CN1218061C - Calcium processing vanadium-nitrogenium-titanium micro-alloying non-quenched and tempered steel and preparation technology thereof - Google Patents

Abstract

The present invention relates to micro-alloy non-tempered steel and a process for preparing the non-tempered steel, and particularly relates to calcium processed vanadium-nitrogenium-titanium micro-alloyed non-tempered steel and a process of preparing the calcium processed vanadium-nitrogenium-titanium micro-alloying non-tempered steel. The present invention solves the defect that the hardness and the structural homogenity of the inner part of the existing vanadium micro-alloyed non-tempered steel with the large cross section, and has the technical proposals that the calcium processed vanadium-nitrogenium-titanium micro-alloyed non-tempered steel is composed of Fe, C, Mn, Si, V, Cr, N, S, Ti and Ca, wherein all the elements have the weight proportion of 0.25% to 0.40% of the C, 1.0% to 70% of the Mn, 0.30% to 0.70% of the Si, 0.05% to 0.20% of the V, 0.30% to 2.0% of the Cr, 0.005% to 0.0250% of the Ti, 0.0080% to 0.02% of the N, 0.005% to 0.025% of the S, 0.0005% to 0.0050% of the Ca, and the rest percentage of impurities. The present invention has the preparing process that according to the design scheme of the alloy, the steel has the soaking temperature from 1130 to 1280 DEG C, the rolling temperature from 1150 to 1200 DEG C and the finishing temperature from 950 to 1050 DEG C; after hot processed, the steel is firstly cooled to 500 DEG C in the air, and then is cooled in heap. The present invention is mainly used for manufacturing plastic moulds and mould frames with high resistance of atmospheric corrosion, good quality of cutting and machining, and higher hardness from 220 to 280 VHN.

Description

A kind of calcium is handled vanadium-nitrogen-titanium micro-alloyedization non-hardened and tempered steel and preparation technology thereof

Technical field: the present invention relates to a kind of middle carbon microalloy pearlitic steel and preparation technology thereof, particularly a kind of calcium is handled vanadium-nitrogen-titanium micro-alloyedization non-hardened and tempered steel and preparation technology thereof.

Background technology: along with the high speed development of industry such as household electrical appliances, communication, automobile and instrument, surface of plastic products smooth finish requires more and more higher, and correspondingly mold cavity surface finish performance requriements is more and more higher.This just requires the corresponding raising of material hardness as mold cavity, because hardness is high more, polishing performance is good more.Meanwhile and the hardness of the mould bases that matches of die cavity also to improve, to improve wear resistance.For a long time, all use both at home and abroad and roll attitude or normalizing medium carbon steel S50C ~ S55C makes mould bases.It uses hardness to be VHN160 ~ 200, and tensile strength is 610 ~ 700MPa.Its advantage is that cost is low, and machining is easy.Shortcoming is that hardness is on the low side, wears no resistance, and the soldering poor performance, resistance to atmospheric corrosion is poor, can not satisfy the needs of growing mould industry.In order to improve the hardness of mould bases, the user often need carry out modifier treatment to S50C ~ S55C, makes hardness bring up to VHN230 ~ 280.But because the hardening capacity of such steel is poor, can't make the above large section module heart portion through hardening of thick 100mm, thereby can't guarantee that heart portion obtains the above hardness of VHN230.Simultaneously, the thermal treatment meeting increases distortion and tearing tendency, and makes at least 500 yuan of manufacturing cost increases per ton.In addition, this class medium carbon steel produces more serious carbon segregation because carbon content about 0.50%, is smelted casting cycle, makes the heart portion hard spot occur, has a strong impact on machinability.The vanadium micro-alloying non-hardened and tempered steel begins to have obtained increasing application from the seventies in last century in fields such as automobile, but is mainly used in structural part, is used for replacing quenched and tempered steel such as S45C and 40Cr.Usually in steel, add 0.05 ~ 0.20% vanadium, and be aided with the nitrogen microalloying, can make steel after hot-work, produce V (C, N) precipitated phase, thereby the intensity of raising steel in the process air cooler.Japan openly speciallys permit communique in the special permission Room, and clear and 59-136420 has reported and has been used for the cold worked non-hardened and tempered steel of bolt: 0.35 ~ 0.50%C, 0.15 ~ 0.35%Si, 0.50 ~ 1.50%Mn, 0.05 ~ 0.20%V, 0.006 ~ 0.02%N.Cooling rate at 500 ~ 700 ℃ after the requirement hot-work is that 10 ~ 100 ℃/min could guarantee hardness VHN200 ~ 260, and further the hardness after the cold working is VHN220 ~ 280.The lower limit of this cooling rate is equivalent to thick 35mm steel slab surface air cooling speed, but slab heart portion cooling rate when being higher than air cooling.This patent only is suitable for making thickness, perhaps the following part of diameter 35mm.

