A54    
  Quenchable boron steels   Last update: 2011-4-5

Quenchable boron steels are used in applications requiring good wear resistant properties.

 

Properties
   

Quenchable boron steels represent a breakthrough in heat treatment technology. These steels use boron as a hardening agent. The melting and refining process, together with thermomechanical treatment by controlled hot rolling, allow ArcelorMittal quenchable boron steel to attain a remarkable degree of hardness and a very uniform microstructure, resulting in excellent mechanical loading performance after heat treatment of the finished part.

 

Advantages
   

After heat treatment

 

Their extreme hardness after heat treatment makes these grades particularly suitable for applications requiring high wear/abrasion resistance. Their use allows significant weight saving (up to 50% compared with an HSLA grade) in structural and automotive components. The specific advantage of ArcelorMittal quenchable boron steels is their suitability for water quenching, making the process more environmentally friendly (less effluent treatment) than that used for conventional carbon steels. Their hardening performance is excellent with both liquid and gas quenching.

ArcelorMittal offers the following quenchable boron grades: 22MnB5 AM FCE, 30MnB5 AM FCE and 38MnB5 AM FCE. The choice of grade will depend on:

  • The required hardness of the finished part
  • The abrasion resistance required
  • The severity of the forming process envisaged

 

22MnB5 AM FCE, 30MnB5 AM FCE and 38MnB5 can be hot or cold formed.

 

As supplied

 

In spite of their moderate hardness and mechanical properties, boron grades exhibit remarkably good abrasion resistance in their delivery condition, thanks to their composite microstructure consisting of a hard pearlite phase embedded in ferrite. They are therefore very cost-effective solutions for applications requiring good abrasion resistance.

 

ArcelorMittal offers a modified version of 30MnB5, for applications such as concrete mixers, in which steel is used untreated: 30MnB5 DRUM AM FCE. Abrasion tests, confirmed by the practical experience of our clients, show a good performance compared with standard structural grades. As a result, parts have a longer lifetime.

 

30MnB5

Ferrite-pearlite structure

 

Applications
   

Quenchable boron steels are used in applications requiring good wear resistant properties. The main applications for these steel grades after heat treatment are agricultural machinery (discs, plough shares), machinery for public works and mining, cutting equipment etc. A popular application for untreated steel is concrete mixer drums.

 

Recommendations for use
   

Jominy curves

The Jominy curve of both 22MnB5 AM FCE and 30MnB5 AM FCE is shown below. This curve gives the hardness as a function of the distance to the quenched area.

TRC characterisation of 22MnB5 AM FCE

The recommended austenitising temperature is 880C. The temperature at the beginning of the quenching process (i.e. at the maximum cooling rate) is 750C. Ac3 temperature is 860C, for a heating rate of 5C/s. Ac1 temperature is 750C, and Ms (Martensitic Start) starting temperature is 400C.

 

In a tensile test, after austenitisation for 5 minutes at 850C followed by water quenching, the structure of the sample obtained is entirely of the martensite type. In the same test performed at 840C, a few islands of residual ferrite can be observed, regularly distributed.

 

TRC characterisation of 30MnB5 AM FCE

The recommended austenitising temperature is 830C to 850C. The temperature at the beginning of the quenching process (i.e. at the maximum cooling rate) is 730C. The TRC diagrams are available on request.

 

Forming
22MnB5 AM FCE, 30MnB5 AM FCE and 38MnB5 AM FCE can be hot or cold formed.

 

 

Heat treatment
   

Typical mechanical properties of a 6 mm specimen in the rolling direction before and after quenching are indicated below.

 

 Delivery conditionQuenched
GradeRe (MPa)Rm (MPa)A (%)Hardness HRCRe (MPa)Rm (MPa)A (%)
22MnB5 AM FCE35052027451100150010
30MnB5 AM FCE and EN 100834406602550120017008
30MnB5 DRUM AM FCE53075021N/A
38MnB5 AM FCE4807601855130020007

N/A = Not available

 

Changing up from grade 30MnB5 AM FCE to 38MnB5 AM FCE makes it possible to increase hardness by about 10% on the quenched parts. Abrasion tests show that this translates into a dramatic improvement of 40% of the wear resistance.

 

Surface quality
   

22MnB5 AM FCE, 30MnB5 AM FCE, 30MnB5 DRUM AM FCE and 38MnB5 AM FCE are available in A unexposed surface quality only.

 

Fatigue resistance
   

Fatigue resistance is determined after heat treatment and quenching. 22MnB5 AM FCE steel 2.65 mm thick has been fatigue-tested by cyclical tensile loading with a load ratio of Rs = 0.1 after different heat treatments. Specimens were austenitised at 950C for 5 minutes.

