CN102643965A - Production method for reducing surface hardness of steel rod - Google Patents

Abstract

The invention discloses a production method for reducing the surface hardness of steel rod. The layout of a production system is sequentially a roll table for delivering rolled bars, an entrance induction heater, a cold bed feeding roll table, a feeding transverse rack, a cold bed, a blanking chained mode transfer bed, a blanking delivering roll table, an exit induction heater and a bar collection bundling machine; the process steps are sequentially as following: the steel rod is heated to 930-950 DEG C before entering the cold bed; the steel rod is transversely delivered to the cold bed within 7 minutes, and the temperature of the steel rod is more than 800 DEG C when entering the cold bed; the steel rod is delivered to the blanking chained mode transfer bed within 10 minutes; the blanking steel rod is heated to 750-800 DEG C, and the temperature of the steel rod is no less than 650 DEG C when entering a burial pit; and the steel rod is collected and bundled to be lifted into the burial pit to be cooled, and is lifted out of the burial pit after being gradually cooled to the temperature below 150 DEG C.

Description

Reduce the process method of round steel surface hardness

Technical field

The invention belongs to steel-smelting technology, particularly relate to a kind of process method that reduces the round steel surface hardness.

Technical background

Bar in use need carry out processing such as fire is cut, shearing, sawing as widely used raw material in the industrial production in the ferrous materials.For guaranteeing to satisfy the processing requirement of shearing, sawing; Surface hardness and centre hardness for the bar product before the bar product export have certain requirement, do not need heat treated bar product will guarantee that the surface hardness of bar has suitable difficulty before still dispatching from the factory for some.

For example certain steel mill's bar Workshop Production ability can reach 1,000,000 t/a; Product is bar and the pipe of 50 ~ 200mm; Represent steel grade that carbon junction steel, high-quality carbon junction steel are arranged, close knot steel, high pressure and low medium pressure boiler tube steel etc., the cold bed design of production line of bar is to satisfy large diameter pipe, the configuration of large diameter bar product.Scenario can appear in such arrangement: with respect to some bar products than small dia, cold bed overcapacity; The bar product of the small dia temperature that rolls off the production line is low, causes hardness value higher, and the user complains more, requires to return goods; For hardening capacity preferably the Cr-Mo steel, contain for the bar product of Cr; Guarantee in the production small-sized bar product surface hardness and lower envrionment temperature winter bar surface hardness in suitable hardness value scope; Seem particularly difficult, winter in every year, bar was bigger because of the compensation that surface hardness is high, the user shears or the sawing difficulty causes.

In winter particularly in actual production, cold bed temperature is 200 ~ 400 ℃ under the bar, and bar real surface hardness is HB240 ~ 260, can not satisfy the requirement of delivery technical qualification.Follow the tracks of emphasis the temperature drop of each key point is measured, measuring intervals of TIME is 60S, through measuring, finds very fast in the temperature drop speed at traversing stand place.Temperature drop speed is fast at traversing stand place, and former because AT and the steel temperature difference be apart from greatly, go into cold bed after temperature drop mild, because of having in the phase transition process in the heat energy dispose procedure, cause temperature drop little.About 2 ℃/S, but about 0.17 ℃/S that on cold bed, descends must try every possible means the temperature drop of traversing stand is controlled or the temperature of guaranteeing to get into cold bed will have clear and definite requirement or target at the bar temperature drop rate at traversing stand place.Cold bed temperature promptly gets into the bainite transformation TR below 600 ℃ under the bar.Therefore will guarantee into bainite structure not occur before the burial pit, bar temp must be more than 650 ℃.

For satisfying delivery requirements, bar must carry out off-line thermal treatment, makes production cost improve like this, and product craspedodrome rate is low, logistics difficulty in the workshop.But general bar factory does not have the off-line HTFX, can't meet the needs of production.As being transformed, cold bed then needs up to ten million fund inputs; Transform the production needs that the back cold bed can not satisfy big specification, low hardening capacity bar again.

Summary of the invention

The present invention aims to provide a kind of process method that there is the reduction round steel surface hardness of weak point in above-mentioned prior art that overcomes, and rolls the temperature that the back gets into cold bed to improve the high-hardenability round steel, makes round steel at cold bed bainitic transformation not take place; For the thermal treatment of the online elimination round steel of the round steel that rolls off the production line bainite structure, the thermal treatment of cancellation off-line reduces production costs, and improves the craspedodrome rate of product; Satisfy the production needs that general round steel factory produces the high-hardenability round steel simultaneously, take into account the requirement of big specification, low hardening capacity round steel simultaneously cold bed.

