CN102439190B

CN102439190B - Bainitic steel for moulds

Info

Publication number: CN102439190B
Application number: CN201080022236.5A
Authority: CN
Inventors: C·A·巴尔博扎; R·A·梅斯基塔
Original assignee: Villares Metals S A
Current assignee: Villares Metals S A; Villares Metals SA
Priority date: 2009-04-03
Filing date: 2010-04-08
Publication date: 2014-12-31
Anticipated expiration: 2030-04-08
Also published as: RU2011140167A; MX2011010440A; CN102439190A; CA2757754A1; US20120288397A1; WO2011120108A1; JP2013523999A; KR20120125945A; ZA201107591B; WO2011120108A8; EP2557196A1; BRPI0901378A2

Abstract

A bainitic steel for moulds has the following composition of alloying elements, in percentage by weight: 0.05-1.0 carbon; 0.5-3.0 manganese; phosphorus, boron, titanium and vanadium in a ratio NU = [%Ti + %P + 10%B + (%V - 0.10)], where the values of NU range from 0.02 to 0.30, those of titanium are always higher than 0.005, those of boron always lower than 0.010 and vanadium can be entirely or partially replaced by niobium in a proportion of two parts by weight niobium for one part by weight vanadium; nickel, molybdenum and chromium in a ratio G = [0.13% Ni + 0.60% Mo + 0.26% Cr], where the values of G are higher than 0.10 and lower than 1.0; those of nickel are higher than 0.1; those of molybdenum range from 0.07 to 0.27; those of vanadium from 0.1-0.15; those of sulphur do not exceed 0.10; those of silicon range from 0.05 to 3.0; those of nitrogen are lower than 0.10; the calcium content does not exceed 0.02; the aluminium content is lower than 0.5; the chromium content is lower than 1.5; the silicon content ranges from 0.05 to 3.0; the phosphorus content is lower than 0.075 and the remainder consists substantially of iron and inevitable impurities due to the preparation process. In order to produce the bainitic steel for moulds, the final hardness can be obtained by slow cooling in air directly after hot shaping or previous heating in a furnace, even in blocks having a section of up to 1000 mmm; the Vickers hardness values are defined by the equation HV = (450 +- 140)% C + (210 +- 45), for values ranging from 280 to 450 HV (30-45 HRC); for uses requiring high strength, the steel according to the present invention can also be produced by accelerated cooling from temperatures above 900 DEG C in water and oil.

Description

Bainitic steel for moulds

The present invention relates to for the multi-purpose bainitic steel in instrument, mould, mould rack, tool holder, it has the uniform rigidity that obtained by bainite transformation as its principal character, and does not need the expensive element of high-content as nickel and molybdenum or quenching technology.Therefore, such steel provides considerable cost-benefit in alloy with the thermal treatment of their agglomerate body of use.The steel article of the present invention that are carefully designed to based on its microstructure aspect of this alloy provide the hardness close with traditional stell(ite) used in instrument, mould and base and character, but their cost significantly reduces.

Instrument and mould are generally used for other material forming technique, no matter are thermoplastic polymeric material's (being often called plastics) or metallic substance.According to the character for the manufacture of their material, in process envrionment temperature or usually reach 700 DEG C high temperature under use these instruments.Steel of the present invention is specially adapted at ambient temperature or the mould that works at lower than the temperature of 500 DEG C or instrument, and for general purpose mould rack or tool holder.Representative instance of this type of application is usually no more than the plastics forming mould of 300 DEG C.They are also applicable to generally work at ambient temperature but tolerate mould rack and the tool holder of the stress of the instrument used under some conditions.

Therefore, mould of plastics and mould rack can be regarded as the typically used of steel of the present invention.In this type of application, the numerous characteristics of the material that fabrication tool is used is important, and some are relevant to mould purposes, and other are relevant to their manufacture.About the characteristic of mould or mould rack purposes, intensive property is important, usually relevant to the hardness of material and the homogeneity along material section.On the other hand, be such as important for the economy manufacture of character to mould or mould rack of the response of the polishing of material, veining and mechanical process capacity and so on.

In order to reach these requirements, conventional steel by Quench and temper through heat-treated.Quench treatment is complicated for large-sized block, and needs at oil groove or cooling fast with in the water medium of polymer modification.For the block for large mould, use and be greater than 80, the groove of 000 liter, this causes great operational difficulty.Except process for cooling, must use and promote that the element of hardenability is if nickel, manganese and molybdenum are to improve the chemical constitution of these materials.As shown in table 1, these elements exist with remarkable content in the steel of prior art situation, also relevant to the hardness finally needed.

In this sense, new development is carried out.The target of such as patent EP0805220 and US5855846 produces the bainitic steel had compared with low alloyed element content for mould.But, in this invention, obtain hardness (in the same range of DIN 1.2738) with the highest chromium content, thus reduce any possibility income of thermal conductivity and produce higher cost.On the other hand, invention US5695576 illustrates the concept using high Al content and Si content, and this may damage the mechanical process capacity of alloy because there is non-metallic inclusion.As shown in Example 2, high Si content also may damage hardenability.Patent PI9602054-7 and PI0308832-4 follows identical concept, but attempts only to obtain the highest durometer level (430 to 530HB) and the thickness lower than 200 millimeters, but more substantial purposes is the mould of 300HB, does not meet this demand.These patents all do not demonstrate in the embodiment without the need to application in agglomerate body (thickness is greater than 200 millimeters) when quench treatment (that is, using air cooling).They do not describe the possible brittle possibility avoided because Slow cooling causes yet, and no matter are by regulating alloy or heat treatment mode.

Table 1: the alloy of prior art situation.

