger value.About 0.05 % by weight nitrogen content makes the secondary hardening in quenching process have larger potential than larger content.

In a preferred embodiment, chromium content is preferably 1.5 ~ 1.7 % by weight.Low chromium content is delayed the precipitation of chromium carbide in microstructure, is conducive to more heat-staple rich vanadium carbonitride.Therefore, the recovery of material is slowed down and tempering resistance is improved.

In principle, the temperature between softening annealing temperature 820 DEG C and maximum austenitizing temperature 1200 DEG C austenitizing can be implemented.In one preferred embodiment, namely have in the composition of about 0.05 % by weight nitrogen content and about 1.5 ~ 1.7 % by weight chromium content, the austenitizing of steel work, preferably the temperature of about 1050 ~ 1150 DEG C, preferably carries out at 1100 DEG C.Close beta shows that higher austenitizing temperature makes tempered-hardness be offset to higher temperature, and namely secondary hardening peak value can be offset to higher temperature, this means will reach required hardness under higher initial tempering temperature.Therefore, this material can improved tempering resistance, and the processing temperature of instrument can be improved.

Steel work through quenching is preferably the temperature of 500 ~ 700 DEG C, and preferably 550 DEG C ~ 680 DEG C, implement the tempering of at least twice, the hold-time is 2 hours.In the most preferred embodiment of steel compositions, the temperature of 600 ~ 650 DEG C, preferably 625 ~ 650 DEG C, carry out tempering.

By introduce nitrogen can obtain scope 0.05 ~ 0.10 % by weight nitrogen content, its by use Regular casting methods add nitrogen to generate melts, cast this melts to generate ingot, and pass through this ingot of thermal treatment homogenizing.Add nitrogen and can produce nascent rich vanadium M (C, the N) precipitation of bulk, it makes this material hardness uneven on the contrary.But if reduce nitrogen content and carried out the thermal treatment of homogenizing before forging subsequently, the carbonitride that so bulk is nascent can not produce.

In a preferred embodiment of the invention, nitrogen content is preferably about 0.05 % by weight.The larger numerical value of above-mentioned numeric ratio brings better properties.About nitrogen content of 0.05 % by weight gives secondary hardening in quenching process higher potential than larger content, therefore makes this steel have high rigidity.But, show that about amount of 0.10 % by weight makes secondary hardening peakdeviation to favourable tempering temperature higher a little.In addition, the test carried out and model calculate and show that improving requirement of nitrogen improves austenitizing temperature.

In the mutation of steel, be also conceivable than the higher nitrogen content shown in preferred implementation.In above-mentioned mutation, nitrogen can altogether up to 0.30 % by weight.In order to obtain more high nitrogen-containing, Regular casting methods is inadequate.Alternatively, thus add nitrogen preferably by first manufacture denitrogenate beyond the powdered steel of required composition substantially, subsequently by this solid state powder of nitrogen nitrogenize, then at inferior this powder of quiet hot pressing of pressure of the temperature of about 1150 DEG C and about 76MPa to generate ingot.By powder metallurgy fabrication tool steel, avoid the problem producing primary carbide.

This ingot preferably forges at the temperature of about 1270 DEG C, and then softening annealing at the temperature of about 820 DEG C, is cooled to 650 DEG C subsequently with 10 DEG C of speed hourly, and then in atmosphere naturally cooling get ready to be austenitizing.

Embodiment 1

In following table 2, the chemical constitution of three kinds of different-alloys N0.05, N0.10 and N0.30 is listed with the form of % by weight.N0.05 refers to the material of the nitrogen comprising 0.05 % by weight, etc.Notice that these are the actual compositions in experiment ingot.

Object keeps the content of all alloying elements except carbon and nitrogen constant.Compare with the low chromium hot working tool steel of the standard in table 1, chromium also reduces slightly.Molybdenum content slightly reduces, and Fe content increases.For carbon and nitrogen, object is to keep the total amount of these elements to be fixed on about 0.40 % by weight, and this point relatively successfully achieves.

