30 Years of Niobium Steel Development in China

30 Years of Niobium Steel Development in China

Mariana Oliveira(1)

, Steve Jansto(2)

, Hardy Mohrbacher(3)

, Jitendra Patel(4)

, Marcos Stuart(1)

(1) CBMM – Companhia Brasileira de Metalurgia e Mineração

(2) RMC – Reference Metals Company

(3) NiobelCon BVBA

(4) International Metallurgy Ltd

Abstract

Over the past 30 years, niobium (Nb) has become an important asset in the search for

engineering solutions to the most significant challenges facing humanity: environmental

awareness, energy savings and infrastructure for growth. China is an extraordinary example

of this progress since it has been addressing these same issues together with the need for rapid

development. This paper presents successful examples of Nb applications in China over the

last three decades, where all expectations were surpassed in the main steel domains: pipeline,

automotive, structural and stainless. An overview of future trends for the development of

Nb products is also presented along with evidence that Nb will continue to be among the first

microalloying choices and the best solution for new demand. CBMM, together with its

Chinese partners, will continue to optimize Nb applications and new developments, always

striving for higher value added products from the beginning of the supply chain to the end

user.

1. Introduction

Niobium (Nb) was first applied as an industrial material in 1933 to stabilize stainless steels

against intergranular corrosion. Through the late 50s and early 60s, Nb was discovered to

have microalloying properties that simultaneously enhance steel strength and toughness. In

the 70s, Nb was also established as the material of choice for several advanced technological

applications, mainly at high temperatures, in the form of superalloysi.

During recent years, Nb applications have increased tremendously in several business

segments, such as:

Microalloyed steels

Superalloys

Thin films

Medical implants

Titanium and aluminum base alloys

Superconductors and copper alloys

Ceramic and electrolytic capacitors

中国含铌钢技术发展 30 周年国际研讨会论文集 120

As shown in

Figure 1, the main use for Nb was in pipeline steels. More than 55% of the ferroniobium

(FeNb) produced by CBMM was dedicated to this application. Currently, Nb usage is still

concentrated in microalloyed steels, but it is more equally distributed between pipeline (32%),

automotive (20%) and structural (33%) segments. The remaining 12% goes to markets that

show promise for growth, including stainless steels and superalloys.

A milestone for FeNb consumption occurred around the year 2000 when FeNb sales began to

outpace the growth in steel production, Figure 2, eventually more than doubling the growth

rate over the decade. This growth illustrates the strong acceptance of Nb alloying solutions in

the world steel market, caused not only by improvements in traditional materials but also by

the development of new products.

Figure 1: Evolution of CBMM’s worldwide FeNb market by business segment.

* Actual Jan-Oct, estimated Nov-Dec.

30 Years of Niobium Steel Development in China 121

Figure 2: Increase in crude steel production and FeNb sales worldwide over the last 10 years.


China is one of the main reasons for increased Nb consumption, especially over the past 10

years, Figure 3.

Figure 3: Increase of FeNb consumption in China during the last decade.


Sales in China increased an average of CAGR 31% over the previous 10 years, Figure 3,

which completely modified CBMM s sales profile, Figure 4. At present, China is the strongest

FeNb market. This trend is forecasted to continue since Chinese crude steel production is

predicted to continue growing in coming years, reaching 650 million tons by 2013ii.


Figure 4: CBMM’s sales by geographical region in 1999 and 2008.

Despite being the most apparent reason, steel production growth is not the only driver of

increased Nb sales. Another important factor that must be taken into consideration is the rise

of specific FeNb consumption, expressed in grams of FeNb consumed per ton of crude steel

produced. China has more than tripled its specific FeNb consumption from 11g/t in 2004 to

35g/t in 2008, proving that the incubation time necessary to develop the foundation for Nb

technology in China has passed and, therefore the intensity of FeNb consumption will

continue to grow.

Comparing China s FeNb distribution by segment to the world s, Figure 5, it is possible to

conclude that the automotive and stainless steel segments still have room to grow, while the

pipeline and structural steel segments have already matured.

Once China is developing fast the steel industry and producing more value added products,

FeNb specific consumption will continuously grow and reach the same or higher levels of

regions like North America and Europe, Figure 6.


Figure 5: Nb consumption in 2008 by business segment in the world and in China.

Figure 6: Specific Nb consumption in select countries in 2008 (g FeNb / t crude steel).

2. Strategic View

CBMM s main strategy is to apply Nb where it is the best solution for adding value,

particularly in addressing what are considered the main challenges of today: environmental

awareness, energy savings and infrastructure to grow, Figure 7.


Figure 7: Today’s challenges are where CBMM is concentrating efforts to apply Nb for

innovative solutions.

The company s goals are not only to supply the demand for Nb in the form of ferroalloy,

oxide or metal, but also to provide and develop the technological potential involved in the use

of this element to discover how Nb can help to overcome the main challenges worldwide:

growing wisely and in a sustainable way.

