Development of High Strength Construction Rebars

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Proceedingsof InternationalSeminaronProductionandApplicationof HIghStrengthSeismicGradeRebarContainingVanadium

BeijingChina

Development of High Strength Construction Rebars Yang Caifu (Central Iron & Steel Research Institute, Beijing 100081) Abstract: The research, production and application of high strength rebars in China are reviewed.

Microalloying, afterheat treatment and fine-grain strengthening are the most effective methods in developing high strength rebars. V-N microalloyed rebars have noticeable advantages over those microalloyed with other elements. Enhanced nitrogen in vanadium-containing rebars promotes the precipitation of V(C,N) particles which markedly improves the precipitation strengthening effects of vanadium, 50% of which can be saved. The goal of saving costly FeV and reducing costs are realized. Based on carbon steel and 20MnSi steel, grade 3 and grade 4 rebars with yield strength of 400MPa and 500MPa respectively can be produced by afterheat treating, or ultra-fine grain technologies; the alloy consumption is reduced and resources are saved at the same time. In recent years, remarkable progress has been achieved in production and application of high strength rebars. Key words: high strength rebar, V-N microalloying, precipitation strengthing, afterheat

treatment, ultra-fine grain steel, seismic resistant rebar 

0

Currently, the domestic building market is

Introduction

dominated by grade 2 rebars with yield

As the biggest consumer among steel

strength of 335MPa. After years of efforts,

 products in China, rebars account for

some achievements have been made in

one-fifth of total steel production and play

application of 400MPa rebars but the share

an important role in national economic

of high strength rebar is still st ill lower. Grade 2

development. In recent years, the output

rebars account for 60% of all products and

and consumption of hot rolled rebars

the application of 500MPa rebars is almost

haveboth increased significantly to meet

 blank, and not filed in the architectural

the requirements of fast growth of building

design

industry.

production

However, in the developed countries,

growth of rebar in the past decade. It is

rebars for construction have been upgraded

visible from the fig that annual output of

to 400MPa and above. For example, grade

rebar had exceeded 100 million tons by

4 rebars with yield strength of 500MPa

2007, nearly five times that in 1997.

have been widely used in Germany [2].In

Although the production of rebar has

terms of applications of building rebars,

substantially increased in the last years, the

our country lags far behind the world

 product mix has been relatively backward.

advanced level. Rebar consumption can be

Fig.1

shows

the

specification

in

our

country.

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Proceedings of International Seminar on Production andApplication of HIgh Strength Seismic Grade Rebar ContainingVanadium

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saved by 14% if the strength is upgraded

the expense of lower ductility and poor

from grade 2 of 335MPa to grade 3 of

 bonding with concrete. Hot rolling with

400MPa. Similarly, 10% of steel can be

 pre-springing method was once commonly

saved if the strength is upgraded from

used in Europe to produce high strength

grade 3 of 400MPa to grade 4 of 500MPa.

rebar, namely“hot rolled torsion rebar ”, the

Therefore, there will be huge economic

yield strength of which was from 360MPa

efficiency and social benefits from rebar

to 400MPa, and 500MPa grade in a few

upgrading. This paper mainly introduces

cases. For consideration of cost, the torsion

the research, development and applications

rebar was gradually replaced by other hot

of high strength rebars for construction in

rolled rebars with same grades. In 1970's,

China.

welding rebar was developed rapidly, which

1998-2009 Production of Rebars in China 140

promoted

evoluation

of

rebar

 production technologies. A great step

120

forward

  s   n   o    T100   n   o    i    l    l    i 80    M  ,   n   o 60    i    t   c   u    d 40   o   r    P

achieved

when

micro-alloyed rebar was developed 

the [4-9]

.

Micro-alloying elements such as titanium, niobium and vanadium were used to  produce high strength rebars based on low

20

carbon steel with improved toughness,

0 1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

ductility Fig.1

Rebars production in china

[1]

and

welding

performances.