Table 2

Material	C	N	Cr	Mo	V	Mn	Si	Fe
									N0.05	0.38	0.05	1.70	2.77	1.20	1.09	0.30	92.5
N0.10	0.27	0.10	1.53	2.32	1.20	1.85	0.26	92.5
									N0.30	0.08	0.32	1.51	2.20	1.20	1.88	0.29	92.5

Tempering stage relates generally to metastable phase, and the research of previous electron microscope technique has shown in tempering temperature interval, and namely at 400 ~ 700 DEG C, these metastable phases are present in the low chromium hot working tool steel of standard.These Carbide Phases are rich vanadium MC (FCC) and rich molybdenum M mainly ₂c (HCP).Also in standard low chromium hot working tool steel, a certain amount of rich chromium M is found ₇c ₃.

The calculating carried out below is to determine whether these alloys comprising nitrogen have the possibility of sclerosis, if namely enough under austenitizing temperature alloying elements can dissolve in austenitic matrix, thus can generate martensite at quenching.Therefore, the temperature range attracted people's attention is in the reality of softening annealing temperature (820 DEG C) and setting between available maximum austenitizing temperature (1200 DEG C).

The result of these EQUILIBRIUM CALCULATION FOR PROCESS shows in the diagram.That show here is M ₆the molar fraction of C, M (C, N) and bcc matrix is to the function of temperature.Equilibrium phase is austenite.Solid-line curve represents N0.05, and dashed curve represents N0.10, and point curve represents N0.30.Note the M (C, N) even having high-content at up to 1200 DEG C in N0.30 alloy.As expected, unstable higher than bcc phase at 850 DEG C.Find enjoyably, represent that the slope of the profile of equilibrium that M (C, N) measures reduces with the increase of nitrogen content.This shows to compare with N0.05, dissolves M (C, N) more difficult in N0.30.What therefore, it is expected to is after the austenitizing of 1100 DEG C, and content ratio in N0.30 matrix of carbon, nitrogen and vanadium is medium and small at N0.05 matrix.

Due to the M of rich molybdenum ₆a C phase dissolved carbon and not dissolved nitrogen, this has lower carbon content in N0.10 and N0.30, therefore M ₆the amount of C reduces along with the minimizing of carbon content.Be also noted that M under used austenitizing temperature ₆c all dissolves.

In order to estimate the potential of secondary precipitation in N0.05, N0.10 and N0.30, only tempering temperature region is calculated.After the balance obtained can show the sufficiently long time at most, what is met and is present in material.Work before has shown in fact can carry out some automatic tempering in standard low chromium hot working tool steel.This means M ₃c (cementite) can separate out after austenitization.

What show in Fig. 5 is the result calculated in tempering temperature region.Block curve represents N0.05, and dashed curve represents N0.10, and point curve represents N0.30.Usually in 500 ~ 650 DEG C, carry out secondary hardening, and in said temperature interval with regard to M (C, N) amount for, there is no large difference between N0.05 and N0.10.On the other hand, N0.30 but has high and almost constant M (C, N) content, and this is likely due to high vanadium and nitrogen content.

Compare with N0.10, carbon content higher in N0.05 produces more M ₂c phase and matrix balance.And in N0.30, there is the M of much less ₂c.

Based on calculation result above, should estimate at a certain temperature after austenitizing, the potential of secondary precipitation in these alloys.This potential depends on that the metastable equilibrium under tempering temperature and the M (C, N) between the balance under austenitizing temperature are mutually and M ₂the difference of C phase content.In table 3, these differences show with the secondary precipitation potential of three kinds of different-alloys.These values provide with molar percentage.

Table 3

The result of table 3 shows, owing to there is M (C, the N) phase of low levels at 1100 DEG C, N0.05 can have best sclerosis response, and namely a large amount of alloying elements can dissolve in austenitic matrix.This also shows that N0.05 has the best potential of good secondary hardening in the drawing process of 625 DEG C.

Embodiment 2

These two kinds of alloys of N0.05 and N0.10 are conventionally cast as the little ingot of 50kg.First time test and Selection N0.10, and before forging process, Homogenization Treatments is not carried out to above-mentioned ingot.Second time test, N0.05, carries out the Homogenization Treatments reaching 15 hours before forging at 1300 DEG C.3rd alloy, N0.30 has too high nitrogen content so that not by the forging type manufacture of routine.Therefore this alloy uses powdered metallurgy to manufacture.First manufacture powdered steel, then this powder is in the solid state through pressurized nitrogen nitrogenize.Then this powder carries out hot isostatic pressing (HIP) with the pressure of 76MPa at 1150 DEG C.