CBMM has a strong technical group developing Nb applications, acting together with

steelmakers, research universities, institutes and end users. At the moment, the company is

involved with more than 50 research projects around the world, 17 of them are with Chinese

universities and steel companies.

At least 1% of CBMM sales is invested in a research and development program. As part of

this technological effort, 237 researchers in the steel industry attained their university degrees

through scholarships granted by CBMM in areas relevant to Nb. This talent is working around

the world and is receptive to Nb technology, helping to develop Nb worldwide.

To promote environmental awareness, the technology program sponsors the development of

materials that minimize pollution emissions, such as ferritic stainless steels used in vehicle

exhaust systems as well as lighter steels for car bodies that reduce fuel consumption and

extend the components life cycles, which together save energy and raw materials.

Lighter weight is also a focus in the infrastructure area in order to create more resistant steel

structures with less material since nowadays there is a strong commitment to lowering

financial and environmental costs, not to mention feasibility issues in urban infrastructure.

Nb-bearing steel is an ideal solution because it is a higher strength steel, which results in less

material volume for the same project, which not only lowers costs, but also uses less raw

material and generates fewer emissions during the steel production process.


The main challenges regarding energy savings are the need to improve existing processes, like

obtaining higher efficiencies in thermal power plants, and to develop new clean sources. Nb

bearing steels can work at higher temperatures, allowing these higher efficiencies and energy

savings.

Successful examples of these technical efforts in China are described below.

3. Successful Examples of Development in China and Future Trends

3.1. Pipeline

China’s rapid economic growth shows no signs of slowing, with a gross domestic product

increase of over 10% reported for 2008 and an annual growth rate of 9% for the year. China is

now the world’s second-largest and fastest-growing energy consumer and is a major player in

world energy markets. According to EIA projections, by 2030 China will be the world’s

largest energy consumer, Figure 8.

Figure 8: Actual and projected global energy demand - 2005 & 2030 (3).

Although coal is the cornerstone of the country’s energy system, natural gas comprises

approximately 2-3% of total primary energy demand. This share hides the significance of the

large volumes of natural gas consumed and the required demand in linepipe steel needed for

long distance transmission systems. Consequently, this has led to the installation of new steel

mills and hot rolling mills, as well as the need to quickly develop modern and advanced high

strength steels for the construction of energy infrastructure.

The required growth in energy demand has meant a significant expansion of China’s existing

pipeline network. A summary of some of the key transmission lines is provided below:

During 1970-1980 the natural gas trunk pipeline network was formed in Sichuan.


In the 1990s, several famous pipelines were built in China such as Ya-13-1-Hong

Kong Pipeline, the Pinghu-Shanghai Pipeline and the ShaanCi-Beijing Pipeline.

During 2000-2005 a number of major pipelines were built adding significant capacity

to the network, including Sebei-Xining-lanzhou Pipeline, West-East Pipeline, a

second pipeline from ShaanXi to Beijing and Zhingxian-Wuhan Pipeline.

In 2008, the total length was approaching 35,000km and transport capacity amounted

to 81bcm per year.

By 2020, there is an expectation that more than 25,000km of new pipeline will be built and

the national gas pipeline system will be moving gas from the western to the eastern regions

and from the northern to southern regions. Significant future developments are also expected

offshore, where China has only started to make notable developments.

Today there are eight major gas production regions in China. The production amounted to

77.5bcm in 2008 and is expected to reach near 220bcm in 2020. Figure 9 highlights the

concurrent development in production and consumption and also translates directly into the

growth needed in the pipeline network.

For example, the growth in China’s pipeline network can be dramatically seen in Figure 10.

Although the first and second West-East Pipelines make a significant contribution, over the

last 10 years the laying of nearly 20,000km of major trunk and branch lines has been

outstanding.

Figure 9: Annual gas production and consumption in China.


Figure 10: Pipeline lengths per year in China.

In order to cater to the required demand in linepipe, China has seen the construction of over

15 new hot rolling mill projects in the last 10 years, as highlighted in Table 1. With this newly

installed capacity and performance capability, today China has become one of the leading

countries able to develop the necessary high strength plate and hot rolled coil required for the

oil and gas sector, both for domestic use and exports.

Table 1: New plate mills installed in China during the last 10 years.

Producer/Location Plate mill width Year ordered

Yingkou 5,000mm 2009

Baotou 4,100mm 2007

Xiangtan 3,800mm 2007

Shagang No.2 5,000mm 2007

Wuhan 4,300mm 2006

Laiwu 4,300mm 2005

Wuyang 3,800mm 2005

Angang 5,000mm 2005

Shougang 4,300mm 2004

Shagang No.1 5,000mm 2003

Xinyu 3,800mm 2003

Baoshan 5,000mm 2002


The installation of state-of-the-art steel making and rolling facilities has permitted Chinese

steel producers to fully exploit the Nb technology that has been previously enjoyed by other

leading world mills. However, in order to capitalize on this new capability the learning has

been rapid, sustained and above all, successful.

