CN102367538A - Super-thick low alloy high strength Q345C steel plate and production method thereof - Google Patents

Abstract

The invention discloses a super-thick low alloy high strength Q345C steel plate which comprises the following chemical components by mass (unit: wt %): C 0.08 to 0.18, Si 0.20 to 0.40, Mn 1.15 to 1. 50, P <=0.018, S <=0.005, micro-alloying elements of (Nb+Ni+Cr) <=0.020 and Als <= 0.040, with the rest being Fe and residual elements. Carbon equivalent satisfies the following equation: [Ceq=C+Mn/5+(Cr+Mo+V)/5+(Ni+Cu)/15]<=0.43. According to the invention, total grade level of a variety of impurities is enabled not to exceed 2.5 by carrying out a series of processes of converter smelting, LF refining, vacuum refining, casting, heating, rolling, controlled cooling, slow cooling and heat treatment, designing the chemical composition of multielement composite micro-alloy elements and guaranteeing the cleanliness of steel by using the technology of LF+VD, and the grain size of steel is enabled to reach grade 8.0-10.0 through the processing of controlled rolling, controlled cooling and normalization; effective implementation of above-mentioned measures enables the super-thick low alloy high strength Q345C steel plate to be successfully manufactured.

Description

A kind of special thick low-alloy high-strength Q 345 C steel plate and working method thereof

 

Technical field

The invention belongs to the steel plate production technical field, be specifically related to a kind of special thick low-alloy high-strength Q 345 C steel plate and working method thereof.

Background technology

The Q345C steel is a kind of special thick low-alloy high-strength steel plate, and it has higher intensity, good cold deformation ability, and plasticity and low-temperature impact resistance ability are widely used in daily production field preferably, and domestic had a large amount of research to this.But about the guaranteed cost of thickness more than 180mm, protect that flaw detection Q345C steel plate is big with its production difficulty, tooling requires reason such as special to produce, the producer of present domestic this steel plate of stably manufactured is less.

Summary of the invention

The objective of the invention is to avoid above-mentioned weak point of the prior art, and provide a kind of thickness more than 180mm, the special thick low-alloy high-strength Q 345 C steel plate and the working method thereof of guaranteed cost, guarantor flaw detection.

Realize that the technical scheme that the object of the invention adopted is: a kind of special thick low-alloy high-strength Q 345 C steel plate; Comprise following chemical components in mass percent (unit; Wt%): C:0.08～0.18, Si:0.20～0.40, Mn:1.15～1.50, P :≤0.018, S :≤0.005, micro alloying element (Nb+Ni+Cr) :≤0.20, Als :≤0.040, other is Fe and relict element.

Carbon equivalent≤0.43 of said special thick low-alloy high-strength Q 345 C steel plate.

The function analysis of above-mentioned chemical element is following:

C: be most basic strengthening element in the steel, improve intensity, but C influences the welding property of steel and influences toughness.Take all factors into consideration, the content of carbon is hanging down of control as far as possible.

Si: be the solution strengthening element, favourable to the intensity that improves steel plate.

Mn: be the solution strengthening element, all favourable to intensity and the toughness that improves steel plate.

P: unfavorable to welding, and have certain cold shortness, and in this steel grade, belong to harmful element, that should control is low as far as possible.

S: be prone to form the MnS type impurity, have certain red brittleness, in this steel grade, belong to harmful element, that should control is low as far as possible.

Nb: in steel, can combine, form fine carbide or carbonitride, can play crystal grain thinning and dispersion-strengthened action, thereby reach the net effect of the obdurability of effective raising steel with C, N.

Ni: an amount of adding can effectively improve the low-temperature impact toughness of steel plate.

Al: can play the crystal grain thinning strengthening effect.

Cr: can form fine and close sull on the steel surface, improve the passivation ability of steel; Can improve simultaneously the hardening capacity of steel.

Said special thick low-alloy high-strength Q 345 C steel plate thickness is more than 180mm.

