CN101440456A - Hot die steel with excellent heat resistance and high toughness - Google Patents

Abstract

The invention provides a hot die steel with excellent heat resistance and high toughness. The hot die steel comprises the following chemical compositions by mass percentage: 0.28 to 0.35 percent of C, 0.20 to 0.50 percent of Si, 0.20 to 0.80 percent of Mn, 4.50 to 5.50 percent of Cr, 2.00 to 2.80 percent of Mo, 0.4 to 0.80 percent of V, less than or equal to 0.025 percent of P, less than or equal to 0.025 percent of S, 0.05 to 0.20 percent of Nb, 0.01 to 0.03 percent of N, and the balance being Fe and unavoidable impurity elements. The hot die steel has both high high-temperature strength and high toughness so as to improve the service life of the hot die steel.

Description

A kind of hot-work die steel with good heat resistance and high tenacity

Technical field

The present invention relates to metallurgy industry die steel product, refer in particular to a kind of hot-work die steel with good heat resistance and high tenacity.

Background technology

Along with developing rapidly of industrial technology, production extensively adopts precision stamping, pressure die casting, cold extrusion, hot extrusion etc. not to have cutting, few Cutting Process both at home and abroad, mould has become its main forming tool, and has formed hot-work die steel, cold-work die steel, plastic die steel three big serial die steels.

Hot-work die steel is mainly used in to make and is heated to the above metal of recrystallization temperature or the mould of liquid metal compression moulding, as hammer forging die, mechanical press forging die, hot extruding die and transfer mold etc.Hot-work die steel has developed into steel series at present, as is used for 5CrMnMo, the 5CrNiMo of forging die; Be used for the 4Cr5MoSiV1 of hot extruding die and transfer mold etc.

The hot-work die steel general property requires as follows:

Intensity and toughness: the bigger load that mould bears during operation often owing to the intensity and the not enough die cavity edge or the early stage aging phenomenon such as local collapse, tipping and fracture of producing of toughness of material, therefore requires die steel to have the toughness that high intensity is become reconciled after thermal treatment.

Fatigue property: the load that mould bears during one's term of military service is a recirculation, the thermal shocking that mechanical shock of bearing as cold-work die and hot-work die bear, therefore the quality of the anti-stress fatigue of die steel and thermal fatigue resistance has determined the work-ing life of mould, in order to obtain the long lifetime of mould, require die steel should have good anti-fatigue performance.

Processibility: the processibility here comprises two aspects, the one, and the cutting ability of material, the 2nd, the hot workability of material.The heat processing and forming technology is generally all adopted in the production of die steel, therefore requires die steel should have heat processing and forming performance preferably, guarantees carrying out smoothly of hot procedure.The shape of mould is very complicated in addition, and difficulty of processing is bigger, and good machinability can guarantee the dimensional precision of Mould Machining.

Hardenability and hardening capacity: for the mould of large section, high hardening capacity can guarantee that whole cross section hardness is even, improves the use properties of mould.

In the middle of above-mentioned performance requriements, high strength and high tenacity are the most favourable work-ing life to improving hot-work die steel.

The interalloy chromium series hot die steel that with 4Cr5MoSiV1 is representative has obtained widespread use.Its Chemical Composition is: C 0.32～0.45%, Si 0.80～1.20%, Mn 0.20～0.50%, Cr 4.75～5.50%, Mo 1.10～1.75%, V 0.80～1.20%, Fe surplus.The interalloy hot-work die steel is based on Cr5 series, this type of steel Cr content improves a lot than the low-alloy hot-work die steel, add alloying elements such as a certain amount of Si, Mo, V in addition, can separate out a certain amount of M2C and MC type diffusion carbide during tempering again, increase age hardening effect, have certain heat resistance and thermostability.Being adapted at 600 ℃ of following operating modes is on active service.

Depend on the obdurability of material the work-ing life of hot-work die steel, has the material of high strength and high tenacity, and the work-ing life of mould is high more.Yet 4Cr5MoSiV1 is because of the heat resistance deficiency, and the hardness of 600 ℃ of tempering insulations after 20 hours only is HRC36, and laterally non-notch impelling strength is 180J only, and only be about 60,000 times the work-ing life that is used for aluminum alloy die-casting die.