JP78091/93 has reported the non-hardened and tempered steel that is used for auto parts: 0.15 ~ 0.40%C, 0.90 ~ 1.30%Si, 1.2 ~ 3.0%Mn, 0.10 ~ 0.50%Cr, 0.03 ~ 0.10%S, 0.05 ~ 0.50%V, 0.008 ~ 0.02%N.Like this high silicon and manganese content is in order to obtain bainite+residual austenite tissue, to have the intensive work hardening capacity, and machinability is poor.This steel requires 250 ~ 650 ℃ of timeliness after hot-work, so that residual austenite changes, and eliminate stress.Added 0.03 ~ 0.10%S, to improve machinability.So high sulphur content can cause center segregation, influences the tissue and the uniformity of hardness distribution of steel, therefore is not suitable for making large section slab, particularly mould of plastics slab.

Summary of the invention: the technical issues that need to address of the present invention are: improve the hardness of die steel and keep good machinability simultaneously, improve its section structure uniform distribution, improve its welding property, improve its erosion resistance.For solving the problems of the technologies described above, invention thinking of the present invention provides a kind of calcium and handles vanadium-nitrogen-titanium micro-alloyedization non-hardened and tempered steel, the present invention intends adopting the matching Design of alloying elements such as carbon, manganese, silicon, chromium, vanadium and nitrogen, and implement calcium and handle, controlled chilling obtains essential tissue and hardness after hot-work.The general objects that calcium is handled is in order to control inclusion morphology and composition, to improve toughness and machinability.In steel of the present invention, calcium is handled special effect.Plate slab of the present invention is organized as ferrite+perlite after hot-work, ferrite can also improve machinability except improving toughness.

Technical solution of the present invention is: a kind of calcium is handled vanadium-nitrogen-titanium micro-alloyedization non-hardened and tempered steel, and its elementary composition Fe, C, Mn, Si, V, Cr, N, S, Ti of comprising is characterized in that component also includes micro-Ca, and the weight proportion of each element is:

C：0.25~0.40％

Mn：1.0~1.70％

Si：0.30~0.70％

V：0.05~0.20％

Cr：0.30～2.0％

Ti：0.005~0.0250％

N：0.0080~0.02％

S：0.005~0.025％

Ca：0.0005~0.0050％

All the other are iron and unavoidable impurities

A kind of calcium is handled vanadium-nitrogen-titanium micro-alloyedization non-hardened and tempered steel preparation technology: according to above-mentioned alloy designs scheme, and 1220 ~ 1280 ℃ of the soaking temperatures of steel, 1150～1200 ℃ of open rollings, 950 ~ 1050 ℃ of finishing temperatures.Steel first air cooling to 500 ℃ after hot-work, cooling in heap then.Promptly can obtain equally distributed ferrite+pearlitic structure and hardness VHN220 ~ 280 along the cross section.

The invention has the beneficial effects as follows: because the above slab heart of thick 100mm portion exists inevitable carbon, manganese segregation, the ability specific surface that obtains ferritic structure is low, causes heart portion to occur full perlite sometimes, and is unfavorable to uniformity of hardness distribution and machinability.This patent finds that calcic sulfide can be induced ferrite transformation.And often there is more sulfide in heart portion, and is more obvious to the inducing action of ferrite transformation.Therefore, implementing under the calcium disposition, can make heavy slab heart portion still obtain the part ferritic structure, thereby improve the homogeneity of hardness and tissue distribution and the machinability of steel.

Below be the design of alloy and the heat processing technique explanation of relevant steel of the present invention:

C:0.25 ~ 0.40% is to guarantee to obtain more than the hardness VHN230, and is organized as ferrite+pearlitic important element.Too low, proeutectoid ferrite is too many, can not guarantee required hardness.Too high, owing to, can cause finished product slab center segregation, can't form ferrite+pearlitic structure, and form troostitic structures smelting the segregation that casting cycle produces, reduce the machinability and the toughness of steel.

Mn:1.0 ~ 1.70% is to guarantee to obtain to obtain the important element of ferrite+pearlitic structure simultaneously more than the hardness VHN230.Too low, can't guarantee above-mentioned hardness.Too high, owing to, make the slab center can't obtain pearlitic structure, and obtain troostitic structures, reduce the machinability and the toughness of steel smelting and casting cycle generation segregation.