Only demonstrate main alloying element, in units of mass percent and iron is surplus.

* most important in classification.

Therefore, the difficulty related to when obtaining the hardness of tool steel block and cost are obvious, no matter are by chemical constitution or special thermal treatment process.Therefore, obviously need when without the need to using cooling fast and also without the need to using the steel that can be hardened when large alloying element content and produce agglomerate body (cross section is greater than 500 millimeters).And preferably, this steel can meet the whole durometer level being applicable to mould, i.e. 300 to 420HB.

Theme of the present invention meets all these demands.

The bainitic steel proposed in the present invention can be hardened without the need to quenching, and has the poor chemical constitution containing high cost element (as nickel, molybdenum and chromium).

In order to meet above-mentioned condition, alloy of the present invention has and is made up of the alloying element formed as follows by mass percentage:

* carbon: 0.05 to 1.0, preferably 0.1 to 0.7, be typically 0.15 to 0.6.

* manganese: 0.5 to 5.0, preferably 1.0 to 3.0, be typically 1.5 to 2.5.Manganese partially or completely can be substituted by nickel or copper by the ratio of 1 mass parts manganese to 1 mass parts copper or nickel.

* phosphorus, boron, titanium and vanadium: they have similar effect, therefore they must by following ratio dispensing NU=[Ti+P+10B+ (V-0.10)]; Wherein NU must have the value of 0.02 to 0.30, is typically the value of 0.06 to 0.20.The mass ratio that vanadium can be equivalent to 2 parts of niobiums or tantalum by 1 part of vanadium is partially or completely substituted by niobium or tantalum.

* titanium: independent of ratio NU, minimum titanium content is necessary for 0.005, typical in 0.015, preferably higher than 0.020; But it must not higher than 0.10, and preferably lower than 0.05, and typical case is lower than 0.040.

* boron: except above-mentioned ratio, must control largest boron content, makes it lower than 0.010, and preferably lower than 0.007, typical case is lower than 0.004.

* nickel, molybdenum and chromium have similar effect and must by following ratio dispensing: G=[0.13Ni+0.60Mo+0.26Cr]; The value of G higher than 0.1 and lower than 1.0, must be preferably 0.2 to 0.5, is typically 0.25 to 0.4.The mass ratio that molybdenum can be equivalent to 2 parts of tungsten by 1 part of molybdenum is partially or completely substituted by tungsten.Under this ratio, the ratio that Ni can be equivalent to 1 part of copper by 1 part of nickel is partially or completely substituted by copper.

* nickel: apart from the above, minimum nickel content is 0.1, preferably 0.3, typical case 0.4.

* chromium: except being included in ratio G China and foreign countries, maximum chromium content can be 1.5, preferably lower than 1.0, typical case 0.1 to 0.8.

* sulphur: lower than 0.10, preferably lower than 0.05, typical case 0.001 to 0.010.

* calcium: must with at the most 0.010, preferably at the most 0.005, the content being typically 0.0005 (5ppm) to 0.003 (30ppm) exists.

* aluminium: must lower than 0.5, typical case lower than 0.1, preferably lower than 0.02.

* nitrogen: must lower than 0.1, typical case lower than 0.05, preferably 0.003 to 0.015.

* silicon: 0.05 to 3.0, preferably 0.1 to 2.0, typical case 0.3 to 1.5.

Surplus is common metal or nonmetallic impurity in iron and the steel course of processing.

Here is the reason of the composition of regulation novel material, describes each alloys producing.Described per-cent refers to mass percent.

C: carbon primary responsibility responds thermal treatment, is responsible for the hardness of martensite or bainite, and the latter is the most important micropetrological unit of steel of the present invention.Therefore, the gained final hardness of carbon content control steel of the present invention, this can require according to purposes and change.Therefore, carbon content must according to hardness also higher (equation according to below in embodiment 5 definition): hardness HV=(450 ± 140) %C+ (210 ± 45) of following equalities with necessity.

But content must lower than 1.0%, and preferably lower than 0.7%, typical case is lower than 0.60%, and make after quenching, the existence of residual austenite is not very high, and avoids the secondary precipitation carbide facilitating high quantity in grain contours yet.According to above-mentioned ration, carbon content must be enough to required hardness and the physical strength of facilitating material, and should higher than 0.05%, and preferably higher than 0.1%, typical case is higher than 0.15%.

Mn: because cost is high and improve effect of hardenability due to it, manganese must be used in steel of the present invention with high-content.Therefore, its content must higher than 0.5%, and preferably higher than 1.0%, typical case is higher than 1.5%.But when excessive, manganese increases the strain hardening of residual austenite and material, causes the loss of mechanical process capacity, and improves hydrogen solvability and promote that scale (flake) is formed.Therefore, Fe content must be limited in and be 5.0% to the maximum, is preferably 3.0% to the maximum, and typical case is lower than 2.5%.

P, B, Ti and V: these four kinds of elements have vital role in steel of the present invention, their combined action thus reduce diffusion phase (as ferrite or perlite phase) nucleation.Depend on volume fraction, these phases significantly may reduce hardness, and and then make to use this material.The explanation that nucleation reduces is based on the concentration of these elements in austenite crystal profile; These regions have high free energy, and therefore they are initiation regions that ferrite and pearlite is formed.When being occupied by phosphorus or boron or even under the carbonitride of titanium and the carbonitride of vanadium exist, grain contours is not useable for diffusion phase, the formation of ferrite or micropetrological unit perlite phase.Therefore, when these phase times of suppression, thermodynamic condition causes bainite to be formed, and it has higher hardness and is also uniform along bar cross section in alloy of the present invention.