In order further to improve hot-work die steel work-ing life.The metallargist develops the modified version steel grade of hot-work die steel 4Cr5MoSiV1 in succession both at home and abroad, as Chinese patent CN85100822A hot-work die steel, its composition is C 0.30～0.50%, Si 0.20～1.00%, Cr 2.00～4.00%, Mn0.20～1.00%, V 0.80～2.00%, Mo 1.50～3.50%, Ni＜2.00%, Co＜4.00%, Nb＜0.30%, B＜0.01%.Though this invention steel grade has higher high temperature strength, not mentioned toughness index.Add alloying element Co in the steel, except the hot strength that improves steel, but reduced the hot workability of material, the forging deformation temperature range is narrow, forges the final forging temperature height, more than 950 ℃; Add the Co element and increased the fragility of material, reduce toughness; The adding of Co also causes hardening capacity to reduce.Because alloying element Co costs an arm and a leg, cause this invention die steel cost to raise simultaneously, be unfavorable for marketing, be difficult to allow market be accepted.The Mo content lower limit of this invention steel grade is lower, is 1.50% only, is lower than Mo upper content limit among the H13, and is little to improving the thermal stability effect.

Summary of the invention

The objective of the invention is to develop a kind of hot-work die steel, have the hot-work die steel that high hot strength has high tenacity again simultaneously, improve the work-ing life of hot-work die steel with good heat resistance and high tenacity.

For achieving the above object, technical scheme of the present invention is,

A kind of hot-work die steel with good heat resistance and high tenacity, its chemical ingredients mass percent is:

C 0.28～0.35

Si 0.20～0.50

Mn 0.20～0.80

Cr 4.50～5.50

Mo 2.00～2.80

V 0.4～0.80

P ≤0.025

S ≤0.025

Nb 0.05～0.20

N 0.01～0.03

Surplus is Fe and inevitable impurity element.

For the hot-work die steel that requires obdurability, there is certain interaction between the alloying element:

Hardness Y1=-2.39Si% * Mn%+2.14Si% * Cr%-1.39Mn% * V%+0.97Mo% * V%+25.4 (not considering the thermal treatment factor)

Impelling strength Y2=-154.33C%-27.79Mn% * V%+111.63 (not considering the thermal treatment factor)

Definite reference of steel grade alloying element content of the present invention interactive rule between the above-mentioned alloying element, taken into full account intensity and flexible is taken into account.The interactive result of Si and Mn reduces hardness, the interactive result of Si and Cr improves intensity, the interactive result of Mn and V reduces hardness and toughness, therefore consider the interaction between the element, C, Si, Mn, V all decrease than 4Cr5MoSiV1, and add micro-Nb, thereby improve toughness; Improve Mo content, and add the N element and strengthen matrix, the intensity of invention steel grade and toughness are improved simultaneously.

C is to improve the hardness of steel and intensity effective elements the most, and the solution strengthening effect is remarkable, separates out a large amount of dispersing carbide during tempering and has dispersion-strengthened action, is the requisite element of the intensity that guarantees that hot-work die steel can reach.But the C too high levels can cause increasing of carbide quantity in the steel, reduces toughness and welding property.In the middle of many alloying elements, carbon is the most remarkable to the flexible influence, demonstrates fully from above-mentioned impelling strength relational expression.Therefore carbon content is unsuitable too high.And,, therefore under the not high situation of carbon content, still can obtain required intensity by the effect of the solution strengthening effect instead of part carbon of nitrogen in steel by adding a spot of nitrogen element.Therefore suitable carbon content is 0.28～0.35%C.

Contain a spot of Si in the steel desoxydatoin is preferably arranged, but the Si too high levels then reduces the welding property and the machinability of steel, and increase the greying tendency, when in steel, having Cr, Mn element, add the Si element and increase the temper brittleness tendency in addition, therefore suitable Si content is 0.20～0.50%.