Si:0.30 ~ 0.70% is effectively to improve the ferrite mark, can improve the element of hardness again.Owing to promote ferrite to form, Si can active balance since the ferrite fractional that the adding of chromium and manganese causes reduce.And suitable fractional ferrite helps to improve machinability.

V：0.05~0.20％。Match with 0.008 ~ 0.0250%N, forging/rolling the back by V and from ferrite, separating out carbonitride, to improve the hardness and the intensity of steel.

Cr：0.30～2.0％。Add chromium, can improve the hardness and the intensity of steel on the one hand, can improve the corrosion resistance nature of steel on the other hand.

Ti：0.005~0.0250％。Little titanium is handled and is stoped growing up of crystal grain that obvious help is arranged in heat-processed for non-hardened and tempered steel.But its content can not be too high, and not so the TiN particle is thick, not only can not stop grain growth, and can damage the machinability of steel.

N：0.0080~0.02％％。Nitrogen can same vanadium, carbon forms the carbon vanadium nitride together, separates out in rolling the postcooling process, improves the hardness and the intensity of steel.Too high nitrogen then damages the toughness of steel.

S：0.005~0.025％。Certain sulphur content can be improved machinability.In addition, sulfide, particularly calcium are handled sulfide can become the ferrite forming core in steel heterogeneous body core.Sulphur content is too high, then aggravates the segregation of steel.

Ca：0.0005~0.0050％。The purpose that calcium is handled is in order to control oxide morphology, to reduce segregation, improving toughness and machinability on the one hand.Be to obtain calcareous sulfide on the other hand, induce ferrite transformation, thereby further improve machinability and Hardness Distribution.

Table 1 has contrasted the Japanese special permission Room and has openly speciallyyed permit communique, the chemical ingredients and the Application Areas of clear and 59-136420 patent [1], JP78091/93 patent (2) and steel of the present invention.

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Same patent [1,2] is compared, and the most important discovery of present patent application is to have implemented the calcium processing.Calcium is handled and made the sulfide sex change is the spindle shape, and calcic spindle shape sulfide can become the heterogeneous body core of ferrite transformation, induce heavy slab heart portion under element segregation situations such as carbon and manganese, still obtain ferritic structure, thereby improve the homogeneity and the machinability of hardness and tissue distribution.This is most important for the plastic die steel of heavy slab.On the contrary, the sulfide of not handling through calcium does not have this effect.In addition, present patent application also has difference aspect following.

Same patent [1] compares, and the silicone content of steel of the present invention is higher, helps promoting the formation of heart portion ferritic structure.Simultaneously steel of the present invention has carried out little titanium and has handled, and helps controlling growing up of austenite crystal in the equal thermal process.Fig. 6 shows steel 0.30%C of the present invention, 0.50%Si, 1.40%Mn, 0.017%P, 0.012%S, 0.38%Cr, 0.013%N, 0.020%Al, 0.010%Ti, the austenite Continuous Cooling Transformation Curve of 0.0025%Ca under thermal process status. as can be seen, in 0.05 ~ 0.5 ℃/s of cooling rate scope, the ferrite-pearlite phase transformation all takes place in steel of the present invention, and hardness is subjected to the influence of rate of cooling less, for about VHN250.Mandatory declaration be, in the actual industrial production, thick 35 ~ 500mm steel slab surface to heart portion in the rate of cooling under the air cooling condition entirely in this scope.This explanation, present patent application can be made thick 35 ~ 500mm slab, and formerly air cooling obtains VHN220 ~ 280 hardness under the back cooling in heap condition, and tissue and thermal stresses are little, thereby satisfy the demand of high-grade mould bases with plastic die steel.And design according to the composition of patent [1], under the air cooling condition, can't guarantee that the above slab heart of thick 35mm portion obtains the above hardness of VHN220.As use air-cooledly, and obtaining desired cooling rate, the difference of hardness that then causes surface and heart portion simultaneously, increases cooling stress apart from increasing, can cause heavy slab to occur being out of shape in the following process process, even ftracture.Same patent [2] is compared, and the silicone content of steel of the present invention is low, and is organized as ferrite+perlite, and hardness is also lower simultaneously.