The working method of said special thick low-alloy high-strength Q 345 C steel plate comprises following production stage:

Converter smelting: tapping carbon>=0.05%, tapping P≤0.012%, S≤0.005%, point blows number of times and must not avoid slag under the tapping process greater than 2 times;

LF refining: guarantee that the white slag hold-time is controlled at more than the 13min;

Vacuum refinement: the dwell time under≤67Pa is controlled by>=18min;

Cast: adopt the casting of water cooled mo(u)ld ingot casting, before the casting, the soft blow argon time must guarantee >=5min, closes then to open behind the calm 5min of argon gas and waters, and pouring temperature is controlled according to 1550～1575 ℃, goes into the burial pit slow cooling after the steel ingot demoulding 24 hours;

Heating: the holding temperature of dead soaking pit is controlled at 1200 ℃～1300 ℃;

Rolling: adopt the controlled rolling mode rolling, 1050 ℃～1200 ℃ of start rolling temperatures, a stage finishing temperature is at 950 ℃～1000 ℃; The two-stage start rolling temperature is at≤880 ℃, 1.5 times of the steel thickness of drying in the air, and the two-stage takes to depress for a short time rolling; Finish rolling accumulative total draft＞45%, finishing temperature≤860 ℃;

Control cold: return red temperature＜760 ℃, cooling several times, cooling rate is controlled at 3～10 ℃/s;

Slow cooling: go into burial pit temperature >=350 ℃, cooling in heap time >=24 hour;

Thermal treatment: adopt normalizing+water-cooling process, 910～940 ℃ of normalizing temperatures, soaking time 1.8～2.4min/cm, water-cooled time 5S～70S.

Since the present invention through converter smelting, LF refining, vacuum refinement, cast, heating, rolling, control is cold, slow cooling, thermal treatment series of process; And the chemical composition design through polynary composite micro-alloyed element; LF+VD technology guarantees the cleanliness factor of steel; Reach each type impurity rank summation and be no more than 2.5; Make the grain fineness number of steel reach 8.0～10.0 grades through controlled rolling and controlled cooling+normalizing treatment,, successfully produced special thick low-alloy high-strength Q 345 C steel plate through the above-mentioned effective enforcement that waits measure.Hot metal pretreatment is arrived steel plate thermal treatment whole process of production; Worked out strict process point control standard, and strict the execution, the quality in kind of product has reached the GB requirement of Q345C fully; And the performance surplus capacity is bigger; Wherein surrender surplus capacity at 20～60Mpa, the tension surplus capacity is at 30～80Mpa, and the elongation surplus capacity is 3～9%.The steel plate guaranteed cost that the present invention produces, guarantor's flaw detection, the steel plate of producing is satisfied with practical application.

Description of drawings

Below in conjunction with accompanying drawing, the present invention is done further elaboration.

Fig. 1 is a process flow sheet of the present invention.

Fig. 2 is the metallographic structure figure (100X) of TMCP of the present invention after rolling.

Fig. 3 is the metallographic structure figure (100X) after the thermal treatment of the present invention.

Embodiment

Thickness of the present invention more than 180mm, the special thick low-alloy high-strength Q 345 C steel plate of guaranteed cost, guarantor flaw detection comprises following chemical components in mass percent (unit; Wt%): C:0.08～0.18, Si:0.20～0.40, Mn:1.15～1.50, P :≤0.018, S :≤0.005, micro alloying element (Nb+Ni+Cr) :≤0.20, Als :≤0.040, other is Fe and relict element.

Carbon equivalent [Ceq=C+Mn/5+ (Cr+Mo+V)/5+ (Ni+Cu)/15] :≤0.43.