Technical scheme of the present invention: the process method that reduces the round steel surface hardness.Production system is arranged and is followed successively by: bar rolls back rollgang, inlet induction heater, cold bed charging roller, the traversing stand of material loading, cold bed, blanking chain transfer, blanking conveying roller-way, outlet induction heater, bar collection bander.Process step is followed successively by:

A. round steel is heated to 930～950 ℃ with round steel before getting into cold bed;

B. the traversing cold bed of sending in the round steel 7min gets into cold bed temperature greater than 800 ℃;

C. round steel is sent into the blanking chain transfer in 10min;

D. the blanking round steel is heated to 750～800 ℃, eliminates the bainite influence tissue of round steel, round steel is gone into burial pit temperature >=650 ℃;

E. round steel hangs in the burial pit cooling after collecting bundling, slowly cools to below 150 ℃ to go out burial pit, obtains the P+F tissue, the hardness HB of round steel≤220;

The present invention is arranged into mouthfeel between back rollgang and cold bed charging roller and answers well heater rolling, and between blanking conveying roller-way and bar collection bander, lays out mouthfeel and answers well heater; Utilize induction heating to improve the temperature that round steel is gone into cold bed, go into cold bed initial stage temperature and be higher than the bainitic transformation temperature, do not produce the high firmness tissue to ensure round steel; The round steel that rolls off the production line utilizes induction heating to carry out online thermal treatment, eliminates bainite structure, and the temperature that guarantees to get into burial pit is organized as the F+P tissue greater than 650 ℃ after the round steel slow cooling, guarantee the round steel qualified hardness.Therefore, compared with prior art, the present invention has the following advantages:

1. increase online induction heater and solved round steel because of lowering the temperature soon, general bar factory cold bed can't satisfy the requirement of producing the high-hardenability round steel, and making it produce small dimension high-hardenability bar becomes possibility;

2. the temperature of round steel on cold bed makes it not produce bainitic transformation greater than 600 ℃, reduces the high firmness phase in the tissue, for even round steel should evenly provide assurance;

3. the back round steel that rolls off the production line carries out induction heating, has satisfied the temperature requirement of round steel entering burial pit, and round steel goes out the P+F that is organized as of burial pit, and its hardness satisfies wanting of delivery technical qualification;

4. online thermal treatment has reduced production cost, has improved the craspedodrome rate of product, has reduced the logistics in the workshop;

5. electric induction heater can be installed on the track, utilizes hydro-cylinder to position, and extensible production line when producing other products uses flexibly;

6. after increasing online induction heater, cold bed can be taken into account the production of big high and low hardening capacity bar, need not cold bed is transformed.

Description of drawings

Accompanying drawing is the production system layout.

Among the figure: 1-rolls back rollgang, 2-inlet induction heater, 3-cold bed charging roller, the traversing stand of 4-material loading, 5-cold bed, 6-blanking chain transfer, 7-blanking conveying roller-way, 8-outlet induction heater, 9-bar collection bander.

Embodiment

Below in conjunction with accompanying drawing and embodiment invention is further specified.

As shown in the figure, the equipment layout of production system is followed successively by: roll the traversing stand of back rollgang 1, inlet induction heater 2, cold bed charging roller 3, material loading 4, cold bed 5, blanking chain transfer 6, blanking conveying roller-way 7, outlet induction heater 8, bar and collect bander 9.After rolling, be arranged into mouthfeel between rollgang 1 and the cold bed charging roller 3 and answer well heater 2, between blanking conveying roller-way 7 and bar collection bander 9, lay out mouthfeel and answer well heater 8.Process step is following:

A. after rolling, be fit into mouthfeel between rollgang and cold bed charging roller and answer well heater, round steel is heated to 930 ~ 950 ℃ with round steel before getting into cold bed, obtains single austenite structure;

B. the traversing cold bed of sending in the round steel 7min gets into cold bed temperature greater than 800 ℃;

C. round steel is sent into blanking chain type one and is sent machine in 10min;

D. collect installation outlet induction heater between the bander at roll off the production line rollgang and round steel, the blanking round steel is heated to 750 ~ 800 ℃, eliminate the bainite influence tissue of round steel, guarantee that round steel goes into burial pit temperature >=650 ℃;

E. round steel hangs in the burial pit cooling after collecting bundling, slowly cools to below 150 ℃ to go out burial pit, obtains the P+F tissue, the hardness HB of round steel≤220.

Claims (1)

1. reduce the process method of round steel surface hardness, it is characterized in that: production system arranges that being followed successively by bar rolls back rollgang, inlet induction heater, cold bed charging roller, the traversing stand of material loading, cold bed, blanking chain transfer, blanking conveying roller-way, outlet induction heater, bar and collect bander; Process step is followed successively by:

A. round steel is heated to 930～950 ℃ with round steel before getting into cold bed;

B. the traversing cold bed of sending in the round steel 7min gets into cold bed temperature greater than 800 ℃;

C. round steel is sent into the blanking chain transfer in 10min;

D. the blanking round steel is heated to 750～800 ℃, round steel is gone into burial pit temperature >=650 ℃;

E. round steel hangs in the burial pit cooling after collecting bundling, slowly cools to below 150 ℃ to go out burial pit.

Images