Another new technology was rebar heat

1 Research and development of high strength rebars 1.1

was

treatment, known as “ Tempcore ” and “ Thermex ”

[10-11]

, successful applied in

Europe firstly. This was called“afterheat

History

treated rebar ”and“quenching rebar ”. High

High strengthening is an important

temperature after rolling was used for

development trend of construction rebar. In

quenching and residual heat in the central

the beginning, by increasing carbon and

 part was utilized for self- tempering. This

manganese contents, the earliest high

method

strength rebar was produced with carbon

 production process for producing high

content

manganese

strength rebars in Europe. Micro alloying

ranging from 0.90% to 1.45% depending

and afterheat treatment are the main

the size of product and yield strength from

 processes for producing high strength

350MPa to 400MPa. In the meanwhile,

rebars in foreign countries. They are

another method for producing high strength

widely used for producing 400MPa (grade

rebars

3), 500MPa (grade 4) and 600MPa(grade5)

of

was

about

0.35%,

evolved

based

on

cold

deformation[3]. The strength of rebars was improved by drawing low-carbon steel at

is

currently

the

prevailing

high strength rebars. Functional

properties

like

seismic

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Proceedingsof InternationalSeminaronProductionandApplicationof HIgh StrengthSeismic GradeRebarContainingVanadium

Beijing China

resistance, flameproof, corrosion resistance

Mn-Si-Nb, with almost 20 brands, some of

are generally required by construction

which have been brought into the national

rebars, which represent another important

rebar standard. In the 1980’s,

development direction. In order to improve

on

the seismic and safety performances of

 performances and profiles of the low

structures, series of high strength seismic

alloyed rebars were conducted based on the

rebars have been developed by countries all

resources in China and internationally

over the world. Japan takes the lead in the

advanced

field of seismic rebar applications by

microalloyed grade 4 rebar products based

developing series of high strength rebars

on 20MnSi (grade 2) were developed by

with strength ranging from 590MPa to

adding proper elements like vanadium,

1275MPa[12].

placed

niobium or titanium, namely 20MnSiV,

high

20MnSiNb, 20MnTi. In addition K20MnSi

Europe

 performance

has

requirements

like

manufacturing

processes,

technologies.

 produced. In late 1990’s, for the sake of

the

higher

further cost reduction and resources saving,

requirement for construction rebars are put

HRB 400 and HRB 500 high strength low

forward, especially when the building is

cost

under marine environment. One effective

microalloying[15-18]. In the meanwhile, high

method for improving rebar corrosion

strength carbon rebars with

resistance is surface treatment, such as

grain has been developed with the support

epoxy coating and galvanizing treatment.

of

Adding chromium, nickel and copper are

successful developments of these products

effective ways for improving inherent

have effectively promoted the application

corrosion resistance. In order to obtain

of grade 3 rebar in our country. However,

longer service life, non-corrosive rebars

in the field of seismic resistant, flameproof

have been developed and used by some

and corrosion resistant rebars, our research

European and American countries in the

work is still at the initial stage.

recent years[13-14].

1.2

The research and development on rebars in China started in the mid of 1960's. Before

this,

the

rebar

standard

rebars

were

rebars

of

and fatigue property. In order to improve buildings,

3

series

afterheat

of

grade

A

brands,

tensile/yield strength ratio, good ductility durability

treated

researches

developed

by

Production

technology

V-N

ultra-fine

“ 973 ”  project

national

was

[19]

of

.

The

high

strength rebars Rebar performance mainly depends on

was

chemical composition and manufacturing

developed with referrence to the standard

 parameters .As welding techniques are

for the similar products of Soviet Union,

widely used in modern architectures, the

mainly carbon rebar. Since 1960s, our

way of adding carbon or equivalent content

country has successfully developed series

to improve strength is infeasible. In order

of low alloyed rebar products including

to make up for the loss of strength due to

Mn-Si,Si-V,Si-Ti,

decreased

Si-Nb,Mn-Si-V

and

carbon

content,

alternative

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 process routes are available which include

increase significantly as a result of cold

cold

deformation. Therefore, the manufacturing

deformation,

afterheat

treatment,

microalloying, grain refining and etc.

 practice of cold deformation to improve

1.2.1

strength of rebar has become a history.