In this sense, boron causes the strongest effect, determines that it is 10 times of titanium and phosphorus according to experience.In the case of vanadium, the moiety content (about 0.07%) of interpolation is in sosoloid at 700 DEG C, forms perlite or ferrite at such a temperature.Therefore, this ratio treats vanadium by formula (V-0.10).Titanium also promotes the formation of carbonitride, but due to their solubleness low, in this ratio, take into full account titanium.Therefore, we consider the ration of NU, and this is related to the combined action of these elements:

NU＝％Ti+％P+10％B+(％V-0.07％)

When the total amount of this ratio is very low, this means that the effect occupying grain contours is low, and diffusion phase must be formed quickly.The result of several composition shows that the minimum of this relational expression is necessary for 0.02%, is typically 0.06%.

But the high content of phosphorus, boron, titanium or vanadium promotes embrittlement due to some reasons.Titanium and vanadium are strong carbide formers, and when too much, they may promote crack propagation.Too much carbide is also not suitable for mould application, because the mechanical process capacity of their infringement materials and polishing ability.On the other hand, phosphorus promotes brittle by reducing local force of cohesion (making the chemistry between the atom in interface connect to weaken) during excessive segregation in grain contours and other interface.Too much boron also may cause with Phosphorus like act on, but there is large shortcoming: the embrittlement cause and form carbide in grain contours, promoting these regions and material monolithic.For those reasons, the maximum level of these elements must be controlled by the limit of regulation NU ratio.Result shown in embodiment shows that NU must lower than 0.30%, and typical case is lower than 0.20%.

Ti: although describe above, but titanium also has the reaction (because the avidity of titanium and nitrogen is higher than boron and nitrogen) of another effect-" preventing " boron and nitrogen to steel of the present invention.Therefore, it makes boron on profile, have segregation effect, avoids it to be combined with nitrogen.For realizing this effect, titanium must higher than 0.010%, and typical case is higher than 0.015%.

B: owing to confirming the strongest embrittling effect of boron, also must this element of independent limitation, and maximum value is 0.010%, maximum value be preferably 0.007% and typical case lower than 0.004%.

Ni, Mo and Cr: these three kinds of elements promote the raising of hardenability due to it to the effect of diffusion phase growth, no matter are distributed in perlite micropetrological unit or pass through proeutectoid ferrite.After its formation, these have the content of balance mutually, and in order to be formed, the diffusion of secondary element must occur.Time for this diffusion may postpone forming process, and the effect of chromium, molybdenum and nickel is related to this.Routinely, this effect is quantized by hardenability coefficient used in following equation:

G＝[0.13Ni+0.60Mo+0.26Cr]

This equation shows the combined action of three kinds of elements when suppressing the growth of the phase formed.Relevant to suppressing the foregoing coefficient of nucleation, the formation of diffusion phase in proeutectoid ferrite or pearlite morphology can be suppressed, form bainite-there is higher hardness and physical strength thus.Therefore, G value must have the minimum value of 0.1%, and preferably higher than 0.2%, typical case is higher than 0.25%.For thinner size (such as lower than 400 millimeters), lower G value can be enough, the value of such as 0.1% or 0.2%.This meaningfully falls low-alloyed final cost, because nickel, molybdenum and chromium have significant valorization in the nearest several years.Except cost, the content of these elements must be controlled to suppress martensitic formation.If obtain this phase, core core hardness will be significantly higher than in the surface hardness of block or bar.In other words, the too high amount of ratio G also facilitates the loss of the homogeneity of aimed hardness except increasing cost of alloy.G value must lower than 1.0%, preferably lower than 0.5% and typical case lower than 0.4%.This three kinds of elements can be substituted with copper, although copper is the important pollutent of waste material, to hardenability, there is similar effect.If use copper, it must replace nickel, molybdenum or chromium with quality equieffective ratio.

Ni: in addition to those described, can adopt minimum nickel content to avoid Carbide Precipitation and to improve toughness.Beyond these, the minimum content of nickel is necessary for 0.1%, and preferably 0.3%.

Cr: except being included in ratio G, also can adopt maximum chromium content to avoid the loss of thermal conductivity.Therefore, chromium content must be restricted to 1.5%, preferably lower than 1.0%, and is typically 0.1% to 0.8%.

S: in steel of the present invention, sulphur forms the inclusion of manganese sulfide, and it is extended by thermoforming process.Due to extending at the temperature that they produce in mechanical processing process and be liquid, these inclusiones promote that groove rupture and lubricates cutting tool, thus improvement mechanical process capacity.Therefore, sulphur content must higher than 0.001%, and preferably higher than 0.005%, typical case is higher than 0.010%.But, due to and the application of not all needs high mechanical process capacity, the use of sulphur band (band) is optional.Although contribute to machining processes, manganese sulfide inclusion thing damages the surface quality and mechanical properties given by polishing.Therefore, sulphur content must lower than 0.20%, and preferably lower than 0.05%, typical case is lower than 0.010%.

Ca: calcium also has effect to inclusion, its change can damage the hard aluminum inclusion of mechanical process capacity, usually reduces the size (nodularization) of inclusion.But due to the reactivity that it is high, it is complicated that calcium contents controls.Therefore, for those situations needing high mechanical workout and polishing ability, the use of calcium is also regarded as optionally.When deployed, calcium contents must higher than 5ppm, and preferably higher than 10ppm, typical case is higher than 20ppm.Too much calcium contents may promote the erosion for the refractory materials in raceway groove and casting device, excessively increases the ratio of inclusion.Therefore, when adding, final ca content must lower than 100ppm, and preferably lower than 50ppm, typical case is lower than 30ppm.