In the last 10 years Chinese mills have successfully mass produced X70 and X80 linepipe

steel grades for both LSAW and HSAW application. The high quality steel has been designed

around new pipeline design practices such as strain-based design and modern pipe-making

and welding techniques. For example, Figure 11 shows the annual increase in production for

NISCO for API steel grades going from around 25,000t to 350,000t in two years.

Figure 11: Annual NISCO production, 2005-2007 (4).

Another excellent development example is the second West-East Pipeline, Figure 12, the

main characteristics of which are presented in Table 2.

Table 2: Main characteristics of the second West-East Pipeline.

Gas transmission main trunk line length = 4,950km

6 sub-lines giving a total length of 8,800km

X80 - 48” OD at 18.4mm WT for mainline – 12MPa OP

X70 for branch lines

Production and laying 2008-2010

Cost = $19.8bn

Capacity = 30bcm/year

Round bar testing


Y/T max = 0.93 (round bar specimen)

Ave CVN >240J at -20oC

Ave DWTT >85% at -15oC

Figure 12: Second West-East Pipeline.

All efforts resulted in a change of the main linepipe specifications, permitting 0.11%Nb to be

used for X70 and X80 steel grades, Table 3.

This in turn has allowed several, long distance, large diameter pipe projects around the world

to be cost-effectively installed with excellent mechanical properties of the final pipe.

Table 3: Chemical composition of X80 with high Nb content.


a- V+Nb+Ti<0.15%

b- B not allowed.

c- When C is reduced by 0.01%, Mn can be adjusted by 0.05% but cannot be beyond

1.95%.

d- CE II W is not a restriction. It is recommended that the steel plant control it below

0.43.

For example, the Jiangsu Shagang Group successfully developed a 22mm thick X80 plate for

the second West-East Pipeline meeting the technical specifications of high strength and high

low temperature toughness. They successfully optimized the original HTP design and

processing (TMCP) practice to produce an improved 0.1%Nb-bearing linepipe steel, Table 4.

Table 4: Chemical compositions and mechanical properties of X80 used in the second

West-East Pipeline.

C

Si Mn Cr+Ni+Cu Al Ti Nb N

0.05

0.24 1.72 <=0.60 0.038 0.016 0.10 0.039

Type YU (MPa) YS (MPa) El (%) YS/TS CVN -200C

J

DWTT

-150C

HTP

548 662 50 0.83 Av 328 Av 50

OHTP 535 705 44 0.76 Av 372 Av 98


Other noteworthy developments by Chinese mills include developing pipeline steels using the

three basic alloy designs recognized in the industry today. The three basic alloy systems

include C-Mn-V-Nb, C-Mn-Mo-Nb and C-Mn-Nb. The latter, using Nb typically in the

0.07-0.10% range, has been termed by the industry as “High Temperature Processed” or HTP

steels, which have been promoted and further developed by CBMM together with its global

customer base.

Today it is possible to say that China has successfully developed the 0.1%Nb HTP alloy

design for pipeline steel applications in both plate and coil at a variety of thicknesses and in

grades from X70 to X100. Processing parameters and mechanical property results have been

presented at several international and domestic conferences and published in journals for

products produced using the 0.1% HTP alloy design.

Technical and practical knowledge and experience have been acquired and aptly demonstrated

in pioneering projects such as the second West-East Pipeline. The platform to develop

Nb-bearing X100 and X120 linepipe steel has been established and is being eagerly pursued

for the next generation of steel grades.

3.2. Automotive

Key aspects of modern automotive engineering are shown in Figure 13. The main drivers are

safety, fuel economy, reduced emissions, long-life components, high performance and

affordability (5). One common development for many of these needs is the reduction of

vehicle weight, as presented in Figure 14 (5). By reducing vehicle weight, it is possible to

reduce fuel consumption, reduce emissions and increase performance as well as cutting costs

(5). China is motivated to achieve the above, thus the efforts to develop new steel grades in

order to reduce vehicle weight.


Figure 13: Key aspects of modern automotive engineering (5).

Figure 14: Motivations for light-weight design: reduced costs and emissions and increased

performance (5).

China’s automotive market has continued to expand. It is set to become not only the world’s

largest new light vehicle market this year but also the biggest vehicle producer, Figure 15.

Whereas global automotive production shrunk by 30% during the first six months of 2009, it

increased by 15% in China compared to the same period in 2008. Figure 15 illustrates the

impressive growth of Chinese vehicle production from 1999 to 2008 and provides a forecast

up to 2015. The 2008 numbers for two other BRIC countries, Brazil and India, are provided

for comparison.


Figure 15: Evolution and forecast of vehicle production in China.

Total 2008 flat steel consumption in China in the automotive industry was about 10 million

tons, of which 65% came from domestic sources with the remainder imported mainly from

Japan, Korea and Europe. Currently, carmakers rely on imported material for outer surface

panels and high strength grades above 780MPa TS. Future flat steel consumption for

automotive applications will increase to about 17 million tons and China will become

practically self sufficient in supplying this material. Foreign material will come primarily

from joint venture operations like hot-dip galvanizing lines, automotive steel service centers

and component makers.