Cold deformation technology

1.2.2

Cold deformation is one of the earliest

Heat treatment after rolling is the

methods for rebar production. Although

 primary route for producing high strength

strength is obviously improved by cold

rebar in Europe and this method is to

deformation, the ductility is much damaged

obtain tempered martensite on the surface

accordingly. As shown in fig.2, the strength

of rebar to realize strengthening. The yield

of hot rolled low carbon rebar increases

strength of common rebar can reach

significantly while the ductility index  Rm/ Re 

drops

dramatically

after

Afterheat treating technology

400MPa and 500MPa to meet performance

5%

requirements of high strength rebar. On the

deformation.

 basis of low carbon manganese steel, rebar with

yield

strength

600MPa

 produced by afterheat

treated

can

be

process

coupled with microalloying method. Table 1 shows the chemical composition of typical high strength rebar with afterheat treated technology in the foreign country. From the table, it can be seen that through afterheat treatment content of alloying elements in the high strength rebar is lower, (Diameter of rebar: 12mm, stretching strain: 5%)

which shows significant cost advantages.

Fig.2 Effect of cold deformation on

Except

[2]

mechanical ro ert of rebars

one-off

equipment

investment

(water-cooling equipment after rolling),

The strength of cold deformation rebars

there’s little increase in production cost.

increases while ductility drops noticeably,

Therefore, afterheat treating technology is

which can hardly meet the requirements for

an effective way for producing high

construction steel, especially the seismic

strength low cost rebars.

resistant steel. Besides, production costs

Tab.1 Chemical composition of typical high strength rebar produced by afterheat treated process

[2]

V

%

Yield strength level/MPa

C

Si

Mn

400

0.16～0.22

0.20～0.30

0.40 ～0.60

＜0.012

500

0.16～0.22

0.20～0.30

0.60 ～0.80

＜0.012

600

0.16～0.22

0.20～0.35

0.80 ～1.00

0.03～0.04

N

0.010～0.012

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Proceedingsof InternationalSeminaronProductionandApplicationof HIghStrengthSeismicGradeRebar ContainingVanadium

1.2.3

Microalloying technology

research

Microalloying utilizes two advanced technologies

which

strengthening

and

are

fine-grain precipitation

achievements

Beijing China

of

V-N

microalloyed rebars.  Titanium microalloying

Titanium is the earliest micro alloyed

strengthening to improve strength. Micro

element

alloying elements are added to rebar such

significant

as titanium, niobium and vanadium with a

strengthening, small quantity of which can

content ranging from 0.02% to 0.15%.

increase strength significantly. However,

Combined with appropriate process control

titanium has strong binding force with

method, the strength can increase doubly.

oxygen, sulfur and nitrogen, forming

Microalloying technology was one of the

oxides,

most significant achievements in physical

formation of TiC. This will give rise to

metallurgy in latter half of 20 century,

difficulty to control titanium content on a

which provides another economic and

reliable basis, resulting in fluctuation in

effective

high

strength of the steel. Oxides and sulfides of

strength steels. The option of microalloying

titanium are formed in molten steel;

elements depends on the their binding

Similarly, TiC is formed in solidification

abilities

carbon,

 process and can easily become bulky

nitrogen, etc, as well as the carbide/nitride

inclusions. For the above reasons, titanium

dissolvability at different temperatures and

micro alloyed method is abandoned for

specific conditions of production process.

strength improvement and this method has

Besides technical consideration, economic

 been used in the field of Ti-treatment and

viability is also an important factor to

oxide metallurgy. Welding performance is

consider for technological selection. Three

improved by adding small quantity of

kinds

namely

titanium (generally 0.010% to 0.020%) to

Ti-microalloying, Nb-microalloying and

form fine TiO and TiN, A lot of steels

V-microalloying are introduced for rebar

containing titanium such as 20MnTi rebar

 production and emphasis is given to the

in the past are discontinued in our country.

method

with

of

for

oxygen,

producing

sulfur,

technologies,

applied

in

steel.