Al: because it forms hard aluminum inclusion, therefore aluminium content can not be too high, to avoid damaging mechanical workout.It must lower than 0.5%, typical case lower than 0.1%, preferably lower than 0.05%.

N: need nitrogen with the carbonitride of the carbonitride and vanadium that form titanium, they suppress grain growing, contributes to reducing the free energy of grain contours and avoiding the nucleation of diffusion phase.On the other hand, excessive nitrogen may react with boron and suppress this element reducing the effect in grain contours energy.Too high nitrogen content also promotes the higher formation of titanium carbonitride, the mechanical process capacity of this infringement material.Therefore nitrogen must lower than 0.1%, and typical case, lower than 0.05%, is preferably 0.003% to 0.015%.

Si: except it is used as reductor (this is important when aluminium content is low, the situation as at steel of the present invention), silicon has vital role in carbide is formed.This element suppress cementite formation and, as shown in embodiment, suppress to separate out in grain contours and destroy the formation of other carbide of this material.For all these effects, silicone content is necessary for 0.05% to 3.0%, and preferably 0.1% to 2.0%, typical case 0.3% to 1.5%.

Material fabrication process, more especially its thermal treatment are also important.As depicted, this material is designed to have high hardenability and the ability along sectional uniform sclerosis.Therefore, for most of size, this material air can be cooled.Must from from stove higher than critical AC ₃the Heating temperature of temperature (about 850 DEG C) or even directly use this cooling after the thermoforming of material.In order to obtain better toughness, can use and cool faster, such as, by water, oil or forced air convection or even spray water.Therefore, the method for cooling in process of setting can change with the toughness needed for equipment and embody rule.Only when the high hardenability that the meticulous adjustment of reason chemical constitution as defined above provides, this is only possible.

In the following description of the experiment carried out with the composition studied, with reference to accompanying drawing, wherein:

Fig. 1 relates to the diagram distribution of the composition studied of the function as NU and G coefficient, evaluates and tests and starts to cool the rear hardness obtained with 0.05 DEG C/s at 1150 DEG C.The hardness of 30 to 34HRC is considered to suitable (" OK "), because this is the main durometer level of the steel using prior art situation;

Fig. 2 relates to typical continuous cooling transformation (CCT) curve in steel of the present invention, shows formed phase.Region B represents bainite, and M and F refers to martensite and ferrite respectively.Note air cooled thick size, obtain the hardness of about 310HV, produce the 32HRC needed for application;

Fig. 3 relates to typical continuous cooling transformation (CCT) curve in DIN 1.2738 steel of prior art situation, shows formed phase.Region B _sand B _irepresent upper bainite and lower bainite respectively, and M and P refers to martensite and perlite respectively.

Fig. 4 relates to the Hardness Measurement Results in two industrial blocks of two kinds of different sizes, shows high uniformity of hardness.

Fig. 5 relates to the evaluation of the impelling strength of different-alloy 18 to 21.Show size and microgram, to relate to the value utilizing Carbide Precipitation to obtain.

Fig. 6 relates to the microgram obtained the composition 25 to 28 with Different Silicon content.Composition display in table 5.

Fig. 7 relates to the microgram obtained the composition 29 to 32 with different phosphate content.Composition display in table 5.

Fig. 8 relates to the microgram obtained the composition 33 to 36 with different boron content.Composition display in table 5.

Fig. 9 relates to by solubilize thermal treatment, the microstructure slowly cooling to the sample of 950,850,750 and 600 DEG C of temperature subsequently and toughness.Corrode: nital 2%.Increase: 200X.

Figure 10 relates to the evaluation of the gained hardness ratio compared with carbon content: a) accurate calculation value and record comparing of hardness; B) under the change of ± 20HB, predict the equation of the hardness value between upper and lower bound.

embodiment 1: in order to limit the composition of steel of the present invention, manufacturing several alloy and comparing with the alloy of prior art situation.Manufacture experiment bar, the display of gained chemical constitution in table 2, indicates by their sequence number below; In order to compare, carry out the research of typical case's composition of DIN 1.2738 steel (pole is usually used in mould of plastics and other purposes in tool base).Before discussion hardness result, interestingly notice that the alloying element in composition of the present invention significantly reduces in table 3, this is converted to lower cost.

Table 2 shows the NU value and G value that are obtained by aforementioned ratio, grows relevant to suppression nucleation and diffusion phase.For each composition, carry out dilatometry research, the hardness obtained under the rate of cooling of 0.05 DEG C/s is also shown in table 2, and the block that this cooling is equivalent to 400 millimeters carries out air cooling.For the typically used of mould and mould of plastics support, the target value of this hardness is in the scope of 30 to 34HRC.Therefore, the hardness in this scope is referred to as " qualified (OK) ", is marked as high or low in this extraneous intensity.

When these results are in schematic form, as shown in fig. 1, the ideal operation region of the alloy in the present invention is measured; In other words, the combination of NU and G produces the region of the hardness be in target zone.Therefore, this makes us obtain the working limit of alloy of the present invention in the element forming NU (Ti, P, B and V) and G (Cr, Ni and Mo).

Directly related with coring and increment mechanism to the explanation of this result.First, promote that the element that the energy in grain contours reduces is basic, therefore they avoid the formation of the proliferation compound (being no matter proeutectoid ferrite or the ferrite of Morphology of pearlite and cementite) caused compared with soft.The element of the NU coefficient of make-up formula provides this effect.Titanium and vanadium tend in grain contours, form precipitation compounds (carbide or carbonitride), thus reduce the free energy in these regions.Under ferrite or perlite formation temperature (about 700 DEG C), the solubleness of titanium is low, ignores; But the solubleness of vanadium is high, therefore its content reduces by 0.07%, is roughly equivalent to the vanadium in sosoloid at 700 DEG C.On the other hand, phosphorus and boron tend to segregation and concentrate in that region, also cause the reduction of its energy, therefore avoid diffusion phase nucleation.By about 10 times that the effect of experience mensuration boron is phosphorus effect, therefore its coefficient is multiplied by 10.Except the internal action of titanium in carbonitride is formed, these compounds remove nomadic nitrogen from matrix, nitrogen easily and boron react and eliminate the vital role of boron in grain contours during segregation.