And patent [2] relies on high silicon and manganese content to obtain bainite+residual austenite tissue.Another difference is that the sulphur content of steel of the present invention is 0.005 ~ 0.025%, 0.03 ~ 0.10% low than patent [2] report.Too high sulphur content is difficult to guarantee that the sulfide sex change becomes the spindle shape, thereby has lost the promoter action to ferrite transformation.

Description of drawings:

Fig. 1 is the aspect hardness distribution of 1# steel of the present invention

Fig. 2 is the aspect hardness distribution of 2# steel of the present invention

Fig. 3 is the aspect hardness distribution of S48C steel grade

Fig. 4 is 2# steel metallographic structure figure of the present invention, * 100

Fig. 5 is S48C steel grade metallographic structure figure, * 100

Fig. 6 is the 1# steel core metallographic structure figure of portion of the present invention, * 400

The wear of the tool flank spirogram of Fig. 7 milling steel of the present invention and S48C steel

Changes in hardness figure when Fig. 8 soldering steel of the present invention and S48C steel from the parent to the weld seam

Embodiment: according to above-mentioned alloy designs thinking, smelt and forged 8 stove steel in testing laboratory, be cast into the 100kg steel ingot, its chemical ingredients is as shown in table 2.80 * 150mm sample is processed in the steel ingot forging, and 1200～1250 ℃ of Heating temperatures are opened and are forged 1150 ℃ of temperature, and 950 ℃ of final forging temperatures are carried out air cooling and sand cooling respectively to room temperature after the forging.At 1/4 diagonal lines position intercepting metallographic sample, carry out measurement of hardness, the result is as shown in table 2.Why dividing air cooling and sand cooling, mainly is to investigate the susceptibility of the hardness of designed steel to rate of cooling.

The chemical ingredients that table 2 testing laboratory smelts, wt%

Heat	C	Si	Mn	P	S	V	N	Ti	Cr	Ca，pp m	The VHN air cooling	The VHN sand cooling
													1	0.36	0.46	1.50	0.013	0.021	0.11	0.016	0.020	0.30	35	245	230
2	0.32	0.40	1.58	0.014	0.020	0.10	0.020	0.015	0.35		235	230
													3	0.33	0.48	1.51	0.013	0.011	0.10	0.006	0.018	0.32	20	230	220
4	0.32	0.56	1.46	0.015	0.012	0.10	0.020	0.025	0.36		235	220
													5	0.34	0.45	1.25	0.015	0.012	0.12	0.015	0.016	1.20		260	245
6	0.36	0.50	1.35	0.016	0.008	0.14	0.012	0.010	1.30		275	258
													7	0.38	0.55	1.20	0.015	0.013	0.16	0.009	0.012	1.60	35	280	265
8	0.34	0.57	1.25	0.016	0.011	0.14	0.013	0.010	1.40		265	250

As can be seen from Table 2,1～No. 4 steel of design, its chromium content is 0.30～0.40%, and hardness is VHN220 ~ 245,5 ~ No. 8 steel, and its chromium content is 1.20～1.60%, and hardness is VHN245 ~ 280.In addition, air cooling is general more higher only about 10VHN than sand cooling hardness, and gap is little, illustrates that the design steel is insensitive to rate of cooling.The slab that this indication designs with these compositions, hardness is along the good uniformity of cross-sectional distribution.Their microstructure is ferrite+perlite, and wherein 1～No. 4 steel ferrite umber is 30 ~ 50%, and 5 ~ No. 8 steel are 20 ~ 40%.Ca handles, and can increase ferrite content.

According to mentioned component principle of design and testing laboratory's port steel-making work, carried out the industrialness production test, slab thickness 230mm, its chemical ingredients is as shown in table 3.Heat processing technique is: 1200 ~ 1280 ℃ of soaking, and 1150～1200 ℃ of open rollings, ℃ again cooling in heap of back air cooling to 500 is rolled in 950 ~ 1050 ℃ of finish to gauges.Analyzed the Hardness Distribution of slab 1/2 width-1/2 thick section, and contrasted, as Fig. 1, Fig. 2, shown in Figure 3 with the thick S48C that rolls attitude delivery of 150mm.