These all three ingots forge and then sample are cut into the size of 15x15x8mm at 1270 DEG C.Through first these samples of softening annealing thermal treatment at 820 DEG C, after annealing, the order of cooling is per hourly cooled to 650 DEG C with 10 DEG C, and naturally cooling in atmosphere subsequently.After softening annealing, N0.05 austenitizing process 30 minutes at 1100 DEG C.In order to compensate poor precipitation potential, N0.10 austenitizing process 30 minutes at 1150 DEG C, and N0.30 austenitizing process 30 minutes at 1200 DEG C.Be derived from each nine samples of these three kinds of alloys in following temperature tempering: 450 DEG C, 525 DEG C, 550 DEG C, 575 DEG C, 600 DEG C, 625 DEG C, 650 DEG C, 675 DEG C and 700 DEG C.Soaking time is 2 hours, and this process is dual temper, and namely total temper time is 4 hours.After thermal treatment, measure the hardness of these samples.Use the form of non-dissolved particles in the next further study sample of scanning electron microscope (SEM), distribution and size.The SEM instrument used is FEIQuanta600F.

Hardness measurement

The result that hardness measurement obtains shows in figure 6.Can see, the temperature range of 500 ~ 600 DEG C, these three kinds of alloys all have secondary hardening peak value.All temper carry out 2+2 hour.N0.05 has the highest hardness (53HRC) in as-quenched condition, and N0.10 and N0.30 has hardness lower a little.But all three kinds of alloys are considered to hardenable.The hardness curve of the hardness curve of N0.05 and standard low chromium hot working tool steel is closely similar, and this standard low chromium hot working tool steel maximum value as shown in Figure 1 is about 54HRC.

The secondary hardening peak of N0.10 seems to move to a little higher temperature, has peak value of hardness at 600 DEG C.The peak value of hardness of N0.05 and N0.30 is all at 550 DEG C.

Scanning electron microscope

Namely have in the alloy of minimum nitrogen content at the N0.05 of routine casting, undissolved M (C, N) particle has the mean sizes being less than 1 μm.This works as with usual undissolved Carbide Phases in steel.Another being easy in N0.05 to find is the mixture of aluminum oxide and manganese sulfide mutually, and see Fig. 7, it is show medium and small SEM figure (back scattering) not dissolving M (C, N) precipitate 2 and spherical oxide compound-sulfide composite grain 1 of N0.05.This sample at 1100 DEG C austenitizing process 30 minutes and at 625 DEG C temper 2+2 hour.

At N0.05(and N0.10) in have the reason of many non-metallic inclusions to be all experimental ingots under open environment to manufacture and casting.

Austenitizing process 30 minutes at 1150 DEG C at 625 DEG C after temper 2+2 hour, in N0.10, the most common-size of M (C, N) particle is 5 ~ 10 μm of equivalent ring diameters (EquivalentCycleDiameter, ECD).Larger, nascent carbide 3(separates out in the melt) austenite crystal interface before being everlasting finds, see Fig. 8, its back scattering SEM being showing M (C, N) undissolved on austenite crystal interface before, nascent in alloy N0.10 schemes.This sample at 1150 DEG C through austenitizing process 30 minutes and at 625 DEG C temper 2+2 hour.

Fig. 9 is the detailed SEM Photomicrograph of M (C, N) particle 4 nascent in N0.10.They are in SEM, use the INCA feature software from OxfordInstruments automatically to find.They show that they separate out from melt in edge clearly.White portion in figure is the M of rich molybdenum ₆c particle 5.Notice that this sample is the N0.10 through softening annealing in this case.

In the N0.30 that powder metallurgy manufactures, the distribution of sizes (ECD) that undissolved M (C, N) particle 6 has, between 1 ~ 5 μm, is modally of a size of 2 μm, and therefore, although nitrogen content is high, particle is small-particle.Be distributed in these uniform particles in microstructure, see Figure 10.But, as shown in figure 11, find bunches 7 of some M (C, N).