contributor

sulfide

and

to

TiC

[3]

a

precipitation

nitrides

Fig.3 NbC, TiC and VN dissolvability at different temperature

is

prior

to

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Proceedingsof InternationalSeminaron ProductionandApplicationof HIghStrengthSeismicGradeRebarContainingVanadium

  Niobium microalloying

12mm～￠25mm)rebar. Based on 20MnSi,

 Niobium microalloying is widely used in

steel

sheet

and

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production.

after rolling, the technical index of the

However, the application is restricted by

rebar containing niobium of 0.02% to

dissolvability

0.03%

of

strip

coupled with accelerated cooling process

Nb(C,N)

in

rebar

 production .The pass system of wire and

can

meet

grade

3

rebar

requirements,

rod mill is fixed and efficient rolling with

 Vanadium/vanadium-nitrogen

fast speed is adopted. With heating up

microalloying

rolling scheme the temperature of rebar in

The microalloying process is mainly

exit of finishing stand is more than 1100 ℃.

used to develop high strength weldable

Therefore,

meet

rebars around the world. During rebar

technological conditions for Nb-containing

 production process, the high rolling speed

steel

low

and high finishing temperature are quite

deformation.

desirable for application of vanadium

it

is

production

temperature

difficult which

and

to

requires

large

Furthermore, the content of carbon in rebar

microalloying

is from 0.20% to 0.25%, which is relatively

standard issued in China also recommends

higher. It can be seen in Fig.3 that under

the use of vanadium microalloying to

typical composition of rebar (0.20%C),

 produce grade 3 rebars with yield strength

only0.02% of niobium can be dissolved in

400MPa at least[20].However, vanadium

the steel at the heating temperature of

added in rebars will increase the production

1,200 ℃.

costs. It is known that microalloying

Although

the

effect

of

niobium

technique.

carbides/nitrides.

in

have

production

process,

the

rebar

element takes effects by precipitation of its

fine-grain strengthening is difficult to exert rebar

The

Microalloyed

noticeably

better

nitrides

strengthening

 precipitation of Nb(C, N) contributes a

effectiveness than that of carbonides, for

little to strengthening. In order to make use

nitrides particles are more stable. Research

of strengthening effect of niobium, further

results[4-5]  indicate that nitrogen is a

research

cost-effective

has

been

done

which

has

alloying

element

in

 promoted the application of niobium of

vanadium microalloyed steels, and the

grade 3 rebars. The primary measure is to

strength can increase from 7MPa to 8MPa

decrease

 per

precipitation

temperature

and

10ppm

of

nitrogen

successful

 Nb(C,N).

is

nitrogen help to improve strengthening

successfully applied in rebar of grade 3 by

effect of steel containing vanadium,and

accelerated

and

achieve the goals of saving alloy and

trace-titanium treatment which can reduce

reducing costs. In order to further reduce

the adverse effects of Nb(C,N), especially

the costs of high strength rebar and explore

for

the

cooling

widely

microalloying after

used

rolling

small

size(

￠

the

potential

of

of

The

obtain fine precipitate phase particles of Niobium

applications

added.

low-cost

microalloying

steel,

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Proceedingsof InternationalSeminaron ProductionandApplicationof HIghStrengthSeismicGradeRebarContainingVanadium

BeijingChina

extensive researches on production of high

steel to which FeV is added, vanadium

strength rebar with V/N microallying have

exists mainly as solid solution which

 been conducted home and abroad[15-18].

accounts for 56.3% of total vanadium

(1) Effect of nitrogen

content, while only 35.5% of vanadium

Fig.4 shows the effect of nitrogen on

 precipitates in the form of V(C,N).The

strength of rebar containing vanadium.

results

With almost the same content of vanadium,

microalloying

the strength of V-N microalloyed rebars is

containing steel do not work toward

much

vanadium

 precipitation strengthening and it is a waste

microallyed steel. It can be seen that with

of vanadium. On the contrary, in V-N steel,

enhancement of 100ppm of nitrogen, the

70%

yield strength and tensile strength of V-N

 precipitates and only 20% dissolves in the

microalloyed rebar increase by 117.5MPa

matrix. Therefore, nitrogen added to steel

and 135MPa, respectively, compared to

alters the vanadium phase distribution and

vanadium containing steel. Experimental

 promotes

result

dissolved in the matrix, thus improving the

higher

shows

than

that

that

of

nitrogen

markedly

improves the strengthening effectiveness of

YS

TS

  a    P    M 60 0  ,    h    t 50 0   g   n   e   r 40 0    t   s

vanadium

in

forms

precipitation

of

the

vanadium

V(C,N)

vanadium

80% 70%

V V(C,N)

