CN102337464A - Steel for high-strength continuous pipe-mill core rod and preparation process thereof - Google Patents

Abstract

The invention relates to a steel material for a high-strength continuous pipe-mill core rod, which comprises the ingredients calculated by mass percentage: 0.20 to 0.35 percent of C, 0.6 to 1.0 percent of Si, 0.9 to 1.5 percent of Mn, 3.0 to 6.0 percent of Cr, 0.40 to 0.75 percent of Mo, 0.30 to 0.70 percent of V, at most 0.04 percent of Nb and the balance of Fe. The material preparation process comprises the steps of smelting in an electric furnace, electroslag remelting, annealing, forging, annealing and heat treatment (quenching and high-temperature tempering), wherein good machining performance can be obtained after the annealing step after forging. Under the condition of preparing finished products, the impact toughness of a novel steel grade is greatly improved through being compared with that of H13, and the H13 steel can be replaced by the novel steel grade under the condition with severe requirements on the impact performance of the core rod, so the production efficiency is improved, and the production cost is reduced.

Description

High tough mandrel mill is with steel and preparation technology thereof

Technical field

The present invention relates to the tough mandrel mill material of a kind of novel high-strength.The steel that uses in the market is high-alloy hot work die steel such as H13 and H11, and the steel grade that the present invention relates to is a kind of middle-low alloy steel.

Technical background

MPM tandem rolling tube machine in first big mouth of sheath footpath was constructed and put into operation in Italian Da Er exposed penstock factory in 1978 in the world.The appearance of MPM to a brand-new level, owing to the many advantage of MPM at aspects such as technology, quality product and production efficiencys, just obtains rapid promotion and application once coming out with the continuously rolling process technical development in the whole world.Especially since the eighties in last century, received the influence in great demand of oil industry, impelled the develop rapidly of MPM technology oil well pipe.

China introduces many MPM production lines in recent years, the basic dependence on import of its main consumptive material plug, and the major diameter plug is with high content of technology, manufacture difficulty is big, has only few countries such as France, Italy, Germany to have throughput at present.The present plug manufacturing capacity of China with abroad have a long way to go, major diameter plug especially, the plug manufacturing of size more than Φ 280mm specification is still blank; Whole dependence on import; The import plug not only costs an arm and a leg, and delivery cycle is long, and imbalance between supply and demand is very outstanding.

There are two aspects in heavy caliber mandrel mill manufacturing technology difficult point: the one, and the manufacturing technology and the equipment of shortage high quality major diameter mandril blank; The 2nd, lack the precision control of the heat treated organizational controls of plug, long pole mechanical workout and the correlation technique and the equipment of plating hard chromium on surface.

At first, the manufacturing of major diameter mandril blank needs high-quality large-scale hot-work die steel ingot, because dimensional effect, steel ingot is big more, and its metallurgical quality, carbide, segregation control difficulty will increase substantially.The manufacturing of high-quality mandril blank not only needs advanced metallurgical quality opertaing device such as vacuum refinement, esr as pacing items, also needs state-of-the-art technology and equipments such as high temperature homogeneous, multiway forging, microstructure ultra-fining treatment to guarantee.Secondly, according to external experience, need for the large mould product made from steel of elongated type of this type of plug specialty band dual operation machine large-tonnage soon the forging machine produce, domestic almost do not have this type professional equipment.And; Only grasp from large-scale steel ingot metallurgical quality and organizational controls methodically, forge back organizational controls, mandril blank organizational controls; Quenching heat treatment, the complete microtexture control techniques of tempering heat treatment series to plug; Just can give full play to the highly malleablized effect of die steel interalloy element, produce and have the major diameter plug that excellent high intensity has the excellent high H.T. again concurrently, satisfy the actual demand of using.

Summary of the invention

Goal of the invention: the present invention is directed to plug with research work such as the optimizing components of steel, metallurgical quality control, forging, roll process control, applicability technology, develop the high tough plug of novel tandem rolling tube machine and use steel, in the hope of the plug of the costliness that substitutes import.

The invention is characterized in:

1, composition design: on the basis of H13, reduced C content, better formed single-phase homogeneous structure, can guarantee that plug is minimum in the volume change that the phase transformation that in use causes owing to colding and heat succeed each other causes on the plug top layer.Alloy content is lower, makes the toughness of steel significantly rise, and adds the Nb of trace simultaneously, makes the tough proportioning of steel reach a more satisfactory state.

2, alloying constituent: it is (mass percent) that the tough mandrel mill of this novel high-strength uses the main alloy element of steel:

C 0.20-0.35%

Si 0.6-1.0 %

Mn 0.9-1.5%

Cr 3.0-6.0 %

Mo 0.40-0.75%

V 0.30-0.70%

Nb ≤0.04%

All the other are Fe and unavoidable impurities element, S in the impurity element :≤0.005%; P :≤0.01; O :≤30ppm.