The working method that the present invention takes comprises: converter smelting, LF refining, vacuum refinement, cast, heating, rolling, control is cold, slow cooling, thermal treatment; In said converter smelting; Tapping carbon>=0.05%, tapping P≤0.012%, S≤0.005%; Point blows number of times and must not avoid slag under the tapping process greater than 2 times; In said LF refining: take the big quantity of slag to carry out slag making, guarantee that the white slag hold-time is controlled at more than the 13min; In said vacuum refinement: the dwell time under≤67Pa is controlled by>=18min; In said cast: adopt the casting of water cooled mo(u)ld ingot casting; Before the casting; The soft blow argon time must guarantee>=5min, after Argon to temperature meets teeming temperature and requires, closes to open behind the calm 5min of argon gas and waters; Pouring temperature is controlled according to 1550～1575 ℃, goes into the burial pit slow cooling after the steel ingot demoulding 24 hours; Pine in said adding: the holding temperature of dead soaking pit is controlled at 1200 ℃～1300 ℃; Said rolling in: adopt the controlled rolling mode rolling; 1050 ℃～1200 ℃ of start rolling temperatures, a stage finishing temperature is at 950 ℃～1000 ℃, and the two-stage start rolling temperature is at≤880 ℃; 1.5 times of steel thickness dry in the air; Two-stage takes to depress for a short time rolling, finish rolling accumulative total draft＞45%, finishing temperature≤860 ℃; In said control is cold: return red temperature＜760 ℃, cooling several times, cooling rate is controlled at 3～10 ℃/s; In said slow cooling: go into burial pit temperature>=350 ℃, cooling in heap time>=24 hour; In said thermal treatment: adopt normalizing+water-cooling process, 910～940 ℃ of normalizing temperatures, soaking time 1.8～2.4min/cm, water-cooled time 5S～70S.

Embodiment 1

Through converter smelting, LF refining, vacuum refinement, cast, heating, rolling, control is cold, slow cooling, thermal treatment process; Acquisition is described in table 1 below the special thick low-alloy high-strength Q 345 C steel plate Finished Steel of chemical ingredients, and wherein each processing parameter and mechanical property are seen like following table 4,5.

The chemical ingredients of table 1 embodiment 1 steel

C(%)	Si(%)	Mn(%)	P(%)	S(%)	Nb+Ni+Cr(%)	AlS(%)
							0.158	0.30	1.41	0.013	0.003	≤0.20	0.035

Embodiment 2

Through converter smelting, LF refining, vacuum refinement, cast, heating, rolling, control is cold, slow cooling, thermal treatment process; Acquisition is described in table 2 below the special thick low-alloy high-strength Q 345 C steel plate Finished Steel of chemical ingredients, and wherein each processing parameter and mechanical property are seen like following table 4,5.

The chemical ingredients of table 2 embodiment 2 steel

C(%)	Si(%)	Mn(%)	P(%)	S(%)	Nb+Ni+Cr(%)	AlS(%)
							0.160	0.36	1.45	0.013	0.004	≤0.20	0.034

Embodiment 3

Through converter smelting, LF refining, vacuum refinement, cast, heating, rolling, control is cold, slow cooling, thermal treatment process; Acquisition is described in table 3 below the special thick low-alloy high-strength Q 345 C steel plate Finished Steel of chemical ingredients, and wherein each processing parameter and mechanical property are seen like following table 4,5.

The chemical ingredients of table 3 embodiment 3 steel

C(%)	Si(%)	Mn(%)	P(%)	S(%)	Nb+Ni+Cr(%)	AlS(%)
							0.165	0.40	1.39	0.014	0.002	≤0.20	0.040

Operational path of the present invention: slow cooling → surface inspection → thermal treatment → finishing → flaw detection → detection → judgement → salable product warehouse-in is aligned → is rolled off the production line in the dark desulfurization → converter smelting of molten iron KR → LF refining → VD vacuum-treat → ingot casting cast → ingot slow cool → heating → dephosphorization → controlled rolling → controlled chilling → control.