In three kinds of all alloys, the chemical constitution of undissolved M (C, N) phase particle is measured by EDS, and will the results are shown in table 4, which show the chemical constitution of M (C, N) particle in alloy N0.05, N0.10 and N0.30.Above-mentioned numerical value provides with molar percentage.Note, although for light element, such as carbon and nitrogen, the accuracy of EDS is not very high, can find out that carbon during M (C, N) mutually and nitrogen budgets it is expected to based on nominal composition.Provide in table ± value is the value provided in INCA program (OxfordInstruments).The part iron of record may from the matrix of surrounding, especially for alloy N0.05.

Table 4

Industrial applicibility

Method in the present invention and low chromium hot working tool steel are applicable to wish to obtain improving the place using hot-work steel instrument under temperature and the condition of time expand.

Claims

1. a low chromium hot working tool steel, it consists of (in % by weight):

Optionally

Ni＜3

Co≤5

B＜0.01

The outer surplus of the removal of impurity is Fe.

2. low chromium hot working tool steel according to claim 1, it meets following one or more condition (in % by weight):

3. low chromium hot working tool steel according to claim 2, wherein the content of C counts 0.30 ~ 0.35 with % by weight.

4. low chromium hot working tool steel according to claim 2, wherein the content of C+N counts 0.36 ~ 0.44 with % by weight.

5. low chromium hot working tool steel according to claim 2, wherein the content of Mo counts 2.2 ~ 2.8 with % by weight.

6. low chromium hot working tool steel according to claim 2, wherein the content of V counts 1.15 ~ 1.25 with % by weight.

7. low chromium hot working tool steel according to claim 2, wherein the content of Mn counts 1.1 ~ 1.9 with % by weight.

8. low chromium hot working tool steel according to claim 2, wherein the content of Si counts 0.2 ~ 0.4 with % by weight.

9. low chromium hot working tool steel according to claim 2, wherein the content of Ni counts < 0.25 with % by weight.

10. low chromium hot working tool steel according to claim 2, wherein the content of Co counts < 0.20 with % by weight.

11. low chromium hot working tool steels according to claim 2, wherein the content of B counts 0.001 ~ 0.005 with % by weight.

12. according to the low chromium hot working tool steel of claim 1 or 2, and it meets following one or more condition (in % by weight):

13. low chromium hot working tool steels according to claim 12, wherein the content of C counts 0.27 ~ 0.34 with % by weight.

14. low chromium hot working tool steels according to claim 12, wherein the content of Cr counts 1.4 ~ 2.3 with % by weight.

15. according to the low chromium hot working tool steel of claim 1 or 2, and it meets following one or more condition (in % by weight):

N0.042～0.10

C+N0.39～0.41

Cr1.3～2.3。

16. low chromium hot working tool steels according to claim 15, wherein the content of N counts 0.045 ~ 0.10 with % by weight.

17. low chromium hot working tool steels according to claim 15, wherein the content of Cr counts 1.4 ~ 2.1 with % by weight.

18. low chromium hot working tool steels according to claim 12, it meets following one or more condition (in % by weight):

N0.042～0.10

C+N0.39～0.41

Cr1.3～2.3。

19. low chromium hot working tool steels according to claim 18, wherein the content of N counts 0.045 ~ 0.10 with % by weight.

20. low chromium hot working tool steels according to claim 18, wherein the content of Cr counts 1.4 ~ 2.1 with % by weight.

21. according to the low chromium hot working tool steel of claim 1 or 2, and it meets following one or more condition (in % by weight):

22. low chromium hot working tool steels according to claim 21, wherein the content of C counts 0.30 ~ 0.34 with % by weight.

23. low chromium hot working tool steels according to claim 21, wherein the content of N counts 0.045 ~ 0.10 with % by weight.

24. low chromium hot working tool steels according to claim 21, wherein the content of Cr counts 1.5 ~ 1.7 with % by weight.

25. low chromium hot working tool steels according to claim 21, wherein the content of Mo/V counts 1.9 ~ 2.1 with % by weight.

26. low chromium hot working tool steels according to claim 21, wherein the content of Cr/V counts < 1.8 with % by weight.

27. low chromium hot working tool steels according to claim 12, it meets following one or more condition (in % by weight):

28. low chromium hot working tool steels according to claim 27, wherein the content of C counts 0.30 ~ 0.34 with % by weight.