The chemical ingredients of the steel of the present invention of table 3 industrial production test, wt%

Grade of steel	C	Si	Mn	P	S	V	N	Al	Ti	Cr	Ca，ppm
												1	0.340	0.515	1.25	0.015	0.0082	0.145	0.0122	0.018	0.010	1.45	30
2	0.320	0.506	1.45	0.015	0.0120	0.120	0.0115	0.015	0.011	0.33	25

The hardness at all test positions of steel of the present invention all is higher than VHN220, and wherein 1# invention steel hardness is higher, all more than VHN240, more than the high 70VHN of average specific S48C steel.In addition, steel uniformity of hardness distribution of the present invention is better than S48C steel.Fabric analysis shows that whole section structure is ferrite+perlite, and the tissue of steel of the present invention is carefully more much smaller than S48C steel, and ferrite mark more (referring to Fig. 4, Fig. 5).This grain refining of handling with little titanium and calcic sulfide are to the promoter action of ferrite transformation relevant (Fig. 6).Fig. 6 clearly illustrates that calcium promotes the sulfide nodularization, and the sulfide after the nodularization can become the core of ferrite forming core, induces ferrite transformation.This is especially significant for the plastic die steel extra-thick plate blank.Because the heavy slab center is easy to generate segregations such as carbon, manganese, be unfavorable for obtaining ferritic structure, the appearance of calcium sex change sulfide makes heart portion under the segregation situation, still ferritic structure be can obtain, thereby tissue and uniformity of hardness distribution and machinability improved.

The tissue of 2# invention steel is similar with the 1# steel, and only the ferrite mark many about 10～20%.

Carried out the Milling Process test, with the machinability of invention steel 1# and compared steel S48C relatively.The hardness of two kinds of test steel is respectively VHN250 and VHN195.Used milling cutter is the M2 rapid steel, diameter 16mm.Cutting parameter is: depth of cut 3mm, depth of cut 0.067mm/rev, cutting speed 37.5m/min.Measure the wear of the tool flank in the working angles, as the index of estimating cutting ability.Wear of the tool flank is big more, and processing characteristics is poor more.From test-results (Fig. 7), the wear of the tool flank amount of milling steel 1# of the present invention and S48C steel is suitable, shows that both cutting abilities are approaching.

Although steel of the present invention is than the hardness height of S48C steel, the former ferrite umber is more, and crystal grain is thinner, therefore helps improving processing characteristics.In addition, the sulphur content that suitably improves also helps machinability.In use or assembling process, mould bases can wear and tear, and perhaps damages.At this moment just need carry out soldering to mould bases.During soldering, the hardness of weld mould bases unavoidably can improve.For the user, what be concerned about most in the soldering performance is the rising situation of hardness after the soldering.Wish that this hardness does not improve too much, come inconvenience not so can for follow-up grinding and other processing belt.The soldering performance can be represented to the changes in hardness situation of weld seam with parent after the soldering.Use the J707Ni welding rod at room temperature to carry out the soldering test.The test steel is steel of the present invention and S48C, and their hardness is respectively VHN250 and VHN195, is of a size of 40 * 150 * 200mm.

During welding, neither carry out preheating, also do not carry out postweld heat treatment.Parent is to the changes in hardness of weld seam, as shown in Figure 8 after the measurement soldering.As seen, during soldering S48C, the raising degree of its hardness is obviously than soldering steel height of the present invention.The maximum hardness of the former weld seam after soldering is HRC62, and the latter only is HRC48.In addition, the former hardened layer of soldering is darker than the soldering latter.This result shows that the soldering performance of steel of the present invention is better than S48C.

In sum, compare with existing medium carbon steel, make the mould bases of mould of plastics with steel of the present invention, make the hardness of mould bases bring up to VHN220～280 from VHN160 ~ 200, its wearability is improved, and in addition soldering performance and atmospheric corrosion resistance also improve. Machinability is kept similar level simultaneously.

Claims (2)

1, a kind of calcium is handled vanadium-nitrogen-titanium micro-alloyedization non-hardened and tempered steel, and its elementary composition Fe, C, Mn, Si, V, Cr, N, S, Ti of comprising is characterized in that component also includes micro-Ca, and the weight proportion of each element is:

C：0.25~0.40％

Mn：1.0~1.70％

Si：0.30~0.70％

V：0.05~0.20％

Cr：0.30～2.0％

Ti：0.005~0.0250％

N：0.0080~0.02％

S：0.005~0.025％

Ca：0.0005~0.0050％

All the other are iron and unavoidable impurities.

2, the described calcium of a kind of claim 1 is handled the preparation technology of vanadium-nitrogen-titanium micro-alloyedization non-hardened and tempered steel, it is characterized in that: 1220 ~ 1280 ℃ of the soaking temperatures of steel, in 1150～1200 ℃ of open rollings, 950 ~ 1050 ℃ of finishing temperatures, steel first air cooling to 500 ℃ after hot-work, cooling in heap then.

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