Mn is the alloying element of postponing perlitic transformation strongly, help improving the hardening capacity of steel and improve intensity by the solution strengthening effect, but the Mn too high levels has the tendency that makes the crystalline grain of steel alligatoring.Suitable Mn content is 0.20～0.80%

Cr, the vital role in steel of the present invention is to postpone perlitic transformation strongly, helps the raising of hardening capacity; And improve martensitic temper resistance.Cr content when 5% left and right sides and carbon form (Fe, Cr) ₇C ₃(Fe, Cr) ₂₃C ₆The type carbide produces the secondary hardening effect, improves intensity.Cr is the element that dwindles the γ phase region in addition, and the Cr too high levels will obtain ferritic structure, causes intensity to reduce, therefore suitable Cr content 4.50～5.50%Cr.

Mo is the very effective alloying element of heat resistance that improves steel, adds Alloy Elements Mo and form M in steel ₂C type carbide can improve the hot strength and the thermostability of steel.But has only the effect that when Mo content surpasses 2.00%, just has tangible raising thermostability.Mo cooperates adding with Cr, Mn in addition, and its interaction can significantly improve the hardening capacity of steel, but the Mo too high levels then increases the thermal processing distortion drag, reduces the hot workability of steel.Therefore suitable Mo content is 2.00～2.80%.

V, the effect in steel mainly is a crystal grain thinning, improves the obdurability of steel, adds the temper resistance that alloying element V can separate out the carbide generation secondary hardening effect raising steel of MC type small and dispersed in addition in the steel.V content surpasses the high-temperature oxidation resistance that significantly reduced steel at 0.8% o'clock, easily causes hot-work die steel to produce heat and melts the damage phenomenon.Therefore suitable V content is 0.4～0.80%

Nb separates out the very carbide of small and dispersed in steel, play the effect of anchoring crystal boundary, thereby crystal grain thinning improves toughness.Add the effect that 0.05%Nb can play the impelling strength that improves steel in the steel, reduce brittle transition temperature, improve welding property.The Nb too high levels then reduces the hardening capacity of steel, has therefore added 0.05～0.20%Nb.

N is an element with remarkable solution strengthening effect, can play the solution strengthening effect by adding minor N, improves die surface hardness, has created condition for reducing carbon content simultaneously, and the minimizing of carbon content can improve the toughness and the welding property of steel.Too much N forms bubble and rarefaction defect easily, so the present invention has added 0.01～0.03%N.

Beneficial effect of the present invention

1. the present invention has taken all factors into consideration influences the hot-work die steel heat resistance and the toughness in work-ing life, design by reasonable component, C and Cr, Mn, Mo, the solution strengthening of alloying elements such as V and precipitation strength effect have improved hot strength and thermostability, especially add the Nb element and improved the toughness of steel, have the advantages that obdurability has both, 20 hours hardness of 600 ℃ of tempering insulations can keep HRC40, exceed more than the 3HRC than 4Cr5MoSiV1, laterally non-notch impelling strength is up to 300J, at least exceed more than the 50J than 4Cr5MoSiV1, its heat resistance and toughness all are better than 4Cr5MoSiV1, help improving the work-ing life of hot-work die steel, be particularly useful for aluminum alloy die-casting die and hot-extrusion mold.

2. the present invention adopts the micro-N element of interpolation to reduce the proportioning of C in the steel, helps improving the toughness and the welding property of steel.

3. the present invention's wide, easily deformable characteristics that have forging range, final forging temperature can arrive 800 ℃.

Description of drawings

Fig. 1 is thermal fatigue surface topography photo after the hot-work die steel of the present invention circulation 2000 times;

Fig. 2 is thermal fatigue surface topography photo after the contrast steel grade 4Cr5MoSiV1 circulation 2000 times.

Embodiment

Adopt the 100kg medium-frequency induction furnace, smelt the electrode bar that obtains Φ 80mm, again through electric slag refusion and smelting, obtain the 70Kg ESR ingot, ESR ingot is carried out 10 hours high temperature homogenization of 1100～1200 ℃ of insulations handle, be swaged into 60mm * 60mm square stock then, 800 ℃ of final forging temperatures.