Except avoiding nucleation, the existence suppressing the element of diffusion phase growth is important.The element forming this coefficient in alloy of the present invention is manganese, nickel and chromium.The coordinate diagram of Fig. 1 shows these elements of coefficient G consideration, and multiplier index is available from the typical consequence of the hardenability of element.Manganese is not considered, because it is constant in all alloys in G.Under high content, these elements facilitate excessive hardenability, cause forming martensite and excessively improving hardness.Under very low amounts, hardness becomes very low.Even if this is because high NU value suppresses nucleation, but high growth tendency causes the ferrite or the perlite that form significant quantity, thus reduces hardness.

In kind of the alloy of 17 shown in the figure of table 1, as described below, some have showed the alloys producing studied admirably.Alloy 1 and 2 shows the effect of phosphorus content, and it produces low NU value and does not reach required hardness when extremely low.But, when its higher than 0.020% time (alloy 2), hardness is required hardness closely.Alloy 5 and 17 has low chromium, nickel or molybdenum content, therefore destroys ratio G, and does not thus realize required hardness.On the other hand, alloy 7,8 and 9 shows, too high Cr and Ni constituent content causes high G-value, thus causes too high hardness (due to forming section martensite).Alloy 15 shows the importance of vanadium, and it causes the remarkable reduction of NU value and the remarkable reduction of therefore hardness at low levels.Therefore, vanadium can be considered to this alloy absolute demand.

Last and important annotation relates to alloy 10.This alloy is uniquely beyond suggestion list, but reason is simple.Alloy 10 has low titanium content, and this causes NU value to reduce.But the reduction of hardness is more more remarkable than what predict.This is because the shortage of titanium causes hydroboration to lose, because the shortage of titanium leaves more nomadic nitrogens and boron reacts, therefore facilitate its loss acted on (being described as effective boron by some authors).NU and G equation can not explain this synergistic effect, and therefore alloy of the present invention has particular requirement to titanium.

Such as, Fig. 2 shows the CCT curve of exemplary composition of the present invention, and this can compare (in figure 3) with the CCT curve of DIN 1.2738 steel of prior art situation.

Once limit best composition by the preliminary study described in embodiment 1, the some industrial batch of material with different geometrical size as shown in table 4 just can be manufactured.Fig. 4 shows Hardness Distribution and the photo of two agglomerate bodies manufactured according to above-mentioned composition.Both uses all obtain the hardness of about 285 to 310HB (30 to 34HRC), without any downtrending in core core region.

embodiment 2: although there is the uniform rigidity in proper range, but industrial furnace charge (heat), particularly in the block of cross section higher than 400 millimeters, show the toughness being starkly lower than DIN 1.2738 steel (benchmark of this application), the value without the shock test of abaculus (insert) is about 200 joules (samples of 7 × 10mm).Material show toughness value and comparing between microstructure that the major cause of this low value is the precipitation of carbide as shown in Figure 5 in grain contours.Therefore, for alloy of the present invention develops replacement scheme to avoid the precipitation of these carbide and therefore to avoid the embrittlement of agglomerate body.

About chemical constitution, the amount observing carbide improves with Boron contents and increases and reduce when silicone content improves, and phosphorus content has no significant effect; Table 5 shows chemical constitution used in this evaluation.Conclusion can based on the composition of table 6, and result is presented in Fig. 6 to 8.Also observe, as same size alloy 18 and 19 in Figure 5 relatively shown in, nickel has material impact; Alloy 18 shows lower carbide amount due to lower nickel content.

For boron, although to hardenability important (embodiment 1), too much content contributes to forming these carbide: note when boron is increased to 40ppm from 20ppm, the amount (table 6) of carbide is increased to twice.

Possibly, this is owing to high metastability condition, and when high Boron contents concentrates in grain contours, it contributes to Carbide Precipitation.

Stronger for this phenomenon of big rod, there is strong microsegregation effect, cause the partial concn of boron to improve.

Fig. 8 shows this effect, clear enough, improves (simulate the process carrying out cooling higher than the block with core core of 800 millimeters with the pole slow cool down process pair cross-section of 36 DEG C/h and promote this precipitation) having carbide amount in the sample compared with high boron content.

As shown in Figure 7, there is similar effect when silicone content reduces, but not stronger; The silicone content higher than 0.40% is used to tend to the formation reducing these carbide.But as shown in table 6, the increase of Si content reduces the hardenability (essential property) of material of the present invention, particularly higher than (according to table 6, the high ferrite containing in the alloy of 2%Si) under the content of 1.0%.

Therefore, in order to manufacture the big rod with high tenacity and sufficient hardenability, use high silicone content (0.2 to 1.0%) and minimum boron content more suitable, limit this minimum value by the coefficient NU described in embodiment 1.