60%

V M3C V sol

50% 40% 30% 20% 10%

30 0

0%

20 0 V -S teel

S t ee l

elements

of

90%  o   i   t   %  a   R  ,  m  n  u  o   i   i   d   t  a  u  n   b  a   i   V  r   t   f  s  o   i   D

70 0

most

100%

a very effective strengthening element for

80 0

of

that

 precipitation strengthening of vanadium.

vanadium in steel, which means nitrogen is rebars containing vanadium.

reveal

V Steel

V -N S teel

Fig. 5 Vanadium distribution in V-steel and V-N

0 . 1 1 % V - 8 5 p p m[ N ] 0 . 1 2 % V - 1 8 0 p p m [N ]

YS

4 4 2 .5  MPa

TS

5 8 5  MPa

VN Steel

5 60 MPa 7 20  MPa

[15]

steel

Fig. 4 Effect of N on strength of V rebars

Phase analysis result shows that the

[16]

steel

fraction of fine particles with a size of less than 10nm in vanadium containing rebar is

(2) Vanadium distribution and preci pitation phase in rebars

 just 21.1%, whereas, the fraction is up to 32.2% in V-N rebar. The increase of fine

Vanadium distribution is shown in

and dispersed V(C,N) precipitated phase is

Fig.5. It can been seen there is an evident

the primary reason for strength rise of V-N

difference

rebars.

in

phase

distribution

of

vanadium between high-nitrogen steel and low-nitrogen steel. In vanadium containing

σS =85.7+37[Mn]+83[Si]+17.4×D -1/2 +σPR 

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V-Steel：  Rel＝ Rel(20MnSi)＋1056×[V%]

23MPa by fine-grain strengthening and

V-N Steel：  Rel＝ Rel(20MnSi)＋1994×[V%]

86MPa

(3) Strengthening mechanism of V-N rebars

strength of microalloyed steels can be [21]

expressed as

:

totaling

strengthening,

109MPa.Comparison

of

contributing factors to the precipitation

where 37[Mn]+83[Si] is solid solution strengthening

17.4×D -1/2

factor,

fine-grain strengthening factor and  precipitation

strengthening

is

σ PR 

is

factor.

According to experimental results of ferrite grain size and yield strength of the sample the

that σPR

in V-N rebar doubles that in

vanadium

containing

steel.

The

incremental strength from precipitation

σS =85.7+37[Mn]+83[Si]+17.4×D -1/2 +σPR 

contribution

of

each

strengthening factor to the yield strength can be estimated by the above formula and the result is shown in Fig.6.

accounts for 73.2% of total strength increment of the steel. It can be seen that  by addition of nitrogen, vanadium can play a greater role in precipitation strengthening and

fine-grain

strengthening,

which

contribute to significant improvement in yield strength. The result of regression equation shows that the strengthening ability of vanadium in V-N rebars almost doubles that of vanadium-containing rebar. V-Steel：

 Rel＝ Rel(20MnSi)＋1056×[V%]

V-N Steel：

Rel＝ Rel(20MnSi)＋1994×[V%]

(4) Effect of accelerated cooling after

600

rolling

  a 500    P    M

165 65

400

   h    t   g 300   n   e   r    t    S 200    d    l   e    i    Y100

precipitation

strength between the two steels suggests

On the basis of research results, the

steel,

by

preciptation Grain Size

170

200

220

solid solution base

120

The

 produced

85

85

85

 process.