Currently, approximately half of the Chinese automotive flat steel volume is produced on an

ultra-low carbon base with partial or full stabilization of interstitials. For soft grades, both

Ti-IF and Nb+Ti-IF contents are used. Nb stabilization is preferred for high strength IF and

bake hardening steels. There are developments aiming at high Nb IF steels (up to 0.1%Nb) to

achieve either ultra-fine grain size and/or precipitation hardening extending the strength range

of these highly formable steel grades. For advanced high strength steels, development

activities are concentrated on strength levels above 780MPa. Here, the challenge is not so

much in achieving strength as such, but more in reducing the scatter of mechanical properties

to a narrow range. Domestic production of hot stamping grades and operation of respective

press stamping lines has also started recently. On the hot-rolled strip side one can see a trend

to develop ultrahigh strength grades in the range of 550 to 700MPa yield strength. These

grades are interesting in chassis and frame applications for passenger cars as well as trucks.

Ferritic-bainitic steel grades are also gaining importance for wheels and particular structural

parts.

As in mature vehicle markets, the demand for fuel efficiency, reduced emissions and safety

are becoming more prevalent in China. Since the body-in-white is the biggest and heaviest

component of a car, it attracts the highest attention in terms of weight saving efforts.

Simultaneously, the body-in-white is also the key component with regard to passive crash

safety. This complex mix of challenges can only be solved in an economic way by using high

strength steels as construction material. Recent car bodies produced in developed markets are


consisting of 30-60% conventional high strength steel, 5-20% advanced high strength steel

and 5-10% press hardening steel. The change from a predominant use of mild steel to the

recent mix of high strength steel has been achieved during approximately three model

generations in Europe. A similar scenario can be expected for China as the extensive use of

high strength steel will require upgrading of press shop and assembly equipment which will

need some time and investment to be done on a broad scale. Along with that, steel mills are in

the process of developing respective steel grades and completing their product portfolio. The

average share of high strength steel in Chinese car bodies was 17 and 21% in 2007 and 2008,

respectively.

CBMM has been greatly involved in the development of high strength flat carbon steels in

China during recent years using Nb as a key alloying element in these steel grades. Generally

speaking, 70% of currently used flat steel grades for automotive body construction are eligible

for Nb microalloying. Particularly, Nb microalloying is the standard for most of the

conventional high strength steels such as IF-HS, IF-BH and HSLA. In advanced high strength

steels, Nb microalloying is an option that quickly proved valuable in terms of processing

stability and manufacturability. Knowledge about these Nb effects has been broadly

disseminated to Chinese steel mills and fundamental know-how has been created by

collaborative projects. In the future, the focus will be on more specific issues where

difficulties and problems have been identified. This relates to reducing the scatter in

mechanical properties, optimization forming and welding properties and extending the range

of hot-rolled HSLA steels to strength levels above 500MPa.

More recently, initiatives have been started on the development of other automotive materials

such as engineering steels, stainless steel and cast iron. In engineering steels the use of Nb has

not been as widespread as in flat carbon steel. However, also here the introduction of Nb is

growing as demand for the respective components is increasing further. The introduction of

Nb in engineering steels is beneficial in the area of fuel injection systems, springs, gears and

axles, connecting and tie rods as well as wheel hubs. The efforts here are meant to reduce the

dependency of the Chinese automotive industry on foreign parts and component supplies as

well as to establish state-of-the-art metallurgical practices.

Cast iron with Nb alloying has relevance for brake discs. In 2008, the Chinese component

supply company SHAC started producing Nb-bearing disc brake alloys for several

Volkswagen models produced by SAIC for the Chinese market and also for the ROEWE 75

model. The alloys typically have Nb content of around 0.1%.

Increasingly, Nb is developing into a strategic alloying element for automotive iron and steel

products. Nb helps to achieve properties and to provide processing routes that cannot be or are

barely achieved by other alloying elements. Therefore there are two drivers for the growth in

Nb consumption in the automotive industry. First, the natural growth of established steel

grades and second, the introduction of new, superior steel grades and iron alloys in all

automotive markets. Both drivers are very strong in China, pushing Nb development strongly

as described here.


3.3. Structural

Nb is widely applied in numerous high strength structural steels throughout the world. Several

opportunities exist within China to further implement these Nb-bearing technologies into

many steel mills. Nb-bearing steel plate development has resulted in a variety of large-scale

structural applications with improved toughness, weldability and manufacturability for beams,

bridges, pressure vessels, ships, storage tanks and a variety of long product construction

applications.

There is strong competition from alternative construction materials, especially concrete, and

operational cost considerations which has further accelerated the technological progress of

Nb-bearing structural steels globally. Nb provides both technical and value added cost

reduction solutions. For example, Nb is frequently used alone or in combination with other

microalloying elements in the production of numerous structural steel grades such as ASTM

A992 beam, ASTM A572 high strength construction plate steels and ASTM 706 high strength

reinforcing bars. The Nb metallurgy is the same. Two such examples involve low carbon high

strength Nb structural beams with superior toughness replacing V-bearing high carbon steels

and the developing application of Nb steels for seismic and fire resistant steel applications in

rebar and plate applications.