Table 5: be the effect of research P, B and Si content in Carbide Precipitation and the alloy of the present invention that manufactures, carbide causes embrittlement in blocks of large

Alloy	C	Si	Mn	P	S	Cr	Mo	Ni	V	W	Ti	Al	B	N
																				(ppm)						(ppm)	ppm	(ppm)	(ppm)
25	0.23	0.05	1.84	0.026	0.003	0.56	0.26	0.41	0.15	0.03	310	420	59	77
															26	0.23	0.38	1.83	0.026	0.003	0.56	0.26	0.41	0.15	0.03	310	420	57	71
27	0.23	0.95	1.83	0.026	0.003	0.56	0.26	0.41	0.15	0.03	310	450	60	70
															28	0.24	1.94	1.84	0.026	0.002	0.57	0.26	0.41	0.15	0.03	310	470	58	68
29	0.22	0.42	1.89	0.010	0.003	0.58	0.27	0.41	0.15	0.02	340	200	56	75
															30	0.22	0.42	1.89	0.025	0.003	0.58	0.27	0.41	0.15	0.02	340	200	55	75
31	0.22	0.42	1.89	0.050	0.003	0.58	0.27	0.41	0.15	0.02	340	200	55	75
															32	0.22	0.42	1.89	0.075	0.003	0.58	0.27	0.41	0.15	0.02	340	200	55	75
33	0.20	0.41	1.87	0.027	0.003	0.50	0.25	0.41	0.15	＜0.01	310	160	20	78
															34	0.20	0.41	1.85	0.026	0.003	0.49	0.25	0.41	0.15	＜0.01	310	160	40	75
35	0.20	0.41	1.86	0.028	0.003	0.49	0.25	0.41	0.15	＜0.01	310	160	70	68
															36	0.20	0.42	1.86	0.027	0.003	0.49	0.25	0.41	0.15	＜0.01	310	160	120	66

The metallurgy reason of this type of effect has discussed uniqueness herein and explains.Under high-content, boron tends to concentrate in grain contours, particularly forms complicated carbide with Fe and Cr.By the Electronic Micro-Analysis carried out in steel of the present invention, find this two kinds of elements and micro-Mo.Therefore, the reduction of Boron contents eliminates the carbide as problem results.But this reduction can not be excessive, because as described in example 1 above, in order to avoid forming ferrite, require to there is boron in grain contours.On the other hand, silicon has low solubleness in iron carbide (cementite), thus avoids it to be formed in steel.Because these carbide in steel of the present invention also have high iron level, it is identical that silicon mechanism can be understood to cementite.

Table 6: by the volume fraction of the carbide in the combination picture analytical method quantitative measurment grain contours of the carbide of artificial congnition.With 100 × 10 regions of ratio of enlargement analytic sample, altogether 14mm is scanned to each sample ².Before measuring, sample is imposed to the low cooling of solubilize at 1150 DEG C and 36 DEG C/h.Presentation graphics is presented in Fig. 6 to 8.

Composition	The volume fraction (%) of carbide ^*	Ferritic volume fraction
			Alloy 25/0.05%Si	0.40	0％
Alloy 26/0.41%Si	0.30	0％
			Alloy 27/1.0%Si	0.25	0％
Alloy 28/2.0%Si	0.17	30％
			Alloy 28/0.010%P	0.33	28％
Alloy 29/0.025%P	0.36	0％
			Alloy 30/0.050%P	0.42	0％
Alloy 31/0.075%P	0.31	0％
			Alloy 32/20ppm B	0.016	0％
Alloy 33/40ppm B	0.031	0％
			Alloy 34/20ppm B	0.085	0％
Alloy 35/20ppm B	0.24	0％

* the furnace charge of the vicissitudinous B of tool, alloy 32 to 35, has comparatively low carbon content (see table 5); Therefore, they can not change with other and compare, but can compare between which, with the effect of outstanding boron.

embodiment 3: except the change of chemical constitution, avoid a kind of mode of this precipitation to be promote fast cooling-from the high temperature that still there is not carbide.Carry out these tests as shown in Figure 9; Note when lower than 800 DEG C, toughness reduces more remarkable, particularly between 750 DEG C to 600 DEG C, but after this reduction, and Carbide Precipitation.

In order to reduce this strong precipitation, after forging or after austenitizing/solubilize process, this block can be cooled fast.Design this technique based on numerical simulation result, and can be implemented by cooling in oil or in water.In the case of water, be Crack prevention, more aerial steps can be introduced, thus the temperature head existed between reduction surface and core core.Table 7 shows the result of these experiments, when speed of cooling is higher, observes significantly improving of intensity.Obviously, to the situation of the low inherently agglomerate body of rate of cooling or when needs high strength, this technique must be adopted.In the con-trary case, air cooling can be adopted.

Table 7: from the data simulated and the result obtained in shock test body, for the Different Cooling Conditions of bloom body of the present invention.The value of striking energy relates to the test body without abaculus, cross section 7 × 10mm, laterally.

* advise that the technique in water can be carried out in oil; For the size of 400mm × 1000mm, in oil, continue 60 minutes.T _s=surface temperature.

embodiment 4: in embodiment before, be defined to be chemical constitution and the thermal treatment of steel as suggested in the present invention.Owing to using titanium in this chemical constitution, therefore form the grit of carbonitride-cause the higher wearing and tearing of instrument and damage the mechanical process capacity of material.For mould application, mechanical workout aspect is basic.

For avoiding this point, study the sulphur of alloy of the present invention and the most high-content of calcium.The formation of these two kinds of element influences inclusiones.Sulphur forms manganese sulfide, and it has soft and contributes to disconnecting chip and tool lubrication.On the other hand, calcium changes hard aluminum inclusion, produces the complicated inclusion with better mechanical process capacity.The interpolation of calcium also makes inclusion balling, produces better polishing condition, and polishing is also the important operation of mould of plastics.