29. low chromium hot working tool steels according to claim 27, wherein the content of N counts 0.045 ~ 0.10 with % by weight.

30. low chromium hot working tool steels according to claim 27, wherein the content of Cr counts 1.5 ~ 1.7 with % by weight.

31. low chromium hot working tool steels according to claim 27, wherein the content of Mo/V counts 1.9 ~ 2.1 with % by weight.

32. low chromium hot working tool steels according to claim 27, wherein the content of Cr/V counts < 1.8 with % by weight.

33. low chromium hot working tool steels according to claim 15, it meets following one or more condition (in % by weight):

34. according to the low chromium hot working tool steel of claim 33, and wherein the content of C counts 0.30 ~ 0.34 with % by weight.

35. according to the low chromium hot working tool steel of claim 33, and wherein the content of N counts 0.045 ~ 0.10 with % by weight.

36. according to the low chromium hot working tool steel of claim 33, and wherein the content of Cr counts 1.5 ~ 1.7 with % by weight.

37. according to the low chromium hot working tool steel of claim 33, and wherein the content of Mo/V counts 1.9 ~ 2.1 with % by weight.

38. according to the low chromium hot working tool steel of claim 33, and wherein the content of Cr/V counts < 1.8 with % by weight.

39. low chromium hot working tool steels according to claim 1, it consists of (in % by weight):

Optionally

The outer surplus of the removal of impurity is Fe.

40. low chromium hot working tool steels according to claim 1, it consists of (in % by weight):

Optionally

The outer surplus of the removal of impurity is Fe.

41. low chromium hot working tool steels according to claim 1, it consists of (in % by weight):

Optionally

B0.001～0.01

Mo/V1.8～2.3

Cr/V＜2

The outer surplus of the removal of impurity is Fe.

42. low chromium hot working tool steels according to claim 1, it consists of (in % by weight):

Optionally

B0.001～0.01

Mo/V1.8～2.3

Cr/V＜2

The outer surplus of the removal of impurity is Fe.

43. low chromium hot working tool steels according to claim 1, it consists of (in % by weight):

Optionally

B0.001～0.005

Mo/V1.8～2.3

Cr/V＜2

The outer surplus of the removal of impurity is Fe.

44. 1 kinds of manufactures have the method for the low chromium hot work tools steel work strengthening tempering resistance, and it comprises:

A) steel limited any one of Claims 1-4 3 is provided;

B) steel work is formed by described steel;

C) be up to step b at the temperature of 1200 DEG C) in described steel work austenitizing about half hour of obtaining, quench subsequently; And

D) at the temperature of 500 ~ 700 DEG C, by the described steel work tempering at least twice through quenching, each 2 hours.

45. according to the method for claim 44, under it is included in the temperature of 1050 ~ 1150 DEG C, implements austenitizing to described steel work.

46. according to the method for claim 44, under it is included in the temperature of 1080 ~ 1150 DEG C, implements austenitizing to described steel work.

47. methods any one of claim 44 or 45, it is included in the temperature of 550 ~ 680 DEG C, implements tempering to the described steel work through quenching.

48. methods any one of claim 44 or 45, it is included in the temperature of 600 ~ 650 DEG C, implements tempering to the described steel work through quenching.

49. methods any one of claim 44 or 45, it is included in the temperature of 625 ~ 650 DEG C, implements tempering to the described steel work through quenching.

50. according to the method for claim 44 or 45, comprise further and add nitrogen, its by first manufacture denitrogenate beyond the powdered steel of required composition substantially, subsequently by the solid-state powdered steel of nitrogen nitrogenize to provide required composition, and then powder described in hot pressing to form ingot.

51. according to the method for claim 47, comprise further and add nitrogen, its by first manufacture denitrogenate beyond the powdered steel of required composition substantially, subsequently by the solid-state powdered steel of nitrogen nitrogenize to provide required composition, and then powder described in hot pressing to form ingot.

52. according to the method for claim 44 or 45, before it is also included in austenitizing, by the step of ingot homogenizing, forging and softening annealing.

53. according to the method for claim 47, before it is also included in austenitizing, by the step of ingot homogenizing, forging and softening annealing.

54. according to the method for claim 50, before it is also included in austenitizing, by the step of ingot homogenizing, forging and softening annealing.