In addition to several new product development activities in China and around the world, in

2009 CBMM is also focusing on assisting customers in projects to improve steelmaking,

casting and hot rolling practices to enhance product quality for both Nb- and non-Nb-bearing

grades. In these challenging economic times, these cost reduction initiatives are reducing both

production and quality costs for our customers. A few illustrations of these product

development and quality improvement activities and opportunities are described below.

3.3.1. Nb Structural Market & Metallurgical Strategy

The Nb metallurgical structural steel strategy is based on three key product development and

commercial elements with enhanced mechanical property and end user cost reduction benefits.

The technical-commercial elements are:

-Low carbon Nb and/or Nb-Mo synergistic chemistries with low cost melting and

rolling schemes.

-Disciplined and carefully controlled accelerated cooling.

-Clean steel and proper alloying practices with appropriate nitrogen control (6).

The compelling benefits for the end user in the steel supply chain translate into the following

new product attributes:

-Improved low temperature toughness resistance to brittle fracture in beam and plate

structures.

-Ability to sustain higher loads with increased toughness per unit area for earthquake

and hurricane-prone zones in value added rebar,


-Improved elevated temperature strength for plate and rebar construction applications

with the current research and development activities creating a family of new fire resistant

Nb-Mo steel grades.

Considering these metallurgical strategic elements, the following examples illustrate a few

commercial applications being developed and/or implemented globally or locally within the

Chinese market.

3.3.2. ASTM 992 Nb-Near Net Shape Cast Structural Beam Application

The addition of Nb refines grain size, lowers the carbon equivalent and improves toughness.

There is still widespread usage of higher carbon structural steels at 0.15 to 0.22% carbon

levels. Recent Nb research has successfully incorporated a lower carbon (<0.10%C) Nb

microalloyed steel into small, medium and jumbo near net shape structural beams. Over

15MMt of low carbon, Nb beam production shows improved impact properties through grain

refinement and strategic cooling practices during rolling. Near net shape cast structural beams

containing only a single Nb microalloy exhibit double the impact strength compared to a

vanadium-only microalloy system at similar sulfur, phosphorous and nitrogen levels. Figure

16 illustrates the impact strength advantages of Nb to vanadium (V) at similar cooling rates

and Figure 17 shows the effect of increasing cooling rates.

0

20

40

60

80

100

120

140

160

180

-60 -40 -20 0 20 40 60 80

Temperature (F)

Imp

ac

t E

ne

rgy

(ft

-lb

s)

Nb-Steel

V-Steel

Figure 16: Charpy V notch impact Nb vs V same cooling rate (7).


0

50

100

150

200

250

1 2 3

Increase in Cooling Rate

Imp

ac

t T

ou

gh

ne

ss

, ft

-lb

s

Nb Nb

Nb

V

V

Figure 17: Charpy V-notch impact Nb x V at increased cooling rates (8).

The use of Nb microalloyed structural steels allows for the opportunity to reduce weight and

cost and increase quality. This production of high strength beams meets severe standards,

offering an excellent combination of strength, ductility and toughness in both the hot rolled

section and after welding over a wide range of welding heat inputs from 10 to 50kJ/cm (9).

3.3.3. Earthquake and Fire Resistant Steel Development Value Added Reinforcing

Bar and Plate

With the projected increased intensity and frequency of hurricanes, earthquakes and cyclones,

there is a market demand to develop and consistently produce S500 and S600 rebar with

elongations of 25 to 30%. Civil engineers are requesting steelmakers to produce new and

improved reinforcing bars at elongation levels approaching 30%. Microalloying with Nb

and/or molybdenum (Mo) offers the possibility to achieve 600MPa with elongations of 25 to

30% and an ultimate tensile strength to yield strength ratio of 1.28-1.30. In addition to Nb or

Nb/Mo chemistry, customized and disciplined quenching practices are of critical importance

in order to successfully meet the needs of this demanding application.

There exists the complimentary need for fire resistance in construction steels. Fire resistant

steel research has increased in the United States with the intent of developing steel that retains

high strength at elevated temperatures (10). There are very limited commercially available

fire resistant plates produced globally. A huge opportunity exists for development of fire

resistant beams and rebars. The goal of this research is to further develop a Nb-Mo alloy

design that will retain two-thirds of its yield strength at 600°C. Figure 18 exhibits the superior

elevated temperature properties of Nb-Mo steels compared to other ASTM A572 or ASTM

A992 type construction steels.


Figure 18: Nb-Mo elevated temperature property comparison (11, 12, 13).