Table 8 shows the mechanical workout result of steel of the present invention, has this change of sulphur and calcium contents, in alloy 18, do not have this change in alloy 19.By comparing, carry out identical test with DIN 1.2738 steel (benchmark for mould application).By changing (alloy 18 and 19) calcium and sulphur content, the volume of tool processes obviously increases.

A replacement scheme for improvement of mechanical process capacity reduces the volume fraction of carbonitride, alleviates the reason of the accelerated wear test of instrument thus.Use in alloy 37 and reduce carbonitride volume+use high sulphur and the combined action of calcium contents.Although be similar to alloy 19 on composition, relevant to the remarkable reduction of titanium carbonitride volume, mechanical process capacity significantly improves.In this case, by using less bar to improve setting rate, the minimizing of carbide is realized thus.But this also realizes by the content of reduction nitrogen or titanium.Because titanium is important for NU coefficient, as described in example 1 above, it is of paramount importance for therefore using low nitrogen content (controlling factor as carbonitride volume) to confirm.

Table 8: by the comparison (V of the mechanical process capacity of the alloy of the alloy 18,19 that records to the tool processes volume of cycle life tools terminal and prior art situation _b=0.20mm).Test conditions: instrument=with the hard metal P25 of TiN coating, 25 mm dias, cutting speed=270m/min, enters apart from=0.25 millimeter/tooth, depth of cut=0.75mm and processing pile penetration=10mm.Here is the result of chemical constitution.In each sample in 20 regions with 500 × measured the volume fraction of carbonitride by computer image analysis, altogether scan 0.56mm ².

Alloy	C	Si	Mn	P	S	Cr	Mo	Ni	V	Ti	Al	B	N	Ca
																				(ppm)					(ppm)	(ppm)	(ppm)	(ppm)	(ppm)
ET1	0.39	0.4	1.66	0.011	16	1.87	0.17	0.74	＜0.01	＜50	90	＜10	44	17
															18	0.22	0.40	1.90	0.050	20	0.58	0.25	0.34	0.15	320	100	30	80	6
19	0.22	0.44	1.89	0.051	90	0.56	0.07	0.32	0.13	310	100	38	130	15
															37	0.21	0.41	1.88	0.026	70	0.59	0.26	0.34	0.10	260	74	27	74	22

embodiment 5: provide 30 to 34HRC hardness based on the whole design of aforementioned alloy, because this is the main use range of die steel.For conventional steel, the different condition of anneal is used to obtain higher hardness.In steel of the present invention, by forging direct sclerosis, therefore this process can not be carried out.Therefore, the present invention also attempts to provide the alternatives improving hardness by changing chemical constitution.

By the base composition described in embodiment 1, manufacture the composition with different carbon content, be there is by dilatometry simulation the cooling (speed of 0.05 DEG C/s) of the core core in the block in about 400 millimeters of cross sections.Result in table 9 and Figure 10 shows, when using most high-carbon content, obtains higher hardness.Based on these data, obtain the ratio of the hardness after carbon content and Slow cooling experimentally.I.e. following ratio:

Hardness HV=450%C+210

(hardness obtained after cooling with 0.05 DEG C/s, is equivalent to the air cooling of the block of 400 mm thick)

Table 6: the HV hardness value obtained after cooling with 0.05 DEG C/s in the composition with different carbon content

Alloy	C	Si	Mn	P	S	Cr	Mo	Ni	V	W	Ti	Al	B	N	HV
																					(ppm)						(ppm)	(ppm)	(ppm)	(ppm)	Speed 0.05 DEG C/s
38	0.23	0.28	1.88	0.047	0.002	0.61	0.21	0.33	0.14	＜0.01	310	150	31	95	305
																39	0.30	0.28	1.88	0.049	0.002	0.61	0.21	0.33	0.14	＜0.01	320	150	32	98	356
40	0.39	0.28	1.87	0.049	0.002	0.61	0.21	0.33	0.14	＜0.01	320	150	31	88	376
																41	0.45	0.28	1.87	0.051	0.002	0.61	0.21	0.33	0.14	＜0.01	320	150	32	86	412

Therefore, this embodiment shows, by regulating carbon content, can give alloy different hardness of the present invention.Such as, for hardness 315HV (about 32HRC), confirm the scope obtained in embodiment 1,0.23% carbon is necessary.On the other hand, for the hardness of 400HV (about 40HRC), the carbon content of 0.42% is necessary.

As shown in table 1, the steel of prior art situation has significantly higher carbon content within the scope of this same rigidity: the hardness of DIN 1.2738,32HRC and 0.36% carbon, and the hardness of DIN 1.2711,40HRC and 0.52% carbon.This fact has attractive importance to weldprocedure conventional in mould.Because they work with minimum carbon content, compared with the steel of prior art, in steel of the present invention, the hardness of heat affected zone is much lower.For the carbon content of 0.23%, steel of the present invention produces the hardness of about 45HRC in the region affected by welding, and this hardness is about 60HRC and is 64HRC in DIN 1.2711 in DIN 1.2738 steel.The situation that this fact contributes to many machining operations after welding and contributes to after polishing or veining.

The little change of the index of previous equations can produce suitable result in the durometer level that application is required.For in industry usually accreditation ± change of 20HB for, this ratio can change according to Figure 10 b, is described by following relational expression: upper limit hardness=590%C+165, lower limit hardness=310%C+255.Therefore, the final equation of the hardness of the function as carbon content can be described as follows:

Hardness HV=(450 ± 140) %C+ (210 ± 45)

Therefore, according to industrial application and necessary hardness, the carbon content in steel of the present invention must be calculated by above-mentioned equation.