High tough mandrel mill is with the preparation technology of steel, and this preparation technology adopts following steps to carry out:

A. melting: with being positioned in the electric furnace after the prescription batching of alloy by claim 1, carry out melting, cast φ 200mm-φ 800mm electrode bar in the temperature more than 1500 ℃;

B. esr: the parameter of esr is: change slag voltage 50-65V, and electric current 3000-5000A, electric system voltage 57-59V, electric current 11000-12000A, the voltage 57-59V that binds, packing ratio is 0.8;

C. esr after annealing: in 700 ℃ of annealing 8 hours, furnace cooling subsequently;

D. forge: steel ingot is heated to 1150～1250 ℃, carries out rough forge, final forging temperature≤850 ℃, and forging ratio should be not less than 6;

E. forging rear annealing: in 700 ℃ of annealing 8 hours, furnace cooling subsequently;

F. thermal treatment process: 920-940 ℃ quenching, 600-630 ℃ of tempering two hours.

This steel grade contains the alloying element of lower aq, makes the more traditional plug of toughness of steel be increased dramatically with steel, adds the Nb of trace simultaneously, makes the tough proportioning of steel reach a more satisfactory state.Recommending under the thermal treatment process condition, hardness is 344-370HB, and average impact value is about 70J.

Description of drawings

Fig. 1 for the invention steel in the hardness of recommending under the heat-treat condition with finished product H13 solid mandrel, impelling strength is relatively.

Embodiment

1. present embodiment has been produced a kind of steel, and its staple is following:

C 0.33% Si 0.9%

Mn 1.2% Cr 4.34%

Mo 0.52% V 0.52%

Nb 0.03% Fe surplus

2. preparation technology and thermal treatment process:

A. melting: alloy carries out electrosmelting after pressing the mentioned component design, and the admixtion in the above-mentioned prescription is positioned in the electric furnace, carries out melting in the temperature more than 1500 ℃, cast φ 400mm-φ 450mm electrode bar;

B. esr: the content that can reduce gas and inclusion behind the esr; And obtain uniform ingredients, dense structure, steel ingot that quality is high, change slag voltage 58V, electric current 3000-5000A, electric system voltage 57V; Electric current 11500A, the voltage 58V that binds, packing ratio is 0.8;

C. slag remelting after annealing: in 700 ℃ of annealing 8 hours, furnace cooling subsequently;

D. forge: steel ingot is heated to 1150～1250 ℃, carries out rough forge, final forging temperature≤850 ℃, and forging ratio should be not less than 6;

E. forging rear annealing: in 700 ℃ of annealing 8 hours, furnace cooling subsequently;

F. thermal treatment process: 920 ℃ of quenchings, 620 ℃ of tempering two hours 1 time;

G. hardness and impelling strength: under the thermal treatment process condition of recommending, hardness value is 344-371HB, and notched bar impact strength is about 70 J.

Advantage and effect

Through alloy optimization design and recommendation thermal treatment process; The tough mandrel mill of this novel high-strength is greatly improved with the toughness of steel; The impact specimen test result of opening the V2 breach is about 70J, and the H13 of same hardness to open the impelling strength of V2 notch specimen be about 17J.

Claims (2)

1. high tough mandrel mill is used steel, it is characterized in that the composition of this steel is counted with the quality percentage composition: C:0.20-0.35%; Si:0.6-1.0%; Mn:0.9-1.5%; Cr:3.0-6.0%; Mo:0.40-0.75%; V:0.30-0.70%; Nb :≤0.04%; All the other are Fe.

2. high tough mandrel mill is characterized in that with the preparation technology of steel this preparation technology adopts following steps to carry out:

A. melting: with being positioned in the electric furnace after the prescription batching of alloy by claim 1, carry out melting, cast φ 200mm-φ 800mm electrode bar in the temperature more than 1500 ℃;

B. esr: the parameter of esr is: change slag voltage 50-65V, and electric current 3000-5000A, electric system voltage 57-59V, electric current 11000-12000A, the voltage 57-59V that binds, packing ratio is 0.8;

C. esr after annealing: in 700 ℃ of annealing 8 hours, furnace cooling subsequently;

D. forge: steel ingot is heated to 1150～1250 ℃, carries out rough forge, final forging temperature≤850 ℃, and forging ratio should be not less than 6;

E. forging rear annealing: in 700 ℃ of annealing 8 hours, furnace cooling subsequently;

F. thermal treatment process: 920-940 ℃ quenching, 600-630 ℃ of tempering two hours.

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