20MnSi

V-rebar

Fig.6 Strengthening Mechanism of 20MnSi, V rebars and V-N rebar

It can be seen that effect of matrix strengthening

and

solid

three rebars, the strength difference is caused by different effects of precipitation

through Fig.7

accelerated

indicates

and fine-grain strengthening of V-N steel is  better than that of V containing steel,

yield

cooling strength

vanadium containing rebar, V-N rebar and V-N rebar produced by accelerated cooling. 600

V-N rebars (Accelerated cooling)

V-N rebars

   a 550    P    M  ,    h    t    g    n 500    e    r    t    S    d    l    e    i    Y450

V rebars

rebar diameter: 16-32mm

strengthening and fine-grain strengthening. The effect of precipitation strengthening

the

changing with content of vanadium for

solution

strengthening is basically the same for the

meet

with lower content of vanadium can be

90

V-N rebar  

which

requirements of grade 3 and grade 4 rebars

90

0

products

400 0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

V content, %

Fig.7 Effects of V content and ACC process on the strength of rebars

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Proceedingsof InternationalSeminaronProductionandApplicationof HIghStrengthSeismicGradeRebarContainingVanadium

Beijing China

It can be seen that with the same

the strength of carbon rebars and 20MnSi

strength, V-N rebars save V resources

rebars. Common carbon steel is able to

substantially

satisfy the performance requirements of

containing

compared vanadium

with

only

,

rebars with

V

grade 3 rebar with minimum yield strength

consumption decreasing from 0.06% ～

of 400MPa by refining grains. For 20MnSi

0.08% to 0.03% ～ 0.04% for 400MPa

rebar, the strength obtained is more than

rebars, and from 0.07% ～ 0.12%

500MPa.

to

0.06% ～ 0.08% for 500MPa rebars. By accelerated

cooling

process,

the

Grain refining is an effective method for

raising

strength

while

improving

consumption of vanadium can be reduced

toughness at the expense of reducing

to 0.02% ～0.03% for 400MPa V-N rebars

tensile/yield ratio. It can be seen in Fig.8

and 0.04% ～ 0.05% for 500MPa V-N

that tensile/yield ratio of carbon rebars and

rebars. It follows that FeV consumption

20MnSi

and costs will be saved by adopting

strengthening is reduced to 1.20 and below,

microalloying technique combined with

less than the ratio of 1.25, a minimum

accelerated cooling process.

requirement by the seismic rebar. Another

1.2.4

Technology of fine-grain rebars

 problem is weldability of this kind of rebar.

Based on“973”ultra-fine grain steel

The grain of heat affected area will grow

 project, the research work of high strength

due to high temperature during the welding

fine-grain rebars have been conducted in

 process, and welded joint will intenerate at

China. The ultra-fine grain structures can

the same time. Improving tensile/yield ratio

 be obtained through DIFT technique as

and researching connection technology are

well as deformation at Ar3 temperature.

the primary efforts toward promoting

Fig.8 shows the effects of fine grains on

fine-grain rebars in the future.

  a    P   a    M    P

   M    h    t   g      度   n   e      强   r    t   s      伸   e    l      拉    i   s   ，   n   e      度    t    h      强    t   g      服   n   e      屈   r    t   s    d    l   e    i   y        ，

550 500

1.3

450

with

fine-grain

850

1.35

σ

rebars

  a    P    M

  a    P    h    t   M

1.5 σb

1.45

800

1.4

750

       ，

1.25

400 350

1.2

σ

300

1.15

σb/

250

1.1

200 0.17%C-0.60%Mn-0.29%Si-0.012Ti

150

1.05 3

4

5

6

7

8

9

10 11 12

晶粒尺寸 grain size μm µm

  g      度   n      强   e   r      伸    t   s      拉    \   e    l    i      度   s      强   n   e      服    t      屈    h    t   g   n   e   r    t   s    d    l   e    i   y

1.35

   d    l   e    i   y      比    /   e 1.25      屈    l    i      强   s 1.2   n   e    T 1.15

700

1.3 650 600 σb/σs 550

σs

500

1.1

450

1.05

0.22%C-1.46%Mn-0.5%Si

400

1 0

1

2

3

4

5

6

7

8

9

晶粒尺寸 μm grain size µm

Fig.8 Effect of ferrite grain size on the strength of plain C and 20MnSi rebars

2 Production and application of high strength rebars

[19]