The S500 and S600 Nb rebar alloy design strategy involves: (i) lowering the carbon

equivalent to improve weldability, (ii) improving ductility and toughness and (iii) achieving

good defined yield point elongation. Nb is added at a 0.040 to 0.050% level to effect

precipitation strengthening, improve grain refinement and enhance hardenability to

compensate for the strength loss due to the reduced carbon and manganese levels. Additions

of Mo in the 0.05 to 0.10% range will enhance hardenability in order to meet stringent

earthquake applications and improve fire resistance, achieving elongations exceeding 25%

(approaching 30%) consistently. Nb and Mo have a synergistic effect in achieving a ferrite

and bainite core in place of the conventional ferrite and pearlite core with Tempcore (14).

Traditionally, some higher strength grades have been produced with V. However, recent Nb

development combining selective accelerated cooling practices and Nb have been successful

in displacing V and producing the 490 grade. In fact, just recently, ASTM has adopted a

Grade 80 (560MPa) rebar which is being tested for possible seismic applications. Current

research into the development of a family of S500 and S600 grades is underway.

A lower total cost of production may be achieved through a low carbon-Nb alloy design

incorporating the selective accelerated cooling approach in conjunction with better control of

reheat furnace temperatures. For example, in comparing a Nb chemistry rebar with a V

chemistry rebar, the Nb chemistry exhibits the most consistent elongation between 1100 and

1150°C which is the optimal soak zone temperature for both ductility and efficient lower cost

energy consumption. Less yield-to-tensile strength ratio variation is experienced as well with

Nb-bearing versus V-bearing rebar when rolled to these thermal practices which offers quality

improvements and reduced external cost of quality (15).

0 200 400 600Temperature (°C)

0

20

40

60

80

100

En

g. S

tres

s (k

si)

0

200

400

600

En

g. S

tres

s (M

Pa)

0 400 800 1200Temperature (°F)

Nb

V+Nb

Nb

Base

V+Nb

Base

Mo+Nb

Mo+Nb

0 200 400 600Temperature (°C)

0

20

40

60

80

100

En

g. S

tres

s (k

si)

0

200

400

600

En

g. S

tres

s (M

Pa)

0 400 800 1200Temperature (°F)

Nb

V+Nb

Nb

Base

V+Nb

Base

Mo+Nb

Mo+Nb


3.3.4. China-Canada-USA Collaboration – Earthquake Reinforced Steel/Concrete

Design

Seven Chinese delegates visited Canada and the USA in 2009 to discuss Canadian and

American reinforced concrete designs for structures built for earthquake zones. The objective

was a thorough review of earthquake reinforced concrete/steel for civil and materials

engineering considerations in North America. Specifically, the threefold focus of this

one-week technical exchange was: 1) Development and application technology of high

strength reinforcing bar for seismic applications; 2) Reinforced concrete construction and

Canadian/ASTM standards; and 3) Earthquake protection technology applications.

The result of the meetings was to initiate three projects: 1) Development of S500 Nb/Mo high

strength and high performance value added seismic rebar steel; 2) Yield to tensile ratio and

elongation relationships as it applies to seismic-resistant applications and 3) Hot ductility of

microalloy steels (16).

3.4. Nb in Stainless Steels

Burning fossil fuels to generate energy in the form of electricity for industries and homes, or

for passenger or cargo transport, results in the emission of pollutants and greenhouse gases

such as CO2.

In order to reduce the production of these gases there is a need to improve burning efficiency

and to improve the use catalysts. This implies the application of higher processing

temperatures and, therefore, higher temperature resistant materials.

Nb-bearing stainless steels are being increasingly used in power generation plants and in

vehicle exhaust systems since they represent the best cost/benefit solutions, resulting in

components with longer life cycles, leading to lower replacement and maintenance costs.

The following examples will demonstrate how Nb is helping produce materials with better

high temperature performance.

3.4.1. Nb in Stainless Steels for Exhaust System

Combustion of fuels in motor engines generates carbon dioxide and nitrogen oxides in

addition to toxic gases like the carbon monoxide (CO). Reduction in the emission of these

gases can usually be obtained by improvements in engine efficiency and fuel quality or the

installation of a catalytic convertor as part of the vehicle s exhaust system.

Besides improvements to engine efficiency and fuel quality, the installation of catalytic

convertors in vehicle exhaust systems is necessary to accelerate the transformation of toxic

components like hydro carbons, CO and NOx, to non-toxic substances like H2O, N2 and CO2.

The efficiency of these reactions is directly related to temperature: the higher the temperature

of the emitted pollutants, the more efficient the conversion.

In order to obtain improved yield in fuel combustion and in catalyst conversion reactions,

higher temperatures are necessary in the reaction chamber of the engine and in outlet gases,

implying higher working temperatures for the entire exhaust system. Such temperatures can

reach maximum values of 900-950oC , Figure 19.


Figure 19: Exhaust system and range of working temperature.

The solution for these components is the use of Nb-bearing ferritic stainless steels that

simultaneously offer an effective compromise between mechanical properties at high

temperatures, corrosion resistance and economical production costs, Table 5.

Table 5: Main ferritic stainless grades containing Nb used in exhaust systems.