The steel-making composition: because this steel plate thickness is thicker, protecting flaw detection and protecting mechanical property is difficult point and emphasis, in the composition design, must take all factors into consideration, and could effectively reach both unifications.Consider that steel ingot is thicker, setting time is long, inner segregation and loose serious characteristics; So for protecting flaw detection, in conjunction with practical experience, the segregation of carbon manganese is bigger to the flaw detection influence; Therefore take Di Tan ﹑ hang down the manganese route, but carbon manganese crosses and hangs down greatlyyer influence, especially align the steel plate of burning hot processing.Take all factors into consideration above factor, take the route of multicomponent microalloying composition design, remedy jointly, take into account reunification thereby effectively solve both in conjunction with follow-up thermal treatment process.For guaranteeing flaw detection and performance, the link of making steel is simultaneously taked the Clean Steel smelting technology, the steel grade of keeping under strict control [P], [S], [N], [H], [O] five big harmful constituent contents.

Ingot shape is selected: strict to performance index simultaneously owing to protect three grades of flaw detections, in conjunction with practical experience in the past, compression ratio at least >=6.Therefore preferred 48T water-cooled die casting steel ingot, this steel ingot mean thickness 930mm, average compression ratio 5.16 can reach design requirements.

Converter smelting: tapping carbon>=0.05%, tapping P≤0.012%, S≤0.005%, point blows number of times and must not avoid slag under the tapping process greater than 2 times.

LF refining: take the big quantity of slag to carry out slag making, guarantee that the white slag hold-time is controlled at more than the 13min;

Vacuum refinement: the dwell time under≤67Pa is controlled by>=18min.

Cast: adopt the casting of water cooled mo(u)ld ingot casting, before the casting, the soft blow argon time must guarantee >=5min; After Argon to temperature meets the teeming temperature requirement; Close to open behind the calm 5min of argon gas and water, pouring temperature is controlled according to 1550～1575 ℃, goes into the burial pit slow cooling after the steel ingot demoulding 24 hours; Strict with the Q345C slab steel ingot pouring technology control of setting, adhere to " high temperature is annotated slowly, and low temperature is annotated soon " principle.Concrete pouring technology will be asked for an interview to table 4.

Table 4 die casting casting process

Annotate: T _LlRepresent liquidus temperature, motor-car, raising one's hat and taking off the ingot time begins to calculate from having annotated.

Heating: the holding temperature of dead soaking pit is controlled at 1200 ℃～1300 ℃.

Rolling: adopt the controlled rolling mode rolling, 1050 ℃～1200 ℃ of start rolling temperatures, a stage finishing temperature is at 950 ℃～1000 ℃; The two-stage start rolling temperature is at≤880 ℃, 1.5 times of the steel thickness of drying in the air, and the two-stage takes to depress for a short time rolling; Finish rolling accumulative total draft＞45%, finishing temperature≤860 ℃.

Control cold: return red temperature＜760 ℃, cooling several times, cooling rate is controlled at 3～10 ℃/s.

Slow cooling: go into burial pit temperature >=350 ℃, cooling in heap time >=24 hour.

Thermal treatment: adopt normalizing+water-cooling process, 910～940 ℃ of normalizing temperatures, soaking time 1.8～2.4min/cm, water-cooled time 5S～70S is qualified to guarantee performance.

Chemical Composition :C adopts lower limit control as one of strengthening element in composition design internal control scope, when avoiding carbon segregation influence flaw detection, can not cause deterioration to welding property; Mn is one of crystal grain thinning element, in order to improve intensity, reduces the steel brittle transition temperature, improves low-temperature impact toughness, but during the Mn too high levels, unfavorable to toughness and welding property, and cause the Mn segregation easily, flaw detection there is certain influence.So Mn content is controlled at about 1.15%～1.50%.The Nb element has significant crystal grain thinning effect, and the over-all properties of improving steel is apparent in view, but Nb content is when high, and cost is bigger, but singlely adds fashionablely, and the multiple strengthening effect is also not obvious.Consider that this steel plate is thicker, add an amount of alloying elements such as Ni and be used to guarantee low-temperature impact work, so the compound adding of Nb ﹑ Ni is optimal selection.P, S content are controlled in the lower scope, and in a word, whole Composition Control is more stable, satisfy the composition design requirements of Q345C ultra-thick plate.