Fig.9 shows production of grade 3 rebar in China in recent years. In the year

2010

Proceedingsof InternationalSeminaron ProductionandApplicationof HIghStrengthSeismicGradeRebarContainingVanadium

of 2000, its output was only 260 thousand

strength

tons, accounting for 1% of the total rebar

adopted to play a role in strengthening

 production.

had

 precipitation as well as improving strength,

reached 33 million tons, accounting for

saving alloy consumption and reducing

one-third of the total. High strength rebar

 production costs. Through optimization of

 production and application in China has

chemical composition, the consumption of

developed rapidly. It can be seen in Fig.10

vanadium in V-N microalloying high

that increasing output of grade 3 rebar has

strength rebars can be reduced to the

significantly contributed to the product mix.

content ranging from 0.02% to 0.04%, half

Although the output of grade 3 rebar has

that of V-Fe microalloyed rebar.

By

2008,the

output

level.

V-N

-67-

microalloying

is

substantially increased, its share is still

Production experiences indicate that

lower. 20MnSi rebar of grade 2 has the

the mechanical properties of V-N micro

 biggest share in the construction rebar

alloyed rebars are quite stable and the

market, namely 60%.The application of

strength is controlled with a variation of

 building rebars indicate that our country still

75MPa, which can satisfy class- one

lags far behind the world advanced level.

seismic requirements. According to the

V/V-N

microalloying

is

the

statistical

data

of

strength rebars for construction. Based on

affected by dimension specification is

20MnSi, appropriate vanadium or V-N is

identified. As shown in Fig.11, statistical

added

performance

results indicate that the average variation of

requirements of 400MPa and 500MPa high

yield strength is 17MPa while the tensile

strength rebars. Table 2 lists the typical

strength is 19MPa by using billets with the

chemical composition of 400MPa and

same chemical composition to produce

500MPa rebars produced by converter

rebars of different specifications.

 process.

micro

It

to

can

meet

be

seen

that

the

alloyed

that

rebar

 production,

steel

way

V-N

 predominant process for producing high

to

the

mass

rebars

strength

of

is

V-N

different

consumption of vanadium needed in V-N

specifications exhibit similar properties

steel is much less than that in the steel

suggesting that the effects of specification

containing vanadium only with the same

are not evident.

1995-2009 China Rebars Steels Output Total Production

 ,    s    r    a    b    e   s    R   n    f    o    o   t    t    n   u   o    i    p    t    l    l   u   i    O   m    l    a    t    o    T

130 120 110 100 90 80 70 60 50 40 30 20 10 0

Production of Grade 3 Rebars

122 103 102

60 50

88 80 71 58 44

15

15

17

21

25

26

29

12.96 5.89 1.94 0.26 1.07

32.43

32.72

22.74 13.07

40 30 20 10 0

   5    9    6    9     7    9    8    9    9    0    0    0    1    0    2    0    3    0  4    0    5    0    6    0     7    0    8    0    9    9    9    9    1    9    1    9    1    9    2    0    2    0    2    0    2    0    2    0    2    0    2    0    2    0    2    0    2    0    1    1

Fig.9

Production of Grade 3 Rebars in China

 ,    s    r    a    b    e    r    3   s    e   n    d    o    a    r    T    G   n    f    o    o   i    l    l    n   i    o   M    i    t    c   u    d    o    r    P

-68-

Proceedingsof InternationalSeminaronProductionandApplicationof HIghStrengthSeismicGradeRebar ContainingVanadium

Beijing China

2007 China Rebars Mix

2006 China Rebars Mix

Grade V, 0.04%

Grade IV, 0.28%

Grade I, 8.29%

Grade I, 4.60%

Grade IV, 0.16%

Grade III, 23.37% Grade III, 31.55%

Grade II, 63.65%

Grade II, 68.05%

Fig.10

Rebar product mix in China

Tab.2 Chemical composition of 400MPa and 500MPa rebars produced by converter process Grade

Alloy

400MPa

V-N

C

Si

Mn

P，S

0.20-0.24

0.45-0.60

1.25-1.45