 

Specimen heated for 5 minutes at 950C followed by:

Endurance limit

sD (MPa)

Spread (sigma)

(MPa)

Maximum stress sD (MPa)

Water quenching

253

6

562

Oil quenching

260

5

578

Water quenching + heat treatment at 200C for 20 minutes

293

26

651

sD = (smax - smin)/2

 

Remark:

The fatigue resistance of ArcelorMittal's boron quenchable steels is between 40 and 60% higher than S355MC AM FCE low alloy grade. She can be reduced by over 30% if total decarburisation is carried out.

 

Brand correspondence
   
 EN 10083-3:2006NF A 36102DIN 1654 Teil 4BS970 Part 1UNI 3756UNE 36034J1268UNS
22MnB5 AM FCE20MnB520MnB5RR22B2174H2021B321B3/20MnB510B21/15B21H15211
30MnB5 AM FCE30MnB530MnB5RR28B2   15B30H15301
30MnB5 EN 1008330MnB530MnB5RR28B2   15B30H15301
30MnB5 DRUM AM FCE30MnB530MnB5RR28B2   15B30H15301
38MnB5 AM FCE38MnB5       
Grades in italics: not included in the standard


 

Dimensions
    Mill finish
Thickness (mm)22MnB5 AM FCE30MnB5 AM FCE30MnB5 EN 10083, 30MnB5 DRUM AM FCE38MnB5 AM FCE
Min widthMax widthMin widthMax widthMin widthMax widthMin widthMax width
1.70 ≤ th < 2.0068510156851065----
2.00 ≤ th < 2.3012651265
2.30 ≤ th < 2.406006001250
2.40 ≤ th < 3.00146014601370
3.00 ≤ th < 4.001650165060016501575
4.00 ≤ th < 4.50185018501850
4.50 ≤ th < 5.00195019501950
5.00 ≤ th < 8.0021502150--
8.00 ≤ th < 14.00685800
14.00 ≤ th < 15.001370
15.00 ≤ th < 16.00--8001370

Pickled
Thickness (mm)Min width22MnB5 AM FCE30MnB5 AM FCE30MnB5 EN 10083, 30MnB5 DRUM AM FCE38MnB5 AM FCE
Max widthMax widthMax widthMax width
1.70 ≤ th < 2.0066010501050--
2.00 ≤ th < 2.4012601250
2.40 ≤ th < 3.0014501280
3.00 ≤ th < 4.0016301280
4.00 ≤ th < 4.50183011001100
4.50 ≤ th < 5.001930
5.00 ≤ th < 6.002130-
6.00 ≤ th < 7.001550-
7.00 ≤ th < 8.001280



 

Mechanical properties
   

 
Direction
Thickness (mm)
Rm (MPa)
30MnB5 DRUM AM FCET1.7 - 5620 - 750


 

Chemical composition
   

These grades receive a spheroidisation treatment of the manganese sulphides. The efficiency of boron is ensured by the addition of elements that bind nitrogen.

 

Of the proposed grades, the lowest carbon content improves hole expansion performance.


 
C (%)
Mn (%)
P (%)
S (%)
Si (%)
Al (%)
Ti (%)
B (%)
22MnB5 AM FCE 0.200 - 0.250 1.10 - 1.40 ≤ 0.025 0.008 0.15 - 0.35 0.015 0.020 - 0.050 0.0020 - 0.0050
30MnB5 AM FCE 0.270 - 0.330 1.15 - 1.45 ≤ 0.025 0.005 0.17 - 0.35 0.015 0.020 - 0.050 0.0010 - 0.0050
30MnB5 EN 10083 0.270 - 0.330 1.15 - 1.45 ≤ 0.025 ≤ 0.035 0.17 - 0.35 - - 0.0010 - 0.0050
30MnB5 DRUM AM FCE 0.270 - 0.330 1.15 - 1.45 ≤ 0.025 ≤ 0.020 0.17 - 0.35 0.015 0.020 - 0.050 0.0010 - 0.0050
38MnB5 AM FCE 0.360 - 0.420 1.15 - 1.45 ≤ 0.025 0.005 0.17 - 0.35 0.015 0.020 - 0.050 0.0010 - 0.0050
Grades in italics: not included in the standard
Values in bold: tighter than the standard


   
For commercial information (quotations, deliveries, product availability):

For technical questions about these products: fce.technical.assistance@arcelormittal.com
For researchers: click here


All details provided in the ArcelorMittal Flat Carbon Europe S.A. catalogue are for information purposes only. ArcelorMittal Flat Carbon Europe S.A. reserves the right to change its product range at any time without prior notice.