The embodiment chemical ingredients is referring to table 1:

Table 1 unit: mass percent

Embodiment	C	Mn	P	S	Si	Cr	Mo	V	Nb	N	Fe
												1	0.32	0.48	0.011	0.010	0.35	5.12	2.45	0.56	0.09	0.023	Surplus
2	0.28	0.78	0.018	0.007	0.49	5.49	2.52	0.65	0.19	0.011	Surplus
												3	0.30	0.40	0.013	0.008	0.21	4.52	2.78	0.78	0.15	0.015	Surplus
4	0.35	0.22	0.0I0	0.009	0.27	5.06	2.03	0.61	0.06	0.018	Surplus
												5	0.33	0.55	0.009	0.005	0.36	4.85	2.66	0.41	0.12	0.028	Surplus
6	0.34	0.20	0.012	0.008	0.42	4.50	2.80	0.80	0.05	0.010	Surplus
												7	0.33	0.80	0.015	0.006	0.20	5.50	2.00	0.40	0.20	0.030	Surplus
Comparative example	0.38	0.27	0.015	0.005	1.01	5.42	1.26	1.02	-	-	Surplus

Annotate: comparative example is contrast steel grade (H13).

To the room temperature quench treatment, quenching hardness is as follows through 2 hours oil coolings of 1060 ℃ of insulations:

Table 2 embodiment quenching hardness

Embodiment	Quenching hardness (HRC)	Difference (△ HRC) with contrast steel grade H13
			1	56.8	2.7
2	56.2	2.1
			3	56.5	2.4
4	57.2	3.1
			5	57.0	2.9
6	56.3	2.2
			7	56.1	2.0
Comparative example	54.1

The hardness of carrying out to the room temperature quench treatment after 600 ℃ of insulations tempering secondary treatment in 2 hours through 2 hours oil coolings of 1060 ℃ of insulations is as follows:

The table 3 embodiment tempered-hardness of quenching

Embodiment	The tempered-hardness of quenching	Difference (△ HRC) with contrast steel grade H13
			1	46.3	3.1
2	45.8	2.6
			3	46.0	2.8
4	47.2	4.0
			5	46.8	3.6
6	47.0	3.8
			7	46.5	3.3
Comparative example	43.2

As follows through the horizontal non-notch ballistic work that 2 hours oil coolings of 1060 ℃ of insulations carry out to the room temperature quench treatment after 600 ℃ of insulations tempering secondary treatment in 2 hours:

Table 4 embodiment impelling strength

Embodiment	Ballistic work (J)	Difference (△ J) with contrast steel grade H13
			1	>300	>48
2	>300	>48
			3	>300	>48
4	>300	>48
			5	>300	>48
6	>300	>48
			7	>300	>48
Comparative example	252

The hardness of carrying out to the room temperature quench treatment after 600 ℃ of insulations tempering secondary treatment in 2 hours again after 20 hours temper of 600 ℃ of insulations through 2 hours oil coolings of 1060 ℃ of insulations is as follows:

Table 5 embodiment thermal stability

Embodiment	The tempered-hardness of quenching (HRC)	Difference (△ HRC) with contrast steel grade H13
			1	40.3	3.5
2	40.0	3.2
			3	40.5	3.7
4	40.8	4.0
			5	40.6	3.8
6	41.0	4.2
			7	40.9	4.1
Comparative example	36.8

As can be seen from Figure 1, hot-work die steel of the present invention shows good thermal fatigue resistance in thermal fatigue test, and heat fatigue cracking is even, tiny, and shown in Figure 2, the crackle of Comparative Examples is thick.

Hot-work die steel non-notch ballistic work of the present invention reaches more than the 300J, quenching hardness is up to more than the 55HRC, 600 ℃ of tempered-hardnesses are up to more than the 45HRC, 20 hours hardness of 600 ℃ of tempering still keeps more than the 40HRC, its obdurability, thermostability and thermal fatigue resistance all are higher than present widely used 4Cr5MoSiV1 hot-work die steel, and its good obdurability helps further improving the work-ing life of aluminum alloy die-casting die and hot-extrusion mold.

Claims (1)

1. hot-work die steel with good heat resistance and high tenacity, its chemical ingredients mass percent is:

C 0.28～0.35

Si 0.20～0.50

Mn 0.20～0.80

Cr 4.50～5.50

Mo 2.00～2.80

V 0.4～0.80

P ≤0.025

S ≤0.025

Nb 0.05～0.20

N 0.01～0.03

Surplus is Fe and inevitable impurity element.

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