AISI/ASTM C Cr Ni Nb Ti Mo

409

(as a

reference)

0.08 10.5-11.7 - - [6x(C+N)]-

0.75

-

409L 0.03 10.5-11.7 0.5 0.18-0.4 0.05-0.2 -

434 0.08-0.12 16.0-18.0 - [7x(C+N)+

0.1]-1.0

- 0.75-1.25

439 0.05 16.0-18.0 - - [0.15+4x(C+

N)]-0.8

-

441 0.03 17.5-18.5 0.0-1.0 [3xC+0.3]-1.0 0.1-0.6

444 0.03 17.0-20.0 0.0-1.0 [4x(C+N)+0.2]-0.8 1.75-2.5

China already uses ferritic stainless steels in some parts of the exhaust system, starting first

with AISI 409 ferritic grade, monostabilized with titanium.


However, due to distinct conditions of fuels and also the demand for higher temperature

resistant materials, it was found that such grades have limited applications and the need for

longer life cycle materials to contain costs were necessary.

In 2006, a three-year joint project was established between First Automotive Works (FAW),

Tisco, Baosteel, CISRI, USTB and CITIC/CBMM. The objective was to concentrate efforts

from the whole supply chain to solve the issue described above.

The result was a modified AISI439 ferritic grade, dual stabilized with Nb and Ti. After three

years working on the alloy design, corrosion properties, formability and weldability, muffler

prototypes using this new steel were produced for road tests, which have shown excellent

results.

Focus for future years in the Chinese stainless steel industry will be on the development of

higher temperature resistant materials for the application in the hot part (900-950oC) of the

exhaust system. Here, according to studies done in Japan and Europe, Nb has already proved

to be essential, mainly with regards to creep, oxidation and fatigue resistance. Shortly, all

vehicles, light, heavy, trucks and buses will have low-emission exhaust systems that have a

minimum 10-year life cycle.

3.4.2. Nb in Stainless Steels for the Power Generation Industry

Securing available energy at reasonable prices greatly influences quality of life and economic

growth. The increasing demand for energy, together with the rising concern over greenhouse

gas emissions are the main drivers of efforts underway to improve efficiency of power

generation plants. The challenge is to obtain more energy with the same amount of fuel

through higher power generation efficiencies, Figure 20.

Figure 20: Challenge in improving efficiency of thermal power generation units.

Efficiency in thermoelectric units can be influenced by a variety of parameters but high

temperature and high pressure of water vapor used in turbine operation remain the major

barriers to material performance. As a reference, 1% of higher thermal efficiency on an


800MW generation turbine would reduce one million tons of CO2 lifetime emissions (17),

approximately, estimated over 20 years.

To meet these new optimized parameters, new materials are necessary that not only have

improved mechanical resistance to resist the higher pressures, but also having high

temperature and corrosion resistance at the lowest possible cost.

Attention was driven mainly to the development of heat resistant stainless steels, Table 6,

most of them containing Nb as this is an element that helps increase creep and corrosion

resistance at high temperatures.

Table 6: Grades containing Nb used in power generation (18)

Specification Composition Allowable

Tensile Stress at

650oC*

Min. Yield

Strength

(MPa)

Min. Tensile

Strength

(MPa)

Thickness of

Steam Oxidation

Scale (µm)

TP 304 H

(as a

reference)

18Cr-18Ni 42 205 515 35

TP 347H 18Cr-11Ni -0.9Nb 54 205 515 27

TP 347 HFG 18Cr-11Ni -0.9Nb 66 205 550 17

Super 304H 18Cr-9Ni-3Cu-Nb 78 235 590 18

HR3C 25Cr-20Ni-Nb-N 76 295 655 ≤2.5

*Calculated value according ASME

As can be seen, grades with Nb added present higher allowable tensile stresses and improved

oxidation performance, making the use of higher temperatures feasible with relatively small

alloying content.

Efforts to further develop these materials are essential to keep increasing temperatures and

efficiencies at thermal power plant units, generating more energy with less fuel and lower

emissions.

4. Conclusions and Final Considerations

Nb applications have developed significantly over the past 30 years and especially during the

last 10 years. China has played a crucial role in that growth and today it is the strongest

market for Nb in the world.

Since China is the world s biggest steel producer with significant interest in new products and

solutions, there is still plenty of room for growth and applications to be explored. Specific Nb

consumption is increasing very quickly in China and within a few years it will reach the same

levels as seen in countries that initiated Nb development.

Today it is possible to say that China has successfully developed the 0.1%Nb HTP alloy

design for pipeline steel applications in both plate and coil at a variety of thicknesses and in

grades from X70 to X 80. Processing parameters and mechanical property results have been

presented at several international and domestic conferences and in journals for products


produced using the 0.1% HTP alloy design.

Technical and practical knowledge and experience have been acquired and aptly demonstrated

in pioneering projects such as the second West-East Gas Pipeline. The platform to develop

Nb-bearing X100 linepipe steel has been established and is being eagerly pursued for the next

generation of steel grade.