Claims

1. " bainitic steel of mould ", it is characterized in that being made up of the element chemistry formed as follows by mass percentage: carbon 0.05 to 1.0; Manganese 0.5 to 5.0; The phosphorus, boron, titanium and the vanadium that are provided by ratio NU=[Ti+P+10B+ (V-0.10)], NU value is 0.02 to 0.30, and titanium is all the time higher than 0.005, boron all the time lower than 0.010 and vanadium partially or completely can be substituted by niobium in the ratio of 2 mass parts niobiums to 1 part of vanadium; The nickel, molybdenum and the chromium that are provided by ratio G=[0.13Ni+0.60Mo+0.26Cr], the value of G is higher than 0.10 and lower than 1.0; Sulphur at the most 0.20; Silicon 0.05 to 3.0; Nitrogen is lower than 0.10; Calcium contents at the most 0.010; Aluminium is lower than 0.5, and cobalt is lower than 2.0, and all the other are unescapable impurity in iron and the course of processing substantially.

2. " bainitic steel of mould " according to claim 1, it is characterized in that being made up of the element chemistry formed as follows by mass percentage: carbon 0.10 to 0.6; Manganese 0.8 to 3.0; The phosphorus, boron, titanium and the vanadium that are provided by ratio NU=[Ti+P+10B+ (V-0.10)], NU value is 0.08 to 0.30, boron all the time lower than 0.010, titanium 0.005 to 0.10, and vanadium partially or completely can be substituted by niobium in the ratio of 2 mass parts niobiums to 1 part of vanadium; The nickel, molybdenum and the chromium that are provided by ratio G=[0.13Ni+0.60Mo+0.26Cr], the value of G is higher than 0.20 and lower than 0.50; Except this ratio, chromium content is necessary for 0.1 to 1.5, and nickel content is higher than 0.3; Sulphur at the most 0.05; Silicon 0.05 to 3.0; Nitrogen is lower than 0.05; Calcium contents at the most 0.005; Aluminium is lower than 0.1, and cobalt is lower than 1.0, and all the other are unescapable impurity in iron and the course of processing substantially; This material can be manufactured by the block of 850 mm thick at the most, by obtaining the hardness of 250 to 450HV from the temperature air cooling higher than 700 DEG C, provide this hardness value by equation HV=(450 ± 140) %C+ (210 ± 45).

3. " bainitic steel of mould " according to claim 2, it is characterized in that being made up of the element chemistry formed as follows by mass percentage: carbon 0.10 to 0.6; Manganese 1.3 to 3.0; The phosphorus, boron, titanium and the vanadium that are provided by ratio NU=[Ti+P+10B+ (V-0.10)], NU value is 0.10 and 0.20, titanium is all the time higher than 0.010, and boron is all the time lower than 0.0050, and vanadium partially or completely can be substituted by niobium in the ratio of 2 mass parts niobiums to 1 part of vanadium; The nickel, molybdenum and the chromium that are provided by ratio G=[0.13Ni+0.60Mo+0.26Cr], the value of G is higher than 0.25 and lower than 0.40; Except this ratio, chromium content is necessary for 0.1 to 1.0, and nickel content is higher than 0.3 to 1.0; Sulphur 0.001 to 0.010; Silicon 0.20 to 1.5; Nitrogen 0.0040 to 0.0150; Calcium contents 0.0005 to 0.0030; Aluminium is lower than 0.05, and cobalt is lower than 1.0, and all the other are unescapable impurity in iron and the course of processing substantially; This material can being prepared by the block of 850 mm thick at the most, by directly carrying out the hardness that air cooling obtains 280 to 450HV after thermoforming, providing this hardness value by equation HV=(450 ± 140) %C+ (210 ± 45).

4. " bainitic steel of mould " according to claim 1, it is characterized in that substantially being made up of the element chemistry formed as follows by mass percentage: carbon 0.18 to 0.52, chromium 0.30 to 0.60, molybdenum 0.10 to 0.50, nickel 0.30 to 0.50, vanadium 0.04 to 0.10; Boron 0.0010 to 0.0030; Sulphur 0.0010 to 0.0100; Calcium 0.005 to 0.010; Nitrogen 0.0030 to 0.0100; Wherein, for the relatively high size of thickness 100 to 1000 millimeters, directly after forging or lamination, obtain final use hardness, and without the need to using oil or water hardening process; Thermal treatment must be the smooth air cooling under forced convection, to 280 to 420HV, be equivalent to the hardness value of 29 to 42HRC, according to following ratio: HV=(450 ± 140) %C+ (210 ± 45) by alloy carbon content determination vickers hardness number.

5. according to " bainitic steel of mould " of any one of claims 1 to 3, it is characterized in that by mass percentage, Fe content is by nickel or copper equivalent substitution partially or completely.

6. according to " bainitic steel of mould " of any one of claims 1 to 3, it is characterized in that by mass percentage containing elemental niobium, zirconium or tantalum, correspond to 2 parts of niobiums relationship part or substitute element titanium or the vanadium completely that 1 part of vanadium or titanium and 1 part of tantalum or zirconium correspond to 2 parts of vanadium or titanium.

7., according to " bainitic steel of mould " of any one of claims 1 to 3, it is characterized in that showing boron 0.0015 to 0.0030 by mass percentage; Silicon 0.40 to 1.2.

8., according to " bainitic steel of mould " of any one of claims 1 to 3, it is characterized in that showing sulphur 0.005 to 0.010 and calcium 0.0005 to 0.0030 by mass percentage.

9. " bainitic steel of mould " according to claim 1, it is characterized in that, in quality PPM, there is sulphur 0.002 to 0.20 and calcium 0.0005 to 0.010, and the carbonitride volume fraction had in its microstructure lower than 0.25%, be applicable to the situation needing high mechanical process capacity.