Composition and mechanical mechanics property are pressed GB/T 1591 and are carried out, and specifically see table 5.

Table 5 Q345C steel plate mechanical mechanics property

This produces 15 batches of the thick Q345C steel plates of 180mm altogether as a trial, and wherein: ys is controlled at 290～346 MPa, has on average reached 310MPa; Than the rich 35Mpa of standard, tensile strength is controlled at 486～565MPa, has on average reached 526MPa; Than the rich 76Mpa of standard; Elongation is controlled at 20%～27%, on average reaches 24%, than standard rich 6%; 0 ℃ of V-type ballistic work is controlled at 150～180J, has on average reached 168J, and performance index have satisfied the Q345C development requires fully.

Outer inspection and flaw detection: the thick Q345C steel plate of the 180mm of production is examined the percentage of A-class goods 100% outward, detects a flaw by JB/T 2970-2004, and closing the secondary rate is 100%, has reached desired result.

Metallographic examination: 1/4 place has done the metallographic structure check respectively to the product thickness after controlled rolling and the normalizing, and the result sees Fig. 2, Fig. 3.

Metallographic structure after the control bundle of table 6 product and the normalizing

Associative list 6 and Fig. 2, Fig. 3 analysis, the steel plate after the controlled rolling is organized as ferritic and perlite, and grain fineness number reaches 8～9 grades.After the normalizing treatment, ferritic and pearlitic structure in the steel plate are more even, and grain refining reaches 8～10 grades.

Claims (4)

1. special thick low-alloy high-strength Q 345 C steel plate; It is characterized in that: comprise following chemical components in mass percent (unit; Wt%): C:0.08～0.18, Si:0.20～0.40, Mn:1.15～1.50, P :≤0.018, S :≤0.005, micro alloying element (Nb+Ni+Cr) :≤0.20, Als :≤0.040, other is Fe and relict element.

2. special thick low-alloy high-strength Q 345 C steel plate as claimed in claim 1 is characterized in that: carbon equivalent≤0.43 of said special thick low-alloy high-strength Q 345 C steel plate.

3. special thick low-alloy high-strength Q 345 C steel plate as claimed in claim 1 is characterized in that: said special thick low-alloy high-strength Q 345 C steel plate thickness is more than 180mm.

4. the working method of special thick low-alloy high-strength Q 345 C steel plate as claimed in claim 1 is characterized in that: comprise following production stage:

Converter smelting: tapping carbon>=0.05%, tapping P≤0.012%, S≤0.005%, point blows number of times and must not avoid slag under the tapping process greater than 2 times;

LF refining: guarantee that the white slag hold-time is controlled at more than the 13min;

Vacuum refinement: the dwell time under≤67Pa is controlled by>=18min;

Cast: adopt the casting of water cooled mo(u)ld ingot casting, before the casting, the soft blow argon time must guarantee >=5min, closes then to open behind the calm 5min of argon gas and waters, and pouring temperature is controlled according to 1550～1575 ℃, goes into the burial pit slow cooling after the steel ingot demoulding 24 hours;

Heating: the holding temperature of dead soaking pit is controlled at 1200 ℃～1300 ℃;

Rolling: adopt the controlled rolling mode rolling, 1050 ℃～1200 ℃ of start rolling temperatures, a stage finishing temperature is at 950 ℃～1000 ℃; The two-stage start rolling temperature is at≤880 ℃, 1.5 times of the steel thickness of drying in the air, and the two-stage takes to depress for a short time rolling; Finish rolling accumulative total draft＞45%, finishing temperature≤860 ℃;

Control cold: return red temperature＜760 ℃, cooling several times, cooling rate is controlled at 3～10 ℃/s;

Slow cooling: go into burial pit temperature >=350 ℃, cooling in heap time >=24 hour;

Thermal treatment: adopt normalizing+water-cooling process, 910～940 ℃ of normalizing temperatures, soaking time 1.8～2.4min/cm, water-cooled time 5S～70S.

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