Currently, 70% of the flat steel grades used for automotive body construction are eligible for

Nb microalloying. Nb microalloying is the standard for most of the conventional high strength

steels. In advanced high strength steels, Nb microalloying is an option that quickly proved

valuable in terms of processing stability and manufacturability. China is fast approaching the

most modern concepts of the most developed car makers in the world: light, safe vehicles

containing advanced, high strength steels.

Higher temperature resistance and longer life cycles in modern exhaust systems are now a

reality thanks to the use of Nb-bearing ferritic stainless steel and the trend is that this

application will spread to all vehicle classes.

The modern architectural concepts employed in Beijing and Shanghai are expanding to the

rest of the country with the help of a new generation of affordable materials with higher

earthquake and fire resistance as well as increased weldability.

CBMM will never see China as merely a market, but rather as a long term partner for

developing solutions to overcome challenges in the quest for a better future.

5. References

(1) F. Heisterkamp, T. Carneiro, “Nb: Future Possibilities – Technology and the Market Place”.

In: Nb Science & Technology, p.1109-1159, USA, 2001.

(2) CRU Analysis. Crude Steel Quarterly - DR, Hit Metal and Crude Steel. London, August

2009.

(3) International Energy Outlook 2008, www.eia.doe.goc/oitaf/ieo/ieorefcase.html.

(4) D. Stalheim, et al, Development and capability of high temperature processing (HTP)

pipeline steel at Nanjing Iron and Steel Company. Pipeline Technology 2009, Oostend,

Belgium.

(5) H. Mohrbacher, “The use of High Strength Steel in Recent Car Body Designs” Paper

presented in Beijng, SAE Seminar, October 2009.

(6) S. Jansto, “Cost Effective Microalloy Structural Steel Balance of Process Metallurgy and

Materials Engineering,” Materials, Science & Technology Conference, Pittsburgh, PA,

October 2008.

(7) D. Misra, S. Shanmugam, T. Mannering, D. Panda, S. Jansto, “Some Process and Physical

Metallurgy Aspects of Nb Microalloyed Steels for Heavy Structural Beams,” International

Conference on New Developments in Long Products, pp. 179-187.

(8) S. Shanmugan, N.K. Ramisetti, D. Misra, T. Mannering, D. Panda, S. Jansto, “Effect of

Cooling Rate on the Microstructure and Mechanical Properties of Nb-Microalloyed Steels,”

Materials Science and Technology (MS&T), 2006, pp. 829-839.

(9) S. Jansto, “Nb-Bearing Steel Development for Value-Added Structural Applications,”

http://www.eia.doe.goc/oitaf/ieo/ieorefcase.html


International Symposium on New Developments: Metallurgy & Applications of High

Strength Steels, May 26-28, 2008, Buenos Aires Hotel, Argentina.

(10) S. Jansto, “Nb Market and Technical Development for Civil Engineering Structural

Applications,” International Symposium of HSLA Steels for the Construction Industry,

Tianjin, China October 22-23, 2007.

(11) J.G. Speer, S. Jansto, J. Cross, M. Walp, D.K. Matlock, “Elevated Temperature Properties of

Nb-Microalloyed Steels for Fire-Resistant Applications,” 2005 HSLA, Conference, Sanyun,

China.

(12) S.G. Jansto, Nb in Structural Steel and Long Product Applications, International Conference

on Microalloyed Steels, Pittsburgh, PA, June, 2007.

(13) R. Regier, J. Speer, S. Jansto, A. Bailey and D. Matlock, “Thermomechanical Processing

Effects on the Elevated Temperature Behavior of Nb Bearing Fire-Resistant Steel,” Materials

Science & Technology Conference, Detroit, Michigan, September 16-20, 2007. {AIST 2008

Hunt-Kelly Award}

(14) S. Jansto, “Production and Nb Application in High Strength and Earthquake Resistant

Reinforcing Bar,” International Reinforcing Bar Symposium, Beijing, China, May 18-20,

2009.

(15) S. Jansto, “Nb-bearing Steel Development for Weldable Structural Steel Applications,”

International Roundtable on Yield to Tensile Ratio, Beijing, China, June 17-18, 2008.

(16) S. Jansto, Earthquake Reinforced Concrete/Steel Civil and Materials Engineering

Considerations Chinese Delegation Roundtable, Internal CBMM report, May 31-June 5, 2009,

Hamilton & Toronto, Canada and Chicago, USA.

(17) D.V. Thornton and K.H Meyer. apud R. Viswanathan and W.T.Bakker: Materials for boilers

in ultra supercritical power plants. In: Proceedings of 2000 International Joint Power

Generation Conference, Florida, July 2000.

(18) In: http://www.sumitomo-tubulars.com/pipe/thermal/austenitic.htm. Last accessed on 12

November 2009.

http://www.sumitomo-tubulars.com/pipe/thermal/austenitic.htm

Documents

30 Years of Niobium Steel Development in China